To mark his 70th birthday, physicist Professor Stephen Hawking answered a selection of questions from listeners to Radio 4's Today Programme.
ORIGINS OF THE UNIVERSE
1. Was there a "time" when there was "nothing"? - Roland, Lagos
The origin of the universe can be explained by the laws of physics, without any need for miracles or Divine intervention.
These laws predict that the universe was spontaneously created out of nothing in a rapidly expanding state.
This is called inflation because it is like the way prices in the shops go up at an ever increasing rate.
Time is defined only with the universe, so it makes no sense to talk about time before the universe began, it would be like asking for a point south of the South Pole.
FASTER THAN LIGHT?
2. What will be the impact on Einstein's theory of relativity if the neutrino is confirmed to be able to travel faster than the speed of light? - David Pointon, Maidstone
 | WHAT IS OPERA EXPERIMENT? Oscillation Project with Emulsion-Racking Apparatus Collaboration between Cern in Switzerland and Italy's Laboratori Nazionali del Gran Sasso (LNGS) Measures neutrino time-of-flight between Cern and LNGS |
Einstein's theory of relativity predicts that nothing can travel faster than light.
Thus if the Opera experiment is correct and neutrinos do travel faster than light, then relativity theory is wrong.
However, I don't believe the Opera results, because they disagree with the detection of neutrinos from supernova SN1987A.
MULTIPLE UNIVERSES?
3. Some people hypothesise that what we call the universe may only be one of many. Is there any conceivable way that we could ever detect and study other universes if they exist? Is it even falsifiable? - Toby North, Essex
Our best bet for a theory of everything is M-theory [an extension of string theory].
One prediction of M-theory is that there are many different universes, with different values for the physical constants.
This might explain why the physical constants we measure seem fine-tuned to the values required for life to exist.
It is no surprise that we observe the physical constants to be finely-tuned.
If they weren't, we wouldn't be here to observe them.
One way of testing this would be to look for features in the cosmic microwave background radiation which would indicate the collision of another universe with ours in the distant past.
COLONISING SPACE
4. Do you think the human race will survive all potential disasters and eventually colonise the stars?- Matt Dotchon, Cardiff
It is possible that the human race could become extinct, but it is not inevitable.
I think it is almost certain that a disaster such as nuclear war or global warming will befall the Earth within a thousand years.
It is essential that we colonize space.
I believe that we will eventually establish self-sustaining colonies on Mars and other bodies in the Solar System although probably not within the next 100 years.
I am optimistic that progress in science and technology will eventually enable humans to spread beyond the Solar System and out into the far reaches of the Universe.
ALIEN CONTACT
5. What do you think the impact will be on humankind if Kepler 22-b [Earth-like planet found by Nasa's Kepler Space Telescope] does indeed support life?- CazCarpSnail via Twitter
The discovery of intelligent life elsewhere in the Universe would be the biggest scientific discovery ever.
But it would be very risky to attempt to communicate with an alien civilization.
If aliens decided to visit us then the outcome might be similar to when Europeans arrived in the Americas.
That did not turn out well for the Native Americans.
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