6 ms·
Great! Let's go and check it out!
by D_Alex 15y ago
Great! Let's go and check it out!
- pjscott 15y agoIt's 20 light years away, so that could take a while. (I still want to do it, though.)
- palish 15y agoQuestion: In the year 2200, if a 10 year old child were to travel to the planet at a speed of 0.9999c, then were to immediately turn around and travel back to Earth, they would be approximately 50 years old. However, what year would they arrive back on Earth? Assumptions: - no acceleration or deceleration time. - the planet is exactly 20 light years away. - the velocity of the ship remains exactly 0.9999c while in transport. (The answer is not 2240. It's much greater. My question is, how much greater?)
- svrocks 15y ago5028
- deleted 15y ago[deleted]
- DavidSJ 15y agoI think you've got it reversed. From Earth's perspective, it would take exactly 40 years, but the child would age very little.
- forensic 15y agohttp://www.wolframalpha.com/input/?i=time+dilation+traveling+at++.9999c+&a=*FS-_**RelativisticTimeDilationFormula.t-.*RelativisticTimeDilationFormula.to--&f2=40+years&x=7&y=11&f=RelativisticTimeDilationFormula.to_40+years http://www.wolframalpha.com/input/?i=time+dilation+traveling... 2828 years + 2200 = 5028 A.D. says wolfram alpha
- palish 15y agoFascinating. 40 years at 0.90000c = 91.76 years 40 years at 0.99000c = 283.55 years 40 years at 0.99900c = 894.65 years 40 years at 0.99990c = 2828.00 years 40 years at 0.99999c = 8944.00 years
- btilly 15y agoYour problem statement is wrong. The child is traveling 40 light years at 0.9999c, which takes about 40 years + 35 hours. However the child won't arrive back 50, the child will not yet be 11. See http://www.wolframalpha.com/input/?i=time+dilation+traveling+at++.9999c+&a=*FS-_**RelativisticTimeDilationFormula.to-.*RelativisticTimeDilationFormula.t--&f2=40+y&x=6&y=5&f=RelativisticTimeDilationFormula.t_40+y http://www.wolframalpha.com/input/?i=time+dilation+traveling... for the exact age. See http://en.wikipedia.org/wiki/Twin_paradox http://en.wikipedia.org/wiki/Twin_paradox for more on this, including an explanation of why your belief about the age of the traveler is wrong.
- palish 15y agoHow can this be? If the child were moving at 0.9999c (which is less than 1.0000c) and the planet is 20 light-years away, then how could it take less than 20 years for the child to reach it? Let alone ~0.5 years? EDIT: Here's an explanation from a friend: light always travels at c even if you're already moving close to c but it's impossible for anything to travel faster than c so if you're traveling at .9999c the passage of time must be scaled for the traveler to make light on the ship appear to move at c even though it's only moving at 1-.9999c That's... awesome.
- Confusion 15y agoIf the planet is 20 light years away, you're saying we could reach it in less than a year if we attain a velocity of 0.9999c? Yes. In the reference frame of the traveler, very little time passes. However, when he returns, people on earth will have aged more than 40 years. This is also why particles traveling at c cannot possibly decay: no time passes for them. A photon is everywhere at once, from its own point if view.
- aik 15y agoAmazing. I hope to some day wake up and have a deep conceptual understanding of the relationship between velocity and time in relation to the various bodies at play. I also hope to have an understanding of what it means for a photon to be everywhere at once, from its own point of view. In the end, I guess I just want to understand the universe just a bit more than I do.
- deleted 15y ago[deleted]
- blhack 15y agoWhy aren't we sending probes out right now? Yeah, we're not going to hear anything back for (probably) 100 years, but why not start now? If we had sent a probe out back in the 60s, this would be something that I'd see results from within my lifetime. Of course, this is assuming that we can build fast interstellar transit systems...which is a huge if.
- nopassrecover 15y agoIt takes light 40 years to get there and back at 1,079,252,849 km/h, and the fastest spacecraft we have currently are the Helios Solar Probes at 252,792 km/h - it would take over 170,000 years before the probe returned.
- pohl 15y agoLet's grant the speed of light on the return side. Say we invent a method of transmitting probe data using radio waves or something.
- nooneelse 15y agoGetting data back via radio seems physically realistic using the gravitational lensing of EM by our sun. It would require us to put a receiving and relay station very var out beyond the planets, at least 550AU, I think. But by the time we are sending a probe several light years, then 550AU should practically be child's play. A good paper about using such lensing: "Interstellar radio links enhanced by exploiting the Sun as a Gravitational Lens" by Claudio Maccone.
- fhars 15y agoBecause anything we might start now would be overtaken before it is one tenth there by anything we might start five hundred years from now. And if we won't be able to start anything faster by then, there would be no technological civilization left to receive the results. So it would be pointless, space is just too big. Once we can reliably reach 1/10 c we might think about sending a probe to Alpha Centauri, although even that would have more symbolic value as a technological demonstration than scientific value. You would have to wait more than half a century for a science mission of at most a few hours, because decellerating would require so much time and fuel to make the whole mission infeasible. A mission to Gliese 581 is a distant fourth or fifth project after that, and sending a planetary probe like the one we send to mars is even more distant. (For reference, it took several years of swing by maneuvers to get a probe out of the orbital plane of the planets into an orbit that allows to examine the poles of the sun, and that takes far less energy than even reaching 1/100 c.)