it would be nice if we could get time travel to work because who wouldn't like to go back in time and buy a few Bitcoins unfortunately the laws of physics don't want to comply time travel seems to result in paradoxes like when Marty goes back in time and accidentally prevents his parents from meeting and if he was never born how could he have gone back in time but maybe the reason we have difficulties understanding time travel is that we think of it on the microscopic level we think of cars or people maybe time travel makes
sense if we think of it on the level of individual particles that obey the strange rules of quantum physics in a new paper a physicist looked at what had happened on the quantum level if you'd attempt to send an object back in time like through a wormhole the result is both interesting and not when this baby hits 88 mph you're going to see some serious the movie industry deals with time travel in one of three ways the first one is that you allow temporary changes but in the end everything needs to work out so that
the future is that which you actually came from this is how they did it in Back to the Future the second option is that when you go back in time you end up in a parallel universe which has a similar but slightly different history this happens for example in the movie The Butterfly Effect the third option is to stick with a story that's consistent in the first place like in the time traveler wife if that's how it works the only way you can go back in time is if you have already been there our difficulties
with making sense of time travel come from our everyday experience that time has a direction glass breaks but doesn't Unbreak rain falls down but not up people get older but not younger physicists call it the error of time and it points towards a coffin but the error of time doesn't exist on a fundamental level if you look at individual particles they don't know forward in time from backward in time the error of time is usually attributed to entropy increase a phenomenon that only emerges at the level of many particles in the new paper now the
author used a collection of many Quantum particles and calculated what happens to its entropy in A Spacetime with a Time Loop in our own universe we have never seen such a loop in time but it's mathematically possible for example with a wormhole the result of the calculation in the paper is option three of the science fiction Solutions you can only return to the past if you've already been there but with the twist that you also have to get younger as you go back in time you can see what I mean in this figure think of
the red curve as a measure for the order of a system or the opposite of entropy if it's up here the order is large and entropy is small say your system is the ingredients to a dough you mix eggs butter and sugar and stir as you do so order drops and entropy increases if you keep stirring normally the entropy just remains large but if the dough goes in a Time Loop the entropy reverses it decreases this it mean that the dough spontaneously unixes now you might say okay but that's the only mathematically possible solution so
what do we learn from this well we learn that the problem has a solution we learn that it's at least mathematically possible but what does it mean would you really see do and mix I think the answer is no the do in my example illustrates the error of time and the error of time is aligned with our memory this means that in such a Time Loop you wouldn't experience going back in time instead it creates two different ways to go into the future so I think this finding shows that time travel doesn't work on the
quantum level but while that's bad news for time travel it's good news for faster than light travel you see a lot of physicists believe that faster than light travel would also allow time travel this is because of the odd consequences of Einstein's theory According to which a spaceship that goes faster than light for one Observer seems to go back in time for another and because time travel would lead to inconsistencies they think that faster than light travel isn't possible either I've explained in some earlier episodes that this argument is wrong because our universe does For
Better or Worse have an error of time regardless of how fast you travel you can't go back in time against that error of time hence no inconsistencies follow from faster than light trouble and the new finding supports this but just in in case you come from the future could you let me know if history books ever made sense of 2024 did you know there's a free and easy way to learn more about the science behind all the videos that you've been watching yes there is have a look at brilliant all courses on brilliant have interactive
visualizations and come with follow-up questions what you see here is from their data science courses which they just released they all use real world examples like what it means to go viral on next brilliant covers a large variety of topics in science computer science and maths from General scientific thinking to Dedicated courses on algebra or large language models just what I'm interested in and they're adding new courses each month I even have my own course on brilliant that's an introduction to Quantum Mechanics it'll help you understand what a wave function is and what the differences
between superpositions and entanglement it also covers interference the uncertainty principle and B theorem and after that you can continue maybe with a course on Quantum Computing or differential equations sounds good I hope it does you can try brilliant yourself for free if you use my link brilliant.org Sabina or scan the QR code that way you'll get to try out everything brilliant has to offer for a full 30 days and you'll get 20% off the annual premium subscription so go and give it a try I'm sure you won't Reg regret it thanks for watching see you
tomorrow
