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That oughta bring ’em in.
It’s true, though. You’re at a wildly unusual temperature compared to the rest of the universe. You’re so hot, in fact, that you’re constantly giving off light. True, it’s light your eyes aren’t adapted to see, but nonetheless you are a gleaming beacon of hotness in a mostly cold universe.
I was talking with some colleagues about liquid nitrogen today. Liquid nitrogen seems like weird stuff. If I were to submerge my hand in liquid nitrogen, I would suffer major and permanent damage. But the damage isn’t because liquid nitrogen is so abnormally cold. It’s because my hand is so abnormally hot. Were I foolish enough to plunge my hand into liquid nitrogen, an enormous amount of heat would leave my hand in order to warm the nearby nitrogen. The result is quickly boiling nitrogen – and a dead hand.
Think how strange that is! When you touch an unusually hot object, the atoms of that unusually hot object move quite quickly, colliding with your atoms and causing them to move quite quickly, as well – probably boiling the water in your cells and giving you a nasty burn.
Now consider touching something at around the same temperature as you – maybe your favorite teddy bear. In this case, the atoms in your hand and the atoms in the bear are pounding on one another with essentially the same force. No harm, no foul.
Finally, think about liquid nitrogen. It’s like reaching for a rung on a ladder that isn’t there. Your hand’s energy pushes, but the nitrogen barely pushes back at all. The extra movement from your hot hand goes into giving the nitrogen molecules that extra movement they need to escape as gas, and your hand gets a whole lot colder.
In fact, liquid nitrogen itself isn’t all that cold, compared to the universe at large. Next to the chill of isolated deep space, liquid nitrogen is chock full of heat energy. Even solid nitrogen is full of heat energy, until it gets down to around 3 kelvins, the current background temperature of space. Things we generally think of as exceedingly cold – liquid nitrogen, a block of ice from the antarctic, and that slufreezy you purchased at the gas station on the way home that gave you brain freeze – all of these are so full of heat energy that they, too, glow with invisible light, light just a little less energetic than the light coming from you. The reason you think of these things as cold is because you, my friend, are so fantastically HOT!
In this last entry on many worlds, I want to revisit free will. In The Fabric of Reality, Deutsch gives the best argument in favor of free will I’ve encountered. Using the full glory of many worlds, Deutsch completely turns free will on its head.
Classical physics is strictly deterministic. Pierre-Simon Laplace described the situation accurately in 1814 when he said that a being with perfect knowledge of the positions and velocities of all particles at any one time could completely predict the future (and past) of the entire universe. The advent of quantum uncertainty showed that Laplace’s idea, while correct for classical physics, didn’t apply to our universe. But Deutsch shows how completely at odds with reality Laplace’s idea actually is.
One must think of many worlds not as a small add-on to classical physics, but as completely reversing the conception. Everything that can happen does happen. In the many worlds multiverse of Deutsch, every event branches out into different results. Consider a galaxy.
A galaxy forms because of gravitational attraction. But if things had been just a little different at the galaxy’s inception, every detail of that galaxy, including its composition, its placement in relation to other galaxies, and its shape, would have been different, as well. In Deutsch’s view, were one to view the multiverse all at once, a single galaxy would transform into a uniform spread of stars, dust, and debris smeared across enormous distance. Everything that can happen does in some portion of the multiverse.
The key thing about a galaxy is that it doesn’t “kick back”. There’s nothing about the galaxy’s makeup that will cause it to resist any multiversal change in its placement, composition, etc. It just doesn’t care, and as a result ends up all over the place.
Contrast that, though, with a living thing. A living thing does care. It does “kick back.” A living thing is knowledge, and as Deutsch says in The Beginning of Infinity, “(K)nowledge is information which, when it is embodied in a suitable environment, tends to cause itself to remain so.” (BoI, p 123) When looked at in the multiverse, life does something that no non-living entity can do. It molds and shapes the multiverse. It makes great portions of the multiverse look alike. As Deutsch says in The Fabric of Reality, “such places stand out . . . as the location of processes – life, and thought – that have generated the largest distinctive structures in the multiverse.” Knowledge is like a crystal that stretches across the multiverse, differentiating itself from all other structures in the universe.
