Eskay Posted January 24, 2005 Share Posted January 24, 2005 Hey, I'm new to the forum- decided to ask a question that wasn't answered in school! I get the idea that electromagnetic waves are released from photons, but I don't understand how the waves interact with anything if they don't have a mass. Also how do photons emit energy if they don't have a mass? Maybe it's a lack of detail in my syllabus, but it seems that I kind of missed something. Just a few weeks ago our teacher explained E=mc² to us. So there I am under the impression that only something with a mass has any energy (and can therefore give out energy). So how do photons first of all give off the energy (EM waves), and then how do the waves themselves interact with things if they don't have a mass? Sorry if my questions seem simple, I did search the forums before posting. Any answers will be greatly appreciated! Link to comment Share on other sites More sharing options...
swansont Posted January 24, 2005 Share Posted January 24, 2005 E=mc2 isn't the whole story The actual equation is E2=p2c2 + m2c4 and reduces to E=mc2 only for a massive particle at rest (p=0) Within that equation, the m is the invariant mass (aka rest mass), and a photon doesn't have any. It's made up of an oscillating electric and magnetic field - nothing that has mass, but can interact via the EM force. Link to comment Share on other sites More sharing options...
Dhawal Posted January 24, 2005 Share Posted January 24, 2005 That's a perfect answer ! Link to comment Share on other sites More sharing options...
Mart Posted January 24, 2005 Share Posted January 24, 2005 Relativity teaches us the connection between the different descriptions of one and the same reality.- Albert Einstein Interesting! Is Einstein's Special Theory of Relativity a theory of the connection between the different descriptions of reality. Or is it a description of the connection .....? Whatever it is, it doesn't connect with Quantum Mechanical Theory. So it's a pretty incomplete theory or description. Link to comment Share on other sites More sharing options...
ed84c Posted January 24, 2005 Share Posted January 24, 2005 Mabye Quantum Mechanics is incomplete? Link to comment Share on other sites More sharing options...
Mart Posted January 24, 2005 Share Posted January 24, 2005 Mabye Quantum Mechanics is incomplete? Einstein thought so. But that's appealing to his personal authority. Would it be the end of science as an activity if there was a complete scientific theory. Link to comment Share on other sites More sharing options...
JaKiri Posted January 24, 2005 Share Posted January 24, 2005 Whatever it is, it doesn't connect with Quantum Mechanical Theory. It doesn't need to. It works perfectly alongside it. So it's a pretty incomplete theory or description. Only in that it doesn't describe everything, but then it's not supposed to. Is Quantum Mechanics any less useful because it doesn't describe how creatures evolve? Link to comment Share on other sites More sharing options...
ed84c Posted January 24, 2005 Share Posted January 24, 2005 yeh, jakiri's right. The Complete theory is only one that describes how our universe works, not how each individual bit works. Link to comment Share on other sites More sharing options...
swansont Posted January 24, 2005 Share Posted January 24, 2005 Interesting! Is Einstein's Special Theory of Relativity a theory of the connection between the different descriptions of reality. Or is it a description[/b'] of the connection .....? Whatever it is, it doesn't connect with Quantum Mechanical Theory. So it's a pretty incomplete theory or description. These people (or this guy) appear to disagree with you. But they're probably crackpots - NASA? Pacific National Lab? Thomas Jefferson National Accelerator Facility? Sheesh. Link to comment Share on other sites More sharing options...
Eskay Posted January 25, 2005 Author Share Posted January 25, 2005 Within that equation' date=' the m is the invariant mass (aka rest mass), and a photon doesn't have any. It's made up of an oscillating electric and magnetic field - nothing that has mass, but can interact via the EM force.[/quote'] Thanks, that's helped me understand it better. So in E²=p²c² + m²c², is p the movement of the object? Link to comment Share on other sites More sharing options...
Mart Posted January 25, 2005 Share Posted January 25, 2005 Is Quantum Mechanics any less useful because it doesn't describe how creatures evolve? Quantum Mechanics wasn't designed to explain how creatures evolve. It's a theory of physical interactions not biological ones. Einstein was a physicist not a biologist. Quantum Mechanics and Relativity both deal what Einstein called the "one and the same reality". By this Einstein meant physical reality. Einstein could not accept a basic principle of QM that there was an unavoidable randomness in the behaviour of the physical world. This means that the constructs of Einstein's Relativity theory don't include randomness and therefore are at odds with those of QM. Yes, they are two ways of making very accurate predictions about the behaviour of certain aspects of the physical world but the problem for physicists is that they do it in fundamentally different ways and therefore some physicists see a need to unite the two ways. Link to comment Share on other sites More sharing options...
