"Vacuum energy" or "zero-point energy" is the energy density of empty space. It is the amount of energy stored in a given system or region of space per unit volume.

In modern physics, we have two fundamental theories: quantum field theory and general relativity. Quantum field theory takes quantum mechanics and special relativity into account, and it's a great theory of all the forces and particles except gravity. General relativity is a great theory of gravity, but it ignores quantum mechanics. Nobody knows how to reconcile these theories yet. That's what people working on "quantum gravity" are trying to do.

Quantum field theory considers the vacuum ground state not to be completely empty, but to consist of a seething mass of virtual particles and fields. Since these fields do not have a permanent existence, they are called vacuum fluctuations. In the Casimir effect, two metal plates can cause a change in the vacuum energy density between them which generates a measurable force.

Some believe that vacuum energy might be the "dark energy" (also called quintessence) associated with the cosmological constant in General relativity, thought to be similar to a negative force of gravity (see antigravity. Observations that the expanding Universe appears to be accelerating seem to support the Cosmic inflation theory — first proposed by Alan Guth (1981) — in which the nascent Universe passed through a phase of exponential expansion driven by a negative vacuum energy density (positive vacuum pressure).

See also

• Zero-point energy - Vacuum energy
• Virtual particle
• Cosmological constant
• Cosmic inflation

External references

1. Eric weisstein's world of physics - energy density[1]
2. Baez physics - Is there a nonzero cosmological constant? [2].
3. Introductory review of cosmic inflation[3]
4. An exposition to inflationary comsology[4]

Books

• The Inflationary Universe: The Quest for a New Theory of Cosmic Origins by Alan H. Guth (1998)
• Cosmological Inflation and Large-Scale Structure by Andrew R. Liddle, David H. Lyth (2000)