Re: light speed and death

Jason,

Your question really, truly is almost exactly the same as 
the 
question about the headlights!!

As explained in that answer, if you are moving at the speed of light with 
respect to some observer, you CAN'T FIRE your laser cannon at him because, 
as far as he is concerned, time isn't passing for you and you can't move! So
I suppose you could say that the spaceship kills him... and you, the energy
released by two objects colliding at the speed of light would be pretty large.

If you are moving less than the speed of light with respect to an outside 
observer, of course you can kill him with your laser cannon (as long as 
you're not moving away so fast that the light is red-shifted to a harmless 
wavelength like radio waves).

Of course, all of the above is from the point of view of the target. From 
your point of view, the target is moving at lightspeed and your laser cannon 
can't reach him... unless he's on a collision course with you.

But if he were on a collision course with you, at the speed of light, you 
couldn't see him to fire at him until he struck you. We define simultaneity
by light beams (see the excellent website The Light Cone), 
so... it appears that you would collide at the same moment you fired the laser.

A bit like the scene in Ray Bradbury's story "A Sound of Thunder" in which 
time-traveling hunters (who can only shoot dinosaurs that are going to die 
anyway) shoot their quarry at the moment that at tree falls on it.

Dan Berger
MadSci Admin