Is time travel possible?
Time travel has always fascinated us. But what is meant by time travel and could it ever be possible? Where would you like to go, if you could? Back in time or forward?
It is mind-boggling to think about time travel. What if you went back in time and prevented your father and mother from the meeting? You would prevent yourself from ever having been born! But then if you hadn't been born, you could not have gone back in time to prevent them from the meeting.
Time travel is the concept of movement between certain points in time, analogous to moving between different points in space by an object or a person, typically using a hypothetical device known as a time machine. Time travel is a widely-recognized concept in philosophy and fiction. The idea of a time machine was popularized by H. G. Wells' 1895 novel The Time Machine.
But the question is, can we travel in time faster or slower than "1 hour per hour"? Or can we actually travel backward in time, going back, say 2 hours per hour, or 10 or 100 years per hour?
The great 20th-century scientist Albert Einstein developed a theory called Special Relativity, developed in 1905. 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 for anything that travels through space-time, and light always travels the speed limit through empty space.
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Time travel of a sort also occurs for objects in gravitational fields. Einstein had another remarkable theory called General Relativity, which predicts that time passes more slowly for objects in gravitational fields (like here on Earth) than for objects far from such fields. So there are all kinds of space and time distortions near black holes, where the gravity can be very intense.
There may be an out to be found in general relativity, Einstein’s theory of gravity that unites space and time as “spacetime”, which curves in the presence of mass. It allows for the possibility of wormholes – a kind of tunnel through spacetime connecting otherwise very distant parts of the universe.
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.
Say you were 15 years old when you left Earth in a spacecraft traveling at about 99.5% of the speed of light (which is much faster than we can achieve now) and celebrated only five birthdays during your space voyage. When you get home at the age of 20, you would find that all your classmates were 65 years old, retired, and enjoying their grandchildren! Because time passed more slowly for you, you will have experienced only five years of life, while your classmates will have experienced a full 50 years.
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In the past few years, some scientists have used those distortions in space-time to think of possible ways time machines could work. Some like the idea of "wormholes," which may be shortcuts through space-time. This and other ideas are wonderfully interesting. The ideas are based on good, solid science. In all time travel theories allowed by real science, there is no way a traveler can go back in time to before the time machine was built.
We could travel 10,000 years into the future and age only 1 year during that journey. Such a trip would consume an extraordinary amount of energy. Time travel to the past is more difficult.
Even the world-renowned physicist Stephen Hawking was entranced by the idea of time travel before his death when he discussed in the Daily Mail how a black hole could make it possible. "Around and around they'd go, experiencing just half the time of everyone far away from the black hole. The ship and its crew would be traveling through time," he wrote in 2010. However, physicist Amos Iron at the Technion-Israel Institute of Technology in Haifa, Israel, said a machine circling a black hole would probably disintegrate before moving that quickly.
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In 2015, Ali Övgün of Eastern Mediterranean University in Cyprus said wormholes might be possible in zones with dark matter. This is a theoretical form of matter that cannot be seen or otherwise sensed with telescopes but does show itself in its gravitational effects on other bodies. While his equations show wormholes could occur in these regions, Övgün said he is still searching for proof. "It is only mathematical proof," he said. "I hope one day it will be possible to also find direct experimental evidence."