Roger Penrose model of the rebirthing universe

Nobel prize winner Roger Penrose has proposed a model for the faith of the universe. When the dark energy has broken up (this is not the correct term, I know) the universe into only photons, time, as proposed by Robert, no longer exists and therefore, space no longer exists. The universe then collapses into a singularity and the inflation process starts again and this process becomes cyclic with new collapses and new inflations. One thing I think of is that even if space only contains photons, it still contains space time, and therefore also quantum fluctuations. If this is correct, it also still contains mass. I have seen calculations of the density of vacuum and its not zero. I dont know if what I write here is correct and I mean not to spread false information or to misslead. Just correct me if I am wrong. Is this model by Robert something that is discussed seriously, or is it more popular science?

rolnor said:

Nobel prize winner Roger Penrose has proposed a model for the faith of the universe.

Please give a specific reference. (Also, I assume you mean "fate", not "faith".)

rolnor said:

I dont know if what I write here is correct

This is why you need to provide a specific reference--so we can read what Penrose actually says and help you to determine this.

Here is a reference and within the reference there is further references. https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology

And I mean "Fate" I am not native so my english is not perfect. Sorry

rolnor said:

time, as proposed by Robert, no longer exists and therefore, space no longer exists. The universe then collapses

I think you must have misunderstood this part. Collapse takes time, so if time doesn't exist, how can there be collapse?

Its clear when you listen to Roger himself talking about his theory (I have done so on youtube) that he does not know exactly how it works. I dont claim to understand this either, off course. My question was, is the theory serious according to you pros, or is it more of a thinking experiment.
https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology

Her he is talking with Jordan Peterson, Peterson is probably not the best physisist to be found.

rolnor said:

TL;DR Summary: Roger Penrose has suggested a new model for the faith of the universe, is it any good?

Nobel prize winner Roger Penrose has proposed a model for the faith of the universe. When the dark energy has broken up (this is not the correct term, I know) the universe into only photons, time, as proposed by Robert, no longer exists and therefore, space no longer exists. The universe then collapses into a singularity and the inflation process starts again and this process becomes cyclic with new collapses and new inflations. One thing I think of is that even if space only contains photons, it still contains space time, and therefore also quantum fluctuations. If this is correct, it also still contains mass. I have seen calculations of the density of vacuum and its not zero. I dont know if what I write here is correct and I mean not to spread false information or to misslead. Just correct me if I am wrong. Is this model by Robert something that is discussed seriously, or is it more popular science?

If this (Conformal Cyclic Cosmology or CCC) were proposed by anyone other than Penrose, it would just be one of hundreds of speculative cosmological theories/hypotheses that are regularly proposed. Further, it requires significant alterations to the Standard Model of particles to work - and that is a big problem. In most situations though, there is no difference whatsoever in its predictions and those of the more ordinary models. There are other "big bounce" ideas that have been proposed over the years, including a number prior to CCC.

It is fair to say: this is not generally accepted, and would best be labeled as a fringe concept that has a very small following. If future discoveries from the Webb or other sources provide some new support for this idea, I'm sure that added research effort would be forthcoming.

As it is, there is no clear prevailing idea of anything that occurred prior to the Big Bang's initial inflationary period. Essentially, if there were a prior universe: evidence of it was essentially completely erased at the Big Bang. Anyone's conclusions must actually be based on an absence of specific information - and a whole lot of speculation and assumptions.

Thanx, yes, thats was my general feeling, a fun, inspiring idéa but not much more. But its nice to think that the end is not the end, its easy to feel anxious when the universe is just going to evaporate int a thin mist of photons, I prefere some sort of rebirth.

Of all the ideas and proposals for cosmology "before" the big bang, this one is the least speculative.

martinbn said:

Of all the ideas and proposals for cosmology "before" the big bang, this one is the least speculative.

It does not get theological.

rolnor said:

time, as proposed by Robert, no longer exists and therefore, space no longer exists

Where, specifically, in the references you gave does it state this?

He says that in the youtube video. He propose that you need mass to create a clock, and if there is no mass you have no time. Thats how I remember his talk. but the is vauge on this, its not 100% clear. I can be wrong.

Isn't this pretty clear? To establish a frame of reference (in the physical sense, i.e., with "clocks and rods" in the lab) you need massive objects. E.g., a clock must define a timelike vector (in a tetrad as part of the mathematical description of this reference frame) by its world line with its proper time (being importantly a scalar in the sense of general covariance, i.e., a gauge invariant quantity, and only such gauge invariant quantities by definition have meaning as describing physical observables) defining "time" of this reference frame. Then you also need "three massive rigid rods" to define the spacelike tetrads of the reference frame. Of course particularly these "rigid rods" a metaphors for more sophisticated constructions like having a set of clocks and light signals used to synchronize these clocks as, e.g., in the GPS. To study the important general-relativistic aspects of the GPS's functioning is a good example for how accurate rerference frames can be established in the realm of GR (open access):

Ashby, N. Relativity in the Global Positioning System. Living Rev. Relativ. 6, 1 (2003).
https://doi.org/10.12942/lrr-2003-1

rolnor said:

TL;DR Summary: Roger Penrose has suggested a new model for the faith fate of the universe, is it any good?

There is a different sub-forum for cosmology on PF: https://www.physicsforums.com/forums/cosmology.69/penrose (@PeterDonis please move).

[Mentor Note -- Thread moved to Cosmology]

Penrose's CCC (which he first proposed in 2005 so hardly new) has been discussed a number of times on PF e.g.

https://www.physicsforums.com/threads/more-on-penroses-conformal-cyclic-cosmology.442740/
https://www.physicsforums.com/threa...cyclic-cosmology-obeys-thermodynamics.427567/
https://www.physicsforums.com/threads/bgv-theorem-and-penroses-conformal-cyclic-cosmology.994703/
https://www.physicsforums.com/threa...-on-ccc-evidence-or-wishful-thinking.1001217/
https://www.physicsforums.com/threads/on-penrose-cyclic-cosmology.1048758/

rolnor said:

He propose that you need mass to create a clock, and if there is no mass you have no time.

Sort of. What he actually means is that, at least according to his hand-waving model, if there are no massive particles present, you can treat two spacetime geometries that are conformally the same (i.e., all the null curves are the same, but timelike and spacelike ones might not be) as though they were physically the same. That is what allows him to, heuristically, "glue together" the far future of one "eon", where everything has evaporated into massless particles, with the "Big Bang" past starting point of the next "eon".

But this amounts to claiming a new law of physics. It's a claim we can't currently test directly, since our universe currently contains massive particles, but that doesn't make it reasonable. As has already been commented, if it were anyone else but Penrose, the claim would most likely have been dismissed.

Perhaps a good way to describe it is, if you want to have a cyclical cosmology for any particular reason, Penrose has devised a somewhat plausible way to do it, based around the idea @PeterDonis has just described: that if you ever get to a universe of pure massless particles, which follow null geodesics, the nature of spacetime becomes pure null geodesics, so the universe can only keep track of conformally equivalent classes. That somehow makes it lose track of scales, such as temperature, so that a very cold situation ends up acting the same as a very hot one, and you get a new big bang. I'm not following his idea of how that actually works, and it does require new physics, so it is more like a description of how a cyclical universe could work, and still possibly be our universe, rather than a claim that ours is that universe. We might remember that Edgar Allen Poe conceptualized a model of the universe that is a very good nonquantitative version of the Big Bang model, without any observational evidence, just pure horse sense, but it could not have violated any of the existing observations (since it was pretty much correct). It's not really science, but it might stimulate science, just to have the idea out there.