Simple relativity question [two ships]

[nearc]

two identical ships launch on parallel paths r distance apart. the are completely alone [nothing to affect them gravitationally [but themselves]]. once they reach some velocity v [they both reach the same velocity at the same time [everything is identical]] they turn off their engines and coast.

can someone on a ship determine the velocity v by measuring the decreasing distance between the two ships over time? [i.e. the faster they go, the more mass they have and the more they should be attracted to each other?]

 

[Filip Larsen]

Since the two ships remain at rest relative to each other, each would measure the relativistic mass of the other to be identical to the rest mass.

 

[ghwellsjr]

Just a point of clarification: did you mean that the two ships are side by side or one in front of the other or some other arrangement?

 

[HallsofIvy]

two identical ships launch on parallel paths r distance apart. the are completely alone [nothing to affect them gravitationally [but themselves]]. once they reach some velocity v [they both reach the same velocity at the same time [everything is identical]] they turn off their engines and coast.

can someone on a ship determine the velocity v by measuring the decreasing distance between the two ships over time? [i.e. the faster they go, the more mass they have and the more they should be attracted to each other?]

You are not thinking in "relative" terms! The faster they go relative to what? If they are on parallel courses, at the same speed, they are each motionless relative to each other and each would measure the other to have its rest mass.

 

[FtlIsAwesome]

[i.e. the faster they go, the more mass they have and the more they should be attracted to each other?]

No, they do not have increased gravitational attraction.

 

[Naty1]

With increased momentum another thread recently concluded the time to collide would be increased...meaning LESS gravitational attraction...!

I'll post that thread here if I can find it...

 

[nearc]

Just a point of clarification: did you mean that the two ships are side by side or one in front of the other or some other arrangement?

they are side by side

 

[nearc]

With increased momentum another thread recently concluded the time to collide would be increased...meaning LESS gravitational attraction...!

I'll post that thread here if I can find it...

i'd love to see that and another info an this thought.

 

[Antiphon]

I think the gravitational attraction as seen by everyone else is reduced, they would attract more slowly.

 

[ghwellsjr]

Just a point of clarification: did you mean that the two ships are side by side or one in front of the other or some other arrangement?

they are side by side

In that case, what HallsofIvy said here is correct:

...
If they are on parallel courses, at the same speed, they are each motionless relative to each other...

Actually, what he said is also true if one was in front of the other after they reached their final velocity, but during their acceleration, they will be moving farther apart and end greater than the distance r between them.