Why does light move at the speed it does

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Discussion Overview

The discussion centers around the question of why light travels at its specific speed of approximately 300,000 km/s, exploring the implications of unit definitions, physical constants, and the nature of speed itself. Participants examine this topic from various angles, including theoretical, conceptual, and philosophical perspectives.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants argue that the speed of light's value is arbitrary and depends on the definitions of the meter and second, suggesting that changing units would alter its numerical representation.
  • Others propose that the question should focus on dimensionless constants, such as the fine structure constant, which are not dependent on unit choices and whose values remain unexplained.
  • A few participants express a belief that understanding the speed of light has fundamental significance, although this is contested by others who compare it to arbitrary unit definitions.
  • Some contributions emphasize that the speed of light is invariant and that its value is determined by the properties of vacuum, specifically permeability and permittivity.
  • There is a suggestion that the question could be reframed to inquire about the properties of speed rather than its numerical value, particularly in comparison to other wave phenomena.
  • Several participants note that reaching a satisfactory answer may ultimately lead to accepting certain constants as given without further explanation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the significance of the speed of light or the nature of the question itself. While some agree that the speed is defined by unit choices, others argue for a deeper inquiry into the underlying physical constants.

Contextual Notes

Limitations include the dependence on unit definitions and the unresolved nature of why certain physical constants have their specific values. The discussion reflects a mix of philosophical and technical reasoning without definitive conclusions.

  • #61
bob012345 said:
Which is what the impedence of free space is. The ratio of two constants of nature.

The ratio of two constants with different units, i.e., a ratio that has units itself. Not a dimensionless ratio. When I said "ratio" I meant "dimensionless ratio"; I assumed that would be clear from the previous posts in this thread.

bob012345 said:
The speed of light is a constant of nature regardless of the fact that it isn't dimensionless. It's only the representation that's arbitrary. It has nothing to do with units.

I'm sorry, but simply continuing to repeat your contrary position without addressing what has already been said in this thread is pointless.
 
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  • #62
PeterDonis said:
The ratio of two constants with different units, i.e., a ratio that has units itself. Not a dimensionless ratio. When I said "ratio" I meant "dimensionless ratio"; I assumed that would be clear from the previous posts in this thread.
I'm sorry, but simply continuing to repeat your contrary position without addressing what has already been said in this thread is pointless.
Well, I wasn't planning posting here today until got an invitation by email about the site and the various topics asking me to participate. Perhaps you should ask yourself why a person would take up the invitation only to have someone like you always trying to put them down with oneupmanship comments and closing off discussions? Yes, certain points were discussed before, but the point you miss is this, they weren't discussed by me. So please, quit trying to end discussions after inviting my participation. That's more pointless. I didn't come her to be bullied by you.
 
  • #63
bob012345 said:
certain points were discussed before, but the point you miss is this, they weren't discussed by me

But you are not discussing them. You are simply repeating your position without addressing them. That is what I drew your attention to.

bob012345 said:
quit trying to end discussions

I'm not trying to end any discussion. I'm trying to get you to contribute to the discussion. You aren't posting in a vacuum; you are coming to a discussion that has already taken place.
 
  • #64
RobC said:
Why does light move at the speed it does, why not half the speed or double?
It's actually the speed of cause and effect (causality). You can visualize this if you think about it from the changing E&M field view, that is, a changing Electric Field causes a changing Magnetic Field in the direction of propagation. That changing Magnetic Field in turn causes a changing Electric Field, again in the direction of propagation, etc ad infinum. The speed of that cause and effect is the speed of light "c"
 
  • #65
PeterDonis said:
But you are not discussing them. You are simply repeating your position without addressing them. That is what I drew your attention to.
I'm not trying to end any discussion. I'm trying to get you to contribute to the discussion. You aren't posting in a vacuum; you are coming to a discussion that has already taken place.

Sorry, the 'bully' charge was too strong but at the moment that's what it felt like.
 
  • #66
Roger Chase said:
It's actually the speed of cause and effect (causality).

This just rephrases the OP's question (instead of "speed of light", "speed of causality"). It doesn't answer it.

Roger Chase said:
You can visualize this if you think about it from the changing E&M field view

This can help to understand how light propagates, but it doesn't explain why it propagates at a certain speed--or why that speed happens to be the same as the "speed of causality".

The previous discussion in this thread addresses those issues.
 
  • #67
This thread has run its course and is now closed.
 
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