The History of Dark Energy: Discoveries and Theories

 

A Type Ia supernova (bright spot on the bottom-left) near a galaxy


This article provides a detailed history of the discovery and theories of dark energy, from its initial detection to current research and understanding.


Introduction

Dark energy is a term coined by astronomers in the late 1990s to describe the mysterious force that is causing the expansion of the universe to accelerate. This force is still poorly understood, but there have been many discoveries and theories over the years that have helped to shed light on this mysterious phenomenon. In this article, we will explore the history of dark energy, including the major discoveries and theories that have led to our current understanding of this fascinating force.


The Discovery of Dark Energy

The discovery of dark energy can be traced back to the late 1990s when two teams of astronomers, one led by Saul Perlmutter and the other by Brian Schmidt and Adam Riess, made an astonishing discovery. They found that distant supernovae were dimmer than they should be if the universe was expanding at a constant rate. Instead, these supernovae were dimmer than expected, indicating that the universe was expanding at an accelerating rate.


This discovery was unexpected, and it raised many questions about the nature of the universe. One possible explanation for this accelerating expansion was the presence of a mysterious force, now known as dark energy, that was pushing the galaxies in the universe apart at an ever-increasing rate.


Theories of Dark Energy

Since the discovery of dark energy, there have been many theories proposed to try to explain this mysterious force. Here are a few of the most prominent theories:


Cosmological Constant

The cosmological constant is the simplest explanation for dark energy. It is a term that was first introduced by Albert Einstein in 1917 as a way to balance the equations of his theory of general relativity. The cosmological constant represents the energy density of the vacuum of space, and it could be responsible for the accelerating expansion of the universe. However, the value of the cosmological constant that would be required to explain dark energy is much smaller than what would be expected from particle physics, which has led some to dismiss this theory as unlikely.


Quintessence

Quintessence is a hypothetical form of dark energy that is a scalar field that permeates the universe. Unlike the cosmological constant, which has a fixed energy density, the energy density of quintessence can change over time. This theory can explain the accelerating expansion of the universe and could provide a link between dark energy and other unsolved problems in physics, such as the nature of dark matter.


Modified Gravity

Another theory to explain dark energy is modified gravity, which suggests that the laws of gravity may need to be modified on large scales. This theory proposes that gravity weakens on large scales, which could cause the acceleration of the universe's expansion. While this theory has not yet been proven, it is an active area of research.


Holographic Principle

The holographic principle is a theoretical framework that suggests that the entire universe can be described by a lower-dimensional system. According to this theory, the universe is like a hologram, where the information about the three-dimensional world is encoded on a two-dimensional surface. Some researchers have suggested that the holographic principle could be used to explain dark energy, but this is still a topic of active research.


Phantom Energy

Phantom energy is a hypothetical form of dark energy that has a negative energy density. According to this theory, the accelerating expansion of the universe will eventually become so fast that it will cause the universe to rip apart. While this is a frightening prospect, there is no evidence to suggest that phantom energy actually exists.


Observational Evidence for Dark Energy

While the existence of dark energy is still a mystery, there is a growing body of observational evidence to support its existence. Here are a few examples of this evidence:


Type Ia Supernovae

The discovery of dark energy was initially based on observations of distant Type Ia supernovae. These supernovae are known to have a consistent luminosity, making them ideal standard candles for measuring distances in the universe. The observations of these supernovae by the teams led by Perlmutter and Schmidt and Riess showed that the supernovae were fainter than expected, indicating that the universe was expanding at an accelerating rate.


Cosmic Microwave Background Radiation

The cosmic microwave background radiation (CMB) is the oldest light in the universe, dating back to just 380,000 years after the Big Bang. The CMB provides a snapshot of the universe when it was still in its infancy, and it contains information about the early universe that can help us understand the nature of dark energy. In 2013, the European Space Agency's Planck satellite released new data on the CMB, which showed that the universe is composed of approximately 68% dark energy, 27% dark matter, and just 5% normal matter.


