A TWIN PARADOX ????

In Einstein's special theory of relativity, there is no such thing as "time" in the singular. Time passes differently for different observers, depending on the observers' motion. The prime example is that of the two hypothetical twins: One of them stays at home, on Earth. The other journeys into space in an ultra-fast rocket, nearly as fast as the speed of light, before returning home:

Afterwards, when the twins are reunited on Earth, the travelling twin is markedly younger, compared to her stay-at-home sibling. The exact age difference depends on the details of the journey. For example, it could be that, aboard the space-ship, two years of flight-time have passed - on-board clocks and calendars show that two years have elapsed, and both spaceship and travelling twin have aged by exactly that amoung of time. On Earth, however, a whopping 30 years have passed between the spaceship's departure and its return. Just like all other humans on the planet, the twin on Earth has aged by 30 years during that time. Seeing the two (ex?) twins side by side, the difference is striking.

So far, so strange, but undoubtedly real. Space-travel with speeds close to that of light may be unfathomably far beyond the reach of current technology. But sending elementary particles on round trips in a particle accelerator at 99.99999 percent of light speed is routine. The result is in precise agreement with the predictions of special relativity - the "inner clock" of such a travelling particle runs much slower than that of a particle of the same species that remains at rest (cf. the page The relativity of space and time in the section Special Relativity ofElementary Einstein).

The reason the case of the travelling twins is also known as the "twin problem" or even the "twin paradox" is the following. From the point of view of the twin on Earth, one can explain the age difference by appealing to time dilation, a basic concept of special relativity. It involves an observer (more precisely: an inertial observer), for instance an observer that lives on a space station floating through empty space. For such an observer, special relativity predicts the following: For any moving clock, that observer will come to the conclusion that it is running slower than his own. Whether it is a clock on another space station floating past or a clock on an engine-driven rocket, in the time it takes for a second to elapse on the observer's own clocks, less than a second will have elapsed on the moving clock. This slowdown is true not only for clocks, but for everything that happens on the moving space station or in the flying rocket. All processes taking place on these moving objects will appear slowed down for our observer.

Characteristically, there are situations where time dilation is mutual. For instance, if there are two observers drifting through space, each on his or her own space station, and if those two space stations are in relative motion, then for each observer, the time in the other space station appears to run slower than for himself. (If that already sounds like a paradox to you, you might want to read the spotlight topic The dialectic of relativity.)

With the help of time dilation - often abbreviated to "moving clocks go slower" - one can try to explain what happens to the twins. No wonder the travelling twin ages less! After all, the twin on Earth can invoke time dilation: Moving clocks go slower, and so do the clocks of the moving twin. On these slower-moving clocks - and, by extension, in the whole spaceship - less time passes than on Earth, in other words: when the travelling twin returns, he is younger.

No paradox so far. But why can't the travelling twin turn the tables on her sibling? After all, motion is relative. Why can't the twin in the spaceship define herself as being at rest? From that point of view, it would be the Earth that moves away before returning to the spaceship. And if that is so, couldn't the travelling twin apply time dilation ("moving clocks are slower") to everyone who remained on Earth? By that argument, shouldn't it be the humans on Earth that are younger than expected once the twins are reunited? If both twins are on an equal footing, then each one should be allowed to onsider herself at rest and invoke time dilation. But in the end, when the twins meet again, only one of them can be right - then, there cannot be any ambiguity: either the one twin is younger, or the other (or, of course, both twins' arguments are wrong, and they have aged exactly the same). A contradiction - a twin paradox?

A PROOF OF PARTICLES TRAVELLING FASTER THAN SPEED OF LIGHT ....

According to a report by the Associated Press, researchers at CERN have observed a subatomic particle moving faster than the speed of light. That’s right, faster than the speed of light. Like any sane people, these researchers are currently looking for outside sources to verify their results, and with results as mind-boggling as these, who could blame them.

It appears that the actual observation happened several months ago when a neutrino beam was shot 454 miles from the area around Geneva to Italy and arrived 60 nanoseconds earlier than light would. That’s not much over, but the margin of error was only 10 nanoseconds, which means this is a statistically significant discovery. After pouring over the results for months, CERN has now turned to the U.S. and Japan to double check their work. Although a 50 to 70 nanosecond gain over the course of 454 miles might not sound like much, it could actually change the understanding of physics as we know it, or at least as we’ve known in the past century.

