Modern cosmology is based on the American astronomer Edwin Hubble's discovery in 1929 that all galaxies are receding from each other with velocities proportional to their distances. In 1922 the Russian astronomer Alexander Friedmann proposed that the universe is everywhere filled with the same amount of matter. Using Albert Einstein's general theory of relativity to calculate the gravitational effects, he showed that such a system must originate in a singular state of infinite density (now called the big bang) and expand from that state in just the way Hubble observed. Most astronomers today interpret their data in terms of the big bang model, which in the early 1980s was further refined by the so-called inflationary theory, an attempt to account for conditions leading to the big bang. According to the theory, the big bang occurred 10 to 20 billion years ago. The discovery in 1965 of cosmic background microwave radiation, a faint glow or radio transmission almost identical in all directions, fulfilled a prediction of the big bang model that radiation created in the big bang itself should still be present in the universe.
In the early universe only small circles can be made in a very dense curved space. It seems odd, but if you try to draw a straight line in a closed circular universe you quickly come back to the place the line started. As the universe expands outward, the largest possible circle expands. You can imagine the growth of the universe as small circles which grow to become very large circles.
As these large circles grow unimaginably vast, a line through space, even out between the galaxies, seems as if it is perfectly straight, even though deep outer space is still slightly curved by the galaxies. Two parallel straight lines will not stay parallel. The lines will converge or diverge depending upon the actual kind of curvature. Similarly, the surface of the Earth seems flat to us, but we know it is round. Presently the whole known universe is curved in some way. We know with certainty that there is actually no such thing as a straight line, anywhere in the universe. It is simply impossible for a line to be perfectly straight in a universe full of massive objects.
In a way, you might imagine that space can relax or unravel, like a rolled up sleeping bag that is laid flat. One could say the unraveling or relaxing of curved space literally creates the Big Bang and causes the universe to expand. A space that was once extremely curved is now slowly becoming increasingly flattened out like a rolled out sleeping bag.
With space always becoming less round and less curved as the universe expands, the large-scale topology of the whole universe is flattening out. When space is perfectly flat, all lines are perfectly straight. Two parallel lines would then always be parallel. So, as the universe becomes larger, as it unfolds, its internal space is gradually becoming more like the spatial contents of a perfect square or a flat plain. Flat space would extend in all directions.
A perfectly flat space is very unique. There are strict rules about flat space. First, flat space has no things or objects in it. It has absolutely no stars, planets or even atoms in it. You cannot move through it, because you are physically made of matter and matter cannot exist in a flat space. Second, a perfectly flat space extends infinitely in every direction. All straight lines in flat space extend infinitely. Therefore a flat universe is open, not closed like a curved universe can be. If you could somehow travel in such a space, you would travel forever without returning to the same place. Last rule, if you do add any object or thing into flat space, that object would instantly add curvature to all space everywhere within the temporal boundaries of that object. The object would naturally create a gravitational field which would curve the universe and destroy the perfect flatness.
A perfectly flat space is the other extreme of possibility, opposite to infinite density. It is space, so it isn't nothing, but such a space is what we normally would imagine nothing to be like, since flat space is perfectly empty of things. Again, there is just a simple logical conclusion being made. No space could be flatter (or emptier of objects) than a perfectly flat space. And again, it does not matter whether or not our universe ever becomes flat. Flat space is still the extreme limit of what is physically possible of space.
So, space can have positive curvature the same way the Earth does, it can rap around on its self, it can have negative curvature, it can rap away from its self, or it can be flat, that is it is normal and behaves the way you would expect it to and it turns out theorists like this, they like things to be simple and they want the universe to be flat.
Suppose that all the matter detected to date in the universe is all that exists. There would be an average of only about one atom of hydrogen--the most abundant chemical element in the universe--in each 10 cubic yards (7.6 cubic meters) of space. Under these conditions, the universe would be open. According to Einstein's theory, an open universe has an infinite volume and an infinite number of hydrogen atoms. The universe would continue to expand indefinitely and would approach zero density at an infinite time in the future. In the far future, only galaxies in the local supercluster would still be nearby. All other galaxies would have receded to great distances. Eventually, all the stars would have exhausted all the energy that makes them shine, so they would be dark.
