Download STM Intro Script - MSU Science Theatre

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Quantum Mechanics and the STM Show Script!
Version for Elementary & Middle School Students
[Enter QM-STM Group]
P1: Hi! We are a group of undergraduate students from MSU who have been working since 2006
(?) with Dr. Tessmer and Science Theater to prepare a 45-minute crash-course (change as
appropriate to length of revised show) into the wonderful and strange world of quantum physics.
P4: What’s that?
P2: Quantum physics is an important set of scientific ideas that completely changed the way we
think about the world around us.
P1: The word quantum means “how much,” and refers to the smallest possible unit of something.
Accordingly, quantum mechanics says that everything—including this table, electricity, and even
the light that lets us see everything—is made up of tiny building blocks.
P3: Please remember during this performance that the rating of this show is EW for “extremely
weird”. We’ll try to explain everything as clearly as we can, but if anything sounds confusing,
feel free to ask questions at any time—even weird ones!
P1: We have an exciting theater-style show for you today. We have with us a very special kind
of microscope called a Scanning Tunneling Microscope, which uses the ideas of quantum
mechanics to look at things that are very very small. We’ll start by giving you an introduction to
quantum mechanics, then we’ll show you the Scanning Tunneling Microscope and how it works,
and then we’ll talk about other ways we can use quantum mechanics to do cool stuff.
P3: Great! Let’s get started by introducing ourselves!
[everybody gives a brief introduction of themselves, i.e., “Hi, I’m Katie, a senior at Michigan
State University studying physics and professional writing.]
P4: On with the show!
[Einstein leaves the room. Ask sits at the desks among students. STM and Applications Group
members move away. Honcho moves to front of the classroom.]
Honcho: Good morning/afternoon students!
(If pathetic/no response, repeat, “Good morning/afternoon students!” and gestures for response).
(extra inflection with italics, like it’s the coolest thing ever): We are gathered here today to
witness the wonders of the scanning tunneling microscope. But first, we’re going to learn a bit
about quantum mechanics. We’ll start off with a little something called the photo-electric effect.
And who better to tell us about it than the man who explained it, Albert Einstein!
[Enter Einstein, obviously]
Einstein: The most beautiful thing we can experience is the mysterious.
Honcho: So, Einstein, what is the photo-electric effect?
Einstein: Remember how we said earlier that light and electricity were made up of tiny building
blocks? Both kinds of building blocks have names. The particles which make up light are called
photons, and the particles which make up electricity are called electrons.
The photoelectric effect is the phenomena we see when a photon with enough energy hits a
surface and frees an electron.
Ask: I thought light was a wave.
Einstein: It is.
Ask: But you just said it was a particle.
Honcho: Hey, that’s Einstein. You don’t argue with Einstein.
Ask: But he’s contradicting himself!
Einstein: It’s both. Certain experiments show that it can act like a wave, but others, like the one
we’ll do in a minute, show that it can also collide with electrons, like a particle. (Ball
demonstration). Here, I have this blue ball to represent a high energy photon. It strikes this
green ball, which represents an electron, and gives up some of its energy so that the electron is
knocked out of position, like so. This red ball represents a lower energy photon. When it strikes
the electron, the electron remains fixed in place. The red ball doesn’t have enough energy to free
it. Now, I can show you the photoelectric effect with real photons and electrons.
(Einstein moves to the UV wave generator demonstration.)
I have a UV wave generator that generates ultraviolet light in both long and short wavelengths. I
will shine both kinds of wavelengths at this charged metal plate. Charging the plate means that
I’m putting some extra electrons on it, which can be freed if they are hit with a photon with
enough energy. If that happens, the electrons that got knocked out of place will make an electric
current, which will cause the voltage to drop on this voltmeter.
I will begin with the longer wavelength. (Show) Now for the shorter. (Show) As you can see,
only the shorter wavelength induced a current, even though I didn’t change how bright the light
was.
Up until my time, light was widely accepted as being a wave, but this experiment showed that
light also exhibited particle-like properties. Can anyone tell me why? Remember, even though
I used the same intensity of light, only the shorter wavelength induced a current. (Blank Stares)
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Your deafening silence was very common when I first made this discovery.
