Friday, February 18, 2011

The Cosmic Neutrino Background

In the very early universe matter was dense and hot. With the expansion of space, matter cooled down which eventually allowed for the formation of nuclei and later atoms, molecules and increasingly large structures. Atoms could be formed when the average energy of electrons decreased to a value so small that ionization became improbable - an event called recombination. Photons, which prior to recombination were scattered on the free electrons, could then travel almost undisturbed. This happened at a temperature of about 1 eV, or some thousand Kelvin. Due to the continuing expansion of the universe, the photons from that time became redshifted, but are still present today. Their temperature is now at 2.7 K, and they have become famous under the name Cosmic Microwave Background (CMB). The temperature fluctuations in the CMB carry information about the structure of matter at the time of the photons' decoupling from matter. WMAP has measured these temperature fluctuations with great accuracy. (We discussed the CMB and some of what we have learned from it here, here, here and most recently here.)

The photons that we are so used to rely on for "looking" do not allow us to learn anything about the early universe prior to recombination. But we can try to see by other means. Neutrinos are well known for being weakly interacting, which is why they are so difficult to detect. But that they interact only weakly also means neutrinos ceased to scatter on the hot matter in the early universe earlier than photons. This happens at the typical energy scale for the weak interaction, at about 1 MeV or 1010K, after which the scattering of neutrinos and anti-neutrinos to produce an electron-positron pair became very improbable and, briefly after this, nucleosynthesis took place. Today, the temperature of the cosmic neutrino background, CνB, is about 10-4 eV or 2 Kelvin* and it's all around us.

While we have not yet measured the absolute neutrino masses, but only have upper bounds, neutrino oscillations test for the differences of squares of masses. This allows us to conclude that at least some of the neutrino species must have cooled so much that their kinetic energy is smaller than their restmass, which means they are non-relativistic. This is interesting because these neutrinos will then clump in gravitational fields like that of our Milky way. As a consequence, the density of neutrinos on the path of planet Earth is roughly one to two orders of magnitude larger than the average density.

Still, these CνB neutrinos are very difficult to detect. But difficult is not impossible. Neutrino capture on tritium would, with some effort but presently available technology, yield a detection rate of maybe 10 CνB neutrinos per year [reference]. That would be enough to confirm the presence of the CνB, but to measure temperature fluctuations, with that procedure we'd probably have spend some million years doing nothing but gathering statistics, not to mention that tritium doesn't grow on trees. Alternative to tritium, it has recently been proposed to instead capture anti-neutrinos on Holmium, which, with some effort and some luck, might yield comparable detection rates. Direct detection of the CνB is the first step. Since the detection rate depends on the neutrino-density, it would not only confirm our theories about the creation of the neutrino-background, but give us information about the distribution of neutrinos in the gravitational field of our galaxy.

Sure, there's only so much you can learn from 10 neutrinos per year. But who knows what technological progress will bring? Half a century ago, the precision with which WMAP measured tiny fluctuations in a temperature that is tiny to begin with would have seemed a fantasy. Today it's fact. So here I am telling you that the CνB is out there, waiting for us to harvest the information it contains.



* It is (4/11)1/3 times the temperature of the CMB. The conversion factor is partly due to neutrinos being fermions while photons are bosons, and partly due to the photons gaining in density, and thus temperature, when electron-positron pairs annihilate to photons while the opposite reaction becomes increasingly improbable. When this happened, neutrinos had already decoupled.

64 comments:

Steven Colyer said...

a temperature of about 1 eV

I thought electron-volts were a mass measure, and as a neat fringe benefit, a voltage measure or well. Damn I'm dumb if that's not true.

Bee said...

mass is energy is temperature is the inverse of wavelength. You see, I'm a theoretical physicist. For what I am concerned c=\hbar=k=1. Very useful:

http://www.cberthod.homepage.bluewin.ch/vuc/converter.html

Kay zum Felde said...

Hi Bee,

that's what I always also say. To do physics as an experimentalist is to find new ways to measure things. And this means to find new technology which benefits the whole world. The theorist and the mathematical physicist and the mathematician are doing their jobs as well in the chain to develop new technology.

Best, Kay

Arun said...

This allows us to conclude that at least some of the neutrino species must have cooled so much that their kinetic energy is smaller than their restmass, which means they are non-relativistic. This is interesting because these neutrinos will then clump in gravitational fields like that of our Milky way.

I don't quite follow. Unless the neutrinos have a way of shedding energy, I don't see how they clump.

Bee said...

Clumping isn't really the right word... I just meant to say they have overdensities without using the word overdensity.

Steven Colyer said...
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Steven Colyer said...

