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Is Light Matter?

Is LIght Matter

  • Total voters
    105
ponderingturtle said:
Matter generaly refers to fermions and light is not a fermion.
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Generally? There are exceptions? Like photons?

Dunno myself. I'm just wondering how something that has energy and momentum doesn't have mass. I know photons don't have rest mass but, then again, they get no rest. Please 'splain. :confused:
 
Slimething said:
I'm not arguing with you because I don't know that light has mass or no mass. As I indicated back in the seventies and eighties, I was taught that you could push stuff with light which, to me, means it has momentum. To have momentum, you have to have mass. Also, as it has energy, by Einstein's equation, it has to have mass. Since photons are never at rest, they have no rest mass but do they have mass at their speed? Dunno. Perhaps the Theory of Relativity still needs a few codicils.

Gravity is a property of mass so it is not mass. Magnetism is a property of electronic configuration so it is not mass.
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Magnetism can "push" and "pull"
 
ynot said:
Magnetism can "push" and "pull"
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Are you saying that magnetism should be considered energy? I'm not sure enough of my E & M theory here to argue convincingly but something in my brain is saying no to this.
 
Slimething said:
Are you saying that magnetism should be considered energy? I'm not sure enough of my E & M theory here to argue convincingly but something in my brain is saying no to this.
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No, I only responding to what you said - “you could push stuff with light which, to me, means it has momentum. To have momentum, you have to have mass.” If light and magnetism can both “push” (I’m not sure that either actually push) why doesn’t what you’ve said also apply to magnetism?
 
ynot said:
No, I only responding to what you said - “you could push stuff with light which, to me, means it has momentum. To have momentum, you have to have mass.” If light and magnetism can both “push” (I’m not sure that either actually push) why doesn’t what you’ve said also apply to magnetism?
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Well, if we're going to play semantics, I'm taking my ball and going home. :(

What I meant is that you can have an easily-movable object on a level surface and make it move by shining a very bright light on it. You can isolate it in such a manner as to convince yourself that only the light is making it move (put it in a vacuum, shield it from air, etc.) and you can still push it with light. You could do the same thing with a magnetic field but the object would have to be made specifically of a material that interacts with magnetism so that's still an electronic effect and not an effect of mass.

So, someone please post an explanation why, despite light having momentum and energy, and is considered dual in nature (particle and wave), it has no mass. In my opinion, at this point in time, that's something I don't understand yet.
 
Photons are just energy, and whilst they have a mass equivalence (m=hv/c2) and an effective momentum, they do not have actual mass.

Not my area of expertise, but I believe they are generally considered as a force mediation particle.
 
Slimething said:
Well, if we're going to play semantics, I'm taking my ball and going home. :(

What I meant is that you can have an easily-movable object on a level surface and make it move by shining a very bright light on it. You can isolate it in such a manner as to convince yourself that only the light is making it move (put it in a vacuum, shield it from air, etc.) and you can still push it with light. You could do the same thing with a magnetic field but the object would have to be made specifically of a material that interacts with magnetism so that's still an electronic effect and not an effect of mass.

So, someone please post an explanation why, despite light having momentum and energy, and is considered dual in nature (particle and wave), it has no mass. In my opinion, at this point in time, that's something I don't understand yet.
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What makes you think it’s your ball?

“In my opinion, at this point in time“ Steals my ball, then steals my signature! What next? :D
 
My very weak understanding is that light is energy, which can be transformed into mass, but is distinctly different from mass when it's energy.
 
ynot said:
What makes you think it’s your ball?

“In my opinion, at this point in time“ Steals my ball, then steals my signature! What next? :D
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Sorry, ynot, I just saw the ball and figured it wasn't anybody's. I'll put it back. And, when I saw your sig, I just couln't resist!

Seriously, this is why I didn't become a physicist. I need to be able to wrap my mind around the phenomena I claim to know and things like this are just too much for my bean. Suffice it to say that I eked my way through quant by relying on my math skills but the cognitive part is a true weakness.

