Time travel offers you two paths- go to the past or go to the future. Of the two traveling to the past has always been the more desirable. That's because everyone has something in their past that they want to change, be it good or bad.

However, physicists from the most respected institutions have come to the conclusion that traveling back to the past is close to impossible for a number of reasons-logical and theoretical.

The most popular theory suggest that the universe is woven into a fabric called space-time which involves understanding that everything exists in four dimensions. These are length, width, height and time. We humans exist in the third dimensional plane, and we can move freely in it. However, humans cannot move through time, and that is the big hurdle.

To "rip" through the fabric of space and time, scientists say that there's a small chance that humans can access what is known as "wormholes." These wormholes are rifts in the matrix that constitutes reality- a hypothetical tunnel connecting two regions of space-time. The regions bridged could be two completely different universes or two parts of one universe.

Scientists say matter can pass through, so a man in a ship may be able to squeeze in. If he does, he may end up in another location and time in the universe, past or future. He may never find the tunnel that leads where he wants to be in the past, but it's a start.

Another theory is that there may be remnants of what was there before the universe came to be. These are called cosmic strings. These are virtual strings that either loop all over the universe or stretch to infinity. They're made of immense mass and unimaginable energy, making them potentially an avenue where time and space can be warped and that opens the window to the past.

Traveling to the past is hard, but a trip to the future is relatively easier says Professor Michio Kaku. "If you want to know what the Earth is like one million years from now, I'll tell you how to do that," said Greene, a consultant for Déjà Vu - a recent movie that dealt with time travel. "Build a spaceship. Go near the speed of light for a length of time—that I could calculate. Come back to Earth, and when you step out of your ship you will have aged perhaps one year while the Earth would have aged one million years. You would have traveled to Earth’s future."