Who ages more of two brothers who travel at half the speed of light twards each other?

Question

Suppose two twins found themselves at a great distance apart, travelling twards each other at half the speed of light (which is an attainable speed), both starting this journey at the same age. Suppose they are far enough from any celestial body so that they can be considered as being equally affected by any gravitational pull. The question is, what does each brother see when passing the other brother (note that they never stop, nor do they collide - they simply pass by each other, with the crafts engines being set so that they maintain a constant speed in spite of the varying gravitational pull each craft exerts on the other, so that no acceleration or decelleration occurs). According to (what I understand of) special relativity, each brother should see the other as being older than himself, which is clearly impossible. Einstein has answered a simillar question, but that involved departing and returning to earth, which involves an acceleration, which explained this parradox.

Answer 1

Hold onto your chair and read carefully. There's a critical detail you overlooked. They cannot *initially* be the same age in *both* reference frames since the two frames are moving relative to one another *and* they are separated by a distance. If we assume, instead, that they are initially *stationary* relative to each other, then they can agree that they have same initial age. Once they start moving towards each other, though, the mnemonic "leading clocks lag" means that each will observe the other to be younger than himself (even after accounting for the delay in the observation due to the finite speed of light!). However, each will also observe that the other is aging more rapidly than himself so that, as they pass each other (ie, they are instantaneously in the same place at the same time), they both observe the other to be exactly the same age.

Answer 2

The most obvious answer here.. is that they wouldn't have TIME to see each other if they're traveling, combined, at the speed of light.

So what would each see?

Hundreds of millions of dollars worth of space with a (probably imperceptible) blur that was the other 'craft'.

Unlikely, improbable, and completely worthless concept if you consider the false gravity that would need to be established within the 'craft' that would be needed to maintain our fragile bodies at that speed.. which negates the possibility of a controlled environment to the point where aging is considered (I.E. more CO2 in one air may take it's toll more than the other, etc).

Not to mention the fact that being in such a controlled atmosphere would mean that aging would take place as normally permissible once the body reached it's zero-gravity interia of half the speed of light.. this would not be a factor on it's aging nor it's appearance.

So, in essence the answer is.. they would see nothing worth taking the time to create this experiment. besides possibly the front of another 'craft' for less than a split second.

But aging would occur as would be the norm.. hence appearance would be the same.

Answer 3

Not quite -- when they pass each other, each brother would see the other as being YOUNGER than himself. This sounds impossible but it's not. This is because simultaneity is relative, too. If the two brothers stop completely at the point when they pass each other, they will perceive the other as instantly aging to the same age as himself.

Answer 4

It depends on the observer - and there is no privileged observer. The clock that travels through the most space accumulates the least time; ds^2 is locally conserved. If the situation is wholly symmetric, so are the results - and without contradiction.

When you *set up* the experiment you defined the reference frames. It makes no difference if you built the clocks within them afterwards.

Answer 5

if both started out the same age etc etc...they would both age the same as the variances only occur if one is traveling with time in the same flow and the other traveling in the reverse flow .and seeing as time is constant and travels in /through the same time and space at the same rate ..there can be no variances..so age at the same rate..

Answer 6

This website answers the question far better than I could:

http://www.phys.vt.edu/~takeuchi/relativity/practice/problem18.html

Answer 7

Midicholorians

Answer 8

we were taught in physics class that travelling at the speed of light makes a person younger...