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So I was asked a question by someone that "if everything in the universe is expanding, then the lens we use to look at stellar objects is expanding as well, meaning we shouldn't be able to tell the difference at all".

I replied with "local forces overpower expanding forces, hence the lens doesn't change size at all, whereas at cosmic scales, local forces are too weak so things move apart. In other words, the lens doesn't change size, the question is false, the universe is expanding"

He replied with "the lens DOES change size, just at a different rate than stellar objects are moving apart from each other, hence we know the universe is expanding"

So, what's the actual answer?

I also looked into a similar question: Why does space expansion not expand matter?

But here, OP stated in his question (after receiving an answer) that:

The answer seems to be (from Marek in the previous question) that the gravitational force is so much weaker than the other forces that large (macro) objects move apart, but small (micro) objects stay together. However, this simple explanation seems to imply that expansion of space is a 'force' that can be overcome by a greater one. That doesn't sound right to me.

This is exactly what I mean to ask. Is the expansion of space a "force" that can be overcome, or not? Unfortunately, nobody has addressed that part of the question in that thread, hence I'm asking here.

Qmechanic
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Zac
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    Possible duplicate of Why does space expansion not expand matter? – Stéphane Rollandin Jun 15 '19 at 08:23
  • https://physics.stackexchange.com/a/37584/220004 this should be the answer you're looking for. Both you and the other person are right, but you are "more right". – Mauro Giliberti Jun 15 '19 at 08:40
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    Yes, in the Newtonian limit the expansion of space behaves exactly like a very weak force that pulls things apart. It is far too weak for solid objects to be noticeably affected. – knzhou Jun 15 '19 at 08:48
  • Why should lenses etc expand without due cause,as though by magic? Only in fairy tales is the cause-and-effect principle suspended,not in the real world. Science should not become a kind of religion or a series of fairy tales. To quote Richard Feynman,"Reality takes precedence over public relations,for nature cannot be fooled." – Michael Walsby Jun 15 '19 at 10:21

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