×

Usamos cookies para ayudar a mejorar LingQ. Al visitar este sitio, aceptas nuestras politicas de cookie.


image

TED Talks Worth Sharing, Brian Greene: Is our universe the only universe?

Brian Greene: Is our universe the only universe?

A few months ago the Nobel Prize in physics was awarded to two teams of astronomers for a discovery that has been hailed as one of the most important astronomical observations ever. And today, after briefly describing what they found, I'm going to tell you about a highly controversial framework for explaining their discovery, namely the possibility that way beyond the Earth, the Milky Way and other distant galaxies, we may find that our universe is not the only universe, but is instead part of a vast complex of universes that we call the multiverse.

Now the idea of a multiverse is a strange one. I mean, most of us were raised to believe that the word "universe" means everything. And I say most of us with forethought, as my four-year-old daughter has heard me speak of these ideas since she was born. And last year I was holding her and I said, "Sophia, I love you more than anything in the universe." And she turned to me and said, "Daddy, universe or multiverse?" (Laughter)

But barring such an anomalous upbringing, it is strange to imagine other realms separate from ours, most with fundamentally different features, that would rightly be called universes of their own. And yet, speculative though the idea surely is, I aim to convince you that there's reason for taking it seriously, as it just might be right. I'm going to tell the story of the multiverse in three parts. In part one, I'm going to describe those Nobel Prize-winning results and to highlight a profound mystery which those results revealed. In part two, I'll offer a solution to that mystery. It's based on an approach called string theory, and that's where the idea of the multiverse will come into the story. Finally, in part three, I'm going to describe a cosmological theory called inflation, which will pull all the pieces of the story together.

Okay, part one starts back in 1929 when the great astronomer Edwin Hubble realized that the distant galaxies were all rushing away from us, establishing that space itself is stretching, it's expanding. Now this was revolutionary. The prevailing wisdom was that on the largest of scales the universe was static. But even so, there was one thing that everyone was certain of: The expansion must be slowing down. That, much as the gravitational pull of the Earth slows the ascent of an apple tossed upward, the gravitational pull of each galaxy on every other must be slowing the expansion of space.

Now let's fast-forward to the 1990s when those two teams of astronomers I mentioned at the outset were inspired by this reasoning to measure the rate at which the expansion has been slowing. And they did this by painstaking observations of numerous distant galaxies, allowing them to chart how the expansion rate has changed over time. Here's the surprise: They found that the expansion is not slowing down. Instead they found that it's speeding up, going faster and faster. That's like tossing an apple upward and it goes up faster and faster. Now if you saw an apple do that, you'd want to know why. What's pushing on it?

Similarly, the astronomers' results are surely well-deserving of the Nobel Prize, but they raised an analogous question. What force is driving all galaxies to rush away from every other at an ever-quickening speed? Well the most promising answer comes from an old idea of Einstein's. You see, we are all used to gravity being a force that does one thing, pulls objects together. But in Einstein's theory of gravity, his general theory of relativity, gravity can also push things apart.

How? Well according to Einstein's math, if space is uniformly filled with an invisible energy, sort of like a uniform, invisible mist, then the gravity generated by that mist would be repulsive, repulsive gravity, which is just what we need to explain the observations. Because the repulsive gravity of an invisible energy in space -- we now call it dark energy, but I've made it smokey white here so you can see it -- its repulsive gravity would cause each galaxy to push against every other, driving expansion to speed up, not slow down. And this explanation represents great progress.

But I promised you a mystery here in part one. Here it is. When the astronomers worked out how much of this dark energy must be infusing space to account for the cosmic speed up, look at what they found. This number is small. Expressed in the relevant unit, it is spectacularly small. And the mystery is to explain this peculiar number. We want this number to emerge from the laws of physics, but so far no one has found a way to do that.

Now you might wonder, should you care? Maybe explaining this number is just a technical issue, a technical detail of interest to experts, but of no relevance to anybody else. Well it surely is a technical detail, but some details really matter. Some details provide windows into uncharted realms of reality, and this peculiar number may be doing just that, as the only approach that's so far made headway to explain it invokes the possibility of other universes -- an idea that naturally emerges from string theory, which takes me to part two: string theory.

So hold the mystery of the dark energy in the back of your mind as I now go on to tell you three key things about string theory. First off, what is it? Well it's an approach to realize Einstein's dream of a unified theory of physics, a single overarching framework that would be able to describe all the forces at work in the universe. And the central idea of string theory is quite straightforward. It says that if you examine any piece of matter ever more finely, at first you'll find molecules and then you'll find atoms and subatomic particles. But the theory says that if you could probe smaller, much smaller than we can with existing technology, you'd find something else inside these particles -- a little tiny vibrating filament of energy, a little tiny vibrating string. And just like the strings on a violin, they can vibrate in different patterns producing different musical notes. These little fundamental strings, when they vibrate in different patterns, they produce different kinds of particles -- so electrons, quarks, neutrinos, photons, all other particles would be united into a single framework, as they would all arise from vibrating strings. It's a compelling picture, a kind of cosmic symphony, where all the richness that we see in the world around us emerges from the music that these little, tiny strings can play.

