The large hadron collider

Rainbows

Static

Static shocks are as mysterious as they are unpleasant. What we know is this: They occur when an excess of either positive or negative charge builds up on the surface of your body, discharging when you touch something and leaving you neutralized. Alternatively, they can occur when static electricity builds up on something else a doorknob, say which you then touch. In that case, you are the excess charge's exit route.

But why all the buildup? It's unclear. The common (and probably partly correct) explanation says that when two objects rub together, friction knocks the electrons off the atoms in one of the objects, and these then move onto the second, leaving the first object with an excess of positively charged atoms and giving the second an excess of negative electrons. Both objects (your hair and a wool hat, say) will then be statically charged. But why do electrons flow from one object to the other, instead of moving in both directions?

This has never been satisfactorily explained, and a recent study by Northwestern University researcher Bartosz Grzybowski found that it may not even be the case. As detailed in the June issue of the journal Science, Grzybowski found that patches of both excess positive and excess negative charge exist on statically charged objects. He also found that entire molecules seemed to migrate between objects as they are rubbed together.

Clearly, the explanation of static is changing.

Rainbows form as sunlight shines on droplets of moisture in the Earth's atmosphere. The droplets act like prisms, "refracting" or separating light into its component colors and sending them shooting off at a range of angles between 40 and 42 degrees from the direction opposite the sun.

Of course, rainbows are no longer scientifically mysterious. They result from the way light passes through spherical drops: it is first refracted entering each drop's surface, reflected off the back of the drops, and again refracted as it leaves the drops, with all these rebounds giving it its final angular direction. This explanation has been known since the days of the 17th century physicist Isaac Newton.

But imagine how mystical rainbows would have seemed before then! Because they are so beautiful and were so inexplicable they were featured in many early religions. In ancient Greece, for example, rainbows were thought to be the paths made by the messengers of the gods as they traveled between Earth and heaven.

1) How did our universe come to be the way it is?

The Universe started with a Big Bang – but we don’t fully understand how or why it developed the way it did. The LHC will let us see how matter behaved a tiny fraction of a second after the Big Bang. Researchers have some ideas of what to expect – but also expect the unexpected!

2) What kind of Universe do we live in?

Many physicists think the Universe has more dimensions than the four (space and time) we are aware of. Will the LHC bring us evidence of new dimensions?

Gravity does not fit comfortably into the current descriptions of forces used by physicists. It is also very much weaker than the other forces. One explanation for this may be that our Universe is part of a larger multi dimensional reality and that gravity can leak into other dimensions, making it appear weaker. The LHC may allow us to see evidence of these extra dimensions - for example, the production of mini-black holes which blink into and out of existence in a tiny fraction of a second.

3) What happened in the Big Bang?

What was the Universe made of before the matter we see around us formed? The LHC will recreate, on a microscale, conditions that existed during the first billionth of a second of the Big Bang.

At the earliest moments of the Big Bang, the Universe consisted of a searingly hot soup of fundamental particles - quarks, leptons and the force carriers. As the Universe cooled to 1000 billion degrees, the quarks and gluons (carriers of the strong force) combined into composite particles like protons and neutrons. The LHC will collide lead nuclei so that they release their constituent quarks in a fleeting ‘Little Bang’. This will take us back to the time before these particles formed, re-creating the conditions early in the evolution of the universe, when quarks and gluons were free to mix without combining. The debris detected will provide important information about this very early state of matter.

4) Where is the antimatter?

The Big Bang created equal amounts of matter and antimatter, but we only see matter now. What happened to the antimatter?

Every fundamental matter particle has an antimatter partner with equal but opposite properties such as electric charge (for example, the negative electron has a positive antimatter partner called the positron). Equal amounts of matter and antimatter were created in the Big Bang, but antimatter then disappeared. So what happened to it? Experiments have already shown that some matter particles decay at different rates from their anti-particles, which could explain this. One of the LHC experiments will study these subtle differences between matter and antimatter particles.

5) Why do particles have mass?

Why do some particles have mass while others don’t? What makes this difference? If the LHC reveal particles predicted by theory it will help us understand this.

Particles of light (known as photons) have no mass. Matter particles (such as electrons and quarks) do – and we’re not sure why. British physicist, Peter Higgs, proposed the existence of a field (the Higg’s Field), which pervades the entire Universe and interacts with some particles and this gives them mass. If the theory is right then the field should reveal itself as a particle (the Higg’s particle). The Higg’s particle is too heavy to be made in existing accelerators, but the high energies of the LHC should enable us to produce and detect it.

6) What is our Universe made of?

