Your Daily Equation #32: Entropy and the Arrow of Time

everyone welcome to this next episode of your daily equation and today I am going to focus upon a deep issue one that we could spend many episodes talking about many hours talking about but I'm just gonna really try to scratch the surface here on the deep issue of the arrow of time and its relationship to entropy and the second law of thermodynamics so let me just jump right in what's the puzzle the puzzle is this there are a gazillion processes in the world that we only ever witnessed taking place in one temporal order they unfold in one temporal direction and we never see the reverse of those processes right I mean we're all familiar with the wind blows and the the petals of a flower can be blown away but if I showed you a film in which the the flower reassembles itself you'd know that I'm showing you a reverse run film you never actually see that kind of reconstruction taking place in the real world around you we're all familiar for another example someone can jump off the side of a pool and do a whatever somersault and land into a pool but if I showed you a film in which someone jumps out of the water the wall are all coalesced to a nice flat surface and the person lands on the pool surface you know that I'm showing you a reverse run film you've never seen that actual process take place in the world around you in the perhaps third and canonical example we're all familiar it's happened to me you're holding a nice glass of wine maybe it's a Riedel glass you know a real nice one it slips out of your hand and it smashes on the floor awful mess but you and I have never seen the shards of glass on the floor all jump off the floor come back together in just the right way to reassemble a pristine glass filled with wine we never see such processes and the puzzle or the issue frame it down way the issue is to explain this asymmetry why did we see events unfold in one temporal order but we never see those events in Reverse now now one answer the quickest answer would be well maybe the laws of physics allow glasses to smash allow people to jump into pools where the water becomes all agitated they allow for wind to blow petals of a flower whatever they're called parts of a flower to blow off in the wind but they simply don't allow the reverse process to take place that would be a great answer we only see the things allowed by the laws of physics the laws of physics don't allow those perverse processes to take place you can film them in the right order and play the reverse but you can actually see them take place in the real world in the reverse order period end of story that would be great problem is that explanation fails as I'll show you in a moment any motion allowed by the laws of physics the reverse motion is also allowed by the laws if it's the reverse process is allowed by the laws of physics so we're back to square one and trying to find an explanation and the actual explanation that will actually finally be led to is not to try to say that the reverse processes can't happen but rather to said that they can happen it's just that they are extraordinarily unlikely extraordinarily unlikely and they're so unlikely that they effectively never happen in the real world that is the basic idea and trying to make that a little bit more precise will bring in the concept of entropy second law of thermodynamics and at the end though we'll find a little bit of a twist in that to really finish this top level argument we're not going to dig into the nitty-gritty details which are fascinating rich but they will take us down a rabbit hole the twist however that we will encounter is that we will need to bring in properties of the universe near the Big Bang to actually make these ideas complete or at least this approach to be complete not everyone agrees that this approach is the correct approach ok so that's the the basic issue at hand and let's just quickly jump in so the subject that we're talking about is entropy and the arrow of time the fact that there seems to be a built-in orientation to the order in which events unfold that's what we mean by the arrow of time that time has an orientation associated with it with space does not seem to have you can do anything in space but time seems to have this asymmetric quality where does it come from so I really just want to quickly spell out two things number one I just want to convince you quickly that the laws of physics really do allow reverse run processes to take place so reverse processes can happen and then the second thing that we will take a look at once we're convinced that there's an issue right if the reverse process these can't happen there's no issue once there is an issue we will talk about entropy order disorder and [Music] the second law of thermodynamics which we will see talks about the overwhelming tendency of order to degrade into disorder from an orderly glass to degrade into a shattered disorderly glass that's where we're going all right so let's begin with point number one and I'll do this in a specific example but easily generalizable I just want you get a feel for how we argue that the laws of physics once they allow one trajectory one kind of motion they necessarily allow the reverse trajectory how do we do that so I'm gonna do a specific example let's imagine that we have a baseball you know I like baseball even I'll admit it I like the Yankees don't turn off the video okay but