One of the questions I get most often is “Do you really think there are singularities at the centers of black holes?”
No. I don’t. I think we still don’t understand how gravity works on quantum scales. Last week my own thoughts where brought back to the surface as I listened to a talk given by Sean Carroll that was eloquently summarized by Chris Lintott. This post isn’t a summary of Sean’s talk, but it dovetails it.
Ancient maps labeled the unexplored corners of the world with the warning, “Here be dragons.” As cosmologists look back in time to the first moments of our own universe we find ourselves journeying with our minds beyond the safe boundaries of charted land. As time winds back toward zero and densities and temperatures reach the extraordinary levels of 10^93 gm/cm^3 and 10^32 Kelvin, we go beyond the boundaries of where physics functions and into our own world of dragons.
These numbers describe a time called the Planck time. This briefest of moments, 10^-43 seconds after what we call the Big Bang, is the point in time when quantum mechanics takes over. At intervals of time smaller than this Planck time, we can only use statistics to say what might have been, and what was is lost into the soup of what ifs.
At this moment run by probabilities, all the mass in the Virgo Supercluster was compressed into far less space than a common lead atom. At these densities mass could not exist in any normal form, but rather existed as pure energy. Just as mass couldn’t exist as normal matter like electrons and protons, the basic forces also couldn’t exist as normal forces like gravity and magnetism. Instead, according to theorists, the forces tangled together to form a single force.
And here is where things break.
As we work to understand the blending of forces, gravity refuses to play. Just 150 years ago we had 3 well recognized forces: Gravity, Electical Force and Magnetism. Under Maxwell, Electricity and Magnetism became the Electromagnetic Force, and later the Strong and the Weak forces stepped forward to explain how nuclei stay together and decay apart. Through the standard model of particle physics, these forces can be drawn together and explained through their interactions with atomic and sub-atomic particles.
But, 150 years and 2 new forces later, gravity still doesn’t fit in. It breaks at atomic scales and defies the mold of quantum mechanics. It won’t play with the Big Bang mathematical models.
It simply defies our current understanding.
And this is the beauty of physics; we, its practitioners, don’t try to cover its flaws. As a community we know gravity is broken, and we know to tip toe around the topic of quantum singularities. We can play at the math, and work at working out the geometry of the centers of black holes, but in its broken beauty, gravity can only respond with twisted infinities that poke through the fabric of space and time.
But this isn’t a new experience for us. The forces have played hard to get before. Before we understood quantum mechanics, we also predicted light bulbs should give off near limitless amounts of ultraviolet light. This was called the Ultraviolet catastrophe, and it was fixed by quantifying atomic transistions.
It is generally hoped that today’s gravitational singularities â€šÃ„Ã¬ both in black holes and at the first moment of the big bang, will go away once we draw out gravity’s quantum personality. In that moment of mathematical discovery, we may find that the Big Bang is a smooth wave function that flows into a well-defined source; we may find that black holes are simply the homes of free quarks, liberated from their normal nuclei bonds. We don’t know. But we know what we don’t know, and this is powerful. Without fear, I can say, here be the next big mystery, here be the dragon’s treasure waiting for the taking.