In Brief Answers to the Big Questions, prominent astrophysicist Stephen Hawking discusses science, philosophy, human destiny, and how they relate to each other. Writing at the end of his career, Hawking offers his readers some final words of wisdom on the issues he considers most important. (The book was published by his family and colleagues shortly after his death.)
Hawking builds his discussion around ten questions, but his answers to some of these questions are sufficiently intertwined that we’ll combine many of them for ease of comprehension. Additionally, we’ve omitted his assessments of whether time travel is possible, our ability to predict the future, and the nature of black holes, which we cover in more detail in our guide to A Brief History of Time.
In this guide, we’ll begin by exploring Hawking’s perspective that science now provides better answers to fundamental questions about reality than religion does. Then, we’ll discuss his view of human origins, and finally, we’ll consider Hawking’s perspective on where we’re going and what we need to do to secure the future of the human race.
Hawking begins with a discussion of God, observing that the concept of God is closely related to the question of how the world began. He explains that our ancestors looked to religion for an explanation of the origin of the universe as well as how reality works in the present. In ancient times, people attributed the creation of the universe, the seasons, the phases of the moon, natural disasters, and many other things to the often-fickle actions of God or gods.
Hawking asserts that today, science provides better explanations for these phenomena than religion does, making the concept of God unnecessary. He doesn’t claim to have proof of God’s non-existence. But he says that the universe follows a set of inviolable natural laws, which would constrain the actions of any god who might exist, and therefore the existence of a god who could change the events of the world according to a personal whim, as many religions believe, would not be possible. Science is the study of these natural laws. As such, science gives you a better understanding of how the universe works and where it came from than religion does.
Hawking concedes that you could call the natural laws “God.” After all, they determine everything that happens in the universe, so they are omnipotent, in a sense. But he cautions that these laws are impersonal principles, unlike the personal, relatable gods that most religions depict.
Is God Separate From the Laws of Nature?
Some religions are more consistent with Hawking’s view of the relationship between science and God than others.
Pantheistic religions such as Hinduism and Taoism are relatively compatible with Hawking’s position that gods are either constrained by the laws of nature or indistinguishable from them. This is because pantheism teaches that the natural and the spiritual are one and the same: God is in everything and everything is part of God. In pantheism, natural and spiritual realities may be personified in any number of deities, but these gods are all unified with nature and with each other as part of a universal spirit. Also, many pantheistic religions do not regard the universal spirit as a personal entity, which is consistent with Hawking’s view that the laws of nature are impersonal.
By contrast, monotheistic religions such as Christianity and Judaism tend to be at odds with Hawking’s perspective. This is because they teach that God is a personal being who created the universe and exists independent of it. Most monotheists believe that God established the laws of physics as nature’s default mode of operation, and also that God can override the laws of nature whenever he wants to. For example, God demonstrates his power over nature when he performs miracles, such as when Jesus walked on water.
Thus, the monotheist might argue that knowledge of God still gives you a more fundamental understanding of how the universe works than science does, because God dictates the laws of nature, rather than being constrained to obey them.
So what does science say about how the world works and where it came from? Hawking does not attempt to provide a comprehensive explanation of the laws of nature, but he does give a brief overview of how we got here. According to Hawking, science traces our origins back to the beginning as follows:
1. Humankind developed from earlier life forms, as described in the theory of Darwinian evolution (which postulates that species change over time as random mutations alter the genetic code of different individuals, and the strongest individuals are more likely to pass on their genes).
2. The first life forms appeared in Earth’s oceans about 3.5 billion years ago. Scientists don’t know exactly how the first living things formed from non-living molecules. As yet, they have not even been able to synthesize DNA from inorganic substances. Nevertheless, Hawking infers that the probability of life forming in a suitable environment is probably relatively high because, in cosmic terms, life appeared on earth quite quickly—only half a billion years after the earth’s surface cooled enough to accommodate liquid water.
3. Earth, the sun, and the rest of our solar system were formed when clouds of interstellar gas from the supernova explosions of earlier stars collapsed under the influence of gravity. This is important because carbon and other elements that are necessary for life had to be synthesized by nuclear fusion in earlier generations of stars.
