4 ms·
Speaking of moving fast, is there anything in physics that limits how fast things are moving in space? I don't mean the limit of speed (that is already known) b
by m0zg 6y ago
Speaking of moving fast, is there anything in physics that limits how fast things are moving in space? I don't mean the limit of speed (that is already known) but realistically, how likely is there to exist, say, a tiny, fist-sized asteroid moving at a slightly sub-luminal speed? Say, 0.9997C in our frame of reference? And if such a thing were to exist, what would the consequences of it colliding with the Earth be? For the reference, an US quarter coin traveling at that speed has relativistic kinetic energy of 4.85MT TNT. We obviously wouldn't be able to detect an object moving this fast, but how likely is it to be out there?
- whatshisface 6y agoThere is always a reference frame where the rock isn't moving - and we all agree something can stay still, so there's nothing in physics preventing it from going as close to the speed of light as you want. I don't know the details of what it would do if it was moving merely very fast, but curiously if it was fast enough, I'm talking unbelievably overwhelmingly fast, it would probably go right through without interacting. Why? Well, if you whiz through the electromagnetic fields of all the atoms in the earth fast enough, the forces won't have any time to transfer momentum one way or the other.
- m0zg 6y agoYes, I understand that, that's why I'm asking not if such a thing is _possible_ but whether it is even remotely _likely to exist_, given what we know about the universe, how galaxies and stars came to exist, etc. That is, in order for something to have this immense energy in our frame of reference, that something (or Earth) would have to get that energy somewhere. What I'm asking, essentially, is how likely is it that such conditions would exist at some point?
- formerly_proven 6y ago> Well, if you whiz through the electromagnetic fields of all the atoms in the earth fast enough, the forces won't have any time to transfer momentum one way or the other. Yet sun sails work, despite being micrometers thick and interacting with particles going very close to c (from the sail's PoV).
- whatshisface 6y agoSolar sails interact with light. It's matter-matter interactions that drop off in the high speed limit.
- rsa25519 6y agoOne scenario that comes to mind is the frame of reference moving 0.49 c in one direction then the object in question moving 0.49 c in opposite direction.
- the8472 6y agoFrom its perspective it would get hit by interstellar gas at relativistic speeds which would at the very least spall atoms from the surface.
- m0zg 6y agoGood point. So unless there's gas moving in the same direction at a similar speed, the object would, over a sufficiently long period of time, be slowed down by this gas.
- the8472 6y agoThe issue is that the ISM is incredibly thing. So it's one of those multiple incredibly large by incredibly small number cases and intuition doesn't work, you'd have to do the actual math. I.e. the timescales could be large enough that if some process could create such an object they could still cross between galaxies.
- ben_w 6y agoI can’t answer for the chances, but this 0.9c baseball should give you a feel for the effects: https://what-if.xkcd.com/1/ https://what-if.xkcd.com/1/ If I’ve done my sums right, your example would have about 30 times the kinetic energy of that baseball, assuming the same mass.