272 Time Englisch 10 2+ 1759
Kurzbeschreibung
Time (Einstein, Time Travel, Star Trek...)
Inhalt des Referats
Time

1) Time is an Arrow

Seeing Things Different

The Last Century
The Beginning of Time
Sensing Time
The Arrows of Time
Which Direction?
Intelligent Life
A fourth Arrow?

Summary

2) Relativity of Time

The Beginning
Einstein's Start
It's all Relative

Einstein
Day-to-Day Experiences
A Clue
The Solution
Light

Einstein's Dreams

Plot
Results

New Findings
Consequences
Faster than Light

General Relativity

A Solution
The Trojan Horse
Questions

3) Space and Time

A Brief History of Time

Sinking into Space-Time

Einstein
The Universe as a Sheet
Einstein as Idol
Dynamic Space and Time
Gravitational Effects
Solutions?
A Unifying Theory
Dreams
The Physics of Star Trek

4) To Build a Time Machine

The First Thoughts

Change Time
The Time Machine
Time Travel
Introducing a New Theory

Problem: Time Travel

The Risks of Time Travel
My Favourite

Creating the Impossible?

Theoretical Basis
Multiply Connected Universes
Time Travel and Baby Universes
Inside Out

Conclusion

Introduction

Scientific revolutions, almost by definition, defy common sense.

If all our common-sense notions about the universe were correct, the science would have solved the secrets of the universe thousands of years ago. The purpose of science is to peal back the layer of the appearance of objets to reveal their underlying nature. In fact, if appearance and essence were the same thing, there would be no need for science.

Perhaps the most deeply entrenched common-sense notion about our world is that it is three dimensional. It goes without saying that length, width, and breadth suffice to describe all objects in our visible universe. Experiments with babies and animals have shown that we are born with an innate sense that our world is three dimensional. But to record all events in the universe, we need another dimension. If we include time as another dimension, then four dimensions are sufficient. No matter where our instruments have probed, from deep within the atom to the farthest reaches of the galactic cluster, we have only found evidence for these four dimensions.

Time is a very complex dimension. So not only in science, thus also in common usage, time is hard to understand. There are so many possible meanings implied.

What time really is, nobody truly can tell, but scientists try their hardest to find answers to their unanswered questions. In this Special Topic "Time" I would like to give an idea of the momentary situation science is now, and show some possible answers from some of the brightest minds of mankind.

But also scientists do not agree in every respect. They try to fit all their observations in formulas they again try to combine all to get a unifying theory about the smallest and the largest things in our universe we live in.

The aim of science is to penetrate into smaller and bigger dimensions and not to stop until humankind has a complete theory of all forces and particles that appear in nature.

Like Thomas H. Huxley once said, The known is finite, the unknown infinite; intellectually we stand on an islet in the midst of an illimitable ocean of inexpl- icability. Our business in every generation is to reclaim a little more land.

On the next pages I would like to give an easy understandable, brief description of what time is considered to be and want to try to uncover some secrets of Time

1) Time is an Arrow

Seeing Things Different

The Last Century

Before the 20th century, Newton's laws belonged to the basis of physics. But at the end of the 19th century there were discovered two conflicts, with thermodynamics and electro-magnetism, that ultimately led to the formulation of first the theory of relativity and then the quantum theory. Einstein told us that space and time were part of a four-dimensional space-time and both relative. He was the first to count these to physics instead of accepting it as simply “existing”. When it was later discovered that the universe is expanding, scientists quickly realised that everything had to start existing at a certain point in the past, known as the “Big Bang”.

The Beginning of Time

At the Big Bang the universe's density was infinite. Under such conditions all the laws of science, and therefor all ability to predict the future, would break down. If there were events earlier than this time, then they could not affect what happens at the present time. Their existence can be ignored because it would have no observational consequences. One may say that time had a beginning at the big bang, in the sense that earlier times simply would not be defined.

Sensing Time

We are creatures in time and this has a very great effect on how we think about time and the temporal aspect of what is real.

The psychological time is very much different from the physical one. It seems that we are not able to perceive too short events, and that our brain manipulates our perceptions before they become conscious. Based on experiments, psychologists therefore suggest that our consciousness is a whole bunch of parallel processes.

People seem to sense time in a very subjective way, a fact that is in conflict with an universal time. In other cultures, like the Aborigines, there is not even a clear distinction between past, present and future. But the latter vanished in physics too, with the invention of relativity.

Many religions and philosophers believe in a cyclic time, and they are consistent with some scientific theories. Laplace first realised that when everything is predictable, knowledge of the moment is enough to know the situation in every moment, also in the future, thus making time obsolete.

The Arrows of Time

With the laws of thermodynamics physicists then realised that the universe is developing towards maximal entropy, or chaos. This made the perpetuum mobile impossible and put an end to Newton's linear time. It also brought an arrow of time into physics. Based on Boltzmann´s work Poincaré then proved the possibility of a cyclic universe, but with cycles being incredibly long.

Religions like to believe in creation, which cannot be proven to be wrong. The P'an Ku myth of China's third century describes the time before creation like that:

In the beginning, was the great cosmic egg. Inside the egg was chaos , and floating in chaos was P ' an Ku, the divine Embryo.

In India's ninth century, the Mahapurana, one of the most important books was written. In this book, the beginning of time is described as follows:

If God created the world, where was He before Creation?... Know that the world is uncreated, as time itself is, without beginning and end.

It is not entirely impossible that we all live only since some minutes ago, created with memories of past times. Seen out of this respect, the flow of time can never be proven, and time itself may as well be an illusion.

Which Direction?

The increase of disorder or entropy with time is one example of what is called an arrow of time, something that distinguishes the past from the future, giving a direction to time. There are at least three different arrows of time.

