Parallel Worlds Probably Exist. Here’s Why

A portion of this video was sponsored by Norton 360. The classic mechanics are excellent. If you know the state of a system, say the position and velocity of a particle, then you can use an equation, Newton's second law, to calculate what that particle will do in the future. Quantum mechanics, if you know the quantum state of a particle, which is its wave function, you can use the Schrodinger equation to calculate what that particle will do in the future, usually it propagates in time, as it does

here

. Note to make this animation you actually solved the Schrodinger equation, so t

here

is a beautiful symmetry here, if you know the initial state you can use an equation to evolve that state smoothly and continuously into the future.

The problem is that in quantum mechanics we never observe the wave function this way when we measure. If we find the particle at a single point in space, then how are we to reconcile the smoothly evolving extended wave function under the Schrodinger equation with this point as the particle detection? Now I think it is understandable that when the founders of quantum theory approached this problem they considered measurement to be more real than the wave function, after all, measurement was something we had actually observed and coincides with our experience of a world of particles of matter. It was harder to say what exactly the wave function was.

Schrodinger formulated his wave equation because scientists, particularly Debroglie, suspected that matter has wave properties, but it took a third physicist, Max Born, to propose how we should interpret the wave function at each point in space. The wave function has a complex amplitude, essentially just a real number plus an imaginary number. Max Born suggested if we take that amplitude and square it you get the probability of finding the particle there. The fact that you have to square the amplitude actually appears as a last-minute footnote in Boran's article, but that's how probability was introduced into the core of our picture of reality, that is.

A pretty big philosophical leap, I mean, the universe is no longer deterministic. This bothered many scientists, especially Einstein, but the rule of birth, as it is now called, remains at the heart of quantum mechanics because it is spectacularly successful in predicting the results of experiments, so the way quantum mechanics was understood and the way I learned it is that there are two sets of rules. When you're not looking, the wave function simply evolves according to Schrodinger's equation, but when you're looking, when you make a measurement, the wave function collapses. suddenly and irreversibly and the probability of measuring any particular outcome is given by the amplitude of the wave function associated with that outcome squared.

Now Schrodinger himself hated this formulation, which is why he invented the famous Schrodinger's cat thought experiment: putting a cat in a box with a radioactive atom adds a radiation detector that triggers the release of poisonous cyanide gas now, although only was intended as a thought experiment, Schrodinger helpfully points out that this device must be protected against direct interference from the cat anyway, the goal of the experiment is to magnify the state of the atom up to the state of something macroscopic and tangible could have chosen anything not had to be alive but Schrodinger selected a cat if the atom decays the detector detects radiation it releases the poison and the cat dies if the atom does not decay, the detector does not detect radiation, the poison is not released and the cat remains alive that the state of the cat and the detector apparatus are directly related to the state of the atom, we say that they are entangled, where things get strange is that, according to Quantum Mechanics the state of the atom does not have to be decayed or not decayed it is generally in a superposition of both decayed and non-decayed at the same time, assuming no measurements have been made, this superposition state of the atom becomes entangled with the detector and then the cat, so after a while the wave function of everything It is inside the box it is in a superposition of the atom it has not decomposed, the poison has not been released. alive and dead at the same time, only when we open the box and make a measurement does the wave function collapse and the cat actually remains alive or dead these days.

Schrodinger's cat is often used as a way to show how strange quantum mechanics is, but that wasn't Schrodinger's point? He wanted to show that quantum mechanics as formulated was incorrect, so he took up Schrodinger's argument in this video. I want to show that there is a better way to think about Schrodinger's cat, in fact, a better way to think about quantum mechanics altogether. What I would say is more logical and consistent to get there we have to examine the three essential components of Schrodinger's cat superposition, entanglement and measurement to see if any of them are flawed.

Superposition is the idea that quantum objects can be in two different states. At the same time, this seems like a crazy idea and something we would never observe, but we do it indirectly with the double slit experiment, we shoot individual electrons through two slits in a screen and the pattern you see is not just the sum of the electrons passing separately. one slit and the other is an interference pattern, we are forced to conclude that a single electron somehow passes through one slit and the other simultaneously this is superposition, of course, it is easy to understand superposition with waves, they are dispersed in space and is It is clear how the peak of a wave from one slit cancels with the trough of the wave from another slit to produce the interference pattern and, fortunately, we know that when we are not looking the electrons are represented by a wave, the wave function, the double slit experiment.

