(Muzika)
On a typical day at school, endless hours are spent learning the answers to questions, but right now, we'll do the opposite. We're going to focus on questions where you can't learn the answers because they're unknown. I used to puzzle about a lot of things as a boy, for example: What would it feel like to be a dog? Do fish feel pain? How about insects? Was the Big Bang just an accident? And is there a God? And if so, how are we so sure that it's a He and not a She? Why do so many innocent people and animals suffer terrible things? Is there really a plan for my life? Is the future yet to be written, or is it already written and we just can't see it? But then, do I have free will? I mean, who am I anyway? Am I just a biological machine? But then, why am I conscious? What is consciousness? Will robots become conscious one day? I mean, I kind of assumed that some day I would be told the answers to all these questions. Someone must know, right? Guess what? No one knows. Most of those questions puzzle me more now than ever. But diving into them is exciting because it takes you to the edge of knowledge, and you never know what you'll find there. So, two questions that no one on Earth knows the answer to. (Music) [How many universes are there?] Sometimes when I'm on a long plane flight, I gaze out at all those mountains and deserts and try to get my head around how vast our Earth is. And then I remember that there's an object we see every day that would literally fit one million Earths inside it: the Sun. It seems impossibly big. But in the great scheme of things, it's a pinprick, one of about 400 billion stars in the Milky Way galaxy, which you can see on a clear night as a pale white mist stretched across the sky. And it gets worse. There are maybe 100 billion galaxies detectable by our telescopes. So if each star was the size of a single grain of sand, just the Milky Way has enough stars to fill a 30-foot by 30-foot stretch of beach three feet deep with sand. And the entire Earth doesn't have enough beaches to represent the stars in the overall universe. Such a beach would continue for literally hundreds of millions of miles. Holy Stephen Hawking, that is a lot of stars. But he and other physicists now believe in a reality that is unimaginably bigger still. I mean, first of all, the 100 billion galaxies within range of our telescopes are probably a minuscule fraction of the total. Space itself is expanding at an accelerating pace. The vast majority of the galaxies are separating from us so fast that light from them may never reach us. Still, our physical reality here on Earth is intimately connected to those distant, invisible galaxies. We can think of them as part of our universe. They make up a single, giant edifice obeying the same physical laws and all made from the same types of atoms, electrons, protons, quarks, neutrinos, that make up you and me. However, recent theories in physics, including one called string theory, are now telling us there could be countless other universes built on different types of particles, with different properties, obeying different laws. Most of these universes could never support life, and might flash in and out of existence in a nanosecond. But nonetheless, combined, they make up a vast multiverse of possible universes in up to 11 dimensions, featuring wonders beyond our wildest imagination. The leading version of string theory predicts a multiverse made up of 10 to the 500 universes. That's a one followed by 500 zeros, a number so vast that if every atom in our observable universe had its own universe, and all of the atoms in all those universes each had their own universe, and you repeated that for two more cycles, you'd still be at a tiny fraction of the total, namely, one trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillionth. (Laughter) But even that number is minuscule compared to another number: infinity. Some physicists think the space-time continuum is literally infinite and that it contains an infinite number