# Thread: lorentz transformation question..

1. ## lorentz transformation question..

"a space ship goes from earth to planet x.
then it goes to the moon of planet x.when it reaches the moon it detects a energy pulse
and 1.01 seconds later planet x blows up.
the distance between planet x and its moon is 400 million meters
the speed of the space ship relatively to planet x and its moon is 0.980c.

A.what is the time difference between detecting the signal and the blowing of planet x
B.what is the meaning of the time difference
C.did the pulse made the planet to blow up or its other wise "

the question is inside the photo

http://i48.tinypic.com/vo5169.jpg

2. I am not 100% certain of this answer but since no-one else has answered yet....

Let S be the frame in which the space ship is stationary and S' the frame in which the planet is stationary. The relative speed between the two frames is 0.98c so gamma is about 5.

From our seat in S we see the space surrounding the planet in S' to be shrunk by a factor of 5. So we observe the distance to the planet is 400e6/5 or 80 million meters. The information that the planet disappeared travels at 300 million meters per second so it takes 80/300 = 0.27 seconds to reach us.

We conclude that the planet disappeared 1.01-.27=0.74 seconds after the energy pulse. Provided the energy pulse travels faster than 80/0.74 = 108 million meters per second (about 0.36c) then there is no reason to doubt that is could have caused the destruction of the planet.

3. if look from the perspective of the space ship
why in the given table in the first post after time t its (x_0+vt,t)
(the ship moved x_0+vt)

if we always look from the perspective of our ship then the space ship
shouldnt move at all
it should be (0,t)

all the surroundings should change arround it

why we have x_0+vt ???

if we look from the perspective of the ship
??