Changes in Our Solar System: Is Trouble Coming?

For the first time in recent memory, the universe is under scrutiny and the solar system we all learned in grade school may be turned upside down.

Astronomers are now reassessing what makes a planet a planet, so curiosity about our existence in this solar system is peaking.

Could the human race go extinct?

According to Stephen Hawking, one of the world's leading theoretical physicists, the possibility of our extinction should be a wake-up call to us all.

Hawking spoke with ABC News to give his perspective on the devastation our civilization could face in the next century.

Here are a few excerpts from Hawking's conversation with Elizabeth Vargas.

Vargas: How crucial is the next 100 years to the survival of the human race?

Hawking: We face a number of threats to our survival, from nuclear war, catastrophic global warming, genetically engineered viruses, and the number is likely to increase in the future, with the development of new technologies, and new ways things can go wrong.

Although the chance of a disaster to planet Earth in a given year may be quite low, it adds up over time and becomes a near certainty in the next 1,000 or 10,000 years. By that time, we should have spread out into space, and to other stars, so a disaster on Earth, would not mean the end of the human race.

However, we will not establish self-sustaining colonies in space for at least the next 100 years, so we have to be very careful in this period.

Vargas: What do you think is the biggest threat to humanity?

Hawking: Nuclear war is still probably the greatest threat to humanity, at the present time. Even after the end of the Cold War, there are still enough nuclear weapons stockpiled to kill us all several times over, and new nuclear nations will add to the instability. With time, the nuclear threat may decrease, but other threats will develop, so we must remain on our guard.

Vargas: Do you think it is possible that the human race will go extinct in the near future?

Hawking: There is a possibility that the human race could go extinct, but it is not inevitable. This is not a prophesy of doom, but a wake-up call.

Vargas: Conversely, do you ultimately believe that the human race will act in time and make the necessary changes in order to survive? If so, what are the necessary changes?

Hawking: Most of the threats we face come from the progress we have made in science and technology. We are not going to stop making progress, or reverse it, so we have to recognize the dangers and control them. I'm an optimist, and I believe we can.

Vargas: The universe is a vast and powerful place with forces that we are only now beginning to understand. Some of them, such as black holes and gamma ray bursts, though extremely unlikely, are capable of destroying our planet. What do these type of phenomena tell us about humanity's place in the universe?

Hawking: Events like a nearby cosmic ray burst, or a collision with a black hole, would be devastating to life on Earth, but they are extremely unlikely. They haven't happened in the 4½-billion-year history of the Earth so far, so the chance of them occurring in the near future is very low. The Earth is in much more danger from human action than from natural disasters.

Vargas: Asteroids provide a paradoxical example of our relationship with the universe. These near-Earth objects may have cleared the way for our evolution, yet could ultimately destroy our very way of life. What do asteroids tell us about the randomness and fragility of human existence?

Hawking: It seems to be 70 million years since the last mass extinction of species caused by collision with an asteroid. This is probably longer than the average period between major asteroid collisions, and this allowed the human race to develop. One might regard this as pure luck, but there is another way to look at it.

There must be many Earth-like planets in the universe, but only those with long periods between asteroid collisions develop intelligent life, which can then ask the question, "Why were we so lucky?"

The answer is, if we hadn't been lucky enough to have a long period between asteroid collisions, we wouldn't be here to ask the question.

Vargas: The separate threats of nuclear war and bioterrorism make an effective argument that we as humans have tremendous difficulty controlling what we create. What does this say about the human species?

Hawking: Up to now, aggression has been an attribute with definite survival advantages. So it has been hard-wired into our genes by Darwinian evolution. Now, however, it may destroy us all by nuclear or biological war, if we cannot control our instinct by our reason. But our aggression is responsible for only some of the dangers we face. Others, like climate change, arise from instabilities in the increasingly complex structure of our way of life. We need to be quicker to identify such threats, and act before they get out of control.

Vargas: Many scientists in the field of artificial intelligence believe that it is only a matter of time before computers will be autonomous, thinking beings that will surpass humans. Do you think this is possible?

Hawking: I think there's no qualitative difference between the brain of an earthworm and a computer. I also believe that evolution implies there can be no qualitative difference between the brain of an earthworm and that of a human. It therefore follows that computers can, in principle, emulate human intelligence, or even surpass it.

Up to now, computers have obeyed Moore's Law, which says that computers double their speed and memory capacity every two years. Human intelligence may also increase because of genetic engineering, but not so fast. The result is that computers are likely to overtake humans in intelligence, at some point in the next 100 years. When that happens, we will need to ensure that the computers serve us, and not themselves.

Vargas: A majority of scientists now believe that mankind is changing the Earth's climate to an unmistakable and potentially catastrophic degree. Do you think it possible for us to stop global warming from getting worse?

Hawking: The danger is that global warming may become self-sustaining, if it has not done so already. The melting of the Arctic and Antarctic ice caps reduces the fraction of solar energy reflected back into space, and so increases the temperature further. Climate change may kill off the Amazon and other rain forests, and so eliminate once one of the main ways in which carbon dioxide is removed from the atmosphere.

The rise in sea temperature may trigger the release of large quantities of carbon dioxide, trapped as hydrides on the ocean floor. Both these phenomena would increase the greenhouse effect, and so global warming further. We have to reverse global warming urgently, if we still can.

Vargas: Natural phenomenon like supervolcanos seem to prove the point that man is still at the mercy of the natural world. Will we ever be able to tame nature?

Hawking: Life on Earth has survived volcanos for 4 billion years. It is not natural forces that are the great threat, but ourselves.