The Fate of the Universe: Expansion, Matter Decay, and the Ultimate End

[Chalnoth]

One reason to be clear about these things is that I'm wary of evidence by lack of imagination. I don't think that anyone has tried very hard to try to fit the BAO data to a world with antimatter (because there really is no good reason to) so I can't say with any certainty that it can't be done.

The likelihood of such disparate observations coinciding by some other physical process is virtually nil.

One reason to be careful is that the odds that you've overlooked a particular thing is very low. However cosmological models are complex enough so that I think it's highly likely that one assumption of the dozens that we are making is seriously wrong is high.

The chance that one of these things being wrong completely changing the overall picture is, however, almost nonexistent. The problem is that we now have a wide body of evidence using a significant variety of observations that all point to the same general picture. The chance of some wildly-different theory fitting the exact same data is small enough that it isn't worth bothering with.

 

[twofish-quant]

The likelihood of such disparate observations coinciding by some other physical process is virtually nil.

But in the case of anti-matter, we don't have that much in the way of disparate observations. We have

1) lack of gamma ray flux
2) BAO calculations.

Now for other parts of the standard model (say dark matter or expansion of the universe) you can point to six or seven different observations that support that. But we aren't taking about dark matter or the expansion of the universe.

Also, talking to people with different physics backgrounds is useful sometimes. For example, I've found that plasma physicists are much more open to the Alfevin model because if you go up to an expert in astrophysical plasmas and say "no process could possibly reproduce the CMB" they step back and laugh at you, and then come up with six or seven processes that you've never heard of.

Now if you talk to nuclear physicists on the other hand and try suggesting that maybe the BBN numbers are wrong because of someone unknown process, you get a bunch of bricks on you, since those numbers are settled.

The problem is that we now have a wide body of evidence using a significant variety of observations that all point to the same general picture.

I care about the details.

That's much too general a statement to be useful, and it's false for particular details. For example, it turns out to be rather difficult to show that a distant galaxy is made of anti-matter. There's one known way, and the fact that there is one known way is a weakness.

There are some pretty basic things that we don't *know*. For example, we strongly suspect that anti-protons will attract each other with gravity, but showing that this is true turns out to be rather difficult.

The chance of some wildly-different theory fitting the exact same data is small enough that it isn't worth bothering with.

Well...

http://moriond.in2p3.fr/J08/trans/sunday/benoit-levy.pdf

http://www.ipnl.in2p3.fr/IMG/pdf/091022_Dirac-Milne_Chardin_IPNL.pdf

I think that when the dust clears that the the standard model will win but "The chance of some wildly-different theory fitting the exact same data is small enough that it isn't worth bothering with." is something I very, very, very strongly disagree with.

The reason this is interesting is that to get a coasting universe, Levy has to assume

1) the universe is half anti-matter
2) anti-matter and matter repel each other

He has trouble getting BAO to match, but I'll give him a few years to try before declaring it can't be done, and he is coming up with interesting stuff...

http://www.icranet.org/talks/WeeklySeminars/2008/March/Chardin.pdf

Also there is the theoretical aspects. Lot's of stuff changes depending on what comes out of LHC. If we find a supersymmetry particle that changes a lot, and things will change once we actually drop the anti-hydrogen in AEGIS.

And as far as the "nuttiness" factor, I'd put repulsive anti-matter as less "nutty" than supersymmetric GUT's. We know antimatter exists.

 

[twofish-quant]

One reason I'm interested in what Levy and Chardin are doing is because of some of the conversations that I've had here.

There are these long threads on physics forums that go

Poster: Milne universe is cool
Me: Yes it is but it won't work because of X, Y, Z, and A

What's neat about Dirac-Milne is

Poster: Milne universe is cool
Me: Yes, but it won't work because of X, Y and Z
Poster: Well... We've gotten X and Y to work, and we are looking at Z
Me: COOL!

It might be wrong, but it's not *obviously* wrong.

 

[Chronos]

The evidence does not support the idea the universe is half anti matter. The gamma ray background overwhelmingly refutes that possibility.

 

[twofish-quant]

The evidence does not support the idea the universe is half anti matter. The gamma ray background overwhelmingly refutes that possibility.