Thank you Bee, and for that bit on Tritium, too. Yeah, when do you think we'll have fusion power plants? The best guesstimate is 2050, so I'll throw in a factor of safety of 2 and call it 2090. Your girls will live long enough to see the first one, maybe, assuming we (Humanity) behave ourselves. The physics and engineering of fusion is known, it's actually cool how given the tritium shortage engineers have used the process to make more, all of which alas is used again by the process. Darn plasma is a bear to work with though.

Thanks to the main article as well, I had no idea a cosmic neutrino background existed. Now if they do their jobs at the LHC (so far so good) we'll be talking cosmic neutrilino background as well, someday? :-)

Navneeth said...

Steven Coyler,

I had no idea a cosmic neutrino background existed.

Technically speaking, no one does. ;-)

Steven Colyer said...

Technically speaking, no one does. ;-)

LOL, good one, yes. I'm holding out for the Cosmic Wino Background as well, although rumor has it some preliminary work can be done by hanging out at Rutgers New Brunswick bars at closing ttime. :-)

Eric said...

Very interesting article Bee. I had no knowledge of a cosmic neutrino background at all. Is it considered still speculative or does it have a high confidence level?

Bee said...

Hi Eric,

I'm not an astrophysicist, so not a good source of information about the community, but I'd say the existence of the neutrino background has a very high confidence level: it involves only physics we know very well. It would be very surprising if it was not there, or turned out to have a different temperature, etc. It seems to me there's some variation in the literature about the local density, it seems to vary about one order of magnitude. I guess it would also depend on the absolute neutrino masses. Best,

B.

Plato said...

I'm having a deja Vue moment seeing this posting.

I'll be back.:)

Plato said...

The idea is to increase the way in which we view the universe so in such a case how shall we scan the skies when we have the means in which to get a even different view of the universe that it pushes perspective a little further back representing itself as the now.

Astronomers wrapped the Fermi Gamma-ray Space Telescope's first all-sky map over a sphere to produce this view of the gamma-ray universe. Credit: NASA/DOE/International LAT Team How you look at the sun or the moon?


That's the point "the now," encompasses all that was there before but was unseen, is the technology with which our views allow us to see differently.

The first three minutes of the universe becomes the first three seconds you see? Changing our ability to see the early universe maybe a theoretical feat, as time progresses, we were able to map this experience ever more minutely as the energy increases.

Best,

Plato said...

This image is from a computer simulation of the beginning of a gamma-ray burst. Here we see the jet 9 seconds after its creation at the center of a Wolf Rayet star by the newly formed, accreting black hole within. The jet is now just erupting through the surface of the Wolf Rayet star, which has a radius comparable to that of the sun. Blue represents regions of low mass concentration, red is denser, and yellow denser still. Note the blue and red striations behind the head of the jet. These are bounded by internal shocks. See:"ROSETTA STONE" FOUND TO DECODE THE MYSTERY OF GAMMA RAY BURSTS

The point is you are looking for the reasons as to why such motivation expresses itself by means of detection, so while you are examining elements of the early universe, you need key factors "as constituents" to help reveal the cascading of the elements(decay) of the way in which we are allowed to see.


Supernova Starting Gun: Neutrinos

.....Next they independently estimated how the hypothetical neutrinos would be picked up in a detector as massive as Super-Kamiokande in Japan, which contains 50,000 tons of water. The detector would only see a small fraction of the neutrinos. So the team outlined a method for matching the observed neutrinos to the supernova's expected luminosity curve to figure out the moment in time--to within about 10 milliseconds--when the sputtering star would have begun emitting neutrinos. In their supernova model, the bounce, the time of the first gravitational waves, occurs about 5 milliseconds before neutrino emission. So looking back at their data, gravitational wave hunters should focus on that point in time. Bold added for emphasis.

So roughly you have a photon shot from a gun and you have a backdrop for examinimg the spectrum, what else can you use in order to identify "the gamma of that spectrum?" So you choose neutrinos? You see? Open to corrections.

Best,

Plato said...
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Neil B said...

Interesting. Is there still a big problem, as noted in Penrose's books, about explaining entropy ratios and all that (to the extent I recall correctly, he said some feature had only around 10^(10^120) of being right, and it wasn't the magnitude of vacuum energy but about entropy or related.) BTW I used to be the informal tritium monitor at a local shipyard building/services US nuclear navy. Because of low-energy emissions, special considerations are required to test properly. It was more a formality since little trouble was expected, but I got a kick out of them appreciating me being a science buff.

Uncle Al said...

[(4/11)^(1/3)](2.725 K) = 1.945 K and 1.68x10^(-4) eV, so close enough. 336/cm^3 Big Bang neutrinos: 56 each neutrinos and antineutrinos each in three flavors. I calculate 2.1/cm^3 solar neutrinos are incoming hard by lightspeed, 62.97 billion/cm^2-sec or 1.7 curies/cm^2 in a plane normal to the sun at Earth's orbit. Check my numbers.