On the other hand, large amounts of matter may exist in space in some form that has not yet been detected--called dark matter. If the average density of matter in space were as much as 100 atoms of hydrogen in each 10 cubic yards (7.6 cubic meters), the universe would be closed. According to Einstein's theory, a closed universe has a finite volume and a finite number of hydrogen atoms. At some time in the future, perhaps 20 billion to 40 billion years, the expansion would stop. The galaxies would start to come together again, and matter would approach infinite density. This collapse might be followed by another period of expansion, and so on without limit.
Closed: This is a heavy universe; that is, this is material where gravity is caused to bend in on its self.
Open: This is a light universe, this doesn't have much in it and space sort of bends away from its self
Flat: This is somewhere between heavy and light, having zero curvature, which is as the theorists say is just right.
We saw that there was a minimum velocity below which an object could not leave Earth. Above the escape velocity, an object travels on forever; below it, it returns. Now the Big Bang resulted in a cloud of matter and radiation, which we call the universe, spreading outward and continuing to do so until today. For any object, say a planet or a star, there is a net gravitational force exerted on it by all the other objects, and tending to slow it down and pull it back to the center of the universe, wherever that may be. There are two extreme possibilities concerning the future of the universe. One is that the gravitational pull of matter will eventually bring expansion to a stop. In other words, the escape velocity is too great for the expansion to keep going. Just as the stationary arrow at the top of its vertical flight starts to fall back to Earth, so the universe will slow down, an when it is stationary it will start to contract. Finally, so this plot goes, the universe will return to being a tiny, immensely compressed ball. This is the Big Crunch, and a universe that expands and then collapses is termed a closed universe.
An alternatively scenario is based on the assumption that the mass of the universe is not enough to stop eternal expansion and it will go on forever: It will "escape." This is an open universe. In which universe are we living? The answer depends on how much mass there is. When a rough estimate is made, on the basis of the visible objects in the cosmos, it is clear that the mass is far too small to prevent eternal expansion: the universe should expand forever. But what does that theory say?
The equations of general relativity, which formed the basis of the standard model of the Big Bang, do not in themselves contain a prediction of the amount of matter in the universe, any more than Newton's laws of motion tell us what the mass of the Earth is. It is Guth's addition of inflation that alters things. A theory might give a vast range of answers to the question of how much mass the universe contains. The one obtained when inflation is taken into account is extraordinary. The answer is that the universe is neither open or close: it is flat, which is the formal way of saying that the mass is just enough to prevent infinite expansion but not enough to result in eventual contraction. The mass needed for this delicate balance is called the critical mass. The prospect for us is that the present rate of expansion will get slower and slower, approaching zero but never quite reaching it. The calculation gives a density for the present universe of about 10
Experiment says that there is not enough observed mass to stop the universe expanding forever. Theory says that there is. Now we can tinker with the theory in order to convince it to give us the amount of matter that we have observed in the universe, but then we loose two other accurate predictions because the CBR, the hydrogen helium ratio, and the critical mass come as one indissoluble package that emerges conveniently from the theory. Another, Baconian, point of view is to give observation precedence and admit that the calculation could be wrong and the universe is really going to expand endlessly. The theoreticians are stubborn, and on the whole they prefer to cling to the theory and look for the "missing" matter which has come to be known as dark matter.
I think Stephen Hawking puts it best when he says that "according to the no boundary proposal, the universe would have expanded in a smooth way from a single point. As it expanded, it would have borrowed energy from the gravitational field, to create matter. As any economist could have predicted, the result of all that borrowing, was inflation. The universe expanded and borrowed at an ever increasing rate. Fortunately, the debt of gravitational energy, will not have to be repaid until the end of the universe."
A successful creation of a universe from the cosmic foam will not necessarily grow to resemble our universe. With different forces and particles, it may create some very alien objects. If this theory is true then one day our expanding universe may collide into another universe. No one is sure what the result will be.
Far from being merely cosmic sinks, black holes may give birth to other universes. "Baby" universes may "bud" off black holes to grow as universes in completely different dimensions with totally different properties. Depending on the amount of matter in each universe, they will be different sizes, but, like ours, will expand and contract and produce still more universes along the way.
