Os Segredos da Física Quântica #1/2 (Documentário)

beneath the complexities of everyday life the rules of our universe seem reassuringly simple this solid Bridge supports my weight the water flowing underneath always goes downhill and when I throw this Stone it always flies through the air following a predictable path but as scientists peered deep into the tiny building blocks of matter all such certainty [Music] vanished they found the weird world of quantum mechanics deep down inside everything we see around us we found a universe completely unlike our own to paraphrase one of the founders of quantum mechanics everything we call real is is made up of things that cannot be themselves regarded as real around a 100 years ago some of the world's greatest scientists began a journey down the rabbit hole into the strange and the bizarre they found that in the realm of the very small things could be in two places at once that their Fates are dictated by chance and that reality itself defies all common [Music] sense and at stake that everything we thought we knew about the world might turn out to be completely wrong the story of our descent into scientific Madness begins with the most unlikely object Berlin 1890 Germany is a new country recently unified and hungry to industrialize in this newly unified Germany a number of new engineering companies were founded they spent Millions buying the European patent for Edison's new invention the light bulb the light bulb was the epitome of modern technology a great optimistic symbol of progress engineering companies quickly realized there were fortunes to be made building street lights for the new German Empire but what they didn't realize was that they would also unleash a scientific revolution strangely enough this humble object is responsible for the birth of the most important theory in the whole of science quantum mechanics a theory that I've spent my life studying and that's because back in 1900 the light bulb presented a rather strange problem Engineers knew that if you heated the filament with electricity it glowed the physics that underpinned this though was completely unknown but something as basic as the relationship between the temperature of the filament and the color of light it prod uses was still a complete mystery a mystery they were obviously Keen to solve and with the help of the new German State they saw how to steal a march on their [Music] competitors in 1887 the German government invested millions in a new technical Research Institute here in Berlin the physical technicia rstout or PTR then in 1900 they enlisted a bright if somewhat straight lace scientist to help work here his name was Max [Music] plank plank took on a deceptively simple problem why the color of the light changes as the filament gets [Music] hotter to get a sense of the puzzle facing plank I'm going to ride this bicycle with an oldfashioned lamp powered by an old-fashioned [Music] Dynamo obviously the faster I go the brighter the light the more I pedal the more electricity the Dynamo produces the hotter the filament in the lamp and the brighter the light but the light the bulb makes isn't just getting brighter it's changing color too as I speed up the color shifts from red to orange to Yellow right now I'm going to really belt it now the bulb's filament is getting even hotter but although it certainly gets brighter the color seems to stay the same yellow white [Music] why doesn't the light get any Bluer to investigate Plank and his colleagues built this a black body radiator it's a special tube they could heat to a very precise temperature and a way to measure the color or frequency of the light It [Music] produced nowadays over a 100 years later the PTR still do exactly this kind of measurement just much more accurately the temperature inside here is 841 de Centigrade I can feel the heat coming off and it's glowing with a lovely orangey red color it's about the same color as my bike line when I'm cycling slowly but I want to see something hotter still the temperature inside here is about 2000° centigrade and it's glowing with a much brighter whiter colored light to produce light of this intensity in color requires a power of about 40 Kow now that's equivalent to about 400 m on a bike C cycling very fast or the combined output of the entire tour to France although the light is whiter it's red white there's very little blue why is blue so much harder to make than red and further up the Spectrum Beyond blue the so-called ultraviolet is hardly produced at all even when we look at things as hot as the sun even the Sun at a temperature of 55,000 de Centigrade produces mostly white visible light and makes remarkably little ultraviolet light given how hot it is why is this why is ultraviolet light so hard to make this remarkable failure of common sense so perplexed scientists of the late 19th century that they gave it a very dramatic name they they called it the ultraviolet catastrophe plank took a crucial first step to solving this he found the precise mathematical link between the color of light its frequency and its energy but he didn't understand the connection however it was another weird anomaly that would really put the cat amongst the pigeons in the late 19th century scientists were studying the their newly discovered radio waves and how they were transmitted and to do that they were building experimental rigs very similar to this one basically by spinning this disc they could generate huge voltages that caused Sparks to jump across the gap between the two metal spheres but in doing so they discovered something very unexpected to do with light they found that by shining a powerful light Source on the Spheres they could make the Sparks jump across more easily this suggested a mysterious and unexplained connection between light