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Getting In A Twist Over Time


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Date: Mon, 02 Sep 2002 07:14:26 -0000




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Getting In A Twist Over Time


by Michael Brooks


London - May 19, 2001


Ronald Mallett thinks he has found a practical way to make a time


machine. Mallett isn't mad. None of the known laws of physics forbids


time travel, and in theory, shunting matter back and forth through


time shouldn't be that difficult.


The catch usually comes when you try to make it work in practice.


Remember wormholes, those clever little tunnels in space and time


that can supposedly be used to travel from one moment to another? On


paper, they're a perfectly respectable way to travel back in time.


Trouble is, you need a supply of exotic "negative energy" matter to


prise your wormhole open.


But Mallett, a professor of theoretical physics at Connecticut


University, believes he has found a route to the past that uses


something much more down to earth: light. Mallett has worked out that


a circulating beam of light, slowed to a snail's pace, just might be


the vital ingredient for time travel.


Not only is the technology within our grasp, Mallett has teamed up


with other scientists at Connecticut to work towards building


it. "With this device," he says, "time travel may become a practical




It may be hard for us to climb into Mallett's time machine, as


slowing light down requires temperatures close to absolute zero. But


future, advanced civilisations might work out a way to do it. And


they might even come back to tell us how. If it works in the way


Mallett believes it might, his device would provide time travellers


from the future with their first gateway into our history.


Mallett began his journey into the past when he was just ten years


old. In 1955, his father died of a heart attack. "For me, the sun


rose and set on him. It completely devastated me," Mallett says.


But then he came across The Time Machine by H. G. Wells. Even as a


child, Mallett knew his father hadn't taken care of himself. Drinking


and heavy smoking took a toll on his weak heart, and it gave out at


the age of 33. "My notion was that if I could build a time machine, I


might be able to warn him about what was going to happen," Mallett


says. "That became my guiding light."


What started as a childish notion grew into a passionate


investigation of everything ever written about time travel. When


Mallett studied the work of Einstein -- who died in the same year as


his father -- he realised that Wells's novel was right on track: time


travel is, in theory at least, achievable.


Einstein himself found the notion upsetting, but he had only himself


to blame. He showed that the effect we call gravity is a bending of


space and time.


Anything that has mass or energy distorts the space and the passage


of time in its vicinity, a bit like the way the surface of a soft


couch is distorted when someone sits on it. Solving Einstein's


gravitational field equations tells you just how space-time is


distorted by mass and energy.


A lump of matter stretches space and time. So, for example, clocks


run slower in the gravitational field close to Earth than they do far


out in space. And if you set a massive lump spinning, it begins to


whip space and time around after it, like a rotating teaspoon


dragging the foam on a cup of coffee. The denser and faster-moving


the matter, the more strongly it distorts space-time.


Take this idea far enough, and you find that time can be twisted so


much that instead of running in an infinite line from past to future,


it is bent into a ring. Follow this loop around, and you return to a


particular moment, just as a walk around the block brings you back to


your front door.


Theoreticians have found some solutions to Einstein's equations that


include these "closed time-like loops" -- physicists' jargon for a


time machine. The first to do so was the Austrian-born mathematician


Kurt Gsdel, in 1949, but unfortunately his solution required the


whole Universe to be rotating -- which it's not.


Decades later Kip Thorne of Caltech came up with the idea of using


wormholes, which link different regions of warped space-time, to


provide such loops. Other loops can be made by infinitely long,


spinning cylinders -- somewhat hard to come by -- or fast-moving


cosmic strings. In the early Universe, these ultra-dense strands of


matter may have been as common as dirt, but alas, no longer.


Mallett's idea of using light is much less outlandish. "People forget


that light, even though it has no mass, causes space to bend," he


says. Light that has been reflected or refracted to follow a circular


path has particularly strange effects.


