# The Big Bang may be a black hole inside another universe

Jul 27 · 9 min read

# The Standard Big Bang Model

The Standard Big Bang (SBB) model of the universe is that the universe, including time, space, and matter, came into being at a single point 13.8 Bya. From the standpoint of General Relativity, the theory of gravity of Einstein, space itself was compressed into that point. As time began, space began to expand carrying matter with it as it went. This process is still going on and we know this because when we observe distant galaxies, they are all moving away from us. More over, the farther away a galaxy is, the faster away from us it is moving. That is consistent with a theory of the universe where space is expanding. The more space there is between two points the faster they can be moving apart. The standard example of this is a set of dots on a balloon. Blow up the balloon and all the dots move apart. The dots further apart from each other move apart faster.

## Where is the center of the universe?

The center of the universe, where the Big Bang happened is, for us, not anywhere in space, but at a point in time, t=0, at the Big Bang. The balloon analogy is helpful here because the center of the balloon, of course, is not on the balloon. Space, therefore, is like the surface of the balloon with one additional dimension, so it is 3 dimensions instead of 2. The past is like the interior.

## So how can we be inside a black hole?

One of the odd features of general relativity is its ability to bend space and time to the point where time and space can exchange places. Formally, this is where the signature of the spacetime metric changes in General Relativity.

# Why is the BHBBT a good idea?

The BHBBT resolves some problems with the Standard Big Bang model of the formation of the universe. One of the problems with the SBB model is that it doesn’t explain why the universe is so homogeneous. When we look at pictures of the early universe by studying the Cosmic Microwave Background (CMB), for example, the universe looks as if it has been thoroughly mixed. This is sometimes called the horizon problem.

## The Horizon Problem

The horizon problem is a problem with causality. The region over which the CMB is observed to be homogeneous is much larger than is possible for ordinary causality which is limited by the speed of light. The most popular solution to the problem is called the inflationary theory in which space expanded exponentially, carrying light and matter along with it so that everything got thoroughly mixed. You can think of it like God’s blender.

## The Flatness Problem

A second problem with the SBB is called the flatness problem. The universe appears, as far as we can tell, completely flat, meaning that its matter density is such that it is exactly the critical amount = 1 to be neither hyperbolic < 1, meaning it will settle to a constant rate of expansion, nor spherical, > 1, meaning it will eventually stop and collapse in on itself. Thus, it will simply slow down as it expands to zero velocity but never actually stop expanding.

One final point is about the so-called black hole information paradox. Simply stated this theory suggests that when quantum information, in the form of states of quantum particles, falls into the black hole, it disappears from the universe. In the BHBBT, it does not disappear, it simply goes from the mother universe to the daughter universe.

# Is it true?

Right now, the current SBB is highly problematic but it only includes those aspects that we can rigorously demonstrate with experiment and observation. The BHBBT is a compelling theory that can be rigorously formulated within the bounds of Einstein’s theory of General Relativity. It doesn’t require new physics. It also explains why the Big Bang happened at all. And I think it is compelling in many philosophical ways such as the anthropic principle, it explains why we are here, but it is far from being demonstrated empirically.

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