"It was amazing," Hawking said after the flight.
The modified jet carrying Hawking, a handful of his physicians and nurses, and dozens of others first flew up to 24,000 feet over the Atlantic Ocean off Florida. Nurses lifted Hawking and carried him to the front of the jet, where they placed him on his back atop a special foam pillow.
The jet then climbed to around 32,000 feet and made a parabolic dive back to 24,000 feet, allowing Hawking and the other passengers to experience weightlessness for about 25 seconds.
The plane made a total of eight parabolic dips, including two during which Hawking made two weightless flips like "a gold-medal gymnast," said Peter Diamandis, chairman of Zero Gravity Corp., the company that owns the jet.
"We had a wonderful time. It was incredible, far beyond our expectations," Diamandis said.
Hawking, a mathematics professor at the University of Cambridge who has done groundbreaking work on black holes and the origins of the universe, has the paralyzing disease ALS, also known as Lou Gehrig's disease.
The 65-year-old was the first person with a disability to experience the flight by Zero Gravity, which has flown about 2,700 people out of Florida since late 2004 and began offering the flights in Las Vegas this week.
"As you can imagine, I'm very excited," Hawking told reporters before the flight. "I have been wheelchair bound for almost four decades. The chance to float free in zero-g will be wonderful."
Unable to talk or move his hands and legs, Hawking can only make tiny facial expressions using the muscles around his eyes, eyebrows, cheek and mouth. He uses a computer attached to his wheelchair to talk for him in a synthesized voice by choosing words on a computer screen through an infrared sensor on a headpiece that detects motion in his cheek.
He raises an eyebrow to signal "yes" and tenses his mouth to the side to indicate "no."
"I want to demonstrate to the public that anybody can participate in this type of weightless experience," Hawking said Thursday.
Hawking's personal physicians were on hand to make sure nothing went wrong. The physicist was attached to heart, blood pressure and oxygen-measuring monitors during the flight. Medical equipment sufficient for a mini-intensive care unit also was on board, said Dr. Edwin Chilvers, Hawking's personal physician.
"I'm anticipating everything to nothing," Chilvers said before the flight.
Others on the flight included financial backers of Zero Gravity and passengers who bid a total of $150,000 toward charities to go on the flight.
The jet's interior is padded to protect the weightless fliers and equipped with cameras to record their adventure.
Normally, the plane conducts 10 to 15 plunges for its passengers, who pay $3,750 for the ride, although that fee was waived for Hawking. As a further safety precaution, Zero Gravity founders Diamandis and Byron Lichtenberg, who has flown on the space shuttle, were on either side of Hawking so they could lower him to the ground gently at the end of the parabola. Hawking also took a motion sickness pill as a precaution. The astrophysicist hopes the zero-gravity flight is a step toward going on a suborbital flight, which may be offered by private space companies by the end of the decade. "Space, here I come," Hawking said after the flight.