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Searching for chameleons in the dark

Cosmology is the study of the origin, evolution, structure and fate of the universe. Theoretical cosmology, merely a philosophical discussion a few hundred years ago, is now a true science. It all changed with the ability to test Einstein's general­theory of relativity. "While astronomy deals with the study of celestial objects and phenomena and involves building telescopes and taking data, theoretical cosmology is about developing theories to explain the observations and data or to make predictions for what is yet to be seen," says Dr Amanda Weltman, senior lecturer at the Astronomy, Cosmology and Gravity Centre, University of Cape Town.

Weltman has become world-renowned for the development of the chameleon mechanism, a novel theory on dark energy. This theory suggests the existence of 'cameleon particles' which change their mass depending on their surroundings.

 "We understand less than 5% of the universe. Seventy-two percent of the remainder is so-called dark energy, and the rest is dark matter," says Weltman.

In 1998, she says, it was discovered that the expansion of the universe is speeding up. Dark energy is the domi­nant explanation for this acceleration. Weltman's chameleon theory is compelling because it is testable in the laboratory, on a cosmological scale and through astrophysical searches. These particles will not only change the way Einstein's general theory of relativity is viewed but also alter the way we understand dark energy.

Her work has led to hundreds of papers on the topic and to a search for these particles in experiments internationally.

GammeV
Weltman teamed up with experimenters at Fermilab in the United States – a large national particle accelerator facility – to design and build the GammeV and later the GammeV CHASE (CHameleon Afterglow SEarch) experiments. Other experiments on chameleons are also being conducted worldwide.

Consequent to the Fermilab experiments, Weltman has begun training research students in the theoretical aspects of the work to increase human resources in South Africa. With the development of MeerKAT and the Square Kilometre Array (both radio telescopes), South Africa will have world-class resources to study dark energy and chameleon theories.

Her work has received extensive recognition both locally and internationally, with over 1100 citations. In 2011, she was invited to be part of the US government's Intensity Frontier Working Group to determine the future of this area.

Weltman completed her PhD in physics at Columbia University and has received fellowships from Columbia, Nasa and Cambridge University. She was honoured by the department of science and technology Women in Sciences awards for the best emerging scientist in 2009 and has been awarded a P-rating by the National Research Foundation.

This 33-year-old mom has recently given birth to her second son and her current passion is her children. "It's incredible to watch them learn about the universe," she says. "I believe that the best scientists stay fascinated and childlike."

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