But there's a cost to this elegant unification, because years of research have shown that the math of string theory doesn't quite work. It has internal inconsistencies, unless we allow for something wholly unfamiliar -- extra dimensions of space. That is, we all know about the usual three dimensions of space. And you can think about those as height, width and depth. But string theory says that, on fantastically small scales, there are additional dimensions crumpled to a tiny size so small that we have not detected them. But even though the dimensions are hidden, they would have an impact on things that we can observe because the shape of the extra dimensions constrains how the strings can vibrate. And in string theory, vibration determines everything. So particle masses, the strengths of forces, and most importantly, the amount of dark energy would be determined by the shape of the extra dimensions. So if we knew the shape of the extra dimensions, we should be able to calculate these features, calculate the amount of dark energy.

The challenge is we don't know the shape of the extra dimensions. All we have is a list of candidate shapes allowed by the math. Now when these ideas were first developed, there were only about five different candidate shapes, so you can imagine analyzing them one-by-one to determine if any yield the physical features we observe. But over time the list grew as researchers found other candidate shapes. From five, the number grew into the hundreds and then the thousands -- A large, but still manageable, collection to analyze, since after all, graduate students need something to do. But then the list continued to grow into the millions and the billions, until today. The list of candidate shapes has soared to about 10 to the 500.

So, what to do? Well some researchers lost heart, concluding that was so many candidate shapes for the extra dimensions, each giving rise to different physical features, string theory would never make definitive, testable predictions. But others turned this issue on its head, taking us to the possibility of a multiverse. Here's the idea. Maybe each of these shapes is on an equal footing with every other. Each is as real as every other, in the sense that there are many universes, each with a different shape, for the extra dimensions. And this radical proposal has a profound impact on this mystery: the amount of dark energy revealed by the Nobel Prize-winning results.

Because you see, if there are other universes, and if those universes each have, say, a different shape for the extra dimensions, then the physical features of each universe will be different, and in particular, the amount of dark energy in each universe will be different. Which means that the mystery of explaining the amount of dark energy we've now measured would take on a wholly different character. In this context, the laws of physics can't explain one number for the dark energy because there isn't just one number, there are many numbers. Which means we have been asking the wrong question. It's that the right question to ask is, why do we humans find ourselves in a universe with a particular amount of dark energy we've measured instead of any of the other possibilities that are out there?

And that's a question on which we can make headway. Because those universes that have much more dark energy than ours, whenever matter tries to clump into galaxies, the repulsive push of the dark energy is so strong that it blows the clump apart and galaxies don't form. And in those universes that have much less dark energy, well they collapse back on themselves so quickly that, again, galaxies don't form. And without galaxies, there are no stars, no planets and no chance for our form of life to exist in those other universes.

So we find ourselves in a universe with the particular amount of dark energy we've measured simply because our universe has conditions hospitable to our form of life. And that would be that. Mystery solved, multiverse found. Now some find this explanation unsatisfying. We're used to physics giving us definitive explanations for the features we observe. But the point is, if the feature you're observing can and does take on a wide variety of different values across the wider landscape of reality, then thinking one explanation for a particular value is simply misguided.

An early example comes from the great astronomer Johannes Kepler who was obsessed with understanding a different number -- why the Sun is 93 million miles away from the Earth. And he worked for decades trying to explain this number, but he never succeeded, and we know why. Kepler was asking the wrong question.

We now know that there are many planets at a wide variety of different distances from their host stars. So hoping that the laws of physics will explain one particular number, 93 million miles, well that is simply wrongheaded. Instead the right question to ask is, why do we humans find ourselves on a planet at this particular distance, instead of any of the other possibilities? And again, that's a question we can answer. Those planets which are much closer to a star like the Sun would be so hot that our form of life wouldn't exist. And those planets that are much farther away from the star, well they're so cold that, again, our form of life would not take hold. So we find ourselves on a planet at this particular distance simply because it yields conditions vital to our form of life. And when it comes to planets and their distances, this clearly is the right kind of reasoning. The point is, when it comes to universes and the dark energy that they contain, it may also be the right kind of reasoning.

One key difference, of course, is we know that there are other planets out there, but so far I've only speculated on the possibility that there might be other universes. So to pull it all together, we need a mechanism that can actually generate other universes. And that takes me to my final part, part three. Because such a mechanism has been found by cosmologists trying to understand the Big Bang. You see, when we speak of the Big Bang, we often have an image of a kind of cosmic explosion that created our universe and set space rushing outward.

But there's a little secret. The Big Bang leaves out something pretty important, the Bang. It tells us how the universe evolved after the Bang, but gives us no insight into what would have powered the Bang itself. And this gap was finally filled by an enhanced version of the Big Bang theory. It's called inflationary cosmology, which identified a particular kind of fuel that would naturally generate an outward rush of space. The fuel is based on something called a quantum field, but the only detail that matters for us is that this fuel proves to be so efficient that it's virtually impossible to use it all up, which means in the inflationary theory, the Big Bang giving rise to our universe is likely not a one-time event. Instead the fuel not only generated our Big Bang, but it would also generate countless other Big Bangs, each giving rise to its own separate universe with our universe becoming but one bubble in a grand cosmic bubble bath of universes.