First, there is the thermodynamic arrow of time, the direction of time in which disorder or entropy increases. Then, there is the psychological arrow of time. This is the direction in which we feel time passes, the direction in which we remember the past but not the future. Finally, there is the cosmological arrow of time. This is the direction of time in which the universe is expanding rather than contracting.

The psychological arrow is essentially the same as the thermodynamic arrow, so that the two would always point in the same direction.

Intelligent Life

The no boundary proposal for the universe predicts the existence of a well defined thermodynamic arrow of time because the universe must start off in a smooth and ordered state. And the reason why we observe this thermodynamic arrow to agree with the cosmological arrow is that intelligent beings can exist only in the expanding phase of our universe.

However, a strong thermodynamic arrow is necessary for intelligent life to operate. In order to survive, human beings have to consume food, which is an ordered form of energy, and convert it to heat which is a disordered form of energy. Thus intelligent life could not exist in a contracting phase of the universe. This is the explanation of why we observe that the thermodynamic and cosmological arrows of time point in the same direction.

The contracting phase will be unuitable because it has no strong thermodynamic arrow of time.

A fourth Arrow?

Some scientists interpose a fourth arrow, an arrow that helps to explain the causal asymmetry. We use "cause" to mark the earlier and "effect" to mark the later of a pair of events which are related this way. Cause-effect relation is itself asymmetric - that is, that causes and effects can be distinguished in some way.

Scientists are everything else but the same opinion in which direction they themselves should research to find answers to the questions the arrows and the asymmetry of time pose to us. In the respect of the increasing disorder in the course of time, James Thurber was right as he said:

"It is better to know some of the questions than all of the answers."

Because the more answers we find the more questions arise.

Summary

Up to the beginning of our century people believed in an absolute time.

Newton considered time to be moving like a straight arrow, which unerringly flies forward toward its target. Nothing could deflect or change the course of this arrow once it was shot. Einstein, however, abandoned the idea of an absolute time and showed that time was more like a mighty river, moving forward but often meandering through twisting valleys and plains created through matter on a space-time surface. The presence of matter or energy might momentarily shift the direction of the river, but overall the river's course was smooth: It never abruptly ended or jerked backward.

However, successors like Kurt Gödel or Louis Tamburino showed that the river of time could be smoothly bent backward into a circle. Rivers, after all, have eddy currents and whirlpools. In the main, a river may flow forward, but at the edges there are always side pools where water flows in a circular motion.

2) Relativity of Time

Newton's laws of motion put an end to the idea of absolute position in space. The theory of relativity put an end to the idea of absolute time, so any observer can work out precisely what time and position any other observer will assign to an event, provided he knows the other observer's relative velocity. (they are related)

Nowadays we use just this method to measure distances precisely, because we can measure time more accurately than length. In effect, the meter is defined to be the distance travelled by light in vacuum in 0.000000003335640952 seconds, as measured by a caesium clock. So, we must accept that time is not completely separate from and independent of space, but is combined with it to form an object called space-time. (more later)

The Beginning

I want to know how God created this world. I am not interested in this or that phenomenon. I want to know His thoughts, the rest are details.

Albert Einstein

Einstein's Start

When Einstein was born, Newton's theory led to absurd results for the movement of light, leading him to postulate the relativity of time and to set the speed of light as the highest one possible.

Early on in physics, scientists invented an ether to explain the characteristics of light. But Michelson and Morley proved this idea ultimately wrong. This led Einstein to the idea that neither space nor time are fixed. His theory of relativity has been proved often since, as an example with the help of pulsars, and turned out to be right. The speed of light being the absolute top causes time dilatation effects, which allow us to observe myons. But this effect also causes the twin paradoxon, which is absolutely possible on closer examination, and it puts an end to a definite present.

This paradoxon is one of the best known world-wide. It describes twins, one staying on earth the other twin making a journey in a rocket travelling with a velocity near the speed of light. They were exactly the same age when the brother departs but when he comes back after 50 years, the brother that stayed is older than the one that went with the rocket. For the one that lived on earth all the time, 50 years had gone by, whereas for the other one in the rocket, just 5 or 10 or 13 years had passed. (dependent on the velocity he travelled)

It is not that the one in the rocket lived 50 years and got only 13 years older; He lived just 13 years in the rocket. For him and all the watches on board only 13 years passed. And for his brother and all the watches placed on earth 50 years passed. Both of them are right.

That time is not a constant but dependent on the velocity of the system in which it is measured, is an assumption of Albert Einstein. Meanwhile there are very exact atomic clocks that proof his assumption as true.

Einstein's idea was that if the speed of light appeared the same to every observer, no matter how he was moving, another factor has to be variable, what led him to the theory of relativity. And this factor is the velocity with which time goes by, to say, time itself. Out of this thought follows that clocks, carried by different observers, would not necessarily agree.

Seen from an observer outside of the moving system, this interesting effect in the flow of time is called time dilatation. The nearer to the speed of light you get, the slower time goes by.

If an object moves with 100% lightspeed, time would stand still; and the mass would get infinite. That is the reason why travelling with speed greater than the one of light is impossible. The spaceship would have to get through the barrier of infinite mass and no time passing by, the so-called light barrier. The second problem is the slightest problem for the person travelling in the rocket. For his point of view the flow of time is constant all the journey long! He just would not find the same persons he left when he comes back. They will all be dead since millions of centuries.

So if one does not like his century, travelling near the speed of light would offer a realistic possibility to jump into the next without a worth mentioning loss of time.

In this respect the advertisement slogan of Swatch, now seen from another background, gets a completely new meaning:

"Time is what you make of it!"

