Re: ...no time...cont'd

Posted by Pasti on Nov 14, 2002 at 00:34
(129.97.17.135)

Re: ...no time...cont'd (Natalie L. Smith)

When I think of energy,
>>specifically EM energy, radiating from an >>object, I have always had a vague associated >>image of it simply streaming out into some >>void, spewing those little photons out into the >>unknown. But, when I think about it from a >>wave/field perspective, it seems to me that the >>energy "loss" of the radiant object would >>necessarily be tied to an interaction with some >>other responsive particle. If the radiant >>object was, somehow, alone in the universe, >>such that the photon beam/light wave never, >>ever encountered any other matter at all, could >>it really be said to be radiating energy? But, >>then, when I think of it all from a particle >>angle, I have no problem with the concept of a >>particle leaving some collection of particles >>and just heading off into some void.

Really, it is the same imagery that you can use.Instead of particles/photons being ejected, radiated, you have waves that are spewing from the radiating body.

>>But, how
>>can an oscillating field be said to be sending >>out energy if there are no responsive particles >>to interact with?

And where do the photons go if there is nothing to intercept them?
You don't need a test particle/receiver to have fields. A single electric charge produces a field.It is true, it does not radiate energy, but it is an example of a field that exists without any receiver.Suppose that you bring now another charge in some proximity of the first one and you leave it free. According to Culomb's law, a repulsive/attractive force will be exerted between them, and they will start to move relative to each other.Where do you think the energy comes from?From the field, even if it is static. The energy is contained in the resulting field of the two particles, even if you consider it a static fiels(i.e. non-oscillating). So even static fields posess energy.Same things happens with oscillating fields, with the only difference that now energy is transported by the wave. You can imagine this energy(just some imagery again) as being the energy necessary to increase and decrease the amplitude of the electric and magnetic fields of the wave
Now think about this: where do the "TV waves" go when you turn off your TV?
It is very simple and straightforward to show that an EM wave transports energy, that this energy is transported by the wave itself and no receiver is required. You can find something along these lines in Pedrotti& Pedrotti, Optics(or something similar as title), in the chapter regarding the superposition of EM waves.

>>So, if a radiant object was
>>absolutely alone in the universe, would it be >>radiating energy or not?

It will radiate energy.

>>Wouldn't the object
>>have to somehow be energetically static, to >>avoid conservation violations?

No, it would not. Because when you consider energy conservation, you have to account for all the "places" where the radiant energy goes, or in other words,for an isotropic source, you have to take into account all space. You don't necessarily need an energy sink.

I guess, I'm
>>just trying to say that radiant energy would >>REQUIRE there to be a recipient or the energy >>couldn't be said to be radiating. I just never >>thought about it like that before. Does that >>mean a photon can't leave without somewhere to >>go?

I think what you want to say is something along the Schroedinger's cat problem. Is something really there, if we cannot see/measure it? Is the cat really dead/alive or it becomes dead/alive the moment we check on it?
Does reality exist or not beyond our senses? there isn't a really clear cut answer to that. In physics, you have to use Occam's razor.Of course you can assume some theory according to which for example, photons don't leave the source unless there is an observer/receiver to "collect" at least some of them. But such a theory would be more complicated than just assuming that photons are emmited/radiated irrespective of the existence of an observer.So you apply Occam's razor.Of course, there is also experimental evidence that confirms this. Think of stars.Do you think they started to radiate just when someone looked through a telescope to them?

>>By "radiation of energy" in this broader, non->>EM view, do we simply mean any field >>interaction? Wouldn't that then include ALL >>energy transfer?

Could you be moe specific?


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