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Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by DeathArrow on Friday April 17, 2020 @03:22AM (#22896924)
Intuitionist mathematics claims that mathematics is purely the result of the constructive mental activity of humans rather than the discovery of fundamental principles existing in an objective reality. [0]

In intuitionist mathematics there is only potential infinity, no actual infinity. Constructive set theory differs from Zermelo set theory.

That has many consequences in practice. Applying intuitionist mathematics to physics we can come to the conclusion that time flows and it helps reconcile quantum mechanics with general relativity.[1]

[0] https://en.wikipedia.org/wiki/Intuitionism

[1] https://www.quantamagazine.org/does-time-really-flow-new-clu...

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by hliyan on Friday April 17, 2020 @05:39AM (#22897547)
I've always thought math as we know it is a result of both deep underlying relationships between natural constructs and how we perceive them. For example, a species who has no sense of vision will not develop geometry the same way we would. A species that has a sense of vision that also includes a direct distance perception (as opposed to our stereoscopic vision) will probably come up with a very different form of geometry.

Though I'd like to think that most species would come up with some version of calculus, even though the notation will be obviously different. Afterall, two of our own species did so independently.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by sorokod on Friday April 17, 2020 @09:26AM (#22898774)
A species that has a sense of vision that also includes a direct distance perception (as opposed to our stereoscopic vision) will probably come up with a very different form of geometry.

Except once axioms have been fixed, the resulting geometry will be the same wether you perceive reality via visible light or echolocation.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by DeathArrow on Friday April 17, 2020 @09:11AM (#22898648)
Maybe vision is helpful with elementary geometry. I don't know how vision would help with differential geometry, geometry of affine spaces, topology, algebraic geometry.

Maybe visualization is more helpful, but you can visualize things without seeing.

A sense of depth and distance, or any kind of metric is helpful, and senses like vision and hearing might be helpful in forming that, but I'm not sure they are required.

From another point of view, math theories are congruent, and you can explain the same things without using geometry, but using algebra, or differential equations or number theory and so on. You certainly can explain any math concept using just modern set theory - maybe it is not the most convenient thing to do.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by Koshkin on Friday April 17, 2020 @04:09PM (#22902506)
Category theory is thoroughly visual, though.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by phaemon on Friday April 17, 2020 @07:34AM (#22898103)
And yet, most blind mathematicians are geometers, which suggests your theory is incorrect.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by cossatot on Friday April 17, 2020 @10:22AM (#22899195)
We could perhaps modify the theory, thinking of the mechanics of research. Progress is made by an individual in the niches where others have not managed yet. Therefore the advantage in geometry for a blind mathematician may be in a different mental model of spaces.

It is not surprising at all that almost all blind mathematicians are geometers. The spatial intuition that sighted people have is based on the image of the world that is projected on their retinas; thus it is a two (and not three) dimensional image that is analysed in the brain of a sighted person. A blind person’s spatial intuition on the other hand, is primarily the result of tile and operational experience. It is also deeper – in the literal as well as the metaphorical sense. […]

recent biomathematical studies have shown that the deepest mathematical structures, such as topological structures, are innate, whereas finer structures, such as linear structures are acquired. Thus, at first, the blind person who regains his sight does not distinguish a square from a circle: He only sees their topological equivalence. In contrast, he immediately sees that a torus is not a sphere […]

This is a quote from a book by Alexei Sossinsky, quoted here: https://onionesquereality.wordpress.com/2011/07/31/blind-geo...

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by phaemon on Friday April 17, 2020 @02:54PM (#22901787)
Ah! That's where I read it! Thanks, I read that book a year ago and couldn't remember where I'd heard that factoid.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by used_noise on Friday April 17, 2020 @09:45AM (#22898915)
I'm not convinced that blind mathematicians count as their own species, nor that they echolocate, and so it doesn't seem to say much about his theory one way or the other.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by red75prime on Saturday April 18, 2020 @09:56AM (#22907747)
Humans can learn/be taught echolocation. https://en.wikipedia.org/wiki/Human_echolocation
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by Koshkin on Friday April 17, 2020 @04:22PM (#22902609)
> nor that they echolocate

How can you be sure?