And now, when we meld this with string theory, here's the picture we're led to. Each of these universes has extra dimensions. The extra dimensions take on a wide variety of different shapes. The different shapes yield different physical features. And we find ourselves in one universe instead of another simply because it's only in our universe that the physical features, like the amount of dark energy, are right for our form of life to take hold. And this is the compelling but highly controversial picture of the wider cosmos that cutting-edge observation and theory have now led us to seriously consider.

One big remaining question, of course, is, could we ever confirm the existence of other universes? Well let me describe one way that might one day happen. The inflationary theory already has strong observational support. Because the theory predicts that the Big Bang would have been so intense that as space rapidly expanded, tiny quantum jitters from the micro world would have been stretched out to the macro world, yielding a distinctive fingerprint, a pattern of slightly hotter spots and slightly colder spots, across space, which powerful telescopes have now observed. Going further, if there are other universes, the theory predicts that every so often those universes can collide. And if our universe got hit by another, that collision would generate an additional subtle pattern of temperature variations across space that we might one day be able to detect. And so exotic as this picture is, it may one day be grounded in observations, establishing the existence of other universes.

I'll conclude with a striking implication of all these ideas for the very far future. You see, we learned that our universe is not static, that space is expanding, that that expansion is speeding up and that there might be other universes all by carefully examining faint pinpoints of starlight coming to us from distant galaxies. But because the expansion is speeding up, in the very far future, those galaxies will rush away so far and so fast that we won't be able to see them -- not because of technological limitations, but because of the laws of physics. The light those galaxies emit, even traveling at the fastest speed, the speed of light, will not be able to overcome the ever-widening gulf between us. So astronomers in the far future looking out into deep space will see nothing but an endless stretch of static, inky, black stillness. And they will conclude that the universe is static and unchanging and populated by a single central oasis of matter that they inhabit -- a picture of the cosmos that we definitively know to be wrong.

Now maybe those future astronomers will have records handed down from an earlier era, like ours, attesting to an expanding cosmos teeming with galaxies. But would those future astronomers believe such ancient knowledge? Or would they believe in the black, static empty universe that their own state-of-the-art observations reveal? I suspect the latter. Which means that we are living through a remarkably privileged era when certain deep truths about the cosmos are still within reach of the human spirit of exploration. It appears that it may not always be that way. Because today's astronomers, by turning powerful telescopes to the sky, have captured a handful of starkly informative photons -- a kind of cosmic telegram billions of years in transit. and the message echoing across the ages is clear. Sometimes nature guards her secrets with the unbreakable grip of physical law. Sometimes the true nature of reality beckons from just beyond the horizon.

Thank you very much.

(Applause)

Chris Anderson: Brian, thank you. The range of ideas you've just spoken about are dizzying, exhilarating, incredible. How do you think of where cosmology is now, in a sort of historical side? Are we in the middle of something unusual historically in your opinion?

BG: Well it's hard to say. When we learn that astronomers of the far future may not have enough information to figure things out, the natural question is, maybe we're already in that position and certain deep, critical features of the universe already have escaped our ability to understand because of how cosmology evolves. So from that perspective, maybe we will always be asking questions and never be able to fully answer them.

On the other hand, we now can understand how old the universe is. We can understand how to understand the data from the microwave background radiation that was set down 13.72 billion years ago -- and yet, we can do calculations today to predict how it will look and it matches. Holy cow! That's just amazing. So on the one hand, it's just incredible where we've gotten, but who knows what sort of blocks we may find in the future.

CA: You're going to be around for the next few days. Maybe some of these conversations can continue. Thank you. Thank you, Brian. (BG: My pleasure.)

Brian Greene: Is our universe the only universe? Brian Greene: Ist unser Universum das einzige Universum? Brian Greene: ¿Es nuestro universo el único universo? Brian Greene : Notre univers est-il le seul univers ? Brian Greene: Il nostro universo è l'unico universo? ブライアン・グリーン:我々の宇宙は唯一の宇宙なのか? 브라이언 그린: 우리 우주가 유일한 우주인가요? Brian Greene: O nosso universo é o único universo? Брайан Грин: Является ли наша Вселенная единственной Вселенной? Brian Greene: Bizim evrenimiz tek evren mi? Брайан Грін: Чи є наш всесвіт єдиним всесвітом? 布莱恩-格林:我们的宇宙是唯一的宇宙吗? 布萊恩·格林:我們的宇宙是唯一的宇宙嗎?

A few months ago the Nobel Prize in physics was awarded to two teams of astronomers for a discovery that has been hailed as one of the most important astronomical observations ever. Pochi mesi fa il premio Nobel per la fisica è stato assegnato a due team di astronomi per una scoperta che è stata salutata come una delle osservazioni astronomiche più importanti di sempre. Birkaç ay önce, fizikteki Nobel Ödülü, şimdiye kadarki en önemli astronomik gözlemlerden biri olarak kabul edilen bir keşif için iki gökbilim takımına verildi. And today, after briefly describing what they found, I’m going to tell you about a highly controversial framework for explaining their discovery, namely the possibility that way beyond the Earth, the Milky Way and other distant galaxies, we may find that our universe is not the only universe, but is instead part of a vast complex of universes that we call the multiverse. E oggi, dopo aver descritto brevemente ciò che hanno scoperto, vi parlerò di un quadro molto controverso per spiegare la loro scoperta, vale a dire la possibilità che ben oltre la Terra, la Via Lattea e altre galassie lontane, potremmo scoprire che il nostro universo non è l'unico universo, ma fa invece parte di un vasto complesso di universi che chiamiamo multiverso.

