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Does the expansion of space (that started from BigBang) limited to expansion of intersteller space only (as observed by Hubble) or does it happen even in the local observable universe?

Specifically, does the space between two stars in our own galaxy is also expanding? Does the molecular space in an ordinary everyday object expanding as well (even if it is very very tiny)?

hashbrown
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  • Space expands everywhere, but there are a host of local factors (like gravitation, virial motion), that prevent you from immediately realizing the effects. – Sayan Mandal Oct 10 '17 at 17:38
  • Are these other factors as you pointed out prevent the expansion in small distances (molecular distances)? Or does space expands even in molecular distances even though the net effect may not be observable due to other factors? – hashbrown Oct 10 '17 at 17:43
  • I think @SigSeg's answer addresses your concern. – Sayan Mandal Oct 10 '17 at 19:33

2 Answers2

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This one is tricky because we have to admit here that the expansion of space is a model. We don't actually know whether it is the true nature of the universe, or merely a good predictive model of every observation we have made over the course of human history.

That being said, the current preferred model is that the expansion of space occurs everywhere. It is treated as an aspect of the topology of space itself, not just the matter in it.

Given the current estimate for Hubble's Constant of 71.9 km/s / Mpc, we can plug in numbers to determine how fast two points are moving apart. Let's pick a point in Los Angeles and one point in New York. They are 10083km apart (straight line distance through the Earth). That's .00000000000000032676778 Mpc, if you convert km to Mpc. Thus New York and Los Angeles are moving apart due to the expansion of space at a rate of 736 um/yr!

Of course, plate tectonics causes shifts 3 orders of magnitude greater than this, so we don't notice this expansion all that much.

Cort Ammon
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    It's a good analogy, but somewhat misleading. The expansion between 2 cities is negated because various forces pulling the two apart are countered by gravity, atomic bonds, etc. You have 2 boats, one close to shore and getting pulled into shore, the other away from shore and getting pulled away. If you take a rope (gravity) and connect between the two boats, they will never drift apart due to the current (space). For this reason, the distance between two cities is unaffected by the expansion. Trillions of years from now, expansion will exceed the rope's strength, and the rope will snap. – SigSeg Oct 11 '17 at 01:48
  • You can also calculate the equivalent force due to cosmological expansion between LA and NY, and it is so small as to be readily counteracted by the static forces that keep the two cities in their place, plus any other local force. Thing that people forget is that that cosmological expansion represents a hugely diminutive force and effect for anything not at cosmological distances, and standard local forces tend to maintain the static equilibrium, and then add all the other earth-related dynamical forces. Anyway, true that eventually the rope breaks – Bob Bee Oct 11 '17 at 05:35
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According to modern understanding of physics, no.

In fact, if the accelerating expansion continues for trillions of years, space will be expanding so much (everywhere) that it will exceed the weak and strong force and pull everything apart.

EDIT

Alex Fillipenko (Seen a lot on "The Universe" is actually one of the leading experts in the area, so I wanted to include his lecture which he had given several dozen times all around the world from 2013-2016:

https://www.youtube.com/watch?v=CaCEEHtPcSg

SigSeg
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  • It is worth elaborating on the "if", "if the accelerating expansion continues". There is consensus in physics that the rate of expansion may not be constant. The basis for this is the big bang, which formed from a singularity. The only known way in physics for matter not to collapse into a black hole at this density is if it is counter-acted by rapid expansion of space. Like physics beyond the event horizon of a black hole, the big bang is equally puzzling and there may be other unknown forces that explain it beside rapid expansion, but that is the current popular theory. – SigSeg Oct 10 '17 at 18:19