Around 13.8 billion years ago, the universe burst into existence with the phenomenon we now call the big bang. In its initial moments, a rapid expansion occurred, only to be gradually slowed down by gravity over the next nine billion years. However, the cosmic narrative took an unexpected turn as the universe's expansion started accelerating, driven by an enigmatic force scientists have dubbed dark energy.
But what exactly is dark energy?
In straightforward terms, we're not entirely sure. What we do know is that it exists, pushing the universe to expand at an accelerating rate, and it constitutes approximately 68.3 to 70% of the entire cosmic makeup.
The intriguing story of dark energy traces back to the late 1990s, although its roots in scientific exploration extend to 1912. American astronomer Henrietta Swan Leavitt played a pivotal role in this journey, discovering key insights using Cepheid variables—stars whose brightness varies predictably. Leavitt's work enabled astronomers to measure distances between us and these stars in far-off galaxies.
Simultaneously, astronomer Vesto Slipher observed spiral galaxies, noting their redshift—a phenomenon indicating objects moving away from us. This crucial observation, coupled with Leavitt's findings, set the stage for realizing that galaxies were steadily moving farther away, unveiling the concept of an expanding universe.
In 1922, Russian scientist Alexander Friedmann, building on Albert Einstein's theory of general relativity, suggested the possibility of an expanding universe. This notion gained further support in 1927 when Belgian astronomer Georges Lemaître independently corroborated the idea, challenging Einstein's static universe assumption.
The turning point arrived in 1929 when astronomer Edwin Hubble, alongside Milton Humason, confirmed the universe's expansion by studying redshifts and Cepheid stars. This pivotal observation, known as Hubble's Law, laid the foundation for our understanding of an ever-expanding cosmos.
Fast forward to 1998, and the cosmic narrative took an unexpected twist. Astronomers studying distant supernovae noticed they were dimmer than anticipated, challenging the assumption that gravity would eventually slow down the universe's expansion. This revelation, led by astronomers Adam Riess, Saul Perlmutter, and Brian Schmidt, earned them the 2011 Nobel Prize in Physics.
These dim supernovae, specifically Type 1a, were unexpectedly farther away, suggesting an accelerated expansion. Enter dark energy—an unknown force propelling the universe to stretch out at an ever-increasing rate.
The question remains: What is dark energy?
Currently, dark energy is a placeholder term for the mysterious force driving cosmic acceleration. Several theories attempt to explain its nature:
Vacuum Energy: Some propose dark energy as a constant, pervasive background energy in space, known as vacuum energy. This theoretical energy could be tied to the cosmological constant, initially introduced by Einstein and later discarded, creating a conundrum known as the "cosmological constant problem."
Quintessence: Dark energy might be an energy fluid or field filling space, behaving in opposition to normal matter. This concept, dubbed quintessence, draws inspiration from ancient Greek philosophy.
Space Wrinkles: Dark energy could manifest as defects in the fabric of the universe, akin to hypothetical cosmic strings or wrinkles formed in the early universe.
Flaw in General Relativity: Some propose that dark energy is a consequence of a flaw in our understanding of general relativity, suggesting modifications to gravity's role on the observable universe scale.
The future holds promising opportunities to demystify dark energy. NASA's involvement in the Euclid mission (launched in 2023) and the Nancy Grace Roman Space Telescope (expected by May 2027) aims to create a 3D map of the universe, unraveling the impact of dark energy on cosmic structures.
Additionally, the Vera C. Rubin Observatory, set to be operational in 2025, and NASA's James Webb Space Telescope, launched in 2021, contribute to our quest for understanding dark energy. The SPHEREx mission (launching by April 2025) and the Dark Energy Explorers citizen science project further enhance our exploration.
As we stand on the brink of a new "golden age" of cosmology, these endeavors promise to unveil more about the mysteries of dark energy, offering a glimpse into the fundamental forces shaping our vast and expanding universe.
steady state theory what existed before the big bang which event led to the formation of our solar system? what would most likely cause the future acceleration of the expansion of the universe? which event led to the formation of our solar system? a galaxy broke apart. a massive star exploded. a solar nebula collapsed. dark matter materialized. there is a theory that gravity could pull galaxies back together, causing a reverse big bang. which observation makes this theory less likely than the idea that the universe may continue to expand? which of the following are most likely to preserve conditions of ancient environments on the earth? what is the big bang? there is a theory that gravity could pull galaxies back together,