Quick disclaimer: I don't know much about physics, so I don't really know what I'm talking about.

The idea

The idea is that an object traveling fast enough in space will be receiving more radiation than it is giving off.

This is because time runs slower for the object which is traveling near the speed of light, and therefore it loses energy through thermal radiation slower than it is not moving.

The object, on the other hand is still receiving radiation from "outside" at the "normal" rate. From the object's perspective, the radiation "outside" is getting more and more intense as is speed increases, therefore it should heat up.

The problem

According to one hypothesis, the universe is going to end in a heat death where everywhere is the same temperature. But I can stop that by shooting an object into space near the speed of light, assuming it doesn't hit anything, it should continue to go forever gathering energy (from thermal radiation and CMBR) and breaking heat death.

Even if it's slowed down by resistance, by painting its front white and its back black should be able to keep it accelerated, as this will cause it to heat up the gas behind it more to push it forward.

That wouldn't work but there's should be a way to make sure heat is released to the back.

Another thing is it doesn't need to be even close to the speed of light, it just need to have be receiving more energy than it is being slowed down, so there is probably already a bunch of these objects zooming around in space.

If this works then why is it not thought about (that heat death is the most accepted hypothesis), or else can anyone explain what went wrong?

  • $\begingroup$ I once heard Penrose explain that at the very late stage of the universe there will be only supermassive black holes that will evaporate boringly slowly. Your object is likely to be eaten by such a black hole as well... note that even if your object loses one atom in a million years due to random collisions with cosmic rays etc, it basically goes to nothing rather quickly... $\endgroup$
    – Amit
    Mar 4 at 21:52

1 Answer 1


An object moving at relativistic speeds would see the CMB and other background light heavily blueshifted but also aberrated, such that the light is preferentially striking it from the front, slowing it down. (This is like how if you run in a rainstorm, the rain will strike you in the front.)

However, the object will also slow down relative to its surroundings independently of that. The universe is expanding, meaning that everything is moving apart at a speed proportional to its distance. A particle moving rapidly in some direction will move toward a region of space where the local matter is also moving in that direction. Over time, the particle will overtake slower-moving matter, eventually reaching (in the infinite-time limit) a position where it is moving at the same speed as its surroundings.

(This effect is just the cosmological redshift applied to massive particles.)


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.