Time & Space Expansion: What Does It Mean?

[earamsey]

Physicists say that space is expanding. Well, Einstein says that space and time can not be separated so I can assume that timespace is expanding. What does it mean for time to expand?

 

[atyy]

"Space is expanding" depends on a particular separation of spacetime into space and time - quite contrary to the spirit of spacetime - spacetime can be separated into space and time many other ways, and in some of those ways, space is not expanding. Anyway, the particular separation of spacetime into space and time used in "space is expanding" is convenient and conventional.

 

[earamsey]

pardon my ignorance, but what is the answer? I asked question because I keep hearing theory of expanding space and some how it start to not sound correct when one thinks about spacetime. I guess I should not worry about this since I saw a lecture about dark energy that questions the correctness of GR and gravity anyways so maybe I have to wait and see what is the final consensus about it.

 

[atyy]

First divide spacetime into space and time - there are many ways to do it - but by convention we choose a way in which space is expanding with time. Since we already chose a division of spacetime into space and time, that space is expanding does not imply that time is expanding.