Rana Adhikari

Start with the Explosions

Most days, Caltech physics professor Rana Adhikari shoots lasers at mirrors, crystals, and film-coated glasses to see how photons of light interact with them.

What he learns helps him design optical systems and sensors for LIGO, the Laser Interferometer Gravitational-wave Observatory, and its successors.

Gravitational waves ripple through space when black holes or collapsed stars merge with each other or stars explode. The energy of those cataclysmic events curves and stretches space and time.

Adhikari, who won a 2019 New Horizons in Physics Breakthrough Prize, contributed to LIGO’s ability to make the first detection of gravitational waves.

Now, he has a few new goals.

  1. Find the missing, medium-sized black holes.
  2. Discover unknown dimensions of space.
  3. Improve the experience of becoming a physicist.

These grand ambitions feel achievable to Adhikari because of the sense of mutual adventure he has found among Caltech scholars and supporters.

“Where else could you get an hour of free advice from the top atomic physicist in the world? And where else would Kip Thorne call you on the weekend to talk about diffuse light?” he asks, referring to conversations with Jeff Kimble, Caltech’s William L. Valentine Professor of Physics, and Nobel laureate Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, Emeritus.

“Where else would a genius postdoctoral scholar join my group out of pure scientific curiosity?” Adhikari continues. That scholar has latitude to pursue his best ideas because of a fellowship endowed by donors to Caltech and its Break Through campaign.

“I just wouldn’t get this at another institution,” Adhikari says.

The Missing Black Holes

If Adhikari and his colleagues can fine-tune the feedback systems that point mirrors and guide lasers inside each LIGO observatory, astronomers may detect a bonanza of black holes.

Astronomers have discovered merging black holes that are five or 10 times the mass of the sun, and others that are millions or billions of solar masses. “It’s impossible that you could have these little ones and these big ones and nothing in between,” Adhikari says. “But no one’s found anything in between.”

Noise from LIGO’s feedback systems may be drowning out the relevant gravitational-wave signals. To refine these systems, Adhikari plans to team up with experts in control systems design and machine learning. But at first, he couldn’t communicate with them.

“They speak in this mathematical space, and to them I sounded like a time-traveler talking about candle wax and oil,” he explains.

Then, Richard Murray, Caltech’s Thomas E. and Doris Everhart Professor of Control and Dynamical Systems and Bioengineering, took time to translate. “He’s a metacollaborator,” Adhikari says. “He speaks both languages. What makes Caltech so special is the people.”

Artist’s illustration of two merging neutron stars
Artist’s illustration of two merging neutron stars (credit: NSF/LIGO/Sonoma State University/A. Simonnet)

Unknown Dimensions

“Humans see space as three dimensional, and everything we have observed about the universe makes us believe that it is,” Adhikari says. “But what if it’s a little different?

As a thought experiment, he proposes, imagine a near-sighted ant in boots stomping on a table. The ant might see only the two-dimensional surface. But the sound of its footsteps reverberating through the table might lead it to guess that energy is traveling in a third dimension.

Adhikari believes that better gravitational-wave detectors may enable astronomers to learn whether some of the energy from black-hole mergers travels into a fourth dimension.

He also expects that merger signals could be used to graph the expansion of space, and to determine whether the number of spatial dimensions has changed over 10 billion years. But today’s detectors can detect only mergers from about the last two billion years.

“We need to find signals from when black holes started. That will probe the formation history of the universe.”
- Rana Adhikari

Stronger Starts for Physicists

Adhikari learned math from his mother, who had not been encouraged to pursue her own interest in the subject. His curiosity about physics was sparked by a comic-book Monica Rambeau, the second Captain Marvel, who transformed herself into neutrinos to pass through the sun. And Adhikari gained skills and the sureness of hand needed for laboratory work through experience as a car mechanic.

Now, he casts a wide net to prepare others for lives in physics. In his laboratory, high-school students, undergraduate and graduate students, postdoctoral scholars, and international visitors collaborate. The whole group has an edge in the pursuit of unsolved scientific questions because of fellowships that free scholars to focus on research rather than funding. Group members hold fellowships that were established by Dominic Orr (MS ’76, PhD ’82), Caltech’s Walter Burke Institute for Theoretical Physics, the Kavli Foundation, and Ellen and David Lee (PhD ’74, a former student of Kip Thorne’s who now chairs the Caltech Board of Trustees).

In homage to Rambeau, Adhikari fuels students’ excitement in first-year physics classes by discussing exploding stars, time travel, wormholes, and black holes. Once the students are hooked, he reasons, they will be motivated to learn the basics and form their own grand plans for serious study.

To learn how you, too, can help open doors for young physicists, email or call Brian Yocum at byocum@caltech.edu or (626) 395-5705.


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