Nearly a hundred years ago, scientists discovered that the universe is expanding. In 1998, they found something even more surprising: the expansion is speeding up, not slowing down like they thought it would. This led to the idea of “dark energy,” a mysterious force that makes up most of the energy in the universe.
Using Everyday Science to Understand the Universe
Now, a team of scientists in Brazil has used ideas from everyday science to better understand this cosmic mystery. They applied the “Grüneisen parameter,” a tool used to describe how materials respond to changes in pressure and temperature, to the expanding universe.
“The dynamics associated with the expansion of the Universe are generally modeled as a perfect fluid whose equation of state is ω = p/ρ, where ω [omega] is the equation of state parameter, p is pressure, and ρ [rho] is energy density. Although ω is widely used, its physical meaning hadn’t yet been appropriately discussed. It was treated as merely a constant for each era of the Universe. One of the important results of our research is the identification of ω with the effective Grüneisen parameter by means of the Mie-Grüneisen equation of state,” said Mariano de Souza, a professor at São Paulo State University and one of the study’s authors.
By connecting these ideas, the researchers showed that the universe is continuously cooling as it expands. They also proposed that the Grüneisen parameter, and therefore the density of dark energy, may change over time as the universe evolves.
New Insights and Unanswered Questions
This new perspective could lead to important breakthroughs in our understanding of the universe’s expansion. It suggests that the shift from the universe’s initial slowing expansion to its current accelerating expansion may be a kind of “phase transition,” similar to how matter changes from one state to another, like liquid water turning to ice.
However, many questions remain. The study doesn’t rule out the possibility of a “Big Rip,” a hypothetical scenario where the expansion of the universe becomes so fast that it tears apart the fabric of space-time itself.
“Assigning a fixed value to lambda means also assigning a fixed value to omega, but recognition of ω as the effective Grüneisen parameter enables us to infer time dependency for ω as the Universe expands in the dark energy-dominated era. This directly entails time dependency for Λ, or the universal gravitation constant,” Souza said.
While there’s still much to learn, this study offers an exciting new way to investigate one of the biggest mysteries in modern science – the ever-expanding universe that we call home.