Baryon Acoustic Oscillations

Baryon acoustic oscillations (BAOs) are regular patterns of galaxies that are thought to be imprinted on the distribution of matter in the universe shortly after the Big Bang. These patterns can be used as a standard ruler to measure the expansion of the universe. Observations of BAOs have shown that the universe is expanding at an accelerating rate, providing further evidence for the existence of dark energy.


Weak Gravitational Lensing

Weak gravitational lensing is a technique used to study the distribution of matter in the universe by observing the way that light from distant galaxies is bent by the gravitational fields of intervening matter. Observations of weak gravitational lensing have shown that the distribution of matter in the universe is consistent with the existence of dark energy.


Future Research

Despite the growing body of observational evidence, the nature of dark energy remains a mystery. As a result, research in this field is ongoing, with many new experiments and observations planned for the future.


Euclid

Euclid is a space telescope being developed by the European Space Agency to study the dark universe. Euclid will use weak gravitational lensing and BAOs to map the distribution of dark matter and dark energy in the universe. The mission is currently scheduled to launch in 2022.


Large Synoptic Survey Telescope

The Large Synoptic Survey Telescope (LSST) is a ground-based telescope being constructed in Chile that will take panoramic images of the sky every few nights over a 10-year period. The LSST will be used to study a wide range of astrophysical phenomena, including dark energy. The telescope is currently under construction and is expected to begin science operations in 2023.


Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is a new instrument being installed at the Kitt Peak National Observatory in Arizona. DESI will use a technique called galaxy clustering to study the distribution of matter in the universe and the expansion history of the universe. The instrument is expected to begin observations in 2022.


Conclusion

Dark energy is one of the greatest mysteries in modern astrophysics. While we have made significant progress in understanding this phenomenon over the past few decades, there is still much that we do not know. Ongoing research, such as the Euclid, LSST, and DESI missions, will help to shed light on the nature of dark energy and the evolution of the universe. As we continue to explore this fascinating field, we are sure to make many more discoveries and gain a deeper understanding of the forces that shape our universe.


References

  • Riess, A. G., et al. "Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant." The Astronomical Journal, Vol. 116, no. 3, 1998, pp. 1009–1038, doi: 10.1086/300499.
  • Perlmutter, S., et al. "Measurements of Omega and Lambda from 42 High-Redshift Supernovae." The Astrophysical Journal, vol. 517, no. 2, 1999, pp. 565–586, doi: 10.1086/307221.
  • Carroll, Sean. "The Cosmological Constant." Living Reviews in Relativity, vol. 4, no. 1, 2001, pp. 1–39, doi: 10.12942/lrr-2001-1.
  • Copeland, Edmund J., et al. "Dynamics of Dark Energy." Living Reviews in Relativity, vol. 15, no. 1, 2012, pp. 1–116, doi: 10.12942/lrr-2012-6.
  • Ade, P. A. R., et al. "Planck 2013 Results. XVI. Cosmological Parameters." Astronomy & Astrophysics, vol. 571, 2014, A16, doi: 10.1051/0004-6361/201321591.
  • Amendola, Luca, and Shinji Tsujikawa. "Dark Energy: Theory and Observations." Cambridge University Press, 2010.
  • Weinberg, Steven. "The Cosmological Constant Problem." Reviews of Modern Physics, vol. 61, no. 1, 1989, pp. 1–23, doi: 10.1103/RevModPhys.61.1.
  • Albrecht, Andreas, and Constantinos Skordis. "Phenomenology of Dark Energy: General Features and Experimental Possibilities." Physical Review D, vol. 68, no. 2, 2003, 023507, doi: 10.1103/PhysRevD.68.023507.
  • Scherrer, Robert J. "Dark Energy Models." Comptes Rendus Physique, vol. 4, no. 4, 2003, pp. 431–440, doi: 10.1016/S1631-0705(03)00078-6.
  • Huterer, Dragan, and Michael S. Turner. "Probing the Dark Energy: Methods and Strategies." Physical Review D, vol. 60, no. 8, 1999, 081301, doi: 10.1103/PhysRevD.60.081301.

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