We can pragmatically define physical reality as everything that exists in the cosmos, and in it there is no complete vacuum. On the contrary, it seems that the more we learn about nature, the more crowded the space becomes. We can contemplate the idea of a metaphysical void, a complete void where there is nothing. But these are concepts we create, not necessarily things that exist. Even calling nothing a “thing” turns it into something. Leucippus and Democritus, the Greek philosophers credited with inventing atomism – that everything is made of tiny fragments of matter that cannot be divided – suggested the joint existence of atoms and the void. Atoms make up all that exists, but they move in complete emptiness, the void.
Fields that unite the Universe
As an exercise in the ever-changing way we understand things about the world, we can make a list of the things we know to fill in the blank. (The list changes. For example, 120 years ago, it would have included the aether, the medium in which light was supposed to travel.) Starting from 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 creating the field.
In classical physics we know only two forces, gravitational and electromagnetic. Every object with mass attracts every other object. You attract and are attracted to everything that exists: butterflies and whales, the Sun and all the planets of this Solar System and throughout the Universe. The strength of an object’s gravitational field grows in proportion to its mass and decays with the square of the distance from it. In this sense, space is filled with interconnected fields that connect us to the rest of the Universe.
Gravitational fields extend their strings 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 have energy too, of course. But because electric and magnetic forces can be attractive and repulsive, they are usually neutralized and rarely manifest over great distances.
Not a lot of anything is happening
At the quantum level, space becomes even more crowded. Indeed, quantum physics tells us that there is no such thing as zero energy. In the world of atoms and subatomic particles, motion is constant and there is an energy associated with the residual motion of a particle called zero point energyOR vacuum energy. If we now connect this fact to the famous E=mc2 formula, which states that energy and matter can be interconvertible, it is possible that particles of matter arise from the energy of the vacuum — the energy of empty space.
The Universe itself could emerge this way, as we have discussed. The fact that matter can come out of what we would call “nothing” shows that the “nothing” of quantum physics is far from a complete vacuum. Virtual particles they appear and disappear like bubbles in boiling soup. In the current view of quantum physics, the vacuum is constantly seething with the creation and destruction of particles of matter.
We encountered the concept of field in classical physics, but it affects 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 proton is an excitation of the electron or proton field respectively, like small waves drifting on the surface of a lake. Particles are depicted as knots of energy moving in their fields, with physical properties such as mass.
The physical image that emerges is that of space filled with quantum fields bubbling with real and virtual particles. As the Fox said to the Little Prince in Antoine de Saint-Exupéry’s fairy tale, “The essential is invisible to the eye”. This is as true of love and friendship as it is of the “nothingness” of space.
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