Why is Time so Hard to Understand? - Ask a Spaceman!

let's just all admit that time is weird time is weird like it's so hard to describe just how weird time is and the weirdest thing about time is that it has an arrow it has a direction it has a flow to it that space doesn't right I can go left or it can go right it's a breezy I can pick either one doesn't matter I can go forward I can go backward and super easy doesn't matter I can go up I can go down up is a little bit challenging but that's because of gravity but like that but out in space it doesn't matter I can pick any direction I want but I can't pick direction which direction I want to go in time I must go forward in time we all must go forward in time it looks like time traveling to the past is forbidden in our universe and I have other videos explaining some examples and how they're forbidden and we don't fully understand why time traveling to the past is forbidden but even without that it's just like time goes forward all the time I don't know how many time puns I'm gonna accidentally make in this episode is probably gonna be a lot but just time goes for time must go forward and this is a property of the universe that demands explanation we can't just let that go we can't just wave that away say Ya Ya Ya what the time goes forward to games no this is a property of the universe that we must explain now it could be it could be just like a trick of the consciousness like some game our brains are playing in our heads and time doesn't really act this way that it doesn't seem right for various reasons I'm not gonna get into because I'm gonna paint a physics picture of time so I I'm gonna assume that time is real that time does go for this arrow of time is not an illusion it's a real physical thing that's it's the game I'm playing and in this scenario in this picture in this world view the arrow of time must be explained so here we are time has an arrow why why this time has an air have an arrow and we what we do as physicist is look around are there any physical laws any theories any models any equations that have themselves a flow of time baked into them where we can point to and say ok ok guys figured it out the reason time has an arrow is right here equation thirteen point four in this derivation time appears in time has an arrow and it has a direction this physical process has a direction a sense to time that's already baked in and hence the arrow of time flows through that now time the you know the variable time the concept of time appears all over in physics like everywhere but it's just a parameter it's just a parameter that tells you how a particular system involves you can you can tune it you can change its value and so the equations even though many many equations and physics have time inside of them the time appears in the equation there's no particular arrow to that time almost every single physical law that we have time can run forwards and backwards just as easily there is no arrow time appears but if you look at say how particles interact and the forces that govern how they interact thinking they can go forwards and backwards as easily as they please if you look how gravity yeah objects behave inside of gravitational fields like they can go forwards and backwards as they please so the fundamental rules that govern our universe don't care about time aren't fully reversible and yet that totally contradicts what we see in the world most everything we do is not reversible is irreversible there is an arrow there is a flow you can immediately tell you can immediately tell if say this video we're playing backwards you just you just know if you were to look at some process a video of some process or an interaction or a scenario at a macroscopic level you would immediately know you have an intuition say yep that one's backwards backwards forwards that wants words for its backwards backwards back like you just boom boom boom boom you wouldn't even think about it the macroscopic world has an arrow has a direction in time but the microscopic world pretty much doesn't there is this very obscure interaction involving the weak nuclear force that does have an asymmetry in time but I'm not going to talk about that here except to say we don't think it's very important because that interaction basically it's very very rare and so it doesn't seem to be fundamental to the universe happy to talk about that in another video and so I want to focus on something else there has to be something in physics that takes us from the microscopic world which can go back and forth in time as easily as it pleases to the macroscopic world that doesn't that is locked that has a flow that has an arrow there has to be a bridge between those two worlds and there is a branch of physics that provides a bridge in that is the branch called thermodynamics thermodynamics the description in who - who would have guessed who would have guessed that if this be this would be the one that this would be her best guess of explaining the era of time things like temperature and pressure in volume in entropy all this you know car knows cycles in in pistons and cylinders and in particles inside of boxes like raah thermodynamics is actually a way of connecting microscopic behaviors to macroscopic observables and this is done through the language of something we call statistical mechanics when we say like okay we have a bunch of particles inside of a box like it we fill up we fill up a bottle with some gas let's say for example in that gas has a temperature and a pressure this is there something we can measure you stick a thermometer or pressure scale you know whatever you can measure that these are macroscopic observables things you can do on a lab bench that connect to microscopic processes to the individual motions of particles that we can't see the countless numbers of particles inside that volume inside that gas inside that cylinder inside that bottle if the temperature is higher that means the particles are jiggling around fast faster on a microscopic level and if the temperature is lower they're going slower the pressure is just these particles hitting the wall constantly hitting the wall if there's higher pressure they're hitting the ball more often or there's more of them to hit the wall if the pressure is lower it's not so much so you have a macroscopic observable that connects to microscopic behaviors and the technology of thermodynamics and statistical mechanics are what make that possible so we have the just mathematical descriptions of the microscopic stuff of the individual motions of prop of particles and we have the mathematical description of the macroscopic behavior of the ideal gas law and pressure and all that juicy stuff that we all learned in high school so that's potentially interesting here is an apparatus that connects the microscope microscopic to macroscopic world in the problem of time demands appears to demand some sort of connection between microscopic processes and macroscopic processes and this is why we think entropy has something to do with time entropy is a measure of disorder in a system I'm gonna do a whole other video just on entropy for now we're just gonna use that to that definition we the second law of thermodynamics says that in closed systems entropy must go up entropy itself is a macroscopic observable measurement for something happening microscopically entropy goes up entropies must go up you systems must move from disordered - disordered they must become more chaotic with time systems must move into their future systems cannot travel into their past they must travel into their future systems go forward in time systems become more chaotic is this it is that the connection is there reason we have an arrow of time because systems must go from order to disorder must become more chaotic maybe that's best guess thanks so much for watching I hope you enjoyed like I said my next video I'm gonna dig deeper into this concept of entropy but if you liked this don't forget to Like and subscribe shochet share make sure notifications or turn on go to patreon.com/scishow and center to help me help you understand entropy and maybe time I'll see you next time

Channel: Dr. Paul M. Sutter

Views: 38,056

Keywords: space, cosmos, universe, astronomy, physics, astrophysics, cosmology, science, time, time travel, entropy, arrow of time

Id: 4V8E82w34SY

Length: 10min 37sec (637 seconds)

Published: Wed Nov 21 2018