Given nominal 0.2 eV neutrino rest mass, 1.68x10^(-4) eV is non-relativistic. Detector volume sweeps through a primordial random background at Earth's average solar orbital speed of ~18.51 miles/sec. The number of primordial neutrinos intercepted by a detector, swept volume/time, is ~1/380 that of solar neutrino detectors, (18.51/186282)(56/2.1) = 0.26%. Doubling that is still a small fraction of a small fraction.

Tritium has large decay heat, 0.324 watt/gram (44+ watts for nominal 10 detections/year). NOBODY has sufficiently accurately measured tritium decay energy (a blob not a spike) to determine even beta-decay anti-neutrino energy.

"...one would need ten years of observation of a source of 30 kilograms [Ho-163] to have 10 events of signal" with "a resolution FWHM better than 0.33 eV."

Ho-163, half-life 4570 years, is synthetic. Threshold 23 tonnes of stored power reactor fission waste must be processed. Ho-163 thermal fission yield is 0.13%,

http://ie.lbl.gov/fission/endf349.pdf
p. 10

It is a clever idea that cannot be reduced to practice for a long chain of reasons.

Plato said...
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Plato said...

The right spin for a neutrino superfluid Compiled by Steve Reucroft and John Swain, Northeastern University.

Kapusta points out that the condensation temperature would be well below the cosmic background temperature, so it would be quite a feat to make this superfluid. However, Kapusta also notes that a sufficiently advanced civilization might use pulses of neutrino superfluid for long-distance communications.

Oh really?:)

Best,

Plato said...
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Plato said...

The spherical cow will sum it up.

The decay process Uncle al is not complete for you...how can it be?:)Your calculations are limited and do not jive with what is being found in LHC?;)

When you understand ICECUBE or the history of Pierre Auger, the decay chain "is" logical and calculated.

Calorimetric wise, this is determined...and then there are those extra dimensions:)The calculation of loss of energy from the evidence allows you to look deeper into what might help measure the inside of volcanoes and magma flows?:)Gran Sasso.

You have to understand these motivations for expression?:) Smile at the Sun:)

Steven Colyer said...

My head is still spinning that mass = temperature. They sure didn't teach us THAT in engineering school.

The next thing you know they'll be trying to tell us there are 11, no 13 dimensions, with massive photons and massless electrons as well, and that we're not real (take THAT Descartes!) and live in or on a hologram. Sheesh, if I didn't know better, such craziness might launch a thousand papers. Maybe 10,000. Can I hear a 100,000 k? Wolf prize? Yes. Nobel prize? No.

Bee said...

Hi Plato,

I freed your post. Best,

B.

Steven Colyer said...

OK Bee, i get it now. It's called nondimensionalization, and the exact relations can be found in Table 4 here. Cool.

E=M
E= T/2
E= angular frequency
S=ln omega

etc.

Phil Warnell said...

Hi Bee,

An interesting article regarding the implications of a particle which not only is difficult to detect, yet difficult to have adequately defined. For instance if it having (rest) mass or not, which relates to what fields it’s influenced by as opposed to more directly measured consideration. That is the empirical evidence absent of the dictates of theory favours more it being massless, rather than massive from measuring its speed directly and yet the opposite as it’s been demonstrated as able to change from one flavour to another, since the passage of time seems to be needed as part of its reality for this to occur. In such respect I would have thought it more advisable to better understand what it is we are observing before rushing off to consider what conclusions might be reached with its observation.

Best,

Phil

Plato said...

Thanks Bee.

Neil B said...

Steven, if you mean the usual implication of kinetic energy being equivalent to "extra mass" (although there is an interpretational wrangle about that issue, see for example my comments at Uncertain Principles), then it's not so surprising. However, there is something I used to hear in discussions of temperature: there was a maximum temperature in effect, at least if hadrons were involved: past a certain temperature (or, roughly perhaps given variables), collisions create new particles and so the energy can't be sustained. (Example: p + p --> 3p + anti-p + 2γ.) Now I don't hear that so much, not sure why.

I had a similar "WTF moment" (to quote the inimitable Sarah Palin) about Uranus: soon after its Voyager encounter, talk of "water" in the planet's interior, in the apparent sense of kept liquid due to high pressure, being up to around 1000 °F. Well, that is above water's critical point 705 °F, so I wondered about that - maybe under extreme pressure and some impurities there's a weird state, but is it really "water?" (Maybe then by definition a "supercritical fluid.") So it seems there are tricky factors that allow something to go beyond a limit, in some special sense.

