Donald W. Reynolds Razorback Stadium is big — so big it holds more than 70,000 people. Yet, if you were to pick up Razorback Stadium along with the rest of Earth and every other planet observed with modern instruments, you would only be holding less than a measly 5%of the universe. The bulk of the universe’s mass is dark energy, followed by dark matter.   

We are still in the dark with dark energy. Its intricacies are unknown, but Bharat Ratra, a Distinguished Professor of physics at Kansas State University, has dedicated his research to determining whether dark energy is responsible for speeding up the expansion of the universe. In fact, the discovery that cosmological expansion is accelerating is one of the most significant scientific discoveries of the last quarter century.  

Ratra’s research tells us that the universe is expanding, and so are opportunities to learn more with the Honors College. Join us and Ratra for an illuminating chat about dark matter, dark energy and Einstein’s cosmological constant at the next Honors College Mic at 5:15 p.m. Thursday, Oct. 5, in Gearhart Hall Auditorium.    

EXPANSION ACCELERATING 

According to Einstein’s equations, the expansion of the universe was predicted to be in a state of slowing down, but in the late 1990s, physicists discovered instead that the expansion was speeding up. 

“It’s like the person who is powering the universe has their foot on the accelerator rather than the brakes,” Ratra shared. “People were not sure how to deal with that theoretically.” 

If you take Einstein’s theory of general relativity, which governs how the universe evolves, and add normal substances like atoms, molecules and even dark matter into the equation, the theory will predict that the expansion will slow down. To explain the acceleration, however, physicists proposed an unusual substance, now labeled dark energy, according to Ratra. 

We don’t know the intricacies of dark energy because it is incredibly difficult to study.

“You have to look at things like galaxies distributed over extremely large-length scales — over hundreds of millions or billions of light years,” Ratra shared, which makes gathering precise measurements almost impossible. Plus, it takes a lot of time to collect enough light from faint, distant objects, so there’s still quite a bit of observation that has to be done. 

Reading the words “dark energy” and “cosmological expansion” may feel like we are living in our own sci-fi novel, but Ratra’s lecture will distill the expansion of the universe into a digestible concept. 

When considering the expansion of the universe, there are two forces that are important: gravitational and electric, explained Ratra. Electric force is both attractive and repulsive, depending on the charge of the object it is acting on, but gravity is only attractive. On Earth, electric force is the more dominant force, and because of the makeup of atoms, electric force holds us together. Although general relativity creates space where there is less mass, we do not see the effects of that space creation on Earth because electric force is so much stronger than gravity. Zoom out millions of light years where there are equal positively and negatively charged particles, and gravity becomes dominant and creates more space — thus, expansion.

“It’s a strange concept because you build up your intuition skills by learning about how physics operates on scales that you can touch with your fingers or that you can walk over. There’s no guarantee that the physics that works on these human scales is going to be identical to the physics that works on the scale of the universe. It is research people don’t usually get exposed to in their everyday life,” Ratra said. “If you’re curious, it will be an interesting evening.”    

ABOUT BHARAT RATRA

Bharat Ratra, Distinguished Professor of physics, works in the areas of cosmology and astroparticle physics. He researches the structure and evolution of the universe. Two of his current principal interests are developing models for the large-scale matter and radiation distributions in the universe and testing these models by comparing predictions to observational data.

In 1988, Ratra and Jim Peebles proposed the first dynamical dark energy model. Dark energy is the leading candidate for the mechanism that is responsible for causing cosmological expansion to accelerate. The discovery that cosmological expansion is accelerating is one of the most significant scientific discoveries of the last quarter of a century.

Ratra's research has appeared in 140 scholarly publications, which have been cited more than 19,000 times in scientific literature. In the last five years, he has given more than 100 invited presentations at conferences, workshops, national laboratories, academic institutions and public settings around the world.

Ratra has received more than $10 million in individual and collaborative grants, largely from the Department of Energy and the National Science Foundation. Ratra was a National Science Foundation CAREER award winner in 1999. He was named a fellow of the American Physical Society in 2002, a fellow of the American Association for the Advancement of Science in 2005 and a fellow of the American Astronomical Society in 2023. He received the 2012-2013 Commerce Bank Distinguished Graduate Faculty Award at Kansas State University; in 2017, he was awarded the Olin Petefish Award in Basic Sciences; and in 2020, he received the Kansas Science Communication Initiative Science Communication Award.

Ratra joined Kansas State University in 1996 as an assistant professor of physics. He was a postdoctoral fellow at Princeton University, the California Institute of Technology and the Massachusetts Institute of Technology. Ratra earned a doctorate in physics from Stanford University and a master's degree from the Indian Institute of Technology in New Delhi.

About the Honors College: The University of Arkansas Honors College was established in 2002 and brings together high-achieving undergraduate students and the university’s top professors to share transformative learning experiences. Each year the Honors College awards up to 90 freshman fellowships that provide $80,000 over four years, and more than $1 million in undergraduate research and study abroad grants. The Honors College is nationally recognized for the high caliber of students it admits and graduates. Honors students enjoy small, in-depth classes, and programs are offered in all disciplines, tailored to students’ academic interests, with interdisciplinary collaborations encouraged. All Honors College graduates have engaged in mentored research.

About the University of Arkansas: As Arkansas' flagship institution, the U of A provides an internationally competitive education in more than 200 academic programs. Founded in 1871, the U of A contributes more than $2.2 billion to Arkansas’ economy through the teaching of new knowledge and skills, entrepreneurship and job development, discovery through research and creative activity while also providing training for professional disciplines. The Carnegie Foundation classifies the U of A among the few U.S. colleges and universities with the highest level of research activity. U.S. News & World Report ranks the U of A among the top public universities in the nation. See how the U of A works to build a better world at Arkansas Research and Economic Development News.