Speed C is Dependant Upon Source?

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The discussion centers on the nature of light and its speed, asserting that the speed of light is constant and not influenced by its source. Participants explore the implications of light reflecting off surfaces, questioning whether this reflection affects its speed or merely its direction. It is clarified that when light hits a mirror, it is absorbed and re-emitted, which does not change its speed but may involve momentum transfer. The conversation also touches on the principles of relativity, emphasizing that light's speed remains constant regardless of the motion of the source or mirrors. Overall, the dialogue aims to deepen understanding of light's behavior in relation to physics concepts like reflection and momentum.
  • #31
urtalkinstupid said:
Where does this newly emitted photon come from, if it travels in the opposite direction of the absorbed photon?

It doesn't necessarily travel in any direction. When you shine a light on a wall the photons get absorbed then emitted any which way (which is why the whole room lights up).

And you were already told it comes from the energy given to (whatever the incident photon hit).
 
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  • #32
no, alkatran. creating isn't the same as emitting! according to tom, the mirror absorbs the photon and then that energy is given back off in the form of another photon. there is conservation, not creation. to create the photon, the mirror would have to create the energy itself, and it doesn't. it just gives it back off.
 
  • #33
beatrix kiddo said:
no, alkatran. creating isn't the same as emitting! according to tom, the mirror absorbs the photon and then that energy is given back off in the form of another photon. there is conservation, not creation. to create the photon, the mirror would have to create the energy itself, and it doesn't. it just gives it back off.

You just keep on twisting those words, alright?

My point was that you're arguing your point based on an obvious mis-wording.
 
  • #34
what words am i twisting, tran? u're the one who told me that we can all look at creation and emission as the same thing. i was arguing u on that, not tom's mis-wording...
 
  • #35
beatrix kiddo said:
what words am i twisting, tran? u're the one who told me that we can all look at creation and emission as the same thing. i was arguing u on that, not tom's mis-wording...

I said they could be seen as the same thing. But fine, you know what? Just to end this argument: I was wrong. There, now get on with the main topic.
 
  • #36
Hopeless. Quantum transactions are not the same as logical operators.
 
  • #37
the guy said that the photon was absorbed... he also said the it was destroyed in the absorbtion... he said that this exites the electrons, causing one to raise to a higher field, thus becoming unstable, and emmiting a new photon...

what a buch of confusing nonsense... if the speed of light cannot be changed, then tell me what is happening in a prism.

the speed of light CAN be changed as long as it is returned to it's original speed. the photon passes through the glass, hits the silver backing and is stopped. the ENERGY not the PHOTON is absorbed. the energy is then emmited back to the photon and it travels back through the glass at speed c...

there is no need to nuke this... no need to over explain. occhams razor will stand strong
 
  • #38
Kiddies,

When a photon is absorbed, it is destroyed. It ceases to exist. It is no more. It is an ex-photon.

Conversely, when a photon is emitted, it is created at the moment of emission.

urtalkinstupid said:
Thank you for explaining, Tom. I thought matter or energy could not be created nor destroyed?

All the energy is accounted for at all times. An unperturbed atom has energy E1 at time t1. A photon of energy Eγ comes in and promotes an atomic electron to a higher energy state
E2. Conservation of energy demands that E2=E1+Eγ.

Yes, I have taken chemistry. I owned at chemistry! I'm taking Chemistry II AP this coming school year.

OK, so check out the solar system model of an atom. It's a very crude approximation, but it will at least give some mental image of the promotion and de-excitation of an atomic electron (it goes from a lower orbit to a higher one, and back again).

So the excitation of an electron causes decay. What kind of decay is this called? When an electron goes into decay it produces photons? Is that the only product of this decay?

It is an electromagnetic transition of the atom. By the way, it is the atom that decays, not the electron. Electrons are stable. And yes, the photon is the only new particle that is created.
 
  • #39
I'm taking Chemistry II AP this coming school year.

I hope its not as hard as AP Chem II at my school! I didn't take it, but my friends (they use to like chem) who did told me it made their lives a living hell. They had complete labs with full lab write ups due every other day. Not that its a hard subject, I think its just the teacher. :wink:
 
  • #40
Haha, that Chem II AP at your school sounds like the BIO II AP I just took this year. Full labs with a write up on each one. Only grades were labs and tests. Haha, average of class was like 60 or 70, but I managed to keep an A. Chem II AP at our school is supposed to be hard as *%(#. :cry:

Tom:
Anyways, How does the new photon know exactly which direction to go in order to reflect the image? Does it take the vector of the destroyed photon and reverse it? I know about electrons and them absorbing energy. I was simply saying what you were saying. So, I'm assuming it is just photon and energy that is created. Are you also saying that anything that is completely absorbed, all of its energy is destroyed? Essentially the photon isn't destroyed, just it's energy is passed on. I don't know.
 
