Cosmological and doppler redshift

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SUMMARY

Cosmological redshifts result from the metric expansion of space, while Doppler redshifts arise from relative velocities through space. Historically, astronomers distinguished these two causes by observing the uniformity of redshifts across distant galaxies, which supported Hubble's law. The discussion emphasizes the challenge of quantifying the contributions of Hubble flow versus Doppler shift in redshift measurements, highlighting the complexities involved in verifying cosmological models.

PREREQUISITES
  • Understanding of cosmological redshift and its relation to metric expansion of space
  • Familiarity with Doppler effect and its application in astrophysics
  • Knowledge of Hubble's law and its significance in cosmology
  • Basic grasp of observational techniques in astronomy
NEXT STEPS
  • Research the metric expansion of space and its implications for cosmology
  • Study the Doppler effect in the context of astrophysical phenomena
  • Examine Hubble's law and its role in measuring cosmic distances
  • Explore methods for distinguishing between cosmological and Doppler redshifts in observational data
USEFUL FOR

Astronomers, astrophysicists, and students of cosmology seeking to deepen their understanding of redshift mechanisms and their implications for the universe's expansion.

throneoo
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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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It was a question of appearances. It would be very strange if distant galaxies were all moving away from us at random.
 
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?
 

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