5 Things You Don't Understand about Gravity

what goes up must come down gravity doesn't need an introduction it's the familiar force that keeps our feet on the ground and our Earth locked in a stable orbit around the Sun but the mechanisms behind gravity are far more complicated than Meats the eye got of the days when we believe that an apple falling onto Newton's head represented just about everything there was to unpack about this invisible aspect of our universe in today's video we're going to break down five things about gravity that are often oversimplified commonly misunderstood by the public or even still remain just a total [Music] mystery it's commonly taught that all interactions in the universe can be explained by the four fundamental forces these are the strong and weak nuclear forces electromagnetism and gravity however you'll sometimes see these listed under a slightly different name the four fundamental interactions which is often considered to be slightly more accurate because gravity isn't exactly a force like the other three to explain this idea we need to start from the beginning for over 200 years the prevailing theory of gravity had been laid out by Isaac Newton in Newtonian Gravity the attraction between two objects is described as an equal and opposite pole that can be calculated based on the object's masses and relative distance the Earth pulls on you keeping your tether to the ground and likewise you pull on the earth it's just that you've got a lot less Mass so that you don't visibly move the Earth but maybe your mom does this model worked wonders it was easy to understand and experimentally verified however even Newton himself was a bit troubled with one part you see he figured out how to measure and predict gravitational attraction but he still had absolutely no clue what caused it or how this action could occur over such large distances in a letter to Richard Bentley he wrote that one body may act upon another at a distance through a vacuum without the mediation of anything else by and through which their action and force may be conveyed from one another is to me so great and absurd as that I believe no man who has in philosophic matters a competent faculty of thinking could ever fall into it the frustration would be shared by scientists around the world until it was finally resolved by none other than Einstein in his theory of general relativity Einstein revolutionized our understanding of Gravity by showing that it isn't actually a force acting between two objects but rather it is a byproduct of the way Mass distorts SpaceTime as you might have learned in a physics class an object in motion stays in motion unless it's acted upon this means if you are cruising through a vacuum in space your speed and direction would remain unchanged until something affected you Newton was spoton when he came up with this idea and Einstein builds upon it to explain his new understanding of gravity in a Newtonian model your path through space would be a straight line and this straight line would be bz by a gravitational attraction curving your path toward the object as you are pulled in its direction what Einstein did is he showed that it isn't really your path through space that is curved but but rather space itself and this may seem like a pointless distinction to make but it's actually really rather important Mass bends and stretches SpaceTime and as a consequence what you perceive as a straight path is curved along this warped terrain moving you toward the attracting Mass this straight yet curved path is called a geodesic and it's easier to understand with a comparison to passenger airlines airplanes want you to take the shortest route to their destination which is a straight line and from the Pilot's persp effective they indeed take off and fly straight with no deviation however when you zoom out you can see that their overall path was actually curved because despite the surface of the Earth being two-dimensional it curves into a third dimension on the surface of a sphere and thus what they perceived as a straight line followed this curve it's a bit harder to visualize this in three dimensions because we live in three dimensions ourselves but the concept is similar objects travel in a straight line Guided by the curves of SpaceTime this gives the impression that there is a mysterious ious Force pulling a distant planet toward a heavy star but in reality there is no Force no invisible push or pull that is shoving the planet in a New Direction it is simply a consequence of the Stars Mass warping SpaceTime and on a more advanced note if we weren't there already it's not just about Mass the Distortion of SpaceTime is actually created by any form of energy density which is why even though photons are generally believed to have a rest mass of zero they still interact with gravity and you can even technically create a black hole out of an half radiation focused in a small region in space and really what you've just heard is truly just the tip of the iceberg when it comes to how curved space gives rise to gravity we won't get into deeper details but we will leave you with the best explanation of it all a quote from legendary theoretical physicist John archero Wheeler who simplified the whole concept in the single phrase SpaceTime tells matter how to move matter tells SpaceTime how to curve [Music] general relativity refines Newton's findings and provided us with our most accurate model of gravity to date however it is not perfect and has one glaring issue of the four fundamental interactions gravity is the one that has yet to be reconciled with quantum mechanics but simply relativity is used to describe larger objects and quantum mechanics is used to describe the Universe on a subatomic level so when working in the domain of one usually you can safely ignore the other because they describe such different aspects of the universe however there are times when we can't just ignore one of them and need both an understanding of quantum mechanics and gravity working together to fully describe what's going on this is the case in the highest levels of energy such as the moments immediately following the big bang and near the smallest regions of space such as near the singularity of a black hole if we truly want to understand every aspect of the universe these two will eventually need need to find common ground this has led to the decades long search for a more comprehensive theory of quantum gravity or in other cases a so-called Theory of Everything that unifies all domains gravity included without getting into the specifics here there have been many different models put forward over the years such as Loop quantum gravity M Theory String Theory twister Theory and several others but one problem that they all share is that because they are all predicting results on these extremely high energy levels or tiny tiny regions of space they are next to impossible for us to verify with real world experiments using current technology for example Loop quantum gravity predicts that SpaceTime is not continuous and smooth but is actually made of distinct pieces or bits that can't be divided further as a result this Theory makes the shocking prediction that the speed of light is not constant but rather varies ever so slightly depending on a photon's wavelength with higher energy photons moving slightly slower however this difference is so indescribably tiny that we really have no hope of detecting it likewise for several predictions of string theory are particle accelerators simply can't reach the levels of energy required to either prove or disprove the prediction still that's not to say that these theories are simply numbers on a chalkboard even without experimental validity they still have yielded interesting scientific and mathematical contributions it's just that without observable evidence they can't yet be solidified as accepted science and as a result there is no consensus in the scientific Community concerning quantum gravity and the field is currently developing at this very moment it's certainly something to look out for in the coming decades as fresh ideas and technological improvements increase our experimental capabilities and we finally might be able to crack the case for [Music] good one of the most famous findings of Albert Einstein is the relationship between energy and mass summed up in the equation eal mc² where e is energy m is mass and C is the speed of light however the value C isn't just the speed of light light it's actually just the fastest possible speed in the universe of which anything can travel including light massless particles and even information crucially when Einstein formulated his theories of Relativity he found that this Cosmic speed limit also applies to gravity implying the existence of gravitational waves that Ripple outward through SpaceTime when there is a change of energy density say if our sun were to suddenly disappear without a trace the Earth would remain in its current stable orbit for another 8 minutes without any clue that the sun had just vanished because that's how long it would take for the last gravitational waves to reach us but despite his prediction of the existence of gravitational waves well over a 100 years ago they were so small and difficult to directly measure that scientists at the time doubted if there would ever be technology precise enough to detect them fortunately for us that technology does exist and in 2015 scientists announced the first ever direct detection of gravitational waves using the laser interferometer gravitational wave Observatory or ligo Lio is one of the most delicate instruments ever created comprised of two long tunnels in an l-shape with an array of carefully constructed lasers and mirrors inside the idea is that if a gravitational wave of sufficient strength move through the system it will Ripple through and for a brief moment make one of the arms slightly longer and the other slightly shorter this can be detected because the laser inside the machine is split into two beams that then bounce back and forth nearly 300 times in the separate arms before recombining back in the center because the beams are the exact same length and arrive at the exactly the same time when they collide with each other they are completely destroyed by interference however if a ripple of a strong enough gravitational wave comes through stretching the arms of the detector ever so slightly it will disrupt the timing of these beams so that they don't perfectly recombine at the center as expected and instead of destroying themselves some energy will be left over and detected it's obviously far more complex than that in reality because scientists also have to account for background interference of things like the Earth and the Sun but that's the basics of