Stephen Hawking’s 75th Birthday Conference: Impressions

I’m back from Cambridge, where I attended the conference “Gravity and Black Holes” in honor of Stephen Hawking’s 75th birthday.

First things first, the image on the conference poster, website, banner, etc is not a psychedelic banana, but gravitational wave emission in a black hole merger. It’s a still from a numerical simulation done by a Cambridge group that you can watch in full on YouTube.

What do gravitational waves have to do with Stephen Hawking? More than you might think.

Stephen Hawking, together with Gary Gibbons, wrote one of the first papers on the analysis of gravitational wave signals. That was in 1971, briefly after gravitational waves were first “discovered” by Joseph Weber. Weber’s detection was never confirmed by other groups. I don’t think anybody knows just what he measured, but whatever it was, it clearly wasn’t gravitational waves. Also Hawking’s – now famous – area theorem stemmed from this interest in gravitational waves, which is why the paper is titled “Gravitational Radiation from Colliding Black Holes.”

Second things second, the conference launched on Sunday with a public symposium, featuring not only Hawking himself but also Brian Cox, Gabriela Gonzalez, and Martin Rees. I didn’t attend because usually nothing of interest happens at these events. I think it was recorded, but haven’t seen the recording online yet – will update if it becomes available.

Gabriela Gonzalez was spokesperson of the LIGO collaboration when the first (real) gravitational wave detection was announced, so you have almost certainly seen her. She also gave a talk at the conference on Tuesday. LIGO’s second run is almost done now, and will finish in August. Then it’s time for the next schedule upgrade. Maximal design sensitivity isn’t expected to be reached until 2020. Above all, in the coming years, we’ll almost certainly see much better statistics and smaller error bars.

The supposed correlations in the LIGO noise were worth a joke by the session’s chairman, and I had the pleasure of talking to another member of the LIGO collaboration who recognized me as the person who wrote that upsetting Forbes piece. I clearly made some new friends there^^. I’d have some more to say about this, but will postpone this to another time.

Back to the conference. Monday began with several talks on inflation, most of which were rather basic overviews, so really not much new to report. Slava Mukhanov delivered a very Russian presentation, complaining about people who complain that inflation isn’t science. Andrei Linde then spoke about attractors in inflation, something I’ve been looking into recently, so this came in handy.

Monday afternoon, we had Jim Hartle speaking about the No-Boundary proposal – he was not at all impressed by Neil Turok et al’s recent criticism – and Raffael Bousso about the ever-tightening links between general relativity and quantum field theory. Raffael’s was the probably most technical talk of the meeting. His strikes me as a research program that will still run in the next century. There’s much to learn and we’ve barely just begun.

On Tuesday, besides the already mentioned LIGO talk, there were a few other talks about numerical general relativity – informative but also somehow unexciting. In the afternoon, Ted Jacobson spoke about fluid analogies for gravity (which I wrote about here), and Jeff Steinhauer reported on his (still somewhat controversial) measurement of entanglement in the Hawking radiation of such a fluid analogy (which I wrote about here.)

Wednesday began with a rather obscure talk about how to shove information through wormholes in AdS/CFT that I am afraid might have been somehow linked to ER=EPR, but I missed the first half so not sure. Gary Gibbons then delivered a spirited account of gravitational memory, though it didn’t become clear to me if it’s of practical relevance.

Next, Andy Strominger spoke about infrared divergences in QED. Hearing him speak, the whole business of using soft gravitons to solve the information loss problem suddenly made a lot of sense! Unfortunately I immediately forgot why it made sense, but I promise to do more reading on that.

Finally, Gary Horowitz spoke about all the things that string theorists know and don’t know about black hole microstates, which I’d sum up with they know less than I thought they do.

Stephen Hawking attended some of the talks, but didn’t say anything, except for a garbled sentence that seems to have played back by accident and stumped Ted Jacobson.

All together, it was a very interesting and fun meeting, and also a good opportunity to have coffee with friends both old and new. Besides food for thought, I also brought back a conference bag, a matching pen, and a sinus infection which I blame on the air conditioning in the lecture hall.

Now I have a short break to assemble my slides for next week’s conference and then I’m off to the airport again.

