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5 Things You Didn't Know: Time Travel
By Jacob Franek
To traverse time, visit the past or to jump ahead to the future: These are concepts so fascinating that they grip the very mind itself, pulling at our imagination with relentless rigor. Just imagine the possibilities: Would you revisit your childhood? Would you share a thought with Aristotle or a drink with Julius Caesar?
Unfortunately, for the time being, these are questions that one can only imagine the answer to. However, great minds have doubted time travel in the past, only to admit that the possibility simply cannot be excluded. In fact, renowned physicist Stephen Hawking came to this exact conclusion. So, we're here to let you in on some of the futuristic possibilities with 5 things you didn’t know about time travel.
1- Stephen Hawking claimed time travel was impossible
One of the many theories of time travel states that the universe will protect itself from creating paradox (problems associated with time travel) by simply not allowing time machines to be made. “All time machines are likely to self-destruct the moment they are activated,” famed physicist Kip Thorne told Scientific American.
While the idea of an unwilling universe seems a little far-fetched (one can’t help but picture the invisible forces at work in Final Destination), Stephen Hawking openly subscribed to this hypothesis, deciding that there ought to be a law banning time travel from the laws of physics. Hawking proposed the chronology protection conjecture as that law. In the years following his proposal, Hawking became increasingly frustrated as he could find no physical law that would prevent time travel. Unable to prove this impossibility, Hawking changed his mind, making headlines when he said, “Time travel may be possible, but it is not practical.”
2- The universe may not allow change when you time travel
It’s no surprise that Hawking once believed time travel to be impossible; there are simply too many paradoxes involved in the whole procedure. The most famous of which -- the grandfather paradox -- proposes the following conundrum: If you were to travel back in time and kill your grandfather, would you not then cease to exist, never having had the chance to be born? Since its mind-boggling inception, the grandfather paradox has seen many attempts to satisfy its confusion. Perhaps the most successful came from American physicist Hugh Everett III, who first proposed the many-worlds interpretation (MWI) of time travel. Though it has gone through several revisions, the MWI essentially states that many universes may exist, one for every possible outcome to every possible event. Therefore, if you were to travel back in time and kill your grandfather, the universe from which you traveled would remain unaffected and you would live on (albeit as a parricidal sadist) because the universe would shift to keep you alive, however possible.
While the MWI does theoretically seem in concordance with quantum mechanics, it certainly has its share of skeptics and, well, it just seems a little too convenient. A more recent model, however, by physicists, Daniel Greenberger and Karl Svozil, allows quantum mechanical time travel along a single timeline while still overcoming the infamous grandfather paradox. According to Greenberger and Svozil, quantum objects exist as multiple component waves, with each wave following a particular path through space-time. In 2005, Greenberger and Svozil found that when these waves travel back in time they interfere destructively, thus preventing anything from happening differently from that which has already happened. Therefore, if you know the present, you cannot change it: "You go back to kill your [grand]father, but you'd arrive after he'd left the room, you wouldn't find him or you'd change your mind," Professor Greenberger told the BBC.
3- We may have already been visited by a time traveler
Back in 2000, a person who identified himself as John Titor began visiting online sci-fi discussion forums, claiming to be a military time-traveler from the year 2036. Appearing, and later disappearing, without a trace, Titor engaged and entertained the online public providing numerous predictions and details about time travel and the future. According to Titor, U.S. civil war was to erupt following the 2004/05 American presidential elections on account of individual “orders and rights.” Titor made predictions that civil liberties will be lost in preference of national security. He also claimed that by 2015, the civil war will end when Russia launches nuclear strikes on various U.S. targets, whereupon the U.S. will retaliate, perpetuating World War III and leaving over three billion people dead.
Obviously, Titor’s claim of civil war was never realized, neither were numerous other claims that he made at the time. Titor, however, indicated that the many-worlds interpretation of time travel was correct, thus stating that the time line he had traveled from would ultimately differ from ours, further making his claims unfalsifiable. Despite the obvious hoax-y feel to this story, it certainly makes for one interesting read. Some of Titor’s other predictions: America will wage war on Iraq, claiming Iraq has nuclear weapons (this prediction was made prior to 9/11 and any talk of war with Iraq); war will erupt between Israel and its Arab neighbors, and weapons of mass destruction will be used; after 2004, on account of international conflict, the Olympics will be canceled (could he have meant China 2008?). And perhaps the prediction that packed the most punch: The future will judge the present harshly.
4- Time travel may not require a time machine
The majority of models explaining time travel require a machine that can produce some form of exotic matter with negative density. However, does this exotic matter exist, and what exactly is it? Well, the best way to understand negative energy density is to look at black holes. Black holes generate intensely strong gravitational fields, so strong that they could actually bend space-time itself.
