As several respondents noted, we constantly travel through time--just forward, and all at the same rate. But seriously, time travel is more than mere fantasy, as noted by Gary T. Horowitz, a professor of physics at the University of California at Santa Barbara:
"Perhaps surprisingly, this turns out to be a subtle question. It is not obviously ruled out by our current laws of nature. Recent investigations into this question have provided some evidence that the answer is no, but it has not yet been proven to be impossible."
Even the slight possibility of time travel exerts such fascination that many physicists continue to study not only whether it may be possible but also how one might do it.
One of the leading researchers in this area is William A. Hiscock, a professor of physics at Montana State University. Here are his thoughts on the matter:
"Is it possible to travel through time? To answer this question, we must be a bit more specific about what we mean by traveling through time. Discounting the everyday progression of time, the question can be divided into two parts: Is it possible, within a short time (less than a human life span), to travel into the distant future? And is it possible to travel into the past?
"Our current understanding of fundamental physics tells us that the answer to the first question is a definite yes, and to the second, maybe.
"The mechanism for traveling into the distant future is to use the time-dilation effect of Special Relativity, which states that a moving clock appears to tick more slowly the closer it approaches the speed of light. This effect, which has been overwhelmingly supported by experimental tests, applies to all types of clocks, including biological aging.
"If one were to depart from the earth in a spaceship that could accelerate continuously at a comfortable one g (an acceleration that would produce a force equal to the gravity at the earth's surface), one would begin to approach the speed of light relative to the earth within about a year. As the ship continued to accelerate, it would come ever closer to the speed of light, and its clocks would appear to run at an ever slower rate relative to the earth. Under such circumstances, a round trip to the center of our galaxy and back to the earth--a distance of some 60,000 light-years--could be completed in only a little more than 40 years of ship time. Upon arriving back at the earth, the astronaut would be only 40 years older, while 60,000 years would have passed on the earth. (Note that there is no 'twin paradox,' because it is unambiguous that the space traveler has felt the constant acceleration for 40 years, while a hypothetical twin left behind on a spaceship circling the earth has not.)
"Such a trip would pose formidable engineering problems: the amount of energy required, even assuming a perfect conversion of mass into energy, is greater than a planetary mass. But nothing in the known laws of physics would prevent such a trip from occurring.
"Time travel into the past, which is what people usually mean by time travel, is a much more uncertain proposition. There are many solutions to Einstein's equations of General Relativity that allow a person to follow a timeline that would result in her (or him) encountering herself--or her grandmother--at an earlier time. The problem is deciding whether these solutions represent situations that could occur in the real universe, or whether they are mere mathematical oddities incompatible with known physics. No experiment or observation has ever indicated that time travel is occurring in our universe. Much work has been done by theoretical physicists in the past decade to try to determine whether, in a universe that is initially without time travel, one can build a time machine--in other words, if it is possible to manipulate matter and the geometry of space-time in such a way as to create new paths that circle back in time.
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Add CommentBefore the blogs were canceled here on Sci Am I had a blog under the username "PHAYEZ" which dealt with, among other things, time and measurement. I put forward that time only exists as a feature of three dimensional existence. Time is the "velocity/distance of 3D matter relative to the velocity/distance of other 3D matter". Outside of three dimensions "TIME" as such does not exist and infinity is equal to zero "time". Also outside of three dimensions measurements cannot be made of anything which makes mathematics, with all due respect, irrelevant since the language of mathematics has, as a syntax, products of measurement. The existence and non-existence of time is a spatial relationship oxymoron which is difficult to grasp when you are an entity who is wholly dependent on being made up of atoms which are moving through space.
Reply | Report Abuse | Link to thisOne final comment, if I may, on the speed limit of light and the fact that even information cannot exceed the speed of light. At the speed of light time is zero, in other words for the light there is no time that passes so that regardless of where it arrives, it arrives instantaneously. Nothing can move faster than instantaneously, even information...
