Astronomers have tried to explain what we see in the universe around
us. The simplest explanation for everything we know about the
universe is called the Big Bang theory. This theory says that
in the beginning, everything in the universe was all in one
place. Something unknown caused the universe to begin growing. The universe
began growing very quickly, and the universe is still growing even today.
At the beginning, when all the matter in the universe was contained in a very tiny volume, it was very hot. As the universe started to grow, it cooled off very quickly. When the universe was about 500,000 years old, it had cooled enough that it was possible for the atoms that make up stars and galaxies to begin to form. Energy released when the universe was small and dense, the cosmic microwave background radiation, still fills the universe today. By studying this energy, astronomers can learn what the universe was like when stars and galaxies were first able to form.
So how old is the universe? Astronomers argue about the exact age of
the universe for many reasons. But they do agree that it is somewhere
between 10 and 20 billion years old.
The
History of the Universe in 60 Seconds or Less - Dr. Eric Schulman - streaming
RealVideo (1 min. 16 sec.) from NSF
Einstein's Messengers - LIGO Documentary - streaming
RealVideo (20 min. 12 sec.) from NSF
A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF
The theory that best explains the current universe is the Big
Bang theory. This theory states that, in the beginning, the
universe was all in one place. All of its matter and energy were
squished into an infinitely small point, a singularity. The laws of
physics which applied at that instant are not understood at all.
Something unknown caused the universe to explode, and thus began the
expansion that we see today.
The early universe was small, so everything happened very quickly compared to the timescales on which events happen for the present universe. At the start, the universe was very small and dense. This stage was called the primordial fireball. For the first second, only elementary particles, such as protons, neutrons, and electrons, could exist. But the universe quickly cooled and expanded. For about the next 500,000 years, electromagnetic radiation (light) was the most important thing in the universe and hence this time was known as the radiation era. When the universe had cooled to the point where the simplest atoms (hydrogen) could form, radiation no longer dominated and matter took over. The cosmic microwave background radiation was produced at this time. So began the matter era in which the universe exists now.
So how old is the universe? There is much debate over the current age
of the universe among astrophysicists. But everyone agrees that it
is somewhere between 10 and 20 billion years old.
The
History of the Universe in 60 Seconds or Less - Dr. Eric Schulman - streaming
RealVideo (1 min. 16 sec.) from NSF
Einstein's Messengers - LIGO Documentary - streaming
RealVideo (20 min. 12 sec.) from NSF
A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF
The theory that best explains the currently observed state of the
universe is the Big Bang theory. This theory states that, in
the beginning, the universe was all in one place. All of its matter
and energy were squished into an infinitely small point, a
singularity. The laws of physics at that instant are not understood at
all. But something caused the universe to explode, and thus began the
expansion that we witness
today.
The early universe was small, so everything happened very quickly compared to the timescales on which events happen for the present universe. At the start, the universe was very small, dense, and very hot. This stage was called the primordial fireball. For the first second, only elementary particles, such as protons, neutrons and electrons, could exist. But the universe quickly cooled and expanded. For about the next 500,000 years electromagnetic radiation was the most important thing in the universe and hence this time was known as the radiation era. Once the universe had cooled to the point where the simplest atoms (hydrogen) could form, radiation no longer dominated and matter took over, begining the matter era. The cosmic microwave background radiation was produced at this time, as light that had been trapped by free electrons escaped when the electrons combined with protons to form hydrogen.
So how old is the universe? In principle, that's an easy question to
answer. With the rate at which the universe is expanding, called the
Hubble constant, astronomers can determine
how long ago the universe was at size zero - the age of the
universe. In practice, it is not so easy. Despite its name, the Hubble
constant is not constant in time. It changes as gravity takes hold of
the universe and slows the expansion. How much it changes
depends on the density of the universe. To determine this density,
astronomers need to measure the distances to very distant galaxies,
which is a very difficult task. Although there is much debate over the
current age of the universe among astrophysicists, they do agree that
it is somewhere between 10 and 20 billion years old, which is still a pretty
good estimate in astronomical terms.
The
History of the Universe in 60 Seconds or Less - Dr. Eric Schulman - streaming
RealVideo (1 min. 16 sec.) from NSF
Einstein's Messengers - LIGO Documentary - streaming
RealVideo (20 min. 12 sec.) from NSF
A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF
Last modified May 6, 2008 by Randy Russell.
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