RE: Many Worlds

From: Jerry Mitchell (
Date: Tue Jul 24 2001 - 23:03:35 MDT

Without getting into that argument about exact definitions... Id say this
blows the hell out of Moore's law if its true ;)

> -----Original Message-----
> From:
> []On Behalf Of J. R. Molloy
> Sent: Tuesday, July 24, 2001 8:03 PM
> To:
> Subject: Many Worlds
> Taming the multiverse
> Parallel universes are no longer a figment of our
> imagination. They're so
> real that we can reach out and touch them, and even use them
> to change our
> world, says Marcus Chown
> Flicking through New Scientist, you stop at this page, think "that's
> interesting" and read these words. Another you thinks "what
> nonsense", and
> moves on. Yet another lets out a cry, keels over and dies.
> Is this an insane vision? Not according to David Deutsch of
> the University
> of Oxford. Deutsch believes that our Universe is part of the
> multiverse, a
> domain of parallel universes that comprises ultimate reality.
> Until now, the multiverse was a hazy, ill-defined
> concept-little more than a
> philosophical trick. But in a paper yet to be published,
> Deutsch has worked
> out the structure of the multiverse. With it, he claims, he
> has answered the
> last criticism of the sceptics. "For 70 years physicists have
> been hiding
> from it, but they can hide no longer." If he's right, the
> multiverse is no
> trick. It is real. So real that we can mould the fate of the
> universes and
> exploit them.
> Why believe in something so extraordinary? Because it can
> explain one of the
> greatest mysteries of modern science: why the world of atoms
> behaves so very
> differently from the everyday world of trees and tables.
> The theory that describes atoms and their constituents is
> quantum mechanics.
> It is hugely successful. It has led to computers, lasers and nuclear
> reactors, and it tells us why the Sun shines and why the
> ground beneath our
> feet is solid. But quantum theory also tells us something
> very disturbing
> about atoms and their like: they can be in many places at
> once. This isn't
> just a crazy theory-it has observable consequences (see
> "Interfering with
> the multiverse").
> But how is it that atoms can be in many places at once
> whereas big things
> made out of atoms-tables, trees and pencils-apparently
> cannot? Reconciling
> the difference between the microscopic and the macroscopic is
> the central
> problem in quantum theory.
> The many worlds interpretation is one way to do it. This idea
> was proposed
> by Princeton graduate student Hugh Everett III in 1957.
> According to many
> worlds, quantum theory doesn't just apply to atoms, says
> Deutsch. "The world
> of tables is exactly the same as the world of atoms."
> But surely this means tables can be in many places at once. Right. But
> nobody has ever seen such a schizophrenic table. So what gives?
> The idea is that if you observe a table that is in two places
> at once, there
> are also two versions of you-one that sees the table in one
> place and one
> that sees it in another place.
> The consequences are remarkable. A universe must exist for
> every physical
> possibility. There are Earths where the Nazis prevailed in
> the Second World
> War, where Marilyn Monroe married Einstein, and where the
> dinosaurs survived
> and evolved into intelligent beings who read New Scientist.
> However, many worlds is not the only interpretation of quantum theory.
> Physicists can choose between half a dozen interpretations,
> all of which
> predict identical outcomes for all conceivable experiments.
> Deutsch dismisses them all. "Some are gibberish, like the Copenhagen
> interpretation," he says-and the rest are just variations on
> the many worlds
> theme.
> For example, according to the Copenhagen interpretation, the act of
> observing is crucial. Observation forces an atom to make up
> its mind, and
> plump for being in only one place out of all the possible
> places it could
> be. But the Copenhagen interpretation is itself open to
> interpretation. What
> constitutes an observation? For some people, this only requires a
> large-scale object such as a particle detector. For others it means an
> interaction with some kind of conscious being.
> Worse still, says Deutsch, is that in this type of
> interpretation you have
> to abandon the idea of reality. Before observation, the atom
> doesn't have a
> real position. To Deutsch, the whole thing is
> mysticism-throwing up our
> hands and saying there are some things we are not allowed to ask.
> Some interpretations do try to give the microscopic world
> reality, but they
> are all disguised versions of the many worlds idea, says
> Deutsch. "Their
> proponents have fallen over backwards to talk about the many
> worlds in a way
> that makes it appear as if they are not."
> In this category, Deutsch includes David Bohm's "pilot-wave"
> interpretation.
