Nature of the Graviton | Claudia de Rham | TEDxCLESalon

so let me invite you to a journey into your new world without gravity with our gravity objects we just seem to be floating around us in midair and while this may seem as fun for a second let's just contemplate the implications four billion years ago walks would not have collided to create the earth so the earth would simply not exist neither would the moon no any planet neither would the Sun there would be no star and no galaxy in the whole universe carbon oxygen water none of the elements were made of would exist as they wouldn't have been synthesized installs so we would simply not exist at least not in our present form the universe itself would be very different with our gravity the universe would have a likely remain as a boiling soup of fundamental particles a trillions of degrees with our gravity the universe would be very different and if we take an trans perspective the very notion of gravity is related to that of space and time themselves so a world without gravity may well be a world without space a world without time so let's go back to our word with gravity still taking on Sean's perspective the notion of gravity is related to law this curvature of space-time and massive objects like the Sun or the earth curved space around them and if we could zoom into this curved space we would see that at this very moment every single one of us is exchanging virtual gravity waves with the earth we cannot catch them that's why we call them virtual where they are there nonetheless and it's through this exchange that we feel the gravitational attraction to the earth and actually this exchange is present and active between any two objects in the universe every seconds you and me exchanging countless number of virtual gravity waves I may never have seen you before I may never see you again and yet you and me are forever connected through this constant exchange of gravity waves and these exchange links any two objects in universe between you and me between you and your neighbor between you and anyone else on the planet and anything else in the universe and this is not some type of fantasy I'm imagining for you today this is the very way we understand gravity and when the Sun gravity so well that we can predict the motion of the Moon around the earth within a millimeter precision and this is in such impeccable agreement with observations that if you wanted to do any better we will need to account for the leaves growing on the trees in the spring and falling down to the surface of the earth in the fall and changing every soul slightly the gravitational shape of the earth and changing every soul slightly the motion of the Moon around the earth we understand gravity so well that we can look at distant stars spinning around each other some twenty one thousand light years away from us and predict that these two stalls should yet closer to one another at a rate of less than an inch per year and that again is impeccable agreement with observations and a direct confirmation that gravity waves really do exist and while this may seem abstract I can guarantee that every single one of us here today does care and does use this level of accuracy in understanding of gravity while we spend one hour on the surface of the earth GPS satellites on orbit twelve thousand miles above our head fill one hour and a tiny tiny tiny bit more 1.5 microseconds more to be exact that's zero point zero zero zero zero zero one five seconds more this is a ridiculous limit small and yet this very subtle difference due to effects of gravity if not accounted for would accumulate and GPS devices would give you positions which would be miles away from the correct ones so if you got here today using a GPS device I guarantee you would not have found the right place how do you device not compute these very subtle Corrections from general relativity but just contemplate the fact that we're dealing with the position our position on the surface of the earth here and the GPS satellites are no bit just above our head if we already need to account for this level of accuracy in our understanding of gravity to understand a position on the surface of the earth just imagine the level of accuracy we need to reach understand a position in the galaxy and if you're like me I interested in the universe and it stretch it understand why the universe is made of and how it has evolved to be as it is today just appreciate the level of accuracy we need to reach in our understanding of gravity to find a place in universe find an origin and found our fate and what greater question is there and actually when we zoom to cosmic our skills we already have direct evidence that gravity is behaving in very unexpected in intriguing ways rather than galaxies moving away from one another more slowly due to the force of gravity as we would have expected we see that a receding from one another faster and faster the expansion of the whole universe is not slowing down it's accelerating and this is possibly one of the most puzzling observations of modern physics this observation is puzzling because in Ashland zero gravity objects are connected gravitationally no matter how far away they are from one another we say that gravity has an infinite reach and so we would have expected the gravitational pull between galaxies to make the expansion of the universe flow down in Antron theory of gravity objects located on the other side of the universe that is 10 to the 22 miles away from here that's 10,000 million trillion miles away from here still feel some gravitational connection like you and me this is remarkable in action fear of gravity even extraordinary but maybe this is simply too much to ask could it be that's his gravitational connection that we share you and me and that we share with the earth only occurs because we sufficiently close to one another could it be that we stop connecting with objects which are sufficiently far away from us like on the other side of the universe while this is a very natural possibility and one that my collaborators and I have been exploring and of course we're not the first ones to think about that Newton himself contemplated the possibility that gravity could behave differently at very large distances and I plus after him and they come after him am an amazing scientist since then but the seemingly innocent possibility has always been entirely refuted and not because it would contradict observations actually could even help explaining some of the observations but rather because it has been impossible to make sense of it theoretically if you look at the literature on the subject this is what you will read no way it doesn't work instabilities and my favorite one is possibly plagued by ghosts and I guess it's possibly the most terrifying thing I can ever imagine a ghost instability is the worst instability we can know of so while you see instabilities balancing rocks on top of one another it's quite an unstable thing to do and we simply need to push the structure and the whole rocks would fall apart stairs are also in stable situations we may have fallen down the stairs once or twice in our lives but just imagine if these stairs had no end and would just disappear come out of the existence just like that imagine in an instant all the particles of your body all the particles of the earth all the particle of the whole University disappearing decaying coming out of the existence this is what being played by a ghost would be it would be the most terrifying thing you could ever imagine an ephah theories of gravity our theory for the very nature of space and time predicted such an instability we wouldn't know how to make sense of anything anymore and so for decades it was so that the absolutely only possibility to avoid setup of such a pathology was for the force of gravity to have an infinite range and for objects to remain connected gravitationally no matter how far away they would be from one another and that mantra is something I myself have repeated in the past but when looking at potential alternatives with our colleagues we realized that they could potentially be more to the story than what we had originally anticipated and what it is true that this ghost is always there it's actually possible to drop it a bit like this and reality this trap looks more like Penrose tales ways possible to trap the ghost in a constrained space so it cannot make you fall anywhere and you can do no harm and so having taken care of this ghost instability pathology we can actually investigate the possibility that the force of gravity has a finite range and its implications in Angela's theory of gravity we need to postulate a new type of energy which we call dark energy to explain the fact that galaxies are receding from one another at an accelerating rate this energy is unlike any type of matter or radiation that we know of and yet it dominates the energy budget of the universe and this needs to be there to explain the fact that galaxies are receding from one another despite the eye tracking force between galaxies but if as I argued the force of gravity could in principle have a finite range we may not need to postulate the existence of this dark energy and the evolution of the universe may appear as much more natural and while this may seem abstract it could come with its own set of signatures and one of them would be on the speed of gravity so you may be familiar with the notion of speed of light the fact that light travels at a finite speed of 300,000 kilometers per seconds well so does gravity gravity travels us at a finite speed and in Anniston theory of gravity we believe it has the same speed as might but this has never been measured so we don't know for sure to appreciate notion of speed of gravity let's look at the planets in the solar system they spin around the earth thanks to the to the force of gravity and if we were to remove sorry they spin around the Sun thanks to the force of gravity and if we were to remove the Sun we think they would follow straight line and we think it would take three minutes for Mercury six minutes for Venus and eight minutes for the earth to realize that the Sun is gone and start changing trajectory or at least this is based on an strength fear of gravity but of course this has never been done so we don't know for sure and probably we shouldn't do it but if gravity had a finite range it would also be slower and so you might take a tiny bit longer for the planets to realize that Sun is gone and start changing their trajectory and while we can't do this what we may be able to do is measure the speed of gravity waves coming from other objects so you're probably familiar with the notion of waves for instance on the surface of water well gravity waves are not so dissimilar but they live on the fabric of space-time and I mentioned both you and me are generating gravity waves but very tiny one to see bigger ones we should look at bigger objects more massive objects like spinning Sun of spinning stars or black holes and the gravity waves generated by these objects would distort an ocean of space and distances so by making very precise measurements here on earth we may be able to detect these gravity waves but if gravity was slower than light the signal we receive from these objects through light would come before the signal we will see from the subject from gravity waves so there would be there could be a slight time delay in the time of arrival of a detection when we see these objects with the eyes or with our telescope and when we feel these objects with interferometers through the gravitational waves throughout the planet thousands of amazing scientists are dedicated to observing gravity waves and if and that's a greater but if they observe a tiny tiny delay in the arrival time of gravity waves no matter how small that innocent little signal will be a smoking gun signature for new theory of gravity that innocent little signal detected using 2.5 miles laser interferometers here on earth would have unprecedented implications for the in standing of a whole universe and for the in design of gravity on a very fundamental level these very signal could tell us whether or not the universe is filled with some strange type of dark energy fluid and observations from these gravity waves here on earth could tell us if and how we connects with others on the other side of the universe some ten thousand million trillions miles away from here thank you you

Channel: TEDx Talks

Views: 152,811

Rating: 4.67415 out of 5

Keywords: TEDxTalks, English, United States, Science (hard), Physics

Id: ThQ8P1KSFiw

Length: 14min 40sec (880 seconds)

Published: Wed Feb 03 2016