The h Bar

Silly Goose

05:26

do ya'll know of any physicists alive or dead who did not believe in an absolute truth

Silly Goose

06:44

@ACuriousMind Do you know anything about categorical quantum mechanics?

DIRAC1930

@SillyGoose All the great ones. Most seemed to be driven by some kind of aesthetic desire which ultimately produces something greater than just seeking logical truth.

More Anonymous

So I've forgotten some stat mech

what does the pressure distribution look like explicitly?

(not the average)

Mr. Feynman

07:11

@DIRAC1930 Feynman didn't agree with Dirac that theories must be beautiful :P

More Anonymous

@Mr.Feynman Boltzmann: "elegance is for tailors"

Mr. Feynman

Anyways, I would argue that logical truth plays a fundamental role, otherwise we would be throwing our guesses all around all the time

@MoreAnonymous I want to be a tailor then :P

More Anonymous

@Mr.Feynman I did need a tuxedo :P

Mr. Feynman

Sewing the fabric of spacetime

More Anonymous

@Mr.Feynman Watch out for those blackholes :P

Though I do agree with Boltzmann

Mr. Feynman

07:16

You shall ask a laundry for those

Completing my sentence above, we search for logical explanation, then nature doesn't have to be logical at all

More Anonymous

Not even wrong endorsed :P

https://www.youtube.com/watch?v=kya_LXa_y1E

ACuriousMind

@SillyGoose A bit, but not a lot

More Anonymous

Also this resonated with me quite strongly (wondering if its only me)

"The amateur is a narcissist. He views the world hierarchically. He continuously rates himself in relation to others, becoming self-inflated if his fortunes rise, and desperately anxious if his star should fall.

The amateur sees himself as the hero not only of his own movie but also in the movie of others.

He insists in his mind, if nowhere else, that others share this view."

You have to find somewhere more firm to stand rather than exclusively outsourcing your sense of self worth to the whole world around you.

ACuriousMind

@SillyGoose What exactly do you mean by belief in absolute truth? That such a thing in principle exists or that it is intelligible to us?

Silly Goose

ah i see i just found out of its existence and it seems interesting i should learn a bit of category theory if i can :D

i more mean in principle "truth" exists

ACuriousMind

07:31

Because I think the "default" view of most natural scientists is that certainly there is an objective reality about which statements can be absolutely true but that our sciences can only ever be reasonable approximations to this truth ("All models are wrong, but some are useful")

More Anonymous

@ACuriousMind something i agree with

Silly Goose

hm id be interested to see non truth existence frameworks

idk naively, believing in the existence of a "truth" is real convenient

but i am no philosopher so it is hard to think about these things for me ;P

More Anonymous

@SillyGoose i wonder if "i think therefore I am" falls under this

ACuriousMind

perhaps you're looking for something like Feyerabend's epistomological anarchism and his "abundant world"

Also, existentialist philosophies generally say something like "Truth only means something in relation to a subject", i.e. don't really say objective truth "exists" or "doesn't exist", but to them the notion is not really meaningful - all statements, when evaluated for their truth, are thought by someone, and so the idea that a statement could be true or false independent of the one who thinks it is incoherent in such approaches

DIRAC1930

07:47

Feynman was no Dirac. But even then, the problems in the latter half of the last century seemed to more technical issues in an already established framework. Dyson talks about his work in an interesting manner. He was probably somewhere in the middle.

More Anonymous

@ACuriousMind sounds a bit of Buddhism :/ (not that I'm greatly familiar with those texts)

DIRAC1930

I think you need both. A strong aesthetic drive but an ability to partially sacrifice it

More Anonymous

@DIRAC1930 agreed but a lot of physicists seem to be people who had an ability to over commit to a particular viewpoint (due to intuition)

But then there were those whose didn't pan out

Makes me wonder if the whole thing functions akin to evolution

A random intuition generator and a feedback loop

Ryder Rude

11:28

In my philosophy, truth gets its meaning from sets. If u hav a set, u hav truths about it and u hav falsities about it

Mr. Feynman

I wonder if there is any philosophy claiming something like this: if our brains made Mathematics and those very brains are made of matter, can we assert that Math is a manifestation of Physics?

