Imagine, if you can, a place in the Universe completely empty, devoid of any objects, planets, stars, galaxies and even light. A place of pure and complete emptiness. According to a common definition, this is the vacuum: a region of space totally devoid of matter, a place where it contains nothing. But is it really possible for such a place to exist, filled with absolute emptiness? Is there any corner in the Universe where there is complete nothingness?
First of all, we need to understand that the idea and concept of a vacuum is nothing new. The first discussions about the existence of an absolute emptiness of which there are records took place in Ancient Greece, more than 2,000 years ago, between the 5th and 4th centuries BC, with the philosophers Leucippus, Democritus and Aristotle. Whereas the first two believed that a vacuum was the space between atoms where nothing else existed, Aristotle defended the opposite idea, that such a vacuum did not exist. In other words, according to the atomist theory of Leucippus and Democritus, atoms would be the smallest possible constituents of any and all matter, therefore, in the separation between an atom and another there would be nothing, just complete emptiness. Aristotle, in turn, denied this idea: for him, the entire Universe would be permeated by a practically intangible fifth element, the “quintessence”, which was added to the four classical elements of nature of earth, water, air and fire.
The four fundamental elements according to Aristotle, to which the fifth essence was added.Source: Diana KC
This so-called fifth essence reappears in discussions about nature and takes on a new guise centuries later with studies on electromagnetic phenomena. In the nineteenth century, mainly due to the work of the English physicist James Clerk Maxwell and the discovery that light and other electromagnetic waves propagate in the space between celestial bodies, an analogous idea was introduced, the concept of the ether. At the time, in accordance with the physics of wave phenomena, it was thought that electromagnetic waves also needed a material medium to propagate. Thus, the ether arises in response to this idea, being defined as a subtle and elastic substance that would fill all space and allow light to propagate in the Universe.
Although its existence had been postulated and defended by most scientists until the end of the 19th century, several experiments failed to detect it, including the famous Michelson-Morley experiment, built especially to measure the relative motion of matter through the ether. With a series of negative results, the ether theory lost strength and was completely put aside with the emergence of Albert Einstein’s Theory of Relativity, at the beginning of the last century, since it was an unnecessary hypothesis for the construction of the theory and for your predictions. One could then speak again of a vacuum!
Photograph of the original apparatus from Michelson and Morley’s interferometric experiment, mounted on a stone slab that floats in an annular mercury chuteSource: Public domain
Several experiments throughout history have studied the nature of air and how to get it out of an environment. One of the fathers of vacuum technology, German physicist Otto von Guericke, pioneered the construction of so-called vacuum pumps that became more and more sophisticated over time. Today, vacuum pumps and other instruments are based on modern techniques to seal and remove molecules from a given environment and are capable of achieving incredibly low pressure values, with just a few hundred particles per cubic centimeter.
But finally, does the perfect vacuum exist?
The answer is no! However efficient the system, however sophisticated and careful the methods for creating artificial vacuums, there are always remnants of matter and the pressure always reaches a minimum value to which it can no longer be reduced. The same goes for any corner of the Universe, as there will always be atoms and other “lost” particles wandering around. The vacuum of space is, however, of the highest quality, with the equivalent of just a few hydrogen atoms per cubic meter, on average, far below any vacuum ever reached by mankind!
Astrophotography of the spiral galaxy NGC 1055.Source: APOD/Martin Pugh
The surprising thing is that, even if we consider the total absence of any atom or particle, space is still not entirely empty! According to Quantum Field Theory, virtual particle-antiparticle pairs are being formed and annihilated all the time in a vacuum, due to quantum fluctuations in fundamental energy. In simple terms, energy fluctuations in a vacuum can be explained by the uncertainty principle of quantum physics. The validity of this principle, introduced by the German physicist Werner Heisenberg and known to bear his name, implies that at any defined point in space, there must be temporary changes in energy over time. Sometimes this energy is converted into mass and spontaneously generates particle-antiparticle pairs. Most of these newly created pairs recombine and disappear before interacting with anything. Because of this, they are called “virtual particles”, which does not mean, however, that they are not real! Far from being just theoretical speculation, quantum vacuum fluctuations have real and measurable effects on our physical reality, such as the Casimir effect.
Floating virtual particles “in and out of existence” according to the Heisenberg uncertainty principleSource: Towards Data Science
With several experimental evidences, the vacuum no longer shares the idea of being a component of the absolute emptiness: on the contrary, it presents itself as a physical entity in which even the “nothings” are full of “somethings”.
Nicolas Oliveira, has a degree in Physics and a Master in Astrophysics. He is a doctoral candidate at the National Observatory, where he researches orphan stars in galaxy clusters. He has experience in Teaching Physics and Astronomy, with research in Extragalactic Astrophysics and Cosmology. It acts as a scientific communicator and disseminator, seeking the popularization and democratization of science.