Timeline for Why does space expansion not expand matter?
Current License: CC BY-SA 4.0
10 events
| when toggle format | what | by | license | comment | |
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| Feb 17, 2021 at 3:26 | comment | added | BlueRaja - Danny Pflughoeft | This doesn't answer the question. If you draw a coordinate grid on the balloon, the distance between two points on the circle doesn't change, as measured in those coordinates, because everything is expanding alongside space. The fact that the distance increases as measured from outside the system doesn't seem relevant, since we're not able to measure distances from outside our own universe. | |
| Dec 26, 2019 at 19:17 | comment | added | Edouard | @Marek When you're referring to "good old Newtonian gravity", are you referring to the gravity prevalent in that finite universe, occupying part of an infinite void, which Newton hypothesized before 1692-3, or to the infinite static universe which he hypothesized subsequently, after recognizing that that earlier version would've collapsed immediately? As Guth explains algebraically on p.295-297 in the 1997 ed. of "The Inflationary Universe", the 2nd version would've also collapsed, so, given its current tag of "cosmology", your answer doesn't quite apply to this question. | |
| Nov 17, 2018 at 17:56 | history | edited | user191954 | CC BY-SA 4.0 | added 2 characters in body |
| Nov 17, 2018 at 17:44 | comment | added | Andrew Steane | The appeal to "good old Newtonian gravity" might be misunderstood as a suggestion that somehow Newtonian gravity sits on top of or in addition to the spacetime effects described by G.R. (I realise you don't intend to suggest that). | |
| Nov 17, 2018 at 16:53 | comment | added | Andrew Steane | @doublefelix For more insight into why galaxies are not expanding, see my answer to this question. | |
| Oct 13, 2017 at 6:05 | comment | added | anna v | you are being misquoted in the question. | |
| Sep 28, 2016 at 19:15 | comment | added | AGML | @doublefelix Galaxies aren't expanding because they are held together by local gravitational forces that aren't accounted for in the simple cosmological model. This is, in fact, contained in Marek's answer. | |
| Aug 9, 2016 at 6:51 | comment | added | R. Rankin | @user3141592 From an energy perspective (landau lifshitz gravity pseudotensor plus tensor energy conserved), an expanding universe seems to remove energy from local systems (such as the em wave) from this perspective, one can see that expanding a galaxy increases it's energy, thus one might expect (counterintuitively) rather that a galaxy would experience an inward force of contraction. | |
| Nov 3, 2015 at 1:20 | comment | added | spinachflakes | "given enough time, our galaxy should grow. But it doesn't" - source? And after that, your answer is (rephrased): "With the assumptions we made to derive expansion, we assumed that galaxies are points" - So you've only said "our derivation doesn't say anything about finite size galaxies", which is interesting, but the question @SoulmanZ asked is unanswered: Can we explain why galaxies are not expanding? I'd like an answer myself. | |
| Dec 22, 2010 at 0:24 | history | answered | Marek | CC BY-SA 2.5 |