- #1
tom_mi
- 7
- 0
Hello All,
I hope my question isn't too simplistic for this forum. I've been giving my kids this illustration for a couple years, and have begun to doubt my story a bit. Hoping someone here might be able to clarify for me.
It's simple really, here's the setup:
*You're going to a star 10 light years away, 20 light-years round trip.
*You're speed is 90% the speed of light "C"; we'll estimate 30yr round trip time due to only going 90% of C. (I don't think an exact measure matters for this illustration)
*We all know that as you approach C, 'time runs more slowly'. (whatever that really means)
What I've been telling the kids:
You'd return from this trip 30 years older and due to the final statement above, the Earth might be 1000 years older.
But now I'm not so sure.
Perhaps the opposite happens? Perhaps 'time slowing down' means you'd think you're getting there in only a week, and you'd return in exactly the pre-planned 30 Earth-years? Put a little differently, as the astronaut approaches C, can his perception of elapsed time drop BELOW the established 20 light-years, or can that perception only drop toward a fixed lower limit of the original 20-year estimate?
I'm not seeing the 1000 year return time for such a trip as plausible anymore. 'Relativity' means relative to the observers, and your 90% of C velocity results from fuel/acceleration calculations that were done on Earth. .9*C IS your velocity as Earth sees it, and the star's distance is unchanging.
Perhaps a distilled question would be: for a fixed distance, can the traveler experience far *less* time than the observer, and can velocities just below C remove the need for supplies/hibernation etc?
Many Thanks,
Tom
I hope my question isn't too simplistic for this forum. I've been giving my kids this illustration for a couple years, and have begun to doubt my story a bit. Hoping someone here might be able to clarify for me.
It's simple really, here's the setup:
*You're going to a star 10 light years away, 20 light-years round trip.
*You're speed is 90% the speed of light "C"; we'll estimate 30yr round trip time due to only going 90% of C. (I don't think an exact measure matters for this illustration)
*We all know that as you approach C, 'time runs more slowly'. (whatever that really means)
What I've been telling the kids:
You'd return from this trip 30 years older and due to the final statement above, the Earth might be 1000 years older.
But now I'm not so sure.
Perhaps the opposite happens? Perhaps 'time slowing down' means you'd think you're getting there in only a week, and you'd return in exactly the pre-planned 30 Earth-years? Put a little differently, as the astronaut approaches C, can his perception of elapsed time drop BELOW the established 20 light-years, or can that perception only drop toward a fixed lower limit of the original 20-year estimate?
I'm not seeing the 1000 year return time for such a trip as plausible anymore. 'Relativity' means relative to the observers, and your 90% of C velocity results from fuel/acceleration calculations that were done on Earth. .9*C IS your velocity as Earth sees it, and the star's distance is unchanging.
Perhaps a distilled question would be: for a fixed distance, can the traveler experience far *less* time than the observer, and can velocities just below C remove the need for supplies/hibernation etc?
Many Thanks,
Tom