Right. However, the interesting thing is that for stuff like the age of the universe, you have multiple independent lines of reasoning that get you to that conclusion, so if it turns out that you made a mistake in one line of reasoning, it doesn't matter because you have a dozen more that gets you to that conclusion. Dark matter for example has lots of different unrelated things that support it, so if it turns out that we just got galaxy rotation wrong, it doesn't change the conclusion. But off hand, I don't think that's the situation with anti-matter.

The idea that there is not substantial amounts of anti-matter has as far as I'm aware of, two (gamma ray flux and BAO). That means that it's more fragile than other things. For example, if you argue that anti-matter and matter repel each other, then they'll separate into different domains over large time scales, so no gamma ray flux.

There's an interesting problem here. If the cells are too large, then you get CMB anisotropy. If the cells are too small, that hits the flux limits. So it's possible that it won't work. But I haven't run the numbers.

Now, if people go and figure out six or seven independent ways of showing that there is no anti-matter in the universe, then well... Good...

Also, I'm playing defense right now. One reason I've read so much about Milne-Dirac models was I got familiar with them while playing offense. There are some old threads in which I was arguing very strongly against Milne models and the coasting universe, and while playing "offense" I stumbled onto those papers. I mentioned those papers so that someone playing defense could have taken them and argued back, but people didn't.

Since other people are playing offense right now, I'm playing defense.

For people that aren't familiar with how science works, this is an example of how arguments work.

 

[Chalnoth]

But off hand, I don't think that's the situation with anti-matter.

We do have multiple, independent lines of reasoning for the interpretation of the CMB as stemming from a time when our universe was a near-uniform plasma. It is simply not possible for the anti-matter to not have annihilated while our universe was a plasma.

 

[twofish-quant]

We do have multiple, independent lines of reasoning for the interpretation of the CMB as stemming from a time when our universe was a near-uniform plasma. It is simply not possible for the anti-matter to not have annihilated while our universe was a plasma.

Can you cite some papers? The papers I've seen constrain the amount of anti-matter by constraining the energy injection into the CMB. The assumption is that matter/anti-matter annihilation injects energy, and which causes polarization.

http://arxiv.org/abs/astro-ph/0312168

In Dirac-Milne, matter and anti-matter repel which causes them to separate which would sharply reduce annihilation. In both CMB and Dirac-Milne, CMB happens several hundred thousand years after event zero, which is more than enough time for the matter and anti-matter to separate. At which point energy injection arguments disappear, and you are looking for large angle deviations from the standard model, and it's at large angles that we have trouble fitting CMB.

This would have other effects on the CMB, but it's not a five minute discussion to figure out what they would be. What I would imagine is large angle deviations.

Also as far as baryon acoustic oscillations, I took a deeper look at this. What the BAO actually measures is the baryon/photon ratio. It's got nothing to do with anti-matter, so there is nothing in BAO that can be used as any sort of evidence against cosmological anti-matter. The interpretation of BAO *assumes* that there is baryon asymmetry and all of the anti matter got turned into photons. It's not evidence that this what happened.

One thing that I think that the non-standard cosmology guys do which is useful is to challenge people to answer questions. It's not enough to just say "we have lots of evidence". You need to put together a chart saying "this is the evidence." There *are* good reasons for thinking that the universe is mostly matter, but one thing that I go out of reading the papers is that they weren't nearly as strong as I thought they were. If you ask me why we think there is dark matter, I can off the top of my head think of five or six reasons. If the question is why do we think that the universe is mostly matter, I can think of one or two. Granted, these are *good* reasons, but it's less than I would have expected.

 

[twofish-quant]

I don't believe for a moment that you could get that many e-foldings and still have a baryon number worth measuring, because if you did, then the baryons would have been so dense early-on that they would have absolutely overwhelmed the inflaton field and you would have had no inflation at all.

What if the inflaton itself had a non-zero baryon number? Since we know almost nothing about the inflaton field, we don't know if that field can't carry a non-zero baryon number which was transferred over to baryons once the field decayed.

There is a lot of work on baryongenesis with a decay of the inflationary scalar field. However, if you are at the point where you are talking about the inflationary field interacting with baryon number, you might save a step and argue that the inflationary field has a non-zero baryon number ab initio.

Also, one thing about playing defense is that I'm playing defense for two different teams here. Logically it's not possible for *both* primordial baryon asymmetry and Dirac-Milne to be correct, and I realize that.

 

[Chalnoth]

Can you cite some papers?

