Question

Is the space completely empty?
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Why?​

Answer 1

The space between galaxy clusters, called the voids, is probably nearly empty. Some theories put the average density of the Universe as the equivalent of one hydrogen atom per cubic meter.

Answer 2

hmmm no

not at all let's see

empty means it has nothing defined by mass space is not empty at all but there are places were it is empty

having celestial bodies many of them I didn't count it.