magician

[QUOTE]Originally posted by AlexM
[B]Back to contradictions in Nature.

magician

I think it's a pretty safe bet that most of the advancements in science didn't come at the hands of people interested in making safe bets.

Saying that something is unlikely in no way addresses whether it's possible.

The comparison to the briefcase full of money . . . well, I'll leave it to you to assess the relevance of that.

chroot

Garyj,

Okayyyy... boring meeting. Hopefully your Physics in the Classroom website explained more about wave-particle duality. Either way, let me see if I can shed some light on it.

The first thing to realize is that this "contradiction" is really just a failure of the models of classical physics. Classical physics described particles as behaving like small billiard balls. Classical physics also described light as a pure wave phenomenon. Light, however, can exhibit effects of both particles and waves, and therefore the classical model was not complete.

In truth, light is just not like either billiard balls or waves on a lake surface -- it is fundamentally both. First and foremost, let's define how light gets created. A charged object sitting still relative to some observer will appear to fill the space around it with an electric field. The field was originally thought be basically a mathematical construct; classical physics (Maxwell's equations, for example) described the behavior of the field and objects in that field, but never actually attempted to define what the field was. Quantum mechanics explains what the field is, but not without a novel new concept. We'll get to that later. For now, you can imagine it any way you'd like -- the surface of a bowl, etc.

Light, electromagnetic radiation, is created when a charged object is shaken, or oscillated, back and forth. Because no information travels faster than light, the field undulates with the charge's motion. The result is a wave in the electric field, which propagates away from the charge. Now, magnetic fields exist whenever electric fields are changing, and vice versa. The two "fields" are really different examples of the same effect. As it turns out mathematically, these fields are always at right angles to each other. Hence, the waving charge makes a waving electric field, and the waving electric field is synonymous with a waving magnetic field in an orthonormal (right-angled) direction. We then have a picture of light as a wave which propagates with two longitudinal components, electric and magnetic, moving at right angles to each other. The interdependence of electric and magnetic fields is exactly the reason light needs no medium to propagate.

So now you understand the basics of the wave nature of light. As it turns out, light also exhibits some particle properties, as well: the photoelectric effect, for example, is only explainable by assuming that light comes in lumps. The spectrum emitted by a blackbody (i.e. a perfect radiator) is also explainable only by assuming that light comes in lumps. Planck decided to model light as lumps, or quanta, and quantum mechanics was born.

But wait -- light is both a wave and a particle -- right? Right. When you make very slow oscillations (like the electrons make in a radio transmitter antenna), the resulting waves have a long wavelength as compared to things we're familiar with -- the wavelength is comparable in size to people, buildings, and other "human-sized" things. As a result, we can observe that radio waves diffract around, refract through, and reflect from surfaces.

Sound waves are of similar wavelengths (but obviously of different physical origin). We can also observe that sound is a wave by observing that we can hear people shouting around the corners of buildings -- if sound wasn't a wave, it wouldn't diffract around the corner.

Visible light waves, on the other hand, are of much higher frequency (much smaller wavelength). We can observe that we can't see around corners -- the light wavelength is so small compared to the size of the building that no appreciable diffraction occurs. We observe that light basically moves along in straight lines, like a stream of particles. But, if you make tiny slits in an opaque screen (for example), you can observe that light does diffract. Similarly, ultrasound (very high frequency sound) does not diffract nearly as much as normal sound -- the "wave" then travels along straight lines like a stream of particles.

It's the same light, though -- it looks like a particle when you think about seeing around corners, and it looks like a wave when you subject it to travelling through very small slits. It turns out that light really is both wave and particle at the same time -- or rather, it's something completely different than macroscopic things. Low frequency radiation looks more wave-like in human-sized environments. But as the frequency is turned up, the wave nature begins to become less important than the particle nature. Different experiments will examine different components of the nature of light, but all light is the same.

So, again, what is light? Well, quantum mechanics describes it as a non-local particle -- in effect, a particle that does not have a definite position. It is smeared out in space. Furthermore, the exact position can be described by a probability distribution, which is often called a wave function. Both the particle and wave natures can be exhibited by the same light travelling through different parts of the same experiment. The position of the "photon," or particle of light, is represented by a packet of waves (a Fourier superposition, for those that want precision) which collectively moves through space. When confronted with small obstacles, the wave packet appears to be a wave, and diffracts around it. When confronted with large obstacles, the wave packet appears to be a particle.

It turns out that all matter also exhibits the same effect -- electrons have characteristic wavelengths, and when subjected to obstacles similar to those wavelengths, electrons diffract. So do neutrons and helium nuclei. So do people! All matter is composed of particles abiding by the indeterminism represented by a wave packet. As a result, all matter exhibits the same wave-particle duality. It is not a contradiction -- it's just that you have to have the right tools to describe the way things work.

- Warren

magician

Orthogonal.

Good explanation, Warren. (OK, I admit it, I was eavesdropping!)

Does that help, Gary?

Warren, we need more skillful minions arguing against contradictions in Nature. I was hoping for some serious thought on the question, not silliness.

magician

Of course you'd have to say that because a meeting which isn't boring would be a contradiction . . . .

JonBoy

[QUOTE]Originally posted by Jay Li
[B]

My main point was that it's ridiculous to say that if it's not good, it's bad, and vice versa.

chroot

Ooops -- muscle memory makes my fingers type orthonormal automatically. Thanks for the correction.

And, uh... I don't think I'm on your side with this whole Nature-contradiction business.

- Warren

Garyj

Are you kidding. I'm going to have to read it a few more times before I can answer that question!

I did understand this line on the first read and find it interesting. Maybe "models" to the atheist and "faith" to the theist are synonymous. No that's not it. Some have faith in models and some have faith in God.

I'm still saying this forum is one of the best places in the world to gather information. Seems like there are quite a variety of S2000 owners.

Thanks Warren for taking the time.

Jay Li

[QUOTE]Originally posted by JonBoy
[B]
What you are describing here is selfishness.

spike

faith is just that......................FAITH.
your beliefs and my beliefs are just that..............our beliefs

i personally believe that i am a better (nicer, ect.) person by feeling i will be held accountable as to my treatment of my fellow man. you may have different motivations as to how you act.

i believe in an afterlife. if i am wrong, then i am just worm food.

however, if you are wrong, eternity is a long, long time....................spike