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Einstein–Rosen metric

From Wikipedia, the free encyclopedia
Exact gravitational-wave solution to Einstein's field equations
General relativity
Spacetime curvature schematic

In general relativity, theEinstein–Rosen metric is an exact solution to the Einstein field equations derived in 1937 byAlbert Einstein andNathan Rosen describingcylindricalgravitational waves.[1]

Einstein first predicted the existence of gravitational waves in 1916. He returned to the problem 20 years later, working with his assistant, Rosen. Einstein and Rosen thought that they had found a proof for the non-existence of gravitational waves.[2] But an anonymous reviewer—posthumously revealed to beHoward Percy Robertson—pointed out their misunderstanding of the coordinates they were using.[3] Einstein and Rosen resolved this issue and reached the opposite conclusion, exhibiting the first exact solution to field equations of general relativity describing gravitational waves.[2][3]

This metric can be written in a form such that theBelinski–Zakharov transform applies, and thus has the form of agravitational soliton. In 1972 and 1973, J. R. Rao, A. R. Roy, and R. N. Tiwari published a class of exact solutions involving the Einstein–Rosen metric.[4][5][6] In 2021 Robert F. Penna found an algebraic derivation of the Einstein–Rosen metric, using theGeroch group.[7]

Description of the metric

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The Einstein–Rosen metric (withc=1{\displaystyle c=1}) is given by[8]

ds2=e2ν[(dt)2(dρ)2]e2μ(ρdφ)2e2μ(dz)2{\displaystyle ds^{2}=e^{2\nu }[(dt)^{2}-(d\rho )^{2}]-e^{-2\mu }(\rho d\varphi )^{2}-e^{2\mu }(dz)^{2}}

whereμ=μ(t,ρ){\displaystyle \mu =\mu (t,\rho )} andν=ν(t,ρ){\displaystyle \nu =\nu (t,\rho )} satisfy

μtt=1ρ(ρμρ)ρ,{\displaystyle \mu _{tt}={\frac {1}{\rho }}(\rho \mu _{\rho })_{\rho },}
(ν+μ)t=2μtμρ,{\displaystyle (\nu +\mu )_{t}=2\mu _{t}\mu _{\rho },}
(ν+μ)ρ=(μt2+μρ2),{\displaystyle (\nu +\mu )_{\rho }=(\mu _{t}^{2}+\mu _{\rho }^{2}),}

in which the integrability of the functionν+μ{\displaystyle \nu +\mu } is guaranteed. A simple separable solution is given by

μ=AJ0(σρ)cosσt,{\displaystyle \mu =AJ_{0}(\sigma \rho )\cos \sigma t,}
ν+μ=A22[σ2ρ2(J02+J12)2σρJ0J1cos2σt],{\displaystyle \nu +\mu ={\frac {A^{2}}{2}}[\sigma ^{2}\rho ^{2}(J_{0}^{2}+J_{1}^{2})-2\sigma \rho J_{0}J_{1}\cos ^{2}\sigma t],}

whereA{\displaystyle A} is a constant,σ{\displaystyle \sigma } is the frequency andJn{\displaystyle J_{n}} is theBessel function. For Einstein–Rosen waves, theC-energy, defined to beC=ν+μ{\displaystyle C=\nu +\mu },[8] is not constant in time and oscillates periodically.

In the general case, one can write

μ=j[AjJ0(σjρ)cosσjt+BjJ0(σjρ)sinσjt].{\displaystyle \mu =\sum _{j}[A_{j}J_{0}(\sigma _{j}\rho )\cos \sigma _{j}t+B_{j}J_{0}(\sigma _{j}\rho )\sin \sigma _{j}t].}

SupposeBj=0{\displaystyle B_{j}=0}, i.e.,μ{\displaystyle \mu } is given by the cosine series, then we have[8]

ν+μ=12jAj2{σj2ρ2[J02(σjρ)+J12(σjρ)]2σjρJ0(σjρ)J1(σjρ)cos2σjt}ρj<kAjAkσjσkσj+σk[J0(σjρ)J1(σkρ)+J0(σkρ)J1(σjρ)]cos(σj+σk)tρj<kAjAkσjσkσjσk[J0(σjρ)J1(σkρ)J0(σkρ)J1(σjρ)]cos(σjσk)t.{\displaystyle {\begin{aligned}\nu +\mu &={\frac {1}{2}}\sum _{j}A_{j}^{2}\{\sigma _{j}^{2}\rho ^{2}[J_{0}^{2}(\sigma _{j}\rho )+J_{1}^{2}(\sigma _{j}\rho )]-2\sigma _{j}\rho J_{0}(\sigma _{j}\rho )J_{1}(\sigma _{j}\rho )\cos ^{2}\sigma _{j}t\}\\&-\rho \sum _{j<k}A_{j}A_{k}{\frac {\sigma _{j}\sigma _{k}}{\sigma _{j}+\sigma _{k}}}[J_{0}(\sigma _{j}\rho )J_{1}(\sigma _{k}\rho )+J_{0}(\sigma _{k}\rho )J_{1}(\sigma _{j}\rho )]\cos(\sigma _{j}+\sigma _{k})t\\&-\rho \sum _{j<k}A_{j}A_{k}{\frac {\sigma _{j}\sigma _{k}}{\sigma _{j}-\sigma _{k}}}[J_{0}(\sigma _{j}\rho )J_{1}(\sigma _{k}\rho )-J_{0}(\sigma _{k}\rho )J_{1}(\sigma _{j}\rho )]\cos(\sigma _{j}-\sigma _{k})t.\end{aligned}}}

See also

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Notes

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  1. ^Einstein, Albert & Rosen, Nathan (1937). "On Gravitational waves".Journal of the Franklin Institute.223:43–54.Bibcode:1937FrInJ.223...43E.doi:10.1016/S0016-0032(37)90583-0.
  2. ^abWill, Clifford (2016). "Did Einstein Get It Right? A Centennial Assessment".Proceedings of the American Philosophical Society.161 (1):18–30.JSTOR 45211536.
  3. ^abKennefick, Daniel (2005)."Einstein Versus thePhysical Review".Physics Today.58 (9):43–48.Bibcode:2005PhT....58i..43K.doi:10.1063/1.2117822.
  4. ^Rao, J.R.; Roy, A.R.; Tiwari, R.N. (1972). "A class of exact solutions for coupled electromagnetic and scalar fields for einstein-rosen metric. I".Annals of Physics.69 (2):473–486.Bibcode:1972AnPhy..69..473R.doi:10.1016/0003-4916(72)90187-X.
  5. ^Rao, J.R; Tiwari, R.N; Roy, A.R (1973). "A class of exact solutions for coupled electromagnetic and scalar fields for Einstein-Rosen metric. Part IA".Annals of Physics.78 (2):553–560.Bibcode:1973AnPhy..78..553R.doi:10.1016/0003-4916(73)90272-8.
  6. ^Roy, A.R; Rao, J.R; Tiwari, R.N (1973). "A class of exact solutions for coupled electromagnetic and scalar fields for einstein-rosen metric. II".Annals of Physics.79 (1):276–283.Bibcode:1973AnPhy..79..276R.doi:10.1016/0003-4916(73)90293-5.
  7. ^Penna, Robert F. (2021). "Einstein–Rosen waves and the Geroch group".Journal of Mathematical Physics.62 (8): 082503.arXiv:2106.13252.Bibcode:2021JMP....62h2503P.doi:10.1063/5.0061929.S2CID 235651978.
  8. ^abcChandrasekhar, S. (1986). Cylindrical waves in general relativity. Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences, 408(1835), 209-232.
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