FQXi update if I may: On his FB page, T. Dorigo said "Beautiful article ..." about my entry there. To be nice I add that Bee won 2nd place for their last essay contest. The latest responses can be very interesting, as is you wade through lots of weird mutterings but I hope mine is better.

Plato said...

Neil:So it seems there are tricky factors that allow something to go beyond a limit, in some special sense

Circumstances around superfluid "allow" how shall we say multi-dimensional abilities to produce evidence as "gaping holes" in mass distinction lets say from point a to b distance in measure.

Collision point, and the screen, lets say as Gran Sasso.

So it has to be around that "collision point" the effect holds more information then is currently realized for it to produce "effects of measure."

Allowing us to see mass and density distinctions with gaping holes, filled with fluidized movement within that mass.

Cerenkov too, in some idealized fashion, "as evidence of course" beyond the barriers of distinct chains of decay elements?

So what are we seeing naturally in the everyday world, that we would coincide our vision capabilities with that in cosmic particle spallations that also reveal decay chains as monitored by energy calculations that are played out in the LHC.

The dimensional capability of that "collision point" has not been fully determined according to that decay chain, so this indeed leaves room for perspective to be further honed to provide for all routes of energy expression yet to be determined?

I of course could be wrong and of course open to corrections. This is where the research to this point had taken me. I am concentrating on the effect of vortex expressions within the superfluids, as well as, viscosity implications as portals of vortex information transfer.

Best,

Steven Colyer said...

Neil wrote:
I had a similar "WTF moment" (to quote the inimitable Sarah Palin)

Here's the only truly funny thing she ever said, and given her (apparent non-relativistic) IQ, I bet Dennis Miller or Jackie Mason wrote it for her:
"I believe there's room for all of Alaska's animals, right next to the mashed potatoes." ... The Alaskan Airhead

About the critical point of water, it's been a while since I studied the phase diagrams, dew point stuff etc., and yes it's very much related to pressure. If you're really interested, I could dig in the attic for my old textbooks, but in ten minutes I bet you could find the answer online. :-)

About DI, Roland Onnes' book at Andrew Thomas' "What Is Reality" website is about the current "interpretation", right? In fact that's how I met Andrew, though looking up "Decoherence" at Wikipedia, which is disappointing in so many ways, yet mathematically correct, as least by those who post there. Anyway, it's not just Onnes, there are 3 other bigwigs in his camp. Hartle too I think.

Anyway, back on topic, the CMB is the FARTHEST we can look back in time, to date, so in truth the farthest we will have hardcore info about. Everything else is speculation. Interesting speculation, but still speculation.

However, with this post, Bee introduces the old western phrase: "Hold on to your horses, not so fast, cowboy." Meaning, we MIGHT be able to test on stuff we speculate that went on JUST before the CMB de-opaqued the early universe. That would be cool if so, because then we'd have to talk about the CNB not the CMB.

(Although Topologically ... "N" and "M" are the same ... as are "E" and "T" come to think of it .... sorry, thinking maths today).

Eric said...
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Eric said...
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Eric said...

Steven, somewhat off topic to this article by Bee, but not to your post: did you notice table 2 for Planck units in the wiki article you cited here? It shows the five base Planck units of length, mass, time, charge, and temperature. You had mentioned in another thread that I'd forgotten to mention charge being contained in the fine structure constant. You were right. I'd emphasized that G wasn't in it though c and hbar were and also that the FSC was a reliable constant. Notice anything peculiar and in common to all the base constants except the Planck Charge. And the more controversial point is that it would imply that the Planck length, mass, time, and temperature are likely to change with the volume of the universe. This can be deduced from the fact that we know the temperature of the universe cools as it expands. There is one fundamental physical constant, and only one, associated with the difference in reliability between the FSC and the other four basic Planck Units. I know Al thinks I should 't bring up these points since I don't have a complete solution. But the start of resolving a problem is identifying it.

Steven Colyer said...

Eric, it never hurts to think outside the box. It works for Susskind, Hawking, Penrose, etc. In fact, if you can find an unprovable yet unfalsifiable theory in the next 50 years, AND you can back it up with the maths, AND you have a PhD., then tenure, professor emeritus status, and maybe a sweet book deal will be yours.

Now, as far as YOUR idea goes, would you mind sharing a bit about your educational background? Because clicking on your name doesn't reveal much. And yah, this dimensional/dimensionless stuff can get pretty strange, but at least it launches a thousand ideas, and using one's head for something more than a hatrack, which is good, good, and good and which is something you are doing and congrats on that, is my play and I wish it was the way of more of the sheeple than it is.

But. It is was it is. Too many people believe anything the "experts" tell them ("Science" "Journalists" doubly so). What they don't know is how many "experts" in any field disagree with each other. I "thought" Physics would be an exception to that. It's not. Fortunately, some Pros in the field like Bee are blatantly honest, and they're the good ones. Not everyone is in it for a buck. Some actually seek Truth, and that's my play, and I'm thinking, yours too.

