When I arrived at the airport in Frankfurt, I dropped into the next store to get a Coke. And there it was: the print version of Welt der Wunder (World of Wonders), with an article titled 'The worlds most dangerous experiment' about the creation of black holes at the LHC. Citing me as 'expert for mini black holes at the University of California, Santa Barbara' in a completely misleading context.
Some months ago, I gave an interview by phone to the journalist, Mirko Herr. He repeatedly asked me whether the mini black holes could possibly grow and swallow the whole earth. A catastrophe scenario he seemed to be very interested in. I patiently explained him that to our best knowledge this is extremely unlikely, and gave numerous arguments. Being a scientist, at being pushed, I said that the possibility can not be completely excluded. I mean, there is a certain possibility that the world might end tomorrow at 10:30 GMT, it's just extremely unlikely. Maybe time is just a finite coordinate and tomorrow we run out of it?
By reading the article, my worst expectations were confirmed. Apparently, he had heard my arguments before and was instead looking for someone to take the opposite site, and warn that the LHC is 'the worlds most dangerous experiment'. I explained him extensively why this is not the case.
Two weeks after the interview, he wrote me an email, explicitly saying that even though I told him the danger is minimal, he would like to know how a 'worst case scenario' looks like, as a 'Gedankenspiel' (game of thought).
Here is what I am cited with from my answer to this mail :
"Sollte es moeglich sein, dass das schwarze Loch mehr Masse aufnimmt, wird es schlicht wachsen, bis alles in erreichbarer Umgebung hinter dem Horizont verschwunden ist -inclusive dem LHC, Genf, der EU, China und den USA. Das passiert dann aber sehr schnell, und um meine naechste Einkommenssteuererklaerung muss ich mirdann keine Gedanken mehr machen."
The translation is roughly:
"Should it be possible that the black hole gains more mass, then it would grow until everyting in its sourrounding vanished behind the horizon, including the LHC, Geneva, the EU, China and the USA. At least, this will then happen very fast, and I don't have to worry about my next income tax return."
I looked up the email I sent him. What I wrote was: "Should it be possible that the black hole gains more mass THAN IT LOOSES, then it will grow... "
More important however, is the full context of the above quotation, in which I again explain quite lenghty the unlikeliness of the event. I attach the full text below (sorry, it is in German).
The second quotation attributed to me 'Es existiert in jedem Fall ein Risiko. Man kann ein Unglueck nicht mit letzter Gewissheit ausschliessen' ('There definitely is a risk. It is impossible to exclude a catastrophe completely'), caused my mother to look puzzled. Though I might have said something roughly like this in the context mentioned above, that it is just not possible to make 100% statements, I am reasonably sure that I never said this exact sentence. It is just not my vocabulary and not a choice of words I would have used.
I am very, very disappointed about the low scientific content of the whole article and it's dumb search for sensation. Though, I should add for fairness, Mirko Herr seemed to be quite a nice and reasonable man.
If you want to read a sensible popular article on mini black holes and extra dimensions, I can recommend the double-sided article which appeared recently in the Sunday edition of the FAZ: 'In anderen Dimensionen' (In other Dimensions), by Ulf von Rauchhaupt. In contrast to the article by Mirko Herr, the scientific quality of the FAZ article impressed me very much. It is clearly written without going into too many messy details, and it cites me with sentences I actually said, and in the correct context.
This will teach me to be more careful with journalists. Indeed, the journalistic world, is a world of wonders.
I also realized that for some reason or the other I did so far not write any post in my blog about the mini black holes, though I have been working on the topic for several years. I will do so in the next week.
Here is the full context of the above quotation in the article in Welt der Wunder:
Lieber Herr Mirko,
damit Sie das Gefahrenpotential richtig einschaetzen, moechte ich folgendes voranstellen: die Produktionschwarzer Loecher am LHC ist moeglich, falls es extra Dimensionen gibt (was nicht feststeht) und dieseausreichend gross sind (was nicht feststeht).
Wir wissen zwar nicht viel ueber den endgueltigen Zerfalldieser Loecher, koennen aber aus Hawkings Herleitung der Strahlung schwarzer Loecher deren Temperaturrecht verlaesslich angeben. Die Temperatur dieserkleinen schwarzen Loecher ist extrem hoch, ca 200 GeV(das sind etwa 2*10^12 Kelvin). Werden diese Objektein der Kollision produziert, so zerfallen sie direktim Kollisionsbereich, noch lange bevor sie die Detektorwand erreicht haben. Die typische Lebenzeitsind etwa 10 fm/c, oder 10^-22 Sekunden. Darin unterscheiden sie sich nicht viel von den meistenanderen 'Dingern', die in so einer Kollision produziert werden. Fast alles ist sehr kurzlebig, je schwerer, destokurzlebiger.
Selbst wenn ein solches Loch in Materie geraten sollte, so wird es nie mehr Energie aufnehmen koennen, als es durch die Verdunstung abgibt. Daher koennen diese winzigen Loecher auch nicht wachsen auf der Erde.Sie koennen auch nicht wachsen, in irgendeinem uns bekannten Medium (selbst die Dichte eines Neutronen-sternes, inetwa vergleichbar zu der des Quark Gluon Plasmas, ist nicht ausreichend).
Mir ist nicht ganz klar, wie Sie sich ein solchesGedankenspiel vorstellen? Sollte es moeglich sein, dass das schwarze Loch mehr Masse aufnimmt als abgibt, wird es schlicht wachsen, bis alles in erreichbarer Umgebung hinter dem Horizont verschwunden ist -inclusive dem LHC, Genf, der EU, China und den USA. Das passiert dann aber sehr schnell, und um meine naechste Einkommenssteuererklaerung muss ich mirdann keine Gedanken mehr machen.
Sollten Sie weitere Fragen haben, zoegern Sie nicht, mir zu schreiben.
Mit freundlichen Gruessen,
Sabine
Monday, June 19, 2006
Jet-lag
The first semi-conscious act after leaving a plane with a nine hour jet-lag was to fix my parents wireless. Something is seriously wrong with me. Maybe not even wrong. I noticed that Christine unfortunately removed her top-ten lists on String Theory and LQG, apparently due to a whole lot of annoying comments. This is really a pity, cause I did not have the time to completely read her posts, and follow the links, and was kind of looking forward to it.
I also noticed there is a discussion on CIP's blog, as well as a follow up on wolfgang's blog, based on comments in my post Science and Democracy, which circles around Lubos' state of mind. Considered the fact that my post tried to communicate that this is exactly what we do not need to discuss, I find this quite ironic.
Also, it seems that blogger still has some technical problems. I would like to strongly advise you to make a copy of your comments (at least into the clipboard) before you click 'submit'.
Besides this, I am currently in Germany which I hardly recognized. Every street corner and every second car has a German flag. I heard, they are sold out! It seems, after all, the Germans rediscovered their national pride. Apparently, it came in a soccer ball.
More after the jet-lag. Best,
B.
I also noticed there is a discussion on CIP's blog, as well as a follow up on wolfgang's blog, based on comments in my post Science and Democracy, which circles around Lubos' state of mind. Considered the fact that my post tried to communicate that this is exactly what we do not need to discuss, I find this quite ironic.
Also, it seems that blogger still has some technical problems. I would like to strongly advise you to make a copy of your comments (at least into the clipboard) before you click 'submit'.
Besides this, I am currently in Germany which I hardly recognized. Every street corner and every second car has a German flag. I heard, they are sold out! It seems, after all, the Germans rediscovered their national pride. Apparently, it came in a soccer ball.More after the jet-lag. Best,
B.
Note added: Christine put her lists back online. Here are the links
Sunday, June 18, 2006
Black Hole Bag
If my blog had categories then this would be a non-scientific post.
It's a Sunday and - again - I am sitting at an airport, this time waiting to be squeezed into a Boing 747 with what looks about 1 Million of Indians, currently dancing in the boarding area.
Today, a good friend sent me an email reminding me that I have only 5 days to go to my wedding. I realized, she is right. So, I decided it's about time to get in the mood, and bought a bridal magazine. Among other things, I learned that I can insure my wedding against rain, and the latest must-haves in dinnerware: contemporary collections enhanced by stylized designs to help me create dinner parties that reflect my personal style. Wow. I am very worried about my current personal style.
The magazine also has a countdown calendar! Some highlights from this:
- 12 months: Choose a wedding theme and style, meet potential wedding consultants
- 11 months: Research and interview florists
- 10 months: Select and order your wedding gown, discuss attebdants' duties with your maid of honor and bridesmaids
- 9 months: Register for gifts, dicide on food and liquor to be served at your reception
- ...
... and so on, and so on. Can we make that days instead of months?
So far the only contribution I made to my wedding organization was to pick the dress. Scheduled between a visit at PI, a seminar in Frankfurt, and a conference in Paris, this was undoubtly the most entertaining event my mother had in the last month.
The shop assistants were horrified to hear that the wedding would already be in no more than four weeks. After we calmed them down, assuring that we would be uncomplicatd, they called two tailors. One of them one with needles pinned everywhere hardly spoke a word, but vanished every 30 minutes for a cirarrette break. The other a chatty women with an accent from Sachsen, whose eyes began gleaming when she saw me: She's tiny, she said, she will fit in EVERY dress. I was about to run away and marry in jeans.
They placed me on a stool, and dragged a dress over me. Great, I said, it's white, I take it! - Nonono, the assistants, both dressed in pink, said, you have to try this, and this and this. It went on for endless hours, in which they put me in and out of dresses, attached things to my hair, around my neck, and shoes on my feet, while my mother was served coffee and cookies. She had a really good time. I was tought how to sit in a dress, how to make turns with the full armor, and to never, never, never, move backwards.
The shop assistants found everything gorgeous, other customers made comments like: Isn't this absolutely LOVELY? or How cute! A postman who delivered a parcel remarked I look like Cinderella. I definitly felt more like the beast than the beauty.
After f-o-u-r hours we settled on the first dress. Then, one of the shop assistants placed a bag in my hand. I had never seen a bag so tiny before. It was white and a bit shiny. My patience was pretty exhausted, so I asked What the fuck am I supposed to put in this 'bag'? The assistant shrugged her shoulders and insisted, it looked nice. Cigarrets, the quiet tailor said. My mother vetod on that, I doubted the plural 's'. Tampons? the other assistant suggested, not very convincingly. A cell phone, the postman yelled from the back.
Actually, I thought, good point. It would look much better to have the cell in a bag than to attach it to the train or so. Yes! the chatty tailor giggled So her lover could call last minute!, my mother looked appropriately disgusted. I instead saw myself getting a call from my coworker, upset, because he had just scanned the arxiv, telling me that we have been scooped on our new paper. Then I would shout into the ceremony 'I DO, I DO, can you hurry up a bit, where do I sign?', and run away, looking for a wireless network.