According to Einstein’s theory of relativity, which has held up well so far, no particle with mass should be able to accelerate to speeds faster than the speed of light without requiring infinite energy. This one instance may be enough to completely change the way we think the world might work. While special relativity does not exactly prohibit particles the travel faster than the speed of light (see tachyons, theoretical particles that are always moving faster than the speed of light), this instance of a particle being accelerated beyond it is revolutionary because no one has ever actually observed this happening before.

It’s easy to jump off the rails thinking about the possibilities of faster-than-light travel, but everyone is keeping in mind that this might be an error of some sort. Even if it turns out to be completely true, not much happens, other than the theory of relativity as we know needing some reevaluation. It was only neutrinos, and only a 50 to 70 nanosecond gain, but still, it may turn out that the speed of light is an arbitrary limit, which opens up an incredible world of opportunities. After all, particles that move faster than light should be able to go forwards or backwards in time.

PARTICLES THAT TRAVEL FASTER THAN LIGHT ....

European Physicists claim to have detected neutrinos (small sub-atomic particles), travelling at faster than the speed of light.  Researchers on the OPERA, (Oscillation Project with Emulsion-Tracking Apparatus), experiment blasted a beam producing billions upon billions of neutrinos from CERN, which straddles the French-Swiss border near Geneva, to the Gran Sasso Laboratory 450 miles away in Italy.  The particles appear to have been clocked at an astounding 186,415.086 miles per second.  A feat currently forbidden by Einstein’s theory of special relativity, a theory that is a foundation of physics.  The speed of light at 186,282 miles per second is considered the cosmic speed limit.

OPERA’s claim is being greeted with skepticism inside and outside the European lab.  “The feeling that most people have is this can’t be right, this can’t be real,” said James Gillies, a spokesman for CERN.  Alvaro de Rujula, a theoretical physicist who works at CERN, called the claim “flabbergasting.”   “If it is true, then we truly haven’t understood anything about anything,” he said, adding: “It looks too big to be true.  The correct attitude is to ask oneself what went wrong.”

Antonio Ereditato, the physicist who leads OPERA, made it clear that while the team had looked hard for any measurement errors or other mistakes that could explain it, and found none, the results still needed careful checking: “After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement.  While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation.”

John Learned, a neutrino astronomer at the University of Hawaii, said that if the results of the OPERA researchers turned out to be true, it could be the first hint that neutrinos can take a shortcut through space, through extra dimensions.  Joe Lykken of Fermilab said, “Special relativity only holds in flat space, so if there is a warped fifth dimension, it is possible that on other slices of it, the speed of light is different.”

The results were announced at a special seminar at CERN today, which coincided with the publication of a research paper describing the experiments.  The Gran Sasso National Laboratory, the world’s largest underground particle physics Laboratory is located under a mountain in central Italy.  The CERN, (European Center for Nuclear Research), complex operates a network of six accelerators and a decelerator including the worlds largest particle accelerator the Large Hadron Collider or LHC.

Neutrinos are electrically neutral particles so small that only recently were they found to have mass.

NASA : WRAP DRIVE EXPERIMENT ....

As we take our virgin steps into space, there is one thing that could always put a cap on our ambitions.

Despite our desire to explore the stars, we are limited by travelling at less than light speed - and even if we managed to match that pace, we would still be listing our voyages from star to star in years, centuries or millenia.

But, in what could be a huge breakthrough, theorists from Nasa say there is 'hope' that we can achieve faster-than-light travel, after physicists found a theoretical possibility for warp speed travel.

But according to Space.com, Harold 'Sonny' White, from NASA's Johnson Space Center, told the 100 Year Starship Symposium, a gathering of scientists, writers and philosophers in Houston, that new theories could allow Man to reach such speeds with less energy.

He told his audience that, instead of enclosing a space-ship in a space time-bubble, a craft could sit within a 'doughnut' shape - which means the warp drive could be powered by a mass the size of a spacecraft like the Voyager 1 probe - the equivalent size of a small car.

He told Space.com: ''The findings I presented today change it from impractical to plausible and worth further investigation.

'The additional energy reduction realized by oscillating the bubble intensity is an interesting conjecture that we will enjoy looking at in the lab.'

White and his team are experimenting with a mini-version of a warp drive in their laboratory, using laser to try to warp space and time in miniature.

He said his 'humble experiment' was 'trying to see if we can generate a very tiny instance of this in a tabletop experiment, to try to perturb space-time by one part in 10 million.'

SEEING THROUGH TIME .....