There is concrete evidence that this wave allows individual electrons to pass through both slits at the same time, so the superposition is on solid ground. The next concept is entanglement. Consider two electrons fired at each other with equal and opposite velocities. We know they will disperse each other, but. We don't know exactly how their trajectories are given by extended wave functions that only give us probabilities, but as soon as we measure the momentum of one of the electrons, we immediately know the momentum of the other, otherwise it must be equal and opposite. Now conservation of momentum would be violated, this may seem obvious but consider that before the measurement the momentum of each electron was in a superposition of states, measuring one instantly collapsed the wave function of the other and this would be true even if those electrons were light years away. apart these electrons are entangled, what is really happening here is that after interacting the electrons do not have separate wave functions at all, they are described by a single wave function and this is what it means to be entangled, this explains why measuring one immediately affects the state. of the other because the single wave function has collapsed, in fact, if we were rigorous, we would have to say that there is only one wave function, the wave function of the entire universe, which includes absolutely everything, but in the case of particles Isolated, non-entangled quantum particles, we can reasonably talk about their individual wave functions and then once they interact with something else, the result is entanglement, so what we've seen is superposition, which is actually the same thing. than describing systems with waves.

An entanglement means that after the particles interact, they describe each other. by a single wave function these are fundamental parts of quantum theory that describe systems with wave functions that evolve according to the Schrodinger equation that leaves only the measurement. Remember that the measurement postulate was added as a second set of rules to connect the mathematics of quantum mechanics to what we know. we actually observe, but doesn't it seem strange that there should be one rule for how systems evolve when we're not looking and a different rule for when we are when we summarize it? The measurement is just the interaction of the electrons and photons of a quantum system. with another quantum system and we know exactly how to deal with it, we simply evolve its wave functions according to the Schrodinger equation.

So what happens if we throw out all the rules associated with measurement? So in Schrodinger's cat thought experiment, the radioactive atom in a superposition. of decomposed and undecomposed gets tangled with the detector and, in turn, the cat now remembers that we are also made of electrons and atoms that obey the laws of quantum mechanics, so we are quantum mechanics, so when we open the box there is no measurement or wave function. we collapse, we just get tangled with the state of everything inside the box, so we see the cat alive and we see the dead cat now, how is it possible?

I'm guessing you've never seen a live cat and a dead one before, but the solution is because the you who saw the live cat and the you who saw the dead cat actually inhabit separate

worlds

. I mean they

exist

in their own complete realities and those realities will never interact, but where do these separate

worlds

come from? Well, something I have. Not yet mentioned are all the particles in the environment, the air molecules, the photons, everything we are not following if a quantum object in a superposition becomes entangled with the environment, it is said to undergo environmental decoherence, this essentially branches the wave function of the universe. split the universe into two slightly different copies, so a more realistic explanation of Schrodinger's cat is this: the radioactive atom evolves from 100% non-decayed to a quantum superposition of decayed and non-decayed the detector becomes entangled with this state of superimposition of the atom, but the detector is being bombarded by all these air molecules and photons in the box, which would bounce back differently if radiation is detected than if it hasn't, so almost immediately the detector becomes entangled with the state of the environment in which D coheres, branching the wave function. at that moment you are divided into two identical copies, one entangled with each result of the experiment, you continue to be identical until you open the box, but in this case the cat is actually alive or dead, by opening the box you were discovering what We are aware that the other result also happened to someone who is no longer you.

I mean, both observers came from you but they are no longer you and they are no longer identical to each other. This interpretation of quantum mechanics is called many. worlds and was formulated by Hugh Everett and if it is true, wave function branching occurs all the time so frequently, in fact, the speed may well be infinite, creating infinitely many subtly different worlds all the time may seem implausible, for To put it mildly, but consider that all those worlds are naturally part of the mathematics of quantum mechanics, many worlds just take them seriously to get rid of them requires something like wave function collapse and the point is that our experience of reality would be the same in the image of many worlds. just as it is if the wave function collapses but the formalism is much cleaner and more elegant all we have are wave functions that evolved under the Schrodinger equation the implication is that the founders of quantum theory may have understood it exactly backwards wave function is the full picture of reality and our measurement is only a small fraction of it, the part we get entangled with when we interact with a quantum object in a superposition, the universe also becomes deterministic, each outcome occurs the one hundred percent of the time, just don't look at us that way because now we're only experiencing our little slice of the multiverse.

I imagine many of you have questions and possibly objections to this, so I went to the expert. Well, I wanted to make this video about many worlds, but I wasn't there. I was worried I was going to screw it up, so I came here to meet Caltech professor Sean Carroll, who literally wrote the book on many worlds. Look for something deeply hidden, available wherever books are available. Let's

probably

ask the common type of YouTube questions. The good arguments against this. yes, how many worlds are there now, the first is the energization of energy, how energy is conserved, it is completely clear in mathematics, the energy of the entire wave function is one hundred percent super conserved, but there is a difference between the energy all the way. function and the energy that people perceive in each branch, so what you should think about is not to duplicate the whole universe, but to take a certain amount of universe and subdivide it, cut it into two pieces, the pieces look identical from the inside, except that one has turns upwards, the one that hasspin down or something, but they are actually contributing less than the original to the total energy of everything.