Ninety-six percent of our Universe is missing! Much of the missing matter is stuff researchers have called ‘dark matter’. Can the LHC find out what it is made of?

The theory of ‘supersymmetry’ suggests that all known particles have, as yet undetected, ‘superpartners’. If they exist, the LHC should find them. These ‘supersymmetric’ particles may help explain one mystery of the Universe – missing matter. Astronomers detect the gravitational effects of large amounts of matter that can’t be seen and so is called ‘Dark Matter’. One possible explanation of dark matter is that it consists of supersymmetric particles.

1) I have heard that the LHC will recreate the Big Bang, does that mean it might create another Universe and if so what will happen to our Universe?

People sometimes refer to recreating the Big Bang, but this is misleading. What they actually mean is:

· recreating the conditions and energies that existed shortly after the start of the Big Bang, not the moment at which the Big Bang started

· recreating conditions on a microscale, not on the same scale as the original Big Bang and

· recreating energies that are continually being produced naturally (by high energy cosmic rays hitting the earth’s atmosphere) but at will and inside sophisticated detectors that track what is happening

No Big Bang – so no possibility of creating a new Universe.

2) How much did the LHC cost and who pays?

The direct total LHC project cost is £2.6bn, made up of:

· the collider (£2.1bn)

· the detectors (£575m)

The total cost is shared mainly by CERN's 20 Member States, with significant contributions from the six observer nations.

The UK pays ~£95m per year as our annual subscription to CERN.

The LHC project involves 111 nations in designing, building and testing equipment and software, participating in experiments and analysing data. The degree of involvement varies between countries, with some able to contribute more financial and human resource than others.

3) CERN stands for 'Conseil Européen pour la Recherche Nucléaire' (or European Council for Nuclear Research); does that mean that CERN is studying nuclear power and nuclear weapons?

At the time that CERN was established (1952 – 1954) physics research was exploring the inside of the atom, hence the word ‘nuclear’ in its title. CERN has never been involved in research on nuclear power or nuclear weapons, but has done much to increase our understanding of the fundamental structure of the atom.

The title CERN is actually an historical remnant. It comes from the name of the council that was founded to establish a European organisation for world-class physics research. The Council was dissolved once the new organisation (the European Organization for Nuclear Research) was formed, but the name CERN remained.

4) Why is the LHC underground? Is it because it is doing secret experiments that scientists want to hide away?

The LHC has been built in a tunnel originally constructed for a previous collider (LEP – the Large Electron Positron collider). This was the most economic solution to building both LEP and the LHC. It was cheaper to build an underground tunnel than acquire the equivalent land above ground. Putting the machine underground also greatly reduces the environmental impact of the LHC and associated activities.

The rock surrounding the LHC is a natural shield that reduces the amount of natural radiation that reaches the LHC and this reduces interference with the detectors. Vice versa, radiation produced when the LHC is running is safely shielded by 50 – 100 metres of rock.

5) Can the work at CERN be used to build more deadly weapons?

Unlikely for two main reasons. Firstly, CERN and the scientists and engineers working there have no interest in weapons research. They are trying to understand how the world works, not how to destroy it.

Secondly, the high energy particle beams produced at the LHC require a huge machine (27km long, weighing more than 38,000 tonnes – half the weight of an aircraft carrier), consuming 120MW of power and needing 91 tonnes of supercold liquid helium). The beams themselves have a lot of energy (the equivalent of a Eurostar train travelling at top speed) but they can only be maintained in a vacuum, if released into the atmosphere they would immediately interact with atoms in the air and dissipate their energy in a very short distance.

6) Are the high energies produced by the LHC dangerous and what happens if something goes wrong?

The LHC does produce very high energies, but these energy levels are restricted to tiny volumes inside the detectors. Many high energy particles, from collisions, are produced every second, but the detectors are designed to track and stop all particles (except neutrinos) as capturing all the energy from collisions is essential to identifying what particles have been produced. Very little of the energy from collisions is able to escape from the detectors.

The main danger from these energy levels is to the LHC machine itself. The beam of particles has the energy of a Eurostar train travelling at full speed and should something happen to destabilise the particle beam there is a real danger that all of that energy will be deflected into the wall of the beam pipe and the magnets of the LHC, causing a great deal of damage. The LHC has several automatic safety systems in place that monitor all the critical parts of the LHC. Should anything unexpected happen (power or magnet failure for example) the beam is automatically ‘dumped’ by being squirted into a blind tunnel where its energy is safely dissipated.

This all happens in milliseconds – the beam, which is travelling at 11,000 circuits of the LHC per second, will complete less than 3 circuits before the dump is complete.

http://www.lhc.ac.uk/11841.aspx

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