What are the latest thoughts about the timescape cosmology

[Arman777]

I came across a theory called "timescape" cosmology. If I understand the theory correctly it assumes that the universe is not homogenenous due to the large voids and gravitationally bounded system. Also time would be different for the observers on these two different locations.

1- Is CMBR and supernova datas support these ideas ?

2- It seems that the model contains different density parameters, Is this plausable ?

3- I am thinking that LCDM calculations makes some predictions and then we put some values of denisty parameters to match it with the CMBR data. And by doing that we find the actual values.

So is this the real process ? By changing the density parameters we can still fit our data to the CMBR data ?

Here are some links to the model
http://www2.phys.canterbury.ac.nz/~dlw24/universe/

https://arxiv.org/abs/1306.3208

 

[PeterDonis]

If I understand the theory correctly it assumes that the universe is not homogenenous due to the large voids and gravitationally bounded system.

It's not so much that it assumes this (it's no news to any cosmologist that there are large voids and gravitationally bounded systems in the universe), as that it tries to quantitatively estimate the effects of these inhomogeneities and, at least according to the proponents, finds that they are not insignificant (whereas the standard model of the universe that is mainstream in cosmology assumes that any such effects of inhomogeneities are insignificant as regards the dynamics of the universe and how we interpret our observations of distant galaxies).

I think the jury is still out on whether a model like this can match observations as well as the standard mainstream model.

 

[Arman777]

It's not so much that it assumes this (it's no news to any cosmologist that there are large voids and gravitationally bounded systems in the universe), as that it tries to quantitatively estimate the effects of these inhomogeneities and, at least according to the proponents, finds that they are not insignificant (whereas the standard model of the universe that is mainstream in cosmology assumes that any such effects of inhomogeneities are insignificant as regards the dynamics of the universe and how we interpret our observations of distant galaxies).

I think the jury is still out on whether a model like this can match observations as well as the standard mainstream model.

I think the idea makes sense. Time would be different in the voids and near the gravitationally bounded objects.

 

[kimbyd]

I think the idea makes sense. Time would be different in the voids and near the gravitationally bounded objects.

I'm not so sure. Typically, gravitational time dilation is inconsequential unless you are extremely close to a very dense object.

 

[Arman777]

I'm not so sure. Typically, gravitational time dilation is inconsequential unless you are extremely close to a very dense object.

Well maybe, I guess.

 

[kimbyd]

Well maybe, I guess.

I haven't looked deeply into their math, but here's my very rough impressions:

1) On the surface, different observers seeing different times resulting in cosmologically-important results is very surprising. Based on what we know of how time dilation works, it really doesn't seem like it should have a huge impact.
2) The paper itself doesn't just look at time differences. The model incorporates many features of inhomogeneities. So it's not just about time dilation, but about rates of expansion being different in different locations. This makes it at least reasonable for the back-of-the-envelope objection in point (1) to be satisfied by the detailed math involved.

The bigger concern I have, however, is this 2010 paper:
https://arxiv.org/abs/1007.3725

The issue at hand is that models like the timescape model require that our solar system be very near the center of a large void. According to the above paper, which was released three years prior to the timescape model paper, those models can't really fit our current observations of galaxies. It's certainly possible that the timescape model avoids the problems that Adam and his collaborators laid out in that paper, but it worries me that it isn't referenced by them.

 

[kimbyd]

Oh, and one more thing:
My objection that Moss et. al. wasn't cited in Duley et. al. could be satisfied if they did cite another, similar paper. I don't really have the spare time to go through the paper right now, but if anybody on this thread would like to see if a similar paper is cited, please feel free.

 

[PeterDonis]

Time would be different in the voids and near the gravitationally bounded objects.

"Time would be different" is not a very good description of what this proposed model seems to be saying. Nor is it a good way to think about how to test the model against observations. We don't observe clock readings in light from distant galaxies. We observe redshifts, brightness, and angular size (roughly speaking). The specific relationship between those three observables is model-dependent, so the observed relationship is a good way to test models. This proposed model basically seems to be saying that, if we properly account for effects of inhomogeneities, we can construct a model that matches the observed relationship without having to include dark energy. As I said, I think the jury is still out on whether that will actually work; it's an open area of research.

 

[Arman777]

The issue at hand is that models like the timescape model require that our solar system be very near the center of a large void.

That seems like a big issue. I read the conclusion part and it seems that using the inhomogeneity to explain the observational data seems to fail.

Also thanks both of you

 

[kimbyd]

That seems like a big issue. I read the conclusion part and it seems that using the inhomogeneity to explain the observational data seems to fail.

Also thanks both of you

Bear in mind that there has been a lot of back and forth on this over the last 15 years or so, with many very reputable cosmologists pointing out some significant holes in the arguments of those who claim inhomogeneity doesn't explain the accelerated expansion. I don't know that it's settled entirely, but I definitely think that Moss et. al. (and any more recent data papers) really need to be taken into account.

 

[Arman777]

Bear in mind that there has been a lot of back and forth on this over the last 15 years or so, with many very reputable cosmologists pointing out some significant holes in the arguments of those who claim inhomogeneity doesn't explain the accelerated expansion. I don't know that it's settled entirely, but I definitely think that Moss et. al. (and any more recent data papers) really need to be taken into account.

Why its hard to settle it down to a conclusion ?

 

[kimbyd]

Two reasons:
1) There's a lot of ambiguity in observations at different distances.
2) It's really really hard to do proper calculations of how inhomogeneities impact measurements.

 

[Arman777]

Two reasons:
1) There's a lot of ambiguity in observations at different distances.
2) It's really really hard to do proper calculations of how inhomogeneities impact measurements.

I see, well thanks a lot