Inquiring Minds

Questions About Physics

Particle vs. Wave, etc.

You Wrote:
Thank you for writing back. Please try to answer as many questions as you can. Thanks:)

Are quarks particles are waves? What about photons, I have heard from a friend experiments conducted proved it both a particle and a wave? Do quarks have spin? How can you tell? What in an atom is waves? Do protons spin in the same direction as electrons? When you say color do you really mean as you can see a color on a quark or is it just a simplified method of combining? What do you use to break subatomic particles apart? Sorry about all the questions but whenever I try to look things up I never get a straight answer or the info I'm looking for. Also I was wondering what happens to light when you turn off the switch? Why doesn't it just keep bouncing around the room and if it's absorbed by atoms than what do they do with it? Do they remit it back out at a different frequency that changes it to something not light? This might sound unreal but I've noticed sometimes around light I hear a very high frequency, no, I don't think it's just my ears ringing because I got real close to a high beam flash light and heard it and as I walked away it got softer. I asked and he didn't hear it. I walked past the guy with the flashlight a bit later and as I approached I could start to hear it as I got closer. I say this because sometimes after I have turned the light off I can still hear this high sound and I was wondering if it was the light changed to a different frequency. That is what I think happens but that's just my hypothesis and I know I could be wrong.


Dear Taila,

It's great that you are trying to understand the understanding of these fundamental physics phenomenon. You are right in that many textbooks are somewhat vague and/or are written assuming you already know an appreciable amount of math for example. We at Fermilab are trying to bridge the gap between the expertise it takes to make a discovery and the basic appreciation of the discovery and its impact on society. Your questions though have more to do with understanding some basic but extremely important physical phenomena than with the kind of high energy research we specifically do at the lab here. So, one at a time:

The quantum theory teaches us that there are times to view an object as a particle and times to view it as a wave. For example, as a function of position, one can call something a particle (pointlike or limited extent in space) or as a wave spread out over space. The way to describe an object in quantum mechanics is by assigning a (complex) function to the object and the square of that function is the probability of finding the object at a specific position. Of course, it can also be expressed entirely as a function of some other variable such as the velocity instead of position. The shape of the function is why/how you make the distinction. Sometimes we talk about wave packets which are oscillations but only contained over a small region of space.

Quarks in most cases we study, are particles. There is distinction between certain types of particles. Thus a particle like a quark is more like a proton, somewhat like an electron, but very different than a photon. For one, the first two have a mass, the photon does not. There are other more fundamental differences though. It depends on the energy of the photon for one. For example, if one wave packet is contained within a small distance and another is also similarly contained, but they are far away from each other, and they interact, then you can consider them as particles. If their "wave functions" are large compared to their separation, then a wave description is more appropriate.

Quarks have spin. It is a quantum mechanical quantity that is hard to explain why it is there but it is. We do know how it works though. The way an electron scatters when it hits a particle with spin is different than hitting one with zero spin. This example is known as the Mott scattering cross section.

Both protons and electrons can have both types of spin direction (left handed and right handed). There are certain particles like neutrinos which can only be spinning in one way.

It is just a method of describing. You cannot "see" quark color.

We use other high energy particles to break apart subatomic particles by colliding one on the other.

What happens to light when you turn off the switch is that no photons are emitted any more, so you see no light. Light is photons which are either directly emitted from a light source or that scatter or reflect off of a surface. Photons scattering off a surface is how we see most things.

The photons are emitted when you heat up a metal wire (inside the lightbulb, the glass around it is just to make the distribution of photons more uniform and spread out. The energy of photons depends on the temperature. When the temperature is low, the photons are not visible but far infrared. When you heat up a stove, you see infrared and finally visible red. The wire is even hotter than that, like 6-700 deg F. If you don't heat it up, (when the switch is off), you get no visible photons. The ones already emitted are absorbed. Otherwise how would you see if your eye did not absorb the photon energy? Yes, they can reemit at lower energy. For example, the sun hits the pavement of the road. At night, the pavement cools off by radiation (infrared photons which hit air atoms and create heat).

These sounds you hear are most likely a mechanical effect such as the filament inside being vibrated slightly at some frequency perhaps because of fluctuations in the heating or because of electrical ground loops causing fluctuation in the current supplied to the wire, or it could even be power line fluctuations (there are appreciable fluctuations unless you explicitly filter them out such as one would use for a computer. I strongly doubt it has a direct effect from the visible photons, though. Remember light and sound may be described by similar mathematics, but they are fundamentally different physical phenomena and you cannot just link one to the other. You cannot hear light or see sound. Optoacoustic couplers do exist and are big these days in the telecommunications business.


Glenn Blanford, Ph.D.
Fermilab Public Affairs

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last modified 1/31/1997