What is the relative speed of two groups of quasars with different redshifts?

In summary, the conversation discusses the speed of two groups of quasars, one at redshift 10 and another at redshift 6, with the assumption that they are at the same distance. The question asks for the speed of the second group relative to the first, either in percent of lightspeed or in kilometers per second. The response suggests using the Doppler shift formula to calculate the redshift from motion and then finding a minimal velocity, as space is not one-dimensional.
  • #1
CosmologyHobbyist
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TL;DR Summary
speed calculation between two groups at different redshifts : redshift 10 & redshift 6.
If many quasars are at redshift 10, and another group is at redshift 6, what is the speed of the second group relative to the first? The redshift 10 group can be considered "at rest", so the redshift 6 group is heading in our direction at what rate? For this scenario, let us assume all the quasars are at same distance (as suggested by zero time dilation difference). Answer in percent of lightspeed please, but kilometers per second is ok, I can handle that conversion.
 
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  • #2
Cosmological redshift is effectively time dilation. You are asking for two mutually exclusive conditions at the same time. But if you want to put them at the same distance: Calculate the redshift from motion at this place (the relative frequencies stay the same), then plug that into the Doppler shift formula. You won't get a unique result because space is not one-dimensional, but you can get a minimal velocity.
 
  • #3
Thanks for your time, mfb.
 

1. How is redshift speed calculated?

Redshift speed is calculated by measuring the shift in the wavelength of light emitted from a distant object. This shift is caused by the Doppler effect, which is the change in frequency or wavelength of a wave as it moves towards or away from an observer. The amount of redshift is then used to calculate the speed at which the object is moving away from us.

2. What is the formula for calculating redshift speed?

The formula for calculating redshift speed is z = (observed wavelength - rest wavelength) / rest wavelength, where z is the redshift value. This value can then be used in the Hubble's Law equation (v = H0 x d) to calculate the speed of the object, where v is the speed, H0 is the Hubble constant, and d is the distance to the object.

3. Can redshift speed be used to measure the distance to a galaxy?

Yes, redshift speed can be used to measure the distance to a galaxy. This is because the amount of redshift is directly proportional to the distance of the object from us. The farther away an object is, the greater its redshift will be. This relationship is known as Hubble's Law.

4. How accurate is redshift speed in determining the age of the universe?

Redshift speed is a very accurate method for determining the age of the universe. By measuring the redshift of distant objects, scientists have been able to estimate the age of the universe to be around 13.8 billion years old. This is consistent with other methods of age determination, such as the cosmic microwave background radiation and the ages of the oldest stars.

5. Are there any limitations to using redshift speed for calculating distances and speeds in the universe?

Yes, there are limitations to using redshift speed for calculating distances and speeds in the universe. One limitation is that redshift speed can only be used for objects that are moving away from us. It cannot be used for objects that are moving towards us, as this would result in a negative redshift value. Additionally, redshift speed can only be used for objects that are far enough away for their redshift to be measurable, typically beyond our own galaxy. For objects within our own galaxy, other methods such as parallax measurements are used to determine distances and speeds.

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