anyway there isn't any baseball this these days in any event so imagine you have a baseball and it's hit from home plate it soars into say the bleachers in the outfield let's say the trajectory is called X of T and let's say we set it up so that T equal to zero is when the ball is a home plate T equals one when it lands and the bleachers clearly if that was in units of one second that would be a monster shot I don't think anyone has ever hit a ball in one second from home plate to the bleachers but just that one B whatever unit it needs to be so that I can just keep the math looking simple from T equals zero to T equal to one now the question is what about the reverse trajectory that would look like say starting in the bleachers and heading back toward home plate and that trajectory let's call it X tilde of T in terms of its functional form that could be written as X of 1 minus T as you see X tilde at time 0 would be X of 1 which is this location here is X of 1 and X tilde of one would be X of 0 over here as that is X of 0 so that is the reverse run trajectory and what we want to make clear is that if X of T satisfies the equations of motion so does X tilde of T I'm doing this purely classically I'll mention the generalization in a moment now what are the equations of motion well it's just the force of gravity which is equal to the mass of the ball times the acceleration due to gravity is M times D 2 X d t squared that is the equation satisfied by X of T and now we want to see if that equation is satisfied by X tilde of T and that's not hard to work out because let's consider let me keep the colors semi consistent so let's consider D X tilde DT so that is the same as d of X of 1 minus T DT and then of course can be written a d of X of 1 minus T with respect to 1 minus T which is now a dummy variable that I couldn't replace with anything as I will in a moment but let's write that D of 1 minus T DT using the chain rule now this fellow over here derivative of 1 minus T respect to T the 1 derivative the one part just gives you 0 so you get derivative of negative T respect to T so it's just minus 1 that's all that that is so a factor of minus 1 coming in and then this term over here as I said 1 minus T is now a dummy variable which hopefully not confusing me I'll now call T it's just a derivative of a function of a very function of a particular argument and it's called 1 minus T in my equation I'm gonna now call it T just for simplicity whoops that's unfortunate phone ringing where is that phone would you please excuse me for half a second guys hopefully this is not a cologne yet to take oh someone picked it up in the main house I should have gotten rid of this phone before I started this but in any event sorry but we're worried so here we have this expression so we have minus DX DT that makes good sense because the velocity of the ball in the purple starting in the bleachers it's heading out in this direction whereas the red one as it was reaching the bleachers was adding a misdirection clearly this purple is the opposite of this red that makes perfect sense but now let's take the second derivative in order to analyze the question of whether X tilde T satisfies Newton's second law I don't have to do anything at all because look when I took the first derivative oh oh it's so irritating all right I'm gonna have to get rid of this phone I'm gonna break it it's gonna drive me nuts okay how much normally I put the phone out the door after out to do it this time but in any event okay so what do we have here so we have this this minus sign that comes from the first derivative if I take a second derivative it'll just bring in another minus sign minus sign times minus sign is plus sign and therefore let me just switch back over to here so if I have D to X tilde DT squared that will just be D to X DT the minus signs will cancel each other and you just have to choose the argument correctly because I didn't replace that 1 minus T by T just to keep the functional form simple but the point is once you get here you're done because that's the only thing that comes into Newton's second law so bottom line if this trajectory satisfies the equations of motion then so does the reverse one now look this is for a single ball which I'm viewing as a single particle traveling under just the force of gravity and we've shown that any motion the reverse motion satisfies the equations of motion you can completely generalize this to any number of particles acted on any collection of forces even quantum mechanically this is true it gets a little bit more technically involved so in Schrodinger's equation not Newton's second law if you want the wave function to evolve in the reverse temporal order you need to take a complex conjugation and Schrodinger's equation you got the I in there it goes to mine i square root of -1 and so you have to take the compass conjugate of the wave function to make it all work out bottom line though you get exactly the same answer any evolution of the wave function forward in time the reverse run film if you will of the wave function going the reverse temper order will also satisfy the equations motion so I've done the simple case but it totally generalizes so that is point 1 there really is an issue as I said at the outset anything that happens in one order it can happen reverse unfortunately we cannot simply argue that the laws of physics prevent those kinds of phenomena from happening and