Maybe I’m misinformed about this. But I was always told matter cannot be destroyed or created. But I have been told space is constantly expanding. Is this expansion of space not made up of “matter”? Where does it come from?
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Hi /u/Barnshart3!
There are a couple of misconceptions in your question, so let’s work through them one by one:
>But I was always told matter cannot be destroyed or created.
Matter is not a conserved quantity (In fact, matter is not even a well-defined term). Processes like [pair production](https://en.wikipedia.org/wiki/Pair_production) and [matter–antimatter annihilation](https://en.wikipedia.org/wiki/Electron%E2%80%93positron_annihilation) can definitely create and destroy matter.
>But I have been told space is constantly expanding.
The universe is probably infinite and probably has always been infinite (including at the big bang). The expansion of space does not mean that space is added at some edge of the universe. Rather, the distance between all points (that are not gravitationally bound) increases over time. You can imagine this analogously to an infinite number line, where the distance between the markers of any two adjacent whole numbers increases over time. The number line is infinite and remains infinite, but the distance between all pairs of points increases over time.
>Where does it come from?
While matter is definitely not conserved in our universe, energy might *seem* like it is conserved. I am sure you learned that energy cannot be created or destroyed in highschool physics class.
*However*, it turns out, that not even this law of conservation remains true in an expanding universe. Energy is *not* conserved in an expanding universe, and dark energy is, in fact, created from nothing as spacetime expands.
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