Why do historians refer to the dark ages as a period when europe "slept"?

it's for world civilization.

As water is cooled from 4 c to 0 c its density

Which measure of humidity, relative humidity or dew point, best describes the actual quantity of water vapor in a mass of air

Some gamma ray bursts are hypothesized to come from mergers of neutron stars or black holes. if this hypothesis is correct, what else should we in principle be able to detect from such mergers? a. gravitiational waves b. x-ray bursts c. significant disruption of gas thousands of light-years away in the surrounding galaxy d. an "afterglow" of bright visible light, lasting for weeks