In the 1978 episode of 'Super-Friends' - 'Conquerers of the Future', the Legion of Doom, which dedicated to a single objective: the conquest of the universe, left the 20th century and traveled into the future to the year 3984. It was understood 39 represented the year of the start of World War II (1939) and 84 represented George Orwell's vision of the future in the book, 'Nineteen Eighty-Four'.
In the year 3984, the leaders of earth were Yerba and Zemora. They lived in the ruling chamber of the gated domed city. Outside the domed city lived the barbarian-like Barlocks, who were cavepeople. At that time, the earth civilization was gone. Lex Luthor decided to join forces with the Barlocks to take over the domed city in his quest to conquer earth.
Following the takeover, Sinestro smirked, "An entire planet at our feet and all the comfort of the 40th century." Toyman added, "And no Super-Friends." Black Manta chuckled, "Gold! Jewels! Statues erected in our honor!" However Lex Luthor countered, "I say it's not enough! Why be satisfied with the earth when the power at our disposal we could rule the galaxy? With the Barlocks under our command we could conquer every planet within the milky way!" Grodd guffawed, "Why stop there? Before long we could control the entire universe."
To do so, Lex Luthor launched an attack on the ruling planet of sector 13 as well as the ice planet. In order to stop the Legion of Doom, the Super-Friends penetrated the time barrier to travel 10,000 years into the future where Superman found the Book of Revelation (also known as 'A History of Earth from the Year 2000 to 7000'). The Super-Friends successfully returned the earth back to its rightful rulers and returned the Legion of Doom back to the 20th century.
The question remained, "Is time travel possible?" Dr Marc from NASA explained, "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.
"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. So, if your journey began in 2003, it would have taken you only 5 years to travel to the year 2053, whereas it would have taken all of your friends 50 years. In a sense, this means you have been time traveling. This is a way of going to the future at a rate faster than 1 hour per hour.
"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."
Astrophysicist Paul Sutter at space.com informed, "Special relativity teaches us that the three dimensions of space and the solitary dimension of time are woven together like a fabric. It's impossible to think of them as separate entities, only a singular unified entity - space-time. We can't think of motion through space without being mindful of motion through time, and vice versa. Left-right, up-down, back-forth and past-future are all on equal footing. And yet, time does seem a little different.
"We have complete freedom of movement within space, but we cannot avoid our future. Time seems to have an 'arrow', whereas the spatial dimensions are ambidextrous. Given the unity between time and space, it leads to the obvious question: Is time travel, of any sort, possible? Under any circumstances? At all? Many science fiction stories explore humanity's desire to travel back in time. Is such a thing really possible in our universe?
"Oddly enough, the answer is yes! We cannot avoid moving into our futures, but we can control the rate that we move through time. This is a consequence of another lesson from relativity: Not all clocks are the same. The speed at which you move through space determines the speed at which you move through time. In the succinct phrase: Moving clocks run slow. If you could build a big enough rocket to provide a constant acceleration of 1g (9.8 meters per second per second; the same acceleration as provided by the Earth's gravity at its surface), you could reach the center of the Milky Way galaxy — a healthy 20,000 light-years away — in just a couple decades of your personal time."