Why extraterrestrials are not found.
Please see this month's Nikkei Science for details.
They are seeking radio signals
by using frequency of hydrogen form the space as a standard
that exists more than any other elements in the space.
This seems to be appropriate.
And we can suppose the existance of more advanced civilization
than the Earth,as extraterrestrials exist.
Then,we conclude
that they must be able to generate powerful radio wave.
And more,send signals which are intelligible for us.

But,we can't find any signals.
The reports of observations say
there exist no advanced civilization more than the Earth
around to the extent for a several hundreds light-years.
Well,let's argue.

ﾏﾝｿﾞｸ?