Timeline for As space expands, should the Planck length too?
Current License: CC BY-SA 4.0
10 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| May 6, 2021 at 16:12 | vote | accept | Árpád Szendrei | ||
| Jan 14, 2021 at 18:35 | comment | added | benrg | @my2cts See this and this. There is only one kind of redshift in general relativity. The "cosmological", "gravitational" and special-relativistic redshift formulas are special cases applying to spacetimes with certain symmetries. When you can put FLRW, Rindler and Minkowski coordinates on the same spacetime, the formulas all agree, even though the numbers you plug into them look completely different. It's the same physics in different coordinates. | |
| Jan 14, 2021 at 18:31 | comment | added | benrg | @shaunokane001 See my other answer. There is no space expansion effect, neither local (in whatever sense) nor propagated by the gravitational field. The effect of dark energy is real but it's nonpropagating. Sometimes in science a misunderstanding spreads very widely and ends up in many textbooks; this is one of those cases. | |
| Jan 14, 2021 at 14:15 | comment | added | my2cts | If "there is no "space expansion" effect in general relativity" the how do you understand cosmological red shift? | |
| Jan 14, 2021 at 14:12 | comment | added | my2cts | @benrg I see. You mean local as opposed to non-local, where I understood this in the context as opposed to global. | |
| Jan 14, 2021 at 9:50 | comment | added | shaunokane001 | There seems to be some confusion here. Physics defined locally does not mean that something far away cannot have an effect - the influences have to propagate from one local region to the next. In that sense, the "space expansion" effect is real, but probably not detectable as it is dominated by local effects. | |
| Jan 14, 2021 at 4:06 | comment | added | benrg | @my2cts This is mainstream physics. Physics is local in the sense that the behavior of macroscopic objects is described by laws acting independently on each part (above the Planck scale at least). As I said in the other answer, dark energy does exert a force that is in principle locally measurable, because it's present locally (it doesn't clump). What doesn't exert a force is the abstract global notion of the shape of spacetime as captured by the FLRW scale factor $a(t)$. | |
| Jan 14, 2021 at 0:15 | comment | added | my2cts | Is physics local? I consider cosmology as applied physics and it is global. | |
| Jan 14, 2021 at 0:15 | comment | added | my2cts | What you call "popular belief" apparently includes most cosmologists, who keep telling me that space expansion even accelerates. Please explain if your statements are main stream physics or not. | |
| Jan 13, 2021 at 23:58 | history | answered | benrg | CC BY-SA 4.0 |