So, yesterday was my big TEDxAlbany talk. I was the first speaker scheduled, probably because I gave them the title "The Exotic Physics of an Ordinary Morning," so it seemed appropriate to have me talking while people were still eating breakfast...
The abstract I wrote when I did the proposal mentions both quantum physics and relativity, but when I actually wrote the talk, that made for a really awkward transition, so it's all quantum, all the time. I cover quite a bit of ground-- the no-animation-effects version of the slides is 42 slides and Word has it as just over 2500 words written out-- but I'm happy to say that I hit the time mark, and I wasn't even the fastest-talking speaker at the event.
This went about as well as I could've hoped. I fumbled the delivery on one small point, but not in a way that anybody who isn't me would notice. People said nice things about it afterwards, which is always good; they livestreamed the talks and at least one person said on Twitter that they'd watched it. They promise to post video at some point; you can be sure that I'll post it here as soon as it's available.
The above photo of me speaking is cropped down from this tweet:
— See Ma (@SeemaWasTaken) December 3, 2015
(not the greatest facial expression, but I can't don anything about that...)
Here are the slides on SlideShare:
Being a TED-type talk, though, those probably aren't much use to anybody who doesn't have the text memorized-- just a collection of images with next to no text. So, here's the approximate text (approximate because I was speaking from memory, and changed the wording here and there in small ways):
When I say “Quantum Physics,” the phrase probably conjures up some intimidating images. Particles that behave like waves and vice versa. Cats that are alive and dead at the same time. Spooky interactions connecting particles over large distances. Quantum mechanics has been around for a hundred years, and is the subject of innumerable books, but the theory remains famously difficult and troubling. One of the pioneers of quantum mechanics, Niels Bohr, is frequently quoted as saying “Anyone who is not shocked by quantum theory has not understood it,” and that’s just as true today as when he said it in the 1930’s.
There are only a few things that everybody thinks they know about quantum physics: It’s hard to understand. It’s really, really weird. And it’s very far removed from our everyday reality.
Except, that last item isn’t true. It can’t be true. Physicists inhabit the same everyday world as everybody else, and we don’t make theories up for no good reason. The modern theory of quantum mechanics exists because physicists were led to it by observations made right here, in the everyday reality we all deal with.
You might be surprised to learn just how familiar you are with these observations. In fact, you probably see one of the key phenomena every morning, when you cook breakfast. Everything we know about quantum physics starts right here, with the red glow of the heating elements in this toaster.
The glow of a hot object is a very simple and universal phenomenon. Take an object, any object, and heat it up, and it will glow red, then yellow, then white. The precise color depends only on the temperature. Physicists call this “black-body radiation” because it doesn’t matter what the object is made of, or how you get it hot. No matter what you have, if you get it to the same temperature, it will glow in exactly the same way.
This sort of simple, universal behavior is like catnip for theoretical physicists, because it seems like it should have a simple and elegant explanation. And in the late 1800’s, a lot of really smart people tried to explain the light we see from hot objects; all of them failed.
The guy who finally succeeded, in 1900, was the German physicist Max Planck, but to do it, he had to resort to a weird mathematical trick. He found an equation that perfectly described the black-body radiation, but to get it, he had to pretend that the object was made up of imaginary “oscillators,” each emitting a particular frequency of light. And each of those oscillators could contain only discrete amounts of energy—one unit, two units, three units, but never two-and-a-half, or pi. This is what puts the “quantum” in quantum physics—it’s Latin for “how much,” and refers to the fact that in Planck’s model, energy comes in discrete amounts.
The energy unit for each oscillator depends on its frequency, and that’s what leads to the colors we see. Red light has a low frequency, and thus a low energy, so it’s easy to produce at relatively low temperature. Blue light has a much higher frequency, so you need a much higher temperature before you get any blue light at all.
Planck’s model works brilliantly, but he was never completely happy about the trick he had to use to get it, and hoped something better would come along. In 1905, though, Albert Einstein picked this idea up and ran with it. Einstein was trying to explain the photoelectric effect, where light falling on metal knocks electrons loose, another of those phenomena that seem simple but turn out to be surprisingly hard to explain. Einstein’s solution was to apply Planck’s idea to the light itself. He said that light, which everybody knew was a wave, is actually made up of tiny particles, each carrying one “quantum” of energy, with the energy related to the frequency according to Planck’s formula.