I'm not aware of anything specific. My reasoning simply consists of:

1. The plasma which emitted the CMB was a nearly-uniform thermal bath at around 3000K. We know it was almost perfectly thermal because of the almost perfectly-thermal spectrum of the CMB.
2. A 3000K thermal plasma doesn't have anti-matter.

 

[Chalnoth]

What if the inflaton itself had a non-zero baryon number?

My understanding is that the inflaton mass had to be many orders of magnitude higher than the proton mass, so that at best this could account for a minuscule fraction of the baryons.

 

[twofish-quant]

I'm not aware of anything specific. My reasoning simply consists of:

1. The plasma which emitted the CMB was a nearly-uniform thermal bath at around 3000K. We know it was almost perfectly thermal because of the almost perfectly-thermal spectrum of the CMB.
2. A 3000K thermal plasma doesn't have anti-matter.

This won't work in Dirac-Milne. If matter and anti-matter repel each other, when when you look at the CMB you are seeing a 3000K thermal plasma, only that you see 3000K matter plasma at some parts of the sky and 3000K anti-matter plasma at some other part of the sky. Now where the matter and antimatter meet, you'll see "weird stuff" but off the top of my head, if the zones are big enough and people aren't specifically looking for "weird stuff" they won't find it. In particular, the domain boundaries are going to be at large angles, and people have been looking at small angle fluctuations.

Now, I still think that the standard model is going to win, but we are talking about levels of uncertain. I'd be willing to bet US$20,000 that there is insignificant amounts of anti-matter in the universe, but I wouldn't be willing to bet US $1 million. I would be willing to bet say $500,000 that there are large amounts of dark matter. If you asked me to go on an airplane that will blow up if the sun doesn't work with nuclear fusion, I'd get on it, since I'm that sure. If the airplane would blow up if the universe had any substantial amount of antimatter, I wouldn't get on it.

This thing about assigning money to uncertainty isn't merely a game. AEGIS has been budgeted at about a million Swiss francs. If we were sure that antiprotons would respond to gravity the same way protons do, it would be a utter waste of money. But we aren't...

More to the point, if it comes down to deciding whether the articles should get published or whether people should get grant money, I've been very impressed by what the Dirac-Milne people have come up with. Even if they are wrong, they have come up with interesting questions.

For example, one big problem with slow growth cosmologies is that you burn up all the deuterium. Case closed... The first papers just talked about deuterium creation processes that people figured out in the 1970's wouldn't work. But then someone points out that if you have a source of anti-protons, then the conclusions of the 1970's that you can't get large amounts of deuterium goes out the window.

And let's suppose we drop an anti-proton and it falls down. One thing that is an interesting question is if you have domains of matter and antimatter, could they be larger than the observable universe. There's an anthropic "broken symmetry" here. If you have a universe that is equal matter and anti-matter then you don't get physicists. If you have a universe that is asymmetric toward either matter or anti-matter then you will (since physicists in the anti-universe will assume that they anti-matter is matter).

So if you assume that the distribution of baryon number at the start of inflation is *random* what happens?

 

[twofish-quant]

My understanding is that the inflaton mass had to be many orders of magnitude higher than the proton mass, so that at best this could account for a minuscule fraction of the baryons.

That assumes that the inflaton has a limited baryon number. There's no reason that I can think of that a single inflaton couldn't have a baryon number of say a million. That's the nice thing about hypothetical particles, you can make up anything.

Also you can assume that baryon number is stored an a massless field. By analogy, a neutrino with +1 lepton number can interact with a neutron with 0 lepton number to generate an electron with +1 lepton number. You could have large numbers of massless particles with non-zero baryon number interact with the inflation field to create protons. Or maybe they aren't massless. Any reason why something with non-zero baryon number has to interact with the strong force?

Yes, I'm inventing particles at random here, but it's no worse than what the supersymmetry people are doing, and if you can find some constraints on the baryon number of the inflation field, that would be useful to put a leash on that.

 

[Chalnoth]

This won't work in Dirac-Milne. If matter and anti-matter repel each other, when when you look at the CMB you are seeing a 3000K thermal plasma, only that you see 3000K matter plasma at some parts of the sky and 3000K anti-matter plasma at some other part of the sky. Now where the matter and antimatter meet, you'll see "weird stuff" but off the top of my head, if the zones are big enough and people aren't specifically looking for "weird stuff" they won't find it. In particular, the domain boundaries are going to be at large angles, and people have been looking at small angle fluctuations.

