Vast scale of the search for ultimate reality

This ring road near Chicago was built above a giant underground particle accelerator. Two kilometres in diameter, the circular Tevatron is employed in the hunt for the tiniest bits of matter. Beams of protons and antiprotons (the antimatter versions of protons) whizz round the ring-shaped tunnel. They collide at spends approaching that of light, creating energies found at the heart of stars and recreating events that happened at the beginning of time. Scientists are hoping to find among the showers of high-energy particles thus produced, the elusive "top" quark, a fundamental particle that must exist if their theories are right.

Tevatron and Particle spray

DetectorA view of the weird world of particles

Left : As fast- moving particle beams collide in a powerful detector, sprays of new particles are produced. Among the debris scientists search for clues to understanding the fundamentals that underlie nature Inset : subatomic particles created in gigantic machines reveal their exotic cosmic dance as swirling tracks in a bubble chamber.

Science is close to solving the biggest mystery of all - how to make sense of the particles that underlie all things

In this dossier

The next time you put a lump of sugar in your coffee, take a good look at it. Inside are the secrets of the universe. If you could look through a powerful microscope, you'd see that each crystal is made of regular ring-like objects - molecules. Further magnification reveals atoms of carbon, oxygen and hydrogen about one- hundred-millionth of a centimetre across. These atoms - plus a few others - make up all of life.
At greater magnification, you notice that these atoms have a structure. A wavering cloud of insubstantial electrons surrounds a tiny dense nucleus of the order of about one-hundred-million- millionth of a centimetre across.

Democritus, who suggested that matter was made of indivisible particles. The idea did not catch on for more than 2000 years after that Democritus

A nucleus is made of two kinds of particle - protons and neutrons. (Hydrogen nuclei are simplest, with just one proton.) Nuclei are still being created in the furnaces we call stars; its no coincidence that our bodies are composed of the same proportions of the same atoms as the stars.
Electrons are thought to be "elementary" - not made up of more basic constituents - but physicists have confirmed in the past 30 years that protons and neutrons are made up of yet smaller particles: "quarks". Here we are down to the unimaginable scale of 10-15 of a centimetre.
Scientists think the elementary particles were created in the first moments after the Big Bang, about 15 billion years ago.
At CERN, the particle physics laboratory in Geneva, scientists are hoping to build a giant new "genesis machine". The Large Hadron Collider (LHC) will recreate the incandescence of the dawn of creation. They hope this will tell them how matter came to be and reveal what it is.


Cosmic rays

This telescope in Italy is studying gamma rays and other sub-atomic particles coming from space. These zap air molecules and create showers of new particles like those made in accelerators.

This would be a unifying theory - it would explain how quarks, electrons and other particles interact. Scientists try to achieve this by treating as particles the fundamental forces of nature - gravity, electromagnetism and nuclear forces - that act upon the constituents of the atom.
While this concept of "force particles" is relatively new, the notion that matter is made of elementary constituents is old. The Greek mathematician Democritus believed matter was made of atoms. (The Greek atomos means uncuttable.) Isaac Newton, the first to suggest that light is made of particles, supported the theory, but it wasn't till the 19th century that "atomism" gained support - partly because it was useful for explaining chemical reactions. But many scientists still did not regard atoms as real. At the end of the 19th century J J Thompson, a British scientist, showed that electricity is borne by tiny negatively charged corpuscles called electrons, and much less massive than an atom. Ernest Rutherford, experimenting with radioactivity a few years later, observed that alpha radiation fired at gold foil is sometimes deflected. He proposed that gold atoms contain a tiny positively charged nugget of material - a nucleus.
By the 1930s scientists had unravelled the structure of the atom. Also, Albert Einstein had shown that matter and energy are interchangeable, and that light is made of "packets" of energy called photons.
Things didn't stay as simple as that. Paul Dirac suggested that a positively charged electron could exist, and the discovery of "positrons", and of other so-called antimatter particles in cosmic rays, soon followed. Particle accelerators, which smash particles at high energies and create showers of "strange" particles, were developed. The result was that by the end of the 19505 there were dozens of new particles with confusing names like the kaon and the lambda. When the muon was discovered, one exasperated physicist asked
"Who ordered that?"
In 1962 Murray Gell-Mann and Yuval Ne'eman used their notion of symmetry to order the particles into families. Gell- Mann went on to suggest that all particles were built of smaller units - "quarks" (a term from James Joyce's Finnegan's Wake). Evidence of quark-like entities was found in protons, and further particles made of different kinds of quark were discovered.

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