Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe · HackerPapers discussions

Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by ziofill

Wed, 09 Oct 2024 04:45:22 GMT

https://arxiv.org/abs/astro-ph/0310808

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by pdonis

Mon, 29 Apr 2024 19:28:32 GMT

> The density in the observed universe is used to extrapolate the number of galaxies in the non-observed universe. As has already been pointed out, our best current model of our universe is that it is spatially infinite. That means an infinite number of galaxies. The finite galaxy numbers that astronomers give are for the observable universe. > The size and shape of the observable universe also changes. Not the way you are describing, no. The observable universe does increase in size as time goes on, because there is more time for light to travel so the light we see can come from objects…

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by pdonis

Sun, 03 Dec 2023 01:01:54 GMT

> Your statement that matter has average uniform density in all directions around us is obviously only correct in sufficiently large frames of reference Yes, agreed. But the distance to our cosmological horizon is large enough that the averaging assumption is fine on that scale. > You should expand on why the cosmological horizon does not function in the same way the GP's "event horizon" analogue does Fair enough. But first I'll reference an excellent paper by Davis & Lineweaver (2003) [1]. You can find much more detail there than I'm going to give here. Some simple facts about our…

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by dav_Oz

Sun, 20 Aug 2023 14:56:01 GMT

This educational paper [0] titled "Expanding Confusion" (2003) is a classic on the general topic and well worth the read. Holding the two concepts of an accelerated (!) (in terms of objects [1]) expanding universe and the fixed finite speed of light simultaneously in one's Euclidean head can be dizzying, so be prepare to draw and enjoy the hard earned manual labor of counterintuitive conclusions. [0]https://arxiv.org/pdf/astro-ph/0310808.pdf [1]https://bigthink.com/starts-with-a-bang/universe-expansion-n...

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by badosu

Mon, 15 Jun 2020 05:08:55 GMT

I found a good article on this matter: https://arxiv.org/pdf/astro-ph/0310808v2.pdf

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by jobigoud

Thu, 09 Aug 2018 20:51:24 GMT

Here: "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe" https://arxiv.org/abs/astro-ph/0310808

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by jobigoud

Mon, 03 Aug 2015 08:39:02 GMT

> If two points are so far apart that the expansion of space inflates the distance between them faster than light can cross it, then no light can ever reach from one to the other, even if it travels for an infinitely long time Actually, it can. The issue is quite subtle. What you are saying is true only if the Hubble parameter is constant, it is not. (Hubble constant is such a misnomer! It's only constant across space but not time). You may want to re-read paragraph 3.3 of the Lineweaver paper (http://arxiv.org/pdf/astro-ph/0310808v2.pdf) Quotes : > Photons near the Hubble sphere that are…

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by goodside

Wed, 25 Jul 2012 12:45:45 GMT

This is a misconception. If you just want a satisfying mental image of the Universe: It's really big, it doesn't have any point defined as its center, and it doesn't have any wall-like borders. Aliens living 14.6 billion LY away from us see a Universe that looks just like what we see in all directions. If it is limited in size at all, it's because it wraps around on itself ("if you go straight long enough you end up where you were"). Nobody has firm evidence that it actually does wrap around on itself, and there's reason to believe that if it does, it's on a scale that's much larger than we…

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by goodside

Wed, 25 Jul 2012 12:32:16 GMT

The short answer is nobody has a plausible upper bound on the size of the entire Universe, and there's no firm consensus on whether it's literally infinite. If it is finite, there is no "wall" or "center", since it's not a big sphere -- a finite Universe just means that if you go straight long enough, you end up in the same spot. It's analogous to how if you stood on the ground of featureless planet, the land you could inhabit is finite, but it has no borders and no point where you could stick a flag in the ground and say "this is the center of the planet's land". Most of the time when people…

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Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe — mentioned by goodside

Sun, 24 Jul 2011 02:53:10 GMT

The answers to the first two questions are related, and unfortunately complicated. I was almost referring to the Cosmic Microwave Background Radiation (CMBR), but I actually meant a slightly older event, the end of the inflationary epoch. The inflationary epoch is rarely understood, but it's really so qualitatively different from everything that came after that it's worth referencing as a starting point for the Universe as we know it. Intuitively, you can think of the inflationary epoch as an extremely brief flash of time where things were so bizarre that nobody really has any firm idea what…

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