This is a radical suggestion—Einstein himself called it his only revolutionary contribution to physics—and lots of people hated it. Including Max Planck. But Einstein’s model passed every experimental test physicists could throw at it, so people had to take it seriously. The idea of light as a particle—nowadays we call them photons—became part of physics, and quantum mechanics was off to the races.
So, quantum physics isn’t as remote as you might think. Any time you toast a piece of bread for breakfast, or wait impatiently for a pot of water to boil, you’re staring directly at the place where it all began.
Now, you could argue that the quantum-ness of the black-body radiation from hot objects is sort of incidental. After all, you don’t need to understand quantum physics to build a toaster. People were working with hot, glowing objects for a long, long time before Planck explained the origin of the spectrum.
But this points out the way that quantum physics does manifest in the everyday world, if you know where to look. And there are numerous examples of ordinary, everyday objects that do rely on quantum physics to operate properly. For example, I wouldn’t be able to get out of bed in the morning if not for quantum physics.
That’s a picture of the alarm clock whose beeping wakes me up every day. It’s nothing all that special, as clocks go, it just sits there marking the passage of time, second by second into the future.
But the very definition of time is based on quantum physics. Which we owe to this guy, the Danish theoretical physicist Niels Bohr, who followed Planck and Einstein with a radical leap of his own. Bohr was trying to explain another phenomenon relating to light and atoms, one that’s a little more obviously quantum. If you take a gas of atoms of a particular element, they will emit light only at very specific frequencies. If you spread out the different frequencies, you’ll see a discrete set of colored lines. Each element in the periodic table has its own unique set of these “spectral lines,” and these were being used to identify new elements as far back as the 1870’s. But nobody understood why different atoms had different characteristic frequencies.
Bohr picked up on the idea of connecting energy to frequency from Planck and Einstein, and made a radical suggestion about the structure of atoms. Bohr proposed that the electrons inside an atom don’t orbit the nucleus in just any old way they like, but are restricted to certain very special orbits. Each of these orbits has a particular energy, and atoms absorb and emit light only when their electrons move between these orbits. The frequency of the light depends on the difference in energy in exactly the way that Planck and Einstein introduced.
This was a revolutionary idea, and kicked the development of quantum mechanics into high gear. And while Bohr’s initial proposal wasn’t completely correct, the basic paradigm of electrons occupying only certain special orbits remains central to our understanding. It explains the absorption and emission of all forms of light, from radio waves to gamma rays, and provides the conceptual basis for all of modern chemistry, from the periodic table to the formation of molecules.
Bohr’s idea is also the foundation of modern timekeeping. The second is defined as 9,192,631,770 oscillations of the light absorbed by cesium atoms moving between two particular orbits. Every cesium atom in the universe is identical to every other, and their characteristic frequencies are fixed by the laws of physics, making them perfect time references—that number of oscillations of that light defines one second, always and everywhere. The official time for the world is set by atomic clocks that shine microwaves on cesium atoms and adjust the frequency to perfectly match cesium’s characteristic frequency. We can do this to astonishing precision—the best cesium clocks would run continuously for almost a billion years before drifting off by a single second.
And all of this trickles down to the timekeepers we use to start our day. If you use an alarm on a smartphone, you’re getting your time from telecom networks, which are deliberately synched to atomic time. Even if you’re relying on a cheap electronic alarm like mine, it’s measuring time using the alternating current in your wall, and that’s kept at an impressively stable frequency that can also be traced back to atomic clocks. So ultimately, I’m able to get to work on time thanks to the quantum physics of cesium atoms.
Now, maybe that doesn’t seem “spooky” enough. I mean, it’s a little weird that atoms have these special states and all, but my alarm clock isn’t obviously using the magical-seeming properties of quantum physics. But those properties play a key role in another step of an ordinary morning routine—after I get out of bed, and get my breakfast, I sit down to check my email and social media. And the Internet that I use to do it would be impossible without Schrödinger’s Cat.
Schrödinger’s Cat is probably the most infamous thought experiment ever devised, taken from a 1935 paper by the Austrian physicist Erwin Schrödinger, who had grown disenchanted with quantum physics for philosophical reasons. To demonstrate the absurdity of quantum predictions, Schrödinger imagined placing a cat in a sealed box with a device that has a 50% chance of killing the cat in the next hour. The question he posed is, at the end of the hour, just before the box is opened, what is the state of the cat? Common sense would seem to say that the cat is either alive or dead, but Schrödinger pointed out that quantum physics says the cat is both alive and dead at the same time, right up until it’s measured.
