4 ms·
To put it another way, time travel machines are very much theoretically possible, and in fact are “only” an engineering problem (an extremely hard one, however)
by xyzzyz 5y ago
To put it another way, time travel machines are very much theoretically possible, and in fact are “only” an engineering problem (an extremely hard one, however). But, only forward travel is allowed: time travel machine could take you as far forward as its engineering would allow it, but there is no going back.
- nimish 5y agoThey are only theoretically possible if you allow for negative mass and energy--not an engineering problem so much as a "need to find exotic matter" Basically people ran the EFE "backwards" to see what matter distribution makes the wanted curvature. You get either negative mass-energy or the bubble doesn't travel ftl iirc.
- kadoban 5y agoGp is talking about forward-only time travel though, you don't need anything exotic for that at all, just lots of energy and an efficient way to turn it into thrust.
- xondono 5y agoThe Alcubierre drive “beats” the speed of light, for the effects described 0.7-0.9c are more than good enough (if slightly unpractical). We can’t do that either for now, but is way easier on the feasibility scale.
- lovegoblin 5y ago> The Alcubierre drive “beats” the speed of light The Alcubierre drive is only a thought experiment that requires "exotic matter" (aka fairy dust) to work.
- xondono 5y agoI know, I was making reference to this > They are only theoretically possible if you allow for negative mass and energy--not an engineering problem so much as a "need to find exotic matter" Basically people ran the EFE "backwards" to see what matter distribution makes the wanted curvature. You get either negative mass-energy or the bubble doesn't travel ftl iirc.
- baja_blast 5y agoPapers have been published that have found ways to create warp drives without the need for exotic matter: https://arxiv.org/pdf/2006.07125.pdf https://arxiv.org/pdf/2006.07125.pdf
- xyzzyz 5y agoNo, for forward time travel you don’t need any sort of exotic matter. You just need a really fast rocket.
- zamadatix 5y agoAt 1G constant acceleration (both speeding up and slowing down) you can make it on a short vacation to the Andromeda galaxy and back in a lifetime (or 5 million years from the perspective or Earth).
- eesmith 5y agoIt looks like about 57 years. Assuming constant acceleration to the 1/2-way point, flip, deceleration, and using http://www.projectrho.com/public_html/rocket/slowerlight3.php http://www.projectrho.com/public_html/rocket/slowerlight3.ph... : Time elapsed (in starship's frame of reference, "Proper time") T = (c/a) * ArcCosh[a*d/(c^2) + 1] (given acceleration and distance) year = 365.25*24*3600; c = 3E8; a=9.8; d=1.25*1_000_000*(c * year) from math import acosh T = (c/a) * acosh(a*d/(c*c) + 1) print(T/year) => 14.3 years each quarter => 57 years round trip The speed at flip would be 99.99999999993978% c - good thing intergalactic space is mostly empty.
- wruza 5y agoBad news CMB shifts into infrared, visible, uv, xray and then hard gamma.
- deleted 5y ago[deleted]
- eesmith 5y agoOh, what a shame. I was about to install some rockets on my RV and head off to Andromeda. Guess I don't need to put my newspaper subscription on hold now.
- smegger001 5y agosince we are talking insane speeds and energies required to reach them why not just say you are in a bigger ship with more radiation shielding a dozen or so meters of water in the hull and a layer of lead a foot thick aught to stop most of it