- #1
tltmts
- 3
- 0
It takes light roughly 1.3 seconds to travel from the Earth to the moon. I have read that even if you push on one end of a stick, the effect of the push cannot reach the other side of the stick faster than c.
So suppose I held a stick in my right hand and one end of this stick is only 1cm away from the surface of the moon. My right arm is bent at a right angle. I now push my end of the stick toward the moon.
Intuitively, it seems that as soon as my arm pushed forward 1cm it would meet instant resistance that stopped it from moving more than 1cm. But if this really happened, then if I tapped Morse code on the surface of the moon I could send a signal faster than c.
So I'm guessing I would be able to continue to push my end of the stick forward more than 1cm. Indeed, I suppose I could push until I locked out my bent right arm at the elbow. I would not be able to feel the effect until enough time has passed for light to travel to the moon and back---roughly 2.6 seconds.
So suppose at time T=0 seconds I begin to push my end of the stick toward the moon. At T=1.0 seconds I have locked out my right arm---I have pushed my end of the stick forward about, say, 60cm. At T=1.3 seconds the other end of the stick hits the moon. At T=2.6 seconds I feel the effect of the other end of the stick hitting the surface of the moon.
But what will this effect be? My arm cannot remain locked out unless the stick has shortened by 59cm. But the stick has not in fact shortened, right?
So does my right hand experience a rebound at 2.6 seconds that forces it 59cm back from the moon? (I.e. a rebound with a force equivalent to the force it took me to accelerate the stick's mass 60cm toward the moon in 1 second?)
So suppose I held a stick in my right hand and one end of this stick is only 1cm away from the surface of the moon. My right arm is bent at a right angle. I now push my end of the stick toward the moon.
Intuitively, it seems that as soon as my arm pushed forward 1cm it would meet instant resistance that stopped it from moving more than 1cm. But if this really happened, then if I tapped Morse code on the surface of the moon I could send a signal faster than c.
So I'm guessing I would be able to continue to push my end of the stick forward more than 1cm. Indeed, I suppose I could push until I locked out my bent right arm at the elbow. I would not be able to feel the effect until enough time has passed for light to travel to the moon and back---roughly 2.6 seconds.
So suppose at time T=0 seconds I begin to push my end of the stick toward the moon. At T=1.0 seconds I have locked out my right arm---I have pushed my end of the stick forward about, say, 60cm. At T=1.3 seconds the other end of the stick hits the moon. At T=2.6 seconds I feel the effect of the other end of the stick hitting the surface of the moon.
But what will this effect be? My arm cannot remain locked out unless the stick has shortened by 59cm. But the stick has not in fact shortened, right?
So does my right hand experience a rebound at 2.6 seconds that forces it 59cm back from the moon? (I.e. a rebound with a force equivalent to the force it took me to accelerate the stick's mass 60cm toward the moon in 1 second?)
