LTEtext

Preface
What follows is the text for the exhibit kiosks in the "Light, Truth and Existence" pavillion from Burning Man 2003. Bold headings indicate a separate panel. Some of the panels link to ones nearby. There were six experiments and twelve panels, distributed in three kiosks. Some of the related panels have been consolidated into single sections with one heading. Separation of the texts by layout and color is not reproduced below, so some of the continuity will seem jumpy in the absence of additional cues. For instance, the explanations were one color while the directions how to do the experiments were another color.

My thinking has developed further since that time, and some of the things said here I would now say differently. Still, it gives a sense of the kind of explanations that would be used in the Explanade.

Introduction

This is the pavilion of Light, Truth and Existence, where it's all about the trouble you get into
when you ask "what is light?"

To find the answer to that question you must go beyond belief toward truth and knowledge about the physical world. This is the way of science. But we cannot know the importance of our knowledge without philosophy, so there's some of that here too. The facts of science lead to questions about the nature of reality and truth, affecting the way we proceed toward our goal of ultimate enlightenment.

Do the experiments.
Our knowledge of the world is based on observation and experience, which is accessible to everyone. Many of the demonstrations here are things you can do at home, so you can prove it to yourself. That's why science is anti-authoritarian; supreme authority rests with the natural world.

What's said here about light is also true for the entire spectrum of electromagnetic waves, from house current to cosmic rays. Most of it is also true of matter, because energy and matter are so similar, we now know.

There is a lot more to the issues of science and truth than can be said here. The current controversy about empirical (observation based) truth is a major reason why this exhibit was created. Science represents the most reliable knowledge about the physical world, whether or not there are mysteries and uncertainties revealed. To understand the nature of those mysteries, or even get an impression, will help people to determine the validity of the ideas in this debate.

It is hoped that those who come here will leave with questions, and those questions will be answered by the visitors' own engagement with the physical world. Leave belief behind, because beyond there is unending wonder and beauty,
waiting.

Color mixing shows that light is a sensation

Color mixing is:

When you look at two or more colors superimposed, they don't appear separate but seem to "add" to form a new color.

Why this is important:

Your senses are limited, and easily fooled. Sometimes what you see is an illusion, and you can't tell unless you check it some other way. To find Truth, we must not only go beyond our individual subjective limits, but beyond human limits in general. We transcend the limitations of our senses by making instruments which we understand. Then, logic allows us to deduce what we cannot see. Our recent scientific knowledge is based on a long, long string of deductions and inferences which reach far beyond immediate experience.

What to do:

1   Turn the switch to on. The outside colors are constant, while you determine the inside color.
2   Turn all the knobs to the left (off), and then turn one at a time to the right (full on) with the others off, and see what color each knob controls.
3   Turn all the knobs to full on and adjust to make white. You probably have to reduce blue.
4   By adjusting the knobs, try to make all the colors on the outside.

What to look for:

A   What colors are you controlling?
B   What colors appear when you turn on two at a time?
C   What colors appear when you make white and turn off one at a time?
D   With two or three color knobs on, how small a change does it take to make a "new" color?

An explanation:

In your eye there are three types of color sensing cells: for red, green and blue. They are evenly distributed over your retina.

One color sensing cell-—red for instance—will gather a range of colors near red, and then report to your brain "red." The red cell can also sense yellow, and so can the green, because yellow is between them in the spectrum. If yellow light comes into your eye, it will stimulate both the red and green sensing cells, so your brain hears "red" and "green" and figures it's seeing yellow. You can fool your brain by showing the eye only red and green together with no yellow, and your brain still thinks yellow.

You can fool your eye/brain into seeing a whole spectrum of colors by using only the three "primary" colors that correspond to the sensing cells.

Truth is what works

How science defines truth

Switch on the box on this panel. Look at the red spot. Do you see little red speckles? Move your head. De-focus your eyes. How do they change?

One might wonder what's going on, and start to guess reasons for this strange effect. Maybe some test could be done to know more about what's happening. If this is an illusion, other people might see it differently. There is a desire to know the truth behind our observations, especially if they are unusual.