Away Note

I’ll be traveling the next two weeks. First to Cambridge to celebrate Stephen Hawking’s 75th birthday (which was in January), then in Trieste for a conference on “Probing the spacetime fabric: from concepts to phenomenology.”  Rant coming up later today, but after that please prepare for a slow time.

Away Note

I'm in Munich next week, playing with the philosophers. Be good while I'm away, back soon. (Below, the girls, missing a few teeth.)

Away Note

I'm traveling next week and will be offline for some days. Blogging may be insubstantial, if existent, and comments may be stuck in the queue longer than usual. But I'm sure you'll survive without me ;)

And since you haven't seen the girls for a while, here is a recent photo. They'll be starting school this year in the fall and are very excited about it.

Reasoning in Physics

I’m just back from a workshop about “Reasoning in Physics” at the Center for Advanced Studies in Munich. I went because it seemed a good idea to improve my reasoning, but as I sat there, something entirely different was on my mind: How did I get there? How did I, with my avowed dislike of all things -ism and -ology, end up in a room full of philosophers, people who weren’t discussing physics, but the philosophical underpinning of physicists’ arguments. Or, as it were, the absence of such underpinnings.

The straight-forward answer is that they invited me, or invited me back, I should say, since this was my third time visiting the Munich philosophers. Indeed, they invited me to stay some longer for a collaborative project, but I’ve successfully blamed the kids for my inability to reply with either yes or no.

So I sat there, in one of these awkwardly quiet rooms where everyone will hear your stomach gargle, trying to will my stomach not to gargle and instead listen to the first talk. It was Jeremy Butterfield, speaking about a paper which I commented on here. Butterfield has been praised to me as one of the four good physics philosophers, but I’d never met him. The praise was deserved – he turned out to be very insightful and, dare I say, reasonable.

The talks of the first day focused on multiple multiverse measures (meta meta), inflation (still eternal), Bayesian inference (a priori plausible), anthropic reasoning (as observed), and arguments from mediocrity and typicality which were typically mediocre. Among other things, I noticed with consternation that the doomsday argument is still being discussed in certain circles. This consterns me because, as I explained a decade ago, it’s an unsound abuse of probability calculus. You can’t randomly distribute events that are causally related. It’s mathematical nonsense, end of story. But it’s hard to kill a story if people have fun discussing it. Should “constern” be a verb? Discuss.

In a talk by Mathias Frisch I learned of a claim by Huw Price that time-symmetry in quantum mechanics implies retro-causality. It seems the kind of thing that I should have known about but didn’t, so I put the paper on the reading list and hope that next week I’ll have read it last year.

The next day started with two talks about analogue systems of which I missed one because I went running in the morning without my glasses and, well, you know what they say about women and their orientation skills. But since analogue gravity is a topic I’ve been working on for a couple of years now, I’ve had some time to collect thoughts about it.

Analogue systems are physical systems whose observables can, in a mathematically precise way, be mapped to – usually very different – observables of another system. The best known example is sound-waves in certain kinds of fluids which behave exactly like light does in the vicinity of a black hole. The philosophers presented a logical scheme to transfer knowledge gained from observational test of one system to the other system. But to me analogue systems are much more than a new way to test hypotheses. They’re fundamentally redefining what physicists mean by doing science.

Presently we develop a theory, express it in mathematical language, and compare the theory’s predictions with data. But if you can directly test whether observations on one system correctly correspond to that of another, why bother with a theory that predicts either? All you need is the map between the systems. This isn’t a speculation – it’s what physicists already do with quantum simulations: They specifically design one system to learn how another, entirely different system, will behave. This is usually done to circumvent mathematically intractable problems, but in extrapolation it might just make theories and theorists superfluous.

It then followed a very interesting talk by Peter Mattig, who reported from the DFG research program “Epistemology of the LHC.” They have, now for the 3rd time, surveyed both theoretical and experimental particle physicists to track researchers’ attitudes to physics beyond the standard model. The survey results, however, will only get published in January, so I presently can’t tell you more than that. But once the paper is available you’ll read about it on this blog.

The next talk was by Radin Dardashti who warned us ahead that he’d be speaking about work in progress. I very much liked Radin’s talk at last year’s workshop, and this one didn’t disappoint either. In his new work, he is trying to make precise the notion of “theory space” (in the general sense, not restricted to qfts).

I think it’s a brilliant idea because there are many things that we know about theories but that aren’t about any particular theory, ie we know something about theory space, but we never formalize this knowledge. The most obvious example may be that theories in physics tend to be nice and smooth and well-behaved. They can be extrapolated. They have differentiable potentials. They can be expanded. There isn’t a priori any reason why that should be so; it’s just a lesson we have learned through history. I believe that quantifying meta-theoretical knowledge like this could play a useful role in theory development. I also believe Radin has a bright future ahead.

The final session on Tuesday afternoon was the most physicsy one.

My own talk about the role of arguments from naturalness was followed by a rather puzzling contribution by two young philosophers. They claimed that quantum gravity doesn’t have to be UV-complete, which would mean it’s not a consistent theory up to arbitrarily high energies.

It’s right of course that quantum gravity doesn’t have to be UV-complete, but it’s kinda like saying a plane doesn’t have to fly. If you don’t mind driving, then why put wings on it? If you don’t mind UV-incompleteness, then why quantize gravity?

This isn’t to say that there’s no use in thinking about approximations to quantum gravity which aren’t UV-complete and, in particular, trying to find ways to test them. But these are means to an end, and the end is still UV-completion. Now we can discuss whether it’s a good idea to start with the end rather than the means, but that’s a different story and shall be told another time.

I think this talk confused me because the argument wasn’t wrong, but for a practicing researcher in the field the consideration is remarkably irrelevant. Our first concern is to find a promising problem to work on, and that the combination of quantum field theory and general relativity isn’t UV complete is the most promising problem I know of.

The last talk was by Michael Krämer about recent developments in modelling particle dark matter. In astrophysics – like in particle-physics – the trend is to go away from top-down models and work with slimmer “simplified” models. I think it’s a good trend because the top-down constructions didn’t lead us anywhere. But removing the top-down guidance must be accompanied by new criteria, some new principle of non-empirical theory-selection, which I’m still waiting to see. Otherwise we’ll just endlessly produce models of questionable relevance.

I’m not sure whether a few days with a group of philosophers have improved my reasoning – be my judge. But the workshop helped me see the reason I’ve recently drifted towards philosophy: I’m frustrated by the lack of self-reflection among theoretical physicists. In the foundations of physics, everybody’s running at high speed without getting anywhere, and yet they never stop to ask what might possibly be going wrong. Indeed, most of them will insist nothing’s wrong to begin with. The philosophers are offering the conceptual clarity that I find missing in my own field.

I guess I’ll be back.

Away Note

I'll be in Munich next week, attending a workshop at the Center for Advanced Studies on the topic "Reasoning in Physics." I'm giving a talk about "Naturalness: How religion turned to math" which has attracted criticism already before I've given it. I take that to mean I'm hitting a nerve ;)

Away Note

I’ll be in London for a few days, attending a RAS workshop on “Fine-Tuning on the Cosmological and the Quantum Scales.” First time I’m speaking about the topic, so a little nervous about that.

It just so happens that tomorrow evening there’s a public lecture in London by Roger Penrose which I might or might not attend, depending on whether my flight arrives as planned. Feeling somewhat bad because I haven’t read his recent book. Just judging by the title I’m afraid it might have some overlap with mine.

This public lecture is arranged by the Ideas Roadshow, which I mentioned before. It’s run by Howard Burton, former director of PI. They have some teaser videos which you might enjoy:



Speaking of former directors, I believe Neil Turok’s term at PI is about to run out and I want to complain that I haven’t yet heard rumors who’s in the pipe^^.

As for this blog, please expect that comments might get stuck in the queue longer than usual.

Away Note

I'll be in Stockholm next week for a program on Black Holes and Emergent Spacetime, so please be prepared for some service interruptions.

Away Note

I have a trip upcoming to Helsinki. After this I'll be tied up in family business, and then my husband goes on a business trip and I have the kids alone. Then Kindergarten will be closed for a day (forgot why, I'm sure they must have some reason), I have to deal with an ant-infection in our apartment, and more family business follows. In summary: busy times.

