Is the Universe Mostly Empty Space? Do Perfect Vacuums Exist?
In other words, even though the universe and everything in it is mostly empty (to the extent that the human race could fit in a very heavy sugar cube with the space removed), true empty space (a perfect stable vacuum) can’t actually exist in nature.
Phenomena like quark and gluon field fluctuations, and other types of cosmic radiation, permeate what we consider empty space. Even if all matter and energy could be removed from a section of space to create a perfect vacuum, the space could not remain “empty” due to vacuum fluctuations, transiting gamma rays, cosmic rays, neutrinos, and other phenomena in quantum physics.
For an analogy we can think of the way an atom has most of its mass in its nucleus and protons, but has what we can think of as a electromagnetic field surrounding it (i.e. it’s mostly “empty,” aside from the fields created by electrons bouncing around the atom in “quantum superposition” as both a particle and a wave; see electron orbitals). So an atom is a bit like the universe, oddly empty despite having small condensed points of mass and lots of energy.
A video talking about “empty space”.
TIP: This is obvious when you think about it, but the air we breath is a gas mixture made of molecules. Thus the air is filled with molecules, which are mostly empty space, which isn’t actually empty on a quantum level due to quantum fields fluctuations. Not even the most remote part of intergalactic deep space is empty.
FACT: Aristotle said “nature abhors a vacuum” (Horror vacui), Pascal and others would later show that non-perfect vacuums exist, still later it was shown that while vacuums are useful to think about (when we are say trying to find a constant speed of light) nature really does “abhor a true vacuum” in practice. The universe, despite its sparse nature, if filled with “somethings” and we are hard pressed to find literal “nothings”.
TIP: Modern physics says the “Higgs Field,” and fields of all the other particles in the universe, permeate what we think of as empty space. This has been true since the big bang started the expansion of the universe.
Why Is the Universe Mostly “Empty Space”?
Let’s back away from the vast emptiness (or non-emptiness) of space for a moment and look at the atom. Atoms are mostly “empty space” and atoms (and their elementary particle building blocks) essentially make up ALL matter in the universe.
Atoms contain almost all of their mass in a tiny nucleus at the center of the atom (like a marble in a soccer stadium). Surrounding that nucleus are the electrons and protons (which have comparably little mass and take up next to no space). That means atoms are almost entirely made of “empty space”.
Energy Doesn’t Touch, it Attracts, Repels, and Bonds
When we touch something we don’t touch atoms (that would cause a small nuclear reaction), instead what we feel is friction from the electromagnetic force of our electrons pushing against the electrons in the matter we are touching (electron repulsion). Atoms bond together by sharing electrons and the force of combined atoms is what we think of as matter.
Now that we know atoms create all matter, and all matter is “empty space”, it’s easy to understand that, in turn, most of the universe is “empty space”.
Are There Exceptions?
Super dense things like black holes contain so much matter (particles with mass-energy) that they theoretically break the rule. We can think of them as being dense and filling space, but since all the mass-energy in the universe has always been and always will be we know that the amount of “empty space” in the universe is constant.
However, there is one other really important exception that we need to remind ourselves when speaking of this concept; “empty space” isn’t “truly empty”.
Why is “Empty Space” Not Actually Empty?
To expand on the above points, empty space isn’t actually empty, empty space looks empty because electrons and photons (light particles) don’t interact with the even smaller elementary particles and fields that are there.
Atoms Are Made of Quantum Particles
To understand this we need to understand that the nucleus, electrons, and protons of an atom are actually composite particles made up of quantum particles, and all those particles have fields. All forms of energy have fields – from quarks, to electrons, to photons, and beyond. Energy fields are actually the main thing happening in our universe (and this helps explain why we see particles like photons as both waves and particles). In fact all quantum particles have wave-particle duality and all can be understood as vibrations in their respective quantum fields. Something like the nucleus, which has a lot of mass, is really just a composite particle made of interacting quarks and gluons.
Quark and Gluon Fields
As noted above, what we think of as empty space is actually full of activity from quantum particles, specifically quark and gluon field fluctuations. The quantized movements of quarks, and the fields they create, and how those fields interact, are all happening in space we might otherwise consider empty.
However, the above quantum particles and fields aren’t evenly distributed throughout the universe (meaning some space is “more empty”) and some of the “Empty space” in the universe is also filled with things we call “dark matter” and “dark energy” and their related fields.
Dark Matter and Dark Energy
According to NASA roughly 68% of the Universe is dark energy. Dark matter makes up about 27%. The rest – everything on Earth, everything ever observed with all of our instruments, all normal matter – adds up to less than 5% of the Universe. Discovered only in 1998, this invisible stuff fills all of space and it has repulsive gravity.
We don’t really know what dark matter and dark energy are; they could be an unknown quantum field or a byproduct of the vacuum fluctuations of the known fields. Don’t feel bad. NASA doesn’t know yet and so you shouldn’t be expected to either.
Can Empty Space Exist?
Empty space can exist, in a manner of speaking. One can pull a lot of energy and clear quantum particles out of “empty space” and create a nearly empty vacuum (like the one we would measure the speed of light in). However, there are two issues.
- Even in an almost empty vacuum isn’t empty. Fields have their lowest energy (vacuum) state: sometimes this lowest energy state is called “vacuum fluctuations” because the fields are never exactly zero.
- That nearly empty vacuum is unstable, and will quickly fall back into “empty space” full of quantum particle and force interactions.
So while empty space in a vacuum can be shown with mathematics, it doesn’t actually exist in the physical universe. A true “perfect” vacuum is unstable and would collapse into quantum particles. Thus, in the lab they use “partial” vacuums to get close to empty space (ground state = lowest energy state, a non-excited state).
The result is that while we can find mostly empty space everywhere and create false vacuums, there is no naturally occurring true empty space or stable “perfect vacuums” in nature or in the lab (learn more about vacuums and empty space).