Impedance of free space
In electromagnetism, the Impedance of free space, Z0, is a physical constant relating the magnitudes of the electric and magnetic fields of electromagnetic radiation travelling through free space. That is,
where |E| is the electric field strength, and |H| is the magnetic field strength. Its presently accepted value is
Z0 = 376.730313412(59) Ω,
where Ω is the ohm, the SI unit of electrical resistance. The impedance of free space (that is, the wave impedance of a plane wave in free space) is equal to the product of the vacuum permeability μ0 and the speed of light in vacuum c0. Before 2019, the values of both these constants were taken to be exact (they were given in the definitions of the ampere and the metre respectively), and the value of the impedance of free space was therefore likewise taken to be exact. However, with the revision of the SI that came into force on 20 May 2019, the impedance of free space as expressed with an SI unit is subject to experimental measurement because only the speed of light in vacuum c0 retains an exactly defined value.
“Free space theory” most commonly refers to the electromagnetic properties of a vacuum, where space is a perfect vacuum with no matter or fields. It is a reference medium characterized by the permittivity of free space* $ε_0$)* and the permeability of free space* $μ_0$)*, which are fundamental physical constants used in equations describing electric and magnetic fields. In a more theoretical context, there is also the idea of a “Zero Space” theory, which suggests the universe is composed of a single field in a matter and “space fabric” state.
Electromagnetism in a vacuum
- Perfect vacuum: In this theory, “free space” is an ideal vacuum with no matter and no electromagnetic or gravitational fields.
- Fundamental constants: The vacuum’s properties are defined by two fundamental constants:
- Permittivity of free space $ε_0$): This constant describes the ability of a vacuum to permit electric fields. Its value is approximately $8.85 \times 10^{-12}$ F/m.
- Permeability of free space $μ_0$): This constant describes the ability of a vacuum to support magnetic fields. Its value is approximately $4\pi \times 10^{-7}$ T·m/A.
- Maxwell’s equations: These constants are crucial for Maxwell’s equations, which govern electromagnetic fields and waves. For example, they show that the speed of light in a vacuum $c$) is directly related to $ε_0$ and $μ_0$.
- Impedance of free space $Z_0$): This is another physical constant, derived from $μ_0$ and the speed of light, that relates the magnitudes of the electric and magnetic fields of electromagnetic waves in free space.
This video explains the concept of the intrinsic impedance of EM waves in free space: youtube/v=tJiiyyc5vCI (youtube/v=tJiiyyc5vCI)
Zero Space Theory
- A single field: This is a more speculative theory that proposes the universe is made of a single field that exists in two states: a “matter state” and a “space fabric” state.
- “Condensed space”: The “matter state” is referred to as “condensed space,” and the “space fabric” is the free state of matter.
- Origin of matter: This theory aims to describe how the matter state develops from the base field and how this development affects the distribution of matter and the properties of light.
AI responses may include mistakes.
[1] https://www.theochem.ru.nl/~pwormer/Knowino/knowino.org/wiki/Free_space_(electromagnetism).html
[2] https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095834529
[5] https://ui.adsabs.harvard.edu/abs/1999APS..OSS…P01M/abstract
[6] https://fiveable.me/key-terms/principles-physics-ii/permittivity-of-free-space
[7] https://fiveable.me/key-terms/principles-physics-ii/permeability-of-free-space