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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.
. The Twin Paradoxon
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
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?
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