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Clearlybeerly t1_iwnnt0x wrote

Reply to comment by Ape_Togetha_Strong in Ask Anything Wednesday - Engineering, Mathematics, Computer Science by AutoModerator

So what does it mean when it is said that "space is expanding"? Is that misnomer?

How can space expand if it isn't expanding?

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Ape_Togetha_Strong t1_iwno8l3 wrote

I didn't say that it doesn't expand. I asked why you feel that there has to be something for it to expand into for it to expand.

Expand is just the best word we have for what space does, it doesn't mean it has to be exactly like other sorts of expansion you can think of.

Space is expanding. Space is not expanding into anything. The distances between things are just getting bigger.

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nivlark t1_iwnsmrq wrote

"Expand" is simply the closest English word to describe a particular behaviour we observe in distant objects.

For a more precise description, you need to turn to mathematics: an expanding space is one where the "metric tensor" - the mathematical object in general relativity that tells you how to calculate the distance between two points in curved spacetime - is time-dependant.

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Clearlybeerly t1_iwoaqmb wrote

OK, thanks. I looked up metric tensor on wiki and looked up other hyperlinks in the metric tensor entry, and I have a very, very vague understanding, but it sure does help me understand, because while I have a vague understanding, what it mainly does is allow me to cut away the extraneous. So very cool, thank you.

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