Here’s a clue: The photons of shorter wavelength light have more energy than those of light
with a longer wavelength. If you think of the demonstration I did with the hacky sacks earlier,
the light with the longer wavelength is like the red ball, which didn’t have enough energy to free
the electron, and the shorter wavelength is like the blue ball, which sent the electron flying across
the room.
The moral of the story is; it doesn’t matter how intense the light is, but what wavelength of light
you have, since each particle (photon) of blue, short wavelength light has greater energy that the
red, long wavelength light particles. That’s the photoelectric effect.
Honcho: Thank you, Einstein, for that demonstration of the photoelectric effect. Now, we can
get into quantum physics!
Einstein (betrayed!): You used me as a set-up for quantum mechanics?
Honcho: I don’t know if used is the right term…
Einstein (storming out): “The more success quantum mechanics has, the sillier it looks.” “God
does not play dice with the universe!” (simply leaves the room, preferably slamming a door.)
Honcho (solemnly): There goes a great man. Probably mistaken about quantum mechanics, but
great nonetheless. [takes a moment] Now onto our next idea, the Heisenberg Uncertainty
Principle! And here’s your host, Dr. Heisenberg himself.
[Ask gets up from seat and comes to the front of the class and takes a small bow…]
Honcho: Did you even try to look like Dr. Heisenberg?
Ask (shifty eyes): Maybe…do you even know what Dr. Heisenberg looked like?
Honcho: Well, I’m not really certain, but I think he looked a little something like...this? (Hits
mouse for powerpoint slide displaying Dr. Heisenberg!)
Ask (glances at screen): Aren’t you being a little dramatic?
Honcho: They don’t call us Science Theater for nothing.
Ask: Okay, so I don’t look like Dr. Heisenberg. But I can tell you about his principle. (Ask
moves over to pendulum contraption which Honcho is holding up.) We know from every day
experience that if I swing this ball on a string, just like a pendulum in a clock, we know exactly
where it is and how fast it is going all the time. Now let’s pretend the ball is actually an electron.
With particles as small as electrons, things are a little different. Can you hit the lights?
[One of the cast members not on stage plunges room into darkness]
Ask: Now, this is more like quantum mechanics. We can find the position of the ball by shining
a light on it (shine flashlight) but remember, electrons get pushed around by light particles. So
finding the electron really turns out to be like this (turn on hair dryer too, chase ball around for a
few seconds, then turns off the fan). Heisenberg’s uncertainty principle is much like this. If you
know how fast a particle is moving, you don’t know where it is. And if you know where it is,
you can’t know exactly how fast it is moving.
[One of the cast members turns the lights back on.]
Honcho: Thank you Fake Dr. Heisenberg for that excellent demonstration of the uncertainty
principle. (Ask returns to seat)
Next up is Dr. Schrödinger to tell us about his cat.
(Enter Formerly Einstein)
Non-Schrödinger (shakes head): It’s no use. I don’t look anything like him.
Honcho: Well, then here’s _________ to tell us about the paradox, or puzzle, of Schrödinger’s
cat.
Non-Schrödinger: Erwin Schrödinger was a scientist who worked out some of the math that is
used to describe quantum physics.
You’ve probably heard the question, “If a tree falls in the woods and no one is around, does it
make a sound?” More specifically, would someone being there to observe, or hear, the tree
falling down change whether or not it makes noise?
You would normally think, “No, the tree will fall the same way, and make the same noise,
whether or not someone happens to hear it. Observing the event won’t change it.”
Things aren’t quite the same in quantum physics. Schrödinger used a similar thought puzzle
involving a cat to demonstrate this.
In the Schrödinger’s cat puzzle, we imagine placing a cat in a box. Inside this box, there is a
special switch that has a fifty percent chance of switching on. If it switches on, a vial of poison
will open, killing the cat. If not, the cat is safe. Now, let’s say we put the cat in a box and an
hour has passed. How many of you think the cat is alive? (wait for raised hands) How many of
you think the cat is dead?
You’re all right. The cat is both completely dead and completely alive.
Ask: That doesn’t make any sense. You can’t be alive and dead at the same time!
Non-Schrödinger: That’s what makes it such a puzzle. Besides, this isn’t really about a cat.
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Schrödinger was just using the cat as a way to show what happens in the world of particles. It
really means that a particle can be doing two different things at the same time.
Now, can I get a student volunteer to participate in our Schrödinger’s Student demonstration?
(Ask raises hand)
Non-Schrödinger (roll eyes, glare, something): A real student.
Honcho: Hold on there. I can’t have you poisoning students. If we killed someone, no one
would ever want us to come back and do this show again!
Non-Schrödinger: Don’t worry about it. We have another substance in the box. Any
volunteers?
You! Come on up. What’s your name? Well _______, are you claustrophobic, because we
really are going to put you in a box?
(hopefully they’re not)
All right then. Since we don’t actually have fancy (schmancy) switches, we’re going to use this
coin (hold up large cat coin) instead. The coin has one side that says “hat” and one side that says
“no hat.” It has a 50% chance of landing with the “hat” side up and a 50% chance of landing
with “no hat” up, so it’s statistically similar to our switch which has a 50% chance of turning on.
Now, I’m going to give you the coin and have you go into the box. You’ll need to flip the coin
and do what the side that lands up says. Are you ready?
(If they say something about time, whisper that it won’t really be an hour)
All right, then, into the box! (Ask and Honcho close student into box and make sure they flip the
coin before putting the fabric over the top) And now, we wait.
(Ask and/or Honcho walk by holding the “One Hour Later” sign)
(look at watch, surprised): What do you know? An hour has passed. So, how many of you
think that ______ is going to have a hat on? And how many think that s/he won’t have a hat on?
(hopefully a bunch of students raise hands twice)
Excellent! So, are we ready to look in the box? This is the moment of truth…can I get a drum
roll please?
(Ask and Honcho to lift fabric and open box. S/he’s hatted! S/he’s not!)
Now, there is one little thing I didn’t tell you about Schrödinger’s cat. When you open the box
to look inside and see if the cat is dead or alive, you seal its fate. Up until you open the box, it is
both alive and dead, but once you look inside, it is either alive or dead. The same principle holds
true for the quantum world. A particle can be doing several different things at once, however
when you attempt to look at it, the particle has to choose only one of those things and that is
what we are only able to observe. So, in a sense, it can be a very literal case of curiosity killed
the cat.
Thank you, _______. You may return to your seat.
Honcho: Thank you, ________ for that demonstration on Schrödinger’s cat. Now, onto
electron tunneling.
Ask: Can I explain this one?
Honcho: Go right ahead!
Non-Schrödinger: Can I sit at a desk and ask irritating questions?
Honcho: No.
Ask (now at front of class): How many of you think you can stand on one side of a wall, and
appear on the other side?
(if no one raises hand): You’re probably right. But, is anyone willing to try?
(if smart-aleck raises hand): Excellent! Come on up to the front of the class!
What’s your name? So, ________, are you ready to try to tunnel through the wall? (wait for a
nod or a shrug.) Just kidding, our box is too valuable to risk you breaking it. Instead, we’ll have
you throw this ball at the wall and see if it tunnels. The thicker the wall and the bigger the
particle, the less likely it is for tunneling to occur. So, as you can see, when we’re dealing with a
ball and wooden panels like these, there isn’t much of a chance that the ball will go through the
wall. But, let’s go ahead and see if the ball tunnels anyway.
(Honcho asks student to throw the ball at the wall.)
Okay, so the ball didn’t make it through the wall. It’s extremely unlikely anyway, given its size
and the thickness of the wall. However, if the wall was really thin (Einstein and Ask fold out
one wooden panel) and the ball was an electron (use smaller ball), it has a better probability of
making it through. Let’s try it again with a thinner wall and this small ball which represents our
electron.
(Honcho tells the student to throw ball over the wall.)
So the ball made it over the wall, BUT you gave the electron enough energy to get over the
barrier. In tunneling, the electron doesn’t have enough energy, but it appears on the other side
anyway. One more time. We’re going to demonstrate roughly how real quantum tunneling
occurs.
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(Honcho tells student to fake throwing the ball, then Ask produces an identical ball on the other
side as student fakes throwing the ball.)
And there you have it, the same electron tunneling through a wall and appeared on the other side.
Thank you, ___________, let’s return to our seats.
Honcho: Ok! Now that we’ve been through the photoelectric effect, the uncertainty principle,
Schrödinger’s cat, and electron tunneling, it’s time to introduce the star of our show – the
Scanning Tunneling Microscope, a small wonder that uses the ideas we just discussed! And here
are [says A’s name] and [says B’s name] to present the STM to you!
[The Intro Group all sit down. A and B from the STM Group take the stage.]
A: Everyone please give a hand for the last group. Now we have to take a few minutes for the
microscope to get ready, so before that we have a couple demonstrations for you.
B: The Scanning Tunneling Microscope was invented so that we could look at things that are
extremely small, such as atoms—the tiny building blocks of matter. You might be wondering
why we need these special microscopes, why we can’t just use a regular light microscope to look
at atoms. With modern technology, why can’t we just make light microscopes more and more
powerful to see things that are smaller and smaller?
The answer to that can be found in the fundamental properties of light. Remember how we said
that light is a wave? All waves have a wavelength which is a measure of how spread out the
waves are from one another.
When we use light to look at something, we can’t see anything smaller than its wavelength.
Atoms are much smaller than that. To see details as small as individual atoms, we need to use
something other than light. Special microscopes like the STM use electrons to do this. Here is a
demonstration that should help show this idea.
A: Can we get a volunteer please? (picks someone from the audience) Please come right up
here.
I have here a box, and inside of this box is a mystery object, which we are going to pretend is on
the scale of nanometers. There are one billion nanometers in a meter, so they are really small—
if I put three atoms in a line, that line would be about a nanometer long. We want to look at this
mystery object, so first we’re going to use a light microscope, which we’ll represent with this
oven mitt. (Fits the volunteer with the oven mitt and explains the demonstration to him/her
quietly.) The large size of the oven mitt represents the relatively long wavelength of light. (to
the volunteer) Now, reach inside the box—no peeking!—and tell me about what you can feel.
(Demonstration proceeds; the object may be a Mickey Mouse doll, pinecone, or sponge of a
particular shape. Have the student try to tell you as much as they can about the object, which
won’t be very much.)
Ok. We couldn’t see much detail about our mystery object when we used a light microscope.
Now let’s try looking at it with an electron microscope. We’ll represent this by having our
volunteer, ____ reach back into the box, but without the glove this time. This will represent the
increased sensitivity of an electron microscope. Smaller fingers, which represent the smaller
wavelength of electrons as compared to light, can feel smaller features. Ready? Go.
(Demonstration proceeds. By conversing with the volunteer, we will hopefully get them to
reveal that the object is must easier to feel and identify now. Hopefully the volunteer identifies
the object, but if not, at least get them to confirm that they can feel much more detail without the
oven mitt on.)
A: Thank you, ________, for volunteering. You may return to your seat. Now we have a
demonstration on how the scanning tunneling microscope works. Let’s call it STM for short. To
visually demonstrate our next idea about the microscope, we are using something called a Tesla
Coil.
For safety purposes, we ask that if you have any metal devices such as pace makers or metal
plates, please do not sit in the first few rows. Also, if you have an older digital watch or cell
phone, the Tesla Coil may cause some damage to the electric circuits.
B: (Tesla Coil demonstration proceeds. The Tesla coil is loud, so it may be better to talk about
what you expect to see and explain it before you turn it on.) This is a Tesla coil. It uses coils of
wire to build up a high voltage at its tip, which can ionize air to make sparks—just like lightning.
The principles behind this are different than the quantum mechanical ones that the STM uses, but
some effects are similar, so we will use it as a visual to explain how the STM works.
