View Full Version : light<-->matter
canopus
Aug21-04, 08:56 PM
I've been dwelling on this question for hours! Does the light transform a matter? It seems it does..... A high energetic photon transform an electron and a positron. Hmm, how can it transform then?
PS:I guess this subject is much suitable for physics.
Light is energy and matter is energy... so maybe. Sorry I'm no more help :)
ArmoSkater87
Aug22-04, 01:51 AM
Mass and energy are interchangeable, since light is energy, it can be converted into matter. A very high energetic photon of light (xray, gamma ray) can transform into an electron and positron pair. Light transforming into matter is the opposite of the positron and electron anihhilating each other and being converted into two gamma rays, released in opposite directions.
ArmoSkater87
Aug22-04, 03:07 AM
This wesite should explain the pair production to you very well.
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/lepton.html
canopus
Aug22-04, 04:04 AM
Thanks for the detailed information. It really helped me!
pmb_phy
Aug22-04, 04:34 AM
Mass and energy are interchangeable, since light is energy, it can be converted into matter.It is incorrect to say that light is energy. It is correct to say that light has energy.
Pete
It is incorrect to say that light is energy. It is correct to say that light has energy.
Pete
This seems to suggest that light is a thing that has the property, energy. But if you remove all the energy from light, what is left?
Keep on chuggin !!
Vern
canopus
Aug22-04, 03:22 PM
Nothing is left (;
Prometheus
Aug22-04, 03:26 PM
But if you remove all the energy from light, what is left?
Who, specifically, is this "you" that you are talking to? If it isn't some omnipotent god, then forget it, because the suggestion of removing all energy from light is not very meaningful.
Light has 0 rest mass, so it is not energy, you have no mass or energy left.
ArmoSkater87
Aug22-04, 10:11 PM
When antimatter and matter annihilate, they are converted into ENERGY...not something that HAS energy. It so happens that this energy is gamma rays. Therefore light IS energy. If light was something that HAD energy, then if it gave away all of its energy to some substance, there would be a stationary photon left...with no energy, and we all know that this cant be, and isnt true at all.
pmb_phy
Aug23-04, 07:04 AM
This seems to suggest that light is a thing that has the property, energy.
That's like saying that a car as the property of speed. Speed is not an inherent property of a car.
But if you remove all the energy from light, what is left?No energy, no photon. That can never be taken to mean that a photon and energy are the same exact thing. There is a one-to-one relationship. That is all. There is a one-to-one relationship between the volume of a sphere and the radius of a sphere. No radius - no sphere. But it is incorrect to say that radius and volume are different names for the same thing.
When antimatter and matter annihilate, they are converted into ENERGY...not something that HAS energy.That is incorrect. See above.
If light was something that HAD energy, then if it gave away all of its energy to some substance, there would be a stationary photon left...with no energy, and we all know that this cant be, and isnt true at all.
That is incorrect. A photon can give up some of its energy, e.g. by scattering off of an electron. An photon can give up all of its energy by being absorbed by an atom. When it does so the photon no longer exists, it doesn't mean that its at rest.
Pete
That is incorrect. See above.
Pete
what do you mean. When a matter and its anti matter particle anniahlate, they form pure energy.
one question.
light has 0 rest mass, yes? but light is never at rest... so couldn't you take the mass then as the momentum/c?
but then again, this whole business is quite tricky
Tom Mattson
Aug23-04, 02:41 PM
what do you mean. When a matter and its anti matter particle anniahlate, they form pure energy.
No, they form photons. Photons are not "pure energy", they are...well...photons!
PMB had it just right above: Photons are not energy, they have energy.
Photons have spin and parity too, but we don't say that they are "pure spin" or "pure parity". They have those properties, they are not identical to them.
pmb_phy
Aug23-04, 02:53 PM
No, they form photons. Photons are not "pure energy", they are...well...photons!
PMB had it just right above: Photons are not energy, they have energy.
Photons have spin and parity too, but we don't say that they are "pure spin" or "pure parity". They have those properties, they are not identical to them.
I forgot to mention that pair production from a single photon can't occur in a vaccum. It must occur near the nucleus of an atom. The nucleus sort of acts like a catalyst in that way. If pair production from a single photon occured in a vaccum then momentum wouldn't be conserved. The nucleas takes up some of that momentum.
Pete
who told you that anniahlation of an atimatter and matter particle produces photons?
Tom Mattson
Aug23-04, 08:12 PM
who told you that anniahlation of an atimatter and matter particle produces photons?
QFT and experimental evidence say so. In fact, there's nothing else that a pair can produce when they annihilate, because it would violate known conservation laws.
ArmoSkater87
Aug24-04, 02:58 AM
one question.
light has 0 rest mass, yes? but light is never at rest... so couldn't you take the mass then as the momentum/c?
but then again, this whole business is quite tricky
No, that would give you the maximum mass into which that photon of light can be transformed into.
pmb_phy
Aug24-04, 07:14 AM
one question.
light has 0 rest mass, yes? but light is never at rest... so couldn't you take the mass then as the momentum/c?
Yes. In fact (relativistic) mass is defined as the m in p = mv. So when v = c -> p = mc or m = p/c.
Pete
red_fox77
Aug24-04, 08:01 AM
Duality. Wouldn't light be considered energy when it is behaving like a wave, and have energy when it acts like a particle?
I wave can transfer energy from one system to another, while a particle can transfer momentum in the form of thermal energy. So when a light 'particle' strikes a photovoltaic cell (solar cell) to generate current, it would be acting like a wave?
Somebody straighten me out here, I am getting lost.
pmb_phy
Aug24-04, 08:10 AM
Duality. Wouldn't light be considered energy when it is behaving like a wave, and have energy when it acts like a particle?
No. The wave part is statisical only. Too much to explain here what that means and I have to log off now. time to rest. More later.
Pete
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