Now let us look at the arrival of that single quantum of energy, to see how that discrete change can possibly happen without any discontinuity. Consider the simplest possible case: an atom absorbs a photon, including all its energy. This energy transfer does not take place instantaneously. (Forget anything that you may have read about ‘quantum jumps’: they are a myth.) There are many ways in which it can happen but the simplest is this. At the beginning of the process, the atom is in (say) its ‘ground state’, in which its electrons have the least possible energy allowed by quantum theory. That means that all its instances (within the relevant coarse-grained history) have that energy. Assume that they are also fungible. At the end of the process, all those instances are still fungible, but now they are in the ‘excited state’, which has one additional quantum of energy. What is the atom like halfway through the process? Its instances are still fungible, but now half of them are in the ground state and half in the excited state. It is as if a continuously variable amount of money changed ownership gradually from one discrete owner to another.
This mechanism is ubiquitous in quantum physics, and is the general means by which transitions between discrete states happen in a continuous way. In classical physics, a ‘tiny effect’ always means a tiny change in some measurable quantities. In quantum physics, physical variables are typically discrete and so cannot undergo tiny changes. Instead, a ‘tiny effect’ means a tiny change in the proportions that have the various discrete attributes.
This also raises the issue of whether time itself is a continuous variable. In this discussion I am assuming that it is. However, the quantum mechanics of time is not yet fully understood, and will not be until we have a quantum theory of gravity (the unification of quantum theory with the general theory of relativity), so it may turn out that things are not as simple as that. One thing we can be fairly sure of, though, is that, in that theory, different times are a special case of different universes. In other words, time is an entanglement phenomenon, which places all equal clock readings (of correctly prepared clocks – or of any objects usable as clocks) into the same history. This was first understood by the physicists Don Page and William Wooters, in 1983.
In this full version of the quantum multiverse, how is our science-fiction story to continue? Almost all the attention that the quantum theory has attracted, from physicists, philosophers and science-fiction authors alike, has focused on its parallel-universes aspect. That is ironic, because it is in the parallel-universe approximation that the world most resembles that of classical physics, yet that is the very aspect of quantum theory that many people seem to find viscerally unacceptable.
Fiction can explore the possibilities opened up by parallel universes. For instance, since our story is a romance, the characters may well wonder about their counterparts in other histories. The story could compare their speculations with what we ‘know’ happened in the other histories. The character whose spouse’s unfaithfulness was revealed by a ‘random’ event might wonder whether that event provided a lucky escape from what was a doomed marriage anyway. Are they still married in the history in which the unfaithfulness was not subsequently revealed? Are they still happy? Can it be true happiness if it is ‘based on a lie’? As we see them speculating on these matters, we see the ‘still married’ history and know the (fictional) fact of the matter.
They might also speculate about less parochial issues. The story could say that their sun is part of a cluster of dozens of stars, all within a sphere of a few light-weeks’ radius. This has puzzled their scientists for decades, since the composition of the stars shows that they originated from far and wide and became gravitationally bound through a series of very unlikely coincidences. In most universes, these scientists calculate, life cannot evolve in such dense star clusters, because there are too many collisions. So in most universes that contain humans there are no fleets of starships visiting inhabited star systems one after another. They have been trying to discover a mechanism by which the proximity of nearby stars might somehow precipitate the formation of intelligent life, but they have failed. Should they consider it just an astronomically unlikely coincidence? But they do not like leaving things unexplained. Something must have selected them, they conclude. It did. Those people are not just a story. They are real, living, thinking human beings, wondering at this very moment where they came from. But they will never find out. In that one respect, they are unlucky: they were indeed selected by coincidence. Another way of putting that is that they were selected by the very story that I am now telling about them. All fiction that does not violate the laws of physics is fact.
Some fiction in which the laws of physics appear to be violated is also fact, somewhere in the multiverse. This involves a subtle issue about how the multiverse is structured – how histories emerge. A history is approximately autonomous. If I boil some water in a kettle and make tea, I am in a history in which I switched on the kettle and the water became gradually hotter because of the energy being poured into it by the kettle, causing bubbles to form and so on, and eventually hot tea forms. That is a history because one can give explanations and make predictions about it without ever mentioning either that there are other histories in the multiverse where I chose to make coffee instead or that the microscopic motion of the water molecules is slightly affected by parts of the multiverse that are outside that history. It is irrelevant to that explanation that a small measure of that history differentiates itself during that process and does other things. In some tiny sliver of it, the kettle transforms itself into a top hat, and the water into a rabbit which then hops away, and I get neither tea nor coffee but am very surprised. That is a history too, after that transformation. But there is no way of correctly explaining what was happening during it, or predicting the probabilities, without referring to other parts of the multiverse – enormously larger parts (i.e. with larger measures) – in which there was no rabbit. So that history began at the transformation, and its causal connection with what happened before that cannot be expressed in history terms but only in multiverse terms.