But Mathematicians are the nicest, and totally cooperative folks, and if there's a field even more basic than Physics, it's Math. Which is why I'm drawn there. Plus, it tends to be true when you figure it out, meaning very undebatable. A Theorem is True, a Theory can be forever.

Specifically, before tackling Planck units, click here and read about Dimensional Analysis. That's what they teach Engineers, the guys who do the stuff the Physicists figure out, in the Macroscopic world.

But let's be honest and with all due respect to Isaac Newton, the micro-mini-verse in space and time in ten times more fun.

"Are we there yet?"

:-) No.

Eric said...

Well Steven, I have some concerns with the way you couched your question about my background. You pre-poisoned the ground by saying if I had a PhD, tenure, yada, yada, then the world would be my oyster. I'm not looking for any of that. I worked for twenty years doing avionics, am fifty eight now, and was fortunate enough to have retired early from some good investments. Academia is not my thing, nor is it required to know what you are talking about.

I did present a talk in 2005 at a STAIF symposium, (STAIF was an extension of the NASA advanced propulsion program.) It was received well but I learned that there is a lot of politics in physics and I'm not temperamentally suited for the sharp elbows and class consciousness that is part
of it.

I'm still interested in advanced propulsion concepts and actually think there is a lot of possibility for it. As I've said before the speed of light is a constant in your own frame but that does not eliminate the possibility of changing the flow of time in your reference frame. How to do that is another question and I have my ideas. But for now I've undipped my toe in the water primarily because I don't think human beings, and especially life in other parts of the universe, are ready for our aggressive tendencies. I think the technology is ready for us but we are not ready for the technology.

Robert L. Oldershaw said...

Hi Bee,

I looked up "natural units" and found a reference that said you can put c [and many other constants with a diverse array of dimensionalities] equal to one.

But how exactly do you "put" c=1. Let's start with this simplest of constants in order to establish the basic methods being used.

How exactly do you go from L/T dimensionality to dimensionless?
Or does c = 1 really mean c = 1 length unit /time unit?

How exactly do you numerically adjust c so that c = 1?

I will save G = h-bar = 1 for after c = 1 is explained to me.

Many thanks,
RLO

Steven Colyer said...

Oh Eric, don't be concerned, I wasn't talking about YOU personally, but I see the way I started that post you could get that impression so my bad, sorry.

Avionics, huh? Very nice. From Wiki: Avionics is a portmanteau of "aviation" and "electronics". It comprises electronic systems for use on aircraft, artificial satellites and spacecraft, comprising communications, navigation and the display and management of multiple systems. It also includes the hundreds of systems that are fitted to aircraft to meet individual roles, these can be as simple as a search light for a police helicopter or as complicated as the tactical system for an Airborne Early Warning platform.

I had to look that up because I was never sure what it meant, but sure enough, it is as I suspected a very large field. Well, I'm glad to see you invested well, sort of sorry you're retired. Second career? That's where I'm headed, but there are SO many interesting fields out there.

As far as physics goes, many scientists in general have strong egos, and as hard as this may be to believe, several have social development issues. That is a bit of a stereotype, Feynman certainly didn't fit it, then again, we're talking about a lot of knowledge crammed into a few years at an age most would rather be dating and skiing. That doesn't leave a heck of a lot of time for going out, but most of them I've met were nice.

Rob, if Bee doesn't answer that right away I'll give it a shot in the morning. I'm sure the answer is in those 2 links I provided.

Bee said...

Hi Robert,

It's a choice of convention, nothing else. c is a dimensionful constant. In some units, it's one. Light moves at a speed of one lightyear per year. You chose these units, that's it. L/T is never really dimensionless, but the point is you can forget about the dimension in all your calculations and just put in the conversion factors in the end. If you don't want to express your final result in units where c=1, you have to convert accordingly, to km/s or whatever. It's the same with the other constants. Takes some getting used to but slims down the notation without actually losing anything. Best,

B.

Steven Colyer said...

From here at this very blog, using the "Search Backreaction" feature:

Indeed, at this conference I heard PlanckPlanckPlanckPlanckPlanckscale all the time. So what's all that fuss about? Well, the Planck scales - a length and a mass [3] - indicate the limits in which we expect quantum gravitational effects to become important

[3]: With the speed of light set to be equal 1, in which case a length is the same as a time. It you find that confusing, just define a Planck time by dividing the length through the speed of light.

Phil Warnell said...

Hi Steven,

Not as to present myself in any way as being an authority, yet within GR distance and duration in general dimensional context are indistinguishable from one another and thus both equivalently interchangeable.