I'm pretty sure that would quite dramatically change the spectrum of the CMB, and in particular it would change the spectrum in a way that is dependent upon location on the sky that doesn't simply look like a tiny change in temperature.

That assumes that the inflaton has a limited baryon number. There's no reason that I can think of that a single inflaton couldn't have a baryon number of say a million. That's the nice thing about hypothetical particles, you can make up anything.

Except now you're leaping into the realm of incredible implausibility.

 

[twofish-quant]

I'm pretty sure that would quite dramatically change the spectrum of the CMB, and in particular it would change the spectrum in a way that is dependent upon location on the sky that doesn't simply look like a tiny change in temperature.

The trouble with large angle changes is that there's a lot that could get lost in data reduction. For example, if you had a domain wall that was in the galactic plane, you'd never see it.

If people have looked for this and not found it, that's one thing. Have people looked?

Except now you're leaping into the realm of incredible implausibility.

Any particular reason why a field with a large baryon number is implausible? The trouble with inflation is that we aren't bound very much by observation. It's hard to tell what is "plausible" or not. I mean what makes a field with a baryon number of 100000 less plausible than a supersymmetric particle or axions, or all of string theory?

That's a serious question.

Also you don't need a baryon number of 100000. Suppose you have a very massive inflaton that all had +1 baryon number. During inflation, the inflaton decays into baryons. All you have to do is to have the mass proton / mass inflation be less than the baryon asymmetry and everything works out, and that gives you numbers.

The reason that inflation works the way that it does is because it creates a more "natural" theory if inflation wipes out pre-inflationary information and dilution gives a good way of doing it. However, if you trying to keep pre-inflationary information, it doesn't seem that difficult to do that.

 

[Chalnoth]

The trouble with large angle changes is that there's a lot that could get lost in data reduction. For example, if you had a domain wall that was in the galactic plane, you'd never see it.

At around 100GHz or so the anisotropies in the CMB are brighter than even the galactic plane, except very close to the galactic center. And you can use various sorts of multifrequency analysis to get a pretty good map of almost the entire sky that is nearly all CMB. So no, not even that would work.

I also would think that this sort of feature would be vastly, vastly brighter than the CMB anisotropies which are only about one part in 10,000 of the average temperature (which also means that the overall CMB temperature is far brighter than the galaxy everywhere in the sky).

Any particular reason why a field with a large baryon number is implausible?

Quantization generally prevents such things from occurring. Especially if the baryon number comes along with electric charge (which appears to be the case).

Also you don't need a baryon number of 100000. Suppose you have a very massive inflaton that all had +1 baryon number. During inflation, the inflaton decays into baryons. All you have to do is to have the mass proton / mass inflation be less than the baryon asymmetry and everything works out, and that gives you numbers.

Well, what would prevent the inflaton field from decaying into baryons before inflation ends in this scenario? Why wouldn't the inflaton field simply immediately decay into baryons?

My understanding is that reheating normally is thought to occur through a resonance of the inflaton field oscillating around its potential minimum, as opposed to your typical particle decays. I don't believe that this sort of effect would allow any transfer of any particle numbers from the inflaton to the standard model particles.

 

[twofish-quant]

I also would think that this sort of feature would be vastly, vastly brighter than the CMB anisotropies which are only about one part in 10,000 of the average temperature (which also means that the overall CMB temperature is far brighter than the galaxy everywhere in the sky).

Until someone, (perhaps me), actually runs the numbers, I'm not entirely convinced that you can't make something like that disappear. Off the top of my head, you wouldn't be looking for bright spots, you are looking for lines where the brightness is anomolously low, and it would be easy to disregard these features as local scattering.

Also CMB doesn't measure brightness. They measure wavelength distribution, and the error bars at large angles are huge.

http://www.cmu.edu/cosmology/events/cosmic-acceleration/will_kinney.pdf

Quantization generally prevents such things from occurring. Especially if the baryon number comes along with electric charge (which appears to be the case).

There's nothing here that conflicts with quantization. You still have integer baryon numbers. They are merely very high. Also neutrons have +1 baryon number but no charge.

Just look up arxiv.org and look for Q-ball. One you have field theory, you end up with point like topological defects with huge charge and baryon number.

If you can link baryon number with charge they you can come up with firmer arguments.

Well, what would prevent the inflaton field from decaying into baryons before inflation ends in this scenario? Why wouldn't the inflaton field simply immediately decay into baryons?

Alien space bats. Normally we are constrained by observations, but since there are no such constraints as far as inflatons go, I can invoke alien space bats. Now it gets interesting if I invoke alien space bats, and I *still* can't get it to work, that's interesting.

Now if you don't like alien space bats, then if the temperature is much larger than than the mass of the inflaton then we ought to expect the backward reactions to create inflatons to be on the order of the inflaton->baryon reaction rate.

What I'm looking for is an explicit contradiction. For example, if you can show that a baryon number of one million violates Lorenz covariance, that would be a strong argument. However, if you say "to get this to work you need X" then you need to explain why X can't exist. For inflation, that's going to be a hard slog.

For CMB or nucleosynthesis, you can see that there are no alien space bats. My point is that for the inflationary era, you can't.

My understanding is that reheating normally is thought to occur through a resonance of the inflaton field oscillating around its potential minimum, as opposed to your typical particle decays. I don't believe that this sort of effect would allow any transfer of any particle numbers from the inflaton to the standard model particles.

It's actually quite simple.

You have things like the Affeck-Dine mechanism in which some particle field gets baryon numbers due to CP violation during inflation, and then at the end transfers those baryon numbers to the SM particles

see http://arxiv.org/pdf/1108.4687.pdf

Now the wrinkle here is that instead of violating CP during inflation through alien space bats, you argue that the inflation field (or some other field that gets tagged along) has non-zero baryon symmetry before inflation gets started, and rather than generating the baryon asymmetry, the alien space bats merely preserve it.

 

[twofish-quant]

Also, I'm talking about the situation in 2012, one of the nice thing about Planck and LHC is that I won't be able to invoke alien space bats in 2020.

 

[twofish-quant]

Scratch that about alien space bats needed to keep the inflaton from decaying into baryons. I just ran some rough numbers and the simple answer for what keeps the inflaton from decaying into baryons immediately is "absolutely nothing." The inflationary time scale is 10^-32 seconds, and it's trivial to have a inflaton whose decay rate is on that order.

 

[Chalnoth]

Until someone, (perhaps me), actually runs the numbers, I'm not entirely convinced that you can't make something like that disappear. Off the top of my head, you wouldn't be looking for bright spots, you are looking for lines where the brightness is anomolously low, and it would be easy to disregard these features as local scattering.

What you'd be looking for is areas where there is actually less plasma, and instead is the occasional matter/anti-matter annihilation. This wouldn't be an effect on the scale of the tiny temperature anisotropies. This would be significant compared to the overall 2.7K temperature of the CMB, which is 10,000 times brighter, and much brighter than any other source of light in the sky.

Also CMB doesn't measure brightness. They measure wavelength distribution, and the error bars at large angles are huge.

This isn't at all true. Instruments like WMAP and Planck specifically measure relative radiation intensity at different places in the sky at specific wavelengths. Most such instruments aren't very good at measuring the absolute brightness directly: this is inferred through, for example, the dipole in the CMB induced by the motion of the Earth around the Sun. But they are extremely good at measuring relative brightness in different locations. That's what they're built for.

http://www.cmu.edu/cosmology/events/cosmic-acceleration/will_kinney.pdf

The large error bars you see here are not measurement errors alone. They are measurement errors plus cosmic variance. The measurement errors on low multipoles with WMAP are extremely tiny (typically much smaller than the errors on high multipoles). The cosmic variance errors, however, are based upon our theoretical model of the physics that produce the CMB, a model which makes a probabilistic prediction on that just isn't very precise at low multipoles.

In essence, the theoretical prediction of how the CMB should look given a set of cosmological parameters (e.g. normal matter density, dark matter density, dark energy density, etc.) is not a specific value, but a variance. Since the prediction is only the variance, and since low multipoles have a small number of independent components (e.g. 5 components for ell=2), the measured variance can vary dramatically from the theory variance without being inconsistent with the theory.

At higher multipoles, where you have a lot of independent components, the measured variance and the theoretical variance have to match much more closely for the theory to agree with experiment.

There's nothing here that conflicts with quantization. You still have integer baryon numbers. They are merely very high. Also neutrons have +1 baryon number but no charge.

Just look up arxiv.org and look for Q-ball. One you have field theory, you end up with point like topological defects with huge charge and baryon number.

Those aren't particles, though. Those are large collections of particles localized at a specific point.

Anyway, we'll see. But these models seem to me to be highly contrived and thus highly unlikely.

 

[twofish-quant]

What you'd be looking for is areas where there is actually less plasma, and instead is the occasional matter/anti-matter annihilation. This wouldn't be an effect on the scale of the tiny temperature anisotropies. This would be significant compared to the overall 2.7K temperature of the CMB, which is 10,000 times brighter, and much brighter than any other source of light in the sky.

This is not terribly convincing without even rough numbers. If you presume that matter and anti-matter repel each other, then you have several hundred thousand years for the matter and anti-matter to separate, and you can make the matter/anti-matter annihilation end up as low as you want. That gets rid of the non-thermal spectrum.

I did a quick calculation of gamma ray flux and to make the numbers work, you have to assume a suppression factor of 10^-2 or 10^-3. That's not a crazy number if matter and anti-matter repel.

At that point you'd have much less plasma at the domain walls, but the temperature would have time to thermalize at which point that you'd have a thermal spectrum and no temperature anisotropy.

Most such instruments aren't very good at measuring the absolute brightness directly: this is inferred through, for example, the dipole in the CMB induced by the motion of the Earth around the Sun. But they are extremely good at measuring relative brightness in different locations. That's what they're built for.

Right. But if you have domain walls, then the relative brightness over a large chunk of sky is likely to be the same.

The cosmic variance errors, however, are based upon our theoretical model of the physics that produce the CMB, a model which makes a probabilistic prediction on that just isn't very precise at low multipoles.

Which means that if there is something funny happening at low multipoles, you aren't going to see it.

Also, because of gamma ray flux, I doubt that we are missing anti-matter. However, getting to what the observations show or don't show is interesting because we could be missing something else. Cosmic strings or GUT monopoles would produce similar domain wall effects. For that matter, if you have a model of CMB at low monopoles, you might be able to use it to map nearby voids.

At higher multipoles, where you have a lot of independent components, the measured variance and the theoretical variance have to match much more closely for the theory to agree with experiment.

Right, but at high multipoles everything goes thermal so Dirac-Milne gives you the same basic spectrum.

Those aren't particles, though. Those are large collections of particles localized at a specific point.

But the topological defect mechanism as far as I can tell could work for the inflaton. Why do we think the inflaton is a massive particle? It's because we need inflation to happen at a specific time and having a massive particle makes the phase transition happen at the right time. Well, what if you have collections of small particles?

Anyway, we'll see. But these models seem to me to be highly contrived and thus highly unlikely.

Saying that something is unlikely presumes a meta-theory. One problem with meta-theories is that whether something is contrived or not is a matter of taste. One reason Dirac-Milne is interesting is that it seems less contrived than the standard model, but this is a matter of taste, and the problem with aesthetic arguments is that if someone says it "looks contrived" and you disagree, there's no way of easily resolving the argument.

The trouble with "aesthetic arguments" is that all of our standard models are highly contrived. They end up highly contrived because reality is complicated and you have to do messy things to make the models fit reality. For things that we have lots of observations for, it's relatively easy to figure out what those messy things are. For stuff that we don't, it's not.

So we need more data, but then we have to ask what data do we need. It's not a matter of "wait and see" and "wait and see what?"

 

[Chalnoth]

This is not terribly convincing without even rough numbers. If you presume that matter and anti-matter repel each other, then you have several hundred thousand years for the matter and anti-matter to separate, and you can make the matter/anti-matter annihilation end up as low as you want. That gets rid of the non-thermal spectrum.

I did a quick calculation of gamma ray flux and to make the numbers work, you have to assume a suppression factor of 10^-2 or 10^-3. That's not a crazy number if matter and anti-matter repel.

At that point you'd have much less plasma at the domain walls, but the temperature would have time to thermalize at which point that you'd have a thermal spectrum and no temperature anisotropy.

This doesn't help, because it would still be much dimmer at the domain walls, which I would be willing to bet would be glaringly obvious in the CMB spectrum. Specifically, it would be glaringly obvious in the spectrum of the anisotropies (because instead of differences in temperature causing the anisotropies, differences in density would cause some of them, which would lead to different spectral effects).

Which means that if there is something funny happening at low multipoles, you aren't going to see it.