that's why we don't see them that is not how our universe works ok so we want to go on then to the potential answer where we don't try to rule out these reverse run processes but rather we want to argue that they're incredibly unlikely now it's not intuitively it's not hard to get to that conclusion in fact let me show you the smashing wineglass how would you get it to reassemble and then in our show some years ago fabric of the cosmos we did a sort of playful example of it I'll show you here so here's that wineglass again and it's in my hand and I drop it smashes on the table you get all the shards now if I want this to reassemble what would I need to do let's hold it hold still I would need to run around changing the velocity of each and every particle reversing it just like the baseball going to bleachers in Reverse it's coming out of the bleachers I need to reverse the velocity of every single particle making up the glass the air in the room the wine whatever everything involved I need to reverse its velocity and then if I allow it to evolve forward in time with those new reverse velocities it all comes back together into the pristine glass so it can happen and that's how you do it but look how incredibly difficult it is to do it you need to run around and change all of those motions in a completely precise and exact way in order for it to all stitch back together so there you get a sense of how incredibly difficult it would be for that physical process to be set up to unfold in the usual orientation of time going forward shards of glass going forward in time reassembling the glass but now let's see how we find the mathematical version that describes how unlikely this is and that is what brings in this idea of entropy and entropy is a word that I think many people are familiar with in everyday discourse you can think of it as a measure that's not perfect by any means and many people balk at this description but it's it's really not bad especially on a first pass approaches we're doing in this episode entropy is a measure of disorder and roughly we want to quantify the idea that the pristine glass is ordered compared to the completely disordered state of the shattered wineglass and how how will we get a measure of that and and the answer to that really comes from this guy over here Ludwig Boltzmann and you see on his tombstone there's an equation s equals K log W and that formula embodies Boltzmann's definition of entropy and the way in which it can be used to quantify disorder what is the basic idea said in words first and then I'll write down the equation the idea is this if a system is very disordered then there are many rearrangements of its ingredients that leave it looking very disordered you know the canonical example that people use just as an analogy you know if your desk is completely disordered you got the paper clips all over papers and random arrangements coffee cups whatever total miss and if I then come in you're not even looking and I rearrange that disordered mess you walk back in the room you don't even notice that I rearranged it it was a disordered mess when you left the room it's a disordered mess when you came back in the room so there are many many rearrangements of a disordered system that go completely unnoticed that leave the system looking pretty much the same if you have an ordered desk where the paperclips are on their appropriate spot the pages are all in a nice neat stack the books are all alphabetically ordered on the back of your desk whatever almost any rearrangement you will notice because the paperclips won't won't be where they're supposed to be the books won't be in the precise alphabet or the pages won't be in that nice neat stack so there are very few rearrangements of the constituents of an ordered desk that leave it looking pretty much the same and there are a huge number of rearrangements of the ingredients making up a disordered decks that leave it looking the same so the way to quantify order versus disorder is to count the number of rearrangements of the ingredients that leave a system looking pretty much the same that is in essence what Boltzmann said and that's really what his formula is so in some sense then s is a measure of the number of rearrangements that leave the overall properties of a system unchanged and when Boltzmann writes down this formula he writes in terms of the logarithm that's what that log means on his tombstone he uses logarithm it's very important mathematical detail I don't want to get bogged down in the mathematical details here but basically the W on his tombstone is counting the number of rearrangements obviously not for a disordered desk but for a system made up of particles so as an example if I consider the air in this room there are many rearrangements of the particles of air in this room that are unnoticed I'm rearranging them right now okay I'm doing a lot of rearrangement feels the same temperatures pretty much the same I'm breathing the same air the macroscopic properties of the air in this room do not change under an enormous number of rearrangements of the air molecules in this room on the other hand if I had a different circumstance here what if the air was all clustered in a tiny region over here I might be gasping for breath put that to the side but if all the air was right here then I'm severely limited in the number of rearrangements that make that configuration look the same because if I move