Flash animations for commercial and educational purposes
Adobe Flash CS4 is an application for producing modest (and not so modest) animated graphics for display in a website. It is often used to create simple animated logos (as above).
A major step forward in InDesign CS4 is its ability to export documents as SWF files, the native format of Adobe Flash. This is an important development because the current trend in publishing is towards putting the same content on the web and in print simultaneously. For example, a magazine that is produced in InDesign for print can also appear — with some added flourishes obviously, but unchanged textual and image content — in an animated website.
My own interest in Flash lies mostly in its potential for illustrating ideas in science and mathematics. It can also be used to illustrate quite abstract concepts in logic and philosophy. Here is an essay that originally appeared in my blog. It tries to de-mystify the surprising behavior of particles of light.
Why particles of light are a bit like jellyfish
There can be little doubt that light consists of waves. One of the clearest signs that this is so is the way light creates interference patterns, like waves on the surface of the sea. (Ocean-going interference patterns, when superimposed in statistically infrequent ways, can produce monster waves quite capable of sinking large ships. Given enough time, these infrequent occurences become inevitable.)
Interference patterns in light waves can be observed and carefully measured by setting up a “two-slit” experiment. But anyone can see them in a haphazard way by simply half-closing their eyes in orange street-lighting (i.e. by allowing sodium light, which is nearly monochromatic, to pass through the gaps between the eyelashes).
Although there is abundant evidence that light consist of waves, there is also just as much evidence that light consists of particles. A beam of light can be dimmed, further and further, till it consists of just individual particles (called “photons”) leaving the source one after another. Through microscopically small, as few as two or three individual photons can be detected by the human eye, if it is accustomed to total darkness for a decent length of time.
How can light be both a wave and a particle? — It is baffling. (All the same, children are used to sending a "pulse" along a rope lying on the ground, which is a combination of a sort of discrete "thing" and a "wave".) Now prepare yourself for something even more baffling. Suppose you set up a familiar two-slit experiment, with light leaving a source, passing through two slits, and hence forming interference fringes on the other side. Next, suppose you turn down the light source, so that just one photon leaves it at a time. You can turn it right down, to the point where only one photon leaves it per week — or one per year, if you like. You might expect the interference pattern not to form, reasoning that it would require photons to interact with each other like waves. But actually that is not so. The interference pattern still forms, although of course it does so very slowly. In reality, the photons are statistically more likely to end up in the bright bands rather than the dark bands of the interference pattern. The statistical frequency when the light is very dim exactly matches the familiar pattern formed when the light pours out from the source in an unbroken train of waves.
How is this happening? Many will tell you that a single photon must somehow manage to be “in both places at once” at the crucial juncture when it passes through the slits. Some will tell you that there is “no fact of the matter” as to which slit a photon passes through until you observe it. Some will go still further and tell you that there is no such thing as objective reality at all, as the whole thing depends on some mysterious type of “interaction with consciousness”. Some will tell you that the entire universe splits in two whenever alternatives of this sort arise. Some will speak darkly of Yin and Yang…
Speaking as a realist, my advice is to believe none of those “explanations”!
Instead of plumping for a bloated and extravagant metaphysical thesis about multiple universes, or the mystical reality-creating powers of consciousness, I suggest we adopt a more modest course. First, let us honestly admit that we really don’t know for sure what is happening. We can, however, imagine the sort of thing that might be happening by picturing something medium-sized, reasonably familiar, and easy to visualize — something that does pretty much the same thing as the mysterious photons. Instead of taking an extravagant theory literally, let us consider an analogy instead, making sure that we only take it metaphorically, as a model of reality rather than a literal description of reality. I submit that some of the mystery will disappear.
Here goes. Photons actually behave in many ways like jellyfish. Consider the common “moon” jellyfish, which consists of a simple hemispherical bell, pulsing its way forwards through the water. In pulsing, the jellyfish simply flattens its bell, then forms it into a more voluminous shape which captures water inside, which it then squeezes out to jet itself forwards. It does this over and over again.
Like jellyfish, photons also “pulse”. Each photon has its own frequency, and because all photons move at the same speed, a high frequency is the same as a short wavelength. The photons of red light pulse more slowly than the photons of blue light. That again is very easy to visualize with any “swimmers” — some use short, rapid strokes while others use long, slow strokes.
When a jellyfish pulses along, it affects the water all around it, for quite some considerable distance. This can be seen easily if there are little bits of stuff suspended in the water nearby. The water in front gets pushed away from the center to the sides to make room for the advancing jellyfish; the water on either side gets pushed backwards as the jellyfish moves forwards; and the water behind closes up again to form a vortex — a “doughnut” of liquid that “rolls” along its own axis like a smoke ring. When you consider that jellyfish themselves consist almost entirely of water, it’s easy to think of one not as something discrete and sharply differentiated from the water it moves through, but rather as a sort of “center of disturbance” of disturbed water.
Like all subatomic particles, a photon too is a “center of disturbance” of the space it moves through. The word ‘particle’ is rather misleading, as it suggests a tiny billiard ball moving through the void, rather than the center of disturbance of various fields (electric, magnetic, gravitational, etc.). Space itself is hardly the “void” that the Ancient Greeks imagined, but rather an active medium with its own qualities such as “curvature”.
As well as making interference patterns, light does two much simpler, distinctively wave-like things: it changes direction when it passes close to an edge, and it changes direction when it enters a medium it travels at a different speed through (such as glass). So do jellyfish, on both counts, and in the same way.
First, imagine a jellyfish pulsing past an edge of some sort such as the concrete column of a pier. If it passes close enough, the water between it and the solid object cannot move as freely as the water on the far side. This affects its motion, because the jet on the far side will be stronger. This asymmetry causes the path of the jellyfish to “adhere” slightly to the solid object as it passes, bending its direction slightly towards the solid object. An entire shoal of jellyfish passing through a narrow space between two solid objects will spread out, just like a narrow beam of light passing through a slit.
Next, imagine a jellyfish passing into a more dense medium (such as colder water). If it enters a body of denser water head-on, it will just slow down. But if the jellyfish enters the body of denser water obliquely, so that one side enters it first, that entering side will be slowed down, while the other side will keep going for a little bit longer at its original speed. That makes the whole jellyfish change direction. Once again, it does so in exactly the same way as a photon entering a glass prism or lens.
Finally, consider a jellyfish swimming through one of two narrow slits. Although the jellyfish itself passes through just one of them, as a center of disturbance of water, the entire disturbance affects the water around both slits. The vortices I mentioned earlier will form at some angles better than at other angles, because they will divide up as they pass through the slits and re-form on the other side, sometimes with each half “out of step” with the other. Those angles correspond to the angles where photons form bright bands of an interference fringe. Please note that these angles depend on the frequency of pulsing, and do not require any more than a single photon/jellyfish at a time.
So much for my elaborate analogy. Perhaps it is “extravagant” in the same way as the mystical theories I criticized above. Even if it is, I would argue that an elaborate analogy that honestly tries to appeal to our intuitions is not quite as bad as an extravagant theory that purports to literally describe reality.
I repeat: we do not know what photons are really like in all their details. But rather than throwing our intuitions to the winds and embracing a metaphysical outrage, isn’t it better to modestly say, “photons are probably a bit like jellyfish”?