What does expand: Space or Spacetime?

[phinds]

I am confused by this whole thread. I have only a superficial knowledge, so probably nothing fundamental.
1. how do you know things are moving away from each other when there is no constant scale? (Any physical scale itself would expand, would it not?)
2. If it is red-shift, how do you know that photons don't gradually expand in wavelength (like a slow decay from blue to red)?
3. What makes time so great that space always has to change (expand) but time does not have to? Is this related to the fact that we can traverse space at will in any direction but time only in forward direction? (By we I mean matter with a positive rest mass.)

1. The scale is irrelevant. WHATEVER the scale you use, things are moving apart and things farther away are moving apart faster than things closer together.
2. The "tired light" theory was debunked ages ago.
3. You are trying to apply a characteristic to time that does not apply. It's like asking "why isn't the number 3 green?"

 

[N123]

2. The "tired light" theory was debunked ages ago.
3. You are trying to apply a characteristic to time that does not apply. It's like asking "why isn't the number 3 green?"

2. Thank you for pointing me to the "tired light" theories.
3. Which characteristic?

 

[phinds]

3. Which characteristic?

Expansion in a physical dimension.