How can nothing expand? Isn’t space made of nothing? You can’t have 5 pounds of space.
In: Physics
Nothing expanding is actually really easy! If you start with nothing, and now have more nothing, you haven’t actually added anything. This works great with conservation laws.
In the case of space expanding; given two things, after a bit of time, they are now further away than they were before (specifically by a factor of about 10^(-19) per second). The distance between them has grown without either of them moving (for a given value of “moving”).
Space expanding means that things that are far away are constantly getting further apart from each other.
If there *was* stuff in space this would cause us problems, as that stuff would have be being created as the universe expands.
Except – as usual with physics – quantum mechanics and general relativity mess this up. It turns out there is stuff in space (for a given value of “stuff” and “is”), and universal expansion is accelerating. Which means there must be some kind of energy pouring into the universe driving this. Hence “dark energy” – one of the big questions in modern physics.
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