Faster than light information transfer

[DaveC426913]

You cut the cord, the pull from the outer object, which is what causes the tension, begins to pull the cord away.

No, it doesn't matter what force originally caused the tension. The simple fact is that the tension is there in every molecule of the cord, even the ones right next to the cut.

If you cut the cord simultaneously at centre-sphere and at orbiting-sphere the cord would still recoil even at the centre-sphere's surface, even though, ultimately every far away, the original force of the orbiting-sphere pulling is no longer there.

 

[DaveC426913]

I think I've got it. Assume the distance separating the two masses is one light year:
If your standing on the central mass and cut the cord, you immediately witness the cords release. Looking through your telescope, you know the light coming from the outer mass is a year old, so you realize that you will see it coninue in orbit for a whole year. One year later, you see its course change exactly as it should. Which would indicate to you that the change happened instantaneously, and the light took a year to reach you. To the observer on the outside mass, you see a man approach your cord and cut it. As soon as this happens, you feel a change in your velocity, but realize that the light you saw was a year old and that the cord has been cut for some time. The outside observer would witness no delay, only the "helicopter" situation I mentioned above.
Does this seem to hold up?

No. The delay between cutting at ground-level and change in movement of the small body is quite real and will be observed by all in real time.

They would actually be able to watch the wave of tension-release travel up the cord at .5c.

 

[1mmorta1]

Okay I get it. Is it even possible for the two ends to cut "simulataneously" on both ends considering that this is relative?

 

[Dale]

See a new FAQ on a closely related topic:
https://www.physicsforums.com/showthread.php?p=3537287#post3537287

 

[Dale]

Okay I get it. Is it even possible for the two ends to cut "simulataneously" on both ends considering that this is relative?

With some advanced planning it is certainly possible, but if they are cut simultaneously in one frame they will not be cut simultaneously in other frames.

 

[1mmorta1]

Thanks dale, I actually was aware of the information in the Faq, but somehow have always been puzzled by the variables in the question I proposed. Is it odd that I find general relativity more difficult to grasp than any other area of physics? I was curious as to where the FAQ is located. How do I get to it from the physics forums homepage?

 

[1mmorta1]

Disregard! I found it :)

 

[sophiecentaur]

The only time you could remove a force in such a way that there would be no delay would be if you were in a circular path using a rocket. Turn off the rocket and you instantly go off in a tangential direction.

 

[sophiecentaur]

Thanks dale, I actually was aware of the information in the Faq, but somehow have always been puzzled by the variables in the question I proposed. Is it odd that I find general relativity more difficult to grasp than any other area of physics? I was curious as to where the FAQ is located. How do I get to it from the physics forums homepage?

Glad top hear QM isn't a problem.

 

[1mmorta1]

Glad top hear QM isn't a problem.

It really isn't ;) Somehow I find it to be much easier to grasp. Relativity on the other hand...I know that seems backwards. I actually felt different back in high school. Relativity was so cool, and qm made no sense. My how we grow...

 

[1mmorta1]

Although sometime's people chide me for my infatuation with the Copenhagen interpretation. I find it to be more insightful than Quantum Decoherence though :O