Why Physicists Think The Future Changes the Past - Retrocausality Explained

you come across a Burning Tree in a forest as the fire dies down you see the charred trunk return to a pristine tree when the flame is at its smallest you hear a roar of Thunder Roll across the sky and the fire is extinguished by a lightning strike awesome but arguably counter-intuitive effect has come before the cause this is the principle of retro causality or that the future can affect the past and increasingly some physicists are entertaining the idea that in certain places in the universe to explain some of the phenomena we see there this must be true the universe must be able to communicate with its younger self that's what we're going to talk about today don't do anything oh for God's sake foreign s interact with time in a pretty straightforward way we perceive it largely to be flowing in One Direction other than maybe when you're stuck on a customer service line which feels like a never-ending game of musical chairs except the music is a repetitive whole jingle and the only prize is your sanity slowly slipping away thank you virgin media not sponsored we think about this concept both in science and in our lives as the arrow or the direction that time flows in but the problem with observing the Universe on the human level that we are familiar with is that a lot of the strange phenomena of the universe are covered up or obscured the really interesting things happen as you peel back the chaos of the universe and get down to its most fundamental Parts when the universe is stripped down to its smallest building blocks at the level of atoms particles and quantum mechanics you are really forced face to face with how the universe operates and at that level there are some questions and some results that make physicists and everyone else kind of uncomfortable people assume that time is a strict progression of cause to effect but actually from a non-linear non-subjective Viewpoint it's more like a big ball of wibbly wobbly timey why me stuff this ties back to the question that we've already covered on this channel is the universe real or specifically is the universe locally real I'll leave a link somewhere on screen now so you can find the video this is a question that has been fought back and forwards between some of the greatest Minds to ever live with people like Einstein supporting the idea that the universe is in fact real and with people like bore suggesting the universe is not real at the moment the consensus surprisingly is that Einstein is wrong as a quick refresher though I recommend you watch the video for a deeper understanding let's look at that term locally real locality is essentially the idea of cause coming before effect or specifically that a cause can only have an effect nearby locally this is because as far as we have ever observed information cause travels at the maximum speed of the universe the speed of light this is also the speed of cause and effect you can't press a button here and have something instantaneously happen in a galaxy far far away you'd have to wait for the signal to reach that Galaxy that's localness realness or realism is the idea that the Universe has definite properties the objects have a specific position speed rotation color flavor or any other property in between that a packet of crisps that I take out of the cupboard was much like some YouTube comments salty both when I reached for them as well as all of the time prior to that point non-reonis is the idea that only when you observe something does it pick its properties this is the whole argument behind if a tree falls in the forest does it actually make a sound now both of these ideas seem completely reasonable well physicists have proven that at least one of these ideas must be wrong this was the subject of the 2022 Nobel Prize that revolved around an experiment conducted on Quantum particles I'm I want to walk us through this experiment explore just how truly counter-intuitive it is and then offer a substitution scenario that of retro causality and if that is at play does it save us from some of these more confusing concepts of quantum mechanics foreign [Music] so let's take a look at how this actually might play out let's imagine I fire a photon through a special Crystal called a spontaneous parametric down conversion Crystal that splits photons into two I know that the photon I sent into the system had zero spin so to conserve energy in the universe the two photons that are created from this Photon must have equal and opposite spins so that they cancel to zero this is the idea of entanglement that their properties are linked correlated but I don't know which one is which until I actually go to measure one of them we call this collapsing the wave function now the states of the photons are known this is the same idea as Schrodinger's Cat being both alive and dead until you actually go to open the box however counter-intuitively how I measure that Photon matters if I measure it looking for up or down photons the other Photon will always be an up or down Photon however if I measure it looking for spin left or spin right particles then the other Photon will be correlated as either a spin left or spin right Photon a deeper explanation of this like I said can be found in the video here but the question how has this happened and how did the particle on the right know which state to be in well there are three potential explanations explanation number one either the universe is locally real the photons decided what states they would have at the very beginning we just couldn't determine that information this is Einstein's View and this is called hidden variable Theory or we might explain it through things like super