I have a book review to appear on this blog later today, but after this you won't hear much from me for a week or two. Keep in mind that since I have comment moderation on, it might take some while for your comment to appear when I am traveling. With thanks for your understanding, here's a random cute pic of Gloria :)

Hello from Maui

Greetings from the west-end of my trip, which brought me out to Maui, visiting Garrett at the Pacific Science Institute, PSI. Launched roughly a year ago, Garrett and his girlfriend/partner Crystal have now hosted about 60 traveling scientists, "from all areas except chemistry" I was told.

I got bitten by mosquitoes and picked at by a set of adorable chickens (named after the six quarks), but managed to convince everybody that I really didn't feel like swimming, or diving, or jumping off things at great height. I know I'm dull. I did watch some sea turtles though and I also got a new T-shirt with the PSI-logo, which you can admire in the photo to the right (taken in front of a painting by Crystal).

I'm not an island-person, don't like mountains, and I can't stand humidity, so for me it's somewhat of a mystery what people think is so great about Hawaii. But leaving aside my preference for German forests, it's as pleasant a place as can be.

You won't be surprised to hear that Garrett is still working on his E8 unification and says things are progressing well, if slowly. Aloha.

Away Note

I am traveling the next three weeks and things will go very slowly on this blog.

In case you missed it, you might enjoy two pieces I recently wrote for NOVA: Are Singularities Real? and Are Space and Time discrete or continuous? There should be a third one appearing later this month (which will also be the last because it seems they're scraping this column). And then I wrote an article for Quanta Magazine String Theory Meets Loop Quantum Gravity, to which you find some background material here and here. Finally you might find this article in The Independent amusing: Stephen Hawking publishes paper on black holes that could get him 'a Nobel prize after all', in which I'm quoted as the voice of reason.

Away note

I’ll be traveling the next two weeks. First I’ll be going to a conference on “scholarly publishing” in the picturesque city of Tromsø. The “o” with the slash is Norwegian and the trip is going to beat my personal farthest-North record that is currently held by Reykjavik (or some village with an unpronouncable name a little North of that).

I don’t have the faintest clue why they invited me, to give a keynote lecture out of all things, in company of some Nobelprize winner. But I figured I’d go and tell them what’s going wrong with peer review, at least that will be entertaining. Thanks to a stomach bug that my husband brought back from India, by means of which I lost an estimated 800 pounds in 3 days, “tell them what's going wrong with peer review” is so far pretty much the whole plan for the lecture.

The week after I’ll be going to a workshop in Munich on the question “Why trust a theory?”. This event is organized by the Munich Center for Mathematical Philosophy, where I already attended an interesting workshop two years ago. This time the workshop is dedicated to the topics raised in Richard Dawid’s book “String Theory and the Scientific Method" which I reviewed here. The topic has since been a lot on my mind and I’m looking forward to the workshop.

Away Note

I will be travelling the next weeks, so blogging might be spotty and comment moderation slow. I'll first be in Washington DC speaking at a conference on New Directions in the Foundations of Physics (somewhat ironically after I just decided I've had enough of the foundations of physics). And then I'll be at PI and the University of Waterloo (giving the same talk, with more equations and less philosophy). And, yes, I've packed the camera and I'm trigger happy ;)

Hello from Iceland

So here I am on an island in the middle of the Atlantic ocean that's working on its next volcano eruption.

In case you missed yesterday's Google Hangout, FQXi just announced the winner's of this year's essay contest and - awesomeliness alert! - my essay "How to save the world in five simple steps" made it first prize!

I'm happy of course about the money, but what touches me much more is that this is vivid documentation I'm not the only one who thinks the topics I addressed in my essay are relevant. If you've been following this blog for some while then you know of course that I've been thinking back and forth about the problem of emerging social dynamics, in the scientific communities as well as in society by large, and our inability to foresee and react to the consequences of our actions.

Ten years ago I started out thinking the problem is the modeling of these systems, but over the years, as more and more research and data on these trends became available, I've become convinced the problem isn't understanding the system dynamics to begin with, but that nobody is paying attention to what we've learned.

I see this every time I sit in a committee meeting and try to tell them something about research dedicated to intelligent decision making in groups, cognitive biases, or the sociology of science. They'll not listen. They might be polite and let me finish, but it's not information they will take into account in their decision making. And the reason is basically that it takes them too much time and too much effort. They'll just continue the way it's always been done; they'll continue making the same mistakes over again. There's no feedback in this system, and no learning by trial and error.

The briefest of brief summaries of my essay is that we'll only be able to meet the challenges mankind is facing if our social systems are organized so that we can react to complex and emerging problems caused by our own interaction and that with our environment. That will only be possible if we have the relevant information and use it. And we'll only use this information if it's cheap, in the sense of it being simple, fast, and intuitive to use.

Most attempts to solve the problems that we are facing are based on an unrealistic and utopian image of the average human, the well-educated, intellectual and concerned citizen who will process all available information and come to smart decisions. That is never going to happen, and that's the issue I'm taking on in my essay.

I'll be happy to answer questions about my essay. I would prefer to do this here rather than at the FQXi forum. Note though that I'll be stuck in transit for the next day. If that volcano lets me off this island that is.

Away note and Interna

Lara

I'll be traveling the next three weeks, so please be prepared for little or unsubstantial action on this blog. Next week I'm in Reykjavik for a network meeting on "Holographic Methods and Applications". August 27-29 I'm running the Science Writers Workshop in Stockholm together with George, this year on the topic "Quantum Theory." The first week of September then I'm in Trieste for the 2014 conference on Experimental Search for Quantum Gravity, where I'll be speaking about space-time defects.

Unfortunately, this traveling happens just during the time when our Kindergarten is closed, and so it's quite some stress-test for my dear husband. Since you last heard from Lara and Gloria, they have learned to count, use the swing, and are finally potty trained. They can dress themselves, have given up requesting being carried up the stairs, and we mostly get around without taking along the stroller. Yes, life has become much easier. Gloria however still gets motion sick in the car, so we either have to drug her or pull over every 5 minutes. By and large we try to avoid long road trips.

The girls have now more of a social life than me, and we basically can't leave the house without meeting other children that they know and that they have to discuss with whether Friday comes before or after Wednesday. That Lara and Gloria are twins apparently contributes greatly to their popularity. Every once in a while, when I drop off the kids at Kindergarten, some four foot dwarf will request to know if it's really true that they were together in mommy's tummy and inspect me with a skeptic view. The older children tell me that the sisters are so cute, and then try to pad Gloria's head, which she hates.

Gloria

Gloria is still a little ahead of Lara when it comes to developing new skills. She learned to speak a little earlier, to count a little earlier, was potty trained a little earlier and learned to dress herself a little earlier. Then she goes on to explain Lara what to do. She also "reads" books to Lara, basically by memorizing the stories.

Lara on the other hand is still a little ahead in her physical development. She is still a bit taller and more often than not, when I come to pick them up at Kindergarten, Lara will be kicking or throwing some ball while Gloria plays in the sandbox - and afterwards Gloria will insist on taking off her shoes, pouring out the sand and cleaning her socks before she gets into the car. Lara takes off the shoes in the car and pours the sand into the seat pocket. Lara uses her physical advantage over Gloria greatly to take away toys. Gloria takes revenge by telling everybody what Lara did wrong again, like putting her shoe on the wrong foot.

The best recent development is that the girls have finally, after a quite difficult phase, stopped kicking and hitting me and telling me to go away. They now call me "my little mommy" and want me to bake cookies for them. Yes, my popularity has greatly increased with them figuring out that I'm not too bad with cakes and cookies. They don't particularly like my cooking but that's okay, because I don't like it either.

On an entirely different note, as some of you have noticed already, I agreed to write for Ethan Siegel at Starts With A Bang. So far there's two pieces from me over there: How the experiment that claimed to detect dark matter fooled itself and The Smallest Possible Scale in the Universe. The deal is that I can repost what gets published there on this blog after 30 days, which I will do. So if you're only interested in my writing, you're well off here, but check out his site because it's full with interesting physics writing.

Away note

I will be traveling the rest of the week to give a lecture at the Sussex graduate school "From Classical to Quantum GR", so not much will happen on this blog. For the school, we were asked for discussion topics related to our lectures, below are my suggestions. Leave your thoughts in the comments, additional suggestions for topics are also welcome.

• Is it socially responsible to spend money on quantum gravity research? Don't we have better things to do? How could mankind possibly benefit from quantum gravity?
• Can we make any progress on the theory of quantum gravity without connection to experiment? Should we think at all about theories of quantum gravity that do not produce testable predictions? How much time do we grant researchers to come up with predictions?
• What is your favorite approach towards quantum gravity? Why? Should you have a favorite approach at all?
• Is our problem maybe not with the quantization of gravity but with the foundations of quantum mechanics and the process of quantization?
• How plausible is it that gravity remains classical while all the other forces are quantized? Could gravity be neither classical nor quantized?
• How convinced are you that the Planck length is at 10^-33cm? Do you think it is plausible that it is lower? Should we continue looking for it?
• What do you think is the most promising area to look for quantum gravitational effects and why?
• Do you think that gravity can be successfully quantized without paying attention to unification?

Lara and Gloria say hello and wish you a happy Easter :o)

Interna

I’ll be traveling for the rest of the week, so be warned of a period of silence.

Wednesday I’m giving a seminar in Nottingham, and after that I’m attending a workshop in Oxford. The workshop topic is “The Structure of Gravity and Space-time” and it’s part of the project “Establishing the Philosophy of Cosmology”. Sound more ominous than it is: They’ll have a session on the question whether there exists a “fundamental length”, which is what brought me on their invitation list. There will also be sessions on bi-metric gravity, massive gravity and strings and space-time structure, which sounds very promising to me. We’ll see how much philosophy infiltrates the physics. A preliminary program is here.

The girls are doing well, now attending Kindergarten. Our pediatrician didn’t raise any concerns at the 3-year checkup, except for Lara’s vision problems. She’ll get new glasses next week. The ones she has now always slip down and hang on the very tip of her nose, so we hope that the new ones will stay put better.

Lara and Gloria can open and remove all our children safety locks now and I’ve put away the door keys because I’m afraid they’ll lock themselves in. They also picked up lots of swear words since they attend Kindergarten. They don’t really know how to use them properly, which is often unwillingly funny. We’ve made a little progress with the potty training, but unfortunately the kids declare plainly they’re “too lazy” to go without diaper. It is similarly unfortunate that several older children at the Kindergarten still use binkies. Gloria told me the other day she will learn to use the toilet when she can “reach the ceiling”. She also declared that since Gloria came out of mommy’s belly, Lara must have come out of daddy’s belly. Everything far away is “Stockholm” and that’s a magical place where mommy goes and brings back gifts. They’re getting more entertaining by the day.

I finally replaced my old digital camera because some of the buttons were broken, and now have a Canon DSLR (EOS 1100D) which I am so far very happy with, though the learning curve is steep. I used to have a SLR Camera 15 years ago. You know, one of these things were you had to wind back the film and carry it to some store and wait a week just to see how badly you did. Remember that? The DSLR looks and feels quite different from that, as with all the menus that I keep getting lost in. Maybe reading the manual would help. In any case, I spent some weeks hunting after the kids. Below are some of my favorite photos.

Testing Conspiracy Theories

I'm about to fly to Vienna where I'll be attending a conference on Emergent Quantum Mechanics. I'm not entirely sure why I was invited to this event, but I suspect it's got something to do with me being one of the three people on the planet who like superdeterministic hidden variables theories, more commonly known as "conspiracy theories".

Leaving aside some loopholes that are about to be closed, tests of Bell's theorem rule out local hidden variables theories. But any theorem is only as good as the assumptions that go into it, and one of these assumptions is that the experimenter can freely chose the detector settings. As you know, I don't believe in free will, so I have an issue with this. You can see though why theories in which this assumption does not hold are known as "conspiracy theories". While they are not strictly speaking ruled out, it seems that the universe must be deliberately mean to prevent the experimentalists from doing what they want, and this option is thus often not taken seriously.

