"Hello." "My name is Stephen Hawking, physicist, cosmologist, and something of a dreamer." "Although I cannot move and I have to speak through a computer in my mind, I am free." "Free to explore the universe and ask the big questions such as do aliens exist?" "If so, where could they be found?" "What do they look like?" "What are they made of?" "Are they intelligent?" "And if we met them, what would it mean for human kind?" "Check it out!" "Wherever I go in the world, people ask me, "Do aliens exist?"" "It's a good question because it cuts to the heart of how we see our place in the universe." "Are we alone on our small, round blue ball?" "I think probably not because of one fact." "The universe is big, really big." "Our planet is just one of eight in orbit around our sun" "which itself is hardly special, being one of about 200-billion stars in a vast spiral." "Our galaxy, the Milky Way." "It's so big, some days I find it hard to comprehend." "But even the Milky Way is just a tiny drop in the cosmic ocean... just one of 100-billion galaxies, formed into an enormous web, stretching away in all directions." "At this scale, each point of light is an entire galaxy which not only puts our little world in perspective, but also makes it difficult to believe we really are alone." "So to my mathematical brain, the numbers alone make thinking about aliens perfectly rational." "The real challenge is to try and work out what aliens might actually be like," "living in some far off world." "The possibilities are infinite and infinitely intriguing" "Alien life could range from a simple green slime that doesn't do much but drip to more advanced animals." "something with a bit more bite." "But, of course, that's just the start of what could be out here." "In such a massive universe, it's logical to wonder if there are intelligent beings, perhaps even civilizations like those in science fiction TV shows and movies." "Star Wars and Star Trek, two of my personal favorites, may be closer to reality than we think." "Similar scenarios are at least conceivable." "But think about it more and even this is limiting the options." "There could be life forms so strange we wouldn't even recognize them as life." "Perhaps there are really exotic creatures that live at the center of stars... or even huge communities of microorganisms that look like clouds of cosmic dust." "Maybe aliens live and die so fast that they come and go in the blink of an eye." "So in such a vast universe with so many possibilities, how do we know what to look for, or for that matter, where to look for it?" "The answer is right back where we began" "The information we need is here at home, for the simple reason that home harbors the only known examples of life" "The laws of physics appear to be the same everywhere, so it follows that the laws of life should be universal too, even if the detail is different." "We can use life on Earth as a kind of alien-hunters' handbook a field guide to what life actually is and how it works, no matter where it occurs." "Chapter one, in our particular case, takes us back 4.5 billion years to when the Earth was really quite young." "Exactly what triggered life here is still a mystery, but there are several theories." "The most common one is that life began purely by accident in pools of primordial soup, full of chemicals called amino acids." "These molecules would have collided at random for millions ofyears until the perfect combination just happened," "the ultimate lucky break that started the chain of life." "It is extremely unlikely that life could spontaneously create itself." "But I don't think that's a problem with this theory." "It's like winning a lottery, although the odds are astronomical, most weeks someone hits the jackpot." "But there is another intriguing idea called Panspermia, which says that life could have originated somewhere else and have been spread from planet to planet" "by asteroids." "It seems possible that lumps of rock could carry frozen organisms inside them." "Organisms able to withstand extremes of temperature and the vacuum of space." "If so, asteroids could even now be transporting life to other worlds." "Regardless of which theory is right, once life begins, the next chapter starts and that's all about survival." "Survival links you, me, and ET." "And it generates rules all of its own." "Survival demands a source of energy, what we call food, or else it would grind to a halt." "Once nourished, life can then copy itself to protect against the death of any one individual." "Ultimately, that leads to evolution." "Evolution thatwould happen eeen on alien worlds, producing in some instances animals that I think, we would recognize as being alive even ifthey look a bit strange." "So the next step on our alien hunt is to find a place, or places where organisms might find food and replicate and evolve." "And as far as we know, that requires one thing." "Like most people, I find water both beautiful and fascinating." "But it's also the key to all known forms of life, from bacteria to blue whales." "Find water elsewhere and aliens could exist nearby." "The good news is that water is very common indeed out in space." "Frozen water litters the universe, from tiny, single crystals to icy comets the size of mountains." "But to find liquid water, we need somewhere at the right temperature." "Around every star is a region where it's not too hot or too cold, but just right, like the porridge in the story of Goldilocks and the Three Bears." "Around our sun, there are two planets that lie in this Goldilocks' zone:" "the Earth and Mars... which is why one day I'm sure we'll pay it a visit." "Rbots have been exploring Mars since the '70s, but they have yet to find life" "I don't think we should give up." "Beneath the Martian surface," "NASA's Spirit rover discovered these white salts, which are formed in contact with liquid water." "Satellite images reveal drainage patterns and erosion of the kinds caused by rivers and oceans." "There may well still be moisture under Mars' surface, moisture that perhaps could support life." "I hope one day we will find the money to send men and women to Mars." "It would capture the public's imagination, just as the Apollo moon missions captured mine back in the '60s." "If they