**Time travel is one of my favorite topics!**

**We all travel in time. During the last year, I've moved forward one year and so have you. Another way to say that is that we travel in time at the rate of 1 hour per hour.**

**The great 20th century scientist Albert Einstein developed a theory called Special Relativity. The ideas of Special Relativity are very hard to imagine because they aren't about what we experience in everyday life, but scientists have confirmed them. This theory says that space and time are really aspects of the same thing—space-time. There's a speed limit of 300,000 kilometers per second (or 186,000 miles per second) for anything that travels through space-time, and light always travels the speed limit through empty space.**

**Special Relativity also says that a surprising thing happens when you move through space-time, especially when your speed relative to other objects is close to the speed of light. Time goes slower for you than for the people you left behind. You won't notice this effect until you return to those stationary people.**

**Twin paradox**

In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. This result appears puzzling because each twin sees the other twin as traveling, and so, according to an incorrect naive application of time dilation, each should paradoxically find the other to have aged more slowly. However, this scenario can be resolved within the standard framework of special relativity (because the twins are not equivalent; the space twin experienced additional, asymmetrical acceleration when switching direction to return home), and therefore is not a paradox in the sense of a logical contradiction.

Starting with Paul Langevin in 1911, there have been numerous explanations of this paradox, many based upon there being no contradiction because there is no symmetry—only one twin has undergone acceleration and deceleration, thus differentiating the two cases. Max von Laue argued in 1913 that since the traveling twin must be in two separate inertial frames, one on the way out and another on the way back, this frame switch is the reason for the aging difference, not the acceleration per se. Explanations put forth by Albert Einstein and Max Born invoked gravitational time dilation to explain the aging as a direct effect of acceleration.

Consider a space ship traveling from Earth to the nearest star system outside of our solar system: a distance d = 4 light years away, at a speed v = 0.8c (i.e., 80 percent of the speed of light).

(To make the numbers easy, the ship is assumed to attain its full speed immediately upon departure—actually it would take close to a year accelerating at 1 g to get up to speed.)

The parties will observe the situation as follows:

The Earth-based mission control reasons about the journey this way: the round trip will take t = 2d/v = 10 years in Earth time (i.e. everybody on Earth will be 10 years older when the ship returns). The amount of time as measured on the ship's clocks and the aging of the travelers during their trip will be reduced by the factor \scriptstyle{\epsilon = \sqrt{1 - v^2/c^2}}, the reciprocal of the Lorentz factor. In this case ε = 0.6 and the travelers will have aged only 0.6 × 10 = 6 years when they return.

The ship's crew members also calculate the particulars of their trip from their perspective. They know that the distant star system and the Earth are moving relative to the ship at speed v during the trip. In their rest frame the distance between the Earth and the star system is εd = 0.6d = 2.4 light years (length contraction), for both the outward and return journeys. Each half of the journey takes 2.4/v = 3 years, and the round trip takes 2 × 3 = 6 years. Their calculations show that they will arrive home having aged 6 years. The travelers' final calculation is in complete agreement with the calculations of those on Earth, though they experience the trip quite differently from those who stay at home.

If twins are born on the day the ship leaves, and one goes on the journey while the other stays on Earth, they will meet again when the traveler is 6 years old and the stay-at-home twin is 10 years old. The calculation illustrates the usage of the phenomenon of length contraction and the experimentally verified phenomenon of time dilation to describe and calculate consequences and predictions of Einstein's special theory of relativity.

*Close to the speed of light (about 300,000 kilometers per second), time warps become startling. Fly to the star Vega, 25 light years away, and back again at 99% of the speed of light, and when you return to Earth in 2062, you will have experienced only seven years travel time in the spacecraft. In effect, you will have leaped 42 years into Earth's future.*

*Ever since HG Wells ' trailblazing novel " The Time Machine " time travel has been a staple of science fiction . The idea of traveling through time is deeply fascinating : you get into the machine , press a few buttons, and step out not just somewhere else , but " somewhen " else . It's easy to imagine , but can it really be done ?*

*Travel into the future is not only possible , we have done it , although so far only in paltry amounts . How about going back in time ? That is far more problematic and remains an active area of research . Einstein found that not only affects this speed , gravity does too . This runs a little bit faster on the roof , where gravity is imperceptibly weaker , than in the basement , for example .*

*A really big time warp requires an intense gravitational field . Black holes are the best ; near their surfaces and thus slowed almost to a standstill relative to us . Indeed , black holes are black because outgoing light is trapped in slow motion . However , hanging out near a black hole is not only dangerous , it still represents only travel into the future , it gets you to the future quicker . Getting to the past requires something even weirder than a black hole - a wormhole .*

*The Evidence That Time Travel is Happening All Around Us :*

*1.The man often called Time Traveling Hipster from the reopening ceremony of the South Forks Bridge in Gold Bridge , British Columbia , Canada , 1941.This photo*

*has not been digitally tampered with . So what 's the deal with the young man in the contemporary - looking sunglasses , t-shirt , and camera ?*

*2.*

*The Philadelphia Experiment, 1943*

*There were no such experiments, of course, but some reports stated that the U.S. Navy destroyer escort USS Eldrige traveled back in time for about 10 seconds on June 28 in 1943.*

*NIKOLA TESLA: SECRET TIME TRAVEL EXPERIMENTS*

*After Tesla's death in New York City, Tesla's files and notes on death rays and other matters were confiscated by the FBI. Some of the FBI files on Tesla were published on the Internet under the Freedom of Information Act, but these have since been removed.*

*Nikola Tesla was a genius, a man ahead of his time.*

*I think that the U.S. services took all of Tesla's papers which were consistent explained in details. Also, I think that even today the world lives of his draft.I 'm sure that Tesla (New Scientist) made a time machine.*

*anyway,*

*Time travel certainly stirs the imagination of all of us.*

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