What Determines the Speed of Light and Its Limitations?

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Discussion Overview

The discussion revolves around the factors that determine the speed of light, denoted as c, and the reasons for its specific value. Participants explore theoretical, conceptual, and speculative aspects of light's speed, including its behavior in different media and the implications of fundamental constants.

Discussion Character

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

Main Points Raised

  • Some participants propose that the magnetic permeability \mu _0 and electric permittivity \epsilon _0 of space fundamentally determine the speed of light, although the reasons for their specific values remain unclear.
  • Others suggest that the speed of light relates to the rate of emission and absorption of energy, with variations in different media affecting its speed.
  • A participant emphasizes that the value of c can be defined differently depending on the units used, and questions the significance of its specific numerical value.
  • Some express skepticism about ever understanding why the constants of the universe, including the speed of light, have their particular values.
  • According to Special Relativity, massless particles, such as photons, must travel at the speed of light, which raises questions about the nature of this speed and its implications for other theoretical particles like gravitons.
  • There is a discussion about whether light travels slower in a medium due to the absorption and emission of photons, with some participants affirming this idea.
  • One participant notes that the fundamental questions about the speed of light may never be fully answered, emphasizing the limitations of physics in addressing "why" questions.

Areas of Agreement / Disagreement

Participants express a range of views on the factors influencing the speed of light, with no consensus reached on a single explanation. Disagreements exist regarding the significance of emission and absorption rates, the nature of fundamental constants, and the implications of Special Relativity.

Contextual Notes

Some claims depend on specific definitions and assumptions about physical constants and the nature of light, which remain unresolved in the discussion.

phenylalanine
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What gives light its speed? And why does it travel at c, not faster or slower?
 
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The magnetic permeability [tex]\mu _0[/tex] and electric permittivity [tex]\epsilon _0[/tex] of space determine the speed of light. That's about as fundamental as you can get since those are properties of empty space and I don't think anyone knows why they have their particular values.
 
Personally, I think the velocity of light through space has to do with the rate at which the energy is emitted and absorbed. Like in space, it is emitted and absorbed at a rate that allows it to go [itex]3x10^8~m[/itex] in one second. This value differs from water. It is emitted and absorbed to a lesser extent which gives it a slower speed. Those are just PERSONAL thoughts. I strongly agree with the magnetic permeability and electric permitivity; I just think it is easily explained through emission and absorption.
 
h8ter said:
Personally, I think the velocity of light through space has to do with the rate at which the energy is emitted and absorbed. Like in space, it is emitted and absorbed at a rate that allows it to go [itex]3x10^8~m[/itex] in one second. This value differs from water. It is emitted and absorbed to a lesser extent which gives it a slower speed. Those are just PERSONAL thoughts. I strongly agree with the magnetic permeability and electric permitivity; I just think it is easily explained through emission and absorption.

Be careful with personal theories, there is a special section for that. I'll just point out that it doesn't hold if only one photon is emitted, in which case you cannot define a rate.

The value of c is only a matter of what units you use, and it is quite simply the asymptotical value that a mass cannot attain. It is entirely possible to define c = 1 with the appropriate units. If there was another "special speed", one could ask why a certain factor between both, but since it is quite unique, I don't see a meaning to the question.
 
I don't think we will ever know why the constants of our universe are what they are, not only the speed of light, but also, planks constant, the gravitational constant, ect.
 
According to Special Relativity, particles with zero mass must travel with the speed of light. So the reason why photons travel with that speed is because their massless. Gravitons (if they exist) also travel with speed of light. So you could also call it "speed of gravity", and say photons travel with that speed. Same idea.

The question why the speed of light is about 3*10^8 m/s is still open ofcourse...
 
phenylalanine said:
What gives light its speed? And why does it travel at c, not faster or slower?

Well, it travels slower through atmosphere... :wink:
 
Is it true that light travels slower though a medium because the photons are absorbed and emited?
 
phenylalanine
What gives light its speed? And why does it travel at c, not faster or slower?
These are questions so basic to physics that they may never be literally known. That c has the units of velocity or its current numerical value most probably does not translate to some other regions of infinite space (likewise for other fundamental constants). Isn't it said that physics answers only "how" questions?

ArmoSkater87
Is it true that light travels slower though a medium because the photons are absorbed and emited?
I believe you are close to correct.
 

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