This is not an assumption. This is a scientific fact. We are able to see the past through looking at the stars. The light from the distant stars takes a lot of light years to reach the Earth. Hence when we are looking at the beautiful starry sky in a clear night we are actually looking at the past of these stars. Astonishingly enough we are looking at a lot of different pasts simultaneously, as these stars are vastly different in regard to their distance from us

There are many conceivable ways of time travel, and many people who do and do not believe in them (such beliefs do not in fact change any laws of nature).

If time travel were assumed to be possible then many impossibilities would be assumed to appear. For example, if someone were to travel into the past and see himself as a child he could kill himself. Okay, so that would be a pretty dumb thing to do, but the possibility brings up a paradox. If he kills himself, then he could never go back in time and kill himself. The possibility of this situation might lead to believe that time travel into the past is not possible. In fact the only time a paradox could be assumed to happen is when someone travels backward in time, and if this travel proves to be possible it should eliminate the possibility of a paradox (by definition paradoxes never happen). In the above example the man would not be able to kill himself, no matter hard he tried, because he has already got to live into the future without killing himself. Someone who does not agree?

Isaac Newton's ideas were widely accepted and could be accurately applied to most of the universal calculations. It wasn't until a slight discrepancy in the observed Mercury orbit and the calculated one that scientists began to wonder if Isaac Newton was entirely correct. The Mercury orbit differed by exactly 42 arc seconds. Later when it was found that light always appeared to move with the same speed despite one's own velocity, combined with many other observations, the Newtonian universe began to crumble.

It was time for new ideas. Albert Einstein was full of them. His theory of relativity assumed that time was the fourth dimension, he introduced the concept of Space-Time. A large mass would bend the space around it and in doing so would create gravity (a Time-Space cartoon). This was a far fetch from original theories, but it predicted the Mercury orbit exactly. Later it was given further support by a test during an eclipse. The light from a star was bent as it came into the curved space created by the sun.

The time travel aspect of this comes from the curved space. When a mass bends the Space-Time it makes distances longer, it stretches the space. A spaceship traveling into the gravity of a large mass, a star, for example Sirus, going 100,000 miles per hour would look like it was traveling quite fast to someone outside the spaceship. Once the ship enters the gravity of Sirus, the ship would seem to slow down. It hasn't though, ship's computer states a constant velocity of 100,000 miles per hour. The person outside is watching the ship and the ship seems to stopp. The space around Sirus which appears to be an inch is actually, once you get there, 100,000 miles. The man inside the ship feels no differens and he continues to travel what seems to be 100,000 miles per hour, so his time must have slowed down. His hour becomes longer than it is to the observer. His clock still runs in a steady motion but it moves slower in comparison to the clock of the observer. This is called Time Dilation. In fact according to the theory of relativity, by moving at speeds close to the speed of the light, even if this happens in a train, the clock would slow down (in relation to the clock of an observer), and one could in this way travel forward in time.

Ronald Mallett, Professor at the University of Connecticut, has used Einstein’s equations to design a time machine with circulating laser beams. While his team is still looking for funding, he hopes to build and test the device in the next 10 years.

With a brilliant idea and equations based on Einstein’s relativity theories, Ronald Mallett from the University of Connecticut has devised an experiment to observe a time traveling neutron in a circulating light beam. While his team still needs funding for the project, Mallett calculates that the possibility of time travel using this method could be verified within a decade.

“Einstein showed that mass and energy are the same thing,” said Mallett, who published his first research on time travel in 2000 in Physics Letters. “The time machine we’ve designed uses light in the form of circulating lasers to warp or loop time instead of using massive objects.” 

