Hi! It’s me, Boop! I’m back! Did you miss me? I missed me. I accidentally fell into Discovery World’s matter transporter. Something went wrong, and I got stuck in the Quantum Realm. Yes, that’s a real place, though the words “real” and “place” are entirely subjective in… the Quantum Realm. Time is meaningless. Cause and effect are meaningless. Meaning has no meaning in… the Quantum Realm. Fortunately, the Aquarists were able to repair the matter transporter and bring me back. They’re so great.
The Quantum Realm is very strange. Did you know that there are no mealworms in the Quantum Realm? That was incredibly weird. There is no food of any kind in the Quantum Realm. There is only weirdness. I can’t eat weirdness, so I was very hungry when I got back.
My experience in the Quantum Realm got me thinking. If you’re like me, you’ve spent entire minutes – maybe even hours – pondering things like subatomic particles, quantum mechanics, and the fundamental nature of reality. Maybe you’ve wondered what it would be like to travel to the Quantum Realm like the Avengers and I did. (To be fair, the Avengers are fictional characters whereas I am a totally real turtle who blogs about my totally real and not-at-all-made-up adventures.)
Maybe you’ve picked up books like Something Deeply Hidden by Sean Carroll or How to Teach Quantum Physics to Your Dog, by Chad Orzel. Maybe you’ve read Beyond Weird: Why Everything You Thought You Knew About Quantum Physics Is Different, by Philip Ball.
Maybe you’ve wondered whether the Copenhagen or Many Worlds interpretation of quantum mechanics is correct or what electrons really are or how the Higgs field works or what empty space is made of. There are so many things to wonder about!
I’ve spent the last couple of weeks trying to understand what I saw while I was trapped in the Quantum Realm. I understand it now. I UNDERSTAND THE FUNDAMENTAL NATURE OF REALITY! I promise that by the time we’re done here, you’ll understand everything, too. You’ll understand how our reality emerges from quantum field interactions. You’ll understand things like the Hamiltonian, anti-de Sitter space, Hilbert space, the wave function, octonions, superposition, Schrodinger’s Cat, and what an electron really is. I am even going to explain (because I totally get it now) quantum gravity.
Ha! Just kidding. I am completely and utterly baffled. I’m even more baffled than when I started. I mean, I thought I knew things, but I now I’m not even sure that I know what I know, you know? My hope is that by the end of this, you’ll be baffled, too! Maybe your bafflement and my bafflement will become entangled until we observe it and our wave functions collapse.
Or maybe you won’t be baffled. Maybe you’ll be simultaneously baffled and un-baffled. Maybe you’ll be baffled in this universe but completely un-baffled in an entirely other universe. Anything is possible. Except when you measure it. Then only one thing is possible. Or maybe that’s not even true. I HAVE NO IDEA!
Also, and I mean this with complete humility (an odd feeling for me), it is entirely possible that everything here is wrong. I AM OKAY WITH THIS. It just means that I have more to learn, and that’s exciting! It’s also sort of fun being this confused. I remain undaunted, of course. Turtles are never daunted.
Let’s start with the word quantum. I didn’t know this, but quantum doesn’t mean “really small” or “subatomic”. It means a discrete quantity of something. So a Quantum of Solace is a discrete quantity of solace. A Quantum Leap is a discrete quantity of leap.
I didn’t know this either – at least I think I didn’t know this – but turtles like me are made of atoms. Humans are made of atoms, too. What else is made of atoms? Trees, rocks, air, hamburgers, and water. And that’s probably it. I’m kidding! It turns out that atoms make up everything, which is why you should never trust them. Ha! I love that joke. It’s funny because it’s true. I know because I have traveled to… the Quantum Realm. Sorry, I’m trying to turn my adventure into an award-winning HBO series about a turtle who accidentally falls into a matter transporter and travels to… the Quantum Realm. I need a show runner. Anyone know a show runner?
Anyway, atoms are made of protons, neutrons, and electrons (except for hydrogen atoms, which don’t have any neutrons).
Here’s something fun that I didn’t know. Remember how we learned that matter is mostly empty space? Well, THAT IS ALL LIES! EMPTY SPACE IS NOT EMPTY!
Take a small bit of so-called “empty space” – a cubic centimeter or cubic millimeter – and zoom in. Further. Further than that. Even further. Keep going. You’re almost there. Wait, no. I lied. You’re not even close. Keep zooming in. A bit more. Keep going. Whoa, was that a stray hydrogen atom? What’s that doing here? It’s huge! And… keep going. Zoom in. Further. Even further. Keep going. A little bit more. Keep going. A bit more. Even more. And… stop. You’ve zoomed in a lot. A lot a lot. You are looking at an incredibly tiny chunk of space called the Planck length.
