Is the speed of one beam in the LHC nearly twice that of the other?

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Discussion Overview

The discussion revolves around the speeds of two proton beams in the Large Hadron Collider (LHC) and whether the speed of one beam relative to the other approaches 2c. The scope includes theoretical considerations of relativistic speeds and the implications of special relativity.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant suggests that the closing speed between the two beams can be considered as 2c, noting that if one were traveling with one beam, the other would approach at the speed of light, c.
  • Another participant counters that the speed of one beam relative to the other is actually c, not 2c.
  • A similar point is reiterated by another participant, emphasizing that the coordinate distance between the beams decreases at nearly 2c just before collision, but this does not imply that one beam is traveling at 2c relative to the other.
  • One participant questions whether an observer on one beam would perceive the other beam moving at 2c, indicating a misunderstanding of the frame of reference.
  • A mathematical expression is provided to clarify the relative speed of the beams, demonstrating that if both beams travel at 0.99c, their relative speed is approximately 0.99994949750012... c, which is less than 2c.

Areas of Agreement / Disagreement

Participants express disagreement regarding the interpretation of relative speeds, with some asserting that the closing speed can be viewed as 2c while others maintain that the relative speed remains c. The discussion does not reach a consensus.

Contextual Notes

There are unresolved assumptions regarding the definitions of speed and reference frames, particularly in the context of relativistic effects and measurements.

pixel01
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Hi all,
I've learned that the LHC has just started. There are two beams of protons which travel clockwise and anti-clockwise at nearly the speed of light. Then the two beams are to colide into each other. My question is whether the speed of one beam compared to the other is at nearly 2 c ?
 
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Yes the closing speed is 2c, if you were traveling with one bunch of particles you would measure the other bunch approaching you at c (although what you would measure this with - I'm not sure)

This doesn't violate relativity in any way, no THING is traveling at 2c, just the rate of decrease of the distance between them.
 
Last edited:
The speed of one beam wrt other is 'c'. NOT 2c
 
astromandi said:
The speed of one beam wrt other is 'c'. NOT 2c

Just before collision, the coordinate distance in the frame of the Earth between bunches of particles traveling in opposite directions decreases at the rate of (nearly) 2c. This is what mgb_phys meant by "closing speed."
 
George Jones said:
Just before collision, the coordinate distance in the frame of the Earth between bunches of particles traveling in opposite directions decreases at the rate of (nearly) 2c. This is what mgb_phys meant by "closing speed."

So if one man stood on one beam, he would see the second moving at 2c ?. In other way, one beam would travel at 2c if the other beam was considered the frame?
 
If the speed of one beam is u and the speed of the other v (both relative to the ground), then the speed of one of the beams relative to the other is

[tex]\frac{u+v}{1+uv/c^2}[/tex]

For example, if u=v=0.99c (exactly), then the result is (0.99+0.99)c/(1+0.99*0.99)=0.99994949750012... c.
 

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