Why is the (maximum) speed of light the number it is?

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Discussion Overview

The discussion centers around the question of why the speed of light is approximately 3x10^8 m/s, exploring its limitations, the relationship to Maxwell's equations, and the implications of defining physical constants. Participants express curiosity about the fundamental reasons behind this specific value and its expression in terms of other physical constants.

Discussion Character

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

Main Points Raised

  • Some participants suggest that the speed of light is fixed in vacuum and its numerical value is tied to arbitrary definitions of units, specifically meters and seconds.
  • Others propose that the speed of light can be expressed in terms of electric vacuum permittivity and magnetic vacuum permeability, as indicated by the equation c² = 1/(ε0μ0).
  • There is a question about what limits the speed of light and why it takes on that particular value, with some participants noting that such "why" questions may not have definitive answers in physics.
  • One participant mentions that historically, the speed of light was measured through various methods, but it is now defined as the distance light travels in a specific time frame, suggesting that the numerical value is arbitrary based on human definitions.
  • Another point raised is the idea that if different definitions for the meter were used, the speed of light could have a different numerical value, emphasizing the arbitrary nature of the constant.
  • There is a suggestion that to remove arbitrariness, one could consider dimensionless ratios, similar to other unexplained dimensionless numbers in physics.

Areas of Agreement / Disagreement

Participants express a mix of views, with some agreeing on the arbitrary nature of the speed of light's numerical value while others seek deeper explanations for its limitations and specific value. The discussion remains unresolved regarding the fundamental reasons behind the speed of light.

Contextual Notes

Participants acknowledge the limitations of their inquiries, particularly regarding the nature of "why" questions in physics and the dependence on definitions of units. There is also a recognition that some dimensionless numbers in physics lack clear explanations.

gracie
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What limits the speed of light to 3x10^8ms^-1? I was referred to Maxwells equations and have studied them but am not sure if this is the full answer and am unsure where Maxwell's relate anyway, the lectures I watched were unclear apart from relating to Ampere's Law.

As much maths as possible to answer please :)
 
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Physics cannot answer "why"-questions at a fundamental level. Light in vacuum has a fixed velocity. Its numerical value comes from our arbitrary definitions of the units meters and seconds.
It is possible to express the speed of light via the electric vacuum permittivity and magnetic vacuum permeability: c2 = 1/(ε0μ0)

It is possible to invent laws of physics where light has infinite speed. We just don't live in such a universe.
 
Okay but in our universe, through whatever units we use, the speed of light is limited, right? But what is it limited by, and why is it that particular number, why not bigger or smaller?
 
Also why can it be expressed with that equation? Where has that come from?
 
gracie said:
But what is it limited by, and why is it that particular number, why not bigger or smaller?

again you are asking why type questions

That is just the speed it is
 
Historically, we measured the speed of light through various ways. But in modern times we just define the speed of light as a certain value. Or more accurately, we define the meter as the distance traveled by light in vacuum in 1/299792458 second. If we chose a different definition for the meter, then the speed of light would have some different numerical value. So the number itself is arbitrary, invented by humans.

If you want to remove the arbitrariness from the question, you have to take some ratio (or more complicated expression) so the human units all cancel out. Then you get a dimensionless number. We don't have explanations for some dimensionless numbers we find in the universe, like the fine structure constant.
 

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