Chad Orzel > Quotes

“Dogs come to quantum physics in a better position than most humans. They approach the world with fewer preconceptions than humans, and always expect the unexpected. A dog can walk down the same street every day for a year, and it will be a new experience every day. Every rock, every bush, every tree will be sniffed as if it had never been sniffed before. If dog treats appeared out of empty space in the middle of a kitchen, a human would freak out, but a dog would take it in stride. Indeed, for most dogs, the spontaneous generation of treats would be vindication—they always expect treats to appear at any moment, for no obvious reason.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Quantum uncertainty is a fundamental limit on what can be known, arising from the fact that quantum objects have both particle and wave properties.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Uncertainty is not a statement about the limits of measurement, it’s a statement about the limits of reality. Asking for the precise position and momentum of a particle doesn’t even make sense, because those quantities do not exist.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“How do we get a wave packet by combining many waves? Well, let’s start with two simple waves, one corresponding to a bunny casually hopping across the yard, and another one with a shorter wavelength (the graph below shows 20 full oscillations of one, in the same space as 18 of the other), corresponding to a bunny moving faster, perhaps because it knows there’s a dog nearby. Now let’s add those two wavefunctions together. “Wait a minute—now we have two bunnies?” “No, each wavefunction describes a bunny with a particular momentum, but it’s the same bunny both times.” “But doesn’t adding them together mean that you have two bunnies?” “No, in this case, it just means that there are two different states* you might find the single bunny in. When you look out into the yard, there’s some probability of finding the bunny moving slowly, and some probability of finding it moving a little faster. The way we account for that mathematically is by adding the two waves together.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“A particle-like object has a definite position (you know right where it is), a definite velocity (you know how fast it’s moving, and in what direction), and a definite mass (you know how big it is). You can multiply the mass and velocity together, to find the momentum.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“In 1927, two American physicists, Clinton Davisson and Lester Germer, were bouncing electrons off a surface of nickel, and recording how many bounced off at different angles. They were surprised when their detector picked up a very large number of electrons bouncing off at one particular angle. This mysterious result was eventually explained as the wavelike diffraction of the electrons bouncing off different rows of atoms in their nickel target.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Waves don’t even add together in the same way that particles do—sometimes, when you put two waves together, you end up with a bigger wave, and sometimes you end up with no wave at all.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“So, look at the world around you, and if you notice things that don't seem right - injustices, inefficiencies, or just oddities - investigate them further. Think about why and how those things might happen and what you could do to change them for the better. Test your ideas by trying new things, making more observations, refining your models, and repeating the process. And when you find something that works to explain or improve your situation, tell everyone about it, so we can all benefit.”
― Chad Orzel, Eureka: Discovering Your Inner Scientist

“Einstein described a beam of light as a stream of little particles, each with an energy equal to Planck’s constant multiplied by the frequency of the light wave (the same rule used for Planck’s “oscillators”). Each photon (the name now given to these particles of light) has a fixed amount of energy it can provide, depending on the frequency; and some minimum amount of energy is required to knock an electron loose. If the energy of a single photon is more than the minimum needed, the electron will be knocked loose, and carry the rest of the photon’s energy with it. The higher the frequency, the higher the single photon energy and the more energy the electrons have when they leave, exactly as the experiments show. If the energy of a single photon is lower than the minimum energy for knocking an electron out, nothing happens, explaining the lack of electrons at low frequencies.* Describing light as a particle was a hugely controversial idea in 1905, as it overturned a hundred years’ worth of physics and requires a very different view of light. Rather than a continuous wave, like water poured into a dog’s bowl, light has to be thought of as a stream of discrete particles, like a scoop of kibble poured into a bowl. And yet each of those particles still has a frequency associated with it, and somehow they add up to give an interference pattern, just like a wave.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Sound waves are pressure waves in the air. When a dog barks, she forces air out through her mouth and sets up a vibration that travels through the air in all directions.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“To measure the position of an electron, you need to do something to make it visible, such as bouncing a photon of light off it and viewing the scattered light through a microscope. But the photon carries momentum (as we saw in chapter 1 [page 24]), and when it bounces off the electron, it changes the momentum of the electron. The electron’s momentum after the collision is uncertain, because the microscope lens collects photons over some range of angles, so you can’t tell exactly which way it went. You can make the momentum change smaller by increasing the wavelength of the light (decreasing the momentum that the photon has available to give to the electron), but when you increase the wavelength, you decrease the resolution of your microscope, and lose information about the position.* If you want to know the position well, you need to use light with a short wavelength, which has a lot of momentum, and changes the electron’s momentum by a large amount. You can’t determine the position precisely without losing information about the momentum, and vice versa.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Following the experiments of Davisson and Germer and Thomson, scientists showed that all subatomic particles behave like waves: beams of protons and neutrons will diffract off samples of atoms in exactly the same way that electrons do. In fact, neutron diffraction is now a standard tool for determining the structure of materials at the atomic level: scientists can deduce how atoms are arranged by looking at the interference patterns that result when a beam of neutrons bounces off their sample. Knowing the structure of materials at the atomic level allows materials scientists to design stronger and lighter materials for use in cars, planes, and space probes. Neutron diffraction can also be used to determine the structure of biological materials like proteins and enzymes, providing critical information for scientists searching for new drugs and medical treatments.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“What we need is a “wave packet,” a wavefunction that combines particle and wave properties in a single probability distribution, like”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Adding these states together is the origin of the uncertainty principle. If we want a narrow and well-defined wave packet, so that we know the position of the bunny very well, we need to add together a great many waves to do that. Each wave corresponds to a possible momentum for the bunny, though, which gives a large uncertainty in the momentum—it could be moving at any one of a large number of different speeds. On the other hand, if we want to know the momentum very well, we can use a small number of different wavelengths, but this gives us a very broad wave packet, with a large uncertainty in the position. The bunny can only have a few possible speeds, but we can no longer say where it is with much confidence.