found even a few Martian microbes, in my opinion, it will be one of the most exciting discoveries ever made." "But even if Mars is barren, there are other places to look for liquid water." "One ofthem lies a mere 30-million miles from Mars, on a small, mysterious moon that orbits the giant planet Jupiter." "This is Europa." "Europa is tiny, just under 2,000 miles in diameter and it's very cold, minus 260 degrees." "The entire moon is covered in a layer of ice perhaps 15 miles thick." "But Europa may have a hidden heat source beneath the surface." "Europa orbits Jupiter once every 3.6 days in an egg-shaped path." "The gravitational pull from Jupiter changes constantly, stretching then compressing Europa." "This process is like kneading a piece of clay to make it warm and soft." "And the heat produced may be enough to melt the underside ofthe ice sheet, creating a hidden ocean of liquid water, protected from the vacuum of space by the solid ice above." "If so, there could be aliens living here, creatures that have evolved to exploit this dark and ancient water world." "I think it's even reasonable to guess at some oftheir physical features." "Aliens here would probably swim in a similar way to our own ocean life, since liquid water is the same stuff everywhere." "They might use chemicals in their skin to generate their own light as many deep-sea creatures do back homm." "They might even swim in school-like colonies just as aquatic animals do on Earth." "But even if advanced animals do live inside Europa," "I think they're unlikely to be trying to make contact with us anytime soon." "They'd exist cocooned in an icy shell 15 miles thick, so they'd be blissfully unaware of the universe beyond." "To find them, we'd need to send a mission here, which would be even more risky and expensive than visiting Mars." "I hope one day we will discover Europa's secrets." "But before then, it's worth continuing our journey to search for aliens with a wider outlook." "I think we need to leave our solar system and voyage into the vastness that lies beyond." "Stars surround us in the universe." "But until recently, no one knew how many had planets in orbit around them," "let alone if any of those planets could support alien life." "Finding out is tough because stars are big and blindingly bright." "Planets are tiny and dark." "Spotting them requires technology on an enormous scale." "The binocular Keck telescope in Hawaii with its twin 30-feet mirrors is one of the most powerful land-based telescopes ever built." "But even this vast machine can't see distant planets." "Instead, it looks for stars that wobble... the tell-tale sign of an unseen planet in orbit." "A hammer thrower demonstrates the principle." "As he spins, the hammer pulls on his body and he wobbles from side to side." "The same thing happens as a planet swings around its star." "Planets also reeeal themselees ifthey pass between their star and us." "The planet causes regular dimming." "And from the timing, we can even determine if it's inside the star's Goldilocks' zone." "The first distant planet was discovered in 1995." "Since then, hundreds more have been found." "This, I think, is a pretty exciting discovery." "We could be on the verge of a major breakthrough, one that will both redefine ou view of life in the universe and be a real triumph for science itself." "Somewhere out there, pmrhaps not so far away, is a rocky planet a bit like Earth." "A planet with liquid water where life has begun." "Due to the power of evolution, aliens here might be surprisingly familiar even if at first they seem anything but." "Aliens that eat, for example, need an input orifice, or as most people say, a mouth." "Likewise, if they live on a solid surface, they'll probably have legs." "The detail might be different." "But legs are good things to have on land, especially ifthe animal is clinging to the side of a cliff." "If the planet is well-lit, eyes are almost guaranteed." "They let a creature accurately sense its environment." "Even the position of the eyes will follow the same rules as on Earth." "Prey animals tend to have eyes on either side of their head allowing them to look out for predators." "Predators, even alien ones, need forward-facing eyes to accurately judge distance an essential skill when hunting." "Alien struggles of life and death are probably happening right now thanks to the universal power of evolution." "But in my opinion, evolution is so remarkable we can't really be sure of its ultimate limits" "Life forms on Earth-like planets or in hidden oceans are not the only options." "We can go even further into the depths of the universe in search of other kinds of aliens, extraterrestrials that are totally unlike us," "life, but not as we know it." "I like to think of myself as an optimist." "And so in our vast, ancient universe with its countless galaxies, almost any life form that is physically possible is likely to exist somewhere." "So there could be, perhaps should be really bizarre aliens that have followed a different evolutionary path." "Aliens that don't depend on water, but on other chemicals instead." "Nitrogen is one possibility." "It's a gas on Earth." "But it can exist as a liquid when it's very, very cold, minus 320 degrees Fahrenheit." "So is there a world of nitrogen oceans lapping frozen shores, where aliens have evolved in temperatures that would kill a human instantly?" "Life here would need chemistry very different than our own... a cold-weather remix of the ingredients that make us." "Ingredient number one, of course, is water." "The average male holds eight gallons, so let's swap water for liquid nitrogen." "There's also about two pounds of phosphorus, half a pound of salt, enough iron to make a nail, three pounds of lime," "15 trace elements, which might also work in alien biology." "And then this carbon, 45 pounds of it." "But what if carbon was switched with something else, silicon perhaps?" "Silicon has slightly different properties, but it could do the same job." "With the right ingredients, ultra low temperature life might be possible." "If so, I think energy would be scarce, so things around here would move very slowly." "Other possibilities are even stranger." "The astronomers searching for far-off planets have