you should not exist neither should your family or your neighbors or the person who served you in the supermarket earlier today the world should not exist there shouldn't be any great art or music there shouldn't be hunger or the horrors of War there shouldn't be any of it there shouldn't even be a universe let's begin at the beginning at the big bang and plausible and unlikely event a one in 10 to the 10 to the 123 charts 10 to the 10 to the 123 is sometimes called the Penrose number named after the Nobel prize winning British physicist and mathematician sir Roger Penrose it measures the remarkable level of order and precision with which our universe was created order and precision are known to Decay over time you see it with the wires that lead into an old pair of headphones getting more and more Tangled As Time Goes By You See It in the crumbling ruins of an ancient city magnificent buildings carved thousands of years ago by our ancestors reduced to dust and Rubble by the passage of time penr knew that our universe should behave in the same way its order and precision decaying over time just like the cities of ancient Egypt China and meso America he knew that black holes were the crumbling ruins of the cosmos the place where everything ends up eventually where order and precision finally give way to the abyss there are about 10 to the power of 80 protons neutrons and other similar particles scattered across our universe still evading the abyss of black holes still Clinging On to their order and precision this makes our universe special like an ancient artifact that hasn't yet crumbled into dust and when he crunched the numbers Penrose realized that our universe must have been carved with a level of precision that just didn't make sense an incred incredibly low entropy a one in 10 to the 10 to the 123 chance and this impossible number is not alone antimatter is like the mirror image of matter and when the two combine they destroy each other and although there are 10 the^ of 80 protons neutrons and other matter particles in the universe there were only a sprinkling of antiparticles but this is just as well if there had been an equal number of particles and antiparticles created in the Big Bang they would have annihilated each other out of existence almost instantly and yet there is nothing in our best models of the universe that seems to give enough of a preference for matter over antimatter in fact when we extrapolate the results of experiments it looks like the universe should have been born with an equal number everything should have been annihilated you and I should not exist the universe should not exist and yet it does but there is one prediction that worries physicists far more than the lack of antimatter or the remarkably ordered state in which the universe was born it is the weight of the universe when theoretical physicists put quantum mechanics alongside G relativity in a controllable way they find that the Universe should have bent itself into Oblivion within a moment of creation it should have been crushed by an overwhelming weight most of which doesn't come from the planets and stars that are sprinkled throughout the Galaxy but from empty space the vacuum our entire universe should have been crushed by the weight of nothing this is a mystery known as the cosmological constant problem and it has haunted physicists for nearly a 100 years the James web space telescopes mirrors are aligned to about 10 nanom that is 1 10,000 the width of a human hair Precision is important when exploring the universe this video has been sponsored by novium and their hover pens are a fantastic classy gift idea and one that reflects the importance of precision and smart design in space exploration crowned one of time's best inventions of 2022 the novium hover pen is a stylish and eye-catching ballpoint pen that hovers at a 23.5° angle just like the Earth's axial tilt without the aid of electricity just using gravity and neodymium magnets cre created from aircraft grade aluminium it also provides a comfortable and smooth writing experience designed by an actual physicist the hover pen is inspired by outer space and the premium version even comes with a real Shard of meteorite embedded into it the perfect gift for space enthusiasts they also have a new addition which combines a roller ball and fountain pen into one Sleek package so click on the link in the description and use the code H Tu to get 10% off and free shipping on any hover pen with Worldwide shipping thanks to novium for supporting educational content on YouTube Julius Von mayor was a ship's Doctor Who served on expeditions to the Dutch East Indies in the middle of the 19th century whenever a sailor took ill on one of the ships Von mayor would often resort to bloodletting this wasn't unusual bloodletting was a common practice at the time and in in this case it led Von mayor to make a groundbreaking discovery in the hot sun of Indonesia he noticed that the blood running through a sailor's veins was just as red as the blood running through their arteries back home in his native Germany where the weather was not so warm the blood running through the veins of his patients was always a little darker than the arterial blood this was he believed because it was lacking in oxygen which had been used in the slow combustion of food to help keep the patient warm in Indonesia the sailors were bathed in tropical Sunshine they didn't need to burn as much fuel to stay warm so their veins carried blood with higher levels of oxygen and appeared much redder in color Von mayor realized that the heat generated from the combustion of food in the body must be equivalent to the heat absorbed from the sun he realized that heat was just another form of energy but what is energy and what does this have to do with the weight of the universe or even the cosmological constant energy is the most precious commodity of all we need energy to power our vehicles to heat our homes to watch videos on YouTube and as Von mayor realized it comes in many different forms in the 18th century early industrialists were looking for ways to convert trapped energy into useful work that could power their machines that is what energy is stuff that we can convert into work oldfashioned water wheels store potential energy by lifting a heavy bucket of water up high before allowing it to fall converting the energy into useful kinetic energy the energy of motion the steam engines of the Industrial Revolution took the chemical energy stored in coal converted that into heat before once again creating motion and it was Einstein who came to realize that mass was also another form of energy and to understand why we need to remember the cosmic speed limit the speed of light nothing can go faster than the speed of light which is about 299,792,458 m/s this limit applies to everything to the speed of a bullet or a particle whizzing around a collider it even applies to Usain Bolt the legendary Jamaican sprinter of course despite his remarkable Talent bolt never managed to get anywhere near the speed of light but what if he had what if there were a supercharged version of Usain Bolt capable of accelerating all the way up to the speed of light how could he do this to accelerate up to higher speeds The Supercharged bolt would need to take on energy presumably in the form of food as he approached the speed of light he would find it harder and harder to except accelerate this has to be the case if it were not he would be in danger of breaking the speed limit and we know that can't happen but what is it that stops him from accelerating it must be that his resistance to acceleration his inertia is getting bigger and bigger the energy he consumes isn't just going away it's being converted into inertia as he approaches the speed of light it doesn't matter how much energy he takes on board his inertia just grows and grows and stops him from accelerating beyond the speed limit with a thought experiment like this Einstein understood that inertia was just another form of energy and that had to remain true even when bolt wasn't running when he was at rest but what is Bolt's inertia when he is resting it's just his mass and so mass and energy are equivalent and Einstein captured this remark fact with his most famous equation e equal mc² this equation tells you how much energy e you should associate with a certain amount of mass m c in this case is the speed of light at around 300 million m/s that's quite a big conversion factor which means just a small amount of mass is equivalent to a huge amount of energy for example a small dog weighing around 9 kg stores energy equivalent to almost a million trillion jewles or 200 megatons of TNT that's roughly the energy that was released by the eruption of katoa in 1883 whenever nuclear fusion occurs a small amount of mass is converted into a huge amount of heat this happens inside a thermonuclear weapon as isotopes of hydrogen fuse together to form heavier elements with a net loss in the overall Mass it also happens in the core of the Sun powering the lifegiving glow that keeps our planet warm the conversion of mass into other forms of energy is one of the most powerful forces in nature and so when a physicist asks you how much you weigh or how much the universe weighs they aren't asking if you've eaten a little too much over the holidays they are asking about the force of gravity that pulls on you or indeed the universe of course how big it is May well depend on how much you've eaten over the holidays because we normally think of gravity as pulling on mass and the more mass you carry the more you weigh but this is only half the story gravity doesn't just pull on mass once Einstein had realized that mass and energy were equivalent he realized that gravity should pull on any form of energy light for example doesn't have any Mass but it does have energy and that's why gravity pulls it on a bent path around the sun when we ask how much you weigh or how much the universe weighs we are really asking how much energy there is and there is a huge amount of energy hiding in all the mass and radiation we see in the universe it is hiding in the stars and planets that populate the galaxies it is in the very radiation that spreads through the cosmos but this is only a small fraction of the total energy budget much of the universe is made from an unknown invisible Source the so-called Dark Universe this is where it gets most of its work weight and so just like gazing at your scales after the holidays or measuring how much flour you need for your cake it's time for us to weigh the [Music] universe in the city of Syracuse in the 3rd Century BC aredes arguably the greatest mathematician of his time is contemplating the size of the universe there are some who think that the number of the sand is infinite in multitude and I mean by the sand not only that which exists about Syracuse and the rest of sic but also that which is found in every other region inhabited or uninhabited but Archimedes is not convinced by this infinite number of grains of sand and sets about calculating how many could actually fit inside the universe this is his famous sand reckoner and it begins with a poppy [Music] seed laying seeds out side by side Archimedes notes that 40 of them would make up a single Greek dactil a finger width equivalent to around 19 mm in modern units and within each seed he imagines a myriad grains of sand a myriad is 10,000 the largest unit available to Archimedes at the time to compute how many grains of sand there were in the universe he had to invent a new system of numbers and he also had to estimate the size of the universe to our comedies the universe reached as far as a blanket of fixed stars that formed an enormous sphere centered around the sun with a series of clever and crude approximations he estimated the diameter of this sphere to be equivalent to 100 trillion Greek stadia or about two Li years to us bringing everything together he triumphantly concluded that the Universe would not be able to accommodate an infinite number of grains of sand the number would not exceed 10 to the power of 63 how much would such a universe weigh well Archimedes wasn't really worried about that but if we imagine that each grain of sand weighs around 10 mg then aredes sandfill Universe would weigh about 10 billion trillion trillion trillion trillion kilog oddly that is not wildly incorrect [Music] but it was just a fluke Archimedes massively underestimated the size of the universe and the reality is it's not full of sand the universe is Big when we ask how much it weighs we are really asking how much energy it contains energy that is stored in the mass of the stars and planets and clouds of interstellar gas energy that is stored in radiation or even in empty space to figure out how much energy that is we need to be clear what we mean by Universe we mean the observable universe that is a large region of the universe as far as the eye can see or indeed anything else can see the universe was born about 13.8 billion years ago this might seem like a long time but it has not been enough time for us to receive signals from the most distant corners of the cosmos they are simply too far away even if they emit a light signal traveling at the maximum speed possible that signal would still not have reached Us in the lifetime of the universe this boundary between what we can and cannot see is known as the observable universe you might think that it must be about 13.8 billion light years in size since that is the distance traveled by light in the lifetime of the universe however this doesn't take into account the expansion of space when this is considered it turns out we could have received signals from objects that are up to 46.5 billion Li years away and so that is the size of the observable universe about 93 billion light years in diameter of course the universe doesn't actually stop at this point there isn't a giant Cosmic wall at 46 A2 billion light years but we have no way of knowing what it's really like Beyond this point it could be that the Universe goes on forever stretching all the way to infinity or perhaps it eventually comes back on itself like a magnificent Cosmic Sphere reaching far beyond the observable realm this giant sphere would bend the shape of space a little light traveling vast distances towards us could be sensitive to that bendiness and we could hope to detect it but so far we've detected nothing if the universe really is shaped like a sphere it would have to be undetectably large with a diameter of at least 23 trillion light years but whatever the size and shape of the universe there is no way we could try and weigh the unobservable Realms because we have no way of knowing what they contain they could be filled with grains of sand or they could be empty void of any stars and planets the laws of physics might even be different there we just don't know and we can never know so if we really want to be serious about weighing the Universe we need to stick to the observable part stretching 46 and 1/2 billion light years in every direction and weigh [Music] that let's start with the Stars the sun is fairly typical with a mass of order 2 million trillion trillion kilog observations suggest that there are between 100 and 400 billion stars in our galaxy which combine to weigh up to a billion ion billion trillion trillion kilog there are at least 200 billion galaxies in the observable universe each containing an average of 100 billion stars that suggests that there are at least 20 billion trillion stars alog together weighing a grand total of around 20,000 trillion trillion trillion trillion kilog and that's actually not a bad estimate for the stuff we can actually see but the problem is it neglects the mass of other sources stuff like Interstellar gas a better way to measure the mass or energy of the universe is to study its effect on the shape of SpaceTime one way to do this is to study the cosmic microwave background radiation the so-called CMB these are primordial photons left over from the moment the first atoms were formed these photons have traveled large distances across the entire universe from every different direction and throughout most of Cosmic history they could even be detected amongst the static in the old days of analog TV using state-of-the-art satellite telescopes astronomers measure the temperature of the cosmic microwave background radiation in different parts of the Sky by measuring the statistical correlations in the temperature fluctuations in the CMB and understanding how matter radiation and other forms of energy affect the shape of space and time astronomers are able to figure out what the universe is made of and the cosmic microwave background in combination with other methods and probes reveals that the observable universe has around 150,000 trillion trillion trillion trillion kilograms of mass stored in the stuff we can see stars planets clouds of interstellar gas and even the human race that's about 7 and a half times our previous estimate it sounds like a lot but the stuff we can see is only 5% of the energy out there there are two more ingredients and they dominate the universe first there is dark matter this is just like ordinary matter that makes up atoms or humans or stars or planets except it's completely invisible if you shine a torch on it the light will just pass through if you try to whack it with a baseball bat it would be as if you were just swinging the bat in empty space we have no way of touching or feeling Dark Matter except through gravity it carries mass and energy just like ordinary matter and so we can feel its effect on SpaceTime but although dark matter is five times more abundant than visible matter it's still not the dominant ingredient in our universe that is dark energy Dark Energy makes up a whopping 70% of the universe another invisible substance it is responsible ible for pushing the universe apart causing the cosmic expansion to Quicken over time we see this through the light from distant Supernova these explosions are reasonably well understood and yet the more distant ones are dimmer than expected this dimming is easily accounted for by The Accelerated expansion of space by the push of dark [Music] energy so just what is dark energy all the data points towards an exotic substance whose energy density is more or less constant right across the universe and as we will come to understand this is just what you'd expect from the energy of empty space empty space it turns out is not empty it is really a bubbling broth of virtual particles that can never be tamed that are forever popping in and out of existence weighing the Universe down giving it energy giving it weight this energy of empty space goes by many names in the early days of quantum mechanics most people called it the nul seni which is German for Zero Point Energy nowadays people often call it the vacuum energy or sometimes the cosmological constant they all mean the same thing and they are what most scientists associate with dark energy our observable universe can contains Dark Energy equivalent to around 46 trillion trillion trillion trillion trillion tons of TNT and when you put everything together the planets the Stars the dark matter the dark energy you find a universe containing energy equivalent to 67 trillion trillion trillion trillion trillion tons of TNT and that is how much the universe weighs this might seem like a lot but remember all this energy is spread evenly across a large Universe the density is very low dark energy is so dilute that a coffee cup full of it doesn't contain enough energy to crush a fairy fly the smallest insect in the world and that's just as well is this low density is what allowed the universe to grow large and old but in weighing the universe we now run into one of the greatest of all the cosmological puzzles the cosm logical constant problem if you really want to think about dark energy as the energy of empty space then why is there so little of it for when we take our most tried and trusted theories of physics at face value we find that the null Punk energy should be absolutely enormous our universe should not be the gently evolving Cosmos we see today it should have been born a super heavyweight instantly crushed under the weight of its vacuum bent into Oblivion in time and space torn to shreds by the tides of gravity and gone within the blink of an eye our universe should never have grown large and old it should never have allowed intelligent life to evolve it should never have allowed you to exist but our universe did grow large and old it did allow you to exist indeed the truth is the universe is not a heavyweight it's not even a flyweight so the question is why is there so little dark energy where is all the NP Punk enery why hasn't it destroyed the [Music] universe to understand the pun enerie and the puzzle it creates we have to travel back a 100 years to the German city of Hamburg to a cafe overlooking the banks of the inner aler Hamburg is a vibrant City risen From the Ashes of World War I a bustling metropolis and a center of intellectual thought and in the cafe are two physicists two friends uto Stern is a bon vion he enjoys the Finer Things in life good food good wine good company he sometimes takes a flight to Vienna just to have lunch Wolf Gang poy however is a very different character he is currently sporting a black eye sustained the night before in the bars of the reaper Barn in hamburg's Notorious San POI District poy had been brawling as he often did fueled by alcohol and a fiery personality Stern takes a sip of his Brandy and turns to his old friend I'm telling you Wolf Gang the Punk's energy is real I've calculated its effects on the vapor pressure of the Isotopes of neon if it were absent as you say it should be the difference in the vapor pressure of neon 20 and neon 22 would be enormous but poy isn't convinced he begins scribbling down a calculation on a napkin when he's done he looks up triumphantly but what of gravity Otto if the null Punk's energy were real as you say it should be the universe would not even reach the Moon Moon the null Punk energy is the energy of empty space the energy of the vacuum consider the universe around you it is filled with stars that shine their light throughout the cosmos from the Menace of red giants to the sickly glow of white dwarfs there are hostile planets in orbit around these stars giant and minnow too hot and too cold there are the warm and welcoming planets like the Earth jewels in the solar system where life can prosper there are towering clouds of gas monuments of colored nebula where stars are being born and all of this stuff carries Mass it carries energy but suppose a cosmic bayith were to enter the universe and take it all way they take away every Star every planet every human and all other forms of complex life they take away the nebula the black coals the bacteria and dust they take everything alive and dead large and small what would be left a dark and Silent place of true desolation the most empty of empty space naively you might expect this emptiness to be weightless to be free of all energy having been robbed of its Wares by The Cosmic bayth but that is not true at least we don't think it's true quantum theory has taught us that empty space does carry energy it carries the null puns energy the Zero Point Energy the vacuum energy the cosmological constant the celebrated German physicist and father of quantum mechanics Max plank had toyed with the idea of the nun seni as early as 1911 and soon after it was another German Walter nerst who suggested that the vacuum of empty space was not empty but an exotic medium filled with an enormous amount of energy but perhaps the most celebrated German physicist of the time Albert Einstein had a turbulent relationship with the nun seni and also separately the idea of a cosmological constant at first he was a champion of both indeed it was he who came up with the idea of a cosmological constant in 1917 requiring a repulsive Force present throughout all of space to counter the effect of gravity in what he believed at the time was a static Universe he also separately teamed up with auto Stern and computed the effects of the null pun enery on hydrogen molecules their results matching experimental data but he did not connect the two and within a decade Einstein had switched camps on both the cosmological constant and the nun seni supposedly calling the constant his biggest blunder and stating that no theoretician can utter the word Zero Point Energy without breaking into a half embarrassed half ironic smile but it would turn out that Einstein was right in his invoking of a cosmological constant and wrong in his dismissal of the nun enery and the idea of Zer Point Energy really took hold in the mid 1920s for this was when the legendary German physicist Vera Heisenberg entered the game struck down by severe hay fever in the summer of 1925 Heisenberg had fled to the island of heland where he checked into a guest house overlooking the dunes his allergies were so bad that the lady who ran the guest house assumed he'd been in a fight Heisenberg used his escape to think deeply about the spectral lines of the hydrogen atom thoughts that often led to insomnia and indeed it was in the early hours of one particular night that a breakthrough finally came and Heisenberg finally began to understand how the hydrogen atom behaved he was beginning to understand the sorcerer world of quantum mechanics where everything was a game of [Music] chance and as Heisenberg realized it was a game that led to the Zero Point Energy the null Punk zeni to understand how the Zero Point Energy emerges go to the kitchen and take out a large mixing bowl throw a marble into the bowl and wait for it to settle down eventually it'll seem as if it's at rest at the bottom of the bowl but is that really true can we really say exactly where it is and how fast it is moving if you zoom into the microw world the answer is clearly no there are air particles constantly colliding with the marble knocking it to and fro okay but what if you suck out all the air in the room and cool it down to absolute zero what then does the marble finally come to rest at the bottom of the bowl or does it wiggle it Wiggles Heisenberg realized that there was always some uncertainty the key thing to remember is that quantum mechanics is a game of chance you can only deal with probabilities it turns out that the more you know about a particle's position the less you know about its momentum so if we know where a particle is we cannot say how fast it is moving and vice versa this means that if we scale the marble down to the size of a fundamental particle we can never say if it is exactly at rest at the bottom of the bowl as that would mean we had exact knowledge of both its position and its momentum Heisenberg's understanding of uncertainty and the laws of quantum mechanics mean that it's simply not possible to know both exactly in the microscopic world something always has to wiggle and so now we can return to our Cosmic bayth deter determined to empty the universe of all its stars planets and Little Green Men before he arrives the universe is littered with particles electrons and photons quarks and gluons Gage bosons and higs bosons and perhaps even some particles we still don't know about these particles are in actual fact just ripples in the fundamental fields of nature the photon is a ripple in the electromagnetic field the electron a ripple in the electron field the higs boson a ripple in the higs field you can imagine these fields as an ocean swell and the particles as the ripples on top what the baith is really trying to do is get rid of all the ripples all the excitations of these fundamental Fields he is trying to silence the ocean of reality to make it perfectly flat but as we know he can't heisenbergs and un certainty principle means he can never silence the ocean completely there is always that Quantum wiggle tiny short-lived ripples in the fundamental Fields but these remaining ripples don't correspond to real particles like electrons or photons you can touch and perhaps even hang on to if they were real if you could hang on to them the bayith would just grab them and take them away instead they are something more mysterious they are virtual particles these virtual particles are forever popping in and out of existence like a bubbling broth in the vacuum of empty space they're not the kind of particles you can hang on to but they do give the vacuum its energy they give it the nulls energy but is this energy actually real or was it just a figment of Heisenberg's imagination there is a fascinating macroscopic example that helps to answer answer this question the gecko as it scampers freely across walls and ceilings its seemingly magical ability to defy gravity is thought to have its roots in the null Punk eneri it turns out that the energy stored in a vacuum through the bubbling broth of virtual particles depends crucially on the shape of its surroundings change the shape and you can change the energy that means that the vacuum will push and pull on the walls that surround it as it tries to lower its energy this push and pull of the vacuum is a force known as the Casmir Force named after the Dutch physicist hendrik Casmir when the walls of the vacuum are far apart this Casmir force is Tiny But when they're close together this force is big enough to measure changes in the Zero Point Energy also lead to Van deval's forces between atoms and molecules and this is what some biologists think is responsible for the gecko's ability to walk on walls microscopic projections on the soles of their feet surround small pockets of vacuum and by altering the shape the gecko creates a force strong enough to defy [Music] gravity and so now that we've accepted that the vacuum energy is real we can estimate how big we think it should be how much energy would you expect to find in a coffee cup of empty space to figure this out we need to break space up into lots of little pieces like a spectacular Cosmic jigsaw the size of the pieces is going to affect our estimate so we should think about what size we should use you might think the pieces should be as small as the eye can see that would make them little boxes about a millimeter across but why would we allow ourselves to be held back by the limitations of a human eye when poy was doing his calculation in the cafe in Hamburg he imagined jigsaw pieces with sides about a trillion times smaller at around a fentom meter this corresponds to the classical electron radius which was at the limit of experimental physics at the time and this is where Heisenberg comes in with his uncertainty if you can resolve the universe Into jigsa Pieces Just A femometer across you can have extremely precise knowledge about where and when a virtual particle pops in and out of existence Heisenberg says that must come a to price you must lose knowledge of the momentum of the particle this means you must also lose knowledge of its energy as you make the jigsaw pieces smaller and smaller the virtual particles can reach higher and higher energies for jig or pieces like Poes about a feter across these energies reach up to a few trillionth of a jewel for each of our little boxes that doesn't seem like much but remember the boxes are tiny so the density is dangerously High high for a coffee cup of empty space with lots and lots of these tiny little boxes the total energy stored inside the cup comes out to a whopping 100,000 trillion trillion Jews that's enough energy to boil away all the oceans of the Earth but why stop there it's been almost a century since poy performed his calculation in the cafe in Hamburg since then physics has moved on we've developed technology has enabled us to probe deeper and deeper into the microscopic fabric of the universe in the tunnels beneath the mountains on the Swiss French border lies the Large Hadron Collider cern's state-of-the-art particle accelerator a machine that recreates the first moments of the universe colliding subatomic particles head on at almost the speed of light these collisions allow physicists to PE deep into the microw world with unprecedented resolution breaking the universe up into pieces that at 10-19 M across that is 10,000 times smaller than an electron 10,000 times smaller than the jigsaw pieces po had imagined when you break down the universe into pieces this small you can resolve virtual particles popping in and out of existence every billionth of a billionth of a nanc filling the vacuum with enormous amounts of ambient Quantum energy with this estimate a coffee cup of empty space would have enough energy to blow up an entire planet and not just once more than a 100 million times wiping out every planet in the galaxy but again why stop there the collisions in the tunnel at CERN are at the edge of experimental physics as it is today but that is only limited by our technology and of course funding there's no no real reason to believe that physics could not go beyond this point with better machines we could imagine peering even more deeply into the Micro World resolving the Universe on an even smaller scale so how far could we go well we could imagine breaking the universe up into pieces as small as the plank length which is more than a million billion times smaller than the scale of our experiments at CERN the plank length is the distance at which the fabric of space and time ceases to make sense as it becomes overwhelmed by Quantum effects if we tried to break the universe up into pieces smaller than the plank length the very notion of space and time would begin to disintegrate but tiny little boxes of Plank and size are more than enough to worry about if we break the universe up into pieces this small we find that our coffee cup of empty space would contain a Google gigles of energy and that is enough to blow up every planet and St star in the observable universe again and again and again more than a trillion trillion trillion trillion times so should we be worried should it terrify us to learn that empty space must contain such gargantuan energies lurking all around us between the molecules of air even in the empty space between the atoms in your body in a world without gravity there's nothing to fear for this null Punk's energy is constant the energy density of empty space is the same everywhere that's why we sometimes call it the cosmological constant to create weapons that destroy planets and galaxies you need energy differences gradients in the energy density that allow you to generate a force the true underlying vacuum energy of of our entire universe has constant density across all of space there are no gradients you couldn't use it to crush a grape never mind a Galaxy without gravity this vacuum energy cannot touch you but with gravity that's a very different story with gravity the vacuum energy Goes [Music] Wild to understand this we need to understand how gravity Works Einstein taught us that the gravitational force is very different to the other fundamental forces in nature in some senses it's not really a force at all gravity is really the shape of SpaceTime and so it isn't just mass that bends space and time mass is just a form of energy all energy bends the space and time around it creating the Warped shapes in SpaceTime that we perceive as Gravity the null puns energy is no exception the vacuum energy the cosmological constant whatever you want to call it will bend the shape of space and time even if it is the same everywhere and of course the more of this energy you have the more space time should be bent this is why poy declared that the Universe would not even reach the moon e calculated the density of the energy in empty space and worked out how much that would bend SpaceTime quickly seeing that SpaceTime would be bent right back so that the observable realm could not even reach as far as the moon but we've already seen how poy had underestimated the vacuum energy guided as he was by the limits of experimental physics in his day modern estimates suggest that the Universe would contain so much energy in empty space it would be bent into Oblivion crushed under its own weight it wouldn't even reach beyond the end of your nose never mind the moon and now we have to State the obvious the universe does reach beyond the end of your nose in fact it reaches a billion trillion times farther than the moon the edge of the observable universe as we've seen is around 462 billion light years away if the cosmological constant is there it's a whole lot smaller than we expected in fact it should be more than a Google time smaller the energy stored in a coffee cup of empty space cannot be enough to destroy a planet or Star it shouldn't even be enough to crush the smallest insect in the world this is the cosmological constant problem our best and most trusted theories of fundamental physics come together to predict that our universe should be so overwhelmed by the nul pun eni by a terrifyingly large cosmological constant that it simply shouldn't exist and yet it does [Music] why on the 3rd of September 1949 a filter paper on a weather plane flying from Japan to Alaska detected unusually high levels of radioactivity the filter paper was sent to the US scientific Lab at Los Alamos for further analysis and on the 23rd of September US president Harry S Truman announced that the Soviet Union had successfully detonated an atomic device the bomb had been detonated a few days prior to the Flight of the weather plane at 7:00 a.m. local time on August the 29th at the semipalatinsk test site in modernday Kazakhstan 10 km south of Ground Zero were eight men amongst them Yakov zeldovich head of the theory division at the Soviet nuclear Development Center at aramas 16 zeldovich remembered seeing a bright cone-shaped flash with a tongue of Fire coming out of the dust and smoke before stepping down into the safety trench after 30 seconds the sound of the explosion reached the trench like a clap of Thunder some of the men celebrated in Praise of comrad Stalin zeldovich stayed silent to the Soviets zeldovich was a silent Superstar a legendary physicist who played a pivotal role in their nuclear weapons program and one of only 16 people to have been named a hero of socialist labor on three separate occasions whereas Robert Oppenheimer became less active in physics after his involvement in developing the nuclear bomb zeldovich went on to make major contributions to particle physics astronomy and cosmology and it was zeldovich 20 years later in 1967 and 1968 who made made the world take notice of the cosmological constant problem it's not clear if zeldovich knew about Po and his enigmatic calculation in the cafe in Hamburg in the mid 1920s but it didn't matter zeldovich was armed with far more powerful tools than poy ever had at his disposal by the late 60s the general theory of relativity was well established along with its applications to cosmology Quantum field theory was fast becoming the dominant description for a subatomic world it was really zeldovich who saw that the vacuum ought to be a bubbling broth of virtual particles endlessly popping in and out of existence weighing down the vacuum bending the universe back into Oblivion zeldovich knew that something had to be wrong with our understanding of the universe and sensed an opportunity for physics stating that the clarification of the cosmological constant will be of tremendous fundamental significance for the theory of Elementary particles so what can we do about this cosmological constant problem perhaps we should just take an empirical approach the energy of empty space is whatever we measure it to be if it's small it's small who cares about zeld doich and the predictions of quantum field Theory who cares about poy and his idiosyncratic Cafe calculations perhaps that's just not how nature chose to do things but this is not very satisfying the quest is to discover How the Universe works and a wealth of empirical data points towards a Micro World accurately described by Quantum field Theory the relativistic version of quantum mechanics developed in the Years following the second world war we can't just simply abandon it not after so much experimental success elsewhere and then there is the general theory theory of relativity the Zenith of Einstein's genius describing gravity as the shape of SpaceTime accurately predicting exotic phenomena like the bending of light around the sun and the perah helian procession of the planet Mercury a slow but Relentless shift in its elliptical orbit it too has a huge wealth of data supporting it even being added to to this day ligo's detection of gravitational waves in 2015 another feather in its cap but together these two two great pillars of 20th century physics predict a universe instantly destroyed by the overwhelming weight of the vacuum by a Herculean cosmological constant by the nul punk eni as zeldovich realized more than 50 years ago we are obviously misunderstanding something something very important the cosmological constant problem is such a crisis in our understanding of fundamental physics its resolution is expected to lead to something profound a step change in our picture of how the universe really works another example of something similar is the famous black hole information Paradox another problem that zeldovich had a hand in this is the question of what happens to all the information you throw into a black hole does it disappear in violation of the laws of quantum mechanics or does it survive and if so where does it go just like the solution to the cosmological constant problem the answers to these questions are expected to reveal something deep about the fundamental fabric of our physical world and so theoretical physicists are forever looking for the solution to the cosmological constant problem in the half century since zeldovich formulated the problem in modern terms many solutions have come but many have also gone a Common Thread is a assuming that zelich's calculation of the cosmological constant is only part of the story that the elementary particles contribute an overwhelmingly large vacuum energy but that there is another piece another constant from some hitherto hidden sector of the microw world that cancels out the parts that zel doich found how and why it would be able to cancel them out to such an astonishing level of precision is the key piece of the puzzle it's like balancing the weight of a trillion trillion trillion trillion trillion Suns accurate to the mass of a single electron the most popular idea makes use of the Multiverse the idea that our observable universe is just one of many possible universes each with a different value for the overall cosmological constant and perhaps other fundamental constants in most parts of this theoretical Multiverse the scales are off balance and the overall cosmological constant is large and overwhelming but in some rare corners of the Multiverse the balancing works and the overall cosmological constant is small just like it is in our universe String Theory our most promising candidate for a Theory of Everything predicts that such a Multiverse could exist it has all the right sort of hidden sectors with a multitude of different possibilities depending on who you ask string theory predicts between 10 to the power of 500 and 10 to the power of 272,000 different vacua different universes with range of vacuum energies a spectrum of cosmological constants this Multiverse is known as the string theory landscape and it's just what we would need to take on the cosmological constant problem with an Innovative but controversial idea but if small cosmological constants are rare in this possible Multiverse how come we find ourselves in a universe with a tiny cosmological constant this is where some physicists Advocate the anthropic principle the idea is that those universes with a large and overwhelming cosmological constant are uninhabitable because of the enormous weight of empty space if the cosmological constant is too large and positive the universe is blasted apart too quickly so much so that matter is unable to Clump together and stars and planets never get the chance to form if the cosmological constant is too large and negative the expansion of the universe rapidly gives way to an apocalyptic crunch a universe squashed out of existence again before stars and planets ever get to form it is only in these rare universes like ours where the cosmological constant is unexpectedly small the conditions are just right a goldilux universe with a slow and gentle Cosmic Evolution allowing time for stars and planets to form and providing a home home for complex life indeed it is only in these goldilock worlds that someone or something like poy or zeldovich can eventually be born smart enough to ask difficult questions about the cosmological constant about the energy of empty space but not Everyone likes this explanation some people say that the Multiverse and anthropic selection is unscientific that it cannot be falsified although that is not entirely true back in 1997 Nobel laurat Steven Weinberg and his collaborators argued that if the vacuum energy was less than 60% of the total energy budget of the universe anthropic arguments could not explain why it was so small this was a testable prediction of the anthropic solution to the cosmological constant problem and as it happened less than a year later astronomers announced the discovery of dark energy making up around 70% of all the energy in the observable universe the anthropic principle had passed its first test but people are still searching for alternative ideas that don't rely on anthropic reasoning these ideas go by many names super symmetric large extra Dimensions vacuum energy sequestering pan Cosmic relativity to name but a few however the is no consensus and right now the mystery of the cosmological constant remains unsolved and so we set out to weigh the universe and stumbled across one of the most embarrassing problems in fundamental physics we wait the stars and the planets and clouds of interstellar gas we wait the Halos of dark matter that shroud our galaxies and we weighed the vacuum of empty space and it weighed so little where was the weight of the bubbling broth of virtual particles frantically popping in and out of existence it should have crushed the universe within an instant of creation but it didn't our universe is light a gentle giant that allowed you and I to live on a rocky planet orbiting an ordinary yellow star somewhere in a galaxy called the Milky Way you've been watching the entire history of the universe don't forget to like And subscribe and leave us a comment to tell us what you think thanks for watching and we'll see you next time
