Tuesday, June 20, 2006

Doggerel #17: "Quantum"

This Doggerel entry has been replaced with a more accurate version.


Welcome back to "Doggerel," where I ramble on about words and phrases that are misused, abused, or just plain meaningless. With this one, I'm speaking with my layman's knowledge, so if anyone's on break from trying to find one of those sixth quarks or a superstring for the cat to play with, feel free to bombard me with every detail I got wrong or left out.
"If you think you understand quantum mechanics, you don't understand quantum mechanics." -Richard Feynman
"Quantum" is a word woos have fallen in love with, probably because of the weirdness of quantum mechanics: The experts have a hard time dealing with it, so it's easy to dazzle laymen with QM jargon.

The word "quantum" by itself refers to, as I understand it, the smallest possible units of energy. You won't find half a quantum anywhere in the universe. Because of this, quantum mechanics deals with very small stuff, down to fundamental particles. On that scale, our familiar Newtonian assumptions stop working, and probability takes a much bigger role. Particles don't have a simple position and velocity assigned to them: They have a wave function, which "collapses" when "observed." There seem to be plenty of interpretations of what wave function collapse is, but none of the good science ones involve consciousness in any way, like plenty of woos like to claim. The woos probably got it from the use of the term, "observer" in many of those interpretations. Some, like those who made "What the Bleep Do We Know?", don't seem to care about the misrepresentation. As David Albert, one of the scientists they edited said,
I was edited in such a way as to completely suppress my actual views about the matters the movie discusses. I am, indeed, profoundly unsympathetic to attempts at linking quantum mechanics with consciousness.
The realm of quantum mechanics isn't subjective. It's still quite deterministic, like the rest of science. It's just weird and probabilistic.
So, while I'm waiting to be bombarded by people with better explanations, is a quantum mechanic someone who works on very small cars? If he looks at the speedometer, does he get lost?

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9 comments:

Skeptico said...

Werner Heisenberg was stopped one day by the cops for speeding. The officer said to him:

“Excuse me sir, but do you know how fast you were going back there?”

To which Heisenberg replied:

“No, but I know my exact location.”

Bah Boom!

MichaelBains said...

LOL! Nice Skeptico.

I've made it 1/3 of the way thru Brian Greene's The Fabric of the Cosmos and needed to take a break for some old SF. I've never enjoyed mathematics, but am so freakin' glad that some folks love and excel at it.

The book is actually quite well written and I'm enjoying it. It's filled with things that make intuitive sense gettin' blasted by real-world observations of physical experiments (including showing how light acts as both a wave and a particle) so it's sort of making my head spin. For now, it's sitting on the coffee table 'til I'm ready for rapproachment.

The SF is much quicker reading, so I should be ready to pick up where I left off in a week or so.

Hhhmm... Though there is a Volume II of this Brian Aldiss anthology of "Galactic Empires" sitting on the bookshelf as well ...

This is a longish kinda post, B-Dog. I bet it still took less than a lighthour for you to write it, eh. {-;

Chris said...

Didn't you ever wonder why speedometer needles are so wide? It's a safety feature. The thickness of the needle keeps the driver from knowing his exact velocity, so that he can still know his approximate location, too.

JST said...

My mainest problem with people's use of "quantum" is using "quantum leap" to describe a large change. In fact, a change whose magnitude is a single quantum is actually the *SMALLEST POSSIBLE* change in the quantity.

Lifewish said...

My understanding was that there's no such unit as a quantum. The term does indeed refer to the fact that in certain circumstances energy is quantised, but the exact quantisation depends on the circumstances.

For example, in a hydrogen atom, you have a single electron buzzing about in a potential well. Due to the wave nature of the electron, its actual behaviour will be more like that of a taut string - the only allowable wave functions will be those that are stationary at both ends. So you'll get a basic back-and-forth "vibration", a first harmonic, a second harmonic and so on.

If we look at the spectrum of hydrogen, we can see that the quantisation of wavelengths is roughly what we'd expect. It's not perfect, but that's due to the fact that the potential well is a smooth curve not a smooth-sided pit.

So in this sense wavelengths, and hence energy levels, are quantised. However, there's no fundamental unit of energy - you'll get a completely different spectrum for any other atom, and they won't have any noticeable common factor.

Anonymous said...

I looked and looked, for entire quantum lightseconds, but I can't find anything on your site that explains what a "woo" is.

It appears that the name applies to both credulous cretins and hideous charlatans, but I can't think where the name comes from -- is it an acronym, like "willfully obtuse organism"?

Bronze Dog said...

It's a bit of slang among us skeptics. Notice it mostly at the JREF forums.

Anonymous said...

Thanks for the explanation of woo and the link to JREF.

More generally, thanks for the insight, humor, and -- especially -- for all the fish.

Paige said...

I'm majoring in physics, and I took a class on (introductory) quantum mechanics last year. So, it's no surprise that misuse of this word is one of my pet peeves. But your explanation is great, especially considering that it's coming from a layman.

Don't worry about being "bombarded" with corrections - you didn't give us enough ammunition. There's only one little tiny thing that I'd like to clarify, and it's a common enough misconception.

The discrete little bits of energy aren't "quanta" of energy - as lifewish said, there is no such unit. The idea that the term "quantum" refers to is that in a given situation there are certain allowed energy levels; you can go back and forth from one to another, but any other value is forbidden.

Think of it like a staircase: you can be at any height above the ground, as long as there's a step there for you to stand on, but otherwise, forget about it. You can't expect to go up half a step and stay there.

But as I said, a very good explanation overall. I especially liked the speedometer joke - I've never heard that one before.

PS: michael, if you're still feeling ambitious after you finish The Fabric of the Cosmos, you might want to try Greene's other book, The Elegant Universe. The former is a general overview of many areas of physics, while the latter is a more in-depth (but still layperson-oriented) look at his particular field of research, string theory.