[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*To*: starship-design@lists.uoregon.edu*Subject*: starship-design: Re: Spacetime, Shmacetime*From*: TLG.van.der.Linden@tip.nl (Timothy van der Linden)*Date*: Fri, 27 Jun 1997 01:40:48 +0200 (MET DST)*Reply-To*: TLG.van.der.Linden@tip.nl (Timothy van der Linden)*Sender*: owner-starship-design

To Ken, >>So the stationary twin thinks his brother lived slower or equal all the >>time. >>But the moving twin thinks his brother first lived slower, than started >>living hyperfast, and finally slower again. However his brother lived >>hyperfast more than he lived slower, so the net result is that his brother >>lived faster. > >That's correct. I had a sign error in my thinking; things only go >backwards in time when you accelerate AWAY from them, not toward them as is >done in the Twin Paradox. > >The Twin Paradox can be easily modified so that (far away) objects DO seem >to go backwards in time. After the rocket-ship twin turns around toward >Earth, have him turn around a second time, back in the direction that he >was going in the first place. During this process, time on Earth (instead >of zipping forward very fast) zips BACKWARDS very fast. It's a reversable >process: you can accelerate one way to make time go forward, and the other >way to make time go backwards. No paradox, though, because by the time you >get back to Earth time has always gone forwards. Unless, of course, you >have FTL. I think you are wrong again, time doesn't zip backward very fast, it slows down even more but still is going forwards. >This comes directly out of the Lorentz transformation of time: > >t' = gamma *(t - vx). > >If you're at t=0, and you're looking at a far-away object (say x=1), A >space time event that seems like it's "now" (x=1, t=0) is transformed to a >t' = gamma * (-v). If v is negative (i.e. you're accelerating away from x) >then t' is now a positive quantity. But what does that mean? It means >that an event that was once "now", is now happening at a positive time >coordinate; in the future! So something that has "already" happened, now >hasn't happened yet! (In your reference frame). You've just "sent" the >far-away object back in time. Fortunately you can't do this for close-up >objects! Hmmm, it seems that now *you* are confusing real and unreal timedilation. The story right above is about what you see, not about what happens. Try to follow how t' changes when t increases. You'll see that regardless how the sign of v is, t' will increase. (Note |v|<1 ) Timothy

- Prev by Date:
**RE: starship-design: Re: Even less Fun with Spacetime** - Next by Date:
**starship-design: Book Recommendation** - Prev by thread:
**starship-design: Spacetime, Shmacetime** - Next by thread:
**starship-design: Book Recommendation** - Index(es):