Last year, Mallett published a paper describing how a circulating


beam of laser light would create a vortex in space within its circle


(Physics Letters A, vol 269, p 214). Then he had a eureka moment. "I


realised that time, as well as space, might be twisted by circulating


light beams," Mallett says.


To twist time into a loop, Mallett worked out that he would have to


add a second light beam, circulating in the opposite direction. Then


if you increase the intensity of the light enough, space and time


swap roles: inside the circulating light beam, time runs round and


round, while what to an outsider looks like time becomes like an


ordinary dimension of space.


A person walking along in the right direction could actually be


walking backwards in time -- as measured outside the circle. So after


walking for a while, you could leave the circle and meet yourself


before you have entered it.


The energy needed to twist time into a loop is enormous, however.


Perhaps this wouldn't be a practical time machine after all? But when


Mallett took another look at his solutions, he saw that the effect of


circulating light depends on its velocity: the slower the light, the


stronger the distortion in space-time.


Though it seems counter-intuitive, light gains inertia as it is


slowed down. "Increasing its inertia increases its energy, and this


increases the effect," Mallett says.


As luck would have it, slowing light down has just become a practical


possibility. Lene Hau of Harvard University has slowed light from the


usual 300,000 kilometres per second to just a few metres per second --


and even to a standstill (New Scientist, 27 January, p 4).


"Prior to this, I wouldn't have thought time travel this way was a


practical possibility," Mallett says. "But the slow light opens up a


domain we just haven't had before."


To slow light down, Hau uses an ultra-cold bath of atoms known as a


Bose-Einstein condensate. "All you need is to have the light


circulate in one of these media," Mallett says. "It's a technological


problem. I'm not saying it's easy, but we're not talking about exotic


technology here; we're not talking about creating wormholes in




Mallett has already caught the interest of his head of department,


William Stwalley, who leads a group of cold-atom researchers. Their


first experiment will be designed only to observe the twisting of


space, by looking for its effect on the spin of a particle trapped in


the light circle.


If they can then add a second beam, Mallett believes evidence of time


travel will eventually appear. He's not sure how time travel would


manifest itself. Perhaps what starts out as a single trapped particle


would acquire a partner -- the particle visiting itself from the




Stwalley is more interested in the practical challenges of the


experiment, and remains sceptical about possibilities of time


travel. "A time machine certainly seems like a distant improbability


at best," he says.


Last month, Mallett gave his first talk on the idea at the University


of Michigan at the invitation of astrophysicist Fred Adams, who


accepts that the theoretical side of Mallett's work stands up to


scrutiny. "The reception was cautious and sceptical," Adams


admits. "But there were no holes punched in it, either. The solution


is probably valid."


But even Adams isn't convinced that the experiment will work. That's


hardly surprising, as time travel raises disturbing questions. Could


you go back and murder your grandparents, making your birth


impossible? There may be ways out of this problem, but most


physicists think that any attempt to mess with history should be


impossible. The Cambridge astrophysicist Stephen Hawking calls this


the "chronology protection conjecture".


The general theory of relativity, which Mallett used to work out his


theory of time travel, does not take account of quantum mechanics.


Could this be the crucial omission that means time machines won't


work in the real Universe?


Hawking and Thorne say that any time machine would magnify quantum


fluctuations in the electromagnetic field, and destroy itself with a


beam of intense radiation. But to know for sure, we need a theory of


quantum gravity -- a theory that merges quantum theory with




Even Mallett doesn't claim that time travel is definitely within


reach. "Whether it will do what I predict is something that one will


only know by performing the actual experiment," he says. Then there's


the problem of getting on and off the loop of time without destroying


it -- or yourself. "I really don't know whether you could use this in


the sense of H. G. Wells's time machine," says Mallett.


But who knows? In a few years, we may have entered an era when time


travel is possible, and all kinds of strange people, things and


situations from the future might come to visit. One thing seems


certain, though. Even if the Connecticut time machine works, it won't


be taking any Yankees back to the court of King Arthur.


