Stephen Hawking: "My sense of humour keeps me going"

Has using a speech device changed your personality? Has it allowed you, as an introvert, to be more extroverted? — Chris Cooke

I don’t think I’ve ever been called an introvert before. Just because I do a lot of thinking doesn’t mean I don’t like parties and getting into trouble. I enjoy communicating and giving popular lectures on science. My speech synthesizer is very important for this, even though I’ve ended up with an American accent. Before I lost my voice, my speech was slurred, so only those close to me could understand, but with the computer voice I found I could talk to everyone without help. So it has allowed me to express (rather than change) my personality. I am very grateful to those who developed my computer voice, and
to Intel, who continue to work on improving it.

Will the world will end naturally, or will man destroy it first? — Paul Ost

We face a number of threats: nuclear war, global warming and genetically engineered viruses. Although the chance of a disaster on planet Earth in a given year may be quite low, it adds up over time, becoming a near certainty in the next thousand or ten thousand years. By that time we should have spread out into space, and to other stars, so it would not mean the end of the human race.

However, we will not establish self-sustaining colonies in space for at least the next hundred years, so we have to be very careful in this period. Most of the threats we face come from the progress we’ve made in science and technology. We are not going to stop making progress, or reverse it, so we must recognise the dangers and control them. I’m an optimist, and I believe we can.

The laws of physics say that new energy can’t be created, but something must have created the universe’s energy. Can we call it God? — Basil Philipsz

The positive energy of matter exactly balances its negative gravitational energy. So universes can be created for free, without violation of the law of conservation of energy. I’m not sure what this has to say about God, but it’s an idea with a lot of creative potential.

If you were a Time Lord, what moment in time would interest you, and why? —John Brookmyre

I would like to meet Galileo, the first modern scientist. He pointed out that simple observations, such as dropping weights from a height, show that things do not work in the way that Aristotle said they do. This must have been realised by many people, who put it down to imperfect observations, or other reasons.

But Galileo said the ancients were wrong, and started to work out the correct laws from the observations. That makes him the father
of modern science. I was born exactly 300 years after the death of Galileo, I hold the same job at Cambridge as Newton did, and I work on Einstein’s general theory of relativity.

Of the three, I feel closest to Galileo. He followed his nose, and was a bit of a rebel.

If you had to offer a piece of advice to future of scientists, what would it be? — Tara Struthers

Be curious, and try to make sense of what you see. We live in a universe governed by rational laws that we can discover and understand. Despite recent triumphs, there are many new and deep mysteries that remain for you to solve. And keep a sense of wonder about our vast and complex universe, and what makes it exist.

But you also must remember that science and technology are changing our world dramatically, so it’s important to ensure that these changes are heading in the right directions. In a democratic society, this means that everyone needs to have a basic understanding of science, to make informed decisions about the future.

So communicate plainly what you’re trying to do in science, and who knows, you might even end up understanding it yourself.

Stephen Hawking is delivering this year's Reith Lectures, starting on Tuesday morning at 9:00 am on Radio 4 FM