Reasoning practiced in the physical world is a genre of computation, so what matters about physics in enabling reasoning is that it can be used to implement computation, to build computers. The reasoning can then be about all sorts of things, physics being among them but not different from others in a way relevant to what makes computation reasoning.
Sure, I think I agree. My point is that because all known reasoning takes place in physics, we don’t need to assume that any of the other things we talk about exist in the same way that physics does.
I even go a little further than that and assert that assuming that any non-physical thing exists is a mistake. It’s a mistake because it’s impossible for us to have evidence in favor of its existence, but we do have evidence against it: that evidence is known as Occam’s Razor.
There is also little point in saying that physics exists. You can reason about physics the same way as about other things, namely without having any use for the assumption that it exists.
Existence of physics makes sense as a statement about values, a claim of caring about physics more than about some other things (which don’t exist in this sense). This is an ingredient of decision theory, not of reasoning.
The fact that I live in a physical world is just a fact that I’ve observed, it’s not a part of my values. If I lived in a different world where the evidence pointed in a different direction, I would reason about the different direction instead. And regardless of my values, if I stopped reasoning about the physical world, I would die, and this seems to me to be an important difference between the physical world and other worlds I could be thinking about.
Of course this is predicated on the concept of “I” being meaningful. But I think that this is better supported by my observations than the idea that every possible world exists and the idea that probability just represents a statement about my values.
To formulate useful abstractions, it’s important to figure out what data is relevant in what arguments. For existence in the sense that physics exists, I don’t see how it’s relevant for reasoning (including about physics), but I do see how it’s relevant to decision making, and that is the distinction I pointed out. Where the fact itself comes from is distinct from where it’s useful, and I’m pointing specifically at the latter here.
You then say “this is predicated on the concept of “I” being meaningful”. Presumably it’s the argument for reality of physics you gave that’s predicated on this, not something else. Parity of N⋅(N+1) is not predicated on this, it shouldn’t be part of the proof of evenness. So it’s another example for the principle I’m describing in this comment.
(To be clear, I’m not ruling out being wrong about the claim of something not being relevant. But the relevant wrongness would need to be in the form of it turning out to be relevant to the particular arguments in question after all, rather than merely true or known, or relevant to something else.)
Okay, let’s forget the stuff about the “I”, you’re right that it’s not relevant here.
For existence in the sense that physics exists, I don’t see how it’s relevant for reasoning, but I do see how it’s relevant to decision making
Okay, I think my view actually has some interesting things to say about this. Since reasoning takes place in a physical brain, reasoning about things that don’t exist can be seen as a form of physical experiment, where your brain builds a description which has properties which we assume the thing that doesn’t exist would have if it existed. I will reuse my example from my previous post to explain what I mean by this:
To be more clear about what I mean by mathematical descriptions “sharing properties” with the thing it describes, we can take as example the real numbers again. The real numbers have a property called the least upper bound property, which says that every nonempty collection of real numbers which is bounded above has a least upper bound. In mathematics, if I assume that a variable x is assigned to a nonempty set of real numbers which is bounded above, I can assume a variable y which points to its least upper bound. That I can do this is a very useful property that my description of the reals shares with the real numbers, but not with the rational numbers or the computable real numbers.
So my view would say that reasoning is not fundamentally different from running experiments. Experiments seem to me to be in a gray area with respect to this reasoning/decision-making dichotomy, since you have to make decisions to perform experiments.
Reasoning being real and the thing it reasons about being real are different things. Truth of an experiment being real is not the same as relevance of the experiment being real. Would the experiment behave differently if it’s not real? I’d say it would need to be a different experiment to do that, not being real wouldn’t suffice, so the distinction of being real vs. not is not useful for this purpose.
Reasoning being real and the thing it reasons about being real are different things.
I do agree with this, but I am very confused about what your position is. In your sibling comment you said this:
Possibly the fact that I perceive the argument about reality of physics as both irrelevant and incorrect (the latter being a point I didn’t bring up) caused this mistake in misperceiving something relevant to it as not relevant to anything.
The existence of physics is a premise in my reasoning, which I justify (but cannot prove) by using the observation that humanity has used this knowledge to accomplish incredible things. But you seem to base your reasoning on very different starting premises, and I don’t understand what they are, so it’s hard to get at the heart of the disagreement.
