Last updated: : August 29, 2025

Is Absolute Vacuum a Utopia?

Vacuum and Ultrahigh Vacuum: From Magdeburg to the LHC

Nothingness vs. Vacuum: Radically Different Concepts

Do not confuse vacuum with nothingness.

Nothingness is the absolute absence of everything: no matter, no energy, no space, no time. It is a metaphysical concept, impossible to observe or reproduce experimentally.
Vacuum is a physical and philosophical concept referring to the absence of matter in a given volume. Unlike nothingness, vacuum can contain energy (electromagnetic fields, quantum fluctuations).

In everyday language, a "empty" container (a glass, a bottle) is actually filled with air. At atmospheric pressure, one cubic millimeter of air contains about 2 × 10¹⁹ molecules, or two quintillion. This density illustrates the ambiguity of the term: if vacuum is never total, does it deserve its name?

Vacuum in Physics: An Experimental Limit

Physicists define vacuum as the state obtained after removing all detectable matter from a given volume, according to current technological limits. It is therefore a relative vacuum, never absolute.

Ultrahigh vacuum is achieved at pressures below 10^-7 Pa (10^-9 mbar). At this level, molecular density drops to about 2 million molecules per cubic centimeter.
For comparison, interstellar space contains on average 1 atom per cubic centimeter, and intergalactic vacuum drops to 1 atom per cubic meter.

How to create a partial vacuum?

A vacuum pump is used to extract molecules from a sealed volume. The quality of the vacuum is measured by the residual pressure, expressed in:

Pascal (Pa) (SI unit): 1 Pa = 1 N/m².
Millibar (mbar): 1 mbar = 100 Pa (industrial use).
Torr: 1 Torr ≈ 133.322 Pa (historical, based on the pressure exerted by 1 mm of mercury).

On Earth, the best ultrahigh vacuums reach 10^-10 to 10^-12 Pa (e.g., particle accelerators like the LHC). Even under these conditions, molecules remain, and the vacuum remains relative.

Pressure in pascals (Pa): 1 Pa corresponds to a force of 1 newton (N) applied uniformly over 1 square meter.
Definition of the newton (N): SI unit of force. 1 N is the force capable of giving a mass of 1 kg an acceleration of 1 m/s².
Example: An acceleration of 1 m/s² means that an object's speed increases by 3.6 km/h every second (1 m/s = 3.6 km/h).

Vacuum and Electromagnetic Fields: Invisible Energy

Contrary to popular belief, vacuum is not "empty" of energy:

Electromagnetic waves (light, radio, X-rays) propagate through vacuum without a material medium. They correspond to variations in electric and magnetic fields, carrying energy.
In quantum mechanics, vacuum is the site of quantum fluctuations: particle-antiparticle pairs spontaneously appear and disappear (Casimir effect).

A total vacuum would therefore imply the absence both of matter and radiation/energy. Such a state does not exist in the observable universe (where cosmic background radiation fills space at 2.7 K), nor in laboratories.

Einstein and Relativity: The End of Absolute Vacuum?

In Relativity: The Special and General Theory (1916), Albert Einstein (1879-1955) devotes an appendix to the problem of space and vacuum. He cites René Descartes (1596-1650) and Emmanuel Kant (1724-1804), and rejects the idea of a space empty of fields:
« Physical objects are not in space, but these objects have spatial extension. Thus, the concept of empty space loses its meaning. »
Albert Einstein, preface to the 9th edition (1952).
For Einstein, spacetime is a dynamic entity, shaped by matter and energy (equation E = mc²). The "vacuum" then becomes a field of potentials, where even the absence of matter leaves room for geometric properties (curvature of spacetime).

The Magdeburg Hemispheres: A Historical Demonstration of Vacuum

In 1654, Otto von Guericke (mayor of Magdeburg and scientist) conducted a landmark experiment to demonstrate the effect of atmospheric pressure: