Introduction This is a hands-on science museum for adults. It presents not just scientific facts, but the philosophy behind how those facts are obtained, and the controversies about our relation to knowledge in general. Most of the exhibits here discuss quantum physics, because it's so controversial and mind-bending. Also, these exhibits attempt to correct some of the popular misconceptions about quantum physics. The discussion here addresses two basic questions: what is the nature of existence, and what is the nature of knowledge? Debates on these issues continue through thousands of years of philosophy. There is probably no better definition of a profound topic. It seems humans have always sought a connection with the profound. Usually this fact is mentioned in connection with religion. It is hoped that these exhibits will demonstrate how a connection to the profound can be established through a different route. Of course, in limited space (and with limited patience) only a small taste of these vast issues can be given. The attempt to compress ideas will have made some statements oversimplified. The goal here is to give a sense of the big questions-though admittedly from the limited perspective of this author-and to induce the visitor to go learn more. Black boxes Science In science, a black box is something that has inputs and outputs and an unknown mechanism inside, but you don't care what's inside if the box's behavior can be completely described by relating the outputs to the inputs. We study animals this way, usually. Since we can't ask them how they feel and think, and it would be presumptuous or worse to imagine that they felt and thought like us, we just observe their behavior (outputs) when certain stimuli (inputs) are present. We relate behavior to stimuli and derive a predictive description of how the animal lives. This concept was also tried with human behavior, but our minds are so complex, it wasn't a useful approach. As we learn how to probe brains and reveal their inner mechanisms, we can abandon the black box model of behavior in some cases where it was once fruitful. Black box models are good whenever one has no way to probe the workings of a phenomenon, but wants to be able to predict it anyway. Experiment Push the buttons on the boxes and observe the lights. Try different combinations of buttons, until you can derive a rule that predicts what you see. Only then take a peek inside. Can you imagine other ways to design the insides so that they still behave the same way? Would one be justified in suggesting an explanation of what's inside without being able to open them up? Would it matter whether the explanation was true or false, if the boxes were un-openable? Philosophy We don't observe what exists in the physical world, but only the consequences of what exists in the physical world. We observe the effects that world has on our senses and instruments, and infer what must have made them act that way. We then assemble a coherent picture of the world from our inferences, and test it by making more observations. The world might be different from this picture, but there is no way for us to find out otherwise. (God whispers in our ears "You have it all wrong...") Our relation to ultimate physical reality is like a person with a black box. We can manipulate the physical world, observe the resulting phenomena, and make up rules that connect the two, which we call laws or theories. What's "really there" is inaccessible, until we learn to probe further and open the black box, finding several smaller black boxes linked together inside. The goal has always been to find finer and finer detail, getting closer to ultimate reality whether it is ultimately accessible or not. Findings in quantum physics have given us pause. We can observe some physical phenomena which the quantum theory, long considered "complete," doesn't explain. Some say "well obviously, since it can't explain some things, the theory is not complete!" These tend to be people who believe that reality exists independent of us, including details we might never know. They emphasize the Reality part of our Description of Reality. Others say "the theory is complete, telling us what we can know and can't, and it makes no sense to pine after details we can't know." These tend to be people who believe we form a picture of reality only from what we can know, defining the physical world through knowledge. They emphasize the Description part of our Description of Reality. What do we want from science, only description or both description and explanation? Who would be satisfied with a black box they could never open? The White Crow Science You are an ornithologist, studying birds. There is a black bird called a crow, which has certain other characteristics-such as its raucous voice-which apparently always occur together. All the crows you have seen are black, so you suggest the hypothesis that "all crows are black." Every time you see another crow that is black, the hypothesis is further supported, though you have not and will not ever see them all. The more you see, the better the hypothesis is confirmed, though you also run a greater risk of its being contradicted by seeing a white one. Barring that, you have a candidate for a truth. What happens if you see a white one? The hypothesis is false. How much does this matter, in practice? You could modify the hypothesis and say "almost all crows are black," and still be right, in fact more right than you were before. Since white crows are rare, it's still a good bet that the next one you see will be black. Nothing much has changed, except that you can amaze other ornithologists with pictures of the white crow. (In the 19th century you would shoot it, stuff it and show it in a museum of curiosities.) Experiment Press