Any reasonable form of quantum gravity can explain (by phase interference) why, on a large scale, inertial frames seem not to rotate relative to the average matter distribution in the universe without the need for absolute space, finely tuned initial conditions, or without giving up independent degrees of freedom for the gravitational field. A simple saddlepoint approximation to a path-integral calculation for a perfect fluid cosmology shows that only cosmologies with an average present relative rotation rate smaller than about $$T^*H^2 \approx 10^{-71}$$ T ∗ H 2 ≈ 10 - 71 radians per year could contribute significantly to a measurement of relative rotation rate in our universe, where $$T^*\approx 10^{-51}$$ T ∗ ≈ 10 - 51 years is the Planck time and $$H \approx 10^{-10}$$ H ≈ 10 - 10 $$\hbox {yr}^{-1}$$ yr - 1 is the present value of the Hubble parameter. A more detailed calculation (taking into account that with vorticity flow lines are not normal to surfaces of constant global time, and approximating the action to second order in the mean square vorticity) shows that the saddlepoint at zero vorticity is isolated and that only cosmologies with an average present relative rotation rate smaller than about $$T^*H^2 a_1^{1/2} \approx 10^{-73}$$ T ∗ H 2 a 1 1 / 2 ≈ 10 - 73 radians per year could contribute significantly to a measurement of relative rotation rate in our universe, where $$a_1 \approx 10^{-4}$$ a 1 ≈ 10 - 4 is the value of the cosmological scale factor at the time when matter became more significant than radiation in the cosmological expansion. Including inflation with 60 e-foldings in the calculation of the action further restricts relative rotation rate to be smaller than $$\approx 10^{-74}$$ ≈ 10 - 74 radians per year. These calculations are consistent with measurements indicating a present relative rotation rate less than about $$10^{-20}$$ 10 - 20 radians per year. The observed lack of relative rotation may be evidence for the existence of quantum gravity.

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旋转问题

任何合理形式的量子引力都可以解释（通过相位干涉）为什么在不需要绝对空间、微调初始条件或不需要给定的情况下，惯性系在大范围内似乎不会相对于宇宙中的平均物质分布旋转引力场的独立自由度。完美流体宇宙学路径积分计算的简单鞍点近似表明，只有平均当前相对旋转率小于约 $$T^*H^2 \approx 10^{-71}$$ T ∗ H 的宇宙学每年 2 ≈ 10 - 71 弧度对测量我们宇宙中的相对旋转率有很大贡献，其中 $$T^*\approx 10^{-51}$$ T ∗ ≈ 10 - 51 年是普朗克时间，$$H \approx 10^{-10}$$ H ≈ 10 - 10 $$\hbox {yr}^{-1}$$ yr - 1 是哈勃参数的现值。更详细的计算（考虑到涡度流线不垂直于恒定全球时间的表面，并将作用近似为均方涡度中的二阶）表明零涡度处的鞍点是孤立的，并且只有具有当前平均相对旋转速率小于约 $$T^*H^2 a_1^{1/2} \approx 10^{-73}$$ T ∗ H 2 a 1 1 / 2 ≈ 10 - 73 弧度/年可以对我们宇宙中相对旋转率的测量做出重大贡献，其中 $$a_1 \approx 10^{-4}$$ a 1 ≈ 10 - 4 是宇宙膨胀中物质变得比辐射更重要时的宇宙尺度因子值。在计算动作时包括 60 个 e 折叠的通货膨胀进一步限制了相对旋转率小于 $$\approx 10^{-74}$$ ≈ 10 - 74 弧度每年。这些计算与表明当前相对旋转速率每年小于约 $$10^{-20}$$10 - 20 弧度的测量结果一致。观察到的相对旋转的缺乏可能是量子引力存在的证据。这些计算与表明当前相对旋转速率每年小于约 $$10^{-20}$$10 - 20 弧度的测量结果一致。观察到的相对旋转的缺乏可能是量子引力存在的证据。这些计算与表明当前相对旋转速率每年小于约 $$10^{-20}$$10 - 20 弧度的测量结果一致。观察到的相对旋转的缺乏可能是量子引力存在的证据。