< 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.


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.

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.
The self reproducing inflationary universe.
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)

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