BBC Gravity and Me - The Force That Shapes Our Lives

would you like to lose a little bit of weight without doing any exercise or dieting would you like to age just a bit more slowly than your friends well you might be surprised to hear the laws of physics can help the key to unlocking these everyday questions is gravity it sculpts the universe it warps space and time it's a fundamental force of nature but gravity's strange powers discovered by Albert Einstein also affect our daily lives in the most unexpected way [Music] in this film we'll be using cutting-edge scientific techniques to investigate how gravity changes your weight it's got up your height I really have shrunk and even your posture and with the help of thousands of volunteers I'll show you how gravity make us all age a different rate through the day I've just been logging on to the for logging onto the app as a physicist gravity is central to my work oh wow and in exploring it I'll be challenged on how I understand this most mysterious force well okay I'm going to go write this one down and I'll have to tackle the very nature of reality itself gravity it binds together all the matter in the universe and it makes our existence here possible that's in the end it all boils down to one simple question what happens if I drop an object [Music] gravity's many mysteries are all contained in this single action how an object falls here's the first puzzle why does a hammer fall faster than a feather you might think it's because the hammer is heavier but that's not the real reason the answer is air resistance it's not the weight of the object that matters is their shape and I can demonstrate this very easily with these two umbrellas they both have exactly the same weight but if I open one of them you can be pretty sure it'll drop more slowly than the other one in fact all objects would fall at the same rate if you could only remove the air the first person to realize this was the 16th century mathematician Galileo Galilei famously it said he worked it out by dropping objects of the Leaning Tower of Pisa and he was spectacularly proven right in an experiment carried out on the moon in 1971 well my left hand I have a feather in my right hand a hammer and I'll drop the two of them here and hopefully they'll hit the ground at the same time it worked perfectly about that symmetric Galileo was correct and his finest now Galileo was obsessed with a second question - when you drop an object it's actually quite hard to tell if it falls at a constant speed or picks up speed as it drops even in slow motion is pretty hard to tell but Galileo realized this first dropping objects a very short distance it lands with very little impact but of course drop it from higher up [Laughter] this time the ball easily breaks the tile which means it must have accelerated gaining in speed and momentum as it drops Galileo had identified something fundamental to all falling objects they accelerate he realized there might be a way to measure how much falling objects gain in speed what he devised was the first ever attempt to measure gravity itself he built a long wooden ramp rather like this that he had sloping at a shallow angle the idea was to roll balls down the ramp and measure their acceleration the crucial thing is that the ramp had to be at the shallow angle to reduce the effects of wind resistance it also meant that the balls would roll down slowly enough to give him time to measure their speed but the big problem was this how do you measure time accurately in an age when there were no accurate timepieces there alone stopwatches well Galileo came up with an ingenious idea involving the flow of water essentially measuring time from the amount of water collected in a cup so we're going to try and repeat Galileo's experiments I say we because I have a couple of willing volunteers Gavin and Johanna three two one go okay there's one now if you come down a quarter of the way down the ramp go okay so now half of the way down go okay and then 3/4 the way down let's go right turn the tap off okay so we have our four measurements and I can see a progression from fuller to emptier but what we need to do now is find the mathematical pattern by weighing carefully the water in each glass weighing the water should give us an idea of how long each roll took and in our experiment these were the results now there's one immediate thing you can tell the ball really sped up the longer it rolled in fact our results seem to show that the time it took to cover the first quarter of the ramp was about the same time it took to cover the next three quarters so we have a strong hint of a mathematical pattern now we'll see if we're right by placing bells along the ramp at intervals which are based on the results this arrangement looks a bit strange because the gap between the first two build is much shorter than the gap between the third and fourth bells but that's okay because if I've got our calculations right the ball starts off slowly so it covers a shorter distance and as it picks up pace it'll cover longer and longer distances so we should hear the bells ringing at equal intervals in time go beautiful so what does this all mean what's the mathematical formula well this is something that Galileo worked out let's say from the star the ball covers a distance of one meter in the first second after two seconds it'll have covered four meters after three seconds nine meters after four seconds 16 meters and so on if you recognize this progression you'll see that distance goes like the square of time Galileo had found the rate at which gravity speeds up objects and he'd found another fundamental principle you can measure the strength of gravity by how much it causes falling objects to accelerate detecting gravity has become exceptionally sophisticated these days but still uses exactly the same principle this is Hurst mon-sol castle in suffix and in its grounds lies the space geodesy facility here vicki uses an astonishing this sensitive instrument to detect the exact strength of gravity on this one spot okay say Vicki tell me about this incredible gravity meter that you work with okay so this is the dropping chamber and a stripped down version essentially what happens is you've got a cart that gets raised to the top and then we can't accelerate them away from a mass in the middle and so this section here in this box and as it drops it drops under freefall so this component in the middle as it drops is basically just Newton's apples falling to the ground yeah so this is a stripped-down version but but that's the real thing this is the real thing how does it actually work in here it's a vacuum so there's no wind resistance I think there is a trick rider inside a laser is used to measure exactly how fast the mass is accelerating this is the 21st century version of Galileo's ramp the balls rolling down so we can we get it down of course if you just like to press the button on the laptop this one yep okay so it's not communicating with it oh here we go again so wait five seconds then takes mention with a gravity and again oh and as you can see the orders of the results appearing now yeah each of those green dots of measurement of gravity with the actual number that it's getting for each one the unit Viki uses has a similar ring I see that the the number up at the top here so you've got this unit micro gal yes gal is essentially one centimeter per second squared the gal who's named off the Galileo so we've just taken the measurement of gravity here today and it's this highly accurate number nine eight 1 1 to 400 7 micro gals the reading means that the Earth's gravity speeds up a falling objects by around 9.81 meters per second for every second if dropped vicki tells me something intriguing she takes a reading here every week and she's found that the strength of gravity changes by tiny amounts over time heavy rainfall for example can cause gravity to increase slightly presumably if gravity is changing here in one spot it will have different values all around the world and so you can have a gravity map of the entire planet that's right yeah so what's the reason for these strange fluctuations that's what I want to investigate next so gravity changes as we move across the surface of the earth well this lies at the heart of a challenge that I set two young volunteers I've given them a task to try and find the place in Britain where gravity is at its weakest so where objects will weigh the least and I've given them just three days to try and find it the volunteers are estrella Sendra a PhD student I've been living in London for five six years and I'm originally from Seville in Spain and they're interested in taking part in this project because I would really like to know more about how these would work and poppy Begum a journalist who lives in London I did my degree in biomedical science and I did biology and chemistry my a-levels but I haven't done any physics since I left school and fascinated to find out more about gravity and I actually enjoy puzzles I like to challenge now the team can't just weigh themselves to see changes in gravity body weight fluctuates naturally by a couple of kilos over the course of a day whereas changes due to gravity as they travel around the country are going to be tiny in comparison a matter of a few grams so they're going to have to use sophisticated scientific methods if they want to measure gravity accurately and that's why the volunteers will be joined by three specialists in gravity science PhD students so knack bows he'll be in charge of some very sensitive measuring apparatus from the National Physical Laboratory Shawn Hughes a geologist who'll be using a portable gravity meter and Andrew Thompson a cosmologists at University College London will help interpret the results we've taken a collective weight for the team before they set off its 380 kilograms so can they find the place in Britain where that'll decrease they're setting out in Snowdonia National Park in North Wales the railway climbs from here to the thousand meter summit of Snowdon Shawn takes its first gravity reading the inside is a mass on a beam and you turn this counter at this dial until you get the beam central by counting the number of turns of the dial Shawn can calculate the downward pull of gravity acting on the mass inside the machine so neck has a simpler method so inside the box is a two kilogram mass and it's supposed to be sort of as perfectly two kilograms as it's possible to get all right and place it oh it's just coming under isn't it one nine nine eight point two grams so it was two kilos in the laboratory but now here is the good list it's the first puzzle why does a two kilo mass fit the scales at just under two kilos and it's one which gets straight to the heart of what the challenge is really about mass is often confused with a related quantity weight the mass of these dumbbells is fixed it doesn't change it's a measure of how much stuff they contain weight is different it's a measure of the effects of gravity on these dumbbells the downward force pulling them to the ground in the same way that it's keeping my feet firmly stuck to the ground the crucial difference is this if I was holding these dumbbells on the moon they still have exactly the same mass but they would weigh six times less because the moon's gravity is so much weaker than the earth so that's why so next bringing along the 2 kilo mass if it changes weight then this should mean that gravity itself has changed ahead of them is the summit of the highest mountain in England and Wales stained for its stunning scenery oh it would be stunning if you could see it and this is what we came all the way up here for this amazing view at the top of Snowdon you wouldn't know it but honestly we are here so we're now near the summit of Snowden and I've set up the gravimeter again and we're going to see what the difference in the reading is he has to turn the dial again and again to try and get a reading if clear gravity has changed but which way has it got stronger or weaker the team leaves Sean to work out his results and tries to division the scales as close as possible to the summit but the reading is all over the place Oh got a lot - eating quite a lot due to the wear I have to say this is what science is always like even if it's never quite what you want it to be so they head inside to the cafe next to the summits wind was being a bit naughty but hopefully hopefully you know all right one 98.2 down there one 997 we've got it at 0.4 for Grandma the mass weighs a tiny bit left it's lost about 1/5 thousandth of its weight and Sean's found that gravity itself has reduced at the top of the most of the mountain we put the measurements and we discovered it the gravel roads gravity had gone down it had gone down it could notice 206 times of the dial and we worked out less that's equivalent to 219 Milligan's so it's clear from the team's measurement gravity weakens as you go higher and you get a bit lighter it's not an excuse to say where we like the light is who cares but you're the tenth understand is actually really interesting it's like an illustrative example of seen how this is actually fluctuating depending on different factors yeah absolutely and that we could measure it and we could see it with our own eyes it makes you think about gravity in a very active way it's such a fundamental force phenomenon in nature but we don't know not much about it but why does gravity change with altitude to understand that question you have to get to grips with the extraordinary discoveries of the next scientific giant in our story Isaac Newton born in England in the middle of the 17th century he spent his life wrestling with so many apparently separate questions from why things fall to the ground to why planets orbit the Sun it took the genius of mutant to realize that there was one single equation that could answer all these questions and here it is his famous law of gravity it might look complicated but this is one of the most important equations in the whole of science F here is the force now Newton said there's an attractive force between any two objects in the universe on this side of the equation G we call the gravitational constant now Newton knew it had to be there but he didn't know what its value was M 1 and M 2 represent the two objects and R is the distance between them now the equation tells us that the more massive the objects are the bigger m1 and m2 the greater the attractive force but the further apart they are the bigger the value of R here the weaker the gravitational force with Newton what was once mysterious now became clear Newton's equation describes why an object falls to the ground including his famous Apple but it's true genius is that it applies to any object anywhere in the universe so it's a very simple and elegant way of describing some of the seemingly most complicated phenomena in the cosmos his law of gravitation can still be used today to explain how orbits work to predict when a comet will return to describe why galaxies spin or to slingshot spacecrafts around planet Newton tells us to look for the underlying simplicity and natural phenomena for instance how the moon orbits the earth if I let go this Apple it'll fall straight down because of the pull of Earth's gravity but if I throw it to begin with it travels in a horizontal direction that's a direction of travel but Earth's gravity is still pulling it downwards so it ends up following a curved path now if I throw it harder it'll travel further before it hits the ground and in principle if I could throw it hard enough I could put it into orbit and that's exactly what's happening with the moon in orbit around the Earth it's a combination of wanting to travel in a straight line but also being pulled down by the Earth's gravity so it ends up constantly falling around the earth and constantly missing Newton's famous equation also explains the strange effect which the roadtrip team has discovered that objects get lighter as