Page last updated at 19:50 GMT, Saturday, 6 September 2008 20:50 UK
Guide to the Large Hadron Collider

Professor Brian Cox

Professor Brian Cox is one of the LHC scientists at Cern. He answered some of your questions about the project and what it could find out.

Q: Why experiment at all?

Can you tell me why we are doing this experiment? I can understand that you are hoping to reveal the origins of mass by smashing tiny particles together but what advantages (besides increase in knowledge) do you expect to obtain from this? (Stephen)

A: Experiment is the basis of the scientific method, without which there would be no modern world as we know it.

The quest to understand the smallest building blocks of nature and the forces that hold them together arguably began with the ancient Greeks, but it was only when we began to conduct experiments that we discovered the electron (1897), quantum mechanics (triggered by precision observations of the light emitted by elements when heated), X-rays, the atomic nucleus, radioactive decay... the list is practically endless.

I think it is disgraceful that huge sums of cash have been spent on this project
Robert, Spain

Without these experimental discoveries, and the subsequent deepening of our understanding of the Universe, there would be no electronics, no silicon chips or transistors, no medical imaging technology, no nuclear power stations, no X-rays or chemotherapy treatments for cancer... again an almost endless list.

What this should teach us is two things. First, it is virtually impossible to deepen our understanding of Nature without experiments. Second, understanding Nature has never been a bad idea - indeed without the pioneers of the past century, our civilisation would be immeasurably poorer.

I do not know what the continuation of this long and illustrious quest will lead to, but I would be extremely surprised if a writer called upon to defend scientific enquiry at the turn of the 22nd Century does not point to the LHC as the foundation of a hundred new technologies, each considered essential to our quality of life. (BC)

Q: Existence of multi-dimensions

Will the Collider be able to prove to scientists that many other dimensions exist as well as ours? If so, then what will the implications be for our future, and could this be a good explanation for the many UFO sightings around the world. (Ian)

A: The LHC could indeed provide strong evidence for the existence of extra dimensions in our Universe. The fact that they are so hard to see (if they exist), however, means that our world interacts with them very weakly.

In fact, we theorise that if they do exist, the force of gravity is the only influence that can pass between them. This would prevent any material objects from crossing from one set of dimensions to another. So, no, UFO enthusiasts must look elsewhere. (BC)

Q: Understanding "dark matter"

Will the LHC help our understanding of dark matter (which seems to make up most of the Universe) and "dark energy" (which seems to be accelerating the expansion of the Universe)?

Are these phenomena "real" or just a result of our misinterpreting measurements of distance and mass for far away objects? (Russell)

A: Quite possibly, yes, certainly for the case of dark matter. One of the most popular interpretations of the evidence that points to the existence of dark matter is that there are new, as yet undiscovered heavy particles, in the Universe that interact with normal matter only via the weak nuclear force and gravity.

In particle physics, we have a family of theoretical candidates for such particles known as Supersymmetric particles. If these exist, then many theoretical physicists expect them to be made and discovered at the LHC. Dark energy is another mater, because we have very little theoretical understanding of this phenomenon at present.

It may just be that if we get some evidence of extra dimensions at the LHC, which may point the way to a deeper understanding of gravity (a "quantum theory of gravity" along the lines of string theory perhaps), then we may gain some insight into this fascinating discovery.

And yes, you are correct that these phenomena may be due to a mis-understanding of something - perhaps the theory of gravity itself at very large distance scales. I think the experimental evidence that something is missing in our understanding is very strong now, however, and it's not merely an experimental error. (BC)

Q: Multiple Big Bangs

What are the possibilities of multiple Big Bangs creating multiple parallel universes? (Jon)

A: If you're asking about the mini-big bangs at the LHC, then the chances are zero. It's a bit of a misnomer actually to call the collisions mini-Big Bangs - each one has the energy of a mosquito hitting you in the face on a summer's day, albeit confined to a very small space!

But - and this has little to do with the LHC directly - some of the current theories of the origin of our Universe suggest that in fact the Universe has been around for ever.

What we see as the Big Bang was simply something happening to our little piece of space-time 13.7 billion years ago. There could be multiple "sheets" of space-time (sometimes called "branes" floating around in an infinitely large multi-dimensional Universe, with everything we see being confined to just one).

When these sheets bump into each other, they become very hot and expand, so to anyone living on a sheet today it would look like their Universe began at the point of collision. (BC)

Q: Black holes and matter

If you are able to generate even small black holes, will they suck up matter? Do full-sized black holes draw in invisible matter also? You have an exciting project and I wish you a lot of luck in the operation of your new hardware. (Merlin)

A: It's just possible that we could create mini-black holes, although this would require at least that there are extra dimensions in our Universe, for which we have no evidence!

If, however, we did, then the little black holes would bear no relation at all to the black holes created when stars collapse. They would evaporate away very quickly via a process called Hawking radiation (unless we have no understanding at all of quantum theory).

Even if they don't, they would be so very tiny that matter would never get close enough to them to be sucked in! Big black holes do suck matter in, and should also emit Hawking radiation, although they emit it much more slowly and so live for a very long time (much more than the current age of the Universe). (BC)

Q: Applications to everyday life

In terms off what this could achieve for the humanity in the next 20-30 years, can this technology change our everyday lives within our lifetimes? Or do you see humanity waiting a little more patiently before our lives are transformed with wormholes and quantum computing? (Lawrence)

A: I wish I knew! Let me give one positive example from history. Quantum mechanics was developed to maturity as a theory during the 1920s and by 1947 we had the first transistor.