of so-called pocket universes with varying properties. How's your brain doing? Quantum theory adds a whole new wrinkle. I mean, the theory's been proven true beyond all doubt, but interpreting it is baffling, and some physicists think you can only un-baffle it if you imagine that huge numbers of parallel universes are being spawned every moment, and many of these universes would actually be very like the world we're in, would include multiple copies of you. In one such universe, you'd graduate with honors and marry the person of your dreams, and in another, not so much. Well, there are still some scientists who would say, hogwash. The only meaningful answer to the question of how many universes there are is one. Only one universe. And a few philosophers and mystics might argue that even our own universe is an illusion. So, as you can see, right now there is no agreement on this question, not even close. All we know is the answer is somewhere between zero and infinity. Well, I guess we know one other thing. This is a pretty cool time to be studying physics. We just might be undergoing the biggest paradigm shift in knowledge that humanity has ever seen. (Music) [Why can't we see evidence of alien life?] Somewhere out there in that vast universe there must surely be countless other planets teeming with life. But why don't we see any evidence of it? Well, this is the famous question asked by Enrico Fermi in 1950: Where is everybody? Conspiracy theorists claim that UFOs are visiting all the time and the reports are just being covered up, but honestly, they aren't very convincing. But that leaves a real riddle. In the past year, the Kepler space observatory has found hundreds of planets just around nearby stars. And if you extrapolate that data, it looks like there could be half a trillion planets just in our own galaxy. If any one in 10,000 has conditions that might support a form of life, that's still 50 million possible life-harboring planets right here in the Milky Way. So here's the riddle: our Earth didn't form until about nine billion years after the Big Bang. Countless other planets in our galaxy should have formed earlier, and given life a chance to get underway billions, or certainly many millions of years earlier than happened on Earth. If just a few of them had spawned intelligent life and started creating technologies, those technologies would have had millions of years to grow in complexity and power. On Earth, we've seen how dramatically technology can accelerate in just 100 years. In millions of years, an intelligent alien civilization could easily have spread out across the galaxy, perhaps creating giant energy-harvesting artifacts or fleets of colonizing spaceships or glorious works of art that fill the night sky. At the very least, you'd think they'd be revealing their presence, deliberately or otherwise, through electromagnetic signals of one kind or another. And yet we see no convincing evidence of any of it. Why? Well, there are numerous possible answers, some of them quite dark. Maybe a single, superintelligent civilization has indeed taken over the galaxy and has imposed strict radio silence because it's paranoid of any potential competitors. It's just sitting there ready to obliterate anything that becomes a threat. Or maybe they're not that intelligent, or perhaps the evolution of an intelligence capable of creating sophisticated technology is far rarer than we've assumed. After all, it's only happened once on Earth in four billion years. Maybe even that was incredibly lucky. Maybe we are the first such civilization in our galaxy. Or, perhaps civilization carries with it the seeds of its own destruction through the inability to control the technologies it creates. But there are numerous more hopeful answers. For a start, we're not looking that hard, and we're spending a pitiful amount of money on it. Only a tiny fraction of the stars in our galaxy have really been looked at closely for signs of interesting signals. And perhaps we're not looking the