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Displays and experiments
Expanding circles of knowledge
A diagram depicts the increase of scientific knowledge in terms of the areas of concentric circles. Inner circles represent the old theories and their regions of applicability. Outer circles represent new theories which encompass all previous knowledge, and hopefully anything we will encounter in the future. As knowledge expands, sometimes it overtakes the theory, requiring a new one (a new outer circle). (This model implicitly contradicts popular historian of science Thomas Kuhn and his paradigm/revolution model.)
Black boxes of reality
Our knowledge of the “world as it really is” can be compared with our knowledge of a “black box:” a container with inputs and outputs but unknown contents. The visitor is presented with three black boxes with two buttons and a light each. We can act in the world (push the buttons) and observe the results through our senses (see the light light up). But we can’t know what’s inside the box (the thing as it really is, or the “thing in itself” as Kant said). The visitor is invited to theorize about what’s in the boxes. Upon peeking, it is found that the boxes (which all exhibit the same behavior) have three different internal mechanisms, including one with a smaller black box inside.
The white crow
An standard example of the limitations of knowledge based on experience is that of the bird watcher who hypothesizes that all crows are black, after seeing only black ones so far. Maybe there is a white one out there no one has seen, it’s impossible to be certain. Still, it’s a good bet to say the next one you see will be black. The visitor can pull a lever to spin a jackpot-like wheel with (almost all) black crows on it. The visitor can form a hypothesis and test it by spinning the wheel multiple times. The more black crows come up, the more the hypothesis is confirmed, even if there was a white one somewhere not yet seen.
Ferrofluid spikes
A ferrofluid is a liquid filled with magnetic dust. When a magnet is placed below a shallow tray of this material, the fluid is pushed upward, but suddenly the lump of fluid breaks into spikes of uniform size. Why? Nothing in the magnetic dust particles says “you are programmed for spikes.” These arise because it’s easier for the fluid to collapse into zones that constrain the magnetic force inside them than it is to form a uniform lump. All the magnetic particles are connected via the fluid and the magnetic force, producing an “emergent property” of spikiness. This kind of phenomenon results in many of the features of our world that are unexpected unless you look at the big picture. The viewer can vary the magnet strength and see spikes form and disappear. It’s an argument for holism.
The game of life
This computer game demonstrates how life could spring from “dead matter” without a soul. The computer has many square “cells” that follow a simple set of rules that connect adjacent cells. The viewer can change the arrangement of cells or preload patterns, resulting in surprising action that never could have been predicted based on the simple rules. Patterns emit other patterns that move across the screen and are absorbed by other patterns, as some grow and others change. It’s an example of “emergence” and another argument for a big picture approach to complex systems.
Photon counting interferometer
This ambitious experiment reveals the utter strangeness of quantum particles. A light source emits light particles one at a time. The light signal splits into two parallel paths that recombine by crossing. A slight change in the length of one of the paths (controlled by the visitor) determines which final output path all the light appears in. It is argued that only a wave that was simultaneously in both paths could behave this way. Upon examining the signals in each path, the visitor only finds particles in one or the other, not a wave in both. How could this be? This experiment confronts the visitor with deep issues concerning knowledge, existence and time.
Rays are good enough, sometimes
Light used to be considered a ray, that is, something that travels in straight lines. This is good enough to explain why a laser beam is constrained to narrow down as the visitor reduces the diameter of an iris it passes through. But when the iris gets too small, the beam starts to expand into beautiful patterns. This behavior can only be explained by assuming light consists of waves, and the rays are just an approximation. We can still use rays to explain how a pinhole camera works (which the visitor can look through). The older theory wasn’t wrong, just limited in its applicability. But it was the wrong ultimate world view. We still use old theories, but we don’t believe in them.
