Dark Energy

Dark Energy – An Unresolved Mystery

We're all going to be tested. The dark energy is going to knock on all our doors.

- Mike Tyson

A well-suited and a cliché definition of Energy is –

Energy can be neither created nor destroyed but only changed from one form to another. This principle is known as the conservation of energy.

But a new form of energy that is derived and depicted in the mysterious way is called “Dark Energy”.

Dark Energy is presented as an unknown form of Energy that is affecting the Universe on the largest scale as derived by some physical cosmology and astrology.

Early Observation

Since the 1990s, dark energy has been the most accepted premise to account for the accelerated expansion.

The first observational evidence for its existence came from measurements of supernovae, which showed that the universe does not expand at a constant rate; rather, the expansion of the universe is accelerating.

Prior to these observations, it was thought that all forms of matter and energy in the universe would only cause the expansion to slow down over time.

Forms of Dark Energy

There are two proposed forms of Dark Energy, depicted according to its Nature,

1. Cosmological Constant

2. Scalar Fields

Cosmological Constant

It is also called as Einstein's cosmological constant as the work “Cosmological Constant” is a constant term that can be added to Einstein’s field equation of Relativity.

It was first proposed by Einstein as a tool to obtain a solution for finding Gravity equation leading to static universe and found that Dark Energy can be effectively used to balance Gravity.

Scalar Fields

It associates a scalar field or valued function with a value to every point in physical space.

The Scalar may be dimensionless mathematical number or a physical quantity. It is also a potential energy which is associated with a particular force.

It is also use to describe the gravitational field and also represents charged particles.

A blunder in the Finding

Albert Einstein coined the term "cosmological constant" to represent the possibility that even empty space has energy and couples to gravity. Like other astronomers of the time, he thought that the universe was static and so proposed there was a repulsive force from space that kept the universe in balance.

It was later realized that Einstein's static universe would not be stable: local inhomogeneities would ultimately lead to either the runaway expansion or contraction of the universe. The equilibrium is unstable: if the universe expands slightly, then the expansion releases vacuum energy, which causes yet more expansion. Likewise, a universe which contracts slightly will continue contracting. These sorts of disturbances are inevitable, due to the uneven distribution of matter throughout the universe. Further, observations made by Edwin Hubble in 1929 showed that the universe appears to be expanding and not static at all. Einstein reportedly referred to his failure to predict the idea of a dynamic universe, in contrast to a static universe, as his greatest blunder.

Involvement of Space Institute NASA

Observations taken by NASA's Hubble Space Telescope and future space telescopes will be needed in order to determine the properties of dark energy, which makes up about 70 percent of the universe.

Astronomers used NASA's Hubble Space Telescope to hunt for supernovae (an energetic explosive event that occurs at the end of a star's lifetime), using their brightness, astronomers could measure if the universe was expanding faster or slower in the distant past.

In its search, Hubble discovered 42 new supernovae, including six that are among the most distant ever found. The farthest supernovae show that the universe was decelerating long ago, but then "changed gears" and began to accelerate.

The diagram above shows the changes in the rate of expansion since the universe's birth 15 billion years ago. The shallower the curve, the faster the rate of expansion. The curve changes noticeably about 7.5 billion years ago, when objects in the universe began flying apart at a faster rate. Astronomers theorize that the faster expansion rate is due to a mysterious, dark force that is pulling galaxies apart

Future Implications

The implications defines the fate of the Universe,

The future is constantly, unremittingly, and obtrusively here. It can’t stop. It’s happening all the time.

It’s happening to you right now.

So it is safe to let the game run on….

However, because of the accelerating expansion, it is projected that most galaxies will eventually cross a type of cosmological event.

Assuming the dark energy is constant (a cosmological constant), the current distance to this cosmological event horizon is about 16 billion light years, meaning that a signal from an event happening at present would eventually be able to reach us in the future if the event were less than 16 billion light years away, but the signal would never reach us if the event were more than 16 billion light years away.

Planet Earth, the Milky Way, and the Local Group of which the Milky Way is a part, would all remain virtually undisturbed as the rest of the universe recedes and disappears.