Thomas Gold, 84, a theoretical astrophysicist and one of the great celestial thinkers of the last century, died of heart disease June 22 at a hospital in Ithaca, N.Y. Mr. Gold, an emeritus professor at Cornell University, came to full prominence during the Space Age and continued hypothesizing about a range of matters -- from astronomy to zoology -- until his death.

Each theory he held was armed with a ferocious self-confidence that seldom dimmed over a six-decade career. He often resisted widespread expert beliefs contrary to his, saying a scientist's role was to probe.

"In choosing a hypothesis there is no virtue in being timid," he once said. "I clearly would have been burned at the stake in another age."

Starting in the late 1940s, Mr. Gold and the legendary stargazers Fred Hoyle and Hermann Bondi became crusaders for an early explanation of the universe's origin and continuous creation. Their "steady-state" theory argued that the universe is ever-expanding, without beginning or end. They said new matter will be formed as other objects, such as stars, die, thereby filling up space as the universe expands.

The three former Cambridge University students spent years at odds with believers of the "big bang," the instantaneous, violent cosmic start of the universe. The big-bang theorists came to dominate the field as more evidence shifted their way, and Mr. Gold gradually came to see the steady-state theory as "doubtful."

He came to full bloom as a media personality during the struggle to place men on the moon. Working under contract to NASA, he theorized that the moon's surface, constantly bombarded by meteors, was awash in fine dust; this was jokingly called "Gold dust."

Concerned, NASA sent the unmanned Surveyor to make a landing test of the moon's surface. They did not want astronauts sinking in a sea of dust.

When the manned Apollo craft landed safely, it was said to have debunked Mr. Gold's theory. However, the scientist said lunar samples proved him correct, that "in one area as they walked along, they sank in between five and eight inches." Further, he held that they would have sunk more except they weighed one-sixth of what they did on Earth.

Starting in the late 1960s, Mr. Gold did key theoretical work on the newly discovered pulsars, rapidly pulsating radio wave sources. Mr. Gold postulated quickly -- and as it turned out correctly -- that they are collapsed neutron stars that are rotating. That led to further discoveries about the neutron stars.

With the energy crisis of the 1970s, he turned his focus to sources of petroleum. His obsession became proving that oil and gas reserves do not have a biological origin, namely decomposing organic material. He envisioned an all-but-inexhaustible amount of natural gas, in particular methane, trapped below Earth's surface during its formation. Those primordial hydrocarbons were constantly seeping upward, he said -- to much derision.

He found Sweden more hospitable to his quest and raised money for a massive drilling project, which began in 1986. He went to a meteor-made lake north of Stockholm to search for oil and gas that may have flowed upward in the meteor-fractured ground.

Mr. Gold said his team had found something oily, but critics countered that the oil was merely contamination from the drilling. He was defiant, angering geologists, some of whom went so far as to start a campaign to prevent publication of his findings.

The author of more than 280 scientific papers told Omni magazine: "Most men . . . can seldom accept even the simplest and most obvious truth if it obliges them to admit the falsity of conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven thread by thread into the fabric of their lives."

Mr. Gold had a transient childhood. Born in Vienna, he moved to Berlin at 10 and then left for England because his father, a Jewish businessman, foresaw Hitler's rise.

As a young man, Mr. Gold became interested in technology after his father gave him a watch. He dutifully took it apart and reassembled it.

He was a graduate of Cambridge University, where he also received a master's degree in mechanical sciences. For his master's, he postulated that the human ear acts not just as an amplifier of sound but also as an oscillator. This caused great hilarity among his peers, who held that the brain was chiefly responsible for the ability to recognize tones. As the technology developed years later to uncover tiny hair cells that caused feedback to vibrating membranes in the ear, he was proven correct.

At the start of World War II, he was briefly interned as an enemy alien because of his Austrian nationality. He later quipped, "I was probably the first person to go right from internment as an enemy to work on an ultra-secret project like radar."

After the war, he taught physics at Cambridge, was assistant to the astronomer royal at Royal Greenwich Observatory in England and taught astronomy at Harvard University.

From 1959 to 1981, he was director of Cornell's Center for Radiophysics and Space Research, and he became a leading advocate for Americans to dominate space before the Soviets.

He became chairman of astronomy at Cornell, hired Carl Sagan to the faculty and was a recipient of numerous prizes, including the Royal Astronomical Society's highest award. He also was a skilled water and downhill skier and enjoyed tightrope-walking in his back yard.

He was still courting controversy into his late seventies. His 1999 book, "The Deep Hot Biosphere," repeated much of his theory of hydrocarbons deep below the earth. It also went on to startle biologists with the view that life formed from those hydrocarbons, not the other way around. The hydrocarbons, he said, offer sustenance for bacteria deep in the earth.

Anyone who cannot grasp that, he told the London Daily Telegraph, was suffering from "surface chauvinism."

His marriage to Merle Tuberg Gold ended in divorce.

Survivors include his wife, Carvel Beyer Gold, whom he married in 1972, of Ithaca; three daughters from his first marriage; a daughter from his second marriage; and six grandchildren.

Thomas Gold, shown in 1987 at Cornell University, continually courted controversy with theories considered outside the norm.