If the main problem is to instantaneously move to a planet 100 light years away, trying to see the scene of World War II. First of all, the theory of relativity does not allow faster than the speed of light, so there is no show. At present, there are only two ways to move faster than light, one is a warp-speed spacecraft, and the other is wormhole . So the hypothesis of the subject is still possible in theory.
Okay, now I am standing on a planet 100 light years away from the earth. Then the light received from the earth should have been in 1909, when the First Time War had not yet begun. In fact, without considering the expansion rate of the universe, 100 light-years are very close to the earth on the cosmic scale. At this time, the expansion rate is not obvious. For example, the Milky Way and the Andromeda Galaxy are 2.2 million light-years apart, and their cosmic expansion cannot offset their mutual attraction. Therefore, the expansion effect of the universe within a hundred light-years can be ignored.
If you want to see World War II, such as the Japanese invasion of China in 1937 or the German blitz on the Polish battlefield in 1939, it should be on a planet about 80 to 82 light years away from the earth.
To see the real-time situation of the battlefield, at least one must see a tank, an airplane and a person. Then you must choose the smallest thing on the battlefield as a pixel, such as the human body. Otherwise I can't see anything. The scale of the human body is roughly calculated as
with a 1.7m diameter sphere, so the aperture of the telescope should be large, otherwise the only thing that can be seen is the earth as a bright spot.
target length/distance = 1.22 x wavelength / telescope diameter. Target length/distance
target scale/distance=1.7m/82 light-years≈4.8×10^-17
The visible light wavelength range is between 380nm and 780nm, and the median value is 580nm.
then the telescope aperture=1.22×580nm/4.8×10^-17
1.22×5.8×10^-7/4.8×10^-17=45,940,973.9480064589824. A telescope with an aperture of approximately 46 million meters. The diameter of the
telescope is about 46,000 kilometers, while the diameter of Neptune is more than 49,000 kilometers.
So standing on a planet 82 light years away, to see the World War II battlefield, at least a telescope as big as Neptune is needed.
