DarkRange55
Enlightened
- Oct 15, 2023
- 1,760
If you believe that electrons can be in superpositions of being in different locations which everyone who subscribes to quantum mechanics thinks that they can - then things that are made of protons and electrons like you and me and the rest of universe, we should be able to be in superpositions of being in different places, doing different things. Then you have the many worlds whether you like it or not. So all of the other theories have to do work to get rid of the other worlds. Many worlds does not come about by putting in extra worlds, they're there in QM. There are other theories, spontaneous collapse theories, hidden variable theories.
You can call them alternate or parallel universes but then you're not sure whether you're talking about cosmology or QM. In QM what we tend to use the words either worlds, they're separate worlds. Or we talk about branches of the wave function. It's so separate from us that philosophically it doesn't matter what the copies of you are doing. It's not a bad question to ask. You should behave in many worlds in the same way you should behave if you thought the universe really was just probabilistic. That it really was just a random chance that something happens but only one thing ever does happen. So as far as I know there are no moral and ethical implications. Because in a sense, in some sense it really doesn't exist. In a sense.
Even in many worlds, there are still laws of physics. And the laws of physics don't change over time. They're governed by some big overarching set of rules so it's not true for example that in many worlds everything happens. A certain set of things happen. Things that are compatible with the laws of physics. Like electrical charge is conserved in many worlds. You never see an electron turn into a proton in this theory. So it's not easy to solve things like fine-tuning that have to do with the parameters that are built into the laws of physics themselves. Those parameters don't change from branch to branch of the wave function in many worlds. In the simplest version. There might be complicated versions of marrying the cosmological multiverse to the many worlds QM which people have tried to do.
When you look at the wave function collapse of a particle, thats not really the whole story in this paradigm. It's something much bigger. The wave function of the entire universe. Hugh Everette who pioneered the many worlds interpretation referred to what he called the universal wave function and what we now call the wave function of the universe. It's the same thing. Every version of quantum mechanics believes there is something called the wave function of the universe. Where different versions of quantum mechanics differ is whether or not they think there is also something else in addition to the wave function and how the wave function evolves over time. Many worlds says there is nothing else and just says it always obeys the same Schrödinger equation no matter whats going on. Other theories say it evolves differently depending on whats happening. But it's a straightforward implication of that simple view in the many worlds interpretation that when you observe a quantum system, it's not that the wave function collapses. Its that you, the observer become entangled with the wave function of whatever you're looking at and it branches into different possibilities and in each one of these possible branches there's a whole world where there's some measurement outcome and thats what you saw.
But first, what actually causes the collapse of a wave function? What actually happens when a wave function collapses? You have to choose a rigorous formulation of quantum mechanics which Copenhagen is not, it doesn't answer that question. It just says trust us, you know it when you see it. Some in some other much more rigorous and well formulated theories of QM you can answer that question. For example, in many worlds, the answer is there is no such thing as collapse of wave function, they never collapse. So its simply an affect of something else, you have your own wave function and thats plays in. Ans the wave function of the universe branches into different parallel worlds that don't interact with each other. And you can tell precisely when that happens, when some macroscopic object becomes entangled in some microscopic one thats in a superposition with different possibilities.
In a many worlds interpretation, there would presumably be many you. This exact post is going taking place right now with just a slight difference somewhere. There's a radioactive particle that decays in the room in one interpretation that doesn't happen in the world. You can never interact with these other worlds. If I measure the spin of an electron and say I will turn left or right on my walk based on the findings of that measurement, then there will be two different worlds in which I went two different directions. Afterward they don't interact with each other, thats the whole reason it makes sense to call them different worlds. It's just a feature of quantum theory that once that interaction happens and the wave function branches, each branch of the wave function evolves forward all by itself independently.
Let's go back to classical reasoning. Within cosmology you also have this concept of multiverses, many universes. And the two seem to be similar. Is there any relation? It's 98% separate. What cosmologist mean when they talk about many universes, the cosmological multiverse, it's actually a pretty straightforward concept. All it means is that very, very far away from us in the universe, much further away than what we can observe, conditions might be radically different. The sense of particles and forces that we're familiar with could be different. Even the fact that space is three dimensional could be different elsewhere in space. But it's still really part of the same big universe. We call it a multiverse as colorful language and we have no idea whether it's true. Could be. Current state of the art, it's very hard to tell.
Whereas in QM the parallel universes of Everett's many worlds theory, they're not located anywhere. They're not out there a certain distance away. They literally are parallel and simultaneous existing to the universe that we're in and they're being formed all the time. Whenever a radioactive atom decays or doesn't, whenever a spin is observed. Literally all the time new worlds are coming into existence. This theory is much more likely to be true than the cosmological multiverse.
Carrol Sagan said, "the universe is what is, what was, and whatever will be." Is it a separate universe because it can't interact or is still part of the universe? Thats up to you. Our ordinary english language just wasn't designed to talk about these concepts. Clearly what we mean is that there is one quantum mechanical wave function that encompasses all of the worlds of the many worlds interpretation of QM. And further more branching of the wave function happens forward in time but not backwards, so there were fewer worlds in the past. So all the worlds that exist now, we believe came from a common beginning. There's many copies of you that are slightly different but they all came from a common ancestor version of you. But once they split, once they branch then they're separate and they can't talk to each other anymore. So on the one hand they're part of a common system, the wave function of the entire universe, on the other hand they're separate worlds in the sense that you can't interact with them or know whats going on in them. So whatever vocabulary you want to use to describe that situation…
Any human language is weak on description. Only mathematics, in reality equations give you precision. It's not impossible to come up with language that describes this correctly. It's just that we happen to invent it 500 years.
What is collapsing the wave function of the universe? That depends on your favorite interpretation of QM. In many worlds, wave functions never collapse. According to Hugh Everett in the 1950's as a graduate student, at the time he was trying to quantize gravity because they had made a lot of progress on electromagnetism and things like that so it was natural to turn to gravity. He was thinking about the quantum theory of the entire universe at once. He realized that the Copenhagen story where you have a small quantum system and a big macroscopic observer and the system acts quantum mechanically and the observer acts classically, the whole story doesn't hold up once your quantum system is the entire universe. There are no external observers poking at it. All that can happen is other parts of the universe can poke at other parts. So he called his theory the relative state formulation of quantum mechanics because whats happening in one part of the universe is relative to whats going on in other parts. So in many worlds, the wave function doesn't collapse. Parts of the universe come into contact with each other and become entangled. In classical interpretations you run into questions like what happens if no one is observing the universe. Einstein famously asked so you really think the moon is not there when nobody is looking at it because that seemed to be certain interpretations of the Copenhagen interpretation of quantum mechanics.
In many worlds, because there is no collapse of the wave function it's just an effect of the universe within itself interacting with itself so everything is always there. There's no fundamental role for observers or awareness or perception or measurements or anything like that. Those can be described within the theory as ordinary physical interactions. So essentially much of the spookiness is dispelled.
Einstein spent the last 30 years of his career chasing quantum gravity and not getting any further. And he was looking at things like spooky action at a distance and all this stuff saying, "god does not play dice with the universe." In the many worlds interpretation he doesn't and the price you pay is that you have a lot of worlds. The theory is well defined, crisp, austere, rigorous, and simple but the price is you have to accept that there are a very large number of worlds (we don't know how many, if its strictly speaking technically infinite or not). If you have a universe where one atom is out of place compared to another universe then you have a completely separate universe by the rules of quantum mechanics.
You can call them alternate or parallel universes but then you're not sure whether you're talking about cosmology or QM. In QM what we tend to use the words either worlds, they're separate worlds. Or we talk about branches of the wave function. It's so separate from us that philosophically it doesn't matter what the copies of you are doing. It's not a bad question to ask. You should behave in many worlds in the same way you should behave if you thought the universe really was just probabilistic. That it really was just a random chance that something happens but only one thing ever does happen. So as far as I know there are no moral and ethical implications. Because in a sense, in some sense it really doesn't exist. In a sense.
Even in many worlds, there are still laws of physics. And the laws of physics don't change over time. They're governed by some big overarching set of rules so it's not true for example that in many worlds everything happens. A certain set of things happen. Things that are compatible with the laws of physics. Like electrical charge is conserved in many worlds. You never see an electron turn into a proton in this theory. So it's not easy to solve things like fine-tuning that have to do with the parameters that are built into the laws of physics themselves. Those parameters don't change from branch to branch of the wave function in many worlds. In the simplest version. There might be complicated versions of marrying the cosmological multiverse to the many worlds QM which people have tried to do.
When you look at the wave function collapse of a particle, thats not really the whole story in this paradigm. It's something much bigger. The wave function of the entire universe. Hugh Everette who pioneered the many worlds interpretation referred to what he called the universal wave function and what we now call the wave function of the universe. It's the same thing. Every version of quantum mechanics believes there is something called the wave function of the universe. Where different versions of quantum mechanics differ is whether or not they think there is also something else in addition to the wave function and how the wave function evolves over time. Many worlds says there is nothing else and just says it always obeys the same Schrödinger equation no matter whats going on. Other theories say it evolves differently depending on whats happening. But it's a straightforward implication of that simple view in the many worlds interpretation that when you observe a quantum system, it's not that the wave function collapses. Its that you, the observer become entangled with the wave function of whatever you're looking at and it branches into different possibilities and in each one of these possible branches there's a whole world where there's some measurement outcome and thats what you saw.