Now the idea of a multiverse is a strange one. L'idea di un multiverso è strana. I mean, most of us were raised to believe that the word "universe" means everything. And I say most of us with forethought, as my four-year-old daughter has heard me speak of these ideas since she was born. E dico la maggior parte di noi con premura, poiché mia figlia di quattro anni mi ha sentito parlare di queste idee da quando è nata. And last year I was holding her and I said, "Sophia, I love you more than anything in the universe." And she turned to me and said, "Daddy, universe or multiverse?" (Laughter) (Risata)

But barring such an anomalous upbringing, it is strange to imagine other realms separate from ours, most with fundamentally different features, that would rightly be called universes of their own. Ma a parte un'educazione così anomala, è strano immaginare altri regni separati dal nostro, la maggior parte con caratteristiche fondamentalmente diverse, che sarebbero giustamente chiamati universi propri. しかし、そのような異常な育成を除けば、他の領域が私たちのものから分離されていることを想像するのは奇妙です。 And yet, speculative though the idea surely is, I aim to convince you that there’s reason for taking it seriously, as it just might be right. Eppure, per quanto l'idea sia sicuramente speculativa, miro a convincerti che c'è motivo di prenderla sul serio, perché potrebbe essere giusto. I’m going to tell the story of the multiverse in three parts. In part one, I’m going to describe those Nobel Prize-winning results and to highlight a profound mystery which those results revealed. Nella prima parte, descriverò quei risultati che hanno vinto il Premio Nobel e metterò in luce un profondo mistero che quei risultati hanno rivelato. In part two, I’ll offer a solution to that mystery. It’s based on an approach called string theory, and that’s where the idea of the multiverse will come into the story. Finally, in part three, I’m going to describe a cosmological theory called inflation, which will pull all the pieces of the story together.

Okay, part one starts back in 1929 when the great astronomer Edwin Hubble realized that the distant galaxies were all rushing away from us, establishing that space itself is stretching, it’s expanding. Ok, la prima parte inizia nel 1929, quando il grande astronomo Edwin Hubble capì che le galassie lontane si stavano allontanando da noi, stabilendo che lo spazio stesso si sta allungando, si sta espandendo. Now this was revolutionary. The prevailing wisdom was that on the largest of scales the universe was static. La saggezza prevalente era che sulle scale più grandi l'universo fosse statico. But even so, there was one thing that everyone was certain of: The expansion must be slowing down. Ma anche così, c'era una cosa di cui tutti erano certi: l'espansione stava rallentando. That, much as the gravitational pull of the Earth slows the ascent of an apple tossed upward, the gravitational pull of each galaxy on every other must be slowing the expansion of space. Che, proprio come l'attrazione gravitazionale della Terra rallenta l'ascesa di una mela lanciata verso l'alto, l'attrazione gravitazionale di ogni galassia su ogni altra deve rallentare l'espansione dello spazio.

Now let’s fast-forward to the 1990s when those two teams of astronomers I mentioned at the outset were inspired by this reasoning to measure the rate at which the expansion has been slowing. Facciamo ora un rapido salto agli anni '90, quando quei due gruppi di astronomi che ho citato all'inizio furono ispirati da questo ragionamento per misurare la velocità con cui l'espansione stava rallentando. And they did this by painstaking observations of numerous distant galaxies, allowing them to chart how the expansion rate has changed over time. E lo hanno fatto osservando minuziosamente numerose galassie distanti, permettendo loro di tracciare come il tasso di espansione è cambiato nel tempo. Here’s the surprise: They found that the expansion is not slowing down. Instead they found that it’s speeding up, going faster and faster. Invece hanno scoperto che sta accelerando, andando sempre più veloce. That’s like tossing an apple upward and it goes up faster and faster. È come lanciare una mela verso l'alto e sale sempre più velocemente. Now if you saw an apple do that, you’d want to know why. Ora, se vedessi una mela farlo, vorresti sapere perché. What’s pushing on it? What's pushing on it?

Similarly, the astronomers' results are surely well-deserving of the Nobel Prize, but they raised an analogous question. What force is driving all galaxies to rush away from every other at an ever-quickening speed? Quale forza spinge tutte le galassie ad allontanarsi l'una dall'altra a una velocità sempre maggiore? Well the most promising answer comes from an old idea of Einstein’s. You see, we are all used to gravity being a force that does one thing, pulls objects together. Vedi, siamo tutti abituati al fatto che la gravità sia una forza che fa una cosa, unisce gli oggetti. But in Einstein’s theory of gravity, his general theory of relativity, gravity can also push things apart. Ma nella teoria della gravità di Einstein, la sua teoria generale della relatività, la gravità può anche separare le cose.

How? Well according to Einstein’s math, if space is uniformly filled with an invisible energy, sort of like a uniform, invisible mist, then the gravity generated by that mist would be repulsive, repulsive gravity, which is just what we need to explain the observations. Ebbene, secondo la matematica di Einstein, se lo spazio è uniformemente riempito da un'energia invisibile, una specie di nebbia uniforme e invisibile, allora la gravità generata da quella nebbia sarebbe una gravità repulsiva, repulsiva, che è proprio ciò di cui abbiamo bisogno per spiegare le osservazioni. Because the repulsive gravity of an invisible energy in space -- we now call it dark energy, but I’ve made it smokey white here so you can see it -- its repulsive gravity would cause each galaxy to push against every other, driving expansion to speed up, not slow down. Perché la gravità repulsiva di un'energia invisibile nello spazio -- ora la chiamiamo energia oscura, ma qui l'ho resa bianca fumosa così potete vederla -- la sua gravità repulsiva farebbe spingere ogni galassia contro l'altra, guidando l'espansione accelerare, non rallentare. And this explanation represents great progress.

But I promised you a mystery here in part one. Here it is. When the astronomers worked out how much of this dark energy must be infusing space to account for the cosmic speed up, look at what they found. Quando gli astronomi hanno calcolato quanta di questa energia oscura deve essere infusa nello spazio per spiegare l'accelerazione cosmica, guarda cosa hanno scoperto. This number is small. Expressed in the relevant unit, it is spectacularly small. And the mystery is to explain this peculiar number. We want this number to emerge from the laws of physics, but so far no one has found a way to do that. Vogliamo che questo numero emerga dalle leggi della fisica, ma finora nessuno ha trovato un modo per farlo.

Now you might wonder, should you care? Ora potresti chiederti, dovrebbe interessarti? Maybe explaining this number is just a technical issue, a technical detail of interest to experts, but of no relevance to anybody else. Well it surely is a technical detail, but some details really matter. Some details provide windows into uncharted realms of reality, and this peculiar number may be doing just that, as the only approach that’s so far made headway to explain it invokes the possibility of other universes -- an idea that naturally emerges from string theory, which takes me to part two: string theory.

So hold the mystery of the dark energy in the back of your mind as I now go on to tell you three key things about string theory. Quindi tieni il mistero dell'energia oscura nella parte posteriore della tua mente mentre ora vado a dirti tre cose chiave sulla teoria delle stringhe. First off, what is it? Prima di tutto, che cos'è? Well it’s an approach to realize Einstein’s dream of a unified theory of physics, a single overarching framework that would be able to describe all the forces at work in the universe. Beh, è un approccio per realizzare il sogno di Einstein di una teoria unificata della fisica, un'unica struttura generale in grado di descrivere tutte le forze all'opera nell'universo. And the central idea of string theory is quite straightforward. It says that if you examine any piece of matter ever more finely, at first you’ll find molecules and then you’ll find atoms and subatomic particles. But the theory says that if you could probe smaller, much smaller than we can with existing technology, you’d find something else inside these particles -- a little tiny vibrating filament of energy, a little tiny vibrating string. Ma la teoria dice che se potessi sondare più piccoli, molto più piccoli di quanto possiamo fare con la tecnologia esistente, troveresti qualcos'altro all'interno di queste particelle -- un minuscolo filamento vibrante di energia, una minuscola stringa vibrante. And just like the strings on a violin, they can vibrate in different patterns producing different musical notes. These little fundamental strings, when they vibrate in different patterns, they produce different kinds of particles -- so electrons, quarks, neutrinos, photons, all other particles would be united into a single framework, as they would all arise from vibrating strings. It’s a compelling picture, a kind of cosmic symphony, where all the richness that we see in the world around us emerges from the music that these little, tiny strings can play.

But there’s a cost to this elegant unification, because years of research have shown that the math of string theory doesn’t quite work. Ma questa elegante unificazione ha un costo, perché anni di ricerca hanno dimostrato che la matematica della teoria delle stringhe non funziona del tutto. It has internal inconsistencies, unless we allow for something wholly unfamiliar -- extra dimensions of space. Ha incoerenze interne, a meno che non permettiamo qualcosa di completamente sconosciuto: dimensioni extra dello spazio. That is, we all know about the usual three dimensions of space. And you can think about those as height, width and depth. E puoi pensare a quelli come altezza, larghezza e profondità. But string theory says that, on fantastically small scales, there are additional dimensions crumpled to a tiny size so small that we have not detected them. But even though the dimensions are hidden, they would have an impact on things that we can observe because the shape of the extra dimensions constrains how the strings can vibrate. And in string theory, vibration determines everything. So particle masses, the strengths of forces, and most importantly, the amount of dark energy would be determined by the shape of the extra dimensions. So if we knew the shape of the extra dimensions, we should be able to calculate these features, calculate the amount of dark energy.

The challenge is we don’t know the shape of the extra dimensions. All we have is a list of candidate shapes allowed by the math. Tutto quello che abbiamo è un elenco di forme candidate consentite dalla matematica. Now when these ideas were first developed, there were only about five different candidate shapes, so you can imagine analyzing them one-by-one to determine if any yield the physical features we observe. But over time the list grew as researchers found other candidate shapes. Ma nel tempo l'elenco è cresciuto man mano che i ricercatori hanno trovato altre forme candidate. From five, the number grew into the hundreds and then the thousands -- A large, but still manageable, collection to analyze, since after all, graduate students need something to do. Da cinque, il numero è cresciuto fino alle centinaia e poi alle migliaia: una raccolta ampia, ma ancora gestibile, da analizzare, poiché dopo tutto, gli studenti laureati hanno bisogno di qualcosa da fare. But then the list continued to grow into the millions and the billions, until today. Ma poi l'elenco ha continuato a crescere in milioni e miliardi, fino ad oggi. The list of candidate shapes has soared to about 10 to the 500.

So, what to do? Quindi che si fa? Well some researchers lost heart, concluding that was so many candidate shapes for the extra dimensions, each giving rise to different physical features, string theory would never make definitive, testable predictions. Ebbene, alcuni ricercatori si persero d'animo, concludendo che c'erano così tante forme candidate per le dimensioni extra, ognuna delle quali dava origine a diverse caratteristiche fisiche, che la teoria delle stringhe non avrebbe mai fatto previsioni definitive e verificabili. But others turned this issue on its head, taking us to the possibility of a multiverse. Ma altri hanno ribaltato la questione, portandoci alla possibilità di un multiverso. Here’s the idea. Maybe each of these shapes is on an equal footing with every other. Forse ognuna di queste forme è su un piano di parità con l'altra. Each is as real as every other, in the sense that there are many universes, each with a different shape, for the extra dimensions. Ognuna è reale come ogni altra, nel senso che ci sono tanti universi, ognuno con una forma diversa, per le dimensioni extra. And this radical proposal has a profound impact on this mystery: the amount of dark energy revealed by the Nobel Prize-winning results. E questa proposta radicale ha un profondo impatto su questo mistero: la quantità di energia oscura rivelata dai risultati della vincita del Premio Nobel.

Because you see, if there are other universes, and if those universes each have, say, a different shape for the extra dimensions, then the physical features of each universe will be different, and in particular, the amount of dark energy in each universe will be different. Perché vedi, se ci sono altri universi, e se quegli universi hanno ciascuno, diciamo, una forma diversa per le dimensioni extra, allora le caratteristiche fisiche di ogni universo saranno diverse, e in particolare, la quantità di energia oscura in ogni universo sarà diverso. Which means that the mystery of explaining the amount of dark energy we’ve now measured would take on a wholly different character. In this context, the laws of physics can’t explain one number for the dark energy because there isn’t just one number, there are many numbers. Which means we have been asking the wrong question. It’s that the right question to ask is, why do we humans find ourselves in a universe with a particular amount of dark energy we’ve measured instead of any of the other possibilities that are out there? È che la domanda giusta da porsi è: perché noi umani ci troviamo in un universo con una particolare quantità di energia oscura che abbiamo misurato invece di una qualsiasi delle altre possibilità che ci sono là fuori?

And that’s a question on which we can make headway. E questa è una domanda su cui possiamo fare progressi. Because those universes that have much more dark energy than ours, whenever matter tries to clump into galaxies, the repulsive push of the dark energy is so strong that it blows the clump apart and galaxies don’t form. Perché quegli universi che hanno molta più energia oscura della nostra, ogni volta che la materia cerca di ammassarsi nelle galassie, la spinta repulsiva dell'energia oscura è così forte che fa esplodere l'ammasso e le galassie non si formano. And in those universes that have much less dark energy, well they collapse back on themselves so quickly that, again, galaxies don’t form. E in quegli universi che hanno molta meno energia oscura, collassano su se stessi così velocemente che, ancora una volta, le galassie non si formano. And without galaxies, there are no stars, no planets and no chance for our form of life to exist in those other universes.

So we find ourselves in a universe with the particular amount of dark energy we’ve measured simply because our universe has conditions hospitable to our form of life. Wir befinden uns also in einem Universum mit der besonderen Menge an dunkler Energie, die wir gemessen haben, einfach weil unser Universum Bedingungen hat, die unserer Lebensform entgegenkommen. Quindi ci troviamo in un universo con la particolare quantità di energia oscura che abbiamo misurato semplicemente perché il nostro universo ha condizioni favorevoli alla nostra forma di vita. And that would be that. E sarebbe quello. Mystery solved, multiverse found. Mistero risolto, multiverso trovato. Now some find this explanation unsatisfying. Ora alcuni trovano questa spiegazione insoddisfacente. We’re used to physics giving us definitive explanations for the features we observe. Siamo abituati alla fisica che ci dà spiegazioni definitive per le caratteristiche che osserviamo. But the point is, if the feature you’re observing can and does take on a wide variety of different values across the wider landscape of reality, then thinking one explanation for a particular value is simply misguided. Ma il punto è che se la caratteristica che stai osservando può assumere e assume un'ampia varietà di valori diversi nel più ampio panorama della realtà, allora pensare a una spiegazione per un particolare valore è semplicemente fuorviante.

An early example comes from the great astronomer Johannes Kepler who was obsessed with understanding a different number -- why the Sun is 93 million miles away from the Earth. And he worked for decades trying to explain this number, but he never succeeded, and we know why. Kepler was asking the wrong question.

