The Plot is set in the near future where Earth is no longer able to sustain Humanity,So a secret organisation launches a risky mission with a group of Astronauts lead by Cooper to travel through a recently discovered wormhole to find a new planet for the Humans to live.
What happened to Earth ?
The Earth is effected by Blight,its disease that slowly kills all the crops in Earth one by one leaving the humans in Earth on the verge of Food crisis,also the oxygen level is depleting fast and that would result in death of the future generations.
What is Murphy's law ?
Murphy's law states that "Anything that can go wrong will go wrong" ,In the film it is shown that Cooper's Daughter Murphy a.k.a. Murph is scared of the future and Cooper cheers her up with a more realistic Interpretation that "Anything that can happen will happen".
What are wormholes ?
Wormhole also known as Einstein-Rosen bridge is like a tunnel in space with two ends and can supposedly be used as shortcuts in space.Since distances are far from our reach in space, wormholes can be used to save time , For example If it takes 7 years to travel from a Place(A) to Place (B) and then using wormholes a spaceship may get there in less than a hour as depicted in the film.In reality there are several conspiracy theories about wormholes but there is no solid evidence to prove its practical existence.
What is fifth dimension ?
Einstein spent the last 30 years of his life working on something called the Unified theory which would combine the concept of Gravity with three other fundamental forces of Nature : The Strong force,Weak force and Electromagnetic force but failed to do so as Gravity refused to co-operate and but yet as of Today no one has able to prove that this theory is true is or not ,but few physicists have said that If we treat our universe as If it has 5 Dimensions rather than 4 Dimensions in Einstein's theories it may be possible,Nolan incorporated the Idea in the script thus Cooper could communicate with his Daughter at different time periods.
Why Cooper and other crew members never showed any signs of aging ?
There is something called Gravitational time dilation,it has been observed in reality.I'll tell you How it works,Time runs at different rates at different reference frames,If you are in a strong gravitational environment you will age slowly compared to a weak gravitational environment.Earth has a weak gravitational environment compared the Planet Miller, according to the film one hour in Planet Miller is equal to more than 7 years in Earth.
A new worm hole had been discovered in the Solar system orbiting Saturn.
Cooper - Professor Brand is his former Boss, Cooper though is reluctant to leave his daughter,finally makes up his mind and agrees to be a part of the mission.
Amelia Brand - She is the daughter of Professor Brand and a Co-pilot in the mission.
Romily - He is a Physicist
Doyle - He is a Geographer
TARS & CASE - Artificial Intelligence robots TARS talks more and provides Humor , CASE talks less but helps them at when they are in need.
What is the mission all about ?
The prime objective of the mission to find a new suitable planet for human beings to live in. Previously 3 Astronauts had traversed through the wormhole to land in 3 different planets named after them (Miller,Edmunds and Mann) to survey the viability of their respective planets.
Ranger - Its function similar to a space shuttle,it is used to enter and exit a planetary atmosphere
Endurance - The Endurance is the mother ship of the crew and its design is inspired by the ISS(International Space Station)
The Lander - Its design is similar to a Russian Helicopter,it is used to transport the capsules and other equipment to the planetary surfaces.
What happened during their visit to Planet Miller ?
The crew land in Planet Miller and find out that the planet is close to Gargantua , A giant rotating black hole,due to the gravitational pull of Gargantua the time in Planet Miller is extremely slower than the time on Earth.They find the planet is inhabitable as there are tidal waves passing frequently throughout the planet.Doyle dies when struck by the wave and as the data derived by Miller is also supposedly destroyed in the wave.
As they are running out of fuel they are forced to choose between two planets Edmunds & Mann,as they receive signals from Planet Mann possibly from Dr.Mann himself, they decide to go to Planet Mann,However they learn that Dr.Mann had faked the data to help himself escape Isolation,He breaks the helmet of Cooper and sets a bomb for Romily leaving them to die while Romily dies Cooper survives as Amelia comes on with to rescue him with oxygen masks,Dr.Mann reaches Endurance but he is killed when the airlock pressure increases and blasts.
With the help of TARS Cooper gets Endurance back in control. Cooper and Amelia formulate a plan to pilot Endurance to Gargantua's event horizon and to jettison TARS once his shuttle runs out of fuel to shed mass and to gather data on the singularity behind the black hole, which they hope to relay back to Earth. Once the robot transmits the data back to them, they would slingshot themselves on a course to Edmunds's planet. Cooper also releases his shuttle into Gargantua to reduce the Endurance's weight, allowing Amelia to escape the gravitational pull. He ejects before his craft is destroyed, and comes to a halt in an extra-dimensional space where time is not linear. Cooper realises the extra-dimensional beings are in fact a future form of humanity who have evolved to the point of transcending three-dimensional time and space, and have come back in time to create the wormhole to ensure humanity's survival. Now equipped with TARS's data on the singularity, Cooper is able to communicate with Murph across the dimensional barrier from inside a tesseract through gravitational waves, making him the "ghost" from her childhood. With this information, Murph is able to complete Brand's equation, allowing Earth's population to be evacuated.
His mission now complete, Cooper is transported back through the wormhole and rescued by a NASA ship. He awakens aboard the NASA station orbiting Saturn and is reunited with an elderly Murph. She convinces him to go to Amelia, who has located the remains of Edmunds's expedition (and buried his body) and a planet that can sustain life. After saying goodbye, he and the newly repaired TARS steal a NASA ship and begin the journey.
What is tesseract ?
It's a four-dimensional cube that according to the movie, allows anyone who really knows what he's doing, to control those four dimensions. The tesseract is actually outside time and Cooper is able to use it at his will, sort of like how you'd play with a Rubik's Cube to get different color combos. Here, the 'colors' would represent what he wants to move around. Books in the bookshelf in this case.
How did Cooper get out of the black hole Gargantua?
As he had no spaceship anymore, he was probably helped out a bit by other dwellers in 5D and conveniently left near a NASA space ship to be rescued.
The above facts have been collected from Wikipedia,Newspapers and some books to help you understand the science of Interstellar.
So stop treating the film like a fantasy,Its one of the realistic sci-fic films of all time If you could understand it.
I wanted to congratulate Christopher Nolan and the entire cast & Technical crew of Interstellar for making such a amazing film.
I hope they at least recover their total investment($165 Million + $150$ = $315 Million Approx.)
My Box office prediction for the film
Domestic - $165-170 Million
Foreign - $300+ Million
Worldwide - Close to $500 Million