Let's ask the question about how many words there are, how often they branch. We have no idea there is a short. answer to this and I think it's embarrassing that we have no idea that it is certainly common, it is certainly very true that the universe branches every time a superposition quantum system becomes entangled with its environment, which is why you have atomic nuclei in your body which are radioactive. decays 5000 times per second there is a radioactive decay in your body, each one of them decays or not. Do you consider it an overlap? Once it decays, it somehow interacts with what's around it, becomes entangled, and the universe branches its wave function. right, branching is happening many times per second just because a radioactive decays in your body now, is it happening infinitely often?

We don't know because we don't know whether the total number of possible branches is infinitely large or finite. In any case there is a lot of room for all these branches to

exist

and it could well be finite, but the details depend on things we don't understand about quantum gravity and cosmology and the theory of everything and all that, so it is a number big, but we don't know how big, let's deal with the misconception that many worlds means everything that could happen, yes that's not true in many worlds it means that the wave function obeys the Schrodinger equation, that's what which means that the Schrodinger equation predicts that many things could happen, but not all, so, for example, an electron will never become a proton, it would violate the conservation of conservation of mass to charge all these things things of Schrodinger's equation gives zero probability of it ever happening.

How about you become president? Yes, that could happen. There is a world where you are president. There is a world where you are SuperDuper. Of course, I won't be the one who is. President Raney, a version of me, true, true, but there is a fork in the road. They are two separate people now, but there is a version of him who is currently president, yes, that's right, and who was tweeting. It is a very low amplitude world, it is a very small probability. but it's there, yeah, I mean, I think this is the way it feels more complicated or more ridiculous than Copenhagen because Copenhagen is like there's only one world, this is what you experience and, but look at the universe, the Good old universe, forget it. about quantum mechanics, okay, like the cow mantra, the universe where we see all the galaxies and everything we don't see, the entire universe, we see a finite amount because light moves at the speed of light, it's a place beyond which we cannot Look, the universe could be infinitely large, we don't know, it is certainly very plausible, the universe is infinitely large, it is plausible that all parts of the universe look more or less like what we see with galaxies and the stars as a whole, if that be true, there are an infinite number. of copies of people exactly like you some of them are presidents some of them are winning NBA championships some of them are supermodels whatever just because there are a bunch of different mixtures of atoms well it has nothing to do with quantum mechanics or rarity. bothering you does that like rubbing you the wrong way, I think, but, but I agree that it's less strange than the quantum idea and I think in both cases it's because you know that human beings have some cognitive bias, I don't know what it is. called but there is a cognitive bias that says the only probabilities for anything or 0% 50% 100% and when I tell you that something can happen but the probability is really very very very very very very very low, you feel like it could happen, let me focus on that, come on, on that possibility of it happening, I say no, don't do that, it's just not likely enough to be worth worrying about in any way when the world branches here, instantly branches far away, The answer is, it depends on This is the annoying part of the answer.

I can write a description where branching occurs instantaneously throughout space. I use that description to make predictions about what people will see. All of those predictions turn out to be a percentage completely true. I can write an alternative. description in which the branch extends at the speed of light and I make a different set of predictions, but guess which ones are exactly the same predictions, there is no difference between what those two images actually predict and what this reflects. God doesn't know about the branches, there's the wave function of the universe, that's all that really exists.

Okay, breaking up the wave function of the universe into different parts that you and I call branches or worlds is very convenient for us humans, but that's it, it's not constructed. in the fabric of reality itself is exactly the same as for the air in this room instead of listing the position and velocity of each air molecule. I just tell them the temperature and the pressure and things like that. That's a convenient description for us. For humans, it is not the complete description of reality and the branches are exactly the same, so if it bothers you that there are two different ways of describing the branches, you should remember that the whole idea of ​​branches is just a human convenience, Hey, this part of the video is sponsored by Norton 360, a global leader in cybersecurity.

Norton 360 comes with multiple layers of protection for your devices, not only antivirus and antispyware but also things like dark web monitoring powered by LifeLock, this software monitors the dark web for uses of your personal information now of course no one can prevent all cybercrime, but it is important to take a multi-layered protection approach because cyber threats are constantly evolving. That's why Norton 360 also comes with a virtual private network, or VPN. A VPN creates encrypted private data. tunnel that helps prevent cybercriminals from hacking into your Wi-Fi and intercepting the data you send and receive. This is particularly useful when you use public Wi-Fi.

I like to use it when I travel, so when I'm connecting to Wi-Fi it's in hotels, airports or coffee shops, this gives me that extra peace of mind right now. You can get up to 60% off by using the promo code veritasium or by clicking the link in the description. Now Norton 360 has kindly I was given Norton 360 Deluxe to try out for myself and I'm really enjoying it so I want to thank Three-sixty for sponsoring this part of the video and I want to thank you guys for watching it.