and release the red button to make the wheel spin, then observe the image when it stops. What do you expect to see, after a few spins? You become quickly bored, because you can use an hypothesis to predict the outcome of the next spin. Each spin confirms the hypothesis*. Would you rather see your hypothesis confirmed again, or would you like to see something new and interesting? This is how scientists feel too. *Except if you see the white one! Philosophy General knowledge about the world gained through experience is always incomplete, but that seems to work for us most of the time. One can never prove a generalization from specific observations, in the way a mathematical theorem is proved, so that it must always be true. Our experience-based knowledge can be falsified by experience too, if we finally find counterexamples. This doesn't necessarily invalidate our previous knowledge, it just requires us to modify the statements we can make based on our entire experience. At any one time, our overall world view will have to be based on the necessarily incomplete knowledge we have so far, and our best generalized inferences from that knowledge. Perfect knowledge is neither attainable nor necessary. All we need is a good bet. It can be a very good bet, so that we are "certain," even though a bet is not a "certainty." When told something, rather than asking "is this true?" we could ask "how likely is this to be true?" Some things people are asked to believe because "they might be true" are in fact very bad bets. The Uncertainty Principle Science The uncertainty principle is the reciprocal relationship between pairs of measurable attributes of quantum particles. For such a pair, as one attribute is measured more precisely, the other can only be measured less precisely. Here is why: 1. The smallest particles of matter and energy seem to behave like waves. (See the "What is a Wave?" exhibit). That is, their observable properties are wave-like. For instance, position and mass are manifested as wave amplitude (strength) and frequency. The precision of our measurement of the particle's properties is determined by how well we can know its wave characteristics. 2. Waves have certain pairs of characteristics that are related sort of like the ends of a see-saw (called "complementary"). For instance, the more limited a wave is in duration, the more ambiguous is its frequency, and vice versa. The more a wave is constrained at one point in its path, the more it will spread out in direction of travel after that point, and vice versa. 3. Therefore, if we try to measure complementary pairs of properties of a particle, the precision of measurement of each will be limited by the other. For example, we cannot measure the exact location of a moving particle (e.g. by seeing it go through a small hole) and at the same time measure its exact direction of motion. As one measurement improves, the other must grow more uncertain. Experiment A laser pointer in the box emits a stream of quantum particles of light (a light beam made of "photons"). They pass through a narrow slit made of razor blades, so you know the particles' position must be within that slit. Twist the knob to vary the width of the slit. See the pattern on the screen change. The narrower the slit, the wider the pattern. As the slit narrows, you know the position of the particles more precisely. As the pattern widens, you know less about the direction of the particles after they go through the slit. Philosophy We used to think that precision measurements could be made exact, closer and closer to "perfect." As we looked closer, we found the surprising wave action of particles. This set limits, but the limits appear to be kind of arbitrary. We could choose to measure one complementary quantity to any desired precision, and suffer a related imprecision of measurement of the other quantity. How then can we learn what's "really there?" If our picture of reality is based solely on what we can measure, and we carefully avoid baseless speculation, our picture of reality is now ambiguous. Do the two complementary attributes of the particle actually have exact values we can't know? Or can we decide that they have whatever values we measure, even though there is something arbitrary about how we measure them? This last suggestion would lead us to the conclusion that reality is somehow a function of the choices we make, that it is at least partially created by us. And not just in terms of our limited knowledge, but in an actual physically measurable sense. All this is still controversial, even 80 years after the physical theory was first developed. In fact, more controversial now than ever, because of new experiments and new philosophies. Illusions Science Knowledge gained through experience is reliable, even in the presence of illusions, because illusions can be identified and managed. In science, knowledge is gained through experience. Scientists make observations, take measurements, and always use experience in the physical world as the ultimate source of truth. This as opposed to truth from pure theory, or authority, or intuition. It is important therefore, to know when observations are reliable. An observation of an illusion would lead one to a wrong connection between what was observed and the underlying physical reality. If an observation is suspected of being an illusion, it is tested in various ways to see if all the different observations add up to the same conclusion (i.e. are "coherent"). Different people do the same measurement to see if they are consistent, or otherwise if one of them is biased or in error. If all the ways something can be tested agree with each other and with what is already known, the effect is deemed real. This is not to say that it can't be an illusion, just that it is