Anyway, my mother decided for the bag. Now I read in this bridal magazine, what has to be in the brides bag:
'Don't leave for the ceremony without an emercency kit packed with essentials for tackling common wedding-day mishaps like torn hems or broken heels. Some must haves:
- Double sided fabric tape
- A small sewing kit
- Superglue
- Deodorant
- Breath mints
- Clear nail polish
- Nail Kit
- Band Aids and Painkillers
- Tissues
To this we add the 'Emergency Beauty Kit: comb and brush, hair spray, nail glue, nail polish topcoat, pressed powder, mascara and lipstic.' Also, I am supposed to take off my glasses for the photos, these go in the bag as well. Together with the cell phone, cigaretts and tampons. Not to mention worldly stuff like purse, and keys, and the required legal documents (you want to make sure you marry the right person). And my memory stick, without which I never go anywhere, in case the new paper gets scooped...
All this seems to imply that it takes a black hole bag rather than a tiny, shiny, white bag. At least the interior needs infinite volume. So I googled for it. And guess what? Here it is, the black hole bag:
I also found the black hole vacuum cleaner, which I should maybe put on the gift list. That is, if I had registered for one around the time when men still dragged their women around on their hair or so.
When I think about it, the double sided tape acutally could be handy to stop the uncle from talking too much.
Note added: I have been told that 'I DO, can you hurry up!' is not exactly the right thing to say, but that I have to say 'Yes' loud and clearly. Not 'Sure', not 'I think so' or 'That's why I'm here'. It's like when you end up sitting on the plane in an emergency exit row. If you are willing and able to perform the required actions in case of an emergency, please say yes lound and clearly.
Friday, June 16, 2006
Impressions from the SUSY 06
The SUSY conference is always my favourite conference of the year. Despite the title indicating a closeness to sypersymmetry, the topics cover a very broad range - which means it is impossible to find a day completely covered with uninteresting talks and to go to the beach.
Besides sometimes technical supersymmetry and string-session, there are the phenomenological talks about Cosmology and collider physics. I myself favour the parallel sessions about models and alternatives, which are usually quite mixed up. My talk usually ends up being an alternative.
On Wednesday we had an evening plenary session about Naturalness. Naturally, this year the collider signatures are a hot topic, which was also addressed in an evening discussion yesterday. I can not avoid noticing that the closeness of the LHC start-up in 2007 seems to have triggered an increased output of predictions and simulations based on more and more models, which might or might not have something to do with susy, or string-theory. It's like the concern is either now or never, so lets publish some predictions as long as we are are not outruled. The recurring question is of course whether available data would actually allow to distinguish between various scenarios. The amount of work that goes into details of simulations of completely unconfirmed (and sometimes even unmotivated) models, is frightening.
The atmosphere this year is full of good vibes (definitly not those of the wireless which is rather mediocre), though the word 'landscape' is used very carefully, and most often in a defensive tone. I was not even able to depress people with my worst case scenario that they find nothing at the LHC, not even the Higgs. Instead, this morning we had a very good talk by James Rosenzweig (UCLA), about future prospects for the next generation accelerators. Among other things, he talked about the creation of high quality beams through plasma wave excitations with a laser. As he said: "Lasers cost only a few Million $, you can do this essentially at home."
This year, the conference is accompanied by a constant series of flashlights. It is impossible not to notice byen00 with the heavy equipment and the video camera, who seems to be present everywhere at anytime, a living proof for the existence of parallel universes. He has probably been to more talks than many of the participants, certainly to more than I. As I learned from the recent post on Cosmic Variance
he calls himself 'chimpanzee'. He told me he wouldn't do the reporting on scientific events for money, coz then it would stop being fun. You find the pictures
It's rather disturbing to be hit by a flashlight in the middle of a sentence! During my talk yesterday, I lost at least two sentences with every photo, and forgot about half of what I wanted to say. At least I finished in time, which I otherwise hardly ever manage.
Here is a photo taken at the reception on Tuesday evening. I can't quite remember what I said to have everyone look at me as if I am nuts. It might have been that I find it possible that gravity maybe just does not have to be quantized.
Note added: I just remembered that the discussion on the above photo turned towards blogging when byen joined us, and then inevitably spiraled towards Lubos. I caused the plain disbelieve you see on the other's faces by saying that I don't think Lubos is totally crazy.
Wednesday, June 14, 2006
Squeeze my brain
Here, in Newport Beach, the weather is gorgeous, the amount of talks is incredible, and the whole conference SUSY 2006 is very inspiring.
Among other things, this year's bag is equipped with a spare brain, which you can squeeze when things go anthropic.
Among other things, this year's bag is equipped with a spare brain, which you can squeeze when things go anthropic.
Yesterday at the reception, I noticed a guy hanging around with a camera. He came up to us and asked "What's going on at the conference? LHC is coming, huh?". We said, "Yeah, that's about it." He said, "cool", turned around and filmed an empty table instead. This was about the most conclusive discussion about the status of physics I have had in the last years.
To find some of the pictures from the conference, go to
Or make a scenic detour and go two blogs this direction.
Monday, June 12, 2006
Science and Democracy
While I was sitting at the coast throwing stones into the ocean, it seems Lubos has written a very interesting post about an important topic: Science vs Democracy.
I don't quite share the perception of the so-called-crisis-in-theoretical-physics, but we are currently in a situation that requires adjustment to the changes that front research has made during the last decades. Without doubt, the number of people working in theoretical physics has increased a lot. Research fields have become more and more specific. It takes a long time to gain enough knowledge to be able to contribute to the front of research.
This has caused the community to fall apart into many distinct fields. Most often, people working on one field don't know much about other fields. Worse, I even noticed that the basic knowledge that postdocs should have, already begins to be filtered by the supervisor they had, or the topic they were focused on. This is not only annoying, but it also hinders progress.
Reading Lubos', Peter's and other blogs, following articles in newspapers, or recent books, it is pretty obvious that currently there is some controversy about which direction research in theoretical physics should take in the future. This is a question that most likely won't be answered by calling each other names in comments on blogger's posts.
It concerns me very much that this discussion is lead on such a level, without serious attempts to resolve the problem in a constructive way. Our work is based on the support of the society we live in. Research funding has to be distributed to the most promising researchers. These decisions have to be made based on something. These decisions ARE made on the basis of SOMETHING. But something is not good enough.
This is the context in which I mentioned the advisory committee. Not to decide on the number of critical dimensions, as Lubos indicates, but to decide which researchers and projects are worth supporting.
Besides this minor misunderstanding, Lubos essentially agrees on what I say.
Lubos: it is absolutely critical that scientists have the freedom to reveal the truth whatever it is and they are unconstrained by the pre-determined truth defined by someone else...
If that alone was the base on which researchers are supported, I would be very happy! However, one might keep in mind that 'truth' is something to search for in mathematics as well as in physics.
To clarify another statement:
Lubos: The blogger mentioned at the beginning has even proposed to establish "advisory committees" that would be deciding what research directions are promising and what conclusions about general questions that scientists are allowed to make and what conclusions they are not allowed to make. I just can't believe she's serious ...
I certainly never said someone should decide what conclusions scientists are allowed to make. I want to point out again that there ARE people deciding what research is promising in terms of financial support. It is definitely possible, and necessary, to improve this decision making process. It requires an objective analysis of what science is, what it should be, and how it can work best.
Lubos: The more specialized and advanced questions in science we try to answer, the more devastating effect the committees would have. It's simply because the very specialized topics in science are always correlated with very small groups of people who understand these things well.
I am very glad that Lubos understands the problem. Groups of people specialized on things they understand will most likely fail to appreciate important contributions outside their line of thought. Candidates picked on this level are most likely those which pursue research topics the group of people who understand these things well understands well. I.e. when things go wrong, they go really wrong.
Lubos: But it is completely crazy for deciding about highly difficult science questions.
To make this clear one more time: truth is not decided about by committees. When truth remains to be found, and resources are limited, decisions ought to be made where the resources go. How this can be done in a way that hopefully leads out of the so-called-crisis-in-theoretical-physics is exactly the discussion that we need.
Note added: This discussion originated from the comments on Lubos' post Dean of crackpots, Hitler's Pope, and string theory.
I don't quite share the perception of the so-called-crisis-in-theoretical-physics, but we are currently in a situation that requires adjustment to the changes that front research has made during the last decades. Without doubt, the number of people working in theoretical physics has increased a lot. Research fields have become more and more specific. It takes a long time to gain enough knowledge to be able to contribute to the front of research.
This has caused the community to fall apart into many distinct fields. Most often, people working on one field don't know much about other fields. Worse, I even noticed that the basic knowledge that postdocs should have, already begins to be filtered by the supervisor they had, or the topic they were focused on. This is not only annoying, but it also hinders progress.
Reading Lubos', Peter's and other blogs, following articles in newspapers, or recent books, it is pretty obvious that currently there is some controversy about which direction research in theoretical physics should take in the future. This is a question that most likely won't be answered by calling each other names in comments on blogger's posts.
It concerns me very much that this discussion is lead on such a level, without serious attempts to resolve the problem in a constructive way. Our work is based on the support of the society we live in. Research funding has to be distributed to the most promising researchers. These decisions have to be made based on something. These decisions ARE made on the basis of SOMETHING. But something is not good enough.
This is the context in which I mentioned the advisory committee. Not to decide on the number of critical dimensions, as Lubos indicates, but to decide which researchers and projects are worth supporting.
Besides this minor misunderstanding, Lubos essentially agrees on what I say.
Lubos: it is absolutely critical that scientists have the freedom to reveal the truth whatever it is and they are unconstrained by the pre-determined truth defined by someone else...
If that alone was the base on which researchers are supported, I would be very happy! However, one might keep in mind that 'truth' is something to search for in mathematics as well as in physics.
To clarify another statement:
Lubos: The blogger mentioned at the beginning has even proposed to establish "advisory committees" that would be deciding what research directions are promising and what conclusions about general questions that scientists are allowed to make and what conclusions they are not allowed to make. I just can't believe she's serious ...
I certainly never said someone should decide what conclusions scientists are allowed to make. I want to point out again that there ARE people deciding what research is promising in terms of financial support. It is definitely possible, and necessary, to improve this decision making process. It requires an objective analysis of what science is, what it should be, and how it can work best.
Lubos: The more specialized and advanced questions in science we try to answer, the more devastating effect the committees would have. It's simply because the very specialized topics in science are always correlated with very small groups of people who understand these things well.
I am very glad that Lubos understands the problem. Groups of people specialized on things they understand will most likely fail to appreciate important contributions outside their line of thought. Candidates picked on this level are most likely those which pursue research topics the group of people who understand these things well understands well. I.e. when things go wrong, they go really wrong.
Lubos: But it is completely crazy for deciding about highly difficult science questions.
To make this clear one more time: truth is not decided about by committees. When truth remains to be found, and resources are limited, decisions ought to be made where the resources go. How this can be done in a way that hopefully leads out of the so-called-crisis-in-theoretical-physics is exactly the discussion that we need.
Note added: This discussion originated from the comments on Lubos' post Dean of crackpots, Hitler's Pope, and string theory.
