Timeline for Why does space expansion not expand matter?
Current License: CC BY-SA 4.0
6 events
| when toggle format | what | by | license | comment | |
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| Jul 10 at 18:32 | comment | added | Yukterez | The expansion of space as we see it in proper distance coordinates is equivalent to the flowing space in Gullstrand Painlevé coordinates where gᵣᵣ=gᵗᵗ=1 and gₜᵣ=v, while the curved spacetime De Sitter coordinates are equivalent to the Schwarzschild Droste coordinates where the local clocks and rulers are under force. Claiming there was "no concept of expanding space" is like ignoring the river model of black holes. | |
| Jul 10 at 18:19 | comment | added | Yukterez | that wasn't one of his famous blunders, the expansion of space is still the mainstream interpretation of the metric. if it was just the matter that expanded this would just be special relativity, but davis & lineweaver explained why that is not the case. you can transform into coordinates where the expanding space becomes curved spacetime if you use accelerated local reference clocks and rulers instead of geodetic ones, but that is just freedom of foliation, not a question of right or wrong. of course there is a concept of expanding space in GR | |
| Jul 10 at 7:22 | comment | added | benrg | @Yukterez Einstein published a lot of things late in his career that aren't well regarded. That said, I think this paper is fine; they just construct a so-called swiss-cheese solution of GR, consisting of expanding FLRW dust with spherical voids containing Schwarzschild stars at their centers, and conclude correctly that the expansion has no effect on the stars. I wish they (and others) didn't call the expanding dust "expanding space" but there's nothing I can do about it. It's the matter that expands, not the vacuum. | |
| Jul 10 at 4:09 | comment | added | Yukterez | benrg wrote: »There is no concept of "expanding space" in general relativity« - Albert Einstein said something different, and a lot of other sources as well. benrg wrote: »it's an artifact of the choice of coordinates« - you can use comoving coordinates where the comoving distance between the galaxies stays the same, but if you take the line element and translate that into the proper distance and volume as measured with rulers it does expand. | |
| Feb 10, 2023 at 21:08 | comment | added | Edouard | Air making me "slightly" smaller than I'd be in a vacuum seems like an understatement, but I guess that an infinite divisibility of space would justify use of the adjective that I've shown in quotes, at least during the earlier part of the time that the material which the body that "I" currently am would subsequently be spending in that vacuum. (I'm trying, here, to understand Einstein's well-documented support for the concept of "zero-point energy" and a conception of aether, which I may have ignorantly neglected elsewhere on PSE.) | |
| Oct 1, 2019 at 7:59 | history | answered | benrg | CC BY-SA 4.0 |