Lee Smolin - Why is the Quantum so Strange?

Lee today quantum gravity is like the holy grail for the ancient Knights well it seems like all physicists are talking about this let's understand what it means why it's important and how you go about attacking the problem it's important because it's finishing the revolution that Einstein started we have general relativity which is a theory of space and time cosmology gravity structure of the universe as a whole basically the structure of the universe as a whole and space and time what space and time are we have quantum theory which is a theory of matter radiation atoms elementary particles and so forth but they speak two different languages they're based on different principles they conceive of the world differently and nature is one nature is a unity so we want one fundamental theory and that's the problem of quantum gravity is to find that one fundamental even though one is the description of the very small and one is the description of the very largest still we need to combine them together sure if for no other reason to have a sense of coherence to have a sense of what nature is to have something to tell our children what is the world but also because there are experiments that probe regime between them and we want to be able to make predictions for those experiments and tests our ideas and our theories and it said that in certain conditions like theoretically in the center of a black hole or singularity or at the beginning of the universe as a whole but everything was so crunched together that quantum mechanics that actually had an effect on everything because everything was so small yes so so we we have to figure this out yes oh yeah okay okay you sound very confident so so how is the field evolved so there are roughly speaking two kinds of approaches there approaches that ignore the fundamental lesson of general relativity and their approaches that embraces the fundamental lesson of general relativity is that space is not given a priori there's no a priori geometry of space space is something dynamical which evolves just like anything else evolve you know the building the particles flying through the air there's no preferred frame of reference so to speak good one one thing everything is oriented from one and no preferred no preferred geometry the world is not Euclidean spaces we were taught in high school and these approaches we call them background independent and pastimes they were called relational because the geometry of space is a network of relations amongst the different things that happen the different things that are now the rest of physics and the rest of elementary particle physics ignores gravity and therefore takes a fixed space-time and then has things moving in it and those are called background dependent approaches and for the rest of physics it's okay because you don't have to deal with some of the larger issues in what they're dealing with and you don't have to deal with this fundamental insight which is that the structure of space the geometry of space is not fixed it's ever-evolving ever-changing because that fact it doesn't affect when you're dealing like with basic atomic physics or absolutely gravity is just too insignificant in that world because of this mystery that it's so weak you hear to the other four times okay okay so string theory is the only real viable or still possibly viable approach which is background dependent but certainly if it succeeds that's a big if it will have to come to the other side and be background independent so for me the interest and for many of us who work on it we start with this requirement that we have to embrace the basic discovery of general relativity of Einstein and general relativity and indeed there's been a lot of success so one of the things that's often said which is false is that you can't combine generality of any quantum mechanics well you can it was discovered how to do that by a program of research called loop quantum gravity started with a by ashtekar and then several of us contributing ted jacobson carlo rovelli myself and we did find that one could consistently combine just is given the principles and the equations of general relativity and quantum mechanics so there is such a thing I don't know if it is the truth eerie of nature but it is a completely well-defined theory and many people study it what are the problems that it's faced so the big problem is the following just like when you quantize an atom you discover that there are discrete energy levels when you quantize geometry you discover that there are discrete pieces of space that fit together to make all the possible geometries of space and we discovered in loop quantum gravity a precise description of these discrete pieces and they fit together into networks which we call spin networks and so we have a precise picture at the Planck scale this tiny tiny scale of the quantum geometry of space by combining these pieces ok the question is why is it that when you aggregate vast numbers of these tiny pieces of space you get something that looks like three-dimensional geometry that's the problem of the emergence of space and that's a problem that any fundamental approach to quantum gravity must face and and it's the problem on which we begin I think over the last five six years to have a real handle on and there have been some results that show a space emerging from this more discrete quantum geometry so what you're saying is that space is not the most fundamental thing that we have which in common perception seems to be it seems like space is space and we move in it in three dimensions but but you're saying that space is an emergent property like water is the emergence of hydrogen and oxygen in some unusual way that space emerges from something else precisely and just like in the science of materials it's a key question if you put together a lot of atoms a lot of water molecules for example under some conditions you'll get a gas under some conditions a solid and ice with very interesting properties under some conditions a liquid can you derive that from the properties of the material plus the fact that there are a large number of them and and we begin to be able to begin to be some results that show for example that when you combine them that the gravitational force is recovered that gravid gravitational waves propagate correctly and one of the things that's surprising and fascinating is that just like water molecules can combine under different conditions in different phases there can be different phases it's fundamentally someone phases space the way that we see it but there could be other phases where there's nothing like space there's still the fundamental physics going on and one of the more interesting directions is that people start to conceptualize 14 Marco Polo Thomas Canoga and some other people that what was going on in the very early universe might have been a phase transition from this other phase with no space to a spate of phase with space and we call this geometric genesis the genesis of geometry now I noticed you haven't mentioned time because normally and in since relativity we assume space and time or a part of the same thing but you're so for me personally time is the deepest mystery and I do think it's much harder to talk about space-time emerging but I should say some of my colleagues that I work with on this study theories of space and time together using these techniques they're called spin foam models and they also have results about space-time emerging as a whole so let me just understand that what what is the thing then that is the fundamental cause that of from which space emerges it is is this the this the spin Network mm-hmm which is composed of what exactly so imagine a network so there's no it's imaginary Internet okay there are nodes and they're connected by edges yeah and they can you can have a penny graph and the graph is then embedded in three-dimensional space but three-dimensional space only with the properties of topology of connectedness and the nodes give you a little quanta of volumes so if you want to know how much volume is there in some region roughly speaking you cut off the nose and and so the little units of volume and the edges tell you how they're stuck together and that creates the geometry if their aggregate it in a nice way of creates geometry and if they're not there's no space if there's not there's no space

Channel: Closer To Truth

Views: 58,333

Rating: 4.9468751 out of 5

Keywords: Lee Smolin, Closer To Truth, Physics, Quantum Physics, Quantum Mechanics, General Relativity, Albert Einstein, Cosmology

Id: QV5reKDbSqo

Length: 9min 1sec (541 seconds)

Published: Mon Oct 23 2017