Pierre
username: PHAYEZ (Edmonton,Alberta,Canada)
Before considering this question we must ponder whether we understand time properly or whether we know enough about Big Bang. It seems highly likely that an antimatter universe and anti-time was created alongside the world we observe. Antimatter seems the best candidate for Dark Matter, and Anti-time could well explain the bizarre nature of quantum mechanics, given that the Quantum World that we observe can only be described in probabalistic, uncertain terms, compared to the larger scale Relativistic world. It would seem that at Big Bang there was a flip over in the time dimension of the Quantum world, with that of the anti-matter universe. Thus when Quantum observations are performed, we are actually witnessing time-travel in a sense.
Reply | Report Abuse | Link to thisAlso the reason that Gravity propagation has never been detected is most likely because it too propagates in anti-time. This explanation would also explain the phenomenon of Entanglement. Entanglement would seem to be a microcosm of our connection to the Antimatter universe, which has been in place since Big Bang. Gravity thus appears to operate by virtue of this matter/antimatter connection and not due to a mediatory particle such as the Higgs Boson. The best way of understanding the Status Quo of the Matter/Antimatter universe is to consider Entropy, denoted by S. I would propose that S + ~S = K, where ~s stands for anti-entropy. Thus time-travel as such can only be possible if it does not violate this law. if it were theoretically possible to get a body to travel backwards in time, then it would appear that this law would be violated, unless it's equivalent in the antimatter universe were to travel forward in time by an equivalent amount. It would therefore seem that as the two universes are connected, that time travel in one of these universes would be negated by the affect on the other and therefore it would not be possible.
I was watching Into the Universe with Stephen Hawking which was talking about time travel. I was truly fascinated by the show itself, but I did find one flaw in Stephen Hawkings beliefs. I respect the man more than words can describe, but while watching the show he said, I do not believe that we can travel into the past, but I do believe we can travel into the future. He explained that time around objects of great mass is slower than farther away from those objects. He later explained how we could fly around a black hole, which decreases time in half compared to time here on earth. For example, 16 minutes would pass by on earth while only 8 minutes pass on the black hole. I understand what he is talking about, but this same concept can be applied to travel into the past. This means that if someone were to travel around an object (planet, black hole, etc.) that was smaller than earth for an extended period of time, they could travel back in time when arriving back on earth. I remember Stephen talking about paradoxes, one example being if a person were to travel into the past and shoot themselves. I understand how this makes no sense in the laws of physics, but Stephens belief that travel into the past cannot happen makes no sense either. I would appreciate some intelligent feedback on this subject and I mean no disrespect to Stephen or anyone else.
Reply | Report Abuse | Link to thisI was watching “Into the Universe with Stephen Hawking” which was talking about time travel. I was truly fascinated by the show itself, but I did find one flaw in Stephen Hawking’s beliefs. I respect the man more than words can describe, but while watching the show he said, “I do not believe that we can travel into the past, but I do believe we can travel into the future.” He explained that time around objects of great mass is slower than farther away from those objects. He later explained how we could fly around a black hole, which decreases time in half compared to time here on earth. For example, 16 minutes would pass by on earth while only 8 minutes pass on the black hole. I understand what he is talking about, but this same concept can be applied to travel into the past. This means that if someone were to travel around an object (planet, black hole, etc.) that was smaller than earth for an extended period of time, they could travel back in time when arriving back on earth. I remember Stephen talking about paradoxes, one example being if a person were to travel into the past and shoot themselves. I understand how this makes no sense in the laws of physics, but Stephen’s belief that travel into the past cannot happen makes no sense either. I would appreciate some intelligent feedback on this subject and I mean no disrespect to Stephen or anyone else.
Reply | Report Abuse | Link to thisEssentialy your traveling back to the past if you hang out with pluto or an astroid if you look at it that way, but it can also be thought of as traveling to the future slower then earth meaning that earth just gets ahead of you, or you get ahead of it, what ever wich way. So it depends on how you look at it.
Reply | Report Abuse | Link to thisTime travel seems reasonable
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They are offering $50 for the first person to find a verifiable contradiction between their model and observable physics.