Something Deeply Hidden Quotes

“A police officer pulls over Werner Heisenberg for speeding. “Do you know how fast you were going?” asks the cop. “No,” Heisenberg replies, “but I know exactly where I am!” I think we can all agree that physics jokes are the funniest jokes there are. They are less good at accurately conveying physics. This particular chestnut rests on familiarity with the famous Heisenberg uncertainty principle, often explained as saying that we cannot simultaneously know both the position and the velocity of any object. But the reality is deeper than that.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“The enigma at the heart of quantum reality can be summed up in a single motto: what we see when we look at the world seems to be fundamentally different from what actually is.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Quantum Mechanics doesn't deserve the connotation of spookiness in the sense of some ineffable mystery that it is beyond the human mind to comprehend. Quantum Mechanics is amazing; it is novel, profound, mind-stretching & a very different view of reality from what we’re used to.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“As a measurement apparatus interacts with a quantum system, the two become entangled with each other. There are no wave-function collapses or classical realms. The apparatus itself evolves into a superposition, entangled with the state of the thing being observed.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“As far as quantum field theory is concerned, a human being or the center of a star isn’t all that different from empty space.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Quantum reality is a wave function; classical positions and velocities are merely what we are able to observe when we probe that wave function.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Don't play Quantum Russian Roulette.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“The suggestion that reality is described as a vector in an enormous Hilbert space, rather than as matter and energy in good old four-dimensional spacetime, is not one he would have found congenial. But there’s a good chance that he would have been pleased that Everett returns our best description of the universe to one featuring definite, deterministic evolution—and reaffirms the principle that reality is ultimately knowable.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“What would Einstein have thought of Many-Worlds quantum theory? Likely he would have been repulsed, at least at first exposure. But he would have to admit that there are aspects of the idea that fit very well with his picture of how nature should operate.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“maybe all of the information about the state of the black hole—the “inside” as well as the horizon—can be thought of as living on the horizon itself, not buried in the interior. The black-hole state “lives,” in some sense, on a two-dimensional surface, rather than being stretched across a three-dimensional volume. First developed by Gerard ’t Hooft and Leonard Susskind in the 1990s, based in part on a paper by Charles Thorn from 1978, this idea is known as the holographic principle.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“So maybe in the real universe, where gravity certainly exists, Everettian quantum mechanics only describes a finite number of worlds. The number Alice mentioned for the dimensionality of Hilbert space was 210122.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“That raises a problem, one that has become notorious within theoretical physics as the black hole information puzzle. Remember that quantum mechanics, in its Many-Worlds version, is a deterministic theory. Randomness is only apparent, arising from self-locating uncertainty when the wave function branches and we don’t know which branch we’re on. But in Hawking’s calculation, black-hole radiation seems not to be deterministic; it’s truly random, even without any branching. Starting from a precise quantum state describing matter that collapses to make a black hole, there is no way of computing the precise quantum state of the radiation into which it evaporates. The information specifying the original state seems to be lost.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Although relativity treats space and time as if they were on an equal footing, quantum mechanics generally does not. The Schrödinger equation, in particular, treats them very differently: it literally describes how the quantum state evolves with time. “Space” may or may not be part of that equation, depending on what system we’re looking at, but time is fundamental. It’s plausible that the symmetry between space and time that we’re familiar with from relativity isn’t built into quantum gravity, but emerges in the classical approximation. It is nevertheless overwhelmingly tempting to wonder whether time, like space, might be emergent rather than fundamental, and whether entanglement might have anything to do with it. The answer is yes on both counts, although the details remain a little sketchy.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“The behavior of spacetime in general relativity can be thought of as simply the natural tendency of systems to move toward configurations of higher entropy.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Von Neumann showed that, for many purposes, the fact that entangled subsystems don’t have definite wave functions of their own is analogous to having a wave function, but we just don’t know what it is. Quantum subsystems, in other words, closely resemble the classical situation where there are many possible states that look macroscopically the same. And this uncertainty can be quantified into what we now call the entanglement entropy. The higher the entropy of a quantum subsystem, the more it’s entangled with the outside world.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Small ripples in the quantized gravitational field look like particles called gravitons, just like ripples in the electromagnetic field look like photons. Nobody has ever detected a graviton, and it’s possible that nobody ever will, since the gravitational force is so incredibly weak. But if we accept the basic principles of general relativity and quantum mechanics, the existence of gravitons is inevitable.