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by SkyBelow on Friday April 17, 2020 @02:19PM (#22901475)
Assuming a species is intelligent enough to discover math, if they have some significantly different way of experiencing the world I think they would take a different path but would eventually reach the same destination we are heading towards, likely merging with us by the point we are at now.

I could see the layman understanding of geometry being quite different than ours, limited by their own visual system. But their mathematicians and our mathematicians would discover the same math, through different paths and perhaps with different strengths and weaknesses and a different path of educating budding mathematicians from the grade school level to the post doc level.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by Phenomenit on Friday April 17, 2020 @06:17AM (#22897703)
I've always figured it's our visions ability to perceive wholes, one of something. A clear conceptual border between two entities.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by hliyan on Friday April 17, 2020 @06:29AM (#22897764)
Yes, but it's possible to perceive distict objects without vision, except the separation is in time, rather than space. Or, depends on the number of sense organs available (e.g. a blind person can sense two different objects simultaneously by holding one in each hand).
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by Phenomenit on Friday April 17, 2020 @12:58PM (#22900724)
Agreed, I wonder if the same amount of abstract concept would be possible though, can you feel a graph? could you do trigonometry with just hearing and sense of touch?
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by pm321 on Saturday April 18, 2020 @01:29AM (#22905546)
"could you do trigonometry with just hearing and sense of touch?"

Can you get data on this from a Monte Carlo method of study on match play between sighted and blind players playing go and chess at distance and blind which requires a mental model of the board state and translations?

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by henrik_w on Friday April 17, 2020 @09:52AM (#22898970)
I really liked this perspective from Bartosz Milewski in this (very good) podcast episode: mathematics is not inherent to the world, it is inherent to the human brain (paraphrased, around minute 32 in the episode)

https://corecursive.com/035-bartosz-milewski-category-theory...

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by StandardFuture on Friday April 17, 2020 @10:27AM (#22899231)
And really one of the biggest pieces of proof of this is that some of the earliest mathematics developed was planar geometry.

But, planar geometry (primarily involving triangles and squares) does not actually exist in nature. Which means that planar geometry is an approximation technique developed by the brain in order to begin to understand the actual much more complex geometries that appear in the real world.

This also suggests that mathematics is 100% constructed by the human brain, even if it is highly-influenced by relationships found in the physical world.

But, this makes sense because we really don't ask the same question about human language. We almost never ask: is human language constructed or discovered?

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by DeathArrow on Friday April 17, 2020 @11:45AM (#22900018)
>This also suggests that mathematics is 100% constructed by the human brain, even if it is highly-influenced by relationships found in the physical world.

As I see it, mathematics is both discovered and invented.

We can model every existing thing in every possible world using math. Even if both the set of all things that might exist and all possible mathematical constructions are infinite, the later is larger. That's because we can also construct mathematical models of things that doesn't exist.

So it looks that from the set of all possible mathematical constructions, we extracted a subset that maps to objects in reality. That looks like a discovery process.

But we also constructed mathematical models of things that don't have corespondents in reality, so that much be more of an invention process.

Let's pretend for a bit that we forget all what we know and tomorrow we will start inventing things again. Or that a species of aliens start fresh on a planet.

The mathematic theories and notions we and the aliens might discover, build or invent might be different than the theories and notions we know today but would probably be equivalent. That suggests that mathematics just exists somewhere in its own world waiting to be discovered.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by hliyan on Friday April 17, 2020 @08:25PM (#22904275)
I too, subscribe to this view. In my mind, reality is nothing more than a vast integer variable field with interactions between some variables. All our mental models, from vision to math are attempts at approximating that complexity down to a level that our brain's limited processing capacity can handle...

Why integers one might ask. For me, even rational numbers are such an approximation.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by david_w on Friday April 17, 2020 @10:38AM (#22899319)
This. It is discovered in the same sense that humans "discover" facts about humans via science- we're not born with perfect self-knowledge.

