I refer to the Cosmological Constant (denoted by the capital Greek letter, Lambda, which looks like an upside-down "V").
This year's Nobel prize in physics was awarded to three astronomers who, I suppose, "led" the research teams whose measurements of a certain type of supernovae were used to derive a positive value for the Cosmological Constant. For fairness, let us at once recognize that the papers publishing the results had dozens of authors, the prize winners being only the two lead authors and one other selected from the pool . And let us also recognize that use of those supernovae as markers of the structure of the universe has been know for at least 50 years or more. Why purportedly exalted prizes are given to anoint the results of the few doing rather obvious research discussed for decades, but finally realizable with large amounts of taxpayer money and new technology, is an unknowable that perhaps sociologists or anthropologists can explain.
The Cosmological Constant represents an energy density of the universe, and seems to be about 72-74% of the density of the universe today. This energy density contribution to the density of the universe is unchanging over time. Just after the Big Bang, the matter density was much, much larger, but now the matter density and energy density appear to be about in the rough ratio of 1 to 3.
In any case, the Cosmological Constant values bandied about the Internet today are thus, depending on the units chosen:
10−35 s−2, 10−47 GeV4, or 10−29 g/cm3
How big are those numbers? Let's look at the last one, which has normal density units of mass per unit volume. The mass of an electron is ->
As one kilogram has 1,000 grams, the Cosmological Constant derived is about .01 electrons per cubic centimeter, which sounds like a rather small density. For comparison, the warm, ionized interstellar medium has a density in the rough range of 0.2-0.5 atom per cubic centimeters. This represents up to 50% of the volume of the Milky way and is rather well studied and understood. As a proton weighs 1836x more than an electron, the warm, ionized interstellar medium in our galaxy has a density of about 600 electrons per cubic centimeter. Thus, the warm, ionized interstellar medium in the Milky Way has about 60,000 times more density that the equivalent energy density represented by the Cosmological Constant.
As the density represented by the Cosmological Constant now dominates/controls the expansion of the Universe, we can see the Cosmological Constant makes up for its small value in volume ;)
What is it? Why? Does its existence have a purpose? Who put that there?
No none has any idea supported by any evidence.
This quote of Hamlet in Hamlet seems appropriate:
"There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy"
Word of the Day
"Monism" - noun [$10] and "Monist"
Monism means 1. any theory denying the duality of matter and mind; 2. (philosophical and theological) the doctrine that only one supreme exists.
Monist means a person who adheres to monism.
Sentence: (A) (from Great Ideas in Philosophy) "For the ontological monist, only one kind of furniture exists in reality, viz., the physical. (B) The seeming existence of the Cosmological Constant seems to rule out monism as a philosophical foundation for the Universe: dark energy is very, very different from matter. There's something else out there beyond our current knowledge.