(Here's the answer: the light is special, and tends to make patterns in your eye that aren't "real." The light waves are all synchronized, and when they hit the back of your eye they add and subtract from each other, making a speckle pattern. See the interference exhibit for more details.)

The scientific method isn't much different from what we would do normally to find out reasons for physical things. What's important is that the method is grounded in nature, not outside of it.

First, an observant and curious person sees something interesting happening. Looking more closely, they decide there's something worth investigating. They guess possible reasons for what's happening, and devise some tests to see which of their guesses is correct. If the tests confirm one of the guesses is the real reason, the person might tell others "I've determined that whenever this phenomenon happens, here's the reason. I'm proposing this as a general rule. I therefore can predict the results of future tests where this phenomenon is involved."

Other people might disagree, and come up with different reasons and do their own tests. Some might do tests decide to see if the predictions are true. Others might re-do the initial tests to see if the person missed something, or was fooling themselves.

If things seem to confirm the proposed rule, it starts to look like the first person discovered something that can be said about nature that's true. It might be that this rule reflects some rule that nature actually follows. As more information is gathered, especially from results that had been predicted ahead of time, the belief in this rule becomes solid. The rule is used often, and becomes part of our truth toolkit.

Someday, there might be an observation that contradicts the rule. The previous tests and observations weren't wrong, but they were limited in some way. What we want is to have the most general rules possible, because they are most useful, but also to conform our thinking to the way nature actually is (that's the real scientific attitude). So, after the theory-making and experimental process begins anew, there is a new rule created that explains both the new results and the old.

If the old rule is easier to use in the limited practical instances where it works, then people still use the old rule there. What changes most when the new rule comes in is the interpretation of what it means, in terms of our overall picture of nature. There might be several interpretations of the same rules.

Nature is a single, unified system, we believe. It seems that way. We therefore should seek a single set of rules to express our understanding of how nature works. The rules are not nature's but ours, although they seem to work the same way. As we learn more, we get closer to a complete picture of nature. Our understanding helps us make neat gadgets (the operation of which confirms our theories), but it also makes us feel like good citizens of the universe.

Imaging shows that light is made of rays

Imaging is:

Patterns of light in one location are reproduced in another location by a device which manipulates light. Here are two examples of imaging using rays, which are imaginary straight line paths for the light. We usually put viewing screens or film or electronics where the image is formed, to make the picture visible.

Why this is important:

As the other experiments in this pavillion show, light does not consist of rays. Rays are an old idea that has been superseded by theories that explain more. Still, the old idea works well enough to be in constant practical use today, even though it isn't our best picture of "reality."

We can only judge the truth of a scientific theory by how well it works to explain and predict everything we now know. We may yet find the limits of the current theories and move farther toward ultimate truth, but since we are only describing our limited experience, we may never have a perfect picture of reality. Maybe every human theory is like "rays"; useful, but true only within limits.

What to do:

1. Turn on the box on this panel, so the three colored lights go on.
2. Pick up the "camera obscura" box hanging from this kiosk. There are four openings in it: a hole, a lens, and two screens.
3. Point the hole at the lights, and look at the "screen for hole." Try to position the box so you get all three lights on the screen.
4. Turn the box to point the lens at the lights, and look at the "screen for lens."
5. Point the lens around the room and watch the screen.

What to look for:

A   What do you see when the hole is pointed toward the colored lights?
B   Is the orientation of the lights on the screen the same as on the panel?
C   How is the image different when you use the lens? Which image is brighter?
D   What is in focus when you point the lens around?

An explanation:

The simplest camera
If light is made of rays, light will travel in a straight line from the source to an end point where it gets scattered or absorbed. When you point the hole at a light source, the rays go through the hole in a straight line toward the screen, as in the diagram below. This is how an image can be made on the screen, but it is upside down. The image would be sharper if the hole was smaller, but then very little light would get through.

A plastic eye
A lens is a piece of glass shaped to bend light rays so that all the rays that come from a point source in front of the lens are focused to a point in back of the lens. The distances of the points to the lens have to be just right to get a good focus. A lens is better than a hole because more light is gathered and focused on the screen.

Interference shows that light is made of waves

Interference is:

When two or more light waves hit the same place, they can add or subtract, causing patterns of light and dark.

This interferometer is a device which makes two waves interfere, by splitting one wave into two, letting them go through different paths and then recombining them. See the simplified diagram at right. When the relative lengths of the two paths are varied, changes in interference clearly indicate waves.

Why this is important:

An interferometer shows that light is made of waves. At the same time, we know that light is made of photons. Since the interferometer works by splitting a light wave into two, what happens to photons that go through the experiment? They do not split in two, but strangely act as though they did. Interference brings up the mysteries that come from the dual, wave/particle nature of light.

What to do:

1. Flip the switch next to the experiment box to "on."
2.   Look at the screen in the box, at top right. There will be a striped red pattern on it.
3.   Gently push on the button sticking out from the box, while watching the red pattern.

What to look for:

A   How does the pattern change when you push on the button?
B   How many lines move through as you push?
C   How little pressure does it take to move only one line?

When you push on the button, you are bending a rigid plate of metal a tiny amount. Waves of light are so small that a movement you can't see changes the light path by several waves.

An explanation:

What is a light wave?
A water wave is a periodic variation of the height of the water. A light wave is a periodic variation of something called "electric field." If you put an electron in this field, the electron would feel a force tending to make it move, like a floating thing on the water.

Alternating force
In a light wave, the field points alternately in one direction then the other. The transparent plates hanging from this kiosk illustrate this, where the dark and light lines represent electric field pointing up and down, say.

What's happening in the box?
A laser beam hits a partially reflecting mirror. Half of the power goes through to a mirror and back, and half reflects off and goes to another mirror and back. When they return to the partial reflector, the two beams recombine and go to the screen.

When you press on the plate that holds the mirrors, it bends very slightly, but enough to shift one beam path several light waves. This is because light waves are so small, only 1/100th the diameter of a human hair.

Diffraction shows that light is made of waves

Diffraction is:

Any abrupt disturbance of a light wave makes it change direction at that point and spread out. When light waves encounter an obstacle, they don't just make a simple shadow on the other side, but spread into the shadow region and make complex patterns. Even transparent obstacles with sharp features can cause this effect.

Why this is important:

When we consider the results of these diffraction experiments in light of the fact that light is also made of particles, profound mysteries emerge. The single slit illustrates quantum uncertainty, which suggests the end of precise knowledge and objectivity. The double slit shows a property of photons which is different from any real object we know, and questions our concepts of objects and reality.

Experiment 1: Single slit

A laser pointer hits a gap between razor blades.
A screw adjusts the width of the gap.

What to do:
1. On the box, press the button that turns on the "single slit."
2. With the other hand, rotate the knob on the bottom of the box marked "turn left to reduce slit." It only goes part of a turn.
3. Look at the screen above the box and watch the pattern as you slowly turn the knob.

What to look for:
A   When you reduce the width of the slit, what happens to the brightness of the beam?
B   How wide does it get before it shuts off completely?
C   What pattern can you see in the beam?
D   How does this change with slit width?
E   Can you guess a rule?

Experiment 2: Double slits

A laser pointer hits a specially made piece of thin metal with pairs of rectangular holes in it.

What to do:
1. Press the buttons marked "double slit 1x" or "double slit 2x."
2. Examine at the beams on the screen above the box.
3. Turn on the single slit and see if you can turn the knob to make a pattern with the same large features.

What to look for:
A   What new features are visible in the beam patterns, compared with the single slit?
B   What features are the same as the single slit?
C   If the slits in "double slit 2x" are each twice as wide and twice as far apart as the slits in "double slit 1x," can you guess a rule for how the pattern is affected?

An explanation:

Imagine a small stone dropped into a pool. Waves come out from it in all directions. Now imagine a straight stick dropped horizontally into a pool. The waves that come out look more like the stick, in that they are series of lines rather than circles. Most of the wave energy emitted from the stick splash goes out perpendicular to the length of the stick.

