Can someone please explain to me about subatomic particles?

Factual Questions
1

I was watching a personal favorite movie of mine last night, Mindwalk, a movie which I’ve watched at least 30 times in my life. I can follow most of it and everytime I watch it things become a bit clearer. But there’s one part that I just can’t seem to fully get, and I really want to.

Just to give you a little background on the movie:
The whole movie is simply a philosophical conversation between an artist, a scientist, and a politician.
The scientist (Liv Ullman), an ex-physicist attempts throughout the movie to get the politician to understand the idea that the world’s problems cannot be solved by studying them in isolation from each other. i.e. that all the problems of the world are interconnected, forming living systems. Thus, the real problem is a “crises of perception”.

OK, about my question. One of the fascinating metaphors she uses to illustrate her point of view is the nature of matter at the subatomic level. Let’s see if I can paraphrase the conversation well enough to give you an idea:

scientist: the particles within an atom move in vast regions of empty space

artist: well if there’s so much empty space, why don’t we fall through everything, why doesn’t everything fall through everything?

scientist: to understand why matter is so solid they had to question many of their ideas about the existence of matter, and they were eventually forced to admit that matter does not exist with certainty in definite places, but rather shows tendencies to exist in certain places.

(huh?)

scientist: in science we don’t really speak of tendencies, but rather of probabilities.

politician: I seem to remember signing a bill to fund a device which was supposed to tell scientists exactly where an electron is.

scientist: the strange thing is that when you make a measurement of an electron it is in a definite place, but between measurements you cannot say that it is in a definite place or has traveled a definite path.

(double huh?)

politician: but in between measurements the electron has moved from one place to the next, right?

scientist: no

politician: you mean it stays in one place?

scientist: no

politician: well, the electron either moves or it doesn’t move.

scientist: well you can’t say that?

(major HUH?)

scientist: you see, the electron doesn’t move nor does it stay in one place. It manifests itself into probability patterns, and the shape of these probability patterns changes with time, something that might seem like movement.

artist: you mean to say that the electron gets shmeared out over a large region and when you measure it with the measuring gun it collapses to a small point?

scientist: you got it.

artist: well if there are no solid objects at the subatomic level, why are there solid objects at any level?

scientist: well, the probability patterns of these electrons arrange themselves around the nucleus in shells. Within the shells the electrons are everywhere at the same time, but the probability patterns that resemble shells are extremely stable and very hard to compress.

artist: So life’s a bunch of probability patterns runnin around huh? probabilities of what?

scientist: relationships. These probabilities are not of things, but of interconnections. The particle has no independant existence. A particle is a set of relations that reach out to connect to interconnections of other things which are interconnections of still other things. In subatomic physics we never end up with things at all. The essential nature of matter lies not in things, but in interconnections.

(now I’m really confused)
Well, I included a little more than I had originally intended but I wasn’t sure what to leave out. (BTW, I think this movie was from the early 90’s so I don’t know if any of this info has changed).

Anyway, will some brilliant physicist out there explain this to me like I’m really dumb.

If you make many measurements of an electron, with a small enough interval of time between measurements, won’t the points form a straight line at some point? Would that be evidence that the electron has moved from one place to another? If they don’t form a straight line, how can we say that the electron exists at that point instead of still existing simultaneously at all points in the shell? why does it choose to show up where it does? what’s the variable?

How can these particles have no independent existence? Does this mean you can’t isolate a single electron in a vacuum? Are we talking physics here, or metaphysics? If you have 2 particles and you take one away, does the other cease to exist?

I realize I’m asking a lot here so if you can just toss a tidbit or 2 of insight this way I would be grateful.
I have taken General chem and did good in it so I’m am not without any knowledge, but these ideas are just way beyond me.

Thanks in advance

2

Mindalk is, I think, by he guy who wrote The Tao of Physics. He likes to make things sound mystical and confusing.

I don’t know a good, up-tp-date Intro to Particle Physics for the Educated Man or Woman. You might try Asimov’s books on science, if you can find them.

3

I’m going to make an attempt here, and then the real physicists will come in and tell you where I messed up.

As quantum mechanics was developed, some people began to realize that it wasn’t really possible to define certain quantities precisely. Some pairs of particle attributes were linked in such a way that if you tried to be very precise about one of them, you couldn’t be at all precise about the other. The first set of these to be described (by Werner Heisenberg) was position and momentum. Thus, the famous Heisenberg Uncertainty Principle. It turns out that if you try to pin down the position of a particle, you lose track of its momentum (which leaves you without much information about any path it may have taken to that position).

If, instead, you try to track it’s movement (like tracing paths in a bubble chamber), you cannot really get its position at any particular point on that path. In a bubble chamber, the paths are fairly wide and fuzzy (though that isn’t strictly due to uncertainty).

When Einstein saw the uncertainty relations, he tried to point out that they were obviously wrong by showing that the same math could be applied to energy and time. Heisenberg and others (notably, Erwin Schroedinger) looked into it, and found that Einstein was correct (not that Al was glad to be right in this case). Since it was already known that energy and mass are the same thing (remember E=mc[sup]2[/sup]?), this form of uncertainty means that for a short time, matter can appear from nowhere. Since the uncertainty makes it impossible to detect this tiny bit of matter for this tiny bit of time, these ‘virtual’ particles pop in and out of existence all over the place. Which is why you can’t really talk about isolating an electron in a vacuum.

I bet I’ve just confused things. Sorry about that, but at least I got to link to my favorite 'Dope column.