It is often said, I think with some justification, that it is extremely unlikely that transistors could have been developed without the quantum theory.

Perhaps we are on the verge of a similar leap when we deepen our understanding of the sub-atomic world once again at LHC - who knows! (BC)

Q: New forms of fuel?

Do you think that there is a chance of discovering a new fuel source or better ways to create/manage energy during this experiment? I imagine enormous amounts of energy coming out of it... (Dave)

A: No energy comes out of the LHC - we get out of every collision exactly what we put in. I think the best hope for LHC technology helping us with the energy crisis is that the cooling systems developed for LHC are now being transferred to the ITER fusion project in France.

And fusion certainly would be the answer to our energy problems if we can make it work on an industrial scale, which is the goal of ITER by around 2035. (BC)

Q: What if the Higgs boson particle is found?

I also understand that the purpose of the LHC is to find the elusive God particle. If this was found, what would be the implications for science as we know it, and what would the next steps be? (Darren)

A: The Higgs particle is one of our theoretical explanations for the origin of mass in the Universe. If found, therefore, we will understand what mass is!

This is the place where we are "stuck" at the moment in our theories, and answering this question will, we suspect, provide a door to a deeper understanding of the Universe.

If the Higgs theory is wrong, by the way, then we will see whatever it is that is responsible for generating mass - it doesn't HAVE to be a Higgs particle!

The implications are quite profound because this is the point at which our current best theory of reality, the Standard Model, breaks down.

We have been stuck here for several decades, so the LHC is guaranteed to be a giant leap forward whatever we find there. (BC)

Q: What if there is no Higgs boson?

What will it mean if the Higgs boson and other particles are not detected by the LHC? (Alex)

A: See above! It will be more exciting in many ways because it will mean that we have understood much less than we thought about Nature. (BC)

Q: Can bacteria survive?

Would it be possible to put various simple bacteria into the experiment to see if they survive. We are relatively certain that plant RNA probably evolved during the Big Bang.

Animal DNA on the other hand could not and possibly came from meteorites carrying bacteria from other worlds (Panspermia theory). It would put this idea to bed if it couldn't survive the Big Bang. (Mick)

A: It won't! At the temperatures we generate in the collisions at LHC, even protons and neutrons don't survive, never mind atoms and molecules. (BC)

Q: Safety Concerns

Cern have been confident in the prediction that there are no major risks associated with the LHC's operation. How robust is this prediction? In particular, how reliant is it upon unsupported theoretical assumptions? (Chris)

Okay, so how do we know this thing won't make planet Earth implode then? (Stephen)

A: Let me answer all of these at once.

The LHC has absolutely no chance of destroying anything bigger than a few protons, let alone the Earth. This is not based on theoretical assumptions.

It is, of course, essential that all scientific research at the frontiers of knowledge, from genetics to particle physics, is subjected to the most rigorous scrutiny to ensure that our voyages into the unknown do not result in unforeseen, perhaps dangerous outcomes.

Cern, and indeed all research establishments, do this routinely and to the satisfaction of their host governments. In the case of the LHC, a report in plain English is available here:

For the record, the LHC collides particles together at energies far below those naturally occurring in many places in the Universe, including the upper atmosphere of our planet every second of every day.

If the LHC can produce micro black holes, for example, then nature is doing it right now by smashing ultra-high energy cosmic ray particles into the Earth directly above our heads with no discernable consequences.

The overwhelmingly most likely explanation for our continued existence in the face of this potentially prolific production of black holes is that they aren't produced at all because there are either no extra dimensions in the Universe, or they aren't set up right for us to see them.

If black holes are being produced, then next on the list of explanations for our continued existence is the broad theoretical consensus that sub-atomic black holes should fizzle back into the Universe very quickly, billionths of a second after they are created in a little flash of particles via a process known as Hawking radiation.

In other words, they evaporate away very quickly indeed. This process, which is perhaps Steven Hawking's greatest contribution to theoretical physics, is on significantly firmer theoretical ground than the extra dimensions theories required to create the little black holes in the first place.

Even if Hawking is wrong, and therefore much of our understanding of modern physics is also wrong, the little black holes would be so tiny that they would rarely come close enough to a particle of matter in the Earth to eat it and grow.

And even if you don't buy any of this, then you can still relax in the knowledge that we have no evidence anywhere in the Universe of a little black hole eating anything - not just Earth but the Sun and planets and every star we can see in the sky, including the immensely dense neutron stars and white dwarfs, remnants of ancient Suns that populate the sky in their millions and which because of their density would make great black hole food.

So - the only theoretical bit is in the proposition that you can make little black holes in the first place. From then on, observation tells us that these things either (a) don't exist - the most likely explanation; or (b) exist, but do not eat neutron stars and are therefore harmless, probably because they evaporate away very quickly indeed!

I am in fact immensely irritated by the conspiracy theorists who spread this nonsense around and try to scare people. This non-story is symptomatic of a larger mistrust in science, particularly in the US, which includes intelligent design amongst other things.

The only serious issue is why so many people who don't have the time or inclination to discover for themselves why this stuff is total crap have to be exposed to the opinions of these half-wits. (BC)

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