Can Anything Travel Faster Than the Speed of Light?

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Discussion Overview

The discussion centers around the question of whether anything can travel faster than the speed of light, specifically addressing the implications of this limit in the context of special relativity and the nature of spacetime. Participants explore theoretical concepts and interpretations related to speed, mass, and the structure of spacetime.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant asks if anything can travel faster than 3x10^5 km/sec and questions the reasons behind a speed limit for particles.
  • Another participant cites special relativity, stating that the speed of light is a fundamental feature of spacetime, asserting that massive particles cannot reach this speed.
  • A participant introduces the concept of 4-velocity and 4-speed, suggesting that all objects move at a constant speed through spacetime, framing the question as one of understanding this constant speed rather than simply a maximum speed limit.
  • Some participants discuss the mathematical representation of 4-velocity, providing examples for objects at rest and photons, and exploring the implications of these representations.
  • One participant acknowledges a detail about massless particles having a 4-speed of 0 while massive particles have a 4-speed of c, indicating a potential misunderstanding in earlier posts.
  • A participant references external material discussing the variable speed of light in quantum theory, suggesting additional complexity to the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of speed in relation to spacetime and the implications of special relativity. There is no consensus on whether the concept of a maximum speed is adequately understood or if alternative models, such as variable speed of light, should be considered.

Contextual Notes

Some claims rely on specific interpretations of special relativity and the nature of spacetime, which may not be universally accepted. The discussion includes references to external sources that may introduce additional assumptions or frameworks not fully explored within the thread.

likephysics
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simple question - Can light or anything else, travel faster than 3x10^5 km/sec?
If not, why is there a limit on max speed particles/photos can travel at?
 
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From wikipedia on Special Relativity:

Special relativity reveals that c is not just the velocity of a certain phenomenon, namely the propagation of electromagnetic radiation (light) - but rather a fundamental feature of the way space and time are unified as spacetime. A consequence of this is that it is impossible for any particle that has mass to be accelerated to the speed of light.
 
A good way to think about it that I recently came across is that everything is moving at a constant speed. That is, every object has a 4-velocity and a 4-speed of c (speed of light). A 4-velocity is a 4-dimensional vector where the first index is time and the last three are space.

Examples:
Object at rest: v = (c,0,0,0)
Photon: v=(0,c,0,0) *or any vector where the length of the spatial part is c and time is 0

So the question isn't "why is there a maximum speed?", its really "why is everything moving through space-time at a constant speed?".
 
michael879 said:
A good way to think about it that I recently came across is that everything is moving at a constant speed. That is, every object has a 4-velocity and a 4-speed of c (speed of light). A 4-velocity is a 4-dimensional vector where the first index is time and the last three are space.

Examples:
Object at rest: v = (c,0,0,0)
Photon: v=(0,c,0,0) *or any vector where the length of the spatial part is c and time is 0

So the question isn't "why is there a maximum speed?", its really "why is everything moving through space-time at a constant speed?".

For a photon, its tangent vector has the form
Photon: v=(c,c,0,0), for example, so that [tex]c^2-(c^2+0^2+0^2)=0^2[/tex].

Here's my comment on the "speed through spacetime" idea:
https://www.physicsforums.com/showthread.php?p=565681#post565681
 
Last edited:
robphy said:
For a photon, its tangent vector has the form
Photon: v=(c,c,0,0), for example, so that [tex]c^2-(c^2+0^2+0^2)=0^2[/tex].

Here's my comment on the "speed through spacetime" idea:
https://www.physicsforums.com/showthread.php?p=565681#post565681

my bad, I forgot that detail: mass-less particles have 4-speed of 0 while massive particles have 4-speed of c.
 

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