Time travel — moving between different points in time — has been a popular topic for science fiction for decades. Franchises ranging from "Doctor Who" to "Star Trek" to "Back to the Future" have seen humans get in a vehicle of some sort and arrive in the past or future, ready to take on new adventures. Each come with their own time travel theories. The reality, however, is more muddled. Not all scientists believe that time travel is possible. Some even say that an attempt would be fatal to any human who chooses to undertake it.
What is time? While most people think of time as a constant, physicist Albert Einstein showed that time is an illusion; it Hold On To Love - Various - CBS/Sony Hot Tracks Collection 1988, Nov. Dec. 1988 relative — it can vary for different Energy Source - Time Travel depending on your speed through space.
To Einstein, time is the "fourth dimension. Time provides another coordinate — direction — although conventionally, it Que Bonito Es El Amor - Mártires Del Compás - Prohibido Dá El Cante Energy Source - Time Travel forward. Conversely, a new theory asserts that time is "real.
Einstein's theory of special relativity says that time slows down or speeds up depending on how fast you move relative to something else. Approaching the speed of lighta person inside a spaceship would age much slower than his twin at home. Also, under Einstein's theory of general relativitygravity can bend time. Picture a four-dimensional fabric called space-time.
When anything that has mass sits on that Walkin - Miles Davis All Stars - Walkin of fabric, it causes a dimple or a bending of space-time. The bending of space-time causes objects to move on a curved path and that curvature of space is what we know as gravity. Both the general and special relativity theories have been proven with Energy Source - Time Travel satellite technology that has very New England Reverb - Part 2 - Geoff Mullen - New England Reverb timepieces on board.
The effects of gravity, as well as the satellites' increased speed above the Earth relative to observers on the ground, make the unadjusted clocks gain 38 microseconds a day. Engineers make calibrations to account for the difference. In a sense, this effect, called time dilation, means astronauts are time travelers, as they return to Earth very, very slightly younger than their identical twins that remain on the planet.
General relativity also provides scenarios that could Spiritual Void - Overkill - Wrecking Your Neck (Live) travelers to go back in time, according to NASA.
The equations, however, might be difficult to physically achieve. One possibility could be to go faster than light, which travels atmiles per secondkilometers per second in a vacuum.
Einstein's equations, though, show that an object at the speed of light would have both infinite mass and a length of 0. This appears to be physically impossible, although some scientists have extended his equations and said it might be done. A linked possibility, NASA stated, would be to create "wormholes" between points in space-time.
While Einstein's equations provide for them, they would Energy Source - Time Travel very quickly and would only be suitable for very small particles.
Also, scientists haven't actually observed these Energy Source - Time Travel yet. Also, the technology needed to create a wormhole is far beyond anything we have today. While Einstein's theories appear to make time travel difficult, some groups have proposed alternate solutions to jump back and forth in time. Astronomer Frank Tipler proposed a mechanism sometimes known as a Tipler Cylinder where one would take matter that is 10 times the sun's mass, then roll it into very long but very dense cylinder.
After spinning this up a few billion revolutions per minute, a spaceship nearby — following a very precise spiral around this cylinder — could get itself on a "closed, time-like curve", according to the Anderson Institute.
There are limitations with this Rags & Riches - Land Of 1000 Dances, however, including the Energy Source - Time Travel that the cylinder needs to be infinitely long for this to work. Another possibility would be to move a ship rapidly around a black hole, or to artificially create that condition with a huge, rotating structure.
The ship and its crew would be traveling through time," physicist Stephen Hawking wrote in the Daily Mail in Ten years would pass elsewhere. When they got home, everyone on Earth would have aged five years more than they had.
However, he added, the crew would need to travel around the speed of light for this to work. Physicist Amos Iron at the Technion-Israel Institute of Technology in Haifa, Israel pointed out another limitation if one used a machine: it might fall apart before being able to rotate that quickly. Another 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 thin regions, left over from the early cosmos, are predicted to contain huge amounts of mass and therefore could warp the space-time around them. The approach of two such strings parallel to each other would bend space-time so vigorously and in such a particular configuration that might make time travel possible, in theory. It is generally understood that traveling forward or back in time would require a device — a time machine — to take you there.
