Light Speed

The non amateur stuff. Hawking, black holes, that sort of thing

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Cliff
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Light Speed

Post by Cliff »

Dear al(L)
I have happily taken it for granted (for longer that I want to remind myself) that the speed of light is approximately 300,000 kps ie roughly 186,000 mps in a vacuum.
However, in recent times I have felt a bit puzzled because from what I gather space isn't a true vacuum.
So does anyone really know what the speed of light might really be in a true vacuum?
Best wishes from Cliff

stella
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Post by stella »

Yes, the velocity of light in a vacuum is 299,792.458 km/sec.

joe
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Post by joe »

I wonder what the differences are between a vacuum (in the laboratory, for example) and a true vacuum and whether those differences are anywhere near enough to have an effect on light speed? Maybe over vast distances, if anything.
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Steve Young
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Post by Steve Young »

OK so if the speed of light is different between travelling in air and in a vacuum it makes me wonder what is happening when propagating through air or in something close to a vacuum.
Presumably in any fluid or solid for that matter it is a full vacuum between the particles so do the photons travel at full vacuum speed between particles and slow down on encountering one and then speed back up on passing (?) the particle. Where does the energy for the acceleration come from?
Makes you think doesn't it, well it does me anyway !?

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Post by joe »

Steve Young wrote:do the photons travel at full vacuum speed between particles and slow down on encountering one and then speed back up on passing (?) the particle.
A photon is absorbed by the particle and then re-emitted. There is no deceleration/acceleration, as far as I'm aware, although, I think I may have read somewhere about "particle recoil" when a photon is emitted.
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Steve Young
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Post by Steve Young »

So if there is no deceleration/acceleration involved then why is the speed in different materials different?. The particles of the material may as well not be there if they don't affect the speed of the photon.
An opaque material stops all photons, (does it get warmer or heavier), a transparent material passes all? Photons but slows them down, but then they speed up again after passing through?.
Sorry for the rhetorical questions, I regularly read this forum with great interest, lots of questions but no answers!
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Cliff
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Post by Cliff »

Dear Stella, Steve and Joe
First, thanks Stella for stating an accurate speed for light in a vacuum.
That said in my current state of bloody mindedness, I'm inclined to say that I'm not convinced that stated speed is true. My current state of bloody mindedness is telling me that astrophysicists and cosmologists are digging themselves into a sort of hole.
Could the speed of light in a real vacuum actually be infinitely fast - although I cann't help thinking that would cause other compllications
Steve and Joe, my knowledge of astro-physics, cosmology and the associated mathematics is very limited. That said ???
I like to think I have, or at least though I did have a reasonable grasp of newtonian mechanics in my younger days and could and indeed still can accept many aspects of relativity theories (I only say many aspects because there are probably numerous other things about relativity I don't have a clue about.
However, in recent years I have become more sceptical about various aspects of modern astro-physics and cosmology.
My one time faith in mathematics has taken a battering (though not completely demolished because of my own limitations preventing me demolishing it.
However, for quite a long time I have thought it possible that the supposed constants of physics aren't really constant at all.
Although being limited in mathematical ability, which makes me feel inadequate to suggest it, I'm inclined to think that the Universe is not mathematically knowable. I might be inclined to suggest that the universe is 50% mathematically knowable and 50% otherwise knowable (but not using mathematics), or not knowable. However, that would suggest the 50% unknowable bit has some sort of mathematical function ie even if that is only in being 50%.
So I'll say that the universe is 50% mathematical and some otherwise indefinable amount non-mathematical.
However, if that is the case then arguably if the non-mathematical part isn't exactly 50% then the mathematical part cann't be 50%. If that is the case then I might argue the indefinable mathematical part isn't truly mathematical either.
I suppose one way out of my silly conundrum might be to introduce the idea of three parts (instead of only two) let's say, a mathematical part accounting for say a third of the the whole and an ill defined second part making up the weird difference between my rigidly mathematical part (which I arbitarily opted to be exactly a third of the whole) and the non-mathematical part.
I hope you'll excuse me talking the above nonsense, it's just my crude way of trying to justify what might be unjustifiable ie my thought that maths cann't analyse everything and going even further that we'll never know the answer to everything.
As well as that my other current thinking is that good old relativity is still pretty good but possbly needing modifying with a touch of MOND (modified newtonian dynamics).
Now I may well be wrong but it seems a nice simplistic way of semi-understading our universe, whilst accepting we'll never understand everything\anything properly.
Just one other thing at the smaller extremes, we'll never know whether the ultimate bits are particles, strings or waves or whatever but they'll always be nothing better understood than "ultimate bits".
Best wishes from Cliff
PS Who needs Dark Matter Dark Energy and who knows what else - they're just a pain in the bum perhaps.
PPS - 30% mathematical, ?% otherwise knowable and ?% non-knowable.
The two ? marks adding up to 70% of course ! but neither ? being ever known.

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