Why Is Gravity So Elusive? | Frank Wilczek, Erik Verlinde, Laura Mersini-Houghton

[Music] I think there are more problems with gravity and also general relativity in particular so we need a new theory to describe the phenomena that we are observing gravity works well but you should understand that has a lot of ways it really works well unless we understand dark energy and the gravitational force associated with it we will complete it with our universal no after this will crunch into a black hole type all will just continue and smooth expansion forever [Music] so why is a force that's so central to the universe and our science so elusive in its character on my right we have Eric valinda who's Utrecht theoretical physicist and string theorist um on my left Frank will check theoretical physicist and Nobel laureate at MIT and Laura Messina halton professor of physics at the University of North Carolina and her work focuses on cosmology and the birth of universities from the multiverse so if I could I think Eric would you would you stop and tell us why you think gravity is so elusive gravity exists I mean indeed if we can keep our feet on the ground and we sit in our chairs thanks to gravity but what is it it mean is it the fundamental force that we need to assume right from the beginning and then describe it or is it possible to derive it without assuming it mean derive it really from something underlying from the microscopic I'm saying on a say the letter it's our current theory of gravity which is general relativity is it really the correct theory I mean can we describe everything we can observe even with it or is it only the problem with the Planck scale I think there are more problems with gravity and also general relativity in particular so we need a new theory to describe the phenomena that we are even observing and particularly in cosmology but let me start out by saying that general relativity is very successful and is a beautiful theory and there are many things that have been tested I mean the gravity waves is certainly one of the recent successes but it doesn't mean that all predictions that we that are made by general relativity are correct and I want to mention a few that are troublesome first of all our mentioned quantum mechanics but also there's a problem with the value of the vacuum energy the cosmological constant which also has to do with quantum mechanics then there is a black hole I mean black holes are our elusive objects where there are many puzzles in particular about the information that goes in and a thing people are probably generally agree that we haven't really solved those puzzles but what for me actually even stands out is that there are even observations that are not in agreement with general relativity if we look at galaxies we see that the way the gal at the stars are moving in galaxies cannot be explained by simply assuming general relativity namely the stars are moving much too fast the only way we can explain it and save the series by assuming that there is an additional amount of matter that we have not observed yet which we call dark matter but this is a safe way of saving it which is assuming that general relativity is correct and the reason is that we don't see why it should be wrong there's no conceptual reason why that should be the case now that brings me to the puzzles of black holes I mean if you think about black holes and the way to behave they actually are are teaching us the actually laboratory stress there are the thought experiments which teaches that the equations of gravity look like those of thermodynamics the laws that describe heat and temperature and so on and those who know we can derive from something microscopic by treating statistically the microscopic molecules while the same is true for gravity the general relativity equations can be derived from something microscopic and that's the kind of theory I'm working on is precisely describing what is the analog of atoms of space-time that we have to assume and there we go into the quantum phenomena of space-time and there's a microscopic picture of space-time from which you can derive gravity and then you can actually also explain the phenomena that we are observing in galaxies without even assuming the dark matter well I think gravity is elusive because no convincing experimental evidence that gets beyond general relativity has been found nor is there any prospect of any the people who set out to detect gravitational waves started 50 years ago estimating what it would take the estin to detect gravitational waves from for instance black holes merging and they estimated that they would have to set up some mirrors to detect Ripa the warping of space-time which is what a gravitational wave is that would be able to detect motions of these mirrors that are of the size of a thousandth of a nucleus thousandth of the size not of an atom but of an atomic nucleus was a hundred thousand times smaller over a distance of four kilometers so when the mirrors of four kilometers away you have to detect that kind of change and by golly they took 50 years and surmount the difficulty after difficulty and there it was so that's a pretty impressive theory it may need changes there are indications that the equations become singular and very very extreme condition is like it at the center of black holes or in the extremely extremely extremely early moments of the Big Bang but it's easy to say gravity works well and but you should understand that has a lot of weight it really works well under all kinds of circumstances the people who believed in Newton's theory of the planets and Newton's theory of gravity had an anomaly much bigger than the anomaly of Mercury that was troublesome in the early days namely the planet Uranus didn't seem to be moving the right way and so Adams John couch Adams and the very a pronoun the planet that's a big planet that's having gravitational influences I'm causing this distortion of the Uranus's orbit and they could calculate what it would take where would have to be how big it would have to be they told astronomers look for that and they found it the general relativity was so good to predict the orbiter these changes in the orbit orbit of mercury doesn't mean that it's I'm not even sure with the interpretation I mean it doesn't mean the Dark Matter calls for another theory it could vary I would argue on the contrary that there is it's not just one observation that there's a deficit of mass in certain circumstances there are many many different kinds of observations in different circumstances all of which are coherent with the possibility that there's a new kind of particle that makes this Dark Matter I even think I know what the particle is something called an axiom this great theory of general relativity and ok so general undoubtedly is a it has limitations but another thing that I would point out is that it's a theory that's very simply formulated the idea that you should explain something simple in terms of something very complicated I think is a little wrongheaded moreover there are quantitative calculations that relate the strength of the electromagnetic weak and strong interactions to the coupling to the strength of gravity quantitative relations that indicate that they all come together so they all can be treated on the same footing as fundamental forces and I think I would need a lot of persuading to ignore that circumstantial evidence gravity do I believe it's a fundamental force absolutely and I think that the majority of the physicists do consider it to be a fundamental force we have not succeeded so far in unifying it with the other three fundamental forces it doesn't mean that a solution is not possible but the problem with gravity is that first of all in our daily experience is such a weak force that we really didn't need to bother with it until relatively recently in the in the history of scientific endeavor and the other difficulty we have since Einstein's theory came about in the early 20th century is the unification of gravity with the quantum theory we don't have a theory of quantum gravity there are two regimes where gravity is extremely important and it's not the weak force that we can ignore or neglect in our experiment and that is at the moment the universe calls on the Big Bang inflation and a similar system of beta the collapse of a very massive star into one point in both cases if you follow general relativity to the dot you end up with a singularity which is a very exotic mysterious object that quite likely is not physically there is a mathematical solution but but not physically there so in those two cases it becomes imperative that we try to understand what what the force of gravity is and that motivates our effort in into a theory of everything a theory of quantum gravity and so on [Music] [Music]

Channel: The Institute of Art and Ideas

Views: 96,539

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Keywords: what is gravity, the problem with gravity, erik verlinde, frank wilczek, laura mersini-houghton, physics, quantum gravity, quantum physics, quantum mechanics, gravity explained, how to understand gravity, axions, anyons, time crystals, particle physics, nobel prize, entropic gravity, verlinde formula, what is dark matter, what is dark energy, theoretical physics today, cosmology

Id: 7lui9qZ6cDs

Length: 10min 55sec (655 seconds)

Published: Mon Dec 04 2017