Free space
In physics, free space is a concept of electromagnetic theory, corresponding to a theoretical "perfect vacuum".
Definition
Free space simply means that there is no material or other physical phenomenon present except the phenomenon under consideration. Free space is considered the baseline state of the electromagnetic field. Radiant energy propagates through free space in the form of electromagnetic waves, such as radio waves and visible light (among other electromagnetic spectrum frequencies). The constant value is known as the permeability of free space. The permittivity of free space, , is the ratio of the electric displacement field to the electric field in free space. This permittivity is used in the construction of the fine-structure constant. According to relativity, radiant energy in free space propagates at the speed of light, independent of the speed of the observer or of the source of the waves.
Ideal states and real-world applications
Free space conveys that the region is absolutely devoid of matter and has no external fields or forces other than those considered in the problem at hand. Free space, with a gaseous pressure of absolute zero is a mathematical idealization. For example, in the "vacuum" of outer space, there are small quantities of matter (mostly hydrogen), and noise sources. The density of the interplanetary medium and interstellar medium though is extremely low, and, for many applications, the interplanetary and interstellar regions are "free space". The cosmic microwave background radiation is isotropic to roughly one part in 100,000.[citation needed]
See also
External articles and references
- Citations
- Other
- Davida, "What is the significance of permittivity of free space?". Ask A Scientist, Physics Archive.
- Susan Lea, "Electromagnetic waves in free space". (PDF)
- Eric W. Weisstein, "Permittivity of Free Space".
- Eric estrada. Weisstein, "Permeability of Free Space".
- "Characteristic impedance of free space". TechTarget, 2005.