the universe?

Question

why is it dark outside i mean in outerspace?

Answer 1

It's a vacuum and there are no molecules to reflect or scatter light.

Answer 2

Because it doesn't go on infinitely, populated by stars forever. This was the subject of "Olber's Paradox" the answer to exactly your question back in the 18th century.
If the Universe was infinite and uniformly populated by stars, it would be extremely bright in every direction. It was determined that star distribution is adequate to make that the case. Since the night sky is black, we conclude that the Universe is finite, either in distance or in time.
A rather large cosmological issue is invoked by such an innocuous little question. It is, in fact, a major reason for abandoning the infinite, steady state model of the Universe, which dominated opinion for a couple centuries.

Answer 3

Because light is a form of energy, and as huge as space is there is not nearly enough light and energy to fill it. So just like at your house when there's not enough light, things appear dark when you don't turn on the lights.

Now think of space as one mind-blowingly huge, mostly empty room, and each star is just a keychain flashlight. Same thing. If you're standing on the other side of this HUGE empty dark room and I turn on my light, you may not even be able to see it at all.

But it should be noted that space can appear dark to human eyes but still be lit up with background radiation from past events that we need telescopes to observe.