Quantum fluctuation

If we know precisely how long a particle exists in a certain state, we don't know how much energy it possesses.

An immediate ramification of this concept brings us possibly the hardest pill to swallow in all of modern physics, the idea of quantum fluctuation.

Since it is the case that the shorter the lifetime of a particle, the greater the uncertainty in the energy of the particle, it becomes possible for particles to come into existence from nothing, completely without cause, provided that they exist for inconceivably short durations of time.

We call these virtual particles.

While it seems like this just can't be true, that it violates causality and everything we thought we knew about the universe, quantum fluctuation of virtual particles is necessary to explain a number of observations, such as the Casimir effect.

When two completely neutral plates are placed in a complete vacuum just a tiny distance away from one another, they will eventually be pushed together.

This can't be due to gravity or the electromagnetic force.