It's all Relative

Both Aristotle and Newton believed in absolute time. That is, they believed that one could unambiguously measure the interval of time between two events, and that this time would be the same whoever measured it, provided they used a good clock. Time was completely separate from and independent of space. This is what most people would take to be the common-sense view. However, we have had to change our ideas about space and time. Although our apparently common-sense notions work well when dealing with things like apples and planets that travel comparatively slowly they do not work at all for things moving at or near the speed of light.

Einstein

Einstein had worked as a patent officer in Berne, in Switzerland, to earn a living and pay for his academic work while he wrote up his ideas about the laws of physics. In doing this he was rapidly becoming known as the visionary scientist of his time. His first major work was published in 1905, the first of two Theories of Relativity. It is called special Relativity; and the later theory, published in 1915, is called General Relativity. The fundamental postulate, we recall from our time at school, was that the laws of science should be the same for all freely moving observers, no matter what their speed. Both deal with the way an observer and the event he or she observes are related; Special Relativity essentially spells out what happens when there is a constant movement linking the event and the observer, and General Relativity brings in gravity. It also suggests what happens as the speed of any movement increases or decreases. The idea included also the speed of light: all observers should measure the same speed of light, no matter how fast they are moving. This simple idea has some remarkable consequences which I will describe later on.

Day-to-Day Experiences

They are both still very difficult theories to understand fully, but they are nevertheless widely acknowledged as the ideas which placed Einstein on the scientific world stage. Einstein did not set out specifically to explain the nature of time or the universe, but his theories inevitably interested many scientists, because he was in effect rewriting the laws of physics which had been left unchallenged since the time of Newton.

Einstein argued that the laws of physics must be the same, from whatever position they happened to be observed. This idea stemmed from the insight that the same event can appear different to two different observers, depending on their relative positions.

Several day-to-day examples have been suggested to help illustrate the point. One that most of us have experienced at some time or another is when two trains stop alongside each other in a railwaystation. You can be sitting on one train, looking out of the window at the other train, when it seems to move off. For a second or two you are not sure whether it has in fact started to move, or whether it is your own train which is moving off. All you know is that one train must be moving relative to the other; hence Relativity.

Now imagine a situation where one observer is on board a train another is on a railway station platform as the train rushes by. A cup on a table in front of the man on the train will appear to stay 60 centimetres in front of him. So, from his point of view, it will not be moving. However, to the man on the platform who watches the passing carriage windows, the cup will be seen to rush past at great speed as the train hurtles through the station.

A Clue

Einstein's great insight was that the laws of physics had to be rewritten in such a way that the laws of motion would be recognised as being consistent. They would have no account for related concepts such as acceleration and momentum, which were involved in these apparently different views of the cup. And this meant understanding the nature of time and space, and how they affect things.

After all, what causes two different views of the cup are the different positions of the observers relative to the cup in time and space. One is travelling through time and space alongside the cup, so that its relative position is always 60 centimetres in front of him; it stays in his field of vision as long as they are both travelling through time and space in an identical fashion. The other observer is, by comparison, stationary in time and space relative to the moving cup, so that it comes into and moves out of his field of vision in a very short time.

The Solution

Einstein developed mathematical equations to describe these kinds of relationships. Taken together, they defined the nature of time and space; and they had momentaneous consequences for cosmologists. To begin with, it emerged that time and space were mathematically one and the same thing. And, as a consequence, Newton's explanation of gravity had to be totally revised, accurate as it seemed to be.

But more to this in the next chapter about 'Space and Time'.

Light

Contemporary physics states that no object should be able to travel faster than the speed of light

c = 299'792'458 metres per second.

Although the value of c appears enormous when compared with conventional travelling speeds, it suggests a limit which renders a practical realisation of interstellar travel improbable. Whereas another planet in our solar system is reachable within minutes or at least hours at the speed of light, a journey to the nearest star system Alpha Centauri would already demand a travelling time of several years (4,2 Light-years). Surely, the question remains: Are faster-than-light speeds possible? At the present time most scientists believe that the correct answer should be "no". However, it has to be emphasised that there is no definite proof for this claim. Actually, whether superluminal speeds are possible in principle depends on the real structure of the space-time continuum. (more later)

Einstein's Dreams[1]

This book shows what would happen if time was no longer an arrow but anything else. There are several examples of different kinds of appearances of time like being like a stream of water, a circle or even parted in regions where in each time runs at a different speed.

Plot

It is a fiction book, endearingly short, airy and irrational, in simple and beautiful language. The science is gentle and it is cast in language to bring the flush of envy to any one of the many famous writers alive today who has coaxed himself into the delusion that scientists cannot write. It is a celebration of a world in which time does not march brutally through people's lives, but rather skips and gambles, forever quirky and unpredictable. Lightman is exploring fiction's deep space, taking us further than we are used to being taken.

The setting of the story is located in Berne, in Switzerland.

In this book Alan Lightman describes the dreams of Albert Einstein, a young patent clerk had between 14th April 1905 and 28th June 1905. Although the characters and situations in this book are entirely imaginary and bear no relation to any real person or actual happening, it is a breathtaking synthesis of science and imagination.

One witnesses Einstein's dreams of new worlds: extraordinary visions of the effect on people's lives when the direction and the flow of time changes to circular or flows backwards, slows down or takes the form of a nightingale.

In all dreams there are given examples, of how life changes when time is different, and most of them play in Berne, the city Einstein used to live.

The whole book is a flashback that starts after Einstein has finished his work. He reflects back on his time of creating the new theory of time. This ends two hours later. In those two hours Einstein reflects on the past several months, where he had many dreams about time. The book describes some of the dreams and tells the reader that those have taken hold of his research.

Out of many possible natures of time, imagined in as many nights, one seems compelling. Not that the others are impossible. The others might exist in other worlds.