Theorist Roy Kerr postulated that time travel may be possible if you could enter a black hole and exit through a white hole on the other side. While a black hole pulls everything toward it, a white hole would essentially push everything away from it, using -- you guessed it -- matter with negative energy density. Though it sounds like a peachy theory, unfortunately, all known forms of matter have positive density. However, exotic matter is predicted by quantum field theorists to exist, only it has yet to be produced and seems available in quantities far too small for actual time travel. Don't fret just yet, new research now proposes that time travel may be possible -- without using exotic matter.
In 2007, physicist Amos Ori of the Technion-Israel Institute of Technology developed complicated mathematical equations outlining a set of ideal gravitational conditions that would allow space-time to spontaneously bend and loop upon itself to form a donut. In this scenario, no time machine is needed. Space-time becomes the machine needed for time travel. If a person could navigate laps around the donut, they could hypothetically travel back in time with each lap.
5- Time travel could begin in 2008
Back when Hawking thought time travel was impossible, one of his defining arguments was that we have not yet seen any time-traveling tourists. If time travel were possible, Hawking argued, “Why haven't we been overrun by tourists from the future?” Hawking later answered his own question by saying that space-time must be warped in a certain way to permit time travel, and if we cannot warp space-time in such a way until the future, then time travelers would not be able to travel back to an earlier point (think of the gravity donut example above). So basically, one could travel into the past only as far back as the point of creation of the first time portal. OK, great, but what does that have to do with 2008 you might wonder.
Well, in February of 2008, the European Organization for Nuclear Research (known as CERN) unveiled its $9 billion (USD) Large Hadron Collider (LHC) -- the most powerful atom-smasher ever known. The LHC is a modern marvel of technology, and is called the most complicated thing humans have ever built. It measures 27 kilometers in circumference, sits 175 meters underground and facilitates the head-on collision of protons that travel near the speed of light. In fact, the LHC is so powerful that Russian mathematicians, Irina Aref'eva and Igor Volovich, claim that it sets the conditions for the creation of a wormhole, providing a potential doorway for unexpected visitors from the future. Though the doorway is probably too small for humans to pass through, is it possible that we’ll start seeing miniature messengers from tomorrow? Only time will tell.
http://www.askmen.com/entertainment/special_feature_150/198_special_feature.html
By Jacob Franek
To traverse time, visit the past or to jump ahead to the future: These are concepts so fascinating that they grip the very mind itself, pulling at our imagination with relentless rigor. Just imagine the possibilities: Would you revisit your childhood? Would you share a thought with Aristotle or a drink with Julius Caesar?
Unfortunately, for the time being, these are questions that one can only imagine the answer to. However, great minds have doubted time travel in the past, only to admit that the possibility simply cannot be excluded. In fact, renowned physicist Stephen Hawking came to this exact conclusion. So, we're here to let you in on some of the futuristic possibilities with 5 things you didn’t know about time travel.
1- Stephen Hawking claimed time travel was impossible
One of the many theories of time travel states that the universe will protect itself from creating paradox (problems associated with time travel) by simply not allowing time machines to be made. “All time machines are likely to self-destruct the moment they are activated,” famed physicist Kip Thorne told Scientific American.
While the idea of an unwilling universe seems a little far-fetched (one can’t help but picture the invisible forces at work in Final Destination), Stephen Hawking openly subscribed to this hypothesis, deciding that there ought to be a law banning time travel from the laws of physics. Hawking proposed the chronology protection conjecture as that law. In the years following his proposal, Hawking became increasingly frustrated as he could find no physical law that would prevent time travel. Unable to prove this impossibility, Hawking changed his mind, making headlines when he said, “Time travel may be possible, but it is not practical.”
2- The universe may not allow change when you time travel
It’s no surprise that Hawking once believed time travel to be impossible; there are simply too many paradoxes involved in the whole procedure. The most famous of which -- the grandfather paradox -- proposes the following conundrum: If you were to travel back in time and kill your grandfather, would you not then cease to exist, never having had the chance to be born? Since its mind-boggling inception, the grandfather paradox has seen many attempts to satisfy its confusion. Perhaps the most successful came from American physicist Hugh Everett III, who first proposed the many-worlds interpretation (MWI) of time travel. Though it has gone through several revisions, the MWI essentially states that many universes may exist, one for every possible outcome to every possible event. Therefore, if you were to travel back in time and kill your grandfather, the universe from which you traveled would remain unaffected and you would live on (albeit as a parricidal sadist) because the universe would shift to keep you alive, however possible.
