Physics 問題~

In space no one can hear you scream. True enough, more or less, but rather misleading.

Sound can travel through space, because space is not the total vacuum often made out to be. There are gases in space, and it's true that these gases can propagate sound waves just like Earth's air allows sound to travel. The difference is that interstellar gas clouds are much less dense than the Earth's atmosphere. (They have fewer atoms per cubic foot.) So if a sound wave is travelling through a big gas cloud in space and we are out there in space ready to listen, only a few atoms per second if any would strike our eardrums, and we wouldn't be able to hear the sound because our ears aren't sensitive enough. Maybe if we have a very advanced and sensitive microphone we could detect these sounds, but to our human ear it would be silent. It is not strictly true that no sound can travel through space at all, but it is true that we would not be able to hear any sound in space.

The simplest answer:

Because sound wave cannot travel in vaccum.
(Since space is a vaccum)