2020年GeCAA理论第3题-镜子 - 版本历史

2021年6月17日 (四) 03:16 Jingsong Guo

2021-06-17T03:16:51Z

2021年6月17日 (四) 03:16 Jingsong Guo

2021-06-17T03:16:17Z

2021年6月17日 (四) 03:15 Jingsong Guo

2021-06-17T03:15:58Z

2021年6月17日 (四) 03:15 Jingsong Guo

2021-06-17T03:15:42Z

2021年6月17日 (四) 03:15 Jingsong Guo

2021-06-17T03:15:12Z

Jingsong Guo：创建页面，内容为“==英文题目 '''3 Mirror''' A bored cosmologist comes up with a thought experiment to determine the Hubble constant ($$H_0$$) for his model of a Steady-State-Uni…”

2021-06-17T03:14:46Z

创建页面，内容为“==英文题目 '''3 Mirror''' A bored cosmologist comes up with a thought experiment to determine the Hubble constant ($$H_0$$) for his model of a Steady-State-Uni…”

新页面

==英文题目

'''3 Mirror'''

A bored cosmologist comes up with a thought experiment to determine the Hubble constant
($$H_0$$) for his model of a Steady-State-Universe. In this experiment, a large, fully
reflecting flat mirror – carrying several gyroscopes that would maintain its spatial orientation
in the same plane – would be placed at a distance $$D$$ from the Solar System in a
region without gravitational influences. From the Earth, a laser beam would be directed
towards that region for a long period of time. After a time T, the radiation would return
and be detected, allowing the determination of the fixed constant $$H_0$$.

(a) (7 points) Find an expression for $$H_0$$ as a function of $$D$$, $$c$$ (speed of light) and $$T$$.
Consider that the separation $$S$$ between the Solar System and the mirror increases
only due to the expansion of the universe according to the law $$S = se^{H_0t}, where $$s$$ is
the initial separation. You may use $$e^x ≈ 1 + x$$ for $$x≪ 1$$, if necessary.

(b) (3 points) Imagine that such a mirror is located in the vicinity of the star Vega
(which also features on the logo of the 1st GeCAA). Vega was the first star outside the
Solar System to be photographed and one of the first stars whose parallax ($$p = 0.125′′$$)
was accurately measured in 1840 by G. W. von Struve.
Estimate the total duration of this $$H_0$$ measurement experiment.

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−	==英文题目	+	==英文题目==

	'''3 Mirror'''		'''3 Mirror'''

@@ 第23行： / 第23行： @@
 (which also features on the logo of the 1st GeCAA). Vega was the first star outside the
 Solar System to be photographed and one of the first stars whose parallax ($$p = 0.125′′$$)
-was accurately measured in 1840 by G. W. von Struve.
+was accurately measured in 1840 by G. W. von Struve. Estimate the total duration of this $$H_0$$ measurement experiment.

@@ 第15行： / 第15行： @@
 (a) (7 points) Find an expression for $$H_0$$ as a function of $$D$$, $$c$$ (speed of light) and $$T$$.
 Consider that the separation $$S$$ between the Solar System and the mirror increases
-only due to the expansion of the universe according to the law $$S = se^{H_0t}, where $$s$$ is
+only due to the expansion of the universe according to the law $$S = se^{H_0t}$$, where $$s$$ is
 the initial separation. You may use $$e^x ≈ 1 + x$$ for  $$x≪ 1$$, if necessary.