(Submitted January 08, 1997)
What holds the Universe together? What holds us together?
Your very good questions are related to two different forces. The
first, what holds the Universe together, is one that astronomers think
about often. On large scales like the Universe, the most important force
is gravity. Between any two objects the gravitational attraction is
proportional to the product of the masses divided by the square of the
distance between them. Gravity is the force responsible for keeping the
Earth and other planets in our solar system in orbit around the Sun.
Gravity also governs the motions of the Sun and nearly all the stars you
can see in the sky, which are orbiting about the center of the Milky Way
Galaxy. The Milky Way is part of a gravitationally bound collection of
galaxies which includes Andromeda, and is called the Local Group. Apart
from observing that objects large and small are gravitationally attracted
to each other, astronomers also observe that the Universe is expanding: an
after-effect of the birth of the Universe in the Big Bang.
Your second question, what holds us together, is closer to
biochemistry than astrophysics. Human beings are composed of different
types of large molecules: proteins, nucleic acids, lipids, carbohydrates,
etc. These molecules are held together by intermolecular forces. An
example is the peptide bond that links amino acids together. This bond
is formed when atoms of Hydrogen, Oxygen, Carbon and Nitrogen share
electrons. Molecular bonding is governed by the electrostatic force, which
on small scales is much stronger than the gravitational force for
charged particles. We human beings still feel
the effects of gravity though: it keeps us from floating
off the Earth.
for Imagine the Universe!