Inflation and Monopoles: Exploring the Mysteries of Cosmic Expansion

[Chronos]

Garth, that is strangely reminiscent of string theory - a theory suffiiciently flexible to accommodate any observational evidence. I instinctively find such ideas repulsive and useless.

 

[bapowell]

Inflation isn't short on falsifiable predictions, but that's the problem, there are too many of them.

Falsify one and an alternative is proposed, and then another, and then another...

Garth

Then I would argue those aren't falsifiable prediction, or at least, they don't get at generic predictions of inflation but rather deal with predictions of specific models (like whether the scalar tilt is such and such). I can think of one generic prediction of inflation: superhorizon correlations in the EE polarization anisotropy.

 

[palmer eldtrich]

Then I would argue those aren't falsifiable prediction, or at least, they don't get at generic predictions of inflation but rather deal with predictions of specific models (like whether the scalar tilt is such and such). I can think of one generic prediction of inflation: superhorizon correlations in the EE polarization anisotropy.

Can you explain this in laymans terms? "superhorizon correlations in the EE polarization anisotropy'

 

[bapowell]

I'll try. Please let me know if I stray too far off the path here. CMB photons observed on Earth today are polarized. They can be either E-mode (curl-free) polarized or B-mode (curl) polarized. CMB photons are not polarized initially: when CMB photons move through an overdensity, they become E-mode (or scalar) polarized. We can use the pattern of E-mode polarization found in the CMB to reconstruct the field of density perturbations in the early universe. When we measure the polarization of CMB photons from across the sky, we find that there are interesting correlations in the polarizations of photons arriving on Earth from different directions (E-mode from one direction correlated with E-mode from another direction gives EE). The larger the angular separation of the photon directions, the larger the size of the overdensity that caused the polarization. What we find, remarkably, is that there are photon correlations indicating overdensities that were truly large -- larger than the size of the observable universe when the CMB was created. (The CMB was "created" around 350,000 years after the big bang. The size of the observable universe is roughly the distance that light had traveled in those 350,000 years (with the help of the expansion).) So these correlations bespeak an acausal process: the generation of an overdensity larger than the distance light could have traveled since the big bang. Inflation generically creates such "superhorizon" perturbations (overdensities).

 

[skydivephil]

Thanks for that Bapowell. Is this something that alternatives to inflation such as Ekpyrosis, VSL, CCC, string gas cosmology etc can explain as well or is it unique to inflation?

 

[bapowell]

Yes, I believe that many alternatives produce superhorizon correlations as well.

 

[skydivephil]

So in that case, it seems to me that if we see a red tilted primordial gravity wave spectrum with no large devaition from gausianity then we can start handing out Nobel prizes for inflation, but not before? Do you agree?

 

[bapowell]

Indeed, a red-tilted tensor spectrum would rule out many alternatives (ekpyrosis, string gases, matter bounces) and would be strongly supportive of inflation. Yes, Alan Guth might get a phone call from Sweden.

 

[slatts]

The Boltzmann brain concept is probably a leading example of logical reasons for dismissing the idea of a past eternal universe.

I think what Chronos is saying is that in an past eternal universe/multiverse not only Boltzmann brains appear, an infinite number of times, but anything else logically possible you can possibly conceive of does as well an infinite number of times.

There is no way to test such an hypothesis and as a theory of anything is a theory of nothing it is totally outside the province of scientific inquiry. Good for science fiction though!

Garth

Let's look at the three contenders (Boltzmann brains, future-eternal inflation, and past- & future-eternal inflation) as the source of whatever perceptions anyone of us might be experiencing. The Boltzmann brains are plainly the most probable as far as their origin in quantum fluctuations is concerned, but the nearly-equal probability of the disappearance of anyone of them, in a quantum fluctuation that would tend to be very nearly as simple as the originating one, totally reverses their lead. The conventional favorite is inflation at least possibly eternal to the future, which, although it could originate in a quantum fluctuation, would tend to require one almost inconceivably more complex for its ending. But, at least in its formulation modeled by Aguirre and Gratton as a dual universe expanding to one side of a three-spherical boundary surface while contracting to the opposite side of it (with a pair of thermodynamic "arrows of time" each occupying one of those halves, and each pointing in the temporal direction opposite the other's), I'd figure that the past- and future-eternal multiverse would seem to be the most likely, because the inconceivably complex quantum fluctuation able to account for its termination would tend to be exponentially more complex than whatever quantum fluctuation might have alternatively accounted for the conventional one's end. (You might say that it would have survival traits that would be more "evolved" than either of the alternatives', and would consequently have been durable enough to have lasted into our own piece of "global " time.)

 

[Joe Ciancimino]

Do people actually believe in magnetic monopoles? The non-observance of magnetic monopoles is only evidence for inflation if magnetic monopoles can be shown to exist.

I think this is one of those great "Oops" moments in history that got swept under the rug. Most people had totally forgotten about monopoles since they really had not been mentioned since around the 1970's or so. From what I remember of it the original theory stated there would either be a single monopole to seed each instance of a big bang universe, or that the monopoles would be so abundant that they would be virtually everywhere. Some 30 years later we find out that ordinary electrons are monopoles, we just did not have the technology to detect the details of them in the 1970's and is the basis of the new upcoming technology of Spintronics. Of course this would be debatable if the magnetic momentum of an electron matches the details of the prediction shown in the theory, but very close regardless.

Spintronics
https://en.wikipedia.org/wiki/Spintronics

 

[PeterDonis]

Some 30 years later we find out that ordinary electrons are monopoles

I don't see how spintronics shows that. Electrons have been known to have magnetic moments since the 1920's, but they are dipoles, not monopoles. Their magnetic moment arises from the fact that they have both electric charge and angular momentum; the combination of those two things makes a magnetic dipole.

 

[slatts]

Much as the monopole seems to me to have some affinity with that one-sided version of Aguirre & Gratton's double-arrowed twin universes whose hypothesized existence somehow preceded it in theory, I'm more than a little vague on it myself, but earlier today I dug up this 1996 bit by Linde, at

http://www.worldscientific.com/doi/abs/10.1142/S0218271896000515,

in which he sketches theories developed by other physicists between that year and 1971 that put entire universes inside one elementary particle or another, and the monopole seems to have been a special favorite as the "seed" particle within which they would develop. Linde himself had a paper, "Monopoles as big as a Universe", published as recently as 1994, but whatever flaw it had isn't clear from the abstract. Someone more familiar with such cosmologies might be able to say whether the disappearance of the observable contents of the monopoles' field had resulted from its realization as the container itself. My own reading of Guth, left shallow by my sketchy math, is that they were more simply left rare by a more generic expansion.

 

[Joe Ciancimino]

I don't see how spintronics shows that. Electrons have been known to have magnetic moments since the 1920's, but they are dipoles, not monopoles. Their magnetic moment arises from the fact that they have both electric charge and angular momentum; the combination of those two things makes a magnetic dipole.

I stand corrected, I blame some of those bad sources you can find on dumbed down documentaries.

 

[Torbjorn_L]

Inflation isn't short on falsifiable predictions, but that's the problem, there are too many of them.

Falsify one and an alternative is proposed, and then another, and then another...

Garth

I think bapowell answered for me, but I note that when you refer to different inflation models it is science as per usual. Every time you can constrain the parameter space, either in observations or in theory you get more precise observations or less uncertain theory because you got rid of what didn't work.

Of course you can always end up with that some type of theory doesn't work at all. (Say, phlogiston.) But you can only get there by testing and rejecting that which doesn't work.