unlikely to be. We believe that any illusion that has negative consequences for our search for truth can be eventually unmasked by careful tests, revealing the consequences as inconsistencies in a coherent, developing world view. Experiment Here is an illusion you can unmask. It's a hologram, which is a trick for bending light so it appears to come from an object that isn't there. Look into the box and see the green phone. Then push the button to the left to illuminate an object in the background, which you can see right through the phone. Do another experiment. Move your head and see the grainy spots in the scene move (which direction depends on if you are near or far sighted). Squint, and you'll see the grains get larger. This indicates that even the grains are an illusion, created somehow in your eye. They are due to crumpled-up light waves adding and subtracting on your retina. Philosophy The idea that knowledge is gained through experience has had its detractors, skeptics that go back to the ancient Greeks. They suggest that everything you perceive is an illusion, and no one can prove otherwise because the illusion is perfect. It turns out to be hard to refute this assertion in an ironclad, logical way. Related to this are the suggestions that "everything is my dream," or "everything is a thought in some mind." From this perspective, things are not as they seem. On the contrary side is the assertion that everything is just as it seems, at least if you look carefully enough. This last position is the one taken by most scientists, because there isn't much one can actually accomplish with the others. It's also in accord with common sense, which is basically the same type of knowledge as that gained through science (that is, from experience). From a practical point of view, "perfect" illusions with no observable inconsistencies don't have any relevance to our project of understanding the observable world, and are therefore not worth our consideration. If it walks and quacks like the truth, it's the truth. Parallel Views 533 Two butterflies went out at Noon- And waltzed upon a Farm- Then stepped straight through the Firmament And rested, on a Beam- And then-together bore away Upon a shining Sea- Though never yet, in any Port- Their coming, mentioned-be- If spoken by the distant Bird- If met in Ether Sea By Frigate, or by Merchantman- No notice-was-to me- -Emily Dickinson World Without Peculiarity The day is great and strong - But his father was strong, that lies now In the poverty of dirt. Nothing could be more hushed than the way The moon moves toward the night. But what his mother was returns and cries on his breast. The red ripeness of round leaves is thick With the spices of red summer. But she that he loved turns cold at his light touch. What good is it that the earth is justified, That it is complete, that it is an end, That in itself it is enough? It is the earth itself that is humanity . . . He is the inhuman son and she, She is the fateful mother, whom he does not know. She is the day, the walk of the moon Among the breathless spices and, sometimes, He, too, is human and difference disappears And the poverty of dirt, the thing upon his breast, The hating woman, the meaningless place, Become a single being, sure and true. -Wallace Stevens Stanza XXXVIII Which I wish to say is this There is no beginning to an end But there is a beginning and an end To beginning. Why yes of course. Any one can learn that north of course Is not only north but north as north Why were they worried. What I wish to say is this. Yes of course -Gertrude Stein XXIV I saw a man pursuing the horizon; Round and round they sped. I was disturbed at this; I accosted the man. "It is futile," I said, "You can never-" "You lie," he cried, And ran on. -Stephen Crane The Allegory of Spring The blossoming cherry trees were quarreling. She thought this when she was fifty yards away and when she was closer, right in amongst them, she imagined she heard them. One tree said to another: I am prettier than you. And the other said: It is impossible for you to see yourself. But I see you. And I tell you you're wrong. The first tree disputed the illogic of this remark. And so on. She went on walking, and when she came out of the cherry grove, she had been through a lot. She hated quarreling. Dietrich was standing by his boat. Come, can you go out with me? he said. I don't want to quarrel, she said. He didn't understand. Well, will you or not? he said. Yes, she said. Then she said, No. -Kenneth Koch Blossoms at night, and the faces of people moved by music. The man pulling radishes pointed my way with a radish. Red morning sky, snail; are you glad of it? -Kobayashi Issa 861 Split the Lark-and you'll find the Music- Bulb after Bulb, in Silver rolled- Scantily dealt to the Summer Morning Saved for your Ear when Lutes be old. Loose the Flood-you shall find it patent- Gush after Gush, reserved for you- Scarlet Experiment! Skeptic Thomas! Now, do you doubt that your Bird was true? -Emily Dickinson Photon Counter Science Light consists of tiny particles called "photons." Using sensitive instruments, we can detect them one at a time. But each one has so little energy that, for most of history, people thought light (indeed, all energy and matter) was a continuous fluid, infinitely divisible. Observing light was like pouring flour, without hearing or seeing the individual grains, versus pouring sand where the granularity is more obvious. To detect a photon, we let it hit a piece of metal, where it knocks off one electron. We accelerate the electron by applying voltage, so that it hits another piece of metal and knocks off several electrons. Doing this about ten times results in around a million electrons for each photon. We can then easily detect a million electrons with