Amanda Weltman (born 1979) is a South African theoretical physicist. She is best known for co-authoring a series of papers proposing "chameleon gravity" to explain the existence of dark energy. She is currently a professor and South African Research Chair at the University of Cape Town.

Amanda Weltman was first drawn to physics while she was an undergraduate student at the University of Cape Town.^[1] Describing her attraction to being a physicist, she stated that "understanding the way the Universe worked was just about the coolest job anyone could have."^[1]

In 2007, Weltman completed her Ph.D in theoretical physics at Columbia University in New York. She was supervised by theoretical physicist Brian Greene.^[2] She also did post-doctoral research at the University of Cambridge as part of the Centre for Theoretical Cosmology run by physicist Stephen Hawking.^[3] She is currently director of the High Energy Physics, Cosmology and Astrophysics Theory (HEPCAT) group which she founded in 2018.

Weltman was born in 1979^[4] in Cape Cod, Massachusetts, and moved to South Africa with her parents when she was two months old.^[5] She spent her childhood in Johannesburg and Cape Town.^[5][2] She was a competitive gymnast as a child.^[5]

She lives with her husband Jeff Murugan, who is a string theorist at the same university. She met him in 1997,^[1] and has three children with him.^[2][1] She has stated that she was glad to be brought up in a family without gender stereotypes, and that barriers that female scientists faced were particularly harmful when they occurred in the form of stereotypes that children were exposed to.^[1] She and her husband both take time off to care for their children, and frequently travel to conferences as a family.^[1]

Weltman became known when she co-authored a 2004 paper titled "Chameleon Cosmology" with Justin Khoury, which proposed a theory to explain dark energy.^[1] She was a 24-year-old graduate student at Columbia University at the time.^[1] Dark energy is proposed as an explanation for the accelerating expansion of the universe. Khoury and Weltman proposed the existence of a new force that drove this expansion, which changed depending on the environment it was in. It would be weak when particles were densely packed together, and strong when they were far apart.^[1][6] Thus, the theory suggests that in regions where matter is relatively dense, the chameleon force is difficult to detect; but in empty regions of space, it acts to push bodies apart and expand the universe.^[7]

The theory of chameleon gravity is compelling in part because it can be tested in a range of environments including in laboratory tests.^[8] The first ever searches for dark energy in the laboratory were performed as searches for chameleons. In 2007 Weltman joined an experimental team at Fermilab on the GammeV experiment which has been designed to search for axion like particles. The first bounds on chameleon gravity parameters were placed by this experiment in 2008.^[9] The experiment was redesigned and rebuilt as a purpose built chameleon detector, the GammeV CHASE (Cameleon Afterglow Search Experiment),^[10] with first results constraining chameleon dark energy in 2010. These were the first experiments of their kind and were able to place the first direct experimental bounds on the theory. This work pioneered a new subfield of laboratory experiments searching for chameleon gravity, or dark energy more broadly, in the laboratory.^[11] The theory evolved by Khoury and Weltman has been described as leading to "entire sub-fields in cosmology and experimental physics." Her work has been described as a continuation of the work of Albert Einstein.

In recent years Weltman has made substantial contributions to astrophysics, in particular to the field of Fast Radio Bursts (FRBs),^[12] mysterious millisecond-long bursts of radio waves that originate from distant galaxies. One of her main contributions here was a comprehensive catalogue of theoretical models available to explain FRB progenitors.^[13] Among her many other major contributions to FRB physics she has proposed a novel test of a model of FRBs as a result of the Gertsenshtein-Zeldovich (GZ) effect which describes how a gravitational wave passing through a pulsar magnetosphere can be (partially) converted into electromagnetic radiation. One novel feature of this model is its prediction that FRBs should be accompanied by continuous gravitational waves that could be detected by future gravitational wave detectors.

Weltman is playing a leading role in the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) currently under construction in South Africa.

In addition to academic talks, Weltman gives public lectures about cosmology, astrophysics and science more broadly. She has written a number of articles for the public,^[14][15] for Nature News and Reviews^[16] and has given interviews on a range of topics related to science, cosmology and astrophysics for assorted print media.

Weltman has served the science community, especially in South Africa, through leadership roles on national boards and academies. She was elected onto the South African Young Academy of Science in 2012 and elected onto its executive in 2015-2016.

Weltman has served on the Steering Board for the National Institute of Theoretical Physics of South Africa since 2015, and currently serves on the steering board for the National Institute for Theoretical and Computational Sciences.

Weltman has served on the Steering Board for the East African Institute for Fundamental Research in Rwanda since 2018.

• National Women in Science award for the Best Emerging Young Researcher in the Natural Sciences and Engineering,^[5] in 2009^[4]
• Meiring Naude Medal from the Royal Society of South Africa,^[5] in 2011^[4]
• NSTF-BHP Billiton, TW Kambule Award^[5]
• Silver Jubilee medal from the South African Institute of Physics^[5]
• The University of Cape Town Faculty of Science Young Researcher award, in 2010^[4]
• The College of Fellows Young Researcher award, in 2010^[4]
• Selection to the Global Young Academy in 2018^[17]
• Inaugural Next Einstein Fellow Laureate 2016–2017^[5]
• Simons Fellowship, ICTP, Trieste 2020–2025^[18]
• South African Research Chair Award 2016–2020 Tier 2, 2021–2025 Tier 1