Nima Arkani-Hamed - Why is the Quantum so Mysterious?

nema everybody today has heard the concept of the quantum and we know that there's some tremendous developments happening in the field so I really want to understand this but let's start with understanding what is the quantum itself how can we understand quantum theory well in the late 1800s we had two basic kinds of phenomenon that we'd seen in nature things like the light and sound waves and other excitation of different media were described by waves but things like billiard balls and and what they didn't have cars but if they had cars cars and other things were described as as as particles and having these two different kinds of descriptions for phenomenon in in in nature started leading to some confusions for example when people described light as ways and then they tried to figure out something very very simple like how much energy comes out of an oven for example and they applied the usual laws of classical physics they got nonsense nonsensical answers like an infinite amount of energy comes out of so they're paradoxes associated with the with the wave like on the one hand and particle-like on the other hand description of the various phenomenon that we saw in nature and what people realized in the early part of the 20th century was that these two different things that were being described by classical physics wave-like properties on one hand and particle-like properties on the other we're in the end of the day all actually describing particles but particles that don't move according to the laws of classical mechanics but move instead according to laws of quantum mechanics which are very very different than then then then the classical laws that they got particles for example there was the famous uncertainty principle that said that while while in the world of classical physics we associate the movement of a particle through space and time by specifying its position and its velocity it and even in any given point that we can't in fact specify the position of the velocity to Ethan it accuracy and then if we know the position very well we don't know the velocity very well and vice versa and all of this happened in conjunction with the realization that there's a new fundamental concept of nature Planck's constant which which determined when when classical approximations to the real underlying quantum physics was good and when that classical approximation broke down I should also say that there were there many other paradoxes of this sort the one that I mentioned about the infinite energy in an oven was the one that led Planck himself to the first realization that there was something wrong and that the the the the classical rules governing light had to be had to be modified the specific way it had to be modified was rather simple by the way classically we might imagine having a light of some given frequency and we can make the power the intensity or the amount of energy carried in that light beam as small as we want and and Planck realized that that that he could make sense of these difficulties with the infinite amount of energy coming out of an oven by positing instead that for a given wavelength of light or a given frequency of light there was a certain minimum amount of energy that was that was compatible at that frequency and this Greek piece and this isn't the envy of the indeed the the discrete piece the the quantum of quantum physics as it entered Planck's vocabulary was - was itwas it was indeed - a tell us that for a given frequency there was just an absolute meaning amount of energy that light could have and it couldn't go any smaller than so energy comes in pieces so that is so that so that so that the energy and light indeed comes in comes in discrete packets now Pike himself while introducing while you know opening the door this revolutionary concept could never himself believe or by all of its consequences so in fact it took Einstein to really to really make the leap and say that that Planck's discovery meant that light came in little parcels light came in particles photons and that at a given frequency there was a minimum amount there was a minimum energy photon whose energy was given by Planck's constant times its it's a frequency and and that description of light made a number of correct predictions now today we know that that from this there's a large number of observations which we know to be true but would seem counterintuitive to our normal macroscopic lives particles entangled the tunneling effects where things seem to jump from one place to the other and this has seems to be impossible but it is real it is absolutely real and one of the one of the unfortunate things about the way sometimes quantum mechanics is described is that there's there's an awful lot of mysticism associated with it and uncertainty means that everything that we can't be sure of anything and maybe consciousness has something to do with with with the way the world is and and there's an awful lot of nonsense said about quantum mechanics and whereas in fact quantum mechanics is responsible for the absolute stability of everything of everything we're made of atoms for example cuz the electrons rock can't occupy the same position right I mean that there was this old classical picture that an atom was it was like a little solar system with an electron orbiting around with electrons orbiting around the nucleus and there were a variety of problems with that picture one of them was that that you would think that the elect would quickly lose energy and spiral into the nucleus and atoms would be completely unstable and another one or a related one is that even even if you ignore that problem you could imagine lots of different solar systems with lots of different distances and and wire wire all the atoms identical wise wise everything's made out of the same same stuff and both of these mysteries were solved by a quantum mechanics with the realization that was impossible for the electron to fall into the nucleus because if it did you would know both where it was and how quickly it was moving at the same time and and and and the uncertainty principle tells you that that's that's not possible so the uncertainty principle actually creates stability and absolute confidence examine exactly far from introducing all kinds of fuzzy gar-bear right actually allows things to be stable and it's responsible for all the gross properties of matter ok let's fast forward to today and tell me about these serious problems in quantum mechanics and what are some of the potential areas of excitement and possible solutions well in many ways we have we have theoretical crises today that in some ways harken back to the sorts of problems that we had in the in the late 1890s that that that led Planck for example to the two is to introduce quantum mechanics to begin with and it all has to do with the fact that in our understanding of quantum mechanics and also putting quantum mechanics together with special relativity actually putting these two things together force us to introduce anti particles which are or antimatter partners to or to ordinary particles and the two of these things together give rise to to do this interesting fact that that the vacuum of what we like to think of is just emptiness is not in fact really is not really empty and it's a very very rich place with all kinds of interesting dynamics so that's something that's forced on us by both quantum mechanics and special relativity and more or less all of our problems have to do with those quantum fluctuations of particles and antiparticles popping in and out of existence out of the vacuum as allowed by the uncertainty principle making sense of those fluctuations of the vacuum gives rise to a variety of real crises in our inner understanding of physics today two of them have to do with ultimately the question of why it is that we have a universe with such incredibly different than disparate and interesting length scales where we're interesting physical phenomenon happen you know the kindest distances that we've explored that our very highest energy accelerators is something like 10 to the minus 16 centimeters that's around a hundred times smaller than the size of a proton the largest distances that we've explored are something like 10 to the plus 28 centimeters that's around the observable size of the universe and in theoretically in our minds eye we can take all the laws of physics that we know quantum mechanics special relativity and it's generalization to describe gravity general relativity and and and using those we can we can imagine extrapolating to very very short distances around 10 to the minus 33 centimeters called the Planck length so so there are these huge very very disparate interesting length scales apparently in in the universe that that's a very salient fact about the universe so that that that there are incredibly different light scales and yet quantum mechanics and indeed these quantum fluctuations of the vacuum seem to be very much at odds with that very basic fact about the universe so for instance quantum fluctuations of the vacuum have some energy and and Einstein told us that that any energy gravitates any energy gives rise to some curvature of space and time so if we take these quantum fluctuations in the vacuum and we just estimate the amount of energy that they Karrie and figure out what that would do to the universe we get a completely nonsensical answer that that if you just do a back-of-the-envelope estimate you would conclude that the universe is for example doubling in size accelerating very very rapidly doubling in size and the doubling time would be every Planck time that flank time is around 10 to the minus 43 seconds okay so so so you know if you took a theorist and walk through them up in a room and asked them to say please here's the universe here are the laws as we know them please give a prediction for what you think the universe looks like they would not remotely predict the universe that that that we see because this this the energy in the vacuum one we just grabbed grossly larger than what we apparently observe it to be okay so that's that's that's one of the crises that that we have and you've talked about that maybe we're missing something big right so I think the problems with these with taming these quantum fluctuations of the vacuum don't appear to be a little technical problem or something or disagreement between theory and experiment in the six decimal place of some some calculation there are problems of you know roughly 120 orders of magnitude or there is an analogous problem with for trying to understand the question why gravity is so weak there are two the fluctuations of the vacuum want to make all the particles that we know and love much much much heavier and if they were much much much heavier than gravity would be a lot stronger because everything would be a lot heavier and then you and I would be black holes of the very unpleasant universe so so there are those are two two questions that are directly tied to the quantum fluctuations of the vacuum that seemed to want to drag things to as high in energy as short a distance as as possible and one of the problems has to do with why the universe isn't accelerating every kind of a mind doubling in size every 10 to the minus 43 seconds that's called the cosmological constant problem the other problem of why we aren't all black holes it's called the hierarchy problem and they're each sort of very large numerically very large problems they're they're the the amount by which the estimate and the answer off is something like 120 order of magnitude for the first 130 orders of magnitude for the second one and so we think there's going to be some very big new principles missing that that that allow us to figure out why the answers are in fact what they are

Channel: Closer To Truth

Views: 24,064

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Keywords: Nima Arkani-Hamed, Closer To Truth, Princeton, quantum, quantum physics, quantum mechanics, quantum theory

Id: OAvd0XCWtCk

Length: 13min 34sec (814 seconds)

Published: Mon Sep 16 2019