It’s out there; it’s everywhere; scientists may not yet be able to describe it in any known physical terms, but its there just the same, and it represents about 74% of the stuff that is the known universe. It is a force, not in any way related to the Star War’s entity as at least one writer here has speculated, but a force nonetheless which appears to counteract gravity. Although it has been quantified, it can not be seen or detected with conventional technology, but that may be only a temporary impediment to understanding what astrophysicists have coined “dark energy.”
There are a number of quantum states of matter known, indeed proven to exist, but which are not manifest within any perceivable sense of reality. Antiprotons and positrons, essentially antimatter, are an example of such. Gravity is a force we are very well aware of, but which can not be qualified in any physical terms beyond its observable effects. Kepler speculated it must exist, Newton defined it, Einstein codified our understanding of its effect, and yet, nobody to this day can tell you exactly what gravity is or what causes it to occur. Is it a manifestation of the weak nuclear force, like electromagnetism? Is it an effect of the strong nuclear force? If we can’t say exactly what gravity is, how could we any better qualify anti-gravity?
The fact is, the best answer science can offer in response to the question of “What is dark energy?” is we just don’t know, yet. What we do know, is that the existence of dark matter provides an excellent premise for understanding why the perceivable expansion of the universe, based on actual observations by the Hubble Space Telescope (HST) of distant supernovae, seems to be accelerating. Since this realization came to light in the 1990’s, other satellites launched to study and view deep space in the infrared and gamma-ray regions of the electromagnetic spectrum have confirmed the HST findings.
Some astrophysicist have proposed dark energy represents the cosmological constant Einstein used in his original calculations in support of his theory of general relativity. Other physicist speculate dark energy may represent some entirely new quantum entity. Still other speculations promote the idea that dark energy is the refuse of matter torn apart in black holes and ejected into space. The only certainty at this point is that this quandary will require much study before it will be fully understood.
It is, perhaps, a scenario analogous to Einstein’s proposition that light energy was actually comprised of particles of matter he called photons. Nobody believed it or paid Einstein much attention in 1905 when he first published his theory. He suggested, if astronomers would just look at stars close to the sun during an eclipse they would detect movement of the stars denoting gravitational effect, and if light was effected by gravity, photons had to be particles with mass, however minuscule. It turned out Einstein was right and became an instant celebrity.
Just as the effect of gravity on photons is real, neither a photon of light nor mechanism underlying gravitational force are well understood. Whatever dark matter is, its effect on the rest of the matter in the universe is undeniable. Dark matter, by virtue of its observable effect, is therefore a physical reality and one that will obviously reshape human thinking on just how all the pieces of the universal puzzle fit together. That is, when we figure out just what dark matter is in the first place.