Question: can you explain the twin paradox?

Rob Temperton answered on 24 Jun 2015:

I assume you are referring the the thought experiment where you take one twin into space, wiz them around space a bit at high speed, bring them down and the twin who stayed on earth will be older?

If so, it is a phenomenon explained by special relativity which states that the faster you travel, the slower time goes for you.

Now for fun, lets do an example – this will unfortunately involve some maths…. So say your space trip lasts 1 year according to the person on earth and that your super awesome imaginary space ship travels at 50% of the speed of light (so 150000000 m/s – very very fast). We can calculate the amount of time that the person in the space ship would experience:

We use a quantity called the lorrentz factor which equals 1/sqrt(1-(v^2/c^2)) where v is the velocity you are travelling and c is the speed of light. For our case, this factor works out as 1.15. This means that the time experienced by the person in the rocket is going 1.15x slower than it is for the person on the earth. This is the same as saying that the person in the rocket will have only been ageing for 10.5 months when the twins meet after a year of earth time (as time goes slower when you travel quickly).

I realise this is quite complex – it is physics which you do at university level so if you understand it you are doing very well!

Rob