"TImescape" models

[pervect]

Some popular news articles mention https://academic.oup.com/mnrasl/article/537/1/L55/7926647?login=false, "Supernovae evidence for foundational change to cosmological models" as suggesting that "Timescape" cosmological models may be superior to the Lambda-CDM model. My question relates to what is being tested, the so-called "Timescape model", which I've never heard of before. The popular news reporting and description of them is predictably pretty awful as one might expect, though the part about them being only statistically homogeneous (as opposed to the standard FLRW models) did come through.

Does anyone have any idea of what the "Timescape" models referred to in this paper are about? For starters, are they based on standard GR, or something else? Peer-reviewed but introductory references would be most desired, but I'll take what I can get, if I get anything.

 

[renormalize]

Does anyone have any idea of what the "Timescape" models referred to in this paper are about? For starters, are they based on standard GR, or something else? Peer-reviewed but introductory references would be most desired, but I'll take what I can get, if I get anything.

Try these lecture notes by David Wiltshire, in particular starting with section 4:
https://arxiv.org/pdf/1311.3787
And here are slides from a talk based on the above notes:
https://ir.canterbury.ac.nz/server/api/core/bitstreams/91239324-879f-439a-8ccf-f00a2cb419b6/content

 

[PeterDonis]

these lecture notes by David Wiltshire

I see a very odd statement at the start of section 2.1 of this paper:

"General relativity is only well tested for isolated systems – such as the solar system or binary pulsars – for which $T^\mu{}_\nu = 0$."

This is basically saying that only vacuum solutions centered on isolated masses are well tested. I don't think this is true. For the solar system, it's true that the isolated bodies whose interiors have nonzero stress-energy--the Sun and planets--also have negligible GR corrections to Newtonian gravity in their interiors. But that's not true of pulsars: those are neutron stars, and GR corrections are significant in the structure of neutron stars, and pulsar observations allow us to test GR predictions about neutron star structure, as well as GR predictions about changes in orbital parameters due to gravitational wave emission (which is what "binary pulsars" refers to).

 

[pervect]

Try these lecture notes by David Wiltshire, in particular starting with section 4:
https://arxiv.org/pdf/1311.3787
And here are slides from a talk based on the above notes:
https://ir.canterbury.ac.nz/server/api/core/bitstreams/91239324-879f-439a-8ccf-f00a2cb419b6/content

Thanks for the links. I'm not too impressed by the approach itself at this point if the papers are representative of it, but that's a separate matter. It's also based on a very quick reading.

 

[phyzguy]

I started this thread on this topic earlier this year, which you may find interesting.

Graduate Thread 'Models without dark energy'

Jan 4, 2025

Several years ago, I posted about this paper, which claimed to be able to eliminate the need for dark energy by performing cosmological simulations differently, basically intercnaging the order of calculating the expansion rate and the average density. One quote from that paper is, "The algorithm exchanges the order of averaging and calculating the expansion rate and, due to the non-linearity of the equations, the two operations do not commute." They also claimed that this reduced the observed Hubble tension.

Now there are several reports in the popular science channels, like...

• phyzguy
• Cosmological Models Simulations
• Replies: 29
• Forum: Cosmology

• 

 

[pervect]

I started this thread on this topic earlier this year, which you may find interesting.

Graduate Thread 'Models without dark energy'

Jan 4, 2025

Several years ago, I posted about this paper, which claimed to be able to eliminate the need for dark energy by performing cosmological simulations differently, basically intercnaging the order of calculating the expansion rate and the average density. One quote from that paper is, "The algorithm exchanges the order of averaging and calculating the expansion rate and, due to the non-linearity of the equations, the two operations do not commute." They also claimed that this reduced the observed Hubble tension.

Now there are several reports in the popular science channels, like...

• phyzguy
• Cosmological Models Simulations
• Replies: 29
• Forum: Cosmology

• 

Thanks - I did find the thread interesting. The previous papers had too much distracting wordage on things I found irrelevant, like Mach's principle for my taste.

Your summary seems a lot more intelligible with much more focus. Or perhaps it was just that it was simple enough for me to understand. I still don't know how one might get actual numbers on the effect, and I probably won't get that far, sadly.

I would expect that it's the largest structures that would be important, and the galactic voids are arguably very large structures.

I don't think this approach will do much about the dark matter problem, though. That shows up at the galactic scale with galactic rotation curves.