Which statement is true about Redshift and the Hubble constant?

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Discussion Overview

The discussion revolves around the validity of various statements regarding redshift and the Hubble constant, exploring concepts related to the expansion of the universe and the relationship between distance and recession speed of galaxies.

Discussion Character

  • Debate/contested

Main Points Raised

  • Some participants propose that statement A is true, asserting that the apparent speed of recession of a galaxy correlates with the Hubble constant and its distance.
  • Others question the validity of statement D, suggesting that it may not be accurate to claim that distances between galaxies remain constant in an expanding universe.
  • A participant mentions using a cosmology calculator to verify statement C, indicating uncertainty about the look-back time associated with a specific redshift.
  • There is a general agreement that statement B is likely not true, as it contradicts the notion that further galaxies recede faster.
  • Some participants express uncertainty about whether only one statement is true, particularly between A and D.
  • One participant emphasizes that the concept of galaxies moving away implies increasing distance over time.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as multiple competing views remain regarding the truth of the statements, particularly between A and D.

Contextual Notes

Participants reference the need for calculations to determine the accuracy of certain statements, indicating potential limitations in assumptions about redshift and look-back time.

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Which statement is true?

A The apparent speed of recession of a galaxy is given by the product of the Hubble constant and the distance to the galaxy.

B The further away a galaxy is, the lower its apparent speed of motion away from us.

C A galaxy with a redshift of 5.37 is situated at a look-back time of 4.1 billion years.

D Space is expanding uniformly so that the distance between galaxies remains constant.
 
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Which statement(s) do you think is/are true and why?
 
I think statement A is true but I'm not 100% sure whether D is false and there is only one true statement.
 
Well, to rule out C you can have a look at Ned Wrights Javascript cosmology calculator to determine the lookback time. Just plug in 5.37 for the redhshift. The light travel time is the "lookback time".

http://www.astro.ucla.edu/~wright/CosmoCalc.html
 
Well, isn't it generally true that the farther a galaxy is from us, the faster it appears to be receding?
 
Yeah, I didn't think B or C were the answers.
I'm still stuck between whether A or D is the right answer and I really need help.
 
Does it make any sense for the distance between things to remain constant in an *expanding* universe?

When we say that a galaxy is moving away from us, what does that mean? Does it not mean that it is getting farther away with time?
 
Statement A is definitely correct.
 

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