Ryder Rude

And i further speculate that sets exist in the universe's ontology, but only approximately

So when we say "Newtonian mechanics is approximately true in its domain of validity", this is an objectively true statement about the set theoretic structure of universe

@Mr.Feynman yes. I think along these lines too. But physics itself is partially math as the universe's ontology has math in it. So our brain is just a subset of that math discovering the rest of that math

@Mr.Feynman this also depends on what u define to be physics. If physics="all that exists", then math is derived from it. All that exists need not b exhaustively math.

ACuriousMind

11:44

@Mr.Feynman that's more or less a shared feature of the theories Wiki classifies as "embodied mind"

although there is a terminology problem here - do you really mean "manifestation of Physics" and not "manifestation of the physical world"? If you think our brains make math, then you should probably also say they make physics (as the science of the physical world distinct from the physical world itself)

Ryder Rude

@ACuriousMind yes, this is what i mean! Usually, by physics, we only mean the mathematical study of the outer world in our subjective experience. Mr. Feynman's statement is good if we replace physics with ontology of reality

This is also why I have a hard time differentiating "physical vs idealism". Isn't the " Physical world", by definition, all that exists?

ACuriousMind

@RyderRude not if you're a dualist

Ryder Rude

If we define "physical world" to mean an "information theoretic" ontology, then the distinction between physicalism and idealism can make sense

Becuz reality need not b a mathematical struture

@ACuriousMind but what is the definition of the "physical aspects of the world" in dualism?

ACuriousMind

again, "dualism" isn't one kind of philosophy

it's just a name for any philosophy that thinks there's (at least) two fundamentally different kinds of stuff

Ryder Rude

If they define "physical aspects=mathematical aspects", then i can see a distinction

ACuriousMind

11:53

the most frequent examples are body-mind dualists who believe that there is something about the mind that is not a function of the material body

that "something" usually has no "physical extent", i.e. it is indetectable by looking at bodies

Ryder Rude

@ACuriousMind how is material defined here? Is "material body" is defined as a mathematical structure corresponding to the body?

ACuriousMind

what

the material body is the physical stuff you're made of, the flesh, the neurons, etc

body-mind dualists assert that the mind is made of something different - a "soul" - that is not like these things, not composed of atoms, not having any spatial extent. We discussed this already when we talked about Descartes.

Apr 10 at 12:22, by ACuriousMind

just because you don't believe in disembodied souls as a fundamental ingredient of reality that doesn't mean Descartes isn't saying that

Ryder Rude

I got it. They define "material things" to be everything except the mind

So they have "two types of things"

ACuriousMind

Not...exactly, no

e.g. they might also think there's a God that's not material, not just a human mind or soul

Ryder Rude

Oh

Ryder Rude

12:11

I think Relational QM may be in support of my philosophy. Like, any measurement device can collapse the wavefunction in its own personal knowledge. But that is its personal knowledge that is inaccessible to everything else excet the measurement device

So we would need to describe it as a superposition, even though it is actually collapsed relative to personal knowledge of other objects

Everything has a "personal aspect" and a "share-able" aspect

The share-ble aspect is "how something behaves from the outside". The personal aspect is "how something is"

Mr. Feynman

@ACuriousMind Thanks

@ACuriousMind I saw that objection coming and yet I decided to phrase it like that. Yes, I mean a manifestation of the physical world and thus in principle the domain a of Physics (in a very reductionist and ideal sense)

@ACuriousMind Sure, that would also hold for Physics, making it circular (and this is something that makes me doubt how knowledge works because it's like a part of the universe is understanding itself but that is not the focus now). What I was really trying to understand is whether a reductionist point of view has Physics at its lowest end

Ryder Rude

13:13

@Mr.Feynman I would say the "physical world" is trivially at the lowest end. A more interesting question would be whether mathematics of physics serves as a foundation for the rest of mathematics. At first glance, this seems blatantly false because the mathematics of physics is a subset of mathematics

But aftr careful thinking, we can say that the mathematics of classical physics is Turing complete. As in, a physical Turing machine can be designed using Newtonian mechanics

And all the mathematical theorems we have ever proven are actually computations using axioms. So turing machines can serve as a foundation to all of mathematics that we have come up with

@Mr.Feynman So I would say the mathematics of physics (like Newtonian mechanics) is at a reductionist lower end over the rest of mathematics that we have cooked in the Turing machine that is our brain

