20 Aug 2005 [To Steuard Jensen]

I told [your father] I had a speed of light question I couldn't get
the answer to and asked if he would ask you the question. He urged me
to write to you directly.

[...]

At any rate, here is the question:

1.    As I understand it, nothing can go faster than the speed of light.

2.    But, suppose a rocket ship is traveling away from us here on  
earth at 60% of the speed of light. And suppose another rocket ship  
were traveling away from us in the opposite direction at 60% of the  
speed of light.

3.    Can it properly be said that those two rocket ships are  
receding from each other at 120% of the speed of light (from our  
observation point here on earth?)

4a.    If not, why not?

4b.    If so, (AND HERE IS THE CRUCIAL PART OF THE QUESTION)  if  
rocket ship A(RSA)  flashed a light toward rocket ship B (RSB), would  
an observer on rocket ship B ever see the light.

5.    I am guess that the observer on RSB would eventually see the  
light because RSB is receding from the point of flash at only 60% the  
speed of light.

6a. If my guess is correct, then the source point electromagnetic  
disturbance of the light flash is a stationary point in space,  
regardless of the speed or direction of the emitter, doesn't it?

6b. If my guess is incorrect, then it would seem the source point of  
the electromagnetic disturbance is itself moving through space.



This is a sticking point for me as I am trying to learn a little  
about relativity. I asked a retired UNL physics professor the  
question and he said he'd have to read up on it before he could  
answer and then he gave me a Wikipedia link that doesn't answer my  
question in a way I can understand.


So, can you help me?

Do you have time to help me?

Are you willing to help me?


If not, that's okay. I've made it 60 years without understanding  
this, so apparently a thorough understanding of the speed of light  
and relativity is not essential to life as we know it.