discovered that many seem to be giant gas planets" "like our own Jupiter and Saturn." "Perhaps there are aliens made of gas." "Aliens living here would need to consume something." "I imagine they could use the power of lightning storms that constantly rage on planets like these." "If such extreme life forms are possible, then life elsewhere in the universe could be very common indeed." "There are certainly many more planets that fall outside the Goldilocks' regions of stars than fall inside them." "It suddenly seems like there could be life nearly eeerywhere you look." "But ultimately, I think it doesn't really matter what aliens are made of." "To me, it's what they can do that counts." "Are they thinking about the cosmos too, trying to unlock its secrets just as we are?" "In short, has alien life evolved as we have and developed intelligence?" "If the universe is full of intelligent, space-faring aliens," "I think at least some of them might be interested in us, if only as a curiosity." "Of course, many people believe they are already here." "Tales of alien abduction have been common ever since I was an undergraduate in the 1950s and I watched all those B movies too." "The story always goes the same." "A lone individual on a quiet road at night, happens to take an unscheduled detour and finds himself lost." "I'm always a bit suspicious when I hearthese tales." "Look at it from the aliens' point of eiew." "What's the point of crossing vast tracts of the universe in a high-tech ship just to abduct some lone earthling?" "In my opinion, if aliens are here, I suspect the newspapers would be full of the story." "And if governments are involved in their cover up, they're doing a much better job at it than they seem to do at anything else." "So the lack of alien contact raises a serious scientific problem." "Where is everybody?" "We've been listening to space for over 40 years." "And in all that time, we've picked up nothing." "Well, except for one mysterious occasion." "On August 16, 1977, a radio telescope in Ohio picked up a signal that bmcame famous." "The telescope listened to space by scanning the skies as the Earth rotated." "And just once, it recorded a signal that got everyone excited, the Wow Signal, as it became known." "The signal was a steady source of radio waves, just the kind an alien race might send because it stands out from the radio static that fills the universe." "A computer recorded the signal as six letters and numbers." "Astronomer Jerry Ehman saw the data and wrote one word in the margin." "Ehman and others subsequently searched the same patch of sky many times, but found nothing." "The Wow Signal had vanished." "The whole mysterious episode reveals that making contact with aliens via radio is always going to be difficult." "In such a vast universe, messages take a long time to reach their destination." "The Wow Signal appeared to come from a star system 200 light years away." "So it took at least 200 years to reach us." "If we sent a reply, it would take another 200 years to reach them, by which time they might have forgotten they sent anything and stopped listening for a reply." "Worse, they might well have destroyed themselves in the meantime." "The human race very quickly discovered the power ofthe atom bomb." "If the same holds for intelligent aliens, then they might not last long." "Perhaps they all blow themselves up soon after they discover that E equals MC squared." "If civilizations take billions ofyears to evolve, only to vanish virtually overnight then sadly we've next to no chance of hearing from them." "They are simply too far away in space and time to reach." "But there is one last possibility that aliens who have avoided destroying themselves are already colonizing the universe." "The human race has only two options when it comes to looking for advanced aliens." "We can listen or we can be more active and broadcast our willingness to talk." "We'd have to think very carefully about what we might say." "I think this might be just a little too risky." "We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet." "We humans are already capable of manipulating the course of our own evolution." "Exactly the same, presumably, would be true of advanced extraterrestrials." "Ultimately, they could halt aging and become virtually immortal." "What's more, they might have reached that point millions of years ago." "It might sound unlikely, but if you think about it logically, alien technology should be as extraordinary to us as a rocket ship to a caveman." "I imagine they might exist in massive ships like these, having used up all the resources from the home planet below." "Such advanced aliens would perhaps become nomads," "looking to conquer and colonize whatever planets they can reach." "If so, it makes sense for them to exploit each new planet for materials to build more spaceships, so they could move on." "Who knows what the limits would be?" "Perhaps their capabilities would only be limited by how much power they could harness and control." "And that could be far more than we might first imagine." "For example, it might be possible to collect the energy from an entire star." "To do that, they could deploy millions of mirrors in space, encircling the whole sun, and feeding the power to one single collection point." "Such power might make it possible to warp the very fabric of space and create a portal called a wormholm." "This portal would act like a shortcut allowing them to travel huge distances in the blink of an eye." "Like us, they would probably have evolved from a species used to exploiting whatever it can." "So if aliens ever visit us," "I think the outcome would be much as when Christopher columbus first landed in America... which didn't turn out very well for the Native Americans." "So the journey that started with the search for water has led us to far offworlds which I think could exist." "Worlds where the conditions and chemistry allow life to begin, and then change into many different forms." "Even so, little green men are probably pretty rare." "But in such a massive place as the cosmos, we only have to look at ourselves for proof that extremely unlikely things can and do happen all the time." "Let's just hope that if aliens do find us, they'll come in peace."