Timeline for How do we resolve a flat spacetime and the cosmological principle?
Current License: CC BY-SA 3.0
19 events
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Jan 4, 2020 at 23:03 | comment | added | dllahr | @FrankH when you do many calculations in quantum physics you need to sum or integrate over "all space" and the results of those calculations are directly compared to experiment. For example in low temperature, you need to treat a system as having discrete states and sum over them; at higher temperatures you can treat it as effectively continuous and integrate. In these situations you're using two different kinds of infinity and see experimental verification of which one is correct. | |
Dec 18, 2019 at 12:30 | comment | added | dllahr | Woops! Sorry, I meant to write "I completely disagree that there can never be experimental evidence for infinity. More productively I'll look it up. | |
Dec 18, 2019 at 7:59 | comment | added | FrankH | @dllahr, are you trolling me? I said: "There can NEVER be experimental evidence for infinity." Then you said: "1st, I completely disagree that there can be experimental evidence for infinity." How can you possibly be disagreeing with me when that is exactly what I said? | |
Dec 16, 2019 at 12:07 | comment | added | dllahr | 1st, I completely disagree that there can be experimental evidence for infinity. 2nd, if there could not be experimental evidence (indirect, usually) then you would not be discussing science, you would be discussing philosophy or math. | |
Dec 14, 2019 at 4:59 | comment | added | FrankH | @dllahr, there is no experimental evidence for infinity. There can NEVER be experimental evidence for infinity. Did you read my answer? I say: "Given the cosmological principle and the flat space-time observation, the idea is that the flat spacetime is infinite, or at least very much larger than our horizon." | |
Dec 12, 2019 at 12:36 | comment | added | dllahr | So then you're not claiming that the infinity of spacetime is described by Aleph0 (instead of Aleph1)? I'm just asking that if you're making that claim, what is the experimental evidence that supports it. | |
Dec 11, 2019 at 20:59 | comment | added | FrankH | @dllahr, there is only one kind of infinity that I have discussed which is the Aleph0 (number of integers) kind of infinity. The universe can have an A0 number of measuring rods laid end to end across the universe. I have no idea how an Aleph1 (points on a line) kind of infinity would apply to our universe, so I cannot answer your question. | |
Dec 11, 2019 at 13:36 | comment | added | dllahr | What is the physical measurable / experimentally measurable difference between an expansion where they are the same size infinities vs. different size infinities? | |
Dec 10, 2019 at 3:13 | comment | added | FrankH | @dllahr, it is not just "relabeling" distances, the density and temperature of matter decreases with time and light from distant sources is redshifted by an amount proportional to the distance, so this is exactly an expansion of space. Relabelling would not have an effect on this kinds of physics. | |
Nov 4, 2019 at 12:20 | comment | added | dllahr | To amplify, what you've described seems like taking the same volume and just relabeling the spacing within it. If that is the case, why is that explanation preferred over an actual expansion? | |
Nov 2, 2019 at 1:15 | comment | added | dllahr | The math is clear but what is the meaning of the word expansion then? | |
Nov 1, 2019 at 18:04 | comment | added | FrankH | @dllahr, not really. In this case, there are not different sizes of infinities. The number of points between 0.0 and 1.0 on a line is a strictly larger infinity than the number of integers. But the expanding universe is like comparing the number of integers to the number of even integers, which are exactly equal infinities since there is a 1-to-1 mapping between them. Similarly the number of points between 0 and 1 is exactly the same as the number of points between 0 and 2 since there is a 1-to-1 mapping between them. Is that clear? | |
Nov 1, 2019 at 7:22 | comment | added | dllahr | This has been extremely helpful to my understanding. So if space is infinite and it is also said that the universe has/is expanding, does that mean we're talking about different size infinities? | |
Oct 26, 2011 at 20:00 | vote | accept | AdamRedwine | ||
Oct 24, 2011 at 19:45 | comment | added | AdamRedwine | Yes, I think it is thanks. I never conceived as the Big Bang happening at one point and, as I said, I have no difficulty imagining an expansion of an infinite manifold, my problem was in not understanding that the manifold is (believed to be) infinite. In this case, I can imagine how the universe might be up to $t=\epsilon$ and I see how it is impossible to get to $t=0$... it's starting to make sense now. | |
Oct 24, 2011 at 19:41 | comment | added | FrankH | So, @Adam, is everything resolved now? You say "I cannot imagine one "confined" to a singularity such as suggested by the Big Bang Theory" but as I said in the EDIT in the answer above, you just need to think about the singularity filling all of an infinite space at $t=0$ which really means we cannot model or have a theory about $t=0$ we can only do theory at t = ϵ on... | |
Oct 24, 2011 at 11:10 | comment | added | AdamRedwine | You are right that my conception is easily compared to the locality of the Big Bang, but it is slightly different. Going to your example, the observer at 7 billion light years out would see things beyond our horizon, but would they possibly see things as far as 7 billion light years further? And what about the observers 7 billion light years from them? How far do they see? If you continue this process of leaping 7 billion light years (or any other distance), either the universe is infinitely large or you must eventually get back to where you started. | |
Oct 24, 2011 at 2:55 | history | edited | FrankH | CC BY-SA 3.0 |
Added last paragraph
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Oct 24, 2011 at 2:38 | history | answered | FrankH | CC BY-SA 3.0 |