Best,

Neil B said...
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Neil B said...
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Steven Colyer said...
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Neil B said...

Folks, re Planck constant and units: Note the incredible failure, such as it is, of the "natural assumption" in some intuitive way of looking at quantum gravity, that there should be a vacuum energy of around one m_Planck per Planck volume. That is of course way too high by the celebrated amount of around 10^120 compared to actual dark energy (assuming I remembered context well enough.) Which reminds me, is DE considered a constant or something that changes? Note also, that cosmic expansion is an acceleration per distance, yielding net units of T^-2 and hence a time T equivalent. Would be interesting to compare that value to universe age and esp. if former changes.

Steven Colyer said...

I know Phil, I just quoted Bee's words from 2007 because she had a nice way of putting it. Also, it's not just Gen Rev but Spec Rev you're talking about, thanks very much to the genius that was Hermann Minkowski.

Since my student years Minkowski was my best, most dependable friend who supported me with all the depth and loyalty that was so characteristic of him. Our science, which we loved above all else, brought us together; it seemed to us a garden full of flowers. In it, we enjoyed looking for hidden pathways and discovered many a new perspective that appealed to our sense of beauty, and when one of us showed it to the other and we marveled over it together, our joy was complete. He was for me a rare gift from heaven and I must be grateful to have possessed that gift for so long. Now death has suddenly torn him from our midst. However, what death cannot take away is his noble image in our hearts and the knowledge that his spirit in us continue to be active.

. . . David Hilbert

Bee said...

Neil: The Cosmological Constant is constant. It's a special type of dark energy which in general does not have to be constant. We discussed that in this post on the cosmological constant, and it's off-topic here.

Robert L. Oldershaw said...

Thanks Bee.

So to get c = 1, you "define":

1 sec = 3 x 10^10 cm.

I also learned how you get h = 1.

In Wheeler's geometrodynamics one converts all parameters into lengths, such as 1 solar mass = 1.477 x 10^5 cm.

I see that this simplifies the calculations greatly.

My concern is that the distinction between abstract calculating conventions and realworld physics might get blurred by too much emphasis on G=h=c=1 simplification.

As long as physicists "convert" back to reality when making statements about the physical properties of nature, I have no complaint.

RLO

Plato said...
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Plato said...

Going through your links on CMB and related posts it became apparent to me that there was "some change on your part as to the recognition of sound as a basis of perspective change that allowed you to "see differently" as it did with a lot of people looking at the science of things in the CMB.

So their is a shift here in particularization and a shift into how you see, based on the way sound is generated, which to me asks us to look at the "collision points" a lot closer?

To look at the nature of the cosmos a lot closer, to define those things that are produced beyond that collision point, and decay channel for further investigation of the cosmos.

There is a equitable formalization for translation that to me should take place not only in LHC, but of a "computerized efforts to pictorial the cosmos" as we see it according to the way we map sound to colour, and sound to "decay elements."

More and more, this basis of exploration has been forefront of the way my mind has adapted to seeing. The progressiveness with the change I see is most appropriate I think into delving further into the physics of and determinations, to paint a correct picture of nature as it is.

But of course this is speculative and remains to be seen?:)

Best,

Zed said...

Bee: "With the expansion of space, matter cooled down which eventually allowed for the formation of nuclei and later atoms, molecules and increasingly large structures."

I know this is the current orthodoxy but I don't quite get how uniform expansion of space can cool anything.

Sure the wavelength of photons will increase in time but won't the wavelength of atoms and atomic transitions increase in the exact same way?

To me it seems that an observer inside an uniformly expanding universe won't notice any difference, only a hypothetical outside observer with independent length and time references could confirm the expansion (as long as he could prove that it's not his references that are changing).

Neil B said...

Zed, always looks at context and the details of a specific concept and not just some general idea from the words etc. In our context, 'expanding space' means that the distances between galaxies changes, but not 'space and everything in it' as a whole with the contents. It's sort of like, if 'the earth' as a planetary body expanded: the buildings would get farther apart from each other, so we would know. Another analogy used is a balloon blowing up, with spots of constant actual size, or with ants on it, etc. Look up "expanding universe", read about it, then come back with proper understanding.

Bee said...

Zed:

At some point I meant to write a post on this, but then found that it's well covered in many other places. The space that expands is the space between bound systems. Atoms, molecules, galaxies, planetary systems etc are all bound systems, bound by one or the other force, they don't expand themselves. It's sometimes claimed that you don't see expansion on small scales because there is so little expansion. This is just wrong. There is really no expansion. The solution to Einstein's field equations that contains the expansion is simply not valid on these scales. There's cooling with the expansion in the early universe because the temperature drops with the density. Best,

B.

Zed said...

