Effect of CMB (cosmic microwave background) on objects at relativistic speeds

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Discussion Overview

The discussion revolves around the effects of cosmic microwave background (CMB) radiation on objects traveling at relativistic speeds, particularly focusing on potential physical damage and interactions. It includes considerations of the Doppler effect, time dilation, and other forms of radiation and matter that may pose risks to such objects.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether the Doppler effect and time dilation would make the CMB physically damaging to an object moving at a significant fraction of the speed of light.
  • Another participant clarifies that for significant damage, the object must be moving at ultrarelativistic speeds, and mentions that other forms of matter and radiation, such as the interstellar medium and starlight, could be more harmful than the CMB.
  • A different participant introduces the concept of high-energy electrons interacting with CMB photons through inverse Compton scattering, leading to detectable distortions in the CMB spectrum, known as the Sunyaev-Zeldovich effect.
  • One participant discusses the implications of a Doppler-shifted blackbody spectrum of the CMB at high speeds, suggesting that at speeds close to c, the CMB could reach temperatures similar to those of stellar surfaces.
  • Another participant speculates about the possibility of using beamed microwaves as a shield against hypothetical projectiles, while also noting that such projectiles could initiate nuclear reactions upon impact.

Areas of Agreement / Disagreement

Participants express differing views on the extent of damage caused by the CMB compared to other hazards, indicating that there is no consensus on the primary risks associated with ultrarelativistic travel.

Contextual Notes

Participants mention various factors that could influence the discussion, such as the need for calculations to assess the risks accurately and the potential for interactions with other forms of matter and radiation in space.

rorix_bw
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A hypothetical question relating to

1) moving a physical object at a significant % of c.

2) interaction with the cosmic microwave background radiation

Is it the case that doppler effect and time dilation means that the CMB is going to be physically damaging to the object?

Further what would happen if a source of microwave energy (e.g. from a transmitter) was directed towards such an object?

This is from a sci-fi discussion, but I just got this idea and I don't know what would happen.
 
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Sort of, but first off, it doesn't just have to be a significant fraction of c, it has to be ultrarelativistic, i.e., very, very close to c. Also, there are other forms of matter and radiation besides the CMB that would fry you much worse than the CMB. I think the interstellar medium (mostly hydrogen) would be the most damaging. Starlight from the forward direction would also be Doppler shifted into the gamma spectrum.
 
rorix_bw said:
A hypothetical question relating to

1) moving a physical object at a significant % of c.

2) interaction with the cosmic microwave background radiation

Is it the case that doppler effect and time dilation means that the CMB is going to be physically damaging to the object?

I know that there is the possibility of some objects to interact with CMB. It is the case of high energy electrons that can react with CMB photon through inverse Compton scattering. This leads to a detectable distortion of CMB spectrum. It is a way used to detect clusters of galaxies and the anisotropies. This effect is called Sunyaev Zeldovich effect.
 
A Doppler-shifted blackbody spectrum is itself a blackbody spectrum. So at about 150 m/s less than c (time dilation factor = 1000) the CMB will be a blackbody with a temperature around 2700 K, close to stellar surface temperatures.

bcrowell is pretty smart, so he may be right that matter will be a probelm before the CMB. I am not sure, I would have to see a calculation, but certainly the CMB isn't the only hazard to ultrarelativistic travel.
 
Interesting, then I might be on the right track: beaming microwaves in all directions could possibly act as a shield against such a hyopthetical projectile. It's off topic for this thread however I guess. Although it seems to be correct that such projectiles would initiate a nuclear reaction on impact.

EDIT: I think i already mentioned hitting stray hydrogen atoms and space dust in that other thread.
 
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