right way. Maybe as civilizations develop, they quickly discover communication technologies far more sophisticated and useful than electromagnetic waves. Maybe all the action takes place inside the mysterious recently discovered dark matter, or dark energy, that appear to account for most of the universe's mass. Or, maybe we're looking at the wrong scale. Perhaps intelligent civilizations come to realize that life is ultimately just complex patterns of information interacting with each other in a beautiful way, and that that can happen more efficiently at a small scale. So, just as on Earth, clunky stereo systems have shrunk to beautiful, tiny iPods, maybe intelligent life itself, in order to reduce its footprint on the environment, has turned itself microscopic. So the Solar System might be teeming with aliens, and we're just not noticing them. Maybe the very ideas in our heads are a form of alien life. Well, okay, that's a crazy thought. The aliens made me say it. But it is cool that ideas do seem to have a life all of their own and that they outlive their creators. Maybe biological life is just a passing phase. Well, within the next 15 years, we could start seeing real spectroscopic information from promising nearby planets that will reveal just how life-friendly they might be. And meanwhile, SETI, the Search for Extraterrestrial Intelligence, is now releasing its data to the public so that millions of citizen scientists, maybe including you, can bring the power of the crowd to join the search. And here on Earth, amazing experiments are being done to try to create life from scratch, life that might be very different from the DNA forms we know. All of this will help us understand whether the universe is teeming with life or whether, indeed, it's just us. Either answer, in its own way, is awe-inspiring, because even if we are alone, the fact that we think and dream and ask these questions might yet turn out to be one of the most important facts about the universe. And I have one more piece of good news for you. The quest for knowledge and understanding never gets dull. It doesn't. It's actually the opposite. The more you know, the more amazing the world seems. And it's the crazy possibilities, the unanswered questions, that pull us forward. So stay curious.
Uobičajenim danima u školi, provode se beskonačni sati u učenju odgovora na pitanja, ali sada ćemo uraditi suprotno. Fokusiraćemo se na pitanja za koja ne možete da naučite odgovore, jer oni ne postoje. Kad sam bio dečak, zbunjivalo me je mnogo stvari. Na primer: kako to izgleda biti pas? Da li ribe osećaju bol? A insekti? Da li je Veliki prasak samo slučajnost? Da li postoji Bog? I ako postoji, kako smo sigurni da je "on", a ne "ona"? Zašto toliko nevinih ljudi i životinja trpi užasne patnje? Da li je moj život deo nekog plana? Da li budućnost tek treba da bude napisana ili je već napisana, samo je ne vidimo? Ali onda, da li ja imam slobodnu volju? Ko sam, uopšte, ja? Da li sam samo biološka mašina? Zašto onda imam svest? Šta je svest? Da li će roboti jednog dana postati svesni? Pretpostavljao sam da će mi jednog dana reći odgovore na sva ova pitanja. Neko mora da ih zna, zar ne? Znate šta? Ne zna ih niko. Većina ovih stvari me sada zbunjuje više nego ikad. Ali, uroniti u njih je uzbudljivo jer vas vode na ivicu znanja i nikad ne znate šta ćete tamo naći. Evo dva pitanja - pitanja na koja niko na Zemlji ne zna odgovor. (Muzika) Koliko svemira postoji? Ponekad kad sam na dugom putu avionom, gledam kroz prozor sve te planine i pustinje i pokušavam da shvatim koliko je ogromna naša Zemlja. I onda se setim da postoji objekat koji viđamo svakog dana, unutar koga bi stalo milion Zemlji: Sunce. Ono izgleda neverovatno veliko. Ali u velikoj šemi stvari, ono je tačkica, jedna od oko 400 milijardi zvezda u galaksiji Mlečni put koju možete videti u vedroj noći kao beličastu maglu koja se proteže nebom. I postaje još gore. Postoji možda 100 milijardi galaksija koje mogu da se otkriju našim teleskopima. Tako da, ako bi svaka