PDA

View Full Version : Steady State v. Expansion?



Hornblower
2015-May-06, 01:55 PM
From the "Reality" thread in S&T:

I asked the question, would a steady state believer adopt an expansionist model? Of course not, they would choose a steady state model. Now Iím not sure whether we will ever get to directly observe the expansion or not of the universe in the sense of observing that balloon.
I split this specific item from the other thread to avoid derailing that thread from its general principles.

If I am not mistaken, Fred Hoyle's hypothesis was a steady state expansionist model. He argued that the galaxies were receding from one another on a cosmic scale and that new matter was continuously being created and keeping the mean density of the cosmos constant. He derisively used the expression "Big Bang" for the model proposed by George Gamow and others, which he thought was nonsense. He did not deny the expansion explanation of the redshift observed by Hubble.

Any comments?

Ken G
2015-May-06, 02:18 PM
Yes, there are really three different models, the static model of Newton and Einstein (before Hubble's observations) in which nothing moves at all (this model never works because it is not stable), the steady-state model of Hoyle and Burbidge (after Hubble's observations, so it allows expansion but not a finite age of the universe), and the Big Bang (which has a finite age for a universe that is not only expanding, but also changing with time). We know the observations like the CMB and the evidence for celestial dinosaurs like quasars strongly favor the Big Bang model. But ironically, the idea of "eternal inflation" allows all three of those models to make some claims on the truth, if evidence can ever be found that eternal inflation is a better model than the single-universe model. In eternal inflation, we have a multiverse of different Big Bangs that are popping off all the time over a truly vast, or even infinite, array of different "possible universes," if you will. Such a model is locally dynamical, but statistically in steady-state, and globally it is pretty darn close to static, though it is probably better to say that distance and time are not viewed as concepts that bridge between universes, so one can simply not say if it is static or steady or what. But to Hoyle, eternal inflation sounded a lot like the spirit of his own steady-state ideas.

(As a more technical aside, there are several flavors of eternal inflation, and it's not obvious that this is really a scientific model as yet-- it is more like a philosophy for creating models. One version holds that there was still only one Big Bang origin, so all the multiverse has a common age, but inflation is still going on in pockets of that universe, creating separations among the multiverse based on accidents of their history. Other versions have the physical constants varying with position in the multiverse, and still others have various parts of the multiverse undergoing inflation at different times, causing the "age" concept to be different throughout the multiverse, and the whole business would not have any origin at all. Basically, it is a set of models that at this point is so unconstrained it could be used to retrofit to any observation we could do, so it will only be scientifically convincing if we can make observations, choose an inflation model that works for those observations, make new predictions based on that model, and test them.)