Bee: "The space that expands is the space between bound systems. Atoms, molecules, galaxies, planetary systems etc are all bound systems, bound by one or the other force, they don't expand themselves."

Thanks for reply but I still can't understand how it's possible, could you perhaps link or say where one can find some such explanation?

AFAIK atoms, molecules, galaxies, etc, are not independent of space, they are all collections of quantum fields defined on spacetime background, so if the space expands the fields also have to be affected - their associated wavelengths have to increase as well.

For example if I have an electron with some momentum it has an associated de Broglie wavelength, now if the space expands with time this wavelength also has to increase and so the momentum decreases in the same way photons are said to lose their energy due to expansion.

Then there is electron mass which is associated with Compton wavelength, as space expands, the Compton wavelength will also increase and so electron mass will decrease.

The same thing has to hold for all the more complex systems as well. So the way I see it the end result would simply be that all the energy of all systems in the Universe is rescaled by the same factor due to expansion of space which as far as I can see cannot have observable consequences.

So where lies the error in my thinking?

Bee said...

Zed:

The error, as I just told you, is that the space inside atoms etc does not expand. The solution to Einstein's field equations that contains the expansion factor is called Friedmann-Robertson-Walker, look that up. It's an approximate solution that assumes homogeneity and isotropy, it's called the cosmological principle, look that up. That necessitates homogeneity and isotropy of the source which is sometimes referred to as the 'cosmic fluid,' look that up. It's valid only on large enough scales. On shorter scales, look around, homogeneity and isotropy is arguably not a good approximation. On these scales, the solution that contains the expansion factor is just not valid. For example for our solar system you'd use instead the Schwarzschild solution, no expansion already there. On subatomic scales you can forget about gravity altogether, but there's not even in principle an expansion there.

I know there's a paper on the arxiv about the not-expansion of atoms, but don't have the reference at hand. Will see if I find it later. In any case, what I said above you can find in every textbook on general relativity. Best,

B.

Plato said...

Perhaps using our ears could allow us to make full use of the neural networks between themListening to the ATLAS detector


The mathematical basis for sonification as it pertains too, the current existing measure of things. The "same math/experiement," used in a different way?

Can you apply macro-perspective and micro-perspective with analogical changes using sonification?

More ruminations on how we can "see differently" on what we have always seen. Will it help you to see new things?

Once you consumed the math, it became yours, and logical steps to show the progressions, are part of the extenuating circumstance of what has come from before, to the the way things are now. Is this not then a description of the way things have become.

At some point you all own it.

Concepts and conceivable changes once consumed allow this to change you, and it allows you to see differently.

Best,

Plato said...

See also Atlas Experiment.

Zed said...

Ok, thanks for your reply that clarified much more, I did also look those terms up.

It is quite surprising to me that expansion has so little theorethical support and is only a consequence of assuming homogenity and isotropy and is not present at all in other somewhat more realistic metrics.

Assuming expansion is real, this doesn't make much sense to me, as if the space can expand (or contract) it should expand (or contract) everywhere, otherwise it should be static everywhere.

For example if we start with a homogeneous and isotropic model and therefore have expansion, and add a slight localised perturbation to it, the expansion should still be present, sure it may be altered in some ways but I don't see how such a small perturbation can somehow turn the whole of space static.

Adding more perturbations, will alter the expansion even more but it still won't make space static.

This line of reasoning seems to imply that if expansion is real then it has to be present everywhere, sure it may be extremely tiny on everyday scales, and may not be modelled correctly by simple Schwarzschild metric but it has to be there.

Otherwise we would have to admit that space expands in some places but is static in others which seems quite absurd. For example what would define the boundry between those two kinds of space?

Just my 2c, as I said thanks for clarification.

Bee said...

Zed,

You're totally on the wrong track there and also completely off-topic. I have no clue what makes you say that the expansion of the universe has 'so little theoretical support.' I told you it's an approximation. You seem to think that means it's not a good solution. In fact, it's an excellent approximation on large scales. Besides that, it's experimentally confirmed. You should have figured that out from your reading.

Yes, you can add small perturbations to the background, look up 'cosmological perturbation theory.' But structure formation is non-perturbative and gravity is extremely weak compared to the other three forces.

It might seem absurd to you, but that space expands in some places and not in others is exactly what I've been telling you. There is a boundary between both, it's somewhere on the supergalactic level, but in practice it's difficult to find (as in difficult to observe). I also don't know what's absurd about that. If you compress a gas, that doesn't change the size of its molecules, it reduces the space between them. Of course in that case space itself doesn't contract, it's just less of it available, but in both cases it's the density that changes rather than the size of the gas constituents.

In any case, please read our comment rules. This is off-topic and if you have further questions, I recommend you ask them in a forum that's dedicated to these things.
Best,

B.

Steven Colyer said...

Bee, I hear what you said to Zed and pls I apologize for continuing just one teensy bit in that vein, but have you read Marcelo Gleiser's excellent essay at NPR blogs, here?

I have a bone to nitpick with him that I posted and repeat below, but before listing it, is expansion all THAT off-topic, considering that expansion prior to the CMB would definitely affect readings, or at the very least interpretations, of the CNB?

Also, did you respond to Uncle Al yet regarding materials? Because I like that a chemist cares enough about physics to have given such a thoughtful response (so you see you can't be TOO mad at me Bee because at least part of this reply is on-topic. Stefan on the other hand .... lol, just kidding).

I wrote to Gleiser and would love if you'd beat him to his response, assuming he does:

Thank you, Dr. Gleiser. Thanks also for your book this past year that there may in fact be no such thing as a "Theory of Everything", in complete disagreement with String Theorists and others, because that completely messed up my mind ... but in a good way! :-)

This is an excellent essay by a noted physicist. Granted, cutting-edge physicists like to argue like all the cutting-edge people in any profession, but that this occurs in that most base of Sciences: Physics, surprises many. Not me, not anymore.

I have several questions but will ask just one, since when we ask multiple questions the person who answers usually only responds to the last one. So my question is this:

Why did you write "the portion of space that we can measure, what is called our horizon—the distance traveled by light since the beginning of time some 13.7 billion years ago — is flat or very nearly so," that is to say, why did you write "or" ?

I'd thought its been experimentally verified that there is no "or" about it, that space is definitely slightly curved (in Physics-speech: a slightly positive cosmological constant) and therefore it merely appears flat, but is not.

Steven Colyer said...

Sorry, the correct link is here, being "Infinity, The Electron, and Other Inventions by Marcelo Gleiser".

Bee said...

Hi Steven,

The question why atoms don't expand is clearly off-topic. It's also an annoying question because you can easily get the answer elsewhere. Regarding your question, I think it's a confusion of terminology. Gleiser was probably talking about the spatial curvature which we know must have been zero or at least very very close to zero. Look up 'flatness problem.' (Related). You instead are talking about space-time curvature (the trace of the Einstein-tensor). Not the same thing. Best,

B.

Steven Colyer said...

Ah, thank you, Bee, so it's spatial curvature vs space-time curvature, I see. That was my confusion. Great, you saved me much time and that clears up much in my head, because as you know and I now realize Science journalists including some very smart men even Siegfried confuse the two, or at least don't make the simple yet important point you made. Much appreciated.

Were you ever a Girl Scout? Well whether or not I was a Boy Scout and one thing they asked us was to do one good deed each day. In your response I assure you you have done yours. ;-) All sorts of ducks are lining up in a row in my brain, so to speak.

Which reminds me, what mobile do you and Stefan have over the girls' cribs? The planets of the solar system, fundamental particles or molecules, or farm animals? They're all good. :-)

Zed said...

Ok, I won't continue this topic any further but just want to clarify one thing.

Yes, you keep asserting that space on the small scales does not expand, but you did not offer any real support for this assertion (and neither did the explanation of terms you said I should looked up).

All you have offered is that a very crude metric which we use as a model on the scale of our Solar System does not include expansion and also that on atomic scales we can ignore gravity all together. That is all true or course but it doesn't support your assertion.

It's like trying to prove that space and time are absolute by invoking the fact that Newtonian physics works great on everyday scales and it assumes they are absolute.

The expansion we are talking about is extremely tiny, it takes billions of years for the wavelengths of photons from distant galaxies to be stretched to a significant extent, so *of course* it can be safely ignored on the scales of our solar system or on atomic scales, but that certainly doesn't prove that it's not there.

And if it IS there then just as with photons over billions of years the wavelengths of matter fields will also expand to a significant extent and this effect will have to be taken into account to properly model evolution of our strange Universe.

Bee said...

Hi Zed,

If you didn't find an explanation looking up the terms I recommended, maybe look again. You might also have to think about it, I probably should have added this. Some more details on what I told you above are here

http://math.ucr.edu/home/baez/physics/Relativity/GR/expanding_universe.html

And that paper might be useful

http://arxiv.org/abs/gr-qc/0508052/

Though it's not the one I had in mind.

Both of which, I should add, you could have easily found with a Google search. Have fun,

B.

Rhys said...

Zed, if you're still interested, there is an obvious difference between photons and the electrons/atoms/other about which you are worrying: photons are massless, massive things are not! ;-)

The size of a hydrogen atom, for example, is set by the masses of the electron and proton, and the strength of the electromagnetic interaction. These quantities are obviously not affected by the expansion of the universe, as I'm sure you'll agree.