IS TIME TRAVEL POSSIBLE ??

IS TIME TRAVEL POSSIBLE ??

IN TO THE FUTURE...

       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 (don't ask me how, that's an engineering problem) 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 centre of the Milky Way galaxy — a healthy 20,000 light-years away — in just a couple decades of your personal time.

You could stop for a few hours, have a picnic near Sagittarius A* (the black hole at the centre of the galaxy), and then hop back into your rocket and come back to Earth.

By the time you return you'll be eligible for retirement benefits, if the institution providing those benefits is even around, because while you only travelled for a few decades according to the clock on your ship, about 40,000 years would've passed on the Earth.

IN TO THE PAST...

          It's the same story every time (pardon the too-hard-to-resist pun). For every scenario we concoct in general relativity to allow CTCs and time travel into our own past, nature finds a way to confound our plans and rule out the scenario.

What's going on? General relativity allows — in principle — time travel into the past, but it appears to be ruled out in every case. It seems like something funny is afoot, that there ought to be some fundamental rule to disallow time travel. But there isn't one. We can't point to any particle interaction at the subatomic level that clearly prevents the formation of CTCs.

The inevitable progression of time from the past to the future resembles another indomitable law of nature: entropy. That's the iron law of thermodynamics that states that closed systems go from ordered to disordered.