The problem of the cosmological constant

Albert Einstein

The value of the cosmological constant Λ in Einstein's equation has gone through many vicissitudes and alternatives:

• 

  Georges Lemaître

  Einstein introduced it in 1917, and gave it a negative value to ensure that the universe neither expands nor contracts, but remains stable indefinitely. At the time, this was the consensus of most cosmologists.
• The Hubble-Lemaître law, discovered in 1927, showed that the universe is not stable, but expanding.
• In 1930, Arthur Eddington showed that Einstein's static universe would not be stable either, for any random variation would throw it out of stability. It would therefore be in an unstable and short-lived equilibrium.
• In 1931, Einstein declared that the introduction of the cosmological constant in his equation had been his worst mistake. Thereafter, the consensus of cosmologists changed: the value of the cosmological constant was probably zero. In other words, the corresponding term in Einstein’s cosmological equation would disappear.
• In 1998, from the study of supernovae in distant galaxies, it appeared that the universe may be in a state of accelerated expansion. The simplest way to explain this is to resurrect the term of the cosmological constant, but assigning it a positive value.
• The standard cosmological model, developed in the first decade of the 21st century, adjusts the values of the constants in the Einstein equation to fit the data obtained by analyzing the cosmic background radiation. From this analysis, the following value for the cosmological constant has been obtained:

Λ ≈ 10^-52 m^-2

• However, if quantum field theory is applied, the value of the cosmological constant should be about 120 orders of magnitude larger, that is:

Λ ≈ 10⁶⁸ m^-2

This discrepancy is so large that it has been said this is the worst prediction in the history of physics.

To make matters worse, if the cosmological constant had the value predicted by quantum field theory, life would be impossible in the universe. It happens that the value of this constant is one of those critical values that make one think that the universe must have been designed to make life possible. If its value were higher than it appears to be, the universe would expand so fast that matter would disintegrate and no galaxies or stars would form. On the other hand, lower (negative) values would lead to a universe that would contract towards a Big Crunch before life would have had time to appear.

The critical value of this constant is very close to zero. This is precisely the value assigned to it by the standard cosmological model. Therefore, at this point physics has a very important pending problem, which proves again that the two theories on which our current knowledge is based (quantum mechanics and general relativity) are incompatible.

The same post in Spanish

Thematic Thread about Standard Cosmology: Previous Next

Manuel Alfonseca