We now know that there are many planets at a wide variety of different distances from their host stars. Ora sappiamo che ci sono molti pianeti a un'ampia varietà di distanze diverse dalle loro stelle ospiti. So hoping that the laws of physics will explain one particular number, 93 million miles, well that is simply wrongheaded. Instead the right question to ask is, why do we humans find ourselves on a planet at this particular distance, instead of any of the other possibilities? And again, that’s a question we can answer. Those planets which are much closer to a star like the Sun would be so hot that our form of life wouldn’t exist. Quei pianeti che sono molto più vicini a una stella come il Sole sarebbero così caldi che la nostra forma di vita non esisterebbe. And those planets that are much farther away from the star, well they’re so cold that, again, our form of life would not take hold. E quei pianeti che sono molto più lontani dalla stella, beh, sono così freddi che, ancora una volta, la nostra forma di vita non farebbe presa. So we find ourselves on a planet at this particular distance simply because it yields conditions vital to our form of life. Quindi ci troviamo su un pianeta a questa particolare distanza semplicemente perché offre condizioni vitali per la nostra forma di vita. And when it comes to planets and their distances, this clearly is the right kind of reasoning. E quando si tratta di pianeti e delle loro distanze, questo è chiaramente il giusto tipo di ragionamento. The point is, when it comes to universes and the dark energy that they contain, it may also be the right kind of reasoning.

One key difference, of course, is we know that there are other planets out there, but so far I’ve only speculated on the possibility that there might be other universes. Una differenza fondamentale, ovviamente, è che sappiamo che ci sono altri pianeti là fuori, ma finora ho solo ipotizzato la possibilità che ci possano essere altri universi. So to pull it all together, we need a mechanism that can actually generate other universes. Quindi, per mettere tutto insieme, abbiamo bisogno di un meccanismo che possa effettivamente generare altri universi. And that takes me to my final part, part three. E questo mi porta alla mia parte finale, la terza parte. Because such a mechanism has been found by cosmologists trying to understand the Big Bang. Perché un tale meccanismo è stato trovato dai cosmologi che cercano di capire il Big Bang. You see, when we speak of the Big Bang, we often have an image of a kind of cosmic explosion that created our universe and set space rushing outward.

But there’s a little secret. The Big Bang leaves out something pretty important, the Bang. Il Big Bang tralascia qualcosa di piuttosto importante, il Bang. It tells us how the universe evolved after the Bang, but gives us no insight into what would have powered the Bang itself. Ci dice come l'universo si è evoluto dopo il Bang, ma non ci dà alcuna idea di cosa avrebbe alimentato il Bang stesso. And this gap was finally filled by an enhanced version of the Big Bang theory. E questa lacuna è stata finalmente colmata da una versione potenziata della teoria del Big Bang. It’s called inflationary cosmology, which identified a particular kind of fuel that would naturally generate an outward rush of space. Si chiama cosmologia inflazionaria, che ha identificato un particolare tipo di carburante che avrebbe generato naturalmente una corsa verso l'esterno dello spazio. The fuel is based on something called a quantum field, but the only detail that matters for us is that this fuel proves to be so efficient that it’s virtually impossible to use it all up, which means in the inflationary theory, the Big Bang giving rise to our universe is likely not a one-time event. Il carburante si basa su qualcosa chiamato campo quantico, ma l'unico dettaglio che conta per noi è che questo carburante si dimostra così efficiente che è praticamente impossibile consumarlo tutto, il che significa nella teoria inflazionistica, il Big Bang che ha dato origine al nostro universo probabilmente non è un evento occasionale. Instead the fuel not only generated our Big Bang, but it would also generate countless other Big Bangs, each giving rise to its own separate universe with our universe becoming but one bubble in a grand cosmic bubble bath of universes. Invece il carburante non solo ha generato il nostro Big Bang, ma avrebbe anche generato innumerevoli altri Big Bang, ognuno dando origine al proprio universo separato con il nostro universo che diventa solo una bolla in un grande bagno di bolle cosmiche di universi.

And now, when we meld this with string theory, here’s the picture we’re led to. E ora, quando mescoliamo questo con la teoria delle stringhe, ecco l'immagine a cui siamo portati. Each of these universes has extra dimensions. The extra dimensions take on a wide variety of different shapes. The different shapes yield different physical features. And we find ourselves in one universe instead of another simply because it’s only in our universe that the physical features, like the amount of dark energy, are right for our form of life to take hold. And this is the compelling but highly controversial picture of the wider cosmos that cutting-edge observation and theory have now led us to seriously consider.

One big remaining question, of course, is, could we ever confirm the existence of other universes? Well let me describe one way that might one day happen. Bene, lasciatemi descrivere un modo in cui un giorno potrebbe accadere. The inflationary theory already has strong observational support. Because the theory predicts that the Big Bang would have been so intense that as space rapidly expanded, tiny quantum jitters from the micro world would have been stretched out to the macro world, yielding a distinctive fingerprint, a pattern of slightly hotter spots and slightly colder spots, across space, which powerful telescopes have now observed. Perché la teoria prevede che il Big Bang sarebbe stato così intenso che, man mano che lo spazio si espandeva rapidamente, minuscoli nervosismi quantistici dal micromondo si sarebbero estesi al macromondo, producendo un'impronta digitale distintiva, uno schema di punti leggermente più caldi e leggermente più freddi. macchie, attraverso lo spazio, che potenti telescopi hanno ora osservato. Going further, if there are other universes, the theory predicts that every so often those universes can collide. Andando oltre, se ci sono altri universi, la teoria prevede che ogni tanto questi universi possono scontrarsi. And if our universe got hit by another, that collision would generate an additional subtle pattern of temperature variations across space that we might one day be able to detect. E se il nostro universo venisse colpito da un altro, quella collisione genererebbe un ulteriore sottile schema di variazioni di temperatura nello spazio che un giorno potremmo essere in grado di rilevare. And so exotic as this picture is, it may one day be grounded in observations, establishing the existence of other universes.

