Alex Filippenko, a popular astronomer and professor at the University of California, will deliver the 42nd annual Oppenheimer Lecture in Los Alamos on Monday. As usual for this distinguished series of talks, the aura of a Nobel Prize and academic prizes yet to come will be in the air.

Filippenko’s topic, “Dark Energy and the Runaway Universe,” will revisit the discovery that won the Nobel in physics last year for Saul Perlmutter, Brian Schmidt and Adam Riess, leading members of two teams that separately concluded that the universe was expanding over larger distances and expanding faster with time, rather than more slowly as expected.” Their finding led in turn to the conclusion that a mysterious effect, known as dark energy, was responsible for pushing the universe apart.

Filippenko was one of the authors of research papers on both teams, analyzing the data that measured the distances to a particular class of exploding stars, known as Type 1a supernovae that provide a reliable standard for plotting astronomical distances.

“I was the guy who got time on the telescopes to get spectra of the supernova candidates and also to get the redshifts of the galaxies in which the supernovae were located,” he said in a telephone interview this week from California. (The distance to a celestial object is called its “redshift,” which is related to how far its light has been stretched to redder and longer wavelengths.)

The calculations developed by the two teams turned out to be closely related to a factor known as the “cosmological constant” — once proposed and then abandoned as an error by Albert Einstein, who devised the formula as a fudge factor needed to keep the universe at a constant size.

A gifted teacher and prolific contributor of texts, learning videos and educational television series, Filippenko has been one of the primary messengers and interpreters of the implications of these findings over the last decade. That the universe is accelerating at an unstoppable pace is now widely accepted by astronomers, but in a chapter he wrote in the book State of the Universe 2008, Filippenko calls the invisible and unknown dark energy at work, which seems to make up nearly three-quarters of existence, “the most important observationally motivated, unsolved problem in all of physics.”

One of the ultimate questions for both science and philosophy comes down to where the universe is headed. After arriving at the Big Bang theory, in which the contents of the universe were formed and flung outward, astronomers thought at first that an expanding universe would eventually be overtaken by gravity and fall back to a central point. Filippenko jokingly calls this the “gnaB giB,” or the “Big Bang in reverse,” a regression that might lead in time to a crunch and potentially to an eternal cycle of expansion and contraction. But this view has now been overtaken by the new cosmological model in which the galaxies and stars will continue to disperse perhaps for another 40 billion years, losing touch among themselves and exhausting their energies, growing farther and farther apart.

For now, the universe seems irreversible and unstoppable, although Filippenko acknowledges that “the physical nature (and future behavior) of dark energy is not yet understood.” Adding uncertainty to the scenario of the runaway universe, follow-up investigations of the expansion have determined that the so-called constant has not been altogether constant, that the universe was actually decelerating until about 5 billion years ago. This phenomenon, known as the “cosmic jerk,” is explained as a shift from a relatively tightly packed universe dominated by gravity to a vaster space dominated by dark energy.

Filippenko said dark energy was important as a clue to a “Theory of Everything,” which might resolve the differences between the dominant but incompatible theories of general relativity and quantum physics. “We didn’t even know dark energy existed 15 years ago,” he said. “We’d like to know what it is.”

Filippenko is highly regarded for his ability to make these sometimes difficult concepts understandable. For his fluency and clarity, not to mention his 40 episodes of The Universe series on the History Channel, he has been compared to Carl Sagan, the great popularizer of astronomy at the end of the 20th century. Filippenko’s teaching and communication skills have earned him a Carl Sagan Prize and a Professor of the Year Award from the Carnegie Foundation.

Having achieved prominence for his descriptions of the universe’s apparent fate over the long term, it’s only natural that he has also been asked about how the world began.

“I don’t know why the world exists, other than the laws of physics permit it to exist, and universes can arise spontaneously given the laws of physics,” he said in a recent email. “But I don’t know why there are laws of physics or whether they predated the universe.

I don’t think we will ever know the answer to why laws of physics exist. Science can’t produce a definitive answer because the hypothesis can’t be tested.”

The J. Robert Oppenheimer Memorial Committee sponsors lectures in memory of the founding director of the science laboratory at Los Alamos. Last year’s speaker was Paul Nurse, a cell biologist and president of the Royal Society, who won a Nobel Prize in 2001. Two years ago, Ahmed Zewail, an Egyptian-born chemist who won the Nobel Prize in 2005, gave his lecture.