Reflectorites
Check out this New Scientist article which pours cold water on the
Anthropic Principle, and the idea that multiple universes would have
different laws of physics, because if string theory is true, they are hardwired
in!
I apologise that I haven't got the time to summarise it.
I like this bit:
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But if Steinhardt wins the bet, the consequences may be uncomfortable.
The theorists hope that string theory will be mathematically inevitable-the
only logically consistent theory of the Universe. But if so, and if string
theory pins down every physical constant, then the fine-tuning for life will
turn out to be hard-wired into mathematics. "In that case, string theory will
be a great argument for design," says Tegmark. He is reminded of Carl
Sagan's novel, Contact, in which mathematicians calculate to billions of
decimal places and suddenly find the digits getting non-random. "It turns
out there is a message written in a fundamental constant of mathematics-a
message from the Creator," says Tegmark. Likewise, if the mathematics
makes life inevitable, people might start using string theory as an argument
for the existence of God. String theorists believe they are following a path
to an ultimate rational theory that is a cut above the anthropic alternative.
They might be upset, to say the least, to find God in their equations.
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Steve
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http://archive.newscientist.com/archive.jsp?id=22424600
New Scientist
Out in the cold 10 Jun 00
The cosmos doesn't need us any more. Marcus Chown finds a growing
chorus of dissent against the anthropic principle
THE UNIVERSE is the way it is because if it weren't we wouldn't be here
to see it. Profound insight or empty truism? This is the "anthropic
principle", and in the past few years it has been embraced by many
cosmologists to explain some of the most mystifying features of the
Universe. But it leaves other scientists feeling deeply troubled.
One of them is cosmologist Paul Steinhardt of Princeton University in New
Jersey, who claims that the anthropic principle is sloppy and unscientific.
"It's corrupting science," he says. His view is shared by physicist Gordon
Kane of the University of Michigan in Ann Arbor, who believes that string
theory will make the anthropic principle redundant. The pro- and anti-
anthropic camps are debating just about the most profound question there
is: why are we here? But the final answer might not please either side.
What makes the debate more difficult is that a precise definition of the
anthropic principle is hard to come by. Roughly speaking, it asserts that our
existence restricts the possible values of any physical constants, because
simply to be observed, the Universe must allow life to exist. If we assume
that life anywhere in the Universe must be broadly like that on Earth, for
example, the Universe must allow stars to form. And the Universe must be
old enough for those stars to have created plenty of heavy elements-the
building blocks of biological molecules-in order to allow life to evolve.
Arguably, British astronomer Fred Hoyle was the first to evoke the
anthropic principle. In 1952, he used the fact that carbon exists to predict
that carbon-12 had an "excited" energy state unknown at the time. If the
state did not exist, Hoyle reasoned, nuclear reactions inside stars could not
assemble carbon and all heavier elements from lighter nuclei, and so
carbon-based life such as ours would not exist.
The principle has gained popularity because of the apparent fine-tuning of
physics. For example, if the strong nuclear force were just a few per cent
stronger, the Sun would burn all its hydrogen fuel in less than a second-not
long for intelligent life to evolve. "Many instances have been found in
which if a certain fundamental force were slightly weaker or stronger, or if
a certain fundamental particle were slightly lighter or heavier, there would
be no galaxies or stars or planets, and hence no human beings," says Max
Tegmark of the University of Pennsylvania. Martin Rees of the University
of Cambridge agrees: "I think the fine-tuning `coincidences' need some
kind of explanation."
"Either God fine-tuned the Universe for us to be here," says Tegmark, "or
there are many universes, each with different values of the fundamental
constants, and not surprisingly we find ourselves in one in which the
constants have the right values to permit galaxies, stars and life."
Some have dubbed this the "multiverse". Inflation, one theory that aims to
describe the first split second of existence after the big bang, hints that the
observable Universe may simply be one bubble among an infinity of others
in a vast ocean of space. Conceivably, the other universes might be distant
patches of space where the fundamental constants are different.
Tegmark believes that the anthropic principle is becoming more widely
accepted. "Two years ago, at a conference at Fermilab there was an audible
hiss when someone mentioned the A-word," he says. "But a couple of
months ago at another conference in Santa Monica, Steven Weinberg
argued that the anthropic principle may be the best explanation for the
cosmological constant."
The cosmological constant, which is a measure of the curious repulsive
force exerted by empty space, is an embarrassing 10123 times smaller than
that predicted by quantum theory. Weinberg explains this by assuming that
the constant takes on all possible values in all possible universes. Most
universes would accelerate madly (where the constant is large) or make
nothing but black holes (where it is large and negative). Only in a few freak
universes where the constant is tiny would galaxies, stars and planets arise.