you gain in altitude when I weigh myself I'm represented by the first mass m1 the second mass m2 is the earth itself and the force pulling me down my weight depends on the distance between me and the center of the earth and that's the secret of the road trip if you want to find the place where you weigh the least then you have to get as far away as you can from the Earth's core [Music] so it's the afternoon of day 1 and the roadtrip theme had to work out where to go next poppy and Australia have a good idea find somewhere higher than Mount Snowdon from the measurements that we that you guys did at Mount Snowdon altitude clearly plays an important part in gravity so with that in mind we've got to go to the highest point in the UK which is been nervous okay but there's just one thing that we haven't shown you so far we actually brought along an extra experiment so can we please show you this first before you make the final decision yes Phonak actually has the other part of this experiment we always carry around some power tools as physicists always do so let's start off nice and gentle okay and then try and pick up some pea hey I'm proving the point is that when something is spinning kind of gets flung outwards and you can actually use that to make a nice flat piece of pizza and but this also applies to the earth the earth isn't it's perfectly round it's what's known as an oblate steroid it bulges at the equator where the spin is greatest we kind of got two competing effects now we're trying to get away from the centre the actual core of the earth the point at the very centre of this ball but now we can do it in two ways we can either kind of go up something tall or we can just go down towards the equator there's what we find when we're doing gravity surveys is that as you move south it tends to be in effect from latitude which is often usually larger than the essentially altitude so the closer to the equator you go the further you get from the Earth's core and the lighter you get so guys the Sun setting just behind me here this is north from the conversations we've just had it sounds like we've got to go that way down south that right yeah yeah okay let's go the team is starting to uncover the reasons why gravity changes as you cross the surface of the earth our planet has defined it shaped by the complicated forces which act upon it and detecting tiny fluctuations in its gravity field can give us important clues it can help us understand how our world is changing the space geodesy facility at Hearst also is one small part in an enormous global network which uses satellites to detect the tiniest of changes in the Earth's gravity field tell me what exactly your job is here what we're doing with this telescope is measuring very accurately the distances of satellites from here so we're using very short laser pulses which we direct towards the satellite on the satellite there are reflecting cubes which return some of that light to us and we measure how long it takes to like to go to the satellite and back and how far away is it sound like really cracking now one of the Galileo satellite which is about 20,000 kilometres 20,000 kilometres away yes okay so we've got it aimed at the gatherer satellite and you're going to turn the laser on now yes oh wow and that laser beam that's being fired up towards the satellite yeah at the time I'll take to get there and come back again it's a fraction of a second and it is it's about 150 thousands of a second hundred fifty milliseconds and we're sending about 1,000 of those per second this strange-looking object is based on satellite readings it's the highly exaggerated representation of how Earth's gravity field varies over time fluctuations like these can give us important insights into climate change ice caps melting sea levels rising changes in groundwater all of these have an effect on the local strength of gravity so something as important as climate change in order to understand it to do something about it we need to know the distribution of the gravitational field of the earth very accurately absolutely - it's a global measure that we need [Music] for the road trippers is the start of day two and they're heading for the south coast they're stopping off in Herefordshire it's a good location as it's the same altitude as to base the Snowdon but they've moved about 80 miles further south so if they find gravity changes here it must be due to latitude it's not a huge difference but is noticeable our counter reading at the bottom of the mountain was 4840 yeah our counter reading here's four thousand seven hundred and seventeen all right I will do get to see a difference so are actually at the same altitude as a base of Mount Snowdon but because we've traveled further down south over nine gravity less here yeah [Music] they push on and by sunset they reach Cygnus on the south coast [Music] Shawn takes the second gravity reading of the day and poppy improvises a map 12 sort of a map we might not the scale of the top there so I drew this map Scotland a bit squashed Wales is quite high up and Cornwall is is there but you get the idea so Shawn we we've been travelling with you you've done quite a few gravity meter readings can you can you plot them on this lots of scale badly drawn maps Lee sure so if you remember we started off in Mount Snowdon about here and that was the zero measurement for our survey and then we've come all the way down here to the south coast the difference from the base of Snowdon is minus 212 many gals Wow so the difference between going measuring gravity at the base of the mountain and the top of the mountain is about the same as here at this latitude and down here at this latitude there quite clearly at sea level yet gravity here is roughly the same as it is at the top of Snowden that we're next we are here if we want to find out where we are the lightest why don't we travel all the way to the most suddenly point in the UK which is here you can also help us so why not find a place in the country that is both low and latitude but also high in altitude in the terms of height above sea level because that will get us somewhere that is really far away from the core of the earth whilst angle in the country [Music] so the answer to the puzzle lies in a combination of two factors how much further south should they go and how much higher [Music] at the end of day two shores results show that the team weighs about 80 grams lighter in total than back at the base of Snowdon the way that weight changes is just one example of Newton's famous equation in action but Newton had left his masterpiece incomplete he didn't know the value of G the gravitational constant which sets the size of the force to harness the full power of the equation you need to know G and the vital clue came with an incredible experiment conducted in London at the end of the 18th century it was an attempt to work out the mass of the earth itself and it was carried out by an eccentric extravagantly rich aristocrat Henry Cavendish Cavendish was a chronically shy deeply solitary man living in total isolation in his house in Clapham the story goes that one day he accidentally bumped into a female servants on his staircase he was so traumatized by this event they had a new staircase built just to him so this horrible incident could never happen again Cavendish had inherited vast fortunes and was able to dedicate his life to devising pioneering experiments including one particularly extraordinary piece of equipment he set up something a bit like this it's called a torsion balance involves four led spheres two large heavy ones which are held fixed in place and suspended by a very thin wire is a wooden rod six feet long with two smaller balls on either end now the crux of the experiment is a relationship between the large ball and the small ball now of course there's a gravitational pull downwards on both of the balls due to the Earth's gravity but Newton also tells us that there should be a very weak gravitational pull between