Sunday, June 11, 2006
SUSY 2006
Next week, I am in Newport Beach at the
14th International Conference on Supersymmetry and the Unification of Fundamental Interactions
or, short, the SUSY 06. I am looking forward to an interesting meeting, and hope to find some time (and some wireless) to report on it.
Since it's another rainy Sunday here in Santa Barbara, let me recommend a CD I bought recently:
Lights Out
Anti-Matter
"I'm just another casualty of casual insanity."
14th International Conference on Supersymmetry and the Unification of Fundamental Interactions
or, short, the SUSY 06. I am looking forward to an interesting meeting, and hope to find some time (and some wireless) to report on it.
Since it's another rainy Sunday here in Santa Barbara, let me recommend a CD I bought recently:
Lights OutAnti-Matter
"I'm just another casualty of casual insanity."
Wednesday, June 07, 2006
Talks on Planck 2006, Paris
Apparently, the world did not end yesterday. Too bad, I was really looking forward to it. Now I will have to pay all the past due bills that accumulated in my mailbox while I was away.
As I mentioned earlier, I was in Paris last week, on the Planck 2006. The conference was fairly well organized, everything went without major disasters. The only annoyance were the security scans at the entrance every morning, where some uniformed guys repeatedly looked through the trash in my backpack.
Here are some comments about my personal favourite talks:
Most interesting theory talk:
Keith Dienes
Temperature, Duality, And the Hagedorn Transition
Is based on the papers hep-th/0312216, hep-th/0312217, and hep-th/0507201 with Mike Lennek from the University of Arizona. The idea is roughly to find a formulation of thermodynamics that is compatible with string-theoretical expectations by construction. Remember how a finite temperature description is achieved in QFT. One goes from zero, T=0, temperature to a finite temperature, T>0, by compactifying a timelike coordinate on radius 1/T.
Now, to get stringy thermodynamics, assume that T-duality (symmetry under replacing the radius R with a dual radius ~ 1/R) holds for the compactified time-like coordinate. This consequently results in a duality under the replacement T -> Td2/T, where Td is some dual temperature.
However, standard thermodynamics unfortunately does not respect this duality. Instead, it is necessary to introduce a 'covariant' exterior derivative to generate thermodynamical quantities that respect the symmetry. Here, the covariant derivative just defined such that it respects the symmetry.
I will write more about this topic at some point because I really like it. Once the string-compatible thermodynamics is formulated, it provides a useful effective description of stringy effects at high temperatures. This in turn can be quite useful for cosmological implications.
I still wonder why this nice work has gotten so little attention.
Most interesting phenomenology talk:
Ann. E. Nelson
Mass Varying Neutrinos and Neutrino Oscillation Tests
Is based on the very readable paper Dark Energy from Mass Varying Neutrinos (astro-ph/0309800). The possibility that neutrino masses vary with the medium they propagate in has recently received increased attention. Though I don't particularly like this model, it is an interesting proposal.
The concept of the mass-varying neutrinos assumes a relation between neutrinos and the dark energy of the universe through a scalar field, the so-called acceleron. This implies then that the neutrino oscillation parameters in vacuum and a medium could be very different (this is not the standard MSW-effect).
Nelson discussed the implications of these models for neutrino phenomenology, for example in the sun, for cosmology, and astrophysics. Maybe most importantly, it could also explain the LSND data. However, she also pointed out that tests of mass-varying effects are very difficult, since the different experiments obtain data under different conditions, and little or no direct information is available on oscillation parameters in vacuum or air.
I should add that I personally don't like to fix problems by introducing additional, fairly unmotivated, scalar fields. Also, the precise predictions of the mass-varying neutrinos seems to be rather model dependent. For my taste, there are too many ambiguities in the
model.
However, in principle, the idea to connect the dark energy to the smallness of neutrino masses is nice, and it is a reasonable phenomenological model which is experimentally testable.
Most entertaining talk:
John March-Russell
Spoke about the always fascinating topic of TBA. Based on the paper Signals of Inflation in a Friendly String Landscape (astro-ph/0604254), it was a talk delivered with humor and an non-negligible amount of self-confidence.
Nevertheless, it left me with the impression that the consequence of the anthropic principle is that we now look for probability distributions of parameters that favor correlations we observe. Should it happen that a distribution has a high probability for correlations we don't observe, well, then we better look for another distribution. But in any case, there is no need to worry, coz the universe can always be just unlikely.
It seems to me that we have replaced looking for theories with looking for probability distributions. Given some distribution, hopefully motivated in one way or the other, a vacuum energy of value of so-and-so is with probability x correlated to a curvature of this-and-that value. But what do we learn from that?
Most deafening talk:
H. Nielsen
Fine Structure Constant relation and multi Point principle
Despite the enormous volume the talk was delivered in, I have not the slightest idea what it actually was about. I only vaguely recall that the speaker repeatedly mentioned some cheat, where he put factors 3 or 1/2 when necessary.
The lesson I learned from this talk is that with some accent, cheat sounds suspiciously like shit.
As I mentioned earlier, I was in Paris last week, on the Planck 2006. The conference was fairly well organized, everything went without major disasters. The only annoyance were the security scans at the entrance every morning, where some uniformed guys repeatedly looked through the trash in my backpack.
Here are some comments about my personal favourite talks:
- Most interesting theory talk
- Most interesting phenomenology talk
- Most entertaining talk
- Most deafening talk
Most interesting theory talk:
Keith Dienes
Temperature, Duality, And the Hagedorn Transition
Is based on the papers hep-th/0312216, hep-th/0312217, and hep-th/0507201 with Mike Lennek from the University of Arizona. The idea is roughly to find a formulation of thermodynamics that is compatible with string-theoretical expectations by construction. Remember how a finite temperature description is achieved in QFT. One goes from zero, T=0, temperature to a finite temperature, T>0, by compactifying a timelike coordinate on radius 1/T.
Now, to get stringy thermodynamics, assume that T-duality (symmetry under replacing the radius R with a dual radius ~ 1/R) holds for the compactified time-like coordinate. This consequently results in a duality under the replacement T -> Td2/T, where Td is some dual temperature.
However, standard thermodynamics unfortunately does not respect this duality. Instead, it is necessary to introduce a 'covariant' exterior derivative to generate thermodynamical quantities that respect the symmetry. Here, the covariant derivative just defined such that it respects the symmetry.
I will write more about this topic at some point because I really like it. Once the string-compatible thermodynamics is formulated, it provides a useful effective description of stringy effects at high temperatures. This in turn can be quite useful for cosmological implications.
I still wonder why this nice work has gotten so little attention.
Most interesting phenomenology talk:
Ann. E. Nelson
Mass Varying Neutrinos and Neutrino Oscillation Tests
Is based on the very readable paper Dark Energy from Mass Varying Neutrinos (astro-ph/0309800). The possibility that neutrino masses vary with the medium they propagate in has recently received increased attention. Though I don't particularly like this model, it is an interesting proposal.
The concept of the mass-varying neutrinos assumes a relation between neutrinos and the dark energy of the universe through a scalar field, the so-called acceleron. This implies then that the neutrino oscillation parameters in vacuum and a medium could be very different (this is not the standard MSW-effect).
Nelson discussed the implications of these models for neutrino phenomenology, for example in the sun, for cosmology, and astrophysics. Maybe most importantly, it could also explain the LSND data. However, she also pointed out that tests of mass-varying effects are very difficult, since the different experiments obtain data under different conditions, and little or no direct information is available on oscillation parameters in vacuum or air.
I should add that I personally don't like to fix problems by introducing additional, fairly unmotivated, scalar fields. Also, the precise predictions of the mass-varying neutrinos seems to be rather model dependent. For my taste, there are too many ambiguities in the
model.
However, in principle, the idea to connect the dark energy to the smallness of neutrino masses is nice, and it is a reasonable phenomenological model which is experimentally testable.
Most entertaining talk:
John March-Russell
Spoke about the always fascinating topic of TBA. Based on the paper Signals of Inflation in a Friendly String Landscape (astro-ph/0604254), it was a talk delivered with humor and an non-negligible amount of self-confidence.
Nevertheless, it left me with the impression that the consequence of the anthropic principle is that we now look for probability distributions of parameters that favor correlations we observe. Should it happen that a distribution has a high probability for correlations we don't observe, well, then we better look for another distribution. But in any case, there is no need to worry, coz the universe can always be just unlikely.
It seems to me that we have replaced looking for theories with looking for probability distributions. Given some distribution, hopefully motivated in one way or the other, a vacuum energy of value of so-and-so is with probability x correlated to a curvature of this-and-that value. But what do we learn from that?
Most deafening talk:
H. Nielsen
Fine Structure Constant relation and multi Point principle
Despite the enormous volume the talk was delivered in, I have not the slightest idea what it actually was about. I only vaguely recall that the speaker repeatedly mentioned some cheat, where he put factors 3 or 1/2 when necessary.
The lesson I learned from this talk is that with some accent, cheat sounds suspiciously like shit.
Monday, June 05, 2006
Paper Recipe
Ingredients:
1 arxiv mirror
1 12-pt document.
2-3 topics of general interest.
A couple of standard textbooks.
1 handful of good taste.
2 teaspoons of symmetry groups.
1/2 cup of superlatives.
1 box of parameters.
1 scalar field.
Preparation:
The previous day, check the recent papers on the arxives hep-ph / hep-th/ astro-ph and gr-qc. Peel and cut the titles, don't bother with abstracts. Pick out frequently used words, irrespective of their physical content.
Our this year's seasonal recommendations are e.g. 'duality, hidden, AdS, noncommutative, black hole entropy, deconstruct, landscape, emergent, ..."
Also, take the parameters out of their box and pair them with values, e.g. Q_eff ≤ 1/3 and \sigma(2,2) = \sin^2(\Pi/3). For best results, make sure your superlatives contain the all-time favourites 'promising', 'groundbreaking', 'exciting', 'significant' and 'of high interest'.
The Following Day:
1) Prepare the Title.
Prepare the title by using as many of the previously found frequently used words as possible. Mix several of them. Colleagues should ideally feel obliged to cite your paper, but not qualified to actually judge on it.
2) Prepare the Abstract.
Take the 2-3 topics of general interest, wash them thoroughly, until completely free of criticism and discussion. We recommend today 'Dark Energy', 'Quantum Gravity', and 'Large Hadron Collider', or whatever this week's special offer of your local blog scene is. Unwrap the prepared frequently used words, and carefully check whether some have become stale over night.
In a large, non-stick pan, warm the topics of general interest over medium heat. Add the frequently used words and cook until thickened to less than 10 sentences. Add ½ cup of superlatives and mash them with the back of a wooden spoon. Gradually stir in the parameters and simmer together for 4 to 5 minutes.
The result might look as follows:
We examine 'topic of general interest #1' within the 'superlative' scenario of 'frequently used word #1' by taking into account the recent 'superlative' results on 'frequently used word #2'. The relations to 'frequently used word #3' with an additional sector of 'frequently used word #4' are carefully investigated, and allow us to draw 'superlative' new conclusions about 'frequently used word #1'. Using an improved version of the 'frequently used word #2' standard approach, we find Q_eff ≤ 1/3, and \sigma(2,2) = sin^2 (\Pi/3). Furthermore, we discuss the relevance for 'topic of general interest #3'.
Add one handful of good taste. Pour into a 12-pt document. Sprinkle with PACS numbers and keywords.
3) The introduction
Google the topics of general interest and copy and paste for at least 3 paragraphs. Then, claim that recently the importance of 'frequently used words' has been realized. Cite the references looked up the previous day. Refer the interested reader to the reviews. Stir in a little of history. Mix well, but carefully. Make certain not to mash crucial details. Put in a warm spot and leave to rise.
4) The Main Part
Start your investigation by some undoubtedly correct formula, using the standard textbooks. Such might e.g. be the FRW metric, the equal time commutation relations, or the QED Lagrangian. Let stand for one hour. Meanwhile get some coffee. Look up the references from the previous day, hit 'cited by' and randomly repeat various equations from citation #50 and up. Make sure to rename all variables, and not to copy the text prior and after the equations. Add appropriate citations to all equations. Do not interpret the calculation. Knead until you have a smooth text. Let rest for a while, then roll out thin on a clean board.
Add the scalar field. Cut into symmetric shapes, then hide some parts and deconstruct the rest. Sprinkle with symmetry groups. Twist carefully several times.
5) The Results
Preheat the universe. Take main part and cover the entire standard model, let several parameters overhang, and give them unintuitive names. Redefine the variables multiple times, use plenty of not introduced abbreviations, and don't hesitate to apply unmentioned mathematical theorems to rewrite your derivations. Introduce at least one new notation, and drop irrelevant factors 2\Pi or \sqrt{2}.
Stir until smooth and bubbly.
Should open questions appear on the surface, add citations to yourself 'in preparation'.
Plot a random correlation between some parameters, then pick a couple of values you like. Call them typical, and put them aside for later use. Fill the rest of the parameter space into the main part. Cover with discussion. Garnish with footnotes and references to 'private communications'. Bake 30 minutes, or until golden brown.
6) The Conclusions
Take the abstract and punch a hole in the middle. Fill in the typical parameters you put aside earlier. Spell check the document several times.
Best served with a prominent co-author, and acknowledgements of hospitality at top-ranking universities.
PS: Don't forget that the world will end tomorrow 06/06/06, so wear a clean shirt and give your last dollars to the homeless guy on the sidewalk.
1 arxiv mirror
1 12-pt document.
2-3 topics of general interest.
A couple of standard textbooks.
1 handful of good taste.
2 teaspoons of symmetry groups.
1/2 cup of superlatives.
1 box of parameters.
1 scalar field.
Preparation:
The previous day, check the recent papers on the arxives hep-ph / hep-th/ astro-ph and gr-qc. Peel and cut the titles, don't bother with abstracts. Pick out frequently used words, irrespective of their physical content.
Our this year's seasonal recommendations are e.g. 'duality, hidden, AdS, noncommutative, black hole entropy, deconstruct, landscape, emergent, ..."
Also, take the parameters out of their box and pair them with values, e.g. Q_eff ≤ 1/3 and \sigma(2,2) = \sin^2(\Pi/3). For best results, make sure your superlatives contain the all-time favourites 'promising', 'groundbreaking', 'exciting', 'significant' and 'of high interest'.
The Following Day:
1) Prepare the Title.
Prepare the title by using as many of the previously found frequently used words as possible. Mix several of them. Colleagues should ideally feel obliged to cite your paper, but not qualified to actually judge on it.
2) Prepare the Abstract.
Take the 2-3 topics of general interest, wash them thoroughly, until completely free of criticism and discussion. We recommend today 'Dark Energy', 'Quantum Gravity', and 'Large Hadron Collider', or whatever this week's special offer of your local blog scene is. Unwrap the prepared frequently used words, and carefully check whether some have become stale over night.
In a large, non-stick pan, warm the topics of general interest over medium heat. Add the frequently used words and cook until thickened to less than 10 sentences. Add ½ cup of superlatives and mash them with the back of a wooden spoon. Gradually stir in the parameters and simmer together for 4 to 5 minutes.
The result might look as follows:
We examine 'topic of general interest #1' within the 'superlative' scenario of 'frequently used word #1' by taking into account the recent 'superlative' results on 'frequently used word #2'. The relations to 'frequently used word #3' with an additional sector of 'frequently used word #4' are carefully investigated, and allow us to draw 'superlative' new conclusions about 'frequently used word #1'. Using an improved version of the 'frequently used word #2' standard approach, we find Q_eff ≤ 1/3, and \sigma(2,2) = sin^2 (\Pi/3). Furthermore, we discuss the relevance for 'topic of general interest #3'.
Add one handful of good taste. Pour into a 12-pt document. Sprinkle with PACS numbers and keywords.
3) The introduction
Google the topics of general interest and copy and paste for at least 3 paragraphs. Then, claim that recently the importance of 'frequently used words' has been realized. Cite the references looked up the previous day. Refer the interested reader to the reviews. Stir in a little of history. Mix well, but carefully. Make certain not to mash crucial details. Put in a warm spot and leave to rise.
4) The Main Part
Start your investigation by some undoubtedly correct formula, using the standard textbooks. Such might e.g. be the FRW metric, the equal time commutation relations, or the QED Lagrangian. Let stand for one hour. Meanwhile get some coffee. Look up the references from the previous day, hit 'cited by' and randomly repeat various equations from citation #50 and up. Make sure to rename all variables, and not to copy the text prior and after the equations. Add appropriate citations to all equations. Do not interpret the calculation. Knead until you have a smooth text. Let rest for a while, then roll out thin on a clean board.
Add the scalar field. Cut into symmetric shapes, then hide some parts and deconstruct the rest. Sprinkle with symmetry groups. Twist carefully several times.
5) The Results
Preheat the universe. Take main part and cover the entire standard model, let several parameters overhang, and give them unintuitive names. Redefine the variables multiple times, use plenty of not introduced abbreviations, and don't hesitate to apply unmentioned mathematical theorems to rewrite your derivations. Introduce at least one new notation, and drop irrelevant factors 2\Pi or \sqrt{2}.
Stir until smooth and bubbly.
Should open questions appear on the surface, add citations to yourself 'in preparation'.
Plot a random correlation between some parameters, then pick a couple of values you like. Call them typical, and put them aside for later use. Fill the rest of the parameter space into the main part. Cover with discussion. Garnish with footnotes and references to 'private communications'. Bake 30 minutes, or until golden brown.
6) The Conclusions
Take the abstract and punch a hole in the middle. Fill in the typical parameters you put aside earlier. Spell check the document several times.
Best served with a prominent co-author, and acknowledgements of hospitality at top-ranking universities.
PS: Don't forget that the world will end tomorrow 06/06/06, so wear a clean shirt and give your last dollars to the homeless guy on the sidewalk.
Sunday, June 04, 2006
Leaving Home
This weekend is a holiday in Germany - Pentecost, including sunday and monday - and I decided to visit my parents' place. They' re living in a small village in the countryside, a two hours' drive from Frankfurt. It is a very peaceful place in the green, and I really enjoy going there every few weeks or so. At this time of the year, lots of birds are singing all-over in the trees and shrubs, and are feeding their offspring in the many nest boxes my father has put up in the backyard.
Yesterday evening, after arriving and when strolling around in the garden, I was attracted by an especially loud cheeping coming from a nest box in an old cherry tree, just at eye level. This was the home of a family of great tits (Kohlmeise in German, or Parus major), and the youngsters were just about to leave, peeping curiously out of their nest box while waiting for their parents bringing food. I was quite amazed that they were not shy at all, at least against humans, and that I could take photos from a very short distance.
This morning, I wanted to take more pictures, with better light, and I was very lucky: there were two youngsters left in the nest, and they were just about to leave the shelter of their home and to take the step out in the world.
Here it was sitting, the chicken bird, still quite unsure, clamping to a shrub below the nest box, and cheeping for food.
A few minutes later, it was already exploring the lawn nearby.
So, young little bird, good luck to you and your siblings, and beware the cats and magpies...
Yesterday evening, after arriving and when strolling around in the garden, I was attracted by an especially loud cheeping coming from a nest box in an old cherry tree, just at eye level. This was the home of a family of great tits (Kohlmeise in German, or Parus major), and the youngsters were just about to leave, peeping curiously out of their nest box while waiting for their parents bringing food. I was quite amazed that they were not shy at all, at least against humans, and that I could take photos from a very short distance.
This morning, I wanted to take more pictures, with better light, and I was very lucky: there were two youngsters left in the nest, and they were just about to leave the shelter of their home and to take the step out in the world.
Here it was sitting, the chicken bird, still quite unsure, clamping to a shrub below the nest box, and cheeping for food.
A few minutes later, it was already exploring the lawn nearby.
So, young little bird, good luck to you and your siblings, and beware the cats and magpies...
Wednesday, May 31, 2006
Excuse me
The organizers of the conference here in Paris announced there would be no wireless on location. They gave in after three days...
Yesterday, Keith Dienes gave a very interesting talk about his work with Mike Lennek that I will try write more about soon. Also, March-Russell's talk about the 'friendly string landscapes' (astro-ph/0604254) was very, uhm, entertaining.
But since I am very braindead today, now to something completely different.
Here in Paris, the streets are crowded with people from different nations. The French actually seem to be the minority. But it's pretty easy to detect an USAmerican: if you come close to one, you will inevitably trigger an 'Excuse me'.
I wrote in a previous post how weird it is to come back to Germany, and to notice all the small differences to the USA. Amusingly, I just found that the Spiegel intends to write a survival guide for visitors of the soccer world cup in Germany:
Help us write the German Survival Bible
starting from the questions "Why are the shops closed on Sunday?" (Cause things don't change in Europe) to "Are Germans rude?".
This used to irritate me. I always found Germans to be overly polite and discrete. But moving to the US, I had to realize that it's actually true that Germans are considered to be rude, just because of this! I also had to realize that the cultural and sociological differences between Europe and the US are far larger than I thought.
From the article Rules of the Street:
Not that Germans are intrinsically rude. No, mostly they've just learned to come to terms with more day-to-day physical contact that many of us. Walking down the street can often feel like a rugby scrum. In a crowd, many Germans will plow grimly ahead like Arctic ice-breaking ships. Boarding a subway, some Germans like to pretend no one else is there. The guy who tromps on your foot will look surprised -- as if you should be somewhere else.
Even better: if you tromp on an American foot, the foot owner will excuse on a 99% confidence limit :-)
So, excuse me, but I also have to tell you something about the American rudeness, the constant urge to ask 'How are you?'. For most Germans this is considered a very personal question and surely nothing you want to be asked by some Jim or Marc you've never seen before, working at a 7/11, who's just supposed to sell you cigarettes.
To give you an applied example: two months ago I came back to Santa Barbara from a 10 hour trip, my stupid bag had stayed in Denver. Meanwhile they had changed Hammond's lyrics to 'It always rains in Southern California' and I found that the roof in my apartment was leaking. Worse, at 5 to midnight I had to run through the rain -- needless to say I had no umbrella and the car didn't start -- to get to the next groceries store. Standing at the register with painkillers, a pack of tampons, and a Hershey's bar, rain dripping from my hair, the cashier asked me how I am!
I seriously thought about hitting him with a better homes magazine, but that would have been rude. Instead I said: Terrific.
He was lucky not to ask whether I found 'everything alright?'.
Yesterday, Keith Dienes gave a very interesting talk about his work with Mike Lennek that I will try write more about soon. Also, March-Russell's talk about the 'friendly string landscapes' (astro-ph/0604254) was very, uhm, entertaining.
But since I am very braindead today, now to something completely different.
Here in Paris, the streets are crowded with people from different nations. The French actually seem to be the minority. But it's pretty easy to detect an USAmerican: if you come close to one, you will inevitably trigger an 'Excuse me'.
I wrote in a previous post how weird it is to come back to Germany, and to notice all the small differences to the USA. Amusingly, I just found that the Spiegel intends to write a survival guide for visitors of the soccer world cup in Germany:
Help us write the German Survival Bible
starting from the questions "Why are the shops closed on Sunday?" (Cause things don't change in Europe) to "Are Germans rude?".
This used to irritate me. I always found Germans to be overly polite and discrete. But moving to the US, I had to realize that it's actually true that Germans are considered to be rude, just because of this! I also had to realize that the cultural and sociological differences between Europe and the US are far larger than I thought.
From the article Rules of the Street:
Not that Germans are intrinsically rude. No, mostly they've just learned to come to terms with more day-to-day physical contact that many of us. Walking down the street can often feel like a rugby scrum. In a crowd, many Germans will plow grimly ahead like Arctic ice-breaking ships. Boarding a subway, some Germans like to pretend no one else is there. The guy who tromps on your foot will look surprised -- as if you should be somewhere else.
Even better: if you tromp on an American foot, the foot owner will excuse on a 99% confidence limit :-)
So, excuse me, but I also have to tell you something about the American rudeness, the constant urge to ask 'How are you?'. For most Germans this is considered a very personal question and surely nothing you want to be asked by some Jim or Marc you've never seen before, working at a 7/11, who's just supposed to sell you cigarettes.
To give you an applied example: two months ago I came back to Santa Barbara from a 10 hour trip, my stupid bag had stayed in Denver. Meanwhile they had changed Hammond's lyrics to 'It always rains in Southern California' and I found that the roof in my apartment was leaking. Worse, at 5 to midnight I had to run through the rain -- needless to say I had no umbrella and the car didn't start -- to get to the next groceries store. Standing at the register with painkillers, a pack of tampons, and a Hershey's bar, rain dripping from my hair, the cashier asked me how I am!
I seriously thought about hitting him with a better homes magazine, but that would have been rude. Instead I said: Terrific.
He was lucky not to ask whether I found 'everything alright?'.
Monday, May 29, 2006
Paris, Planck 2006
This week, I am in Paris at the conference
Planck 2006: From the Electroweak to the Planck Scale
which is so far really nice. The company is pleasant, the food is excellent, the seats in the auditorium are extremely comfortable to sleep in, and - oh yes - the talks are okay so far.
I can't pass a single chocolaterie without picking some pralines. The coffee tastes like coffee, the cheese tastes like cheese, the traffic is still suicidal, Notre Dame is still here, and the French still smoke in public. That's the nice thing about Europe: it's so reliable.
Vive la France, B.
Planck 2006: From the Electroweak to the Planck Scale
which is so far really nice. The company is pleasant, the food is excellent, the seats in the auditorium are extremely comfortable to sleep in, and - oh yes - the talks are okay so far.
I can't pass a single chocolaterie without picking some pralines. The coffee tastes like coffee, the cheese tastes like cheese, the traffic is still suicidal, Notre Dame is still here, and the French still smoke in public. That's the nice thing about Europe: it's so reliable.
Vive la France, B.
Monday, May 22, 2006
Nonlocality
I am relieved to see that Germany is still Germany. The weather is rainy, people drive like nuts, and everyone is unfriendly. Each time I come back for a visit I find it harder to localize my interactions. Crossing the street without being run over has become a challenge. The currency looks funny. Where do I get coffee to go, or aspirin on a Sunday afternoon? I go through the aisles in the grocery store, mumbling 'excuse me, thank you' and people stare at me with wonder. Not so much because I excuse, but because there is nothing to excuse for. And have avocados always been green?
Besides this, Germany is going nuts because of the soccer world cup. No street corner without advertisements, no magazine without reports, no good German without excitement. Glad to say, I leave before the fun starts.
I mentioned some time ago that I stumbled across this paper:
Relational EPR
Authors: Matteo Smerlak, Carlo Rovelli
quant-ph/0604064
It took me some while to make up my mind, but here is a rough summary of my understanding and my opinion.
The so-called collapse of the wave-function, caused by the measurement process in quantum mechanics, is commonly considered to be a problem because it is non-local. Even though such collapse does not allow to actually transmit information between observers, it is unpretty.
Take a box with two particles, about which you know that the total spin is zero. Then divide your system into two particles, sending one to observer A, one to observer B. Quantum mechanics tells you the state is entangled before any further measurement is made, meaning you can't say what the spin of each particle is. When observer A has made his measurement, the outcome has to be either + or - 1. Let's say, it is +1. Since the total spin is zero, the other particle then has to go into state with spin -1. Instantaneously.
Now the claim of the relational interpretation is that in the above it was omitted to take into account that the measurement device, or the observer himself, also are subject to quantum mechanics. Therefore, strictly speaking, the outcome +1 of the measurement for A is not global. It is +1 as seen by observer A, it is a measurement relative to A.
The main statement is that there is no need for a non-local collapse of the wave-function if one takes this quantum mechanical relativeness of observers really serious. Drop the assumption of the non-locality, and assume instead that A measures something, and B measures something. As long as observer A and B don't compare their measurements, there is no problem. But if they do, their comparison is an interaction, subject to quantum mechanics, and has to be treated like such. As shown in the paper, if you describe the comparison as an quantum mechanical interaction, both observers will always agree on their description of the experiment. "It is clear that everybody sees the same elephant."
As I understand it, this means roughly the following. If A measures +1 and B -1, or vice versa, there is no problem. But if that always were the case then we were back to the collapse. Now the new thing is, let A measure +1, and B measure +1. That doesn't worry us as long as they don't compare their measurements. When they do (back in causal contact) B will find A's measurement in agreement with his, meaning 'A as seen by B' is -1, and also A will find B's measurement in agreement with his 'B as seen by A' is -1.
Should I badly have misinterpreted this, I would be very grateful if someone could enlighten me.
You might also want to look up Alejandro's blog, Christine's blog and the Physicsforums.
It seems to me that this might be possible to write down on a paper. But I can't make too much sense out of it. In particular, I have a problem with the above elephant, alias, the classical limit. As long as they are not in causal contact, observer A and B make up their own stories about what is happening. Yet, when they talk to each other, they both always agree. Not because their stories are identical, but because they interpret to other observer's story through some measurement as being identical to their own story.
But suppose A has a dog, and he agrees with B to kill it when he measures +1. A and B separate, are out of causal contact. Both measure +1. A kills the stupid dog.
Then he comes back into causal contact with B, and of course he takes the dog, which is nothing but a macroscopic result of a quantum measurement. But no matter what, B will always have to find that the dog is alive.
This reminds me of some conversations I have with my grandmother. Being almost deaf she just hears what agrees with her story of the universe. I goes somewhat like this
Me: "I hear his mom is really worried"
My granny: "It's so great he's getting married!"
Me: "No, I mean, they split up recently."
My granny: "Yes, that's how it's supposed to be."
Me: "But he left - HE HAS MOVED OUT."
My granny: "She has every reason to be proud."
I admit that I envy my granny for her ability to make up her own reality. The bottomline of the relational interpretation is essentially, that we all have our own reality, and no matter how hard we try to talk to each other, we will never agree. But we will never notice that we don't. On a philosophical level, I find that to depressing to like it. In addition, I feel specifically non-local today. Looking forward to your feedback, B.
Besides this, Germany is going nuts because of the soccer world cup. No street corner without advertisements, no magazine without reports, no good German without excitement. Glad to say, I leave before the fun starts.
I mentioned some time ago that I stumbled across this paper:
Relational EPR
Authors: Matteo Smerlak, Carlo Rovelli
quant-ph/0604064
We argue that EPR-type correlations do not entail any form of "non-locality", when viewed in the context of a relational interpretation of quantum mechanics. The abandonment of strict Einstein realism advocated by this interpretation permits to reconcile quantum mechanics, completeness, (operationally defined) separability, and locality.
It took me some while to make up my mind, but here is a rough summary of my understanding and my opinion.
The so-called collapse of the wave-function, caused by the measurement process in quantum mechanics, is commonly considered to be a problem because it is non-local. Even though such collapse does not allow to actually transmit information between observers, it is unpretty.
Take a box with two particles, about which you know that the total spin is zero. Then divide your system into two particles, sending one to observer A, one to observer B. Quantum mechanics tells you the state is entangled before any further measurement is made, meaning you can't say what the spin of each particle is. When observer A has made his measurement, the outcome has to be either + or - 1. Let's say, it is +1. Since the total spin is zero, the other particle then has to go into state with spin -1. Instantaneously.
Now the claim of the relational interpretation is that in the above it was omitted to take into account that the measurement device, or the observer himself, also are subject to quantum mechanics. Therefore, strictly speaking, the outcome +1 of the measurement for A is not global. It is +1 as seen by observer A, it is a measurement relative to A.
The main statement is that there is no need for a non-local collapse of the wave-function if one takes this quantum mechanical relativeness of observers really serious. Drop the assumption of the non-locality, and assume instead that A measures something, and B measures something. As long as observer A and B don't compare their measurements, there is no problem. But if they do, their comparison is an interaction, subject to quantum mechanics, and has to be treated like such. As shown in the paper, if you describe the comparison as an quantum mechanical interaction, both observers will always agree on their description of the experiment. "It is clear that everybody sees the same elephant."
As I understand it, this means roughly the following. If A measures +1 and B -1, or vice versa, there is no problem. But if that always were the case then we were back to the collapse. Now the new thing is, let A measure +1, and B measure +1. That doesn't worry us as long as they don't compare their measurements. When they do (back in causal contact) B will find A's measurement in agreement with his, meaning 'A as seen by B' is -1, and also A will find B's measurement in agreement with his 'B as seen by A' is -1.
Should I badly have misinterpreted this, I would be very grateful if someone could enlighten me.
You might also want to look up Alejandro's blog, Christine's blog and the Physicsforums.
It seems to me that this might be possible to write down on a paper. But I can't make too much sense out of it. In particular, I have a problem with the above elephant, alias, the classical limit. As long as they are not in causal contact, observer A and B make up their own stories about what is happening. Yet, when they talk to each other, they both always agree. Not because their stories are identical, but because they interpret to other observer's story through some measurement as being identical to their own story.
But suppose A has a dog, and he agrees with B to kill it when he measures +1. A and B separate, are out of causal contact. Both measure +1. A kills the stupid dog.Then he comes back into causal contact with B, and of course he takes the dog, which is nothing but a macroscopic result of a quantum measurement. But no matter what, B will always have to find that the dog is alive.
This reminds me of some conversations I have with my grandmother. Being almost deaf she just hears what agrees with her story of the universe. I goes somewhat like this
Me: "I hear his mom is really worried"
My granny: "It's so great he's getting married!"
Me: "No, I mean, they split up recently."
My granny: "Yes, that's how it's supposed to be."
Me: "But he left - HE HAS MOVED OUT."
My granny: "She has every reason to be proud."
I admit that I envy my granny for her ability to make up her own reality. The bottomline of the relational interpretation is essentially, that we all have our own reality, and no matter how hard we try to talk to each other, we will never agree. But we will never notice that we don't. On a philosophical level, I find that to depressing to like it. In addition, I feel specifically non-local today. Looking forward to your feedback, B.
This used to be my playground
This used to be my childhood dream
This used to be the place I ran to
Whenever I was in need
Of a friend
Why did it have to end
And why do they always say
Don't look back
Keep your head held high
Don't ask them why
Because life is short
And before you know
You're feeling old
This used to be my childhood dream
This used to be the place I ran to
Whenever I was in need
Of a friend
Why did it have to end
And why do they always say
Don't look back
Keep your head held high
Don't ask them why
Because life is short
And before you know
You're feeling old
Thursday, May 18, 2006
Monday, May 15, 2006
The Principle of Finite Imagination
Airports have a strange atmosphere. I frequently receive emails from friends who sit at airports, and contemplate their lives, go into philosophical meditations about the meaning of reality, or the mystery of our existence. Yesterday, I was stuck on such a meditation place, even worse, I was stuck there with nothing else to read but Susskind's book, "The Cosmic Landscape".
The last dinners I had in the company of physicists inevitably ended up with a discussion of the anthropic principle. At which point I very suddenly got very tired and left early. Being asked recently for my opinion on the matter I said I have none. As Stefan told me, that's not good, I am supposed to have an opinion about everything! No matter if it is a sensible one.
To get to my opinion or it's absence, let me introduce you to Oliver. I got to know Oliver as 'Olli_6703' in some online discussion around 2001. Since then he lost his job, his long-time girlfriend, an had an unfortunate accident that left him with a permanent limp. By now he is an alcoholic. I guess, drinking is his way to arrange himself with the insight that life sucks.
It's hard to say why he ended up like this. He's been very sportive, and suddenly being confined to slow-motion was really tough on him. It might also have mattered that his girlfriend did better in her job than he did, and she chose to live alone instead of with him - something he repeated endlessly and was unable to understand. Had she cheated on him and moved in with someone else it might have made more sense to Olli. But she stayed ALONE! Or then why did he have to loose his job in the first place, which started the whole series of unfortunate events? The company he worked for installed phone systems. They went broke cause the companies that were in need of these systems went broke. I am neither a therapist, a sociologist, nor an economist and don't know what the reason is. Maybe it's "just" the genes.
Sorry for the sad story.
Now imagine you are an atom in one of Olli's liver cells. You are a smart atom and have figured out the Standard Model. You had no need for some weird assumption like gravity, but you have found very elegant laws that describe the exchange of molecules in you cell. You even managed to measure the extension of the liver! To your very surprise you found that it has been growing recently. You and the other atoms are very puzzled by this, and you try to come up with a theory to explain it.
Maybe you introduce some a-essence that causes the liver to grow, but where does it come from and why has it only become important recently? Some of your colleagues have suggested that there are other meta-livers outside yours which obey different laws, but hey, you are a serious scientist, and that's just too weird. Besides this, it doesn't really explain anything. Some insist on a fourth force, based on some kind of a principle (you keep forgetting the name). But this force would only be important on completely unobservable distance scales. Though they claim it's important for a theory of everything you fail to see the point. Some even work on an extension of this theory that implies that the cosmos is nothing but a braid, but you can't really follow their arguments.
Then there are some others who found a beautiful string-like winding structure which they claim contains all the information necessary to explain the liver and probably more! But they are unable to predict anything from it. They keep repeating it's elegant, and keep making conjectures about things they don't even know what they are.
However, none of these incredible theories was able to help you understanding the strange place that you live in. Recently, it's been dubbed a crisis in liver-physics.
How smart has the atom to be to imagine the existence of a human being? To imagine several billions of them? Of the world they live in? With all the global and sociological problems? How smart has the atom to be to imagine the existence of the earth, the solar system, our galaxy, the universe, or even multiverses? The poor atom was just looking for a theory of everything, just some few equations that extend the Standard Model such that they explain the observed liver growth.
To come back to the anthropic principle: It is certainly right, if we weren't here then we wouldn't worry why we are here. But I am a physicist because I hope that I can understand at least part of the games that nature is playing on us. Retreating to the anthropic principle means to me to give up the believe that there is something to understand.
Maybe I am just just stubborn.
But I am surprised that just because we currently can not imagine a way out of the so-called 'crisis' in theoretical physics, so much effort goes into explaining why we can't explain what we want to explain. So much time goes into arguing why we can't argue. And smart physicists declare bugs to features, instead of looking for other ways to find insights.
Needless to say, I believe that there is a reason why the universe is the way it is. It might just be very hard to find. Try to imagine there is an universe in every gluon, and our universe is a gluon in an atom in some liver-cell of an alcoholic cosmic terrorist, who aligns his angular momenta on the axis of evil while his followers are forcing cosmological natural selection on innocent citizens.
I would rather come to the (admittedly depressing) conclusion that the human mind just might not be able to solve the problems we are currently facing, than being satisfied with the statement that there is nothing to explain. Going anthropic is not a solution to anything. If anything it's reason to quit physics.
Fortunately, it is in the nature of human beings to never be satisfied. Therefore, I have no doubt that this crisis is temporarily.
That's the reason why I don't spend time on thinking about the anthropic principle and the meaning of the string landscape, not even at airports. There are just more interesting topics.
(Like, where is the next Starbucks, and what do the Americans do with their milk foam without spoons?)
See also Alejandro's recent post about the lamdscape.
The last dinners I had in the company of physicists inevitably ended up with a discussion of the anthropic principle. At which point I very suddenly got very tired and left early. Being asked recently for my opinion on the matter I said I have none. As Stefan told me, that's not good, I am supposed to have an opinion about everything! No matter if it is a sensible one.
To get to my opinion or it's absence, let me introduce you to Oliver. I got to know Oliver as 'Olli_6703' in some online discussion around 2001. Since then he lost his job, his long-time girlfriend, an had an unfortunate accident that left him with a permanent limp. By now he is an alcoholic. I guess, drinking is his way to arrange himself with the insight that life sucks.
It's hard to say why he ended up like this. He's been very sportive, and suddenly being confined to slow-motion was really tough on him. It might also have mattered that his girlfriend did better in her job than he did, and she chose to live alone instead of with him - something he repeated endlessly and was unable to understand. Had she cheated on him and moved in with someone else it might have made more sense to Olli. But she stayed ALONE! Or then why did he have to loose his job in the first place, which started the whole series of unfortunate events? The company he worked for installed phone systems. They went broke cause the companies that were in need of these systems went broke. I am neither a therapist, a sociologist, nor an economist and don't know what the reason is. Maybe it's "just" the genes.
Sorry for the sad story.
Now imagine you are an atom in one of Olli's liver cells. You are a smart atom and have figured out the Standard Model. You had no need for some weird assumption like gravity, but you have found very elegant laws that describe the exchange of molecules in you cell. You even managed to measure the extension of the liver! To your very surprise you found that it has been growing recently. You and the other atoms are very puzzled by this, and you try to come up with a theory to explain it.Maybe you introduce some a-essence that causes the liver to grow, but where does it come from and why has it only become important recently? Some of your colleagues have suggested that there are other meta-livers outside yours which obey different laws, but hey, you are a serious scientist, and that's just too weird. Besides this, it doesn't really explain anything. Some insist on a fourth force, based on some kind of a principle (you keep forgetting the name). But this force would only be important on completely unobservable distance scales. Though they claim it's important for a theory of everything you fail to see the point. Some even work on an extension of this theory that implies that the cosmos is nothing but a braid, but you can't really follow their arguments.
Then there are some others who found a beautiful string-like winding structure which they claim contains all the information necessary to explain the liver and probably more! But they are unable to predict anything from it. They keep repeating it's elegant, and keep making conjectures about things they don't even know what they are.However, none of these incredible theories was able to help you understanding the strange place that you live in. Recently, it's been dubbed a crisis in liver-physics.
How smart has the atom to be to imagine the existence of a human being? To imagine several billions of them? Of the world they live in? With all the global and sociological problems? How smart has the atom to be to imagine the existence of the earth, the solar system, our galaxy, the universe, or even multiverses? The poor atom was just looking for a theory of everything, just some few equations that extend the Standard Model such that they explain the observed liver growth.
To come back to the anthropic principle: It is certainly right, if we weren't here then we wouldn't worry why we are here. But I am a physicist because I hope that I can understand at least part of the games that nature is playing on us. Retreating to the anthropic principle means to me to give up the believe that there is something to understand.
Maybe I am just just stubborn.
But I am surprised that just because we currently can not imagine a way out of the so-called 'crisis' in theoretical physics, so much effort goes into explaining why we can't explain what we want to explain. So much time goes into arguing why we can't argue. And smart physicists declare bugs to features, instead of looking for other ways to find insights.
Needless to say, I believe that there is a reason why the universe is the way it is. It might just be very hard to find. Try to imagine there is an universe in every gluon, and our universe is a gluon in an atom in some liver-cell of an alcoholic cosmic terrorist, who aligns his angular momenta on the axis of evil while his followers are forcing cosmological natural selection on innocent citizens.
I would rather come to the (admittedly depressing) conclusion that the human mind just might not be able to solve the problems we are currently facing, than being satisfied with the statement that there is nothing to explain. Going anthropic is not a solution to anything. If anything it's reason to quit physics.
Fortunately, it is in the nature of human beings to never be satisfied. Therefore, I have no doubt that this crisis is temporarily.
That's the reason why I don't spend time on thinking about the anthropic principle and the meaning of the string landscape, not even at airports. There are just more interesting topics.
(Like, where is the next Starbucks, and what do the Americans do with their milk foam without spoons?)
See also Alejandro's recent post about the lamdscape.
Perimeter Institute
This is the first time I see Waterloo not covered by snow. When I was here in December last year, I took the wrong exit from the building and found what I thought was a large untouched field of snow. After too much brain activity during the day, I wasn't in the mood to figure out how the key-card works. I decided I could manage 3 inches white fluffy stuff on the pavement. After some steps however, I stumbled down an invisible edge, and stood more than knee-deep in snow. I was cursing whoever constructed this stupid yard.