It is "created" because there is no guarantee that our efforts correspond to reality. In that sense we are just playing in the sandbox of what we can conceive.

The fact that mathematics corresponds so "unreasonably" to objective reality is because what we call objective reality is mediated by our brain's own idiosyncrasies and limitations of thinking.

It's no more surprising that external objective reality is mathematically predictable and describable than it is that our eyes can see shapes and some, but not all, light. That's the purpose of eyes and they tell us enough of what we need to know that we can survive.

Our brains are exactly the same thing- they tell us a story in a way which helps us to survive. Actual reality may be beyond our capacity to conceive of or worse, may seem like nonsense to us because it's aggressively illogical or specifically contradictory and reality therefore makes no "sense" to us.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by SkyBelow on Friday April 17, 2020 @02:23PM (#22901517)
>It is "created" because there is no guarantee that our efforts correspond to reality. In that sense we are just playing in the sandbox of what we can conceive.

But doesn't this dance kinda near the notion that I am a brain in a vat and none of you exist (read this question with me as the speaker or with yourself as the speaker)?

I would say our brains do have limits. I can't well envision a 4D object. But once we reduce things down to simple logical axioms and constructs, these exist as much as anything can be said to exist. Even if I was a simulation that didn't even have a brain, much less eyes, the concepts I come up with would exist more than the flesh I incorrectly thought I had.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by david_w on Saturday April 18, 2020 @12:04PM (#22908611)
>>But once we reduce things down to simple logical axioms and constructs, these exist as much as anything can be said to exist.

I agree.

But this assumes logic and at least the principle of non-contradiction: not both A and not A - is how reality "really" is.

We can't get past the idea that it must be this way because only provable nonsense lies on the other side of this assumption. But our brains may be fundamentally unable to process ultimate reality and the nonsense a contradiction represents may be a statement not about reality but our brains, our thinking.

So logical contradictions aren't actually nonsense, they're the sound of us hitting the walls of what our minds can conceive of. All animal have such limits. We assume those limits look like darkness- stuff we can't peer into. What if they look like impossibility instead?

That's the point of view I'm entertaining here. I am not saying this is true. It certainly isn't useful or provable as far as I know, but it is possible.

The practical value of such an exercise, if it has any (and I think it does) is to twofold.

One seems to expand my imagination to the maximum extent pops me out of the assumptions that frame my thinking and this seeps into my thinking about things, technical problems, generally.

Two it confers humility and a certain openess and makes me less judgmental. So that, for example, when I hear or read people with claims to spiritual knowledge I don't automatically blow them off as crazy / bitter / ignorant because what they're saying "makes no sense".

Thinking and talking about Ultimate Reality capital U capital R, ought to fill us all with humility if we're being intellectually honest by our own standards. Yet, I find people totally lack that humility. They make huge pronouncements about Ultimate Reality which they can't really be sure of, and the effect this has on the world, and how we think of each other, and therefore how we treat each other, and even the effect on one's own mind, is one of diminishment generally.

Mea culpa, I was one of those people and I didn't like it.

If you get down to the core of knowledge and how we know something, this is what's really there, and it's good to be reminded of it.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by jbotz on Friday April 17, 2020 @06:33AM (#22897792)
"two of our own species [discovered calculus]"..? Which two species are those? I assume by "own own" you mean Terran species, and one of them is Homo Sapiens, which is the other one? Really curious...
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by red75prime on Friday April 17, 2020 @06:48AM (#22897871)
Leibniz and Newton. Two [members] of our own species.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by sunstone on Friday April 17, 2020 @09:23AM (#22898749)
And Archimedes makes three.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by satori99 on Saturday April 18, 2020 @09:16AM (#22907494)
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by jerf on Friday April 17, 2020 @04:02PM (#22902440)
Probably Homo Econimus. If Homo Econimus is good at one thing, it's math, to the exclusion of pretty much everything else.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by bregma on Friday April 17, 2020 @02:57PM (#22901813)
Take your stinking paws off me you damn dirty ape!
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by lazyant on Friday April 17, 2020 @01:27PM (#22901041)
Not exactly the same but 2-dimensional beings on a curved surface can discover the 3rd dimension using math, we did this proof in a differential geometry class.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by Koshkin on Friday April 17, 2020 @04:26PM (#22902640)
I think you may be talking about the curvature of the surface (the Riemann tensor). It is intrinsic, i.e. does not depend on the notion of the surface being embedded into a higher-dimensional space.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by lavp on Friday April 17, 2020 @01:30PM (#22901077)
I would love to see a proof of it if you happen to have it!
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by lazyant on Friday April 17, 2020 @01:41PM (#22901166)
https://fsw01.bcc.cuny.edu/luis.fernandez01/web/texts/dgcs.p...

