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A new era of physics at the Large Hadron Collider
What would you be most excited to see
in the LHC’s detectors?
It would be extremely exciting if they
saw evidence for our theory, which
would consist of a particle
that is called the Kaluza-Klein partner of the graviton. You’d see something
that looks like a graviton,
which communicates gravity, but it would really be
from an extra dimension.
You’ve said that physics is entering a
“new era.” What do you mean by that?
At the high energies of the LHC, you’re
getting very precise, and you’re getting to, in some sense, simpler systems
where you can see the more basic and
more fundamental rules of physics
going on.… Studying higher energies is
the same as studying smaller scales. We
have this target scale, the weak energy
scale that the LHC is exploring — that is
to say, the scale at which we know particles are somehow acquiring mass associated with the Higgs mechanism.
What would the physics community be
most surprised to see in the LHC data?
Something we haven’t
thought of. If they don’t
see anything, of course,
there’s going to be a long
period where we have
to see: Are they not seeing anything because of
experimental deficien-cies, or are they not seeing
anything because there’s
really nothing there? We
really do expect there to
be something there playing the role of the Higgs
boson … but one of the
things you find as a theorist when you work out
the details is that there
could be a lot of stuff there
that we just miss.
Explain the theory that you and
Raman Sundrum developed to resolve
the “hierarchy problem,” namely that
gravity is much weaker than quantum
physics would predict.
The scenario we had in mind is that
some stuff is stuck on an object called a
brane, which exists in three dimensions,
but there can be an extra dimension of
space where gravity can be concentrated
away from us. That would explain why
gravity is so weak for us.… By an extra
dimension, I really do mean another
dimension beyond the three we’re
familiar with: left-right, up-down and
top-bottom. These extra dimensions
are hidden somehow and part of the
If the LHC finds a Kaluza-Klein particle, what does
that mean for the Higgs
mechanism and string
theory?
The Higgs could be there
whether or not there are
extra dimensions. If we
found the Kaluza-Klein
particle, it would be a nice
target for string theory.
It would be
extremely
exciting if they
saw evidence
for our theory,
which would
consist of a
particle that
is called the
Kaluza-Klein
partner of the
graviton.
When we first wrote down
this theory, string theorists
told us, “Oh, that’s very
nice, but it doesn’t happen
in string theory.” Actually
they didn’t even say it was very nice.
But a year later they found it in string
theory. The energy of the Kaluza-Klein
particle is much too low to prove or
disprove string theory, but it gives you
different ways to think about what the
possibilities are in string theory. If this
warped geometry exists, they’d have to
say it’s part of whatever model comes
out of string theory.
If you could design a
machine to test your
ideas, how would it look?
The SSC [the Supercon-
ducting Super Collider, an unfinished
project in Texas that was canceled by
the U.S. Congress in 1993] would have
been a great machine. It would have
had almost three times the energy of
the LHC, and that would really cover
a lot of what we’re looking for. Obvi-
ously, six times the energy would have
been great too. The higher the energy,
the more chances you have of seeing
things at a small scale. I do think that
at the SSC energy levels I would have
felt much more confident. But the LHC
is still a fantastic machine.… It’s the
highest energy, highest luminosity,
highest intensity, biggest machine in
the world. s
Could the LHC find a Kaluza-Klein
particle before reaching full power?
We know roughly the energy of this
thing. It could be that it’s an energy
a little higher than the LHC. It could
be that it’s the energy of the LHC. It