Results

The result of all those dreams was the special theory of relativity. It was a completely new point of view. Although it cost Einstein a lot of energy, he believed that it was worth it. The picture of time that got its final shape while it was dreaming, was so obvious, so clear to him. Other people might also have such visions, but Einstein had the ability to write it down as a physical concept.

New Findings

Consequences

The essence of Einstein's equations is that the matter and energy content of an object determines the amount of curvature in the surrounding space and time.

Faster than Light

The question whether the speed of light is a true physical limit has no definite answer yet. It depends on the real structure of space-time. If there is an absolute time preserving causality (by preventing time-travel paradoxes), then faster-than-light speeds - and even faster-than-light travel - are possible, at least in principle. On the other hand, if superluminal processes are to be discovered, then absolute time will

probably have to be reintroduced in physics. Although the theory of special relativity states against absolute time and superluminal phenomena, it does it not by proof, but only by assumption.

Are there indications that absolute time and faster-than-light processes exist ? My opinion is "yes" !

The theory of relativity does not make faster-than-light moving completely impossible, it only forbids the crossing of the light barrier, thus principally allowing tachyons that always move faster than light, but are not manipulatable by us. Based on the equivalency principle and the Doppler effect Einstein concluded that also gravity influences light, putting an end even to sub-atomic perpetuum mobiles.

Another example where particles can travel faster than light is given in the quantum theory. There exists a phenomenon called the tunnel effect. It turned out that it is impossible to measure the length of the tunnelling time. Some other experiments also showed that one cannot determine which way a photon has taken in an experiment. The photons even seemed to communicate to each other faster than light! Quantum theory therefore proposes the concept of multiple realities.

General Relativity

A Solution

In 1949, Einstein was concerned about a discovery by one of his close colleagues and friends, the Viennese mathematician Kurt Gödel. Gödel found a disturbing solution to Einstein's equation that allowed for violation of the basic tenets of common sense: His solution allowed for certain forms of time travel. For the first time in history, time travel was given a mathematical foundation.

If one followed the path of a particle in a Gödel universe, eventually it would come back and meet itself in the past. He wrote, "By making a round trip on a rocket ship in a sufficiently wide curve, it is possible in these worlds to travel into any region of the past, present, and future, and back again."

His solution let time bend into a circle, called a closed timelike curve (CTC).

The Trojan Horse

Einstein's equations, in some sense, were like a Trojan horse. On the surface, the horse looks like a perfectly acceptable gift, giving us the observed bending of starlight under gravity and a compelling explanation of the origin of the universe. However, inside lurk all sorts of strange demons and goblins, which allow for the possibility of interstellar travel through wormholes and time travel. (more later)

The price we had to pay for peering into the darkest secrets of the universe was the potential downfall of some of our most commonly held beliefs about our world - that its space is simply connected and its history is unalterable.

Questions

But the question still remained: Could these CTCs be dismissed on purely experimental grounds, as Einstein did, or could someone show that they were theoretically possible and then actually build a time machine?

3) Space and Time

Because of the non-existence of an absolute rest, the lack of an absolute position in space and time is explained !

A Brief History of Time[2]

"A Brief History of Time" is a book that tries to explain the main theories of today physics in a quite "non-technical" language so everybody can understand them. This book starts at the beginning of science with the Greek philosopher Aristotle and goes on until the youngest theories about our universe like the superstring-theory which needs 10dimensions.

We go about our daily lives understanding almost nothing of the world. We give little thought to the machinery that generates the sunlight that makes life possible, to the gravity that glues us to an Earth that would otherwise send us spinning off into space, or to the atoms of which we are made and on whose stability we fundamentally depend. Except for children, few of us spend much time wondering why nature is the way it is; where the cosmos came from, or whether it was always here; if time will one day flow backward and effects precede causes; or whether there are ultimate limits to what humans can know. Was there a beginning of time? Could time run backwards? Is the universe infinite or does it have boundaries? These are just some of the questions considered in an internationally acclaimed masterpiece which begins by reviewing the great theories of the cosmos from Newton to Einstein, before diving into the secrets which still lie at the heart of space and time.

This book tries to answer at least some of these questions that can be answered now. To get some answers we can only follow the theories of Stephen Hawking, which are very good explained in his best-seller.

Sinking into space-time

Einstein

As I already mentioned, Einstein developed mathematical equations to define the nature of time and space. These equations had momentous consequences for cosmologists. To begin with, it emerged that time and space were mathematically one and the same thing. And, as a consequence, Newton's explanation of gravity had to be totally revised, accurate as it seemed to be. Einstein argued that two objects do not directly attract each other as Newton has thought; rather, each of the two objects affects time and space, and any gravitational effects are a consequence of this. That was the moment when he found out that space and time are warped.

The Universe as a Sheet

If this concept is difficult to grasp, imagine a heavy object (such as a cannon ball), representing the sun, being placed in the middle of a taut rubber sheet [{ einfügen Bild in files }], creating a cone-shaped dent all around it - rather reminiscent of the surface of a vortex of swirling water rushing down a plunge hole.

Einstein argued that whenever something heavy bent space-time like this, it would naturally affect the path of anything lighter travelling nearby. So a smaller ball representing the Earth or one of the other planets could be rolled across the stretched rubber sheet representing space-time, towards the dent around the cannon ball sun.

If it was travelling too slowly, it would fall directly into the dent and quickly reach the surface of the sun (just like Newton's apple falling to the surface of the Earth). If it was travelling too fast, it would have its path deflected towards the cannon ball sun, but would only dip into the dent then climb out of the other side, before continuing on its journey. But at just the right speed, the small planet ball would be going fast enough not to fall right into the dent, but too slowly to escape it completely. With nothing else to stop it or slow it down, it would find its level on the 'side' of the dent in space-time, rather like a motorcycle stunt rider going round and round the 'wall of death'. It would have found its static orbit around the sun.