Mallett's circle of light won't allow anyone to travel back beyond


the point where time first formed a closed loop. So it will be


impossible to go back to a time before it was set up. "A later person


could only travel back to the time when the machine is turned on,"


Mallett says.


This may explain why we have never been overrun by visitors from the


future. It also means that although Mallett might change the


Universe, he won't ever achieve his childhood dream. Mallet's father


will remain forever beyond his reach.


Paradox lost


Time travel is littered with paradoxes. The most notorious is the


idea of travelling back to the time before your parents were born and


killing your grandparents, making it impossible that you would ever


exist. And if you didn't exist, you wouldn't be able to travel back,


so you wouldn't kill your grandparents, so you would be born after


all ... Any influence on the past can lead to self-contradictory


logical loops like this.


People have dreamed up ways to try to break out of the loop. One is


the "consistent histories" approach, which says that you must be


somehow forbidden from doing anything that would change the past.


However hard you try, something will stop your killing spree. But


this is uncomfortably deterministic. In a universe with time travel,


should everything be predetermined?


Another way out is the "alternative histories" hypothesis. In this


idea, you go back to a different history from the one you left. You


are free to do anything in this alternate version of history --


killing your grandparents included. It won't change anything in the


history where you originated.


This has parallels in the "many worlds" interpretation of quantum


mechanics, an explanation of how the bizarre quantum laws allow


unobserved particles such as atoms and electrons to be in two places


at once.


Every time an observation forces them to choose one position or


another, a new universe is created -- one where they took one


position, one where they took the other. So perhaps a time machine


would take you into a parallel universe.


Michael Brooks is a Features Editor at New Scientist. This article


was first published in the May 19, 2001 issue of New Scientist




Mr. Daniel E. Lauireraka: Commander Zxavier :devil:



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This is a fairly old editorial. Many agree this will never work as these conditions are already abundant on earth. Example: The ocean slows and bends light in the same way this experiment does. Fish, submarines and divers do not travel through time under the ocean.


A strong man doesn't waste his time trying to predict the future; He makes his own.



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Yeah i think if you build a time machine you may only be able to go back to the point it was built,


this certainly protects our past without a doubt,but doesnt protect our future,


if such a device was built you could preserve existance up to that point,but you could still cause chaos after that point becuase of the very machine exists.


Its not hard to create paradoxes,any information gained from the future is dangerous cos it changes decisions and actions in the past,the time machine could be preserved but once its been built the walls of reality could come crumbling down,the world would become chaotic because the human brain will only remember something if it has happened,if something doesnt happen because something was changed,you wouldnt notice it cos you wouldnt know what it was like before,its like a blank videotape recording and being re-edited over and over with any change.


The problem with the idea of parrallel universes is the simple fact that once YOU are in the other universe you leave the other one behind,which means that its selfish towards the other universe cos as far as there concerned you just vanished never to be seen again,from your perspective your in the same universe


except any changes you make to the parrallel one will not affect or do anything at all to the previous one,


each time you travel you will end up split off from the previous universe where they too will think you disapeared.


As for the continous historys,well its flawed


ill tell you why:


suppose you try and kill your grandparents before you are born,


now when you were younger they didnt mention such a thing happening,so surely it didnt happen.


Now you go back and make the attempt but fail,surely this will cause ripples where there is change,


its what you call a logical problem because its suggesting things are the way they are now because of future time travel,


i cant see how logically you can fail,if you managed to build a time machine you should be able to get hold of a decent gun and kill your grandparents,theres no way you can miss with an ak-47 and a few grenades,throw in some semtex maybe a nuclear bomb whatever lol


:devil: ,if all that dont work then yeah everything is predetermined and we are all actors in a big play reading out lines that are prewritten,so you go back and all you can do is observe what went before but cannot touch or change actions,itll always swing back to what it was supposed to be.



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