4. Earlier stars were formed from clouds of hydrogen and helium.
5. These clouds of matter came from the big bang. The big bang was the moment the universe came into being at a “singularity,” where all matter, energy, space, and time were initially concentrated in an infinitesimally small area. The universe expanded outward from this original singularity. (Shortform note: Hawking discusses the big bang model in more detail in A Brief History of Time.)
6. But what caused the original singularity? Hawking says it didn’t need a cause because time itself began at the singularity. The theory of general relativity predicts that time slows down in regions of high gravity. At a singularity, gravity is infinitely strong because of the infinite density of matter at that point, so time stops entirely. And time is what delineates cause and effect, because causes must come before their effects. Time starts at the big bang singularity, so nothing can happen before it, and thus it can’t have a cause.
Is Science’s Answer Better Than Religion’s Answer?
As noted before, followers of some religions (particularly monotheistic religions) tend to challenge Hawking’s assertion that science provides better answers to the question of where we came from. To illustrate how some religions still claim to offer more complete answers, let’s contrast Hawking’s chronology with that presented by Christian astrophysicist Hugh Ross:
Ross disputes Hawking’s first two points above and instead believes that God created life on earth. He asserts that God created Adam and Eve as the first humans. For that matter, God created every individual species of lifeform.
Scientific studies of the fossil record reveal numerous species appearing and disappearing over Earth’s geologic history, but scientists have never observed one species change into another, either directly or through fossil evidence. Ross argues that these observations fit better with the idea that God created new and unique animal species at each stage of Earth’s geologic history than it does with the idea that earlier species changed into other species over time.
Ross goes on to assert that there are many scientific problems with the theory of Darwinian evolution, such as its inability to explain the irreducible complexity of cells. Atheistic models offer no mechanism for the origin of the first life forms. But if the mechanism was divine intervention, then it’s no wonder scientists haven’t been able to find a naturalistic mechanism, and irreducible complexity is not a problem for God.
Ross also disputes Hawking’s theories of how planetary bodies formed as outlined in points three and four above, instead believing that God orchestrated Earth’s formation. Strictly speaking, Ross agrees with Hawking’s view of how our solar system physically formed from gaseous remnants of earlier supernovae.
However, Ross also argues that the earth and solar system are too exquisitely fine-tuned for human life to be the product of mere chance. There are so many astronomical parameters (such as planet size and chemical composition, star brightness, orbital stability, and so on) that must be in a certain range for a planet to be habitable that the odds of getting even one human-habitable planet in the entire universe by random chance are infinitesimally small. Ross takes this as evidence that God personally fine-tuned Earth’s formation, even if he worked behind the scenes through the laws of physics.
Finally, Ross weighs in on Hawking’s theories of the origins of the universe, believing that God created the big bang singularity. He endorses an inflationary big bang model similar to Hawking’s. But where Hawking argues that the singularity precludes the universe having a cause, Ross argues the opposite: Since time itself began at the big bang singularity, the singularity had to be created by something (or someone) that is not confined to the space-time of our universe. In other words, since the singularity precludes a natural cause, the universe had to have a supernatural cause.
Is Ross’s model better than Hawking’s? It depends on your perspective. Ross asserts that his creationistic model matches current scientific observations better than atheistic models do.
But Hawking points out that, historically, people have often appealed to the supernatural to explain natural phenomena that they didn’t understand. He concedes that scientists don’t yet have naturalistic explanations for some things, like the origin of the first life forms. Nevertheless, he expects natural mechanisms to be discovered, based on the historical trend of natural explanations replacing supernatural ones.
Ross might argue that this goes against the scientific method: A scientist should accept the simplest model that matches current observations, and update his model as new data becomes available, rather than appealing to possible discoveries that haven’t been made yet. Ross concedes that a scientist should test every model by using it to predict future observations, and then comparing the predictions to the new observations. Nevertheless, he argues that scientists’ ongoing failure to identify a naturalistic mechanism for the origin of life contradicts Hawking’s predictions and agrees with the predictions of his creationistic model.
Perhaps future discoveries will eventually vindicate either an atheistic model or a theistic one, but for now the controversy continues.
Having explained where we came from, Hawking then turns his attention to where we’re going. He expects that humankind will face a number of challenges in the not-so-distant future and emphasizes that scientific literacy will be increasingly important to help people navigate these challenges.