it to understand it on the simplest level if SpaceTime is nice and calm the lasers will destroy each other and an indicator stays dark but if SpaceTime is messed up some energy from the lasers survives and an indicator lights up detecting this minuscule change is a process so extremely precise that it's hard to even put it into perspective the arm of the ligo detector the long tunnel through which the lasers travel is 4 km in length or 2 and 1/2 miles and a strong gravitational wave will change the length of this arm by smaller than the thousandth of a diameter of a proton on the official ligo website they compare this change to measuring the distance to the nearest star 4.2 light years away to the accuracy of the width of a human hair it is simply incredible in 2015 after getting some modernized upgrades the detectors gave the first indication that a gravitational wave had been measured with the main terminal giving off a short audible chir the tiny beep not only earned several people a Nobel Prize in physics but was also evidence that Einstein had indeed been correct over a hundred years ago long before the technology was around to pull off an experiment like this to determine where these gravitational waves had originated from a joint effort was launched across the astronomical Community combining the findings of ligo with Sky surveys and Gamma rate detections to give them a head start on their search though scientists at least knew what general part of the sky to start looking in because the waves have been detected by two SE Lego Systems in the United States one in the state of Washington and one in the state of Louisiana because the waves traveled at the speed of light there was about a 7 millisecond delay between the two sites giving researchers a general direction of the source there is one other gravitational wave system on earth that is believed to be sensitive enough to detect it and that's located in Italy but unfortunately this third one was shut off and undergoing maintenance during the event the consensus is that the origin of the Waves was the merging of a pair of binary black holes each around 30 times the mass of our sun most likely located about a billion light years away in the direction of the melanic clouds and remember because these gravitational waves travel at the speed of light the actual event that created them happened in the distant distant past long before vertebrates that even evolved on [Music] Earth perhaps the strangest of Einstein's predictions are those related to time dilation there are two types of time dilation one that arises as a result of velocity and one that arises as a result of gravity which is the one that we could be going over today because that's what this video is about gravitational time dilation is a crazy concept that our brain just isn't wired to understand intuitively but we'll do our best to break it down for you according to relativity the closer an observer is to a gravitational Source the slower time passes for them relative to an observer that is further from the gravitational Source this means that technically a person living on the surface of the Earth would Age more slowly someone living on the moon because the person on Earth experiences a stronger gravitational effect though when we're talking about time dilation with things like the Earth the difference is absolutely tiny M fractions of a fraction of a second over a human lifespan however it is interesting to note that because the strength of gravity is much stronger at the center of the planet if you had some stopwatches running from the moment the Earth formed You' find that its core is about 2 and 1/2 years younger than its surface time dilation was displayed perfectly in the movie Interstellar where 1 hour spent on Miller's planet is equal to 7 years spent back on Earth due to the fact that Miller's planet is in close proximity to a large black hole the time dilation caused by this black hole is also how the main protagonist ends up younger than his own daughter by the end of the film confirming time dilation experimentally was only limited by the accuracy of clocks which improved greatly throughout the 20th century and led to multiple confirmations of Einstein's theories even the simplest of experiments yielded the expected results such as placing one atomic clock at sea level and the other on the top of a mountain if your clocks are accurate enough you'll find each and every time that the clock taken to the higher elevation takes a fraction of a second faster now it's easy enough to take this at face value and move on but a bit more analysis is needed to truly understand the why of this the key here is remembering the time half of SpaceTime according to Einstein the two are inseparable when a large mass stretches and distorts SpaceTime it is also stretching and distorting time which is what causes the difference in how quickly time passes think of time like a one Ray Road on which you're always driving forward at a constant speed now imagine that every M there is a sign indicating that one year has passed a pair of twins will go their lives passing by these Mal markers at the exact same time reaching ages 5 10 and 20 simultaneously because they both live on the surface of the Earth and their roads of time are identical now picture the one of the twins is teleported near to the event Horizon of a black hole a place with immense