PBS Space Time - Season 2022 (2022)

If you used every particle in the observable universe to do a full quantum simulation, how big would that simulation be? At best a large molecule. That’s how insanely information dense the quantum wavefunction really is. And yet we routinely simulate systems with thousands, even millions of particles. How? By cheating. Using the ultimate compression algorithm: Density Functional Theory (DFT). Let’s learn how to cheat the universe.

We routinely simulate the universe on all of its scales, from planets to large fractions of the cosmos. Today we’re going to see how it’s possible to build a universe in a computer - and see whether there’s a limit to what we can simulate.

Fact: in a black hole, all of the mass is concentrated at the singularity at the very center. Fact: every black hole singularity is surrounded by an event horizon. Nothing can escape from within the event horizon unless it can travel faster than light. Fact: gravity travels at the speed of light. So how does a black hole manage to communicate its gravitational force to the outside universe? How does gravity escape a black hole?

Objective Collapse Theories offer a explanation of quantum mechanics that is at once brand new and based in classical mechanics. In the world of quantum mechanics, it’s no big deal for particles to be in multiple different states at the same time, or to teleport between locations, or to influence each other faster than light. But somehow, none of this strangeness makes its way to the familiar scale of human beings - even though our world is made entirely of quantum-weird building blocks. The explanations of this transition range from the mystical influence of the conscious mind to the grandiose proposition of multiple realities. But Objective Collapse Theories feels as down to earth as the classical world that we’re trying to explain. Let’s see if it makes any sense.

Reality has cracks in it. Universe-spanning filaments of ancient Big Bang energy, formed from topological defects in the quantum fields, aka cosmic strings. They have subatomic thickness but prodigious mass and they lash through space at a close to the speed of light. They could be the most bizarre undiscovered entities that actually exist.