Question

Can anyone explain grandfather paradox,wormhole, and gravitational waves ?

Answer 1

This appears to be physically impossible, although some scientists have extended his equations and said it might be done. ... While Einstein's equations provide for them, they would collapse very quickly and would only be suitable for very small particles. Also, scientists haven't actually observed these wormholes yet

Answer 2

These terms are related to space and space time. I will try to teach you in simple ways. Firstly lets talk about grandfather paradox.

Grandfather paradox - Suppose if time travel is possible. You don't like your  grandfather and so one day think of killing him. So you go in the past and killed your grandfather before his marriage. Now here comes interesting part, If you killed your grandfather before his marriage then your grandfather never met your grandmother and how your father will born and so you. If you never born then how you go in the past to kill your grandfather ? This paradox is called grandfather paradox. What do you think about it ?

Now coming to the wormhole. Einstein purposed this theory. Wormhole is only imagination of him. It does not exist or invented yet. What exactly is wormhole ? If I try to explain you in simpler words. It is a shortcut for going to different place without traveling the actual distance. Remember Doraemon's door ?  

Acc. to space.com the definition for wormhole is -

A wormhole is a theoretical passage through space-time that could create shortcuts for long journeys across the universe. Wormholes are predicted by the theory of general relativity. But be wary: wormholes bring with them the dangers of sudden collapse, high radiation and dangerous contact with exotic matter.

Now, What are Gravitational Waves?

Gravitational waves are 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the Universe. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. Einstein's mathematics showed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that 'waves' of distorted space would radiate from the source (like the movement of waves away from a stone thrown into a pond). Furthermore, these ripples would travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself.