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How to Travel in Time?Some theories about time traveling ... |
By Stefan Anitei, Science Editor
9th of March 2007, 12:23 GMT
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Would you like to have the chance of taking advantage of all the missed opportunities of your youth?
Only a time travel could fix it.
It looks like fiction, but some scientists imagine this possibility.
"There are a handful of scenarios that theorists have suggested for how one might travel to the past," said Brian Greene, a physicist at Columbia University and expert in string theory.
"And almost all of them, if you look at them closely, brush up right at the edge of physics as we understand it."
Physical time is regarded as a dimension much like length, width, and height: moving through a spatial direction is in all three spatial dimensions: length, width and height but also in time, the fourth dimension.
"Space and time are tangled together in a sort of a four-dimensional fabric called space-time," said Charles Liu, an astrophysicist with the City University of New York, College of Staten Island.
"Space-time can be thought of as a piece of spandex with four dimensions. When something that has mass-you and I, an object, a planet,
or any star-sits in that piece of four-dimensional spandex, it causes it to create a dimple. That dimple is a manifestation of space-time bending to accommodate this mass."
One can go backwards or forwards in the three spatial dimensions, but time lacks this multi-directional freedom.
"In this four-dimensional space-time, you're only able to move forward in time," said Liu.
A handful of proposals exist for time travel.
The most popular proposal for time travel involves a wormhole-a hypothetical tunnel connecting two regions of space-time, which could be two different parts of one universe.
Matter would be passed from one mouth of the wormhole to the other side.
"Wormholes are the future, wormholes are the past," said Michio Kaku, a physicist at the City University of New York.
"But we have to be very careful. The gasoline necessary to energize a time machine is far beyond anything that we can assemble with today's technology. To punch a hole into the fabric of space-time would require the energy of a star or negative energy, an exotic entity with an energy of less than nothing," said Kaku.
Greene concepts matter in a minimum of 10 dimensions.
"The basic idea if you're very, very optimistic is that if you fiddle with the wormhole openings, you can make it not only a shortcut from a point in space to another point in space, but a shortcut from one moment in time to another moment in time."
Other popular concepts are the cosmic strings, narrow tubes of energy stretched across the entire length of the ever-expanding universe and containing vast amounts of mass, warping the space-time around them.
"Cosmic strings are either infinite or they're in loops, with no ends," said J. Richard Gott, an astrophysicist at Princeton University.
"So they are either like spaghetti. The approach of two such strings parallel to each other will bend space-time so vigorously and in such a particular configuration that might make time travel possible, in theory. This is a project that a super civilization might attempt," said Gott.
"It's far beyond what we can do. We're a civilization that's not even controlling the energy resources of our planet." he added.
"Mathematically, you can certainly say something is traveling to the past. But it is not possible for you and me to travel backward in time," said Liu.
"Maybe if there were a theory of everything, one could solve all of Einstein's equations through a wormhole, and see whether time travel is really possible. But that would require a technology far more advanced than anything we can muster. Don't expect any young inventor to announce tomorrow in a press release that he or she has invented a time machine in their basement." said Kaku.
"If you want to know what the Earth is like one million years from now, I'll tell you how to do that," said Greene.
"Build a spaceship. Go near the speed of light for a length of time-that I could calculate. Come back to Earth, and when you step out of your ship you will have aged perhaps one year while the Earth would have aged one million years. You would have traveled to Earth's future."
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