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Established equationsGeneral relativity

Einstein field equations

The equations of general relativity: not an unsolved problem, but highly nonlinear PDEs with famous exact solutions.

Exact statement

Rμν−12R gμν+Λgμν=8πGc4 TμνR_{\mu\nu}-\frac12 R\,g_{\mu\nu}+\Lambda g_{\mu\nu}=\frac{8\pi G}{c^{4}}\,T_{\mu\nu}
Vacuum, Λ=0:Rμν=0\text{Vacuum, }\Lambda=0:\quad R_{\mu\nu}=0

Ten coupled nonlinear partial differential equations for the space-time metric g, relating curvature (left side) to energy and momentum (right side).

Status

Not an open problem: established physics since 1915, with many exact solutions. Deep open questions remain about their general solutions (for example cosmic censorship).

Posed: 1915, Albert Einstein.

In plain words

The left side measures how space-time curves (Ricci tensor RμνR_{\mu\nu}, scalar curvature RR, cosmological constant Λ\Lambda); the right side is the stress–energy tensor of matter. 'Matter tells space-time how to curve; space-time tells matter how to move.'

There is no single 'answer'. You solve them for a given physical situation, usually with symmetry assumptions or on a computer (numerical relativity, used to predict the gravitational waves LIGO detected in 2015).

Key results so far

  1. 1952: Choquet-Bruhat proves the equations have a well-posed initial value problem (local existence).
  2. 1965–1970: Penrose and Hawking singularity theorems.
  3. 1993: Christodoulou and Klainerman prove the nonlinear stability of Minkowski space.
  4. open: Weak and strong cosmic censorship (Penrose, 1969) remain open in general.

Exact special solutions and solved cases

Schwarzschild (1916)

ds2=−(1−rsr)c2dt2+(1−rsr)−1dr2+r2dΩ2,rs=2GMc2ds^{2}=-\Big(1-\frac{r_s}{r}\Big)c^{2}dt^{2}+\Big(1-\frac{r_s}{r}\Big)^{-1}dr^{2}+r^{2}d\Omega^{2},\quad r_s=\frac{2GM}{c^{2}}

Outside a non-rotating, uncharged spherical mass; contains the simplest black hole.

FLRW cosmology (Friedmann 1922, Lemaître 1927, Robertson–Walker)

ds2=−c2dt2+a(t)2[dr21−kr2+r2dΩ2],(a˙a)2=8πG3ρ−kc2a2+Λc23ds^{2}=-c^{2}dt^{2}+a(t)^{2}\Big[\frac{dr^{2}}{1-kr^{2}}+r^{2}d\Omega^{2}\Big],\quad \Big(\frac{\dot a}{a}\Big)^{2}=\frac{8\pi G}{3}\rho-\frac{kc^{2}}{a^{2}}+\frac{\Lambda c^{2}}{3}

A homogeneous, isotropic expanding universe; the basis of Big Bang cosmology.

Kerr (1963)

Rotating black hole; Reissner–Nordström (1916–1918) adds electric charge; de Sitter (1917) is the vacuum with Λ > 0.

What our solver can and cannot do

The Einstein field equations are established physics, not an open problem. The solver shows the equations, famous exact solutions and their history; solving them for a new physical situation needs specialised numerical methods. Open the solver.

Frequently asked questions

What do the Einstein field equations say?
Ten coupled nonlinear partial differential equations for the space-time metric g, relating curvature (left side) to energy and momentum (right side).
Are the Einstein field equations an unsolved problem?
Not an open problem: established physics since 1915, with many exact solutions. Deep open questions remain about their general solutions (for example cosmic censorship).
Can MathGPT solve the Einstein field equations?
MathGPT shows the statement, who settled it and how, with references; the proof itself is in the cited papers.

References

  • A. Einstein, 'Die Feldgleichungen der Gravitation', Sitzungsberichte Preuss. Akad. Wiss. (1915).
  • C. Misner, K. Thorne, J. Wheeler, Gravitation (1973).
  • R. Wald, General Relativity, Chicago (1984).