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submitted 2 months ago by fossilesque@mander.xyz to c/science_memes@mander.xyz

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[-] Rhaedas@fedia.io 57 points 2 months ago

Good visualization but inaccurate. Space between galaxies in a cluster and even the stars in a galaxy is also growing. The difference is in scale. There's so much distance between galactic clusters and the largest structures of the universe that added up that expansion amount is so much bigger. The balloon analogy with galaxies as dots on the surface is closer since the dots also do grow some, but the balloon would have to be huge to capture a good scale comparison.

[-] Tlaloc_Temporal@lemmy.ca 20 points 2 months ago

Are you sure that galaxies are growing? They're gravitationally bound enough to have organized orbits, do those orbits get larger over time?

[-] davidgro@lemmy.world 6 points 2 months ago

My understanding was that in a gravitationally bound system like that, the orbits would be slightly larger (or slower for the same distance) based on the rate of expansion and the distance, but not grow any unless the rate of expansion increases. Like maybe the earth is a few angstroms farther from the sun than in a not expanding universe, but that number doesn't change as long as the expansion keeps going the same. Same for galaxies and clusters.

[-] Tlaloc_Temporal@lemmy.ca 6 points 2 months ago

At the planetary scale, such a change would be completely overpowered by other orbit defining effects, like resonance, mass flow/loss, and even drag.

At the cluster scale, I can absolutely see spacetime expansion overpowering gravity.

At the galaxy level, I can't tell. Does spacetime expansion limit the size of galaxies? Is that limit shrinking due to the acceleration of expansion? Are galaxies under that limit larger than otherwise expected? Is this effect large enough to effect the speed of galaxy rotation and does it need to be taken into accout when measuring the effects of dark matter?

[-] Rhaedas@fedia.io 7 points 2 months ago

At the cluster level it will depend on the velocities and distances. For example, using very rough numbers the current expansion rate means that space between us and the Andromeda galaxy is expanding at 55 km/s. Seems fast until you realize the distance needed to see the effect build to this level. For perspective I found someone's calculation to reduce it to solar system level to end up with ~10 meters/AU/year. But of course at this distance gravity dominates so we can't measure that directly and it may not even be large enough to consider.

A larger and slower moving galactic cluster would be more affected than a tighter one. I don't know what our Local Group would be considered to be, but there are a hundred or so galaxies around us that appear blue shifted, so they are moving towards us even with the expansion.

[-] Tlaloc_Temporal@lemmy.ca 1 points 2 months ago

That wouldn't significantly affect most galaxies though, would it? The rasin bread model might insinuate that the space in a galaxy isn't expanding (which is wrong), but it is accurate in thst gslaxies themselves are not growing larger.

[-] Rhaedas@fedia.io 2 points 2 months ago

Correct, the differences make the analogy good enough to visualize the concept. It does however suffer from the same problem as the balloon one, in which someone can get the impression the expansion has a center. The wiki for the expansion of the universe goes through the various analogies and where they break down.

I would suggest Dr Becky's Youtube channel for a number of excellent videos on the expansion as well as the current problem of getting an accurate measurement of the correct Hubble expansion rate. The James Webb telescope was hoped to solve that dilemma, but we still aren't sure.

[-] wholookshere@lemmy.blahaj.zone 0 points 2 months ago

I see where this is diverging a little bit.

But everything is expanding. Including matter. But the mass isn't chaning.

But this also includes the space in between the objects.

So objects are getting further apart, but so are the objects getting bigger at the same rate.

The mind bend for me was realsing it's not space that expanding really, it's distance.

This is why distant light is red shifted. Because what started out as white, has had the wavelength expand with the universe, making it appear more red.

[-] Tlaloc_Temporal@lemmy.ca 5 points 2 months ago

Yes, all distances are expanding, but not everything in space is expanding. Atoms aren't expanding because atomic forces are far stronger than expansion is, for example.

Yet the distance between galaxies is increasing, so there must be a crossover point where one structure can stay structured but a slightly bigger structure is torn apart.

My question was if this size is larger or smaller than galaxies, and it seems to be quite a bit larger than galaxies at the moment.

The interesting thing is that the expansion is increasing, so this size limit is shrinking. Unless some change in forses happens (like inflation or some kind of false vacuum collapse) the limit will eventually be smaller than galaxies and they'll get ripped apart. Eventually star systems will be ripped apart too, then stars (if any remain at that point) then planets, molecules, atoms, and bosons; and if if that continues to quarks funny things start happening that kind of look like the big bang.

That last part is still speculation of course, but I do still wonder if the expansion of the universe affects galaxy formation and dynamics, and if ancient galaxies were different in part because of this.

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[-] Gradually_Adjusting@lemmy.world 9 points 2 months ago

Metaphors are great if you assume they're mostly wrong

[-] Mango@lemmy.world 2 points 2 months ago

Am I getting bigger too?

[-] Lemming6969@lemmy.world 2 points 2 months ago

There's still a center of the balloon and bread

[-] WolfLink@sh.itjust.works 4 points 2 months ago

There’s no center of the surface of the balloon (approximating the balloon as a sphere and ignoring the nipple).

If you are standing on the earth, there is no center of the surface of the earth. The actual center of the earth requires movement in the 3rd dimension, but the surface is 2 dimensional.

If our universe is hyper spherical, the “center” would be something unreachable; it would require moving in the 4th spacial dimension.

[-] Lemming6969@lemmy.world 2 points 2 months ago

Yeah I get that, but there is no evidence of a 4th spacial dimension, so it's really just creative writing at this point.

[-] WolfLink@sh.itjust.works 3 points 2 months ago

There is evidence of space time being curved

[-] Lemming6969@lemmy.world 1 points 2 months ago

Yes, but just because the discrete distance between 3D points isn't constant does not mean a 4D space exists that allows for what is being proposed.

[-] WolfLink@sh.itjust.works 1 points 2 months ago

Yes.

In summary, for the purposes of this analogy, a balloon has no center.

[-] buddascrayon@lemmy.world 14 points 2 months ago

Also, don't forget to flour your galaxies in order to keep them in their respective places and prevent them from all rising to the top of your universe.

[-] ICastFist@programming.dev 3 points 2 months ago

It's important to butter the baking pans so the galaxies can come off more easily

[-] Sotuanduso@lemm.ee 14 points 2 months ago

I read "3cm" as "Jam" somehow and was very confused. For a bit, I thought the raisins were holes to inject the jam into to make a jam-filled cookie.

[-] dharmacurious@slrpnk.net 7 points 2 months ago

I would buy this delicious jam filled galactic cookie if you bake it

[-] Sotuanduso@lemm.ee 4 points 2 months ago

If you bake it, he will buy.

[-] dharmacurious@slrpnk.net 3 points 2 months ago

Read this at first as "if you bake it, he will come" and I was like "I dunno if I'd go that far. Depends on what kind of jam, to be honest"

[-] Sotuanduso@lemm.ee 4 points 2 months ago

Apparently dyslexia is contagious.

[-] marcos@lemmy.world 10 points 2 months ago

But those raisins are growing!

[-] RamblingPanda@lemmynsfw.com 4 points 2 months ago

It's bad_science_memes now

[-] mvirts@lemmy.world 10 points 2 months ago

Can we just not use metaphor for everything? It's like building a new car only out of old parts people are familiar with. 😹

[-] Mango@lemmy.world 4 points 2 months ago

Is this the metaphor straw that broke the metaphor camel's back metaphorically? Can we have this metaphor but axe some other metaphors? Why do I gotta choose?