How is new space created as the universe expands? Einstein discovered that empty space is not nothing, so what is responsible for new space appearing into existence, when energy and matter cannot?

Question

[Nasa.gov](https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy) explains dark energy like a property of space, and go on to say:

> Albert Einstein was the first person to realize that empty space is not nothing. (…) The first property that Einstein discovered is that it is possible for more space to come into existence.

But they never elaborate on how Einstein knows this. I know this is a field without concrete answers, but I’m curious about Einstein’s explanation.

In: Physics

Answer 1

Conservation of energy only applies to a closed system. An expanding universe is not a closed system. Further more the energy ‘created’ in the new space isnt the same thing as we typically think of when talking about energy. In the case of dark energy the ‘new’ energy isn’t doing any work, rather it is a property of empty space itself. The energy density never changes, just the absolute amount.