the balls and this is effectively what Cavendish was trying to measure any slight movement of the small ball towards the large one should cause a twist in the torsion wire and that's what Cavendish was trying to detect of course this is all much easier said than done the experiment was incredibly sensitive the tiniest of vibrations of slightest breeze changes in temperature could all influence the measurements so Cavendish had to isolate the apparatus inside a box and the Box within a shed he even realized that his mere presence next to the apparatus could influence things so he had to remove himself outside the shed what he's ended was sit outside the shed and through a small hole in the shed wall looked through a telescope to detect the tiniest of twists in the wire it was an incredibly difficult process but after many months he finally felt confident enough that he had a reliable results [Music] Cavendish found that the small balls did move a tiny four millimeters he calculated as a result by comparing the density of the balls with the density of water in the end the result of Cavendish experiment and subsequent calculations was that the density of the earth was about five and a half times that of water or put another way the mass of the earth was five point nine trillion trillion kilograms what's most remarkable is that Cavendish got this number right to within an accuracy of one percent with Cavendish's astonishing result scientists were able to work out G then the equation could be used to determine the mass of any celestial body in orbit around another [Music] so astronomers were able to calculate the mass of the Sun and the planets and the moon and eventually even distant galaxies [Music] at the end of day two the team were in cydnus on the south coast looking for the place in britain where they'll weigh the least they've worked out the answer lies in a combination of two factors the right mix of going south and being higher up and for the final leg of the journey I'm going to meet up with them I asked them to drive a short distance west to one of the most remote areas in mainland Britain Dartmoor National Park it's only 40 miles from the southernmost tip of Britain hello nice and it's very high very hilly territory Jim the team got to the south coast yesterday yeah we defined gravity at its weakest but we haven't quite figured out whether it's altitude or latitude do we go further now hold and go higher you're right to ask do we go as far south as possible or as high as possible that's why I've brought you here sadar more and we've charted the most important points on this map here let's have a look so we are here two bridges these four dots represent these hills up there behind us which are at about 500 metres above sea level so that's what we want to check out these hills are close to the south coast and they're also the highest in the whole of the South of England so logic suggests they must be the right combination of latitude and altitude well there's another reason why this makes perfect sense one which we haven't looked at yet and that is the effect of the underlying rocks on gravity and I've got a map here that shows you're going to Trump my map value here we are down here in these blue areas are the lowest areas according to the density of the rocks underneath the rocks around here are made of granite which will make gravity weaker still so they're helping as well as the altitude and the fact that we're further south yep also playing a part well we have a plausible theory but now we need to test it if I'm right then at the top our gravity readings should be by far the lowest reading of the trip of course there's another effect of gravity to deal with now it's mackerel when you head uphill okay so I think this is pretty much the start of the hills we've located on the map so let's see if this is the lightest place Sean if you want to get the gravity meter out and we'll take another reading here yep okay Shawn sets up his equipment one more time let the news well the bottom of Mount Snowdon was our zero for this test we found we lost a certain amount by going up to the top of Mount Snowdon we found we liked a certain amount coming south to the south coast not only have we beaten that we've smashed it brilliant we were - 219 Milligan's lower at the top of Mount Snowdon here on Dartmoor we're - 347 milling out well yeah so it is a combination of three things we're far south so that's the latitude we're at altitude with a high up and we're surrounded by all this granite rock which is low-density anyway I hope you all think it was worth to climb up here anyway there you go boom science now we already know that the altitude of these hills takes us much further from the Earth's core than anywhere else further south in Britain so gravity must be weakest here there's extra evidence to the British Geological Survey has compiled tens of thousands of gravity readings made in the UK and the lowest reading ever recorded were all taken around here on the high hills of Dartmoor what do we do to celebrate we weigh ourselves of course thank you thanks very much so when the sella pancakes for breakfast IBP is right I can tell you that you should weigh something like 20 grams less than you did at the base of Mount Snowdon guys I'm guessing something like 25 to 30 grams less so if you want to weigh as little as possible this is the place in Britain to cup it indicated such a tiny amount that it's going to be wiped out entirely by whatever it was you had for breakfast this morning gravity what goes up must come down all of our lives we abide by its rules it dominates our every action but there's one select group of humans who know what it's like to live free of gravity one zero [Music] everybody's used to gravity we're used to the oppression of it gravity is the ultimate oppressor it grinds us under its heel 24/7 with no release until you're in space and then suddenly you're free from gravity you are you're weightless in orbit Canadian astronaut Chris Hadfield and five months onboard the International Space Station you can pull your knees up to your chest and just tumble or if you take a wet cloth and you get a dripping wet and everybody at Earth knows what'll happen when you're wringing out all the water will fall inevitably if you do that in weightlessness the water stays there and it actually because of the surface tension starts crawling up your arms [Music] it's a little bit mesmerizing and hypnotic to be in weightlessness if you're weightless you don't need a bed you don't need a mattress you don't need a pillow your body is floating completely suspended like magic movement becomes effortless push off with one finger and fly and tumble you don't need to hold yourself where you are with with muscle you can just with the delicate fingertip pressure you can stay where you are but there is a price to pay astronauts bones atrophy and their muscles wither away one of the things we do on board a space station is exercise purely to simulate gravity if we don't do something then our heart will shrink our ability to pump blood to our head will diminish our bones will start to dissolve our muscles will waste away our key separation comes from timers off back in a way at a rate of just a little over 1/10 of a meter per second re-entering gravity is a punishing experience to come back to earth is violent it can be five times the force of gravity or eight times the force of gravity crushing you down into the floor of the ship for quite a long time then of course you hit the ground and tumble and roll to a stop and and now you're the victim of your past you're the victim of your decision-making lying there trying to shake your head and get used to beating and gravity again I remarked at the time that I had forgotten that my lips have weight and my tongue has weight you don't think about it but if you try and talk articulately standing on your head you'll notice that you have to sort of control your lips in your tongue a little differently