Many people have written to us recently with concerns
about the forthcoming experiments at the LHC. These have
often come from things they have read on blogs or in the
news media.
We have seen concerns about a variety of topics. Here we
focus on the most common concern -- that the LHC might
produce microscopic black holes. But the nature of the answer
is quite similar for all these concerns.
As you might guess, the physicists at the Large Hadron
Collider have given considerable thought to this subject.
If there really were danger, we would be as concerned as
anyone else. We all have families and want to be certain
that everything we do is perfectly safe. Detailed studies
reviewed by highly respected independent bodies have
concluded without doubt that the LHC and its experiments are
absolutely safe. You can read about it at:
http://public.web.cern.ch/public/en/LHC/Safety-en.html
We are starting the LHC because there is no danger.
Let us explain.
According to some theoretical models, microscopic black
holes could be produced in collisions at the LHC. Most
people think it is very unlikely, but it would be
fascinating if it were possible, and definitely harmless.
They would decay into ordinary particles extremely quickly,
and those particles would be detected by experiments
(the tinier the black hole, the faster it evaporates).
How do we know that they are harmless? Cosmic rays are
continuously bombarding Earth's atmosphere with far more
energy than protons will have at the LHC, so cosmic rays
would produce everything LHC can produce.
They have done so throughout the 4.5 billion years of
the Earth's existence, and the Earth is still here. The
LHC just lets us see these processes in the lab (though at
a much lower energy than some cosmic rays).
We have read in the news media that a few people propose
(despite the predications of physics) that black holes do
not decay but are stable. Even if this speculation were
true, a still more powerful piece of data rules out any
concern. Such microscopic black holes would be produced
by cosmic rays hitting neutron stars and be absorbed, and
would turn the neutron stars into black holes. If this
were true, we would not see any neutron stars, but of
course we do.
In conclusion, no matter what assumptions one makes,
microscopic black holes pose no concern to anyone. Also
keep in mind that it is extremely speculative to imagine
microscopic black holes being created, since it requires
the existence of extra dimensions of space, and several
other highly unlikely assumptions.
We hope this reassures you about the complete safety of
the Large Hadron Collider. We also hope you will share
with us the incredible excitement of great discoveries
that the LHC may make over the next few years.