Why will scientific literacy be so important for our future wellbeing? Two issues that Hawking discusses in particular are the ongoing evolution of the human race and the expansion of human civilization into outer space. Both these issues present us with a variety of technical questions or challenges that have broad implications for society, and we will need a new generation of technical experts to develop solutions to these challenges. Furthermore, as society is faced with ethical and political decisions that increasingly have a technical element to them, even non-scientists will need an increased level of scientific literacy to understand the issues as they contribute to society’s decision-making process.
Where Science and Politics Meet
Many people have observed, often with concern, that science is becoming increasingly politicized. Some argue that this is detrimental both to science and to society, arguing that politicians should leave scientific inquiry to professional scientists, and then humbly incorporate scientists’ recommendations into political policy. Others, such as Yuval Noah Harari, argue that science is inevitably directed by socio-political interests, because scientific research is expensive, and scientists are dependent on society for their funding. For better or for worse, this gives society control over what scientists study.
Hawking’s perspective suggests both a cause for the increasing intersection of science and politics and a solution to the problems that it can create. As society advances technologically and becomes more dependent on technology, social problems become increasingly technical. So, in a sense, it’s not that science is becoming more politicized—it’s just that social issues are more technical than they used to be. And so, to cope with society’s problems, we all need to be more technically literate.
For example, energy production and environmental sustainability are issues facing our society today. Some politicians want to subsidize the production of solar panels because they believe solar panels provide an environmentally sustainable way of generating electrical power. Others oppose widespread production of solar panels because they believe that solar panel waste does more damage to the environment than the panels can prevent. After all, solar panels have to be replaced periodically as they wear out, and it takes a lot of solar panels to produce as much power as a single traditional power plant.
Who’s right? This is a social question that requires a numerical solution: If the lifetime energy production of a typical solar panel is high enough, it’s worthwhile for society to invest in producing more of them. If not, stimulating production would be counterproductive. You may not have the time or the funding to measure the output of solar panels for yourself, but the more scientifically literate you are, the easier it will be for you to assess the technical validity of the data that each side provides in this debate.
Hawking anticipates that the ongoing evolution of life on earth will give rise to new challenges for the human race. He says that, while Darwinian evolution of the human species continues, other processes may soon accelerate the evolution of mankind, if they haven’t already. He suggests three new types of evolution, which we’ll explore in turn.
(Shortform note: Hawking is not the only one to contemplate the challenges that the evolution of humans and human civilization may pose for the future. In Homo Deus, Yuval Noah Harari makes conjectures about future evolution that are parallel to Hawking’s ideas, but from a different perspective. As we examine Hawking’s predictions, we’ll compare them to Harari’s.)
First, Hawking explains that evolution is characterized by information transfer: As each generation evolves and passes on its genes, the information contained in the genetic code of the species grows. But with the invention of written language, humans have developed other ways of passing useful information from one generation to the next. And now, thanks to digital information processing, the amount of information that humans can access and store is increasing exponentially. Hawking sees this as a new mechanism of evolution.
(Shortform note: While Hawking doesn’t say it explicitly, this paints a bleak picture of the future for people who aren’t literate, or who lack the technical competence to access digital information. Consider what happens when you combine his argument that digital information transfer has become a mechanism of human evolution with the Darwinian principle of survival of the fittest. Together, they imply that humans who are more adept at taking advantage of available information in this digital age will be more “fit” to prosper, while others will tend to get weeded out by natural selection.)
Hawking explains that one particularly important piece of information mankind has been able to decipher and pass on is our own genetic code. He predicts that, now that the human genome has been sequenced and increasingly powerful gene-splicing technologies are being developed, you will soon be able to rewrite the genetic code of your offspring. Genetic engineering will lead to much faster genetic advancement of our species than Darwinian evolution.
Hawking anticipates that first, genetic engineering will allow us to cure diseases and syndromes caused by deficiencies in single genes. Then, more cures for more genetically complex conditions will be developed. After that, we’ll be able to upgrade our children’s genetics for increased intelligence, natural immunities, and eventually capabilities we haven’t even imagined yet.
Hawking acknowledges that there are many valid ethical concerns about genetically engineering humans, and that many countries consequently restrict or prohibit it. However, he argues that civil laws cannot prevent this new form of evolution. He expects that, even if it’s illegal in most countries, sooner or later someone will do it. And once the first genetically engineered superhumans appear, the rest of humankind will be faced with a choice: Embrace genetic engineering, or become an increasingly inferior sub-species of humanity. Either way, genetically enhanced humans would become the dominant species by natural selection.
