Why doesn't light go faster than c?

[Neandethal00]

hi,
it's my first post in this forum so I hope I'm in the right section. I've asked three different physics teachers in my high school an explanation for this to no avail. if acceleration is inversely proportional to mass, and photons have no mass, why don't they have infinite acceleration? in other words, what poses a boundary to the speed of light?

I'm not sure if anyone before pointed out another definition for speed of light which depends on the properties of EMPTY SPACE, permittivity (e_o)and permeability (u_o).

c = 1/SQRT(e_o*u_o) = 3x10⁸ m/sec (current value)

If we half the current values of each, permittivity and permeability,

c = 6x10⁸ m/sec

If we double the current values

c = 1.5 x 10⁸ m/sec

If we lower the current values by 10 times

c = 3x10⁹ m/sec.

In other words, you have to go to another universe with different space-time properties to have higher or lower speed of light in VACUUM.

 

[Danger]

In other words, you have to go to another universe with different space-time properties to have higher or lower speed of light in VACUUM.

That's a cool post, which I can't even begin to understand. Your mention of vacuum, however, demands that you specify which light speed you refer to. Photonic speed and 'group velocity' are different. An individual photon travels at c regardless of the medium. It's the collision with atoms factor that impedes propagation of the 'beam'.

 

[Neandethal00]

Your mention of vacuum, however, demands that you specify which light speed you refer to. Photonic speed and 'group velocity' are different. An individual photon travels at c regardless of the medium.

http://upload.wikimedia.org/wikipedia/commons/2/27/Frontgroupphase.gif

red dot --> front velocity
green dot --> group velocity
blue dot --> phase velocity

I see, physicists have now a new velocity in addition to phase and group velocity, it is 'front velocity', which is 'c' for light. Note, group and front velocity in the picture are equal.
ε_o and μ_o are the lowest in vacuum but higher in transparent objects.

I must admit, I exaggerated a bit when I said 'you have to go to another universe'. Because there are some experiment where they have found the 'space' is not completely isotropic in all directions from earth. Speed of light may be different in different regions inside the universe.

 

[Danger]

It might be because I just finished my 31st beer, but that animation did nothing for me other than to make my eyes go wonky.
The beer store might be closed today, so I have an emergency stash of Ballantine's that I'm about to crack open. Perhaps that will be more conducive to my understanding of the subject.

 

[YummyFur]

@Danger, splendid.

@DarioC, it's not just the little round balls, it's the whole wave/particle concepts. Waves and particles were words coined to describe quantum objects long before the whole concept of a quantum object was even the tiniest spark in someone's mind.

Which is why they hunted the ether, because really speaking a wave MUST have a medium because that is what a wave is. Same with 'particle', it a very very very tiny little bit of something, just as Democritus supposed.

So a quantum object is not a wave at all never was never will be, and as for particle, that's just a word that we call bits of atoms, but it's not the same word in the sense of its meaning as say the other way we use particle in the classical world.

Therefore when someone asks the question is a photon a particle or a wave, they are referring to the classical meaning of the words. They must be because they would not ask the question otherwise.

A photon when it displays an interference pattern is not really even behaving like a wave, because it can't. What it could be said to look as if it's doing is behaving as if it was a classical object in some sort of substance and this substance glowed like light and interfered with itself just like a water wave does. But of course there is no substance that's waving, so it's not like that at all and really speaking it can't be.

What is interfering then? Really no one knows. That is just the same as asking 'what is a photon really'. Which is an invalid question. I might snip out a bit from one of Feynman's lectures and post his answer to the 'is it a wave or particle' question.

 

[sophiecentaur]

@Danger, splendid.

@DarioC, it's not just the little round balls, it's the whole wave/particle concepts. Waves and particles were words coined to describe quantum objects long before the whole concept of a quantum object was even the tiniest spark in someone's mind.

...

That is just the same as asking 'what is a photon really'. Which is an invalid question. I might snip out a bit from one of Feynman's lectures and post his answer to the 'is it a wave or particle' question.

