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I have already asked this on Astronomy.SE but I couldn't understand the answer there.

According to Hubble's Law, the farther a galaxy is, the farther it is moving away. But do we take into account the fact that we are actually looking in the past?

For example, there are two galaxies A and B at distance of 5 and 10 billion light years respectively. Now, when we observe A we are looking at how it was moving 5 billion years ago. The same applies for B. So, now we conclude that 5 billion years ago space was expanding at a slower rate while it was expanding comparatively faster 10 billion years ago. What's wrong with this conclusion?

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Yashbhatt
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  • You mean "distance of 5 and 10 billion light years". – Steeven Jul 14 '14 at 17:19
  • Yes. Made the edit. – Yashbhatt Jul 14 '14 at 17:20
  • @JohnRennie Can you please shed some light on this question? – Yashbhatt Jul 14 '14 at 17:21
  • The answer on Astro.SE is correct. If you cannot understand it, try asking questions to try and clarify what you don't understand about that answer, instead of asking the same question again. I almost posted an answer, but then read the Astro.SE one and realized I was just going to say essentially the same thing. – Kyle Oman Jul 14 '14 at 17:56
  • All I understood from the answer is that we should expect distant objects to move faster as we are looking at them as they were in the past. So, suppose we look at galaxy A which is $x$ billion light years away and measure at what rate it is receding. Then, we look at another galaxy B which is $y$ billion light years away such that $x$ > $y$. Then, we calculate at what rate the expansion rate decreases and find that the rate decreased but that does not agree with something. I don't know what's that something. – Yashbhatt Jul 15 '14 at 16:17

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