Scientists said the project dwarfs anything else in the field, known as the Search for Extra Terrestrial Intelligence. Globally, less than $2 million annually is spent on SETI, said Dan Werthimer, an adviser to Milner's project and the astrophysicist who directs the SETI@home project affiliated with the University of California in Berkeley.
Given technological improvements, including in computing power and telescope sensitivity, $100 million will go much farther than in the early 1990s, the last time SETI had significant funding, scientists said.
The advances allow scientists to monitor several billion radio frequencies at a time, instead of several million, and to search 10 times more sky than in the early 1990s.
But any signals the scientists detect will likely have been created years ago, perhaps even centuries or millennia earlier. Radio signals take four years simply to travel between Earth and the nearest star outside our solar system.
In 10 years, with his $100 million, Milner figures scientists can listen for radio transmissions in the Milky Way galaxy, plus the 100 nearest galaxies.
One of the biggest costs lies in booking time at radio telescopes, including at Australia's Parkes Observatory in New South Wales and the Radio Astronomy Observatory in Green Bank, West Virginia. Milner plans to book about two months a year at each site, a boon to scientists who normally might get two days a year on the telescopes.
The team, led by scientists such as Peter Worden, who until earlier this year directed the NASA Ames Research Center, will organize the radio signals they find, make the data public, and examine the data for patterns.
The goal lies less in understanding the signals than in establishing whether they were created by intelligent life rather than natural phenomena.
Scientists say the fact that humans have developed radio signaling makes it a good bet that others may use it as well.
"It doesn't tell you anything about the civilization, but it tells you a civilization is there," said Frank Drake, who with Carl Sagan sent the first physical message into space in 1972, the Pioneer plaques on board the Pioneer 10 U.S. spacecraft. An adviser to Breakthrough Listen, Drake is also chairman emeritus of the SETI Institute.