The idea that we are living inside a black hole isn’t as crazy as it sounds. Black holes warp space and time to the point where space and time reverse roles. For anyone falling into a black hole, the radial dimension, towards the singularity, becomes time and the time dimension becomes like space.
The two well known predictions from this are that, from inside a black hole event horizon, (a) you cannot escape because the way out is back in time and (b) black hole singularity covers a “spacelike” region of spacetime that exists like a barrier so that anything that falls in strikes the barrier simply at different spatial points along the singularity’s extent.
Another prediction is that the infinitely compressed central singularity of the black hole lies in your future as you fall in. When you reach it, nobody knows what happens because the laws of physics as we know them literally break down. Whatever the theory of quantum gravity ends up being might explain it, but for now we have no idea.
The basic idea for the Black Hole Big Bang Theory (BHBBT) is that matter from a mother universe collapses into a black hole. The singularity of this black hole is at a single point in space with respect to anyone in the mother universe. But, because of the reversal of time and space for anyone inside the daughter universe, that point in space r=0 become their initial point in time, t=0. Hence, what was a singularity in space is now a singularity in time, just like the Big Bang.
This means that any matter falling in from the mother universe will disappear from that universe and emerge at the initial t=0 point of the daughter universe thoroughly scrambled.
Not only that, but what emerges at the Big Bang is not just the matter that was there at the black hole’s formation but all matter that ever fell into it. That is because time at the black hole’s singularity is essentially perpendicular to time in the mother universe outside.
The reason why a whole other universe can be contained inside another one has to do with the strange way in which time and space can be warped, stretched, compressed, and twisted. What appeared to be a deadend at the center of a black hole, can instead be a passage way into the birth of a new universe.
You can have many interconnected universes this way, in which mothers give birth to daughters which give birth to more daughters, and so on ad infinitum. Thus, far from being only 13.8 Bya (Billion years ago), the whole interconnected cosmos can be infinitely old or more properly timelike paths can be infinitely long into the past passing from universe to universe.
This is not the same as the Many Worlds Interpretation of quantum mechanics that I have criticized in recent articles of course. There is no constant splitting of universes based on quantum observations. Rather, this is a process that occurs through black hole formation, and each universe would be essentially unique, although daughter universes would share characteristics of their mothers. There wouldn’t be exact copies of you running around.
Indeed, some have argued that a process of natural selection may take place with these universes, since the only universes that can reproduce are those that can form black holes. It is also a potential resolution of the anthropic principle, the theory about why human beings exist, since each universe may have slightly different laws of physics. Just as not all planets can support life, not all universes can. No many worlds interpretation required just many distinct universes within a single spacetime.
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.
Black holes, on the other hand, have their centers at a point in space, r=0 in coordinates centered on the black hole singularity. Thus, they are fundamentally different from the Big Bang singularity.
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.
The metric is what tells us how space and time behave and what distances mean at any given point. Intense concentrations of matter can warp space and time so that the metric changes what space and time mean for different observers.
For an observer outside a black hole, called the far observer, the singularity is at a point in space. For the observer inside the event horizon, however, the sign of the r and t elements of the spacetime metric change places. Now, for the near observer, the singularity is at a point in time, some time in the future.
The BHBBT suggests that, at least for certain types of singularities, once matter reaches it, it enters a new universe where time at the singularity is the initial point of that universe.
To visualize this, imagine you are an ant crawling on a table. As you crawl along, you crawl down a slope. The slope gets steeper and steeper until it is completely vertical from the direction you were crawling in. Suddenly, it ends in a point. This is typical of how black holes are portrayed. But now, instead of ending in that point, it expands out again from the point, flaring into a cone. Through some miracle of quantum mechanics, you pass through the point and emerge into the cone. Now you are in a new universe perpendicular to the one you left.
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.
Inflationary theory doesn’t solve a number of other problems including the fluctuation problem, super-Planck scale physics problem initial singularity problem, or the cosmological constant. It doesn’t matter exactly what all these mean. The point is that it is far from a panacea.
The horizon problem is address by the BHBBT model simply by pointing out that matter falling into the black hole has plenty of time to interact with other matter falling in before reaching the singularity. While this is not on the daughter universe’s clock yet, it is in that quasi-time that exists within the black hole event horizon that is neither part of the mother universe nor the daughter but is somewhere in between.
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.
Why the universe has exactly the correct matter density to be flat, called the critical density, is one problem. What that matter is is another: we don’t know. The universe has three general types of matter: baryons, which are what we think of as matter, dark matter, and a third form. We call it dark energy and we have no idea what it is. Dark matter, at least, we can observe in the rotations of galaxies and other gravitational behavior. Dark energy we only see in the expansion of the universe and to explain it we introduce a constant into Einstein’s equations called the cosmological constant which makes the universe’s density even out to the critical density.
We believe that if the critical density were not 1 then we would not be here. If it were more than one, the universe would have collapsed long ago, perhaps only an instant after the Big Bang, if it were less than one, the universe would have expanded so rapidly that galaxies would not have formed.
The BHBBT resolves the flatness problem by connecting the black hole interior to what is called a de Sitter space, which represents our universe, with an infinite amount of time. Thus, the observer inside the black hole approaches the singularity and emerges into de Sitter space and continues on for infinite time into that space.
It turns out that the only solution that allows a de Sitter space to connect to a black hole is a flat one. Thus, dark energy isn’t a form of matter energy but is actually the result of a spatial topology (shape) inherited from the black hole.
Black Hole Information Paradox
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.
[Updated: The previous version of this article said the future of the universe could be seen from inside the black hole event horizon. This can only happen if the black hole is rotating and/or charged.]
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