11–20 of 88 posts
Earlier quoted context omitted.
Out of interest, why ice and not (say) steel?
Water is really good at blocking proton radiation (those stray hydrogen atoms in the interstellar medium become really dangerous once you go fast enough). Plus you can drink it. You also don't want to stop particle radiation too quickly, or you get x-ray Bremsstrahlung. So something a little less dense than steel works better in practice.
Earlier quoted context omitted.
Out of interest, why ice and not (say) steel?
Water is really good at blocking proton radiation (those stray hydrogen atoms in the interstellar medium become really dangerous once you go fast enough). Plus you can drink it. You also don't want to stop particle radiation too quickly, or you get x-ray Bremsstrahlung. So something a little less dense than steel works better in practice.
Note that tachyonic particles are not very particle-like at all, so I prefer the name 'tachyonic interaction':
Tachyons cannot be properly localized, there's a critical frame where they have no energy, their 'life-time' is space-like, both endpoints of the interaction may have the same (intrinsic) type (absorption-absorption, emission-emission), to name just some of the peculiar properties.
Recami argues (imo convincingly) that you cannot use such tachyons to violate causality.
Point 13 is also somewhat questionable, but this is more of a matter of semantics. While each of the galaxies are at rest (or in free fall, if you prefer), they are not at rest relative to one another according to parallel transport along the light ray (otherwise, there would be no red-shift). This is imo the correct way to handle relative velocities in a general-relativistic setting; the fact that their comoving distance is constant doesn't mean they are at rest in any physically meaningful way, but one can at least argue this point both ways.
Earlier quoted context omitted.
You want a big block of ice in front of your ship.
Out of interest, why ice and not (say) steel?
A negative to this is a proposed solution to Fermi's Paradox
One way would be to fire an entangled photon down both ends of fibre optic cable in the middle. On the sending end you could observe/ ignore it, and on reviving end you'd observe it. We'd have to develop cables capable of preserving the entangled state of light particles, and a beam splitter that's more reliable. You could improve the bandwidth considerably by measuring the polarisation of the particle, even more if…
I think there was a HN link a while ago about ideas to use this as a perfectly secure key exchange mechanism for crypto. I don't know how serious this idea is, though.
One way would be to fire an entangled photon down both ends of fibre optic cable in the middle. On the sending end you could observe/ ignore it, and on reviving end you'd observe it. We'd have to develop cables capable of preserving the entangled state of light particles, and a beam splitter that's more reliable. You could improve the bandwidth considerably by measuring the polarisation of the particle, even more if…
Pretty harsh to downvote this person for writing out an idea - ok, if you know the physics you might dismiss this, but dismiss with words not votes!
I personally find it a bit insulting to propose something like this, as it assumes all those physicists working on quantum physics and relativity over the last hundred years were too dumb to think of this. Yet they all go around saying FTL communication is impossible? To suggest such a thing, you'd have to think they were all very stupid or you'd have to not be thinking at all.
One way would be to fire an entangled photon down both ends of fibre optic cable in the middle. On the sending end you could observe/ ignore it, and on reviving end you'd observe it. We'd have to develop cables capable of preserving the entangled state of light particles, and a beam splitter that's more reliable. You could improve the bandwidth considerably by measuring the polarisation of the particle, even more if…
However because when you observe the photon it collapses randomly and there is no way to tell if the photon has collapsed before you observed it or for the first time as you are observing it you don't actually have any information on if the other side observed it or not.
One way would be to fire an entangled photon down both ends of fibre optic cable in the middle. On the sending end you could observe/ ignore it, and on reviving end you'd observe it. We'd have to develop cables capable of preserving the entangled state of light particles, and a beam splitter that's more reliable. You could improve the bandwidth considerably by measuring the polarisation of the particle, even more if…
However because when you observe the photon it collapses randomly and there is no way to tell if the photon has collapsed before you observed it or for the first time as you are observing it you don't actually have any information on if the other side observed it or not.