ACuriousMind

@Mr.Feynman there might be reductionist views in general that reduce to something other than physics; what you're describing is more specifically called physicalism

2

user4539917

By "the mathematics of physics" are you referring to "mathematical physics"

Ryder Rude

I mean a specific axiomatic model of physics like Newtonian mechanics can simulate a Turing machine which can later compute all the other mathematics and theorems that we have come up with

user4539917

13:33

sounds similar to hilbert's program, but Gödel's incompleteness theorems showed that most of the goals of Hilbert's program were impossible to achieve

Ryder Rude

Oh no. I dont mean "foundation of mathematics" in the Hilbert sense. After all the, the models of physics are themselves founded in set theory.

I mean "foundation of mathematics" in the sense of what ontologically comes first

user4539917

whelp, in physics experiments come first

Ryder Rude

The models of physics are engrained in the ontology of the reality. The mathematics of physics allows the physical existence of Turing machines like our brains which we use to cook up the rest of mathematics

In this sense, the mathematics of physics is at the lower end in terms of physical existence

In terms of logical foundations, set theory is at the lowest end (or something equivalent like Category theory)

user4539917

Apr 20 at 12:33, by user 85795

We can't even understand the brain of a fruit fly.

Ryder Rude

13:50

Yes. You are correct @user4539917 . But the computationalist model of brain works upto a great approximation in predicting our thoughts. It's still not the lowest thing in the ontology imo. It emerges from something deeper. I'm just saying that it's relatively lower compared to the rest of mathematics we have come up with (as it can all be explained using an approximate Turing machine model of the brain)

Mr. Feynman

@RyderRude In that case the distinction between Physics and physical world becomes crucial

Ryder Rude

Like, we store axioms in our memory and we do computations on them. This explains the rest of mathematics using a Turing machine model of brain @user4539917

Mr. Feynman

@RyderRude I wouldn't make this distinction, because that's just about the laws that we have discovered and for those we have used some specific mathematics to model it. Here the discussion is not about a specific mathematical concept, rather about mathematics itself being physical

Ryder Rude

@Mr.Feynman It would depend on what you mean by "physical". I personally define physical to mean " All that exists", because I prefer physicalist monism

Mr. Feynman

@ACuriousMind Oh, thanks again

Ryder Rude

13:59

This is why I said this version of the discussion may get trivial. So I switched to other discussion of the mathematics of physics being lower than the rest of mathematics

ACuriousMind

@RyderRude this is nonsense, our brains are not Turing machines and we regularly do mathematics that would be impossible for finite Turing machines

Ryder Rude

The other discussion is just a matter of opinions of whether you believe the outer world is physical, dual, or ideal whatever. Whatever you believe to be the outside world, mathematics is derived from it

@ACuriousMind example of such mathematics? I thought we derive theorems from axioms

Is there any mathematics that we do that a turing machine cant do?

ACuriousMind

@RyderRude Turing machines (of arbitrary length, unlike our finite brains!) are essentially equivalent to first-order logic

mathematics is more than first-order logic

user4539917

much more

Ryder Rude

You mean computers cant do second order logic?

ACuriousMind

14:04

@RyderRude computers and Turing machines are two completely different concepts

Ryder Rude

Second order logic is just first order logic with the existential working on sets

ACuriousMind

our computers are not Turing machines, either

Ryder Rude

I mean they r turing equivalent

ACuriousMind

Okay, so if you don't want to use the usual formal equivalence between logic and Turing machines, why is it relevant to model the brain as a Turing machine and not just something that can do computations?

Ryder Rude

Oh my argument does not rely on Turing machines specifically. I just did it to establish Turing completeness of the brain. My argument is just : "Newtonian mechanics can simulate the computation of any theorem from axioms that we ever have done in mathematics"

So as long as u believe classical computers can do any math we have done, and that newtonian mechanics can simulate classical computers, my argument works

ACuriousMind

14:11

and also: Yes, I am claiming that computers/Turing machines can't do second-order logic, cf. math.stackexchange.com/q/3637201/143136

(the subtle question is: Do you believe we can do second-order logic? :P)

@RyderRude the brain is obviously not Turing complete because the usual notion is that we have a Turing machine with arbitrarily large tape but the memories of our computers and brains are obviously finite

again, the devil is in the details and you should stop with the handwaves

Ryder Rude

@ACuriousMind i really was aware of this part. I didnt mention it becuz this detail neither hurts nor helps my argument.