just because gravity's pushing them the other way and it's the same sort of thing raising your arm holding your head up about turning your head when everything wants to tumble just keeping your balance all of those things it's a little bit like like relearning to walk again like it's like an infant [Music] gravity on earth grinds us all down over the course of the day it actually squeezes your spine an effect you can see for yourself if you use a measuring rod okay that's half percent in the morning just got up and I'm going to see how full and before gravity drags me down [Music] 178 centimeters or just over five foot ten over the course of the day gravity compresses the fluids in your spine right it is just past 11 p.m. I've been standing up for most of the day so let's see if gravity has had an effect on my height that is 176 centimeters so I really have shrunk by just over half an inch over the course of today in the longer term gravity can affect your posture permanently but there are exercises you can do to counteract this effect part of my research has been looking at the effects of gravity on the human body the people might not be aware or they might not always think about the effective gravity on our physical state on our house and particularly on our posture however because it's such a constant force gravity has a massive impact over the course of our lifetime as you get older you can develop a stoop which is damaging to your mobility doctor here's actually got a very good posture but I'd like you to just show not so good posture so when poor posture is really rounded shoulders and then loss of the the curve and the back as well I can't ask you to raise up your arms when you're in that posture so no and then just come back down shoulders back and on and then raise your arms you can see the effects of posture on function ironically the exercises which many gym goers do actually make your posture worse that's if you only exercise the frontal muscle like the chest and abdominal so it's recommended you exercise the back muscles just as much to straighten you out and counteract the effects of gravity [Music] gravity shapes our bodies and molds our planets nothing happens on earth without its power and influence the Isaac Newton explains so many of its effects using one simple equation and in the centuries that followed his laws of physics led to breakthrough up to breakthrough spurring on the Industrial Revolution but in the first decade of the 20th century the next genius in our story challenged the very foundations of our understanding of gravity a young German scientist called Albert Einstein was churning something over in his mind he thought that something in Newton's laws didn't quite add up [Music] imagine I'm the Sun and this tennis ball is the earth in orbit around me Newton's laws can describe very precisely the path the earth takes around the Sun in terms of the mutual gravitational attraction between the two bodies but what Newton can't explain is what connects them in reality of course there is no invisible string between the Earth and the Sun holding the two together there's just empty space a complete void and yet according to Newton the Earth and Sun pull on each other instantaneously across a vast distance how can gravity act in this way when there's nothing to connect it or transmit it after years puzzling over this Einstein had a blinding flash of inspiration just like Galileo and his ramp or Newton with his Apple Einsteins breakthrough came because he was thinking about one simple action what happens when something Falls to explain I'm visiting this 400 foot high power in Northampton built to safety 10 lifts one day in 1907 Einstein had what he called the happiest thought of his life what if I was standing in a stationary lift completely isolated from the outside world not feeling anything apart from the pull of gravity on my feet what if then the lift cable breaks and I start falling one of the forces that I will feel as I'm plummeting to the ground [Applause] well I'm not going to try that fortunately there's another way to test this without me having to plunge down a lift shaft sorry to disappoint you this little device here that I've stretched this plastic toy is an industrial accelerometer so it measures acceleration now I've got it connected to my laptop and it's showing a measurement of 1g now that's the downward acceleration due to the pull of Earth's gravity so basically it works just like a gravity meter but what happens if I were to drop it presumably of carry on measuring 1g because it's falling in Earth's gravity okay well let's try that and see [Music] so you can see here along this line at the bottom that's when I was holding it still and it's measuring an acceleration of 1g these oscillations here is when I stood up and a bit of disturbance that this spike along here is the moment I released it and this short duration along here is the time it was falling and you see while it was falling it was registering an acceleration of zero now if you think about it this is really odd the accelerometer is accelerating downwards is plummeting in the full grip of Earth's gravity and yet it's measuring no acceleration at all it's as though gravity has completely disappeared [Music] Einstein's insight was that when something Falls it no longer feels the pull of gravity in fact falling is like floating in empty space this is the essence of Einstein's happy thoughts what we now call is principle of equivalence [Music] Einstein's point is that when the man in the lift falls he doesn't just feel weightless he is weightless Einstein said the man feels no force pulling on him because there is no force pulling on him gravity doesn't act on him it acts on the space and time around him what we now call the geometry of space-time this was a radical redefinition Einstein says forget the idea of gravity as a force acting mysteriously between two objects now we have to think of it as the shape of space-time changing you think Newton saw space and time as independent fixed and immutable that three-dimensional space is the stage in which things happen but time is separate it ticks by at the same rate everywhere in the universe according to Newton an object will travel through space in a straight line unless acted upon by a force like gravity it will cause it to deviate from that path but Einstein said that space and time aren't fixed and immutable they're interconnected meshed together in what is known as space-time and he said that space-time can be looped that matter curves space and time around it so after Einstein we no longer see gravity as an invisible string pulling objects together instead a body like the earth warped the structure of space and time around it and an object in orbit follows a path which is as straight as possible through that space-time it's a fundamental part of Einstein's vision of reality space and time can't be disentangled you can't talk about space separately from time so matter warped time as well as space it's known as gravitational time dilation and it's possibly the strangest of all of Einstein's discovery [Music] I've got two identical clocks here now because the clock lower down is closer to the center of the earth it feels msf lightly a stronger gravitational pull than the clock higher up Einstein theory says that the lower clock will pick by at a slightly slower rate than the higher clock basically gravity slows time down it's an extraordinary conception of reality that Einstein describes based his being curved and time is being distorted so why can't we perceive this in our everyday life Einstein had a rather nice way of explaining it most of us have had the experience as children of trying to work out what our parents do for a living well imagine your father as Albert Einstein when he was about 12 years old young Edward Einstein asked his father why he was so famous what he'd discovered well this poor eye Stein's senior on the spot but he came up with a beautifully simple