The laser-illuminated single slit, when it is almost closed, is like the dropped stone. It is similar to a perfect point emitting light, so the light tends to spread out in all directions. The wider the slit gets, the more it is like the stick, in that waves tend to come out horizontally and not spread so much.

The dashed pattern that appears is caused by light waves from one half of the slit cancelling out waves from the other half. At some point on the screen where there's a dark spot in the beam pattern, the distance to that point from one half of the slit is a half wave more than the distance to that point from the other half. At this point the waves always apply force in opposite directions, so the net effect is zero.

The double slits make dashed patterns within the larger dashed pattern because of a similar process. Here, light is spreading out from each slit. The beam patterns of the two slits overlap on the screen, so there is a larger pattern like the single slit. Where there are dark spots within the larger pattern, this is where light waves from the two slits are cancelling each other out.

The uncertainty principle revealed

Check out the diffraction experiment next door before reading this, because you will then be familiar with the setup described here.

We can imagine doing the single slit diffraction experiment with a very dim laser, where only one photon goes through the slit at a time. This will tell us how an individual photon behaves, which is really no different from how it behaves in the presence of other photons

The first uncertainty: position
We can know approximately where the photon was when it went through the slit, because we know the width of the slit. We know it was somewhere in the slit, but we are uncertain as to exactly where. We say the slit width is the amount of uncertainty.

The second uncertainty: momentum
There is another uncertainty: how far the photon will depart from a straight trajectory after it leaves the slit. If it goes straight, the photon will hit the center of the pattern. The distance it’s traveled off center tells how much vertical momentum it has. The width of the pattern on the screen is an indicator of the uncertainty in this vertical momentum, because the photon could wind up anywhere within the pattern.

Their relation
It should now be apparent that the uncertainty in position and momentum seem to trade off. Less uncertainty in vertical position means more uncertainty in vertical momentum and vice versa.

This is the famous uncertainty principle. It involves certain pairs of related quantities. If you are more certain of one of these related quantities, you are less certain of the other.

Uh-oh, deeper issues...

We want to know more
One might wonder what caused the photon to go exactly where it did after leaving the slit. We could conjecture that the exact angle is related to the exact position where the photon went through the slit.

But can’t
If we narrow the slit to find out the photon’s exact trajectory, the photon’s direction becomes even more uncertain. You can’t beat the uncertainty principle, so one can’t know the answer to the question.

So the exact behavior of the particle—its choice of trajectory—is something for which we can’t know the cause. Maybe something specific is happening in the photon’s little life there, or maybe it’s just random chance, but we can never know.

Despair
It’s the end of the journey of cause-and-effect, because here’s an effect for which we can know no cause. It’s the end of the journey of increasing precision because here’s a level of uncertainty we must always accept.

Hope
We might seek a different kind of certainty. If we only want to know the statistics, the averages of where the photon is likely to go, we can know that with great precision, it turns out. Put enough photons through the slit, and you get an accumulated pattern on the screen that can be predicted exactly.

The macroscopic world we know so well is comprised of vast collections of photons and other tiny objects, so we are always seeing only the averages. The precision of statistical predictions gives us the appearance of certainty and solidity, even though there is uncertainty at the tiniest levels. Our everyday experience needn’t change, though we know certainty is never perfect.

Look! Fun! Not too tough!

Try this at home:

If you want to play with single-slit diffraction, here’s a handy experiment.

Find a distant, bright light at night, one that sort of glares at you. Get some nail clippers or wire cutters, where the edges come together parallel, not slicing like scissors. Hold the clippers very near your eye (carefully), and look through the cutting part at the light. Sort of “cut” the light rays coming toward you.

You will see the light seem to expand sideways into the cutting edges before it disappears. The image is expanding because of diffraction and the uncertainty principle.

Try this at home two:

If you want to play with double-slit diffraction, you can do something similar with a piece of hair.

Go find a distant, bright light again. Take a single strand of hair and stretch it taut between your hands. Then put the hair right near your eye, so it crosses your field of view (again, carefully), and goes right across the bright light. You will see a streak of light that crosses the bright light, at right angles to the hair. If you look closely you might see it’s a dashed line, and has rainbows in it if the light is white.

You are seeing the same dashed pattern as with the double slits. In this case, all you have is the opaque gap between the slits, and the slits have no outsides, but it’s similar enough.

Try different thickness hairs. Can you figure out a way to determine how fine someone’s hair is?

Uncertainty shows that light is made of you

Observer-dependent reality

You should do the diffraction experiment and read the associated uncertainty principle panel before reading this one, because the ideas here are a continuation.

Consider again the single slit diffraction experiment, where there's a laser beam that hits a narrow slit. On the other side there's a screen, and instead of a narrow beam like the laser made, there is now a wide pattern. The slit has made the laser beam spread out. Now imagine that the beam is so weak that only one photon goes through at a time. The photons will hit the screen in random places, gradually building up the pattern as before, although we are uncertain as to where any one of them will hit.

A clever scheme
Let's imagine someone is using this arrangement as a way to measure the exact trajectory of a photon. It comes from the laser, which is a nice source of identical photons. Then we make it go through a slit in order to know where it is in space at that point. If we draw a line between the laser and the slit, we then know where the photon is going.

Doesn't work!
But wait. The photon is not going in the same straight line after it goes through the slit. It heads off in some random direction. We now don't know the trajectory at all.

It looks like we made an experimental faux pas: we somehow caused the photon to change direction. We didn’t want to do that; we just wanted to measure its position and let it go on its way, like a quiet bird watcher. But we affected it, and we can’t imagine not doing so, if all our measurement apparatus is in principle similar to the slit.

Uncertainty vs. objectivity
We thus can’t make a measurement from a purely objective, removed point of view, but must now account for how our measurement (the imposition of the slit) seems to affect—or define, really—the actions of the photon (its subsequent trajectory).

It becomes impossible to speak of "the photon's trajectory" because just by trying to know that trajectory we determine what it is. The reality of the photon's path is due in part to our efforts to know it. We no longer stand outside the reality that we study, but become a part of it. The reality we are studying in the photon's case is sometimes called "observer-dependent."

Different kinds of subjectivity
We need to make a distinction between objectivity versus observer-dependence, and objectivity versus subjectivity. Objectivity can mean that we are completely independent from the thing we observe, or it can mean that no matter who observes it, the thing appears the same. In modern physics, the former is false, but the latter is true. Therefore, observer-dependence doesn't imply subjectivity. We needn't accept all the theories of knowledge that say we create reality in our heads.

Different ideas of existence
This observer-dependence puts limits on what we can know, and what questions it makes sense to ask. If we accept the idea that nothing exists unless it's at least in principle measurable, then the photon's exact trajectory doesn't exist. We can only speak of it in speculation, although that speculation would not be science. It would be metaphysics, which is the study of existence in general, and of things we're not sure exist.

There is another school of thought that is more constraining, which says that things can only be said to exist if in fact they have been measured or observed. Reality is then completely observer-dependent. This is not necessarily to deny that there is a physical reality apart from us, but to define reality as knowledge, and the universe as a universe of ideas. This puts so much dependence on our knowledge of things that it seems to make consciousness the center of everything, an idea distasteful to most scientists. Still, it is interesting to see where this leads.

If something can only be said to exist if it is observed, this is quite different from saying that the thing springs into existence because it is observed. The difference is in the direction of cause and effect. On the one hand, something existing causes you to be able to observe it, and on the other hand your observation causes it to exist. The problem is, if you deny any pre-existence before your observation, you are left with the notion that you caused the existence.

Mystification
This notion leads to all sorts of ideas about the importance of thought as a force, and the responsiveness of matter to our whim. Mysticism and supernatural forces become explicable by recourse to observer dependence and the uncertainty principle. At least one author claims that quantum mechanics explains why you should be able to cure cancer by meditating. This sort of reasoning should indicate a wrong turn in our efforts to interpret the discoveries of quantum physics.

