The Known Universe
Universe, what is it, who created it, where do
we exist, couple of questions always puzzle my mind. I asked my teachers,
friends and read some books, and this is what i knew about universe.
According to Big Bang theory our
universe concentrated into a single point which have infinite density and zero
volume. Early time it was so hot and according to Lambda CDA, universe age is 13.7
billion years (that’s so big, very very big). Our general relativity says that
at the beginning of the Big Bang, was a singularity, it showed that the
universe could have had a singularity, a beginning of time. According to
general relativity gravity is always attractive by this fact scientist showed
star that collapse under its own gravity is trapped in a region where boundary
eventually shrinks to zero size. This mean that all the matter in the star will
be compressed into a region of zero volume, so the density of matter and the
curvature of space time become infinite. In other words, one has a singularity
contained within a region of space time known as Black Hole, but that’s a
different topic first you should know what is singularity- it’s a location
where the quantities that are used to measure the gravitational field become
infinite in a way that does not depend on coordinate system(seems
interesting).
Nobody knows where it came from?, who
created it?, why should the universe have begun at the Big Bang? And why was
the early universe so hot?
God (creator) caused the Big Bang, he
made it happen, perfectly reasonable answer. This seems to help many questions
with unsatisfying prospect of an event without a cause. But problem is that
from where did the creator of universe come? If the answer is- he always
existed then we have situation that is no more satisfying than a universe that
come out from Nothing. A Creator that has always existed is an entity that
somehow exist without a cause.
Actually we can’t predict anything beyond the time of Big Bang because
itself time had a beginning at the Big Bang. Time and space had a finite
beginning that corresponds to the origin of matter and energy. If there were
events before Big Bang, then they could not affect what happened at the present
time. Their existence can be ignored because it would have no observational
consequences.
We can’t predict what would come out
of the singularity because predictability would break down at the Big Bang.
Event before Big Bang have no consequences according to Stephen Hawking. All
the known laws of science would break down at such a point(that were the bad
news for some scientist).
In order to predict how the universe
should have started off, one needs laws that hold at the beginning of time or
space time singularity. So if you are intelligent enough to suggest laws that
hold at the singularity then you can answer, from where did the universe come
In other words our universe looks
like this
No matter how good our telescopes and
technology, we can’t see through that infinitely small hole into The Before.
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Earlier I thought that universe is
expanding in a infinite space. As I studied
that matter occupy space, so that was normal to think that( for me ), there is already
a infinite space and universe is expanding in it. Actually Big Bang is not a
explosion of matter moving outward to fill an empty space. Instead, space
itself expand with time everywhere and increasing the physical distance between
two co-moving points. According to theory, Big Bang is not a explosion in space
but rather an expansion of space.
Before the twentieth century no one
had suggested that the universe is expanding or contracting. It was generally
accepted that either had existed forever in a unchanging state. In 1992, Edwin
Hubble observed that wherever you look, distant stars are moving rapidly away
from us. Every single one galaxy is moving away from us and farther the galaxy
is, the faster it is moving. In other words universe is expanding. This mean
that earlier time objects would have been close together and this proves that
there is a singular point in the universe, at a time, the distance between
neighboring galaxies must have been zero. The discovery that universe is
expanding one of the great revolution of the twentieth century
In particular, it might seem that as
we must be at the center of the universe and universe also looks the same in
every direction as seen from any other galaxy(roughly on a large scale).
The situation is rather like steadily
blowing up a balloon which has a number of spots painted on it, as the balloon
expands, the distance between any two spots increases but there is no spot that
can be said to be the center of the expansion and also farther apart the spots
are, faster they will be moving apart. Similarly speed of which two galaxies
are moving apart is proportional to the distance between them.
According to Friedmann model, that the universe is not infinite in
space, but neither does space have any boundary. Gravity is so strong that
space is bent round onto itself, making it rather like the surface of the
Earth, if one keeps
travelling in a certain direction on the surface of the
Earth, one never comes up against an impassable barrier or falls over the edge.
It’s like, when one try to reach at
the end of the Earth but eventually comes back to where one started. According
to Stephen Hawking the idea that one could go right around the universe and end
up where one started makes good science fiction, but it doesn't have much
practical significance because it can be shown that the universe would re-collapse to zero size before one could get around. You need to travel faster
than light in order to end up where you started before the universe came to an
end, and that is not possible, our theory doesn't allow it.
We can also determine the present rate
of expansion by using Doppler effect, so all we know is that the universe is
expanding by 5 per cent and 10 per cent every thousand million years.
Is it enough to halt the expansion of universe or it will expand
forever. First we need to know the present rate of expansion and present
average density. If the mass density of the universe is greater than the
critical density, it would become denser and hotter again, ending with a state
similar to that in which it started- A Big Crunch.
If the density in the universe is
equal to or below the critical density, the expansion would slow down but never
stop. Stars formation would cease with the consumption of interstellar gas in
each galaxy stars would burn out leaving white dwarf, neutrons stars and black
holes. The average temperature of the universe would asymptotically approach
absolute zero- A Big Freeze
The present evidence therefore,
suggests that the universe will probably expand forever( Don’t bank on it ).
Still now less than 5% of all matter
and energy is directly detectable, we have to discover a lot so don’t forget to
keep looking Up.
The Universe is yours to Discover.
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