determinism which is a preferred explanation as far as I can tell of internet and real-life physicists like Sabine this explanation feels both intuitive and at the same time intuitive these photons are created in the same place at the same time they are locally correlated so absolutely it feels allowable that they could transfer some information between the two of them but it feels very strange that that information could be encoded in such a way that it doesn't allow us to access it option number two would be that the Universe isn't locally real the photons really really do not make up their minds until the moment of measurement and at that moment they adopt their chosen States they communicate instantaneously with each other to tell which states the other one should be in no matter how far away they have been separated the results of the Nobel prize-winning experiment concluded that option two the universe is not locally real was correct follow an experiment around the Bell inequality they really are actually both spinning up and down left and right or some combination of the above until the point of measurement this I think seems doubly frustrating as an explanation the photons both haven't made up their minds and they have to be able to instantaneously communicate to one another it feels like the worst possible outcome but this is the generally accepted principle among the physics Community but what would happen if we had another explanation last night's time travel experiment was apparently a complete success [Music] let's look again at this situation and envisage a retro causality explanation according to Retro causality as soon as the measurement was made on the first particle that decision was correlated back through time to the very moment where these two photons were created allowing that correlation to influence and embed in both photons so that they agree on their spin Direction when measured at some future point in time okay potentially I can buy that as an idea but I guess the question becomes so what what is the benefit to actually conceptualizing of the universe in this way with a retro causal model we could remove that confusion about realism and locality at the point of creation the photons could have definitely decided their states and we wouldn't need a mechanism to either explain how they communicated their collapse across the Galaxy or how they were hiding information from us that encoded States in a way that we couldn't perceive another possible payoff would be that retro causality is the idea that the wave function now would just be a mathematical encoding of our incomplete knowledge about a system essentially saying that a wave function doesn't have to amount to anything actually physically real it isn't both a particle that is spinning up and spinning down we just don't know which one it is so we're going to write the maths in a way that lets it be both until we've clarified it at the point of measurement interestingly this makes the universe feel much more classical potentially giving us a much more compatible way of integrating the quantum world into our theories for things like general relativity and The Wider Universe this seems promising and potentially interesting but ultimately to me this feels like a bit of a bait and switch yes we get to feel comfortable about things being real and having definite properties and we no longer need to think about photons communicating Magic quickly with each other instantaneously across the universe but we do now need a mechanism that explains how things can correlate backwards through time we've swapped two uncomfortable ideas for one idea that's almost twice as uncomfortable and I would ask is that progress retro causality would rely on our universe being something called time symmetric that the laws of the universe would work the same way going backwards in time as forwards in time and according to the second law of Thermodynamics this isn't true entropy disorder is always increasing and preventing things from moving backwards in time could it be a possibility maybe that this is just a macroscopic effect and the the universe at its absolute most fundamental level is time symmetric and allows things to move in either direction maybe but I'm not so sure regardless time-based correlation is different to sending information back through time which has all sorts of causality breaking problems associated with it that we won't go into right now ultimately I think retro causality feels like a very roundabout way of getting back to a theory like super determinism which is equally unpopular among the physics Community but via a Time Loop where the ride operator hopes you kind of don't notice that you're going back in circles but what does this actually mean does this then suggest that actually that measurement was always predetermined and that the starting conditions of those two photons was equally correlated to that measurement condition that the universe is starting to conditions have been set for a very long time and it's just naturally playing out in a deterministic fashion if I asked you to hit the like button was it always predetermined on a Quantum level whether you will or not I'm hoping that you are super determined to what do you think I'd be interested to know your thoughts in the comments section down below potentially I will use it as the topic of a future video thanks very much for watching I'll see you next time goodbye [Music] foreign

Channel: Dr Ben Miles

Views: 315,139

Keywords: science, startup, spinout, research, how to run a business, business, innovation, future, investment, deep tech, deep science, future technology

Id: WugRN6xe9XQ

Length: 12min 32sec (752 seconds)

Published: Sun Mar 26 2023