If our Universe is a black hole, then it has a finite and predictable lifetime. At the Big Bang, the Universe starts expanding as a series of inflating balloons. The galaxies and the other constituencies of the Universe lie on the skin of the balloon, which represents space and carries the galaxies apart as it swells. The history of the Universe is shown on successive strips of the balloons. The Universe expands until it reaches its maximum size; then gravity wins over the momentum from the big bang. The Universe begins to contract. The galaxies move closer together and collapse into another singularity the Big Crunch.
Black holes and Big Crunches can both provide "budding sites" where new universe can start. From the universe, they can spawn a network of independent universes. Although each baby universe is different, it will inherit some of its parents "genes." This be how our universe came to be. American cosmologist Ed Harrison even suggests that our Universe is so ideally suited for the development of intelligent life that it may have been created by an advanced civilization in another universe. Perhaps the scientists in that universe reached the stage of making black holes in the lab, and one budded off to become our Universe. We may be just the result of someone's experiment.
Thus far, theorists have not been able to establish whether the universe will continue to expand forever. The problem centers on the amount of mass estimated to exist in the universe, because current estimates do not fit in neatly with other predictions of the big bang theory. Based on these estimates, gravitation is insufficient to halt the expansion. Some scientists, however, support the concept of an oscillating universe, which requires more mass than current estimates support. They suggest that the missing mass exists in intergalactic space or in black holes. Another theory is that the supposedly massless elementary particle called the neutrino actually does have mass. Neutrinos flood the universe, so their total added mass could be sufficient to keep the universe expanding and contracting forever.
1: Either gravity will stop expansion and the universe will collapse in on itself. That now seems more unlikely than ever.
There is a modest number of convincing applications of chaos theory to real systems, including cardiac rhythms and certain chemical reactions. The theory is here to stay, and as computers become more powerful, it will be possible to tackle an in-creasing number of problems using models that are nearer to reality than humans maintaining their balance in life to a time until the sun explodes, which some people actually think is not just possible but likely.
Some would argue for the third possibility on the grounds that if there were a complete set of laws that would infringe Gods freedom to change his mind and intervene in the would. It's a bit like the old paradox; can God make a stone so heavy he can't lift it. But the idea that God might want to change his mind is an example of the fallacy of imagining God as a being existing in time, time is a property only of the universe that God created. Presumably he new what he intended when he set it up.
It has been pointed out that if the relative strengths of the forces in the universe had not been as they are, then life would never have developed. Furthermore, there is no priori physical reason for the universe to be as it is. If gravity had been somewhat stronger, the stars would have been compressed more strongly, and because collisions would have been more frequent, they would have burned out far quicker. The life of the universe might not have been ling enough to allow life to develop. If gravity had been somewhat weaker, the stars would never have formed no solar system, no planets, no Eve, no Adam. If the strong force had been a bit stronger, protons would be able to hang onto each other without the necessity of neutrons being around. The single proton, the nucleus of hydrogen, would have been unstable with respect to a double proton. Hydrogen would not have existed. If the strong force had been a bit weaker, nuclei would never have formed. The only chemical element in the universe would have been hydrogen - no life. In short, it looks like something of a miracle that the fundamental forces had the strengths that they did, strengths that appear to be almost essential for the existence of a universe conducive to the emergence of life.
Some cosmologists, notably Robert Dicke and Brandon Carter, have suggested that our own universe is uniquely tuned to produce life, the way a plant exists to grow a flower. We might be in effect the crown of creation. By this admittedly self centered logic, known as the anthropic principle, the universe is the way it is because we are here, but then why is the universe the way we see it? The anthropic principle has been developed into a variety of theses, each supported by all kinds of coincidences that shown not only to be highly improbable, but also to be conditions for the existence of life.
Several prominent physicists, including Steven Hawking, have pushed the idea, apparently first voiced in 1957 by Robert Dicke, that we are not dealing with luck here. Einstein wondered if God had any choice in the matter, so does the physicist John Wheeler, any universe without life," Wheeler suggests, "Is a meaningless one, an impossible concept." This extraordinary suggestion that a universe in which life could not develop would never have come into existence is commonly dismissed by many scientists. But one thing is certain: no one would have known if it had been created. The idea is related to those of another physicist, Robert Dicke, whose chain of reasoning starts with the question: If there is no one to see it, what point is there in being a universe? Thus, the condition for there being a universe is that there be a living creature capable of appreciating that the universe exists. In that case all the laws of nature and all the forces would have to be such that this cosmic super observer who is literally the center of the universe shall have evolved.
