Good afternoon, dear visitors! Today I want to talk about emptiness. Yes, yes, about absolute emptiness. Wikipedia defines the concept of “emptiness” as “incompleteness, the absence of something,” as well as “the complete absence of any particles in space – a vacuum”. In the English version of “emptiness” as “the state of being empty, i.e., not containing anything” or “lack of matter, or vacuum”. The Oxford Student Dictionary describes “emptiness” as “having nothing or nobody”; Lexico online dictionary defines “emptiness” as “The state of containing nothing”; etc. As a result, all sources come to the idea that the concept of “emptiness” is equivalent to the concept of “nothing.”
But is it correct? Can emptiness be considered as just a state of the absence of everything? Or is it still a completely different and unique form of matter that we simply have not studied enough? It is not in vain that physicists have long been concerned about the mystery of the energy of vacuum; and this, logically, contradicts the idea of complete absence, because nothing can’t produce something measurable… Our respected expert, you have the floor!
Dmitri Burshtyn: Vacuum is, probably, the most mysterious concept in physics.
In classical physics, the concept of vacuum is simple and clear – it is a region in space in which there are no particles.
But in quantum physics, a vacuum is something completely different. In quantum field theory (in particular, in quantum electrodynamics, the most accurate experimentally verified physical theory), the physical vacuum is the lowest (ground) energy state of a quantum field with zero momentum and other zero quantum numbers. This state is not an absolute emptiness. Quantum field theory claims that, in accordance with the uncertainty principle, virtual particles are constantly born and disappear in a physical vacuum: occurs so-called zero-field oscillations.
That is, a physical vacuum is not emptiness, but a “soup” of particle-antiparticle pairs constantly born from a vacuum and then annihilates back into a vacuum.
It looks paradoxical and fictional, but nevertheless, it is real and proven experimentally.
A striking example is the Casimir Effect.
Place two parallel metal (grounded) plates in a vacuum very close to each other. The vacuum energy between the plates is slightly lower than the vacuum energy in the space outside of the plates. This difference in the energy of the vacuum outside and between the plates leads to the appearance of a force that attracts the plates to each other.
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This effect was theoretically predicted by Casimir in 1948, first experimentally tested in 1958, and with great accuracy (95%) – in 1998.
One of the most mysterious aspects of vacuum energy is that, in accordance with the calculations of quantum field theory, it is infinite! And these are the same calculations that very accurately predicted the experimentally measured value of the force acting on the plates in the Casimir effect!
[Stephen Reucroft, John Swain, “What is the Casimir effect?”, Scientific American, June 22, 1998]
Another example is sonoluminescence.
Sonoluminescence is the occurrence of flashes of light during the collapse of bubbles generated in a liquid by a powerful ultrasonic wave. That is, if a wave of high power is generated in a bath with some liquid, then the exploding micro-bubbles of air create strong flashes of light as if the air temperature inside the bubbles rises to tens of thousands and even millions of degrees. There is still no clear explanation for this phenomenon, discovered in the 30-s of the last century, but the main candidate fort he theory behind sonoluminescence is the Dynamical Casimir Effect. That is, it is the vacuum energy released by collapsing walls of micro-bubbles, which moves with great acceleration towards each other during a collapse.
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But still, the most global manifestation of vacuum energy is dark energy, which accounts for 68% (!) of total energy in the universe. According to the Standard Cosmological Model (Λ-CDM model), Λ is the cosmological constant (= dark energy), responsible for the accelerated expansion of the universe. The nature of dark energy is still an open question in modern physics, but the majority of physicist agrees that dark energy is vacuum energy.
The complex structure of the quantum vacuum is the basis that determines the fundamental properties of our world. A vacuum can generate not only particles but also worlds. Spontaneous vacuum fluctuations can generate multiple universes with a different set of fundamental constants.
[S. Carlip “Hiding the Cosmological Constant” Phys.Rev.Lett. 123, 131302; Sean M. Carroll “The Cosmological Constant” Living Rev. Relativity, 4, (2001), 1]
Summarizing all of the above, from the point of view of modern physics, a vacuum is not “emptiness”, but a sea of particles born from “nothing” and disappearing into “nothing”. A vacuum is a complex dynamic system with energy, which is continuously redistributed between virtual particles, and its structure and dynamics define fundamental properties of our world.