Monday, June 01, 2009

Quick ideas to become a cosmology atheist

As I said in the other post, and not for the first time, I don't take cosmology too seriously. I find that there are many uncertainties in the observed data and also in the interpretations. Because of that I hadn't bothered to think too much about that questions.

In the last post Kea sugested me to read the Louise Riofrio theory, which resulted to be a version of the VSL (variable speeds of light) cosmologies. I have partially readed some of their statements, and also made the usual googling abbout the topic. The first thing that one finds is a mention of Von Riemman space. Well, I have no idea of what that is supposed to be. of course that could be because iI am not spetialist in the field so I googled for it and Ireached a physiscs forum's thread where other people also agreed that they didn't know it. Well, there som other points in her papers whose motivation I don't see clear. Beeing so I can't say too much else about the general theory

Another apect where she seems to see a point, independent of the general model, favouring her theory of a VSL is the following argument. In some epoch ths sun , according the standard model o solar evolutions, radiates a 75% of the energy that it radiates now. Ok, according to that she claims that earth should be a ice ball contradicitng the fact that there was life in it. The VSl solves the problem because someway the VSl implies tht the sun luminosity should be corrected to the right factor.

Without going into the detaill I must say that I find very unlikely that conventinal astronomy wouldn't have considered that possibbility before. Also there is another consideration. Earth is hot by itself. The friction energy that leaded to it's formation is accumulted inside it. In the XIX there was a controversy among the geologists and a prominent physics I don't remember for sure but I think that it was kelvin). The geological observations dated the antiquitie of earth in a number of years that was imcompatible with its temperature. Using the heat equation and the conventional data for earth materials one could see that earth would have frozen long time sooner that the age estimated bby the geologists. Later Somerfeld said that the reconciliation of the two viewpoints was the prsence of radiactive materials inside earth. Beeing sommerfeld such a well qualified physicist the argument was accepted as valid withouth criticism.

Well, in fact if one does the actual calculationsit can be shown that the radiactive materials are not enought to achieve the hotting of earth,. The reaosn earth is still hot (inthe outside) is that the heat equation used by Kelvin was not right. One needs to consider also trasnport phenomena, that is, convection. Doing so
it canbe shown that earth is hot bbecause of it's inner hot adquired within it's formatioin.

Beeing so I am not sure of how much of the riofrio argument makes too much sense. Also I find that history interesting because it whos explicitly how cautous one must be with arguments not based in observations made inlaboratory controlled conditions. Simply there are too many uncertaintiees.

Well, It has coincided that this mount the spanish edition of scientific american has an article where the cosmological arguments leading to the cosmological constant where revised. Being a divulgative article, that is, easy to read, I did so (it didn't take too mcuh time) The idea is that the observational reason why we belive univserse is expanding aceleratedly is that we see that far supernovaes light arrives to us with less intensity that what it would be expected from it's red shift it the univserse would be under a decelerating FRW (Friedman-Robertson-Walker) expansion. In the article they offert an alternative explanation. They say that it we would be in a particularly empty region of space-time the local decelartion of the universe would be slowest here that in distant points (for example the points near the observed supernovae. It contraicts the copernican principle that says that we are not in a particular place in space time. But tht can be circunvated in a natural way. If in the early universe there would e a random distribution of density inhomogenities that respected that principle the evolution would make that the less dense parts would increase it's size bby a factor ggreater than the more dense ones. In that way it would be mor probable that we would be in a relatively empty region of the universe. The last part of the argument is very similar to the nucleation mechanism that susskind used to explain the cosmological constant (but there are also diferences, of course).

Well, afther reading all that I wondered if I myself could ideate a mechanism to go agains the conventional big bang + inflaction scenary. Well, indeed I could.

The firs thing I did is to think about how fiabble is the red shit factor. Certainly the usual idea, that the expansion of universe generatees red shit is reaonable. And things like the BBN (big ang nucleosinthesys) respald that oservation. But the thing is that maybe there are aditional contributions to red shift. I have not had time to thnk for detailed mechanims. One of the first things that I have thought is that photons have mass. To be more explicit they have energy, and energy is a source of gravitation. One traditional way to put maths on that idea is to asign a mass to the photon MUhV whre v is it's frecuency. Themetiric corresponding to that mas is the Aichelbburg-Sexl solution (basically a Lorentz boost to v=c of the Schwarschild solution). Once one realizes that photons can radiate (and that they indded should radiate) one can think that it must llose energy. That loose would mean an aditional red shift. Ok, one could do the calculation for four dimensions, but that's not the whole history. If one thinks of a Randal-Sundrum like scnary one could expec that there is aditionanl radiation of energy to the one corrspoonding to four dimensions, that is, some energy would be radiated to the bulk. The RS scenary means that there are a range of possible values to the radiated energy that could be used to fit observations (that is, the aditioal red shiths would mean that the univser could have n smaller size that the expected oneand so advoid the problem of thermaliztion of causally disconected zones, usually solved by inflation, or, in other non-sntandrd scenaries, bby VSL). It also has another point. The warp factor could be variating in time. That could mean that the radiated energy could have been greater in the past and that would explain the cosmological constant. This is a particlar mechanis for aditional distant depending red shift, but surely one could guess many others I think.

