Thread: Time travel

If i travel in the speed of light for one year and i leave my friend when he was two years when i back how old he will be.

Your friend is two years old?

OK, then he would be three. However, you wouldn't have aged a second, nor noticed any time passing at all.

Doesnt that depend who is accelerating and who's year you are counting?

Also moving this to Q/A

Originally Posted by grapes

Your friend is two years old?

OK, then he would be three. However, you wouldn't have aged a second, nor noticed any time passing at all.

Originally Posted by tom

Doesnt that depend who is accelerating and who's year you are counting?

There are different ways to interpret the question, but since the OP says "i leave" I've assumed that the OP is traveling away at the speed of light and coming back. If the OP is traveling at the speed of light, they will sense no passage of time, so I assumed that the "year" was from the point of view of the other observer, the two-year old, making them three.

Yes Grapes is correct, except for the time it takes to accelerate to C, and then deccelerate of course.

But, if say your friend was able to flick a switch and you jumped instantaneously to C travelling away for 1/2 a year measured by himself. Where he flicked a switch once more instananeously reversing your direction without you losing speed. After another 1/2 year measured by your friend you would return. To you it would appear that you'd gone nowhere yet your friend had instantaneously aged one year as soon as you saw him flick the switch.

Hey its a good way to live longer relative to everyone else, thats if you are willing to miss a few years in between time

Although! based on our current understanding of physics this scenario is completely impossible in many ways. So I wouldn't get to hung up on the details. Grapes gave you the layman mainstream answer.

Hmmm ... I may have to disagree with you ... whatever time frame you are in ... your time is passing normally. Lets say you have been travelling at the speed of light since the beginning of time and you traveled for 1 year your time ... that is totally fine ... now the problem is that the rest of the universe would be infinitely old even after one of your seconds.

Now ... the way I interpreted the questions is not at the speed of light ... but NEAR the speed of light ... which also for the local traveler time does not stop ... a year is a year ... and light travels at c ....

The point I am making is that for all frames ... time travels similarly ... 1 second is 1 second ... no ?

Originally Posted by grapes

There are different ways to interpret the question, but since the OP says "i leave" I've assumed that the OP is traveling away at the speed of light and coming back. If the OP is traveling at the speed of light, they will sense no passage of time, so I assumed that the "year" was from the point of view of the other observer, the two-year old, making them three.

I'm not sure what you are disagreeing with!