In simple cases like that, there is a ready-made approximative language in which we can minimize mention of the rest of the multiverse: the language of random events. This allows us to acknowledge that most of the high-level objects concerned still behaved autonomously except for being affected by something outside themselves – as when I am affected by the rabbit. This constitutes some continuity between a history and a previous history from which it split, and we can refer to the former as a ‘history that has been affected by random events’. However, this is never literally what has happened: the part of that ‘history’ prior to the ‘random event’ is fungible with the rest of the broader history and therefore has no separate identity from it: it is not separately explicable.
But the broader of those two histories still is. That is to say, the rabbit history is fundamentally different from the tea history, in that the latter remains very accurately autonomous throughout the period. In the rabbit history I end up with memories that are identical to what they would be in a history in which water became a rabbit. But those are misleading memories. There was no such history; the history containing those memories began only after the rabbit had formed. For that matter, there are also places in the multiverse – of far larger measure than that one – in which only my brain was affected, producing exactly those memories. In effect, I had a hallucination, caused by random motion of the atoms in my brain. Some philosophers make a big issue of that sort of thing, claiming that it casts doubt on the scientific status of quantum theory, but of course they are empiricists. In reality, misleading observations, misleading memories and false interpretations are common even in the mainstreams of history. We have to work hard to avoid fooling ourselves with them.
So it is not quite true that, for instance, there are histories in which magic appears to work. There are only histories in which magic appears to have worked, but will never work again. There are histories in which I appe
ar to have walked through a wall, because all the atoms of my body happened to resume their original courses after being deflected by atoms in the wall. But those histories began at the wall: the true explanation of what happened involves many other instances of me and it – or we can roughly explain it in terms of random events of very low probability. It is a bit like winning a lottery: the winner cannot properly explain what has just happened without invoking the existence of many losers. In the multiverse, the losers are other instances of oneself.
The ‘history’ approximation breaks down completely only when histories not only split but merge – that is to say, in interference phenomena. For example, there are certain molecules that exist in two or more structures at once (a ‘structure’ being an arrangement of atoms, held together by chemical bonds). Chemists call this phenomenon ‘resonance’ between the two structures, but the molecule is not alternating between them: it has them simultaneously. There is no way of explaining the chemical properties of such molecules in terms of a single structure, because when a ‘resonant’ molecule participates in a chemical reaction with other molecules, there is quantum interference.
In science fiction, we have a mandate to speculate, even to levels of implausibility that would make for quite bad explanations in real science. But the best explanation of ourselves in real science is that we – sentient beings in this gigantic, unfamiliar structure in which material things have no continuity, in which even something as basic as motion or change is different from anything in our experience – are embedded in multiversal objects. Whenever we observe anything – a scientific instrument or a galaxy or a human being – what we are actually seeing is a single-universe perspective on a larger object that extends some way into other universes. In some of those universes, the object looks exactly as it does to us, in others it looks different, or is absent altogether. What an observer sees as a married couple is actually just a sliver of a vast entity that includes many fungible instances of such a couple, together with other instances of them who are divorced, and others who have never married.
We are channels of information flow. So are histories, and so are all relatively autonomous objects within histories; but we sentient beings are extremely unusual channels, along which (sometimes) knowledge grows. This can have dramatic effects, not only within a history (where it can, for instance, have effects that do not diminish with distance), but also across the multiverse. Since the growth of knowledge is a process of error-correction, and since there are many more ways of being wrong than right, knowledge-creating entities rapidly become more alike in different histories than other entities. As far as is known, knowledge-creating processes are unique in both these respects: all other effects diminish with distance in space, and become increasingly different across the multiverse, in the long run.
But that is only as far as is known. Here is an opportunity for some wild speculations that could inform a science-fiction story. What if there is something other than information flow that can cause coherent, emergent phenomena in the multiverse? What if knowledge, or something other than knowledge, could emerge from that, and begin to have purposes of its own, and to conform the multiverse to those purposes, as we do? Could we communicate with it? Presumably not in the usual sense of the term, because that would be information flow; but perhaps the story could propose some novel analogue of communication which, like quantum inference, did not involve sending messages. Would we be trapped in a war of mutual extermination with such an entity? Or is it possible that we could nevertheless have something in common with it? Let us shun parochial resolutions of the issue – such as a discovery that what bridges the barrier is love, or trust. But let us remember that, just as we are at the top rank of significance in the great scheme of things, anything else that could create explanations would be too. And there is always room at the top.
TERMINOLOGY
Fungible Identical in every respect.
The world The whole of physical reality.
Multiverse The world, according to quantum theory.
Universe Universes are quasi-autonomous regions of the multiverse.
