According to the current understanding of the laws of physics, we have already established that it is possible to move forward in time relative to the observer. In a basic sense, we could technically time travel into the future – according to Einstein's theory of special relativity, which has to do with the warping of space and time.
However, another German physicist by the name of Rudolf Clausius theorised the second law of thermodynamics. This crushed the science fiction enthusiast's dreams of potentially travelling back in time one day as science and our understanding of physics progressed.
The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. The key here is the idea and understanding of entropy, and how natural phenomena always follows from a low entropy state to a high entropy state and never the reverse.
This fundamental understanding of the second law of thermodynamics, in turn, serves to prove that time itself flows from low entropy to high entropy. This directly translates into a forward continuous motion, and never from a high entropy state to a low. Thus, time always moves in one direction.
Take a look at the video below by the YouTube channel, BBC, on Brian Cox explains why time travels in one direction – Wonders of the universe – BBC Two.