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TITLE>Nobel Essay
This is an essay I wrote as my contribution to a contest in connection
with the 2001 Nobel prize. It was limited to 2500 words(in Swedish it's
almost precisely there) and an introduction on 250 words.
THE CREATION AND DEVELOPMENT OF THE
UNIVERSE
Up till just recently, scientists have been
rather certain on the beginning and development of the universe. The Big-bang
model accompanied by inflation is able to account for the properties of the
observed universe with an astonishing degree of accuracy. But they leave some
questions unanswered, like why the conditions for life are so very well meet and
inflation requires some parameters to be fine-tuned. Although this might be look
as more of a philosophical aspect of it, a theory which requires that you to but
in a lot of values 'by hand' for each experiment, can't be said to have much
predictive power which is what we want. And lately, new material like the
accelerating expansion of the universe and predictions made by the new, string
theory has emerged showing us that we might have to reconsider some of the very
foundations of modern science. In this essay I'll briefly explain some of the
modern theories that intend to describe our universe, and look forward to the
coming theories that will bridge the conceptual difficulties encountered by
today's ideas.
How did the universe arise? The dominating
view today is that it arose through what is called the big-bang. This view is
most common because it predicts: A) It predicts that the universe is
expanding, which it does. This leads to that if we think backward in time the
universe would be contracting. This would lead to that once everything has been
gathered on one place, and therefore has arisen through a primordial-explosion;
big-bang. B) It predicts that the universe should be made of 25% helium,
which is correct. C) It predicts the background radiation. When the universe
had just been created it was very hot which means that there where a lot of
radiation. As the universe then cooled a lot of the radiation disappeared but
some still exist and this is the background radiation. Furthermore it is
considered to be the theory that requires the least amount of unconfirmed
assumptions to make these predictions. In other words it is the easiest way to
explain them.
Big-bang also has some problems, the main problem is the
so called horizon problem: All parts of the universe seem to have the same
temperature on average and they also look very similar. This suggests that they
sometime have been in contact with each other so that they could have had their
temperature equally distributed. The problem is that there simply doesn't seem
to have been enough time for all parts in the known universe to have come into
contact with each other. One can calculate the time the universe seems to have
existed by measuring the distance to galaxies and the speed with which they move
away from each other. Since the speed of light in vacuum is constant one can
calculate how far light(and therefore radiation) could have travelled since the
beginning of the universe. We then look at how big the universe seems to be(how
much of it we can see). Picture our field of vision as a sphere(with the earth
at its' centre), we can see everything inside this sphere. The galaxies on one
side of the sphere looks exactly like the galaxies on the opposite side, which
means that they have been in contact, but when one calculate the distance
between the opposite galaxies one comes to the conclusion that the distance
between them are greater then the distance light could have travelled since the
beginning of the universe. So they cannot have been in contact, with the normal
expansion model.
The solution to this problem is called inflation.
Inflation is a powerful, but brief, expansion of the universe in its beginning.
This solves the problem by directly after the universe had begun the expansion
was rather calm and the different parts had time to come into contact with each
other, but after a while(a very short while actually) inflation started and the
universe expanded enormously on just a fleeingly short moment. Where after the
expansion continued as normal. This makes it possible for the universe to be as
large as we sees it today and at the same time there where a calmer moment in
the beginning when every thing could come into contact and even out the
temperature. Then what drove this large expansion? It has been speculated in
so called scalar fields, which are energy fields that should exist throughout
the universe. The universe rate of expansion is proportional to it's density.
This means that the lower the density is the slower it expands. When the
universe expands the density drops since the mass gets scattered over a vaster
area. According to relativity energy has gravitation just as mass, you can
say that mass and energy are different sides of the same coin. So these scalar
fields thereby contribute to the density of the universe. When the universe
expands the matter gets thinned out fast, the density drops. But the energy of
the scalar fields gets thinned out much slower then matter. This sluggishness
has the effect that the density of the scalar fields remained almost constant
for some time. The decreasing gravitational pull between matter(because of
the matter getting more spread out) made it harder for the universe to contract
and in combination with an almost constant density thanks to the scalar fields,
made it possible to instead of and escalating deceleration of the expansion,
have an escalating expansion before the scalar fields "caught up" with the
expansion and dropped to the density it should have. This is called false vacuum
since the universe contained more energy then what should have
existed.