But really, this is a very misleading interpretation of superdeterminism. All that superdeterminism means is that a state cannot be prepared independently of the detector settings. That's non-local of course, but it's non-local in a soft way, in the sense that it's a correlation but doesn't necessarily imply a 'spooky' action at a distance because the backwards lightcones of the detector and state (in a reasonable universe) intersect anyway.

That having been said, you might like or not like superdeterministic hidden variables theories, the real question is if there is some way to test if that's how nature works, because one can't use Bell's theorem here. After some failed attempts, I finally came up with a possible test that is almost model-independent, and it was published in my paper "Testing super-deterministic hidden variables theories".

I actually wrote this paper in the hospital when I was pregnant. The nurses kept asking me if I'm writing a book. They were quite disappointed to be drowned in elaborations on the foundations of quantum mechanics rather than hearing a vampire story. In any case, in the expectation that the readers on this blog are somewhat more sympathetic to the question whether the universe is fundamentally deterministic or not, here a brief summary of the idea.

The central difference between standard quantum mechanics and superdeterministic hidden variables theories is that in the former case two identically prepared states can give two different measurement outcomes, while in the latter case that's not possible. Unfortunately, "identically prepared" includes the hidden variables and it's difficult to identically prepare something that you can't measure. That is after all the reason why it looks indeterministic.

However, rather than trying to prepare identical states we can try to make repeated measurements on the same state. For that, take two non-commuting variables (for example the spin or polarization in two different directions) and measure them alternately. In standard quantum mechanics the measurement outcomes will be non-correlated. In a superdeterministric hidden variables theory, they'll be correlated - provided you can make a case that the hidden variables don't change in between the measurements. The figure below shows an example for an experimental setup.

A particle (electron/photon) is bounced back and forth between
two mirrors (grey bars). The blue and red bars indicate measurements
of two non-commuting variables, only one eigenvalue passes, the
other leaves the system. The quantity to measure is the average time
it takes until the particle leaves. In a superdeterministic theory,
it can be significantly longer than in standard quantum mechanics.

The provision that the hidden variables don't change is the reason why the test is only 'almost' model independent, because I made the assumptions that the hidden variables are due to the environment (the experimental setup) down to the relevant scales of the interactions taking place. This means basically if you make the system small and cool and measure quickly enough you have a chance to see the correlation between subsequent measurements. I made some estimates (see paper) and it seems possible with today's technology to make this test.

Interestingly, after I had finished a draft of the paper, Chris Fuchs sent me a reference to a 1970 article by Eugene Wigner where, in a footnote, Wigner mentions Von Neumann discussing exactly this type of experiment:

“Von Neumann often discussed the measurement of the spin component of a spin-1/2 particle in various directions. Clearly, the possibilities for the two possible outcomes of a single such measurement can be easily accounted for by hidden variables [...] However, Von Neumann felt that this is not the case for many consecutive measurements of the spin component in various different directions. The outcome of the first such measurement restricts the range of values which the hidden parameters must have had before that first measurement was undertaken. The restriction will be present also after the measurement so that the probability distribution of the hidden variables characterizing the spin will be different for particles for which the measurement gave a positive result from that of the particles for which the measurement gave a negative result. The range of the hidden variables will be further restricted in the particles for which a second measurement of the spin component, in a different direction, also gave a positive result...”

Apparently there was a longer discussion with Schrödinger following this proposal, which could be summarized with saying that the experiment cannot test generic superdeterminism, but only certain types as I already said above. If you think about it for a moment, you can never rule out generic superdeterminism anyway, so why even bother.

I'm quite looking forward to this conference, to begin with because Vienna is a beautiful city and I haven't been there for a while, but also because I'm hoping to meet some experimentalists who can tell me if I'm nuts :p

Update: Slides of my talk are here.

Interna

Lara, putting on her shoes.

May 1st is a national holiday both in Sweden and in Germany. A good opportunity, I thought, to update you on our attempts at normal family life.

Lara and Gloria are now talking basically non-stop. Half of the time we have no idea what they are trying to say, the other half are refusals. Gloria literally wakes up in the morning yelling "Nein-nein-nein". Saying it's difficult to get her dressed, fed, and to daycare makes quantizing gravity sound like an easy task. Yesterday she insisted on going in her pajamas. Good mother that I am, I thought that was a brilliant idea.

Gloria is proud of her new hat.