Einstein as Idol

The mathematical formula of Einstein could apart from even describe the orbit of Mercury, what was not possible with Newton's rather simpler equation. This was impressive evidence that Einstein's theory was correct, or at least an improvement on Newton's explanation of gravity. It was natural for physicists to begin to think: if it fits in with Einstein's theories, it is probably going to be true.

Dynamic Space and Time

It was while studying these equations of Einstein's that Lemaître, a priest and Belgium's most famous astronomer, discovered something which really excited him. One of the consequences of Einstein's maths was that the universe was not static; it was dynamic.

It is simply enough to see why. If time and space are 'dented' by anything with mass, then, as one body passes another, it will be drawn closer to it.

If the universe is static, then all objects will eventually be drawn to each other; all mass will congregate together at the bottom of the largest dent in space and time.

This was the same problem which had worried Newton when he came up with his theory of gravity; how could all the matter in the universe still be widely spread out after billions of years? Why hadn't it been pulled together by gravity into one conglomerate lump? But, whereas Newton's idea had confined itself to the attraction of objects, Einstein's theory involved the mathematics of how space and time change when an object with mass affects them. Thus Newton's system had no way for the coming together of all objects to be avoided but Einstein's maths did. Einstein needed space and time to be able to change in the presence of mass. So space and time had to be dynamic, rather than static.

Consequently, space-time, and so the universe, could not remain still; and if it had to change it could only really get bigger or smaller. Hence it ought to be gently expanding or contracting.

Gravitational Effects

It is gravity that governs and shapes the large-scale structure of the universe and thus even time.

The laws of gravity were incompatible with the view held until quite recently that the universe is unchanging in time: the fact that gravity is always attractive implies that the universe must be either expanding or contracting.

According to general theory of relativity, there must have been a state of infinite density in the past, the big bang, which would have been an effective beginning of time. (Scientists today generally agree on an age of the universe of about 13 billion years.)

Similarly, if the whole universe recollapsed, there must be another state of infinite density in the future, the big crunch, which would be an end of time. Even if the whole universe did not recollapse, there would be singularities in any localised regions that collapsed to form black holes. These singularities would be an end of time for anyone who fell into the black hole.

In every case there are certain locations in space that effect time, seen from an different, innocent, and independent observer.

Solutions?

Schwarzschild calculated a solution to Einstein's equations where the time dilatation is infinite from a certain radius on, out of which evolved the idea of black holes. Wheeler found out that Schwarzschild´s solution included a singularity, but also proved its possibility. (The first black hole was found in 1964 in the system Cygnus X-1.)

Hubble proved the even expanding of space, which allowed to calculate the Big Bang. Einstein therefore introduced a new term into his theory of relativity, the “cosmic term”, which he later thought of as his biggest error, because it would have caused the universe to become unstable.

In the search for “theories of everything”, which try to unite relativity and quantum mechanics, the possibility of a cosmic term returned.

A Unifying Theory

When scientists like Stephen Hawking combine quantum mechanics, with general relativity, there seems to be a new possibility for him that did not arise before: that space and time together might form a finite, four-dimensional space without singularities or boundaries, like the surface of the earth but with more dimensions. It seems that this idea could explain many of the observed features of the universe, such as its large-scale uniformity and also the smaller-scale departures from homogeneity, like galaxies, stars, and even human beings. It could even account for the arrow of time that we observe.

At the end of A Brief History of Time Stephen Hawking concludes that, if we do discover a complete theory that could describe everything, its basic principles and implications should in time be understandable by everyone. And once we all understand the true nature of the universe, we all, philosophers, scientists and just ordinary people, can take part in the discussion of the question of why it is that we and the universe exist. Should we ever resolve this question, he suggests, it will be 'the ultimate triumph of human reason - for then we would know the mind of God'.

Perhaps, for many of us, that challenge will seem a step too far. There are millions of us who have never before got close to discovering the nature of the universe. We may just have not tried; more likely we were convinced that it was beyond our limited capacity to understand.

But I think that our opinion is changing. Changing towards knowing more and more about the world and universe we live in. And that is the reason for me to belief that in no way research in this field will find a sudden end.

Already Yogi Berra said : “It ain’t over till it’s over”

Dreams

I think that these concepts will come to seem as natural to the next generation as the idea that the world is round. Imaginary time is already a commonplace of science fiction. But it is more than science fiction or a mathematical trick. It is something that shapes the universe we live in.

An example of how the human race could cope with the progress made in all scientific directions is given in Star Trek. It shows how much we know already and how much we will be able to do with our knowledge in the near future.

The Physics of Star Trek[3]

It is a popular science book, trying to tell most modern science in a simple language. " The Physics of Star Trek" is a book to be read many times as long it is up-to-date with our time (till we cross the milky ways of our and other galaxies). It offers a lot of exotic science to anyone who wants to make a small investment of imagination. Perhaps accidentally, Krauss also does a useful job in explaining some important physics, using Star Trek as a pop culture example: the physics of Newton, Einstein and Stephen Hawking all figure in the highly successful analysis. It is a book on physics, but it is written in such a spirit of fun, it might even make you want to watch Star Trek. This book is fun, and Mr. Krauss has a nice touch with a tough subject. Krauss is smart, but speaks and writes the common tongue.

In this entertaining book the physics professor Lawrence Krauss looks at how the imaginary science of the Star Trek universe stacks up against the real thing. Krauss speculates on the possibility of alien life, touching on whether any kind of life is such an improbable phenomenon.

There are impressively clear explanations of difficult and up-to-date concepts in information theory, quantum mechanics, particle physics, relativity, mechanics and cosmology. The book goes where not even the show's laudable tradition of scientific evangelism has gone before.

