Читать книгу How to Make a Human Being: A Body of Evidence - Christopher Potter, Christopher Potter - Страница 15

1 | Until the 1920s scientists believed in an independent reality that could be measured. But then from the 1920s there was quantum mechanics.

I think I can safely say that nobody understands quantum mechanics.

Richard Feynman

2 | The physicist Niels Bohr once said that quantum mechanics only makes sense if you change the meaning of the word ‘understand’.

3 | Quantum mechanics tells us that the world is best described by a wave of superimposed probabilities. The most famous wave formulation is the Schrödinger equation. It is a linear superposition of different states of reality that evolves smoothly in time. Each possible observed reality has a certain probability attached to it.

4 | From the perspective of a molecule, nature is a single quantum wave of probability. From the perspective of a human being there are separate things, and particular events occurring at particular moments. The fundamental problem of quantum mechanics is how a reality that is described by a smooth wave also describes the world that we witness at our human scale. How are these two different perspectives commensurate?

5 | Various mechanisms have been put forward to explain how the sinuousness of the quantum world, in which everything is entangled in probability, becomes a world of separate things that actually happen, or appear to happen (the appearance being what we take to be the actual), but each is problematic.

6 | The Copenhagen interpretation, the most famous interpretation of quantum mechanics, devised largely by Niels Bohr and Werner Heisenberg in the 1920s, argued that quantum mechanics does not describe a physical reality but probabilities attached to the act of measuring itself. The wave of possibility collapses when a measurement is made, and we find ourselves in that world out of the many possible worlds contained within the wave. All the other possible worlds disappear.

7 | Light is both wave and particle. Light is made out of photons that in particle physics are understood to be particles. But light diffracts when it passes around the edges of a slit (or more evidently when it passes through a double slit). Light behaves as if it is a wave: troughs of light coincide to make the bands of darkness of a diffraction pattern. Even when the light is thinned so that single photon particles pass through the slits one at a time the diffraction pattern remains. It is as if each particle knows that it is part of the pattern. But how can a single particle know where to go? Follow the particle with a detector to see exactly when and where it decides which slit to pass through and the diffraction pattern disappears. The Copenhagen interpretation of quantum mechanics claims that it is the measurement itself that changes reality.

8 | The Copenhagen interpretation raises problems about what defines a measurement. It implies that the act of looking, of conscious attention, affects the outcome of an event. The attention of the observer creates the very thing we call reality.¹ But how much attention, and the attention of what? As Einstein once asked, would a sidelong glance from a mouse suffice?

9 | The problem of how to interpret quantum mechanics became mixed up with the problem of how to define consciousness. If humans are uniquely conscious, as the Copenhagen interpretation seems to claim, then humans become highly privileged, a problem if the Copernican principle is to be upheld.

With human consciousness the universe became aware of itself. It might even be claimed, as the neurophysiologist John Eccles once did, that the universe cannot be said to have existed until there was human consciousness; the universe’s past falling into place only retrospectively. What claim could be more arrogant, or anti-Copernican? Yet if we see reality as a conversation between human consciousness and what we take to be outside ourselves, the arrogance fades away. Other forms of consciousness have their own conversations with the universe.

10 | For Einstein, quantum mechanics only makes sense if there is some hidden variable which, once found, turns the world back into a world of cause and effect.

Without being aware of it … we exclude the subject of cognizance from the domain of nature that we endeavour to understand. We step with our person back into the part of an onlooker who does not belong to the world, which by this very procedure becomes an objective world.

The physicist Erwin Schrödinger (1887–1961) refutes Einstein’s belief in an independent reality

11 | If an observing mouse is a separate physical system, where does the system begin and end? With a few atoms it is clear, because atoms have lost their thingness. Out of pure thought alone, we might guess that a world of elementary particles has to be indistinguishable as things. How would elementary particles know where the boundary of the system is? By the time we reduce the world to atoms, the world has become a place of limited sameness. The molecules of our bodies are continually in motion in and out across our boundaries, they do not know where we start and end. As complex structures of a certain size, humans lose their grip on reality and fall into the illusion of a world of things.

Nature opens its eyes and sees that it exists.

Friedrich Schelling (1775–1854), philosopher

12 | On the radio I hear Simon Saunders, a philosopher of physics, attempting to explain the measurement problem: Look, there’s a fairly straightforward dilemma here, well trilemma really …

13 | In Hugh Everett’s ‘many worlds’ interpretation of 1957, reality is a single wave function, a superposition that never collapses of every state of everything in the entire universe. In the quantum world there is a rule: whatever can happen, happens. The many worlds interpretation of quantum mechanics says that all possibilities contained within the wave equation actually do happen. God does not play dice, all possibilities exist.

We see only part of the wave equation. Other selves see other parts of the wave equation in other parts of the universe. The idea of a coherent self is undermined. What we take to be our self is the illusion that arises out of being trapped in a particular perspective of the multiverse. Somewhere in the multiverse we are doing everything that it is possible for us to do.

14 | Nature is a single superposition. It is only with great effort that scientists create a rival superposition, a rival nature. At any instant Nature pounces to claim its own. The information of our rival laboratory-made superpositions will easily leak into the much larger superposition that is all of nature outside the laboratory. The leaking of this information gives the illusion that the wave collapses, but it is only an illusion: the larger wave absorbs the smaller wave.

Scientists have found ways to keep a molecule made of some twenty carbon atoms in its own superposition (outside the superposition that is Nature). It requires the creation of an extremely cold environment. The small molecule does indeed, under these extreme conditions, reveal its ‘true’ nature: being in two or more places at the same time, for example – behaviour that would have counted as magic less than a hundred years ago.²

We are far from working out how to keep something as complex as a cat separate from the superposition that is Nature. I once heard a scientist say that if we look hard enough, one day we might find cats and chairs embedded in the wave equation. Perhaps, but somehow I doubt it.

15 | The chance that all the molecules that make up a glass of water being together as a glass of water in some other part of the universe and not here cancel out all the possibilities of where it could also be, and it ends up being where we most likely take it to be, what we call ‘here’. The rules of quantum mechanics tell us that all possibilities exist, but added together the unlikely ones cancel each other out, leaving what we acknowledge as the possible, the world of things. It is the addition of these possibilities that gives the illusion of a single reality, of a glass of water that exists very close to where we find it.

16 | Heisenberg said that the meaning of quantum mechanics is in the equations. Bohr, his mentor, pointed out that we still have to talk about the equation in words.

Mathematics is a great tool, but the ultimate governing language of science is language.

Lee Smolin

17 | The theoretical physicist David Bohm said that the quantum world is process based. Such a world is most readily described in verbs rather than nouns. He said that the problem with European languages, as in sentences like ‘The cat sat on the mat,’ is that we are dealing with well-defined nouns, a world of things. He believed the process that the verb describes is the deeper reality from which the illusion of thingness emerged, not the other way about. It has been suggested that the Algonquin languages of the Blackfoot, Micmac and Ojibwa tribes are particularly suitable processed-based languages in which to see the world as it is described by quantum mechanics. For these tribes, the world is alive. Singing is generative. The world was sung into existence.

Explanations of processes by which things come to be produce a feeble impression compared with the mystery that lies under the process.

T.S. Eliot (1888–1965), poet and essayist

18 | There are physicists who are still uncomfortable with the world quantum mechanics describes. Many attempts have been made to undermine quantum mechanics as a description of how reality actually is, but all attempts have failed. Pragmatically, scientists all agree that quantum mechanics works, and most don’t worry about how it should be interpreted.