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Margaret Geller, senior scientist at the Smithsonian Observatory, is recognized by astronomers for discovering that galaxies are lined up in walls and filaments that are millions of years long. She gave a talk about the dark matter of the universe on April 19 as a part of the UC Irvine’s Chancellor’s Distinguished Fellows Series.
Geller is also known for contributing to new mapping techniques that helped define galaxy patterns and the location of invisible dark matter.
‘Dark matter makes up 20 percent of the universe,’ Geller said. ‘We know where it is because it gravitates, but we don’t know what it is.’
Most of the mass in the solar system is detected because of the photons of light that reflect off of it. Only 0.1 percent of the solar system is dark matter.
Geller explained the difference between black holes and dark matter.
‘Black holes are massive objects confined to a small radius. … We sometimes can see the radiation,’ Geller said. ‘Dark matter cannot be seen.’
Geller reminded attendees of how unimaginably large the universe is. She said that it is time, not space, which limits our perception of the universe.
‘We’re doomed to only see a miniscule part of it,’ Geller said. ‘We see only the tiny fraction from which light is able to reach us.’
However, Geller and other scientists’ modern mapping techniques, such as the red shift survey, have advanced their ability to measure the distribution of mass throughout our perceived universe.
‘Today, we can make maps of matter in the universe of about three or four thousand galaxies per square degree,’ Geller said.
Geller gave an overview of physics discoveries that have simultaneously led to the advancement of modern-day astronomical hypotheses and increased skepticism about our knowledge about the quantity of mass in the universe.
Geller began her lecture talking about Newton’s theories on gravity. Later, she introduced Fritz Zwicky’s discovery of dark matter in the Coma Cluster in 1933 and Vera Ruben’s discovery of dark halos in the 1970s. Geller also mentioned Einstein’s general relativity theory about how matter moves and stretches geometric space.
‘Matter changes geometric space, which changes the way matter moves,’ Geller said. ‘Space is dynamic, stretching like a ball pressing down on a rubber sheet. Large objects like planets produce a dip in space. Light bends to conform to the shape of space, [creating a] distortion of how we view objects.’
The talk came to a close with a humanistic note on the scientific concept of dark matter.
‘It shows the reach of the human mind,’ Geller said. ‘The thing that makes us grand is that we ask questions about the universe and that we can answer them.’
After hearing the lecture, Sahil Gandhi, a second-year computer engineering major, was skeptical about our knowledge about dark matter.
‘We still don’t really know what dark matter is,’ Gandhi said. ‘It’s an interesting way of explaining a phenomenon in the universe, but it may not be completely accurate.’

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