I'm sorry to have kept you waiting. Now let me work out an answer
to the question 'why night is dark?'
When I presented a question [why night is dark?' I gave you notice
that an answer was judged 'to be 'correct' based on the knowledge
or theories of 'astronomy' and 'cosmology' at the time of the opening
of the 20th century when the question was firstly presented or at
the time of the early 20th century when the answer was recognized
to be 'tentatively correct', hence nobody knows whether this 'correct
answer' would correct for ever. Such situation is something like
a 'circadian rhythm of living beings/ which natural science has
had from its birth, it may be 'fate' or a 'chronic disease' OR 'freshness'
However, the 'answer' has been accepted as a persuasive 'synopsis'
by 'astronomy' or 'cosmology' in 2005, I dare say.
Repeating the question, it was that 'Provided that numerous stars
equally exist in the cosmos, even though the sun exists near the earth,
by collecting light of numerous stars, the total would be equal or
brighter than light of one sun, hence the light when the sun hides
itself behind the dark side of the earth, i.e. the 'nighttime', should
be the same as that when the sun exists on the light side of the earth,
i.e. the 'daytime', shouldn't it? Theoretically it should be so though,
actually the 'nighttime' is dark and it only becomes faintly lighter
by 'moonlight' or 'starlight'. Why is it so?'
The answer which was guaranteed as 'correct' by then most authorized
scientists among numerous answers from around the world, thanks to
the extraordinary prized money, was 'the cosmos has been expanding'
that seemed too much simple, or contemptuous uninteresting one even
the one we wanted to involuntarily throw a question back to somebody
'isn't that right?' Because everybody else expected a most unexpected
answer. Of course it is difficult for us to quickly imagine 'the cosmos
has been expanding', even after being lost in thought of it, that
is an extraordinary idea, so dare say I.
Even though the belief, almost near the religion, that the cosmos
has never been and will never be changed from the earliest times to
the eternal future has occupied 99.9% of the human history, however
not a few observatory findings which gave an impetus to asking 'By
some chance the cosmos is expanding?' began coming out one after another
in those days already. The 'red shift phenomenon' that clarifies why
more distant stars go away from the earth more quickly is one of the
typical samples, we can find the similar phenomenon in the change
of a steam whistle from a distant train.
I think that the biggest key in this question is in this 'leap of
idea' which connected the question 'the cosmos may be expanding' with
the answer 'because the cosmos is expanding night is dark'.
Everybody thinks that if the cosmos is expanding what was the origin
before expanding, reached the theory of the 'big bang' I described
in the 'rise and fall of the cosmos', and further asked whether the
cosmos will continue expanding or begin shrinking. Asking such a question
leads to an interesting story of 'interstellar materials' or 'black
matters', however I recommend you to read some appropriate guide books
answering those questions.
Let's review the above story once more. I the cosmos is expanding,
in particular more distant stars are going away from the earth more
quickly, even though light of numerous stars is accumulated, brightness
of light of the sun nearby the earth, i.e. the sun goes away from
the earth most slowly, overwhelms the star light, doesn't it? That
was an answer to the question 'Why night is dark?'
The attached photograph is the 'Hubble Telescope' named after Edwin
Hubble, astronomer, who discovered the 'red shift' which is said to
be evidence of the expansion of the cosmos. The telescope has been
sending us, one after another, excellent images of the cosmos observed
from the outside of the earth's atmosphere.