The question of the darkest thing in the universe involves examining how matter and space interact with electromagnetic radiation. Cosmic darkness can be defined by the lack of visible light, the complete absorption of light, or the non-interaction with any form of electromagnetic energy. Understanding ultimate darkness requires exploring these three distinct concepts, from the vast emptiness of space to extreme physical objects and the mysterious, unseen components of the cosmos.
The Cosmic Vacuum
The most common form of darkness is the vast, empty space between galaxies and stars, often referred to as the cosmic vacuum. This environment has an extreme sparsity of matter, meaning there is very little to emit, reflect, or scatter light. Despite the billions of stars in the universe, the night sky appears dark because the vacuum of space acts as a backdrop devoid of light sources.
This phenomenon resolves the long-standing astronomical puzzle known as Olbers’ paradox. The paradox suggests that in a static, infinite universe filled with stars, every line of sight should end on a star, making the night sky uniformly bright. However, the universe is neither static nor infinitely old.
The two main factors keeping the cosmic vacuum dark are the finite age of the universe and its expansion. The universe is approximately 13.8 billion years old, so light from objects beyond the observable universe has not had enough time to reach Earth. Furthermore, the expansion of space stretches the wavelength of light from distant galaxies, causing cosmological redshift. This stretching shifts visible light into the non-visible infrared and microwave regions, effectively dimming the distant cosmos until it becomes invisible.
Black Holes
The darkest physical objects in the universe are black holes, which achieve their profound darkness through overwhelming gravitational force. A black hole is a region of spacetime where gravity is so intense that nothing, not even light, can escape its grasp. The boundary marking this point of no return is known as the event horizon.
Once a photon crosses the event horizon, it is forever trapped and pulled toward the central singularity. The escape velocity required to leave this region exceeds the speed of light. Because light cannot be emitted or reflected from within the event horizon, a black hole acts as a perfect absorber, analogous to an ideal black body in physics.
The visible darkness of a black hole results from its perfect absorption of all incoming electromagnetic radiation. While the black hole itself is dark, it is often surrounded by a swirling accretion disk of superheated gas and dust that emits intense radiation. This makes the black hole visible only by the contrast of its dark shadow against the bright matter around it.
Dark Matter
A different form of cosmic darkness is represented by a mysterious substance known as Dark Matter. Unlike a black hole, which perfectly absorbs light, Dark Matter is considered “dark” because it does not interact with the electromagnetic force at all. This means it neither emits, absorbs, nor reflects light, making it truly invisible across the entire electromagnetic spectrum.
The existence of Dark Matter is inferred from its gravitational effects on visible matter and the structure of the universe, not from its light. Observations show that galaxies spin too fast to be held together solely by the gravity of their visible stars and gas. This rotational velocity requires a significant amount of unseen mass, which is attributed to Dark Matter.
Gravitational lensing, where the path of light from distant galaxies is bent by the gravity of foreground matter, provides strong evidence for this unseen component. By measuring the distortion of the background light, scientists can map the mass distribution in galaxy clusters. They find that the gravitational influence is far greater than what visible matter accounts for. Current cosmological models suggest that Dark Matter constitutes approximately 85% of the total matter in the universe.
The Darkest Material
In contrast to the vast, invisible darkness of space, scientists have engineered materials that represent the darkest known physical substance on Earth. The most notable example is Vantablack, a coating designed for terrestrial and aerospace applications. This material achieves its extreme darkness through a microscopic structure rather than chemical composition alone.
Vantablack is composed of a dense “forest” of vertically aligned carbon nanotubes (VANTA), which are tiny cylinders of carbon standing upright on a substrate. When light strikes the surface, photons enter the spaces between the nanotubes and become trapped instead of reflecting. They bounce around within the structure, being repeatedly absorbed by the carbon until the light energy is dissipated as heat.
The original Vantablack coating absorbs up to 99.965% of visible light, making it appear as an almost perfect void to the human eye. This extreme absorption ability erases any sense of dimension or contour, causing three-dimensional objects coated in the substance to look like flat, two-dimensional shapes. While Vantablack is the darkest substance known to human engineering, its absorption rate is slightly less than the perfect absorption achieved by a black hole’s event horizon.