This does not mean, however, that you should forget everything you know; that would be a catastrophe. If ignorance were all that was required, only those who knew nothing would be able to understand the world around us. You must perform a delicate balancing act: retain your knowledge, but at the same time open your mind to ideas that may not fit with what you already know. This is a skill which does not come naturally once you have grown up, and is difficult even when you are still a child. We can learn much from Lewis Carroll's Alice, who constantly received lessons during her trips to Wonderland that instructed her in this skill:
"I ca'n't believe that!" said Alice.
"Ca'n't you?" the Queen said in a pitying tone.
"Try again: draw a long breath and shut your eyes."
Alice laughed. "There's no use trying," she said: "one ca'n't
believe impossible things."
"I daresay you haven't had much practice," said the Queen. "When
I was your age, I always did it for half-an-hour a day. Why, sometimes
I've believed as many as six impossible things before breakfast" (Lewis
127).
Are your eyes closed yet? Good. We are almost ready to begin our tour of the quantum. But there is one more thought to keep in mind, as we study these strange phenomenon; they may not be real. "What?" you exclaim, "I thought you just told me to be open minded!" Well, I did. But you should also be aware that there can never be absolute truth in physics-only absolute falsehood. As Einstein once said, "The scientific theorist is not to be envied. For Nature, or more precisely experiment, is an inexorable and not very friendly judge of his work. It never says 'Yes' to a theory. In the most favorable cases it says 'Maybe,' and in the great majority of cases simply 'No.' ...Probably every theory will some day experience its 'No'-most theories, soon after conception " (Dukas 18). Physicists' beliefs vary almost as much as religious beliefs, and in the end you must be the one to decide who you believe: what views you wish to follow. We are traveling to a place where you have no eyes to see, no hands to touch, no ears to listen and no tongue to taste. Other ways must be found to explain what we find there. That is the job of a physicist, and the results they produce are only as good as the way in which they are found and interpreted. Now, that said, let us explore the quantum zoo.
The quantum world is a term that is used to describe the very, very small. In order to understand exactly how small we must make comparisons. If you were to place a small green pea in the middle of six football fields (spread out to form a rough square), that would approximate the size of a gold atom's nucleus compared to it's outer shell (Lederman 155). But that is just the beginning. Within that tiny green pea are 79 protons and approximately 118 neutrons. Yes, it sounds a little crowded in there, but these particles are so small in comparison that it isn't too tight of a fit.
Now, let's stretch our minds a lot further, and go down to the size of an electron. "So what is the size of an electron?" you say? Well, that is a very good question. It is generally accepted that an electron has a radius of zero (yes, zero). And, as is the case with a radius, if you multiply it by two you get the diameter-once again, zero. So here we have what you can think of as a true point particle, with no size, how do we know it is anything at all? We know it exists because it has other properties of matter that we can measure, with names such as charge, mass and spin. "Think of Lewis Carroll's Cheshire Cat. Slowly the Cheshire Cat disappears until all that's left of it is its smile. No cat, just smile. Imagine the radius of a spinning glob of charge slowly shrinking until it disappears, leaving intact its spin, charge, mass and smile" (Lederman 142). [See Figures 1 and 2] To complete our earlier model, 79 of these zero-sized particles are scattered out within the six football fields of the gold atom.
Figure 1 The Cheshire Cat
Figure 2 No cat, just smile
Electrons are also peculiar in other ways. They can only exist in certain allowed orbits, or states. These orbits can be thought of like planets orbiting around the Sun (the nucleus). Electrons change orbits by making a quantum jump. The confusing part is that when an electron takes a quantum jump, it disappears from its current orbit, and instantaneously reappears in its new orbit, without ever actually traveling in between the two! The electron either emits or absorbs energy, depending on if it is going to a lower or higher orbit, which allows it to make these crazy jumps.
Everything I have described so far has been about matter. But in 1928 the English physicist Paul Dirac "...noticed that Einstein's famous equation E=mc^2 [Energy equals Mass times the Speed of Light, squared] was actually not quite correct. (Einstein realized that the correct version is E=±mc^2 [Energy is equal to plus or minus Mass times the Speed of Light, squared] but did not concern himself with the minus sign because he was creating a theory of forces.) ...The minus sign was puzzling because it seemed to predict an entirely new form of matter" (Kaku 179).
This new form of matter, antimatter, acts just like regular matter, with one important exception: it has an opposite charge from that of its twin. For example, our friend the electron has a negative charge. It whizzes with its buddies around the nucleus of an atom. The antimatter counterpart of an electron is known as a positron. Yes, you guessed it, it has a positive charge. Other than that, it seems just like an electron: it has a zero radius and the same mass.
