# Physics/Essays/Fedosin/Gravitational characteristic impedance of free space

The **Gravitational characteristic impedance of free space**, is a physical constant that relates the magnitudes of the gravitational field strength and the gravitational torsion field in covariant theory of gravitation (the gravitoelectric and gravitomagnetic fields in gravitoelectromagnetism) in gravitational radiation travelling through free space:

where
is the gravitoelectric gravitational constant in the set of selfconsistent gravitational constants,
is the gravitational constant,
*c* is the speed of light,
is the gravitomagnetic gravitational constant.

As in electromagnetism, the characteristic impedance of free space plays a central role in all radiation problems, such as in a comparison of the radiation resistance of gravity-wave antennas to the value of this impedance in order to estimate the coupling efficiency of these antennas to free space. The numerical value of this impedance is extremely small, but the impedance of all material objects must be “impedance matched” to this extremely small quantity before significant power can be transferred efficiently from gravitational waves to these detectors.

The gravitational characteristic impedance of free space may be connected with other constants:

where is the Planck constant, is the fine structure constant for the elementary charge , is the electric constant, is the Stoney mass.

The gravitational characteristic impedance of free space for the atoms and nucleons level of matter is:

where is the strong gravitational constant, and are the masses of proton and electron.

## History

editDue to McDonald ^{[1]}
first who used Maxwell equations to describe gravity was Oliver Heaviside. ^{[2]}
The point is that in the weak gravitational field the standard theory of gravity could be written in the form of Maxwell-like gravitational equations. ^{[3]}

In the 80-ties Maxwell-like equations were considered in the Wald book of general relativity. ^{[4]} In the 90-ties Kraus ^{[5]} first introduced the gravitational characteristic impedance of free space, which was detailed later by Kiefer ^{[6]}, and now by Raymond Y. Chiao, ^{[7]} ^{[8]} ^{[9]} ^{[10]} ^{[11]}
who is developing the ways of experimental determination of the gravitational waves.

## Typical gravitational impedance at the megascopic scale

editIn the general case only planets (with their sattelites) and stars could be considered "as free, as possible" to be used as some "antenna" to the gravitational waves detection. Spherical megascopic bodies have the folloving characteristic impedance:

where

- is the equatorial velocity,
- is the spherical body radius and
- is the body mass.

- Solar planetary system

Object | Radius, m | Equator velocity, m/s | Mass, kg | Impedance | |
---|---|---|---|---|---|

Human | 2 | 1 | 100 | ||

Sun | 317.4 | 1.32ˑ10^{–2}
| |||

Mercury | 2.99 | ||||

Venus | 1.807 | ||||

Earth | 465 | ||||

Mars | 240.6 | ||||

Jupiter | 12644 | ||||

Saturn | 10248 | ||||

Uranus | 3952 | ||||

Neptune | 2771 | ||||

Planetary data were taken from the textbook. ^{[12]} As could be seen from the Table, only the Mercury has characteristic impedance close to the free space value.

- Planet's satellites

Object | Radius, m | Equator velocity, m/s | Mass, kg | Impedance | |
---|---|---|---|---|---|

Moon | 4.36 | ||||

Titan | 276.8 | ||||

Ganymede | 1116 | ||||

Callisto | 252.7 | ||||

Satellites' data were taken from the textbook. ^{[12]} As could be seen from the Table, only the Moon has the closest value of characteristic impedance about 12-times greater then for free space.

- Stars

Object | Radius, m | Equator velocity, m/s | Mass, kg | Impedance | |
---|---|---|---|---|---|

Sun | 317.4 | ||||

O5 | |||||

F5 | |||||

Globular cluster | |||||

In this table designations "O5" and "F5" define stellar types. ^{[12]} As it is seen from the Table, some stars could have characteristic impedance value about the same as the impedance of free space.

## See also

edit## References

edit- ↑ K.T. McDonald, Am. J. Phys. 65, 7 (1997) 591-2.
- ↑ O. Heaviside, Electromagnetic Theory (”The Electrician” Printing and Publishing Co., London, 1894) pp. 455-465.
- ↑ W. K. H. Panofsky and M. Phillips, Classical Electricity and Magnetism (Addison-Wesley, Reading, MA, 1955), p. 168, 166.
- ↑ R. M. Wald, General Relativity (University of Chicago Press, Chicago, 1984).
- ↑ J. D. Kraus, IEEE Antennas and Propagation. Magazine 33, 21 (1991).
- ↑ C. Kiefer and C. Weber, Annalen der Physik (Leipzig) 14, 253 (2005).
- ↑ Raymond Y. Chiao. "Conceptual tensions between quantum mechanics and general relativity: Are there experimental consequences, e.g., superconducting transducers between electromagnetic and gravitational radiation?" arXiv:gr-qc/0208024v3 (2002). [PDF
- ↑ R.Y. Chiao and W.J. Fitelson. Time and matter in the interaction between gravity and quantum fluids: are there macroscopic quantum transducers between gravitational and electromagnetic waves? In Proceedings of the “Time & Matter Conference” (2002 August 11-17; Venice, Italy), ed. I. Bigi and M. Faessler (Singapore: World Scientific, 2006), p. 85. arXiv: gr-qc/0303089. PDF
- ↑ R.Y. Chiao. Conceptual tensions between quantum mechanics and general relativity: are there experimental consequences? In Science and Ultimate Reality, ed. J.D. Barrow, P.C.W. Davies, and C.L.Harper, Jr. (Cambridge:Cambridge University Press, 2004), p. 254. arXiv:gr-qc/0303100.
- ↑ Raymond Y. Chiao. "New directions for gravitational wave physics via “Millikan oil drops” arXiv:gr-qc/0610146v16 (2009). PDF
- ↑ Stephen Minter, Kirk Wegter-McNelly, and Raymond Chiao. Do Mirrors for Gravitational Waves Exist? arXiv:gr-qc/0903.0661v10 (2009). PDF
- ↑
^{12.0}^{12.1}^{12.2}Allen C.W.(1973). Astrophysical quantities. 3-d edition. University of London, The Athlone Press.