The speed of light, denoted by "c," is a fundamental constant in physics, representing the maximum speed at which information or energy can travel in a vacuum. In the context of the theory of special relativity, proposed by Albert Einstein, the speed of light plays a crucial role. Its value is approximately 299,792,458 meters per second (approximately 186,282 miles per second).
In other words, in a vacuum, light travels at this constant speed, and nothing with mass can travel faster than c. This principle has far-reaching consequences for our understanding of the universe, such as time dilation and length contraction at relativistic speeds.
As for dark energy, it is a mysterious form of energy that is hypothesized to permeate space and contribute to the accelerated expansion of the universe. It is one of the most significant unsolved mysteries in cosmology. Observations of distant supernovae in the late 1990s revealed that the universe's expansion rate is actually increasing over time, contrary to what was initially expected.
Dark energy is believed to be a repulsive force that counteracts the gravitational attraction between galaxies, causing the expansion of the universe to accelerate. The exact nature of dark energy remains unknown, and it is one of the key topics of research in modern cosmology.
The majority of the universe is composed of dark energy (about 68%) and dark matter (about 27%), with the rest being regular matter (the stuff that makes up stars, planets, and us) and radiation (such as light and other electromagnetic waves).
While dark energy's existence is inferred from observational data, its origin and true nature are still subjects of ongoing investigation and speculation in the scientific community.