No one keeps track of time better than Ferenc Krausz. In his lab at the Max Planck Institute of Quantum Optics in Garching, Germany, he has clocked the shortest time intervals ever observed. Krausz uses ultraviolet laser pulses to track the absurdly brief quantum leaps of electrons within atoms. The events he probes last for about 100 attoseconds, or 100 quintillionths of a second. For a little perspective, 100 attoseconds is to one second as a second is to 300 million years.

But even Krausz works far from the frontier of time. There is a temporal realm called the Planck scale, where even attoseconds drag by like eons. It marks the edge of known physics, a region where distances and intervals are so short that the very concepts of time and space start to break down. Planck time—the smallest unit of time that has any physical meaning—is 10-43 second, less than a trillionth of a trillionth of an attosecond. Beyond that? Tempus incognito. At least for now.

Efforts to understand time below the Planck scale have led to an exceedingly strange juncture in physics. The problem, in brief, is that time may not exist at the most fundamental level of physical reality. If so, then what is time? And why is it so obviously and tyrannically omnipresent in our own experience? “The meaning of time has become terribly problematic in contemporary physics,” says Simon Saunders, a philosopher of physics at the University of Oxford. “The situation is so uncomfortable that by far the best thing to do is declare oneself an agnostic.”

Time is a state of the mind. Time is measured only by the human mind. Indeed time travel would be possible, but not with a physical being.

Actually it would be possible to send something through time, and I'll simplify it for you.

Only light can travel at the speed of light, everything else can travel 99.99% the speed of light maximum. If a train were to be travelling 99.99% the speed of light time on the train would slow down to make sure it never reaches the speed of light by a passenger getting up and running forward which would add to the trains speed.

So if everything is slow motion on the train time would be going by slower on the train but anything outside of the train would be going at normal speed. If the train were to move at this speed for 5 months years would've passed outside of the train but the passengers only experienced 5 months, thus making them time travellers.

But since time travel is possible from a scientific standpoint wouldn't that mean time is more than a form of measurement?