While the MWI does theoretically seem in concordance with quantum mechanics, it certainly has its share of skeptics and, well, it just seems a little too convenient. A more recent model, however, by physicists, Daniel Greenberger and Karl Svozil, allows quantum mechanical time travel along a single timeline while still overcoming the infamous grandfather paradox. According to Greenberger and Svozil, quantum objects exist as multiple component waves, with each wave following a particular path through space-time. In 2005, Greenberger and Svozil found that when these waves travel back in time they interfere destructively, thus preventing anything from happening differently from that which has already happened. Therefore, if you know the present, you cannot change it: "You go back to kill your [grand]father, but you'd arrive after he'd left the room, you wouldn't find him or you'd change your mind," Professor Greenberger told the BBC.
3- We may have already been visited by a time traveler
Back in 2000, a person who identified himself as John Titor began visiting online sci-fi discussion forums, claiming to be a military time-traveler from the year 2036. Appearing, and later disappearing, without a trace, Titor engaged and entertained the online public providing numerous predictions and details about time travel and the future. According to Titor, U.S. civil war was to erupt following the 2004/05 American presidential elections on account of individual “orders and rights.” Titor made predictions that civil liberties will be lost in preference of national security. He also claimed that by 2015, the civil war will end when Russia launches nuclear strikes on various U.S. targets, whereupon the U.S. will retaliate, perpetuating World War III and leaving over three billion people dead.
Obviously, Titor’s claim of civil war was never realized, neither were numerous other claims that he made at the time. Titor, however, indicated that the many-worlds interpretation of time travel was correct, thus stating that the time line he had traveled from would ultimately differ from ours, further making his claims unfalsifiable. Despite the obvious hoax-y feel to this story, it certainly makes for one interesting read. Some of Titor’s other predictions: America will wage war on Iraq, claiming Iraq has nuclear weapons (this prediction was made prior to 9/11 and any talk of war with Iraq); war will erupt between Israel and its Arab neighbors, and weapons of mass destruction will be used; after 2004, on account of international conflict, the Olympics will be canceled (could he have meant China 2008?). And perhaps the prediction that packed the most punch: The future will judge the present harshly.
4- Time travel may not require a time machine
The majority of models explaining time travel require a machine that can produce some form of exotic matter with negative density. However, does this exotic matter exist, and what exactly is it? Well, the best way to understand negative energy density is to look at black holes. Black holes generate intensely strong gravitational fields, so strong that they could actually bend space-time itself.
Theorist Roy Kerr postulated that time travel may be possible if you could enter a black hole and exit through a white hole on the other side. While a black hole pulls everything toward it, a white hole would essentially push everything away from it, using -- you guessed it -- matter with negative energy density. Though it sounds like a peachy theory, unfortunately, all known forms of matter have positive density. However, exotic matter is predicted by quantum field theorists to exist, only it has yet to be produced and seems available in quantities far too small for actual time travel. Don't fret just yet, new research now proposes that time travel may be possible -- without using exotic matter.
In 2007, physicist Amos Ori of the Technion-Israel Institute of Technology developed complicated mathematical equations outlining a set of ideal gravitational conditions that would allow space-time to spontaneously bend and loop upon itself to form a donut. In this scenario, no time machine is needed. Space-time becomes the machine needed for time travel. If a person could navigate laps around the donut, they could hypothetically travel back in time with each lap.
5- Time travel could begin in 2008
Back when Hawking thought time travel was impossible, one of his defining arguments was that we have not yet seen any time-traveling tourists. If time travel were possible, Hawking argued, “Why haven't we been overrun by tourists from the future?” Hawking later answered his own question by saying that space-time must be warped in a certain way to permit time travel, and if we cannot warp space-time in such a way until the future, then time travelers would not be able to travel back to an earlier point (think of the gravity donut example above). So basically, one could travel into the past only as far back as the point of creation of the first time portal. OK, great, but what does that have to do with 2008 you might wonder.
Well, in February of 2008, the European Organization for Nuclear Research (known as CERN) unveiled its $9 billion (USD) Large Hadron Collider (LHC) -- the most powerful atom-smasher ever known. The LHC is a modern marvel of technology, and is called the most complicated thing humans have ever built. It measures 27 kilometers in circumference, sits 175 meters underground and facilitates the head-on collision of protons that travel near the speed of light. In fact, the LHC is so powerful that Russian mathematicians, Irina Aref'eva and Igor Volovich, claim that it sets the conditions for the creation of a wormhole, providing a potential doorway for unexpected visitors from the future. Though the doorway is probably too small for humans to pass through, is it possible that we’ll start seeing miniature messengers from tomorrow? Only time will tell.
http://www.askmen.com/entertainment/special_feature_150/198_special_feature.html