[ilovemath]

v = H₀d tells us that the recession velcotiy of a galaxy is directly related to its distance from us on earth.
However, as the planets move further apart, their potential energy increases (and hence kinetic energy decreases).

How can these two phenomena both exist. In fact the only one that seems correct is the latter (kinetic energy MUST decrease if PE increase as energy cannot be created/destroyed)

???

[Pangol]

It's a bit tricky to apply the conventional energy way of thinking here, because the recession of galaxies is not caused by their motion through space, but by the expansion of space itself.

[ilovemath]

(Original post by Pangol)
It's a bit tricky to apply the conventional energy way of thinking here, because the recession of galaxies is not caused by their motion through space, but by the expansion of space itself.

eh....could you link we a good site to explain this?

[Pangol]

Try this.

[ilovemath]

(Original post by Pangol)
Try this.

I have done a little reading about and it seems the situation is quite complex...would I be correct in assuming this question would not show up at A-level (we have not covereed relativity at all)

[Pangol]

While it's great that you've thought around what you've been taught, I think that it's very unlikely you'll be asked for anything other than Hubble's Law.

[ilovemath]

(Original post by Pangol)
Try this.

I have been thinking about what you said and yes, it makes sense their velcotiy is caused by recession through space but here is another issue.
The PE between planets is increasing....thus energy is not being conserved. ?????