Is Space a Perfect Vacuum?

Check out this answer from Consensus:

While the concept of a perfect vacuum is useful in theoretical discussions, it is not achievable in practice. Quantum theory and practical limitations ensure that some matter or energy will always be present in any given space. Therefore, space is not a perfect vacuum.

The concept of a perfect vacuum, a space entirely devoid of matter, has been a subject of scientific inquiry and philosophical debate for centuries. While the term “vacuum” is often used to describe spaces with significantly lower pressure than atmospheric pressure, the idea of achieving a perfect vacuum remains theoretical.

Key Insights

• Theoretical Concept of Perfect Vacuum:
  • A perfect vacuum, defined as a space completely devoid of matter, is a theoretical construct that cannot be fully realized in practice3 4 5.
• Quantum Fluctuations:
  • Quantum theory suggests that no volume of space can be perfectly empty due to quantum fluctuations, which means that even in a vacuum, particles and antiparticles are constantly being created and annihilated4.
• Practical Definition of Vacuum:
  • In practical terms, a vacuum refers to a space where the pressure is significantly lower than atmospheric pressure, but it is never completely devoid of matter3 5.

Is space a perfect vacuum?

Antonija Grubisic-Cabo has answered Extremely Unlikely

An expert from Monash University in Physics, Materials Science

Perfect or absolute vacuum means that there is a region with no particles present.

While space is probably the closes approximation of a perfect vacuum (due to very low number of particles, low density and pressure), it is not a perfect vacuum because there are still some particles present.

For example, the most abundant atom in space, hydrogen, has an average density of 1 atom per cubic centimetre in space, and there are also virtual particle pairs (particle and its anti-particle) constantly being created and annihilated, making space no completely empty of particles.