Discernamant

REDEFINE the concept of free will? Only a Nobel laureate would have
the nerve. Last year, the Dutch physicist Gerard 't Hooft announced
that the weird effects that spring from quantum mechanics arise from a
deeper deterministic reality based on classical physics. People
objected that his theory appeared to rob us of free will, and now 't
Hooft has responded by moving the goalposts. No, we don't have free
will as it is commonly understood, he says - but that's because the
way it is commonly understood is wrong.

't Hooft, of the University of Utrecht in the Netherlands, shared a
Nobel prize in 1999 for laying the mathematical foundations for the
standard model of particle physics. Like Einstein, he was troubled by
the indeterminism at the heart of quantum mechanics, according to
which particles do not have clearly defined properties before you
measure them, and you can never predict with certainty what the
outcome of your measurements will be. So 't Hooft constructed a
deterministic alternative which showed that fundamental states which
exist on the smallest scales do start out with clearly defined
properties. Information about these states gets blurred over time,
until we are no longer able to tell how they initially arose - leading
to their apparently probabilistic quantum nature, he says.

However, mathematicians John Conway and Simon Kochen at Princeton
University showed that if 't Hooft's theory is true, then people's
ability to make instantaneous, unpredictable choices on a whim is
similarly constrained - we don't have free will (New Scientist, 4 May
2006, p 8).

The revelation has been a stumbling block for his theory, 't Hooft
admits. "It's not the mathematics that loses other physicists," he
says. "It's this metaphysical worry about free will. Why worry at all
about a notion so flimsy as 'free will' in a theory of physics?"

Imagine you are holding a cup of coffee. "I can't change my mind in an
instant about whether to drink the coffee or hurl it across the room.
My decision must have roots in brain processes that occurred in the
past," he says. "What's important is that I have freedom to calculate
what happens if I throw my coffee cup. Equally, I have the freedom to
calculate the effects after I drink from my cup." What we lack is the
freedom to instantaneously switch between which of these initial
states we start from. 't Hooft calls his new formulation the
"unconstrained initial conditions postulate".

Hans Halvorson, a philosopher of physics also at Princeton University,
agrees that our ideas of free will need to be revised. "It's likely
that our naive gut reaction about what free will is may need to be
radically rewritten in just such a way, if we really want to consider
what's happening at the deepest levels," he says.

Conway and Kochen say a deterministic theory denies us the freedom to
choose what to measure about a particle's characteristics. The only
way 't Hooft's theory matches experimental results, they say, is if
nature is conspiring to prevent physicists measuring certain
characteristics of a quantum particle by changing its properties at
the same moment that they decide what to measure.

't Hooft sees nothing mysterious about this. Any decision about what
to measure must have been influenced by environmental factors in your
recent past, and it will take time to enact your choice as you modify
your measuring apparatus. It's safe to assume that in this time, the
particle you plan to measure will also be influenced by these
environmental factors - a disruption that accounts for nature's
ability to tweak what you are able to measure, he says.

However, Antoine Suarez, a physicist at the Center for Quantum
Philosophy in Zurich, Switzerland, remains troubled. "If 't Hooft is
really correct, then the work for which he is famed was not carried
out as a result of his free will. Rather, he was destined to do it
from the beginning of time," he says. "In that case, maybe his Nobel
prize should rightfully have been presented to the big bang instead."

Suarez has performed an experiment that he claims proves 't Hooft
wrong. 't Hooft's deterministic theory and his redefinition of free
will rely on fundamental states obeying causal laws, so that a chain
of events can be calculated precisely, given the starting conditions.
By bringing the effects of special relativity into play in a standard
entanglement experiment, Suarez and his colleagues were able to check
how time flow interacts with the quantum world (see "Effects without
causes"). "We tested the very concept of time," says Suarez.

The result was a resounding success for quantum mechanics, says
Suarez. His team showed that the well-behaved time-ordering 't Hooft
needs simply doesn't exist: there is no causality at a deep level.
Suarez is submitting his paper to Foundations of Physics, a journal
that is edited by 't Hooft. "I think it will spark an interesting
debate," Suarez says.

't Hooft is ready to meet that challenge. Although his theory cannot
yet explain the results, he is confident that it will eventually do
so. "After all, we know that quantum mechanics produces eccentric
results," he says. "That's exactly why I am looking for an
alternative."

Effects without causes

To test 't Hooft's deterministic theory, Antoine Suarez at the Center
for Quantum Philosophy in Zurich, Switzerland, and his colleagues
performed an entanglement experiment with a relativistic twist.

Entangled particles are inextricably intertwined, so that making a
measurement on one instantaneously affects its partner. In standard
experiments, two entangled photons, A and B, follow different paths
until they come to a beam splitter, which allows the photon to follow
either a longer path or a shorter one to continue its journey (see
Diagram). In every case, A and B make the same choice, proving they
are entangled.

A deterministic theory can explain the result if A hitting the beam
splitter somehow affects the environment of B, encouraging B to take
the corresponding path - a straightforward causal link. To test this,
the team exploited an effect of special relativity, which causes two
events to appear to occur in a different order to different observers
if those observers are moving relative to one another.

Suarez's set-up uses a pair of beam splitters that are moving apart.
An observer sitting at the first beam splitter, BS1, would observe
photon A hitting BS1 - and making its path choice - before photon B
hit BS2. An observer sitting at BS2, would see the reverse - that
photon B made its choice before A (www.arxiv.org/abs/0705.3974).

If a deterministic theory such as 't Hooft's is correct, any
entanglement should disappear. This is because it is not possible for
either photon to "tip off" its partner about its choice before its
partner chooses its own path, since both photons are making their
choices both before and after their partner, depending on which beam
splitter you observe from. Yet the team continued to observe
entanglement. "Quantum mechanics beat both time and 't Hooft," says
Suarez.



"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.
"Abandoning the uncertainty of quantum physics means we must give up
the cherished notion that we have free will"

"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.
"Our lives would be like the second showing of a movie, playing out as
though we are free, but freedom is an illusion"

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."

.

Relevant Pages

  • Re: Discernamant
    ... deeper deterministic reality based on classical physics. ... Hooft has responded by moving the goalposts. ... standard model of particle physics. ... the indeterminism at the heart of quantum mechanics, ...
    (soc.culture.romanian)
  • Baba cu colacii...
    ... in quantum mechanics, we have no choice," if two new studies are ... beyond physics: abandoning the uncertainty of quantum physics means we ... Gerard 't Hooft of Utrecht University in the Netherlands, ... for the standard model of particle physics. ...
    (soc.culture.romanian)
  • Maybe my last post to sci.physics 8^(
    ... (The Feynman Lectures on Physics, ... "First, he assumed that there is always associated with a particle of mass m a periodic internal phenomenon of frequency ƒ. ... he equated the rest mass energy mc² to the energy of the quantum of the electromagnetic field hƒ. ... Starting with this we get the quantum mechanics of a single particle, ...
    (sci.physics)
  • What is a particle?
    ... physics. ... a particle is something that carries linear momentum and ... no meaning classically. ... was restricted to quantum mechanics, but it appears to be much more ...
    (sci.physics)
  • A theoretical physics FAQ
    ... (This lack of growth is due to the fact that I currently have almost no free time for discussing physics. ... Postulates for the formal core of quantum mechanics ... Why does QFT look so different from QM? ... Is quantum mechanics compatible with general relativity? ...
    (sci.physics.research)
Loading