STUFF we ought to know 2

 THE FLUIDITY OF TIME

Time is not a fixed dimension. What this means is that what we experience as steadfast, comparable, measurable time,  to mark the days of our lives is actually fluid. 

 EINSTIEN'S THEORY OF RELATIVITY (1917) revolutionised the laws of physics as we knew them then. Time and space are two aspects of the same thing, which is famously reffered to as Spacetime. 

Time for us goes in a linear direction, from now (present) to then (future.) We are aware of the division of days in 24 hour slots, which are then divided into minutes and seconds. This is time we use to schedule our daily activities, school, office hours, wedding dates, anniversaries and so on. And to us this time goes only in one direction - forward. This is commonly known as 'the arrow of time.'

This clock time is the same in every part of the earth, time zones may vary and they certainly do, but duration of a minute, an hour stays the same on earth. Why the qualification 'on earth?' This is because time is not the same in every place in the universe. Time like space is affected by gravity - the pulling force exerted by a body of mass, the bigger and denser the mass, the more the gravity or its gravitational pull. 

Earth, moon, Sun all have gravitational fields of varying degrees. And every body in the universe has gravity. How does this affect time and space? Space is not a large void or a deep hole which is populated by planets and stars. It is rather like a trampoline on which heavy bodies create dips and curves. Just like if heavy balls are placed on the trampoline it will bend and curve the surface, space is somewhat like that. As space bends around heavy celestial bodies so does time. I know this is a rather hard concept to grasp but just try. 

Stars and planets make time run slower, the force of the gravity makes time move at a slower pace than in relatively sparse regions of space. The gravity of these massive bodies make time drag and hence move slower than in outer space. Therefore, the example that if you had a twin and she travelled in space, on return she would be lot younger than you who'd be here on Earth. The gravity of earth makes time run slower than in space. Thus the image of a fixed time is an illusion. 

We also know by experience that time feels different when we are suffering, waiting, anxious - it takes longer to pass, than when we are happy, on holiday or generally having a good time. 

Scientists have ruled out the possibility of time travel to the past, because that raises the paradoxical situations of 'effect before cause', which within the known universal laws is an impossibility. But, time travel to the future is possible, at least theoritcally. There are ways, rather ruptures in spacetime through which it could be possible to travel to a distant time in the future. 

Although if we understand the speed of light then it is possible to appreciate the fact that when we look up into the night sky the light of the stars that we see is billions of light years old. Lightyear is the distance light travels in one year. A 186,000 miles per second, that means it can go around the globe 7 times in less than a second! Nothing can go faster than light. This is the speed limit of the Universe, and nothing can reach the speed of light also. Hence, coming back to our starlight in the night sky, the stars we witness tonight might have ceased to exist millions/billions of years ago, we are seeing the light that left those that many years ago!!!! so in a way we are seeing into the distant past!!! so much for impossibility of time travel.