The Big Bang is a giant machine that is one of the bosses in Elex. You must face it during the main quest with the same name that you receive from Duke Logan in The Fort (the Outlaws' headquarters). Defeating The Big Bang is more troublesome than the rest of regular fights with monsters. You can't weaken that enemy by only using your standard attacks. Instead, you must use a little bit of creativity.
The battle with this boss takes place after you are sent to search for Konrad (after finding all parts that are necessary for creating a bomb). You reach Ruins of the Dome. Watch out because strong enemies roam the terrains near the base, such as Moloch and Slime Drakon.
Your goal is to reach the destroyed dome, presented in the picture, BEFORE you jump down on the "arena". Save your game and be sure that you have good weapons or attacks (magic etc.) for ranged combat (plasma and laser rifles will work great here). Entering the dome starts a cut-scene during which you learn that Konrad created The Big Bang robot. You must defeat this giant machine alone (your companion is send back to the team's camp).
Don't try to attack the giant levitating machine because it is protected by a force field. Use the nearby walls to avoid its energy attacks. You should also watch out for its powerful ground hits (you shouldn't stand near it).
Even if you didn't bring any ranged weapons with you, you can find Laser Blaster LSR-T (presented in the picture). Check its requirements.
Wait for a moment when a smaller machine, called Big Bang Workshop, emerges from the levitating robot. It always goes towards one of the nearby Elexit deposits and starts mining it. Attack it when it is in the air (picture 1) or use melee attacks when it gets low enough so you can reach it (picture 2). You must also keep moving constantly when the smaller machine mines Elexit because the bigger one will throw explosive charges - stay away from them.
Destroying Big Bang Workshop allows you to proceed to the second stage of the fight. Here, the big levitating robot will use a flamethrower. If you don't have armor and abilities that increase your resistance to that element then you shouldn't allow the boss to get closer to you. Use ranged attacks to weaken the machine. Continue attacking The Big Bang until the boss loses all health.