3 ms·

My physics isn't great, but I have questions based off what I have (mis) learned: 1. If you jettison a 1kg rock at 99.999% the speed of light, it'll not really

My physics isn't great, but I have questions based off what I have (mis) learned: 1. If you jettison a 1kg rock at 99.999% the speed of light, it'll not really be 1kg anymore because of something with energy and mass being the same near the speed of light? 2. At that point you'd be jettisoning raw energy? 3. Could you make a single molecule act like a very heavy object this way? 4. What would happen if that single molecule hit a planet? 5. Would fusion (or fission) be capable of creating more mass through velocity than the weight of the reactor? As in, using a couple molecules to create enough energy to speed up a molecule so much that it acts massive.

ianai 6y ago
c is the speed energy travels at and less than c is the speed matter travels at in the universe. You’re right that ultimately matter is energy, but you typically have to introduce it to it’s antiparticle to turn it into energy. (I’m less clear on how you go from energy to mass. I think you can knock a photon into an electron with enough force to escape its nucleus but you’re not going to get new matter out of it. I wonder whether further knowledge of the Higgs Boson would give us some ideas in this area.) So photons can’t transmit forces dependent upon mass - but they can transmit momentum. I remember being told this is what keeps a stars gravity from collapsing the matter into a singularity or otherwise blowing apart. I think you’re probably right that speeding matter up to significant fractions of c would increase its effect on your opposite velocity, but it’s probably hard to benefit from as an engineered system. Like having a particle accelerator the size of our orbit around the sun to make meaningful thrust-hard.
btilly 6y ago
Answers. 1. The relativistic mass is the rest mass / sqrt(1 - (v/c)^2) which in this case is 223.607356769625 kg. The kinetic energy is the change in mass, so 222.607356769625 kg which through the conversion E = mc^2 is about 2 * 10^19 Joules. The momentum is mass times velocity which is about 6.7 * 10^10. 2. No. You'd be jettisoning a very nasty rock. That will immediately explode on impact. 3. There is no limit to the mass it could have. 4. The first thing it hit, would convert into highly energized particles still moving in the same direction, which would hit new particles and so on. The result of the cascade will be to generate a shower of high energy particles with the same energy and momentum as the original. Or in short, BOOM! 5. Because of conservation of energy/mass, no. Even with 100% efficiency, the reactor would have to lose the same amount of mass that shows up as kinetic energy in the ejected particle.

ianai 6y ago

c is the speed energy travels at and less than c is the speed matter travels at in the universe. You’re right that ultimately matter is energy, but you typically have to introduce it to it’s antiparticle to turn it into energy. (I’m less clear on how you go from energy to mass. I think you can knock a photon into an electron with enough force to escape its nucleus but you’re not going to get new matter out of it. I wonder whether further knowledge of the Higgs Boson would give us some ideas in this area.) So photons can’t transmit forces dependent upon mass - but they can transmit momentum. I remember being told this is what keeps a stars gravity from collapsing the matter into a singularity or otherwise blowing apart. I think you’re probably right that speeding matter up to significant fractions of c would increase its effect on your opposite velocity, but it’s probably hard to benefit from as an engineered system. Like having a particle accelerator the size of our orbit around the sun to make meaningful thrust-hard.

btilly 6y ago

Answers. 1. The relativistic mass is the rest mass / sqrt(1 - (v/c)^2) which in this case is 223.607356769625 kg. The kinetic energy is the change in mass, so 222.607356769625 kg which through the conversion E = mc^2 is about 2 * 10^19 Joules. The momentum is mass times velocity which is about 6.7 * 10^10. 2. No. You'd be jettisoning a very nasty rock. That will immediately explode on impact. 3. There is no limit to the mass it could have. 4. The first thing it hit, would convert into highly energized particles still moving in the same direction, which would hit new particles and so on. The result of the cascade will be to generate a shower of high energy particles with the same energy and momentum as the original. Or in short, BOOM! 5. Because of conservation of energy/mass, no. Even with 100% efficiency, the reactor would have to lose the same amount of mass that shows up as kinetic energy in the ejected particle.