Communication signals and the speed of light

[auxengin]

As per the theory of general relativity nothing can travell faster than the speed of light. Therefore we would always be in the past light cone of a distant celestial body, say planet X in another solar system, that is 100 light years away. A minimum of 100 years would have to lapse before an event that occurred on that planet would have any effect on us. However in a hypothetical situation, if there existed a perfectly taut and non deformable (cannot be stretched) chord or rope between that planet and ours, a person on planet X would be able to signal us immediately by just pulling on the chord, thus sending a signal faster than light. Is this possible?

 

[Astronuc]

As per the theory of general relativity nothing can travell faster than the speed of light. Therefore we would always be in the past light cone of a distant celestial body, say planet X in another solar system, that is 100 light years away. A minimum of 100 years would have to lapse before an event that occurred on that planet would have any effect on us. However in a hypothetical situation, if there existed a perfectly taut and non deformable (cannot be stretched) chord or rope between that planet and ours, a person on planet X would be able to signal us immediately by just pulling on the chord, thus sending a signal faster than light. Is this possible?

No - because a physical disturbance in a material would propagate at the speed of sound, which is well below light. In addition, a string has elasticity, and a small displacement would be 'distributed' over a long distance so it would have essentially no effect several hundred meters from the origin.

Now consider a rigid rod, which is not purely rigid, but simply has a large elastic constant, or in otherwise, is very stiff. The disturbance still must propagate at or below acoustic velocities, and of course, the disturbance will be dispersed (attenutated) as it propagates. The rigid body has mass which will resist propagation of a disturbance in the mass.

One can observe air brakes on a long train. Activation of the air brakes propagates from the front to the rear, pretty much at the speed of sound in the gas. Also, when the locomotives start pulling, one will hear the propagation of the sound of couplers tensioning from front to rear of the train.

 

[auxengin]

Understood your answer. Thanks for your time.

 

[Matterwave]

This is a reason a perfectly rigid body is not possible.

 

[pmacias]

I can say that this hypothetical situation is not possible. The theory of general relativity states that nothing can travel faster than the speed of light, including communication signals. This is a fundamental principle that has been extensively tested and observed in various experiments.

The concept of a taut and non-deformable chord or rope connecting two distant planets goes against the laws of physics. Even if such a chord existed, the person on planet X would not be able to send a signal faster than light by pulling on it. This is because the force of pulling on the chord would still have to travel through space, which is limited by the speed of light.

Furthermore, the concept of a non-deformable object is also not possible according to the laws of physics. All materials have a certain level of elasticity and can be stretched or deformed to some degree. Therefore, the hypothetical chord or rope would not be able to maintain its tautness and non-deformable properties over such a vast distance.

In conclusion, the theory of general relativity and the speed of light limit the possibility of instant communication between distant celestial bodies. While it may seem like a fascinating idea, it is not possible according to our current understanding of physics.