Rethinking Space and Time: The Quantum Perspective | Sylvie McKnight-Milles | TEDxStJohnsCollege

i'd like to take a moment to ask you to forget everything you think you know about reality but what exactly is reality to be honest nobody's really sure but we can try to figure it out we'll start off easy picture yourself trying to get your morning newspaper you get out of bed put on your bathrobe and walk down the driveway and you bend down to pick up the paper seems simple right every one of your actions had a direct and immediate consequence and time flowed in one direction but what happens if you do the same thing at the speed of light if you take a proverbial step back from time the first thing you notice is that nothing is moving rather past and present are overlaid upon each other like images in a stop-motion animation video you're in the driveway and bending down to pick up the paper all at the same time and your hand is in the paper the very dis the very idea of spatial distance seems to have become meaningless congratulations you're beginning to see what life is like for a quantum particle except they seem to exist this way nearly all the time as a superposition of different states of being given that reality for a quantum particle appears to be an amalgamation of many realities all twisted and tangled together physicists prefer to assign something called a wave function to a quantum system a wave function is basically a large mathematical object that sums together all the probability states of where a particle might be at any given moment and what state it might be in now this probability function or wave function does not operate like our traditional ideas of the cartesian coordinates in that a particle is everywhere at once now this might sound contradictory how can a particle a fixed quantized object exist everywhere it wants as a wave well it turns out that this isn't a unique feature of the quantum world in fact it's everywhere in quantum mechanics decades ago scientists resolved that light itself is made up of both a particle and a wave so it's not one or the other it's somehow both it's a wave until it's observed and then once it's observed or interacted something in our world the probability function collapses into a single probability into a single state of being so in that way particle of light is both a particle and a wave doesn't this seem to contradict nearly all of our traditional ideas about what reality is in causality space and time how can something be affected instantaneously by something on the other side of the universe and then collapse from something continuous into something discrete in an instant well seems like that's just how the quantum world functions we may seem like we have an issue with this on the grounds that it violates our terms of what constitutes reality but in fact this is reality for the quantum world so the issue clearly doesn't lie with the quantum world which does follow these rules it lies with our issue an issue of our understanding of ideas such as causality and locality and even major principles such as space and time and these will have to be re-evaluated if we want to truly understand how causality works at the quantum level so macroscopic laws won't work with quantum events if the x makes that startlingly clear so basically i'm going to start with the notion of two different quantum particles we'll name one alice oh there we go there's alice oh wait no it's not on your screen it's on mine okay there's alice this is alice and the other quantum particle is named bob now alice and bob have a very special relationship we could even say that they're soul mates now whatever state alice is in we'll call this state up which is basically this state up is just a mathematical representation of something called angular momentum which i won't get into now because it's very wordy and complicated but and we know that if alice is in the upstate of angular momentum that bob will also be correlated to alice's state no matter how far away they are from each other so if alice is up then bob is down it's important to keep in mind that one of the funny features of the quantum world is that until they interact with each other quantum particles are considered to exist in a superposition of many states of being or reality so alice and bob are both up and down at the same time until they're measured which is not normal so let's do a little experiment we'll send bob a hundred thousand light years across the known universe that should suffice and we'll take a measurement of alice we find out that alice is in the down position can we predict bob's state even though they're so far away can alice even affect bob at this distance well it turns out that it can we take a measurement of bob somehow and figure out that it is up it will always be up when alice is down regardless of how much distance is between the two instantaneous communication that's quantum mechanics for you this process is an example of a non-local interaction in physics in that it violates our traditional ideas of causality and locality physicists refer to this particular relationship as quantum entanglement but how can quantum how can the quantum world violate our ideas of reality so blatantly this just doesn't really make any sense well it's possible that the quantum world follows a unique structure of cause and effect that is hidden from our prying eyes because the quantum world clearly doesn't follow you know our traditional notions of time and space and what's the deal with wave functions anyways why do wave functions always have to be expressed in terms of probabilities that is where a particle might be at any given moment why can't it have a fixed position when these particles are definitely interacting and they definitely exist this seems like again a flaw with our current understanding of quantum mechanics so let's get into a possible structure of what cause a possible cause and effect structure that quantum mechanics might follow well if we think about it one thing that quantum mechanics seems to have differently from our world is that quantum quantum objects don't seem to regard distance as anything of importance to them that could be because they don't have any like inclination to follow our idea of time at all so if they aren't privy to our notion of time then by virtue of this distance means nothing as we saw in the introduction where things were distance became nothing when you step outside of time but why would this happen and what would a quantum world lying beyond our reach even look like how could we imagine something existing not within time or without time but beyond time well it's possible that the quantum world itself creates the space time the very fabric that we are and is all around us it seems likely that the quantum world has something to do with the creation of space time in that quantum processes underlie everything we know about the known universe and in fact if quantum mechanics does create the arrow of space and does create space and the arrow of time then it makes a lot of sense to assume that quantum mechanics wouldn't necessarily follow a sort of causality that's dependent upon the time it creates in other words by creating our arrow of time quantum mechanical objects must follow some other arrow of time or at least causal relationship this causal relationship