Ctrl-F for "2D" (2-dimensional creatures), although I can't find the "discovery", maybe I remember it wrong.

Btw, this was one of the mindfucks I learned studying physics. Other ones are:

  - dimensional analysis: checking if formulas can be wrong, and more importantly, finding formulas (eg, period of a pendulum) just by analyzing units that can be involved (no constants obv)  
  - similarly, rate of growths in dimensions: why giants can't exist (bone resistance is proportional to section area and load (weight) is proportional to volume  
  - Conservation laws derive easily from symmetries (energy from invariance in time, momentum from invariance in direction etc)
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by lavp on Friday April 17, 2020 @02:03PM (#22901347)
This is brilliant, thank you!
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by Kaiyou on Friday April 17, 2020 @06:08AM (#22897662)
Combining the words "most" and "species" feels a little bit silly. Among all the millions of species on this planet only humans have displayed the intelligence necessary to contemplate any of this.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by foldr on Friday April 17, 2020 @11:02AM (#22899559)
That's only true if you limit this to conscious thought. Lots of organisms perform impressively complex calculations. The desert ant odometer is one classic example:

https://jeb.biologists.org/content/210/2/198

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by ableal on Friday April 17, 2020 @10:55AM (#22899476)
> on this planet

Location was not specified ...

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by tartoran on Friday April 17, 2020 @03:43AM (#22897026)
From the wikipedia source: In the philosophy of mathematics, intuitionism, or neointuitionism (opposed to preintuitionism), is an approach where mathematics is considered to be purely the result of the constructive mental activity of humans rather than the discovery of fundamental principles claimed to exist in an objective reality. That is, logic and mathematics are not considered analytic activities wherein deep properties of objective reality are revealed and applied but are instead considered the application of internally consistent methods used to realize more complex mental constructs, regardless of their possible independent existence in an objective reality.

And Im wodering why Im not looking more into the philosophy of math, i find this interesting because I am mainly an intuition driven person. Any ideas for courses online?

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by dnautics on Friday April 17, 2020 @04:06AM (#22897118)
The mathematical definition of intuition is not the colloquial definition. For example, in intuitionistic mathematics, you can't proof by contradiction, which means that some things that are "intuitively true" in the colloquial sense, are inaccessible.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by peterburkimsher on Friday April 17, 2020 @06:34AM (#22897795)
Tell me more about the difference between "potential infinity" and "actual infinity".

Recursive functions in computer programming, or fractals in maths, are infinite but can be described. Each small part looks like the whole, but the whole can never be fully known within a finite universe. Is that "potential" or "actual" infinity?

I've been thinking a lot about infinity this past week, mostly because of Conway's lectures. I'm trying to figure out whether the following logic makes sense.

- Assuming that the universe is finite -> Infinity cannot be approximated with finite numbers (MIP* = RE) [1] -> Numbers cannot have infinite strings of digits -> The future can never be perfectly preordained (Gisin) [2] -> Free will exists (Conway) [3]

This is not a proof that free will exists! But I think this is a consistency proof that free will is finite.

Now you're telling me that there's another kind of infinity, and I want to know what that means for this thought.

[1] https://www.quantamagazine.org/landmark-computer-science-pro...

[2] https://www.quantamagazine.org/does-time-really-flow-new-clu...

[3] https://www.youtube.com/watch?v=tmx2tpcdKZY&feature=youtu.be...

