Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

If a person on Earth today is looking at a star, say, 10 billion light years away, is it possible that some of the atoms he is looking at will eventually go on to make him?

share|cite|improve this question
If the atoms travel at half the speed of light, wouldn't you have to live another 10 billion years for them to reach you? – RedGrittyBrick Jan 19 '13 at 22:42
If you like this question you may also enjoy reading this Phys.SE post. – Qmechanic Jan 20 '13 at 6:26
As pointed out, the atoms of that star would have had to travel faster than light to reach earth in time to form you. But if you really want to look back in time at yourself, a mirror will do the trick. And the farther away you stand from it, the further back in time you will see yourself. :) – Wouter Jan 20 '13 at 10:21
Thanks team! Wouldn't it be incredible to 'see' the reflected light rays from Earth's history today?? We could point our cameras at a big mirror somewhere in the universe and 'see' the Library of Alexandria, the dinosaurs etc etc!! – wideangle123 Jan 20 '13 at 10:56

I don't think so because the atoms would have had to travel faster than the speed of light to get to you (to form you) before the light they reflected got to you, and from what I understand, nothing travels faster than light.

share|cite|improve this answer
Hi T-Fox. I don't provide contradiction to your quote: "Nothing travels faster than light". Actually, objects with zero mass, can travel at $c$. Whilst on the other hand, objects having negative mass, can travel faster than light. By saying mass, I really meant rest mass. The problem is, we haven't observed any superluminal objects yet and we won't. Maybe that's the reason I didn't argue with your quote ;-) – Waffle's Crazy Peanut Jan 20 '13 at 5:09

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.