A revolutionary discovery by Edwin Hubble in 1929 really shook the grounds of
many astronomers. He found that Universe was expanding at enormous speed. Hubble
noted that galaxies outside our own Milky Way were all moving away from us,
each at a speed proportional to its distance from us. He quickly realised what
this meant that there must have been an instant in time (now known to be about
14 billion years ago) when the entire Universe was contained in a single point
in space. The Universe must have been born in this single violent event which
came to be known as the "Big Bang."
Astronomers combine mathematical models with
observations to develop workable theories of how the Universe came to be. The
mathematical underpinnings of the Big Bang theory include Albert Einstein's general theory of relativity along with standard
theories of fundamental particles.According to the theories of physics, if we
were to look at the Universe one second after the Big Bang, what we would see
is a 10-billion degree sea of neutrons, protons, electrons, anti-electrons
(positrons), photons, and neutrinos. Then, as time went on, we would see the
Universe cool, the neutrons either decaying into protons and electrons or
combining with protons to make deuterium (an isotope of hydrogen). As it
continued to cool, it would eventually reach the temperature where electrons
combined with nuclei to form neutral atoms. Before this
"recombination" occurred, the Universe would have been opaque because
the free electrons would have caused light
(photons) to scatter the way sunlight scatters from the water droplets in clouds.
But when the free electrons were absorbed to form neutral atoms, the Universe
suddenly became transparent. Those same photons - the afterglow of the Big Bang
known as cosmic background radiation - can be observed today.
Enormous amount of energy produced in this explosion is
enough to inflate the universe. But the question is when the energy that is
transformed to matter creates a gravitational pull that can retard the
inflation. Still the expansion is accelerating. Something, not like matter
and not like ordinary energy, is pushing the galaxies apart. This
"stuff" has been christened dark energy, but to give it a name
is not to understand it.
