You Can't Travel Back in Time

[Owlscrying]

Mar. 9

The urge to hug a departed loved one again or prevent atrocities are among the compelling reasons that keep the notion of time travel alive in the minds of man.

While the idea makes for great fiction, some scientists now say traveling to the past is impossible.

There are a handful of scenarios that theorists have suggested for how one might travel to the past, said Brian Greene, author of the bestseller, “The Elegant Universe” and a physicist at Columbia University.“And almost all of them, if you look at them closely, brush up right at the edge of physics as we understand it. Most of us think that almost all of them can be ruled out.”

The fourth dimension

In physics, time is described as a dimension much like length, width, and height. When you travel from your house to the grocery store, you’re traveling through a direction in space, making headway in all the spatial dimensions—length, width and height. But you’re also traveling forward 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 and co-author of the book “One Universe: At Home In The Cosmos.”

Space-time, Liu explains, 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,” he said. “That dimple is a manifestation of space-time bending to accommodate this mass.”

The bending of space-time causes objects to move on a curved path and that curvature of space is what we know as gravity.

Mathematically one can go backwards or forwards in the three spatial dimensions. But time doesn’t share this multi-directional freedom.

“In this four-dimensional space-time, you’re only able to move forward in time,” Liu told LiveScience.

Tunneling to the past

A handful of proposals exist for time travel. The most developed of these approaches involves a wormhole—a hypothetical tunnel connecting two regions of space-time. The regions bridged could be two completely different universes or two parts of one universe. Matter can travel through either mouth of the wormhole to reach a destination on the other side.

“Wormholes are the future, wormholes are the past,” said Michio Kaku, author of “Hyperspace” and “Parallel Worlds” and 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, Kaku explained, would require the energy of a star or negative energy, an exotic entity with an energy of less than nothing.

Greene, an expert on string theory—which views matter in a minimum of 10 dimensions and tries to bridge the gap between particle physics and nature's fundamental forces, questioned this scenario.

“Many people who study the subject doubt that that approach has any chance of working,” Greene said in an interview . “But 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.”

Cosmic strings

Another popular theory for potential time travelers involves something called cosmic strings—narrow tubes of energy stretched across the entire length of the ever-expanding universe. These skinny regions, leftover from the early cosmos, are predicted to contain huge amounts of mass and therefore could warp the space-time around them.

Cosmic strings are either infinite or they’re in loops, with no ends, said J. Richard Gott, author of “Time Travel in Einstein's Universe” and an astrophysicist at Princeton University. “So they are either like spaghetti or SpaghettiO’s.”

The approach of two such strings parallel to each other, said Gott, 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,” Gott told LiveScience. “It’s far beyond what we can do. We’re a civilization that’s not even controlling the energy resources of our planet.”

Impossible, for now

Mathematically, you can certainly say something is traveling to the past, Liu said. “But it is not possible for you and me to travel backward in time,” he said.

However, some scientists believe that traveling to the past is, in fact, theoretically possible, though impractical.

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, Kaku said. “But that would require a technology far more advanced than anything we can muster," he said. "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.”

For now, the only definitive part of travel in the fourth dimension is that we’re stepping further into the future with each passing moment. So for those hoping to see Earth a million years from now, scientists have good news.

“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, a consultant for “Déjà Vu,” a recent movie that dealt with time travel. “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.”

go

[Four Winds]

I've known I can't travel back in time for a while now

Edited March 9, 2007 by Razer

[Lotus Flower]

I travel back in time all the time - in my thoughts lol. Everytime I remember something my mind is travelling back.

I think it is a good job we can't do it physically, God knows what would be going on.

[Shadow Hunter Ryzi]

I've been discussing this with my friend during math class.

And it's rather unusual we came to the same conclusion the people quoted in this topic did, and hence, decided to build a spaceship.

From our point of view, backwards time travel is impossible, while forwards "Time-Travel" is almost certainly possible.

Or going back in time could be possible to try, but you'd most likely be 'lost' in time.

Edited March 10, 2007 by Shadow Hunter Ryzi

[Legatus Legionis]

traveling back in time is probable. but not like traveling forward in time. traveling forward in time all you need to do is rather exceed or reach the speed of light and hang on as long as you can. but traveling back in time needs a working time machine that would be turned on "now" and will be turned on forever. if the machine is turned on for a Century , The person in the future can send back items, information thru the machine . and the items, information would rather simply go back when the machine was first turned on. both options. like traveling forward in time and traveling backward in time is most likely impossible for this period of time, which is called "the present". because of the tricky physics law, if you try to travel forward in time in the speed of light you would likely have an VAST/ infinite amount of Mass. ofcourse more mass needs more power/energy. therefore infinite mass=inifinite energy.

PS: I'f i'm wrong, please correct me... or comment me.. i am open to all comments. thanks