Why is outer space dark, even though there is the Sun? Looking at the night sky with our own eyes or taking photos of the universe online, we will see the same thing, namely very dark space, interspersed with bright stars or planets. Why is it black?
Why is outer space colorless, like the blue daytime sky on Earth? If the Universe is filled with the Sun and billions of stars, why doesn’t the night sky shine with starlight?
This is a classic question that astronomers call the Olbers paradox, after the German astronomer Heinrich Olbers. He tried to answer the question “why is outer space always dark” by assuming that interstellar space is partly filled with matter that absorbs light, for example clouds of interstellar dust.
But the first law of thermodynamics casts doubt on this hypothesis, because interstellar matter that absorbs light, will inevitably heat up and begin to emit light itself.
Olbers’ paradox was finally solved in the 20th century. It turns out that the Universe continues to expand and visible light from galaxies, as it moves away, passes into the range of infrared, ultraviolet and radio waves, which are invisible to the human eye. Unless we can see microwaves, all of space will glow.
Another question of course is, if space is dark, why is Earth bright? Quoted from Orbital Today, this phenomenon can be explained https://www.atrbpnkabserang.com/ by the presence of the atmosphere. Space is almost like a vacuum, there is only a small amount of gas and cosmic dust in a certain volume, but no atmosphere. And the light needs to bounce off something.
Why is Space Dark
Light will travel in a straight line until it hits an object. Once light hits and reflects off an object, it is the atmosphere that provides the “scattering” in the spectrum visible to the human eye. Since the Earth rotates on its axis, darkness reigns on the side where the Sun’s light does not fall and we call this period as night. During the day, atmospheric atoms, molecules and dust interact with photons, causing them to scatter.
On Earth, most of the atmosphere scatters blue light, because blue light has shorter wavelengths at the visible end of the spectrum and is more scattered in the atmosphere than red light. Therefore, the daytime sky on Earth appears blue.
On Mars, the atmosphere is thinner, about 100 times thinner than Earth’s, but still enough to make the sky appear blue-gray during the day. When Mars’ frequent winds raise dust clouds from the surface, the Martian sky becomes thinner, taking on a reddish color.
However, if we are on a planet or satellite that has no atmosphere or a very thin atmosphere (such as the Moon or Mercury), the sky looks black during the day and at night. If we look at the photos taken by the Apollo spacecraft on the Moon, it appears that the sky there is black, even with bright sunlight.
As far as astronomers who study the observable universe know, only about 5% is made up of matter. The rest, or most of it, consists of dark matter or dark matter (around 27%) and dark energy (around 68%). Dark matter is invisible matter that does not emit its own light and only interacts with normal matter through gravity, evidence of which we can see in galaxies and galaxy clusters. But considering that it is five times more abundant than ordinary matter, scientists are of course looking for direct evidence of its existence.
One approach to finding it, perhaps counterintuitive because dark matter explains what we see in stars and galaxies, is to head underground. There are several underground facilities around the world where physicists look for signs of Weakly Interacting Massive Particles (WIMPs), such as measuring neutrino impacts, among other things.
WIMPs Must Pass Earth All the Time
The idea is that WIMPs should pass by Earth all the time as they move through space, so to detect them we just need a detector sensitive enough to pick up such weak interactions.
“In the Stanford LUX-ZEPLIN experiment, two large electrical networks applied an electric field across the volume of the liquid, which pushed the released electrons towards the surface of the liquid,” said Hugh Lippincott, Associate Professor of Physics at the University of California, Santa Barbara, quoted from The Conversation.
“As they penetrate the surface, they are drawn into the space above the liquid, which contains xenon gas, and accelerated by another electric field to create a second flash of light. Two large arrays of light sensors collect these two flashes of light, and together they allow researchers to reconstruct the position, energy, and the type of interaction that occurs,” he said again.
These detectors are impressive, and even if they don’t know what dark matter is, they can help constrain what dark matter isn’t. But the problem is that if you place them on the surface, they will detect too much noise.
“However, on Earth, we are constantly surrounded by low levels and harmless radioactivity originating from trace elements, especially uranium and thorium in the environment, as well as cosmic rays from outer space,” Lippincott continued.
“The goal of hunting for dark matter is to build detectors that are as sensitive as possible, so they can see dark matter, and place them in places as quiet as possible, so that dark matter signals can be seen against the background of radioactivity,” he explained.
Therefore, dark matter detectors are placed deep underground. In Ontario, Canada, scientists must travel every day 2 kilometers underground, then walk deeper into a working mine to reach SNOLAB, the world’s deepest clean laboratory.
Events recorded from the LUX-ZEPLIN experiment, deep beneath the Black Hills in South Dakota, occur about five times a day, far lower than the trillions of events detected at the surface.
However, scientists have ruled out dark matter as a potential cause of all this. But as the experiments continue, there is hope that they can find evidence of all the lost objects in the universe, deep underground.