@ACuriousMind thanks for this. I shall read it and try to modify my philosophy

ACuriousMind

it's just the old incompleteness theorem again just in the language of Turing machines

I don't really think you want to ground mathematics as formal computations we do anyway because historically we've done a lot of informal math

you might believe that mathematics "really is" about the formal structures, but the fact is that most mathematicians do not practice entirely formal mathematics, and the proofs they produce are not formal proofs any Turing machine could check

the social construct of mathematics as practiced by humans is different from the formal construct of it we employ when we do logic or meta-theory

Ryder Rude

@ACuriousMind But the computational model can be used to predict people's thoughts 10s in advance. I think this should be able to predict informal reasoning too

ACuriousMind

I don't know how that is a response to what I said

you claimed

13 mins ago, by Ryder Rude

So as long as u believe classical computers can do any math we have done, and that newtonian mechanics can simulate classical computers, my argument works

Ryder Rude

Yes, I again weakened my argument even more :P

ACuriousMind

14:24

my point is that we don't do math like the computers do, as evidenced by the fact that computers can compute stuff much better than we can

Ryder Rude

U keep refuting it, so I have to weaken it

ACuriousMind

I'm not denying that it is possible our minds are algorithms, I'm saying "the brain does math like a computer" is wrong

Ryder Rude

Okay. I will stick to the weaker version: "our minds r algorithms". And, in ur opinion, these algorithms r manifestates of mathematics of physics just like other physical processes are?

ACuriousMind

I don't know what that means

Ryder Rude

So we could say that the mathematics of physics derives the rest of mathematics

@ACuriousMind like how other physical processes have an approximate one-to-one correspondence with the mathematical models of physics. We cud say the same for the algorithm of our brain

And this algorithm is at the root of the rest of mathematics tht we make

ACuriousMind

14:29

I really don't know what you're talking about, and I think it is not evident that whatever our brain implements is really an algorithm as we usually think

you can believe that the biological processes in our brain determine our actions without believing that those processes can necessarily be modeled as an algorithm

Ryder Rude

I just personally think that mathematical reasoning seems explainable using algorithms. I agree this is not necessarily true @ACuriousMind

I think this becuz mathematical reasoning doesnt seem as mysterious to me as qualia

So it's a matter of opinion i guess

ACuriousMind

@RyderRude This is likely because you live in the era after Turing and von Neumann where algorithms are a universal metaphor for thought and mathematics

people 200 years ago did math and didn't really have so much as a concept of an "algorithm"

2

Ryder Rude

Yes, people have done informal math for most of human history

I just think that computationalist model can predict all thoughts becuz it's very successful at predicting thoughts

user4539917

let's just agree to disagree

Ryder Rude

I'm not debating. I'm just discussing

ACuriousMind

14:35

@RyderRude and the only "explanation" of mathematical reasoning via algorithms is not really an explanation: You just have to say that the brain is an algorithm at least as opague as modern language models, and somehow it produces math

you're right that "math" isn't as mysterious as qualia but that's just because math, like every other action, is an output of humans, not because math as practiced by humans is any closer to computations and algorithms than, say, football

qualia aren't measureable outputs, they are invisible "features" inside the "algorithm"

Ryder Rude

@ACuriousMind yes. This is y. I expect mathematics physics to model the outputs to a great accuracy. I expect this to hold for informal reasoning too.

But this is not necessarily true, I agree

Becuz we cud have free will and stuff @ACuriousMind

ACuriousMind

@RyderRude I'm not sure what you mean by expecting "mathematics physics to model the outputs to a great accuracy"

our current physics is terrible at predicting humans

as in, no one even really knows how we'd start in principle

Ryder Rude

Yeah

Also free will is maybe relevant too. Maybe we have free will

Then we would not be predictable, even in principle

I'm not sure what free will really means tho

Things can either be random or determistic.

ACuriousMind

I'm not talking about free will, I'm just asking what you mean when you say you expect "great accuracy" from physics in predicting humans

because currently I don't see anyone using physics to try to predict humans

Ryder Rude

I mean, in principle, I expect physics to predict humans just like it predicts the Solar system. I dont't mean in practice

In practice, things get chaotic

ACuriousMind

14:43

so you're not actually talking about predictions, you just mean that in principle humans follow the same physical laws as everything else

Ryder Rude

Yes!