Even inflation has problems: Why was the expansion so precisely
suited to create a universe we could live in? Had the expansion been a bit
slower the universe would soon have collapsed back into nothing and had it been
a bit faster galaxies and stars wouldn't have formed. Why everything seems
to be so perfectly suited for life is also in general a mystery. Had certain
properties, such as the strength of the different forces, gravitation,
electromagnetism and the weak and the strong force been different, the elements,
stars and galaxies would never have formed. Not that this configuration of the
universe is unlikely, it's just that there's simply so many more possibilities
for what the universe could have looked like which in most of them life couldn't
exist. This has, so far, no physical solution. Instead you refer to the
antrophic principal, which states that everything is as it is because if it had
been different we wouldn't be here to observe that it is as it is. This might
sound odd but it means that if the universe wouldn't have the properties it has,
life wouldn't have arisen and we wouldn't be here to ask us the question why the
universe is as it is.
An alternative to inflation is that the speed of
light wouldn't be constant; instead it would slow down over time. In this way
the speed of light could have been bigger in the beginning of the universe and
since radiation travels with the speed of light the different parts of the
universe could have come into contact and got the same
temperature.
Another interesting question is how the universe could be
created out of nothing(which we persume). The answer to this question lies in
quantum mechanics and Heisenberg's uncertainty principal. This means that on a
subatomic level you can't know two properties to 100%. The more you know about
one of them the less you can know about the other. This relation exists between
e.g time and energy; if you want to know the energy level more exact you have to
measure it under a longer time. This means that the energy level is uncertain
under small time intervals. This uncertainty leads to that the energy level can
fluctuate up and down and the larger the fluctuations are the less time they can
exist. So energy can arise out of nothing, therefore the universe could be one
big quantum vacuum fluctuation. The universe contains so incredibly much energy
that if it where a vacuum fluctuation it shouldn't have existed for billions of
years as it has? Energy has gravity and in physics you can say that gravity has
negative energy. This is seen when looking at an objects potential energy. If
you take a hamster and lifts him up on a cliff you will have expended energy
when you lifted him up, you therefore have given the hamster energy(since it was
he who benefited from you expending of energy), but when you then throw him of
the cliff the gravity will make him fall downwards. He will then loose the
energy you gave when lifting him up. Gravitation therefore has a negative effect
on the energy level(at least the energy level in a hamsters). So an objects
negative gravitational energy would cancel out it's own positive energy and
thereby creating a total energy level of zero. And if the total energy level of
the universe is zero it could exist forever.
Gravitation in general
relativity is bending of spacetime, if you picture a membrane and an object on
top of it which bends the surface of the membrane you have a pretty good picture
of spacetime. So it is this bending that would cancel out an objects positive
energy and create a total energy of zero. What happens if the universe already
is bend(a possibility)? Then there would be a surplus of negative energy that
eventually would be forced to disappear and therefore the universe would be
forced to collapse. So if the universe is flat it can exist forever, but if
it is bend it will disappear. And there has been recent measurements of the
background radiation using a satellite named COBE, and it was found with a high
degree of accuracy that the universe is flat. A flat and a bend universe would
give different results at measurements of the background
radiation.
Another interesting(although somewhat speculative) idea about
the creation of the universe is that it has arose when a black hole was created
in another, already existing, universe. The collapse of the star that creates a
black hole in our universe could be an expansion in another. This also is in
line with string theory(se below).
In the wake of string theory(a new
theory which unifies general relativity and quantum mechanics) a couple of new
proposals for the creation of the universe has arisen. Though they are mainly
for explaining what's behind the creation of the universe, what came before and
to find an alternative to the inflation model, so large parts of the big-bang
model is intact in these theories:
The Pre-big-bang model:
Instead of starting with a universe that is: hot, filled with matter and who's
spacetime is highly bend(because of the mass being very tightly confined), one
begins with one that is: empty, cold and flat. Instead of a universe that is
very fine tuned for life, this pre-universe isn't stable. These instabilities
leads to that an expansion can occur spontaneously in different parts of this
universe. The possibility is then that we live in such a place where an
expansion has occurred spontaneously. In this way you get inflation "for free",
and the need for fine tuning isn't necessary either since the inflation period
is limited by properties in the previously existing universe. Although there has
now been found things pointing towards that also this model needs fine tuning,
because the universe must be almost completely flat for the inflation period to
last the "right" amount of time.