  • #41
tom, it hurts my feelings when u call me kiddie... atleast make it kiddo..

u really shouldn't use words like created or destroyed, though, because it gives a false representation of what is occurring on the mirror. a photon is energy release. since no energy gets created or destroyed, then, technically, the photon really isn't destroyed either. absorption and emission cannot be viewed as destruction and creation.
entropy, chem II ap at our school is pretty hard. the teacher is nice and all, but she gives really hard tests, and labs, etc. (i am taking it next yr... but this is what I've heard from her former students)
 
  • #42
urtalkinstupid said:
Anyways, How does the new photon know exactly which direction to go in order to reflect the image?
A photon doesn't "know" anything. Conservation of momentum dictates in which direction the atom will emit the photon.
So, I'm assuming it is just photon and energy that is created. Are you also saying that anything that is completely absorbed, all of its energy is destroyed? Essentially the photon isn't destroyed, just it's energy is passed on. I don't know.
The photon is destroyed when it is absorbed, but the energy doesn't vanish, its incorporated into the atom that absorbed it. It manifests itself by the electron jumping to a higher energy level.
 
  • #43
urtalkinstupid said:
Anyways, How does the new photon know exactly which direction to go in order to reflect the image?

Ignoring the creation and destruction of photons for a minute, and just focusing on the photon states before and after the reflection, there is a total momentum and total energy in each state. In other words, this annihilation and creation of photons has to take place under the same constraints as a collision. The conservation of momentum in the direction parallel to the mirror imposes one constraint, and conservation of energy imposes another (the photon energy is unchanged in the reflection). That means that the momentum of the photon normal to the mirror can only be equal and opposite to the original normal component.

So now your question can be reduced to "Why are energy and momentum conserved in the process of reflection?"

And the answer is: "Because that's the way it is."

Are you also saying that anything that is completely absorbed, all of its energy is destroyed?

Not destroyed, but converted. It is transferred to the atom in the form of a promoted electron.

Essentially the photon isn't destroyed, just it's energy is passed on. I don't know.

The photon is destroyed. For as long as the excited atomic state exists, there is no photon. A new photon is emitted when the atom de-excites.
 
  • #44
beatrix kiddo said:
tom, it hurts my feelings when u call me kiddie... atleast make it kiddo..

Lighten up, kiddo. :wink:

u really shouldn't use words like created or destroyed, though, because it gives a false representation of what is occurring on the mirror.

No, it doesn't. And I use those words because those are the words that are used in quantum field theory, which is the best theory we have for the interactions between photons and electrons.

Actually, it's the best theory we have, period. (It has been verified to 10+decimal places).

a photon is energy release. since no energy gets created or destroyed, then, technically, the photon really isn't destroyed either.

No, the photon "technically" is destroyed. If it were not, then the atom could not be promoted to a higher energy level.

absorption and emission cannot be viewed as destruction and creation.

Can too. :-p
 
  • #45
Tom Mattson said:
Lighten up, kiddo. :wink:

hehehe...

i still disagree. i mean a photon is energy right? well if the energy isn't destroyed then the photon isn't destroyed. maybe stewarta is correct. maybe the photon gets stopped by the mirror and then the photon is accelerated at c, back off the mirror.
 
  • #46
Oh, no, Janna, that is contradicting with the constancy of light's velocity. Let's not do that! It's bad to go against theories, even though they aren't full proof. I'd have to agree with you! The photon can not be destroyed. Well, I believe matter and energy can be destroyed and created, but I thought there was some kind of law stating that they can not be destroyed or created? Maybe I'm just hearing things. *looks around really quick*

I believe the photon is stopped. The energy that is emitted to an electron excites that electron. Once that electron returns to it's original energy state, it emitts the energy back out accelerating the photon in the opposite direction. WOO, another one of my outrageous ideas!
 
  • #47
hahahaha.. there we go. now let's really get the ball rolling and just come and say that anyone who says the photon is destroyed contradicts einstein! i don't agree with sir Albert (on many levels), but tom does. so make a choice. either the photon gets destroyed or the velocity of light changes.
 
