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.
(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.