4) To Build a Time Machine

The First Thoughts

Change Time

Since ever, humans wanted to change the past and know about the future. Just to know the results of a bet of tomorrow today or to mend a decision, made in the past.

Since it was not possible for scientists to build machines to look or travel through time, it was the duty of science fiction authors to speculate about possible ways, how a time machine would look and work like.

The Time Machine[4]

It is a science fiction novel about the Victorian future which is more than a fantastical yarn. It raises chilling questions about progress, social orders, so called civilisation and the ultimate fate of the world. It tells the story from the present until the end of our sun-system, a cold, almost lifeless earth with a dying sun.

Wells wrote this novel mainly because Charles Darwin published and proved his theory of Evolution, which was the greatest scientific rumpus since the trial of Galileo.

It is a story about evolution brought to the reader as an adventure of an old scientist, who has invented a time machine. Although Wells doesn’t tell the reader the names of the Victorian scientist and the Narrator, he creates a personal relationship with the reader, which is very difficult and proves again that H.G.Wells is one of the best writers.

The Time Traveller lives in a house in London, in Richmond. In the cellar he has his laboratory, his workshop. The Time Traveller shows his disbelieving dinner guests a device he claims is a Time Machine.

He tries to convey his dinner guests that he found a machine to interrupt the floating time stream an though have the possibility to move through time as one wants.

In real time a week later the dinner guests visit the Time Traveller again, but instead of a settled old man they find him raged, exhausted and garrulous. The tale he tells is of the year 802,701 AD of life as it is lived on exactly the same spot, what once had been London. He has visited the future, he has encountered the future -race -elfin, beautiful, vegetarian, helpless, leading a life of splendid idleness.

But this is not the only race, these are not our only descendants. In the tunnels beneath the new Eden there lurks another life form.

The end of the book is open because the Time Traveller disappears in front of the eyes of the Narrator and hasn’t come back for three years although he said he’ll need only half an hour for his journey.

Time Travel

Can we go back in time?

Like the protagonist in H.G. Wells's The Time Machine, can we spin the dial of a machine and leap hundreds of thousands of years to the year 802,701? Or, like Michael J. Fox, can we hop into our plutonium-fired cars and go back to the future?

The possibility of time travel opens up a vast world of interesting possibilities. With time travel, we could go back to our youth and erase embarrassing events from our past, choose a different mate, or enter different careers; or we could even change the outcome of key historical events and alter the fate of humanity.

For example, in the climax of Superman, our hero is emotionally devasted when an earthquake ravages most of California and crushes his lover under hundreds of tons of rock and debris. Mourning her horrible death, he is so overcome by anguish that he rockets into space and violates his oath not to tamper with the course of human history. He increases his velocity until he shatters the light barrier, disrupting the fabric of space and time. By travelling at the speed of light, he forces time to slow down, then to stop, and finally to go backward, to a time before Lois Lane was crushed to death.

This trick, however, is clearly not possible. Although time does slow down when you increase your velocity, you cannot go faster than the speed of light ( and hence make time go backward ) because special relativity states that your mass would become infinite in the process. Thus the faster-than-light travel method preferred by most science fiction writers contradicts the special theory of relativity.

Einstein himself was well aware of this impossibility.

Most scientists, who have not seriously studied Einstein's equations, dismiss time travel as poppycock, with as much validity as lurid accounts of kidnappings by space aliens. However, the situation is actually quite complex.

To resolve the question, we must leave the simpler theory of special relativity, which forbids time travel, and embrace the full power of the general theory of relativity, which may permit it. General relativity has much wider validity than special relativity. While special relativity describes only objects moving at a constant velocity far away from any stars, the general theory of relativity is much more powerful, capable of describing rockets accelerating near supermassive stars and black holes. The general theory therefor supplants some of the simpler conclusions of the special theory. For anyone who has seriously analysed the mathematics of time travel within Einstein's general theory of relativity, the final conclusion is, surprisingly enough, far from clear.

Proponents of time travel point out that Einstein's equations for general relativity do allow some forms of time travel. They acknowledge, however, that the energies necessary to twist time into a circle are so great that Einstein's equations break down. In the physically interesting region where time travel becomes a serious possibility, quantum theory takes over from general relativity.

Einstein's equations state that the curvature or bending of space and time is determined by the matter-energy content of the universe. It is, in fact, possible to find configurations of matter-energy powerful enough to force the bending of time and allow for time travel.

However, the concentrations of matter-energy necessary to bend time backward are so vast that general relativity breaks down and quantum corrections begin to dominate over relativity. Thus the final verdict on time travel cannot be answered within the framework of Einstein's equations, which break down in extremely large gravitational fields, where we expect quantum theory to become dominant. But quantum corrections, in turn, may actually close the opening of the wormhole, making travel through the gateway impossible.

Introducing a New Theory

This is when the ten dimensional hyperspace theory can settle the question. Because both quantum theory and Einstein's theory of gravity are united in ten dimensional space, scientists expect that the question of time travel will be settled decisively by the hyperspace theory. But wormholes and dimensional windows which could be used for time travel might only be understood completely when one incorporates the full power of the hyperspace theory.

Because of this reason it will take some time until enough scientists can research in this direction and decide whether these wormholes are physically relevant or just another crazy idea.

However, the most bizarre consequence of wormholes is that physicists can not only show that wormholes allow for multiply connected spaces, but that they allow for time travel as well. This is the most fascinating, and speculative, consequence of multiply connected universes. (more later)

Problem: Time Travel

If what one does could be predicted, then the fact of making that prediction could change what happens. It is like the problems one would get into if time travel were possible. If you see what is going to happen in the future, you could change it. But that action would change the odds. One only has to see Back to the Future to realise what problems could arise.