Don't be fooled by optical illusions
Illusions are the bane of knowledge based on sense experience. How do you know your perceptions are not just illusions? Well, you can test them. The viewer sees a hologram, which is convincing until one puts one’s hand through it. An illusion of motion is created by a pattern that is clearly stationary when you look closely at its parts. An illusory color is found to be comprised of three primary colors when the visitor can turn each off and on at will. We needn’t be afraid that illusions dominate our experience of the world, because they have the hallmarks of illusions rather than the hallmarks of reality, which careful tests reveal.
What is a wave
It can be strongly argued that the entire universe consists of waves of one sort or another. What is a wave? The visitor can manipulate some electronic and sound waves to see how amplitude (loudness), frequency (tone), phase (delay), resonance (ringing) and interference (mutual cancellation) work. These concepts apply to everything from earthquakes to atoms. The concept of a wave is one of the most powerful explanatory tools in physics. We recognize wave phenomena from experience with sound, so sound is emphasized in this exhibit, which allows the visitor to play until the concepts become intuitive.
Decoherence: from the perfect to the ordinary
How does the everyday world emerge from the underlying quantum world? They are very different, yet one is made up of the other. This exhibit shows an example of a phenomenon that forms the basis of one possible answer. A laser emits nearly perfect light waves, like the waves of quantum particles when they are alone. The viewer can see a special quality of this light when reflected from a rough surface: the surface seems to be speckled, but the speckles move as the viewer moves their head. This is because the waves of light are slightly crinkled by the surface, and interfere with each other in the viewer’s eye (which links to the illusions display). The light passes through several diffusing surfaces, and as the light waves get more crinkled, the speckles get smaller until the light looks just like ordinary light with no speckles. This is analogous to how a quantum particle has its wave wrecked by interaction with the real world, and becomes more like what we recognize. After much buffeting about, complexification makes the quantum weirdness go away. (This display links to the photon counting interferometer display.)
When does ultimate truth matter?
Does it matter that things are made of atoms, not some continuous material? It depends on what you do with the material. It’s like dots on a color printed page. Look closely enough and the dots do matter, but far away you don’t notice or care. We know the world is made of atoms, but we don’t have to believe that it is when pouring water or cutting metal. For most ordinary activities, we could adopt the world view of Aristotle and reject the idea of atoms entirely. But we know this is not ultimately true, because looking close reveals atoms again. There are practical world views and ultimate world views. The visitor is invited to examine objects with a microscope, including color printing.
A deterministic machine
In the 19th century, it was thought that if an omniscient being could know every position and motion of every atom at one moment, they could predict the future and know the past precisely. This was called determinism, the idea that the course of all events is determined by the laws of nature. We now know that nature has many unpredictable elements that comprise it, so such a perfect prediction would be impossible. Still, the deterministic universe is an attractive idea. A mechanical toy is presented, where figures move according to gears and cams. The visitor can observe the driving mechanism, playing 19th century God.
The speed of light
No energy or information can move faster than light. This fact erases any concept of simultaneity or absolute time, a la Special Relativity from Einstein. To show that this speed is not infinite, we measure it with a simple instrument and some pulses of light. The visitor can move a reflector back and forth and see how the echo time for a reflected light pulse changes. The delay inside the explanade can only be a few billionths of a second. This means that the view you see of things around you is not how they look at present, but a few billionths of a second ago. Light from the distant mountains conveys news that’s a few millionths of a second old. The visitor is invited to look outside at night, at a specified point in the heavens, to see the 2.8 million year old light from the Andromeda galaxy. Given this limitation to the freshness of our knowledge, the idea of “now” kind of melts away.
Foucault pendulum
A carefully suspended pendulum swings in one plane, while a platform it’s attached to can be rotated by the visitor with no effect on the pendulum’s motion. If the platform was the earth (and the pendulum was at the north or south pole) the pendulum would still swing in one plane and ignore the earth’s rotation. Presumably the pendulum ignores the motion of the earth’s orbit around the sun as well. Well then, what is its reference? It’s stationary with respect to what? Itself, during previous swings. Such unperturbed objects with kinetic energy are indicators of straight lines and flat planes in what we call spacetime. The pendulum is aligned with respect to its history. This says something about continuity in our world view, and the present reality of past things.