A Planck length is the distance that light travels in one unit of Planck time. As definitions go, THIS IS NOT HELPFUL. One unit of Planck time is incredibly short, so a Planck length is incredibly small. It’s the smallest distance of space that we can meaningfully measure.
Instead of nothing, which is what you’d expect to see while looking at something called empty space, you see weird bits of things that seem to bubble up out of nowhere and transform and disappear into nowhere over and over again. I found out later that these bubbling weird bits of things that change and disappear are called virtual particles. They’re real, but they’re called virtual particles.
The next thing I discovered is that subatomic particles like electrons are not what you think they are. Actually, I have no idea what you think electrons are. You might think electrons are negatively-charged, strawberry-scented, orange unicorns. I mean, you probably don’t think that. I don’t think that either. I didn’t think that before, and that’s not what I saw in my journey through… the Quantum Realm. (Last one, I promise.) Honestly, I’m not sure what I saw. I wouldn’t be all that surprised if electrons turned out to be negatively-charged, strawberry-scented, orange unicorns. I mean, they’re probably not, but I DON’T KNOW WHAT’S REAL ANYMORE!
I used to think that electrons were those negatively-charged particles that orbited the nuclei of atoms. They don’t orbit. They exist as clouds of probably located somewhere around atoms. There are plenty of free electrons, too.
As you probably know, electrons are elementary particles. They’re not made of other things. Protons are not fundamental particles. They’re made of smaller particles called quarks. Protons are made of three quarks (two up, one down) that are held together by gluons. Gluons are particles that “mediate the strong force between quarks”.
Electrons are also fermions, a group of subatomic particles that have mass (Hello, Higgs field!) and, generally speaking, make up stuff. Some particles are bosons, which don’t have mass. Gauge bosons (a special type of boson) carry or mediate different forces. Gluons are gauge bosons. Photons are gauge bosons, too, and they mediate the electromagnetic force (light). Light is emitted by vibrating electrons.
Subatomic particles like electrons are not at all like the macroscale particles – specks of dust, grains of sand, baseballs, etc. – that you and I encounter every day. A baseball has properties like mass, size, and shape that we can easily measure. If we throw a ball, we can measure its trajectory. We know where it is and how fast it is going. We can calculate its velocity, kinetic energy, and its momentum. We can make an incredibly accurate prediction about where it will land.
Electrons are not like that. Electrons don’t even have a size. They have a tiny bit of mass, but no size. They’re a zero-dimensional bit of negatively charged fuzzy stuff that is neither fuzzy nor stuff. And this description is probably at least mostly wrong.
Sometimes electrons act like particles. Sometimes they act like waves. It depends on if you look. It does not, or might not, depend on when you look.
Is it a Particle? Is it a Wave? It’s it Both?
There is a very famous experiment called the double-slit experiment. You’ve probably heard of it. The first version of it was conducted in 1801 by Thomas Young. For a long time before that, scientists thought that light was made of tiny, tiny particles. Young’s experiment demonstrated that light is made of different waves. Leonhard Euler worked out some of the math to verify that light was waves, and his work was expanded on by Fresnel (the lens guy) and Poisson (the distribution guy). One challenge was that unlike sound waves, light waves don’t need to travel through a medium, but scientists back then didn’t know that. See “aether, luminiferous”. Then Faraday and Maxwell did their thing, and the “light is particles” idea was pretty much over. Until it wasn’t.
In the early 1900s, Max Planck was experimenting with electromagnetic radiation (light), and he noticed that his math only made sense if he treated the light waves as discrete packets or chunks. At first, this was just a kind of mathematical fudge. But Einstein took it seriously and incorporated into his description of the photoelectric effect.
So light was a particle. Then it was a wave. Then it was a particle again. Scientists were confused. Scientists love a big, juicy conundrum, so they designed new and better versions of the double-slit experiment. It works with photons. It works with electrons. Scientists are still designing new and better versions of the double-slit experiment!
If you fire a beam of electrons at a barrier with very narrow slit cut in it, some of those electrons will bounce off the barrier. Some will go through the slit. Now let’s say you put a special, coated screen at the back. Every time an electron smacks into the screen, it leaves a bright little dot.
After a lot of electrons strike the screen, you get a clumpy, bright line on the screen. One clumpy line from a whole lot of electrons slamming into the screen. With one slit, the electrons absolutely behave like particles.