However, today I solved the mystery of the annoying edge: it was the pool! (see photo below).
Greetings from Canada,
B.
Friday, May 12, 2006
Emmy Noether
I made my PhD at Frankfurt University in August 2003. From 2001 on Stefan, Marcus, and I lead a group we called LXD - Large eXtra Dimensions. Its official supervisor was Horst. From the very beginning on this group was quite successful and it seemed to be very attractive for young students. Soon we had several undergraduate and graduate members who were very interested in working with us. Temporarily, we even had encounters with mathematicians from the other side of the building in our group meetings!
During the first years, we managed to use money from other sources to support the group members, but soon it became clear that we would need an own grant to enable ongoing research. We applied for support at the German Research Foundation (DFG). The support was declined at the end of 2003. In January 2004, I moved to the US.
Here is a photo of (most of) the group (missing: Katja Poppenhaeger), taken around Christmas 2003. From left to right: Marcus Bleicher, Stefan Hofmann, Sabine Hossenfelder, Christoph Rahmede, Ulrich Harbach, Joerg Ruppert, Sascha Vogel, Horst Stoecker.
I am traveling the next 3 weeks, so the frequency of my posts will crucially depend on the speed of my internet connection.
During the first years, we managed to use money from other sources to support the group members, but soon it became clear that we would need an own grant to enable ongoing research. We applied for support at the German Research Foundation (DFG). The support was declined at the end of 2003. In January 2004, I moved to the US.
Here is a photo of (most of) the group (missing: Katja Poppenhaeger), taken around Christmas 2003. From left to right: Marcus Bleicher, Stefan Hofmann, Sabine Hossenfelder, Christoph Rahmede, Ulrich Harbach, Joerg Ruppert, Sascha Vogel, Horst Stoecker.
While I was sitting in Arizona and cursing the blisters from my Flip-flops, I had plenty of time to wonder about the complete absence of future my life suddenly suffered from. Then I found that the DFG has an excellent program, named the Emmy-Noether-program. Its purpose is:
To provide outstanding researchers with the opportunity to rapidly qualify for a leading position in science and research or for a university teaching career by leading an Independent Junior Research Group and assuming relevant teaching duties.
To recruit young, outstanding postdocs working abroad (back) to Germany.
In summer 2004 I applied for this program, as it was one of the little choices that seemed to make sense to me. Not only would it have meant a 5-6 year position, but I would have been able to hire collaborators, and to actually pursue my research interests! (As opposed to, say, cursing my blisters). This was such a great opportunity that it seemed worth the effort to write a proposal despite the small chances to finally get the grant (all of a sudden I heard from about thousands of people who did not get it).
Unfortunately, during the time my application was being processed, the guidelines for the program changed significantly. (The original version consisted of two separate phases). In February 2005, I received the decision from the DFG. They wrote they had to reject my application. I did not fulfill the requirements for the new guidelines. According to these, I needed at least two years of stay abroad, one of which was missing. Instead, the DFG was very generous and offered me to instead provide a scholarship for this missing year. After this year, I could apply again for the Emmy Noether program. Joerg and I found that very funny. Essentially they said: "You are great, please stay in the US."
I applied again for the program in summer 2005. The regulations had become significantly more difficult and bureaucratic. Among other things, the application had to be typeset in Arial, printed on A4 paper and two-hole-punched (you don't believe that? Read Section IV: Proposal Formats and Submission). Living in the US, the latter two requests I found almost impossible to fulfil. (Well, if you live in Germany, try to print 50 pages on letter format and get them 3-hole-punched).
Since I had no problem picturing me being unemployed and sleeping on the beach any time soon, I also applied for regular postdoc positions around November 2005. To make a long story short, I accepted the offer from the Perimeter Institute in January 2006. Then, in February, the DFG told me that I got the grant for the Emmy Noether. I asked them whether it was possible to postpone the starting date for one year. They said no. PI assured me every possible kind of support for a collaboration with Germany, so I offered the DFG that I would initiate and support the project from Canada (though I had to be talked into making this offer). Again, they said no, the grant is attached to my person, and no one else but me can make Phenomenological Quantum Gravity (such the title of the proposal) in Germany. They asked me to reconsider my decision.
Yesterday, I wrote them a lengthy explanation why I would stick to my decision, go to Canada, and decline the German offer.
This, I guess, is the end of the story I started in a previous post. I find it very sad that the possibility to start a group on Quantum Gravity in Germany fails due to a lack of flexibility in program guidelines.
Dear reader: should you qualify for the Emmy Noether Program and consider applying for a grant, please feel free to contact me. ESPECIALLY, if you are interested in Phenomenological Quantum Gravity, as it seems, the DFG is in principle willing to support such research.
I am traveling the next 3 weeks, so the frequency of my posts will crucially depend on the speed of my internet connection.
Wednesday, May 10, 2006
The Minimal Length Scale
Yesterday, I gave a seminar here at UCSB about my recent work, and so I will use the opportunity for some self-advertisement. You find the slides (PDF) online:
Here is a brief summary about the main statements. In 2003 my collaborators and I worked out a model that includes the notion of a fundamental minimal length into quantum mechanics and quantum field theories. It builds up on earlier works, most notably by Achim Kempf, but extends these approaches -- and is less mathematical but instead focused on applications. The model turned out to be useful to derive modifications to Feynman rules, and allowed us to compute cross-sections (at least at tree level).
I talked about quantum field theories with a minimal length scale, their interpretation, application, and their relation to Deformed Special Relativity (DSR). The talk is mainly based on my recent paper:
And the basics of the model are from our '03 paper
Here is a brief summary about the main statements. In 2003 my collaborators and I worked out a model that includes the notion of a fundamental minimal length into quantum mechanics and quantum field theories. It builds up on earlier works, most notably by Achim Kempf, but extends these approaches -- and is less mathematical but instead focused on applications. The model turned out to be useful to derive modifications to Feynman rules, and allowed us to compute cross-sections (at least at tree level).
Modifications of such a minimal length should become important at energies of about the inverse of that length. The Planck length is expected to play the role of such a minimal length. In case there exist large extra dimensions, the 'true' Planck length might be about 10-4 fm and be testable at the LHC. Actually, what one would find in this case is that there is nothing more to find. Once one reaches the minimal length scale, it is not possible to achieve a higher resolution of structures, no matter what. (And thus there's no point in building a larger collider.)
The motivations for the existence of such a minimal length are manifold, you can e.g. look up my brief review
Essentially the reason for the emergence of a fundamentally finite resolution is that at Planckian energies spacetime gets strongly distorted and it's not possible anymore to resolve finer structures. Also, such a minimal length acts as a regulator in the ultra-violet, which is a nice thing.
The basic idea of my model is to effectively describe such a finite resolution by assuming that no matter how high the energy of a particle gets, it's wavelength never becomes arbitrarily small. To do so, just drop the usual linear relation between wave-vector and momentum. With this, one can then quantize, 2nd quantize, etc. Note, that in my model, there is no upper bound on the energy. There is instead a lower bound on the wave-length. The energy and the momentum of the particles have the usual behavior and interpretation.
While writing the paper in 2003, I could not avoid noticing some kind of a problem with Lorentz-invariance. Apparently, a minimal length should not undergo a Lorentz-contraction and become smaller than minimal. However, it turned out that the quantities with the funny transformation behaviour never entered any observables. It was thus completely sufficient to assume that such a transformation exists, without knowing how it actually looked like.
It was only 2 years later that I realized the connection of this model to DSR which apparently has become enormously fashionable over the last years. (I just found that by now there is even a textbook on DSR available.) By now there are a vast number of papers on the subject. The one half are very phenomenological, the other half are very algebraical investigations. However, as far as I am aware, DSR-theories are still struggling to formulate a consistent quantum field theory. (There was a very notable recent attempt by Tomasz Konopka to set up a field theory with DSR, but imo the model has more than one flaw.)
Most importantly, DSR faces two problems: the one is the soccer-ball problem, the other one is the question of conserved quantities. To briefly address those:
- In DSR there is an upper limit on the energy of the particle. Such a limit should not be present for macroscopic objects (e.g. a soccer-ball). The problem is how to get the proper multi-particle limit for which the deformed Lorentz-transformation behaviour should un-deform. (There has been recent progress towards this direction, see. e.g. Joao's paper, but I think the issue is far from being solved).
- The second problem is that since in DSR the 'physical' momenta do not transform linearly, they do not add linearly, and thus one has to think about what quantities are conserved in interactions - or, how they are defined in the first place. To take a very simple example: usually, the square of the center of mass energy s for two particles with momenta p and q is s = (p+q)^2. Usually, s is Lorentz-invariant (its a scalar), and since the tranformation is linear on p and q, the result of boosting p+q is the same as boosting p, boosting q and then adding both. Not so in DSR. So, which quantity is the center of mass energy? Is it still a scalar? Is it conserved? The situation gets worse for more particles. (Again there has been progress, see e.g. the paper by Judes and Visser, but I think the issue is far from being solved.)
I should admit that I maybe just don't understand that. At least, it is confusing to me, and even after thinking about it several months, I still can't make sense out of it.
Therefore, lets get back to what I understand and that is how things work in my model. Free particles do not experience any quantum gravitational effects. They behave and propagate as usual. When they make an interaction with high center of mass energy and small impact parameter, quantum gravitational effects can strongly disturb the spacetime. An exchange particle in this region then experiences the effects of DSR. It's wavelength has a lower bound, and there is a limit to the resolution that can be reached in such an interaction. This is schematically shown in the figure below
The quantities that are conserved are as usual the asymptotic momenta of the particles. Composite objects do not experience any effects since they are not usually bound such that the gravitational interaction is very strong. Thus, both of the above mentioned problems of DSR are not present using this approach.
I should be so fair to point out that in my scenario there is no modification of the GZK-cutoff, which is the most popular prediction from DSR.
To briefly recall the problem: protons propagating through the universe can make cosmic rays when they hit the earth's atmosphere. The total energy of these events can be measured (at least a lower bound). A proton with very high energy however, should be able to make pions by interacting with photons of the CMB. If the energy of the proton is such high, it can not travel far enough, will not reach the earth, and can not produce a cosmic ray. This cutoff is expected to occur at a certain energy, the so-called GZK-cutoff. There are some events that seem to indicate that cosmic rays above this cutoff have been detected (data has to be confirmed). This has lead to a huge amount of speculation for the cause of the non-presence of the GZK-cutoff.
To come back to main subject, the reason why there is no modification of the GZK-cutoff in my model is very easy to see: the cutoff is a sudden increase in a cross-section as a function of the center of mass energy. Both, the center of mass energy and the cross-section are Lorentz-scalars. The cut-off has been measured on earth at a certain center of mass energy (about one GeV). Boosting it into the reference frame of the fast proton does not change the necessary center of mass energy.
