### Video instructions and help with filling out and completing Who Form 2220 Compute

**Instructions and Help about Who Form 2220 Compute**

Theoretical physics what does that make you think of maybe added physics in school or maybe you think of one of the greats like Albert Einstein maybe you think of fundamental particles the elementary building blocks of our universe I'm a theoretical physicist and and I think of these things but I spend an awful lot of time thinking about knots what I usually want to know about knots is whether one knot is the same or different from another knot what I mean by this is can the knot on the right be twisted and turned around and turned into the knot on the left without cutting without using scissors if you can do this we say they're equivalent knots and otherwise we say that in equivalent surprisingly enough this question of equivalence of knots is very important for certain types of fundamental particles furthermore it's important for the future of technology this is what I'm going to tell you in the next 15 minutes to get started we need some of the results from relativity now relativity is a pretty complicated subject I'm not going to explain much of it but one of the themes that we learn from it is that space and time are mostly the same thing so I have a little story to tell to explain this it's a story of Einstein's world and his day so we have his home his work his cinema on the screen and there's a clock in the upper right hand corner so keep your eye on the clock during the day so Einstein starts his day he goes to work then after a while he comes home for lunch clock keeps ticking he goes back to work clock keeps ticking in the afternoon he decides to go to the cinema goes to the cinema clock keeps ticking and then eventually he goes home well the physicist would look at this and we want to treat time more similarly as space and the way we do this is we plot space on an axis and we bought time on another axis Einstein's so-called world line is this dark red line which tells you where in space is he at any given time it's called his world line because it tells you where in the world is he at any given time now we can go through the day and keep your eye on the dark red ball the ball goes up one step every hour as we go through the day it goes back and forth in space tracing Einstein's position so the world line is just a convenient way of keeping track of where Einstein is at any point in the day we can do the same thing with a more complicated world so here we imagine looking down on Einsteins neighborhood from a helicopter above so Einstein starts this day at home he goes to work he goes to cinema he goes back home a student on the same day starts at home goes to the library goes to the pub and goes home now if we follow them both on the same day Einstein goes to work student goes the library Einstein goes the cinema student goes the plot of Einstein goes home student goes home it starts to look pretty complicated but we can simplify it by looking at the space-time diagram of what happened we do that by turning the neighborhood sideways plotting time vertically and you notice I've drawn a blue vertical line at the position of every object in the neighborhood that doesn't move such as the library or the pub they stay fixed in space and they move through time I'm signing the students world lines move around in the neighborhood as they go through time now you can kind of see where I'm going with this Einstein and the students world lines have wrapped around each other if you pull those tight you'll discover that you have them knotted then we need one more thing from the theory of relativity we need e equals MC squared again this is a thing that I'm not going to explain to you in much depth but roughly what it means is that energy and mass are the same thing so if we have a particle in our world like an electron that's a particle of matter now each particle of matter has an opposite particle of antimatter in the case of an electron the antimatter particle is called a positron both the electron and the positron have mass if you bring them together however they can annihilate each other giving off their mass as energy usually as light energy the process works in Reverse just as well you can put in the energy and get out of the massive particles now we're going to do the same thing we did with Einsteins neighborhood we're looking down in a neighborhood we put in energy to create a particle and the antiparticle we put in energy to create a particle in the antiparticle then maybe we move one particle around another we bring them back together we rien aisle eight them and rien aisle eight them releasing the energy again now if we look at that in a spacetime diagram it looks a little bit like this time's running vertically we put in the energy we put in the energy we wrap one particle around the other and we annihilate them and we annihilate them again you can see quite clearly here that the world lines have knotted around each other do the same thing with more particles by putting in more energy move them around in some very complicated way and bring them back together the space-time diagram would look a little bit like this making a very complicated knot now here's the amazing fact upon which the rest of my talk relies certain particles called an eons exist in two plus.