Does modern physics allows for creation from nothing? Here I will explain what physicists mean when we say that particles can come from “nothing” for a very simple case. The “Universe from Nothing” case is more complex, but the spirit is the same.
Caveat: this is an explanation for the lay audience; necessarily, many things are simplified and the very idea of rigor is treated more as a suggestion.
First, a couple of lessons from quantum field theory (the most successful physical theory of the 20th/21st century):
- Fields are the stuff that fills the Universe, not matter or energy.
- Particles are oscillations of fields
Those statements might mean nothing to you. Let’s explain things one by one.
What are Fields?
To understand fields, one need to first understand harmonic oscillators. Imagine the following apparatus laying flat on a table:
Perhaps when you first buy it from the ball-on-a-spring store, it will look more like this:
Where all of the spring is coiled together. If I pull the ball away from the spring and let go, I impart energy on the system. This causes the ball-on-a-spring to oscillate:
L here is the length of the spring when it is fully stretched. It depends on how far I pull the ball away from the spring, and on therefore on the amount of energy I impart on the system.
Now, imagine a whole bunch of these ball-on-a-spring systems:
Each of them has different energies, so each spring has different L’s.
Now suppose I have so many ball-on-a-spring that they blur together:
Each point in that blue line is a ball on a ball-on-a-spring system, I just have so many of them that it’s easier to draw them as a single line. I also forego drawing the springs, because it gets ridiculous.
This collection of many ball-on-a-spring systems is what a quantum field theorist would call a field.
Particles are oscillations of fields
In quantum field theory, particles are oscillations of fields. This means exactly what it sounds like:
- The underlying objects are fields
- If the field is oscillating, we (and our experiments) detect this oscillation as particles
To reiterate, there are no particles in this system:
This blue line is a bunch of mass-on-a-spring systems that are completely at rest. If I zoom in enough, each of them looks like
In contrast, this system has particles in them:
Why are particles “oscillations of the field”? I can motivate it by appealing to the fact that you probably have heard of the “wave-particle” duality. Particles are just waves, i.e. oscillations.
Quantum mechanics and creation from "nothing"
In quantum mechanics, there is a relation called the time-energy uncertainty relation, which in math reads
\Delta t \Delta E \ge \frac{1}{2} \hbar
This is a cousin of the more famous Heisenberg Uncertainty Principle, i.e. the one saying that position and momentum of a particle cannot both be pinned down exactly. Similarly, what the time-energy uncertainty relation essentially says is that for every chunk of time \Delta t (which could be seconds, minutes, whatever), there is an intrinsic variance in the amount of energy of the system \Delta E. The energy could not be pinned down exactly unless the chunk of time we consider in our experiment is infinity.
Now, because the energy in a ball-on-a-spring system is related to how far the spring stretches, this is what the field looks like if the energy is always zero:
each of the individual ball-on-a-spring system does not stretch at all. This is just the no particles case.
But because of the time-energy uncertainty relation, the energy can not be pinned down exactly. There is always a variance in the energy, which causes a variance in “how far each spring stretches”, so this “energy is always zero”, i.e. the “no particles” case is impossible.
We can also see this from the standard Heisenberg Uncertainty Principle, that position and momentum of each particle cannot both be known simultaneously. In the “energy is always zero” case, the position of each ball is exactly at the center line, and their velocity is exactly zero. This is a case where we know both exactly and thus violates the Heisenberg Uncertainty Principle. So again, this case is impossible.
What physicists call quantum vacuum or ground state or lowest energy state, is the state of the system that has the lowest energy allowed by quantum mechanics. They are the closest to the no-particles case allowed by the Heisenberg Uncertainty Principle, but they are not the no-particles case. There are always wiggles in the blue line, and as we learn, these wiggles are what our experiments detect as particles.
This is what physicists mean when we say creation from nothing: in the closest thing to actual nothingness that is allowed by quantum mechanics, the field regularly oscillates, and thus particles regularly pop in and out of existence. Also, they do this without needing any energy input.
A philosophical point
Obviously, this is not actually creation from nothing. For one, we need to have fields, which is not nothing, and we need to have the laws of physics, which again is not nothing.