So what of free will? We see now that free will is not just the ability to make different things happen. Everything has that ability in the multiverse. Consider a single uranium atom. It might decay this second, or next second, or not for billions of years. It might fire an alpha particle north, south, up, down, or in any other direction. It is fundamentally unpredictable. So is every other microscopic process. Variability isn’t hard to achieve in the multiverse, it’s natural and automatic.
What is hard to achieve is consistency. And this, Deutsch argues, is the heart of free will. Here’s his argument, which he presents in a chart in Chapter 13 of FoR:
After careful thought I chose to do X; I could have chosen otherwise; it was the right decision; I am good at making such decisions. What do each of these statements mean when looked at through the multiversal lens?
After careful thought I chose to do X: in the multiverse view, this means that some proportion of all the versions of me, including the one speaking, chose to do X.
I could have chose otherwise: in the multiverse view, some other versions of me did choose otherwise.
It was the right decision, I am good at making such decisions: in the multiverse view, the vast majority of all the versions of me made this decision – I have molded the multiverse by my decision-making.
From a deterministic world in which we really have no choices, Deutsch has given us a uniform cloud called the multiverse. It’s up to us to mold and shape that cloud into the form we want. The multiverse is ours for the making.
One must be careful, of course, to not accept an idea simply because it is attractive. Beware the ideas you want to be true. I’m still not fully sold on the quantum multiverse. As Deutsch says again and again, our ideas are always fallible. Many worlds may well be wrong. What Deutsch and the other writers have done for me, however, is convince me that a working hypothesis, no matter how crazy its consequences might seem, is better than no hypothesis at all. If many worlds is wrong, I think someone needs to show why its wrong, rather than just dismissing it as a silly extravagance.
As quantum technology brings these strange effects more and more into the world of the macroscopic, we will have an answer. Already there are proposed experiments that will be possible in the near future. These experiments will make one prediction for many worlds, another for rival ideas. Soon we won’t have to speculate, we will know. I for one (or maybe for many?) can’t wait to find out.
I’ve never purchased a lottery ticket, which I’m pretty sure is why I’ve never won. Lotteries are of course examples of zero sum games (or even worse than zero sum, since the state’s not running the lottery just for something to do – they’re making money!) However, some people have pointed out that if many worlds is true, you have a sure-fire way of winning the lottery.
First, build a suicide machine.
Next, go buy a lottery ticket. A single ticket will do just fine.
Now set up the suicide machine so that it will kill you in your sleep if you don’t win.
Go to sleep (sweet dreams!)
If you wake up (as, according to many worlds, you must in some history), then you’ve won the lottery!
Sounds pretty grim, but the idea comes from the fact that every possible outcome must happen in some history, so that somewhere your lottery ticket is the lucky one. And since any “you” that results from the many worlds splitting is in fact you, then you’ve just guaranteed yourself a big payoff.
The problem, of course, is that in the vast majority of histories you’ll be dead. Maybe you don’t care, but I might. I kinda like you, and chances are that in my history your infernal machine just snuffed you out. So don’t do it!
It sounds like a sick joke, sort of Schrodinger’s cat meets The Hunger Games , but such ideas are the topics of serious conversation in the many worlds debate.
Another version says that in some history I will live forever. In another history you will, too. In a vanishingly percentage of histories, we both will, but they’re so rare that we’ll ignore them for now. Here’s the idea. When I get to a potentially life-ending event (as I must every moment of every day), I will always find myself in the history in which I survive. Since there’s always some history in which I survive anything, I will live forever. Even as I grow old and grey (ok, older and greyer), something happens that causes my continued existence. I’ll notice the rest of the world passing by as normal, but I will find myself becoming the oldest living human, first by just a little, then by a decade, then a century, and so on.
I doubt this. For one thing, it seems to require either cause-effect problems or else historical discontinuities. For instance, I may be hit by a cosmic ray today that will start a slow cancer. The cancer might kill me in, say, ten years. So ten years from now in this history I’m ready to die, but somehow I don’t. Maybe I just barely survive. OK, fine.
But what about this? Right now there is an asteroid in deep space that, with the right nudge, could find itself on a collision course with the Earth. This is no ordinary Cretaceous Era asteroid that will wipe out 90% of life on the planet. No, this is a world-shattering asteroid that will turn the Earth itself into a pile of rubble. It is unfathomable that I could survive such a cataclysm. But how does my current history know to avoid the branch in which that asteroid tumbles Earthward? If you don’t think the asteroid is final enough, consider nearby supernovas, or disasters that destroy the Sun itself.
