How did the first black hole form?

Answer

1) Black holes can form as end products of massive stars. These stars end their “life” by means of a supernova explosion, which also leaves a small core as a neutron star, or in the extreme case, as a black hole, if the star was one of the most massive. Such a black hole can indeed attract nearby matter, for example when it occurs in a binary star and the other star expands into its red giant phase, causing matter from the other star to spiral into a disk around the black hole and partly into the black hole ends up. Massive black holes also exist in the center of the galaxy.

2) Then regarding the 2nd statement : “a black hole becomes a big bang” : that is “way over”. A black can slowly evaporate due to Hawking radiation, losing matter, and the temperature continues to rise. This process may end in an explosion of gamma rays, that is correct, but that is something completely different from a big bang.

3) Quatun mechanically matter can indeed arise spontaneously from radiation and vice versa, but that is certainly not limited to black holes. A gamma photon that enters our atmosphere (you know, a gamma photon has a huge energy) will interact with particles in the atmosphere, creating a whole bunch of elementary particles, so real matter. This process repeats like a waterfall downwards, and the remnants can be observed at ground level with special gamma telescopes. Conversely, a particle and an antiparticle can animate each other, converting matter into energy in the form of radiation. This, too, is effectively observed, apart from black holes.

Finally, the story of several parallel universes : short and concise, there is currently no indication that this exists. It may be theoretically possible, or rather, not theoretically contradictory to the models, but even then there is no guarantee that it will also occur in reality. Compare it with the well-known wormholes : these do not contradict current relativistic models, but that does not mean that they do not contradict reality either : do they exist right ? Can they really exist? If so, for how long are they stable? Do they perhaps disappear after a fraction of a microsecond? Can matter actually tunnel through it? Can we make them ourselves, wherever and whenever we want? ….. all in science fiction literature, but in science? The same goes for a multiverse.
A model is always an idealization of reality, and this also applies to the theory of relativity. We can never be sure that a model can accurately describe reality 100 percent. Popular science literature and TV programs often give unreasonable attention to such ideas.
It is also dangerous to jump at odds if they arise from reasoning in which something impossible is studied for an infinitely long time. In mathematics this corresponds to a product of zero x infinity, and this is called an indeterminacy. It can actually be anything.