and [Music] electricity to understand what was happening scientists use this it's called a gold leaf electroscope it's basically a more sensitive version of the spark gap apparatus now first of all I have to charge it up what I'm doing is adding an excess of electrons that are pushing the two gold leaves apart now first I take red light and shine it on the metal surface and nothing happens even if I increase the brightness of the light still the gold leaves aren't affected now I'll try this special blue light rich in ultraviolet immediately the gold leaves [Music] collapse light can clearly remove static electric charge from the leaves it can somehow knock out the electrons I added to them but why is ultraviolet light so much better at doing this than red light this new puzzle became known as the photo electric effect the ultraviolet catastrophe and the photoelectric effect were big problems for physicists because neither could be understood using the best science of the time the science that said quite unequivocally that light was a wave all around us we see light behaving in a perfectly Common Sense wavy way look at the shadow of my hand it's fuzzy around the edges we understand this as the light hitting the sides of my hand and bending and smearing out slightly just like water waves around an obstruction perfectly Common Sense wavelike behavior and here's something else something rather beautiful look at these soap bubbles shine a light on them and gorgeous colored patterns emerge from nowhere and this was easily explained if you accept that light was a wave reflecting off the outer and inner layers of the thin soap film and breaking up into the colors of the rainbow rather like ripples on the surface of water light was simply ripples of energy spreading through space and this was a firmly accepted as the fact that the Earth was round but although this wave theory worked perfectly well for shadows and bubbles when it came to the ultraviolet catastrophe and the photo El electric effect the wheels started coming off the problem was this how could light do this to truly grasp how absurd this phenomenon was it might be useful to consider how waves in water behave [Music] hey this is the wave tank at the RN headquarters in Dorset it's used to train Lifeboat teams to deal with a range of different kinds of water waves first small waves just 30 cm High these waves don't have much energy hardly enough energy to knock this top can off the other but when the waves grow to over a meter and a half it's a very different proposition and they're really throwing me about there's no way I can keep this can balanced on the top it's clear what water waves are telling us bigger more intense waves have more power they easily knocked me and the cans around so if light was a wave more intensity should knock out more electrons but that's not what happened remember no matter how intense the red light was it still didn't budge electrons from the metal but weirdly weak ultraviolet works within seconds so thinking of light as a wave just wasn't adding [Music] up to resolve this someone needed to think the unthinkable and in 1905 someone did you may well have heard of him his name was Albert [Music] Einstein this is the Arenal stvar observatory in Berlin perched on top is a strange huge Iron and Steel construction but it's not a gun it's actually a telescope built in 1896 the telescope was one of the largest of its kind in the world and made the observatory the go-to place to engage and Astound the public in new science Albert Einstein gave a very famous public lecture here on his theory of relativity which is of course what he's most famous for but it's not the work that won him the Nobel [Music] Prize in 1905 he'd also come up with a new Theory to explain the photo electric effect and what he suggested was revolutionary and even heretical he argued that we have to forget all about the idea that light is a wave and think of it instead as a stream of tiny bullet-like particles the term he used to describe a particle of light was a Quantum to Einstein a Quantum was a tiny lump of energy and although in 1905 the word wasn't knew the idea that light could be a Quantum seemed crazy and yet following Einstein's heretical line of thought to its logical conclusion solved all the problems with light at a single [Music] stroke I'll try to explain how this helps using a rough analogy of course like all analogies it's far from perfect but hopefully it'll give you a sense of the physics to help you understand why thinking of light as a stream of particles solves the mystery of the photoelectric effect in this analogy these red balls represent Einstein's light Quant and those cans over there are the electricity held in the metal now in the original experiment they made electricity flow from the surface of of the metal by Shining Light on it in my analogy I'm going to try and knock those tinan over using these red [Music] balls absolutely no effect that's just like red light according to Einstein each particle of red light carries very little energy because red light has a low frequency so even a very bright red light with many red light particles can't dislodge any electrons from the metal plate just like the red balls now I'm going to use heavier balls like these blue golf balls and I'm going to try and knock off the tink hands with these they're like the ultraviolet lights in the experiment now each individual light particle carries more energy because ultraviolet light is higher [Music] frequency just a few of them like a dim ultraviolet light are enough to knock the electrons out of the metal plate and collapse the gold leaf so Einstein's idea that light is made up of tiny particles or Quant is a wonderful explanation of the photoelectric effect I remember when I first learned about this