How can we know if our big bang is a one side of a wormhole?

According to Hawking, he proved that (excluding quantum mechanics) the big bang started at a singularity. Hence showing a connection between the mathematics of the big bang and black holes.

Equally, looking out at the Observable Universe we are looking back in time, and in any direction we eventually will see back to the big bang singularity. Or at least to the event horizon of that singularity.

Hence, the observable Universe (or any time-slice of the Universe that has bounds at the big bang) could be represented on the surface of a sphere with you at one pole and the big bang singularity/event horizon at the antipode. Like a giant black hole on the far side of the sphere.

Now, according to solutions of General Relativity a blackhole can be a wormhole. According to Susskind and others, this is the equivalence of two entangled black holes.

For our big-bang / observable-universe-horizon, if this was a wormhole it would, presumably, have to link to the big bang of another mirror universe running in the oppose direction. (I suppose this is just like the trick in electrostatics where it is useful to assume a mirrored version of a half-plane in order to get good boundary conditions).

In fact if this were true, (a 2D slice of) the observable Universe might resemble the top surface of a pizza, with the bottom of the pizza as the mirror universe, and the rim of the pizza as the big-bang event horizon. Every black hole could be a wormhole tunnelling through the pizza to the other side.

So, anyway, I wonder if there would be any tests or consequences we could measure to tell if our big bang was one side of a wormhole. (I am not sure if this is related to the tunnelling hypothesis of Quantum Cosmology). Or whether the wormhole hypothesis could be merely a mathematical trick with no Platonic reality to it. If it was a wormhole, would this be considered a boundary condition for our Universe? i.e. an initial condition?

• Note that the Big Bang singularity and black hole singularities are different. The Big Bang singularity is timelike while a black hole singularity is spacelike. You seem to be assuming that they are the same. Commented Nov 17, 2022 at 19:13
• @JohnRennie Well it depends how you look at it. The big-bang event horizon is space-like in the sense one can see it with a telescope. And note, it is event horizons that are the physically important thing as singularities probably don't exist.
– user84158
Commented Nov 17, 2022 at 20:20
• @JohnRennie This 1973 paper by Penrose says that the Big Bang was a “past-spacelike” singularity (not a timelike one) and black holes are a “future-spacelike” singularity. Are there various definitions in use? Commented Nov 17, 2022 at 21:43
• @zooby "And note, it is event horizons that are the physically important thing as singularities probably don't exist." -> And how are you elevating these statements to "facts"? Commented Nov 17, 2022 at 22:32
• @Avantgarde I think the word "probably" means that they are not facts but likelihoods. Singularities don't exist as GR breaks down on such small scales and quantum gravity takes over. A singularity is by definition a failure of the theory as it is dividing by zero.
– user84158
Commented Nov 18, 2022 at 5:06