But first, what actually causes the collapse of a wave function? What actually happens when a wave function collapses? You have to choose a rigorous formulation of quantum mechanics which Copenhagen is not, it doesn't answer that question. It just says trust us, you know it when you see it. Some in some other much more rigorous and well formulated theories of QM you can answer that question. For example, in many worlds, the answer is there is no such thing as collapse of wave function, they never collapse. So its simply an affect of something else, you have your own wave function and thats plays in. Ans the wave function of the universe branches into different parallel worlds that don't interact with each other. And you can tell precisely when that happens, when some macroscopic object becomes entangled in some microscopic one thats in a superposition with different possibilities.
In a many worlds interpretation, there would presumably be many you. This exact post is going taking place right now with just a slight difference somewhere. There's a radioactive particle that decays in the room in one interpretation that doesn't happen in the world. You can never interact with these other worlds. If I measure the spin of an electron and say I will turn left or right on my walk based on the findings of that measurement, then there will be two different worlds in which I went two different directions. Afterward they don't interact with each other, thats the whole reason it makes sense to call them different worlds. It's just a feature of quantum theory that once that interaction happens and the wave function branches, each branch of the wave function evolves forward all by itself independently.
Let's go back to classical reasoning. Within cosmology you also have this concept of multiverses, many universes. And the two seem to be similar. Is there any relation? It's 98% separate. What cosmologist mean when they talk about many universes, the cosmological multiverse, it's actually a pretty straightforward concept. All it means is that very, very far away from us in the universe, much further away than what we can observe, conditions might be radically different. The sense of particles and forces that we're familiar with could be different. Even the fact that space is three dimensional could be different elsewhere in space. But it's still really part of the same big universe. We call it a multiverse as colorful language and we have no idea whether it's true. Could be. Current state of the art, it's very hard to tell.
Whereas in QM the parallel universes of Everett's many worlds theory, they're not located anywhere. They're not out there a certain distance away. They literally are parallel and simultaneous existing to the universe that we're in and they're being formed all the time. Whenever a radioactive atom decays or doesn't, whenever a spin is observed. Literally all the time new worlds are coming into existence. This theory is much more likely to be true than the cosmological multiverse.
Carrol Sagan said, "the universe is what is, what was, and whatever will be." Is it a separate universe because it can't interact or is still part of the universe? Thats up to you. Our ordinary english language just wasn't designed to talk about these concepts. Clearly what we mean is that there is one quantum mechanical wave function that encompasses all of the worlds of the many worlds interpretation of QM. And further more branching of the wave function happens forward in time but not backwards, so there were fewer worlds in the past. So all the worlds that exist now, we believe came from a common beginning. There's many copies of you that are slightly different but they all came from a common ancestor version of you. But once they split, once they branch then they're separate and they can't talk to each other anymore. So on the one hand they're part of a common system, the wave function of the entire universe, on the other hand they're separate worlds in the sense that you can't interact with them or know whats going on in them. So whatever vocabulary you want to use to describe that situation…
Any human language is weak on description. Only mathematics, in reality equations give you precision. It's not impossible to come up with language that describes this correctly. It's just that we happen to invent it 500 years.
What is collapsing the wave function of the universe? That depends on your favorite interpretation of QM. In many worlds, wave functions never collapse. According to Hugh Everett in the 1950's as a graduate student, at the time he was trying to quantize gravity because they had made a lot of progress on electromagnetism and things like that so it was natural to turn to gravity. He was thinking about the quantum theory of the entire universe at once. He realized that the Copenhagen story where you have a small quantum system and a big macroscopic observer and the system acts quantum mechanically and the observer acts classically, the whole story doesn't hold up once your quantum system is the entire universe. There are no external observers poking at it. All that can happen is other parts of the universe can poke at other parts. So he called his theory the relative state formulation of quantum mechanics because whats happening in one part of the universe is relative to whats going on in other parts. So in many worlds, the wave function doesn't collapse. Parts of the universe come into contact with each other and become entangled. In classical interpretations you run into questions like what happens if no one is observing the universe. Einstein famously asked so you really think the moon is not there when nobody is looking at it because that seemed to be certain interpretations of the Copenhagen interpretation of quantum mechanics.
In many worlds, because there is no collapse of the wave function it's just an effect of the universe within itself interacting with itself so everything is always there. There's no fundamental role for observers or awareness or perception or measurements or anything like that. Those can be described within the theory as ordinary physical interactions. So essentially much of the spookiness is dispelled.
Einstein spent the last 30 years of his career chasing quantum gravity and not getting any further. And he was looking at things like spooky action at a distance and all this stuff saying, "god does not play dice with the universe." In the many worlds interpretation he doesn't and the price you pay is that you have a lot of worlds. The theory is well defined, crisp, austere, rigorous, and simple but the price is you have to accept that there are a very large number of worlds (we don't know how many, if its strictly speaking technically infinite or not). If you have a universe where one atom is out of place compared to another universe then you have a completely separate universe by the rules of quantum mechanics.
