Time travelling has been an interesting yet controversial topic for decades!
In some point in our life we all have wished to go back in time and change our past.
Let’s say someone wanted to go back so badly and invented a time machine. We’ll call him Sam.
Sam goes 100 years back to where his grandfather spent his childhood. But… somehow…. Because of Sam’s arrival his grandfather gets killed.
Let’s take a look at Sam’s family hierarchy….
Now that Sam’s grandfather is dead, he won’t get married to grandmom…. So one of Sam’s parents won’t be born. Then Sam will never be born.
If Sam wasn’t born, then he won’t travel back in time and kill his grandfather. So he will marry grandmom and then one of Sam’s parents will be born. So Sam will be born to travel back in time…
Wait what????
This is called Grandfathers Paradox!
A confusing endless loop happens in backward time travelling.

Let’s consider another incident.
You learn a new scientific theory in school which has been discovered by a famous scientist 50 years ago. You travel back in time and meet the scientist before he made his discovery. Then you tell him about the theory you learned. Later on he publishes the theory and becomes world famous. He knew the theory because of you told him… But would never learn it in the first place if the scientist didn’t discover it. Where is this information originally come from?
This is Bootstrap paradox!

Not confused enough???

Someone travels 60 years back and meets a beautiful woman which, happens to be his mother in future. They get married and have a baby. This baby will be growing in to the man who travels back in time in the first place. Take a minute to think about this…. This person’s farther is he himself. But where did he originally come from? What’s the origin of his DNA?
This is called Predestination Paradox!

There is a common factor in all these paradoxes. Something happened in the past is caused by the incident or a person in present. Therefore, the origin of the information or object has become unknown.
Because of these paradoxes most scientists believe backward time travelling can never be done! But some of them has come up with explanations for these paradoxes. We’ll discuss about them in another video.