> Bohm's idea is that a quantum wave guides particles along their
> trajectories. Then the strange shape of the pilot wave can be used to
> explain all the odd quantum behaviours, such as interference
> patterns. In
> effect, says Deutsch, Bohm's single universe occupies one groove in an
> immensely complicated multi-dimensional wave function.
> "The question that pilot-wave theorists must address is: what are the
> unoccupied grooves?" says Deutsch. "It is no good saying they
> are merely
> theoretical and do not exist physically, for they continually
> jostle each
> other and the occupied groove, affecting its trajectory.
> What's really being
> talked about here is parallel universes. Pilot-wave theories are
> parallel-universe theories in a state of chronic denial."
> Back and forth
> Another disguised many worlds theory, says Deutsch, is John Cramer's
> "transactional" interpretation in which information passes
> backwards and
> forwards through time. When you measure the position of an
> atom, it sends a
> message back to its earlier self to change its trajectory accordingly.
> But as the system gets more complicated, the number of
> messages explodes.
> Soon, says Deutsch, it becomes vastly greater than the number
> of particles
> in the Universe. The full quantum evolution of a system as big as the
> Universe consists of an exponentially large number of
> classical processes,
> each of which contains the information to describe a whole
> universe. So
> Cramer's idea forces the multiverse on you, says Deutsch.
> So do other interpretations, according to Deutsch. "Quantum
> theory leaves no
> doubt that other universes exist in exactly the same sense
> that the single
> Universe that we see exists," he says. "This is not a matter of
> interpretation. It is a logical consequence of quantum theory."
> Yet many physicists still refuse to accept the multiverse.
> "People say the
> many worlds is simply too crazy, too wasteful, too mind-blowing," says
> Deutsch. "But this is an emotional not a scientific reaction.
> We have to
> take what nature gives us."
> A much more legitimate objection is that many worlds is vague
> and has no
> firm mathematical basis. Proponents talk of a multiverse that
> is like a
> stack of parallel universes. The critics point out that it
> cannot be that
> simple-quantum phenomena occur precisely because the
> universes interact.
> "What is needed is a precise mathematical model of the
> multiverse," says
> Deutsch. And now he's made one.
> The key to Deutsch's model sounds peculiar. He treats the
> multiverse as if
> it were a quantum computer. Quantum computers exploit the
> strangeness of
> quantum systems-their ability to be in many states at once-to
> do certain
> kinds of calculation at ludicrously high speed. For example,
> they could
> quickly search huge databases that would take an ordinary computer the
> lifetime of the Universe. Although the hardware is still at a
> very basic
> stage, the theory of how quantum computers process information is well
> advanced.
> In 1985, Deutsch proved that such a machine can simulate any
> conceivable
> quantum system, and that includes the Universe itself. So to
> work out the
> basic structure of the multiverse, all you need to do is
> analyse a general
> quantum calculation. "The set of all programs that can be run
> on a quantum
> computer includes programs that would simulate the multiverse," says
> Deutsch. "So we don't have to include any details of stars
> and galaxies in
> the real Universe, we can just analyse quantum computers and
> look at how
> information flows inside them."
> If information could flow freely from one part of the
> multiverse to another,
> we'd live in a chaotic world where all possibilities would overlap. We
> really would see two tables at once, and worse, everything
> imaginable would
> be happening everywhere at the same time.
> Deutsch found that, almost all the time, information flows
> only within small
> pieces of the quantum calculation, and not in between those
> pieces. These
> pieces, he says, are separate universes. They feel separate
> and autonomous
> because all the information we receive through our senses has
> come from
> within one universe. As Oxford philosopher Michael Lockwood
> put it, "We
> cannot look sideways, through the multiverse, any more than
> we can look into
> the future."
> Sometimes universes in Deutsch's model peel apart only locally and
> fleetingly, and then slap back together again. This is the
> cause of quantum
> interference, which is at the root of everything from the two-slit
> experiment to the basic structure of atoms.
> Other physicists are still digesting what Deutsch has to say. Anton
> Zeilinger of the University of Vienna remains unconvinced.
> "The multiverse
> interpretation is not the only possible one, and it is not even the
> simplest," he says. Zeilinger instead uses information theory
> to come to
> very different conclusions. He thinks that quantum theory
> comes from limits
> on the information we get out of measurements (New Scientist,
> 17 February, p
> 26). As in the Copenhagen interpretation, there is no reality
> to what goes
> on before the measurement.
> But Deutsch insists that his picture is more profound than
> Zeilinger's. "I
> hope he'll come round, and realise that the many worlds
> theory explains
> where the information in his measurements comes from."