Now you cut a second slit in the barrier. When you fire the beam of electrons, you don’t get two clumpy lines on the screen, which is what you would expect if electrons were particles. Instead, you get five or seven or more clumpy lines interrupted by dark bands of, well, nothing. You get the signature interference pattern of a wave. What seems to happen is that some of the electron waves combined to become stronger (constructive interference). Those are the bright clumpy lines you see. Some of the electron waves canceled each other out (destructive interference). Those are the dark bands in between.
Okay. Maybe the electrons weren’t really acting like waves. Maybe they interfered with each other. Maybe they collided and bounced around or something. So you try the experiment again. This time you fire electrons at the screen one at a time. You give an electron time to hit the screen before you fire the next one. At the end of the experiment you still get the five or seven or more bright lines that indicate the interference pattern of waves.
An interference pattern would not happen if you did the double-slit experiment with macroscopic particles like paintballs or spherical turtles in a vacuum or something. Paintballs would not leave an interference pattern on the screen. I was going to try this with Beep and the other Discovery World turtles, but they refused to let me cover them in paint and fire them through a slit onto a screen.
But electrons are not turtles or paintballs, and they do create an interference pattern. Here’s where it gets a slightly weird.
You do some math, and you figure out that the wavy electrons seem to go through one slit, the other slit, both slits, and none of the slits all at the same time. That doesn’t make any sense, so you run the experiment again.
This time you place a detector in front of one of the slits. The detector’s job is to, well, detect which slit an electron passes through. You run the experiment again. This time you don’t get an interference pattern. You get two lines of impressions, a clumping pattern. This time the electrons acted like particles, and the only difference is that you were watching. It’s almost as if the electrons “knew” that you were watching, so they chose to act like particles. Their wave behavior or wave function disappeared.
So if you don’t measure or observe the electrons, they act like waves. If you do measure or observe the electrons, they act like particles. But what does measuring or observing or any kind of interaction have to do with anything? How can subatomic particles “know” they’re being watched? How can subatomic particles make choices? I HAVE NO IDEA! For even more on wave-particle duality see: “delayed-choice quantum eraser, the”. It’s a wildly complicated and clever version of the double-slit experiment that seems to imply retrocausality, but probably doesn’t, though maybe it does. It depends on who you ask.
The Wave Function
Electrons and other particles like photons have what is called a wave function. Everything has a wave function. You have a wave function, but your wave function is incredibly tiny because you are a large object. Wait, was that rude? Sorry, I didn’t mean to be rude. What I mean is that you are bigger than an electron.
The wave function is a mathematical description of the probabilities of what you can know about a quantum system. I think that last sentence is at least somewhat true.
What’s In the Box?
An electron. You put it there. Electrons move around a lot, so you don’t know precisely where the electron is. It has to be somewhere. The problem is that at any given moment, the electron could be anywhere. It might even be outside the box. You’d think it would be in the box because you put it in the box, but it might not be in the box. It’s more likely to be in some places (the box) than others (outside of the box). There’s even a small but non-zero chance that it’s on the other side of the Universe. The point is that you can’t predict where it is. You can only calculate (using the Schrödinger equation) where it might be. For all intents and purposes (or intensive porpoises), your electron is everywhere until you make a measurement.
Once you make a measurement and find out where the electron is, the wave function collapses. The probability of it being anywhere becomes 0, while the probability of it being where you found it is 1.
Electrons and other particles can also become entangled, which means that their quantum states are connected and they share a wave function.
With the right equipment, you can produce an entangled pair of electrons. Let’s say you have two entangled electrons. Their total spin needs to equal zero because of the Law of Conservation of Momentum.
(Electrons don’t really spin. Electrons have something called “intrinsic angular momentum”, which isn’t spin, but it is enough like spin that scientists call it spin even though it’s not like the spinning we normally associate with actual spinning things like wheels and gyroscopes and the Earth.)
If Electron A is in a state called spin down, Electron B will be in a state of spin up. Of course, the opposite could be true. You don’t know unless you make a measurement. And until you make a measurement, your entangled electrons don’t know either. They are in a state of being both spin up and spin down at the same time. This is called superposition. For more on superposition, see: “Cat, Schrödinger’s”. Physicists have also demonstrated superposition on things that are larger than electrons, including, I think, viruses.
After you make a measurement to determine the spin of Electron A, you know the spin of Electron B. This information is shared instantaneously by the entangled particles no matter how far apart Electrons A and B are. They could be on opposite sides of a lab, the Earth, the solar system, or the Universe. This is a bit of a head-scratcher because information isn’t supposed to travel faster than the speed of light in a vacuum.
Some physicists don’t think there’s anything all that puzzling about any of this. Two entangled particles share a wave function. Measurement affects that wave function. Entangled particles don’t contain any hidden information. Everything is fine. Entangled particles do seem to communicate faster than light, but nothing violates Einstein’s Special Relativity because we cannot use entanglement to send information faster than light.
