What's the cosmological constant!?

Human stupidity.

I don't know but I hear that baby is about as constant as you can get.

0.260 eV/cm^3 (4.17 × 10^-14 J/m^3) which yields approximately 411 photons per cubic centimetre. The Cosmic Microwave Background, which permeates through the entire universe.

The cosmological constant, denoted by the Greek letter lambda (Λ), is a term in Einstein’s field equations of general relativity that represents the energy density of space, or vacuum energy. It was originally introduced by Albert Einstein in 1917 to achieve a static universe, which was the prevailing belief at the time. However, after Edwin Hubble’s discovery of the expanding universe, Einstein abandoned the constant, considering it his “greatest blunder.”

Despite this, the cosmological constant made a comeback with the discovery in 1998 that the universe’s expansion is accelerating. This acceleration implies that the cosmological constant may have a positive value. In modern cosmology, the cosmological constant is associated with dark energy, which accounts for about 68% of the mass-energy density of the universe and is used in the current standard model of cosmology known as the ΛCDM model.

The cosmological constant is essentially a measure of the energy density of empty space, or the vacuum energy that arises from quantum mechanics. It acts as a repulsive force, working against the gravitational pull of matter in the universe. The exact nature of the cosmological constant and dark energy remains one of the greatest mysteries in physics, with many physicists believing that understanding the vacuum holds the key to a full understanding of nature.