Einstein's "greatest blunder" may turn out to be his greatest gift to science
Einstein's "greatest blunder" may turn out to be his greatest gift to science
Dark Energy explained...
Maybe you have to know the darkness before you can appreciate the light. -Madeleine L'Engle
Greetings, fellow Bohron
Dark Energy is an undiscovered form of repulsive force that acts opposite to the attractive nature of gravitational force. As per our current knowledge, dark energy is attributed as the reason for the mysterious accelerated expansion of the universe.
Cosmological Constant
A mathematically permitted but optional term occurs in Einstein field equations, known as cosmological constant(denoted by Ω or Λ). This rather unnecessary-looking term opposes the ability of gravity to clump the whole universe together into a single ball and help Einstein fulfill his belief in a static universe.
Alexander Friedmann’s work was like last rites before the demise of the static universe hypothesis was confirmed by the discoveries of Edwin Hubble and others. Now embarrassed, Einstein abandoned the idea of Ω calling it his life’s ‘greatest blunder’.
However, Ω continues to trouble physicists to date. Remember the saddle-shaped Friedmann model (Ω < 1) which hinted at a forever accelerating universe. Recent observations have found something similar.
History
Type 1a supernovae serve as excellent means of measuring large intergalactic distances due to their consistent peak luminosity. In 1998, two teams led by astrophysicists Saul Perlmutter, Brian Schmidt and Adam Reiss discovered that dozens of such distant supernovae appeared dimmer than expected.
In two separate papers, they proved that the recession velocities of galaxies housing such supernovae were strictly increasing over time. This meant that the universe was undergoing accelerated expansion, a discovery for which Saul, Brian and Adam won the 2011 Nobel Prize in physics.
This was the first evidence that a mysterious ‘dark’ force that opposed gravity permeated through space. There doesn’t seem to be any other natural explanation for this than Einstein’s Ω.
How Ω causes the universe to expand?
The vacuum of space is not completely empty but beaming with particle-antiparticle pairs popping in and out of existence every now and then. Such short-lived perturbations in vacuum are called Quantum Fluctuations.
The most acceptable answer is that dark energy is a quantum effect, an intrinsic property of the vacuum itself.
Vacuum energy creates particle-antiparticle pairs(known as pair production) which annihilate after a very brief period releasing back the energy that created them. For the howsoever tiny amount of time such virtual particles exist, they exert an outward repulsive vacuum pressure which causes the spacetime fabric to stretch. Vacuum pressure is however very difficult to measure.
As the vacuum grows, the matter-energy density decreases, and the vacuum pressure increases creating more vacuum which in turn causes greater repulsive pressure forcing an endless cycle of accelerating universe.
What do we know?
When the amount of this repulsive vacuum pressure is calculated, the result is 10¹²⁰ times larger than the experimentally determined value of Ω. Whoa! This is the greatest mismatch in the history of science.
Current measurements suggest that dark energy is responsible for 68% of all the mass-energy in the universe, 27% is attributed to dark matter while normal matter corresponds to a mere 5%.
Even after a century, the physical reality of Ω remains a mystery. We are still looking for ways to detect this mysterious stuff. NASA’s Roman Space Telescope, which is planned to launch in the mid-2020s may help us solve this mystery.
Without a doubt, Einstein’s greatest blunder was having declared that the cosmological constant was his greatest blunder.1
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