Questions you'd like answering, regardless of how trivial they may seem

[laurentian]

Who says it has stopped?

If it slows by just a metre per second per year, that is probably beyond our current capability to measure.

Universe is approximately (and, I guess, arguably) 13.8 Billion years old so slowing at 1 m/s per year down to where we are now would mean it would have been, well, bloody fast at the beginning of the universe!

I am far from an expert on this but I would imagine that even a small reduction in the speed of light (and all electromagnetic waves) would have been detected and probably have caused us lots of problems . . . but then its all relative so . . .

 

[ebikeerwidnes]

but if it slows down, then how long is a metre?

basically, it is one of the fixed constants of the Universe
so other things are measured by it

so a meter is the distance travelled by
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of ⁠1/299792458⁠ of a second, where the second is defined by a hyperfine transition frequency of caesium.[2]

so if light slows down then the metre shrinks as it is a man made definition rather than a physical constant based on nature

 

[Profpointy]

Who says it has stopped?

If it slows by just a metre per second per year, that is probably beyond our current capability to measure.

I'd have thought that would easily show up in observations of the distant, ie a long time ago, universe as the physics would show very differently if one of the key (so say) constants of nature varied significantly. I've not done the calculations, and would struggle to think of where to start, but I would he surprised if this wouldn't have been the subject of papers pretty much as soon as the constancy of the speed of light was mooted

 

[FishFright]

in a vacuum

true

So there is an arguement that in the very early universe whcih contained alll matter/energy already was much denser than a vacuum so the speed of light was indeed different .

I've not seen any models that show this yet so it remaind conjecture on my part

 

[Ming the Merciless]

wouldn't that imply that it is constantly slowing over time?

It would imply nothing about a rate of decline in the speed of light. Why assume it’s a constant deceleration? We have not been measuring the speed of light for that long in the scheme of things. How many times have we actually measured it?

 

[laurentian]

So there is an arguement that in the very early universe whcih contained alll matter/energy already was much denser than a vacuum so the speed of light was indeed different .

I've not seen any models that show this yet so it remaind conjecture on my part

Would that not be a different speed due to the interaction of light with the matter (refractive index) as opposed to a change to the speed of light itself?

 

[FishFright]

Would that not be a different speed due to the interaction of light with the matter (refractive index) as opposed to a change to the speed of light itself?

Honestly I don't know .

 

[laurentian]

Honestly I don't know .

Nor me! Though I do find this stuff fascinating and try my hardest to understand it all