those particles outside that little cluster then I can notice it it's only if I keep them tightly clustered and therefore a limited number of rearrangements will keep that configuration of air molecules unchanged so if the air is in a nice tiny orderly package very low entropy if it's widely dispersed and moving this way and that in my room in this office here then it has higher entropy it is more disordered and the basic idea of the second law of thermodynamics is that there is a natural tendency for systems to evolve from order toward disorder or in terms of entropy now from low entropy to high or higher entropy and the reason for that is again quite straightforward for low entropy there are very few configurations available for a high entropy by definition there are many more configurations of the constituents available and if the constituents are randomly moving about thermally jiggling this way and that then just by the law of numbers it's much more likely that they're going to find themselves in a higher entropy configuration since there's so many configurations that fit that bill and quite unlikely that they'll find themselves on a low entropy configuration because they're very few of those so if I had the gas clustered in a small little region here as the gas randomly jiggles about it's going to ultimately fill the room it will go from the ordered low entropy to the high entropy and that is the natural course of events simply by the logic of numbers in the logic of probabilities and I like to give you a little more of a feel for that using another analogy concrete example that I find particularly useful which is imagine you have a hundred pennies and the match in those hundred pennies are are on on my desk here and they're all heads up now that is a very orderly configuration right if you think about the degree of freedom to simply change a head to a tail or a tail to a head there's only one configuration that has all heads you can't change the disposition of any coin and keep it all heads if I then were to have the penny subject to thermal jostling let's ask so I can pick the table making the pennies bounce around some of them will then flip over from heads to tails and if I keep on going some of the tails will go back to heads but many more heads will turn into tails so over time the juggling pennies will go from the ordered configuration of all heads to a far more disordered configuration which has more of a mixture of heads and tails simply because there are many more such configurations and I want to just make them that quantitative for you and half a second and do a little fun little simulation on that so take those hundred pennies as our system and if I ask myself if I'm looking at a configuration that has all heads how many rearrangements of that configuration maintain all heads and by rearrangement I'm just talking about changing heads to tails and tell us that it's not rearranging them in terms of their locations just whether it's heads or tails and there's only one arrangement or rearrangement every single penny has to have heads period end of story there are no other possibilities that meet the stipulation that you have all heads very unlikely configuration say if you drop the pennies for it to land in them because of that but what if I had not all heads but ninety-nine heads at one tail how many configurations have one tail well now there are a bunch of rearrangement let's say the first coin is tail and the other 99 our heads you can rearrange that make it the second coin tail in the first is back two heads that still has 99 heads or the fifth coin is tails or the lone tail is the seventeenth corner the loan tells the 99th coin you see there are hundred possibilities there are a hundred States if you will that meet the stipulation of having 99 heads and so if your randomly throwing coins on the table its 99 it's a hundred times more likely that you get 99 heads then you will get a hundred heads and therefore much more likely that you'll have at least one tail but you can keep on going what if you have 98 heads well now think about it the two tails could be coins one and two or coins one and three or coins two and three or four and five or six and seventy-seven right they're all in fact 100 choose two if you know a little combinatorics for the number of configurations have two tails 100 choose to that's a hundred times 99 divided by two so it's 50 times 99 I think that's four thousand nine hundred and fifty and so it's almost five thousand times more likely that you'll have two tails than no tails keep on going but if you have 97 heads you work that one out again three tails get bitcoins one two and three or coins one two and four coins one two and five or points two five and seven you know it just keeps on going and how many are they believe there are 160 1700 possibilities in that particular case which is an interesting large factor by were to be more likely to have the number of heads compared to the number that I started out with with there was no heads what about 96 heads I don't really know that one off of the top of my head so I'm gonna just estimate it I believe it's about 4 million so I can't give you the exact number there if you're interested it's easy to work out there's 100 choose 4 and this keeps on going and the point is I don't care about these exact numbers that we have here I just care about the trend that is being Illustrated the trend is that if