How does the theory end up in such a bizarre place? Well, it goes back to Niels Bohr and his special orbits. These work brilliantly to explain what’s going on with spectral lines and chemistry, but have one tiny problem: there’s no obvious reason why those orbits should be special.
But a French Ph.D. student named Louis de Broglie pointed out that you can easily explain Bohr’s rule for picking out the special orbits if electrons behave like waves. Bohr’s special orbits are ones where an integer number of electron wavelengths fit perfectly around the circumference of the orbit. For those orbits, the wave reinforces itself, and is stable, while other orbits get wiped out.
Wave nature for electrons is a radical notion, but there’s a nice symmetry to it, when paired with the particle nature of light introduced by Planck and Einstein. If light, which everyone knew is a wave, behaves like a particle, then it’s not unreasonable to think that an electron, which everyone knew is a particle, might behave like a wave. It’s also an eminently testable idea, and within a few years of de Broglie’s proposal, physicists in the US and UK had seen direct experimental evidence of electrons behaving like waves.
These days, we can beautifully demonstrate this dual nature, by firing electrons one at a time at a barrier with slits cut in it. Each electron is detected on the far side in a particular place at a particular instant, like a particle, but if you repeat the experiment over, and over, and over, all of the electrons together trace out a pattern of bright and dark stripes that’s characteristic of wave behavior. Electrons are particles that behave like waves, and vice versa.
By 1930, physicists knew that electrons have both particle and wave nature and are properly described by a quantum wavefunction,; Schrödinger himself shared a Nobel Prize for developing one of the equations physicists use to calculate those wavefunctions.
How does this lead to half-dead cats? Well, the thing about waves is that they can’t be nailed down the same way particles can. Particles are found at one position at any instant, but waves are necessarily spread out, a disturbance filling some region of space. So, quantum particles like electrons with wave nature can occupy multiple states at once, not just here or there, but here and there, until they’re measured. The idea that quantum objects exist in multiple states, and observation picks out the single reality we see was deeply disturbing to classically trained physicists like Schrödinger and Einstein. These philosophical issues drove them to abandon the theory they had helped create.
But this spreading out to multiple states is essential for understanding solid objects. The electrons in an atom behave like waves, extending over space. If you bring two atoms close together, the electrons end up shared between the two. An individual electron, like Schrödinger’s Cat, isn’t stuck to just Atom A or Atom B, it’s on both A and B at the same time.
This continues as you add more and more atoms. An electron inside a chunk of solid silicon, say, isn’t associated with a single atom, but spread through the entire thing. This profoundly changes the way electrons move inside materials. Fully understanding that motion demands quantum physics.
And because we understand quantum physics, we can use it to control the way electrons move inside materials, which lets us make transistors out of chunks of silicon. And packing millions of those together lets us make the semiconductor chips that power all our computers and telecommunications devices. Without quantum physics, none of that would be possible. So, the Internet isn’t just for sharing pictures of cats, it’s possible because of the physics behind Erwin Schrödinger’s infamous zombie cat.
Those are just a few of the ways that the exotic physics of quantum mechanics manifests itself in the course of an ordinary morning. It’s all too easy to fall into thinking of exotic physics as something with no practical relevance, that only matters in giant accelerators or around black holes. This is partly the fault of physicists, who are prone to over-emphasizing the weird and extreme.
It’s important to remember, though that as weird as quantum ideas may seem, they profoundly affect everything around us. There’s no separate “quantum realm” where the weird stuff happens; we live in a quantum world, from top to bottom. From the alarm that gets me out of bed, to the appliances I use to cook my breakfast, to the social-media apps that help me ease into the day, getting off to work in the morning would be impossible without quantum physics.
I’m telling you this not because I want to take away the magic of quantum physics, and drag it down to the mundane level of a weekday breakfast. Quite the contrary. I’m telling you this to enhance the everyday. Knowing how ordinary, everyday objects trace their behavior back to quantum physics can add an element of awe and wonder to even the most mundane morning.
Quantum physics is one of the greatest intellectual achievements in human history, and that’s something we should appreciate more. The great thing is, it’s everywhere, all around us, if we just know where to look.