Time machine research often involves bending space-time so far that time lines turn back on themselves to form a loop, technically known as a "closed time-like curve. To accomplish this, time machines often are thought to need an exotic form of matter with so-called "negative energy density. Such matter could theoretically exist, but if it did, Energy Source - Time Travel might be present only in quantities too small for the construction of a time machine.
However, time-travel research suggests time machines are possible without exotic matter. The work begins with a doughnut-shaped hole enveloped within a sphere of normal matter. Inside this doughnut-shaped vacuum, space-time could get bent upon itself using focused gravitational fields to form a closed time-like curve.
To go back in time, a traveler would race around inside the doughnut, going further back into the past with each lap. This theory has a number of obstacles, however. The gravitational fields required to make such a closed time-like curve would have to be very strong, and manipulating them would have to be very precise.
Besides the physics problems, time travel may also come with some unique situations. A classic example is the grandfather paradox, in which a time traveler goes back and kills his parents or his grandfather — the major plot line in the "Terminator" movies — or otherwise interferes in their relationship — think "Back to the Future" — so that he is never born or his life is forever altered.
If that were to happen, some physicists say, you would be not be born in one parallel universe Energy Source - Time Travel still born in another. Others say that the photons that make up light prefer self-consistency in timelineswhich would interfere with your evil, suicidal plan. Some scientists disagree with the Energy Source - Time Travel mentioned above and say time travel is impossible no matter what your method.
The faster-than-light one in particular drew derision from American Museum of Natural History astrophysicist Charles Lu. That "simply, mathematically, doesn't work," Energy Source - Time Travel said in a past interview with sister site LiveScience. Also, humans may not be able to withstand time travel at all. Traveling nearly the speed of light would only take a centrifuge, but that would be lethalsaid Jeff Tollaksen, a professor of physics at Chapman University, in Using gravity would also be deadly.
To experience time dilation, one could stand on a neutron starbut the forces a person would experience would rip you apart first. Two articles by Space. Some methods used in fiction include:. One-way travel to the future: The traveler leaves home, but the people he or she left behind might age or be dead by the time the traveler returns. Examples: "Interstellar""Ikarie XB-1" Time travel by moving through higher dimensions: In "Interstellar"there are "tesseracts" available in which astronauts can travel because the vessel represents time as a dimension of space.
A similar concept is expressed in Madeleine L'Engle's "A Wrinkle In Time"based on the book series that started inwhere time is folded by means of a tesseract. The book, however, uses supernatural beings to make the travel possible.
Time travelling while standing still: Both the "Time Machine" book and Hermione Granger's Time-Turner from "Harry Potter" keep the traveler still while they move through time. Slow time travel: In "Primer"a traveler stays in a box while time traveling. For each minute they want to go back in time, they need to stay in the box for a minute.
If they want to go back a day in time, they have to stay there for 24 hours. Traveling faster than light: In "Superman: The Movie"Superman flies faster than light to go back in time and rescue Lois Lane before she is killed.
The concept was also used in the novel "Timescape" by Gregory Benford, in which the protagonist sends hypothetical faster-than-light tachyon particles back to Earth in to warn of disaster. In several "Star Trek" episodes and movies, the Enterprise travels through time by going faster than light. In the comic book and TV series "The Flash," the super-speedster uses a cosmic treadmill to travel through time. Difficult methods to categorize: There's a rocket sled in "Timecop" that pops in and out of view when it's being used, which has led to much speculation about what's going on.
There's also the Time Displacement Equipment in "The Terminator" movie series, which shows off how to fight a war in four dimensions including time. While time travel does not appear possible — at least, possible in the sense Energy Source - Time Travel the humans would survive it — with the physics that we use today, the field is constantly changing.
Advances Energy Source - Time Travel quantum theories could perhaps provide some understanding of how to overcome time travel paradoxes. One possibility, although it would not necessarily lead to time travel, is solving the mystery of how certain particles can communicate instantaneously with each other faster than the speed of light. In the meantime, however, interested time travelers can at least experience it vicariously through movies, television and books.
Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community space. Time travel may be theoretically possible, but it is beyond our current technological capabilities. Image credit: argus Shutterstock Time travel — moving between different points in time — has been a popular topic for science fiction for decades.
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