Can a Strong Cable Connect Planets Faster Than the Speed of Light?

In summary, my friends had asked me a question which I thought was rather troubling and provoking. The problem is that is actually seems to violate the law that states that nothing travels faster than the speed of light. Their question was: Suppose two planets (planet A and planet B) which are one thousand light years apart to be connected with a strong cable. Then the living beings on planet A tugs at the end of the cable. Now the problem is: Would the life forms on planet B, which is the other side of the cable, feel the pull instantly even when the two planets are a thousand light years apart?
  • #1
physicskid
75
0
My friends had asked me a question which I thought was rather troubling and provoking. The problem is that is actually seems to violate the law that states that nothing travels faster than the speed of light. Their question was:

Suppose two planets (planet A and planet B) which are one thousand light years apart to be connected with a strong cable. Then the living beings on planet A tugs at the end of the cable. Now the problem is: Would the life forms on planet B, which is the other side of the cable, feel the pull instantly even when the two planets are a thousand light years apart?
 
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  • #2
physicskid said:
My friends had asked me a question which I thought was rather troubling and provoking. The problem is that is actually seems to violate the law that states that nothing travels faster than the speed of light. Their question was:

Suppose two planets (planet A and planet B) which are one thousand light years apart to be connected with a strong cable. Then the living beings on planet A tugs at the end of the cable. Now the problem is: Would the life forms on planet B, which is the other side of the cable, feel the pull instantly even when the two planets are a thousand light years apart?

No. You're assuming that the cable is rigid. In special relativity nothing is rigid. Think of the cable as an elastic band. The tug on the cable propagates down the length of the cable at a finite speed which is always less than the speed of light.

Pete
 
  • #3
The cable is indeed elastic and if the elasticity modulus is E in Newton (kg*m/s²), and the linear density Lambda (kg/m), the wave propagation speed isequal to:

c = sqrt(E/Lambda)

Which will be quite a bit lower than the lightspeed. Typically in the order of several hundred to thousand meters per second.
 
  • #4
pmb_phy said:
The tug on the cable propagates down the length of the cable at a finite speed...
A.K.A "the speed of sound."

Relativity or not, there is no such thing as a perfectly rigid substance (yes, even a rock has elasticity).

Whether it was set up on purpose or not, this is a common trap people fall into where they try to evaluate the implications for physical reality of something that can't be physically real. Ie, start with impossible assumptions and you can draw any conclusions you want.
 
  • #5
also you are saying that the tug would be felt immediately - not that they would see it immediately - this has nothing to do with light speed
 
  • #6
europium said:
also you are saying that the tug would be felt immediately - not that they would see it immediately - this has nothing to do with light speed


It isn't just seeing. Although we talk about "the speed of light" and that one inertial frame "sees" the dilation in the other, it is really causation that can not be communicated faster than light. Faster than c that is, where c is the conversion factor between time and space (so many length units for each time unit).
 
  • #7
What? Even a rock is elastic? Hell, I did not know that.

Anyway, thanks for everyone's replies so that I am now able to prove to my friend who is the real physics expert!
 
  • #8
physicskid said:
What? Even a rock is elastic?
If rock wouldn't be elastic, how do you think you would get earthquake waves?
 

1. What is the Faster than Light Paradox?

The Faster than Light Paradox is a thought experiment that explores the consequences of traveling faster than the speed of light. It is based on the theory of relativity, which states that the speed of light is the maximum speed at which anything in the universe can travel.

2. Can anything travel faster than the speed of light?

According to our current understanding of physics, it is not possible for anything to travel faster than the speed of light. As an object approaches the speed of light, its mass increases and it requires an infinite amount of energy to accelerate it further. This makes it impossible to reach or exceed the speed of light.

3. What are the implications of the Faster than Light Paradox?

If it were possible to travel faster than the speed of light, it would lead to a number of paradoxes and violations of the laws of physics. For example, traveling faster than light would cause time dilation, where time would pass at a different rate for the traveler compared to those remaining on Earth. This would create a paradox known as the "twin paradox" where one twin traveling at near-light speeds would age slower than the twin who stayed on Earth.

4. Could the Faster than Light Paradox ever be resolved?

It is highly unlikely that the Faster than Light Paradox will ever be resolved, as it is based on fundamental principles of physics that have been extensively tested and proven to be accurate. However, there are ongoing efforts by scientists to better understand the universe and potentially find new explanations that could shed light on this paradox.

5. How does the Faster than Light Paradox impact our understanding of the universe?

The Faster than Light Paradox challenges our current understanding of the laws of physics and the limits of the universe. It shows that there are still mysteries and unknowns in the universe that we have yet to fully comprehend. The paradox also encourages further research and exploration to push the boundaries of our knowledge and potentially uncover new discoveries about the nature of the universe.

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