Mart Posted January 25, 2005 Share Posted January 25, 2005 These people (or this guy[/url']) appear to disagree with you. But they're probably crackpots - NASA? Pacific National Lab? Thomas Jefferson National Accelerator Facility? Sheesh. Not crazy at all. This is my point. These are attempts to unify QM theory and Relativity theory because they are seen to be on their own incomplete. Einstein claimed that "Relativity teaches us the connection between the different descriptions of one and the same reality" but it can't be doing what he claimed because it doesn't include QM. Link to comment Share on other sites More sharing options...
swansont Posted January 25, 2005 Share Posted January 25, 2005 Thanks' date=' that's helped me understand it better. So in E²=p²c² + m²c², is p the movement of the object?[/quote'] Momentum Link to comment Share on other sites More sharing options...
swansont Posted January 25, 2005 Share Posted January 25, 2005 Not crazy at all. This is my point. These are attempts to unify QM theory and Relativity theory because they are seen to be on their own incomplete. Einstein claimed that "Relativity teaches us the connection between the different descriptions of one and the same reality" but it can't[/b'] be doing what he claimed because it doesn't include QM. If that was your point, I fear you didn't make it very well by saying that SR and QM "don't connect" since they obviously do. When did Einstain say that? SR precedes QM by what, about two decades or so? So it's entirely possible that it's been ripped, kicking and screaming, out of context. Saying that theories are incomplete is hardly a revelation. I guess I read too much into your statement. My mistake. Link to comment Share on other sites More sharing options...
bloodhound Posted January 25, 2005 Share Posted January 25, 2005 can anyone explain how a photon can have momentum when it doesnt have any mass. or is in this case momentum completely difference from the momentum we define in classical mechanics. Link to comment Share on other sites More sharing options...
Mart Posted January 25, 2005 Share Posted January 25, 2005 If that was your point' date=' I fear you didn't make it very well by saying that SR and QM "don't connect" since they obviously do.[/quote'] Not obvious to me but clearly obvious to you. Can you tell me in what ways SR and QM connect? I would like your understanding of the connection. Link to comment Share on other sites More sharing options...
swansont Posted January 25, 2005 Share Posted January 25, 2005 Not obvious to me but clearly obvious to you. Can you tell me in what ways SR and QM connect? I would like your[/b'] understanding of the connection. What part of "relativistic quantum mechanics" is giving you problems? Link to comment Share on other sites More sharing options...
Mart Posted January 25, 2005 Share Posted January 25, 2005 What part of "relativistic quantum mechanics" is giving you problems? QM is fundamentally a method of calculating the outcomes of certain events. I have no problem with that or of applying relativistic corrections to equations. In that sense QM and SR can be made to work together. However, QM predicts brilliantly but fails (or refuses) to explain. If accurate prediction is all that is required then there is no problem. Most people want explanations as well as predictions. Link to comment Share on other sites More sharing options...
swansont Posted January 25, 2005 Share Posted January 25, 2005 QM is fundamentally a method[/b'] of calculating the outcomes of certain events. I have no problem with that or of applying relativistic corrections to equations. In that sense QM and SR can be made to work together. However, QM predicts brilliantly but fails (or refuses) to explain. If accurate prediction is all that is required then there is no problem. Most people want explanations as well as predictions. What people want has little bearing on the issue. Science explains (as best it can) how nature behaves. Science doesn't explain why nature behaves that way. Link to comment Share on other sites More sharing options...
Mart Posted January 25, 2005 Share Posted January 25, 2005 Science doesn't explain why nature behaves that way. Agree about the why. My question was about the how - like how does that happen. We try to find explanations. Hot air rises because . . . Boats float on water because . . . Link to comment Share on other sites More sharing options...
JaKiri Posted January 25, 2005 Share Posted January 25, 2005 This means that the constructs of Einstein's Relativity theory don't include randomness and therefore are at odds with those of QM. This doesn't matter in the slightest for Special Relativity. It matters for General Relativity, but that's not what you're talking about. Link to comment Share on other sites More sharing options...
swansont Posted January 25, 2005 Share Posted January 25, 2005 Agree about the why. My question was about the how - like how does that[/i'] happen. We try to find explanations. Hot air rises because . . . Boats float on water because . . . You get to the advanced physics and the explanations are mathematical. Things act the way they do because they have to be solutions to the Schroedinger equation. Link to comment Share on other sites More sharing options...
Mart Posted January 25, 2005 Share Posted January 25, 2005 You get to the advanced physics and the explanations are mathematical. Things act the way they do because they have to be solutions to the Schroedinger equation. Pythagorus would have agreed with you - he believed the universe was fundamentally mathematical. He also believed that eating peas was a sin. As I understand it theories are descriptions not prescriptions meaning that we make models of the universe's behaviour. Our ideas have to explain its behaviour. If it has to obey the solutions of our equations then that turns my ideas upside down. I suppose the pre-Copernican astronomers might have thought that the heavens obeyed their system of epicycles. Maybe the heavens did? Link to comment Share on other sites More sharing options...
Guest SuperNoa Posted January 27, 2005 Share Posted January 27, 2005 The Main problem of Quntum Mechanic is time.... Link to comment Share on other sites More sharing options...
JaKiri Posted January 27, 2005 Share Posted January 27, 2005 I'd argue that the main problem of QM is its incompatability with GR. Link to comment Share on other sites More sharing options...
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