I just hold faith in physics

ACuriousMind

then say that :P

Ryder Rude

Yes, I don't mean predictions in practice :)

So if, in principle, if the mathematics of physics predicts human thoughts and memories and every behavior and output of humans, then the mathematics of physics derives the rest of mathematics we have come up with

@ACuriousMind ooh i see where i got misunderstood. It's the "great accuracy" part :P

By great accuracy, I didn't mean "great accuracy" in practice. I meant that I believe every model of physics is always approximate, even in principle

user4539917

sounds like the unreasonable effectiveness of mathematics

Ryder Rude

This is a personal belief

So I never expect it to completely predict human output with 100% accuracy

I only expect human output on the level of mathematical reasoning to be predictable, in principle

user4539917

14:52

but

Unreasonable ineffectiveness of mathematics

The unreasonable ineffectiveness of mathematics is a phrase that alludes to the article by physicist Eugene Wigner, "The Unreasonable Effectiveness of Mathematics in the Natural Sciences". This phrase is meant to suggest that mathematical analysis has not proved as valuable in other fields as it has in physics. == Life sciences == I. M. Gelfand, a mathematician who worked in biomathematics and molecular biology, as well as many other fields in applied mathematics, is quoted as stating, Eugene Wigner wrote a famous essay on the unreasonable effectiveness of mathematics in natural sciences. He meant...

Ryder Rude

15:08

@ACuriousMind I just realised that much of natural language is lost in formal languages. So I think I am wrong in expecting that informal and intuition-based reasoning can be derived from algorithms

Intuition and reasoning cud b something mysterious like qualia

I will have to modify my philosophy

My previous philosophy was : All that exists derives Mathematics of physics derives Algorithm of brain derives All of Human thought derives All math we have made

But all of human thought is probably not derivable from the previous step

I will now attribute the origin of mysterious components of human thought to : All that exists minus Mathematics of physics

So these r the non-mathematical aspects of the ontology. This is the same place I am attributing qualia to

DIRAC1930

16:30

What's the best way to learn string theory if you are interested in physical consequences?

Physics Meta

16:56

0

Q: On-topic question about wavelengths

I made several edits to a question about wavelengths. Each version of this question was marked as off-topic. Since I cannot post new question on the Physics site, I need to work on improving my existing questions by editing them to comply with the site's guidelines and address any feedback I have...

DIRAC1930

18:26

Is there anything I can learn about QFT by studying string theory?

Mr. Feynman

I dislike the interpretation of the Feynman propagator $D_F(x-y)$ as a transition amplitude for a particle to go from $x$ to $y$. We don't even have a position operator in relativistic QFT

There is that discussion about $\hat{\phi}(\vec{x})\lvert 0\rangle\sim\lvert\vec{x}\rangle$ but the RHS is just handwaving in the relativistic theory

DIRAC1930

18:45

In the non-rel case you can show it explicitly by inserting a complete set of position states between the field operator and vacuum but I'm guessing the story is different in the rel case

Mr. Feynman

18:56

In the non relativistic case you have by construction that $\hat{\Psi}^\dagger(\vec{x})\lvert 0\rangle=\lvert\vec{x}\rangle$ and the RHS is well defined

imbAF

19:10

In nuclear physics, why do we make the assumption that the room temperature can be approximated to zero ?

DIRAC1930

It would be interesting to see how the non-rel limit is achieved

Don't we get an inconsistency from L&L 4 chapter 1. In the rest frame of the electron we will have a wavefunction that makes sense (since we are in the non-rel limit), however viewing the electron from a different (relatively high velocity) frame, the wavefunction becomes a meaningless concept.

Maybe I should just forget about this

DIRAC1930

20:00

en.wikipedia.org/wiki/… This is interesting

So is the idea of collider experiments to make the incident particles of energy $m c^2$ where $m$ is the mass of a new hypothetical particle created if the interaction will allow it?

I suppose this is similar to adding a perturbation to a QM Hamiltonian and it jumping to a higher energy level

imbAF

What is the one body potential ? In the context of an effective nucleus potential

Silly Goose

23:51

does anyone know a good introduction to category theory (especially if it is motivated by physics)

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