you have evermore tails it's ever more likely that if you randomly drop the coins you'll have that number of tails in fact this keeps on going until you get to the upper 50 heads and 50 tails when it's an equal split and that one it's not it's trying to bring up I do want to show you that number I can find if it I guess I have it here so I'm going up on the screen there it is I don't know how to pronounce that number so I won't try but it's a big number it's a big number so if you think about these numbers as the entropy of the state which should be the log of it you see that the number is 1 for all heads and is this huge number for 50 heads and 50 tails which means if I had these coins on my table and I bang them jostle them around kick the table as I described you would expect over time you would approach 50 heads or 50 tails or something very close to that because there are so many ways to realize that state and so few ways to realize the low entropy state of all heads and I want to show you this drive from order toward disorder from say the configuration with all heads to one that has a mixture of 50/50 I have a little simulation that a guy at the world science about really smart guy Danny Swift made for me asked to me I want a little computer simulation to show the folk on your daily equation how the coins 100 pennies evolve over time and he quickly came up with this which is really cool let me see if I know how to make it work there it is all right so it asks me how many coins are there let me actually do a thousand make it even more dramatic not a hundred just because the numbers are even more extreme then it says how many heads are up I'm gonna start in a completely ordered state of say I'm gonna do all tails what difference does it make I'm start with all tails so no heads up and then it says how many we'd like to flip so this is saying I'm kicking the table how hard he kicking the table on average how many coins will flip over and I'm gonna say roughly speaking 25 coins on each kick are gonna change their disposition either from tail to head or head to tail they're gonna be randomly chosen by the simulation and how many times you want to kick the table well it's a computer after all so I don't have to kick it literally so let me just say I don't know 2000 times that happens and then how many tosses per frame that's when I'm plotting it out how quickly the plot will go oh no let me go 4 per frame I don't even know if that's a good number or not and you know that the graph is gonna come out here so I'm going to quickly try to bring it over once that starts to go there it is there's my graph notice that I started in the ordered state down here over time we're going closer and closer to the 50-50 split which here would be 500 heads and 500 tails we've now gone from order all the way up more entropy more disorder more disorder and once we hit the 50/50 split then we pretty much stay in that range there be some fluctuations when I kick the table and I get a little more heads than tails or I don't know what you know yeah a little more heads into house little more tails and heads over here but for the most part once we reach that maximal entropy state we pretty much just meander there it's not that we can't go back to an ordered state like all heads are all tails it's just so fantastically unlikely how unlikely there's only one state that has all heads whereas we have this huge number that I showed you before that hundred I don't know what is what is a hundred billion billion or whatever it is and I'd have to count or maybe one hundred billion billion billion have to count the number of digits but there are so many states that have this roughly 50/50 split and that's why we ran during around them some heads go to tails some tails go to heads but on average we're pretty much staying in the 50/50 split in this case 500 heads and 500 tails for us to go down to here would be an incredibly unlikely move we'd have to have the coins all just flip in the right way that singular way to yield all heads or all tails which is highly unlikely to happen and this is a nice example to illustrate the move from low entropy to higher entropy from order to disorder and how unlikely the reverse process is so if you think about for instance this ordered state as our wineglass very few rearrangements of the molecules of the wineglass will leave it intact compared to the number of rearrangements of the shards that leave the shards in a disordered mess you start moving the molecules of the wine glass around it breaks it deforms it warps whatever it doesn't look the same any longer but you start moving around the molecules of the shards of glass and the splattered wine and it's like the messy desk pretty much looks like a disordered mess before pretty much looks like a disordered mess after so there are so many ways for the molecules of that glass to be disordered that high entropy state so few ways for the molecules to be ordered in that beautiful Riedel glass that once you go the progression from order to disorder it is very unlikely for the reverse process to happen and we saw how difficult the reverse process is you have to change the velocities of all the shards in just the right way for them to come back together for that to randomly happen in the real world is incredibly unlikely right and the there aren't people running around changing the velocities of molecules and atoms and the real world is just