4

If it helps, think of the electron’s location as being like a cloud. You can clearly see a cloud in the middle of a clear sky. You can easily point to places where the cloud is and where it isn’t. But if you tried to approach it and measure exactly where it started, you’d fail. And if you went into the deepest part of the cloud and tried to gather a sealed jar of “cloud” to take out and examine, you’d find that your sample was no longer a cloud when you got it to the lab.

Besides, there’s really no such things as electrons. They’re actually interdimensional strings which vibrate in such a manner that they occasionally act like electrons. Does that clear thing up?

5

Gary Zukav’s book The Dancing Wu Li Masters does a great job of explaining subatomic particles and probabilistic theory (Which Einstien refused to accept). It’s a great book in general, though a bit Zen and the Art of Motorcycle fixin’-up. Highly recommend it.

6

Yikes. Big topic. (well, small…quantum…topic)

I think the key thing to grasp is that at the subatomic level (the bits that make up atoms), you can no longer picture matter as little marbles stuck together (like atoms in a model of a molecule). Instead, subatomic particles are more fuzzy in their existence and, on their own, exist through probability waveforms rather than at definite locations. When these fuzzy particles interact, they combine into atoms which have a resulting force that we can more readily get a hold of as “matter”.

I think an electron (a fundamental particle) CAN exist on its own, but you would not be able to know both its position and momentum, like Saltire said. It sounds like the movie was being a little dramatic here. I think these particles do exist on their own, but their existence is ‘fuzzy’ until they are interacting with other particles.

As far as tracing a straight line…yes, you can generalize a straight line, but that line gets fuzzier as you zoom in for a closer look. A higher resolution view of the world at the subatomic level shows that things are very different from our normal low-res/macroscopic view.

Just ask about double-slit experiments with electron beams to get really confused.

7

I think one of the problems here is that this is physics via Hollywood. It is true that atoms are mostly empty space. I often heard the analogy that if the nucleus of an atom were the size of an acorn, the volume of space occupied by the electroms would be roughly the size of a baseball stadium. Gives you a rough idea of scale, anyway. So why doesn’t your hand simply pass through the tabletop if there is so little matter? Because of electrostatic forces. The electron clouds act like little negative magnets and repel each other. So while you can’t tell where a specific electron is, you can tell that the entire region around an atom will have a negative charge. So what feels like to material objects touching to us is really several umptibillion negatively charged electron clouds not being able to further encroach on each other’s territory.

-b

8

This experiment always gets me (BTW – this experiment can be done in most high school physics labs…it’s pretty simple). Basically this experiment gets you to the wave/particle duality of matter. Depending on your experiment a particle can behave like a wave (think of a wave travelling down a rope that you shake) or a particle (think of a BB).

The double-slit experiment really gets you because even if you setup the experiment such that you ‘know’ you are using particles (i.e. a machine that emits one photon at a time) you still get wave like behavior. Essentially, the particle is shot at a target that has a screen with two slits cut into it between the source and the target. One would suppose that the particle has to travel through one slit or the other but at the target you see light and dark lines formed by interference. The problem is how can a single particle interferre with itself? The implication of this is that the particle has travelled through both slits (yes…one particle travelling through both slits simultaneously so it is, in effect, in two places at once). Counter-intuitive? Sure is but the experiment has been perormed jillions (scientifically speaking) of times and the results are always the same.

This gets you back to the probability aspect of particles. You can’t “know” which slit the particle travels through but only assign a probability to where it might be at a given time. Right slit? Left slit? Both slits? You can never know for certain.

The only speculation I’ve heard for how a single particle can interfere with itself is an argument for parallel universes. Essentially there is a parallel universe that is identical to our own except in the other one the particle travels through a different slit than the one in our universe and the two particles interact and interfere with each other. I don’t think any serious physicists buy this explanation though if for no other reason than it is completely untestable and thus remains pure speculation. Speculation may be good for sci-fi but it’s not something any self-repsecting scientist would hang their hat on.

As to matter being mostly empty space that is true. IIRC the floor you are standing on is something like 90% empty space. You don’t fall through the floor thanks to the repulsive effect of the electromagnetic force. Gravity wants to suck you through the floor but gravity is by FAR weaker than any of the other three fundamental forces (strong nuclear, weak nuclear and electromagnetic). The only flip side to gravity being weaker is that it is the only force of the four that you can’t shield yourself from (there is no such thing as an antigravity room where the floor blocks out gravity allowing you to float).

9

I think Phobos explained things well. The assumptions we’ve picked up from living at a length scale of meters just don’t work on a microscopic level.

I love the two-slit experiment. It’s chock full of physics, and it’s very elegant.

You send a beam of low-mass particles (electrons, photons, etc.) through two closely-spaced slits. You get a series of fringes from the interference between the two slits, where the output of one slit is out of phase with the output of the other and they cancel each other out. This is a property of waves, and from this we learn that both electrons and photons can behave like waves.

Now, we turn down the beam, until we’re just sending a single particle at a time at the slits. And we get the same pattern, indicating a single particle has wave-like properties.

However, if we put detectors over the slits, to measure what is passing through each one, the pattern changes to resemble point particles passing through, with no interference.

What this all means is that very small, light things are fuzzy (“delocalized”). Even though an electron is a discrete object, with non-zero mass, this doesn’t mean that it has to be at a single pinpoint location in space. When you try to measure a fuzzy particle, though, you have to interact with it. Any interaction significant enough to gain information about which state the particle is in will force it to be only in one of those states. So putting detectors over the slits forces the particle to pass through only one of them.

Quantum mechanics has been proved to be non-local (meaning putting a detector over one slit instantaneously changes the wavefunction at the other slit), which is both non-intuitive and really interesting.