zvezda bila veličine zrna peska, samo Mlečni put bi imao dovoljno zvezda da se ispuni komad plaže veličine 10x10 metara peskom dubine od jednog metra. A cela Zemlja nema dovoljno plaža da se predstave zvezde iz celog svemira. Takva plaža bi se protezala bukvalno stotinama miliona kilometara. Stivena mu Hokinga, to je mnogo zvezda. Ali, on i drugi fizičari danas veruju u stvarnost nezamislivo veću od toga. Kao prvo, 100 milijardi galaksija u dometu naših teleskopa su verovatno majušni deo od ukupnog broja. Sam svemir se širi ubrzanim tempom. Ogromna većina galaksija udaljava se od nas tako brzo da svetlost sa nijh možda nikad neće stići do nas. Pa ipak, naša fizička realnost ovde na Zemlji je u bliskoj vezi sa tim udaljenim, nevidljivim galaksijama. Možemo misliti o njima kao o delu našeg svemira. One čine jednu ogromnu građevinu, pokoravaju se istim fizičkim zakonima i napravljene su od istih atoma - elektrona, protona, kvarkova, neutrina - od kojih smo sačinjeni i vi i ja. Ali, nedavne teorije u fizici, uključujući i teoriju struna, govore nam da bi moglo postojati bezbroj drugih svemira sačinjenih od drugih vrsta čestica sa drugačijim osobinama i koje se podvrgavaju drugim zakonima. Većina ovih svemira ne bi nikada mogli da podrže život i mogli bi da se pojave i nestanu u jednoj nanosekundi. Ali bez obzira na to, u kombinaciji čine ogroman multiverzum mogućih svemira do u 11 dimenzija i sadrže čuda koja nadmašuju našu najluđu maštu. Vodeća verzija teorije struna predviđa multiverzum sačinjen od 10 na 500-ti svemira. To je jedinica sa 500 nula, broj tako ogroman da ako bi svaki atom u našem vidljivom svemiru, imao svoj sopstveni svemir i svi ostali atomi u svim tim svemirima, imali svoj svemir i kad biste to ponovili još dva kruga, još uvek biste imali mali deo od ukupnog broja, odnosno milijardu milijardi milijardi milijardi milijardi milijardi milijardi milijardi milijardi milijardi milijardi milijardi milijardi milijardi triliona. Ali čak i taj broj je majušan u poređenju sa drugim brojem: večnošću. Neki fizičari misle da je prostor-vreme kontinuum bukvalno beskonačan i da sadrži beskonačan broj takozvanih džepnih univerzuma sa osobinama koje variraju. Kako vam je mozak? Kvantna teorija dodaje novu začkoljicu. Mislim, teorija je potvrđena bez sumnje, ali njena interpretacija je zbunjujuća i neki fizičari misle da možete da je odgonetnete jedino ako zamislite taj ogromni broj paralelnih univerzuma kako se množe u svakom trenutku i svaki od njih bi bio kao svet u kome se nalazimo sa višestrukim kopijama vas. U jednom od tih univerzuma biste diplomirali i oženili se osobom svojih snova, a u drugom ne bi bilo tako. A ima i drugih naučnika koji bi rekli: besmislica. Jedini smislen odgovor na pitanje koliko ima univerzuma je jedan. Samo jedan univerzum. A nekoliko filozofa i mistika bi reklo da je čak i naš univerzum iluzija. Tako da, kao što vidite, ne postoji slaganje kod ovog pitanja, čak ni blizu. Sve što znamo je da je odgovor negde između nule i beskonačnosti. Pa, pretpostavljam da znamo još jednu stvar. Da je ovo super vreme da se studira fizika. Možda upravo prolazimo kroz najveću promenu paradigme u znanju koju je čovečanstvo ikada videlo. (Muzika) Negde u tom ogromnom svemiru mora da postoje bezbrojne druge planete koje bujaju životom. Ali zašto mi ne vidimo dokaze za to? Ovo je čuveno pitanje Enrikea Fermija iz 1950: Gde su svi? Teoretičari zavere tvrde da nas vanzemaljci stalno posećuju i da se izveštaji samo zataškavaju, ali iskreno, ovo nije veoma uverljivo. Ali to ostavlja pravu zagonetku. U toku prošle godine, u svemirskoj opservatoriji Kepler pronašli su stotine planeta, samo oko okolnih zvezda. Ako izvedemo vrednosti za te podatke, čini se kao da može da postoji pola triliona planeta samo u našoj galaksiji. Ako bilo koja u 10 000 ima uslove koji mogu da podrže neki oblik života, to je još uvek mogućih 50 miliona planeta koje imaju živi svet blizu nas na Mlečnom putu. Evo zagonetke: naša Zemlja se nije stvorila sve do oko 9 milijardi godina nakon Velikog praska. Nebrojene druge planete u našoj galaksiji bi trebalo da su se formirale ranije i dale priliku da se razvije život milijardama, ili svakako brojnim milionima godina pre nego što se to desilo na Zemlji. Ako je samo nekoliko od njih stvorilo inteligentne oblike života i počelo da stvara tehnologije, te tehnologije bi imale milione godina da postanu kompleksne i moćne. Na Zemlji, videli smo koliko dramatično tehnologija može da se ubrza za samo 100 godina. Tokom miliona godina, inteligentna vanzemaljska civilizacija je veoma lako mogla da se raširi galaksijom, stvarajući možda ogromne artefakte za stvaranje energije ili flote svemirskih brodova za kolonizaciju ili veličanstvena umetnička dela koja ispunjavaju noćno nebo. U najmanju ruku pomislili biste da bi oni otkrili svoje prisustvo, namerno ili ne, kroz elektromagnetne signale ili nešto slično. Ipak, ne vidimo nikakve ubedljive dokaze za ovo. Zašto? Pa, postoje brojni mogući odgovori, a neki od njih su prilično zloslutni. Možda je jedna ultrainteligentna civilizacija zaista osvojila galaksiju i naredila strogu radijsku tišinu zato što se boji potencijalnih suparnika. Samo sedi tamo, sprema da uništi bilo šta što joj postane pretnja. Ili možda nisu toliko inteligentni, ili je možda razvitak inteligentnih bića sposobnih da stvore sofisticiranu tehnologiju dosta ređi nego što smo pretpostavljali. Uostalom, to se desilo samo jednom na Zemlji za četiri milijarde godina. Možda je i to bila puka slučajnost. Možda smo mi prva takva civilizacija u našoj galaksiji. Ili civilizacija možda sa sobom nosi seme sopstvenog uništenja kroz nesposobnost da kontroliše tehnologije koje stvara. Ali postoje drugi brojni odgovori koji nose nadu. Za početak, ne tražimo baš detaljno, i trošimo mizerne sume novca na to. Samo delić zvezda u našoj galaksiji je detaljno proučeno i pretraženo za znakove ili zanimljive signale. Možda ne gledamo na pravi način. Kako se civilizacije razvijaju, možda brzo otkrivaju tehnologije komunikacije daleko sofisticiranije i korisnije od elektromagnetnih talasa. Možda se sva radnja dešava u misterioznoj tamnoj materiji koja je nedavno otkrivena, ili tamnoj energiji, koje, čine se zauzimaju većinu mase univerzuma. Ili možda gledamo na pogrešnoj skali. Možda inteligentne civilizacije shvate da život na kraju čine samo kompleksni šabloni informacija koji međusobno deluju na predivan način, a to može biti efikasnije na manjem obimu. Isto kao što su se na Zemlji kabasti ogromni radio uređaji smanjili do predivnih, malih ajpoda, možda je i sam inteligentni život postao mikroskopski, kako bi smanjio svoj uticaj na okolinu. Sunčev sistem možda vrvi od vanzemaljaca, ali ih mi prosto ne primećujemo. Možda su same ideje u našim glavama oblik vanzemaljskog života. U redu, to je luda zamisao. Vanzemaljci su me naterali da kažem to. Ali super je to što ideje kao da imaju svoj život i nadživljavaju svoje tvorce. Možda je biološki život samo prolazna faza. Pa, u sledećih 15 godina bismo mogli da počnemo da viđamo prave spektroskopske informacije od obećavajućih planeta u blizini, koje će otkriti koliko su naklone životu. U međuvremenu, SETI, Potraga za vanzemaljskom inteligencijom, sada javno objavljuje podatke tako da milioni građana-naučnika, uključujući možda i vas, mogu da doprinesu moći masa i pridruže se potrazi. A ovde na Zemlji se vrše neverovatni eksperimenti u pokušaju da se stvori život ni iz čega, život koji bi mogao da bude veoma drugačiji od DNK koju poznajemo. Sve ovo će nam pomoći da razumemo da li univerzum buja od života ili smo tu zaista samo mi. Oba odgovora ulivaju strahopoštovanje na svoj način, jer čak i ako smo sami, činjenica da mislimo i sanjamo i postavljamo ova pitanja se može ispostaviti kao jedna od najbitnijih činjenica o univerzumu. Imam još jednu dobru vest za vas. Potraga za znanjem i razumevanjem nikada ne posustaje. Nikada. Zapravo je suprotno. Što više znate, svet se čini neverovatnijim. Te lude mogućnosti i pitanja bez odgovora su ono što nas gura napred. Stoga ostanite radoznali.