Or what about this? I hold a gun to my head and fire. In the fraction of a second after the bullet starts to move, but before it enters my brain, I’m still conscious. I’m still in that universe where a bullet is flying toward me but I’m alive. How in that history do I avoid death? And when exactly does the death avoidance happen?
Still, maybe there is some utterly unlikely way to survive. I suppose the test is this – if I find myself in situations again and again where I should die but don’t, then the hypothesis of quantum immortality is supported. Of course, if that doesn’t happen, I’ll never know about it, now will I?
But here’s another point. None of us live in such a universe, where some really old guy is living out his quantum immortality history. Yet if I were such a person living forever, I’d be surrounded by younger people who would see my odd immortal state. But who would those people be? What if (OK, this is really getting into the realm of fantasy now) they were actually my children? If not for my odd immortality, they would never exist. So they would only know a universe in which the reality of quantum immortality was manifest. Yet none of us, alive in this universe, can know this. So I ask again, who are these people? Another way of looking at it is, why aren’t we living in a universe where one, two, or more people are immortal?
All this assumes, of course, that there’s something special about consciousness. I’m not sure that’s a justified assumption, and neither does David Deutsch:
“There is the so-called ‘quantum suicide argument’ in regard to the multiverse . . . However, that way of applying probabilities does not follow directly from quantum theory . . . It requires an additional assumption, namely that when making decisions one should ignore the histories in which the decision-maker is absent . . . the theory of probability for such cases is not well understood, but my guess is that the assumption is false.”
So go buy a lottery ticket if you must, but as for your quantum suicide machine, don’t do it!
For the last entry in this series on many worlds, I’ll revisit a topic I’ve written about before, the reality of free will.
One of the strangest claims in The Beginning of Infinity is that fiction that doesn’t disobey the laws of physics is, in some part of the multiverse, true. This I find utterly bizarre.
It isn’t the first time that I’ve encountered this “every possibility is realized” sort of thinking. In fact, even without the quantum multiverse there are lots of ways that such a thing might come about. If this universe, the one we know, is in fact infinite, then by definition every possible configuration of matter must occur somewhere within it. In fact, every possible configuration of matter must occur an infinite number of times, so that there are infinite versions of me typing these words.
But how could this possibly be? Consider that if any of these multiverse ideas, quantum many worlds or otherwise, are true then somewhere there is an Earth exactly like this one except that every person has the last name of Mixelplix.
This seems utterly unlikely to me. Wouldn’t some smart demographer point out the silliness of everyone sharing the same last name? It certainly would make using the phone book quite a task. Again, somewhere there’s an Earth exactly like this one except that all copies of Huckleberry Finn on that Earth end with Huck being elected president. Again, wouldn’t someone point out that he’s only eleven years old? And, as Deutsch points out, there’s an Earth where Huckleberry Finn actually happened, and many other Earths where something very like Huck Finn, but different in slight details, happened, too.
My gut tells me that we’re getting something wrong here. Is there really an Earth where Santa Claus just walked through our glass door and handed me a chocolate pie? And another where it looks like a chocolate pie but is actually, um, something else?
Deutsch makes the point that in some of these universes, unlikely coincidences would lead to rare configurations of matter, and that if the scientists in those universes tried to explain those rare configurations, they would fail. There would be no tendency of nature toward these rare configurations – such configurations make sense only in the context of the multiverse.
I don’t know. This idea that anything that can happen does happen leads to a lot of proposals that I just can’t accept. In some part of the multiverse, did I just now stand up and kick my dog? In another part, did I just now drop everything to go join the circus? (I know that can’t be, because I’m afraid of clowns!)
And in some part of the multiverse, I will live forever. You will, too. I guess that means we didn’t run into any killer clowns.
I’ll talk about this idea of quantum immortality next.
