Travelling to the future (paradox)

[alexmahone]

Some time ago, I watched a Stephen Hawking documentary which said that you could travel to the future if you went at a fraction of the speed of light for some amount of time.

The explanation was this: Consider an observer O at rest. Let the time traveller be T. O sees T whiz past him and concludes that T's clock is running slower than O's. So when T stops (assume that he remains in the same geographic time-zone), O knows that his own clock will be ahead of T's and so T will get the impression that he has traveled to the future.

But now consider T's frame of reference. He sees O whiz past him and concludes that O's clock is running slower than T's. So when T stops, he thinks that his own clock will be ahead of O's.

Who is right?

 

[ghwellsjr]

Some time ago, I watched a Stephen Hawking documentary which said that you could travel to the future if you went at a fraction of the speed of light for some amount of time.

The explanation was this: Consider an observer O at rest. Let the time traveller be T. O sees T whiz past him and concludes that T's clock is running slower than O's. So when T stops (assume that he remains in the same geographic time-zone), O knows that his own clock will be ahead of T's and so T will get the impression that he has traveled to the future.

But now consider T's frame of reference. He sees O whiz past him and concludes that O's clock is running slower than T's. So when T stops, he thinks that his own clock will be ahead of O's.

Who is right?

They're both right but I'm sure the documentary pointed out that the traveler T has to eventually turn around and come back to observer O at which point they will both agree that T is much younger than O.

 

[alexmahone]

They're both right but I'm sure the documentary pointed out that the traveler T has to eventually turn around and come back to observer O at which point they will both agree that T is much younger than O.

Assume that T does not turn around. Instead, he whips out a phone when he alights and calls up O to ask the time. (Assume that the distance traveled by T is not much.)

 

[Ryan_m_b]

It's a good question that everyone seems to think of at some point. I believe the difference is that both can agree that T is at some point in an accelerating reference frame whereas O is not. I'm pretty sure the proper name for your observation is the twin paradox which is not considered a true paradox.

 

[ghwellsjr]

If they both use the same reference frame in which they are mutually at rest, they will agree that T is younger, but that doesn't make it absolutely true because in the inertial reference frame in which T was traveling, or in other reference frames, there ages can be different. This is the issue of relativity of simultaneity.

 

[gopolks]

Was this the doco that Hawking said, if you built a train track around earth, and the train went 186000 miles per second, in 150 years, the people will get out the train, and would've only aged a week, and thus you have time travel.

 

[alexmahone]

Was this the doco that Hawking said, if you built a train track around earth, and the train went 186000 miles per second, in 150 years, the people will get out the train, and would've only aged a week, and thus you have time travel.

Exactly!

 

[gopolks]

So basically what is keeping people from time traveling as someone on these boards pointed out, is just a engineering issue.

 

[alexmahone]

So basically what is keeping people from time traveling as someone on these boards pointed out, is just a engineering issue.

Every time we hop into a vehicle or even walk, we are traveling to the future compared to someone who is at rest. However, we travel by a negligibly small amount. What's keeping us from traveling into the far future is an engineering issue.

 

[ghwellsjr]

If the engineering issue is ever solved, then it will become an economic issue, just like the engineering issue of going to the moon was solved decades ago but the Apollo program was cut short due to economic factors and has never been funded since.

 

[gopolks]

Its the fact that it's possible to travel to future in terms of physics, I think that should excite people, even though it won't happen.

 

[sweet springs]

Hi.
To the future it is easy, "Rip van Winkle", but impossible is to the past.
regards.

 

[Millenniumf]

Of course, you realize that if the engineering problems were solved, what we get may be something like this:

http://www.xkcd.com/989/