Wednesday, September 10, 2008

Is the Large Hadron Collider safe?

The Large Hadron Collider, usually referred to by scientists as the LHC, had its first preliminary test today.  All went well.  But what does the LHC do, and is it safe?

What is the LHC?

The LHC is a "particle collider".  It has two main parts: beams and detectors.  Two beams of protons will be channeled at near the speed of light around a tunnel 27 km in circumference, one clockwise, one counterclockwise, by a pair of rings made of 9000 superconducting magnets.  The beams will cross in several places, allowing the particles within them to collide (hence the term "collider").  The by-products of those collisions will be observed by two enormous detectors (as well as two somewhat smaller ones).  It short, it collides beams of particles and detects what happens.

What is the LHC for?
Physicists have learned a lot about the fundamental constituents of matter by bashing particles together.  The higher the energy scale of the collisions, the deeper, in a sense, one can probe.  We now understand what particles make up all the matter we can see, and what particles are responsible for forces.  For example, as I said in a previous post, we understand about electrons and their siblings (yes, I know I haven't gotten around to doing the followup posts yet), and we understand that the electromagnetic force comes from the particle of light, the photon.  In fact, we have understood how these particles and forces behave in terms of some rather beautiful symmetries.  A symmetry is an invariance, as in "looks the same in a mirror", or "runs the same if you switch all the red and black cables for one another".   A key point is that a symmetry can be broken.  For example, you don't look the same in a mirror.  Even if you part your hair down the middle, there is always some freckle to give away that it is a mirror image.

Our theory of particle physics using symmetries works great, except for understanding why most of the particles have mass.  If the symmetries of the theory were not broken,  these particles would have to be massless.  We need to understand how the symmetries are broken—we have to find the freckles.   The main freckle is called the Higgs boson (please, can we stop using the awful term "God particle"!).  It has never been seen.  We think that is how the electron gets its mass, but we don't know for sure.  And we don't understand how the Higgs boson might fit into a more complete theory.

The LHC is designed to find the Higgs boson, and we hope it will point us to a more complete theory of matter and energy.  It may also shed light on the dark matter, but that is a post for another day.

Is the LHC Safe?
Sometimes the LHC is described as "recreating the Big Bang".  This sort of language is colorful, and conveys the grand nature of the endeavor, but it also makes it sound scary, and, more to the point, is completely inaccurate.  The LHC will probe a new frontier for humans, but the kinds of collisions that will take place in it happen in and around the Earth all the time.  Cosmic ray protons hit protons in the atmosphere and create sprays of particles just like in the LHC.  If you were to wait in one location, it would be quite rare that you would see a collision at the same energies as the LHC, but across the whole atmosphere they happen all the time.  If these collisions were dangerous, they would have done their damage long ago.  

One worry that has been stated in the press is that the LHC might produce mini black holes.  Well, that is a possibility if there are extra dimensions of space that become visible just at the LHC energy scale, but that is unlikely (not quite as crazy as it sounds though).  But such mini black holes would not be like the monsters you may have seen in Sci Fi.  They would be tiny (way smaller than protons) and would decay in a fraction of a second.

Could these mini black holes be stable?  First of all, even if they were, a mini black hole would take hundreds of millions of years to grow appreciably in size in the Earth, so it could not be the doomsday machine some have feared.  But everything we know about the theory says that such mini black holes must decay very rapidly due to quantum processes.   Mini black holes are essentially  just another kind of particle that decays. 

If all of that is not enough to convince you that the LHC is safe, here is a final comfort:  we have seen pulsars.  Comforting eh?  You see, pulsars are like canaries in the coal mine.  They are spinning neutron stars.  Neutron stars are dense cinders of dying stars that just barely avoided collapsing on themselves into black holes (the large kind).  They would feel the effects of a mini black hole much much faster than the Earth would.  They too are bombarded by cosmic rays all the time.  They recreate the LHC experiments each second.  If particle collisions created mini black holes that somehow were stable, all neutron stars would quickly be triggered into collapsing.  We see pulsars, so that can't have happened.

So the LHC is not a threat.  It is just a tool to look for freckles.

An engineer leans on a magnet in the 27km-long tunnel that houses the Large Hadron Collider (BBC News; Image: Cern/Maximilien Brice)


Leslie GP said...

I feel somewhat more reassured now about those mini black holes.

But I'm starting to get a little nervous about freckles . . .

JTankers said...

Hawking Radiation has been debunked.

Physicists who re-examined Hawking Radiation in the last decade determined that micro black holes do not evaporate. Their papers conclude:

"black holes do not radiate"[1] "the effect [Hawking Radiation] does not exist."[2] "infinitely delayed Hawking radiation" [3]

Dr. Rössler, a physicist famous for invention of Chaos theory's Rössler Attractor and for founding Endophysics, calculates exponential micro black hole growth (years or decades to consume the planet).[3]

If the Large Hadron Collider WILL create micro black holes, then the odds of danger might be... possibly... a probability?

[1] Do black holes radiate?. Prof. Dr. Adam Helfer (2003)

[2], On the existence of black hole evaporationyet again, Prof. VA Belinski (2006)

[3] BLACKHOLE.pdf Abraham-Solution to Schwarzschild Metric Implies That CERN Miniblack Holes Pose a Planetary Risk, Prof. Dr. Otto Rössler (2008)

eyesopen said...

Note that none of these papers have been published in a refereed journal. The consensus opinion of those who have extensively studied the issue is that black holes do decay via Hawking radiation. People can post virtually anything they want on the arXiv. If they said the Earth was flat, that wouldn't make it so.

Hawking radiation arises from quantum field theory, which has been extremely well tested, in what is called the semiclassical regime--where gravitational fields are not strong enough to mandate a full quantum gravity treatment. In other words, we have every reason to believe the calculations are correct.

But note that my argument did not even rely on black holes decaying. I simply noted that LHC-like collisions happen all the time, and would have had some very obvious effects if they were dangerous.

I should say that I think it is important to ask the question, "is this safe?", but I think one also has to accept the answer if it is a resounding "yes", as in this case.

JTankers said...

If CERN is certain they are correct, then they should not oppose a safety conference, but apparently they do.

I studied Hawking Radiation and I think Reverse Hawking Radiation is very plausible.

Regular HR with Dr. Hawking's requirement for reverse time travel and negative energy is not at all compelling to me and particularly non-compatible with dark energy conjecture.

Apparently Dr. Hawking thought he could explain where all the anti-matter went but failed to realize that anit-matter is energy, not negative energy.

Reverse HR however would explain much I think, have you read the open source conjecture at[1]

I don't know if micro black holes will be created, Dr. Hawking estimates a 1% chance for them and bet $100 against finding the Higgs![2]

I also don't know how fast a stable micro black hole would grow.

I am concerned that at this rate Sir Martin Rees's conjecture of a 50/50 chance of humans surviving probably man's most dangerous century sounds very plausible. We will probably survive millenia if we manager to survive the next few centuries.

[1], The Pre-Big Bang Universe Model, Open Source Speculative Physics Projects

[2] Threats Won't Stop Collider, Sep 9, 2008