analogy Einstein told his son when a blind beetle crawls over the surface of a curved branch it doesn't notice that the track it has covered is curved I was lucky enough to notice what the beetles didn't notice this is what Einstein meant the beetle is free to move in any direction on the branch it can move forwards backwards left and right but it has no concept of a direction up off the branch it's as though for the beetle the universe is missing the third dimension the beetle may think it's moving in a straight line along the branch but we can see that the surface is walking on itself curving and twisted Einstein's point was that what we see and the twists and curves of the branch feel to the beetle like forces pushing and pulling it okay so consider this rather strange example imagine we have two beetles perched on this pumpkin and for whatever reason they want to walk up towards the top now if they start at the equator pointing you north as they walk there we'll begin by moving parallel to each other that means their paths should never meet but as they get closer to the top their paths get closer together now if they have clever beetles they might try and figure out what's going on and they could imagine that there's some mysterious force that's pulling them closer together but for us from our perspective we can see there is no such force all they're doing is following straight paths over a curved surface just as the beetles have no sense that the surface of the branch is curved we completely failed to perceive the bizarre ways that gravity shapes the reality we live in Einstein's problem was proving that he was right after years more thought you realized that there was a way by looking far out into the solar system incredibly here in the grounds of her sponsor castle it housed one of the original telescopes that were used to prove Einstein was correct in 1915 when Einstein developed his general theory of relativity it was just that it was a series it had no proof in fact many people found it completely outlandish but then just four years later in 1919 this telescope and allow me to geek out of it here and I'll give it its correct name this is the 13 inch Astro graphic reflector this telescope proved that I sign wasn't that right that gravity does curved space itself [Music] Marit Cocula is the public astronomer at the Royal Observatory in London and he's recently rediscovered a neglected treasure in their archives this is perhaps one of the most important scientific artifacts we have in the collection here in Greenwich and for an astrophysicist like me it's almost a holy relic it's a glass plate photo of a solar eclipse taken in 1919 as part of a famous scientific expedition British astronomers who traveled all the way to Brazil and the west coast of Africa to take photographs which they hoped would prove Einstein right what we're saying here is the eclipses of 1919 you can see the black disc of the Moon silhouetted against the Sun blocking its light around it is the solar corona the sun's outer atmosphere in this spectacular prominence of gas leaping off the surface but it's not the Sun that we're really interested in the fundamental point that this photo and others from the expedition's show is that the positions the apparent positions of the stars in the sky are altered and shifted from where we would expect them normally to be and that proves this very strange thing that general relativity predicts that the mass of the Sun ends for space and time around it and that so she is gravity this is a negative of one of the photos it has markings showing where the stars positions seems that have shifted since then observation art observation have confirmed that matter curves space and slows down time so the simple question of why things fall the way they do let us deeper and deeper into the very nature of space and time itself gravitational science shows us how galaxies stars and planets fall by measuring gravity we've discovered the existence of dark matter that 80% of the mass of our universe is invisible and we don't know what it's made of and we've detected exotic objects with extreme gravity like neutron stars which have more mass than our Sun here are only twenty kilometres across but it's another mysterious aspect of Einstein's universe that I want to explore in my next gravity project here at the University of Surrey some colleagues and I have been working on it for months what we're doing is devising a nationwide citizen science project we're developing a smartphone app so it uses the GPS contained on your phone to explore one of the strangest properties of gravity how it affects the rate at which we age I formulated the equations myself and a small team of computer scientists and software developers is using them to devise the app Einstein discovered that as gravity changes so does the rate that time ticks this means the strength of gravity you feel affects how quickly or slowly you aged the aim of my app is to demonstrate this effect it works by using a phone's GPS data to estimate your local gravity and it also calculates the average speed at which you move because this too affects the rate at which you age it then uses the equations I've written which are based on Einstein's theory of relativity to calculate overall how fast or slowly you're aging once the app is ready I tweet about it [Music] thousands of people download it and we start to gather results from across the country some people send me videos giving me their results how fast they're aging compared with how time picks out in space in zero gravity over the past day I have aged left by about 172 microseconds I have aged less by ten ten point zero two milliseconds so since downloading the app I am aged less by one point forty military seconds opening time warp I have aged less by two point six milliseconds our aim is to use their results to build up a map of how time flows because of gravity my smartphone project provides just one insight into the space and time which Einstein's theories describe [Music] gravity and it's strange ways have given us astonishing insights into the dark secrets of our universe perhaps the weirdest objects in the universe of black holes collapsed stars whose gravity is so strong that not even light can escape their grip now for the first time ever their effects have been felt on earth and they've been detected through the medium of gravity itself it's a story that has revolutionized the study of modern cosmology 1.3 billion years ago in a galaxy far far away to black holes swirled around each other closer and closer together until they finally collided with incredible violence in that final fraction of a second at the precise moment that they merged a disturbance was created that sent ripples out through the universe gravitational waves are a key prediction of Einstein's theory matter doesn't just curve space-time it can cause ways ripples which expand outwards exactly like a stone dropped in water this particular wave was unimaginably large the energy released was greater than all the lights being given out by all the stars in the universe the wave rippled through space at the speed of light in 1.3 billion years it covered a distance of over 10 billion trillion kilometres until on the morning of the 14th of September 2015 it arrived here the streets and cafes of New Orleans in fact everything in America and on earth expanded and contracted very very slightly with the wave passed through no one noticed that by the time it arrived here the distortion was phenomenally tiny except that one science laboratory did notice and I'm going to see it [Music] a thousand scientists across the world are collaborating on it it's the culmination of over 50 years of effort and is one of the most sophisticated experiment ever designed by humanity so I'm pretty excited too fear it's a rather unusual setting Here I am in the middle of rural Louisiana about an hour's drive outside New Orleans I don't expect to find such a multimillion-dollar cutting-edge research facility as this and yet this is the place where recently one of the most important scientific discoveries in human history was made this is like oh the laser interferometer gravitational-wave Observatory is an enormous construction shaped like an L with a sophisticated laser system bouncing up and down the two arms so we're standing on top of one of Lai goes to arms so this is the first Lego arm and in that tube we with there's a laser beam that we bounce back and forth between a mirror in the end station and a mirror in this building and the other bit goes that way four kilometers perpendicular to the arm we first saw the L che Big L on the ground so the light bounces back and forth in that arm and bounces back and forth in this arm and what we actually measure with leghul is the length of this arm as measured by the light between the two mirrors and the length of that arm as measured by the light between two mirrors and then the laser interferometry measures the difference between those two arm lengths so is the gravitational wave passed through the lasers picked it up they detected that my goes to arms changed in length to a very very tiny degree the signal that we saw was just a few thousandth of the size of the of the atomic nucleus the biggest the signal ever got so so far far smaller than the size of a single atom or much much smaller yeah that one and you need something this huge to pick that out that's right and so this is one of the most biggest biggest source of energy in the universe one of the biggest events you'd ever measure and we just barely saw it the LIGO scientists turned the gravitational waves into sound waves so what you're about to hear is in a very real sense the sound of two black holes colliding it was the first observation of any kind of pairs of stellar-mass black holes stellar-mass means you know several or a bunch of Suns in weight and and so we learned that they exist we learned that there enough of them that occasionally they run into each other and coalesce and and we also learned by comparing the wave form we observed with general relativity calculations that general relativity is as far as we know dead-on right [Music] the long concrete bunker to my left houses the beamline one of the lie goes laser arm the detail and and the effort that's gone into isolating the beam from the outside environment reminds me very much of Cavendish's famous experiment he too had to worry about isolating his experiment from external disturbances only of course LIGO takes things too far far greater degree inside the arm is one of the largest and purest vacuums in the world atmospheric pressure in there has been reduced to one trio of the pressure outside the mirrors inside are so reflective that they only absorb one in 3 million photons and at the end of my little trip neither British success story [Music] well I made it all the way to the end of one of the LIGO arms so be honest it took me a bit longer than I thought especially in that thing but housed inside this building is one of the reflecting mirrors that bounces the laser beam all the way back down the four kilometer arm to the main control center and the technology that went into developing these mirrors is quite remarkable it was developed in the UK at the University of Glasgow this is what the mirror looks like its surface is extraordinarily smooth no bump bigger than a few billions of a meter high equally amazing are these fused silica fibers a few times the thickness of a human hair designed by the University of Glasgow in conjunction with scientists from other British universities they isolate the mirror completely so it hangs perfectly still you could say that in there is the quietest place on earth despite this outside event do sometimes interfere with the work here as I witnessed for myself I've wandered into the control room here at LIGO because I'm told something kicked off a few hours ago and they're all very busy the image that's flickering up there is not meant to be like that essentially what they've picked up is a seismic disturbance an earthquake now that's not an earthquake down the road it started on the other side of the planet in Japan so it just gives us a sense of the tremendous challenges faced by LIGO and the team here and the level of sensitivity needed that an earthquake on the other side of the earth can disrupt their measurements and they and have to reset everything all over again one of the scientists involved in developing this extraordinary place put it quite succinctly once we were blind but now we can see throughout the entire history of astronomy we've studied gravity and how it affects matter in the universe and how it wilts space-time but only by looking at the light that enters our telescopes now for the first time we can study the universe in a different way the discovery of gravitational waves means we can see objects that cause extreme warping of space-time and its effect on gravity directly this essentially opens up a new era in astronomy gives us a new way of looking out at the universe professor Sheila Rowan was one of the scientists who spearheaded the British effort for LIGO for her and her colleagues gravitational wave detection is just in its infancy new instruments even more sensitive than LIGO and now being developed there's so much that we don't understand about the universe every weapon and this is suddenly given us a new tool a new way to probe the dark crew safeties in the universe because every time we make the observatory is more sensitive we can sense gravitational wave signals from further away from father oh and the universe from further back and cosmic history things like supermassive black holes spiral and into quite small black holes orbiting dragon supermassive black holes tracing out the dates and space-time of those super massive objects a long-term goal is to probe back further towards what we think of as the Big Bang the airiest moment that we understand of the universe as we know it [Music] if you think about it time and time again in the history of science unlocking the mysteries of gravity have led to a deeper understanding of the universe Galileo and his ramp Newton and his Apple I starred in the falling man in the lift each of these characters challenged the scientific consensus of the day and even today understanding the true nature of gravity remains one of the biggest challenges in science which brings me back to the smartphone app and it's at this point that our story to me at least takes a completely unexpected turn unfortunately it's all gone a bit pear-shaped ok so here's what's happened a couple of months ago we launched the app and it was all going really well thousands of people downloaded it and have been sending us their results we've been collecting the data to create this nationwide map to show how time flows at different rates for different people around the country unfortunately I've just realized there's a big problem you see I was going over the scientific literature and I came across this subtle point about relativity which basically made me sit bolt upright there was this horrible dawning realization that I've made a mistake in the equations that gets fed into the app so what this means is all the results we've been gathering are wrong the issue lies in the strange and subtle effects of Einstein's theories of relativity and it's fundamental to the way time flows across the surface of the globe now what if I use my smart phone app where I live here on the south coast of England and then go and spend a few days down near the equator so here on the west coast of Africa now we know from the road trip that gravity is weaker by the equator so that means time ticks faster there there's another important factor we have to take into account movement you see when I'm here near the equator I'm moving more quickly than I was back in Britain because of the rotation of the earth Einstein says movement slows down time so clocks will tick slower at the equator this is where the error crept in you see I had taken into account these two effects but I'd missed a crucial point they cancel each other out exactly in fact the earth bulges out exactly the right amount for its rotational speed to make sure they cancel out so all clocks on the surface of the earth at sea level tick at exactly the same rate so now I'm having to go right back to square one and completely rewrite the equations for the end [Music] and the test if it's working I'm going to use it over the course of a normal working week this is where I live this is Portsmouth which means I'm very close to sea level and this is how I thought most mornings catching the train to work the app records my speed as I'm on the Train and calculates how this slows down my personal clock I think the train journey should have slowed my time down by a tiny few trillions of a second I'm heading for the BBC's headquarters in central London and gravity should be a bit weaker here I'm a few metres above sea level I get here so there'll be a speed up of my time because of altitude the app compares the way my time flows with a stationary clock at sea level so what's my results on an average day my movement makes me age slower by a third of a nanosecond that's a third of a billionth of a second but the weaker gravity on him means I age faster overall half a nanosecond faster I've also given the app to some other volunteers to compare how they aged over an average day Nik flies cargo planes he flies from Chicago to Germany [Music] tomorrow morning we have to leave to go to first to Milan and then on to Tokyo this travel slows down his aging but much weaker gravity at high altitude speeds his clock up by just a bit more overall his aging 5 nanoseconds faster than a stationary clock at sea level Vanessa runs a pub in the Yorkshire Dales I'm going to take outside to see the weather conditions here so here we are outside - Tom Hillen will is right in the middle national park on the moor the tan Hill Inn is famous as Britain's highest altitude pub at over 500 metres above sea level how many neighbors just a sheep her altitude means she ate his faster every day by around four nanoseconds compared to someone at sea level there's Kevin a mountaineer in the Highland I'm on a mountain in Glencoe course Cornelia I've been an altitude generally of between 2,000 to 3,000 feet for a lot of the day throughout the day I've just been logging on to the for logging onto the app and just checking out and having a look and I've been watching it get bigger you're watching the value get bigger and bigger so be quite a lot of fun on an average day of climbing Kevin's personal clock goes faster by one nanosecond [Music] Gary works for a Scottish water retailer my job takes me all over the UK dealing with amateur consultant and amateur brokers spot up north is Inverness spot on sofas London proximately do about thousand miles a week sometimes more depending on the number of meetings I have Gary's car journeys do slow his time down a bit but being above sea level means he's still ages faster by three-quarters of a nanosecond our final volunteer is Walter he lives close to sea level at the iconic John O'Groats I run a tourism business and I started about fifty years ago so when people come here they can actually physically speak to someone who's been born with drama groups and FPS questions I can tell all sorts of useless information because are full of useless information so our final results show that if you want to age more slowly try to live near sea level like Walter oh there is another way to do it get a job on the International Space Station it's 17,000 mile an hour orbits will give you a boost we did the math for the astronauts every month you are about 1 millisecond younger so you know a thousandth of a second so after six months you are that much younger than people on earth so I'm younger than I should be hope I hope I look it of course for us on earth time dilation is so utterly minuscule a few billions of a second between ER you might think it's too frivolous to even bother about and yet in the long and difficult process of designing the app I've come to an extraordinary conclusion the different ways that time flows may not be some quirky byproducts of gravity it may actually be gravity it may be the cause of gravity the reason why objects fall [Music] one of the colleagues have been consulting is kicked form he's one of the world's leading theoretical physicists and a driving force behind the creation of LIGO while I was going back over some of the basic physics behind the app I came across an intriguing idea of his it's a very interesting and different way of describing gravity this is what Kip says everything likes to live where it'll age the most slowly and gravity pulled it their hips based at Caltech in California and is one of the most respected theoretical physicists in the world firstly a theorist thank you for helping out with the debacle over the house well I sympathize I made so many errors in my own over the years that I totally separated one of the things that struck me thinking about this is something you wrote Kip you said everything likes to live where it'll age the most slowly and gravity pulled it there was this a way of explaining something that you felt was a neat explanation or is there something because profound about that I think there is something deeply profound in some sense but it's a lovely description of Einstein's first major insight about gravity in 1912 he realized that gravity that we feel on earth is due to a slowing of time on earth so time comes before gravity in that sense here that did on the earth surface time runs more slowly and that accounts for why gravity wants to keep us there well I think in a very deep sense this is true objects want to fall it that the flow of time or the rate of flow of time is the thing that produces the gravity it is the thing that is ultimately responsible for the fall so somehow it's in the nature of all objects to move towards a region they're kind run Kitt's formulation works anywhere in the universe where the gravitational field is such as on earth the difference in the gradient flow of time is tiny at high altitude and on the surface of the earth the difference in the rate of flow of time is one second in 100 years that's not very much but that is enough that is precisely the right amount to produce the gravitational pull that we feel and produce the accelerations we're talking about Wow okay I need to go and write this one down [Laughter] so my investigation deep into the weird ways of gravity has finally left me face-to-face with one of the greatest mysteries in all of physics the nature of time itself it sounds like such a simple question why does the Apple fall and yet hundreds of years of scientific inquiry investigating this single action have led us to completely redefine the way we think about the very nature of space and time and now them presented with this extraordinary proposition that somehow in some profound way the Apple falls because it's seeking out the place where time runs the slowest so does gravity dictate the flow of time or the time itself define gravity could this hint to fundamental new laws of physics as yet undiscovered I think I'm going to have to think about this a bit more [Music] filtering through what's really in the air we breathe understanding our atmosphere available now on BBC iplayer vision on sound on stereo ready next on BBC four for the opening night that helped invent television as we know it how the box was born next you

Channel: Documentaries Only Please

Views: 193,427

Rating: 4.6454611 out of 5

Keywords: documentary, documentaries, document, only, please, factual, science, hd, 720p, 1080p, HDTV, x264, full-lenght, full, lenght, politics, psychology, sociology, history, film, dokumentalne, dokumentalny, nauka, historia, polityka, psychologia, socjologia, geologia, reportaż

Id: aNeR_fHcQSs

Length: 88min 46sec (5326 seconds)

Published: Wed Aug 23 2017