What is an electromagnetic wave?

[Soapy Sam]

Turtles.

All the way down.

 

[GodMark2]

It is, but that doesn't mean that photons are NOT particles, only that: at the level of QE, the diference of meaning between a particle and a wave becomes rather fuzzy.

It seems to me that the concept of a "particle" is actually an approximation, and there is no such thing as a "particle" as the term traditionally was used.

There is also no such thing as a 'wave' as the term was traditional used, both 'particle' and 'wave' are used to describe the set of actions that these QM 'doohickies' seem to be able to do, and both are approximations.

 

[MattusMaximus]

Please forgive my ignorance, but if you are 'sending' photons they should be visible, as even single photons can be seen in a dark room. Yet swinging a magnet does not produce light. "Huge numbers" of photons should make quite a bit of light. Why the disparity?

Ummm, well it depends upon what you're using to detect those photons. The human eye has a lower limit on what it can detect, so it is conceivable that you could be firing these single photons (or small groups of them) at one's eye and sense nothing at all. Which is precisely why more sensitive equipment in the lab (such as CCDS, etc) are required for these experiments.

But yes, you are correct in saying that the larger the number of photons, the brighter the light.

And actually, swinging a magnet or lump of electric charge back and forth *will* produce light - it's just invisible light. Likely the kind of light you'd generate in this manner is going to be radio waves, since I'm rather certain that you wouldn't be able to vibrate a magnet back & forth at a frequency of about 10^14 Hertz, roughly the frequency of visible light.

The only difference in the generation of visible vs. non-visible light is simply the rate at which the magnetic & electric fields oscillate to and fro. Do it slowly and you'll get radio waves, go faster and you'll get microwaves, faster still and you've got infrared, then visible light (ROYGBIV), go faster still and you leave the visible range and go into UV, even faster and you have X-rays, etc.

Cheers - Mattus

 

[MattusMaximus]

If anything, why isn't it touted as conclusive proof that light is a wave? If you perform the experiment in 2D with water and watch 'single' waves propagate, you see the same patterns.

Actually, it *is* proof that light *behaves* like a wave. And there are other experiments, such as the Photoelectric Effect, that give proof that light *behaves* like a particle.

Light behaves like both - maddening to some of you I'm sure, but there it is. You cannot argue with the experimental results - I know, I've done all of these experiments, and more, that confirm everything I'm saying in this forum.

Cheers - Mattus

 

[BPScooter]

Wow, I'm happy that others are interested in this sort of thing at my level of non-mathematical but curious. I've recently been reading Martin Gardner's book collections and he occasionally reviewed some books and talked about QM. I'm way behind and finally getting around to reading Nigel Calder's "Einstein's Universe" if that tells you anything.

One thing I saw recently-- early universe models now say that particles and anti-particles were created in abundance in the Big Bang, and that some initial asymmetry occurred to where now we have our versions of particles vs. the anti-particles. So the positron (anti-electron) was a theoretically predicted thing until we could make and observet them, briefly, in giant accelerators. OK, I can get that. But a brief comment was that a photon is its own antiparticle. That was a little strange. I guess I need to keep at it.

 

[hammegk]

... If a static magnet produces a static field and fields must be explained by photons, then either the photons are static, which is impossible by definition, or there must be an infinite supply of constantly renewed photons. Which sounds worryingly like something Fred Hoyle might have said. (It was always hard to know when Sir Fred was kidding).

IIRC, Fred thought one photon would be enough, and why not?

So what is it with this "field " business? How do we get there from photons?

We know a field is a mathematical construct. What did we say a "photon" is?

Turtles.

All the way down.

Now you're just stringing us along.

 

[BPScooter]

Ho ho! I follow for 10 to the -23 second! I guess I'm swimming in "quark soup" for the moment. Jolly wishes to physicists, I for one am interested in what you all come up with. For me it constitutes a personal amusement, not existential life-or-death curiosity. However one might hope for an answer to human issues from precision measures of small things (microscope, atoms, molecules) or big things (galaxies, dark matter, hydrogen clouds) those human answers still sit here on the level of people.

Just speaking as a social "scientist" with some fascination with philosophy, etc. like many here.

*edited to fix bad typing*

 

[rockoon]

"So is a photon a particle or a wave?"

The answer is "no"

 

[hammegk]

And "yes", and "maybe". Damned things (or is it just one thing ) ignore Aristotelian logic.