I’ll conclude with a striking implication of all these ideas for the very far future. You see, we learned that our universe is not static, that space is expanding, that that expansion is speeding up and that there might be other universes all by carefully examining faint pinpoints of starlight coming to us from distant galaxies. Vedete, abbiamo appreso che il nostro universo non è statico, che lo spazio si sta espandendo, che quell'espansione sta accelerando e che potrebbero esserci altri universi, il tutto esaminando attentamente deboli puntini di luce stellare che ci arrivano da galassie lontane. But because the expansion is speeding up, in the very far future, those galaxies will rush away so far and so fast that we won’t be able to see them -- not because of technological limitations, but because of the laws of physics. Ma poiché l'espansione sta accelerando, in un futuro molto lontano, quelle galassie si allontaneranno così lontano e così velocemente che non saremo in grado di vederle -- non a causa dei limiti tecnologici, ma a causa delle leggi della fisica. The light those galaxies emit, even traveling at the fastest speed, the speed of light, will not be able to overcome the ever-widening gulf between us. So astronomers in the far future looking out into deep space will see nothing but an endless stretch of static, inky, black stillness. And they will conclude that the universe is static and unchanging and populated by a single central oasis of matter that they inhabit -- a picture of the cosmos that we definitively know to be wrong. E concluderanno che l'universo è statico e immutabile e popolato da un'unica oasi centrale di materia che abitano -- un'immagine del cosmo che sappiamo definitivamente essere sbagliata.

Now maybe those future astronomers will have records handed down from an earlier era, like ours, attesting to an expanding cosmos teeming with galaxies. Ora forse quei futuri astronomi avranno registrazioni tramandate da un'era precedente, come la nostra, che attestano un cosmo in espansione brulicante di galassie. But would those future astronomers believe such ancient knowledge? Ma quei futuri astronomi crederebbero a una conoscenza così antica? Or would they believe in the black, static empty universe that their own state-of-the-art observations reveal? O crederebbero nell'universo nero, statico e vuoto che le loro stesse osservazioni all'avanguardia rivelano? I suspect the latter. Sospetto quest'ultimo. Which means that we are living through a remarkably privileged era when certain deep truths about the cosmos are still within reach of the human spirit of exploration. Il che significa che stiamo vivendo un'era straordinariamente privilegiata in cui alcune profonde verità sul cosmo sono ancora alla portata dello spirito umano di esplorazione. It appears that it may not always be that way. Sembra che non sia sempre così. Because today’s astronomers, by turning powerful telescopes to the sky, have captured a handful of starkly informative photons -- a kind of cosmic telegram billions of years in transit. Perché gli astronomi di oggi, puntando potenti telescopi verso il cielo, hanno catturato una manciata di fotoni fortemente informativi, una specie di telegramma cosmico in transito di miliardi di anni. and the message echoing across the ages is clear. Sometimes nature guards her secrets with the unbreakable grip of physical law. A volte la natura custodisce i suoi segreti con la morsa indistruttibile della legge fisica. Sometimes the true nature of reality beckons from just beyond the horizon.

Thank you very much.

(Applause)

Chris Anderson: Brian, thank you. The range of ideas you’ve just spoken about are dizzying, exhilarating, incredible. La gamma di idee di cui hai appena parlato è vertiginosa, esilarante, incredibile. How do you think of where cosmology is now, in a sort of historical side? Come pensi di dove sia ora la cosmologia, in una sorta di lato storico? Are we in the middle of something unusual historically in your opinion?

BG: Well it’s hard to say. When we learn that astronomers of the far future may not have enough information to figure things out, the natural question is, maybe we’re already in that position and certain deep, critical features of the universe already have escaped our ability to understand because of how cosmology evolves. Quando apprendiamo che gli astronomi del lontano futuro potrebbero non avere abbastanza informazioni per capire le cose, la domanda naturale è, forse siamo già in quella posizione e alcune caratteristiche profonde e critiche dell'universo sono già sfuggite alla nostra capacità di comprensione a causa di come si evolve la cosmologia. So from that perspective, maybe we will always be asking questions and never be able to fully answer them.

On the other hand, we now can understand how old the universe is. We can understand how to understand the data from the microwave background radiation that was set down 13.72 billion years ago -- and yet, we can do calculations today to predict how it will look and it matches. Possiamo capire come comprendere i dati della radiazione di fondo a microonde che è stata stabilita 13,72 miliardi di anni fa, eppure oggi possiamo fare calcoli per prevedere come apparirà e come corrisponde. Holy cow! Mucca sacra! That’s just amazing. So on the one hand, it’s just incredible where we’ve gotten, but who knows what sort of blocks we may find in the future. Quindi, da un lato, è semplicemente incredibile dove siamo arrivati, ma chissà che tipo di blocchi potremmo trovare in futuro.

CA: You’re going to be around for the next few days. CA: Sarai in giro per i prossimi giorni. Maybe some of these conversations can continue. Thank you. Thank you, Brian. (BG: My pleasure.)