Sean Carroll

They might not even float in the air anymore. But individual molecules is an interesting physics point. Let's start with an individual atom. An individual oxygen atom—oxygen atoms can be in different states, but by different states what we mean is the electrons in those oxygen atoms can have different energy levels, okay?

They might not even float in the air anymore. But individual molecules is an interesting physics point. Let's start with an individual atom. An individual oxygen atom—oxygen atoms can be in different states, but by different states what we mean is the electrons in those oxygen atoms can have different energy levels, okay?

As we talked about earlier, when you're in a higher energy level for an electron in an atom, you tend to relax, you tend to decay down to the lowest allowed energy level. And so typically oxygen atoms are going to be in their lowest allowed energy levels. And all oxygen atoms that are in the same lowest energy level are indistinguishable from each other.

As we talked about earlier, when you're in a higher energy level for an electron in an atom, you tend to relax, you tend to decay down to the lowest allowed energy level. And so typically oxygen atoms are going to be in their lowest allowed energy levels. And all oxygen atoms that are in the same lowest energy level are indistinguishable from each other.

They are literally indistinguishable particles in the quantum field theory sense of the term. So there's no marker, there's no way to say this is this oxygen molecule, that one is that oxygen molecule, or atom I should say. But even as you get to molecules, Molecules are more complicated. They have more moving parts, so it becomes slightly easier for more things to happen.

They are literally indistinguishable particles in the quantum field theory sense of the term. So there's no marker, there's no way to say this is this oxygen molecule, that one is that oxygen molecule, or atom I should say. But even as you get to molecules, Molecules are more complicated. They have more moving parts, so it becomes slightly easier for more things to happen.

Molecules can vibrate and stuff like that. But if we're talking about things as simple as a water molecule, there's not an interesting set of vibrations that it can have, and even those vibrations decay away, so they all look alike. So no, you cannot really watermark the molecules.

Molecules can vibrate and stuff like that. But if we're talking about things as simple as a water molecule, there's not an interesting set of vibrations that it can have, and even those vibrations decay away, so they all look alike. So no, you cannot really watermark the molecules.

It's true that if Julius Caesar breathes a breath, the atoms that he's just breathed out will, for the moment, mostly be near him. They're not going to instantaneously spread through the universe or spread even through the Earth's atmosphere, right? So when people make these statements, they are absolutely not just using numerology about how many atoms there are.

It's true that if Julius Caesar breathes a breath, the atoms that he's just breathed out will, for the moment, mostly be near him. They're not going to instantaneously spread through the universe or spread even through the Earth's atmosphere, right? So when people make these statements, they are absolutely not just using numerology about how many atoms there are.

they need to make statements about how quickly the Earth's atmosphere mixes, how quickly a test particle, if you have one particle in the air that is floating randomly, well, you know what the temperature of the air is, you know what the typical velocity is, and it's doing a random walk, it's bumping into other molecules.

they need to make statements about how quickly the Earth's atmosphere mixes, how quickly a test particle, if you have one particle in the air that is floating randomly, well, you know what the temperature of the air is, you know what the typical velocity is, and it's doing a random walk, it's bumping into other molecules.

So you can ask the question, how long does it take to sort of randomly go throughout the whole Earth's atmosphere? And the answer is less than 2,000 years. So that's why there is some quantitative sensibility to that kind of statement, even if you can't actually look at the individual molecules.

So you can ask the question, how long does it take to sort of randomly go throughout the whole Earth's atmosphere? And the answer is less than 2,000 years. So that's why there is some quantitative sensibility to that kind of statement, even if you can't actually look at the individual molecules.

DMI says, is the feeling that only the present we see is real, even though nothing in the physics equations makes it more fundamental than any other slice of spacetime, could that be the same kind of illusion that gives us the feeling that only the branch of the wave function we see is real, even though nothing in Schrodinger's equation makes it more fundamental than any other branch?

DMI says, is the feeling that only the present we see is real, even though nothing in the physics equations makes it more fundamental than any other slice of spacetime, could that be the same kind of illusion that gives us the feeling that only the branch of the wave function we see is real, even though nothing in Schrodinger's equation makes it more fundamental than any other branch?

Kind of, I guess. I like the analogy and I'm trying to decide whether or not I think it's a completely accurate analogy or not. The wave function case is actually easier in this particular example because even though the wave function itself is very abstract, it is indisputable that if you believe any of the usual Everettian story, any individual agent is located on one and only one branch.

Kind of, I guess. I like the analogy and I'm trying to decide whether or not I think it's a completely accurate analogy or not. The wave function case is actually easier in this particular example because even though the wave function itself is very abstract, it is indisputable that if you believe any of the usual Everettian story, any individual agent is located on one and only one branch.

of the wave function, and that's the branch they see, and that's the branch they naturally attribute reality to. And that's true across time, right? Not just for a moment, but in future moments as well. Whereas for the presentism question, you have to say, well, you have to distinguish between the agent at one moment and the agent at another moment, right?

of the wave function, and that's the branch they see, and that's the branch they naturally attribute reality to. And that's true across time, right? Not just for a moment, but in future moments as well. Whereas for the presentism question, you have to say, well, you have to distinguish between the agent at one moment and the agent at another moment, right?