Scientist say you can't travel back in time

[Kreshna Aryaguna Nurzaman]

Yahoo News

You Can't Travel Back in Time, Scientists Say

Sara Goudarzi

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 many.

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.”
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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.
Video: Can You Time Travel?

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.”
Video: How to Time Travel!

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.”

Excuse me, but am I the only one who think that this is just another Captain Obvious Article?

[frigidmagi]

Excuse me but shouldn't this be in Science and Logic?

[Comrade Tortoise]

KAN... this does not belong here. It belongs in my dominion.

[Rogue 9]

[Kreshna Aryaguna Nurzaman]

Duh. Wrong sub-forum.

Back to the topic, is there really anything new with the article? I have read it over and over again but as far as I'm concerned, it's just a 'No Shit Sherlock' article.

[Hedgecore]

Way to crush my dreams, Science.

[Comrade Tortoise]

Well sometimes science has to finally put an end to the bullshit that people insist on clinging to

[SirNitram]

'Current science and technology doesn't allow for time travel in reverse'.

Wow. Did the DoD give you 7 million for that? Have you checked psychic teleportation?

What pisses me off is it's all on string theory, which is still not anywhere near perfected. And all is says is you need the power of a star to create a wormhole; gee, there aren't any stars around! Oh wait..

Time travel in reverse is a tricky, odd subject. But this is just saying 'Well, not with anything we can do now'. No fuckin' duh.

[Destructionator XV]

Did the DoD give you 7 million for that?

The sad part is I wouldn't be surprised at all if that were true.

And all is says is you need the power of a star to create a wormhole; gee, there aren't any stars around! Oh wait..

I'm not familiar with the theory at all, but 'power of a star' can mean a lot of things. It might mean total luminous power output of a star (which vastly varies among stars), it might mean the total energy output of a star over its entire lifetime, it might mean the energy of the star if all its mass was converted to energy. The luminous power would be my guess, but with lay terms, one can not be sure what was really meant.

In any case though, not only is it not very specific (it might mean many stars; a wide range), it also presents a serious practical problem: how to you harness all this energy anyway?



On reverse time travel in general, I am personally of the camp that it is simply impossible, and thus anything that may cause it is also impossible (including, FTL travel, in any form). It just would cause too many causality problems (heh, that sentence is funny to me).

[Ra]

The Vulcan Science Commission has determined that time travel is impossible.

And they were right, bitch!

Yeah, this does seem kinda obvious, though interesting nonetheless. The last part is just basic time dilation put to use.

[SirNitram]

Did the DoD give you 7 million for that?

The sad part is I wouldn't be surprised at all if that were true.

And all is says is you need the power of a star to create a wormhole; gee, there aren't any stars around! Oh wait..

I'm not familiar with the theory at all, but 'power of a star' can mean a lot of things. It might mean total luminous power output of a star (which vastly varies among stars), it might mean the total energy output of a star over its entire lifetime, it might mean the energy of the star if all its mass was converted to energy. The luminous power would be my guess, but with lay terms, one can not be sure what was really meant.

In any case though, not only is it not very specific (it might mean many stars; a wide range), it also presents a serious practical problem: how to you harness all this energy anyway?

Given the way he's talking about wormholes, he's probably talking about the collapse of a supermassive star into a black hole, as you need one of those to link to another to form the Einstein-Rosen bridge. Then you need negative energy to stretch the fucker out.

Of course, if you can harness negative energy, for alot less negative energy, you've got a servicable FTL drive, which should allow backwards time travel anyways.

On reverse time travel in general, I am personally of the camp that it is simply impossible, and thus anything that may cause it is also impossible (including, FTL travel, in any form). It just would cause too many causality problems (heh, that sentence is funny to me).

The idea that 'It'd cause problems = It must be impossible' is immeasurably silly to me.

[Destructionator XV]

The idea that 'It'd cause problems = It must be impossible' is immeasurably silly to me.

"It'd cause problems" is an understatement. Without casualty, physics fall apart. The definition of a paradox is that there is no solution; logic fails.

An analogous situation would be a free energy device. It would cause problems with conservation of energy, so they are simply discarded as impossible. Also a reactionless engine; if you accelerate without an equal but opposite force, that causes a problem with conservation of momentum, and is again, discarded as impossible until extraordinary evidence can be procured.

It is an oldie, but if you traveled back in time and killed your grandfather before you were born, what happens?

Even ignoring the casual disconnect, how about conservation of energy. If you go back in time, isn't there now two copies of the molecules that make you up at this new point in time? If so, time travel is also a free energy device.

If you have any evidence whatsoever that anything that causes even a minor problem with casualty or conservation of energy on this scale is possible, please enlighten me. Until then, anything that doesn't jive with these fundamental laws of physics - including the very foundation on which physics is based - cause and effect - is simply impossible in my mind.