Dark energy is a uniform negative pressure that makes up 70% of the universe’s mass/energy and causes its accelerating expansion. Its exact form is unknown, but the cosmological constant theory is believed by most physicists. Dark energy’s existence has implications for the universe’s ultimate fate, including the “heat death” caused by decreasing density and increasing hostility to life.
Dark energy is a very scattered and uniform negative pressure that permeates the entire observable universe. It accounts for 70% of the mass/energy in the universe and is responsible for its accelerating rate of expansion. Dark energy is different from the energy we know because it is not locally concentrated, as is the case in stars and galaxies, conventional manifestations of matter and energy. There are several other important differences between conventional energy and dark energy, which physicists continue to study.
The exact form or working mechanism of dark energy is unknown. In this respect it is similar to its cousin, dark matter, which can only be observed by its influence on normal matter and energy.
There are two main theories for the shape of dark energy, although one is more important than the other. The first theory, the quintessence, describes dark energy as a fluctuating field that changes its intensity based on location. The second theory, that of a cosmological constant, describes dark energy as constant and uniform. It is this second theory that is believed by most physicists and forms the basis of the Lambda-CDM model, the prevailing model of the structure of the cosmos.
The negative pressure of the cosmological constant is thought to originate from vacuum fluctuations on extremely small scales throughout space. So-called virtual particles are continually being created and destroyed in this vacuum, creating a quantum foam that itself has energy.
The existence of dark energy has implications for the ultimate fate of the universe. If dark energy is an intrinsic property of space, as it appears to be, then it will continue to exist indefinitely. If dark energy is the cause of the accelerating expansion of the universe, then it will also be the cause of decreasing the average density of any space particle in the long run. As the universe becomes thinner and thinner, it will also become colder and more hostile to life. Therefore, dark energy can rightly be blamed for causing the “heat death” of the universe.
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