Back to the Future, Men in Black, Terminator, Looper, Deja Vu... time travel is a common theme in movies, and many of us are fascinated by it. According to physicists, it isn't as fictitious as you might think it is.Traveling back in time? That's a tough one...It's really hard for a lot of us to even imagine this being possible. Most physicists also think it's impossible. However, there is a way of doing it that experts agree on.This method uses a strange concept called "wormhole." What is a wormhole? It's hard to explain because it doesn't exist. Well... we don't know if it exists. It's a concept imagined by Albert Einstein.These hypothetical objects would, hypothetically, connect two places like a tunnel. But it goes even further. Instead of connecting two physical places, it would connect two regions of space-time. This would make it possible to move faster, provided that it travels faster than the speed of light.Suffice to say that it is kind of a fantasy, especially since we don't know if these wormholes exist. And even if they existed, could we get through?A trip to the future? That's more likely!Unlike traveling to the past, which physicists can't agree on, scientists are unanimous when it comes to traveling to the future. In a video for Business Insider, Brian Greene, professor of physics and mathematics at Columbia University in New York, explains how that could come to be."We know how to do it because Einstein showed us the way over a hundred years ago. It’s surprising how few people actually really know about this in their bones. He showed that if you go out into space and travel near the speed of light, and you turn around, and you come back, your clock will be ticking off time more slowly. So, when you step off it's going to be the future on planet Earth. You will have time traveled into the future."So it's doable, provided you travel at the speed of light, meaning 299,792,458 m\/s... Otherwise, Einstein came up with another option. If you approach the edge of a source where gravity is strong, like a black hole, but you really stop at its edge, time will move slower for you than for everyone else. Once you return to Earth, you'll be in the future.Machines made for time travel?Man has always dreamed of having a "time machine." It's often pictured as a device, an object, or a car, like in Back to the Future. But none of these have proven to be even plausible.Still, Ron Mallett, an American astrophysicist, is convinced that it is possible to make a time machine. He has spent much of his life studying theories of time travel and is now convinced that he has the answer.His idea is to "twist" time in a loop with a laser beam. So we'd be able to travel to the past, then return to the present by going around the loop. He has created a prototype but will need more funds to run some tests. Is this real or just fantasy?