Caltech President Jean-Lou Chameau notified the institution in an e-mail that Lange apparently took his own life Friday.
Lange checked into a Pasadena hotel Thursday and the next morning housekeepers found him dead, apparently due to asphyxiation, said Det. Lt. John Dewar of the Pasadena Police Department.
"It appears to be a suicide," Dewar said.
Lange recently resigned as chairman of the Division of Physics, Mathematics and Astronomy, Caltech said.
Lange was best known as co-leader of project "Boomerang," which in 1998 used a telescope, carried over Antarctica by a balloon for 10 1/2 days, to study the so-called cosmic microwave background -- a gas of thermal radiation left over from the embryonic universe.
The experiment showed the spatial geometry of the universe is flat and supported theories that it will expand forever and not collapse upon itself.
The observations were considered the first detailed images of the infant universe, according to Caltech. They largely matched predictions and suggested that scientists are on the right track in understanding the earliest moments of the universe, its age and the amount of so-called dark matter that holds galaxies together.
"It is an incredible triumph of modern cosmology to have predicted their basic form so accurately," Lange said when the research was published in 2000.
A flat universe also supports the "inflation" theory that the universe underwent a rapid expansion in a fraction of a nanosecond after its birth.
Lange and Italian team leader Paolo De Bernardis of Rome's La Sapienza University were awarded one of Italy's 2006 Balzan prizes, annual awards of 1 million Swiss francs, for contributions to cosmology. ("Boomerang" was short for Balloon Observations of Millimetric Extragalactic Radiation and Geophysics.)
Lange was born July 23, 1957, in Urbana, Ill.
He graduated from Princeton University in 1980, earned a doctorate at UC Berkeley in 1987, and was a visiting associate at Caltech in 1993-94. He was appointed a full professor in 1994 and named the Marvin L. Goldberger Professor of Physics in 2001.
In 2006, he became a senior research scientist at NASA's Jet Propulsion Laboratory and was appointed chairman of Caltech's physics, mathematics and astronomy division in 2008.
Lange had three young sons, according to Caltech. A complete list of survivors was not immediately available.