“I don’t have time” or “I need some time to finish this” or “Time heals everything” are some of the common statements we hear in our lives. And we also do what is common: hear them, understand them and then forget them. But sometimes, we may ponder on what this time really is, is the ticking of the clock all there is to it, or it is something more complex and subtle?
Also, all of us have come across the word Time Travel at some point or the other in our lives. We know that, in essence, it is about travelling anywhere other than the present. It also brings out some of our most weirdest and fascinating imaginations.
Various sci-fi movies have demonstrated time travel of different sorts. But, till now, we know that it hasn’t been possible. However, there is much more to the theories of time travel then just having a time machine. The following are some of the most amazing things about time and time travel.
Time Is The Rate Of Change Of The Universe
Time can be described in its most basic form as the rate of change of the universe. It is common knowledge that all properties of matter occur when they are in space. However, there is something called the Space-time continuum which states that space cannot exist without time, and vice versa.
Therefore, everything that happens in space happens in time also. And since time is the rate of change of the universe, everything that relates to change is related to time. For example, an iron slowly rusting, or we all slowly getting older and then eventually dying, are all acts of time. Although we might think we know this already, but right now we are witnessing change around and within us through a different angle, through time in its basic and universal sense.
Gravitational Time Dilation
This term might seem quite scientific, but it is really very easy to understand. First let us understand gravity. As we all know, gravity is the resultant force of a body towards its surface, due to its mass. So, gravity involves mass, and anything having mass curves space-time. Let us take an example.
Suppose four of us are holding each end of handkerchief. and applying a force which makes it flat. Now we put a stone on top of the handkerchief. What happens? The stone takes the handkerchief a bit downwards. It is similar to how is it with space-time. However space-time has four dimensions, time being the fourth dimension. But the effect can be understood with the example.
The handkerchief is the space and earth is the stone, say. Then, basically earth (and any other body having mass) curves space. And due to the space-time continuum discussed earlier, the earth also curves time. Therefore, the rate at which time is going on earth is not the rate at which time is going on space. So, if we are in orbit, time passes faster for us, since earth’s mass drags the time. The changes are very minute, though.
Also, speed also plays a role in how we experience time. The mass of a body increases as its speed increases, and hence time passes more slowly as speed increases. Although not a very practical example, we can say that if we run then time passes more slowly for us. And so, if a body moves at the speed of light, its mass becomes infinite, That is why it is only theoretically possible to travel time till now since a body’s mass cannot be infinite. If it becomes infinite, however, time stops for it.
Time travel to the past
We can see that if there are some innovations made in technology at a very high level, then time travel to the future may be possible. But what about time travel to the past? Say, we apply the theories and reach the past, at a time where we weren’t even born. But that would be weird. Because a consequence cannot come before action. Or, a cause leads to an effect, which is also called the law of causality. Our birth is a cause, and our existence right now is an effect of our birth. So, if we reach at a time before we were born, we defy the law of causality. However, this problem can be solved by using the concept of Multiverse, discussed later.
Ways to travel time (in theory) through Kerr Rings, Wormholes and Cosmic String
Kerr Black Holes, proposed by New Zealand mathematician Roy Kerr, is a kind of black hole created by a dying star collapsing into a rotating ring of neutron stars. Their centrifugal force prevents the infinite gravitational pull from the black hole, and so we can pass through it. It is also postulated that it will bring us out through a white hole, probably into another time. But it is just a theory.
Another way to travel time is Wormholes, shown very clearly in the movie “Interstellar”. Wormholes are tunnels in the space caused due to various masses putting pressure in the universe. And this tunnel would bring together two separate times, at least in theory.
Cosmic Strings are stringlike objects thought to be created during the Big Bang. They are very thin with a lot of gravitational pull, and if brought close to another cosmic string or a Blackhole, it can form a close timelike curve, and time travel could be done by using the gravity produced.
Time travel paradoxes
Time travel presents with itself a lot of paradoxes. Here are three major ones.
i) The Grandfather Paradox: Suppose we go back in time, and kill our grandfather. This presents a complication: How will we be born if we kill him? And then we would never be able to travel back time and kill him in the first place.
The solution is the existence of Multiverse. It is a theory that, with every choice taken by anyone and everyone, there is different realities or ‘universes’, in a way that each outcome of the choice is possible. Of course this is not the perfect definition, but it gives a solution to the Grandfather Paradox. We may go into a separate universe in the past so that our present universe is not affected by it.
Predestination Paradox: Suppose we go to the past, and in a series of events, be the only reason why we exist. For example, we become the reason why our parents met. So, the problem here is we have to come back from the future every time and do the exact same things to make our parents meet, otherwise we cease to exist.
Bootstrap Paradox: Suppose, we steal a book from someone in the future, write it in the present, and publish it in our own name. Then, later on, it gets stolen- by our own younger self. So the question is, whose book is it actually? Who is the actual author? This is the Bootstrap Paradox.
Time is a very mysterious matter, and time travel brings with it a lot of problems and paradoxes. Perhaps someday we will be able to unravel the mysteries and find the ultimate theory- The Theory Of Everything.