Why is space dark ??

 1.  Lack of atmosphere

                           On earth, sky looks blue. It is called Reyleigh scattering.  Since space lacks an atmosphere to scatter light, it looks black.

2.  Absence of light source

                           Space is vast and mostly empty. It has few light sources

3. Vacuum of space

                           Space is near perfect vacuum.  There are  no particles to reflect or difuse light. 

4.  Inverse square law

                          Light intensity decreases with distance.  So, distant stars appear dim.

5.  Human eyes limitations 

                      Human eye needs certain amount of light to see. In the dark regions of space, there is no sufficient light.

6. Olber 's paradox

                      Light from distant stars has not reached us yet.

7. Cosmic expansion

                      Universe is expanding beyond the visible spectrum making space more darker to human eye.