Getting In A Twist Over Time

[Zxavier]

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

 

Subject: TIME MACHINE

 

Reply-to: [email protected]

 

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

 

possibility."

 

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

 

space."

 

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

 

future.

 

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

 

relativity.

 

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

 

http://www.gpgwebdesign.com.au

 

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

 

 

[Raidzuo]

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.

 

 

[NATAS_999_SYADDNE]

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.