By David Pearce
Intuitively, there shouldn’t be anything to explain. Bizarrely, this doesn’t seem to be the case. One clue to the answer may be our difficulty in rigorously specifying a default state of “nothingness” from which any departure stands in need of an explanation. A dimensionless point? A timeless void? A quantum vacuum? All attempts to specify an alternative reified “nothingness” – an absence of laws, properties, objects, or events – just end up smuggling in something else instead. Specifying anything at all, including the truth-conditions for our sense of “nothingness”, requires information. Information is fundamental in physics. Information is physical. Information, physics tells us, cannot be created or destroyed. Thus wave functions in quantum mechanics don’t really collapse to yield single definite classical outcomes (cf.). Decoherence – the scrambling of phase angles between the components of a quantum superposition – doesn’t literally destroy superpositions. Not even black holes really destroy information. (cf. )
So naturally we may ask: where did information come from in the first place?
Perhaps the answer is that it didn’t. The total information content of reality is necessarily zero: the superposition principle of QM formalises inexistence.
On this story, one timeless logico-physical principle explains everything, including itself. The superposition principle of quantum mechanics formalises an informationless zero ontology – the default condition from which any notional departure would need to be explained. In 2002, Physics World readers voted Young’s double-slit experiment with single electrons as the “most beautiful experiment in physics”. (cf. Wojciech Zurek) The universal validity of the superposition principle in post-Everett QM suggests that the mystery of our existence has a scientific rather than theological explanation.). Richard Feynman liked to remark that all of quantum mechanics can be understood by carefully thinking through the implications of the double-slit experiment. Quite so; only maybe Feynman could have gone further. If Everettian QM (cf. ) is correct, reality consists of a single vast quantum-coherent superposition. Each element in the superposition, each orthogonal relative state, each “world”, is equally real. (cf. ) Most recently, the decoherence program in post-Everett quantum mechanics explains the emergence of quasi-classical branches (“worlds”) like ours from the underlying quantum field-theoretic formalism. (cf.
What does it mean to say that the information content of reality may turn out to be zero? Informally, perhaps consider the (classical) Library of Babel. (cf.) The Library of Babel contains all possible books with all possible words and letters in all possible combinations. The Library of Babel has zero information content. Yet somewhere amid the nonsense lies the complete works of Shakespeare – and you and me. However, the Library of Babel is classical. Withdrawing a book from the Library of Babel yields a single definite classical outcome – thereby creating information. Withdrawing more books creates more information. If we sum two ordinary non-zero probabilities, then we always get a bigger probability. All analogies break down somewhere. Evidently we aren’t literally living in Borges’ Library of Babel.
So instead of the classical Library of Babel, let us tighten the analogy. Imagine the quantum Library of Babel. Just as in standard probability theory, if there are two ways in QM that something can happen, then we get the total amplitude for something by summing the amplitudes for each of the two ways. If we sum two ordinary non-zero probabilities, then we always get a bigger probability. Yet because amplitudes in QM are complex numbers, summing two amplitudes can yield zero. Having two ways to do something in quantum mechanics can make it not happen. Recall again the double-slit experiment. Adding a slit to the apparatus can make particles less likely to arrive somewhere despite there being more ways to get there. Now scale up the double-slit experiment to the whole of reality. The information content of the universal state vector is zero. (cf. Jan-Markus Schwindt, “Nothing happens in the Universe of the Everett Interpretation“).
The quantum Library of Babel has no information.
Caveats? Loose ends? The superposition principle has been experimentally tested only up to the level of fullerenes, though more ambitious experiments are planned (cf. “Physicists propose ‘Schrödinger’s virus’ experiment“). Some scientists still expect the unitary Schrödinger dynamics will need to be supplemented or modified for larger systems – violating the information-less zero ontology that we’re exploring here.
Consciousness? Does the superposition principle break down in our minds? After all, we see live or dead cats, not live-and-dead-cat superpositions. Yet this assumption of classical outcomes – even non-unique classical outcomes – presupposes that we have direct perceptual access to the mind-independent world. Controversially (cf. Max Tegmark, “Why the brain is probably not a quantum computer“), perhaps the existence of our phenomenally-bound classical world-simulations itself depends on ultra-rapid quantum-coherent neuronal superpositions in the CNS. For if the superposition principle really broke down in the mind-brain, as classical neuroscience assumes, then we’d at most be so-called “micro-experiential zombies” – just patterns of discrete, decohered Jamesian neuronal “mind-dust” incapable of phenomenally simulating a live or a dead classical cat. (cf. David Chalmers’ “The Combination Problem for Panpsychism“)
This solution to the phenomenal binding problem awaits experimental falsification with tomorrow’s tools of molecular matter-wave interferometry. (cf. )
What about the countless different values of consciousness? How can an informationless zero ontology possibly explain the teeming diversity of our experience? This is a tough one. Yet just as the conserved constants in physics cancel out to zero, and just as all of mathematics can in principle be derived from the properties of the empty set, perhaps the solutions to the field-theoretic equations of QFT mathematically encode the textures of consciousness. If we had a cosmic analogue of the Rosetta stone, then we’d see that these values inescapably “cancel out” to zero too. Unfortunately, it’s hard to think of any experimental tests for this highly speculative conjecture.
“A theory that explains everything explains nothing”, protests the critic of Everettian QM. To which we may reply, rather tentatively: yes, precisely.
David Pearce is a personal inspiration. He recently had a conversation with Peter Singer, Hilary Greaves and Justin Oakley. I encourage anyone interested in hard core stuff to watch it 🙂