Most basically, the STM consists of a very sharp metal tip which is scanned over the surface we
want to look at. It is close enough that electrons that are in the atoms of the sample can actually
tunnel into the tip. Here, instead of a wooden panel, the barrier that they are crossing is the gap
between the sample and the tip.
Here we have this large metal ball and here we have a sharp needle charged with electricity. The
metal ball is going to represent an atom, and the pointed needle is going to represent the tip of
the STM. When the atom passes to within about a half nanometer of the tip, tunneling occurs
and electricity flows. But the tunneling effect shuts off dramatically if the atom is just a little bit
farther, say a full nanometer. That effect is used to “feel” the position of the atoms. A computer
that is connected to the STM can detect changes in how many electrons are tunneling at a certain
spot, and draws a picture accordingly. It puts light colored spots where a lot of tunneling occurs,
and dark colored spots where few electrons are tunneling.
Now that we’re done with the demonstrations, it’s time for us so show you what the STM in
action.
A: Up on the screen I have the computer software we use to control the microscope. I’m going
to start it scanning and zoom in gradually.
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(Lets the microscope scan through a couple times, use zoom feature to try and get a close up
view of a smooth spot on the graphite)
Remember, this microscope is extremely sensitive to how sharp the tip is, and how far away the
tip is from our sample. Because of this even small vibrations or imperfections can affect the
quality of our image. (If the image is fuzzy or atomic resolution can’t be achieved, explain that it
is a consequence of this.) It is so sensitive that even the sound of my voice…or of people
clapping can affect the image. Let’s do an experiment: on the count of three, everyone please
clap loudly, and watch what happens to the picture on the screen. Ready? One, two, three! As
you can see the there’s a large area where the scan is very noisy; that’s where you clapped. Just
the vibration from that noise caused the STM to vibrate and caused a problem.
That’s it for the STM, thanks for listening! Next up is ___ to talk to you more about technology
which is related to quantum mechanics.
After the STM demo, Person 2 walks on stage. Einstein lurks somewhere, inconspicuously
sipping a cup of water.
Person 2: Thank you ___ and ___ for that demonstration of the STM. Let’s quickly review
what we’ve learned so far. First Einstein told us about the-Person 1 (running in, interrupting): Person 2, I have to tell you what I just saw on TV! It could
mean the difference between life and death.
Person 2 (incredulously): What did you see?!
Person 1: I was watching this TV special about little machines that were made to clean up a lab.
Well, things got out of hand and they started to multiply and stopped following the coded
instructions for cleaning and tried to TAKE OVER THE WORLD!!! That’s when I got scared
and turned off the TV.
Person 2: I think you were watching a movie. It was on last night. I saw it too.
Person 1 (relieved): Phew! I thought it was real…but wait, the scientists kept talking about
something called nanotechnology. I’ve heard that word before and not just in movies.
Person 3 walks on the stage, reading a newspaper.
Person 3: Nanotechnology? I was just reading about that.
Person 1: Really? Can you tell me what nanotechnology is?
Person 3: Well I could, but why have me do it, when we could bring in another noble prize
winning physicist to describe it? How about Richard Feynman?
Person 1: Wait, did you just call a physicist a fine man?!
Person 3: No, Feynman is his last name. (looks toward Einstein storming across stage)
Einstein (with inaudible grumbling): grumble. I think that one noble prize winner is enough for
this show. grumble. Bah, QUANTUM MECHANICS!
Einstein throws water on Person 3’s pants.
Person 3: Phew…good thing these were stain proof!
Person 1: How are they stain proof?
Person 3: Through the wonders of nanotechnology! (Person 1 rolls eyes.) Well that’s what the
tag said when I bought the pants.
Person 1: Well ok. But what is nanotechnology. Nano…I’ve heard that before. It means
something small doesn’t it?
Person 2: Yes, nano refers to a scale which is 1 billion times smaller than a meter. A strand of
hair is thousands of nanometers thick!
Just to give you an idea of how small a nanometer is, here we have a binder with its pages
covered in dots. (Show the million-dot book) There are one million dots in this book. A billion
is one thousand million—one thousand binders like this would contain a billion dots. If you
were to divide a millimeter, the smallest markings on a meter stick (show a meters stick) into one
million pieces, you would have a nanometer.