ordinary circuits. Experiment A flashlight emits a light beam, which is actually a stream of about ten million billion photons per second. They enter a box where most of them get lost in a black maze. The few that get through (a small, constant fraction of those that went in) hit a sensitive detector. The signal from this detector is amplified and sent to a speaker, where a "tick" is heard each time a photon hits the detector. (There are a few extra ticks a second, due to imperfections in the detector.) To hear these, turn on the switch at bottom right. You should hear many ticks. Then, block the light from the flashlight with your hand, and hear the ticks decrease. Gradually move your hand to control the number of ticks. It sounds like a Geiger counter, which is a particle detector too, but for much more energetic (and destructive) particles. This here is just plain old light. Remember to turn off the sound when you leave. Philosophy When you hear a click, you know a photon has arrived. One can speak of the "granularity" of light, as if it was sand. Yet, before the photons hit the detector, they were wave-like (see the "Uncertainty" and "Wave" exhibits), and not like sand at all. For instance, we know that before detection, photons must have no specific location, spread out instead over an area set by the experiment. Why do we then detect them in a localized spot, like a sand grain? "The wave function collapses" says Quantum Physics, but gives no explanation as to why or where. We don't see anything wave-like or fuzzy about our experimental results, so we know the wave had to disappear before our awareness of the outcome. Although nothing in the standard interpretation of quantum physics prevents it from staying a wave up till then. "Maybe it does" say some thinkers, "and our awareness of it is what collapses the wave function." This leads to an emphasis on consciousness as a key element of quantum physics, and opens the door to philosophies of existence that claim that mind is central to what exists, or mind is all that exists ("idealism"). Reality is said to be "observer dependent." But this puts humans at the center of the universe again, long after heliocentric cosmology shoved them out. Our self-importance overshadows the differences between us and Nature. Also, we never observe our apparatus acting like a wave. Rather, we find the wave function to be delicate and easily destroyed by any interaction with anything else, exactly what it takes for us to observe it (which-aha!-is why we never see it). This could be happening all the time without our knowing, because we simply don't look. Quantum physics is not about what we know, but about what we could know. Thus, when the photon hits the detector tube, the wave magic disappears and we have a "sand grain". If reality is observer dependent, this little detector tube is an observer. What is a Wave? Science A wave is an idea that we can apply to certain types of phenomena in the physical world. The surface of water, electromagnetic fields, sound, earthquakes, electrons, gravity-all behave in a way that we can characterize as "wave-like." It is important that we can so characterize things, because it allows us to quickly explain and predict actions of the physical world. A wave is a traveling "back and forth" oscillation of something (e.g. water, air, electric field, "quantumstuff"). How frequently it oscillates is the "frequency". How far it oscillates is the "amplitude". Where a wave is in it's oscillatory cycle is the "phase" (like the phase of the moon, which has a monthly cycle we break up into quarters, but which is always continuously changing). How fast it travels is its speed. Waves can add or subtract from each other when they collide (called "interference"). Something is wave-like if it exhibits these characteristics. Experiment Play with waves. Turn up the "amplitude" (loudness) knobs and hear sounds that correspond to the electrical waves you see on the oscilloscopes (instruments that make oscillations visible). Change the frequency and amplitude with the knobs. Notice what happens when the waves are added. You can add two different waves or make them the same with the switch. With them both the same, and frequency "A" tuned to a high note, move your head left or right, listening for the sound changing loudness. Cover one ear and see if you can find a place where the sound in the other ear disappears. Philosophy It's striking how widely applicable the concept of a wave is. Many important inventions (radio, for instance) are based on wave action. The paradoxes of quantum physics are due to particles acting like waves. In fact, all modern electronic gadgets are based on the fact that electrons (well known as particles) act like waves when traveling through crystals. Ultimately, everything that constitutes the universe can be seen as consisting of waves. But what does this mean? Are we simply imposing a handy idea on nature and then reaping the benefits, unaware of alternative realities? Or is there something fundamental in nature that exhibits itself as waves everywhere? A realist would say the latter, because one could not use this idea successfully in so many situations without nature's cooperation. Expanding Knowledge Over time, our knowledge increases in scope, but we can never know all. Therefore theories (explanations) based on our knowledge will always be approximations, applicable within a limited range. Theories are collected together to form a coherent world view. Eventually we discover facts that the current theories can't explain, and must develop new ones, ultimately discarding the previous world view. The new theories explain all the knowledge we have, both new and old, although the old theories are still used where possible, because they are simpler.