- The Harmonic Concordance
- "The chart heard 'round the World"
|
|
|
|||
|
| Annotated
T.O.C. Astrology
Portal Spirituality
Portal Science
Portal The Ascended Relationship The
Chart e-group Feedback Contributors Chat Room Links Experiencing
the Harmonic Concordance with Astrological
Ritual Ceremonial
Gemstones Our
Visitor's Say: Have
you seen the |
Taming the Multiverse
Marcus Chown 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. 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." 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." From
New Scientist 14 July 2001.
|
|