Person 1: Wow. We’re talking about things at the level of atoms and molecules right? Isn’t that
where the things we just learned about quantum mechanics become really important?
Person 2: Exactly. ‘Person 3’, what does Richard Feynman have to do with that anyway?
Person 3: He’s believed to be one of the first to address the possibility of the field of
nanotechnology. About 50 years ago, he offered a prize to the first person who could build a
motor the size of a pinhead and a page of a book smaller than the width of a human hair. It took
some time, but eventually someone succeeded at doing both.
Person 2: Everyday uses of nanotechnology have only been around for the last few years.
That’s not long when you compare it to other technology like light bulbs and airplanes which
have both been around for more than 100 years.
Person 3: That’s right. Nanotechnology is relatively new.
Person 1: So what is nanotechnology actually used for?
Person 3: A lot of things! For example, scientists can design things called nanomaterials. There
are substances with special properties that the scientists can control by using their knowledge of
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the small particles that the substance is made of.
Person 1: Like making your pants stainproof?
Person 3: Exactly.
Person 2: The STM is an example of nanotechnology too. It’s what can be called a nano-tool
because it can manipulate other objects on the nanometer scale. Both engineers and scientists are
working on developing machines that operate on the level of nanometers.
Person 3: Nanotechnology is also very useful in medicine. Research in nanotechnology is
helping people to walk, see, and recover from accidents.
Person 1: Now I’m beginning to understand that nanotechnology is not just for the future. Other
than your pants, what other kinds of every day objects use nanotechnology?
Person 2: Nanotechnology is a big part of the computers and electronic equipment we use all the
time, such as cell phones and video games! It allows us to make them as small and compact as
they are…and allows us to invent even newer and fancier gadgets. For example, computer
screens that can be rolled up have already been developed.
Person 3: Nanomaterials are also used to make things like paint and makeup. It’s even used in
stain-proof pants!
Person 2: So you see, developments in nanotechnology affect everyone, not just scientists. No
matter what you decide to be when you grow up, it will undoubtedly be a part of you life—so
knowing a little of the science behind it is a really good thing!
Person 1: (Looking at watch) Well, I’ve got to go soon. I’ve learned so much about
nanotechnology today, and I hope everyone else has too.
Person 3: I’m glad to hear it. Like all parts of science, there will always be more to learn about
nanotechnology, even for the smartest scientists out there, so be sure to ask questions whenever
you are curious about something.
Person 2: And with that suggestion, we end our show. Thank you all for coming and listening.
If you have any questions, you can ask them now. If not, you are free to come up here to look at
the STM and to chat with us or ask any other questions.
Last update: 3-13-09
Demonstrations and Supply List:
All Groups:
 Laptop (for various powerpoint components of each segment)
Intro Group:
 Einstein wig
 Blue ball (for Einstein’s photoelectric effect)
 Green ball (for Einstein’s photoelectric effect)
 Red ball (for Einstein’s photoelectric effect)
 photoelectric apparatus
 Pendulum Contraption (for Ask’s Uncertainty Principle)
 Flashlight/Fan Contraption (for Ask’s Uncertainty Principle)
 Wooden Box (Schrödinger’s Cat demonstration)
 Large Fabric (to cover over box for Former Einstein’s Schrödinger’s Cat demonstration)
 Stuffed toy cat (for Schrödinger’s Cat demo)
 Hat and coin (for Schrödinger’s Cat demo)
 “One Hour Later” Sign
 2 or 3 identical ping pong balls (for Ask’s Quantum Tunneling demonstration)
STM Group:
 Secret-viewing box apparatus (for electrical microscopes demonstration)
 Mystery object (block S)
 Oven mitt (for electrical microscopes demonstration)
 Tesla Coil with special round metal rod (for visual tunneling example demonstration)
 Model of atomic lattice
 Model of STM tip
 STM and STM’s laptop (for STM Demonstration)
Applications Group:
 Powerpoint slideshow of Applications of Nanotechnology
 Meter stick
 Million dot book
 Newspaper
 Cup of water
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