Well, surelly there are drawacks in the argument.But I have used around an hour to think about the question. I think that for the inverted time I have got a well sounding arguments (certainly there are many imprecisions on the exposed arguments, don't look at them as definitive serious proposals). I have also imaginated another possibility, but it sounds less convincing. Well, don't take the idea too seriously (althought I don't totally dislike it as an a priory total crap one). But the point is that if in so short time ihave ideated an alternative to the standard scenary, even if it is false, possibly there are ther many more options.

1)Not too surprisingly my idea about additional redshift for photons was not new. It dates back to as soon as 1929 made by Fritz Zwicky. See the entry Tired Light in wikipedia for additional details. To be honest my idea has some differences with that proposals. To beguine with I didn't intend to create an alternative to the BBT but to modify it by a small amount. ON the other hand the kind of ways I had thought for the tired light phenomena where very different to what is exposed in wikipedia. The main objection I have read there is that there is no observed redshift for photons within our galaxy and any tired light mechanism would operate in it, and not only in the light from distant galaxies. Maybe I'll make some additional thinking about this topic, to see if the diferences in my proposals save something, but the proposal very probably will dimmer without success.

Anyway, it was only a quick idea. It is not bad to see that it has been considered before by important people. Also it means that the BBT is solid enough to resist elementary attacks. Still the arguments of the scientific american article keep making some sense. Also applies to the uncertainties in the nature of CMB anisotropy explained in the previous entry.

2) For VSL theories you can see this recent post (not the first one he does) about the toic on Lubos blog


air monitoring said...

I have always had trouble wrapping my brain around the notion that all of the universe started as a small point of energy. For one thing, our measurement of distance is based on the rate of light propagation, so how can you know the size of the universe at such small sizes? This got me to hypothesize that the universe is not expanding, but that its "spaces" are dividing into ever smaller proportions of the universe. Since we are in the universe, we perceive the division as expansion.

Mahndisa S. Rigmaiden said...

While a varying speed of light is a possibility that could be acceptable, nowhere in Riofrio's theory is its mechanism really explained.

BTW: I hope you can help Matti with his computational difficulties. Now his theory, what little I can understand, makes sense.

Javier said...

air monitoring:

Certainly when one goes near the planck scale (for example, in the begining of a FRW or de Sitter like universe) general relativity is expected to fail and tobbe replaced by a quantum gravity.

LQG people havea whole discipline devoted to the topic, named LQC (loop quantum cosmology) nd get some rerults.

Of course string theory people don't trust LQG and try to study that problems in the context of string theory. I am not an expert in string cosmology, but by waht I know there are very diferent uses of string theory in cosmology, depending on the time (or size) of the universe they are studiying. For example, as I said here, the F-theory models have been used for the analisys of the thermalization afther inflation and it's consecuences for BBN with the reslt that they get a natural explanation for the lithium shortness probblem based onthe saxion. This is a "late time" cosmological problem. The reasons for this is that local model F-theory GUT models are decoupled from grvity and can investigate earlier questions where gravity becomes important.

There are other attemps that try to use string theory to guess potential forms for inflation fields (and even suggest inflation fields not available in other theories). You can see, for an example of this approachs a post in U-duality about tachyonic inflation, But, certainly, there are many more proposals.

In an even earlier time (minor radius) one needs to trate diferent problems. I don't know all that is beeing made, but I know that one thing is to investigate string gas and to study it's consequences for Hagedorn temperatures and phase changes. This last line of research wuld be the oe that is nearest of our concerns, but I can't tell you too much about the recen results (I have localized a review paper aout the topic, but haven't read it still).

There exist also alternatives to big bang in scenarios implied y string theory. Those scenaries argue that what is thought as a big ang is in fact a rane collision. Our universe would be a 3-brane. Near it there would be another one that would from time to time become to closer to our and colliedes with ti. As a result our universe (our brane) get`s a lot of energy and it looks as a bbig ang. The most famous (I am not sure if the only one in fact) of this kind of models is the ekpiroctic universe proposed by Neil Turok (actual director of the perimeter institute). I must saytht as far as I know althought the model is string inspired it doesn't have the beneplacit of the string theory comunity.

Aout your proposl, wlell, withouth going into deeper considerations just to say that it is too much ad hoc. you ntroduce a mechanism that is usefull only for this purpose and that has no any natural part into any other part of phyisic. As such it is quite unmotiated and one wouldn't accept such kind of considerations untill any better alterntives should be discarded. Still so If my memory is not wrong that proposal had been considered before by some people in the early years of FRW cosmology, withouth acceptnce, mainly by the reason I told.

Javier said...

Yes Mandisa, I fully agree. I think that ther is not full , well organized, exposition of riofrio's theory so one can't judge a theory that is not properly exposed. If Riofrio or Kea read tis and disagree they can point me to the right papers, or answer the questions.

About matti prolems I guess that there will be solutions, it is only a question of searching the best one ;-).

Mahndisa S. Rigmaiden said...

I've asked her about it years ago and there was a void of responses and only Kea or Nigel would answer queries.

With that in mind, I will look into F-theory, of which I am unfamiliar. I studied a bit of lqg for a while and there are some troubling details that need to be worked out. The mathematics is so complex that it will likely take me a few more years to understand its underlying foundations, although by that time it might be proven correct or incorrect... ;)

You suggested GNU Octave to run matlab code. I hope they have patches for it because it can be kind of glitchy sometimes. But I must admit that its capabilities are great once you get the hang of it.

For Matti's computations Lord knows how many computational resources are necessary to run one of his calculations:) I hope you can help him. One day when I get rich, I wanna meet him and learn...