Cosmological and doppler redshift

In summary, astronomers originally distinguished cosmological redshifts and doppler shift by observing the appearance of distant galaxies and questioning the randomness of their movements. With the use of Hubble's law and the standard cosmological model, it was determined that the Hubble flow is responsible for the redshifts, but it is still unclear how much is contributed by doppler shift.
  • #1
throneoo
126
2
cosmological redshifts are caused by the metric expansion of space, whereas doppler shift is a result of relative velocities through space. So before the development of the modern cosmological models, how did astronomers originally distinguish these two causes of redshifts (e.g. when they tried to verify the Hubble's law) ? Even with the use of Hubble's law and the standard cosmological model, can we tell how exactly these two mechanisms contribute to these redshifts?
 
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  • #2
It was a question of appearances. It would be very strange if distant galaxies were all moving away from us at random.
 
  • #3
mathman said:
It was a question of appearances. It would be very strange if distant galaxies were all moving away from us at random.

doesn't that only imply the existence of the Hubble flow? I mean how did astronomers ascertain how much of the redshift of a single object is caused by the Hubble flow and how much by doppler shift?
 

Related to Cosmological and doppler redshift

1. What is cosmological redshift?

Cosmological redshift is a phenomenon where light from distant objects in the universe appears to be shifted towards the red end of the electromagnetic spectrum. This is caused by the expansion of the universe, which stretches the wavelengths of light as it travels through space.

2. How is cosmological redshift measured?

Cosmological redshift is measured using a unit called redshift (z), which is calculated by comparing the observed wavelength of light from a distant object to its known rest wavelength. A higher redshift value indicates a larger shift towards the red end of the spectrum and therefore a greater distance from Earth.

3. What is the difference between cosmological redshift and Doppler redshift?

Cosmological redshift is caused by the expansion of the universe, while Doppler redshift is caused by the relative motion between an object and an observer. In cosmological redshift, the distance between the object and the observer is constantly increasing, while in Doppler redshift, the distance between the object and observer can vary due to their relative motion.

4. Can cosmological redshift be used to determine the age of the universe?

Yes, cosmological redshift can be used to estimate the age of the universe. By measuring the redshift of distant objects and using the known rate of expansion of the universe, scientists can estimate how long it has been expanding and therefore determine its age.

5. How does cosmological redshift support the Big Bang theory?

Cosmological redshift is one of the key pieces of evidence supporting the Big Bang theory. The redshift of light from distant galaxies indicates that the universe is expanding, which is a fundamental principle of the Big Bang theory. Additionally, the amount of redshift observed in different objects can be used to trace the history of the expansion of the universe and support the concept of a primordial singularity at the beginning of the universe.

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