So why does Steinhardt so vehemently oppose the anthropic principle? "I
have several reasons," he says. "First, the anthropic principle is not testable,
which means it is not science."
According to Steinhardt, a statement has scientific meaning only if it can be
tested by an experiment or observation. He maintains that there is no such
test for the anthropic principle. "This makes it entirely different from, say,
Newton's general principle that the laws of physics are deterministic," he
says. "This was tested and found to be false in the realm of the atom."
Tegmark, however, argues that the anthropic principle is no more
sophisticated or controversial than the principles of logic that underpin a
statement like 1 + 1 = 2. "If I have two competing theories, the anthropic
principle merely selects the theory which gives the greatest likelihood of
seeing what I see, given that I am here," he says. "The anthropic principle
is no more than an application of probability theory. Unfortunately, the
word `principle' suggests there is something deep about it. In fact, there's
nothing to test."
But Steinhardt has a more telling criticism. One of the characteristics of
science, he says, is that you begin with a little and get out a lot. It's an
efficient way of gaining knowledge. "What does the anthropic argument
get you? I'm not sure there's enough to fill the back of a postage stamp."
Take the cosmological constant. The anthropic principle seems to provide a
rational explanation for why this constant has the value it has-but does that
really tell us anything? Isn't it just a way of feeling comfortable with the
way the Universe is? Contrast this with Newton's law of universal
gravitation. Newton developed his theory to explain the orbits of the
planets in our Solar System, but it has many other observable
consequences-it predicts the existence of lunar tides and the movements of
comets, moons, asteroids and other stars.
So is the anthropic principle a useless but essentially harmless idea?
Steinhardt thinks it's worse than that. He says it "dulls sharp problems with
an air of explanation"- it stops people from struggling to find really
fundamental solutions. He sees its increasing popularity as partly due to
impatience. "People want to know all the answers right now, but we have
to accept that this is not possible," he says. "I'd rather say `I don't know'."
Another serious objection to the anthropic principle is that "there are no
rules of the game", says Steinhardt. He points out that there is no
justification for the belief that physical constants vary from one universe to
another. The problem, he says, is that there is no underlying "metatheory"
which predicts how they vary.
We know that some parameters, such as the distance between the Earth
and the Sun, can vary. Before Newton, there had been high hopes that this
distance would turn out to be a fundamental constant, perhaps fixed by the
geometry of cubes and other solid figures. However, Newtonian dynamics
allowed a whole continuum of Sun-Earth distances. This is a little like the
sort of metatheory that Steinhardt is talking about. For life to exist on
Earth, the Earth must be neither too cold nor too hot-so we shouldn't be
surprised that the Earth-Sun distance is just right for water to flow on the
Earth's surface.
But even this application of the principle is flawed. "Even now we cannot
say how common planets are, or whether planets need to be like ours to
foster life," says Steinhardt. For instance, if silicon-based machines could
evolve, they might find themselves on a planet closer than Mercury is to the
Sun. If it turned out that life could exist in a huge range of physical
environments, we would find ourselves in the special position of being
cool, watery, carbon-based observers. The anthropic principle would lose
its power.
But in the case of the cosmological constant, says Steinhardt, there isn't
even a theory predicting that it can take on a range of values. He maintains
that such a theory, like Newtonian dynamics, would be bound to have other
consequences-perhaps in the microscopic world-which could be measured.
"If there's a breakthrough and the anthropic people can come up with an
abundantly predictive, testable metatheory, I would be happy to accept it."
Rees believes that such a metatheory could come from Andrei Linde's idea
of eternal inflation. In that model, space spontaneously "inflates" to give
birth to new universes, which give birth to yet more universes, and so on,
ad infinitum. "There are two key questions for 21st-century
physics/cosmology," he says. "When we understand the physics of the
inflationary era, will it indeed predict multiple big bangs, as in the
simulations of Linde and his colleagues? And do the underlying physical
laws allow the different big bangs to end up governed by different low-
energy physics?" According to Rees, if the answer to both these questions
is "yes", then anthropic selection would explain the apparent fine-tuning in
our Universe.
Tegmark would like to see this fine-tuning quantified. He believes that
scientists have not performed such calculations because of
"anthropophobia"-the principle makes them uneasy. The build-up of heavy
elements inside stars, for example, depends on the electromagnetic and
strong coupling constants, which determine the strengths of the
electromagnetic and strong nuclear forces. "If someone calculated the
detailed consequences for stars of varying these parameters, we could find
out how small is the island in parameter space we live on," he says. That
would tell us just how finely tuned the Universe is. Rees adds that if we
found ourselves living on a highly improbable part of this island, that would
invalidate the anthropic principle.