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by TheOtherHobbes on Friday April 17, 2020 @09:32AM (#22898824)
Free will is a philosophical concept which is essentially dualist. It's an attempt to reconcile two subjective experiences - the feeling of making a decision, and the fact that sometimes we can't predict the actions of others - with universal determinism.

There's no reason why universal determinism and free will need to be related. So trying to "prove" free will with math makes as much sense as "proving" free will with weather forecasting.

Even if that weren't true you still can't get to Conway's Step 3, because "free will" could just be statistical noise, and not willed in any sense at all.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by coldtea on Friday April 17, 2020 @09:51AM (#22898960)
>Free will is a philosophical concept which is essentially dualist.

Is it though? I came to the conclusion that one could consider free will the self-realization of a person in space-time -- in other words, free will is the only and only choice one can make (at each decision they face), that they make because of who they are thus far.

In that sense, "free will" is the same as the "person" (or the person's essense) -- and would it make sense for it to be any other way? Randomness wouldn't be free will, and having a second entity (e.g. a soul in dualism) do the decision making just moves the question and degree upwards (from "how the person has free will?" to "how the person's soul has free will?")

If a person faced with a choice A or B could go either way, then I wouldn't call that really free will (even though for some reason that's what most people have in mind when talking about the subject).

Either a person is a concrete personality/being and that manifests through its choices (which means that when faced with the A or B dillema they can only chose one or the other based on who they are), or they have some degree of randomness in their decision making (which makes them less of a person in my eyes -- randomness is not tied to our person, it is, as the name reveals, random).

When some people say "free will" they actually mean "free (independent) from the person". But that's not a will then -- a will denotes something being tied to a person (a person is their will).

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by naasking on Friday April 17, 2020 @11:12AM (#22899686)
> Free will is a philosophical concept which is essentially dualist.

It's not, although many people think this. Consider that the majority of philosophers are actually Compatibilists, in which free will is compatible with determinism, and so they would disagree with your definition. If the majority of practicing experts disagrees with your view on their subject, it's probably time to revise your view.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by throwaway17_17 on Friday April 17, 2020 @11:51AM (#22900076)
First, I would take strong issue at your describing the majority of philosophers as Compatiblists. I can find no support for such a broad statement. Also, one of the primary criticisms of Compatiblism, dating back as early as Kant, is that what Compatibilists define as ‘free will’ is not free will as most people, including philosophers understand it. Pulling a quick quote, the Compatibilist position can typically expressed by the following:

Arthur Schopenhauer famously said, "Man can do what he wills but he cannot will what he wills." In other words, although an agent may often be free to act according to a motive, the nature of that motive is determined.

This position that the ‘free will’ people experience is the ability to ‘decide’ to take some and then take it, while then saying the the decision to do so was predetermined, is not what is meant (especially in the vernacular) by free will.

Therefore, while I will not support a metaphysical dualist basis for ‘free will’ it is clearly incorrect to dismiss an argument of such based on 1) an appeal to authority which is unsupportable (in that your claim about the position of a majority of ‘experts’ seems unsupported), and 2) that even if it was supported, that said appeal to authority is a valid refutation of an argument. Further, dismissal of an argument by choosing to substitute a contested definitional term (the meaning of free will) for one that is clearly not the same is not rhetorically valid.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by naasking on Friday April 17, 2020 @12:56PM (#22900700)
> First, I would take strong issue at your describing the majority of philosophers as Compatiblists. I can find no support for such a broad statement

Almost 60% Compatibilist, the remainder evenly split among three other options: https://philpapers.org/surveys/results.pl

> Arthur Schopenhauer famously said, "Man can do what he wills but he cannot will what he wills." In other words, although an agent may often be free to act according to a motive, the nature of that motive is determined.

You're assuming this is relevant. Turns out, it's not.

> Also, one of the primary criticisms of Compatiblism, dating back as early as Kant, is that what Compatibilists define as ‘free will’ is not free will as most people, including philosophers understand it.

Nobody definitively understands free will. Some people conjecture it has certain properties, mainly incompatibilists. So far they have mostly been wrong.

