Cain explains that German Astronomer Heinrich Wilhelm Olbers first asked the question in 1823. It’s known as Olber’s Paradox and states that the night sky should be lousy with stars if the universe is infinite, static, and timeless. However, the night sky is more connected to the dots than pointillism.
Edwin Hubble solved the paradox in 1929. He observed that everywhere he looked in the universe. All the stars’ spectrums were slightly red, which stretched the light. It means the space itself light was traveling through was expanding.
Ergo, the universe isn’t static, and there must be stars so far away. Their light hasn’t had time to reach yet. It means that the farther away something is, the faster the space between it and us stretches out. After a long distance, space will stretch out faster than light can close the gap.
If the universe expands away from everything else, it stands to reason that it was all clumped together if you go far back enough. It is where the theory of the big bang comes in. The expansion of space solves the riddle. In 1964, Arno Penzias and Robert Wilson were working on an unrelated experiment with a radio telescope, and they couldn’t shake this unwanted static.
After ensuring everything was functioning correctly, even cleaning the antennae inside for bird droppings for hours, they realized the signal was coming from everywhere. Nobody can’t stop the signal. They concluded that the Cosmic Microwave Background Radiation must have been the light from the big bang. But it had been stretched out after billions of years until it was low-energy microwaves that our eyes couldn’t see.
Why is space black?
Space appears black because it is mostly empty and lacks significant visible light sources. Here are a few reasons why space appears black:
Lack of Atmosphere: Space is a vacuum devoid of air and other gases. Earth’s atmosphere scatters and diffuses sunlight, so we see a blue sky during the day. However, in the vacuum of space, there is no medium to scatter or reflect sunlight. As a result, when we look at space from Earth or space-based telescopes, the absence of scattered light gives the appearance of darkness.
Low Matter Density: Space is predominantly empty, with vast distances between celestial objects. In interstellar and intergalactic regions, the density of matter is extremely low. Without matter to reflect or emit light, these regions appear black to our eyes.
Absorption: Objects in space, such as planets, stars, and galaxies, can absorb light. When light encounters an object in space, it may be absorbed by that object rather than reflected toward us. This absorption contributes to the darkness of space.
Background Radiation: While space appears black, it is not entirely energyless. As mentioned earlier, space contains Cosmic Microwave Background (CMB) radiation, a remnant of the Big Bang. The CMB radiation has a low energy density and is predominantly in the microwave range outside the visible spectrum. Thus, we cannot directly perceive this background radiation as visible light.
Galaxies aren’t a solid light source. These light sources are dimmer. They appear as less light from that source reaches our eyes because of the inverse-square law. The light’s intensity depends on the source’s radius because the further the light travels, the more it spreads over a larger surface area. It means the observer observes the intensity is reducing.
However, the sky wouldn’t be black if people lived in an infinite, static universe with endless stars, no expansion, and no beginning or end. But instead, as bright as the surface of a star or even infinitely bright. This concept is known as Olber’s Paradox. It wouldn’t matter where you looked in the sky in an infinite universe.
What about clouds and dust that would obscure the view of background stars? These will also be as bright as stars as they receive and reflect so much light in an infinite universe. It is one of the grand pieces of evidence that the universe is not everlasting but has a beginning and an end. It is also evidence of the expansion of the universe.
- The Hubble Constant has shown that the universe expands at roughly 70km/s every 1 megaparsec.
The universe likely has an age of roughly 13.8 billion years. It is dynamic and expanding. It means a sphere around Earth that we can’t see beyond. Galaxies beyond that sphere are moving away from us faster than the speed of light.
It means that even with a telescope capable of infinite magnification, there would be patches of space in the sky containing nothing from the human perspective. Distant galaxies become redder due to the stretching of light wavelengths through the universe’s expansion, known as redshift.
The redshift of galaxies can become so extreme that light is emitted in the visible light spectrum. Billions of light-years away are stretched so much that they eventually reach us through infrared wavelengths beyond our eye’s ability to see.
Scientific explanation: Human eyes are well adapted to life on Earth, during the day anyway. The Sun gives an excellent level of light. So therefore, everything around us is beautiful colors. At night, it is dark because the light of the Sun is no longer there. Each one of the stars is like a Sun in its location.
Why is the space so black if all the stars are given all this light? We should probably explain why the Earth has so much light and color to determine this answer. The Earth is surrounded by an atmosphere that contains gas, water, dust, and dirt. When the light of the Sun hits any of these objects, it scatters or bounces off. The Rayleigh Scattering process makes the sky blue during the day. It causes us to see the various colors.
- Eyes can only detect light in a tiny portion of the electromagnetic spectrum, but most of the light isn’t even within this spectrum.
So, the atmosphere allows one to see the light and the colors. This scattering effect lets us see the blue sky and the gorgeous tones of the sunrise and sunset. Space does have gas and cosmic dust, but it doesn’t have any atmosphere. Light will travel in a straight line until it hits something. The surrounding space appears black because there isn’t a strong enough atmosphere to cause the scattering effect.
The light from the stars at the farthest end of the galaxy will take longer to reach our eyes than those closer to the Earth because light travels at a constant speed. So as the universe keeps on expanding, the wavelength of light gets longer and longer. Therefore, we have less visible light until there is no light that we can see.
How dark is space?
Scientists want to know how dark space is. Can that tell us about the number of galaxies in the visible universe? Nasa uses the new Horizon spacecraft to figure out how dark space is. When you look at the night sky away from city lights, the space between stars appears dark. Outside the Earth’s atmosphere, outer space gets even darker.
Space is not black. A faint glow of countless distant stars and galaxies lights the universe. But it’s not easy to measure this glow. Like the Hubble space telescope, satellites and telescopes inside our solar system cannot correctly calculate the light emitted. Dust and particles illuminated by the sun fill the region around the earth and the inner solar system. This creates a diffuse glow in the sky.
Scientists must use a spacecraft outside our solar system to measure that faint glow that fills the universe. Scientists have used observations from NASA’s new horizons mission to Pluto and the Kuiper belt to determine this cosmic optical background’s brightness.
New Horizons is far from significant light pollution sources, billions of kilometers from Earth. Therefore, the surrounding sky is about 10 times darker than the darkest sky visible to Hubble. It enables the probe to take much more accurate measurements.
“Space – Physics and Metaphysics.” Encyclopædia Britannica.
Refer to Plato’s Timaeus in the Loeb Classical Library, Harvard University, and his reflections on Khora.
Carnap, R. An Introduction to the Philosophy of Science. New York: Dove. (Original edition: Philosophical Foundations of Physics. New York: Basic Books).
Space from Zeno to Einstein: classic readings with a contemporary commentary. Huggett, Nick.
Janiak, Andrew. “Space and Motion in Nature and Scripture: Galileo, Descartes, Newton.” Studies in History and Philosophy of Science.