might take the form of interactions through another dimension that's either too small or too large for us to be able to visualize or interact with quantum mechanical objects may be temporally related that is across another dimension of time or they may not be physically related in our in our dimensions so they may be infinitely far away from each other in space and still able to communicate because their probability states in some sort of way overlap temporally now i'd like to draw your attention to the following slide the red dots depict a particle which is in its current position just existing in space which is very unlikely to find a particle in one spot but for the sake of this demonstration so the blues the blue dots represent the future probability states or the states that the particle will um possibly become in the future so probability states the green probability states are yet another step removed in time from the blue now what does this mean well it draws to mind ideas of randomness like how do we know which state the particle is going to choose well quantum particles are a lot in this way like molecules of air floating around we may not know where a given molecule of air will be at any given time and it doesn't seem to matter in the context of the wider system but when you think about the interactions of every other particle you can deduce where one particle will be likewise in quantum mechanics interactions that may seem completely random may depend upon the motions of every other quantum particle in the states of every other quantum particle in the entire universe so it's no wonder that quantum mechanics seems a little random when you're taking into account literally every variable there is so under this model we can draw a conclusion quantum particles neither exist outside the arrow of time nor are they completely immune to it in that they still follow some sort of they can still interact with each other within the scope of our dimension of time rather by virtue of creating it they exist within it and thus aren't beholden to the consequences of violating our idea of causality but before before i get into what i promised a few minutes ago that is to explain how quantum entanglement and quantum relationships might create the space-time structure itself i'd like to get into a process that seems wholly dependent upon our notion of of a unidirectional of a one directional excuse me line of time and the name of that process is entropy you may have you may have heard of entropy before after all it's a staple of every chemical engineering class basically the just the gist of entropy is that the more randomness a system has that is the more probabilities it has of evolving into a more spatially randomized body the more entropy it has so in this graphic the teacup on the on your left represents a system with very low entropy it has a low probability of evolving into some other state or interacting with other systems in a way that will change its physical composition whereas when the teacup is dropped it shatters into pieces each of these pieces have their own probability states they can interact with a multitude of other systems now this sounds a lot like quantum mechanics when you think about probability states increasing in when entropy increases so as time goes on entropy increases because the number of probability states in a quantum system increase now this particular definition of entropy might sound strange and that's because it's from a very strange discipline in physics that is black hole physics it's derived from a definition which will become very important to listen carefully the basically in black hole physics the gist of this relationship is that the more entropy there is inside the black hole that is the more quantum relationships are going on inside the black hole the greater the area of the horizon is now the horizon you can think of as being like a boundary of sorts for the black hole so the more that's going on inside the black hole the more entropy and randomness quantum interactions there are the greater the area of the horizon but what does this have to do what we've been talking about earlier all the quantum malarkey well what if the relationship between time and entropy is reciprocal this might seem to have come out of the blue but i promise i'll get into it if you superimpose that diagram of a black hole well it's kind of a rudimentary diagram but the the idea is still there on to our idea of the universe then the horizon of the black hole would have correspondence with what we see as our present moment in time that is a sliver in time which we perceive as well as our three dimensions of space so the world around us would be equivalent to the horizon of some cosmic black hole that is in this case the entropy in the system would come from the interactions on the quantum level which permeate the entire universe these interactions in turn would cause space and time to expand if space and time are in fact the horizon of this cosmic black hole so the more entropy there is within the universe as a whole that is the more interactions of the constituents of the universe the more space we get space expands outwards and time moves forwards in one direction that is our arrow of time in this way entropy could give rise to time so to briefly recap in a black hole the more entry entropy there is the greater the area of the horizon likewise if we consider the horizon of our universe to be our current slice of time and three dimensions of space space and time are expanding as entropy increases within the universe it's like a quantum web permeating the entire universe facetime would be a web based on quantum probability states and entropy now this brings to mind a very important relationship you might recall from einstein that the theory of gravity that is means that when the space-time curves objects move that is move towards the center of that curvature so gravity is basically just curvature in space-time now if space-time has quantum origins that could mean that the gravitational force itself is dependent upon the objects which it impacts just as much as the objects which it impacts are dependent upon gravity so it's a reciprocal relationship in a way quantum interactions give rise to space-time by virtue of having probability states through their various interactions with one another these probability states can be counted as entropy which drives the engine of space time forwards then in the air the excuse me the arrow of time forwards and the area of space time outwards and then the fact that time is moving forwards and that there continues to be space means that gravity occurs and that objects interact with each other relative to this gravity these quantum interactions in turn give rise to more probability states more entropy more space time gravity and it goes back to quantum interactions so the universe is like a giant machine driving itself forwards it turns out that by looking at the quantum world we can learn so much about our own reality by taking the perspective of alice and bob you learn something very crucial and that is that the quantum world drives reality thank you for your time

Channel: TEDx Talks

Views: 10,230

Keywords: English, Physics, Science, TEDxTalks, [TEDxEID:33118]

Id: NzEjNOrNJnw

Length: 14min 27sec (867 seconds)

Published: Thu May 05 2022