Recent content by codeman_nz

General relativity says that nothing can go faster than the speed of light when measured against local landmarks. What counts as a local landmark? What is the boundary between a local and distant landmark?

OK I will put it another way. The source of the light and the travellers starting point are both at rest relative to each other and they have synchronized their clocks. At a specific time the source of light emits a constant light beam and the traveller starts moving towards the source of the...

Relativity says that the speed of light is constant for all observers regardless of their state of motion. So does that mean even if you are heading towards a light beam at a constant velocity that the light beam would take the same amount of time to reach you as when you are at rest relative...

Hi everyone, I am having a little trouble with the difference between a covariant vector and contravariant vector. The examples that I come across say that an example of a contravariant vector is velocity and that a contravariant must contra-vary with a change of basis to compensate. So...

Hi everyone, Can anyone recommend some good books about relativity. I read Relativity Demystified by David McMahon and Paul M. Alsing which excellent as it explained the mathematics with simple examples. So I am after something similar. Thanks in advance.

Yes but why? The paper only introduces constant acceleration when he calculates total co-ordinate time. Until then he makes no mention of it so aside from getting up to speed I just do not see the need for it.

Can you explain? I see nothing in there that says that constant acceleration is required. Also I don't get how he derives the volume expansion equations.

Yes I know you need to accelerate to faster than the speed of light but from what I read it is constantly accelerating for half the trip and then decelerating for the rest of it. What I am confused about is why does it need to constantly accelerate? What can't it get up to speed and then...

I know what it says in relativity but this whole thing about light cones and causality confuses me. Say a star 10 light years away explodes so we will not know about it for 10 years. If you could jump instantaneously from Earth to the star you would find that it is no longer there. Just...

Hi everyone, I have been reading the fascinating paper by Miguel Alcubierre about the warp drive and one thing is confusing me. He says that the total co-ordinate time is T= \left[d/v + \sqrt{(D-2d)/a}\right] Would that mean that the warp bubble is constantly accelerating so its...

Hi everyone, What is a co-variant derivative? I have looked online but the explanations are not clear. I just want a simple explanation with a simple example more specifically the co-variant of a 3-metric. Thanks.