Lara isn't quite as difficult as Gloria, but she is very easily distracted. If I ask her to get into the stroller, she'll first spend five minutes inspecting the stones by the road or take off her shoes and put them back on, just because.Time clearly flows very differently when you're two years old than when you're forty. I try to use the occasions to check my email. Time flows through my iPhone, I'm sure it does.

We finally made progress on our daycare issue, which is presently only half a solution. A new daycare place opened in the area, and due to my time spent on the phone last year, asking people to please write down my name and call me back if the situation unexpectedly changes, somebody indeed recalled my name and we made it top of the list for the new place. So there'll be another adaption phase at another place, but this time it's a full-day care that will indeed cover our working hours. It is also, I should add, considerably less expensive than the present solution with a self-employed nanny. This, I hope, will make my commuting easier for Stefan to cope with.

I'm really excited about the workshop for science writers that I'm organizing with George. We now have an (almost) complete schedule, I've ordered food and drinks and sorted out the lab visit, and I'm very much looking forward to the meeting. Directly after this workshop, I'll attend another workshop in Munich, "Quantum Gravity in Perspective", where I'll be speaking about the phenomenology of quantum gravity. I have some more trips upcoming this summer, to Bielefeld and Aachen and, in fall, to Vienna to speak at a conference on "Emergent Quantum Mechanics."

I was invited to take part in this KITP workshop on black hole firewalls but I eventually decided not to go. Partly because I'm trying to keep my travels limited to not burden Stefan too much with the childcare. But primarily because I don't believe that anything insightful will come out of this debate. It seems to me there are more fruitful research topics to explore, and this discussion is a waste of time. I also never liked SoCal in late summer; too dry for my central-European genes.

Lara and Gloria, eating cookies at a visit to the zoo.

We'll be away for the next couple of days because Stefan's brother is getting married. This means a several-hours long road trip with two toddlers who don't want to sit still for a minute; we're all looking forward to it...

Interna

Lara with her new glasses.

When you last heard from Lara and Gloria, they could utter a few single words. Within a couple of weeks, they have transitioned to speaking full sentences, answer to questions with "yes" and "no", and are very clear in expressing themselves. "Jacke an, Bagger gucke" (Jacket on, watch digger), they might say when they want to go for a walk. They still refer to each other as Gaakie and Gookie though. And they are struggling with German grammar, especially finding the right articles.

Lara now has glasses that are meant to help correct her squinting. She wears them without complaint. It probably helps for her acceptance that I too wear glasses.

The half-day daycare solution is working reasonably well, except that it's prohibitively expensive. The nanny has taught the kids to drink from a cup, to wash their hands, to paint and to jump. I'm sure our downstairs neighbors are as excited about the jumping as the kids. My commuting to Stockholm is not working quite so well. It leaves all of us terribly exhausted and is a huge waste of time, not to mention money. The time that I gain by having the kids in daycare is mostly spent on catching up on life's overhead, paperwork, the household, piles of unread papers and unanswered emails that wait for me upon return.

That having been said, I have a bunch of trips coming up. March 15 I'm in Bergen giving a seminar, apparently on the topic "Siste nytt om kvantegravitasjon". On April 12 I'm in Reykjavik. I haven't been able to find anything resembling a seminar schedule on the department website, but it's the same seminar as in Bergen. In May George and I are running the previously mentioned Workshop for Science Writers in Stockholm, and at the end of May I'll be attending a workshop on "Quantum Gravity in Perspective" in Munich. I have some more trips coming up, but plans haven't proceeded further than that. If you're located in any of these places and feel like  meeting up, send me a note.

Besides this, I've been told that the current issue of the Finnish magazine Tähdet ja avaruus ("Stars and Space") has an article by Laura Koponen about quantum gravity, featuring Renate Loll, Robert Brandenberger, and me. It's in Finnish so I have no clue what it says, but the photos look nice. Though... something about the photo of me didn't feel quite right, and after some forehead frowning it occurred to me that the NorthFace logo on my shirt fell victim to Finnish photoshopping. I actually like it better this way; I prefer my clothes without logos if possible. In any case, should you by any chance speak Finnish and have read the article, let me know what you think.