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4. Back to the beginning page 14
Fundamentally right
Like Democritus (see page 3), we are still searching for a full understanding of the fundamental particles and forces of nature. Scientists think that they have found most of these in large particle accelerators.
Photo of discharge tube
Picture 4.1 The large particle accelerator at Cern, in Switzerland, is buried underground. The 27 km tunnel runs in a circle under the border with France. Find out more about accelerators in A world of particles.

Which particles are fundamental?
Electrons are fundamental particles and, as far as we know, cannot be made simpler. The electron is a member of the lepton family of fundamental particles.

Protons and neutrons are not fundamental and can be broken down into smaller, fundamental parts. Each proton and neutron contains 3 particles called quarks.

Quarks and leptons are fundamental particles. We think that all of matter is made up from these two families of particles.

The model that describes quarks, leptons and the forces between them is called the Standard Model. You can find out more about this in the resource A world of particles.

Where did they come from?
As well as helping us understand what makes the matter in the Universe, the Standard Model helps explain where it all came from. We now think that the Universe was born in a Big Bang about 14 billion years ago. Quarks and leptons were the first particles to be born soon after the Big Bang.

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Question 13
Look at the particles below.
a) Which of the particles are fundamental?
b) Which one particle is the simplest particle found inside the nucleus?
particle a) fundamental b) simplest in
   nucleus
quark
proton
lepton
electron
neutrons
atom