How to Teach Quantum Physics to Your Dog 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

“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

“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

“Zero-point energy is one of the most counterintuitive ideas in quantum physics, telling us that nothing can ever be perfectly at rest. It means that there is always some energy present in any system, no matter how hard you try to extract all the energy. Even empty space has zero-point energy, which leads to some surprising consequences, including the spontaneous emission of photons from atoms and tiny forces (called “Casimir forces”) between metal plates in a vacuum.”
― 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

“Electrons must always have uncertainty in both their position and momentum, and that means that the energy of an electron in an atom can never be zero. To have zero energy while still being part of an atom, an electron would need to be not moving, sitting right on top of the nucleus. This is impossible, as we’ve already seen—the closest we can come is to make a narrow electron wave packet centered on the nucleus, which will include lots of different states with nonzero momentum”
― 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

“When we account for the wave nature of the electron, we are forced to discard the whole idea of electrons as planets. Instead, the electron hovers around the nucleus in a fuzzy sort of “cloud,” with a position that is uncertain, but confined to a region near the nucleus, and a momentum that is uncertain, but limited to values that keep it near the nucleus. Bohr’s idea of allowed energy states still applies—the electron will always have one of the limited number of energy values predicted by Bohr’s theory—but these states no longer correspond to electrons moving in particular orbits.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Louis de Broglie’s wave model of the electron provided the missing theoretical basis, but while particle-wave duality justifies the idea of allowed states, it requires us to discard the image of electrons orbiting the nucleus like planets orbiting the sun.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Most humans, and even many dogs, picture atoms as tiny little solar systems, with negatively charged electrons orbiting a positively charged nucleus. This picture originated with Niels Bohr in 1913, when he proposed the first”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Looked at in terms of wavefunctions, then, we can see that this relationship is much more than just a practical limit due to our inability to measure a system without disturbing it. Instead, it’s a deep statement about the limits of reality. We saw in chapter 1 that quantum particles behave like particles—photons have momentum and collide with electrons in the Compton effect (page 25). We also saw that quantum particles behave like waves—electrons, atoms, and molecules diffract around obstacles and form interference patterns. The price we pay for having both of these sets of properties at the same time is that position and momentum must always be uncertain. The meaning of the uncertainty principle is not just that it’s impossible to measure the position and momentum, it’s that these quantities do not exist in an absolute sense.”
― 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

“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

“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

“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

“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

“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

“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

“Imagine you have a bunny in the yard whose position and velocity you would like to know very well. When you attempt to make a better determination of its position (by getting closer to it), you inevitably change its velocity by making it run away. No matter how slowly you creep up on it, sooner or later, it always takes off, and you never really have a good idea of both the position and the velocity.”
― 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

“Well, in the picture where you attribute everything to the effects of measurement, you implicitly assume that whatever you’re measuring has some definite and well-defined properties, and the uncertainty in those values arises only from perturbations that occur through the act of measuring them. That’s not what happens, though—in quantum theory, there are no definite values for those quantities. They’re not uncertain because of limits on your measurement, they’re uncertain because they are not defined, and they can’t be defined, due to the quantum nature of reality.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“It’s not just that measurement changes the state of the system, it’s that what we can measure is limited by the fact that position and momentum are undefined until we measure them.”
― 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

“As the mass of a particle increases, its wavelength gets shorter and shorter, and it gets harder and harder to see wave effects directly. This is why nobody has ever seen a dog diffract around a tree; nor are we likely to see it any time soon. In terms of physics, though, a dog is nothing but a collection of biological molecules, which the Zeilinger group has shown have wave properties. So, we can say with confidence that a dog has wave nature, just the same as everything else.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“So, if all material objects are made up of particles with wave properties, why don’t we see dogs diffracting around trees? If a beam of electrons can diffract off two rows of atoms, why can’t a dog run around both sides of a tree to trap a bunny on the far side? The answer is the wavelength: as with the sound and light waves discussed earlier, the dramatically different behavior of dogs and electrons encountering obstacles is explained by the difference in their wavelengths. The wavelength is determined by the momentum, and a dog has a lot more momentum than an electron.”
― 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

“Electrons reflecting from all these different rows of atoms behaved like waves.”
― 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

“The idea has a certain mathematical elegance, which was appealing to theoretical physicists even in 1923, but it also seems like patent nonsense—solid objects show no sign of behaving like waves.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog

“Also in 1923, a French Ph.D. student named Louis Victor Pierre Raymond de Broglie* made a radical suggestion: he argued that there ought to be symmetry between light and matter, and so a material particle such as an electron ought to have a wavelength. After all, if light waves behave like particles, shouldn’t particles behave like waves? De Broglie suggested that just as a photon has a momentum determined by its wavelength, a material object like an electron should have a wavelength determined by its momentum: γ = h/p which is just the formula for the momentum of a photon (page 24) turned around to give the wavelength.”
― Chad Orzel, How to Teach Quantum Physics to Your Dog