Dark energy, a concept that has intrigued scientists for decades, may be more dynamic than previously believed. Recent research posits that dark energy could be evolving over time, which would significantly alter our understanding of the universe's expansion and the nature of dark energy itself.

For years, we have accepted that the universe is predominantly dark, with stars and galaxies scattered throughout. However, the visible matter, which includes protons and electrons, constitutes a mere 5% of the total universe's mass. The remaining 95% consists of dark matter, which accounts for 27%, and dark energy, which makes up 68%. The latter is theorized to be an energy intrinsic to space that appears to drive the universe's accelerated expansion.

New observational data is challenging our existing views on dark energy. If validated, this could lead to a revolutionary shift in our understanding of cosmology.

The most effective way to determine the universe's composition isn't through direct measurements, which would leave us blind to the vast majority of it. Instead, we utilize a principle of General Relativity: various forms of matter and energy influence the very fabric of spacetime, as well as its evolution over time.

By examining the current expansion rate and its historical variations, we can deduce the universe's composition using data from supernovae, large-scale structures, and cosmic microwave background radiation. This has led to the widely accepted model of 5% normal matter, 27% dark matter, and 68% dark energy.

Dark matter appears to behave similarly to normal matter in terms of gravity, maintaining a consistent total mass. As the universe expands, its density decreases. Dark energy, on the other hand, behaves differently; it seems to remain constant as space expands, ultimately dominating the universe's energy balance and causing accelerated expansion over time.

Historically, astronomers have measured cosmic expansion using two main methods:

1. Standard Candles: By knowing the inherent properties of a light source and measuring its brightness, we can estimate its distance, helping us understand cosmic expansion.
2. Standard Rulers: By recognizing the physical size of an object and measuring its angular size, we can infer its distance and contribute to our understanding of the universe's expansion.

Both methods rely heavily on the assumption that our understanding of these intrinsic properties is accurate.

Our current best standard candles have allowed us to look back approximately 4 billion years into the universe's history. In contrast, scientists have begun utilizing X-ray emitting quasars, which shine brightly and can be observed even when the universe was only 1 billion years old. A recent study by Guido Risaliti and Elisabeta Lusso leverages quasars as standard candles to probe further back in time, revealing some unexpected findings.

Their investigation, which utilized data from around 1,600 quasars, confirmed previous findings about dark energy's existence and its substantial contribution to the universe's energy composition. However, they also noted deviations from the expected behavior of dark energy at greater distances, suggesting a potential increase in density over time.

Risaliti's blog elaborates on these unexpected results:

> "Our final Hubble Diagram revealed surprising outcomes: while our measurements aligned with supernova data for distances common to both datasets, incorporating more distant quasars indicated a significant deviation from standard cosmological expectations. If this deviation is attributed to dark energy, it implies an increasing density over time."

This measurement poses challenges, as there may be questions about the reliability of quasars as standard candles. Past attempts to use gamma-ray bursts as distance indicators revealed that they were not standard, highlighting potential biases in detecting such phenomena.

While resolving these issues will be complex, the evidence does not necessarily convince skeptics that dark energy is constant.

What if the new findings are accurate? If dark energy is indeed evolving, this could fundamentally alter our understanding of the universe's fate. The implications of a changing dark energy are profound, as the equation of state, denoted as w, could vary from the expected value of -1.

If w is less than -1, dark energy may weaken over time. Conversely, if w is more negative than -1, it indicates an accelerating expansion that could lead to a catastrophic end known as the Big Rip, where cosmic structures would eventually be torn apart.

The quest to comprehend the universe's ultimate fate has captivated humanity for centuries. With the tools of modern astrophysics, we can explore these profound questions scientifically. Determining whether the universe will continue expanding, collapse, oscillate, or be torn apart hinges on our understanding of dark energy and its properties.

Ultimately, unraveling the mysteries of dark energy may reveal that it is not a constant, and only through careful observation and analysis of the cosmos can we hope to uncover the truth.

Starts With A Bang is now featured on Forbes and republished on Medium thanks to our Patreon supporters. Ethan has written two books: Beyond The Galaxy, and Treknology: The Science of Star Trek from Tricorders to Warp Drive.