Caltech crowd basks in Hawking radiation
Stephen Hawking is the last of the 20th century’s celebrity scientists. As did Albert Einstein, Richard Feynman, Carl Sagan and a handful of others, he has the rare gift of being able not only to think deeply about the mysteries of the cosmos, but also to capture the imagination of the public with his ideas.
That celebrity was on full display Wednesday night, when more than 2,000 people, some of whom waited in line for hours in lawn chairs, showed up at the Caltech campus in Pasadena to hear him speak.
Hawking, 66, delivered a prerecorded talk about black holes, sprinkled liberally with humor about his failure to win a Nobel Prize for his theory about Hawking radiation, a leakage of radiation from the massive gravity of a black hole.
At the end of his talk, he answered five questions submitted by Caltech students.
Hawking’s close friend Kip Thorne, a Caltech physicist, described the painstaking process by which the British theoretician, who has Lou Gehrig’s disease, programs his computer to speak for him.
According to Thorne, it took Hawking several days to program answers to the students’ questions. “He is about the most patient, stubborn man I know,” Thorne said.
Everyone depicts black holes as round objects, but are doughnut- or pretzel-shaped black holes possible?
One of the results I obtained when I was a [postdoctoral student] was that a black hole in four dimensions has to be round. There are no doughnut-shaped black holes in four dimensions. However, one of my former students found there could be doughnut-shaped black holes in five dimensions.
Given that any extraterrestrial colonies that we develop would likely be wholly dependent on Earth for support, do you think we should be involved in manned space exploration?
Any extraterrestrial colonies we establish will depend on Earth for support at first. However, the aim should be to make them self-sustaining before too long. Only then will the future of the human race be safe from disasters on Earth. It would certainly be necessary for the colonies to be self-sustaining as we go to other stellar systems. Just to send a message to Earth that more supplies were needed would take at least four years. And it would take hundreds or thousands of years to actually send the supplies.
Could the cosmic microwave background radiation be a form of Hawking radiation?
[The context to this question is Hawking’s radical prediction in 1974 that black holes could emit thermal radiation, thereby allowing some black holes to ultimately shrink and disappear. The cosmic microwave background radiation is the remnant radiation left over from the Big Bang.]
In the slow inflationary scenario, the cosmic microwave background radiation is not Hawking radiation. However, the fluctuations in the microwave background detected by WMAP [a NASA spacecraft] can be regarded as Hawking radiation from the inflationary period. Thus, in a sense, Hawking radiation has already been observed. So maybe I should get a Nobel Prize.
According to general relativity, white holes, the opposite of black holes [and] which spew matter into the universe, can exist. But we’ve never found them. What would we see with our telescopes if we did?
When black holes are large, things fall in. But they give off very little Hawking radiation. So they are essentially black. But when they are very small, they radiate more than they accrete. So they are essentially white. Black and white holes are the same, just with different boundary conditions. If the boundary conditions are that particles are going in but nothing is coming out, we call it a black hole. On the other hand, if the boundary conditions are that particles are going out but nothing is coming in, we call it a white hole.
If black holes are created in the Large Hadron Collider, will we be in danger of getting eaten up by them?
[This question refers to the construction outside Geneva, Switzerland, of the world’s most powerful collider, which is expected to begin operations this summer. Some skeptics fear it will generate such powerful energies that it could create mini-black holes.]
The LHC is absolutely safe.
There is no danger that collisions between particles at the LHC will cause a rip in space-time and destroy the universe.
Particles from collisions far greater than those in the LHC occur all the time in cosmic rays, but nothing terrible happens.
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After his talk, Hawking was wheeled out of Beckman Auditorium to a standing ovation. He then took a victory lap in his wheelchair around the building, while the crowd snapped pictures and shouted: “We love you, Stephen.”
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