Expanding circles of knowledge
A diagram depicts the increase of scientific knowledge in terms of the areas of concentric circles. Inner circles represent the old theories and their regions of applicability. Outer circles represent new theories which encompass all previous knowledge, and hopefully anything we will encounter in the future. As knowledge expands, sometimes it overtakes the theory, requiring a new one (a new outer circle). (This model implicitly contradicts popular historian of science Thomas Kuhn and his paradigm/revolution model.)
Black boxes of reality
Our knowledge of the “world as it really is” can be compared with our knowledge of a “black box:” a container with inputs and outputs but unknown contents. The visitor is presented with three black boxes with two buttons and a light each. We can act in the world (push the buttons) and observe the results through our senses (see the light light up). But we can’t know what’s inside the box (the thing as it really is, or the “thing in itself” as Kant said). The visitor is invited to theorize about what’s in the boxes. Upon peeking, it is found that the boxes (which all exhibit the same behavior) have three different internal mechanisms, including one with a smaller black box inside.
The white crow
An standard example of the limitations of knowledge based on experience is that of the bird watcher who hypothesizes that all crows are black, after seeing only black ones so far. Maybe there is a white one out there no one has seen, it’s impossible to be certain. Still, it’s a good bet to say the next one you see will be black. The visitor can pull a lever to spin a jackpot-like wheel with (almost all) black crows on it. The visitor can form a hypothesis and test it by spinning the wheel multiple times. The more black crows come up, the more the hypothesis is confirmed, even if there was a white one somewhere not yet seen.
Ferrofluid spikes
A ferrofluid is a liquid filled with magnetic dust. When a magnet is placed below a shallow tray of this material, the fluid is pushed upward, but suddenly the lump of fluid breaks into spikes of uniform size. Why? Nothing in the magnetic dust particles says “you are programmed for spikes.” These arise because it’s easier for the fluid to collapse into zones that constrain the magnetic force inside them than it is to form a uniform lump. All the magnetic particles are connected via the fluid and the magnetic force, producing an “emergent property” of spikiness. This kind of phenomenon results in many of the features of our world that are unexpected unless you look at the big picture. The viewer can vary the magnet strength and see spikes form and disappear. It’s an argument for holism.
The game of life
This computer game demonstrates how life could spring from “dead matter” without a soul. The computer has many square “cells” that follow a simple set of rules that connect adjacent cells. The viewer can change the arrangement of cells or preload patterns, resulting in surprising action that never could have been predicted based on the simple rules. Patterns emit other patterns that move across the screen and are absorbed by other patterns, as some grow and others change. It’s an example of “emergence” and another argument for a big picture approach to complex systems.
Photon counting interferometer
This ambitious experiment reveals the utter strangeness of quantum particles. A light source emits light particles one at a time. The light signal splits into two parallel paths that recombine by crossing. A slight change in the length of one of the paths (controlled by the visitor) determines which final output path all the light appears in. It is argued that only a wave that was simultaneously in both paths could behave this way. Upon examining the signals in each path, the visitor only finds particles in one or the other, not a wave in both. How could this be? This experiment confronts the visitor with deep issues concerning knowledge, existence and time.
Rays are good enough, sometimes
Light used to be considered a ray, that is, something that travels in straight lines. This is good enough to explain why a laser beam is constrained to narrow down as the visitor reduces the diameter of an iris it passes through. But when the iris gets too small, the beam starts to expand into beautiful patterns. This behavior can only be explained by assuming light consists of waves, and the rays are just an approximation. We can still use rays to explain how a pinhole camera works (which the visitor can look through). The older theory wasn’t wrong, just limited in its applicability. But it was the wrong ultimate world view. We still use old theories, but we don’t believe in them.
Don't be fooled by optical illusions
Illusions are the bane of knowledge based on sense experience. How do you know your perceptions are not just illusions? Well, you can test them. The viewer sees a hologram, which is convincing until one puts one’s hand through it. An illusion of motion is created by a pattern that is clearly stationary when you look closely at its parts. An illusory color is found to be comprised of three primary colors when the visitor can turn each off and on at will. We needn’t be afraid that illusions dominate our experience of the world, because they have the hallmarks of illusions rather than the hallmarks of reality, which careful tests reveal.