Suffice it to say that I will accept yours, wollery's and kellyb's arguments that photons have no mass. That would fit into my observation that photons generally don't make divots in my head because they're traveling so close to the speed of light. (sorry, couldn't resist that)

:solved2
 
Slimething said:
Suffice it to say that I will accept yours, wollery's and kellyb's arguments that photons have no mass. That would fit into my observation that photons generally don't make divots in my head because they're traveling so close to the speed of light. (sorry, couldn't resist that)
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The fact that they're travelling at the speed of light (being, in fact, light) is one of the ways that we know they have no mass.
 
wollery said:
The fact that they're travelling at the speed of light (being, in fact, light) is one of the ways that we know they have no mass.
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Yes, I know, wollery. It was yet another sample from my vast arsenal of bad jokes. Didn't you notice the apology? ;)
 
It depends on your definition, but in general, yes, light is matter. All particles are matter. Yes, the photon happens to massless, but it is almost certainly not the only massless particle. There is certainly no such thing as "pure energy", energy is a property of matter. A particle can have energy, it cannot be energy. The energy contained in fields is in fact contained by force mediation particles. When it comes down to it, all matter is basically the same stuff. You can consider it as a particle, a wave, or both. What you can't do is argue that one particular thing is definitely one or the other while everything else isn't. Either photons are matter along with everything else, or photons aren't matter and neither is anything else.

Matter generaly refers to fermions and light is not a fermion.
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No. A fermion is simply a particle with half-integer spin. A boson is a particle with integer spin. Arguing that only fermions are matter is arguing that, for example, hydrogen is not matter.
 
My finger points at the moon another finger covers a star therefore the star and the moon are not the same because my fingers tell me so.

False dichotomy based upon language usage.(Yes the star and the moon are different but not because of angular seperation.)

All human thoughts are constructs we place over the reality that our senses interact with. Words have no inherent meaning, they simply refer to objects of sensation and perception.

Don't mistake the map for reality.

Ynot: are electrons matter?
 
Slimething said:
I'm not arguing with you because I don't know that light has mass or no mass.
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This depends on how you define mass. But having mass would still not make light matter, as you generally need to obey the Pauli exclusion principle to be considered matter.(if you can put an infinite number of the same objects in exactly the same place it is likely not matter)
As I indicated back in the seventies and eighties, I was taught that you could push stuff with light which, to me, means it has momentum.
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Light certainly has momentum, but that is not the sole definition of matter.
To have momentum, you have to have mass.
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Again this depends on how you define mass. Currently mass means the rest mass, and relativistic mass is not part of common usage and generally considered to be not a really helpful concept.
Also, as it has energy, by Einstein's equation, it has to have mass. Since photons are never at rest, they have no rest mass but do they have mass at their speed? Dunno. Perhaps the Theory of Relativity still needs a few codicils.
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Wrong, E=mc^2 is only total energy if you put the momentum into the mass.
 
Slimething said:
Generally? There are exceptions? Like photons?

Dunno myself. I'm just wondering how something that has energy and momentum doesn't have mass. I know photons don't have rest mass but, then again, they get no rest. Please 'splain. :confused:
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So you think that being unable to occupy the same space at the same time is not a general property of "Matter"

The real problem here is that matter is no really a definition that a physicist would use, they would specify the type of particle and such. And the generally is based on that especially theoretical physicists can come up with really weird definitions and I am not comfortable enough with high energy particle physics to make it an absolute statement.
 
Slimething said:
Well, if we're going to play semantics, I'm taking my ball and going home. :(
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This is fundamentaly a semantic issue though. You need to define what matter is before you can say if light is or is not matter.

So, someone please post an explanation why, despite light having momentum and energy, and is considered dual in nature (particle and wave), it has no mass. In my opinion, at this point in time, that's something I don't understand yet.
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It does not obey the Pauli exclusion principle so you can put as many photons as you want in the same quantum state. If matter could do this think about all the storage options that that would make for you house? You could pile an infinite ammount of things in the corner!
 
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