Vacuum

A vacuum is the space devoid of matter. the word is derived from the Latin adjective vacuus for "vacant" or "void". An approximation to such(a) vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would arise in a perfect vacuum, which they sometimes simply invited "vacuum" or free space, and ownership the term partial vacuum to refer to an actual imperfect vacuum as one might pull in in a laboratory or in space. In engineering and applied physics on the other hand, vacuum mentioned to all space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is used to describe an thing that is surrounded by a vacuum.

The quality of a partial vacuum noted to how closely it approaches a perfect vacuum. Other things equal, lower gas Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space.

Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was non studied empirically until the 17th century. Evangelista Torricelli delivered the first laboratory vacuum in 1643, & other experimental techniques were developed as a a thing that is caused or produced by something else of his theories of atmospheric pressure. A Torricellian vacuum is created by filling a tall glass container closed at one end with mercury, as well as then inverting it in a bowl to contain the mercury see below.

Vacuum became a valuable industrial tool in the 20th century with the first design of incandescent light bulbs and vacuum tubes, and a wide layout of vacuum technologies has since become available. The development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general.

Classical field theories

The strictest criterion to define a vacuum is a region of space and time where all the components of the stress–energy tensor are zero. This means that this region is devoid of power to direct or establishment and momentum, and by consequence, it must be empty of particles and other physical fields such(a) as electromagnetism that contain power to direct or develop and momentum.

In general relativity, a vanishing stress–energy tensor implies, through Einstein field equations, the vanishing of all the components of the Ricci tensor. Vacuum does non intend that the curvature of space-time is necessarily flat: the gravitational field can still gain curvature in a vacuum in the have of tidal forces and gravitational waves technically, these phenomena are the components of the Weyl tensor. The black hole with zero electric charge is an elegant example of a region totally "filled" with vacuum, but still showing a strong curvature.

In classical electromagnetism, the vacuum of free space, or sometimes just free space or perfect vacuum, is a requirements reference medium for electromagnetic effects. Some authors refer to this member of extension medium as classical vacuum, a terminology intended to separate this concept from QED vacuum or QCD vacuum, where vacuum fluctuations can produce transient virtual particle densities and a relative permittivity and relative permeability that are not identically unity.

In the abstraction of classical electromagnetism, free space has the coming after or as a a thing that is caused or produced by something else of. properties:

The vacuum of classical electromagnetism can be viewed as an idealized electromagnetic medium with the constitutive relations in SI units:

relating the electric displacement field D to the electric field E and the magnetic field or H-field H to the magnetic induction or B-field B. Here r is a spatial location and t is time.