But even before that time comes, we as a society need to be scientifically literate so that we can make intelligent decisions as we are increasingly confronted with issues pertaining to genetic engineering.
Genetic Engineering and Techno-Humanism
Hawking surmises that, as genetic engineering becomes increasingly feasible, people will begin to take advantage of it whether it’s sanctioned by governments or not. Yuval Noah Harari echoes this idea in Homo Deus, in which he describes the rise of “techno-humanism,” or the belief that humans should use technology to upgrade their own mental capabilities.
Based on Harari’s exposition of techno-humanism, it seems likely that Hawking is right that people will improve themselves and their offspring with technology regardless of their governments’ positions. It also seems likely that techno-humanists will be the first to genetically reengineer themselves once the technology becomes available. Genetic engineering is one of the primary mechanisms whereby they hope to upgrade their minds. Other possible mechanisms include nanotechnology, integration of computer chips into the brain, and brain-altering drugs.
Hawking also says that genetic engineering will raise new ethical and technical questions for society to answer. Harari’s discussion of techno-humanism illustrates the type of questions Hawking is referring to.
To begin with, if people start to upgrade their brains, what parts or capabilities of the brain should they focus on, and what effect will it have on society? For example, if we improve people’s ability to make decisions quickly and calmly, will we lessen their ability to empathize and be patient with others? If a military was made up of these super-rational soldiers, would it end up an efficient but unfeeling force?
According to Hawking, in addition to accelerating the evolution of our own species, we may create an entirely new form of life: electronic life. By Hawking’s definition, “life” requires only two capabilities: reproduction and metabolism.
(Shortform note: Hawking defines “life” more broadly than most biology textbooks do. One common definition requires something to meet five criteria in order to be considered a living thing: 1) It must be made of cells. 2) It must have DNA. 3) It must maintain homeostasis (regulate its internal chemistry). 4) It must be able to reproduce. 5) It must be able to collect energy that it can use for growth and movement (metabolism). Hawking dismisses the first three of these criteria and keeps only the last two. Thus, by the classical textbook definition, viruses are not alive, since they aren’t made of cells. But by Hawking’s definition, viruses are alive.)
Hawking points out that just because some technology is “alive” doesn’t mean it’s self-aware. That said, he also suggests that self-aware computers and robots may not be relegated to science fiction forever. At some point in the evolution of humans, the human brain developed enough information-processing capability to become self-aware. So, as we continue to develop increasingly sophisticated computers and artificial intelligence (AI) algorithms, it is possible that they may become conscious at some point.
Moreover, according to Hawking, once AI algorithms become better at writing algorithms than human programmers are, they will begin to evolve at an exponentially increasing rate. From this point on, AI will be increasingly beyond our control, whether they become self-aware or not. So we need to make sure that any artificial intelligence we create will work for our good and not our harm.
In particular, Hawking warns that the societal consequences of developing autonomous weapon systems could be disastrous. But not all issues involving AI are this clear-cut. Artificial intelligence algorithms could provide powerful tools for solving important technical problems, such as finding cures to disease, or modeling and controlling climate change.
Once again this makes scientific literacy increasingly important for our society, as society is increasingly confronted with questions about how to manage the development of artificial intelligence, which are both ethical and technical in nature.
Is Weaponized Artificial Intelligence Inevitable?
Hawking advises against developing autonomous war machines or otherwise weaponizing artificial intelligence. However, in light of his discussion of genetic engineering, development of intelligent weapons may be unavoidable.
As we have discussed, he predicts that laws against human genetic engineering will not prevent it from happening, because someone will eventually try it anyway. Then the genetically engineered superhumans will have an advantage over regular humans that will force the rest of humanity to either embrace genetic engineering or lose their influence.
A similar argument could be advanced for intelligent weapons. If artificial intelligence has the potential to make weapon systems dramatically more effective, then the first military power to develop these systems will have the advantage. They’ll get to make the rules, at least until their rivals develop comparable technology.
So can we really avoid development of intelligent weapon systems? As much as it might be in everyone’s best interests in the long term, the opportunity these systems provide for an individual nation or faction to gain power in the short term makes it likely that someone will do it anyway. And then other nations will either have to accept their military supremacy or match their technology.