Metaphysical realism is OK
The alternative to defining reality as that which is observed would be to say reality pre-exists our observations and consciousness, in some form which we then discover abeit imperfectly. This is what most scientists believe. The problem is, you cannot show such a universe to exist, because then you would be observing it, and we're back to the universe being only what we observe. The existence of a reality beyond observation has to remain a belief, and be part of metaphysics. Such an idea motivates us to continue to explore, because we know there is more out there to find.

The mysteries of the uncertainty principle can be clarified by saying that the photon's behavior is not observer-dependent but context-dependent. If we do the experiment a certain way, the photon acts accordingly. It would do so in the same situation whether we were there or not. We have only to recognize what attributes of the photon are affected in this way, and accept them in their variability as part of reality.

Photoluminescence shows that light is made of particles

Photoluminescence is:

A material is struck by light of one color, and gives off light of a different color. It's not like colored paint, which simply absorbs some of the light that hits. Photoluminescence makes a new color that wasn't in the original light.

Why this is important:

The continuous afterglow of glow-in-the-dark materials shows that the time each molecule holds energy is random, although governed by averages. This randomness is basic, so we can't know precisely when an atom will emit, or equivalently, why it went off when it did. It's an effect for which we can't know the cause, and what we can't know doesn't exist, so we have reached the limit of cause-and-effect, the philosophical basis of science.

What to do:
1. Turn the knob to select a color.
2. Push either button to make light emit from the box. The square button turns it on continuously.
3. Take the palette of photoluminescent materials hanging from the kiosk, and put it under the light.
4. Look through the transparent plate at the top of the box, toward the center of the box. You should see the colors separated in a front-to-back direction.
5. Try different colors with different materials.
6. Put the infrared sensor under the violet light for a few seconds, then select infrared light.

What to look for:
A   Which colors do the materials absorb?
B   Which ones do they reflect or transmit?
C   How long does it take the materials to stop glowing?
D   Which colors make them glow, and what color is the glow?
E   Can you guess a rule?

An explanation:

What molecules do
When a light particle (photon) hits a molecule (or atom), depending on the photon energy and on the molecule, various things can happen. Refer to the cartoons below, showing a molecule catching a photon and storing its energy. The glowing materials here illustrate fluorescence and phosphorescence, which are the same except phosphorescence takes longer.

Energy is conserved
Any color more toward the violet end of the spectrum has more energy per photon than any color more toward red. The energy of the photons in the glow must always be the same or less than the energy of the photons that hit the molecule originally, because the total energy is constant, and some is always lost. Therefore the color of the glow must always be more to the red than the color that originally hit.

An anomaly
One of the materials violates this rule: the infrared sensor. High energy photons charge it up. Then, when an infrared photon hits it, it's "triggered" to re-emit some of the energy as orange light.

Makeshift spectroscope
The plate on the top of the box has a "diffraction grating" in it, which works like "rainbow glasses," bending different colors of light in different directions.

Free will and knowledge

Fluorescence and free will

Early in the development of physics, it seemed as though the actions of all matter and energy could be predicted with absolute precision, if you knew where things started, where they initially were going, and the rules that governed their development. It seems like a reasonable idea, if you have confidence in the rules you've discovered, and optimism about being able to measure things exactly. If you could, using the laws of physics, make such predictions, you could know the future.

The universe machine
In this view of things, the future becomes the eventual state of some giant machine, which is continually churning out the present. The advent of mathematical physics enabled people to know the mechanism of the machine, and hope to know its evolution.

That the universe was a precisely programmed machine was not a new idea. For thousands of years people had tried to predict the future by marking the motions of the planets, the most precise machine they knew. It was thought that time was so exactly programmed that when the planets all lined up as they did when the world was created, the world would be destroyed and remade anew. Then it would play out the progression of history exactly as it did the first time. The new physics allowed such greater exactitude in predicting planetary orbits, the goal of knowing the future in detail might finally be realized.

Newtonian automatons
In a leap of imagination, it was also realized that we as humans, being comprised of matter and energy, ultimately function according to the laws of the universe machine. In this view of things, we become very complex robots without a metaphysical soul that would operate outside the laws of nature.

