What does the cosmological constant tell us about the universe?

Figure 1: The cosmological constant was originally introduced by Einstein in 1917 as a repulsive force required to keep the Universe in static equilibrium. In modern cosmology it is the leading candidate for dark energy, the cause of the acceleration of the expansion of the universe.

Why is the cosmological constant important?

The main attraction of the cosmological constant term is that it significantly improves the agreement between theory and observation. The most spectacular example of this is the recent effort to measure how much the expansion of the universe has changed in the last few billion years.

Why did Einstein create his fudge factor?

In 1915, Einstein derived the equations of general relativity that describe the workings of a gravity-dominated cosmos. He added a fudge factor called the cosmological constant to ensure that, in keeping with contemporary tastes, the universe described neither expanded nor contracted.

Why did Einstein include the cosmological constant?

Einstein included the cosmological constant as a term in his field equations for general relativity because he was dissatisfied that otherwise his equations did not allow, apparently, for a static universe: gravity would cause a universe that was initially at dynamic equilibrium to contract.

What is a fudge factor used for?

A fudge factor is an element inserted into a calculation, formula or model to allow for error or uncertainty. Fudge factors are also used to make something congruent with an observed or desired result. The word fudge, in this context, means to be intentionally unclear or imprecise.

Is the expansion of the universe accelerating?

Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time. The unexpected result was that objects in the universe are moving away from one another at an accelerated rate.

Is the universe expanding at a constant rate?

But in a dark energy-filled Universe, the expansion rate is constant, so as a galaxy gets more distant, it moves away faster and faster. The largest contributors to our Universe’s energy today are matter (at ~32\%) and dark energy (at ~68\%).

Does the cosmological constant explain dark energy?

Cosmological constant The simplest explanation for dark energy is that it is an intrinsic, fundamental energy of space. This is the cosmological constant, usually represented by the Greek letter Λ (Lambda, hence Lambda-CDM model).

Is the cosmological constant a fudge factor?

Although the cosmological constant is often referred to as a “fudge factor,” that is a misnomer. Such a constant is required in Einstein’s equation, although no value is given for it. If positive, it produces a gravitational repulsion.

What is the cosmological constant in physics?

In the context of cosmology the cosmological constant is a homogeneous energy density that causes the expansion of the universe to accelerate. Originally proposed early in the development of general relativity in order to allow a static universe solution it was subsequently abandoned when the universe was found to be expanding.

What is the coincidence problem in cosmology?

Coincidence Problem. Many argue that to be living in that moment is too unlikely to be coincidence. This has been called the coincidence problem, and has motivated theories beyond the cosmological constant with more general forms of dark energy that may change with time.

How does the cosmological constant affect the energy density of vacuum?

The cosmological constant has the same effect as an intrinsic energy density of the vacuum, ρvac (and an associated pressure ).