The Infinity Stones are the driving force of the Universe; without these, there is no Universe. That means no MCU.
The infinity stones are the balance of the Universe, the reason that anybody in the MCU is alive at all. Thanos wants to court the Lady Death, an ancient being behind the creation of the Universe. The other entities are Infinity, Entropy and Eternity. Combining them all, we get the stones seen in the Marvel Universe.
The Science Behind the Stones
The stones are the controlling powers for their respective name. The reason for their existence is said to be the existence of the ancient beings themselves. Coming to the science behind the Infinity Stones, they are said to be made of immense Gamma Rays, as Bruce Banner suggests.
Could Infinity stones possibly exist in reality?
There is little to no real chance for Gamma energy to be stored inside of small shining stones we call Infinity Stones throughout the MCU. Gamma Rays exist in our reality because of the fate of the stars. When supermassive stars die out, they send out Gamma-ray bursts. These events occur on a daily basis. You don’t want to be anywhere close to one, trust us.
The Infinity Stones Theory
In the Marvel Cinematic Universe, Infinity stones exist because the ancient creators- Eternity, Infinity, Entropy and Death make them. There is no real reason known as to why they create them, perhaps it is in order of The One Above All. We really have no idea.
This is the stone that is able to manipulate any being to its will. This has unprecedented power. When in possession of this, you have the power to control any being in your vicinity. This is first seen in Loki’s sceptre. He uses it to manipulate various people throughout the MCU storyline and he is the reason for Avengers to come together at all.
Perhaps the most powerful thing in the entire Marvel Universe, this stone is able to manipulate and create immense bursts of Energy. It can destroy an entire planet with one blow and has the ability to provide its wielder with infinite power. The most famous wielders of this stone are the celestials. Not much is known about these beings yet but we may yet see them in Eternals.
The reality stone can shape and bend reality to the will of its holder. When in possession of the reality stone – also known as Ether. While it sounds like a dumb thing, it means that you can destroy, create and use anything that exists as you will it to be. You can ruin a planet or create one just for fun.
The space stone in MCU allows its wielder to move anywhere in the universe without a shred of sweat. Instant teleportation is what this stone allows for anyone in possession of this Infinity stone.
All the stones need each other to reach their complete potential and that is why the Infinity Gauntlet is such an important relic in the Marvel Universe. It is the ultimate weapon when culminated with all the gems, giving the ability to finish all life in the Universe if needed. A snap of Infinity stones means that everything is over.