Monday, January 22, 2007

Waves and Spectra... or the post with the most mentions of Gummby ever

There is more light zooming around us than the sharpest eyed humans can see. Only birds can see the near ultraviolet hues that are all around us, and they use this extra information in ways that we can’t really imagine.

But do birds see the whole picture?

Nope. Birds don’t see all the light there is to see. Actually, with the use of technology we can “see” much more light than birds can.

But what is it we are seeing? Light is hard to describe.

Light is a thing, and it moves. Light travels from point A to point B, and it takes time to do it. Light does not travel instantaneously.

Light is not a thing, yet it moves. Light has no mass. Massily speaking, light is nothing. How can nothing move? Very strange. (The answer to this is that you don’t have to have mass to be something. Light is pure energy, which Einstein among others demonstrated is just mass in another form.)

Light comes in little discrete packets called photons. It is reasonable to speak of a photon as a particle of light. Yet light travels in what we can best describe as waves. You may say, “of course it would… waves of photon particles…”, but you would be wrong. It is reasonable to speak of light as a wave without any particle constituents such as photons. Confused? It gets worse.

A single photon (which is a tiny little thing, about the size of an electron (if in fact it has any meaning to speak of the size of a thing that has no mass)), will behave as if it is part of a wave, even if it is the only photon in the universe. This fact would be stunning, if I weren’t so inept at explaining it.

Waves have properties known as wavelengths, which is the physical distance between successive crests of the wave (or troughs). To understand wavelengths, think of the distance between whitecaps when it’s stormy at the beach. Waves also have frequencies… the elapsed time between the arrival of crests. Again, think of the beach, and the seconds that elapse between the crashes on the beach, as wave follows wave.

Back to our single photon in the universe. Let’s call it Gummby. Gummby is a particle and a wave at the same time. Gummby is heading towards a piece of paper with two slits in it. These slits are spaced to cause an interference pattern if a wave goes through them. Think of a breakwater with two openings. The crashing waves will find their way through the two openings into the sheltered harbour and interfere with each other in the harbour. There will be a grid pattern of double troughs and crests as the waves pass through each other.

Anyways, microscopic Gummby photon passes through one of the slits. You would expect him to pass straight through, right? But he doesn’t. He ends up in a weird unexpected spot on the far side of the paper. Oh well, Gummby carries on and decides that that was pretty fun. He takes a hard banking turn and comes around for another pass at the slits. He passes through one of the slits and ends up in a different spot than he did last time. Fun, wow! Gummby does this over and over, and each time his trajectory takes a little jig as he passes through one of the paper slits.

What’s going on? Is he deflecting off the edge of the slit? No, he’s not. Even though slits are narrow, they are millions of times wider than Gummby. He’s the size of an electron, remember?

What is happening is that Gummby the wave-particle is doing a wave interference dance as he goes through the slits, just like the waves in the protected harbour. But who is he interfering with? Gummby is the only photon in the universe. There is no one for him to interfere with. The answer lies in quantum mechanics. At the nanoscopic level, Gummby operates in the world of quantum mechanics, whose rules say that if we know Gummby’s velocity, it is impossible to nail down exactly where he is at any moment. All we can say is that it is probable that Gummby is here, and less probable that Gummby is there.

When Gummby passes through the slits and causes an interference pattern, what he is interfering with is the probability that he will be there, or here, or perhaps a little bit over to the left. Gummby is interfering with himself, with alternate locations for himself. It has been said that light is at its heart, a probability wave. But that would be attaching to much speciality to light, because when you get as small as photon Gummby, everything is just a probability wave, according to quantum mechanics.

The preceding spiel was intended to bafflegab the lone remaining reader into conceding that light is a wave, and thus has a wavelength and a frequency. Light always moves at the same speed, so that means the shorter the wavelength, the higher the frequency. And since every photon is a little wave-packet of energy, higher frequencies also mean higher energies.

Visible colours are nothing more than light with different wavelengths and frequencies. The lowest wavelength visible colour (and thus least energetic) is deep red. All other colours fall somewhere in between. The highest wavelength is deep violet. Take a good look at the next rainbow you see, and you’ll notice that the light is ordered by wavelength. The violet and red colours are at opposite ends of the rainbow spectrum.

Now, transfer your consciousness into a pelican and take a look at that rainbow. Your birdbrain sees below the deep violet another colour… ultraviolet. What’s it look like? Well, it looks like ultraviolet, silly! Ultraviolet has shorter wavelengths than violet, is more energetic than ultraviolet (which is why it causes sunburns!).

Let’s keep shortening the wavelength of the light and see what we get. We will get a lot of increasingly energetic ultraviolet light, but if we shorten it enough we will get something called X-Rays. Keep going. Increase the frequency and energy, and reduce the wavelength, and eventually you will come up with gamma rays, the most energetic form of light.

Now let’s go to the other side of the rainbow. Lower the frequency and lengthen the wavelength past red and you get infrared. Infrared light is something that we sense with our skin as radiated heat, but it is less actually less energetic than, say green light, which may seem surprising.

Next along the spectrum we run into microwaves, and then television and radio waves. Ever wonder why AM radio reception is not usually as good as FM in concrete buildings? The answer is that the AM wavelength is longer than FM, sometimes longer than the building itself, and there is just not enough room in the concrete jungle for the AM wave to resolve itself.

What is light? Is it only that stuff that we see? If so, what do we do with colourblind people, who would say that light is only as much as they see. What do we do with birds, who would scoff at our paltry vision, had they brains capable of scoffing? One of the only appreciable differences between aquamarine blue light and an x-ray is the wavelength of their respective photons. One of the only appreciable difference between pumpkin orange and Erv Weinstein's Eyewitness News broadcast on WKBW Channel 7, Buffalo, New York, is the wavelength of their respective photons. But they are all just different types light.

Light covers the entire electromagnetic spectrum, from Very Low Frequency radio waves (with wavelengths of over a thousand miles) to high energy gamma rays, with wavelengths smaller than you can even imagine.

When God created Light, this is what He created.


Very cool. Yes I know the very last reader gave up six paragraphs ago and that I’m talking to myself. Still, it's very cool.

4 comments:

Gummby said...

I actually knew the part about AM & FM radio. I feel so proud.

The Mains said...

Wow...very interesting.

Anonymous said...

Gummby is cool...

Herbie the robot is boss...

Wrymouth said...

Now, throw in a discussion about Faraday and Maxwell's work, in nailing down the connection of magnetism to electricity... pretty clever, for being dogmatic, faith-based "scientists" without computers or tv shows or movies to go to. How did they do it?

And then, of course, there's the reports of the surprising two-slit experiments, wherein the Gummby changes his behavior if we place a "camera" at one slit to observe him.

How does he know we're watching?

Knowledge is information, and information is energy. "Logos," indeed!