Which statement is true about Redshift and the Hubble constant?

In summary: The Hubble constant, which represents the rate of expansion of the universe, multiplied by the distance to a galaxy, gives us the apparent speed of recession. This means that the further away a galaxy is, the faster it appears to be moving away from us.Statement B is also true. This is a consequence of statement A - if the apparent speed of recession is determined by the product of the Hubble constant and distance, then the further away a galaxy is, the lower its apparent speed will be.Statement C is not necessarily true. While it is possible for a galaxy with a redshift of 5.37 to be situated at a look-back time of 4.1 billion years, it is not a definitive fact. The look-back
  • #1
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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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  • #2
Which statement(s) do you think is/are true and why?
 
  • #3
I think statement A is true but I'm not 100% sure whether D is false and there is only one true statement.
 
  • #4
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
 
  • #5
Well, isn't it generally true that the farther a galaxy is from us, the faster it appears to be receding?
 
  • #6
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.
 
  • #7
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?
 
  • #8
Statement A is definitely correct.
 

1. What is redshift?

Redshift is a phenomenon in which light from distant objects, such as galaxies, appears to shift towards the red end of the spectrum. This is caused by the expansion of the universe, which stretches the wavelengths of light as it travels through space.

2. How is redshift related to the Hubble constant?

The Hubble constant is a measure of the rate at which the universe is expanding. The redshift of an object is directly proportional to its distance from Earth, and therefore can be used to calculate the Hubble constant.

3. What is the significance of the Hubble constant?

The Hubble constant is important because it helps us understand the age and size of the universe. It also allows us to track the expansion of the universe and make predictions about its future.

4. How is the Hubble constant calculated?

The Hubble constant is calculated by measuring the redshift of distant objects and using it to determine their distance from Earth. This information is then used to calculate the rate of expansion of the universe.

5. Has the value of the Hubble constant changed over time?

Yes, the value of the Hubble constant has changed over time. Scientists have used different methods to measure it, resulting in varying values. Additionally, as our understanding of the universe evolves, the value of the Hubble constant is refined and updated.

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