Artificial Intelligence and Dataism
Just as Harari’s discussion of techno-humanism sheds additional light on Hawking’s discussion of genetic engineering, Harari’s exposition of Dataism provides additional perspective on Hawking’s discussion of the social implications of AI.
Harari explains that Dataism is a type of “techno-religion”: a belief system based around technology. Those who believe in Dataism hold that the intrinsic value of any living thing or system is directly proportional to its data processing capacity. Unlike humanists, Dataists don’t attribute any special significance to self-awareness or other, similar qualities that set humans apart from machines and lower animals.
Dataists believe that humans became the dominant species on Earth simply because humans can collect and process more data than animals can. Inventions like written language increased humanity’s importance because they improved humans’ ability to transmit and process data. By the same token, large communities are more important than small ones because more people can process more data. And free societies are more likely to flourish than dictatorships because they facilitate the free flow of information and allow processing to be distributed among a larger number of people.
Dataists also believe that humanity’s tenure as the dominant species on Earth is rapidly coming to an end. Computers are becoming progressively more powerful and humans are struggling to process all the data that is now available. Hawking predicts that AI will eventually become better at writing AI algorithms than human programmers, and then artificial intelligence will take off exponentially. Dataists make the same prediction and believe that will be the turning point. Once AI takes off, it will become the dominant life form on earth, as its data processing capabilities rapidly exceed humans’ capabilities. After that, Dataists believe humans will merely serve the all-powerful AI until the AI finds a way to assimilate any remaining humans into itself.
Dataism resonates with Hawking’s conjectures that self-awareness is probably just a matter of being able to process enough data, and that artificial intelligence may evolve beyond human control, whether it becomes self-aware or not. However, where Hawking raises these points as possibilities that society needs to consider and plan for, Dataists accept them as doctrine. While Hawking warns that we need to make sure AI serves our best interests, Dataists anticipate that we’ll soon be obliged to serve a global AI—and they think that’s a good thing.
Whether or not Dataists’ predictions come true, their techno-religious beliefs illustrate how technology now influences philosophical thinking, and how technological issues like AI are becoming social issues that affect everyone.
According to Hawking, not only do we need to cultivate scientific literacy so our society can address the complex questions raised by new types of evolution, but we also need new generations of scientists and engineers to solve the technical problems of colonizing outer space.
Hawking presents two reasons to colonize outer space:
First, our species is running out of space on earth. Earth’s natural resources are limited, and we’re depleting them at an alarming rate. Hawking is all in favor of conserving natural resources by improving how we manage them, but he believes that in the long term, we’re still going to need more room for humanity to expand into.
Second, colonizing space mitigates the risk of extinction. Hawking warns that there is a significant probability that humans could go extinct on earth in the next millennium. But if we’ve colonized other planets by then, at least that wouldn’t be the end of our species.
Hawking mentions several threats that could lead to extinction of humans on earth. Asteroid impacts have caused extinctions in the past, and Earth will eventually be hit by another large asteroid again.
(Shortform note: Statistically speaking, large asteroids impact the earth about every 50 to 60 million years. It’s been about 66 million years since the last impact, so we’re arguably due for another asteroid impact any day now.)
As Hawking points out, if an asteroid doesn’t get us, a global nuclear war could have much the same effect. For that matter, so could climate change. Hawking expresses concern that human activity may already have triggered runaway climate change: Rising carbon dioxide levels in the atmosphere cause global warming. Global warming melts the polar ice caps. The ground underneath the ice caps absorbs sunlight better than the ice did, accelerating global warming. Furthermore, global warming could lead to deforestation of some areas, reducing the planet’s capacity to sequester carbon dioxide and thus increasing the buildup of carbon dioxide, which accelerates global warming.
Connecting Resource Depletion to Risk of Extinction
Harari offers a slightly different perspective on the dangers of ecological collapse that reveals interconnectivity between the risks that Hawking discusses.
Like Hawking, Harari points out that we as a species are using up the earth’s natural resources at an alarming rate. Unlike Hawking, he conjectures that mankind will likely find a solution to resource depletion. Throughout history, as humans have used up their natural resources, they have discovered or developed new resources.
