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The trouble is that, although it has no 'inertial mass', it still shows a property, momentum' which makes it behave as if it had some. I think people find this confusing because momentum doesn't get its proper status; it is treated as a second class quantity. Whereas the conservation of momentum is a more rigorous 'law' than the conservation of energy, in many ways.
With that said how exactly does light display momentum and not inertial mass, and what is the difference? Also why is this?
however if you shine a beam of light on a reflective surface
since light displays particle properties does it also display the effects of inertia [MOD: modified subject to make it a question. CS]
since light displays particle properties does it also display the effects of inertia.
The answer is: yes, with a caveat. Matter causes gravity, but E=mc2 tells us that matter is "made" of energy, hence energy causes gravity. You can understand this when you put a photon in a mirrored box. The additional photon energy means the mass of the box+photon system is increased, and that increased mass will cause more gravity. Hence a photon causes gravity, hence two light beams will attract one another gravitationally. However a huge mass like the earth deflects light by only a tiny amount, so the very small energy of a photon will deflect another photon by such a small amount it won't be measurable any time soon.
It has a finite inertia related to its momentum. So we are all agreed with this?
Quote from: Mr. Scientist on 22/11/2009 22:41:53It has a finite inertia related to its momentum. So we are all agreed with this?Hmmn. Looking at what soulsearcher and pmb said, it seems to be a matter of definition. If you look at Inertial mass and say you can't make a photon go faster or slower, the answer is no. But you can use the Compton effect to change the direction of that photon, and that's an acceleration. So then you say the answer is yes. But most people associate inertia with rest mass, so I'm saying no, but then momentum and inertia are like two sides of the same coin depending on who's moving, and I'm saying yes again. And looking at the original post afresh, this isn't anything to do with light displaying particle properties. A wave conveys energy-momentum, but if you said it was you moving but not the wave, it wouldn't deliver a bump, it would be a bump and you'd say it had mass instead of momentum.Interesting. But when it comes to mass, I think the important point is that you can make an electron out of a massless photon, and then it's got mass because it isn't moving at c any more. And that means the photon is boson enough. The mass isn't there because the electron is interacting with the Higgs field. The only thing "in there" going round and round is a 511keV photon, so the only thing it can be interacting with is itself.
Farsight? "But you can use the Compton effect to change the direction of that photon, and that's an acceleration." You're sure about that?
What 'acceleration' a photon might have will only be expressed in a different wavelength as far as I know? Like a 'higher energy' relative the observer.
And that is also a very 'relative' expression defined by you observing.
... But you can use the Compton effect to change the direction of that photon,...
I know. If you look at this thread it's clear that issues revolve around definition, and what things mean. And when you think about it, that's pretty much the whole issue when it comes to physics. But hey, we're getting there.
Lightarrow: a mirror isn't so clear cut, because the wavelength isn't reduced.
I don't ignore all that detail PhysBang, not at all. You do, just as you ignore what people say and contribute only spoiler bile.
And as for getting banned from "serious forums" time and time again, it isn't true. Care to provide an example to back up your claim?
Oh, and I don't think anybody will be impressed by your insinuation that this isn't a serious forum.
Did you mean the wavelenght or the frequency? Anyway, if you also want to reduce the frequency it's very simple, you make the mirror recede at speed v with respect to the EM wave:f' = f(c-v)/(c+v).
As for photons accelerating, That's a 'nono'. As for direction changes? Well, what we see after that direction change is in fact not our 'original photon'
Quote from: LightarrowDid you mean the wavelenght or the frequency? Anyway, if you also want to reduce the frequency it's very simple, you make the mirror recede at speed v with respect to the EM wave:f' = f(c-v)/(c+v).Sorry, I meant frequency. I prefer Compton scattering because it's just a free electron and a photon, it's cleaner. Quote from: yor_onAs for photons accelerating, That's a 'nono'. As for direction changes? Well, what we see after that direction change is in fact not our 'original photon'I don't like photons accelerating either. But what can you do? Re original photons, if all you've got is a photon and a free electron, there's no bond there to absorb and re-emit the photon. Thin gruel, Physbang. A partial bar on Dawkins for mentioning a book (the irony!), and a temporary suspension on Baut for not answering questions, despite answering about two hundred. I contribute to physics discussions. Might be an idea if you did too, instead of being a stalker and a troll intent on spoiling them.
Because if you contrive multiple Inverse Comptons so that the photon ends up travelling in its original direction albeit it with a increased frequency, that means you've accelerated it. But it's still going at the same speed. It's acceleration Jim, but not as we know it!
As for photons accelerating That's a 'nono'As for direction changes? Well, what we see after that direction change is in fact not our 'original photon', ah, mainstream seen (if 'photons' now are 'traveling' at all?)
Usually "inertia" refers to "inertial mass" and a beam of light has zero mass.
when someone fires a high power laser beam, does a force push back on the device that fired the laser beam, in a direction opposite of the direction of the laser beam.