And according to Einstein, whenever you do something to space, you also affect time. Twisting space causes time to be twisted, meaning you could theoretically walk through time as you walk through space.
“As physicists, our experiments deal with subatomic particles,” said Mallett. “How soon humans will be able to time travel depends largely on the success of these experiments, which will take the better part of a decade. And depending on breakthroughs, technology, and funding, I believe that human time travel could happen this century.”
Step back a minute (sorry, only figuratively). How do we know that time is not merely a human invention, and that manipulating it just doesn’t make sense?
“What is time? That is a very, very difficult question,” said Mallett. “Time is a way of separating events from each other. Even without thinking about time, we can see that things change, seasons change, people change. The fact that the world changes is an intrinsic feature of the physical world, and time is independent of whether or not we have a name for it.
“To physicists, time is what’s measured by clocks. Using this definition, we can manipulate time by changing the rate of clocks, which changes the rate at which events occur. Einstein showed that time is affected by motion, and his theories have been demonstrated experimentally by comparing time on an atomic clock that has traveled around the earth on a jet. It’s slower than a clock on earth.”
Although the jet-flying clock regained its normal pace when it landed, it never caught up with earth clocks - which means that we have a time traveler from the past among us already, even though it thinks it’s in the future.
Some people show concern over time traveling, although Mallett - an advocate of the Parallel Universes theory - assures us that time machines will not present any danger.
“The Grandfather Paradox [where you go back in time and kill your grandfather] is not an issue,” said Mallett. “In a sense, time travel means that you’re traveling both in time and into other universes. If you go back into the past, you’ll go into another universe. As soon as you arrive at the past, you’re making a choice and there’ll be a split. Our universe will not be affected by what you do in your visit to the past.”
In light of this causal “safety,” it’s kind of ironic that what prompted Mallett as a child to investigate time travel was a desire to change the past in hopes of a different future. When he was 10 years old, his father died of a heart attack at age 33. After reading The Time Machine by H.G. Wells, Mallett was determined to find a way to go back and warn his father about the dangers of smoking.
This personal element fueled Mallett’s perseverance to study science, master Einstein’s equations, and build a professional career with many high notes. Since the ‘70s, his research has included quantum gravity, relativistic cosmology and gauge theories, and he plans to publish a popular science/memoir book this November 2006. With help from Bruce Henderson, the New York Times best-selling author, the book will be called Time Traveler: A Physicist’s Quest For The Ultimate Breakthrough.

THE COSMIC SUPER STRINGS' THEORY ....

Under normal circumstances, the effects of time dilation are negligible. You aren’t going to find yourself in the 23rd century just by running extra fast. But, when objects (or, theoretically, people) move at what Greene terms “a significant fraction of light speed,” time dilation is very pronounced.

Yet another theory for how we might travel back and forth through time uses the idea of cosmic strings, proposed by Princeton physicist J. Richard Gott in 1991. These are - as their name suggests - string-like objects that some scientists believe were formed in the early universe. These strings may line the entire length of the universe and are under immense pressure - millions upon millions of tons.

These cosmic strings, which are thinner than an atom, would generate an enormous amount of gravitational pull on any objects that pass near them.

Objects attached to a cosmic string could travel at incredible speeds, and because their gravitational force distorts spacetime, they could be used for time travel. By pulling two cosmic strings close together, or one string close to a black hole, it might be possible to warp spacetime enough to create closed time-like curves. 

A spacecraft could be turned into a time machine by using the gravity produced by the two cosmic strings, or the string and black hole, to propel itself into the past. To do this, it would loop around the cosmic strings. However, there is still much speculation as to whether these strings exist, and if they do, in what form. Gott himself said that in order to travel back in time even one year, it would take a loop of string that contained half the mass-energy of an entire galaxy.

Cosmic superstring loops wiggle and oscillate, producing gravitational waves, then slowly shrink as they lose energy until they disappear.

Cosmic strings are theoretical fault lines in the universe, defective links between different regions of space created in the moments after the Big Bang. And they might be theoretical no longer - distant quasars show the fingerprints of these strings.

Compared to cosmic strings, black holes seem downright sensible. These strings - no relation to the subatomic strings of theoretical physics - are one-dimensional objects, meaning they have length, but no height or width. They are defects in the fabric of the universe, a byproduct of the universe cooling in the first instants after the Big Bang. The easiest way to think about these strings is to see them as the cosmic equivalent of the cracks that form in ice over a frozen lake.

Of course, that doesn't capture the full measure of their one-dimensional weirdness. Since they have no width or height, they are incomprehensibly narrow, with a diameter that would make even a tiny photon look fat. They're also dense, as a string that's even a mile long would weigh considerably more than Earth. These strings expanded right along with the universe, ultimately stretching across the entire known universe in a more or less straight line, or forming massive rings many thousands of times bigger than our galaxy.

We've not yet directly observed these strings, but researchers at the University of Buffalo say they've found clear indirect proof. They studied 355 quasars - incredibly bright galaxies with super-massive black holes at their center - at the furthest corners of the observable universe. All quasars emit massive energy jets pointed in a particular direction, and through very careful study it's possible to figure out the directions of the jets.

183 of those quasar jets lined up to form a pair of enormous rings in the sky, suggesting two massive circular structures exist - or had existed - to orient the direction of the jets. The only known candidates for such colossal structures are cosmic strings, providing compelling indirect evidence for them. If we confirm the existence of cosmic strings, it will greatly improve our understanding of the formation of the earliest galaxies.

This isn't clinching proof - some scientists, like Arizona State's Tanmay Vachaspati, are skeptical cosmic strings that formed nanoseconds after the Big Bang could last long enough after the Big Bang to affect quasars in this way.