To build a time machine

The First Thoughts . Change Timebr />
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

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


. Logical Paradoxon

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.

. Time Paradoxes

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.


. Evading the Light Barrier

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?