Does the CMB move or is it static?

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Discussion Overview

The discussion centers on the nature of the Cosmic Microwave Background (CMB) radiation, specifically whether it is static or exhibits motion. Participants explore the implications of the CMB being quantum fluctuations from the early universe, considering both theoretical and observational aspects.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants propose that if the CMB consists of quantum fluctuations, it should be expected to move rather than be static, likening it to a dynamic process rather than a still image.
  • Others question the feasibility of observing any motion in the CMB, noting the vast distances involved and the challenges in detecting movement over the short observational time frame of decades.
  • One participant mentions that CMB photons were separated by much closer distances when the universe was only 380,000 years old, suggesting that there might be more motion than observed in stars, which do not appear to move significantly on human time scales.
  • Another participant raises a mathematical consideration regarding the angles subtended by objects moving at relativistic speeds, questioning how such speeds would affect visibility over vast distances.

Areas of Agreement / Disagreement

Participants express differing views on whether the CMB is static or moving, with no consensus reached on the nature of its motion or the implications of its distance on visibility.

Contextual Notes

Limitations include the assumptions about the nature of quantum fluctuations, the observational constraints of detecting movement over billions of light years, and the mathematical considerations regarding relativistic speeds.

MarcJo
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If the CMB is quantum fluctuations of the primordial universe, I would expect it to move, not be static like a photograph. Quantum fluctuations do not hold still, nor has time itself seem to have dilated to the point where it would look constant.

Can somebody take a movie of it and see? All that we see is the famous photograph, but no one has seen the motion picture.

Thanks,

Marcjo
 
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MarcJo said:
If the CMB is quantum fluctuations of the primordial universe, I would expect it to move, not be static like a photograph. Quantum fluctuations do not hold still, nor has time itself seem to have dilated to the point where it would look constant.

Can somebody take a movie of it and see? All that we see is the famous photograph, but no one has seen the motion picture.

Thanks,

Marcjo

At a distance of dozens of billions of light years, just how fast would any part of it have to be moving in order for us to see visible movement in the few decades we have been observing?


Hint: it is difficult enough for us to visually detect movement of stars in our own galaxy, some millions of times closer.
 
We are looking at CMB photons that were separated by by much closer distances, when the universe was only 380,000 years old. I would expect much more motion than the stars, which don't seem to move on day to day human time scales. How much motion, I don't know.
 
MarcJo said:
We are looking at CMB photons that were separated by by much closer distances, when the universe was only 380,000 years old. I would expect much more motion than the stars, which don't seem to move on day to day human time scales. How much motion, I don't know.
The point is, at a distance of 14 billion light years, things would have to be traveling at outrageous speeds for their motion to be visible at all over such a short time frame.

What is the angle of a triangle whose short side is .5 light years wide and 14 billion light years long? That is the angle an object would subtend traveling at .5c over one year.
 

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