The Risks of Time Travel

The peculiar risk lies in the possibility of the time traveller finding some substance in the space which he, or the machine, occupies. As long as the traveller travels through time at a high speed, this scarcely matters, but to come to a stop would involve the jamming of him, molecule by molecule into whatever lies in his way. That would result in a far reaching explosion and would blow him and the apparatus out of all possible dimensions into the 'Unknown'.

Here one could raise the question weather air or water is also a substance which leads to an explosion or if these substances are exceptions because of their low density. Another interesting case that could happen would be if a feather is just gliding through the air, exactly at the place in space where the time traveller stops. When he stops and the feather is exactly under his nose, he will sneeze. When he stops and it is there where his lounges are, he will cough it up. But what will happen when the feather is there where his leg or head is going to be?

Avoidable but risky problems are also posed by time paradoxes, but more to this later on.

Another risk is that you never know the exact situation in which you stumble in stopping the machine. At your destination a suddenly appearing earthquake could surprise and kill you without giving you a chance to flee through time in the last moment.

In the movie Time Cop one of the greatest risks is described very vivid. The same object cannot exist in the same place, at the same time! It would erase itself out of the universe. From that time on it would stop to exist as matter.

But already while the time traveller is making or entering the machine, he has to accepted these possibilities as unavoidable risks, some of the risks a time traveller has to take.

To understand the problem with time travel, it is first necessary to classify the various paradoxes. In general, most can be broken down into one of two principal types:

1. Meeting your parents before you are born
2. The man with no past

The first type of time travel does the most damage to the fabric of space-time because it alters previously recorded events. For example, remember that in Back to the Future, our young hero goes back in time and meets his mother as a young girl his age, just before she falls in love with his father. To his shock and dismay, he finds that he has inadvertently prevented the fateful encounter between his parents. To make matters worse, his young mother has now become amorously attracted to him! If he unwittingly prevents his mother and father from falling in love and is unable to divert his mother's misplaced affections, he will disappear because his birth will never happen.

The second paradox involves events without any beginning. For example, let's say that an impoverished, struggling inventor is trying to construct the world's first time machine in his cluttered basement. Out of nowhere, a wealthy, elderly gentleman appears and offers him ample founds and the complex equations and circuitry to make a time machine. The inventor subsequently enriches himself with the knowledge of time travel, knowing beforehand exactly when stock-market booms and busts will occur before they happen. He makes a fortune betting on the stock-market, horse races, and other events. Decades later, as a wealthy, ageing man, he goes back in time to fulfil his destiny. He meets himself as a young man working in his basement, and gives his younger self the secret of time travel and the money to exploit it. The question is: Where did the idea of time travel come from?

My Favourite

My favourite time travel paradox is one of the second type. It was cooked up by Robert Heinlein in his classic short story All You Zombies--.

A baby girl is mysteriously dropped off at an orphanage in Cleveland in 1945. "Jane" grows up lonely and dejected, not knowing who her parents are, until one day in 1963 she is strangely attracted to a drifter. She falls in love with him. But just when things are finally looking up for Jane, a series of disasters strike. First, she becomes pregnant by the drifter, who then disappears. Second, during the complicated delivery, doctors find that Jane has both sets of sex organs, and to save her life, they are forced to surgically convert "her" to a "him." Finally, a mysterious stranger kidnaps her baby from the delivery room.

Reeling from these disasters, rejected by society, scorned by fate, "he" becomes a drunkard and drifter. Not only has Jane lost her parents and her lover, but he has lost his only child as well. Years later, in 1970, he stumbles into a lonely bar, called Pop's Place, and spills out his pathetic story to an elderly bartender. The sympathetic bartender offers the drifter the chance to avenge the stranger who left her pregnant and abandoned, on the condition that he join the "time travellers corps." Both of them enter a time machine, and the bartender drops off the drifter in 1963. The drifter is strangely attracted to a young orphan woman, who subsequently becomes pregnant.

The bartender then goes forward 9 months, kidnaps the baby girl from the hospital, and drops off the baby in an orphan age back in 1945. Then the bartender drops off the thoroughly confused drifter in 1985, to enlist in the time travellers corps. The drifter eventually gets his life together, becomes a respected and elderly member of the time travellers corps, and then disguises himself as a bartender and has his most difficult mission: a date with destiny, meeting a certain drifter at Pop's place in 1970.

The question is: Who is Jane's mother, father, grandfather, grandmother, son, daughter, granddaughter, and grandson? The girl, the drifter, and the bartender, of course, are all the same person.

And the reason why it is my favourite is because it makes your head spin, especially if you try to untangle Jane's twisted parentage. If You draw Jane's family tree, we find that all the branches are curled inward back on themselves, as in a circle. You will come to the astonishing conclusion that she is her own mother and father! She is an entire family tree unto herself.

Creating the Impossible?

Special warpings of space-time would make time travelling possible. In warped space-time also wormholes are possible, although all current models require exotic matter, to say imaginary matter, to generate negative pressure and so negative gravity.

Theoretical Basis

Using Einstein's equations, it is perfectly possible to predict changes to the shape of space and time which would affect us in ways we have so far found no way to experience - like time warps.

Most people imagine the universe to be a bit like an ever-inflating balloon, with us somewhere inside it. But perhaps the balloon is hardly inflated at all, and is instead a loose and flexible bag. Perhaps we are inside a universe where time and space can be so bent and flexed that the balloon can be folded back on itself. Eventually two parts of the outer skin could somehow get close enough to each other to be linked by wormholes - strange tunnels through space and time through which we might one day be able to move from one end of the universe to the another.