History A set of fungible universes, over time. One can also speak of the history of parts of a universe.
Parallel universes A somewhat misleading way of referring to the multiverse. Misleading because the universes are not perfectly ‘parallel’ (autonomous), and because the multiverse has much more structure – especially fungibility, entanglement and the measures of histories.
Instances In parts of the multiverse that contain universes, each multiversal object consists approximately of ‘instances’, some identical, some not, one in each of the universes.
Quantum The smallest possible change in a discrete physical variable.
Entanglement Information in each multiversal object that determines which parts (instances) of it can affect which parts of other multiversal objects.
Decoherence The process of its becoming infeasible to undo the effect of a wave of differentiation between universes.
Quantum interference Phenomena caused by non-fungible instances of a multiversal object becoming fungible.
Uncertainty principle The (badly misnamed) implication of quantum theory that, for any fungible collection of instances of a physical object, some of their attributes must be diverse.
Quantum computation Computation in which the flow of information is not confined to a single history.
SUMMARY
The physical world is a multiverse, and its structure is determined by how information flows in it. In many regions of the multiverse, information flows in quasi-autonomous streams called histories, one of which we call our ‘universe’. Universes approximately obey the laws of classical (pre-quantum) physics. But we know of the rest of the multiverse, and can test the laws of quantum physics, because of the phenomenon of quantum interference. Thus a universe is not an exact but an emergent feature of the multiverse. One of the most unfamiliar and counter-intuitive things about the multiverse is fungibility. The laws of motion of the multiverse are deterministic, and apparent randomness is due to initially fungible instances of objects becoming different. In quantum physics, variables are typically discrete, and how they change from one value to another is a multiversal process involving interference and fungibility.
12
A Physicist’s History of Bad Philosophy
With Some Comments on Bad Science
By the way, what I have just outlined is what I call a ‘physicist’s history of physics’, which is never correct . . .
Richard Feynman, QED:
The Strange Theory of Light and Matter (1985)
READER: So, I am an emergent, quasi-autonomous flow of information in the multiverse.
DAVID: You are.
READER: And I exist in multiple instances, some of them different from each other, some not. And those are the least weird things about the world according to quantum theory.
DAVID: Yes.
READER: But your argument is that we have no option but to accept the theory’s implications, because it is the only known explanation of many phenomena and has survived all known experimental tests.
DAVID: What other option would you like to have?
READER: I’m just summarizing.
DAVID: Then yes: quantum theory does have universal reach. But if all you want to explain is how we know that there are other universes, you don’t have to go via the full theory. You need look no further than what a Mach–Zehnder interferometer does to a single photon: the path that was not taken affects the one that was. Or, if you want the same thing writ large, just think of a quantum computer: its output will depend on intermediate results being computed in vast numbers of different histories of the same few atoms.
READER: But that’s just a few atoms existing in multiple instances. Not people.
DAVID: Are you claiming to be made of something other than atoms?
READER: Ah, I see.
DAVID: Also, imagine a vast cloud of
instances of a single photon, some of which are stopped by a barrier. Are they absorbed by the barrier that we see, or is each absorbed by a different, quasi-autonomous barrier at the same location?
READER: Does it make a difference?
DAVID: Yes. If they were all absorbed by the barrier we see, it would vaporize.
READER: So it would.
DAVID: And we can ask – as I did in the story of the starship and the twilight zone – what is holding up those barriers? It must be other instances of the floor. And of the planet. And then we can consider the experimenters who set all this up and who observe the results, and so on.
READER: So that trickle of photons through the interferometer really does provide a window on a vast multiplicity of universes.
DAVID: Yes. It’s another example of reach – just a small portion of the reach of quantum theory. The explanation of those experiments in isolation isn’t as hard to vary as the full theory. But in regard to the existence of other universes it’s incontrovertible all the same.
READER: And that’s all there is to it?
DAVID: Yes.
READER: But then why is it that only a small minority of quantum physicists agree?
DAVID: Bad philosophy.
READER: What’s that?
Quantum theory was discovered independently by two physicists who reached it from different directions: Werner Heisenberg and Erwin Schrödinger. The latter gave his name to the Schrödinger equation, which is a way of expressing the quantum-mechanical laws of motion.
Both versions of the theory were formulated between 1925 and 1927, and both explained motion, especially within atoms, in new and astonishingly counter-intuitive ways. Heisenberg’s theory said that the physical variables of a particle do not have numerical values. Instead, they are matrices: large arrays of numbers which are related in complicated, probabilistic ways to the outcomes of observations of those variables. With hindsight, we now know that that multiplicity of information exists because a variable has different values for different instances of the object in the multiverse. But, at the time, neither Heisenberg nor anyone else believed that his matrix-valued quantities literally described what Einstein called ‘elements of reality’.
The Beginning of Infinity Page 36