Physics of Consciousness - Sean Carroll

Sean Carroll - Cosmology

Sean Carroll

Sean Carroll is a Research Professor in Physics at the California Institute of Technology. His research focuses on fundamental physics and cosmology.

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Sean
Carroll

Theoretical Physicist, Caltech

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Robert Lawrence Kuhn:

Sean, consciousness has been one of my focuses of life. My doctorate's in neuroscience because I wanted to try to understand consciousness, of course, one had very little to do with the other at that point, but I've continued to focus on it as – as perhaps the – the, ah, key to under – to really understand reality. Now, you may disagree with that. I know you're a radical physicalist, so how do you deal with consciousness?

Sean Carroll:

I think that consciousness is a way of talking about the physical world, just like many other ways of talking. It's one of these emergent phenomena that we find is a useful way of packaging reality, so we say that someone is conscious of something that corresponds to certain physical actions in – in the real world. I don't think that there is anything special about mental properties. I don't think there's any special mental realm of existence. I think it's all the physical world and all the manifold ways we have of describing it.

Robert Lawrence Kuhn:

Okay. Give me another example of an emergent phenomena.

Sean Carroll:

Well, the classic example of an emergent phenomenon is the fluid description of the air around us. The fact that even though it's made of discrete particles—atoms and molecules—we talk about it as a continuum with a pressure and a temperature and stuff like that. It's a – it's a macroscopic coarse grain view.

Robert Lawrence Kuhn:

Great. Great example. The wetness of water would be something similar. Okay. Now, I would believe, ah, that consciousness is a qual – qualitatively different from that because there is a, um, there – there is something that is like to have the feelings that I'm seeing. You call it an internal movie, whatever you want to call it, that the phenomenology of – of – of this is – is a – a radical difference from the – getting the wetness of water from individual molecules or the fluidity of air.

Sean Carroll:

Right. And—

Robert Lawrence Kuhn:

You must disagree with that.

Sean Carroll:

I do disagree with that. Uh, I think there is this – there is an irreducibility but it's not in the reality, it's in how people talk to each other about it. I – I – and I – there's – there's something that—

Robert Lawrence Kuhn:

But you see it. You live it. You feel it.

Sean Carroll:

Of course. That's right. And [Crosstalk] describe it in physical terms perfectly well. When – when you say like—[Crosstalk] I now have experienced the, ah, redness of red. I think that that is a set of words that can be mapped on in a very direct way to certain physical things happening in my brain.

Robert Lawrence Kuhn:

Oh, nobody doubts that. There's—

Sean Carroll:

There are people who doubt that, but yes. Many people do not doubt that.

Robert Lawrence Kuhn:

Okay.

Sean Carroll:

And I think that's all there is. Is – is [Crosstalk]—

Robert Lawrence Kuhn:

At least among – at least among my friends nobody doubts that.

Sean Carroll:

You know, when you talk about the existence of a cat, you know, this is – this isn't a category, it is not to be found in the fundamental laws of physics, a cat. A game of basketball is not to be found because they're useful categories for describing the world. I think that consciousness, self-awareness, experience, intersubjectivity, very useful categories for describing the world.

Robert Lawrence Kuhn:

No, but you know some physicists, ah, see consciousness as – as sitting below, ah, the wave function, not just part of the wave function but actually sitting below it as the most fundamental thing [Crosstalk]...

Sean Carroll:

Some physicists deny global warming. [Laughter.] I mean, some physicist, it's not a very good beginning to almost any sentence.

Robert Lawrence Kuhn:

Okay. Alright, I accept that. Um, so – but – but with – with consciousness your, um, one philosopher has said that consciousness, ah, is an output of the brain like urine is the output of the kidneys. Is that something you would subscribe to?

Sean Carroll:

It's – ah, no, I don't – I'm not sure I would use that exact metaphor. I mean, again, I think it's a very, very useful construct at a higher level of description, right? I can't imagine doing without consciousness as a way of talking about the world. I know what it means when people say I'm conscious of this, I know what it is like to be that. These – these are real ways of describing the underlying physical reality.

Robert Lawrence Kuhn:

When you're saying I'm conscious of it, that's sort of a – a – a – an English locution that means I'm aware of something, but – but it – but you could – you could almost be conscious or aware of something in a – in – in a – in a – in a mechanical or a zombie like way in terms of behavioral reaction. But I'm talking about this – the – the phenomena that we all feel seems so radically different from anything that you see in the brain. I mean, I dealt with that. You deal with the probing of electrodes and electrochemistry and, ah, and the genetic expressions. Do you believe that the – the phenomen – phenomenology of what we see is, in an identical theory sense, two descriptions, like ah, the morning star or the evening star is – is the same as Venus.

Sean Carroll:

Yes, that's right.

Robert Lawrence Kuhn:

Is the same thing. I'm just calling it by different – because I didn't know that they were the same.

Sean Carroll:

Absolutely. And I think that actually, to me, zombies, the idea of the philosophical zombie, something that acts in exactly the same way as a conscious creature but just lacks the consciousness, lacks that inner subjective experience, is a great argument for my position in the sense that it's very hard to really take self consistently this idea of the philosophical zombie because if you met a zombie you ask them what are you experiencing right now. They would tell you exactly the same thing that a regular person would say. And – and you say, well, at least I know I'm not a zombie. Do you really know that? Of course, you're telling yourself you're not a zombie. You're experiencing. But so, would a zombie. A zombie would say they're not a zombie. I think that there's really no way of boiling that thought experiment down to a consistent holding of the idea there could be something that physically acts exactly like me, yet lacks an important element of consciousness.

Robert Lawrence Kuhn:

The zombie would say that I'm not a zombie and describe the inner feelings, but would still be a zombie. SC: That – well that – that is the – that is the proposal [Laughter] and I'm – I'm just pointing out how – how silly it begins to sound—

Robert Lawrence Kuhn:

Okay.

Sean Carroll:

—because they would be sincere.

Robert Lawrence Kuhn:

Okay. Look, I think anything—

Sean Carroll:

They would really think they're experiencing it.

Robert Lawrence Kuhn:

[Laughs.] They would really say that they—

Sean Carroll:

Why would they lie?

Robert Lawrence Kuhn:

—it – it would be – it's – it's sort of a behavioral reaction, you know, it – it – it's sort of an input output.

Sean Carroll:

That's right. And the difference between me and someone who thinks that there's something phenomenologically different about consciousness is that that is all there is.

Robert Lawrence Kuhn:

So, an implication of your view, I – I think, is that you have to be 100% sure that at some, ah, time in the future, with future technologies, some people would say 20 or 100 years, some people may say a thousand years, you would be able to upload your, ah, individual first-person consciousness to a – another medium, whether it's non-biological or another person. You – you would have to be 100% sure of that.

Sean Carroll:

Well I'm not 100% sure—

Robert Lawrence Kuhn:

Why wouldn't you be?

Sean Carroll:

—of anything in the world. I'm not 100% sure that the universe is [Crosstalk].

Robert Lawrence Kuhn:

Well, no – given – come on – given your presupposition as a radical physicalist to consciousness, that's what – that's the given.

Sean Carroll:

Yeah. I see no – I think the way I'm happy to say it is I see nothing special about an organic human being that could not be duplicated to arbitrary accuracy.

Robert Lawrence Kuhn:

Or – or if there were something then you could just duplicate it in an organic – you could create a human being.

Sean Carroll:

And we all know there are thought experiments so we – we do believe, most people believe, that I could take out one neuron from my brain—

Robert Lawrence Kuhn:

Okay. Alright, no, we've been through that.

Sean Carroll:

—replace it with an electronic brain.

Robert Lawrence Kuhn:

Right, right.

Sean Carroll:

And then I still just as conscious—

Robert Lawrence Kuhn:

Right, right.

Sean Carroll:

And what happens when I take out two and to me that – that's not even an issue. Like, yeah, sure, just as conscious all the way down.

Robert Lawrence Kuhn:

Okay, so you go all the way down and you've placed 100 billion and 1 neurons and you're – and you will – and, since we – the thought experience – perfectly reproduced every neuron, every connection, every reaction, etcetera, that you will noticed no difference during the whole process.

Sean Carroll:

Right.

Robert Lawrence Kuhn:

Okay. So, let me take that one step further that every time I put that neuron in, and we both agreed it was a perfect replication, I made two of them, and I put one over here. And – and then I made another and when I got to the 100 billion and you – you haven't felt any difference.

Sean Carroll:

Right.

Robert Lawrence Kuhn:

I – I have a 100 billion of another – another one, another, ah, Sean, right here.

Sean Carroll:

That's right.

Robert Lawrence Kuhn:

And so, so not what – what – where's the consciousness? Where's the first person—[Crosstalk]

Sean Carroll:

There's two conscious things.

Robert Lawrence Kuhn:

There's two conscious things, but that's not your consciousness here.

Sean Carroll:

No, well that – no. Even if I'm the one here, that's another one.

Robert Lawrence Kuhn:

What do you mean? [Clears throat.] So then – then—

Sean Carroll:

It's just like a branching of the wave function of the universe. There's now two copies of me that go their own ways.

Robert Lawrence Kuhn:

But – but – but you have no awareness of this one?

Sean Carroll:

That one has its own awareness, I have my own awareness.

Robert Lawrence Kuhn:

And you have no – it's not like you have a shared consciousness?

Sean Carroll:

No, certainly not.

Robert Lawrence Kuhn:

Right. And you don't have a fractional consciousness.

Sean Carroll:

Right.

Robert Lawrence Kuhn:

So – so this – this – this is going in – so this is like your twin?

Sean Carroll:

Yeah, exactly.

Robert Lawrence Kuhn:

So, that's not you.

Sean Carroll:

No. That's – that's a copy. There's two copies there.

Robert Lawrence Kuhn:

So then, how – okay. So then, but I just made a perf – ah, this is 100% the same as what you have.

Sean Carroll:

Right, but this is a – philosophical – this is a mereological question. Ah, this is the ship of Theseus, right?

Robert Lawrence Kuhn:

No, I don't think so. I don't think – you're the ship.

Sean Carroll:

I think it is.

Robert Lawrence Kuhn:

If – if I didn't have the second one you'd be the ship of Theseus.

Sean Carroll:

Right, but the point is that if you just – if you want to sort of really get down to what the identity is, at every moment of time there's a different thing, right? There's a different configuration of stuff. There's this configuration of stuff at this moment of time, this configuration of stuff at this moment of time. If you were reifying the idea that there was some unified flow of conscious experience through time, I'm going to deny that.

Robert Lawrence Kuhn:

Yeah, I'm – I'm not – I'm not at that point. I'm just – I'm just at the skeptical position of – of – of following what follows from your analysis that consciousness—

Sean Carroll:

Yeah. I have no trouble believing that there's these two separate conscious creatures now.

Robert Lawrence Kuhn:

[Crosstalk] but – but – if that's not – if that second one is not you, what is the difference because at – at T zero—

Sean Carroll:

But you're reifying you-ness.

Robert Lawrence Kuhn:

Literally – at – at T zero, from the physical point of view, we – we would both agree they are exactly the same.

Sean Carroll:

Right.

Robert Lawrence Kuhn:

They're – they're just in two different places.

Sean Carroll:

That's right, yes.

Robert Lawrence Kuhn:

Okay? And so—

Sean Carroll:

It's the question of which one is you is just meaningless. There are just two of them.

Robert Lawrence Kuhn:

And it – it becomes meaningful if – if – if we – if we take the original, which was you with all your neurons replaced, and, um, and – and burn it.

Sean Carroll:

Well, there's two people. There's two conscious creatures. If you want to start burning them, then, you know, by ordinary moral standards that would be a bad thing to do. Uh, yeah.

Robert Lawrence Kuhn:

But—

Sean Carroll:

Just like having a duplicating machine.

Robert Lawrence Kuhn:

Yeah, so, okay. You have the duplicating machine but – but the you that you that didn't experience any difference during the – the, ah, the switching process with neurons, you haven't experienced anything of that, and you may not even be aware of this other thing that I've created on the side because I didn't tell you, um, and then if you're destroyed, your individual first person experience will go out of existence, because you have this other one here.

Sean Carroll:

Yeah. Right.

Robert Lawrence Kuhn:

Is that right?

Sean Carroll:

Yeah, I mean, they will have identical experiences but—

Robert Lawrence Kuhn:

They – they won't – they don't – memories experiences but they won't have your first person. You won't – if – if—

Sean Carroll:

No. They will have everything that I had by construction.

Robert Lawrence Kuhn:

Right, but there – there would be two of them.

Sean Carroll:

There's two of them, you destroy one, and there's one of them, right. And they will go their own future ways.

Robert Lawrence Kuhn:

Right. But – but in terms of your internal sense of this individual – you didn't know that this existed and – and you were made to not exist, burning or something else, you would go out of existence.

Sean Carroll:

Yes.

Robert Lawrence Kuhn:

Okay. So – so if that's true, then you – then that individ – personal one – ah, a first-person experience cannot be uploaded.

Sean Carroll:

No, that has a first-person experience.

Robert Lawrence Kuhn:

That has—

Sean Carroll:

That is the same as mine.

Robert Lawrence Kuhn:

But it's like an identical twin, the same as – it's not—

Sean Carroll:

It's much better than identical twin, it's really identical. Yes. That's right.

Robert Lawrence Kuhn:

But it – it doesn't have your first person—

Sean Carroll:

I think you are attaching some metaphysical continuity to this experience. Some – some uniqueness to it. At every moment of time, there is a set of things that are having conscious experiences. You've described an elaborate way to take one of those and make two of them and both of them can persist or not persist, talk to each other, never talk—like all of those are possible and none of that gives, in my mind, any special weirdness to the physicality of consciousness.

Robert Lawrence Kuhn:

We're not – we're not at that stage yet. I'm just saying that you – you – if we – if you are unable then to be uploaded with your first-person experience because you can be uploaded, but you would be the same as this other entity over here, which would be a set – a – a very close identical twin with all your memories, but it wouldn't have your first-person experience.

Sean Carroll:

So, I don't think you can say these statements you're saying without using the word "you." I think that's the problem. There is a person here who has consciousness experiences. You're creating a way of making an – an identical twin of them. There are now two people with conscious experiences. They're both going to go on and – and do whatever they do. Uh, is there any objection to that? No. I mean, I think that the—

Robert Lawrence Kuhn:

Is there a difference? Let me ask it this way. Is there a difference between uploading you and now you're uploaded, and I'm not sure whether we destroy the original or we don't, and having this duplicate here? It sounds like the same thing.

Sean Carroll:

Yeah, it's the same thing, right.

Robert Lawrence Kuhn:

It's the same thing. So, um, if – if you would be uploaded, do you feel – would that give you a virtual immortality, when I'm using the word "you" in terms of your first-person experience, or would you feel like it's a very close relative that would go on like – like child but it's – it's a – it's – it's more than a child.

Sean Carroll:

I – I – I really think that you are attaching some, ah, magical reality to you-ness or me-ness. Like, me now is not the same as me a day from now, right? So, which is two—

Robert Lawrence Kuhn:

[Crosstalk] You have the internal coherence. You have the internal coherence—

Sean Carroll:

They're related. They're certainly very related, just as I would be to this uploaded thing. But two consciousnesses.

Robert Lawrence Kuhn:

So – so you—[Crosstalk]

Sean Carroll:

The uploaded one and then there is the physical one.

Robert Lawrence Kuhn:

So, your argument is, is that, a Sean Carroll now and Sean, Sean Carroll tomorrow morning is the same relationship as Sean Carroll here and Sean Carroll that would be uploaded?

Sean Carroll:

It's very similar, obviously. It's not exactly identical because of the terms of the thought experiment, but it's essentially the same, yes.

Robert Lawrence Kuhn:

Okay. So that – that would, um, that would mean that in – in – in your mind, consciousness is, ah, is certainly not an important fact in the universe, it's a – a contingent accident of what – what happened here at some point.

Sean Carroll:

Depends on what you mean by important. It's very important to me. It's as important as cats and baseballs and so forth, yeah. It's a very useful way to think about what happens in our world.