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Offline m.levert

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speedoflight
« on: 12/09/2007 00:27:30 »
if light goes slower in glass than air, where does the energy come from to speed it back up again on the way out of the glass into air?

why does this not violate the law of conservation of energy?

this is keeping me up at night...seriously, if anyone knows?...


 

Offline syhprum

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« Reply #1 on: 12/09/2007 09:36:30 »
The light travels at normal speed between the atoms in the glass but it is adsorbed by the electron shells around them and then re emitted with a slight delay this is why it appearers to slow down.
When it leaves the glass it encounters very few atoms in the air so travels at almost the correct speed that it does in a vacuum.
 

Offline JP

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« Reply #2 on: 12/09/2007 17:09:08 »
Also, since a photon has no mass its energy is given by the frequency of the light, not its speed.  If it were to lose energy passing through something, you would notice fewer photons coming out the other side, but they'd all still be going at the speed of light.
 

Offline m.levert

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speedoflight
« Reply #3 on: 14/09/2007 03:08:54 »
AHA! very clear,thanks.

that`s a funny thing about photons though, having no mass. presumably, this is why they can go so fast,without experiencing time and mass dilation - so any journey by a photon will take no time whatsoever (from the photon`s point of view)

i hope they find the higgs boson soon, since it may be the key to some kind of mass cancelling technology, enabling light speed travel for solid objects (like a spacecraft)

if you could travel at the speed of light, would you be blind? every light ray would be left behind, and you`d pop out of the light cone into..what? how would you navigate?

if you acheived actual light speed,prsumably the time dilation factor rises to infinity, and the entire history of the universe would flash by in an instant while you`re gone, so when you stop, when and where would you be?

 

Offline lightarrow

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speedoflight
« Reply #4 on: 14/09/2007 12:38:55 »
AHA! very clear,thanks.

that`s a funny thing about photons though, having no mass. presumably, this is why they can go so fast,without experiencing time and mass dilation - so any journey by a photon will take no time whatsoever (from the photon`s point of view)
Photon's point of view doesn't exist.

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i hope they find the higgs boson soon, since it may be the key to some kind of mass cancelling technology, enabling light speed travel for solid objects (like a spacecraft)
Higgs Boson existence would make Special Relativity violated?  I don't think so.

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if you could travel at the speed of light, would you be blind?
You can't. You can (in theory) travel very close to c but not exactly at c.

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every light ray would be left behind, and you`d pop out of the light cone into..what? how would you navigate?

if you acheived actual light speed,prsumably the time dilation factor rises to infinity, and the entire history of the universe would flash by in an instant while you`re gone, so when you stop, when and where would you be?


"When" referred to which frame?
"Where", is a good question. I presume in every place of the universe you want, but the question is: of which universe? Certainly not the one we can observe now, since light travelled for many billions of years from the most distant object we see, to come to us.
 

Offline m.levert

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« Reply #5 on: 17/09/2007 00:59:00 »
hmmm... i just love wild speculation.

i mentioned the Higgs particle/ field since rumour has it that it`s the origin of mass, so i thought it possible that applying a counter-field could cancel out mass and thus inertia, avoiding mass dilation and the law of diminishing thrust returns,thus enabling light speed travel.

of course i realise photons are not concious entities, but still must have objective existence to be affected by other phenomena. recent laboratory experiments have ``slowed down`` photons to almost standstill, which you might think would make them easier to study, but deep mystery still surrounds their functionality.

going back to my first question, if light is transmitted by photons being absorbed and re-emitted by electron shells in order to travel, what happens in vacuum in the absence of matter? they just ``become`` electromagnetic waves?

but what is it that is ``waving``?

also, how is the information in a photon preserved when it supposedly hops from one atom to another? light from a distant object has been re-transmitted billions of times when it gets to the eye so why is absloutely no information   
lost in the process due to accumulation of entropy?

 in what way can it be said to be the same photon?



 

Offline m.levert

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« Reply #6 on: 17/09/2007 01:06:19 »
P.S- i didn`t say at all that the higgs would violate relativity, just that cancelling/dampening the higgs field would eliminate mass therefore sidestepping the issue of dilation at superluminal velocities.
 

Offline lightarrow

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« Reply #7 on: 17/09/2007 11:23:35 »
hmmm... i just love wild speculation.
i mentioned the Higgs particle/ field since rumour has it that it`s the origin of mass, so i thought it possible that applying a counter-field could cancel out mass and thus inertia, avoiding mass dilation and the law of diminishing thrust returns,thus enabling light speed travel.
Good for a science-fiction movie...

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of course i realise photons are not concious entities, but still must have objective existence to be affected by other phenomena. recent laboratory experiments have ``slowed down`` photons to almost standstill, which you might think would make them easier to study, but deep mystery still surrounds their functionality.
I don't understand "photons are not concious entities" and how this could be related to their objective existence. Anyway, photons weren't actually slowed down; what was slowed down is light propagation through a particular medium; it's not the same thing.

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going back to my first question, if light is transmitted by photons being absorbed and re-emitted by electron shells in order to travel, what happens in vacuum in the absence of matter? they just ``become`` electromagnetic waves?
The problem for most of us is that the word "photon" becomes automatically translated in the word "light's travelling particle". In Quantum Mechanics, instead, the word "photon" actually has another meaning, that is, it means "quantum of electromagnetic field". As you see, there's no mention of "travelling particle" in this definition; indeed, this hasn't been proved yet; the main problem comes from the fact it hasn't mass, so it's impossible to define the position operator for such object, that is, it's impossible to define the observable position; translation: it's impossible theoretically to know where it is (and how big it is).

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but what is it that is ``waving``?
Electromagnetic Field. And if you ask: "but what is EM field made of"? I would answer that probably you need to see particles as the origin of everything, otherwise I could ask you: "what particles are made of"? And my answer would be: fields...

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also, how is the information in a photon preserved when it supposedly hops from one atom to another? light from a distant object has been re-transmitted billions of times when it gets to the eye so why is absloutely no information   
lost in the process due to accumulation of entropy?
It depends on which information and on how light is absorbed and then re-transmitted: if you observe a distant star which is located behind a dense cloud of gas and powders, you won't get much information from it.
« Last Edit: 17/09/2007 11:28:48 by lightarrow »
 

Offline Soul Surfer

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speedoflight
« Reply #8 on: 17/09/2007 12:41:29 »
Let me just clarify this absorption and reemission process as light travels through a dense transparent medium like glass.  The fact that the material is transparent means that the light photons do not interact with the electrons and nuclei in any significant way i.e most of the photons cannot permanently affect the electrons and atoms in any way so these absorptions and emissions are limited by the uncertainty principle which mans that the light photon must come out after a short delay in essentially the same direction that it went in.

The electromagnetic wave requires no conventional medium to propagate itself because a moving electrical charge creates a magnetic field and a changing magnetic field creates an electrical charge so you can visualise the energy in the field constantly changing between electrical fields and magnetic fields as the wave propagates.
 

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speedoflight
« Reply #8 on: 17/09/2007 12:41:29 »

 

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