HMS may be unaware that sober scientists have this sudden urge to walk on the wild side. Their imagination has been stimulated in part by something intriguing (Pythagorean) relationships between the numbers that characterize the universe. A simple example resolves around the number 1039, which is roughly equal to the ratio of the electrostatic force between an electron and a proton to the gravitational force between them. But it is also roughly the ratio of the radius of the known universe to the radius of the electron and, lo and behold, when squared it gives 10
The anthropic principle and particularly the cosmic number game have provoked either the awe that comes from seeing the light, or the ridicule engendered by scientology.
We are rather certain that the time we measure with clocks had a beginning. But we don't yet fully understand the universe enough to be certain about the momentum of time, meaning we cannot answer questions such as "will the fourth dimension cease to exist some day?" So we aren't certain about the future, but he new data that tells us the rate of expansion is increasing is very powerful, but for now there are still a lot of unanswered questions.
Here are the last unanswered questions:
This Universe is
:
The following theories are subjected to very high levels of scrutiny to most if not all people who hear them, but seeing as how no-one really yet knows what it is that we live in these theories cannot yet be denied, weather they can be confirmed is another matter all together. The following are some general possibilities for what the universe is (excluding the main leading theories that have already been explained):
1. Cosmic Foam:
If you look at the surface of the ocean from an airplane it looks smooth. But view it from a rowing boat and the perspective is completely different there are huge waves, turbulence and all kinds of violent activity. It is just the same with space. Seen on the smallest scale of all around 10-33 cm, or less than a trillion-trillionth the size of an atom, it seeths and bubbles like billowing foam. This cosmic foam could be the source of countless baby universes that bubble up from nowhere. Most of them start to expand but never get further. Well before they reach even the size of a proton, they contract and vanish within a fraction of a second. Each is a tiny closed universe in its own right. But if a universe manages to undergo inflation it is set for a long future.
The process goes like this:
1st: The multi dimensional foam bubbles with baby universes. Most expand for a fraction of a second before collapsing and disappearing.
2nd: Our own universe manages to get further than its own siblings, and grows steadily.
3rd: Suddenly our universe inflates enormously, propelling its self into a dramatic phase of accelerated growth. After that its existence is guaranteed.
2. A Black Hole:
Some scientists have suggested that the entire universe is a huge black hole, of a rather different kind. It is not surrounded by an event horizon, but curves back on itself like the surface of a balloon. The result is the same: you cannot escape. The universe has no central singularity. Instead, it had a singularity in the past, the Big Bang in which the universe began and it may collapse back into a singularity in the future, the Big Crunch. The theory links black holes and universe so closely that it predicts a black hole can actually create a new universe.
The Beginning, of a black hole universe:
No one knows what caused the Big Bang: it may have been fluctuations out of literally nothing. Fractions of a second afterwards, the temperature and density in the cosmic fireball were almost infinite. In the inferno, dozens of strange particles were created which, as the universe cooled and expanded, formed the nuclei of the first atoms. Around 2 billion years later, these crumpled together to make quasars violent young galaxies with black holes in their hearts. Meanwhile the universe continued its expansion.
The End, of a black hole universe:
After perhaps a million million million years gravity will draw everything in again the Big Crunch. About a year before galaxies will collide, and the temperature of space will rise to higher than the surface of a star. An hour before, supermassive black holes in the centers of galaxies will merge and the universe will dramatically collapse into a point of infinite density.
3. A Grey Hole:
As well as black holes and white holes, relativists sometimes talk about 'grey' holes. A black hole is an object into which matter and radiation fall, but nothing escapes. A white hole is an object from which matter and radiation escape, but nothing falls in. A grey hole is an object from which matter and radiation escape, rise to a certain distance above the event horizon, and then fall back in. And because this is rather like the description of the universe, as emerging from a big bang, expanding for a while and then contracting into a big crunch. Some people think we live in a grey hole.
The End:
There are four general possibilities for the end of the universe:
2: Perhaps space will expand forever, becoming nearly flat but never perfectly flat. That theory also is now in question if the rate of expansion increases.
3: Or, maybe there is something we haven't learned yet about the universe that allows space to unfold completely so that time as we know it ends perfectly flat.