That's all quite true and anyone who demands an answer to advanced questions in elementary terms will usually be disappointed.

But it has to be true to say that the wave model explains a lot of phenomena very well so it is well worth using. (Which is more than can be said for the bullet model).

 

[my_wan]

I must admit, I exaggerated a bit when I said 'you have to go to another universe'. Because there are some experiment where they have found the 'space' is not completely isotropic in all directions from earth. Speed of light may be different in different regions inside the universe.

Yes. In General Relativity the speed of light light is not an absolute constant but in some sense varies with gravitation depth. However, since gravitation depth also determines determines the spacetime metric for local observers the local speed of light is always constant at all gravitational depths. You can also have two observers, both in flat spacetime, which nonetheless have differing gravitational depths. The easiest example is an observer inside a uniform massive hollow sphere such that no gravitational acceleration is locally present. Yet this observer will still be gravitationally time dilated by the same amount as an observer on the surface where gravitational acceleration is at a maximum.

This implies that the observer in another Universe with a higher or lower speed of light may still measure their local speed of light as the same constant we do. No different from the speed variability under General Relativity.

 

[YummyFur]

this is Feynman's take on the wave/particle thing http://youtu.be/7HKOm8fffgU

 

[OCR]

I know that definitions are difficult when discussing this type of subject matter , and maybe this is being 'picky', however...

Speed of light may be different in different regions inside the universe.

Using the word inside, wrt 'the universe', also seems to imply an outside, wrt 'the universe'.

I believe the common thinking is, there is no outside... the universe.

Maybe a better way to express the thought would be...?

"Speed of light may be different in different regions of the universe".




Again, definitions...

Same with 'particle', it a very very very tiny little bit of something, just as Democritus supposed.

A 'bit of something' could depend on how the definition of the word 'particle' is applied.

http://en.wikipedia.org/wiki/Particle

http://en.wikipedia.org/wiki/Elementary_particle

By the bye... your name is somewhat disturbing on a couple of different levels, and

I can't figure out which one I like best

I have absolutely no ambiguity about that... lol



OCR

 

[YummyFur]

A 'bit of something' could depend on how the definition of the word 'particle' is applied.
OCR

Like this for example...

...and as for particle, that's just a word that we call bits of atoms, but it's not the same word in the sense of its meaning as say the other way we use particle in the classical world.

 

[Danger]

I have absolutely no ambiguity about that... lol
OCR

Oboy...
At least one of you had damned well better be female, or I'll never live this down.

 

[YummyFur]

Ok, it's a comic by cartoonist Chester Brown, circa early 90's.

 

[YummyFur]

As opposed to non quantum terms?

 

[Neandethal00]

I know that definitions are difficult when discussing this type of subject matter , and maybe this is being 'picky', however...

Using the word inside, wrt 'the universe', also seems to imply an outside, wrt 'the universe'.

I believe the common thinking is, there is no outside... the universe.

Maybe a better way to express the thought would be...?

"Speed of light may be different in different regions of the universe".


OCR

I hesitated a few seconds before using the words inside universe.
But then again, I'm one of those few people who 'thinks' (not believe)
the universe if finite.

 

[rcgldr]

One puzzling issue is the fact that photons are emitted from electrons at c, inspite of the velocity of the electrons. In the case of lasers, the photons are emitted with the same velocity (and phase?) as the photons that triggered the release.

Regarding acceleration, light curves in gravitational fields, which is acceleration in terms of the direction of velocity so there is acceleration in a Newtonian universe. Can the curving only be explained in GR?

As a side question, how long does it take for an electron to emit a photon (it seems it would be related to the size of a photon / c), and transition to a lower energy state?

 

[Danger]

Regarding acceleration, light curves in gravitational fields, which is acceleration in terms of the direction of velocity

I'm not sure that you can count that as an acceleration, since the light 'perceives' its path as a straight line. It doesn't curve within space; the space itself is curved.