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Comment by d_tr | Hacker News Reader

> It’s not like the universe is just expanding everywhere uniformly, ...

I thought this is exactly what most modern physicists believe.

The wavelength of photons travelling in space is supposed to scale perfectly with the expansion of the universe, like an ink dot on a balloon getting wider as the balloon is being inflated.

This is why we have the Cosmic Microwave Background consisting of photons that would have been maybe in the UV range when emitted by excited atoms back when the universe became "transparent".

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This is hard to communicate so I’m sure I’ve been misleading.

“Space” is expanding uniformly, yes. But not the matter that exists in space, nor is the distance between local matter increasing.

It’s not like the entire universe is undergoing a magnification of scale where everything is enlarging including each individual atom.

So it’s misleading to say “the space between your fingers is expanding”, because it might give the impression that the distance between your fingers will actually be larger as time passes. This is not the case.

If “space is expanding”, but the matter inside this space is unaffected by said expansion, then you’re left with a very subtle phenomena which is easy to misunderstand.

So then all our parts are "falling" together constantly through this expanding space? I say falling, but I understand it is other local forces besides gravity.

I struggle to wrap my mind around what that means for concepts I learned long ago in college physics... what is an inertial frame of reference then? What about the speed of light and relativistic effects?

I suppose the answer is back to the original statement that the effect is really only noticable at cosmological scales. Locally, it's well below any margin of error?

I actually find your "it is and it isn't" to be much more confusing than "it is but the other forces recompact matter faster than the new space emerges".

> This is hard to communicate ...

True. I think that the best way to explain this to someone who does not know about the phenomenon is to start with the phrase "existing space continuously creates new space" and everything should follow from this fact.

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