gravitational force compared to the earth in this environment of intense Gravity the road will be stretched and lengthened making the distance between each mile longer than those of his twin back on Earth this means that even though they are moving forward through this time Road at the same speed the twin near the black hole has more distance to cover in order to age a single year and thus it takes longer compared to his twin on Earth and he ages more slowly still the point of Relativity is that each twin doesn't notice the difference in the passage of time on their own for each individual Observer time appears to pass at the normal rate and time dilation is only noticeable when you compare two different locations the Einstein field equations are a group of equations published as part of general relativity that describe the geometry of SpaceTime only a few months after they were published in 1915 Carl Schwarz child found a peculiar solution to them a point in space where when matter reached to certain density some of the terms of the field equations became infinite today we know this as a singularity around which the force of gravity is so strong that not even light can escape creating the infamous black hole you could fill a library of books dedicated to understanding black hole singularities and the strangeness that occurs at such high levels of gravity so we're going to go through just a few things that most people aren't aware of for starters the popular perception of black holes is that they suck matter into them as they move around the universe like like a hungry Cosmic vacuum cleaner but that's not true as long as you haven't crossed the Event Horizon the point of no return the gravitational pull exerted by a black hole is no different than the gravity exerted by any other object of that size for instance if you were to replace our sun with a small black hole of the exact same mass the planets would continue orbiting as usual as if nothing had changed of course our planet would become inhospitable without the warmth of the Sun but the point is that we wouldn't suddenly be sucked into the center of the solar system and eaten by the black hole which is a very popular misconception instead we would just keep cruising around on our stable yearly orbit in fact it's not just objects that can orbit a black hole but even light itself there's a specific radius from the black hole which light is trapped in a perfectly circular orbit balanced on the perfect trajectory to avoid both falling past the event horizon or escaping into free space this point is called the photon sphere it leads to some interesting thought experiments such as standing in the perfect spot so that light bouncing off your head travels all the way around the black hole and into your eyes allowing you to see the back of your own head but in reality the photon sphere is not only a one-dimensional line having no thickness but also orbits on the line would be highly unstable as even the slightest interaction would disrupt the perfect distance now let's say that you were trying to set up this little experiment and accidentally fell past the Event Horizon Whoops a Daisy most people understand that this is the point from which you can't return to the outside world but Les's break down exactly why that is for every celestial object there is something known as escape velocity this is the speed you need to reach in order to escape its gravitational pull for the Earth it's about 25,000 mph for the sun it's closer to 1.4 million mph that's really fast but it's still within the realm of possibility if you've got a nice spaceship with a powerful enough propulsion system the issue with black holes is that once you pass the Event Horizon the escape Velocity becomes higher than the speed of light and since we know that this speed is impossible to reach or surpass you are now trapped but it gets even Stranger Than simply not being able to go fast enough once you've passed the Event Horizon SpaceTime becomes increasingly stretched and warped beyond anything imaginable to the point where no matter which path you take the singularity is unavoidable not just in space but also in time it becomes an inevitable point in your future to understand this think back to our analogy of the time Road or when we discussed these time roads before the length was infinite All We Care about was how stretched it became under intense gravity but once you're past the Event Horizon of a black hole and under the grip of its gravitational pull SpaceTime becomes so curved that your time road now has a concrete end a Finish Line at the singularity no matter which direction you face or how fast or slow you try to move every single path you could possibly take through SpaceTime ends with you meeting the singularity it is inevitable and it's all thank thanks to gravity [Music]

Channel: Sideprojects

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Keywords: megaprojects, construction, engineering, projects, sideprojects, mysterious facts about gravity, earth shattering facts about gravity, 10 most mysterious facts about gravity, facts about gravity, top 10 facts about gravity, gravity, mysterious gravity facts, how gravity works, gravity facts, gravity on earth, weird facts, gravity on other planets, gravitational forces, amazing facts, interesting facts

Id: NEtilzJOWgs

Length: 19min 40sec (1180 seconds)

Published: Fri Jun 21 2024