Redshift is due to the expansion of the universe

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SUMMARY

The cosmological redshift is a phenomenon resulting from the expansion of the universe, where light from distant galaxies is shifted to longer wavelengths. This occurs because light travels at a constant speed, and its wavelength changes based on the relative motion between the source and the observer, as explained by special relativity. Gravitational redshift, a concept from general relativity, occurs when light is emitted from objects in a gravitational field, causing the light to be 'stretched'. The effects of cosmological expansion are significant only over vast distances, not within smaller scales like those of everyday objects.

PREREQUISITES
  • Understanding of special relativity and its implications on light and motion
  • Familiarity with general relativity and gravitational effects on light
  • Basic knowledge of wave theory, particularly in relation to light and sound
  • Awareness of cosmological concepts, including the expansion of the universe
NEXT STEPS
  • Research the principles of special relativity and how they apply to light propagation
  • Study general relativity, focusing on gravitational redshift and its implications
  • Explore the Doppler effect and its applications in both sound and light waves
  • Investigate the current understanding of cosmic expansion and its observational evidence
USEFUL FOR

Astronomers, physicists, and students of cosmology seeking to deepen their understanding of redshift phenomena and the expansion of the universe.

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Okay, from what I understand, the cosmological redshift is due to the expansion of the universe. I'm confused as to how this works. I don't understand why, if the universe is expanding, that the waves don't just have farther to travel. I also don't understand what is waving or why other things don't get 'redshifted'. Why isn't my bed farther from the wall than it was yesterday? Also, how do we know that the redshift isn't due to a heavy object near the 'edge' of the universe? Could someone explain redshifting in further detail?
 
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The waves do have farther to travel. But since the light moves at the same speed regardless of how fast their source is moving (special relativity), its wavelength is different when viewed by someone who's not moving at the same speed as the source.

It's not just light from distant galaxies that gets shifted. All light that's emitted by a moving (relative your frame of reference) object gets shifted (in your frame of reference).

Then there's gravitational redshift, which is due to general relativity. In brief gravity curves space-time, so things in a gravitational field get 'stretched'; including light.
 


None of this has anything to do with quantum physics, by the way, just classical wave theory.

Why isn't my bed farther from the wall than it was yesterday?

Gravity holds, say, Earth to rotating around the sun; mostly electrostatic forces hold the Earth together, and even gravity between your bed and the wall is much stronger than any separation effects. The cosmological expansion or redshift is called that because it's only over vast cosmological distances, not even within a galaxy for example, where the expansion overcomes everyday forces of attraction.

I don't understand why, if the universe is expanding, that the waves don't just have farther to travel. I also don't understand what is waving or why other things don't get 'redshifted'.

They do, even sound waves from a passing vehicle or train for example...

You can get some physical explanations and diagrams here:
http://en.wikipedia.org/wiki/Doppler_shift
 

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