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Everything in the universe is subject to the uncertainty principle, and has an uncertain position and velocity.” “That can’t be right. I mean, I can see my bone right over there, and it has a definite position, and a velocity of zero.” “Ah, but the quantum uncertainty associated with your bone is dwarfed by the practical uncertainty involved in measuring it. If you look at it really carefully, you might be able to specify its position to within a millimeter or so—” “I always look at my bone carefully.” “—and with heroic effort, you might bring that down to a hundred nanometers. In that case, the velocity uncertainty of your hundred-gram bone would be only 10-27 m/s. So, the velocity would be zero, plus or minus 10-27 m/s.” “That’s pretty slow.” “Yeah, you could say that. At that speed, it would take the age of the universe to cross the thickness of a single atom.” “Okay, that’s really slow.” “We don’t see quantum uncertainty associated with everyday objects because they’re just too big. We only see uncertainty directly when we look at very small particles confined to very small spaces.” “Like electrons near atoms!”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“You can measure how often the wave repeats itself in a given amount of time—how many times the duck reaches its maximum height in a minute, say—and that gives you the “frequency” of the wave, which is another critical number used to describe the wave. Wavelength and frequency are related to each other—longer wavelengths mean lower frequency, and vice versa.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“When we add these two waves together, we find that there are some places where they are in phase, and add up to give a bigger wave. In other places, they’re out of phase, and cancel each other out. The wavefunction we get from adding them together (the solid line in the figure) has lumps in it—there are places where we see waves, and places where we see nothing. When we square that to get the probability distribution, we get the bottom graph: The dashed curves in the top graph show the wavefunctions for the two different wavelengths (shifted up so you can see them clearly). The solid curve shows the sum of the two wavefunctions. The bottom graph shows the probability distribution resulting from adding them together (the square of the solid curve in the top graph).”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“The photoelectric effect ought to be readily explained by thinking of light as a wave that shakes atoms back and forth until electrons come out,”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Planck’s trick amounts to treating light, which physicists thought of as a continuous wave, as coming in discrete chunks, like particles. Planck’s “oscillators” could only emit light in discrete units of brightness. This is a little like imagining a pond where waves can only be one, two, or three centimeters high, never one and a half or two and a quarter. Everyday waves don’t work that way, but that’s what Planck’s mathematical model requires.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“The apparent bending of sound waves around corners is an example of diffraction, which is a characteristic behavior of waves encountering an obstacle. When a wave reaches a barrier with an opening in it, like the wall containing an open door from the kitchen into the dining room, the waves passing through the opening don’t just keep going straight, but fan out over a range of different directions. How quickly they spread depends on the wavelength of the wave and the size of the opening through On the left, a wave with a short wavelength encounters an opening much larger than the wavelength, and the waves continue more or less straight through. On the right, a wave with a long wavelength encounters an opening comparable to the wavelength, and the waves diffract through a large range of directions. which they travel. If the opening is much larger than the wavelength, there will be very little bending, but if the opening is comparable to the wavelength, the waves will fan out over the full available range.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“This tiny residual motion is called zero-point energy, which is the minimum quantum energy associated with a particle due to its confinement. Zero-point energy provides an absolute lower limit to the energy a confined particle can have—no matter how carefully you prepare the system, the particles in that system will always be in motion, with small random fluctuations constantly changing the magnitude and direction of their velocity.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“If we add together three different waves, the region where we have a good probability of seeing the bunny gets narrower, and with five different waves, it’s narrower still. As we add more and more waves, the regions of high probability get narrower, and the spaces between them become wider and flatter. What we end up with starts to looks like a long chain of wave packets.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“The apparent bending of sound waves around corners is an example of diffraction, which is a characteristic behavior of waves encountering an obstacle. When a wave reaches a barrier with an opening in it, like the wall containing an open door from the kitchen into the dining room, the waves passing through the opening don’t just keep going straight, but fan out over a range of different directions. How quickly they spread depends on the wavelength of the wave and the size of the opening through”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“uncertainty principle: it is impossible to know both the position and the momentum of an object perfectly at the same time. If you make a better measurement of the position, you necessarily lose information about its momentum, and vice versa.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“The most striking difference between light and sound in everyday life has to do with what happens when they encounter an obstacle. Light waves travel only in straight lines, while sound waves seem to bend around obstacles.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“You know, Heisenberg’s uncertainty principle? The uncertainty in the position of an object multiplied by the uncertainty in the momentum is greater than Planck’s constant over four pi? Which means that when one uncertainty is small, the other must be very large.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“The first person to talk seriously about light as a quantum particle was Albert Einstein in 1905, who used it to explain the photoelectric effect. The photoelectric effect is another physical effect that seems like it ought to be simple to describe: when you shine light on a piece of metal, electrons come out. This forms the basis for simple light sensors and motion detectors:”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“What does it mean to add together lots of different waves with different wavelengths in this way? Well, each wave corresponds to a particular momentum—a different velocity for the (single) bunny moving through the yard. When we add them all together, what we’re doing is saying that there’s a chance of finding the bunny in each of those different states”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Interference and diffraction are phenomena that only happen with waves, though, so after Young’s experiment (and subsequent experiments by the French physicist Augustin Fresnel), everybody was convinced that light was a wave. Things stayed that way for about a hundred years.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“At walking speed, a twenty-kilogram dog like you has a wavelength of about 10-35 meters. You need your wavelength to be comparable to the size of the tree—maybe ten centimeters—in order to diffract around it, and you’re thirty-four orders of magnitude off.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog