Cosmic Voids Aren’t Empty – They’re Full of Something Far Stranger

Cosmic voids are not truly empty but are filled with vacuum energy that powers the universe’s expansion.

If you could somehow strip away everything inside the vast cosmic voids, removing all normal matter, neutrinos, dark matter, cosmic rays, and even radiation, what would remain?

At first glance, it might seem like the answer is nothing at all. But that conclusion would be wrong. Even in the most remote and seemingly barren regions of the universe, empty space is still there. And that “emptiness” is not truly empty.

Empty space is not nothing

That’s because the vacuum of space-time is not truly empty. It contains something. Not in the usual sense of matter or radiation, but something more fundamental. It exists within the underlying fabric of reality itself. It can be difficult to describe precisely in everyday language, but what I’m referring to are quantum fields.

In quantum field theory, the particles that make up our universe, such as electrons, top quarks, neutrinos, and even dark matter, are not fundamental objects on their own. What we call a particle is actually a manifestation of something deeper. The truly fundamental entities are the fields. Each type of particle has a corresponding field, and these fields extend through every region of space and time. They have been present since the Big Bang and fill every corner of the universe.

When we point to something and say, “Look at that electron zooming by,” what we are really observing is an excitation, a vibration, or a wave in the underlying field. That localized disturbance is what we interpret as a particle. Even if all particles were removed, even if all the matter and radiation were gone, the field itself would still remain.

Vacuum energy drives expansion

That underlying field carries energy. Because of the Heisenberg uncertainty principle, even what we think of as empty space cannot have zero energy. The details of that principle are a topic in their own right. When physicists try to calculate how much energy exists in the vacuum, the results vary wildly, ranging from staggeringly large values to formally infinite ones… which is also a discussion for another time.

What matters here is that this energy produces a measurable effect. We call that effect “dark energy,” the name given to the phenomenon responsible for the universe’s accelerating expansion.

Observations of cosmic acceleration tell us that the actual amount of vacuum energy is small compared with many theoretical predictions. However, it is not zero. Dark energy, or vacuum energy if you prefer, has almost no impact in regions packed with matter. In dense environments, its influence is negligible. On Earth, for example, matter is so concentrated that it completely overwhelms any effect dark energy might have.

If dark energy suddenly vanished, life on Earth would look exactly the same. A baseball would follow the same path when thrown. A burrito would take just as long to heat in the microwave. Nothing in our daily experience would change.

The same holds true for galaxies, galaxy clusters, filaments, walls, and every other dense structure in the cosmic web. In those regions, gravity and matter dominate the dynamics.

Cosmic voids are different. These vast expanses contain very little matter. In such places, the vacuum of space-time itself becomes the dominant component. If you were positioned at the center of a cosmic void, dark energy would be the primary influence surrounding you.

Voids are where dark energy wins

In fact, voids are the places where dark energy is doing its job of accelerating the expansion of the universe. It’s not happening in any dense places like galaxies or clusters. It’s only happening in the voids. The voids don’t just empty out to build the cosmic web.

The voids themselves are expanding. They are literally tearing the cosmic web apart. What we see as these very large, beautiful, and intricate structures in the universe are temporary. Over the course of the next 5-10-20 billion years, the exact number doesn’t matter, the cosmic web is going to evaporate. And it will do that through the action of the voids pressing against everything else.

So the voids are full. They are vibrating with fundamental quantum energies. They are doing work on the rest of the universe to accelerate its expansion. And they are the only places in the universe that can do this, and the only reason they can do this is that they are devoid of everything else.

So yes, voids are empty of matter. This is how we discover them. This is how we measure them. This is how we define them. But the emptiness of matter means that they are full of dark energy. And so no matter where you go in the universe, whether it’s to a nearby Galaxy or the deepest interior of the emptiest void, you will never ever quite be alone.

Adapted from an article originally published in UniverseToday.

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