Different times

[Jackmason]

If two twins were given a watch with excactally the same time on them, and one was to travel around the world and one stay were she was. Would the Twin who travelled have a different time on her watch and would she be slightly younger?

[mibn2cweus]

Do their watches have billionths of a second hands?

an historic flight

[wildwood]

I don't understand mibn2cweus. Why would Katie only be 15.5 if she spend 50 years traveling?

[jake-the-peg]

Because time doesn't work the way you think it does.

It passes at different rates for different people depending on things like how fast they're going compared to you or how strong gravity is.

In the example Katie spends 50 years travelling by Shannons' watch but for her only half a year has passed.

A good example of this from real life are muons.

These particles are created high in the upper atmosphere by cosmic rays but they're very short lived so even at speeds close to the speed of life we should hardly see any reaching us on Earth.

But because they travel so fast time is slower fro them and many many more reach the ground before they decay tens of thousands more.

see here:
http://hyperphysics.phy-astr.gsu.edu/hbase/rel ativ/muon.html

[mibn2cweus]

They should have specified that Katie's trip took 50 years in Shannon's time which passes much faster than Katie's time:


Relativity does not prohibit traveling 50 light years in six months although this would require a lot of energy. What relativity states is that within the reference frame from which you departed you could not travel 50ly in less than 50 years.

In the process of accelerating to say 90% of the velocity of light you are no longer in the reference frame from which you first started your acceleration. If you then stop accelerating and coast at 0.9c you are then in a new reference frame in which you are inertially at rest, however your time does not pass at the same rate as a clock in your initial rest frame. From your new rest frame you are not prohibited by relativity from again undertaking an �identical� acceleration to 90% of the velocity of light. What allows this is the dilation of time because time does not add linearly from one rest frame to the next.

While at first it might appear to you that you have broken the speed limit of light because of the distance you have traveled in relation to your elapsed time, your time is dilated in relation to the passage of time in the reference frame you departed from. As observed from the reference frame of your original departure the two accelerations you experienced do not add up to 1.8 times the velocity of light but are squeezed together so that they always remain within the velocity of light as observed in that reference frame no matter how many times you carry out the same acceleration.

cont . . .

[mibn2cweus]

Time and distance must always yield to the elusive velocity of light and are adjusted by relativity to maintain a constant velocity of light no matter how long one continues to accelerate to a greater and greater velocity. Reaching 90% of the velocity of light would require an enormous amount of energy and due to the equation of relativity those energy demands grow exponentially as you accelerate closer and closer towards the velocity of light.

jake, There you are, it's about time.

[Loosehead]

For interest this experiement was done using 2 cesium clocks. They started off syncronized, one was flown around the world and one left on the groud. When compared again the travelling clock was slightly slower than the staionary one. The amounts where in line with Einstien's predictions.

[Loosehead]

Should have read the link first I guess! Doh!