Comments

  • Fall of Man Paradox
    It probably doesn't make sense to roll an infinite sided dice in the first placeflannel jesus

    Why not? In a recent post to Javra, I described an object of finite size with infinite sides that could function as a die. Adam could certainly hold it in his hand. We would just need to trust God to ensure its fairness. Just to clarify, I'm not aiming for a religious debate here. I mention God in the story simply because it seems to me that objects with infinite properties could only exist within a supernatural realm.
  • Fall of Man Paradox
    The limitation of possible representation is still an issue here; there must be a finite maximum magnitude for the game. Infinity cannot be a stipulation.Nils Loc

    Do you believe that the set of all natural numbers exists? Is it reasonable to stipulate its existence? If infinite sets can exist in some realm, why can infinite dice not exist in God's realm?

    You could fix the problem with doing away the limit of natural numbers and including the negative integers to infinity.Nils Loc

    Addressing a problem by focusing on a completely different issue is like sweeping the original problem under the rug.

    Maybe it's undefined for the natural numbers also.Nils Loc

    But at what point does the math fail? The calculations don't seem to get much simpler.
  • Fall of Man Paradox
    Just as a polygon with infinite sides of equal length would be empirically indiscernible form a perfect circle—this irrespective of how close one observes it, say with a quantum microscope—so too would a die with infinite sides of equal length be empirically indiscernible from a perfect sphere, even when analyzed with a quantum microscope.javra

    Your argument merely skims the surface, focusing only on the impossibility of the story occurring in our physical world. Let's remember, this is a die created by God, and the story takes place in the Garden of Eden, where ordinary physical laws don't hold. Nonetheless, I'll engage with your point since you're considering mine.

    The die doesn't have to be polyhedral; it simply needs to be fair. Imagine a line segmented as follows: the first half represents roll 1, the first half of the remaining line represents roll 2, the first half of what's left represents roll 3, and so forth.

    wnsE6sU.png

    If we roll this line into a faceted arc, we achieve an object with infinite sides. All that's left is a little divine magic to ensure it rolls fairly, and extraordinary vision for the players to discern the minuscule markings on those higher rolls.
  • Fall of Man Paradox
    There would be no way to read the numbers because any of them could appear to be unlimited and by the physical limitations of the universe would therefore be impossible.Nils Loc

    I concur that this narrative couldn't unfold in our physical reality, but your argument doesn’t address the core of the paradox. The inclusion of God and the Garden of Eden in the story was specifically to lift us beyond our finite limitations.
  • Fall of Man Paradox
    "Infinite" is not a number as an amount of sides but is that which cannot be gotten to since it never completes, but to play along, the die is ever becoming more of a higher and higher resolution smoother sphere.PoeticUniverse

    No, the die in the story remains unchanging and complete with a side for every natural number. This distinction matters because the potentially infinite die you describe doesn't concern me.
  • Unexpected Hanging Sequel
    It gives your paradox a much easier angle of angle of attack than the unexpected hanging has. You can point out the error in the formulation. That "an adjacent pair of real numbers" doesn't exist.fdrake

    Agreed, however, this is precisely why I find the sequel valuable. As I stated in my latest post to @flannel jesus, the sequel is not paradoxical because it's obvious that unobserved moments exist between any two instances, providing ample opportunity for surprise. Isn't it plausible that in the original paradox, a comparable scenario arises—between the states of being alive and deceased, there must exist unobserved moments. I understand this challenges our classical physics intuitions, but does it contradict our intuitions derived from quantum physics?

    I also wouldn't like to call it a sequel to the unexpected hanging because your riddle isn't (at least at face value) anything to do with induction (the mathematical reasoning concept) or self reference.fdrake

    In this paradox, the details of the prisoner's punishment don't explicitly involve induction or self-reference. In the sequel, I offer a perspective in which the conditions of the initial sentence remain entirely logical. Through this lens, both induction and self-reference become redundant. These elements only emerge through the prisoner's flawed reasoning, rooted in classical physics. Therefore, it isn't the sentence itself that's paradoxical, but rather the prisoner's interpretation of it.

    So you can't detect the exact points a step change in a function ([0,1]->red,green) would occur by putting in any countable list - at least your guesses have probability 0 of being right if God's not been too human about it.fdrake

    I believe there's a misunderstanding of my point. It's not enough for the prisoner to identify the initial moment when the light turns green. They must also pinpoint the final moment it was red. This step is crucial to confirm that the moment they observed was truly the first instance of the light turning green. Therefore, it's not about the prisoner's probability of finding a solution being zero; it's that a solution does not exist at all.