4: But, if the measurements of modern-day scientists are correct then the universe has infinite size, but we can never see it because it is expanding away from us at always increasing speeds, it will last forever. This immortal universe will continue to expand faster and faster until the entire universe has expanded beyond our ability to see it. This would be my best guess.
Practical Chaos:
Of what practical significance is the study of chaos? The distinguished Belgian physicist David Ruelle, the "inventor" of the strange attractor, has said, "The physics of chaos, however, in spite of frequent triumphant announcements of 'novel' breakthroughs, has had a declining output of interesting discoveries." The initial excitement has cooled slightly. The realization that nature is replete with nonlinear systems and that some of them display chaotic behavior encouraged those in the field to think that chaos theory could be fruitfully applied to an enormous range of problems. It is possible that it can, but although it has had some fascinating successes in some fields, the complexities of many systems frustrate the easy application of theory. But the general feeling is that it will find more and more applications. The scientifically important fields in which attempts have already been made to use the theory include weather prediction, astronomy, certain chemical reactions, the nature of turbulent flow, medical statistics, electronics, mechanical engineering, and the behavior of biological systems. It is even intruding into economics, where 1 suspect that it has a natural home. The movement of some asteroids has been shown to be chaotic - their orbits are unpredictable. The same is true of the planet Pluto, and in a very muffled way of the whole solar system. The physical reason is the fact that the paths of all the bodies in the solar system are affected by several other bodies. We have seen that an attractor can be localized in a region of space. Our luck is that the attractors for the chaotic motion of the planets are quite limited in extent. In the past, some asteroids, which circulate mainly in a dense belt between Jupiter and Mars, seem to have had large attractors; in other words, their orbits were "wild." The spatial spread of the attractor depends on the forces on the asteroids, and those whose orbits were in a certain relationship to that of Neptune displayed chaos dramatically enough to have left their companions, most of whom continue to circulate in reasonably settled paths. Their original orbits are empty, and the asteroid band has gaps in it that were previously a mystery but are no longer.
Unified Field Theory:
Einstein's general theory of relativity did not completely satisfy him because it did not include electromagnetism. Beginning in the late 1920's, he tried to combine electromagnetic and gravitational phenomena in a single theory, called a unified field theory. Einstein failed to establish a unified field theory, though he spent the last 25 years of his life working on it. Toward the end of his life, he remarked that it would be worthwhile to show that such a theory did not exist. He worried that if he neither produced a theory nor showed that one was impossible, perhaps no one ever would.
But is there really a complete unified theory of physics. There seem to be three possibilities:
1: There really is a complete unified theory, which we will some day discover if we are smart enough.
2: There is no ultimate theory of the universe, just an infinite sequence of theories that describe the universe more and more accurately.
3: There is no theory of the universe, events cannot be predicted beyond a certain extent, but occur in a random and arbitrary manner.
Was the Universe made for you and me:
Newton's demonstration that the gravitational constant, G, applied to the solar system as well as to gravity on Earth, was quoted as proof that there was one supreme designer. In recent times scientists have found what some see as convincing evidence for more than chance in the structure of the universe.
The question of why the universe is the way it is is far from trivial. Thus all electrons have the same mass. Why? And why that particular mass? And what determined the ratio of the gravitational to the electromagnetic? Again the simplest answer is: that's how it happened, but this is not satisfactory.
We don't understand the mechanism by which the hosts of elementary particles turned out to be like the standardized products of a production line rather like the idiosyncratic pebble on a beach.
Time No Longer:
The scientific community is slowly realizing the significance of this new information. There were previously only two major cosmological models of the future. One main theory, the Big Crunch model, predicted gravity would win the battle and bring the universe crashing in on itself. The other less talked about theory, the Heat Death scenario, predicted the universe would expand at a decreasing rate forever.
This new data destroys the Big Crunch idea, and endless expansion may not be an option either. The issue now becomes how long and how far can the universe expand. Here are just a few of the new questions:
Can an increasing rate of expansion continue forever? If not, is there an omega point. Is the universe expanding toward an extreme state? What will increasing expansion do to the stars, galaxies and all matter? Will time end? If so, what kind of state will the universe end up in?
Will the universe collapse inward? Or will space continue to expand forever, making ever larger circles. Or is it possible that the universe will one day finally stop, and ordinary time, or the time we measure with clocks will end?
So far we have only been able to speculate on these matters and we probably will not get much further than that.
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