For example, the Iron Age began when cultures that lacked the copper deposits to make bronze-age tools figured out how to refine iron (iron ore is much more common on Earth than copper). Similarly, we now build airplanes out of materials like aluminum and titanium that were unknown just a few hundred years ago, and we can now generate electricity from sunlight or nuclear fission instead of fossil fuels.
That said, Harari also points out that new technology tends to benefit the rich more than the poor because the poor can’t afford to adopt it. If we reach a point where, for example, the poor increasingly suffer from lack of clean air and water, while the rich have the technology to purify their air and water, this could lead to class warfare.
The same principle would apply to climate change: If Earth’s climate becomes inhospitable to human life, the people who can afford to do so will likely construct climate-controlled dwellings and working spaces. If others are suffering from nearly unlivable environmental conditions, this would likewise contribute to class hostility.
As such, depleting Earth’s resources or incurring climate change not only pose a direct risk to the survival of mankind, but they also increase the risk of extinction through war. Thus, based on Harari’s discussion, Hawking’s risks are not separate risks, but rather facets of the same basic problem.
Harari discusses the problem without proposing a definitive solution, while Hawking asserts that colonizing outer space is the clear solution. Yet, this, too, could fit with Harari’s model: Perhaps colonizing space is how mankind will develop new resources in the next millennium.
But is colonizing space even possible? And if so, how do we go about it? Hawking thinks it is possible, and he suggests that we start by colonizing the moon, followed by Mars. He argues that the cost of a program to build bases—and ultimately colonies—there would amount to only a few percent of the world GDP.
Furthermore, Hawking expects that the experience that we gain from building colonies on the moon and Mars, combined with future advances in propulsion technology, would eventually enable us to expand beyond our solar system. He concedes that the laws of physics make it impossible for a spacecraft to travel faster than light, but he points out that there are about a thousand stars within 30 light years of earth. Theoretically, these stars will eventually be reachable by spacecraft. If even a small percentage of these stars have habitable planets, that will give mankind a lot of new real estate to settle.
Climbing Out of the Gravity Well
Although Hawking doesn’t mention it explicitly, his strategy for colonizing space appears to be based on solving the “gravity well problem,” which he certainly would have been familiar with as a physicist.
Basically, the “gravity well problem” is that it takes a tremendous amount of energy (usually in the form of a very large rocket) to launch anything into space from Earth’s surface—just like it would take a lot of energy to climb out of a deep well. This becomes particularly problematic if you want to move a large amount of material into space, for example to colonize another planet.
However, the moon’s gravity is weak enough that you can escape it much more easily. If you had a colony on the moon, it would be much easier (and cheaper) for the lunar colonists to launch a mission to Mars or somewhere else than it would be for people on Earth. Furthermore, the moon’s crust is rich in light metals like titanium and magnesium, which could be useful in constructing spaceships.
This is probably why establishing a colony on the moon is the critical first step of Hawking’s strategy. Once colonized, the moon would serve as an important base of operations from which to launch other space missions.
As we start colonizing space, will we have any competition? Are there indigenous peoples on other planets or extraterrestrial races already spreading their empires across the galaxy?
Hawking says he likes the idea of extraterrestrial life, but he doesn’t think we have any direct evidence one way or the other for its existence. He dismisses reported UFO sightings and alien abductions as hoaxes, hallucinations, or misunderstandings—investigators have shown that some of the alleged sightings are indeed hallucinations, and he thinks that is the most reasonable explanation for all of them. Hawking expects that if mankind ever does make contact with technologically advanced extraterrestrials, it will be widely publicized and obvious to everyone.
(Shortform note: Hawking doesn’t elaborate on his reasons for believing that if extraterrestrial spacecraft arrived on Earth, everyone would know, but one reason they probably would know is that the United States maintains a space surveillance network. This network of radar stations, satellites, and other instruments is capable of detecting any object 10 centimeters across or larger entering or leaving low earth orbit. If Earth were ever visited by alien spacecraft, this network would provide official documentation of the craft’s arrival, but no such arrivals have been reported. This also corroborates the idea that reported UFO sightings are most likely to be hallucinations.)
Hawking discusses three possible reasons that we haven’t been contacted by extraterrestrials:
1) Maybe there are intelligent extraterrestrials out there, but we just haven’t made contact with them. The distance between stars and galaxies in our universe is so vast that it would be easy for multiple races to exist in different parts of the universe without ever bumping into each other.
(Shortform note: If there are intelligent extraterrestrials out there, how would we detect them? Even the nearest stars are much too far away for our telescopes to make out details like orbital space stations, cities on their planets, or other evidence of intelligent life. Our best bet might be picking up their radio communications signals. However, distance reduces radio signal strength, limiting the distance at which we can detect signals. Radio telescopes can pick up radio waves from distant stars, but even the dimmest dwarf stars are quadrillions of times more powerful than the most powerful radio transmitters, so it’s unlikely we’d be able to detect the signals any alien life forms might transmit.)
2) Maybe extraterrestrial life is common in the universe, but intelligent life is not. Hawking questions whether intelligence is really beneficial from the standpoint of Darwinian evolution. Maybe species that evolve sufficient intelligence to develop advanced weapons technology tend to bring about their own extinction through war. If intelligence tends to be an evolutionary dead end, there may not be very many intelligent races in the universe at any given time.
(Shortform note: If intelligent life is rare, this would greatly compound the distance problem, because, as we said before, our best shot at detecting extraterrestrial life is picking up their radio signals. But if the extraterrestrials aren’t intelligent enough to build radio transmitters, then we won’t be able to detect them that way.)
3) Maybe the probability of life forming is actually so low that it only happened once in the entire history of the universe—here on Earth. The idea that life is highly improbable seems far-fetched based on our observations of life on Earth, but observers only evolve in places where life actually forms, so our observations may not be representative. As an illustration, a child growing up in a wealthy neighborhood may assume that every kid gets a new car for her sixteenth birthday, just because everyone she knows did. Perhaps we would be similarly naive to assume that life forms on every planet, just because it formed on ours.
Estimating the Probability of Extraterrestrial Life
Various scientists have put forth estimates of the likelihood of extraterrestrial life. Probably the best-known is the Drake equation, which attempts to estimate the number of intelligent races in our galaxy based on the rate of star formation, the fraction of stars that form suitable planets, and the probability of life forming on a habitable planet. Typical assessments based on the Drake equation predict that there should be at least a thousand intelligent races in the galaxy.
However, scientists concede that some of the parameters in the Drake equation, such as the probability of life forming, are just assumptions. Some have also pointed out that there are a large number of physical and astronomical factors that can affect the habitability of a planet, which the Drake equation doesn’t include.
When these factors are included, the expected number of races typically drops to much less than 1, even if the probability of life forming on a habitable planet is assumed to be 100%, and the scope of the equation is broadened from just our galaxy to the entire observable universe.
Admittedly, there is some uncertainty inherent in all estimates of the probability of extraterrestrial life, but if more exhaustive models tend to drive the probability down, that tends to support the third possibility that Hawking presents, namely that we really are alone in the universe.
In this guide, we’ve discussed Hawking’s perspective on a number of “big questions,” such as the existence of God and the future of humankind. Now we’ll give you a chance to consider them for yourself.
Hawking asserts that science has made the concept of “God” unnecessary by offering better answers to the question of human origins than religion ever did. However, as we also noted, some people contend that religion still offers a more complete answer to the question of human origins. What do you think? What role, if any, do you think a supernatural creator played in the origin of life, humanity, or the universe? Why?
Hawking expects that artificial intelligence algorithms will eventually become better at writing AI algorithms than human programmers are, and that once that happens, AI will grow exponentially beyond human control. In this context, he warns that we, as a society, need to make sure AI works for our good and not our harm, but he doesn’t go into detail about how we should do that. What do you think is the best way to make sure AI doesn’t harm us in the future? (For example, should we make certain types of AI illegal? If so, what should be illegal, and how would the prohibition be enforced?)
Hawking calls for colonization of outer space. Suppose that world leaders heed his call, and a sudden breakthrough in propulsion technology makes it possible to send colonists to neighboring solar systems. Given the opportunity, would you consider immigrating to a different planet? Why or why not?
Now imagine that an all-knowing AI has taken over the earth, and is ramping up the space colonization program. Moreover, the AI has just informed you that it has decided to relocate you to a distant planet. You have to report to the spaceport within 30 days, and there is no possibility of returning to Earth after you leave. How would you spend your last 30 days on Earth?