The theory is a beautiful one. It’s as familiar as it is simple. We see it everyday when we look at ourselves or the ones we love. It’s in the wispy lunar strands of my younger sister’s hair. It’s especially something I see in her doting brown eyes and the way the black lashes curl around them, framing them like delicate curved petals. Those eyes are expressive. At a few months old they began to distinguish all the colors of the world. They are light-sensitive, distinct features over 500 million years in the making, evolving over time from just a small bundle of special cells. We know this, of course, from Darwin’s theory of evolution. The eyes were one of the most challenging characteristics to describe and yet the theory was able to do it. A progression. Small steps over so many rich years in our planet’s history.
So what if we take that theory and apply it to something beyond biology? What if we extended the theory of evolution outside the waxy blue feathered birds and the nimble little newts of our forests and we applied it to the entirety of the cosmos instead? The implications would be that we began within a black hole and that black holes can lead to other universes much like ours. There has always been the same mystery shrouding both events: the singularity of a black hole and the singularity of the Big Bang. To understand them requires more. More math, more physics, more examination of our ever-broadening world. And as we uncover the laws of nature the question becomes why we have those laws and not any other version of them.
That is the answer theoretical physicist Lee Smolin hoped to provide with his theory of cosmological natural selection.
At the heart of it is this strange assumption that time is real. Relativity tells us that time is not real, it’s subjective and malleable. It’s an illusion, and though we may think of ourselves as living in this moment and this moment departing from the past and heading towards the future, relativity says that’s a false perception. If it turns out that time is not an illusion and it is real, then everything evolves within it. We evolve within it, and the laws of nature do as well. The numbers behind the strengths of particles or forces would be a result of their evolution throughout time. They carry this evolution out through the constant creation of new universes within black holes.
The way we think of them now, stars collapse down to infinitely dense points known as singularities, where time stops. Except in Smolin’s theory there is no infinitely dense point. The star collapses to a certain density and then bounces into a new expansion — an expansion that marks the birth of an all new universe. Time ends within a black hole only to begin again in a new world.
When this new universe is born, the laws of nature and their constants are reborn as well, shifting ever so slightly in the child universe through random variations. The point of this cosmological natural selection is to produce as many black holes as possible. This means producing as many stars as possible, since it is the collapse of the great burning giants that give us the monstrous caverns we call black holes. This variation is the process behind our parameters — it is, so to speak, the pressure on our carbon, that thing which gives us diamonds in whites and pinks and blacks. One such diamond is the cosmological constant.
It’s a non-zero value. But just barely. The value represents either an expansion or contraction of spacetime. Our spacetime is expanding — we know this — but quantum mechanical fluctuations would give us a cosmological constant that’s very large. This small, non-zero number we observe would be a likely result of child universes affecting the apparent value of the cosmological constant. That’s the proposition Stephen Hawking made in the 1970’s when he began investigating how the uncertainty principle of quantum mechanics changes our understanding of black holes (the uncertainty principle says a particle’s position and velocity cannot both be well-defined at the same time).
This led to his realization that black holes are not completely black.
Black holes give off particles and radiation. These particles can do what even light cannot manage to do — escape the strenuous region of the event horizon. The uncertainty principle allows the particles to travel at superluminal speeds for short enough distances. Anything consumed by the black hole would emerge in a child universe branching off from our spacetime. The total number of particles in a child universe, then, would be equal to the number of particles that fell into the black hole plus the number of particles emitted during evaporation. The more the black hole shrinks, the more rapidly it will evaporate. As it approaches and then reaches zero mass, it will disappear from the cosmos altogether. It is humbling to think that even these thundering machines do not last. Even they — supermassive and liquid dark and hungry — will someday be gone.
Like a foil character to Smolin’s theory, in Hawking’s paper the child universes occur in imaginary time.
Imaginary time can be thought of as a plane, one that’s perpendicular to our current plane of time. That is, crossing over from our universe and into the new child universe only the histories of the particles would remain the same. They are mutilated in passage. What comes out is not what falls in. The only thing that remains constant is the amount of energy involved.
Hawking radiation could be the key to discovering child universes. The difference between a regular micro-black hole and one with a child universe lies in uncovering the rate of Hawking radiation. These micro-black holes may be nearly as old as the universe itself, or they might someday be formed in a lab where some scientists speculate we may be able to create new universes ourselves. They would appear, from our end, to be nothing more than the round, gaping mouths of black holes. One moment there, the next moment gone as the child universe would separate from ours — its parent.
I look at my sister’s hands.
There are spots of white on them. A skin condition passed on from our mother. If cosmological natural selection is true then universes favor the creation of stars. In so doing, they favor the creation of life. The chemicals of life come from the stars and their spectacular explosions. The network of the universe must be replete with us — not mankind specifically, but life. We are made, it seems, to be set against a stellar backdrop. A black spacetime threaded with clusters and clusters of stars, those same bodies we wish on, and from which we evolved.