What happens when light stops?

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The problem with that is that photons don't accelerate. They are created travelling at the speed of light.
 
James R,

Obviously, when electrons emit photons the electrons are not moving at light speed. I also doubt that photons are actually bouncing off the inside of electrons at light speed before they are emitted. Therefore, the photons accelerate to light speed as soon as they are emitted.

Tom
 
Joeblow,

Your conclusions don't follow from your premises. No, the electrons are not travelling at light speed. But photons don't exist "inside" electrons - that's not how photon emission works. As I said, photons are created travelling at light speed.
 
James R,

You're not making sense.

Please explain how a particle(electron), moving at velocity much slower than light, can emit a second particle(photon), which travels at the speed of light, without the second particle having to accelerate to the speed of light. Is it magic!!??

Tom
 
I'm sure James R will differ in understanding, but from what I've deduced in theory, an electron is just a matrix of photons anyway. (A photon collaberation caused by blackhole acceleration/compression)

From the information I've obtained, what you see appears slower than it actually is. (thats why if an atom is split it releases so much energy)

I think how James R meant wasn't that a photon was absorbed, but it creates a Quanta Ripple that's re-applied during an impact.
(The Photo-Electric effect)

Of course feel free to correct.
 
Joeblow (can I call you Tom?),

<i>Please explain how a particle(electron), moving at velocity much slower than light, can emit a second particle(photon), which travels at the speed of light, without the second particle having to accelerate to the speed of light. Is it magic!!??</i>

As I said before, the photon does not exist inside the electron, so it doesn't have to travel at the same speed as the electron at any time. It is created travelling at the speed of light.

Any particle with zero rest mass is constrained to travel at the speed of light, always. It cannot slow down or speed up (accelerate) by any mechanism.


Stryderunknown:

An electron is not made up of photons.
 
Hi all,

I'd like to add something to James R's post:

"As I said before, the photon does not exist inside the electron, so it doesn't have to travel at the same speed as the electron at any time. It is created travelling at the speed of light."'.

Joeblow, what you are probably asking yourself is where the photon comes from then. The answer is quite simple actually: photons can be created from the energy the electron has. More important, the photon's speed is the same for all observers. This means that regardless of the speed of the object the photon originated from, it will always travel at lightspeed.

Stryderunknown,

Care to elaborate how you've come to the conclusion that electrons consist of photons ? At the moment, the general accepted theory is that the electron is one of the fundamental particles (along with the quarks and other leptons).

Bye!

Crisp
 
James R,

Sure you can call me Tom.

First, you still didn't explain how one particle which is not traveling at light speed can create a particle which is traveling at light speed without the created particle having to accelerate. As Crisp pointed out, the photon could have been created from the electron's electric field. If that was the case, the electric field would have to be composed of particles that are traveling at light speed already. Unfortunately, I believe the electric field of an electron is stationary, so Crisp's idea would not apply.

You also stated that since a photon has no rest mass, it must travel at light speed. Why can't a massless particle just float around?

Last but not least, this whole discussion is about the acceleration of photons. If you don't take the creation of a photon into consideration, a photon decelerates as it enters a denser material, such as glass, then accelerates back to light speed as it exits the material. What force do you believe causes this acceleration?

Tom
 
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Tom,

<i>As Crisp pointed out, the photon could have been created from the electron's electric field. If that was the case, the electric field would have to be composed of particles that are traveling at light speed already. Unfortunately, I believe the electric field of an electron is stationary, so Crisp's idea would not apply.</i>

The electric field is not made of particles. I don't really want to get into exactly what a field is right now, though, so let's stick with photons. Photons are created from <b>energy</b> that the electron has for whatever reason. That energy can be electromagnetic or kinetic, or some other type. Photons are not created inside the electron, since the electron (as far as we know) is structureless and dimensionless. Instead, photons are created out of the vacuum using the energy of the electron. They are created travelling at the speed of light.

<i>You also stated that since a photon has no rest mass, it must travel at light speed. Why can't a massless particle just float around?</i>

I'm not sure exactly, but feel free to check on my statement if you doubt me. Massless particles always travel at the speed of light. I'm pretty sure there are relativistic reasons for that. There is no such thing as a stationary photon.

