Question

What keeps space empty?

Answer 1

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Space is not empty. a point in outer space is filled with gas, dust, a wind of charged particles from the stars, light from stars, Cosmic rays, radiation left over from the big Bang, Gravity, electric and magnetic fields, and neutrinos from nuclear reaction
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Answer 2

Space is not empty, instead contains fleeting electromagnetic waves and particles that pop into and out of existence. According to modern understanding, even if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, dark energy, transiting gamma and cosmic rays, neutrinos, along with other phenomena in quantum physics. In modern particle physics, the vacuum state is considered as the ground state of matter.

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