Looking up in the sky with self eyes or looking at the images of the universe online, one will see the same thing: the blackness of space, punctuated by spacecraft, planets, or bright stars. But why is it black? Why isn’t it colorful?
According to Tenley Hutchinson-Smith, a graduate student of astronomy and astrophysics at the University of California, Santa Cruz, “You would think that since there are billions of stars in our galaxy, billions of galaxies in the universe and other objects, such as planets, that reflect light, that when we look up at the sky at night, it would be extremely bright. But instead, it’s actually really dark.”
Hutchinson-Smith said this contradiction, known as Olbers’ paradox in physics and astronomy circles. The theory of space-time expansion can explain this, the idea that “because our universe is expanding faster than the speed of light … the light from distant galaxies might be stretching and turning into infrared waves, microwaves, and radio waves, which are not detectable by our human eyes.
According to Miranda Apfel, who is also a graduate student of astronomy and astrophysics at UCSC, Lights in all colors are given by stars, even colors not visible to the human eye, like ultraviolet or infrared. If microwaves could be seen, all of the space would glow, and this because of the cosmic microwave background from the Big Bang light energy that was scattered by electrons and protons existing during the early universe still fills all of space.
Another reason interplanetary and interstellar space appears dark is that space is a nearly perfect vacuum. Space is a near-perfect vacuum meaning it has exceedingly few particles; there’s virtually nothing in the space between planets and stars to scatter light to in eyes. And with no light reaching the eyes, it is seen as black.
A study in The Astrophysical Journal of this year suggests that space may not be as black as scientists thought. Through NASA’s new Horizon Mission to the Kuiper Belt and Pluto, researchers have been able to see space without light interference from Earth or the sun. The images taken by the spacecraft the team shifted through and subtracted all light from known stars, possible galaxies, and Milky Way, as well as any light that might have leaked in from camera quirks. They found that the background light of the universe was still twice as bright as predicted.