# A and B are twins,A notice B moving away from him with velocity v

1. Nov 23, 2009

### IPhO' 2008

A and B are twins,A notice B moving away from him with velocity v, so A notice that B is youngerv than him (time dilation) , In the same way, B notice that A is younger than him.
What happen?

2. Nov 23, 2009

### Staff: Mentor

Re: twins

Search this forum for "twin paradox." There have been many discussions of this. In fact, there's one going on right now, with the title "Need help understanding the twins."

3. Nov 23, 2009

### Hans de Vries

Re: twins

Image 4.26 in section 4.15 (Reversal of Time dilation) explains this all:

http://physics-quest.org/Book_Chapter_Non_Simultaneity.pdf

Regards, Hans

4. Nov 23, 2009

### HallsofIvy

Re: twins

Actually, in this case, nothing is happening! Both are completely correct. Each sees the other as being younger than himself. This only becomes a "paradox" when the two twins are back in the same "frame of reference" (i.e. at rest relative to one another) together again. And that requires acceleration of one of the twins.