Baba cu colacii...
- From: "Prof. Dr. Ing. IPS Raspopitul Esq." <raspopitul@xxxxxxxxx>
- Date: 18 Aug 2006 17:57:12 -0700
Argon Gates wrote:
Ai vrea tu. Dar s'a carat baba cu colacii.... discernamantului ;-)
Free will - you only think you have it
* Exclusive from New Scientist
"WE MUST believe in free will, we have no choice," the novelist Isaac
Bashevis Singer once said. He might as well have said, "We must believe
in quantum mechanics, we have no choice," if two new studies are
anything to go by.
Early last month, a Nobel laureate physicist finished polishing up his
theory that a deeper, deterministic reality underlies the apparent
uncertainty of quantum mechanics. A week after he announced it, two
eminent mathematicians showed that the theory has profound implications
beyond physics: abandoning the uncertainty of quantum physics means we
must give up the cherished notion that we have free will. The
mathematicians believe the physicist is wrong.
"It's striking that we have one of the greatest scientists of our
generation pitted against two of the world's greatest mathematicians,"
says Hans Halvorson, a philosopher of physics at Princeton University.
Quantum mechanics is widely accepted by physicists, but is full of
apparent paradoxes, which made Einstein deeply uncomfortable and have
never been resolved. For instance, you cannot ask what the spin of a
particle was before you made an observation of it - quantum mechanics
says the spin was undetermined. And you cannot predict the outcome of
an experiment; you can only estimate the probability of getting a
certain result.
"Quantum mechanics works wonderfully well, but it's not complete," says
Gerard 't Hooft of Utrecht University in the Netherlands, who won the
Nobel prize for physics in 1999 for laying the mathematical foundations
for the standard model of particle physics. One major reason why many
physicists, including 't Hooft, yearn for a deeper view of reality than
quantum mechanics can offer is their failure so far to unite quantum
theory with general relativity and its description of gravity, despite
enormous effort. "A radical change is needed," says 't Hooft.
For more than a decade now, 't Hooft has been working on the idea that
there is a hidden layer of reality at scales smaller than the so-called
Planck length of 10-35 metres. 't Hooft has developed a mathematical
model to support this notion. At this deeper level, he says, we cannot
talk of particles or waves to describe reality, so he defines entities
called "states" that have energy. In his model, these states behave
predictably according to deterministic laws, so it is theoretically
possible to keep tabs on them.
However, the calculations show that individual states can be tracked
for only about 10-43 seconds, after which many states coalesce into one
final state, which is what creates the quantum mechanical uncertainty.
Our measurements illuminate these final states, but because the prior
information is lost, we can't recreate their precise history.
While 't Hooft's initial theory explained most quantum mechanical
oddities, such as the impossibility of precisely measuring both the
location and momentum of a particle, it had a major stumbling block -
the states could end up with negative energy, which is physically
impossible. Now, 't Hooft has worked out a solution that overcomes this
problem, preventing the states from having negative energy
(www.arxiv.org/quant-ph/0604008). "It was an obnoxious difficulty," he
says. "But having solved it I am more and more convinced that this is
the right approach."
Essentially, 't Hooft is saying that while particles in quantum
mechanics seem to behave unpredictably, if we could track the
underlying states, we can predict the behaviour of particles.
Others are impressed. "This is a very beautiful theory that tells us
about the world on the smallest scales," says physicist Willem de
Muynck at Eindhoven University of Technology in the Netherlands. "But
these are scales that current experiments cannot reach, so if anything
the theory is before its time."
As enticing as 't Hooft's theory may be to physicists, it has an
unexpected and potentially frightful consequence for the rest of us.
Mathematicians John Conway and Simon Kochen, both at Princeton
University, say that any deterministic theory underlying quantum
mechanics robs us of our free will.
"When you choose to eat the chocolate cake or the plain one, are you
really free to decide?" asks Conway. In other words, could someone who
has been tracking all the particle interactions in the universe predict
with perfect accuracy the cake you will pick? The answer, it seems,
depends on whether quantum mechanics' inherent uncertainty is the
correct description of reality or 't Hooft is right in saying that
beneath that uncertainty there is a deterministic order.
Conway and Kochen explored the implications of 't Hooft's theory by
looking at what happens when you measure the spin of a particle. Spin
is always measured along three perpendicular axes. For a spherical
particle, the particular axes that you choose and the order in which
you carry out the measurements are up to you. But are your choices a
matter of free will, or are they predetermined?
What the mathematicians proved is this: if you have the slightest
freedom to choose the axes and order of measurement, then particles
everywhere must also have the same degree of freedom. That means they
can behave unpredictably. However, if particles have no freedom, as
implied by 't Hooft's theory, the mathematicians proved that you have
no real say in the choice of axes and order of measurement. In other
words, deterministic particles put an end to free will
(www.arxiv.org/quant-ph/0604079).
Arguments about free will are as old as philosophy itself, and ever
since quantum mechanics was proposed people have attempted to connect
free will to the indeterminacy at the heart of this theory. "We're
proud because this is the first solid proof relating these issues,"
says Conway.
Kochen and Conway stress that their theorem doesn't disprove 't Hooft's
theory. It simply states that if his theory is true, our actions cannot
be free. And they admit that there's no way for us to tell. "Our lives
could be like the second showing of a movie - all actions play out as
though they are free, but that freedom is an illusion," says Kochen.
Since the mathematicians believe that we have free will, it follows for
them that 't Hooft's theory must be wrong. "We have to believe in free
will to do anything," says Conway. "I believe I am free to drink this
cup of coffee, or throw it across the room. I believe I am free in
choosing to have this conversation."
Halvorson says the debate really boils down to a matter of personal
taste. "Kochen and Conway can't tolerate the idea that our future may
already be settled," he says, "but people like 't Hooft and Einstein
find the notion that the universe can't be completely described by
physics just as disturbing."
For philosophers, both arguments can be troubling. "Quantum randomness
as the basis of free will doesn't really give us control over our
actions," says Tim Maudlin, a philosopher of physics at Rutgers
University in New Brunswick, New Jersey. "We're either deterministic
machines, or we're random machines. That's not much of a choice."
Halvorson, however, welcomes the work by 't Hooft, Conway and Kochen.
"Philosophy has separated itself from science for far too long," he
says. "There are very important questions to be asked about free will,
and maybe physics can answer them."
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