No soul and no volition
If you could know the future, you could know human actions before they were thought. No one could make a decision contrary to the revealed plan. Even those who knew the plan would be subject to it because they were part of the universe machine too.

Thus free will would no longer exist.

There are of course practical impediments to knowing where every atom was at a particular time, and where those atoms were all headed. Only somebody like God could know that much. But even if no one but God could predict all your actions, you still would not have free will.

New physics rescues free will
As physics progressed, we discovered that there are unpredictably random elements in nature. Beyond knowing the statistics of certain processes, we cannot know what will happen in any particular instance. An example is how long it takes for a fluorescent molecule that captures a photon to give up the photon's energy. The molecule will grab the energy, hold it for some time and then re-emit the energy as light. We know the statistics of each molecule and photon combination very well, but no one can predict the time any one molecule will take. That's why glow-in-the-dark materials shine continuously after you put them in light. There are lots of molecules, and each one takes its own time.

The knowledge of basic random processes makes a precisely predictable universe machine impossible. If those random processes have an influence on human actions, our actions will be unpredictable, even by God. That is, if he follows his own natural laws, which is not guaranteed. We therefore can probably be said to have free will. At least, science gives reason to hope.

Neo's
Quantum 8-Ball!

Tired of the omniscient almighty knowing your
every move? Can't stay one step ahead of the
totalitarian police state?

The solution is the new Quantum 8-Ball!

Let your decisions be determined by a random
process that no one—and we mean NO ONE—can
predict! Physics has proven prior knowledge of the
outcome of this process to be IMPOSSIBLE!!

Unlike the cheap knock-offs, the original Neo's
Quantum 8-Ball uses no radioactive elements! Only
safe and efficient quantum electronic tunneling for
reliable, random results. Thousands of responses
are possible, to keep the control freaks scratching
their heads!

And it's so unpredictable, even God will never know!!!

The photoelectric effect shows that light is made of particles

What this means:
Light consists of units of energy we call photons.
The photoelectric effect was a mystery until explained in this radical new way in 1905. This explanation changed the way we understood light, and along with other developments in quantum physics, changed the way we understood the physical universe and the nature of reality.

Photoelectric effect is:
Some material is struck by light, and electrons are knocked loose, becoming an electric current.

The experiment:
There is a little glass tube visible in the box. It has a curved metal plate which is struck by light. There is a wire in front of the plate which catches electrons knocked off the plate by the light. You can control the light color and power. You can also apply a variable opposing force against the electrons to make them stop before they're caught by the wire. This lets you measure how energetic they are, when they can barely oppose the force and reach the wire.

What to do:
1. Make sure the bottom knob, marked
"stopping force" is turned all the way to the left.
2. Turn the color knob to select a color.
3. Adjust the power (photon flow rate) of the light, and watch the current (electron flow rate) meter. Try it with different colors.
4. With a color turned up to the maximum power,
slowly turn the stopping force knob to the right
until the electron flow rate just barely reaches zero.
5. Note what energy the "energy removed by stopping force" meter says.
6. Turn the barrier down to zero and try this again with different colors.

What to look for:
A   What is the relation between photon flow rate and electron flow rate?
B   How does the "energy removed" affect the electron flow rate?
C   How does the color affect how much the "energy removed" has to be in order to stop the electron flow? Can you guess a rule?

An explanation:
When a photon hits an atom, a piece of the atom—an electron—can be forcefully knocked off. The electron flies away with all the energy of the photon, minus the energy it took to break the electron loose.

The more photons that hit the material, the more
electrons are knocked off. We see the moving electrons as electric current.

Through the visible spectrum, photons toward the violet end have more energy than photons toward the red end. If we try to stop the electrons by making them struggle against an opposing force, we can see how much energy they have. Electrons knocked off by high energy photons will have more energy than electrons knocked off by low energy photons, and will go through a stronger force.

If light was a continuous flow of energy rather than particles, the color would not determine how much energy electrons get from the light. What might matter is how long you shined the light and at what intensity. The light power control here doesn't appreciably change the electrons' energy (except for some spurious
effects it's hard to get rid of in a simple setup).