<i>If you don't take the creation of a photon into consideration, a photon decelerates as it enters a denser material, such as glass, then accelerates back to light speed as it exits the material. What force do you believe causes this acceleration?</i>

Photons do not accelerate or decelerate in glass. What happens is that photons are constantly absorbed and re-emitted by glass atoms. There is some delay between absorption and re-emission, which means the photons take longer to pass through glass than they do to pass through a vacuum of the same length. Between glass atoms, photons travel at the usual speed - the speed of light in a vacuum.
 
Hi all,

"Massless particles always travel at the speed of light. I'm pretty sure there are relativistic reasons for that. There is no such thing as a stationary photon."

Indeed, a massless particle can always be reduced to a photon - since massless implies that the particle consists only of energy (which is manifested only as photons). We know that photons travel at lightspeed hence all massless particles travel at lightspeed ;).

"As Crisp pointed out, the photon could have been created from the electron's electric field. If that was the case, the electric field would have to be composed of particles that are traveling at light speed already. Unfortunately, I believe the electric field of an electron is stationary, so Crisp's idea would not apply. "

I never talked about an electric field. As James R correctly pointed out, I was refering to particle creation from whatever energy the electron might have. And also, electric and magnetic fields are observer-dependant, and only in the electron's frame of reference is its electric field stationary. All other observers will see an electric and magnetic fields produced by the electron.

Bye!

Crisp
 
Crisp,

"Indeed, a massless particle can always be reduced to a photon - since massless implies that the particle consists only of energy (which is manifested only as photons). We know that photons travel at light speed hence all massless particles travel at light speed"

You assume that since a photon doesn't have mass, it isn't matter. Gravity does not have to be a characteristic of all matter. You also didn't indicate why a massless particle must only travel at light speed.

This whole discussion is about a misunderstanding. You and James R believe that a photon is pure energy, and therefore can do "magical" things. I, on the other hand, believe that a photon is a particle, and is therefore it is matter, even though it's gravitational field is ignored(curved space crap). I believe that energy can't exist without matter, energy is a characteristic of matter. Therefore in order for the matter in a photon to reach light speed it must accelerate, or be created from matter that is already at light speed.

Tom
 
I on the other hand believe that mass is frozen energy (matter myth, Paul Davies)
 
Imahamster,

Interesting link. Maybe you can store energy this way(photonic battery).

Tom
 
Crisp:

I disagree that the photon is the only massless particle. What about gluons, for example? I also disagree that photons are "pure" energy, whatever that is. Photons are electromagnetic entities.


Tom:

<i>I, on the other hand, believe that a photon is a particle, and is therefore it is matter, even though it's gravitational field is ignored(curved space crap).</i>

A photon is a particle, but it is not matter. It is a gauge boson. Matter has (rest) mass. A photon should also have a gravitational effect, though a tiny one.

<i>I believe that energy can't exist without matter [etc.]</i>

I would say energy is a property of a <i>system</i>, not a particular particle of matter (e.g. consider potential energy).
 
Hi all,

James R,

"I disagree that the photon is the only massless particle. What about gluons, for example? I also disagree that photons are "pure" energy, whatever that is. Photons are electromagnetic entities. "

Hrm, didn't know that gluons have zero mass. I knew I shouldn't have skipped that part when studying for my elementary particles exam ;).

You say photon's are electromagnetic entities. Isn't this a bit circular reasoning ? An electromagnetic field consists of photons (e.g. the Coulomb force is mediated by photons), so defining photons as electromagnetical entities makes the definition of an electromagnetic field kinda hollow. However, I agree with your point that the term "pure energy" can be misleading; it is also not entirely what I meant to say in my previous post - I tried to point out that a photon only manifests itself in the form of energy, e.g. in absorption or emission phenomena. So IMHO for all practical purposes we can say that a photon consists of energy (even though energy is a fictous concept, something man made up for easing calculations). The deeper underlying structure can probably be found in QED with photonfields.


Tom,

"You assume that since a photon doesn't have mass, it isn't matter. "

Exactly. I consider matter to be objects that have restmass, which a photon doesn't have.

"Therefore in order for the matter in a photon to reach light speed it must accelerate, or be created from matter that is already at light speed. "

If matter were to travel at lightspeed, that would violate the theory of special relativity, which we assume to be correct. Concerning the acceleration of photons: Why should it accelerate in the first place ? A new particle is created, of which we know it travels at lightspeed. There's no need for acceleration complicating the description we have at the moment.

Bye!

Crisp
 
check out National Geographic, october 2001

Scientist Lene Hau brings a laser-beam to a stop with some kind of gas.
 
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