  • #48
Now, we know the velocity of light can't change unless there is a shift in frequency! :cry:
 
  • #49
urtalkinstupid said:
I believe the photon is stopped.
See, this is what I was talking about in the other thread. That's just not how science works. You can't just pull things out of the air and choose to believe them (or not believe them). You're setting yourself up to take a huge fall here. An active imagination is a good thing, but don't let it get the better of you. Your imagination isn't reality.
 
  • #50
NOTICE HOW I CORRECTED MYSELF BY SAYING FREQUENCY SHIFT! That compensates for the decceleration.
 
  • #51
beatrix kiddo said:
hahahaha.. there we go. now let's really get the ball rolling and just come and say that anyone who says the photon is destroyed contradicts einstein! i don't agree with sir Albert (on many levels), but tom does. so make a choice. either the photon gets destroyed or the velocity of light changes.
That's nonsense.
 
  • #52
I thought there was a law that said nothing can be created or destroyed. Energy and matter wise. Is that true?
 
  • #53
how is it nonsense russ?? the velocity of light changes because the photon (the light) is stopped. or do u believe the photon gets destroyed? and if u believe the photon gets destroyed, but u don't think the energy gets destroyed, that is in itself a contradiction because a photon is energy.
 
  • #54
A photon can't be destroyed, it can be converted into an electron/positron pair. (At least gamma can, i think)
 
  • #55
It doesn't get converted. Doesn't it decay?
 
  • #56
Just a test

sorry about this.
 
  • #57
urtalkinstupid said:
I thought there was a law that said nothing can be created or destroyed. Energy and matter wise. Is that true?
Matter and energy can't be created or destroyed, only converted from one to the other. Photons aren't matter and they aren't energy (though they carry energy). Think of it this way: a sound wave is created at your speaker and destroyed when it is absorbed by your eardrum. The energy is conserved.
the velocity of light changes because the photon (the light) is stopped. or do u believe the photon gets destroyed? and if u believe the photon gets destroyed, but u don't think the energy gets destroyed...
I don't believe, I know. There is a big differnece. Light does not stop, photons are destroyed, and energy is conserved. This has been explained now about half a dozen times.
...a photon is energy...
Maybe this is the problem. See my sound wave analogy above.
 
  • #58
In the early measurements of the speed of light, I know, they interpreted the interference patterns created by a split beam. Do they still measure it this way, or has a higher tech system been developed that uses a different method?
 
  • #59
I just thought of something. Take an object and accelerate it to .8c and then let it go about a constant velocity. Right when that object reaches .8c and light beam next to it wille mitt. How fast will that light beam be going with respect to the object. If the speed of light does not change, would it be c? I don't think it would c. I don't know though. Maybe there is a way around this paradox.
 
  • #60
beatrix kiddo said:
the velocity of light changes because the photon (the light) is stopped.
The photon keeps going full throttle till all of a sudden there is no more photon. Instead there is a more energetic electron. There is no time lag between the transition in which you could say there is a photon with no velocity, a "stopped" photon.

All the energy the photon had is now possessed by the electron which will jump to a higher orbit, meaning it is traveling in a circle of larger diameter than before (to use the solar system model). It takes more energy to travel in a circle of larger diameter. The electron can do this now because it has all the energy the photon once had, on top of the energy it, itself, had when the photon hit it. The photon's energy is not destroyed.

If you swing a rock tied to a string around it takes a certain amount of energy to keep it swinging. If you let more string out you'll find you have to swing harder to keep the rock in motion: it takes more energy to maintain a larger diameter orbit. Same with electrons. If you zap the electron with more energy by hitting it with a photon it just naturally jumps to the higher orbit. And there's no more photon.

Since it takes less energy for a smaller diameter orbit, the electron releases its extra energy, when it falls back to the lower orbit, in the form of a photon. Is this the same photon that it absorbed in the first place? They haven't figured out a way to tell, but there is nothing to indicate that it is. The electron has a certain total amount of energy and there is no reason to suppose any part of that energy can be distinguised from any other part. The new photon is simply whatever part of it's total energy that is convenient for it to release when it drops down to the lower orbit.

On the level of a single photon it is by no means certain that it will fly off at an angle equal to the angle of incidence. Light only seems to do that on average. I have just been reading about this in QED by Feynman. The best they can do for a given individual photon is calculate a probability for its direction. Only on the level of masses and masses of photons do they all add up to the neat and tidy angle of incidence equaling the angle of reflection.
 

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