Multiply Connected Universes

Multiply connected is the opposite to simply connected what means, that our windows and doorways are not entrances to wormholes connecting our home to a far-away universe.

Although the bending of our universe in an unseen dimension has been experimentally measured, the existence of wormholes and whether our universe is multiply connected or not is still a topic of scientific controversy.

Many physicists, who once thought multiply connected spaces in which regions of space and time are spliced together, are now seriously studying multiply connected worlds as a practical model of our universe.

These models are the scientific analogue of Alice's looking glass. When Lewis Carroll's White Rabbit falls down the rabbit hole to enter Wonderland, he actually falls down a wormhole.

One can visualise a wormhole as the tube between two sheets of paper, connected through holes.

If you fall into the wormhole, you are instantly transported to a different region of space and time. Only by retracing your steps and falling back into the wormhole can you return to your familiar world.

Time Travel and Baby Universes

Although wormholes provide a fascinating area of research, perhaps the most intriguing concept to emerge from this discussion is the question of time travel.

Wormholes may connect not only two distant points in space, but also the future with the past.

Since travel through the wormhole is nearly instantaneous, one could use the wormhole to go back in time. Unlike the machine portrayed in H.G.Wells's The Time Machine, however, which could hurl the protagonist hundreds of thousands of years into England's distant future with the simple twist of a dial, a wormhole may require vast amounts of energy for its creation, beyond what will be technically possible for centuries to come.

Another bizarre consequence of wormhole physics is the creation of "baby universes" in the laboratory. We are, of course, unable to re-create the Big Bang and witness the birth of our universe. However, a few years ago some physicists of the Massachusetts Institute of Technology shocked many physicists, when they claimed that the physics of wormholes may make it possible to create a baby universe of our own in the laboratory. By concentrating the intense heat and energy in a chamber, a wormhole may eventually open up, serving as an umbilical cord connecting our universe to another, much smaller universe. If possible, it would give a scientist an unprecedented view of a universe as it is created in the laboratory.

One could then find out how the starting conditions of a universe look like; if time is already one of those conditions or if it is just a product, created by chance.

When Carl Sagan wrote a novel called Contact, he wanted to make his book as scientifically accurate as possible and though wrote to the well known physicist Kip Thorne weather there was any scientifically acceptable way of evading the light barrier.

Sagan's request piqued Thorne's intellectual curiosity. A serious request that demanded a serious reply. Fortunately, because of the unorthodox nature of the request, Thorne and his colleagues approached the question in a most unusual way: They worked backward. Normally, physicists start with a certain known object and then solve Einstein's equation to find the curvature of the surrounding space.

However, Thorne and his colleagues started with a rough idea of what they want to find. They wanted a solution to Einstein's equations in which a space traveller would not be torn apart by the tidal effects of the intense gravitational field. They wanted a wormhole that would be stable and not suddenly close up in the middle of the trip. They wanted a wormhole in which the time it takes for a round trip would be measured in days, not millions or billions of earth years, and so on. In fact, their guiding principle was that they wanted a time traveller to have a reasonably comfortable ride back through time after entering the wormhole. Once they decided what their wormhole would look like, then, and only then, did they begin to calculate the amount of energy necessary to create such a wormhole.

They did not care if the energy requirements were well beyond twentieth-century science. To them, it was an engineering problem for some future civilisation actually to construct the time machine. They wanted to prove that it was scientifically feasible, not that it was economical or within the bounds of present-day earth science.

Much to their delight, they soon found a surprisingly simple solution that satisfied all their rigid constrains. It was not a typical black hole solution at all. They christened their solution the "transversible wormhole," to distinguish it from the other wormhole solutions that are not transversible by spaceship.

They were so excited by their solution that they wrote back to Sagan, who incorporated some of their ideas in his novel. (and this year in the identically named film Contact.)

Inside Out

Scientists are not quite sure what happens inside a black hole. There are solutions of the equations of general relativity that would allow one to fall into a black hole and come out of a white hole somewhere else. A white hole is the time reverse of a black hole. It is an object that things can come out of but nothing can fall into. The white hole could be in another part of the universe. This would seem to offer the possibility of rapid intergalactic travel. The trouble is it might be too rapid. If travel through black holes were possible, there would seem nothing to prevent you from arriving back before you set off. You could then do something, like kill your mother before you were born. You must then cease to exist. But if you cease to exist, you could not have gone back and killed your mother. But if you didn't kill your mother, then you have not ceased to exist. To put it another way: if you exist, then you cannot exist, while if you don't exist, you must exist.

This is the most famous paradox to be found in both science fiction and physics. (It belongs to the first type)

Perhaps fortunately for our survival ( and that of our mothers), it seems that the laws of physics do not allow such time travel. What seems to happen is that the effects of the uncertainty principle would cause there to be a large amount of radiation if one travelled into the past. This radiation would either warp space-time so much that it would not be possible to go back in time, or it would cause space-time to come to an end in a singularity like the big bang or the big crunch. Either way, our past would be save from evil-minded persons.

But the best evidence that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.

But, are we alone?

Conclusion

Why it matters

In what sense do these issues matter? Why shouldn't we ignore the view from nowhen, and go on in physics, philosophy, and ordinary life just as we always have? After all, we cannot actually step outside time, in the way in which we can climb a tree to alter our viewpoint. Isn't it better to be satisfied with the viewpoint we have?

We cannot step outside time, but we can try to understand how the way in which we are situated within time comes to be reflected in the ways in which we talk and think and conceptualise the world around us. What we stand to gain is a deeper understanding of ourselves and of what is external to us. This is a reflective kind of knowledge: we reflect on the nature from the standpoint from within, and thereby gain some sense, a sense-from-within, of what it would be like from without.

If the reflexivity w
Quellenangaben des Verfassers
keine Angaben