Here is something that still puzzles me: DSR is argued to be observer independent. Now I wonder how can it be that in the one system the cut-off is at a different center of mass energy than in the other system. And if it was so, couldn't one then use exactly this to distinguish between observers?
Anyway, the bottomline is that my model is an alternative interpretation of DSR. It has less problems, but is also less spectacular. I am a particle physicist, and I would really like to see a self-consistent formulation of a QFT with the 'usual' DSR interpretation - maybe that would help me to understand it.
Update Dec. 9th 2006: see also Deformed Special Relativity
Monday, May 08, 2006
Why do we live in 3+1 dimensions?
People warned me that writing a blog would take a lot of time. Hopelessly naive as I am, I thought, well, I would just not post anything if I am too busy. It seems, I underestimated the persistent interest of my fellow readers.
So, I wrote last week that I volunteered to bring an Honest Question to our gravity lunch. This meeting takes place here at the Department pf Physics at UCSB every Friday at noon. Lately, the discussion has been mostly about black thingies. I tried to come up with a question that would roughly fit into the string dominated atmosphere and the time constraint, and eventually settled on "Why do we live in 3+1 dimensions?"
The last time I wrote this question down, someone was so nice to tell me that 3+1=4. Therefore, let me point out that the question actually consists of two parts: a) why 3 spacelike dimensions and b) why Lorentzian signature -- I will only discuss a) in the following.
But of course I had to make the question more complicated to be appropriate for the gravity lunch. To do so, I picked the paper
Relaxing to Three Dimensions
Authors: Andreas Karch, Lisa Randall
Phys.Rev.Lett. 95 (2005) 161601 (hep-th/0506053)
Last time I was at PI, I happened to hear a seminar by Lisa Randall about the paper, you can find it online at the streaming seminars (click on "seminar series", then "filter by presenter" Lisa Randall - comes under L not R, and hit "search" -- they promised they are working on an improvement...).
While writing this post, I also found an article about the paper from economist.com
A braney theory: An explanation for the anthropic principle comes a little closer
Here is a quick summary: The idea is to take a 9+1 dimensional non-compactified spacetime. Fill it with gases of d-branes, each with an energy density and pressure. And let it expand with a Friedmann-Robertson-Walker (FRW) ansatz, i.e. homogeneous and isotropic. The paper is quite impressing, as it only contains 4 equations, which are the FRW equations in higher dimensions.
Now the question is what happens to the gases of the d-Branes.
- When the branes don't interact, the energy density will dilute slower the larger the dimension of the brane - because it can dilute only into the dimensions it does not occupy. In terms of the FRW scale parameter a, the density goes with a power -9+d.
- But they can interact, i.e. branes can meet anti-branes and decay. This decay goes slower the larger the dimensionality of the brane - because there is less space to decay into. In terms of the time t, the density goes with -9+d.
- Then the question remains whether d-branes do find each other to interact. It turns out from dimensional arguments that they will generically find each other and attempt to decay when 2*(d+1) is larger or equal 9.
From 3. it follows that 3-branes are those with the largest dimensionality that will not interact. From those that will not interact, they are also those whose energy density will dilute the least. For d larger than 3, the 9-branes do always overlap and therefore are gone. The 8-branes are apparently more complicated, but can be argued away. The only argument for the latter that I understood was that in some scenarios there just are no 8-branes. Let's assume that works.
Then, in terms of energy densities, 3-branes and 7-branes will dominate. Such the conclusion of the paper. I understand why one would like to have 3-branes. As to the 7-branes, the paper states
A configuration that is a natural candidate for four-dimensional gravity is the intersection of three 7-branes where the intersection has spacetime dimension four.
Among others, a question I raised on Friday was why this is natural. I learned that the physics on such an intersection allows chiral fermions. That explains why they write it is natural to live at this intersection. But not why it is natural.
More importantly, I fail to see why the densities of the gases are relevant for the question why we experience three dimensions. Even if the higher dimensional thingies decay, the lower dimensional ones are still around, no matter what their density is. Why is the energy density the selection criterion?
And another point that I still don't understand is how it is possible that the ongoing time-dependence in the bulk does not influence the physics (locally localized gravity) on the brane or brane/intersection. I mean, one has to make sure that things we call constant actually are constant (restrictions apply).
Bottom-line: I like the paper, I like the idea and the minimalistic setup. Unfortunately, it seems to me some of the arguments are more wishful thinking than strict conclusions.
I have certainly heard weirder things. I once sat through a seminar while the speaker explained that our universe has 10 dimensions because Pi^2 is approximately 10, and we live on a 3-dimensional submanifold because Pi is close by 3. No, I can't recall the name of the speaker, and I never heard of him again.
On the other hand, it is indeed puzzling that dimensional regularization works only in 4 dimensions, isn't it?
For those of you who are interested, here are some further references
Why do we live in 3+1 dimensions?
Ruth Durrer, Martin Kunz, Mairi Sakellariadou
Brane Gases in the Early Universe
S. Alexander, R.Brandenberger, D.Easson
On the dimensionality of spacetime
Max Tegmark
(thanks to Garrett for the reference)
Why is Space Three Dimensional
Ingemar Bengtsson
Oh, and due to a certain lack of volunteers, I agreed to bring another question for the next gravity lunch. Any suggestions?
Tuesday, May 02, 2006
Honest Questions
I volunteered!
I volunteered to bring a question to our gravity lunch next Friday. Now I am wondering what to ask the brainy guys. How about: why are there hundreds of postdocs discussing the existence, properties and numerical investigation of black holes, black branes, black strings, black rings, or short: black things? (Though I have been told the technical term is black THINGIES.) Black thingies may be boosted, rotating, magnetic, deformed, bumpy or bumpier, potentially unstable, but mostly extreme, and certainly in extra dimensions.
Other questions that currently puzzle me is what a particle is, or why women plug out their eyebrows and then paint them back on. But I figure none of these interesting questions is really appropriate.
Besides this I am preparing a seminar I have to give next week here at UCSB. Since the unwritten law is that questions I can answer won't be asked, I currently wonder what a quantum algebra is (don't ask) -- not that it has anything to do with the seminar.
However, thinking about questions, I wasted time classifying the type of questions I have encountered in multiple seminars and parallel sessions:
1. The commenting question
Starts most often with the words: "It is more a comment than a question..." and serves to prove that the person asking knows something about something, most likely his/her own work. This is the most comfortable question to encounter, and can actually be very interesting, even if it has nothing to do with your talk.
2. The completely irrelevant question
Is the most common question, and one that you might want to practice when you like to draw attention to yourself. To give an example, I have been asked once how many pions a black hole emits (couldn't care less). Here are some very universally applicable members of this family
Starts most often as an interruption -- say on slide 2 -- and has the answer: I will come to that later -- say on slide 34. Not satisfied with this answer, the person asking will insist on further and further details, thereby completely destroying the structure of your talk which you have been thinking about for the last weeks. If the chair person fails to pull the pump-gun, my advise is to simply ignore the questions.
Another kind of never-ending question is asked in the end of your talk, and requires you to remember every detail of every calculation, parameters of the numerical investigation, factors 4 Pi, references to people whose names you can't pronounce, starting dates of experiments you can't remember, rotation directions in complex planes, and will make you ask yourself why the fu*k you did this work at all. Maybe we can discuss that in the coffee break.
4. The stupid question
Requires very much politeness, since we don't want to embarrass anybody, do we? Stupid questions are frequently asked by those who missed the beginning of your talk. Like: what is d, when you have been talking about the number of extra dimensions for 1 hour.
5. The dangerous question
Is most often asked by senior scientists and frequently comes with an attempt to appear harmless, like "It is probably a stupid question, but..." or "I must have missed something, but..." In case you encounter such a question, consider faking a heart attack on stage.
6. The honest question
And then there are the occasional honest questions from people who genuinely try to understand your work. Honest questions have made me realize many times what direction to look for further insights, and have brought up viewpoints I might have completely missed on my own.
See also: my new poem Honest Questions.
I volunteered to bring a question to our gravity lunch next Friday. Now I am wondering what to ask the brainy guys. How about: why are there hundreds of postdocs discussing the existence, properties and numerical investigation of black holes, black branes, black strings, black rings, or short: black things? (Though I have been told the technical term is black THINGIES.) Black thingies may be boosted, rotating, magnetic, deformed, bumpy or bumpier, potentially unstable, but mostly extreme, and certainly in extra dimensions.
Other questions that currently puzzle me is what a particle is, or why women plug out their eyebrows and then paint them back on. But I figure none of these interesting questions is really appropriate.
Besides this I am preparing a seminar I have to give next week here at UCSB. Since the unwritten law is that questions I can answer won't be asked, I currently wonder what a quantum algebra is (don't ask) -- not that it has anything to do with the seminar.
However, thinking about questions, I wasted time classifying the type of questions I have encountered in multiple seminars and parallel sessions:
1. The commenting question
Starts most often with the words: "It is more a comment than a question..." and serves to prove that the person asking knows something about something, most likely his/her own work. This is the most comfortable question to encounter, and can actually be very interesting, even if it has nothing to do with your talk.
2. The completely irrelevant question
Is the most common question, and one that you might want to practice when you like to draw attention to yourself. To give an example, I have been asked once how many pions a black hole emits (couldn't care less). Here are some very universally applicable members of this family
- What about the Cosmological Constant?
(Yeah, what about it?) - Can you couple a massive scalar field to your model?
(Sure, but why would I?) - Does that work in an arbitrary number of extra dimensions?
(Some particular number? 10 or 11 by any chance?) - Can you say something about chiral symmetry?
(Plenty, but that's got nothing to do with my talk) - Is there any relation to the recent work by XYZ?
(No idea, never heard of them.)
Starts most often as an interruption -- say on slide 2 -- and has the answer: I will come to that later -- say on slide 34. Not satisfied with this answer, the person asking will insist on further and further details, thereby completely destroying the structure of your talk which you have been thinking about for the last weeks. If the chair person fails to pull the pump-gun, my advise is to simply ignore the questions.
Another kind of never-ending question is asked in the end of your talk, and requires you to remember every detail of every calculation, parameters of the numerical investigation, factors 4 Pi, references to people whose names you can't pronounce, starting dates of experiments you can't remember, rotation directions in complex planes, and will make you ask yourself why the fu*k you did this work at all. Maybe we can discuss that in the coffee break.
4. The stupid question
Requires very much politeness, since we don't want to embarrass anybody, do we? Stupid questions are frequently asked by those who missed the beginning of your talk. Like: what is d, when you have been talking about the number of extra dimensions for 1 hour.
5. The dangerous question
Is most often asked by senior scientists and frequently comes with an attempt to appear harmless, like "It is probably a stupid question, but..." or "I must have missed something, but..." In case you encounter such a question, consider faking a heart attack on stage.
6. The honest question
And then there are the occasional honest questions from people who genuinely try to understand your work. Honest questions have made me realize many times what direction to look for further insights, and have brought up viewpoints I might have completely missed on my own.
See also: my new poem Honest Questions.
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