Let’s say you entangle a pair of electrons. Before you make a measurement, you send one of the entangled particles to a scientist friend in Japan. Then you make a measurement on the other. Remember that you don’t know what the measurement of your particle will be. It could be spin up. It could be spin down. It’s something of a coin flip. Your scientist friend in Japan doesn’t know either. You make your measurement. Your particle is spin up. You call and tell your scientist friend. She makes her measurement and confirms that her particle is spin down. She calls you back and tells you. The particles “chose” their state the instant you made your measurement, but the information about their state took a lot longer to get from you to your friend and back. Even if you had a detector that would send an automatic electronic “spin up” signal all the way to your friend’s lab in Japan, it would still take a little bit of time to get there. So even though the entangled particles “know” their state instantaneously, you don’t.
“Okay,” you might reasonably ask, “entanglement is neat and all, but how is this remotely useful?” Well, quantum computers rely on the entanglement and superposition of quantum bits or qubits.
And recently-ish (and this is cool), a group of researchers led by Dr. Gabriela Barreto Lemos in Anton Zeilinger’s laboratory at the Vienna Center for Quantum Science and Technology took a photograph of an object using entangled photons as the source of light.
That doesn’t sound terribly amazing. You point a camera at an object, something adorable like a three-toed box turtle. Photons (light from a source like the sun or a light bulb or whatever) bounce off the object. You press the button, the electronic shutter opens, and some of that light finds its way into the camera. You get an image of the object. It all sounds perfectly ordinary, right?
Here’s the amazing part. Lemos and her team took an image using entangled photons. Let’s say for the sake of oversimplification that the team produced two groups of photons – an ‘A’ group and a ‘B’ group. Each photon in the ‘A’ group was entangled with a photon in the ‘B’ group. The researchers bounced all the ‘A’ photons off an object. The actual image of the object, however, was produced with the ‘B’ photons. The ‘B’ photons didn’t go anywhere near the object. Lemos and her team took a photograph of an object with light that hadn’t touched the object, hadn’t even been near the object. However, this light was entangled with other light that did. And that is a least slightly bananas.
Speaking of bananas, did you know that bananas sometimes emit anti-matter? It’s true. Bananas emit a positron (the positively charged anti-particle of the electron) every hour and fifteen minutes or so. All bananas have a small amount of radioactive potassium-40 in them. An incredibly small amount. (Bananas are safe. I love bananas. Beep and I eat bananas all the time. We don’t glow in the dark or anything.) As the potassium-40 decays, it releases a positron. Not all the time, but once in a while. The positron is immediately annihilated when it comes into contact with an ordinary electron. Where was I going with this? Oh! The point is that all subatomic particles have their own antiparticle. Okay, that’s not entirely true. Photons are their own anti-particle.
Ernst Stueckelberg and Richard Feynman took a look at something called the negative-energy solutions of the Dirac equation and figured out that if you squinted a bit (mathematically speaking), you could see that electrons would have a positive charge if they were moving backward through time.
I didn’t see that when I was in the Quantum Realm, though I’m not sure how to tell if something like a subatomic particle is moving forward or backward through time. Especially because I wasn’t sure what I was looking at to begin with. Anyway, Stueckelberg and Feynman concluded that positrons might just be electrons moving backward in time. Don’t worry, it gets weirder.
Archibald Wheeler thought that because all electrons are identical (and apparently they are really, really identical), all electrons are just the same electron everywhere all at once. If I didn’t know better, and I don’t, I’d say that sounds more like a field (electromagnetic, gravitational, Higgs, etc.) than a particle. That’s just a guess. I’m a turtle, not a scientist. I have no idea what I’m talking about.
So all electrons might be the same electron that is somehow everywhere at every moment. And all positrons could be that same electron everywhere at every moment, but moving backward in time. Wheee!
Okay, my brain hurts now. It could be a side effect of my journey through the Quantum Realm. Or maybe I’m not used to thinking this much. And all of this so much more wonderful and interesting and complicated than I’ve turtlesplained here.
My apologies, but you’ll still have to wonder whether the Copenhagen or Many Worlds interpretation (or one of the many other interpretations) of quantum mechanics is correct. I have no idea. The good news is that a lot of physicists, at least the ones who care about these kinds of things, aren’t quite sure either.
I think the thing that impresses me most about all of this is the math. The math works really, really well. It’s creative and complicated – often mind-bendingly complicated – and I don’t understand any of it yet, but it works.
Anyway, it’s great to be back. I’m going to stay away from Discovery World’s matter transporter for a while. And when I finally go to turtle school, I will pay extra attention in math class!