I still remember my Commodore 64. I used BASIC to build a starship Enterprise and create a star field behind it. Then my starship went sailing through the star field, starting at a different height on the screen each time because of a random number generator I’d entered into the code. Later I had the starship randomly visit various randomly generated stars, discovering what kind of star it was only after arrival (I guess the viewscreen must have been out). Sometimes the star was actually a BLACK HOLE, which caused the whole program to end with a dark screen. I saved the whole program on my tape drive and then I could reload it any time I wanted. Pretty spiffy.
That’s about as far as my computer education went. So you shouldn’t expect much from me regarding quantum computers.
David Deutsch (who is a renowned pioneer in the field) has an entire chapter in The Fabric of Reality on quantum computers. Colin Bruce talks extensively about them in his book, as well. And the truth is after reading these sections again and again I still have no idea how quantum computers actually work. Right now I’m working my way through a series of six lectures by David Deutsch on quantum computation; they’re intense and mathematical, but I’m not without hope.
Anyway, the actual operation of a quantum computer is not really the point of this blog entry, so I’ll just do some handwaving. The essential idea is this. A classical computer is made of bits which can hold a value of either 0 or 1. To increase the power of the computer, you increase the number of bits. A quantum computer doesn’t use bits, but qubits. These can also be 0 or 1, but also can be a superposition of these two values. This essentially gives the quantum computer hugely more computational power, because it can use all these different possible values in its computations.
As Deutsch pointedly says, the quantum computer is a fundamentally multiversal device, because all these values of the qubit occur there. To work effectively, the qubit must be isolated from the rest of our universe. The result is a multiversal object, existing in a quantum interference superposition, calculating away in a huge number of histories, until the interference is canceled and the qubit recombines in a single history (our history), its calculation complete (this is the handwaving part, as I’m not at all clear how this actually happens).
One particular calculation that Deutsch discusses is the factorization of 250-digit numbers using something called “Shor’s Algorithm.” Shor’s algorithm can factor numbers using quantum processes in a matter of minutes that would take millions of conventional computers millions of years to factor. The quantum computer would need to complete only a few thousand calculations in each history, but it performs these calculations not in one or even a few histories, but in the staggering number of 10^500 histories!
As Deutsch says, “Where was the number factorized? There are about 10^80 atoms in the entire visible universe, an utterly miniscule number compared with 10^500. So if the visible universe were the extent of physical reality, physical reality would not even remotely contain the resources required to factorize such a large number. Who did factorize it, then? How, and where, was the computation performed?” (Fabric of Reality, page 178).
Of course, quantum computers do not yet exist in anything like the form needed to factor these large numbers. But when they do, Deutsch’s challenge will still be there. If not via many worlds, then how do quantum computers work?
The point I’d like to make about quantum computers, though, is this. Many worlds is still seen by many physicists as mathematically useful fiction, or worse. The same used to be true of the heliocentric theory, field theory, atomic theory, quark theory, and many others. Each time the theory was taken seriously, instead as just a fiction, tremendous progress resulted. David Deutsch isn’t the only physicist who has done important work on quantum computing, of course, and not all those physicists themselves accept many worlds. And yet . . .
Deutsch makes the point in Beginning of Infinity that the “shut up and calculate” school of quantum mechanics and the Copenhagen Interpretation that spawned it are particularly bad philosophies not because they’re wrong, but because they make criticism taboo. The tradition of criticism that led inexorably toward better explanations, including heliocentric theory, electromagnetic field theory, atomic theory, and so on also led to the technologies that we’ve used to transform the world.
Might the final rejection of “shut up and calculate” and the restoration of a tradition of criticism lead to a similar explosion of new knowledge? Could quantum computers be just the beginning of the advances we might make if we take many worlds seriously? Could many worlds, like all those “mathematical fictions” that came before it, be the better explanation that leads to our next great transformation?
Now I’ll take a look at some of the weirder possible consequences of many worlds.
In their recent book The Grand Design, Stephen Hawking and Leonard Mlodinow describe a way of looking at the world called “model-dependent realism.” The idea is that one model of the world is as good as another if it describes the results of experiments just as well as that other model. We use whatever model is most useful. From the book:
“According to model-dependent realism, it is pointless to ask whether a model is real, only whether it agrees with observation. If there are two models that both agree with observation … then one cannot say that one is more real than another. One can use whichever model is more convenient in the situation under consideration.”
