We show assuming small data that massless solutions to the reflection symmetric Einstein–Vlasov system with Bianchi VII₀ symmetry which are not locally rotational symmetric, can be arbitrarily close to and will remain close to isotropy as regards to the shear. However in general the shear will not tend to zero and the Hubble normalised Weyl curvature will blow up. This generalises the work (Nilsson et al 2000 Class. Quantum Grav. 17 3119–34; Wainwright et al 1999 Class. Quantum Grav. 16 2577–98), which considered a non-tilted radiation fluid to the massless Vlasov case. This represents another example of the fact that almost Ehlers–Geren–Sachs theorems do not hold in general and that collisionless matter behaves differently than a perfect fluid.

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关于几乎 Ehlers-Geren-Sachs 定理

我们假设小数据表明，具有 Bianchi VII ₀对称性的反射对称 Einstein-Vlasov 系统的无质量解不是局部旋转对称的，可以任意接近并将保持接近关于剪切的各向同性。然而，一般来说，切变不会趋于零，哈勃归一化外尔曲率会爆炸。这概括了工作（Nilsson等人2000班级。量子引力 173119–34；温赖特等人1999班级。量子引力 162577–98)，它考虑了无质量 Vlasov 情况下的非倾斜辐射流体。这代表了几乎 Ehlers-Geren-Sachs 定理一般不成立并且无碰撞物质的行为不同于完美流体这一事实的另一个例子。