Right, but domain walls would affect multipoles on many scales, because they are linear features.

Right, but at high multipoles everything goes thermal so Dirac-Milne gives you the same basic spectrum.

Why? The optical thickness of the CMB washes out features at high multipoles overall, but the effect of the domain walls should be visible at all scales relative to the CMB anisotropies (which are also washed out at high multipoles due to this effect).

But the topological defect mechanism as far as I can tell could work for the inflaton. Why do we think the inflaton is a massive particle? It's because we need inflation to happen at a specific time and having a massive particle makes the phase transition happen at the right time. Well, what if you have collections of small particles?

The inflaton is typically modeled as a field, with the quanta of that field being inflatons. I'm not sure a field of solitons makes sense.

Saying that something is unlikely presumes a meta-theory. One problem with meta-theories is that whether something is contrived or not is a matter of taste. One reason Dirac-Milne is interesting is that it seems less contrived than the standard model, but this is a matter of taste, and the problem with aesthetic arguments is that if someone says it "looks contrived" and you disagree, there's no way of easily resolving the argument.

I would be willing to bet that Dirac-Milne simply cannot work on purely empirical grounds, just given our current observations of the CMB, regardless of any arguments regarding simplicity.

As for simplicity, however, there are reasonably good measures of simplicity, such as the number of parameters required to describe the model. If a model requires more parameters to describe it, it sure as heck had better explain a lot more experimental evidence than the competing model, or else it's most likely wrong. Even though it's not possible to prove that this is a good way of doing things, and even though there are sometimes arguments about just how simple or complex various theories are, it seems to be a pretty good heuristic that has worked rather well in the past. And there are some rather rough probabilistic justifications for it that at least seem reasonable.

So we need more data, but then we have to ask what data do we need. It's not a matter of "wait and see" and "wait and see what?"

Yes, it is a matter of wait and see, because it takes an overwhelmingly-compelling theory to push people to base new experiments about it.

 

[twofish-quant]

Why? The optical thickness of the CMB washes out features at high multipoles overall, but the effect of the domain walls should be visible at all scales relative to the CMB anisotropies (which are also washed out at high multipoles due to this effect).

A lot depends on the geometry of the domain walls, and on the processing that people do to get the multipoles. If the thickness of the domain walls are large compares to the features that people care about, then the only thing in the higher order multipoles are going to be harmonics and it's not hard for those to get lost.

One thing is that if some says "yes I've actually put in domain walls" here is what they look like, that would convince me, but I think that the Dirac-Milne have put enough of a case that I don't think that it's valid to dismiss their challenges without some numbers.

The inflaton is typically modeled as a field, with the quanta of that field being inflatons. I'm not sure a field of solitons makes sense.

What if the inflaton is a soliton? The reason you need a high mass particle is so that you get the phase transition at the right time. You can have the inflationary particle be relatively low mass but the phase transition happen because of a soliton.

Also, this is a different argument than Dirac-Milne.

I would be willing to bet that Dirac-Milne simply cannot work on purely empirical grounds, just given our current observations of the CMB, regardless of any arguments regarding simplicity.

It's not that one is willing to bet but how much. I'd be willing to bet US $25K-$50K that Dirac-Milne is wrong. I wouldn't bet my life on it. As far as primordial baryongenesis. I'd be willing to bet several hundred dollars that primordial baryon number is irrelevant, but I wouldn't bet any more than that.

Yes, it is a matter of wait and see, because it takes an overwhelmingly-compelling theory to push people to base new experiments about it.

Or one weird observation. All that has to have happen to have people take Dirac-Milne seriously is to drop some anti-protons and watch them go up.

 

[Chalnoth]

One thing is that if some says "yes I've actually put in domain walls" here is what they look like, that would convince me, but I think that the Dirac-Milne have put enough of a case that I don't think that it's valid to dismiss their challenges without some numbers.

It's up to them to put forward their case, not the rest of us to disprove it. And yes, I really think that the domain walls would produce brightness anisotropies that are much, much larger than the temperature anisotropies we see.

Or one weird observation. All that has to have happen to have people take Dirac-Milne seriously is to drop some anti-protons and watch them go up.

Well, right, and there are groups that are trying. The problem is that it's really, really hard given that gravity is some 40 orders of magnitude weaker than electromagnetism, so that the electric charges of the anti-protons tend to react far more strongly than do their masses.