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“There are two big ideas that go under the name of “the theory of relativity,” the special theory and the general theory. Special relativity, which came together in 1905, is based on the idea that everyone measures light to travel at the same speed in empty space. Combining that insight with an insistence that there is no absolute frame of motion leads us directly to the idea that time and space are “relative.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“By poking a quantum field in one tiny region of space, it’s possible to turn the quantum state of the whole universe into literally any state at all. Technically this result is known as the Reeh-Schlieder theorem, but it has also been called the Taj Mahal theorem. That’s because it implies that without leaving my room, I can do an experiment and get an outcome that implies there is now, suddenly, a copy of the Taj Mahal on the moon. (Or any other building, at any other location in the universe.)”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“we’re seeing a manifestation of what we talked about in the context of the uncertainty principle: when we observe a quantum state, we typically see something quite different from what the state was before we looked.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Sometimes the circumstances aren’t right; inside a proton or neutron, even though we often speak about quarks and gluons as if they’re individual particles, it’s more accurate to think of them as diffuse fields. As physicist Paul Davies once titled a paper, with only a bit of rhetorical exaggeration, “Particles Do Not Exist.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“This is the basic answer to the question of why we see the particular worlds that we do: the preferred-basis states are those that describe coherent objects in space, because such objects interact consistently with their environments. These are often called pointer states, as they are the states in which the pointer of a macroscopic measuring device will indicate a definite value, rather than being in a superposition. The pointer basis is where a well-behaved classical approximation makes sense, and therefore it’s that kind of basis that defines emergent worlds. Decoherence is the phenomenon that ultimately links the austere simplicity of Everettian quantum mechanics to the messy particularity of the world we see.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“The feature that makes space special is locality. Interactions between different objects happen when they are nearby in space. Two billiard balls bounce off each other when they come together at the same spatial position. Nothing of the sort happens when particles have the same (or opposite) momenta; if they’re not in the same location, they just keep going their merry way. That’s not a necessary feature of the laws of physics—we could imagine other possible worlds where it wasn’t the case—but it’s one that seems to hold pretty well in our world.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Textbooks in introductory quantum mechanics sometimes give the impression that classical behavior is inevitable once objects become very big, but that’s nonsense.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Everettian worlds are the same way. We don’t need to keep track of the entire wave function to make useful predictions, just what happens in an individual world. To a good approximation we can treat what happens in each world using classical mechanics, with just the occasional quantum intervention when we entangle with microscopic systems in superposition. That’s why Newton’s laws of gravitation and motion are sufficient to fly rockets to the moon without knowing the complete quantum state of the universe; our individual branch of the wave function describes an emergent almost-classical world.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“There are right and wrong ways to divide the wave function into branches, and the right ways leave us with independent worlds that obey approximately classical laws of physics. Which ways actually work is ultimately determined by the fundamental laws of nature, not by human whimsy.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“To say that something is emergent is to say that it’s part of an approximate description of reality that is valid at a certain (usually macroscopic) level, and is to be contrasted with “fundamental” things, which are part of an exact description at the microscopic level.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Even when we explicitly move to quantum mechanics, physicists generally start by taking a classical theory and quantizing it. But nature doesn’t do that. Nature simply is quantum from the start; classical physics, as Everett insisted, is an approximation that is useful in the right circumstances.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Einstein’s general relativity, which describes the curvature of spacetime. General relativity is itself a field theory—it describes a field pervading all of space, in this case the gravitational field. And we have very well understood procedures for taking a classical field theory and quantizing it, yielding a quantum field theory. Apply those procedures to the known fields of fundamental physics, and we end up with something called the Core Theory. The Core Theory accurately describes not only particle physics but also gravity, as long as the strength of the gravitational field doesn’t grow too large. It is sufficient to describe every phenomenon that happens in your everyday experience, and quite a bit beyond—tables and chairs, amoebas and kittens, planets and stars.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“by which they interacted were described by fields. These days we know better; even the particles that we know and love are actually vibrations in fields that suffuse the space around us. When we see particle-like tracks in a physics experiment, that’s a reflection of the fact that what we see is not what there really is. Under the right circumstances we see particles, but our best current theories say that fields are more fundamental.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

“Maybe quantum mechanics and consciousness are somehow interconnected; it’s a hypothesis we’re welcome to contemplate. But according to everything we currently know, there is no good evidence this is actually the case.”
― Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime