0:00:02 > 0:00:06These are the Appennine mountains in Central Italy.
0:00:08 > 0:00:10Buried underneath them
0:00:10 > 0:00:13is one of the most sophisticated science labs in the world.
0:00:16 > 0:00:19Last month, an international group of scientists
0:00:19 > 0:00:21working here on a particle physics experiment
0:00:21 > 0:00:24called OPERA made an astonishing claim.
0:00:27 > 0:00:30They said they had detected particles that seemed to travel
0:00:30 > 0:00:33faster than the speed of light.
0:00:33 > 0:00:36It was a claim that contradicted
0:00:36 > 0:00:39more than 100 years of scientific orthodoxy.
0:00:39 > 0:00:41It has created a furore.
0:00:41 > 0:00:43If it's true the implications are amazing.
0:00:43 > 0:00:47They're mind-blowing. They really will turn things on their heads.
0:00:47 > 0:00:48This is earth-shaking if true.
0:00:48 > 0:00:51You would be able to travel back in time.
0:00:51 > 0:00:55We have to tear up all the textbooks and start again.
0:00:56 > 0:00:57My name's Marcus du Sautoy.
0:00:57 > 0:01:01I'm a mathematician and as a mathematician,
0:01:01 > 0:01:05I'm used to dealing with ideas that seem impossible in the real world.
0:01:05 > 0:01:08For me, it's moments like this
0:01:08 > 0:01:12when data clashes with theory that are always rather thrilling.
0:01:12 > 0:01:15You can almost feel the shudder that passes through the entire
0:01:15 > 0:01:19scientific community when a result as strange as this comes out.
0:01:19 > 0:01:21Everybody's talking about it.
0:01:23 > 0:01:26Is this the moment for a grand new theory to emerge that makes
0:01:26 > 0:01:31sense of all the mysteries that still pervade physics?
0:01:31 > 0:01:35Or has there just been a mistake in the measurements?
0:01:35 > 0:01:37I'm going to explore one of the most dramatic
0:01:37 > 0:01:40scientific announcements for a generation.
0:01:40 > 0:01:43What does it mean and why does it matter?
0:01:52 > 0:01:54Our story starts with light.
0:01:55 > 0:01:59For centuries, light has fascinated us.
0:02:01 > 0:02:03Our ancestors built monuments to capture light
0:02:03 > 0:02:07from the sun at particular times of the year.
0:02:08 > 0:02:12Light gives us colour. It's how we see the world.
0:02:15 > 0:02:17Light floods the cosmos.
0:02:19 > 0:02:23But it has always been mysterious.
0:02:23 > 0:02:28One of the biggest mysteries about light is how fast does it travel?
0:02:28 > 0:02:31Unravelling this question, would lead to one of the greatest
0:02:31 > 0:02:34and most surprising leaps in the history of science.
0:02:37 > 0:02:39Until 350 years ago,
0:02:39 > 0:02:43many scientists argued that light didn't really travel at all.
0:02:43 > 0:02:46It was transmitted instantaneously from source to eye.
0:02:48 > 0:02:51But then an astronomer, making careful observations
0:02:51 > 0:02:55of the moons of Jupiter showed it took a finite period
0:02:55 > 0:02:59of time for light waves to reach Earth.
0:02:59 > 0:03:02That meant light travel couldn't be instantaneous.
0:03:02 > 0:03:05It had to have a finite speed.
0:03:05 > 0:03:07Another puzzle remained.
0:03:07 > 0:03:11If light was a wave, then scientists concluded it must be travelling
0:03:11 > 0:03:16through some medium, in the same way as sound travels through air.
0:03:16 > 0:03:19This medium was given a name - the ether.
0:03:24 > 0:03:29It was thought that the ether was able to flow like the wind.
0:03:29 > 0:03:33Therefore, light waves that were travelling in the same direction
0:03:33 > 0:03:37as the ether should travel faster than those fighting against it.
0:03:39 > 0:03:42In the 1880s, scientists tried to measure variations
0:03:42 > 0:03:46in the speed of light travelling in different directions.
0:03:46 > 0:03:49But to their surprise, they found no difference.
0:03:49 > 0:03:54However you measured it, light always went at the same speed.
0:03:56 > 0:03:58As the 20th century dawned,
0:03:58 > 0:04:01scientists were still wrestling with the strange behaviour of light
0:04:01 > 0:04:06and in particular, what speed it travelled at.
0:04:06 > 0:04:09The stage was set for the arrival of a genius who would unravel
0:04:09 > 0:04:11the mysteries of light
0:04:11 > 0:04:16and in the process, transform our understanding of the universe.
0:04:24 > 0:04:29In 1902, a young physicist arrived in the Swiss town of Berne.
0:04:29 > 0:04:33He trained as a physics and maths teacher in Zurich,
0:04:33 > 0:04:36but had been unable to find a teaching job.
0:04:36 > 0:04:40Eventually, he found work in the Swiss patent office.
0:04:40 > 0:04:43It was far from a lofty, academic institution,
0:04:43 > 0:04:47but it turned out to be just the environment he needed.
0:04:47 > 0:04:49His name was Albert Einstein.
0:04:56 > 0:05:01An amateur scientist, someone who didn't have an academic position.
0:05:01 > 0:05:04This patent clerk who worked on physics
0:05:04 > 0:05:07when he wasn't doing his day job
0:05:07 > 0:05:10was quite an unusual person to be the one
0:05:10 > 0:05:13who revolutionised our ideas of space and time.
0:05:13 > 0:05:16I don't know what the workload was in the patent office.
0:05:16 > 0:05:19Maybe there weren't so much patents coming in
0:05:19 > 0:05:22in Switzerland in those days and he had a lot of time to think.
0:05:22 > 0:05:25Anyway, somehow or other, he was able to think
0:05:25 > 0:05:27very long, very hard and very deep.
0:05:27 > 0:05:30The clerk's work gave Einstein time
0:05:30 > 0:05:34to ponder thought experiments, deceptively simple scenarios
0:05:34 > 0:05:38that enabled him to explore the most complex of concepts.
0:05:39 > 0:05:44Einstein was very much an individual, lone scientist
0:05:44 > 0:05:48thinking his deep thoughts and, perhaps precisely because
0:05:48 > 0:05:52he was working by himself, he got insights other people hadn't seen.
0:05:54 > 0:05:58Einstein was fascinated by the mysterious behaviour of light.
0:05:58 > 0:06:02It was a wave, yet it also had the properties of a particle,
0:06:02 > 0:06:04what came to be known as a photon.
0:06:06 > 0:06:10How fast did it travel, he wondered? And did it have a speed limit?
0:06:10 > 0:06:14From the age of 16, Einstein had been pondering a thought experiment.
0:06:14 > 0:06:19If I look into this shaving mirror and I accelerate faster and faster
0:06:19 > 0:06:25towards the speed of light, then does my image suddenly disappear?
0:06:25 > 0:06:28If you think about it, the photons from my face have got to travel
0:06:28 > 0:06:31the distance from my face to the mirror and if I am going
0:06:31 > 0:06:35at the speed of light, then those photons have to go travelling faster
0:06:35 > 0:06:39than me. Namely, the light is travelling faster
0:06:39 > 0:06:41than the speed of light.
0:06:41 > 0:06:44Now, Einstein believed his image wouldn't disappear,
0:06:44 > 0:06:48so he started to think about how to resolve this paradox.
0:06:51 > 0:06:54In the spring of 1905, Einstein was ready
0:06:54 > 0:06:57to launch his ideas on the world.
0:06:57 > 0:07:02In that one year, Einstein published four papers, any one of which
0:07:02 > 0:07:05would have been enough to create a sensation in their own right.
0:07:05 > 0:07:09It was, arguably, one of the most sustained and extraordinary bursts
0:07:09 > 0:07:12of scientific creativity the world has ever seen.
0:07:13 > 0:07:17One of those papers transformed our understanding of light.
0:07:22 > 0:07:25And here it is, all 31 pages of it.
0:07:25 > 0:07:28It's an astonishing paper in many different ways, not least
0:07:28 > 0:07:31because if I look at one of the papers I have published,
0:07:31 > 0:07:36then, at the end, I reference 39 other papers that I rely on.
0:07:36 > 0:07:40In Einstein's paper there are no references at all.
0:07:42 > 0:07:47It contains a set of scientific laws that define not just our world,
0:07:47 > 0:07:50but also our entire universe.
0:07:50 > 0:07:54At the centre of these is the statement that the speed of light,
0:07:54 > 0:07:58when it travels through a vacuum, is absolute.
0:07:58 > 0:08:00Nothing can travel faster.
0:08:02 > 0:08:05It was an incredibly audacious piece of reasoning.
0:08:05 > 0:08:09Einstein realised that the way we looked at the universe was wrong,
0:08:09 > 0:08:14particularly our intuitive sense of how time and space worked.
0:08:14 > 0:08:18We can see how, by doing a thought experiment of our own
0:08:18 > 0:08:22with the help of the 12.12 to Ashford.
0:08:23 > 0:08:26If I shine this torch while standing still on the platform,
0:08:26 > 0:08:29then the beam of light from the torch
0:08:29 > 0:08:31is going to be going at the speed of light.
0:08:31 > 0:08:33That's straightforward.
0:08:35 > 0:08:39But what happens to the same beam of light went I'm on a moving train?
0:08:42 > 0:08:46Now, I've just asked the conductor how fast the train is going.
0:08:46 > 0:08:49He says it's going at 140 miles an hour.
0:08:49 > 0:08:53This is the same torch I had on the platform.
0:08:53 > 0:08:55If I switch it on, the question is,
0:08:55 > 0:08:57for somebody standing outside in the field,
0:08:57 > 0:09:00how fast do they think the light is travelling?
0:09:00 > 0:09:03Because logic would suggest that the light is travelling
0:09:03 > 0:09:06at the speed of light from the torch, but then I need to add on
0:09:06 > 0:09:09the 140 miles an hour that the train is going.
0:09:09 > 0:09:13But Einstein said no. The speed of light is a constant.
0:09:13 > 0:09:16It doesn't matter where you are in the universe, how you measure it,
0:09:16 > 0:09:18on a train to Ashford or on a spaceship
0:09:18 > 0:09:22travelling across the universe or standing still outside,
0:09:22 > 0:09:24the speed of light is the same.
0:09:25 > 0:09:28Einstein's brilliance was to realise
0:09:28 > 0:09:30that if the speed of light was the same regardless
0:09:30 > 0:09:35of where you measured it from, then something else had to give.
0:09:36 > 0:09:40He concluded that it was time that was changing.
0:09:40 > 0:09:41Time was not a constant.
0:09:41 > 0:09:46Instead it changed depending on how quickly you were moving.
0:09:47 > 0:09:51The faster you travel, the slower time passes.
0:09:51 > 0:09:56Einstein's view of the universe was seen as radical at the time
0:09:56 > 0:09:59and it's still hard to grasp.
0:09:59 > 0:10:04But over the years, countless experiments have proved him right.
0:10:04 > 0:10:07These theories have a practical impact in the real world,
0:10:07 > 0:10:12an example being the GPS or Global Positioning System.
0:10:14 > 0:10:17'US Naval Observatory Master Clock.
0:10:17 > 0:10:19'At the tone, Mountain Daylight Time
0:10:19 > 0:10:22'18 hours, 48 minutes, 5 seconds.'
0:10:22 > 0:10:23BEEP
0:10:25 > 0:10:28GPS uses a network of satellites orbiting
0:10:28 > 0:10:32at speeds of 14,000 kilometres per hour
0:10:32 > 0:10:35to accurately pinpoint locations all over the globe.
0:10:35 > 0:10:41To ensure precision, it's vital that the time kept by the satellites
0:10:41 > 0:10:45is the same as the time kept by the receivers on the ground.
0:10:45 > 0:10:51But the satellites travel so fast that, compared to the receivers
0:10:51 > 0:10:56on earth, time runs slower by seven microseconds a day.
0:10:56 > 0:11:00If we didn't use Einstein's theories and take this into account,
0:11:00 > 0:11:02the accuracy of our GPS systems would drift
0:11:02 > 0:11:05by more than two kilometres a day.
0:11:07 > 0:11:09Einstein didn't stop there.
0:11:09 > 0:11:13He theorised that not only did light travel at a constant speed,
0:11:13 > 0:11:18but that speed was also the speed limit of the universe.
0:11:18 > 0:11:20Nothing can travel faster.
0:11:22 > 0:11:26That's because of the relationship between mass and energy.
0:11:26 > 0:11:31Einstein said that mass and energy were two sides of the same coin.
0:11:31 > 0:11:36That means that if the amount of energy an object has increases,
0:11:36 > 0:11:38then so does its mass.
0:11:38 > 0:11:43Crucially, increasing an object's speed increases its energy.
0:11:47 > 0:11:51The faster I travel on this train, the more mass I gain.
0:11:51 > 0:11:55For example, if I was travelling at 90% of the speed of light,
0:11:55 > 0:11:59then my mass would be twice that as if I was stationary.
0:11:59 > 0:12:03The more I accelerate, the more my mass increases
0:12:03 > 0:12:06and the more energy I'm going to need to make me accelerate.
0:12:06 > 0:12:08Until, when I reach the speed of light,
0:12:08 > 0:12:12the equations force my mass to be infinite.
0:12:12 > 0:12:15I'm going to need an infinite amount of energy to get there.
0:12:15 > 0:12:19But no-one can possess infinite energy however hard they tried.
0:12:19 > 0:12:22That's why, according to Einstein, it's impossible
0:12:22 > 0:12:25to cross the speed of light barrier.
0:12:25 > 0:12:28From a thought experiment,
0:12:28 > 0:12:31Einstein was able to radically alter our view of the world.
0:12:33 > 0:12:36He concluded that the speed of light is constant
0:12:36 > 0:12:40and that nothing with mass can travel faster than the speed.
0:12:41 > 0:12:45These concepts are at the heart of our modern understanding
0:12:45 > 0:12:47of the universe.
0:12:47 > 0:12:51The results picked up by the OPERA team in Italy were so shocking
0:12:51 > 0:12:55because they raise serious questions not just about Einstein's theory,
0:12:55 > 0:12:59but all the evidence that's been gathered to support it.
0:12:59 > 0:13:02That said, in some ways, we shouldn't be so shocked
0:13:02 > 0:13:05by the results because the OPERA scientists were studying
0:13:05 > 0:13:09one of the strangest and least understood particles there is -
0:13:09 > 0:13:11the neutrino.
0:13:11 > 0:13:14And if there was one particle that was going to break the rules,
0:13:14 > 0:13:15it was this one.
0:13:16 > 0:13:20The neutrino's been the bad boy of physics,
0:13:20 > 0:13:23basically, putting physicists out of their comfort zone.
0:13:23 > 0:13:25I think that's the best way to put it.
0:13:25 > 0:13:28A lot of unusual things have been revealed by the neutrino,
0:13:28 > 0:13:31so maybe we shouldn't be surprised by this novelty.
0:13:33 > 0:13:37There are 16 types of fundamental particles that are the smallest
0:13:37 > 0:13:40and simplest building blocks in the universe.
0:13:40 > 0:13:44Together, they explain the world and what holds it together.
0:13:45 > 0:13:48Three of those elementary particles are neutrinos.
0:13:48 > 0:13:52Their assistance was first predicted in 1930
0:13:52 > 0:13:56by Austrian physicist Wolfgang Pauli.
0:13:56 > 0:14:00But Pauli didn't think it would ever be possible to find one,
0:14:00 > 0:14:04because their properties make them incredibly difficult to spot.
0:14:04 > 0:14:09It's a very anti-social particle. It doesn't like to talk to the world.
0:14:09 > 0:14:12Right now, you are being crossed by billions of neutrinos per second,
0:14:12 > 0:14:15and you don't feel them because they go through you.
0:14:15 > 0:14:19They go through the earth, through everything without interacting.
0:14:19 > 0:14:22And still, the universe is pervaded by them. It's full of them.
0:14:22 > 0:14:24There is a swarm of neutrinos going around,
0:14:24 > 0:14:27many more neutrinos than particles of light and atoms
0:14:27 > 0:14:29and anything you are used to.
0:14:31 > 0:14:35It order to understand how neutrinos are able to travel straight
0:14:35 > 0:14:37through matter without being noticed,
0:14:37 > 0:14:40we need to think about what matter is made of.
0:14:40 > 0:14:42Every physical thing in the world around us,
0:14:42 > 0:14:46from mountains and buildings to you and me, is made of atoms.
0:14:46 > 0:14:51And atoms are made up of a nucleus at the centre,
0:14:51 > 0:14:54surrounded by orbiting electrons,
0:14:54 > 0:14:58a bit like a solar system with a sun and orbiting planets.
0:15:00 > 0:15:03The mind-boggling thing about matter is that, although it looks
0:15:03 > 0:15:07and feels solid, it's actually mostly empty space.
0:15:07 > 0:15:10There are vast swathes of nothingness between the tiny nucleus
0:15:10 > 0:15:13and the orbiting electrons.
0:15:13 > 0:15:16And the neutrino is so small without any charge,
0:15:16 > 0:15:19that it can pass through this space very easily.
0:15:19 > 0:15:23In fact, the neutrino's so tiny that if the atom
0:15:23 > 0:15:28is the size of the solar system, the neutrino is the size of a golf ball.
0:15:30 > 0:15:35These tiny particles existed in theory for a quarter of a century
0:15:35 > 0:15:38without anyone being able to see them.
0:15:38 > 0:15:41But then something happened to change that.
0:15:44 > 0:15:46The nuclear bomb.
0:15:48 > 0:15:52The power of a nuclear bomb comes from a chain reaction
0:15:52 > 0:15:55of spitting atomic nuclei.
0:15:55 > 0:15:58In the 1950s, a young researcher called Fred Reines
0:15:58 > 0:16:02realised that this chain reaction would produce
0:16:02 > 0:16:04an intense burst of neutrinos,
0:16:04 > 0:16:08and so be the perfect place to hunt for the elusive particle.
0:16:10 > 0:16:14But detecting neutrinos from a nuclear explosion wasn't practical.
0:16:14 > 0:16:17So Reines turned his attention to the much more controlled
0:16:17 > 0:16:19chain reaction in a nuclear reactor.
0:16:21 > 0:16:24Although most neutrinos produced by the reactor passed through
0:16:24 > 0:16:29the gaps inside atoms, so many neutrinos were produced
0:16:29 > 0:16:33that every now and then, one would collide with an atom's nucleus.
0:16:33 > 0:16:37When it did, a charged particle would be ejected.
0:16:37 > 0:16:41He set up his experiment, which he called Project Poltergeist,
0:16:41 > 0:16:45and waited for the characteristic signal of this interaction -
0:16:45 > 0:16:47a distinctive double pulse of energy.
0:16:49 > 0:16:55In June 1956, Reines announced that he had detected the neutrino.
0:16:59 > 0:17:03Since that discovery, we've become a bit more adept at creating
0:17:03 > 0:17:07and observing this most elusive of particles.
0:17:07 > 0:17:11We've created neutrinos in man-made particle accelerators
0:17:11 > 0:17:13like the ones in CERN in Geneva,
0:17:13 > 0:17:17as well as detecting them naturally in cosmic rays and from the sun.
0:17:17 > 0:17:22We now know they are essential to our existence.
0:17:22 > 0:17:25All of the elements are made by nuclear reactions
0:17:25 > 0:17:28that would be impossible without neutrinos.
0:17:30 > 0:17:33We also know that despite their tiny size,
0:17:33 > 0:17:38they do still have a small mass, which means, according to Einstein,
0:17:38 > 0:17:42they can't travel faster than the speed of light.
0:17:48 > 0:17:52But that theory has now been challenged by a small group
0:17:52 > 0:17:55of scientists working in one of the most unusual science labs
0:17:55 > 0:17:57in the world.
0:17:57 > 0:18:01Assergi is a sleepy town nestled beneath Gran Sasso,
0:18:01 > 0:18:05a 3,000 metre peak in the Apennines of Central Italy.
0:18:05 > 0:18:08In the early 1980s, a new road was planned here
0:18:08 > 0:18:11that would cut right through the mountain.
0:18:11 > 0:18:14Italian scientists had a brilliant idea.
0:18:14 > 0:18:18They realised that the road would give them
0:18:18 > 0:18:22a unique opportunity to create a physics lab like no other.
0:18:22 > 0:18:26It would give them easy access to the heart of the mountain,
0:18:26 > 0:18:30the perfect place to build a neutrino detector.
0:18:30 > 0:18:32Here we have 15 different experiments,
0:18:32 > 0:18:38and there are roughly, 100 physicists per day working here.
0:18:42 > 0:18:46Neutrinos so rarely interact with matter that it is easy
0:18:46 > 0:18:49for an experiment to be swamped by false readings,
0:18:49 > 0:18:53readings triggered by naturally occurring radiation
0:18:53 > 0:18:56and charged particles such as cosmic rays hitting the experiment.
0:18:59 > 0:19:04The only way to study neutrinos is to find some way to weed out
0:19:04 > 0:19:08as many of these interfering particles as possible.
0:19:12 > 0:19:15Now we are in the middle of the gallery.
0:19:15 > 0:19:17And near here, we have the experiments.
0:19:17 > 0:19:22On top of us, we have 1,400 metres of rock,
0:19:22 > 0:19:25the top of Gran Sasso mountain.
0:19:25 > 0:19:29Here, the cosmic rays are very few, because outside,
0:19:29 > 0:19:32there are 200 per square metre per second.
0:19:32 > 0:19:36Here, just one per square metre per hour. This is a very huge shielding.
0:19:39 > 0:19:41Thanks to the mountain above it,
0:19:41 > 0:19:46this vast chamber is a natural laboratory for neutrino research.
0:19:46 > 0:19:50It was here, in 2008, that scientists began work
0:19:50 > 0:19:53on a sophisticated experiment designed to study
0:19:53 > 0:19:55the nature of neutrinos.
0:19:55 > 0:20:00It was called the Oscillation Project with Emulsion Tracking Apparatus,
0:20:00 > 0:20:03or OPERA for short.
0:20:03 > 0:20:08At this stage, they had no idea of the impact that OPERA would have.
0:20:08 > 0:20:12The OPERA experiment is an experiment designed to study
0:20:12 > 0:20:14the properties of neutrinos.
0:20:14 > 0:20:17It consists of a huge detector which is designed
0:20:17 > 0:20:19to try and find as many of them as it can.
0:20:19 > 0:20:21Once it's found them and counted them,
0:20:21 > 0:20:25it wants to test their properties and enable us to know more about
0:20:25 > 0:20:28what they're doing, what their nature is
0:20:28 > 0:20:31and in fact, anything we can find out about them.
0:20:32 > 0:20:35To begin with, measuring the speed of neutrinos
0:20:35 > 0:20:38was not at the forefront of the scientists' minds.
0:20:38 > 0:20:42They were trying to understand how the three different types
0:20:42 > 0:20:45of neutrinos were formed and how they behaved.
0:20:45 > 0:20:49The first step of the experiment was to create some neutrinos.
0:20:49 > 0:20:52For this, they turned to another underground lab,
0:20:52 > 0:20:55CERN in Switzerland.
0:20:56 > 0:21:00CERN is most famous for the Large Hadron Collider.
0:21:00 > 0:21:04But it was two much less-heralded particle accelerators
0:21:04 > 0:21:06that began the OPERA experiment.
0:21:06 > 0:21:11The scientists started by generating a beam of protons
0:21:11 > 0:21:14which they accelerated around CERN's Proton Synchrotron.
0:21:14 > 0:21:18The proton beam was then passed into the Super Proton Synchrotron
0:21:18 > 0:21:20to accelerate them even further.
0:21:20 > 0:21:23The resulting high-energy beam of protons
0:21:23 > 0:21:25was slammed into a graphite target.
0:21:25 > 0:21:29This produced a cocktail of exotic sub-atomic particles,
0:21:29 > 0:21:33including neutrinos, which then flew off through the Earth
0:21:33 > 0:21:35in the direction of Gran Sasso.
0:21:37 > 0:21:43The 730 kilometre journey took them 2.4 milliseconds.
0:21:43 > 0:21:48They came from that direction. Geneva is in that direction.
0:21:49 > 0:21:52Several billions of neutrinos are produced every day
0:21:52 > 0:21:54at the CERN accelerators.
0:21:54 > 0:21:59They go through the Earth's crust and they reach the OPERA detector.
0:22:01 > 0:22:05Even with billions of neutrinos streaming into the laboratory,
0:22:05 > 0:22:07detecting them still wasn't easy.
0:22:07 > 0:22:12The key was the huge detector at the heart of the Gran Sasso lab.
0:22:14 > 0:22:21It's made from 150,000 bricks of lead, and weighs 4,500 tonnes.
0:22:23 > 0:22:25Lead is particularly dense,
0:22:25 > 0:22:29which increases the chances of a neutrino encountering a nucleus.
0:22:32 > 0:22:35As the neutrinos smashed into the lead nucleus,
0:22:35 > 0:22:37they created charged particles,
0:22:37 > 0:22:40which are detected as tiny flashes of light.
0:22:42 > 0:22:47You can see that with OPERA, it's a waiting game.
0:22:47 > 0:22:49You fire a neutrino beam and you wait,
0:22:49 > 0:22:52and you count as many of these interactions as you can.
0:22:52 > 0:22:56The process generated about 30 flashes of light a day,
0:22:56 > 0:22:58and provided a chance to test more
0:22:58 > 0:23:01than just the type of neutrino arriving.
0:23:01 > 0:23:05The nice thing about this experiment is, although it was set up
0:23:05 > 0:23:08to study the behaviour of neutrinos in a very fundamental sense
0:23:08 > 0:23:11and the types of neutrinos and how they might change into each other,
0:23:11 > 0:23:15is that you can also study more basic properties of them.
0:23:15 > 0:23:18And what OPERA decided they could measure was the speed
0:23:18 > 0:23:20at which neutrinos travel.
0:23:20 > 0:23:24That's quite an easy thing to measure because you know a distance,
0:23:24 > 0:23:26you know where neutrinos were produced,
0:23:26 > 0:23:29you know where you're finding them and how long they took to get there
0:23:29 > 0:23:32if you have a clock where you produced it
0:23:32 > 0:23:35and a clock in your experiment where you've made the measurement.
0:23:35 > 0:23:37That's speed. Speed is just the distance covered
0:23:37 > 0:23:39in a certain amount of time.
0:23:41 > 0:23:44Nobody had anticipated what happened
0:23:44 > 0:23:48when they started measuring how long it took the neutrinos to arrive.
0:23:48 > 0:23:53They seemed to arrive early. Earlier than the laws of physics allow.
0:23:53 > 0:23:5760 billionths of a second, or 60 nanoseconds sooner
0:23:57 > 0:24:00than a beam of light would, if it were to cover the same distance.
0:24:00 > 0:24:04That meant that the neutrinos had travelled at just over
0:24:04 > 0:24:08two thousands of 1% faster than the speed of light.
0:24:08 > 0:24:12If I was on a motorway, I wouldn't expect to get into trouble
0:24:12 > 0:24:15for exceeding the speed limit by that small amount,
0:24:15 > 0:24:17but not in physics.
0:24:17 > 0:24:20The thing about an absolute speed limit is that it is absolute -
0:24:20 > 0:24:23it can't be exceeded in any circumstances,
0:24:23 > 0:24:26by however small an amount.
0:24:26 > 0:24:28Under our current understanding of the universe,
0:24:28 > 0:24:30this just isn't possible.
0:24:33 > 0:24:37The researchers themselves were pretty shocked by the results.
0:24:37 > 0:24:40They spent many months looking for mistakes.
0:24:40 > 0:24:42They brought in outside experts.
0:24:42 > 0:24:45They pored over the figures hundreds of times,
0:24:45 > 0:24:47searching for an error.
0:24:47 > 0:24:50They even made sure they'd factored the movement
0:24:50 > 0:24:52of the continents that changes the distance
0:24:52 > 0:24:55between Italy and Switzerland by small amounts.
0:24:56 > 0:25:03But they couldn't find any mistakes, so they decided to publish.
0:25:03 > 0:25:06When the news broke, it caused a sensation.
0:25:09 > 0:25:13The theory that nothing travels faster than the speed of light is challenged.
0:25:13 > 0:25:16The measurements could be wrong or there's some unknown...
0:25:16 > 0:25:19Scientists have discovered that some tiny particles
0:25:19 > 0:25:20seem to break that rule.
0:25:20 > 0:25:23They seem to be travelling faster than the speed of light.
0:25:23 > 0:25:26For physicists, this is earth-shaking if true.
0:25:26 > 0:25:32It has created a huge furore, basically because if it was true,
0:25:32 > 0:25:36then it would be so astonishing and important.
0:25:36 > 0:25:40If the velocity of light turned out not to be absolute,
0:25:40 > 0:25:45we just have to tear up all the textbooks and start all over again.
0:25:45 > 0:25:49For me, it would mean the direction
0:25:49 > 0:25:53of my own research was wrong.
0:25:53 > 0:25:56So...it WOULD be a revolution, but to me,
0:25:56 > 0:26:00it would also mean that nature's just playing tricks with us.
0:26:00 > 0:26:05On the other hand, it would be nice if it were true.
0:26:05 > 0:26:07Ever since the paper was published,
0:26:07 > 0:26:10the internet has been buzzing with debate.
0:26:10 > 0:26:15There are over 100 papers that have been uploaded in the last few weeks.
0:26:15 > 0:26:19For me, this is a great example of science in action.
0:26:19 > 0:26:22The OPERA team found some data that they couldn't explain.
0:26:22 > 0:26:26For months, they'd been questioning it, doubting it, repeating it,
0:26:26 > 0:26:30and only after intense scrutiny did they eventually publish it,
0:26:30 > 0:26:35not in some triumphalist way, but asking the scientific community
0:26:35 > 0:26:37to see where they might have made a mistake.
0:26:40 > 0:26:43Not surprisingly, many of the responses have been sceptical.
0:26:43 > 0:26:47And there are good reasons for doubting the figures,
0:26:47 > 0:26:50based on both theory and experimental data.
0:26:51 > 0:26:55The first problem is that the finding calls into question
0:26:55 > 0:26:57one of the fundamental principles
0:26:57 > 0:27:00that underpins our understanding of the universe -
0:27:00 > 0:27:02cause...
0:27:02 > 0:27:04and effect.
0:27:05 > 0:27:09Cause and effect is a simple, yet powerful idea.
0:27:09 > 0:27:13One thing follows another in a logically-ordered sequence.
0:27:13 > 0:27:17The important thing is that events stay in the same order.
0:27:17 > 0:27:21If I drink my coffee, I drink the coffee before I put the cup down.
0:27:22 > 0:27:26A happened before B.
0:27:26 > 0:27:28That's important cos A might have caused B.
0:27:32 > 0:27:34Einstein's theory respects the relationship
0:27:34 > 0:27:39between cause and effect, because with an absolute speed limit,
0:27:39 > 0:27:43the speed of light, time can only flow in one direction.
0:27:43 > 0:27:44If that isn't the case,
0:27:44 > 0:27:48then the world can quickly become a very strange place indeed.
0:27:48 > 0:27:51Here's an example of what might happen.
0:27:53 > 0:27:55I'm going to send a text to my friend
0:27:55 > 0:27:59with the winning lottery ticket numbers which were just announced.
0:27:59 > 0:28:04The lottery numbers were...
0:28:04 > 0:28:112, 3, 5, 7, 11, and 13.
0:28:11 > 0:28:13Press "send".
0:28:13 > 0:28:16Now, let's suppose my friend and I have both got phones
0:28:16 > 0:28:19that can send messages faster than the speed of light.
0:28:19 > 0:28:23For this to work my friend has got to be moving relative to me,
0:28:23 > 0:28:25so let's suppose that she's on a spaceship.
0:28:25 > 0:28:30It's a spaceship that travels close to the speed of light.
0:28:30 > 0:28:34This means that if I send a message that can travel faster
0:28:34 > 0:28:36than the speed of light,
0:28:36 > 0:28:39then, as far as she's concerned, it would arrive
0:28:39 > 0:28:41before it had been sent.
0:28:43 > 0:28:47Then, it's possible for me to send her a text
0:28:47 > 0:28:50and for her to reply so that I get the reply before
0:28:50 > 0:28:54I've even sent the original text, which is pretty weird.
0:28:55 > 0:28:57Things get even weirder
0:28:57 > 0:29:01if you start to think whether I can actually act on my friend's text.
0:29:01 > 0:29:04I could now change my lottery numbers to the winning numbers
0:29:04 > 0:29:06and become a millionaire.
0:29:06 > 0:29:11I can change my past, which just doesn't make sense.
0:29:11 > 0:29:16With the order of events all scrambled up, we find ourselves
0:29:16 > 0:29:20in a universe more traditionally inhabited by science fiction.
0:29:20 > 0:29:23If something can travel faster than the speed of light,
0:29:23 > 0:29:28then, in principle, time travel is possible.
0:29:28 > 0:29:32You'd venture into that forbidden region where you are influencing
0:29:32 > 0:29:34things that you shouldn't, according to Einstein.
0:29:34 > 0:29:37This causes paradoxes because you can go back in time
0:29:37 > 0:29:41and kill your grandmother before you were born, all this nonsense.
0:29:42 > 0:29:46For physicists, a consistent theory of the universe in which
0:29:46 > 0:29:49we can travel back in time to win the lottery or kill
0:29:49 > 0:29:52our grandmother is almost impossible to imagine.
0:29:54 > 0:29:55It makes you wonder,
0:29:55 > 0:30:01are the speeding neutrinos playing some sort of joke on us?
0:30:01 > 0:30:04A barman says, "Sorry, we don't serve neutrinos."
0:30:04 > 0:30:07A neutrino walks into a bar.
0:30:09 > 0:30:12In other words, neutrinos that travel faster
0:30:12 > 0:30:15than the speed of light imply all sorts of ideas
0:30:15 > 0:30:20that don't tally with our everyday experience of the universe.
0:30:20 > 0:30:23Another reason why many scientists are sceptical
0:30:23 > 0:30:26that neutrinos really can break the light barrier
0:30:26 > 0:30:29is because it contradicts previous results.
0:30:29 > 0:30:33This is not the first time that the speed of neutrinos
0:30:33 > 0:30:35has been measured.
0:30:35 > 0:30:39In fact, there's one particularly famous observation
0:30:39 > 0:30:41that was made back in the 1980s.
0:30:41 > 0:30:44The reason you probably haven't heard about it
0:30:44 > 0:30:46is because the results were in perfect accord
0:30:46 > 0:30:51with Einstein's theories, so no news headlines and no TV programmes.
0:31:02 > 0:31:07The action began on February 23rd, 1987.
0:31:14 > 0:31:16Astronomers realised that a star on the fringes
0:31:16 > 0:31:21of the Tarantula Nebula in the Large Magellanic Cloud had exploded.
0:31:21 > 0:31:25It's called a supernova, one of the most violent
0:31:25 > 0:31:28and destructive events in the universe.
0:31:30 > 0:31:36We observed it in 1987. It actually happened over 100,000 years ago
0:31:36 > 0:31:39and it took the light from that supernova,
0:31:39 > 0:31:43the energy from that supernova, over 100,000 years to reach us.
0:31:47 > 0:31:51This star exploding threw out enormous amounts of energy.
0:31:51 > 0:31:54Most of it was in neutrinos, some of it was in light.
0:31:54 > 0:31:58The light from the supernova and the neutrinos from the supernova
0:31:58 > 0:32:02reached us almost at exactly the same time.
0:32:09 > 0:32:13Scientists calculated that the neutrinos travelled
0:32:13 > 0:32:16just a tiny bit slower than the speed of light,
0:32:16 > 0:32:19just as you'd expect if Einstein was right.
0:32:22 > 0:32:24Had the neutrinos from the supernova
0:32:24 > 0:32:27travelled at the speed that the OPERA scientists recorded,
0:32:27 > 0:32:30in other words, a little bit faster than the speed of light,
0:32:30 > 0:32:33then they would have arrived here
0:32:33 > 0:32:36four years before the light from the supernova.
0:32:36 > 0:32:38That didn't happen.
0:32:40 > 0:32:43Given this rock-solid verification of Einstein's theory,
0:32:43 > 0:32:46it's not surprising that when the OPERA results were published
0:32:46 > 0:32:50this year, suggesting that neutrinos travelled faster than light,
0:32:50 > 0:32:53most people thought that, somewhere along the line,
0:32:53 > 0:32:55they must have made a mistake.
0:32:57 > 0:33:02When I first heard the result, I was...sceptical
0:33:02 > 0:33:07and I think that most of my colleagues were very sceptical also.
0:33:07 > 0:33:11I heard about this result in the coffee bar at CERN
0:33:11 > 0:33:14about two weeks before it came out and I laughed.
0:33:14 > 0:33:17I was like "Ah, well, they've got something wrong, haven't they?!"
0:33:17 > 0:33:21Data error seems plausible when you consider the details
0:33:21 > 0:33:23of what they were measuring.
0:33:23 > 0:33:27Remember, those neutrinos arrived 60 billionths of a second,
0:33:27 > 0:33:29that's 60 nanoseconds, early.
0:33:29 > 0:33:32It's not the sort of measurement where a standard stopwatch
0:33:32 > 0:33:33would be much use.
0:33:39 > 0:33:43It's worth considering the astonishing nature
0:33:43 > 0:33:46of the measurements we're talking about.
0:33:46 > 0:33:48The world of athletics provides a good comparison,
0:33:48 > 0:33:53a high precision sport relying on super accurate measurements.
0:33:55 > 0:33:58In a 100 metre sprint the race is often so close
0:33:58 > 0:34:01that it results in a photo-finish.
0:34:03 > 0:34:06The winning athletes may be separated from the rest by just
0:34:06 > 0:34:10100th of a second. A gap of 100th of a second in time
0:34:10 > 0:34:14translates into roughly ten centimetres in distance.
0:34:17 > 0:34:22Now, compare that to the neutrinos' journey from Switzerland to Italy.
0:34:22 > 0:34:25The neutrinos that arrived in Gran Sasso
0:34:25 > 0:34:29did so just 60 billionths of a second ahead of schedule.
0:34:30 > 0:34:36If a 100 metre sprint were to be won by 60 billionths of a second,
0:34:36 > 0:34:39then that would mean the winner would have been just under
0:34:39 > 0:34:421,000th of a millimetre ahead of the field.
0:34:49 > 0:34:53So the OPERA team were attempting to measure time
0:34:53 > 0:34:55over almost inconceivably small periods.
0:35:01 > 0:35:05Even the tiniest error could have huge implications.
0:35:08 > 0:35:12The scientists themselves have admitted that there are inaccuracies
0:35:12 > 0:35:13with their measurement.
0:35:13 > 0:35:17Firstly, they could have got the distance between CERN
0:35:17 > 0:35:22and Gran Sasso wrong, but only by about 20 centimetres.
0:35:22 > 0:35:26It is also difficult to pin down the exact moment the neutrinos hit
0:35:26 > 0:35:29the target at Gran Sasso.
0:35:29 > 0:35:33But by far the biggest uncertainty comes from recording exactly
0:35:33 > 0:35:34when the neutrinos left CERN.
0:35:34 > 0:35:39Yet, even adding together all the potential errors identified so far,
0:35:39 > 0:35:43it only gives you around ten nanoseconds.
0:35:43 > 0:35:47That still doesn't come close to explaining why the neutrinos
0:35:47 > 0:35:50arrived 60 nanoseconds early.
0:35:54 > 0:35:58But some of the physicists who have been poring over the results
0:35:58 > 0:36:02reckon that a much larger inaccuracy could be lurking
0:36:02 > 0:36:05deep in the detail of when exactly the neutrinos started their journey.
0:36:09 > 0:36:16So what they do is measure this kind of pulse of the protons at CERN
0:36:16 > 0:36:20and these things leave with some kind of shape.
0:36:20 > 0:36:23Then, in OPERA, they sit there waiting.
0:36:23 > 0:36:27There are billions of protons at CERN producing lots of neutrinos.
0:36:27 > 0:36:32Very few of those neutrinos actually interact in the OPERA detector,
0:36:32 > 0:36:35so you sit there and wait and you get a bang. There's one, bang.
0:36:35 > 0:36:36There's another one.
0:36:36 > 0:36:40Over time you build up a shape of the arrival time of the neutrinos
0:36:40 > 0:36:43and you fit the two together. You fit the proton pulse shape
0:36:43 > 0:36:45and you fit the neutrino arrival shape.
0:36:45 > 0:36:49But the neutrino arrival shape is made up of many fewer events
0:36:49 > 0:36:51than the proton one.
0:36:54 > 0:36:57John Butterworth is concerned that the OPERA scientists
0:36:57 > 0:37:00have assumed that these two shapes are the same
0:37:00 > 0:37:04when there are good reasons why they might not be.
0:37:04 > 0:37:08As far as I can see, they assume that the underlying shape
0:37:08 > 0:37:11of the neutrino arrival is identical to the underlying shape
0:37:11 > 0:37:13that they know very well, of the protons leaving.
0:37:13 > 0:37:15It's not obvious to me that that's true
0:37:15 > 0:37:21because the OPERA experiment, you see a very small fraction of the beam.
0:37:21 > 0:37:23The beam is much bigger than the detector.
0:37:23 > 0:37:28It's a kilometre across and the detector's much smaller than that.
0:37:28 > 0:37:32Also, these protons, a lot happens to them before they become neutrinos.
0:37:32 > 0:37:34There are various ways in which that shape
0:37:34 > 0:37:38could be slightly different. You don't need much of a difference
0:37:38 > 0:37:40to undermine the precision of the measurement.
0:37:40 > 0:37:43I'm not saying this is definitely a mistake,
0:37:43 > 0:37:46but I'm surprised that they didn't treat that more seriously
0:37:46 > 0:37:49and I think I'd have gone, "That needs to be checked."
0:37:55 > 0:38:00So far, dozens of suggestions have been made about potential errors
0:38:00 > 0:38:02in the experiment, but none of them
0:38:02 > 0:38:07have yet been proven to explain the faster than light measurement.
0:38:07 > 0:38:10What strikes me about the paper the team have prepared
0:38:10 > 0:38:11is just how meticulous it is.
0:38:11 > 0:38:15This must be one of the most accurate measurements ever made.
0:38:15 > 0:38:18So, at this stage, I think it's right to keep a sceptical,
0:38:18 > 0:38:20but open mind.
0:38:21 > 0:38:24There's one intriguing additional piece of evidence
0:38:24 > 0:38:27that offers some support for the OPERA team.
0:38:27 > 0:38:30In 2007, scientists from Fermilab,
0:38:30 > 0:38:34the high energy physics laboratory just outside Chicago,
0:38:34 > 0:38:38made a similar, but less precise, neutrino measurement
0:38:38 > 0:38:41using an experiment called MINOS.
0:38:41 > 0:38:45MINOS fired neutrino beams similar to those detected at OPERA
0:38:45 > 0:38:50to a detector in a mine 800 kilometres away in Minnesota.
0:38:53 > 0:38:56They measured the time between Chicago where the particles
0:38:56 > 0:39:00are produced and the this mine in Minnesota and they get an effect
0:39:00 > 0:39:04which goes in the same direction as what OPERA has seen,
0:39:04 > 0:39:07so that the neutrinos are a bit faster than you'd expect.
0:39:08 > 0:39:12The MINOS neutrinos did seem to be moving faster
0:39:12 > 0:39:14than the speed of light.
0:39:14 > 0:39:17However, because their equipment was less precise,
0:39:17 > 0:39:21the MINOS scientists had to allow for a larger uncertainty
0:39:21 > 0:39:23than the Italians.
0:39:23 > 0:39:25And when this lack of precision was accounted for,
0:39:25 > 0:39:29the results didn't appear to be statistically significant.
0:39:32 > 0:39:35So nobody got really very excited about this at the time.
0:39:35 > 0:39:41Now, this will mean, with this new result coming out,
0:39:41 > 0:39:46that MINOS and another experiment in Japan, which is called T2K,
0:39:46 > 0:39:52will both work very hard to get a similar measurement
0:39:52 > 0:39:55with a similar position in the next few years.
0:39:55 > 0:39:58But it will take a few years, I think.
0:39:59 > 0:40:02So until we've got evidence there really is an error
0:40:02 > 0:40:06in the OPERA results, it only seems fair to explore other options.
0:40:06 > 0:40:09This is where it becomes particularly interesting,
0:40:09 > 0:40:12especially if you're a mathematician.
0:40:12 > 0:40:14Because there's a whole range of other theories
0:40:14 > 0:40:16that could explain this.
0:40:16 > 0:40:18At stake is one of the greatest prizes of science,
0:40:18 > 0:40:21a theory of everything.
0:40:25 > 0:40:28The first issue is to consider whether the speed of light
0:40:28 > 0:40:33is really the absolute barrier that Einstein described.
0:40:33 > 0:40:37There are at least two arguments that suggest it might be possible,
0:40:37 > 0:40:41in certain circumstances, to travel faster than the speed of light.
0:40:41 > 0:40:45The intriguing thing is that, mathematically speaking,
0:40:45 > 0:40:48travelling faster than the speed of light isn't quite as difficult
0:40:48 > 0:40:52as the popular interpretation of Einstein's series suggest.
0:40:52 > 0:40:56In fact, from a mathematical point of view, it isn't impossible at all.
0:40:56 > 0:41:00To understand why, you need to explore the relationship
0:41:00 > 0:41:03between physics and maths.
0:41:05 > 0:41:08There are many examples in the history of physics
0:41:08 > 0:41:11where maths predicts something that, at first sight,
0:41:11 > 0:41:15seems counter-intuitive only for the maths to then to be proved right.
0:41:18 > 0:41:20Back in the 1920s,
0:41:20 > 0:41:24a scientist called Paul Dirac came up with equations to describe
0:41:24 > 0:41:28what happened to electrons when they travel close to the speed of light.
0:41:30 > 0:41:33But his equations led to a peculiar conclusion.
0:41:38 > 0:41:43They predicted that every particle had an equivalent antiparticle
0:41:43 > 0:41:46with an opposite electric charge.
0:41:46 > 0:41:50These antiparticles would combine to form antimatter.
0:41:52 > 0:41:55At the time, the idea of antimatter seemed mad,
0:41:55 > 0:41:58but eventually, incontrovertible evidence
0:41:58 > 0:42:00for its existence was found.
0:42:02 > 0:42:06And we've seen something similar happen with the prediction
0:42:06 > 0:42:11that neutrinos would exist before they'd been observed.
0:42:11 > 0:42:14So maths can sometimes suggest solutions that appear impossible
0:42:14 > 0:42:19in the real world, but then turn out to be feasible after all.
0:42:22 > 0:42:24Surprisingly enough, there are mathematical solutions
0:42:24 > 0:42:28to Einstein's equations which do allow particles to go faster
0:42:28 > 0:42:30than the speed of light.
0:42:30 > 0:42:33We even have a name to describe these theoretical particles
0:42:33 > 0:42:36that can do this. They're called tachyons.
0:42:36 > 0:42:39Now, I have to admit that, on the surface,
0:42:39 > 0:42:41tachyons are pretty strange.
0:42:41 > 0:42:43Most notably, their mass is an imaginary number,
0:42:43 > 0:42:49but however strange that sounds, it doesn't mean they couldn't exist.
0:42:49 > 0:42:51A surprisingly large part of the universe
0:42:51 > 0:42:54is built on imaginary numbers.
0:42:54 > 0:42:56So what's special about tachyons?
0:42:56 > 0:42:59How could they travel faster than the speed of light?
0:42:59 > 0:43:00The key is this...
0:43:00 > 0:43:05Einstein's formula forbids any particle to travel THROUGH the speed
0:43:05 > 0:43:10of light, because as it accelerates, its mass get greater and greater.
0:43:10 > 0:43:13But if a particle is formed when it's already travelling
0:43:13 > 0:43:17BEYOND the speed of light, then it gets past this problem.
0:43:17 > 0:43:20Even before these results, a few scientists have suggested
0:43:20 > 0:43:23that neutrinos might have a tachyonic behaviour.
0:43:23 > 0:43:28In other words, there might be a link between tachyons and neutrinos.
0:43:28 > 0:43:32At this stage, it's too early to say whether this theory has any legs,
0:43:32 > 0:43:36but it's still good to know from a mathematical perspective
0:43:36 > 0:43:40that it IS possible to travel faster than the speed of light.
0:43:44 > 0:43:48There's another reason for doubting that Einstein's speed limit
0:43:48 > 0:43:50is quite as absolute as it appears.
0:43:50 > 0:43:53In fact, there are certain circumstances where the idea
0:43:53 > 0:43:57of an ultimate speed limit doesn't make any sense.
0:43:59 > 0:44:03The exciting thing for me about controversial results like these
0:44:03 > 0:44:05are that they shake things up.
0:44:05 > 0:44:08They provoke lots of questions, demand new ideas.
0:44:08 > 0:44:12In doing so, they shine a light on theoretical problems that tend
0:44:12 > 0:44:15to get swept under the carpet.
0:44:16 > 0:44:19Unless you study science, you could be forgiven
0:44:19 > 0:44:22for thinking that the theories used by academics to describe
0:44:22 > 0:44:27the universe all join up nicely, but that's not always the case.
0:44:31 > 0:44:34Obviously, this result contradicts what you find in textbooks,
0:44:34 > 0:44:38but if you're actually working in the frontier of physics
0:44:38 > 0:44:43and trying to find new theories, this is not as tragic as you might think.
0:44:43 > 0:44:46It's a crisis, but we need a crisis because there are lots of things
0:44:46 > 0:44:51in physics, in those textbooks, which don't really make any sense.
0:45:05 > 0:45:08Einstein's theories describe with astonishing accuracy
0:45:08 > 0:45:10the universe we can see.
0:45:12 > 0:45:17The planets, the stars, even the distant galaxies.
0:45:26 > 0:45:30And here, the speed of light is indeed the ultimate speed limit.
0:45:32 > 0:45:34But even within this familiar universe,
0:45:34 > 0:45:38there are places Einstein's theories don't work.
0:45:41 > 0:45:46In extreme conditions, the rules break down.
0:45:47 > 0:45:50Physics hasn't yet developed the language to understand
0:45:50 > 0:45:54what happens inside a black hole, for example.
0:45:57 > 0:46:01Einstein's ultimate speed limit also causes problems
0:46:01 > 0:46:03in trying to explain how the universe evolved
0:46:03 > 0:46:05from the birth of everything...
0:46:05 > 0:46:07EXPLOSION
0:46:07 > 0:46:09..the Big Bang.
0:46:13 > 0:46:16Physicists think that at the moment of the Big Bang,
0:46:16 > 0:46:20everything in the universe was crammed into one tiny point,
0:46:20 > 0:46:23smaller than an atom.
0:46:27 > 0:46:32At the Big Bang, the universe expanded at astonishing speed.
0:46:32 > 0:46:36As it expanded, it cooled, allowing fundamental particles,
0:46:36 > 0:46:41then protons and neutrons, to condense out of the energetic soup.
0:46:41 > 0:46:44All of this happened in less than a second.
0:46:50 > 0:46:52Over the next 400,000 years,
0:46:52 > 0:46:56the universe cooled enough to allow the first hydrogen atoms to form,
0:46:56 > 0:47:00creating vast clouds of gas that finally began to collapse
0:47:00 > 0:47:03into the familiar stars and galaxies
0:47:03 > 0:47:05that make up the universe as we see it today.
0:47:16 > 0:47:18But here's the big problem.
0:47:18 > 0:47:22Accepted science only seems to account for what happened
0:47:22 > 0:47:25just after the Big Bang.
0:47:25 > 0:47:28If you want to understand what happened to our universe
0:47:28 > 0:47:30in its very first moments, Einstein can't help you.
0:47:32 > 0:47:36And there's a particular problem with Einstein's idea
0:47:36 > 0:47:40of a constant cosmic speed limit, the speed of light,
0:47:40 > 0:47:42when you apply it to the Big Bang.
0:47:46 > 0:47:49Some physicists believe that for the universe around us
0:47:49 > 0:47:53to be as we see it today, then that speed limit must have been
0:47:53 > 0:47:57broken in these instants immediately after the Big Bang.
0:48:01 > 0:48:05In cosmology, it's very difficult to explain why the Big Bang universe
0:48:05 > 0:48:09is what it is if you have the speed limit which is very constraining
0:48:09 > 0:48:10in the early universe.
0:48:10 > 0:48:14You don't have enough time to produce the universe if you have this
0:48:14 > 0:48:18speed limit which limits your range of action and ties your hands.
0:48:18 > 0:48:21So raising the speed limit could be exactly the missing ingredient
0:48:21 > 0:48:23for explaining the Big Bang.
0:48:26 > 0:48:29This is a controversial theory.
0:48:35 > 0:48:40But it does support the idea that there are extreme circumstances
0:48:40 > 0:48:41in which the speed of light
0:48:41 > 0:48:44is not the ultimate speed limit of the universe.
0:48:48 > 0:48:51However, the most exciting attempt to explain
0:48:51 > 0:48:54how neutrinos could travel faster than light
0:48:54 > 0:48:59comes from the very frontier of theoretical physics.
0:48:59 > 0:49:04Scientists are attempting to create a unified theory of everything.
0:49:04 > 0:49:09At the moment, there are two sets of theories that explain the universe.
0:49:09 > 0:49:12Einstein's theories which explain the world of the large,
0:49:12 > 0:49:15the things we can see in the universe.
0:49:15 > 0:49:19And a second theory, called quantum mechanics, describes the world
0:49:19 > 0:49:22of the small, like subatomic particles.
0:49:24 > 0:49:26And they just don't join up.
0:49:26 > 0:49:29The dilemma we faced at the beginning of this century is that the two main
0:49:29 > 0:49:34pillars of the last century's physics seem to be mutually incompatible.
0:49:35 > 0:49:38So if something big has to give...
0:49:38 > 0:49:42and this August, perhaps, a new scientific revolution.
0:49:42 > 0:49:45There are, however, a number of candidates
0:49:45 > 0:49:49for this grand unifying theory. The main one is string theory.
0:49:49 > 0:49:51And the exciting thing that's beginning to form
0:49:51 > 0:49:54in some scientists' minds is that perhaps the OPERA results
0:49:54 > 0:49:57are the first experimental proof of it.
0:50:00 > 0:50:03String theory is based on the idea that we only have
0:50:03 > 0:50:06a very partial view of the universe.
0:50:06 > 0:50:10It suggests that the fundamental particles we see in the universe
0:50:10 > 0:50:13are all related to each other through a string.
0:50:15 > 0:50:19In string theory, the particles are still there,
0:50:19 > 0:50:22but they no longer occupy centre stage.
0:50:22 > 0:50:26The fundamental object is a one-dimensional string.
0:50:26 > 0:50:30One can think in an analogy of a violin string.
0:50:30 > 0:50:34The string can vibrate and each mode of vibration, each note,
0:50:34 > 0:50:38if you like, represents a different elementary particle.
0:50:38 > 0:50:43So this note is an electron, that note a quark,
0:50:43 > 0:50:46and yet another note could be a Higgs boson.
0:50:46 > 0:50:50So it's a much more economical way of describing dozens
0:50:50 > 0:50:53of elementary particles by a single string.
0:51:00 > 0:51:02There are plenty of mathematical equations
0:51:02 > 0:51:04that describe string theory,
0:51:04 > 0:51:07but they lead to a rather uncomfortable conclusion.
0:51:07 > 0:51:09The universe needs a lot more dimensions
0:51:09 > 0:51:11than we are used to dealing with.
0:51:13 > 0:51:18We are used to the idea of living in a three-dimensional world.
0:51:18 > 0:51:22Forwards, backwards, up, down, left, right.
0:51:22 > 0:51:24And time is the fourth dimension.
0:51:24 > 0:51:28But string theory says there have to be an extra six.
0:51:28 > 0:51:32But they'd have to be curled up to one unobservably small size,
0:51:32 > 0:51:35or else rendered invisible in some other way,
0:51:35 > 0:51:39if they're to describe the universe we find ourselves in.
0:51:41 > 0:51:44Scientists have come up with wonderful language
0:51:44 > 0:51:46to describe this multi-dimensional world.
0:51:46 > 0:51:50The 3D universe we are familiar with is known as a membrane,
0:51:50 > 0:51:52or "brane" for short.
0:51:52 > 0:51:55But this is just part of something much larger,
0:51:55 > 0:51:58which includes all the other membranes or dimensions.
0:51:58 > 0:52:03And this all-encompassing entity is known as the bulk.
0:52:03 > 0:52:07A one possibility is that our universe, you, me
0:52:07 > 0:52:10and everything in it, is a three dimensional brane...
0:52:14 > 0:52:18which lives itself in a higher dimensional bulk space time
0:52:18 > 0:52:21which may have 10 or 11 dimensions.
0:52:21 > 0:52:25And there can be other universes parallel to ours.
0:52:25 > 0:52:30The analogy would be slices of bread in a loaf.
0:52:30 > 0:52:34So the bulk is the loaf, the brane is the slice of bread.
0:52:34 > 0:52:40And we live on the brane, and light is confined just to the brane.
0:52:40 > 0:52:42It doesn't travel in the bulk.
0:52:43 > 0:52:47So here, then, is one possible explanation.
0:52:47 > 0:52:51The neutrinos left CERN travelling at just below the speed of light
0:52:51 > 0:52:52on our brane.
0:52:52 > 0:52:56They then took a short cut through the bulk and popped back
0:52:56 > 0:53:00into our universe or membrane in time to be picked up at Gran Sasso.
0:53:01 > 0:53:04If a particle were to leave the brane,
0:53:04 > 0:53:09travel in the bulk and reappear on the brane,
0:53:09 > 0:53:12it would create the impression to someone living on the brane
0:53:12 > 0:53:14that it had travelled faster than light.
0:53:33 > 0:53:37There are a couple of rather satisfying elements to this theory.
0:53:43 > 0:53:46First, Einstein's theories still hold.
0:53:46 > 0:53:51Light still forms the ultimate speed limit in our membrane,
0:53:51 > 0:53:53just as Einstein said.
0:54:01 > 0:54:05But if particles like neutrinos can travel in the bulk,
0:54:05 > 0:54:07they can do so at a faster speed.
0:54:23 > 0:54:27Second, it might explain why the supernova neutrinos
0:54:27 > 0:54:32that were detected in 1987 travelled slower than the speed of light.
0:54:33 > 0:54:35Think of it this way.
0:54:35 > 0:54:38Most of the time, when ocean waves form, they behave
0:54:38 > 0:54:41in a predictable way, because the energy that forms them
0:54:41 > 0:54:43is fairly consistent.
0:54:43 > 0:54:46But every now and then, there's a freak wave
0:54:46 > 0:54:50formed from a particularly violent collision.
0:54:50 > 0:54:54In the same way, neutrinos created at CERN are the products
0:54:54 > 0:54:58of incredibly violent collisions, and this could be enough to throw
0:54:58 > 0:55:02some of them briefly out of our membrane and into the bulk.
0:55:11 > 0:55:13It all sounds rather elegant.
0:55:13 > 0:55:15If this explanation is right,
0:55:15 > 0:55:19then these faster than light neutrinos offer tantalising evidence
0:55:19 > 0:55:23that string theory could indeed be a theory of everything.
0:55:23 > 0:55:25But it's only fair to say that many string theorists
0:55:25 > 0:55:27are far from convinced.
0:55:27 > 0:55:33I've been working on the idea of extra dimensions for over 30 years.
0:55:33 > 0:55:37So no-one would be happier than I if the experimentalists were
0:55:37 > 0:55:40to find evidence for it.
0:55:40 > 0:55:44However, to be frank, although I like the idea of extra dimensions,
0:55:44 > 0:55:48this is not the way they are going to show up, in my opinion.
0:55:48 > 0:55:53So I am not offering extra dimensions as an explanation
0:55:53 > 0:55:57for the phenomenon that the Italian physicists are reporting.
0:56:02 > 0:56:07So for the time being, there is no theory that convincingly explains
0:56:07 > 0:56:11how the neutrinos appeared to break the speed of light barrier
0:56:11 > 0:56:15travelling between Geneva and Gran Sasso.
0:56:15 > 0:56:18All scientists have is some idea of the right place
0:56:18 > 0:56:22to look for a theoretical explanation.
0:56:22 > 0:56:25This could be one of those moments that turns our understanding
0:56:25 > 0:56:29on its head yet again, lets us see further into the universe,
0:56:29 > 0:56:32lets us understand more about how it ticks, how it sticks together,
0:56:32 > 0:56:34how things are related inside it.
0:56:34 > 0:56:38If it does that, if we understand more, then it is one of those
0:56:38 > 0:56:41magical moments that you get in the history of physics
0:56:41 > 0:56:46that just twists your understanding and brings the universe into focus.
0:56:46 > 0:56:49If we are seeing the start of that now and we're documenting it,
0:56:49 > 0:56:53then we're really, really privileged to be doing so.
0:57:01 > 0:57:04At this stage, the argument is nicely poised.
0:57:04 > 0:57:07Measurement error, or the beginnings of a seismic breakthrough
0:57:07 > 0:57:09in our understanding of the universe?
0:57:09 > 0:57:12Nobody knows. What's needed, of course,
0:57:12 > 0:57:15is the thing that underpins all of science.
0:57:15 > 0:57:19The scientific method demands replication of the results.
0:57:19 > 0:57:23If other scientists can't repeat the findings coming from Italy,
0:57:23 > 0:57:26we have to begin to doubt the accuracy of those measurements.
0:57:26 > 0:57:31However, if they do repeat them, the stage is set for a major challenge
0:57:31 > 0:57:36to Einstein and the creation of a grand unifying theory of everything.
0:57:42 > 0:57:44Subtitles by Red Bee Media Ltd
0:57:44 > 0:57:46E-mail subtitling@bbc.co.uk