Origins of the
The universe has not always appeared as
it does today. Most theories agree that the universe of 15 billion
years ago was vastly different that the present universe. Three
theories have gained widespread acceptance in the scientific
The Big Bang
Theory: This theory states that
15 billion years ago the universe and all of the matter in it was
compressed into a very small, dense and hot fireball. At this time
there was no such thing as planets, stars or galaxies. The entire
universe consisted of nothing more than the rubble of smashed and
broken atoms. Everything, including space itself, was squeezed into
this fireball by the tremendous forces of gravity. We really don't
know how long the universe existed in this condition. We do know that
about 15 billion years ago, something big happened. To call it just
"an explosion" just doesn't do justice to this event. This universe
of ours started to expand. Sort of like a balloon being inflated, the
universe began to get larger. As the fireball expanded, it began to
cool off. This process took millions and millions of years.
Eventually, the matter within the universe cooled enough for simple
hydrogen atoms to form. Lumps and clumps of this expanding matter
began to form. These early lumps and clumps of material would
eventually become the first stars and galaxies. Concentrations within
these lumps and clumps eventually became planets and moons. 15
billion years later, after a lot of expanding and cooling, the
universe appears as it does today. It is roughly spherical in shape,
perhaps 30 billion light years from side to side. In this universe
are about 100-200 billion galaxies, each containing about 100-200
billion stars. According to the Big Bang Theory, nothing will ever be
as powerful as the force of the big bang. Even gravity will never be
able to reverse the expansion that began so long ago. In the very
distant future, when all the stars have used us their fuel and the
last galaxies' light winks out, the universe will be cold, dark and
empty, and still expanding ever larger. The expansion will continue
forever. Not exactly a bright and cheery future, but keep in mind
that "distant future" means hundreds of billions of years from now.
Our universe has only been around for a mere 15 billion years, so
there is still a lot of time left.
Universe Theory: This is a
slightly more modern version of the Big Bang Theory. It has found
acceptance by about half of the scientific community today. The other
half tends to accept the Big Bang Theory. The first part of the theory
is exactly the same as what you learned for the Big Bang Theory.
Fifteen billion years ago the universe formed with a big bang, it
began to expand, and galaxies, stars and ultimately YOU formed from
lumps and clumps of the expanding universe. The basic difference
the power of gravity, and therefore, how much matter there actually
is in our universe. Recall that in the big bang theory, the most
powerful force ever is thought to be the force of the big bang.
Nothing, not even gravity, will have enough power to stop the
expansion of the universe. This theory contends that the ultimate
winner in the battle of the forces will be the force of gravity.
Proponents of this theory believe that there IS enough matter in the
universe to make enough gravity, to one day stop the expansion.
According to this theory, gravity will eventually slow the expansion
of the universe, gradually brining it to a full stop. After a time,
the ceaseless force of gravity will actually reverse the expansion,
and cause the universe to begin to contract. This is a time period
known as the "Big Crunch". This contraction will go
on for many years, until all matter and space in the universe is once
more contained in a fireball. This fireball for exist for some amount
of time, then it will to experience another big bang! (It's only
reasonable to expect that if it happened once, it's likely to happen
again!!) After this second "bang", this universe will begin an era of
expansion once again, only to see the expansion stopped by gravity,
begin contracting and end up as a fireball again. According to this
theory, this cycle will continue forever, as the universe forms,
destroys and reforms itself again and again!
The Steady State
Theory: This theory is
much different from the other two. The steady state theory really
isn't all that well accepted by the scientific community these days,
but it used to be, so I'm including it here for historical purposes.
The steady state theory has four points:
- The universe never "began" and it will
never "end", it simply has always existed and always will!
- The universe has always appeared and
will always appear much as it does now.
- As some galaxies die, new ones will
take their place.
- Stars produce the raw materials from
which other stars are constructed