There is no such thing as a void in the Universe.
We can define physical reality pragmatically as all that
which exists in the cosmos, and there is no such thing as complete emptiness in
it. Quite the opposite, it seems that the more we learn about nature, the
busier space becomes. We can contemplate the idea of a metaphysical emptiness,
a complete void where there is nothing. But these are concepts we make up, not
necessarily things that exist. Even calling nothingness a “thing” makes it into
something. Leucippus and Democritus, the Greek philosophers credited with the
invention of atomism — that everything is made of tiny bits of matter that
cannot be divided — suggested the joint existence of atoms and the void. Atoms
make up everything that exists, but they move in a complete emptiness, the
void.
Fields that link the Universe
As an exercise in the always evolving way we figure things
out about the world, we can make a list of the things we know fill up empty
space. (The list does change. For example, 120 years ago, it would have
included the ether, the medium in which light was supposed to propagate.)
Starting with classical physics, the key concept is that of a field. A field is
a spatial manifestation of a source. If an object sensitive to the field is
placed within its range, it will respond in some way, usually by being
attracted to or repelled by the source that creates the field.
In classical physics we know of only two forces,
gravitational and electromagnetic. Every object with mass attracts every other
object. You attract and are attracted by everything that exists — by
butterflies and whales, by the Sun and all the planets of this Solar System and
across the Universe. The intensity of an object’s gravitational field grows in
proportion to its mass and decays with the square of the distance to it. In
that sense, space is filled with interconnected fields that link us to the rest
of the Universe.
Gravitational fields extend their threads to all corners of
space. Since fields carry energy, we can say that space is filled with the
energy of these gravitational fields. Electromagnetic fields also have energy,
of course. But since electric and magnetic forces can be attractive and
repulsive, they usually are neutralized and rarely manifest themselves at great
distances.
A whole lot of nothing going on
At the quantum level, space gets even busier. Indeed,
quantum physics tells us there is no such thing as zero energy. In the world of
atoms and subatomic particles, movement is constant, and there is an energy
associated with a particle’s residual motion called zero point energy, or
vacuum energy. If we now connect this fact to the famous E=mc2 formula, which
states that energy and matter may be interconvertible, it is possible for
particles of matter to spring out from the energy of the vacuum — the energy of
empty space.
The Universe itself could emerge in this way. The fact that matter may come out of what we would call “nothing”
shows that the “nothing” of quantum physics is far from a complete void.
Virtual particles appear and disappear like bubbles in a boiling soup. In the
current view of quantum physics, the void bubbles continuously with the
creation and destruction of matter particles.
We met the concept of fields in classical physics, but it
carries over to quantum physics with even more dramatic effects. We no longer
refer to particles, in fact, but to the fields that create them. An electron or
a proton is an excitation of the electron or the proton fields, respectively,
like small waves drifting on the surface of a lake. Particles are pictured as
knots of energy moving in their fields, with physical properties like mass.
The physical picture that emerges is that of space filled
with quantum fields that boil up with real and virtual particles. As the Fox
said to the Little Prince in Antoine de Saint-Exupéry’s fable, “What is
essential is invisible to the eyes.” This is as true for love and friendship as
it is for the “nothingness” of space.
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