Visualization of a quantum field theory calculation showing virtual particles in the quantum vacuum. (Specifically, for the strong interactions.) Even in empty space, this vacuum energy is non-zero. As particle-antiparticle pairs pop in-and-out of existence, they can interact with real particles like the electron, providing corrections to its self-energy that are vitally important. On Quantum Field Theory offers the ability to calculate properties like this. (DEREK LEINWEBER)

This Is Why Quantum Field Theory Is More Fundamental Than Quantum Mechanics

And why Einstein’s quest for unification was doomed from the start.

If you wanted to answer the question of what’s truly fundamental in this Universe, you’d need to investigate matter and energy on the smallest possible scales. If you attempted to split particles apart into smaller and smaller constituents, you’d start to notice some extremely funny things once you went smaller than distances of a few nanometers, where the classical rules of physics still apply.

On even smaller scales, reality starts behaving in strange, counterintuitive ways. We can no longer describe reality as being made of individual particles with well-defined properties like position and momentum. Instead, we enter the realm of the quantum: where fundamental indeterminism rules, and we need an entirely new description of how nature works. But even quantum mechanics itself has its failures here. They doomed Einstein’s greatest dream — of a complete, deterministic description of reality — right from the start. Here’s why.

If you allow a tennis ball to fall onto a hard surface like a table, you can be certain that it will bounce back. If you were to perform this same experiment with a quantum particle, you’d find that this ‘classical’ trajectory was only one of the possible outcomes, with a less than 100% probability. Surprisingly, there is a finite chance that the quantum particle wwll tunnel through to the other side of the table, going through the barrier as if it was no obstacle at all. (WIKIMEDIA COMMONS USERS MICHAELMAGGS AND (EDITED BY) RICHARD BARTZ)