Useless speculation
All this may be useless speculation, however, because there are reasons to
believe the constants can't vary. "I would say the examples of fine-tuning
people have found aren't really there," says Steinhardt. He cites Grand
Unified Theories (GUTs), which attempt to unify the three non-
gravitational forces of nature. In GUTs, the strengths of the
electromagnetic and strong nuclear forces are intimately linked. "If you
vary one, the other changes too," says Steinhardt. So the argument that all
the constants must be individually fine-tuned begins to look shaky. Kane
agrees: "It's simply not so that increasing the strong force or decreasing the
electromagnetic force affects how the Sun works," he says. "Most of the
old arguments are just misleading numerology."
Kane believes that string theory provides even more powerful arguments
against fine-tuning. In string theory, the fundamental entities of reality are
tiny strings vibrating in 9-dimensional space, and all the constants of nature
depend on a single fundamental parameter. "So if the theory is right there
will be no room to vary any of the constants the anthropic people like to
vary," says Kane. He and his colleagues, Malcolm Perry and Anna Zytkow
of the University of Cambridge, have just written a paper outlining this
argument, titled "The beginning of the end of the anthropic principle".
But string theory does allow the vacuum to adopt a range of different
states in different universes, which should, for example, have different
cosmological constants. "In a sense, the ensemble of universes is replaced
by something with a better theoretical basis, the many vacua of string
theory," admits Kane. "Different vacua will lead to different universes, and
only some will be right for life to emerge."
So have string theorists, in rejecting the anthropic principle for a final
theory, let it in by the back door? Is string theory the metatheory that
Steinhardt is looking for? "Sure, superstring may some day prove to be a
metatheory with lots of predictive power," says Steinhardt. "But I don't
think Newton's theory or string theory include the anthropic principle-I
think they replace it."
Kane is also dubious. "Until the vacuum structure of string theory is
understood better, it looks a lot like the multiple universes, but not the
same," he says. That's because the various regions might be causally
connected, affecting each other's states.
For his part, Tegmark is sceptical of string theory. "It is emerging as the
modern version of the emperor with no clothes," he says. "So far, it has
predicted the value of none of the physical constants, and I'm willing to bet
that numbers like the electromagnetic coupling constant will never be
derivable from pure math." "Is he serious?" responds Steinhardt. "Where
can we line up to take that bet?"
But if Steinhardt wins the bet, the consequences may be uncomfortable.
The theorists hope that string theory will be mathematically inevitable-the
only logically consistent theory of the Universe. But if so, and if string
theory pins down every physical constant, then the fine-tuning for life will
turn out to be hard-wired into mathematics. "In that case, string theory will
be a great argument for design," says Tegmark. He is reminded of Carl
Sagan's novel, Contact, in which mathematicians calculate to billions of
decimal places and suddenly find the digits getting non-random. "It turns
out there is a message written in a fundamental constant of mathematics-a
message from the Creator," says Tegmark. Likewise, if the mathematics
makes life inevitable, people might start using string theory as an argument
for the existence of God.
String theorists believe they are following a path to an ultimate rational
theory that is a cut above the anthropic alternative. They might be upset, to
say the least, to find God in their equations.
Further reading:
: Just Six Numbers by Martin Rees (Weidenfeld & Nicolson, 1999)
The Anthropic Cosmological Principle by John Barrow and Frank Tipler
(Oxford University Press, 1988)
Marcus Chown
From New Scientist magazine, vol 166 issue 2242, 10/06/2000, page 32
(c) Copyright New Scientist, RBI Ltd 2000
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"I have quoted some voices of dissent coming from biologists in eminent
academic positions. There have been many others, just as critical of the
orthodox doctrine, though not always as outspoken - and their number is
steadily growing. Although these criticisms have made numerous breaches
in the walls, the citadel still stands - mainly, as said before, because nobody
has a satisfactory alternative to offer. The history of science shows that a
well-established theory can take a lot of battering and get itself into a
tangle of contradictions - the fourth phase of 'Crisis and Doubt' in the
historic cycle and yet still be upheld by the establishment until a
breakthrough occurs, initiating a new departure, and the start of a new
cycle. But that event is not yet in sight. In the meantime, the educated
public continues to believe that Darwin has provided all the relevant
answers by the magic formula of random mutation plus natural selection -
quite unaware of the fact that random mutations turned out to be irrelevant
and natural selection a tautology." (Koestler A., "Janus: A Summing Up",
Picador: London, 1983, pp.184-185)
Stephen E. Jones | sejones@iinet.net.au | http://www.iinet.net.au/~sejones
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