being blown away by Sheer Elegance and simplicity but what's more Einstein's Nifty idea also helped solve Plank's mystery of the light bulb there was more red than ultraviolet because ultraviolet Quant took so much more energy to make about a 100 times more energy no wonder there are so few of them that moment at the beginning of the 20th century signaled a genuine Revolution because it demonstrated that the kind of uh physical science that people were doing right back to Newton and llas and people like that that you needed a completely new approach physics has never recovered from that moment in the sense that it's built on that moment that's where Modern physics really began but Einstein's theory also left physicists with a dizzying paradox defying all common sense light was definitely a wave which explained shadows and Bubbles and now it was definitely a particle too Einstein's quantum explaining the photoelectric effect and the ultraviolet catastrophe then just a few years after Einstein's brilliant crazy idea the Paradox got a lot deeper and a whole lot weirder because what seemed to be a curious mystery about light was about to become a Battleground about the nature of reality itself [Music] 1922 the Western world is in the grip of a revolution a cultural revolution James Joyce's unes is published Stravinsky is at the height of his powers and chaplain has just released his first serious movie the Ottoman Empire collapses Europe is still recovering from the war to Endor Wars in which milli millions of men lost their lives Russia is newly communist meanwhile America is exporting Jazz to the world thank [Music] you in art politics literature economics there was an insatiable appetite for change this was the birth of modernism you got a heart that there's no way of knowing see where you are but can't see where you're going and I'm stuck here still I'm tangled up with you this whole world can un but and I might get in trouble for saying this I would argue that the upheaval that took place in physics at this time would Eclipse them all and have far longer lasting consequences it had begun with the discovery of the weird and contradictory wave particle nature of light it ended up as an epic battle fought between the greatest minds and science for the highest possible Stakes the nature of reality itself I know I deserve you I know you're my savior when I observe you you change your behavior so one side a new wave of modernist revolutionary scientists and their leader the brilliant Danish physicist Neils bore on the other side the voice of reason Albert Einstein at the height of his powers and now world famous a formidable [Music] adversary the battle raged for decades actually in some ways it still does it was fought across the world in Universities at conferences in bars and cafes it would reduce grown men to tears and it began with a deceptively simple experiment this whole world can be so un but weirdly it was an experiment that wasn't even about light it was about the particles that make electricity else in the mid 1920s an experiment was carried out at Bell Laboratories in New Jersey In America which uncovered something entirely unexpected about electrons now at the time it was accepted without question that electrons were these tiny lumps of matter small but solid particles like miniature billiard balls in the experiment they fired a beam of electrons at a crystal and watched how they scattered now that's entirely equivalent to take taking a beam of electrons say from an electron gun and firing it at a screen with two slits in it so that the electrons pass through the slits and hit another screen at the back what the Bell scientist found shocked the physics world to the [Music] core to understand why consider a similar experiment with water waves I've set up a simple experiment I have a water ripple tank placed on top of an overhead projector I have a generator producing waves that pass through two narrow gaps the projector beams the image of the Waves onto the back wall you can see as the waves come in from the left and squeeze through the two gaps they spread out on the other side and interfere with each other what this means is that when you get the crest from one wave meeting the crest from another they add up to make a higher wave but when the crest from one meets a trough they cancel out this gives rise to these characteristic lines leading to the signature wave pattern bands of light and dark whenever you see these light and dark bands the signature wave pattern you know without doubt that you've got wavelike Behavior [Music] so guess what they saw in New Jersey now it seemed that firing electrons tiny solid particles through the two gaps produced exactly the same kind of pattern bands of light and dark first light for a long time believed to be a wave was found to sometimes be behave like particles and now electrons for a long time believed to be particles were behaving like waves but it was actually Stranger Than That the wave pattern wasn't merely some result of the entire beam of electrons more recently this experiment has been repeated in labs around the world by firing one electron at a time through the slits onto the screen at first first each electron seems to land randomly on the screen but gradually a pattern forms the signature wave pattern let me be quite clear about just how weird this is remember from the wave tank experiment where the signature wave pattern only exists because each wave passes through both slits and then its two pieces interfere with each other but here every individual electron each single particle is passing alone through the slits before it hits the screen and yet each single electron is still contributing to the signature wave pattern each electron has to be behaving like a wave to explain this strange result Neils Bor and his colleagues created quantum mechanics a crazy theory of light and matter that embraced contradiction and didn't care that it was almost impossible to understand as neilb himself said anyone who isn't shocked by quantum theory hasn't understood it so viewers I'm going to take our tiny electron and use it to delve deep into the heart of reality and yes prepare to be shocked because this is the only way to explain what we observe when a single electron travels through the slits and hits the screen quantum mechanics says this we can't describe what's traveling as a physical object all we can talk about are the chances of where the electron might be this wave of chance somehow travels through both slits producing interference just like the water wave then when it hits the screen what was just the ghostly possibility of an electron mysteriously becomes real let me try and capture just how weird this is with an analogy if I spin this coin then all the time it's spinning it's a blur I can't tell if it's heads or tails but if I stop it I force it to decide and it heads so before it was sort of not heads or tails but a mixture of both but as soon as I've stopped it I've forced it to make up its mind this is what B and his supporters claimed was happening with our [Music] electrons in a sense as it spins the coin is both heads and tails similarly the electron's wave of chance passes through both slits two par S at the same time our Corin then stops at heads the Ethereal wave of probability hits the screen and only then becomes a particle the quantum world was unlike anything ever seen before it's hard to overstate just how crazy this is B was effectively claiming that one can never know where the elect actually is at all until you measure it and it's not just that you don't know where the electron is it's weirdly as though the electron itself is everywhere at once bear in mind that electrons are among the commonest and most basic building blocks of reality and yet here's B saying that only by looking do we actually conjure their position into existence it's like there's a curtain between between us and the quantum world and behind it there is no solid reality just the potential for reality things only become real when we pull back the curtain and look and this view ladies and gentlemen became known as The Copenhagen [Music] interpretation persuasive as it might seem many people couldn't stomach Neils B's outlandish ideas and they found a natural leader in the most powerful man in science Albert Einstein hated this interpretation with every fiber of his being he famously said does the moon cease to exist when I don't look at it he was very unhappy because it uh gave limits to knowledge that he didn't think should be final he thought there should be a better underlying Theory over the next 10 years Einstein and bour would argue passionately about whether quantum mechanics meant giving up on reality or not then with two other scientists Nathan Rosen and Boris Podolski Einstein thought they'd found a way to win the argument he was convinced he'd found a fatal flaw in the Copenhagen interpretation and it's claimed that reality was summoned into existence by the act of looking at it at the heart of Einstein's argument was an aspect of quantum mechanics called entanglement now entanglement is this special incredibly close relationship between a pair of quantum particles whose Fates are intertwined for example if they were created in the same event let me try and explain this by imagining the two particles are Spinning Coins imagine these coins are two electrons created from the same event and then moved apart from each other quantum mechanics says that because they're created together they're entangled and now many of their properties are forever linked wherever they are remember the Copenhagen interpretation says that until you measure one of the coins neither of them is heads or tails in fact heads and tails don't even exist and here's where entanglement makes this weird situation even weirder when we stop the first coin and it becomes heads because the coins are linked through entanglement the second coin will simultaneously become tails and here's the crucial thing I can't predict what the outcome of my measurement will be only that they will always be opposite Einstein seized on this because it meant that something was happening between the two coins that was almost too crazy to imagine it's as if the two coins are secretly communicating communicating instantaneously across space and time even even if the first corn was on earth and the other was on Pluto Einstein refused to believe this instantaneous faster than light communication his theory of relativity said that nothing could travel that fast not even information so how could one coin instantaneously know how the other would land he disparagingly called it spooky action at a distance and claimed it was a fatal flaw in the Haagen interpretation what's more he had a better idea Einstein believed there was a simpler interpretation that somehow the destiny of the two coins whether or not they ended up heads or tails was already fixed long before we observed them he said that although it seemed the coin was deciding to be say heads at the moment of observation actually that decision was taken long before it was just hidden from us in Einstein's mind Quantum particles were nothing like Spinning Coins they were more like say a pair of gloves left and right separated into boxes we don't know which box contains which glove until we open one but when we do and find say a right-handed glove then immediately we know that the box contains the left-handed glove but crucially this requires no spooky action at a distance neither glove has been altered by the act of observation both of them were either left