Send Information Faster than Light: Point A to B

Click For Summary

Discussion Overview

The discussion revolves around the concept of transmitting information faster than light using a hypothetical iron tube connecting two points, A and B, separated by 10 light years. Participants explore the implications of moving the tube versus sending a light pulse, examining the physical limitations of materials and the nature of signal propagation.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that moving the iron tube would allow for instantaneous communication to point B, while sending a light pulse would take 10 years.
  • Others argue that any change in the iron tube would propagate at the speed of sound in the material, which is significantly slower than the speed of light.
  • Some participants emphasize that the concept of a rigid rod is flawed, as all materials exhibit flexibility at a microscopic level due to atomic interactions.
  • A participant challenges the initial claim by proposing that releasing the tube in a gravitational field could allow the bottom to move before light arrives, but this is met with skepticism regarding the speed of signal propagation.
  • Several replies reference the behavior of a slinky to illustrate the limitations of rigid materials and the propagation of waves through them.
  • One participant expresses frustration at the assumption that a non-physicist could identify flaws in established physics, highlighting the importance of understanding material properties.

Areas of Agreement / Disagreement

Participants generally disagree on the feasibility of transmitting information faster than light using the proposed method. Multiple competing views remain regarding the nature of rigidity and signal propagation in materials.

Contextual Notes

Limitations include assumptions about the rigidity of materials, the dependence on definitions of speed and signal propagation, and the unresolved nature of how gravitational effects might influence the scenario presented.

jonjacson
Messages
450
Reaction score
38
We have two points A and B, separated by 10 light years away.

WE have an iron tube conecting the two points, so this tube its 10 light years long.

We are at point A and want to communicate with B, we have two options:

-move slightly the iron tube---> instantly the observer at B will receive the news

-send a light pulse---> we will need to wait for 10 years until B observes the light

Isn't the first method faster?
 
Physics news on Phys.org
A tube is made of atoms which interact through electromagnetic forces which propagate at or below lightspeed. The rod cannot be rigid, therefore.

In fact, the compression wave you set off by tapping the end of the rod will travel at the speed of sound in the rod, which is a couple of kilometres per second. Much slower than c.
 
Unfortunately, no.

Any changes to the iron bar will propagate at the speed of sound in iron, which is still much slower than the speed of light.

For example, if you moved one end of it really fast, say by striking it with a hammer, that vibration would move along the bar at the speed of sound in iron.

The atoms in the iron bar are held together by electromagnetic forces just like many other chemical bonds. This puts an upper limit to how fast information can travel along the iron bar as the speed of light (light being an electromagnetic wave, and all).
 
Jimmy said:
No.

https://www.physicsforums.com/insights/can-i-send-a-signal-faster-than-light-by-pushing-a-rigid-rod/

Ibix said:
A tube is made of atoms which interact through electromagnetic forces which propagate at or below lightspeed. The rod cannot be rigid, therefore.

In fact, the compression wave you set off by tapping the end of the rod will travel at the speed of sound in the rod, which is a couple of kilometres per second. Much slower than c.

jfizzix said:
Unfortunately, no.

Any changes to the iron bar will propagate at the speed of sound in iron, which is still much slower than the speed of light.

For example, if you moved one end of it really fast, say by striking it with a hammer, that vibration would move along the bar at the speed of sound in iron.

The atoms in the iron bar are held together by electromagnetic forces just like many other chemical bonds. This puts an upper limit to how fast information can travel along the iron bar as the speed of light (light being an electromagnetic wave, and all).
Jimmy said:
No.

https://www.physicsforums.com/insights/can-i-send-a-signal-faster-than-light-by-pushing-a-rigid-rod/

You said no too fast.

What about just leting the bar move. I mean, imagine that we are in a gravitational field, and we are holding the tube at point A (top point) , after releasing it, there is no wave traveling, the center of gravity will start accelerating due to gravity and the whole bar will move, so B (bottom point) will observe it before light gets there.
 
Google "slinky drop videos". The bottom doesn't start moving for quite some time after the top is released. Certainly slower than light.

Edit: again, releasing the top sets off a relaxation wave moving down the rod at the speed of sound. The bottom doesn't start moving until the wave reaches it.
 
  • Like
Likes   Reactions: Dale
Ibix said:
Google "slinky drop videos". The bottom doesn't start moving for quite some time after the top is released. Certainly slower than light.

Edit: again, releasing the top sets off a relaxation wave moving down the rod at the speed of sound. The bottom doesn't start moving until the wave reaches it.

Its hard to imagine that with a rigid tube.
 
jonjacson said:
Its hard to imagine that with a rigid tube.
Rigid requires an infinite speed of sound. But the atoms are held together by forces that travel at or below the speed of light. So there is no such thing as perfect rigidity in relativity.

The reason you think of an iron bar as rigid is that you'd need one a hundred metres long to see the "slinky" effect to unaided human senses. Good luck picking it up... So "rigid" is a decent approximation for most purposes.

But even the Earth is flexible. If you believe otherwise I've got some property on the San Andreas fault I'd like to sell you. :wink:
 
jonjacson said:
Its hard to imagine that with a rigid tube.

Nevertheless, it is true.

The assumption in this thread, that without studying physics in any depth that somehow you have spotted something people who have studied it have missed for more than a century is horribly arrogant.

The second assumption, that the universe is compelled to limit itself to what you find easy to imagine is even more so.

Both of these are standing in the way of your understanding.

Now, go back to the slinky example. Imagine two slinkies, one more springy than the other. While quantitatively the behavior of the slinkies will differ, qualitatively it will not. Now imagine a slinky as stiff as an iron tube. What will happen then?
 
  • Like
Likes   Reactions: m4r35n357 and davidge
  • #10
jonjacson said:
Its hard to imagine that with a rigid tube.
Vanadium 50 said:
Nevertheless, it is true.
Er -- just to clarify: the real answer here is that there is no such thing as a rigid tube. All materials are essentially made of a collection of little springs. It just isn't noticeable on the scale we are used to dealing with for something like an iron pipe. But they really don't need to be that long before you start noticing the issue if you look closely/think hard. For example, if you strike it with a hammer, it rings like a bell. Why?
 
  • Like
Likes   Reactions: Lunct and SiennaTheGr8
  • #11
jonjacson said:
Isn't the first method faster?
Not even close. It is orders of magnitude slower.
 
  • Like
Likes   Reactions: SiennaTheGr8

Similar threads

Graduate 1-Way Speed of Light
  • · Replies 42 ·
2
Replies
42
Views
3K
High School Why can't energy or information go faster than light?
  • · Replies 32 ·
2
Replies
32
Views
3K
High School Would We See the Same Light After Traveling Back to Earth Faster Than Light?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Information traveling faster than light? (thought experiment)
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Conventionality of the One-Way Speed of Light
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad The Einstein Clock aka Light Clock
  • · Replies 34 ·
2
Replies
34
Views
3K
Undergrad Faster-than-Light Causality-Flip: Thought Experiment Reference?
  • · Replies 3 ·
Replies
3
Views
2K
High School New Paradox Discovered, I Think
  • · Replies 98 ·
4
Replies
98
Views
9K
High School Can Info Travel FTL? Understanding Speed of Information
  • · Replies 6 ·
Replies
6
Views
2K
High School Why is it impossible to go faster than the speed of light?
  • · Replies 21 ·
Replies
21
Views
5K