thermal motion banging things around and for the random thermal motion to happen to be just right to make all the molecules and all the shards of glass to do what I showed you in that film extraordinarily extraordinarily unlikely so there's our arrow if you will of time that's natural progression from order toward disorder from low entropy to I entropy and let me just make well three staples number one this is the second law of thermodynamics the natural tendency to go from order to disorder and you see that it doesn't really require I mean if you take this in a statistical mechanics course this will be laid out in more rigor and more formalism will be developed but in the end of the day it's nothing but logical reasoning with numbers and you know it's but there very few ways to be ordered and a huge number of ways to be disordered and things are randomly sampling the possibilities and it's more likely that they will find themselves in disordered States compared to orderly once nothing to it in some sense and that's why Einstein I believe that's why Einstein described these kinds of ideas as the only ones that he was confident would never be overthrown right he knew that his general theory of relativity and special relativity they had to be just approximate descriptions of the world he was realistic about that he imagined that one day they might be and would be superseded but when it came to these kinds of ideas he didn't think that they'd ever be superseded because they don't rely upon anything but kind of logic and numbers okay that's sort of point number one point number two the second law of thermodynamics is not a law in the conventional sense it's only as we see a statistical likelihood in fact if you don't mind I'm going to do one other example if I can bring this up on the screen just to show you what I mean it's not that entropy can't go down is just that it's unlikely to go down in fact in a simple system let me not do so many coins let me do 10 coins and let me imagine that I don't know but start with let's start with five up so we're going to start completely disordered five heads five tails and let's say we flip I don't know three on each time we're jiggling around or let's not do three let's do let's do I don't know no no no three maybe that's okay whatever I'm not sure how many times you guys do it many times let's do it I don't know 10,000 times and how many toss I better do a lot we're gonna be it forever the computer's gonna take forever so let me do sort of I don't know 100 tosses as we plot this let me bring over here so I can bring that over quickly that graph okay there it is oh and look at that you see we started right here in the middle at the 50-50 but notice over time we are going we're fluctuating to highly ordered states where we have all heads and all tails the reason is because we only got ten coins but my point is here's an example that accentuates the likelihood of that rare fluctuation from disorder to order the reverse of what we are used to and that's kind of beautiful because we see that the second law is just a statistical tendency it is not a law I mean Newton's second law is along it is not a tendency Schrodinger's equation is meant to be a law not a likelihood the second law of thermodynamics is however a tendency an overwhelming tendency but a tendency nevertheless entropy can go down it is just unlikely for that to happen okay what is my third point my third point is this have we answered the question of the arrow of time you might think we have because now we understand why glasses shatter and we don't ever see them unshod we now understand why whatever a candle burns but we never see it unburned we never see all the the fumes come back together in order to recreate the candle in it reforms we never see that because those would be entropically decreasing processes which can happen as it just hope does it just unlikely they become ever more unlikely when the number of particles involved is ever larger that's why I only use 10 pennies and the example where I wanted you to see fluctuations to lower entropy but have we fully enter the question not not really because you still want to ask yourself if the high entropy states are the more likely ones why do we ever have any order at all why do we have a pristine wineglass where did its order come from if if it's unlikely to have ordered States and more likely that disordered states why don't we just as always disordered where did the order come from and to try to answer that question it's natural to think temporarily you can say ok today the universe has a certain amount of entropy if the second law holds do you think that yesterday you'd have less entropy in the day before less entropy and if you follow this all the way back then you're led to the Big Bang and you're led to imagine that the Big Bang was a highly ordered low entropy state the lowest entropy that the universe has ever had and we don't have an argument that establishes that the Big Bang was highly ordered that it had low entropy we posit it it's a hypothesis is usually called the past hypothesis I believe David Albert gave this hypothesis that name it's not that everybody believes that this is the right way to go but I'm describing one chain of reasoning which at least holds together albeit under the assumptions that it makes and the assumption is that for whatever reasons the early universe had extraordinarily low entropy extraordinary