Time Travel Stephen Hawking style

[Gazabone]

I'm fascinated by Stephen Hawking's programmes.  A while back I watched the one about time travel and I accept (I certainly don't claim to understand!) that proximately to a mass and travelling very fast will bend the space time continuum and have the effect of slowing down time.  I can accept the idea that someone can get into a (yet to be invented) spaceship, travel near light speed for what will be a few weeks whilst in the same time for those of us on Earth, 80 years or so will have passed.......so far so good.

The next analogy is getting on a "near light speed train" and would go around the Earth 7 times a second.  He illustrates that if a passenger ran forward on the train, they could still never reach light speed (but that aspect wasn't what puzzled me). That got me thinking (always fatal I know).  Suppose (just to make the maths easy) the train was going for 1 hour (on board train time) and in that same time 10 hours passed for the rest of us not on the train.  Suppose there is a counter on the station that clicks once every time it "sees" the train pass through (7 times a second) and suppose that the was also a counter on the train itself to count how many times it passed the station (which would still be 7 times a second even though it's "on board train time".

Presumably, for the duration of the journey, the counters would read as follows;

Train - 7 x 60 x 60 x 1 = 25,200 times (7 times a second, x 60 seconds a minute x 60 minutes an hour x 1 hour).

Station - 7 x 60 x 60 x 10 = 252,000.

Either the train goes past the station or it doesn't!

Would they show those counts or not?  I think the root cause of my confusion is that the number of "passes" has to be the same whether you're on the train or not. but if that's the case then it would seem time would have to pass at the same rate whether you're on board or not.

This one has really got me baffled, I suspect that the explanation will be beyond my poor little brain but it seems an interesting conundrum.

Anyone with any ideas?

[andrew s]

53 minutes ago, Gazabone said:

which would still be 7 times a second even though it's "on board train time

I think you need to think about this statement a bit more. Who's clock are you using and why still 7 per second?

Strictly, this experiment is not within the bound of SR as the train is not in an inertial frame.

Regards Andrew

[Dave In Vermont]

Not going to touch it - I already gave myself a migraine trying to analyze such when I was 18. But I'll drop off these:

http://quoteinvestigator.com/2013/12/19/lady-bright/

Relativity.

There was a young lady named Bright
Whose speed was far faster than light;
She set out one day
In a relative way
And returned on the previous night.

Yikes!

Dave

[Gazabone]

Lol, Dave, I like it.  Staving off a headache over it myself. Just as well I don't have to make a living from astrophysics!

 

hi Andrew,

re the clock; isn't it the point though that the train will record 7 laps per second in its own time just as the station clock wll do the same (I.e. In "normal" Earth time)? I knew I would struggle with understanding this.

[andrew s]

No. It is like a multi trip twin paradox. They agree on the number of trips but disagree on how long each trip or circuit takes. If you Google the twin paradox and look for a space time diagram that explains it you should get the right idea. SR says observers agree on the number of events (assuming they are in their past light cones) but not on the timing.

Regards Andrrw

[Sai Samarth]

I agree with " Proto Star ". Both counters will show same value, but will click at different rate which is dependent on the observer. A person in the train will see's the counter on the station and in the train tick at the same time.. as he is the observer. The same will happen to an observer on the station. If there had to only one observer, it would disagree with Relativity because, the train has to slow down for both the counter's to tick with the same value.