What is a wave
It can be strongly argued that the entire universe consists of waves of one sort or another. What is a wave? The visitor can manipulate some electronic and sound waves to see how amplitude (loudness), frequency (tone), phase (delay), resonance (ringing) and interference (mutual cancellation) work. These concepts apply to everything from earthquakes to atoms. The concept of a wave is one of the most powerful explanatory tools in physics. We recognize wave phenomena from experience with sound, so sound is emphasized in this exhibit, which allows the visitor to play until the concepts become intuitive.
Decoherence: from the perfect to the ordinary
How does the everyday world emerge from the underlying quantum world? They are very different, yet one is made up of the other. This exhibit shows an example of a phenomenon that forms the basis of one possible answer. A laser emits nearly perfect light waves, like the waves of quantum particles when they are alone. The viewer can see a special quality of this light when reflected from a rough surface: the surface seems to be speckled, but the speckles move as the viewer moves their head. This is because the waves of light are slightly crinkled by the surface, and interfere with each other in the viewer’s eye (which links to the illusions display). The light passes through several diffusing surfaces, and as the light waves get more crinkled, the speckles get smaller until the light looks just like ordinary light with no speckles. This is analogous to how a quantum particle has its wave wrecked by interaction with the real world, and becomes more like what we recognize. After much buffeting about, complexification makes the quantum weirdness go away. (This display links to the photon counting interferometer display.)
When does ultimate truth matter?
Does it matter that things are made of atoms, not some continuous material? It depends on what you do with the material. It’s like dots on a color printed page. Look closely enough and the dots do matter, but far away you don’t notice or care. We know the world is made of atoms, but we don’t have to believe that it is when pouring water or cutting metal. For most ordinary activities, we could adopt the world view of Aristotle and reject the idea of atoms entirely. But we know this is not ultimately true, because looking close reveals atoms again. There are practical world views and ultimate world views. The visitor is invited to examine objects with a microscope, including color printing.
A deterministic machine
In the 19th century, it was thought that if an omniscient being could know every position and motion of every atom at one moment, they could predict the future and know the past precisely. This was called determinism, the idea that the course of all events is determined by the laws of nature. We now know that nature has many unpredictable elements that comprise it, so such a perfect prediction would be impossible. Still, the deterministic universe is an attractive idea. A mechanical toy is presented, where figures move according to gears and cams. The visitor can observe the driving mechanism, playing 19th century God.
The speed of light
No energy or information can move faster than light. This fact erases any concept of simultaneity or absolute time, a la Special Relativity from Einstein. To show that this speed is not infinite, we measure it with a simple instrument and some pulses of light. The visitor can move a reflector back and forth and see how the echo time for a reflected light pulse changes. The delay inside the explanade can only be a few billionths of a second. This means that the view you see of things around you is not how they look at present, but a few billionths of a second ago. Light from the distant mountains conveys news that’s a few millionths of a second old. The visitor is invited to look outside at night, at a specified point in the heavens, to see the 2.8 million year old light from the Andromeda galaxy. Given this limitation to the freshness of our knowledge, the idea of “now” kind of melts away.
Foucault pendulum
A carefully suspended pendulum swings in one plane, while a platform it’s attached to can be rotated by the visitor with no effect on the pendulum’s motion. If the platform was the earth (and the pendulum was at the north or south pole) the pendulum would still swing in one plane and ignore the earth’s rotation. Presumably the pendulum ignores the motion of the earth’s orbit around the sun as well. Well then, what is its reference? It’s stationary with respect to what? Itself, during previous swings. Such unperturbed objects with kinetic energy are indicators of straight lines and flat planes in what we call spacetime. The pendulum is aligned with respect to its history. This says something about continuity in our world view, and the present reality of past things.
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