> This position that the ‘free will’ people experience is the ability to ‘decide’ to take some and then take it, while then saying the the decision to do so was predetermined, is not what is meant (especially in the vernacular) by free will.

Experimental philosohy suggests pretty definitively that people's moral reasoning agrees with Compatibilism: https://www.researchgate.net/publication/274892120_Why_Compa...

> that even if it was supported, that said appeal to authority is a valid refutation of an argument.

The other poster provided no argument, they just made an unsupported claim.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by otabdeveloper4 on Friday April 17, 2020 @10:00AM (#22899020)
You're conflating different kinds of randomness here.

A coin flip and a hand of cards are both random, but obviously cards are 'more random'.

This can be quantified - 'more random' is information complexity, or information entropy. (Two names for the same thing.)

If free will exists, then it must necessarily be a singularity of infinite information complexity, which is the same thing as a singularity of infinite randomness.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by gowld on Friday April 17, 2020 @09:01AM (#22898583)
The video timestamp you linked does not say "free will exists". Is says "humans has free will implies element particles have free will".
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by peterburkimsher on Friday April 17, 2020 @03:09PM (#22901959)
His definition of free will is quite limited. He only suggests that free will is limited to a "free" choice between options within one's power.

Conway said that there either is determinism or free will. If the future can be perfectly preordained (Gisin) due to infinite possibilities, then there is no free will. But if there are finite options, I think that there is "free will" for particles and people to choose between those options.

https://youtu.be/tmx2tpcdKZY?t=1074

https://en.wikipedia.org/wiki/Free_will_theorem

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by ShamelessC on Friday April 17, 2020 @11:46PM (#22905161)
While there is technically no proof, there is a lot of evidence that the universe is infinite. In particular it's curvature is flat within the margin of measurement error which implies an infinite universe outside the observable universe.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by Koshkin on Friday April 17, 2020 @04:36PM (#22902730)
"Actual infinity" is merely an abstraction, not unlike many others. It is very useful. Abstract thinking is part of what separates humans from (other) animals.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by miscPerson on Friday April 17, 2020 @09:42AM (#22898899)
Potential infinities are just saying, you don’t have an infinity in your hand — you just have a recipe for arbitrarily large numbers (or arbitrary accuracy on real numbers, etc).

Eg, the “natural numbers” are a recipe to make as many as you want (by taking the successor of the last one) but not an actual (as in existing) infinite collection — the only ones which exist are the ones you construct, and the “potential infinity” refers to the fact that you can always make a new one.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by mikorym on Friday April 17, 2020 @04:11AM (#22897144)
The reason why intuitionist mathematics is useful in QM is because it can be viewed as resource based logic.

But remember that (as far as I know) you can do intuitionist mathematics in classical mathematics, but not the other way around. So you can think of intuitionist mathematics as being embedded in classical mathematics.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by h-cobordism on Friday April 17, 2020 @04:20AM (#22897178)
I think in your first paragraph you're confusing intuitionistic logic and linear logic --- intuitionistic logic still lets you "clone" and "delete" propositions freely.

The second paragraph is somewhat true --- at its base, the modern use of the term "intuitionistic logic" refers merely to not accepting the law of the excluded middle. However, there are varieties of intuitionism that are very, very inconsistent with classical logic, like those adopting the idea that "every function between real numbers is continuous".

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by mikorym on Friday April 17, 2020 @08:41AM (#22898464)
When you separate internal and external logic, for example in topos theory, the external logic is still classical.

For example, any topos has internal logic on subobjects of at least a Heyting algebra. In some cases you specialise to a Boolean algebra.

However, when you write things down such as your arguments around functors and constructions, you argue according to classical mathematics externally. When you enter into the category (which is chosen not to be Boolean) and argue on the subobject structure, then you are entering intuitionistic logic. This is what I mean when I say that classical logic can be argued to have intuitionistic logic embedded in it.

