What to do, what to do:

Two spaceships flying together thousands of light years from any star or other mass, the space drive is one that accelerates every atom inside the craft at the same time so even though the craft is accellerating at 10 G's, nothing is felt inside each craft. So one craft, call it spacecraft A, doubles its G rate, causing spacecraft a to shoot ahead of spacecraft B. The captain on the bridge of B notices A shooting ahead. Does he call engineering to ask why we are slowing down or what? His radio broke and he can't just call A. How can he figure out which one is causing the shift in positions? His own craft slowing down or the other one speeding up?

Originally posted by sonhouse
Two spaceships flying together thousands of light years from any star or other mass, the space drive is one that accelerates every atom inside the craft at the same time so even though the craft is accellerating at 10 G's, nothing is felt inside each craft. So one craft, call it spacecraft A, doubles its G rate, causing spacecraft a to shoot ahead of spacec ...[text shortened]... ne is causing the shift in positions? His own craft slowing down or the other one speeding up?

You would not be able to use Doppler affect, since that does not distinguish between A accelerating or B decelerating.

Originally posted by sonhouse
Two spaceships flying together thousands of light years from any star or other mass, the space drive is one that accelerates every atom inside the craft at the same time so even though the craft is accellerating at 10 G's, nothing is felt inside each craft. So one craft, call it spacecraft A, doubles its G rate, causing spacecraft a to shoot ahead of spacec ...[text shortened]... ne is causing the shift in positions? His own craft slowing down or the other one speeding up?

You said, can't JUST call A, so why doesn't he just call base and A?

Originally posted by sonhouse
Two spaceships flying together thousands of light years from any star or other mass, the space drive is one that accelerates every atom inside the craft at the same time so even though the craft is accellerating at 10 G's, nothing is felt inside each craft. So one craft, call it spacecraft A, doubles its G rate, causing spacecraft a to shoot ahead of spacec ...[text shortened]... ne is causing the shift in positions? His own craft slowing down or the other one speeding up?

You said, can't JUST call A, so why doesn't he just call base and A?

Originally posted by Alethia
You said, can't JUST call A, so why doesn't he just call base and A?

Well, the two craft are several thousand light years from anywhere so a call to base would take say, 6000 years for a reply so that's probably out of the question. But his radio is broke anyway so he has to try to figure out what happened, his ship or his buddy. I think he would call engineering and ask if anyone applied the brakes. Of course some sabateur could have snuck in a hack that took over and even engineering wouldn't know what happened. So now what? Like one guy said, doppler won't tell you much more than the change in velocity, not who did what.

jettison something, observe, etc.

Originally posted by sonhouse
Two spaceships flying together thousands of light years from any star or other mass, the space drive is one that accelerates every atom inside the craft at the same time so even though the craft is accellerating at 10 G's, nothing is felt inside each craft. So one craft, call it spacecraft A, doubles its G rate, causing spacecraft a to shoot ahead of spacec ne is causing the shift in positions? His own craft slowing down or the other one speeding up?

The shift in positions is relative and in some senses it may not be relevant to answer your question, since both causes would produce the same outcome - B speeding up or A slowing down - it makes no difference. The only reliable information has to concern his own craft internally and the measure of distance from the other craft. He can ask engineering what action would be required to compensate for the change and re-establish a stable relative position. He has no reliable information about the internal affairs of the other craft so can only surmise based on what he knows about his own craft, its current use of energy, any record of change such as a sudden acceleration or deceleration. I do not believe that a doubling or halving of speed could take place without consuming energy and that must be detectable if it took place within his own craft unless it struck an invisible and undetectable source of friction to slow him down - which surely ought to be unlikely.

Originally posted by finnegan
The shift in positions is relative and in some senses it may not be relevant to answer your question, since both causes would produce the same outcome - B speeding up or A slowing down - it makes no difference. The only reliable information has to concern his own craft internally and the measure of distance from the other craft. He can ask engineering what ...[text shortened]... isible and undetectable source of friction to slow him down - which surely ought to be unlikely.

All true, but I like sloth's solution, dump something overboard (outboard?) and watch. If you are in accel or decel, the stuff dumped will go bye bye but if not, it will stay with you. Nice. I like that.