a watched pot never boils and a watched Quantum particle doesn't move that's the quantum Xena effect in a nutshell if you think that sounds weird it's actually weirder is it a real effect Oh yes totally the best way to understand the quantum Xeno effect is to use a Quantum particle that can be in only two states let's just call them one and two the particle starts out in state one and has some probability to switch to state two if it was a non-quantum particle that just mean it sits in state one until at some point it doesn't but for a Quantum particle the probability is just a way to describe what happens if You observe the particle as long as you don't observe the particle it's in both States at the same time and then when you look it has some probability to be in state too now let's imagine that you have a lot of those particles you put them up in the first state and the then you wait for some time and then you measure how many of them have dropped down to state two you put them back up wait for a longer time and measure and so on this gives you a probability as a function of time the Xeno effect now is that if you look whether the particle is up here then the probability of it falling down decreases indeed if you look at the particle all the time it doesn't drop at all strange stuff you might say but if you look at the particle you're interacting with it you're doing something to it so that's not so surprising well here's where it gets really weird because you don't have to look at the particle you can instead just check that the particle is not in the state to because if it isn't there you know it's still up in state one even though you didn't look at it and that works too oh yes there have actually been experiments showing that this is indeed what happens here is a little example that might have help you understand what's going on suppose you're a prison guard and your job is to watch a prisoner your shift is 4 hours long and if you don't watch your prisoner for some period of time he'll Escape let's say that after 1 hour of not checking after The Prisoner the probability of him having escaped is 12.5% and it doubles each hour so after 2 hours the probability of him having escaped is 25% 3 hours it's 50% and after 4 hours he's gone for sure and also you're now unemployed your prisoner however knows when you come to look for him so each time you go and check after him the probability increase resets suppose you check after him after 2 hours the chance that he's there is 100us 25 so 75% you go away and check after another another 2 hours so 4 hours in total then the chance he's still there is 75 * 75% which is about 56% so that's noticeably larger than when you didn't watch him the interesting thing is now that the more often you watch after him the higher the probability he'll still be there after 4 hours if you watch after him every hour then the probability he'll still be there after 4 hours is 67% watch after him every 10 minutes and it'll be higher still and if you watch him constantly he won't Escape at all now you might say that isn't so terribly surprising is it it's not so surprising if you're watching a person with a memory someone who knows you've been checking on him but a particle doesn't have a memory and yet the same thing happens for a particle and that's the quantum Zeno effect and yes that's a real effect it was theoretically predicted already in the 1970s and has since been confirmed experimentally many times you might wonder now what's with radioactive decay if I watch plutonium does that mean it won't Decay unfortunately not and that's for an interesting reason radioactive decay doesn't have a memory the probability of a radioactive nucleus decaying is given by what's known as a parur distribution it has the funny property that no matter how many events have happened in the past the probability of an event happening at some time in the future stays the same it's the same with Quantum particles moving around and other common examples none of those will display a Xeno effect this might sound like a tangential Point P what memory but in nature you mostly expect events to happen without memory this means that if you want to see a Zeno effect you need to set up a rather special system like this two-state system that I started out talking about so it's a real effect but it only happens under certain circumstances and not for all Quantum processes everywhere it's also an example of how a seemingly strange and mysterious Quantum process suddenly doesn't look all that mysterious anymore if you know a little bit about the maths yes I've been talking about quantum physics again it's definitely my favorite topic but did you know that I have a quantum mechanics course that you can take for free on brilliant.org my course will help you understand what a wave function is and what the differences between superpositions and entanglement it also covers interference the uncertainty principle and Bell's theorem and after that you can continue maybe with their course on Quantum Computing or differential equations all courses on brilliant have interactive visualizations and come with follow-up questions I found it to be very effective to learn something new it really gives you feeling for what's going on and helps you build general problem solving skills they cover a large variety of topics in science computer science and maths from General scientific thinking to Dedicated courses on differential equations or large language models and they're adding new courses each month it's a fast and easy way to learn and you can do it whenever and wherever you have the time and of course I have a special offer for users of this channel if you use my link brilliant.org zabina you'll get to try out everything brilliant has to offer for full 30 days and you'll get 20% off the annual premium subscription so go and check this out thanks for watching see you tomorrow