Tedward
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I understand that the universe is expanding, and the evidence is that all observable points are moving away from us. And by moving away I mean the expansion of space itself.

But surely the space occupied by earth is expanding too? And the same for an arbitrary galaxy we point our telescope at?

So proportionally, why would it appear as if the distance between us is increasing if we are increasing with it?

Confusing point, hopefully someone can help!


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lerjj
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(Original post by Tedward)
I understand that the universe is expanding, and the evidence is that all observable points are moving away from us. And by moving away I mean the expansion of space itself.

But surely the space occupied by earth is expanding too? And the same for an arbitrary galaxy we point our telescope at?

So proportionally, why would it appear as if the distance between us is increasing if we are increasing with it?

Confusing point, hopefully someone can help!


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The space we're in isn't expanding as well, I used to think this too. I honestly can't remember the reason why- gravity maybe?
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haydentaylor
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Think as the big bang as a grenade... (-(-(-(-(-(o-)-)-)-)-) as you can see the space isn't expanding from near the center, instead the space continues to expand from the outwards layers! dunno if this helped? i'm only studying A2 physics haha!
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Tedward
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(Original post by lerjj)
The space we're in isn't expanding as well, I used to think this too. I honestly can't remember the reason why- gravity maybe?
Ahh gravity is good point. I think the space we occupy is expanding, just at a reduced amount in comparison with areas with less gravity...perhaps?


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Tedward
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(Original post by haydentaylor)
Think as the big bang as a grenade... (-(-(-(-(-(o-)-)-)-)-) as you can see the space isn't expanding from near the center, instead the space continues to expand from the outwards layers! dunno if this helped? i'm only studying A2 physics haha!
I think I have an idea what your saying but 1. There's no particular reason why we'd be near the "centre" and not an outer layer. And also I'm not sure whether there is even a centre since all points arose from a single point so in a way the whole universe is the centre...don't take my words as gospel though, I'm not an expert!


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interstitial
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I'm not completely sure, but this is what makes sense to me - The force causing the universe to expand is very very weak in comparison to other forces and only really has a noticeable effect on (virtually) empty space as it's not strong enough to overcome the forces joining other atoms together. The universe is only expanding when averaged out on a massive scale, and atomic forces do not follow the typical geodesic paths associated with expansion.

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lerjj
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(Original post by Arithmeticae)
I'm not completely sure, but this is what makes sense to me - The force causing the universe to expand is very very weak in comparison to other forces and only really has a noticeable effect on (virtually) empty space as it's not strong enough to overcome the forces joining other atoms together. The universe is only expanding when averaged out on a massive scale, and atomic forces do not follow the typical geodesic paths associated with expansion.

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This is correct I think, kinda what I meant when I said 'gravity' but couldn't think up the full explanation. I don't actually know what geodesic means, so that'll occupy me for a while :-) (I also just bought a tent that is supposedly 'geodesic' so it's becoming a real issue)
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amtheril
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Space may be expanding, though that doesn't mean that matter is (although Paul Dirac's LNH suggests otherwise): imagine a background of 'space' expanding but that not having any affect of the mass of the earth. @haydentaylor its not like an explosion because an explosion starts in a certain location and explodes through a pre-existing volume of space. Expansion has no centre (everywhere in the universe is the centre if you look at it that way, as all space in the universe derived from this small starting point).
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DrQuantum
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Because the gravity of the earth and intermolecular forces pull the earth back in faster then this almost negligible expansion does. Things only move apart when they are far enough away from us that the gravitational attraction is not enough to stop the recession.

Hubbles constant however seems to be increasing so if this continues at some point this will be significant over small distances and molecules themselves could be separated.
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BestProfileName
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(Original post by Tedward)
I understand that the universe is expanding, and the evidence is that all observable points are moving away from us. And by moving away I mean the expansion of space itself.

But surely the space occupied by earth is expanding too? And the same for an arbitrary galaxy we point our telescope at?

So proportionally, why would it appear as if the distance between us is increasing if we are increasing with it?

Confusing point, hopefully someone can help!


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The fabric of spacetime is expanding, but not us. You could think of it as bubbled within a big bubble. The big bubble can expand whilst the little bubbles remain a constant size. In other words, you can have local pockets of order in an ocean of disorder.

Our solar system has way more mass than the average volume of spacetime, so of course, gravity is going to hold it together as we hurtle, as a collective, through space.
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