/sci/ - Science & Math » Thread #12857270

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Anonymous Sat 20 Mar 01:20:37 2021 No.12857270 View Reply Original Report

Quoted By: >>12857291 >>12858158 >>12858204

What does it mean when we say the universe is expanding? I understand that it's not "expanding into something" because by definition the universe is everything that exists. But then how are objects able to keep moving away from each other?

Does this imply that the universe is infinite? What happens if you keep going in a single direction, do you like loop around or what?

And is it gay if I'd be down to making out and cuddling with femboys but wouldn't put my dick in them or take their dick up my ass?

Anonymous

Anonymous Sat 20 Mar 2021 01:28:59 No.12857291 Report

Quoted By: >>12857302

>>12857270
they don't know beyond the statement that the vacuum of space itself is getting larger.

Anonymous

Anonymous Sat 20 Mar 2021 01:33:47 No.12857302 Report

Quoted By: >>12857306 >>12858054

>>12857291
So what does that mean? Is it like being in a large field where you only see the field in all directions, not knowing if there's an ending and the people on the field are slowly moving away from each other?

Anonymous

Anonymous Sat 20 Mar 2021 01:36:40 No.12857306 Report

Quoted By: >>12857313

>>12857302
it's like if the ground was made of elastic rubber, celestial objects were dots glued on the rubber, and the elastic rubber was being stretched.

Anonymous

Anonymous Sat 20 Mar 2021 01:38:40 No.12857313 Report

Quoted By: >>12858093 >>12858118

>>12857306
I see. Pretty hard to wrap my head around this concept. Because the rubber is still expanding "into" something but that doesn't apply to the universe

Anonymous

Anonymous Sat 20 Mar 2021 06:43:44 No.12858054 Report

Quoted By:

>>12857302
Picture a chess board and stars and galaxies and shit are the pieces. The pieces stay (roughly) on their squares, but the squares themselves get bigger.

Anonymous

Anonymous Sat 20 Mar 2021 07:12:06 No.12858093 Report

Quoted By:

>>12857313
Brainlet idea but maybe beyond the universe there’s just an infinite void of protons and shit in absolute stasis, where nothing happens

Anonymous

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Anonymous Sat 20 Mar 2021 07:17:20 No.12858102 Report

Quoted By: >>12858183

H33LLO FREN ANONS

Anonymous

Anonymous Sat 20 Mar 2021 07:26:16 No.12858118 Report

Quoted By: >>12858133 >>12858413

>>12857313
yes it is hard to imagine the universe expanding without some ambient space. but actually it is a common thing in GR to think about “embedding” 4D space time into a 5D mathematical space. then for example you could think of the universe like a rubber balloon that expands in 3D within a 4D euclidean. space over time (an additional dimension to the 4D space that embeds our 3D space). this is a perfect way to model space time, but it carries a caveat: the 5D flat space (minkowskian with one time dimension and the remaining 4 euclidean) is not actually real. so even though it is useful for envisioning 4D curved space time, usually it isn’t taught to students because it is easy to mistake it as a real thing, and if you make that mistake you can easily fuck up, so generally the didactics focus on getting students used to 4D curved spaces without embedding them.

Anonymous

Anonymous Sat 20 Mar 2021 07:35:14 No.12858133 Report

Quoted By:

>>12858118
maybe to follow up. for example you can think of a 2D spacetime. let’s say the x axis is time and the y axis is space. a 1D space that also has time. ok. you can have your particles in this space move along the y axis over time.

now let’s imagine the y axis is actually compactified. what i mean by this is that the y dimension is finite, say it goes from 0 to some length d, but if a particle tries to cross the boundary at d then it loops back over to the bottom at 0 and continues happily on its way, like on the maps of the Civilization games.

in that case you might want to think about trying to connect the upper edge at d with the lower edge at 0. that makes sense. but to connect it like that, you need to envision a third dimension and the. wrapping it around to form a cylinder. so even though you started out with a 2D space with a fairly simple rule for how you cross boundaries, it helps a lot to think about it in a higher dimensional space with some topology going on. but the third dimension is just not real here, it was just introduced to help you think about it topologically

the same thing happens with embeddings in GR

Anonymous

Anonymous Sat 20 Mar 2021 07:55:34 No.12858158 Report

Quoted By: >>12858173

>>12857270
Space itself is getting bigger. It's not expanding "into" something, that would mean that only the 'edges' stretch out. But space is inflating across the board.
tldr - it's god's work.

Anonymous

Anonymous Sat 20 Mar 2021 08:02:48 No.12858173 Report

Quoted By:

>>12858158
however, it is totally possible that there are no edges and yet it can still expand. free yourself from the idea of edges, it is not a good idea for anyone trying to understand this. if theee are edges that is no problem but you shouldn’t constrain your thinking to there always being edges

Anonymous

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Anonymous Sat 20 Mar 2021 08:07:14 No.12858183 Report

Quoted By:

>>12858102

Anonymous

Anonymous Sat 20 Mar 2021 08:17:54 No.12858204 Report

Quoted By:

>>12857270
Am I supposed to see a merchant face in that image or should I spend less time on 4channel?

Anonymous

Anonymous Sat 20 Mar 2021 09:42:40 No.12858413 Report

Quoted By:

>>12858118
>it is a common thing in GR to think about “embedding” 4D space time into a 5D mathematical space

General relativity knows no 5th dimension. It defines spacetime as a 4d differentiable manifold with a pseudo-Riemannian metrics that leads to a causal structure. The Einstein field equations are differential equations, i.e. as defining local entities like e.g. the metric, by themselves they do not exclude wormholes or other topologic peculiarities from the beginning. However, for all this to work, no embedding in a higher-dimensional space is needed. This is all intrinsic geometry as already regarded by Gauss 200 years ago.

Anonymous

Anonymous Sat 20 Mar 2021 10:47:53 No.12858635 Report

Quoted By:

The way I get around this quagmire is to think of a circle. Just after time zero the circle is full of immensely hot energy. That is the Universe as it was. What is contained in the circle is the Universe. It is everything. There is nothing existing outside the circle.

Then as time goes on the circle remains the same size. It doesn't get bigger. But everything inside shrinks, coalesces into stars and galaxies, gets cooler. As everything shrinks the relative space between objects becomes proportionally greater.

I asked on another forum whether this model actually had any credibility. Some of the people, who seemed bright and qualified enough, said that as far as cosmologists are concerned there is no effective difference. So this is what I go with, at least until anyone picks a hole in it.

TLDR. The Universe remains the same size, everything within it is shrinking.

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