Stephen Hawking is one of the most brilliant minds of the 21st century. He is known throughout the world for his disability, his scientific brilliance, and even for his interest in acting. But Stephen Hawking also had a weird habit that most people may not be aware of. He was a fan of making wagers. Throughout his life, he made several wagers with other scientific minds over pressing scientific questions. In this blog post, I discuss some of Stephen Hawking's bets.
Stephen Hawking's bets
In the early 1970s, when people's interest in black holes spiked, Hawking made a rather controversial scientific wager.
1. Cygnus X-1
At that time, the most brilliant minds in science thought that Cygnus X-1, a strong source of X-rays, was a black hole. By observing the X-rays coming from Cygnus X-1, they suspected that Cygnus X-1 and a nearby supergiant star were orbiting their common center of mass. They deducted that the material sucked in from the star might have created a hot accretion disk around Cygnus X-1, which emitted the X-rays. They inferred its minimum mass to be at least six times that of the sun. So, theoretically, the chance of Cygnus X-1 being a black hole was pretty high.
But Stephen Hawking made a bet against another theoretical physicist, Kip Thorne, that Cygnus X-1 was not a black hole. The prize was a magazine subscription. In his book 'The Brief History of Time,' Stephen Hawking explains that the bet was a form of insurance policy for him. He says,
I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would bring me 4 years of the magazine Private Eye.
But in 1990, more than a decade later, Stephen Hawking conceded the bet, even though scientists were still not sure if Cygnus X-1 was actually a black hole.
2. Naked Singularity
But losing that bet did not stop Stephen Hawking from betting again. Just one year later, he bet against Kip Thorne and his colleague John Preskill that a naked singularity cannot exist
A singularity is a point where the variable or variables in a mathematical function become infinite. When that happens, the behavior of the function, which is normally predictable, becomes upredictable or undefined. The functions in question here are Einstein's Field equations which represent his Theory of General Relativity. And a singularity in these equations means infinite mass and infinite curvature, i.e., in simple terms, infinite gravity.
Such a singularity exists theoretically in every black hole. Stephen Hawking bet that such a singularity can exist only behind the event horizon of a black hole. But Thorne and Preskill bet that it was possible for a singularity to exist even without an event horizon. (The event horizon is the boundary of a black hole, beyond which nothing, not even light, can escape from the black hole).
In 1997, Hawking conceded that bet too and reframed it as "a naked singularity cannot form under generic conditions." This bet has still not been resolved.
3. The Blackhole information paradox
In 1974, Hawking proposed that black holes can emit radiation. Since this radiation is in the form of heat and independent of what fell into the black hole previously, it gave rise to the black hole information paradox.
But before we can look at what the Blackhole information paradox is, we have to understand what information is.
What is information?
In Physics, one thing is very important, and that thing is determinism, i.e., when one knows the parameters of a system, it must be possible to predict how the system behaved in the past and how it will behave in the future. Regardless of whether it is a single particle, a big chemical reaction, or the whole universe, once we know its properties, physics lets us predict its past and future states.
So, if we know everything that is to be known about a system or an object, like the number of particles it has, their positions, velocities, spins, electric charges, etc., then we can predict these particles' behavior in the past and future. Hence, the raw information in a system (whatever we can know about it) is always preserved across time. It never gets created or destroyed; it only gets rearranged.
But this is not so easy when it comes to black holes, at least not after Hawking discovered Hawking's radiation.
A black hole's gravitational field is so strong that nothing can escape from it once inside its event horizon. So, regardless of whatever you throw inside the black hole, that object disappears. For example, if you throw a book inside a black hole, it disappears. We know what happens afterward, but we can guess that it will be stripped apart. But the book had a lot of information before being thrown into the black hole, like the number of particles it was made of, its chemical composition, etc., besides the obvious human-readable content it contained. So, what happens when the book is thrown into a black hole? If it gets stripped apart into its constituent particle, what happens to the information it earlier contained?
Earlier I told you that when you throw something into a black hole, it disappears.
Well...
It's not completely true.
If you are an observer outside the event horizon of the black hole, and if you throw the book into the event horizon, the book just passes through it. You don't know what happens afterward. Maybe, the information the book contained is somehow preserved in the black hole.
But in 1974, Hawking proposed that a black hole can emit radiation in the form of heat. This in itself is not the problem. The real problem is that, because of the radiation it emits, the black hole shrinks with time and eventually disappears. But what happened to the information about all the objects that the black hole had sucked in?
What happened to the information contained in the light, asteroids, planets, and stars it sucked in?
What happened to the information contained in the book you threw in?
Would the information somehow leak through Hawking's radiation? Hawking tells us that it's not the case. So, if the information about the book you threw into the black hole does not come out through Hawking's radiation, and the black hole disappears, what happened to the information? Where did it go? This indeterminism about the information inside a black hole created the paradox - The black hole information paradox.
The wager about the Blackhole information paradox
In 1997, Stephen Hawking made a wager once again with Kip Thorne and John Preskill regarding the Blackhole information paradox.
This time, Hawking and Thorne were on the same side. According to the Theory of General relativity, the gravitational field of a black hole is so strong that not even light can escape from it. That is, the escape velocity of a black hole (The velocity an object needs to escape from the black hole's gravitational pull and travel to outer space) is more than the speed of light. And since nothing can travel faster than the speed of light, nothing can escape a black hole. So, the information inside cannot leak from a black hole through Hawking's radiation. Hence, the information carried by Hawking's radiation must be new information and not from inside the black hole. Therefore, Hawking and Thorne bet that Quantum Physics needs to be rewritten.
On the other hand, Preskill bet that the Theory of General Relativity must be modified because Quantum Mechanics says that the information contained within the radiation emitted from black holes must somehow relate to the information that fell into the black hole at an earlier time.
In 2003, he conceded this bet as well.
4. Higgs Boson
In the early 2000s, Hawking bet against a physicist called Gordon Kane that the Higgs Boson could never be found. But the particle was eventually found in 2012. Hawking, who had obviously lost the bet, hailed Peter Higgs, the person who had theorized the existence of Higgs Boson almost 48 years earlier, and told that he should be given a Nobel prize.