Colin Bruce says something similar in Schrodinger’s Rabbits. Bruce describes a game played by advanced aliens (“gods” in his wording) that turns out to have three equivalent descriptions. The simplest, at least for the way our brains work, is tic-tac-toe. Bruce argues that many worlds is like the tic-tac-toe version of the aliens’ game. It is the simplest description for our human minds. Whether many worlds is true is irrelevant.
David Deutsch will have none of this. For Deutsch, many worlds is reality, because many worlds appears in our best explanations. Here’s how Deutsch describes “realism”:
“The commonsense, and true, doctrine that the physical world really exists, and is accessible to rational inquiry.” (BoI, page 23)
However, Deutsch also emphasizes that our knowledge is fallible, and will always be imperfect (infinitely imperfect, in fact). We are always at the beginning of infinity. For Deutsch, many worlds (the multiverse in his words) is real because it is the consequence of our best explanation of single-particle interference. “We should conclude,” Deutsch writes, “that a particular thing is real if and only if it figures in our best explanations of something.” (BoI, page 30)
But is that “really” real? What happens when a better explanation comes around (as it must, if we’re at the beginning of infinity)? Here’s what Deutsch says:
“Sweeping away the entities through which a theory makes its explanation is not the same as sweeping away the whole of the explanation. Although there is no force of gravity, it is true that something real (the curvature of spacetime), caused by the sun, has a strength that varies approximately according to Newton’s inverse-square law, and affects the motion of objects, seen and unseen.” (BoI, page 108)
So what of many worlds. Are they really there? Something real causes single-particle interference. That something behaves an awful lot like photons.Could that something have some other explanation? Of course it could. Many worlds could be the wrong explanation. Our knowledge is always fallible. And whether it is right or wrong will have real consequences for what is to come. But Deutsch has something to say about that, as well. It isn’t so much what we know, it’s how we use what we know.
“The ability to create and use explanatory knowledge gives people a power to transform nature which is ultimately not limited by parochial factors, as all other adaptations are, but only by universal laws. This is the cosmic significance of explanatory knowledge – and hence of people . . .” (BoI, page 60)
This passage affected me more than almost any other in the book, because it helped me see that knowledge (what one might see as pure science) and transformation (what one might see as technology) are intimately linked. There is no separating them. The path to knowledge and the path to transformation are one and the same – the only way to improve our explanations is to use them to transform (and through that transformation learn yet more about) the world.
And that leads me directly into one of the most exciting ideas of many worlds – the quantum computer. Next time.
Quantum mechanics, though weird, is fantastically accurate. The accuracy, though, is of a strange kind. Instead of giving values, quantum mechanics gives probabilities of finding values. This creates a unique problem for Many Worlds.
The situation is simple when the probabilities are 50/50. Either a photon passes through a half-silvered mirror, or else it bounces off. Simple, in one possible world possibility A occurs, in the other it’s B. No problem.
But what if most of the silver is scraped off the mirror, so that the probability of transmission is 90%. Does that mean that, instead of dividing into two worlds, the division is into ten, with 9 photons passing through and only 1 being reflected back? What if the probability is 88.6273%? You see the problem. How can many worlds reproduce the fantastic accuracy of quantum mechanics if its main tool is the splitting of worlds? Are we to believe that every pane of glass splits the world not just in two, but into an essentially infinite set of universes?
Yes, says David Deutsch. In Schrodinger’s Rabbits, Colin Bruce discusses the measure problem and describes Deutsch’s approach, constructed along with another Oxford researcher named David Wallace. Deutsch and Wallace have created the mathematical foundations for many worlds-style probability, and have derived the basic probability that emerges from traditional quantum mechanics from their new approach. It’s a stunning achievement, one mentioned by Brian Greene in The Hidden Reality, as well.
Though there are certainly still skeptics, it certainly appears that convincing progress has been made on the measure problem in many worlds. The cost, however, is high. Rather than an ordinary universe that might occasionally split into two when a quantum “decision” is made, we now see that many worlds describes a universe that is constantly dividing, not just into two alternate worlds, but into essentially infinite worlds. Many worlds is not just a necessary add-on; it is, in fact, the fabric from which reality is stitched. And this changes everything, as we will see.
Compared to entanglement, the double slit experiment is nothing for paradoxical behavior. Einstein (with two collaborators named Rosen and Podolsky) pointed out the strangeness created by entanglement in their famous EPR paper of 1935. John Bell revealed in 1964 that what had looked like an insoluble philosophical dilemma in fact made measurable predictions that could be tested by experiment. And several experimenters in the 1970s and 1980s actually did the test.
Here’s the basic idea. Create two particles that, due to the nature of their creation, have correlated properties. For instance, perhaps two electrons have exactly opposite spins, or two photons have exactly opposite polarization. Call the particles A and B. Let them jet away from one another toward laboratories X and Y. After some time, do an experiment in laboratory X to determine the property of particle A. This action determines the properties not just of particle A, but of particle B, as well. In other words, you’ve determined the properties of particle B without ever measuring it.
This is not a paradox at all if you assume that the particles had their particular properties from the beginning. It is no more surprising than discovering a brown and black sock in your suitcase and realizing that you must have another brown and black pair back at home. However, traditional quantum theory says this is the wrong view. Traditional quantum mechanics says that until you measure particle A, it does not have specific properties (spin up, say, or clockwise polarization). According to quantum mechanics, the act of measuring the particle determines its properties.
Hence the paradox. How could measuring particle A in laboratory X instantly affect particle B in laboratory Y, in principle miles or even light-years away? This is called entanglement by most physicists, but Einstein called it “spooky action at a distance” and could not accept that the universe worked this way. Despite the clear mathematics of quantum theory, Einstein believed there must be “hidden variables” that instructed the particles how to behave even before they were measured.
Unfortunately, there seemed to be no way of choosing between the quantum view and Einstein’s hidden variable view. So it might have remained, but for a brilliant insight by Irish physicist John Bell. Bell showed that, far from being purely a philosophical problem, the question was amenable to experiment. Bell’s achievement was realizing that if a pair of particles had not just one or two but at least three entangled properties, Einstein’s hidden variables and traditional quantum mechanics made radically different predictions for their behaviors. And conflicting predictions about experiment are the bread and meat of physics.
For a beautiful account of Bell’s Theorem, read the section on it in Brian Greene’s Fabric of the Cosmos. While most authors just hand-wave Bell’s theorem away (as I’ve just done), Greene creates a stunningly clear description of it, one that I won’t even attempt to mimic here. Trust me; read the book (in particular, the section called “The Red and the Blue” beginning on page 84, but really getting into the heart of the matter on page 105 with the section called “Reality Testing.”)
Careful measurements show that Einstein was wrong. Local hidden variables are ruled out by experiment. Although non-local solutions are still possible, they are themselves as weird and convoluted as the traditional quantum explanation that says properties don’t exist until they’re measured. And so things stand, until we consider many worlds.
The crux of the entanglement conundrum is that somehow particles “know” about each others’ behavior instantly, even over vast distances. When the particles “decide” what property to display, they decide together, in perfect lockstep, despite the distance separating them.
In Many Worlds, the particles don’t decide. Rather, the particles choose every possible property, in direct proportion to the probabilities predicted by quantum mechanics. It is only when we experimenters compare the results of measurement in one particular history that we notice something remarkable.
Consider our original particle A. As it flies away from its origin, it spreads into David Deutsch’s multiverse. Our particle A becomes a multiversal object, existing along with innumerable shadow particles. Then, when A reaches laboratory X and is measured, the measurement entangles particular instances of A with particular histories. And in one of those particular histories, a version of you the experimenter observes A to have a particular (apparently randomly determined) property.
So far so good. But what happens next? Suppose you call your colleague in laboratory Y. Here’s where things get weird, because you discover that particle B, which was just measured there, showed a perfect correlation with particle A. The properties match up perfectly. From Bell’s theorem you know there are no local hidden variables, so how did the correlation happen?
The answer seems to be that your phone call (or telegraph, or smoke signal, or whatever system you used to communicate to laboratory Y) caused your part of the universe (laboratory X) and your colleague’s part of the universe (laboratory Y) to become entangled together. But (and here’s the weird part) the entanglement happened in just the right way to preserve the weird connection between particle A and particle B. In essence, you couldn’t reach a laboratory Y with the “wrong” answer – that version of the laboratory, while real in some other history, was unavailable to you.
