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Although some compelling evidence exists to support the idea that a repulsive force similar to dark energy exists, it has yet to be directly observed or measured.
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To circumvent this uncomfortable missing piece of the cosmological puzzle, physicists have developed alternative theories explaining the acceleration of universal expansion that don’t rely on dark energy.
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A new theory, posited by a physicist at the University of Alabama in Huntsville, suggests that multiple singularities blinking in and out of existence could provide the energy and matter seen in decades of observations.
In 1998, two independent projects—the Supernova Cosmology Project and the High-Z Supernova Search Team—confirmed that the expansion of the universe was accelerating. But there was a problem: our current understanding of physics couldn’t explain this phenomenon. Scientists hypothesized that there must be some unknown “dark energy” in the universe that propels the universe ever outward, but as theoretical cosmologist Katie Mack states: “We can’t see it, we don’t know what it is, and we’re not even sure how it can exist at all.”
In the decades following this discovery, independent pieces of evidence have supported the idea, but this elusive form of energy—estimated to make up 70 percent of the universe—has still never been directly observed or measured. Because science abhors an epistemological vacuum, alternative theories of this universal acceleration have emerged in an attempt to circumvent this dark energy conundrum with names like Modified Newtonian Dynamics (or MOND) and “timescape cosmology,” the latter of which essentially attributes dark energy to a misunderstanding of kinetic energy expansion at universal scales.
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Now, Richard Lieu, a physicist from the University of Alabama in Huntsville, has a new approach to explaining the universe that has no need for dark energy—or even the Big Bang. The results of the study were published in the journal Classical and Quantum Gravity.
Lieu isn’t a stranger to out-of-the-box cosmological thinking, grabbing headlines just last year for intimating that gravity can exist without mass (though, the idea relied on negative mass, which is as hypothetical as dark energy). This new study builds a cosmological model around the central idea being that universal acceleration is caused by multiple singularities blinking in and out of existence. And as Lieu notes, this concept doesn’t rely on negative mass or negative density to work.
“The new model can account for both structure formation and stability, and the key observational properties of the expansion of the universe at large, by enlisting density singularities in time that uniformly affect all space to replace conventional dark matter and dark energy,” Lieu said in a press statement.
These “transient temporal singularities,” as Lieu calls them, create step-like bursts that periodically flood the universe with matter and energy. The kicker is that because they happen so quickly, they’re nearly impossible to observe before they disappear entirely. Lieu isn’t the first to propose the idea that the universe creates energy over time—from the 40s to and 60s, a hypothesis known as the “steady-state” theory was the main rival of the Big Bang theory. Lieu claims his theory fixes one of steady-state theory’s biggest shortfalls.
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“[The steady-state] hypothesis violates the law of mass-energy conservation,” Lieu said in a press statement. “In the current theory, the conjecture is for matter and energy to appear and disappear in sudden bursts and, interestingly enough, there is no violation of conservation laws […]. The origin of these temporal singularities is unknown—safe to say that the same is true of the moment of the Big Bang itself.”
Like every other alternative theory that forgoes dark energy, this model has no empirical data to back up its claims. Thankfully, the Nancy Grace Roman Space Telescope (which launches in 2027) is purpose-built to explore the cosmos for evidence of dark energy. For now, cosmologists postulate different methods for explaining the observational acceleration of universal expansion. But it will require cold, hard data to prove whether dark energy—or some other alternative, like multiple singularities—is the long-sought-after energy force behind the unexplainable.
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