Question

what is grand father paradox...?

Answer 1

Grandfather patadox is a paradox in which time travel takes place. In it irregular manner of change of time takes place.

Answer 2

The grandfather paradox is a paradox of time travel in which inconsistencies emerge through changing the past. The name comes from the paradox's common description: a person travels to the past and kills their own grandfather before the conception of their father or mother, which prevents the time traveler's existence.