how fast?

[cristache]

earth travels with the speed of light and rocket is stationary. How the one on earth is older?
Remember we can put the referential system anywhere we like - per Einstein relativity theory.

[Neo-X]

Huh? I did not notice it.. This time the one on the rocket was older. Your post was confusing and please post only a logical example. At speed of light time will completely stop. Some scientist think that when we travel faster than speed of light, time goes backward. Its means we can travel back in time. But for me its impossible, my theory is when we travel faster than speed of light, we can teleport. The time difference of departure and arrival is depend on how many times faster you are compared to the speed of light. 

[cristache]

Whatever, closer to the speed of light. Same idea, you get a contradiction since you cannot tell which is older just by changing the reference system.
The reality is the same, one travels compared with the other closer to the speed of light
Another example is to put the referential system traveling at high speed between rocket and earth. Now both of them have the same speed compared with this new reference system

[Neo-X]

I already said the one on the rocket was the older because he was not moving and the earth was moving. I just confuse at first thats why my first post was wrong. You will never ever find the absolute time because all galaxy including our own galaxy are expanding very fast so our time now are quite slow even we are not moving.

[cristache]

You missed the point.
earth and rocket are moving one relative to another with 0.9c
If you put the referential system on the rocket, the twin on rocket gets older
if you put the referential system on earth, the twin on earth gets older
if you put the referential system always half distance, moving at constant seep between earth and rocket the twins have the same age at experiment end.
Since there is one phenomenon there should be one single outcome, regardless of the referential system.
A twin cannot be in the same time older and younger than the other.