> Why are physicists reluctant to accept many worlds? Deutsch
> blames logical
> positivism, the idea that science should concern itself only
> with objects
> that can be observed. In the early 20th century, some logical
> positivists
> even denied the existence of atoms-until the evidence became
> overwhelming.
> The evidence for the multiverse, according to Deutsch, is equally
> overwhelming. "Admittedly, it's indirect," he says. "But
> then, we can detect
> pterodactyls and quarks only indirectly too. The evidence that other
> universes exist is at least as strong as the evidence for
> pterodactyls or
> quarks."
> Perhaps the sceptics will be convinced by a practical
> demonstration of the
> multiverse. And Deutsch thinks he knows how. By building a
> quantum computer,
> he says, we can reach out and mould the multiverse.
> "One day, a quantum computer will be built which does more
> simultaneous
> calculations than there are particles in the Universe," says
> Deutsch. "Since
> the Universe as we see it lacks the computational resources to do the
> calculations, where are they being done?" It can only be in
> other universes,
> he says. "Quantum computers share information with huge
> numbers of versions
> of themselves throughout the multiverse."
> Imagine that you have a quantum PC and you set it a problem.
> What happens is
> that a huge number of versions of your PC split off from this
> Universe into
> their own separate, local universes, and work on parallel
> strands of the
> problem. A split second later, the pocket universes recombine
> into one, and
> those strands are pulled together to provide the answer that
> pops up on your
> screen. "Quantum computers are the first machines humans have
> ever built to
> exploit the multiverse directly," says Deutsch.
> At the moment, even the biggest quantum computers can only
> work their magic
> on about 6 bits of information, which in Deutsch's view means
> they exploit
> copies of themselves in 26 universes-that's just 64 of them.
> Because the
> computational feats of such computers are puny, people can
> choose to ignore
> the multiverse. "But something will happen when the number of parallel
> calculations becomes very large," says Deutsch. "If the
> number is 64, people
> can shut their eyes but if it's 1064, they will no longer be able to
> pretend."
> What would it mean for you and me to know there are
> inconceivably many yous
> and mes living out all possible histories? Surely, there is
> no point in
> making any choices for the better if all possible outcomes
> happen? We might
> as well stay in bed or commit suicide.
> Deutsch does not agree. In fact, he thinks it could make real choice
> possible. In classical physics, he says, there is no such
> thing as "if"; the
> future is determined absolutely by the past. So there can be
> no free will.
> In the multiverse, however, there are alternatives; the quantum
> possibilities really happen. Free will might have a sensible
> definition,
> Deutsch thinks, because the alternatives don't have to occur
> within equally
> large slices of the multiverse. "By making good choices,
> doing the right
> thing, we thicken the stack of universes in which versions of us live
> reasonable lives," he says. "When you succeed, all the copies
> of you who
> made the same decision succeed too. What you do for the
> better increases the
> portion of the multiverse where good things happen."
> Let's hope that deciding to read this article was the right choice.
> Interfering with the multiverse
> You can see the shadow of other universes using little more
> than a light
> source and two metal plates. This is the famous double-slit
> experiment, the
> touchstone of quantum weirdness.
> Particles from the atomic realm such as photons, electrons or
> atoms are
> fired at the first plate, which has two vertical slits in it.
> The particles
> that go through hit the second plate on the far side.
> Imagine the places that are hit show up black and that the
> places that are
> not hit show up white. After the experiment has been running
> for a while,
> and many particles have passed through the slits, the plate
> will be covered
> in vertical stripes alternating black and white. That is an
> interference
> pattern.
> To make it, particles that passed through one slit have to
> interfere with
> particles that passed through the other slit. The pattern
> simply does not
> form if you shut one slit.
> The strange thing is that the interference pattern forms even
> if particles
> come one at a time, with long periods in between. So what is
> affecting these
> single particles?
> According to the many worlds interpretation, each particle
> interferes with
> another particle going through the other slit. What other
> particle? "Another
> particle in a neighbouring universe," says David Deutsch. He
> believes this
> is a case where two universes split apart briefly, within the
> experiment,
> then come back together again. "In my opinion, the argument
> for the many
> worlds was won with the double-slit experiment. It reveals
> interference
> between neighbouring universes, the root of all quantum phenomena."
> --<>-- --<<<+>>>-- --<>--
> "May we all live in eternity's sunrise,
> on the seashore of endless worlds."
> --Blake/Tagore

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