OK, that probably doesn’t feel any better to you than traditional quantum mechanics. How do histories match up like that? I was bothered by the same question, and to some extent I still am. But David Deutsch himself actually answered my question about this issue:
me: How are particles supposed to know which universe they’re allowed to be in?
David Deutsch: The same way they know what sort of particle they are, what their energy is, what their half-life is, what other particles they should decay into, and with what probabilities, where they are in space, how fast they are moving, and all their other attributes.
OK, that’s sort of like saying, “hell if I know, but that’s hardly the biggest mystery here.” But still, it was kind of thrilling for me to get an answer from the man himself, and it does put the question into perspective. Particles seem to “know” an awful lot of stuff, so why not this one more piece of information, which really could just be some kind of key code saying, “you are in my version of the universe, but you are not.”
Looked at in this way, entanglement becomes no more mysterious than the bank’s understandable (though unfortunate) practice of placing Fabio’s paycheck in his account instead of mine.
In the same way that inserting Fabio’s paycheck into my bank account would cause some sort of cosmic rift, notice that entanglement always occurs in such a way as to preserve the conservation laws – momentum, angular momentum, and so on. So whatever “code” is attached to particular instances, it must contain quite a lot of information. How is that information stored? How is it communicated to the rest of the universe? How is it that such a wild mixture of possibilities always results in the sensible, rule-following universe we observe?
Tough questions, and I’m far from satisfied. But that’s what makes this so much fun!
Criticisms I’ve read of many worlds focus on its baroque violation of Occam’s razor. Creating an essentially infinite number of other worlds to explain a few small effects in this one does seem over the top. But when you actually read about many worlds, you discover that the motivation is exactly the opposite.
Schrodinger’s equation describes the world with beautiful and amazing accuracy. If the equation says that some event A will occur 98.6% of the time, you can bet that when you set up the experiment 1 million times, 986 thousand of the trials will give you A. But what happens to the other 1.4%?
As David Deutsch points out in Chapter 12 of Beginning of Infinity, quantum physicists adopted a rule of thumb:
“Whenever a measurement is made, all the histories but one cease to exist. The surviving one is chosen at random, with the probability of each possible outcome being equal to the total measure of all the histories in which that outcome occurs.” The Beginning of Infinity, page 273
You might recognize this as the famous “collapse of the wave function” of the traditional Copenhagen interpretation.
And as Brian Greene points out in both Fabric of the Cosmos and The Hidden Reality, there is no mathematical justification for this rule of thumb.
“The collapse does not emerge from the mathematics of quantum theory: it has to be put in by hand, and there is no agreed-upon or experimentally justified way to do this.” – Fabric of the Cosmos, page 116
Many worlds, by contrast, simply accepts the mathematics as it is. The wave function does not collapse. Instead, we become part of the wave function, part of the probability it describes. We measure event A 98.6 % of the time because 98.6% of the time we find ourselves in an instance of the universe in which A occurs. The other 1.4% still exist, but we are forever separated from that outcome.
Deutsch again in Chapter 12 (page 274)
“(Q)uantum theory (was) clearly describing some sort of physical process that brought about the outcomes of experiments. Physicists, both through professionalism and natural curiosity, could hardly help wondering about that process. But many of them tried not to. Most of them went on to train their students not to. This counteracted the scientific tradition of criticism in regard to quantum theory.” (italics in original)
and on page 276
“And in Dublin in 1952 Schrodinger gave a lecture in which at one point he jocularly warned his audience that what he was about to say might ‘seem lunatic’. It was that, when his equation seems to be describing several different histories, they are ‘not alternatives but all really happen simultaneously’ . . . Here is an eminent physicist joking that he might be considered mad. Why? For claiming that his own equation – the very one for which he had won the Nobel prize – might be true.”
My point here is not to prove that many worlds is correct. Instead, I want to point out that in some sense many worlds is the most straightforward and least strange interpretation of the most successful theory in the history of science. To me, this revelation came as quite a shock.
It seems that many good explanations began as mathematical constructs that no one really took seriously. Copernicus’ sun-centered system, atoms, Faraday and Maxwell’s fields, the neutrino, and most recently quarks. Later, all turned out to be real, and many became crucial to technologies and discoveries that made us masters of the world. Could many worlds be of the same character? Could it move from useful fiction to a fundamental reality? And could that change again alter the world?