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The year 2024 was significant for space science in numerous ways; it might turn out to be the most crucial year for the universe’s most perplexing and enigmatic “component,” dark energy, since its identification nearly thirty years ago. This year marked the first occasion that researchers received an exhilarating observational clue suggesting that the force responsible for the accelerating expansion of the universe could be “growing up.”
Dark energy poses a substantial challenge for researchers. Accounting for 68% of the universe’s entire matter-energy framework, this force propels the accelerated expansion of the universe. This occurrence is distinct from the universe’s initial inflation, caused by the Big Bang, which had nearly ceased when dark energy took control!
To illustrate the concern, imagine giving a child on a swing a single push, seeing them come to a stop, and then, inexplicably, they start swinging again, with increasing speed.
This late-time acceleration was identified in 1998 by two groups of astronomers conducting distance measurements utilizing supernovas in distant galaxies. “Dark energy” was merely a temporary term assigned to the force causing this acceleration, with the expectation that a more precise concept and terminology would eventually be developed.
Related: What is dark energy?
Nevertheless, dark energy has persisted in our universe’s recipe, its existence serving as a reminder that the principal component of the cosmos still remains an enigma. You could liken this to Colonel Sanders’ hidden mixture of herbs and spices, but it’s akin to dining at KFC while not knowing what chicken is or its origins! Quite concerning.
Although 2024 did not provide a more definitive resolution to this enigma than any of the previous 25 years, a notable crack has emerged in the façade of dark energy, a captivating clue that could steer researchers toward unraveling this urgent cosmological conundrum.
2024 was DESI’s year
These fresh dark energy indications emerged from the first year of data provided by the Dark Energy Spectroscopic Instrument (DESI), resulting in one of the most in-depth maps of the cosmos ever created.
The 5,000 robotic sensors of DESI gather light from millions of galaxies spanning over a third of the Earth’s sky, breaking this down into a spectrum of colors. The results from DESI have enabled researchers to measure the alteration in the wavelengths of light emitted by distant galaxies as they move away from us on the expanding fabric of space-time, a phenomenon referred to as “redshift.”
Findings from DESI provided researchers with a suggestion that dark energy is evolving over time. Specifically, it seems that this enigmatic force is diminishing.
This is essential, as in our current most accurate model of cosmology — the Standard Model or the Lambda Cold Dark Matter (LCDM) model — dark energy is represented by the cosmological constant (denoted by the Greek letter lambda). The cosmological constant is expected to remain constant over time in the LCDM framework.
“The unveiling of these results marked a remarkable day for cosmology, indicating a ‘decreasing’ influence of dark energy over time, implying that it is evolving and, therefore, not constant after all,” stated Luz Ángela García Peñaloza, a former DESI team member and a cosmologist at the Universidad ECCI in Colombia, during an interview with Space.com in April 2024 when the DESI findings were released. “The identification of evolving dark energy would be as transformative as the recognition of the accelerated expansion of the universe itself if validated with forthcoming data.”
Space.com engaged with García Peñaloza to further discuss the significance of this discovery and contemplate how future cosmologists may evaluate the year 2024.
“Until this year, most observations were consistent in recognizing dark energy as the cosmological constant. However, 2024 was replete with hints suggesting this may not be true,” García Peñaloza remarked. “Several cosmic surveys have cast doubt on the cosmological constant, showing promising results indicating that dark energy could be evolving over time.”
Dark energy becomes dynamic!
The suggestion that dark energy might be weakening, or undergoing any changes, came as a genuine surprise to cosmologists. As García Peñaloza noted, until now, observations have aligned with an “equation of state” for the universe wherein both the cosmological constant and dark energy are stable over time.
García Peñaloza mentioned that this deviation from that consistency “opens the door” to cosmic models that incorporate a type of dark energy that varies with time. This could signify the conclusion of the cosmological constant and the rise of “dynamical dark energy.”
One favored dynamical dark energy concept that García Peñaloza supported even before the release of DESI data was an “early dark energy” (EDE) model. This concept revolves around the idea that, while dark energy currently dominates the universe, that was not always the scenario.
Until approximately 4 billion to 5 billion years ago, matter prevailed in the universe, and prior to that, radiation responsible for Big Bang-related inflation was the primary force. EDE models propose that dark energy did not simply emerge from nowhere to begin its dominance over the cosmos when it reached 9 to 10 billion years; rather, dark energy had always existed, playing a significant role.
This means that it is dynamic and evolving. The preliminary DESI data appears to support that idea.
Related: What is the Big Bang theory?
Cosmologists will likely not be disheartened to see the end of the cosmological constant if dark energy indeed proves to be evolving.
Projections of the cosmological constant indicating the “vacuum energy” of space…
made utilizing theory differ from observations of this metric by as much as 10 to the power of 121 (that’s 10 followed by 120 zeroes).
It is hardly surprising that the cosmological constant has posed a challenge for cosmologists for many years and has been referred to as “the most significant theoretical miscalculation in the history of physics.”
However, let us not dismiss lambda too hastily. Additional information will be necessary to refute this model. Plus, data that could achieve this is already en route!
The DESI survey commenced operations from the Mayall Telescope situated atop Kitt Peak near Tucson, Arizona, in 2021, and is scheduled to function for a duration of five years, concluding in 2026. Thrillingly, the outcomes we have already examined suggest a potential paradigm shift for dark energy research stemming from just the initial year of findings.
To instigate a substantial reevaluation of dark energy, researchers must encounter additional data indicating that this cosmic component may change over time. Fortunately, the DESI Year 2 and Year 3 data are anticipated in Spring 2025.
“Dynamical dark energy might align more closely with DESI Year 1 findings than the cosmological constant does,” García Peñaloza asserted. “That said, it is not definitive yet; they are merely hints favoring dark energy as an evolving [entity] rather than the conventional cosmological candidate. Nevertheless, it is indeed quite thrilling.
“Maybe it’s still premature to declare we are unraveling this enigma, but I would say that we now possess a bit more insight into the behavior of this enigmatic element.”
García Peñaloza elaborated on the advancements in dark energy research she anticipates for the upcoming year. DESI will receive some assistance in its pursuit to unveil the mysteries of dark energy, she noted, through additional data from the Euclid space telescope.
The European Space Agency’s (ESA’s) “dark energy investigator” was launched in July 2023 and has been astonishing scientists with its remarkable images of the universe since October of that year. In the coming year, it could deliver the same with concrete data.
“Firstly, Euclid will be unveiling the initial datasets, which have been eagerly awaited by the community. Additionally, other indicators of the universe at larger scales will be releasing their findings that complement recent discoveries from the James Webb Space Telescope,” García Peñaloza concluded. “The latest high-resolution numerical simulations will persist in revealing new clues about the nature of dark energy and likely generate new inquiries regarding the connection between dark energy and other cosmological occurrences.”
Much like the universe itself, our enthusiasm for 2025 and the discoveries it will bring is swelling at an ever-increasing pace!
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