Time Travel

Time Travel: The Fascinating Question of Reality or Fiction

When the topic of “Time Travel” comes up, we immediately think of that imaginary, strange device from various Hollywood movies or cartoons, often referred to as a time machine.

In these movies or cartoons, it’s shown that by riding this strange device, one can travel from the present to the past or from the present to the future.

For example, a person might ride a strange machine and travel from the year 2021 to 2521 to see how the future world will be. Or someone might travel back from 2021 to 1521 to observe how the world was at that time. In movies, these things are shown very easily, almost like fulfilling a casual wish.

But the question is, is it actually possible to make that strange device, the time machine, that we see in movies and cartoons?

After watching these movies, you might think, “Oh, if only I had a time machine like that! I could go back to the past and correct the mistakes I made. Those mistakes that are now having a bad impact on my present life.”
Or, you might think about going to the future to see what your upcoming life will be like. Will it be filled with happiness, or will it be filled with sorrow?

Many times, people have all sorts of thoughts swirling in their heads about time travel. This is because humans have been able to control almost everything, but they have not yet been able to control time.

Time still remains for us an uncontrolled train, whose speed and destination we are not yet able to control.
But today, the discussion is about how realistic time travel actually is.

What is Time?

To understand time travel, we first need to know what time is. Where did time begin?

Mathematically speaking—

• Time is a continuous flow that differentiates between the past, present, and future. It is believed that time began just moments after the Big Bang. There is no clear idea about whether time existed before the Big Bang.

Time is an important part of the fundamental structure of the universe. It is connected with space to form (Space-time). And all cosmic objects exist within this space-time.

Time is one of the four dimensions of the four-dimensional universe. 

Because of time, all physical events in the universe (both those that are directly happening and those that are indirectly happening) occur in a sequence. Essentially, time is a physical quantity, but it is possible to measure it.

Einstein’s Theory of Relativity and Time

According to Einstein’s theory of relativity, the flow of time in the universe is like a movie or a film. In this flow, the moments of the past, present, and future are arranged sequentially.

In other words, this suggests that your upcoming future is already determined. It means that the events that will happen in your future are already fixed.

From the perspective of the observer, only the events currently being experienced are the present, the moment just before is the past, and the moment after the present is the future.

In simple terms, time is like a movie, and we are like viewers who can’t fast-forward the scenes. For us, only the current events are unfolding; we can’t see past scenes or future ones. We are only able to watch the current ones.

However, in the case of a regular movie, we can use a CD player to rewind and view past scenes or fast-forward to see future scenes. But is such a thing possible with time?

Time is Relative

According to Einstein’s theory of relativity, time is relative ,meaning time moves slowly in some places, quickly in others, and stands still in certain places. But what is the reason for this relativity of time? Have you ever thought about that?

Einstein’s theory of relativity explains that speed and gravity have the most significant influence on time.
This is why time moves slowly near heavy objects and quickly near light objects. Similarly, time moves slowly for fast-moving objects and quickly for slow-moving objects.

Why does time move slowly near heavy objects and quickly near light objects?

We can imagine the universe as a flat surface. All the cosmic objects, such as satellites, planets, stars, black holes, etc., are placed on this flat surface. Time, which flows over this surface, moves in a straight line across the universe.

Moving in a straight line is one of the key features of time. Think about it, who wants to travel on a crooked path? You and I both prefer to walk on a straight path, don’t we?
But when a heavy object bends the flat surface of the universe, time, too, is forced to follow a curved path. This creates a curvature in space-time.

This concept might be a bit difficult to understand, so let’s look at a simple example.
Imagine that you are time, and the universe is a desert. Of course, you want to cross the desert in a straight line rather than a zigzag path because it would save both time and energy.

Just like time, which wants to travel in a straight line across the universe. But while walking across the desert, you suddenly encounter a pit. Now, what will you do? Will you turn back? But there’s no way to go back! The journey you started must be completed!

You have to cross the pit and move forward! If the pit is small, you can easily and quickly cross it because it’s not very deep, requiring little effort and time to pass.
But if the pit is large, it will take more effort and time to cross it because of its depth.

Similarly, when time passes near a light object, it can cross the slight curvature of space-time created by that light object, much like quickly crossing a shallow pit.

However, when time passes near a heavy object, the space-time curvature is greater due to the object’s immense mass. Time moves more slowly, just like a person who takes longer to cross a deep pit.

This is why time moves slowly near heavy objects and quickly near light objects.

Why does time move slowly for fast-moving objects and quickly for slow-moving objects?

Let’s imagine a slow-moving bicycle passing by a railway track. Let’s say the bicycle is moving at 15 km/h. While the bicycle is crossing the track, suddenly a train speeds by on the railway line. Let’s assume the train is moving at 80 km/h. Here, the slow-moving bicycle is like an object moving at a low speed.

The train, moving at a much higher speed, is like time itself. The fast-moving train quickly overtakes the slow-moving bicycle.

In the same way, time moves quickly past slow-moving objects.

Why does time stop at the speed of light?

To understand this, let’s consider an example.
Suppose your friend is traveling in a bullet train, and you want to join your friend.

But on foot, by bicycle, or even by motorcycle, there’s no way you can catch up to the train because none of these vehicles can move at the speed of the bullet train. To catch up with your friend, you would need a vehicle capable of moving at the same speed as the train.

From this, it becomes clear that for an object to appear stationary relative to another, they must move at the same speed. Since time moves at the speed of light, time appears to stop at that speed.

You’ve probably experienced something similar in real life. When you’re on a bus and see another bus moving at the same speed as yours, you notice that both you and the passengers on the other bus appear stationary relative to each other. This is because both buses are moving at the same speed.

Why does time stop near extremely strong gravitational forces?

The universe is like a desert, and you are time trying to cross it. Suddenly, some small and large pits block your path. If the pit ahead of you is shallow, you can quickly cross it.

If it’s a bit deeper, it will take more time. But if the pit is huge and deep, you won’t be able to cross it at all. Similarly, when time passes near a very massive object, the curvature of space-time becomes so great that time essentially falls into the pit and never reaches the other side.

As a result, time becomes completely frozen in the vicinity of such an object, and time itself ceases to exist there.
This is why time freezes near black holes due to their immense gravitational pull, which warps space-time to such an extent that time can no longer pass through it.

The Science of Time Travel: Moving Forward to the Future but Not to the Past