Planck Time - The shortest measure of time

we've looked at the smallest thing in the universe we've even looked at the hottest thing in the universe and i think my head's now recovered from that so what about the shortest amount of time possible well this is plank time and it's very strange indeed let's find out more plank time is defined as a time taken for light in a vacuum to travel one plank length now i've already made a video about the plank length now you can go and watch but spoiler alert the plank length is really tiny that means that the time taken for light to travel across one plank length is very short indeed in fact it's 5.9 times 10 to the minus 44 seconds that's about this much okay so we're going to try and imagine just how mind meltingly short the planck time is but just like we did with the plank length and plank temperature we're going to get there in stages right then let's start with a frame of reference that hopefully we can all understand so let's start with a second on screen at the moment a light is flashing it stays on for one second and then goes off for a second seconds are the beats that time our lives the average heartbeat takes just less than one second so let's think about some things that last for one second avoiding the obvious jokes roughly six lightning strikes hit the earth every second also in one second the earth travels about 19 miles around the sun or roughly 30 kilometers so for every second of this video the earth is 30 kilometers further in its orbit of the sun for this year but if you thought that was fast light in one second travels 300 000 kilometers strictly speaking it travels 299 792 kilometers in one second that's just over three quarters of the way to the moon okay so what's next well let's think about one tenth of a second or not point one seconds don't worry i'm gonna miss out a lot of these otherwise this is gonna be a really long video in one tenth of a second a world-class sprinter can run about a meter sound at sea level will travel about 34 meters and a bumblebee beats its wings about 20 times the average i blink lasts for about 0.1 seconds so this is 0.1 seconds or 10 to the minus 1 seconds now 10 times smaller than that and we find a hundredth of a second a formula one car travels about one meter in a hundredth of a second most timed sporting events such as a hundred meter sprint a time to the nearest one hundredth of a second our eyes work at rates around this speed even though our eyes really don't see in frames per second it's a convenient way of thinking about things our eyes are thought to refresh at a rate between 30 and 60 frames per second and this is all to do with how our eyes detect light light coming into the eye interacts with chemicals in the light detecting cells called rods and cones this causes an impulse to be sent from the rods and cones to the brain but then after that there's an enforced rest period the rods and cone cells can't now send back any more impulses for a short period of time so to make sure that our vision isn't jerky our brains retain the previous image until a new image is sent from the eyes to update the image being perceived this then means that our view of the world is updated roughly between 30 and 60 times per second a millisecond is one thousandth of a second in one millisecond light will travel about 300 kilometers that's roughly equal to the distance from london to york one millisecond is 10 to the minus 3 seconds and some sporting events are timed to the nearest thousandth of a second let's speed things up a little bit and now move on to a micro second this is one millionth of a second and now we're starting to get seriously quick and the kind of times we can only now start to imagine the elementary particle the muon has a lifetime of 2.2 microseconds also the 2011 earthquake in japan was so powerful that it altered the rotation of the earth slightly and days are now 1.8 microseconds shorter than they were before it even at a millionth of a second we're nowhere near to plank time so let's press on a nanosecond or a billionth of a second is 10 to the minus 9 of a second in one nanosecond light will travel 30 centimeters in a vacuum atomic clocks are the way that we keep an accurate measure of time today accurately knowing the time is essential for gps satellites to work properly the standard that we use is the number of vibrations of an atom of cesium 133 so one second is defined as 9 billion 192 million 631 770 oscillations of a cesium-133 atom so one oscillation of one of these atoms would come in roughly here in our journey through the minuscule end of the time scale let's go even shorter in time and look at the femtosecond this is 10 to the minus 15 of a second or one millionth of one billionth of a second in this time light will travel about 0.3 micrometers that's about the size of a large virus chemical reactions happen when bonds break or are made this process is very quick and it takes about 200 femtoseconds also the elementary particle the tau on has a lifespan of 290 femtoseconds at our next stop on this journey through time albeit short times we have the ato second this is 10 to the minus 18 of a second or this small and now we're getting seriously brief there are as many ato seconds in one second as there are seconds in 31.7 billion years that's more than twice the current age of the universe at 10 to the minus 21 of a second we have the zepto second and this is one billionth of one trillionth of a second and here we have the shortest time that we've measured we've measured the amount of time it takes for a photon of light to cross a hydrogen atom and that by the way takes zeptoseconds and yet even here we're nowhere near to plank time but before we get on to how unbelievably small this is let's have a quick think about where this idea comes from and what the implications are like all the other plant units planck time is derived from some of the universal constants and in order to derive planck time the planck constant the gravitational constant and the speed of light are used as i've already mentioned planck time is the time taken for light to travel the planck length which is we already know is very small indeed our understanding of the universe breaks down at time scales on the planck level and this affect our understanding of the start of the universe the universe is governed by four fundamental forces the strong nuclear force which holds atoms together the weak nuclear force which governs nuclear disintegrations among other things electromagnetism which affects how charged particles interact and gravity which is the attraction between two bodies that have mass it is thought that at the planck time after the big bang all these forces were combined as a single force following the big bang the universe expands but before the planck time after the big bang there is no space and no time if string theory is correct then the universe consists of ten-dimensional quantum foam and our explanations of space-time have no way of describing the behavior of the universe before the first planck time after the big bang and this is known as the planck epoch okay so let's try and imagine just how tiny the planck time is and we're going to try and imagine how many planck times there are in just one second so let's go and i'm going to do this in two ways firstly our universe is currently almost 14 billion years old and i'm going to call that one universe as a measure of time there are more planck times in one second than there are seconds in 10 million trillion universes of time let's think of it another way our galaxy the milky way contains about 100 billion stars that's a hundred thousand million stars and there are many estimates of how many galaxies there are but some of the upper estimates suggest about 2 trillion galaxies that's 2 million million galaxies each with about 100 billion stars so let's imagine every star in the universe has 300 identical planet earths on each of these planets orbiting every star in the universe if you counted every grain of sand on every one of those planets orbiting every one of those stars in every one of the two trillion galaxies then you'd be in the right kind of ballpark for the number of planck times in one second that's how unbelievably tiny the planck time is however before we finish just do something for me please move a part of your body an arm or a leg or even a finger that body part moved a certain distance during one plank time it had to otherwise you didn't move at all and the amount that it moved during one plank time must have been smaller than the planck length so planck time is something that we live through we just can't experience it anyway i do think i need to go for a little lie down now and if you've enjoyed this video then don't forget to hit subscribe for more geeky videos and until next time thank you for watching [Music] you

Channel: Learning Curve

Views: 613,123

Keywords: Planck time, Planck time explained, planck time, quantum mechanics, planck scale, shortest unit of time, shortest unit of time ever measured, planck units, plank time, learning curve planck length, max planck, learning curve, learning curve planck

Id: aTvBdLm7bqM

Length: 11min 33sec (693 seconds)

Published: Wed Dec 22 2021