Can fast objects get cooked by Cosmic Microwave background?

In summary: The person on the ship would detect them as well, because they would have the right energy to kick an electron into a higher energy state.
  • #1

jfizzix

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Awhile ago, I was considering what sort of dangers a spacecraft moving at relativistic speeds would face in interstellar space. Aside from the obvious pieces of space dust being relativistic bullets in the ship's frame of reference, the cosmic microwave background (CMB) would become a big problem.

In particular the CMB in front of the ship would be blue-shifted into the infrared, visible, ultraviolet, and beyond.
Let's say we put a gamma ray detector on this ship; something whose chemical composition changes by exposure to gamma radiation, but not with lower energy photons. Then, in the ship's frame of reference, it will start detecting gamma rays from the CMB. However, in say, a planet's frame of reference, the CMB is just microwaves, while the ship is moving very fast.

My question is this
: How can a gamma ray detector record gamma rays that exist in one frame of reference, but not in others? Surely the detector must register detections in both reference frames, even if where and when those events take place is frame-dependent. However, in the planet's frame of reference, there's no gamma radiation for the detector to detect (it all being microwaves instead).
It seems a conundrum...
 
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  • #2
Perhaps I'm missing something but it seems to me that your argument is exactly the same as saying that since a swimmer can move about freely on the surface of a lake, it is bizarre that a person hitting it at 500 mph would feel it like at brick wall.
 
  • #3
phinds said:
Perhaps I'm missing something but it seems to me that your argument is exactly the same as saying that since a swimmer can move about freely on the surface of a lake, it is bizarre that a person hitting it at 500 mph would feel it like at brick wall.

It's a bit different because the speed of the photons in the "cosmic lake" is a constant in both reference frames. In neither frame would the ship be smacking into a wall of photons because light doesn't pile up in front of a spaceship the way sound might (or maybe it does?).
What's different between the frames (among other things) is due to the relativistic Doppler effect.
 
  • #4
I don't really understand how gamma rays are detected (Compton ray scattering) so I'll use visible light instead. The extrapolation should still be valid though.

If you're viewing a spaceship going close to the speed of light with respect to your reference frame on a planet then you will observe the spaceship's visible light detector (the Captain's eyeball) going close to the speed of light as well. In order for the cones and rays in the captain's eyeballs to register a photon, it must encounter a photon with just the right amount of energy to kick an electron in a retinal molecule into a higher energy state.

When the Captain is encountering those cool microwaves in front of the ship, because the Captain is going so fast those photons only need a tiny amount of energy to kick the retinal electron into a higher energy state. Most of the energy is provided by the Captain, while only a tiny amount is provided by the photon.

Keep in mind that everything I just described is from the frame of reference of the planetside observer.

From the Captain's perspective, he is absolutely still. The photon distribution in front has been piled up into a higher energy band (visible light), while the photon distribution behind him has been lowered such that it becomes difficult, if not impossible to measure.
Those visible light photons give just enough energy to kick an electron into the higher energy state, which transforms the retinal molecule into a different, more stable shape, which triggers a protein conformation that triggers an electrical pulse to the brain.

I believe you need the Lorentz transformations to figure out mathematically exactly what's going on.
 
  • #5
jfizzix said:
My question is this: How can a gamma ray detector record gamma rays that exist in one frame of reference, but not in others? Surely the detector must register detections in both reference frames, even if where and when those events take place is frame-dependent. However, in the planet's frame of reference, there's no gamma radiation for the detector to detect (it all being microwaves instead). It seems a conundrum...

Both would agree that the gamma ray detector should register detections. The person on the planet, knowing how to calculate events in the spacecraft 's frame of reference, would determine that gamma rays would be encountered there even though they are not in his frame of reference.
 

1. Can fast moving objects actually get cooked by the Cosmic Microwave Background (CMB)?

Yes, it is possible for fast moving objects to get cooked by the CMB, but it would require extremely high speeds close to the speed of light. This is because the CMB has a very low energy density, meaning it has a low amount of energy per unit volume. Therefore, it would take a lot of exposure time to the CMB for any significant heating to occur.

2. How is the CMB related to cooking?

The CMB is not directly related to cooking in the traditional sense. It is the residual radiation left over from the Big Bang and is present throughout the universe. However, due to its low energy density, it would take a long time for it to have any noticeable effects on objects, even at high speeds.

3. Is the CMB dangerous for fast moving objects?

No, the CMB is not dangerous for fast moving objects. As mentioned before, it has a very low energy density and would not have any immediate or significant effects on objects, even at high speeds. It is a natural and harmless part of the universe.

4. Are there any known instances of objects getting cooked by the CMB?

There are no known instances of objects getting cooked by the CMB. However, there have been experiments conducted where small objects were exposed to the CMB for extended periods of time and showed slight heating. This is not practical or feasible for everyday objects and would not occur in nature.

5. Can the CMB be harnessed for cooking purposes?

No, the CMB cannot be harnessed for cooking purposes. As mentioned before, it has a very low energy density and would require a very long exposure time to have any noticeable effects on objects. It is not a viable or efficient source of heat for cooking.

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