Why is the speed of light what it is?

[Dadface]

http://cds.cern.ch/record/618057/files/0305457.pdf
This may be a useful source of relevant information.

 

[OldYat47]

Look up the Lorentz transform. There are excellent articles that explain why the speed of light is constant for all observers even if their individual frames of reference are moving at different velocities.

 

[AgentSmith]

This statement is correct for dimensionless physical constants like the fine structure constant.
However, it's not correct for $c$; its value was chosen by a committee.

The committee did not pick a value out of thin air. It was ultimately based on experimental values.

 

[Nugatory]

The committee did not pick a value out of thin air. It was ultimately based on experimental values.

To be precise, it was chosen to fall within the error bars of the previous definition of the meter. There's a conceptual shift here, in that earlier experimental measurements of the speed of light are reinterpreted as measurements of the length of the meter.

 

[AgentSmith]

deleted OP

To be precise, it was chosen to fall within the error bars of the previous definition of the meter. There's a conceptual shift here, in that earlier experimental measurements of the speed of light are reinterpreted as measurements of the length of the meter.

I know that. But still the new definition had to fit within experimental results. (We could and have set it to 1, but there would be a ripple effect.)

 

[Dale]

But still the new definition had to fit within experimental results.

No, it didn’t. They chose to have it fit within the error range of previous experimental results, but they most certainly did not have to. They chose to keep it within previous experimental ranges for convenience, but if they had decided to be inconvenient then they could have chosen any arbitrary value whatsoever.

There is simply no way to get an exact value through experiment, and c is an exact value in SI units. It is purely the outcome of a committee.

 

[AgentSmith]

No, it didn’t. They chose to have it fit within the error range of previous experimental results, but they most certainly did not have to. They chose to keep it within previous experimental ranges for convenience, but if they had decided to be inconvenient then they could have chosen any arbitrary value whatsoever.

There is simply no way to get an exact value through experiment, and c is an exact value in SI units. It is purely the outcome of a committee.

No way to get an exact value through experiment. Glad you're here to tell me these things, professor. Of course they could have chosen any value whatsoever, but that would be pretty d**m stupid. Ya think there is a reason they chose not to be stupid?

 

[Dale]

No way to get an exact value through experiment. Glad you're here to tell me these things, professor.

Me too, thanks!

Of course they could have chosen any value whatsoever,

Good, you understand. The value of c in SI units is not experimental.

but that would be pretty d**m stupid. Ya think there is a reason they chose not to be stupid?

Sure, there were lots of great reasons to not be stupid. But anyone working with committees knows that they are fully capable of being stupid anyway.

 

[Vanadium 50]

Glad you're here to tell me these things, professor. Of course they could have chosen any value whatsoever, but that would be pretty d**m stupid. Ya think there is a reason they chose not to be stupid?

You do know that the 1799 definition of the meter was known to be incompatible with the 1798 definition? So historically there have been examples of "pretty d**m stupid".

 

[AgentSmith]

You do know that the 1799 definition of the meter was known to be incompatible with the 1798 definition? So historically there have been examples of "pretty d**m stupid".

We are now into the 21st century. Hopefully we have progressed a bit.

 

[phinds]

We are now into the 21st century. Hopefully we have progressed a bit.

Ah, you optimist you.