The Ekpyrotic universe: It seems
string theory predicts the existence of parallel universes. This model is based
on two such universes existing next to each other. Through an instability in one
of them, a piece of it is ripped off and starts to move toward the other
universe. When the piece hits the other one energy is created in the collision,
the piece and the universe it hit fuses together and the normal big-bang model
takes over. Inflation isn't needed here since the collision that created the
universe had the same effect everywhere, which leads to that all parts of the
universe should have got the same temperature. This model is called the
Ekpyrotic after the old Greek model of the universe, in which it was destroyed
and recreated regularly by a big fire. The process is called Ekpyrosis. The name
is fitting since there's nothing stopping a new piece from another universe to
get ripped off and colliding with our universe again. This would annihilate ours
the way we see it today and start everything over from the big-bang stage.
If we now move on to the fate of the universe it is very uncertain. It
seems like everything will get darker and eventually completely dead. This is
because of the second law of thermodynamics. Which states that the entropy in a
closed system always rises. Entropy is a measurement of disorder, so then the
entire universe should end in chaos. This means that everything should be
dead. In stars and galaxies, which are energy rich, entropy is lower then it
would be if everything was dead and "burned out". But we can't be certain on
this; thermodynamics is pretty old and it has been found in newer theories that
the second law is broken in some situations.
Another possibility for
complete destruction of the universe is false vacuum(with all these
possibilities for apocalypse it's strange that the suicide rate for astronomers
aren't extremely high). It's stated above that in the beginning the universe had
more energy the it should and that this wasn't stable, which lead to that the
energy level was forced to drop. It is then possible that the universe today
also has an energy level that is larger then it should. This false vacuum should
also be forced to disappear and when it disappeared the energy level of the
entire universe would drop, which leads to that matter would decay and force
fields be weakened. This would, to say at least, not be such a good thing for
life.
The fate of the universe will depend heavily on: Dark matter and
Quintessence.
Dark matter: The universe doesn't contain enough
matter. E.g stars orbits around galaxies to fast and galaxies wouldn't hold
together at all if they only contained the visible matter. More matter is needed
who's gravity could accelerate stars and hold the galaxies together. Since we
don't see this matter it's called dark matter(and it also sounds cool). Dark
matter could be made up by different "kinds" of matter: MACHOS(MAssive
Compact Halo Objects): Could be matter that we're used to, i.e made up by
protons and neutrons. This could be ordinary, although dark, celestial bodies
such as meteorites and black dwarfs(which is what is left after a small star
dies) WIMPS(Weakly Interacting Massive Particles): Exists so
far only in theory. Could possibly constitute a large part of the dark matter,
but they would only communicate weakly with ordinary matter(weakly interacting)
and so with our measuring devices and should therefore be hard to
find. Neutrinos: These are known to exist. Neutrinos have a very small
mass, but on the other hand there are very many of them so it evens
out. Parallel universes: Again string theory. The dark matter doesn't
have to exist in our universe, instead it could be the matter in another
universe which exerts a gravitational pull on the matter in ours. This could
also explain why the dark matter seems to be gathered in rings around galaxies.
Gravitation pulls two masses together, two masses in different universes would
then lay as close to each other as they could. Picture two sheets of paper as
two universes. Two galaxies in them would then lay themselves on top of each
other. This leads to that(as seen from our universe) the galaxy in our universe
will block out most of the galaxy in the other universe, so we only notice the
gravitation in the outskirts.
Quintessence: Comes from the Greek
word for the fifth, perfect, element. It has recently been found that the
expansion of the universe is accelerating! This wasn't expected, instead it has
been believed that the expansion would slow down because of the gravitation
between the objects in the universe that constantly tries to pull them together.
So the main question has long been if there's enough matter in the universe to
one day turn the entire expansion around and make it start to contract to a
big-crunch or if there's to little so that the universe always will continue to
expand but in a decreasing rate. But that it's now expanding in an accelerating
fashion suggests that there's some new kind of force acting as an anti gravity.
This force would also have the properties that it should increase over time,
again in contrast to gravity in the universe that decrease as the matter spreads
out. This doesn't mean that the universe will expand forever; quintessence seems
to be able to change over time so it could get "normal" gravity and we would end
up in a big-crunch. But so far nobody even knows what quintessence is.
References: Books: Brian Greene: The elegant universe. Stephen
Hawking: A brief history of time. Steven Weinberg: De tre första
minuterna(The first three minutes). Internet pages: Inflation for
beginners. (http://www.biols.susx.ac.uk/home/John_Gribbin/cosmo.htm) The
self reproducing inflationary
universe. (http://www.sciam.com/specialissues/0398cosmos/0398linde.html) Others: A
simple/short introduction to pre-big-bang physics/cosmology. (arXiv:
hep-th/9802057) The Ekpyrotic universe: Colliding Branes and the origin of
the hot big bang. (arXiv: hep-th/0103239)