Assume that the expansion of the universe stops and it starts to contract again. What would happen?
Would only distances between objects get smaller, or are there other effects we can expect?
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$\begingroup$ Global warming would eventually become less of a thread compared to the CMB. $\endgroup$ – pela Apr 2 '19 at 12:22
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2$\begingroup$ What timeframe for "effects" do you have in mind? A Big Crunch in xx billion years? What causes the contraction, and is it isotropic (does it apply to the whole universe)? Do the normal laws of physics still apply? NB given that the expansion is currently accelerating, you would need this acceleration to reduce to zero, and then the rate of expansion to decline to zero, before contraction can start. $\endgroup$ – Chappo Hasn't Forgotten Monica Apr 2 '19 at 12:40
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$\begingroup$ @Chappo but if the universe find the limit like a wall or a wave in a cliff? $\endgroup$ – Nicolas Oñate Apr 2 '19 at 12:54
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Given that the expansion of the universe shows us that the distance between galaxies (or rather moreso between galaxy clusters) is increasing, without any change in the distances within or between atoms, or between stars within galaxies (apart from normal stellar motion), and that galaxies themselves are also not expanding, we could assume that a contraction would manifest as a decrease in the distances between galaxies/galaxy clusters.