One way of explaining antimatter is that it is normal matter traveling backwards though time. The two would be indistinguishable from each other by our methods of measurement. "For example, if we push an electron with an electric field, it moves, say, to the left. If the electron was going backward in time, it would move to the right. However, an electron moving to the right would appear to us [with our measuring equipment] as an electron with positive, not negative, charge. Therefore an electron moving backward in time is indistinguishable from antimatter moving forward in time" (Kaku 181). [See Figure 3]
"I don't understand you," said Alice. "It's dreadfully
confusing!"
"That's the effect of living backwards," the Queen said kindly:
"it always makes one a little giddy at first--" (Carroll 125).
Figure 3 The positively-charged Positron curves right.
When exploring the quantum Wonderland, another strange concept comes into play: the Heisenburg Uncertainty Principle. This tells us that it is not possible to know both the exact velocity (speed) that a particle has and its exact position at a point in time. If you know one, you cannot know the other, no matter how precise the equipment you are using. Just the fact that you are measuring the velocity of the particle changes its position, and vice versa. For example, suppose we are trying to find out the exact position of a car that we have shown to have a speed of 60 mph traveling west on Highway 64. If the car were a quantum particle, we couldn't tell if the car were in Williamsburg, Richmond, or Charlottesville. Conversely, if we have found out that the car is in Richmond, then we cannot know its exact speed.
Remember, when we are dealing with quantum particles, everything is very small, and they are very easily disturbed (changed) by the act of measurement. To bring it in perspective, imagine that the only way to tell where the car is, is by throwing huge boulders at it. If a boulder bounces back, we know that we have hit the car. Where we threw the boulder was the exact position of the car at that moment. The problem is that the car is no longer traveling at 60 mph eastward down Highway 64: it is rolling sideways down a steep embankment to a patiently waiting ditch.
Remember Einstein's equation E=mc^2? It tells us that the amount of energy a particle has is directly related to how much matter it has. The speed of light is a really large number, and if you square it, you get an even larger number. Since the amount of energy is equal to the amount of mass times a really large number, a very small amount of mass can be converted to a great deal of energy, and vice versa. We have all seen the conversion of mass to energy in the films of atomic bomb blasts at Hiroshima and Bikini Atoll.
With our car example, we were talking about two particular variables, velocity and position. The uncertainty principle also applies to other variables, including energy and time. You can never know the exact energy a particle has and exactly when it had that particular energy. One, or the other, but not both. So if we pinpoint an exact time, we cannot say exactly how much mass a quantum particle has at that exact moment. It is this idea that leads us to the concept of virtual particles. "In other words, we could have a sequence...where a single particle becomes, for an instant, a pair of particles. No measurement we can make will tell us that this is or is not happening" (Trefil 48). In this scenario a great deal of the energy of a particle could change, for an incredibly short amount of time, into matter. [See Figure 4] "'Curiouser and curiouser!' cried Alice" (Carroll 10).
Figure 4 Creation of a Virtual Particle / Normal Particle Pair.
The Heisenburg Uncertainty Principle governs how big a particle can be created, and for how long it can exist. "In a sense, the [uncertainty] principle plays the same role in [the creation of a virtual particle] as the clock played in the Cinderella story—so long as the [virtual] particle gets home from the ‘ball’ before the time runs out, it will not turn into the subatomic equivalent of a pumpkin" (Trefil 49).
Subatomic fairy tales are not the only things you should consider. Most people have at some point joked that a ‘watched pot never boils,’ without realizing that in physics this is an entirely true statement:
The watched-pot-never-boils [quantum] effect . . . was experimentally verified, perhaps for the first time, in 1989. ...The "water" in [the] experiment consisted of 5,000 beryllium ions trapped by magnetic fields. During a time interval of 256 seconds, a radio wave drove some of the ions from a ground state to an excited state of higher energy (representing "boiling"); call it level two. While this was going on, the experimenters occasionally sent in a brief pulse of laser light, which can drive ions up to a level three. An ion can only make the transition to the third level if it is in the ground state when the laser pulse arrives; it then drops quickly back, emitting a photon of the same color as the laser. [See Figure 5] Thus the amount of light coming out of the trap after a pulse is sent in reveals the fraction of ions still in the ground state.
When the experimenters "peeked" with the laser after a 256-second interval, essentially all the ions had jumped to level two. If they peeked twice, once at 128 seconds and once at 256 seconds, only about half made the jump; if they looked four times, the figure dropped to a third. At 64 peeks, almost all the atoms stayed in the ground state. The water never boiled (Wick. p.149).
