Saturday, September 13, 2008

Crashing Things Together is Fun and Educational

It’s in our nature. We humans often get a kick out of crashing things into each other. I remember watching Demolition Derby on TV when I was young. It was fascinating to watch drivers crash cars into each other on purpose until only one was left running.

And remember when David Letterman used to throw things off the top of a tall building just to see how they would smash upon impact with the ground.

Imagine shooting two bullets directly at each other from high-powered rifles. What would happen to the bullets when they hit each other in mid-air? The collision would take place so quickly and the bullets are so small, that the actual impact would probably be anticlimactic. But if you placed a high-speed video camera at the impact site, you could slow down the collision and watch in awe as the bullets annihilated each other.

Ordinary matter doesn’t really seem ordinary when looked at up close. I mean really up close. For example, more than 99 percent of the mass of any atom is located in a tightly-packed, tiny center called the nucleus. The two heaviest particles that make up an atom, protons and neutrons, are located there. Electrons are, by contrast, featherweights that whirl around the nucleus. So most of the atom is nothing but space.

If you were to scale up the size of an atom so that its nucleus was the size of a pea, and if you placed that pea in the center of the 50 yard line of a football field, the first ring of electrons would be located out along the uppermost seats in the nosebleed section. Even with binoculars, the closest electrons could not see their own nucleus.

So in our hypothetical rifle bullet collision, despite the fact that the bullets would be deformed beyond recognition and probably fragmented into tiny bits, none of the atomic nuclei in any of the atoms of the lead in those bullets would be affected in the least. The entire reaction would be handled by the outer rings of electrons, far away from the nucleus.

Inside the nucleus of every atom reside one or more tiny particles called protons. They carry a positive electric charge and were thought for many years to be an indivisible building block of the atom. Protons were assumed to be solid particles that could not be broken down into anything else.

But in the 1930s, physicists began shooting atomic nuclei at each other at high speeds just to see what would happen. Amazingly, the protons in them broke apart into new particles. Protons were not indivisible. They were made of other, smaller, particles. Scientists have been playing demolition derby with subatomic particles ever since.

The latest and greatest (and most expensive) atom smashing toy of the nuclear physicists was recently completed in Europe. It is the Large Hadron Collider, or LHC. Hadrons are a family of subatomic particles, such as protons and neutrons. It came on line last week.

Within a year, it will be up to full power and scientists will start shooting protons at each other at a speed as close to the speed of light as they can get. The speed of light is the theoretical speed limit of matter. Nothing can go that fast because to do so would require an infinite amount of energy. But the protons in the LHC will be moving pretty close to that speed.

Scientists hope that, by looking at the debris left over when the protons collide, they can find some of the elusive particles that are predicted to exist but haven’t yet been found. At the energies that will be used to crash two protons together in the LHC, the scientists will be recreating the environment that existed within a fraction of a second after the Big Bang. So the LHC is something like a time machine for subatomic particles.

What they discover from these collisions will probably produce more questions than answers. But scientists are fairly certain the results will lead them closer to an understanding of the ultimate question. How was the universe created?

See, crashing things together can be both fun and educational.

No comments: