# Speculations on the variable speed of light

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I speculate that my physics professor was correct sixty years ago about the variable speed of light.

The evidence he showed us was a simple nine-dollar magnifying glass.

He said light goes slower in glass than in air, and that's why its path is bent in the lens.

I don't have any mathematics on that, nor any other evidence. It just makes sense.

Maybe he had some more to show us on that, but he didn't.

Maybe he had some math on the subject, but he didn't show it to us.

But I speculate he was right. And if he wasn't, nobody ever showed up to tell us any different.

And here's a further speculation: WestStar is going over half the speed of light away from CenterStar.

EastStar is going over half the speed of light away from CenterStar in the other direction. And yet the light from EastStar arrives at WestStar at the speed of light. Hmmmmmmm? Come to think of it, that same physics professor told us this story that same day over sixty years ago.

I therefore speculate that we don't know everything about the speed of light in all circumstances.

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Light travels at c in a vacuum. Through a medium, the propagation speed slows down.

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If I say light is slowed down in a medium, that is speculation, because I have no supporting evidence.

But now that you-all tell me so, it is no longer speculation, but settled science.

And since you tell me light travels at c in a vacuum, that is settled science as well.

In the professor's three-star story, does the same light travel at c RELATIVE to all three stars? He said it does, so that makes it sixty-year settled science, but what does it MEAN?

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Light travels at c in any inertial frame. Because of this, time and distance are relative, rather than being absolute.

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The real question is why does it go slower in glass than in air than in vacuum ??.

Perhaps light travels at the same speed always.

Perhaps a photon suffers delays as it passes through atoms.

Perhaps delays are due to bendings (ie longer path), or due to absorption & later emission (ie longer path).

Bending is supposedly explained by waves. But it is equally explained by every photon having an effective width & height (& length).

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Light travels at c in a vacuum. Through a medium, the propagation speed slows down.

the impact of light on a concert wall does it !~ no? so any substance contenting mass has the ability to do So !

I'm I Ok ?

Edited by Roger Dynamic Motion
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the impact of light on a concert wall does it !~ no? so any substance contenting mass has the ability to do So !

I'm I Ok ?

Was that Pink Floyd?

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Sounds more like Wild Man Fischer to me.

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The real question is why does it go slower in glass than in air than in vacuum ??.

Perhaps light travels at the same speed always.

Perhaps a photon suffers delays as it passes through atoms.

Perhaps delays are due to bendings (ie longer path), or due to absorption & later emission (ie longer path).

The quantum explanation is that photons are absorbed and re-emitted (and travel at c between the atoms).

The classical explanation is that the speed of light changes because of the different permittivity and permeability.

Bending is supposedly explained by waves. But it is equally explained by every photon having an effective width & height (& length).

The classical explanation is because the waves change speed.

The quantum explanation has nothing to do with the size of the photons but is rather more complex. I recommend Feynman's lectures on QED - available as a book or you can find videos online of him explaining it.

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I speculate that not every aspect of the speed of light is regarded as "settled science".

It has been delightful to read some different opinions on the subject.

Anyone remember the old science fiction story about "slowglass" -- thru which it supposedly might take YEARS for light to pass? Fun! Speculation!

Swansort,

"Inertial frame". Is that anything that has mass and that thereby might have inertia?

See, that is what got us off a century or two ago into the "aether" sidepocket.

What you say is no doubt correct.

The Aether thing (except poetically!) has been proven wrong.

Please offer the appropriate explanations for us new guys.

Edited by frankglennjacobs@gmail.com
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"Inertial frame". Is that anything that has mass

Please offer the appropriate explanations for us new guys.

Yes massless particles follow null geodesics. A null geodesic is not an inertial. Inertial frames are your spacelike geodesics.

Edited by Mordred
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The Aether thing (except poetically!) has been proven wrong.

Er, yes it has.

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