What's so special about light?

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Discussion Overview

The discussion revolves around the nature of light and its relationship to the speed of light (c), particularly in the context of massless particles and electromagnetic theory. Participants explore various definitions and implications of c, its fundamental role in physics, and its broader applicability beyond light.

Discussion Character

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

Main Points Raised

  • Some participants question whether light travels at c simply because it is light or because it is a massless particle, suggesting a deeper connection between masslessness and the speed of light.
  • One participant proposes that "the speed of light" is actually a "universal speed limit," indicating that all massless particles, including gravity waves, travel at this speed.
  • There are inquiries about alternative definitions of c beyond its relation to permittivity and permeability constants, with some suggesting that these constants are presented for practical reasons rather than reflecting fundamental truths.
  • Another participant emphasizes that while c is tied to electromagnetic interactions, it is defined as the speed of propagation in a vacuum, which does not inherently make light special, but highlights the significance of its invariant nature.
  • Some participants express the view that c relates fundamentally to geometry and sequencing in physics, though this perspective is met with some confusion from others.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of c and its implications, indicating that multiple competing perspectives exist without a clear consensus on the relationship between light, massless particles, and the speed of light.

Contextual Notes

Some statements reflect assumptions about the definitions of physical constants and their implications, which may not be universally accepted or resolved within the discussion.

copernicus1
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Hi, I confused about the relationship between light and [itex]c[/itex] on the one hand and massless particles and [itex]c[/itex] on the other. Does light travel at c because it's light and that's all there is to it, or does it travel at c because it just happens to be another massless particle?

I know that classically [itex]c=1/\sqrt{\epsilon_0\mu_0}[/itex], which seems to indicate that the speed of light has everything to do with electromagnetism, but then why does the speed of light apply so much more broadly?
 
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What you call "the speed of light" is really "the universal speed limit". That is, it isn't what it is because it's the speed that light travels at, it is a more fundamental thing than that and light travels at it because light is a massless particle. Any massless particle will travel at the universal speed liimit. Also, gravity waves are believed to travel at that speed
 
Okay, thanks, that's sort of what I thought. Are there other ways of defining c besides in terms of the permittivity and permeability constants? This seems to tie c to the electromagnetic interaction in some special way.
 
copernicus1 said:
Okay, thanks, that's sort of what I thought. Are there other ways of defining c besides in terms of the permittivity and permeability constants? This seems to tie c to the electromagnetic interaction in some special way.
c is the fundamental constant in Maxwell's Equations. It's a mistake to think in terms of two fundamental constants ε0 and μ0, which are presented that way to satisfy the engineers. Recall that μ0 is nothing more than a defined number, 4π x 10-7.
 
copernicus1 said:
Okay, thanks, that's sort of what I thought. Are there other ways of defining c besides in terms of the permittivity and permeability constants? This seems to tie c to the electromagnetic interaction in some special way.
It is well known that c is tied to electromagnetic interactions as light is electromagnetic, but c is defined as the speed of propagation in vacuum (for sound, c is the speed of sound and for light it's the speed of light). In other words, the fact that electromagnetic properties allowed to predict the propagation speed of electromagnetic waves does not define that speed - but those constants are definitely tied together. And since SR we know that c is also the limit speed of everything material; that was the mathematical outcome from the observations that the speed of light is not only a constant c, independent of the source, but also invariant. That doesn't make light special, but it does make its vacuum propagation speed c special.
 
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I agree, I can't help but feel c is ALL about geometry & sequencing (ordering). From there physics happens.
 
nitsuj said:
I agree, I can't help but feel c is ALL about geometry & sequencing (ordering). From there physics happens.

Uh ... huh ?
 

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