high order which means and I can just go back over here for a second to give a better picture so I can have a nice have to show this with so if we do our thousand 0:25 say let's do it one thousand times and let's make this go really fast cuz I don't have time to wait and I'm the graph is happening here every well you can sort of see it pretty fast but the point is the beginning of the universe highly ordered over time the entropy has been increasing and we're sort of here we're in a part of the unfolding an interesting question is does the universe have a maximum entropy I don't need to go all the way up here but we're over here say where the universe still has some residual order from the Big Bang so the idea is the reason why there can be ordered structures my wine glasses and candles and flowers and planets and people and stars the reason why there can be ordered structures in the universe is because the Big Bang was so fantastically ordered that in route to ever greater disorder and route on that journey there is still residual order from the Big Bang along the way so I like to say you know when you drop a wineglass in it smashes or an egg splatters on the floor you are actually witnessing something that's deeply connected to the Big Bang itself because the very existence of the wineglass the very existence of the egg relies upon the orderly BIGBANG for there to be any order today which can be embodied in say a wineglass or an egg or a planet or a person or any of the structures that are ordered in the world around us so this is key to the arrow of time it's not just that entropy increases over time it's not just that order degrades into disorder it's also that there's an anchor you have to explain why there's any order at all or else there wouldn't be any opportunity for order to degrade into disorder and to explain why there's any order at all we're led right back to the Big Bang and the that the Big Bang was a highly ordered low entropy state and with that assumption the past hypothesis that the beginning was highly ordered and with the second law of thermodynamics and the tendency overwhelming tendency of entropy to increase over time we get a natural orientation of time a natural notion of what it means to head toward the future so the laws of physics agnostic about past and future as we started out any trajectory that can unfold toward the future the reverse trajectory also solves the equations of motion so the laws of physics agnostic about what we call past and future but with the past hypothesis low entropy beginning and the second law of thermodynamics we have an orientation to time that then emerges is that the end of the story no I mean we want to understand can we give an explanation for why the Big Bang was highly ordered can we give some deeper principle that explains how that order came to be or do we need to simply accept that we have say one universe and that's how began period end of story that's it or as some have suggested maybe there's a pre maybe there's another side to time maybe time doesn't begin at the Big Bang and maybe as some have suggested if you go through the Big Bang and should be increases in a symmetric way so maybe you start with a very high entropy infinite pass it comes down to our Big Bang and then from there and heads again back toward very high entropy that would be completely symmetric that's a possibility to that people talk about but in any event the one that at least at the moment that I find most convincing past hypothesis second law of thermodynamics entropy tending to increase from the highly ordered beginning and that is where the asymmetry and our experience comes from that's why we never see those things that make us laugh in Reverse run films those things that look up surd they're not absurd based upon the laws of physics they're absurd based upon our assumption about the orders of the Big Bang and our understanding from entropy in the second law of thermodynamics have this overwhelming tendency to head from order toward disorder okay that's all I wanted to say today and maybe a natural next step at some point soon will be to apply these ideas of entropy relating to information maybe something an information theory with Shannon would be good but also to relate them to the physics of black holes where entropy and these ideas really flower in an unexpected and deep way anyway that's for the future but after today our of time entropy Big Bang past hypothesis that's all I wanted to say for today until next time this has been your daily equation take care

Channel: World Science Festival

Views: 92,338

Keywords: Brian Greene, Black Holes, why time slows down near a black holes, why time slows down in a fast moving spacecraft, time slows, why black hole slows time, slows, how do black holes impact time?, learn, light years, slow down time, time slow down, time near black hole, why there is no time at black hole?, bizarre phenomena, the universe and time, what happens to time near a black hole, how time dilation is real, #YourDailyEquation, #DailyEquation, daily series, math series

Id: x4iU76Qj2mU

Length: 44min 28sec (2668 seconds)

Published: Wed Jun 03 2020

Reddit Comments

[u/greggregory689]

Prof Green said the arrow of time is powered by the ordered explosion of the Big Bang . Question how can an explosion be ordered ? White noise has greatest disorder for a given power . When white noise becomes ordered it's called MUSIC.