or right-handed glove from the beginning and the only thing that has changed is our knowledge so which is the true description of reality BS coins which only become real when we look at [Music] them and then magically communicate to each other or Einstein's gloves which are hidden from us but AR definitely left or right from the beginning in other words is there an objective reality as Einstein believed or not as bore maintained in the late 1930s as the world plunged into war there was no way to answer this question the battle to understand the nature of reality was deadlocked the war rolled across Europe and many of the leading scientists fled to the United States then as the second world war led inexorably to the Cold War American Science backed by dollar bills and a new vision of the future boomed remember after the war physic came back raring to go and try to apply uh the ideas of of quantum theory to uh to to atoms the interaction between electrons and and light and what have you you didn't need to worry about the philosophical side of things uh to make progress with that so as you say it really took a back seat quantum mechanics led to a profound understanding of semiconductors which helped create the modern electronic age It produced lasers revolutionizing Communications breathtaking new medical [Music] advances and breakthroughs in nuclear power quantum mechanics was so successful that most working physicists deliberately chose to ignore Einstein's objections it simply didn't matter to them because it worked they even coined a phrase for it shut up and calculate [Music] and the price for this success was that Bor and Einstein's debate on the reality of the quantum world was simply brushed under the [Music] carpet and amidst all this success and pragmatism there were few who still worried what it all meant but as the 50s rolled headlong into the 60s one lone denter worked out how to settle the argument once and for all John Bell I think it's fair to say isn't well known to the general public but to physicist like me he's well a hero he was an original thinker with real courage in his convictions and the story of his rise to become one of the great sop physics is made even more remarkable when you consider how he started he was born in Belfast in the 1920s into a poor workingclass family his father was a horse dealer and they really struggled to get him into Queens University Belfast to study Physics in fact he was the only one in his family to even finish school this I believe made him insatiably curious fiery and stubborn I remember meeting John Bell in 1989 a year before he died we were both at a conference in America and we happened to be sharing a lift just after both attending a talk on quantum mechanics Keen to say something to the great John Bell I said I thought the the the speaker conclusions were completely crazy he he stared at me with his piercing blue eyes and for a moment I thought my fledgling physics career was going down the drain but as the lift doors opened and he was about to leave he said yes I completely agree with you haven't they heard of the helium problem to this day I'm not quite sure what the helium problem is but I was just so relieved that John Bell and I [Music] agreed for many years he worked here at Britain's atomic energy rearch Center at Harwell who built this early experimental nuclear reactor called Dao it was here that he started pondering the deep and worrying questions that quantum mechanics raised did the quantum world only exist when it was observed or was there a deeper truth out there waiting to be discovered in fact he was so troubled he began to wonder if there were was a problem at the heart of quantum mechanics he famously said I hesitate to think it might be wrong but I know it is rotten and so in the early 1960s B decided to try and resolve the crisis at the heart of quantum physics it was an epic challenge after all how do you check if something is real there something is or isn't there all without looking how do you look behind the curtain without pulling it open but John Bell came up with a brilliant way of doing exactly that I think this is one of the most ingenious ideas in the whole of physics it's certainly one of the most difficult to understand and explain but I'm going to try and have a go and yes I'm afraid I'm going to use another analogy this time I'm going to play a game of cards but it's one for the highest possible Stakes the nature of reality itself the card game is against a mysterious Quantum dealer the cards he deals represent any subatomic particles or even Quant of light photons and the game we'll play will ultimately tell us whether Einstein or B was right now the rules of the game are deceptively simple the dealer is going to deal two cards face down if they're the same color I win if they're different colors I [Music] lose so I have a red so I need another red to win it's black I lose again opposite colors I've lost both those that's four in a [Music] row that's six pairs in a row that I've lost okay I think I know what the dealer is doing here clearly the deck has been rigged in advance so that every pair come out as opposite colors but there's a simple way to catch the dealer out so what we can do now is change the rules of the game this time if they are the opposite color I [Music] win but once again every time my evil Quantum opponent beats [Music] me but again I can see what the crafted dealer could could have done maybe while I wasn't looking he's switched the pack and and and rigged it so that it always lands in his favor now every pair is the same [Music] color rigged decks remember were what Einstein thought was really happening in the entanglement experiment he said that just like the gloves were already placed in the box so the evil dealer stacked the cards before we played but Neil's B's idea was very different he said red and black don't even exist until you turn them over Belle's genius was that he came up with a way of deciding once and for all who was right Einstein or bore this is how he did it I'm now not going to tell the dealer which game I want to play same color wins or different color wins until after he's dealt the car CS now because he can never predict which rules I'm going to play by he can never stack the deck correctly now he can't win or can he so now the rules are different wins the same okay same color [Music] wins this gets to the very heart of Belle's idea if we now start playing and I win as many as I lose then Einstein was right the dealer is just a trickster with a gift for slight of hand reality may be tricky but it does have an objective existence but what if I lose well then I'm forced to admit that there is no sensible [Music] explanation each card must be sending secret signals to the other across space and time in defiance of everything we know I'm forced to accept that at the fundamental Quantum level reality is truly [Music] unknowable Bell reduced this idea into a single mathematical equation that tells us once and for all what seemed unanswerable how reality really is John Bell published his idea in 1964 and the extraordinary thing is at the time the entire physics Community ignored him total radio silence it seems the world simply wasn't ready perhaps it was because his equation seemed untestable or just because nobody thought it was worth investigating but that was about to change and the change would come from a very unexpected place the of the age of Aquarius AG of Aquarius [Music] aquar America was in crisis over Vietnam water gates feminism the Black Panthers and while all this was going on a small group of hippie physicists were working at the University of Berkeley in California they did all the hippie things they smoked do they popped LSD they debated things like Buddhism and telepathy and they loved quantum mechanics in its weird version of reality they saw parallels with their own esoteric [Music] beliefs their hippie New Age style physics also caught the attention of the public who read their crazy hippie books that mixed quantum mechanics with Eastern mysticism books like the tower physics the dancing woly Masters and my personal favorite space time and Beyond towards an explanation of the unexplainable but more importantly for our story the story of quantum mechanics these hippie physicists also turn their attention to Einstein's now famous thought experiment and what it told us about the nature of reality they saw Neil's B's secret signaling as proof that physics supported their own ideas because if two particles could spookily communicate across space then ESP telepathy and Clairvoyance were probably true as well if only they could prove it really existed then in 1972 they realized that with a bit of mathematical slight of hand they could take Bell's equation and experimentally test it one of their group John clauser borrowed some equipment from the lab he was working in and set up the first genuine and ultimate test of quantum mechanics this is a picture of that first experiment built of leftovers and stolen equipment over the next few years it was improved by a team led by Alan aspect in Paris making its results more reliable over 10 years after Bell first proposed his equation finally it could be put to the test this is a modern version of the experiment first carried out by John clauser and then Alan aspect here a crystal converts laser light into pairs of entangled light Quant photons making two very precise [Music] beam these photons are passed round and bent back again until they pass through these detectors the two photons are like the two cards the evil dealer places in front of me we'll measure a property of the photons called polarization which is equivalent to the color of the playing cards in my game so for instance winning with two matching red cards might be the same as two photons with matching polarization but because this is quantum mechanics it's more complicated than my simple card game and these dials here allow me to measure a second property of the photons as well now that's equivalent to me not only trying to guess the color of the face of the cards but also trying to guess the color of the back of the cards okay so we're now going to switch on the laser and start the [Music] experiment so this number here here gives me the number of photon pairs coming through the experiment that's equivalent to the pairs of cards in my game the graph here dropping down gives me the probability that I can win that I'm guessing right the more photons the more accurate it becomes I'll stop with an uncertainty of about 1% and The Final Answer is. 56 so if I put that into my equation I now need to run the experiment three more times corresponding to the four different settings of these dials each run is now like a different set of rules for the quantum dealer and when I add them up and get the answer if it's less than two then einan was right if it's greater than two then B was right okay so now for the second setting just remember what the experiment will show if the numbers come out less than two then it's proof the dealer has been stacking the deck this was Einstein's view okay so the number I get this time is . 82 now reset for run three but if the result is greater than two then the deck cannot be stacked and something else is at work okay so the run three result is minus .

59 and finally run [Music] four this last number will finally reveal if the world follows common sense or something much more bizarre okay so our final result is in and it's 0. 56 so if we turn the laser [Music] off right I better just work out the answer and there we have it 2.