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Questions That Plague Physics: A
Conversation with Lawrence M. Krauss
Lawrence M. Krauss speaks about unfinished
business
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Image: MARK
JENKINSON
LAWRENCE M. KRAUSS is
a man of many opinions. One is that string theory has failed to shed
light on the nature of dark energy.
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Chair of the physics department at Case Western Reserve University,
Lawrence M. Krauss is famed in the research community for his prescient
suggestion that a still mysterious entity called dark energy might be
the key to understanding the beginnings of the universe. He is also an
outspoken social critic and in February was among 60 prominent
scientists who signed a letter entitled "Restoring Scientific Integrity
in Policymaking," complaining of the Bush administration's misuse of
science. The public, though, might know him best as an op-ed writer and
author of books with mass appeal. His 1995 work, The Physics of
Star Trek, became a best-seller, translated into 15 languages. He
is now finishing his seventh popular title, Hiding in the Mirror:
The Mysterious Allure of Extra Dimensions,
which he describes as "an exploration of our long-standing literary,
artistic and scientific love affair with the idea that there are hidden
universes out there." Krauss recently discussed his many scientific and
social passions with writer Claudia Dreifus.
SCIENTIFIC AMERICAN: What are the top questions
bedeviling physicists today?
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LAWRENCE KRAUSS: Three
that I find fascinating are: What is the nature of dark energy? How can
we reconcile black hole evaporation with quantum mechanics? And,
finally, do extra dimensions exist? They are all connected. And they
are all going to require some new insights into quantum gravity. But
someone is going to have to come up with a totally new and remarkable
idea. And it's hard to predict when that is going to happen. In 1904
you couldn't have predicted that Albert Einstein would come up with a
remarkable idea in 1905.
I think the resolution to these problems is likely to be
theoretical and not experimental. This is because direct experimental
signatures that might point us in the right theoretical directions in
these areas probably lie beyond the realm of current experiments. I'd
also bet that the solution to these problems is not going to resemble
anything being done now, including string theory.
SA: Is string theory the physics equivalent of
The God That Failed, as some people used to say about communist
ideology?
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Image: JAY LaPRETE AP
Photo
KRAUSS (standing)
spoke to the Ohio State Board of Education Standards Committee on March
11, 2002, in an effort to keep religious teachings out of the public
school science curriculum. The board agreed, although creationists have
not given up the fight.
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LK: Not exactly. But I do think its time may be
past. String
theory and the other modish physical theory, loop quantum gravity, both
stem from one basic idea: that there's a mathematical problem with
general relativity.
The idea is that when you try to examine physical phenomena on ever
smaller scales, gravity acts worse and worse. Eventually, you get
infinities. And almost all research to find a quantum theory of gravity
is trying to understand these infinities. What string theory and what
loop quantum gravity do is go around this by not going smaller than a
certain distance scale, because if you do, things will behave
differently. Both these theories are based on the idea that you can't
go down to zero in a point particle, and that's one way to get rid of
mathematical infinities. The main difference, I think, between the two
theories is that string is intellectually and mathematically far richer.
String theory hasn't accomplished a lot in terms of solving physical
problems, but it's produced a lot of interesting mathematical
discoveries. That's why it fascinates. Loop quantum gravity hasn't even
done that, at least in my mind.
"We live in a society
where it's considered okay for intelligent people to be scientifically
illiterate."
SA: Are you saying that string theory hasn't
really gotten us anywhere?
LK: Neither string theory nor loop quantum
gravity has told us
much about the key unsolved physical problems--most important, why does
the universe have dark energy? That's the biggest question right now.
One thing that has come out of string theory is the idea of plural
universes or extra dimensions, and that's because string theory is
based on extra dimensions. The only consistent string theory originally
had 26 dimensions, and then it got lowered to 10. But the universe we
live in is four-dimensional [three spatial plus time]. A lot of talk
went into explaining how all these extra dimensions were invisible.
Recently some people have been trying to turn that defect into a virtue
by suggesting that the extra dimensions might actually be detectable.
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