Edit: I understand that using observation of the physical world to justify that it exists is a bit circular. However, I think that premises based on things that everyone has to at least act like they believe is the weakest possible sort of premise one can have. I assume you also must at least act like the physical world is real, otherwise you would not be alive to talk to me.
I don’t see how reality of physics is used in your reasoning. I did see that you claim that you do use it, and that you mentioned it in the posts, but I don’t see how it’s doing some work in some argument. I don’t see how humanity accomplishing incredible things has anything to do with the world being real, we could similarly accomplish incredible things in a world that isn’t real.
My frame is grounded in thinking about decision theory, where one thing that keeps coming up is counterfactuals, reasoning about what would happen under conditions that at some point are revealed to in fact fail to hold. This is reasoning about situations and worlds that are not real, and for this form of decision making to make sense, it’s necessary for the reasoning about worlds that are not real to reach meaningful conclusions. This makes discussion of detailed claims about worlds that are not real a normal thing, not something strange. And when that crystallizes into an intuitive way of looking at things in general, it becomes apparent that if our physical world wasn’t real in a similar sense, literally nothing about anything would change as a result. Relevance of the world being real is largely an illusion.
What matters about the world being real is that it seems to be the case that we care about what happens in the physical world, possibly more than about what happens in some other hypothetical worlds. That’s a formulation of the meaning of the physical world being real that’s more clear to me than how these words are normally used (i.e. without a satisfactory clarification or an argument for truth of the claim that might also serve that purpose).
I completely agree that reasoning about worlds that do not exist reaches meaningful conclusions, though my view classifies that as a physical fact (since we produce a description of that nonexistent world inside our brains, and this description is itself physical).
it becomes apparent that if our physical world wasn’t real in a similar sense, literally nothing about anything would change as a result.
It seems to me like if every possible world is equally not real, then expecting a pink elephant to appear next to me after I submit this post seems just as justified as any other expectation, because there are possible worlds where it happens, and ones where it doesn’t. But I have high confidence that no pink elephant will appear, and this is not because I care more about worlds where pink elephants don’t appear, but because nothing like that has ever happened before, so my priors that it will happen are low.
For this reason I don’t think I agree that nothing would change if the physical world wasn’t real in a similar sense as hypothetical ones.
What I mean by reaching meaningful conclusions about counterfactuals is that you start with a problem statement, a description of a possibly counterfactual situation, and then you see what follows from that. You don’t get to decide that pink elephants follow just because the situation is counterfactual, any pink elephants would need to follow from the particular problem statement that you start with. Existence of other counterfactuals (other possible worlds) with pink elephants is completely irrelevant, because we are not reasoning about them at the moment.
Similarly, if you reason about the physical world that isn’t real, it doesn’t matter that there are other alternative physical worlds that are also not real with different properties, because we are reasoning about this particular not-real world, not those other ones. The problem statement constrains the expectations, not reality of the thing referenced by the problem statement.
let’s forget the stuff about the “I”, you’re right that it’s not relevant here
No, I believe I’m wrong. I reversed the point about “I” in the grandparent about 10 minutes after posting, which turns out to be too late. I originally said that I don’t see how that’s relevant at all, but then noticed that it’s not true, since it’s relevant to your argument about reality of physics. Possibly the fact that I perceive the argument about reality of physics as both irrelevant and incorrect (the latter being a point I didn’t bring up) caused this mistake in misperceiving something relevant to it as not relevant to anything.
My point is that because all known reasoning takes place in physics, we don’t need to assume that any of the other things we talk about exist in the same way that physics does.
I can’t follow your syntax, but clearly physical brains can think about non physical things.
It’s a mistake because it’s impossible for us to have evidence in favor of its existence, but we do have evidence against it: that evidence is known as Occam’s Razor.
But it’s not conclusive in every case, because the simplest adequate explanation need not be a physical explanation.
clearly physical brains can think about non physical things.
Yes, but this is not evidence for the existence of those things.
But it’s not conclusive in every case, because the simplest adequate explanation need not be a physical explanation.
There is one notion of simplicity where it is conclusive in every case: every explanation has to include physics, and then we can just cut out the extra stuff from the explanation to get one that postulates strictly less things and has equally good predictions.
But you’re right, there are other notions of simple for which this might not hold. For example if we define simple as “shortest description of the world which contains all our observations”. Though I think this definition has its own issues, since it probably depends on the choice of language.
Still, this is the most interesting point that has been brought up so far, thank you.
Edit: I was too quick with this reply and am actually wrong that my notion of simplicity is conclusive in every case. I still think this applies in every case that we know of, however.
Edit 2: I think the only case where it is not conclusive is the case where we have some explanation of the initial conditions of the universe which we find has predictive power but which requires postulating more things.
Yes, but this is not evidence for the existence of those things.
I didn’t say it was.
But it’s not conclusive in every case, because the simplest adequate explanation need not be a physical explanation.
There is one notion of simplicity where it is conclusive in every case: every explanation has to include physics, and then we can just cut out the extra stuff from the explanation to get one that postulates strictly less things and has equally good predictions.
Why posit that an explanation has to include physics even in cases, like this, where it adds nothing? In those cases it’s simpler not to include physics.
Reasoning practiced in the physical world is a genre of computation, so what matters about physics in enabling reasoning is that it can be used to implement computation, to build computers. The reasoning can then be about all sorts of things, physics being among them but not different from others in a way relevant to what makes computation reasoning.
Sure, I think I agree. My point is that because all known reasoning takes place in physics, we don’t need to assume that any of the other things we talk about exist in the same way that physics does.
I even go a little further than that and assert that assuming that any non-physical thing exists is a mistake. It’s a mistake because it’s impossible for us to have evidence in favor of its existence, but we do have evidence against it: that evidence is known as Occam’s Razor.
There is also little point in saying that physics exists. You can reason about physics the same way as about other things, namely without having any use for the assumption that it exists.
Existence of physics makes sense as a statement about values, a claim of caring about physics more than about some other things (which don’t exist in this sense). This is an ingredient of decision theory, not of reasoning.
The fact that I live in a physical world is just a fact that I’ve observed, it’s not a part of my values. If I lived in a different world where the evidence pointed in a different direction, I would reason about the different direction instead. And regardless of my values, if I stopped reasoning about the physical world, I would die, and this seems to me to be an important difference between the physical world and other worlds I could be thinking about.
Of course this is predicated on the concept of “I” being meaningful. But I think that this is better supported by my observations than the idea that every possible world exists and the idea that probability just represents a statement about my values.
To formulate useful abstractions, it’s important to figure out what data is relevant in what arguments. For existence in the sense that physics exists, I don’t see how it’s relevant for reasoning (including about physics), but I do see how it’s relevant to decision making, and that is the distinction I pointed out. Where the fact itself comes from is distinct from where it’s useful, and I’m pointing specifically at the latter here.
You then say “this is predicated on the concept of “I” being meaningful”. Presumably it’s the argument for reality of physics you gave that’s predicated on this, not something else. Parity of N⋅(N+1) is not predicated on this, it shouldn’t be part of the proof of evenness. So it’s another example for the principle I’m describing in this comment.
(To be clear, I’m not ruling out being wrong about the claim of something not being relevant. But the relevant wrongness would need to be in the form of it turning out to be relevant to the particular arguments in question after all, rather than merely true or known, or relevant to something else.)
Okay, let’s forget the stuff about the “I”, you’re right that it’s not relevant here.
Okay, I think my view actually has some interesting things to say about this. Since reasoning takes place in a physical brain, reasoning about things that don’t exist can be seen as a form of physical experiment, where your brain builds a description which has properties which we assume the thing that doesn’t exist would have if it existed. I will reuse my example from my previous post to explain what I mean by this:
So my view would say that reasoning is not fundamentally different from running experiments. Experiments seem to me to be in a gray area with respect to this reasoning/decision-making dichotomy, since you have to make decisions to perform experiments.
Reasoning being real and the thing it reasons about being real are different things. Truth of an experiment being real is not the same as relevance of the experiment being real. Would the experiment behave differently if it’s not real? I’d say it would need to be a different experiment to do that, not being real wouldn’t suffice, so the distinction of being real vs. not is not useful for this purpose.
I do agree with this, but I am very confused about what your position is. In your sibling comment you said this:
The existence of physics is a premise in my reasoning, which I justify (but cannot prove) by using the observation that humanity has used this knowledge to accomplish incredible things. But you seem to base your reasoning on very different starting premises, and I don’t understand what they are, so it’s hard to get at the heart of the disagreement.
Edit: I understand that using observation of the physical world to justify that it exists is a bit circular. However, I think that premises based on things that everyone has to at least act like they believe is the weakest possible sort of premise one can have. I assume you also must at least act like the physical world is real, otherwise you would not be alive to talk to me.
I don’t see how reality of physics is used in your reasoning. I did see that you claim that you do use it, and that you mentioned it in the posts, but I don’t see how it’s doing some work in some argument. I don’t see how humanity accomplishing incredible things has anything to do with the world being real, we could similarly accomplish incredible things in a world that isn’t real.
My frame is grounded in thinking about decision theory, where one thing that keeps coming up is counterfactuals, reasoning about what would happen under conditions that at some point are revealed to in fact fail to hold. This is reasoning about situations and worlds that are not real, and for this form of decision making to make sense, it’s necessary for the reasoning about worlds that are not real to reach meaningful conclusions. This makes discussion of detailed claims about worlds that are not real a normal thing, not something strange. And when that crystallizes into an intuitive way of looking at things in general, it becomes apparent that if our physical world wasn’t real in a similar sense, literally nothing about anything would change as a result. Relevance of the world being real is largely an illusion.
What matters about the world being real is that it seems to be the case that we care about what happens in the physical world, possibly more than about what happens in some other hypothetical worlds. That’s a formulation of the meaning of the physical world being real that’s more clear to me than how these words are normally used (i.e. without a satisfactory clarification or an argument for truth of the claim that might also serve that purpose).
I completely agree that reasoning about worlds that do not exist reaches meaningful conclusions, though my view classifies that as a physical fact (since we produce a description of that nonexistent world inside our brains, and this description is itself physical).
It seems to me like if every possible world is equally not real, then expecting a pink elephant to appear next to me after I submit this post seems just as justified as any other expectation, because there are possible worlds where it happens, and ones where it doesn’t. But I have high confidence that no pink elephant will appear, and this is not because I care more about worlds where pink elephants don’t appear, but because nothing like that has ever happened before, so my priors that it will happen are low.
For this reason I don’t think I agree that nothing would change if the physical world wasn’t real in a similar sense as hypothetical ones.
What I mean by reaching meaningful conclusions about counterfactuals is that you start with a problem statement, a description of a possibly counterfactual situation, and then you see what follows from that. You don’t get to decide that pink elephants follow just because the situation is counterfactual, any pink elephants would need to follow from the particular problem statement that you start with. Existence of other counterfactuals (other possible worlds) with pink elephants is completely irrelevant, because we are not reasoning about them at the moment.
Similarly, if you reason about the physical world that isn’t real, it doesn’t matter that there are other alternative physical worlds that are also not real with different properties, because we are reasoning about this particular not-real world, not those other ones. The problem statement constrains the expectations, not reality of the thing referenced by the problem statement.
No, I believe I’m wrong. I reversed the point about “I” in the grandparent about 10 minutes after posting, which turns out to be too late. I originally said that I don’t see how that’s relevant at all, but then noticed that it’s not true, since it’s relevant to your argument about reality of physics. Possibly the fact that I perceive the argument about reality of physics as both irrelevant and incorrect (the latter being a point I didn’t bring up) caused this mistake in misperceiving something relevant to it as not relevant to anything.
I can’t follow your syntax, but clearly physical brains can think about non physical things.
But it’s not conclusive in every case, because the simplest adequate explanation need not be a physical explanation.
Yes, but this is not evidence for the existence of those things.
There is one notion of simplicity where it is conclusive in every case: every explanation has to include physics, and then we can just cut out the extra stuff from the explanation to get one that postulates strictly less things and has equally good predictions.
But you’re right, there are other notions of simple for which this might not hold. For example if we define simple as “shortest description of the world which contains all our observations”. Though I think this definition has its own issues, since it probably depends on the choice of language.
Still, this is the most interesting point that has been brought up so far, thank you.
Edit: I was too quick with this reply and am actually wrong that my notion of simplicity is conclusive in every case. I still think this applies in every case that we know of, however.
Edit 2: I think the only case where it is not conclusive is the case where we have some explanation of the initial conditions of the universe which we find has predictive power but which requires postulating more things.
I didn’t say it was.
Why posit that an explanation has to include physics even in cases, like this, where it adds nothing? In those cases it’s simpler not to include physics.