The cardinality of the reals being equal to the cardinality of the naturals is then something you have to construct inside the topos. So you need to construct along the spirit of a natural numbers object (perhaps a real numbers object) and then use the internal logic to argue about continuity.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by mikorym on Friday April 17, 2020 @08:46AM (#22898497)
I think you are right about the comment about linear logic. I must be confusing A U A with A U ^A.

I checked the paper that I was thinking about and the condition that I saw there is distributivity being dropped rather than double negation being dropped.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by cwzwarich on Friday April 17, 2020 @12:42PM (#22900530)
> But remember that (as far as I know) you can do intuitionist mathematics in classical mathematics, but not the other way around.

There are a number of embeddings of classical logic into intuitionistic logic. The most popular/obvious is the double-negation embedding that maps a proposition to its double negation.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by mikorym on Friday April 17, 2020 @12:47PM (#22900590)
You shouldn't be mapping propositions, you should be mapping theories. See my comment below on the internal logic of a topos.

What you are referring to as a proposition is an element of the Heyting algebra or the Boolean algebra.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by cwzwarich on Friday April 17, 2020 @12:53PM (#22900666)
Why do you think the same thing doesn't apply to theories? Since you mention topos theory, the double-negation topology is actually a basic construction in topos theory, used to construct a dense Boolean subtopos of a given topos.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by mikorym on Saturday April 18, 2020 @01:48PM (#22909537)
You can always generate substructures with closure properties. The subobject structure comes from all the subobjects—so it is the default logic of the topos. Of course you can do the same thing here as you mentioned since it is a Heyting algebra at the least.

My point is something else: I don't know of a way to have a intuitionistic exterior logic and a classical internal logic.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by analbumcover on Friday April 17, 2020 @09:43AM (#22898900)
It's the other way around, classical logic is a restriction of intuitionistic logic that arises when you affirm the Law of Excluded Middle.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by ironSkillet on Friday April 17, 2020 @10:06AM (#22899052)
I think you're both right in a certain sense. The set of provable statements in intuitionist logic is a subset of what is provable in classical logic, which is what I believe the parent was referring to.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by analbumcover on Friday April 17, 2020 @11:14AM (#22899713)
You're certainly right that any constructively provable statement is classically provable, that follows from intuitionism/constructivism generalizing classical logic. But I don't see how we could interpret the following to mean that.

> you can do intuitionist mathematics in classical mathematics

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by hyw on Friday April 17, 2020 @03:43AM (#22897025)
> Applying intuitionist mathematics to physics we can come to the conclusion that time flows

Can you expound on this a little more? I'm completely new to the idea of intuitionistic mathematics and much more so to its applications in physics; the constructive approach to thinking about objects and properties is very refreshing and I'd like to hear how you've related those principles with the paradox of time in the context of classical physics.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by DeathArrow on Friday April 17, 2020 @04:10AM (#22897133)
>Can you expound on this a little more?

Unfortunately no. I got the info from Quanta Magazine article. I am not knowledgeable enough to respond on this. Even though I did some high level math courses in University, I wasn't interested enough.

I am sure other HN users understand this stuff better.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by naasking on Friday April 17, 2020 @11:04AM (#22899578)
> Intuitionist mathematics claims that mathematics is purely the result of the constructive mental activity of humans rather than the discovery of fundamental principles existing in an objective reality. [0]

The "mental activity" part isn't strictly necessary. A constructive mathematics will produce results that are largely the same. What matters most is that mathematical objects are proven by construction, and so proofs have a direct translation to computation.

Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by maxiepoo on Friday April 17, 2020 @11:47AM (#22900043)
I think you and OP are talking about different things because the term "intuitionist" has been used for both the philosophy that EJ Brouwer espoused (which matches what OP said) and the large field of constructive mathematics that has been greatly influenced by Brouwer's philosophy but has embraced approaches like formal logic which Brouwer himself disliked.
Re:Roger Penrose – Is Mathematics Invented or Discovered? [v... by naasking on Friday April 17, 2020 @12:57PM (#22900718)
I was merely pointing out that the "mental" dependency of intuitionism isn't strictly necessary. Take it out, and you're left with an equally valid constructive logic.