How do we know what we know?
Particles like protons, electrons, and force carriers
are too small to see with even our most powerful microscopes.
So how do we know that such particles exist and what they're
Particle Family Album
images, which reveal tracks of various types of particles,
help physicists prove that particles exist. Scientists
can learn how particles interact by studying the relationships
between different particle tracks in each image.
While we can't see the particles themselves, physicists
have designed ingenious experiments that allow them to see
the paths, or tracks, of moving particles. Just as skid
marks on a road can tell you about a car's behavior just
before an accident, particle tracks tell scientists a lot
about how the building blocks of matter behave.
In fact, particle tracking has allowed physicists to identify
more than a hundred different kinds of particles and learn
important information about them -- such as their size and
mass, how they interact with other particles, and their
role in the universe.
One experiment commonly used to see particle tracks involves
a special container filled with alcohol vapor called a cloud
chamber. When some particles pass through this chamber,
they make alcohol vapor molecules stick together, leaving
a track of condensed alcohol.