    In that respect the kind of ambiguities in the framing are already solved problems, and it's a riddle about something completely different from the unexpected hanging.fdrake

    The main goal of the sequel is to offer a resolution to the original paradox, so I find myself at odds with that assertion. Essentially, the sequel's lack of paradox stems from the inability to witness every moment. My argument is that the initial paradox, much like the sequel, can be addressed by accepting the impossibility of observing every day. If one reviews the records and notes that the prisoner was alive on Monday but deceased by Wednesday, then choosing not to examine Tuesday's footage maintains the ambiguity of the exact time of death. On the other hand, if one decides to view Tuesday's footage and discovers the prisoner was already deceased, the only way to sidestep a paradox would be to alter the historical record, thereby erasing the observation from Monday. This means, in the revised history, the prisoner's death could have occurred on the now unwatched Monday or the scrutinized Tuesday. While this notion may seem far-fetched, it mirrors occurrences in the quantum realm: https://en.m.wikipedia.org/wiki/Delayed-choice_quantum_eraser.
  • Unexpected Hanging Sequel
    Well, I don't think the "paradox" even makes sense here. If he manages to find a moment when the guillotine is going through his neck (different example), the light should shine green.Lionino

    Yes, but he will never be certain that that moment is the first moment the guillotine is going through his neck.

    Besides, it is not a paradox.Lionino

    I agree that there's nothing paradoxical about the sequel, but that's my point. I'm trying to present a perspective (an eternalist view) from which the original paradox is not paradoxical. I explained my view further in my last message to flannel jesus.
  • Unexpected Hanging Sequel
    I think you're wrong to call it a sequel to the hanging paradox. It's conceptually nothing like the hanging paradox, other than the fact that both word problems both involve a hanging - which is just a superficial similarity. Conceptually it has more in common with zenos paradox of motion, which also has to do with problems of infinites and infinitely divisible units.flannel jesus

    While I concur that this sequel shares conceptual similarities with Zeno's paradox, I diverge in the assessment that its resemblance to the hanging paradox is merely superficial. My contention is that unless the hanging paradox is approached from an eternalist perspective, a satisfactory resolution remains elusive.

    In this sequel, the essence of surprise persists because nestled between any two real numbers exists another number—indeed, an infinite multitude of them. This signifies that amidst any observed moments lies a realm of unobserved moments wherein change could have transpired.

    Dissimilar to the sequel's continuum of infinite points awaiting measurement, the original paradox comprises only five discrete points—Monday through Friday. From my eternalist standpoint, not all five of these points can be directly observed. While we ascertain his vitality on Sunday and his demise the ensuing Saturday, I posit that a fundamental limitation exists in our ability to fully witness all five points in the recording. An inherent barrier prohibits us from directly observing every point between his state of vitality and his demise, thus preserving the element of surprise.

    My central contention is that change transpires when our gaze is averted. Indeed, such is the essence of reality's behavior (https://en.wikipedia.org/wiki/Quantum_Zeno_effect).
  • Unexpected Hanging Sequel
    Hold on a second! What is a "pair of adjacent real numbers"?Pierre-Normand

    That's why I called it a hopeless task.

    Consider also that most statements of the paradox have the prisoner ignorant of the day on which they will be hung. The days are discrete and hence don't span a continuum.Pierre-Normand

    Yeah, this is a fair point. But then again, I'm presenting it as a sequel, not a remake of the original.
  • Real numbers and the Stern-Brocot tree
    I didn't say that I'll only consider formalizations. I have been interested in the earlier proposals though not formalized. Rather, I said that I'm not inclined now to study your latest revisions.TonesInDeepFreeze

    Fair enough.

    Somehow, I don't believe you. To formalize you'd have to know what formalization IS. Be honest: Learning what goes into an axiomatic formulation is not a goal for you.TonesInDeepFreeze

    Formalization is the way for an idea to be treated seriously. Learning how to get there would require a huge investment of time and money. If the idea seems very promising and my finances were just right I would pursue it. Let's not debate my motivations.

    So, hopefully, you understand now that there's no "cake and eating it too" about the S-B tree and Cauchy sequences in set theory, or generally in set theory having both finite algorithms and infinite sets.TonesInDeepFreeze

    If ZFC is consistent then there's no cake and eating it too.

    No, set theory shows how the paradoxes with the naive notion of sets are avoided.TonesInDeepFreeze

    We've been down this road already.

    Set theory is quite intuitive to me. I listed the axioms for you. I find each of them to be eminently intuitive.TonesInDeepFreeze

    Given that everything fits nicely together for you and in your view the paradoxes are addressed, I can see how you're not motivated to pursue a potential infinity solution.

    -----------------

    Let's leave it at that. Thanks again!
  • Real numbers and the Stern-Brocot tree
    Then you added more apparatus that doesn't seem to me to improve the more basic and original goal that was not being addressed. Then you went further about "higher dimensions". I'm not sufficiently interested in whatever that's about to invest time and energy on it, while instead my curiosity is with the original questions of defining ordering and the operations.TonesInDeepFreeze

    Going to higher dimensions helps explain my position and would more clearly demonstrate why 'more apparatus' improves my position. But yes, it would take time to try and understand what I'm saying and time is limited. You're right, I've taken this discussion beyond the original question and it is reasonable for you to not want to come along with me. You've already been generous with your time. Thanks.

    So while the mathematician is still in the pre-formalized stage, deepening and extending the intuitions, she is putting herself into a kind of "intellectual debt". That is, the mathematician eventually is going to have to "pay" for the intuitive commitments with the hard cash of formalizing them.TonesInDeepFreeze

    I agree. I suppose as this conversation evolved I wanted to bounce my pre-formalized idea off of someone to see whether it was worth me investing in formalizing it. Although I'm disappointed, I acknowledge that it is reasonable for you to not want to discuss it until it is formalized.

    So, in set theory, there is both the tree that doesn't have a final row or "row infinity" and the continuum. This is not having our cake and eating it too. Whatever we have comes from proofs from the axioms. The axioms are productive enough to proof the existence of many things including: the continuum, the S-B tree, finite algorithms, etc.TonesInDeepFreeze

    Yes, the proofs come from the axiom and unless I can prove the axioms to be inconsistent there's no point discussing my musing.

    You are in an intuition stage. If you ever followed through to write some mathematics, then you would confront the debt you're accumulating and pay it off with rigorous formulations. But, in the meantime, one still needs discipline to not just mouth a bunch of incoherent mental picture stories. Even with intuitions, one would like not to commit to informal contradictions (unless one wants to base the proposal in a paraconsistent logic). Which is to say, crankery is a dead end.TonesInDeepFreeze

    I agree with the first sentence. I also agree that many times I have not been clear. While I would have deeply appreciated you trying to truly understand what I'm trying to say, I fully acknowledge that it is reasonable for you to not want to invest the time into it.

    You seem to have a notion that we have to distinguish numbers. No, every object is a set.TonesInDeepFreeze

    I think I understand what you're saying. Start with a small set of axioms and everything else follows. Numbers follow. Points follow. You do not want to discuss this on an intuitive level and want to stick with formalities. This is not how one would explain what should be a simple concept to a grade schooler but that's fine if that's how you want to approach it. And I think that's how you have to approach it because when discussing the standard position on an intuitive level many paradoxes arise. The standard position doesn't gel with our intuitions and so we must stick with the formalization. But you and I have been down this road before.

    I don't know the purpose of this exercise.TonesInDeepFreeze

    If you are not willing to discuss basics on an intuitive level then there is no purpose of this exercise.

    ----------------------------

    All in all, it's clear that we want to have different discussions. You want to talk in terms of formalities and I want to talk in terms of intuitions. Neither of us are able to talk on the other person's level. While I'm extremely disappointed that this conversation has come to an end, I once again want to thank you for your time and insights. As I mentioned before, I've gotten great value from this discussion. Thank you.
  • Real numbers and the Stern-Brocot tree
    So what? Lots of things use similar language, but say RADICALLY different things.TonesInDeepFreeze

    Okay, fine. It's significantly different. I suppose I'm coming from the applied side of mathematics and I don't see how my view changes anything in my day to day computations. But yes, if a mathematician were to go from a system based on actual infinities to one based on potential infinites there will be significant differences in the formalization. I should not understate this.

    Okay, let me retrace my steps responding more thoroughly to some of your comments from your earlier post.

    A continuum requires that the ordering is complete, meaning that for every bounded set, there is a least upper bound.TonesInDeepFreeze

    A continuum defined by numbers requires that the ordering is complete. I'm not proposing this. I'm attacking this from the other direction - numbers defined by a continuum. The ordering of numbers in this system does not need to be complete.

    You don't get to incorrectly say what I'm willing to imagine. I don't even have notion of "points are fundamental", let alone that I won't imagine that it's not the case….
    Please don't make pronouncements about what I am willing to imagine.
    TonesInDeepFreeze

    Okay, I take back my comment. But let me ask this. Would you agree to either of the following?
    1) A continuum is defined completely by numbers.
    2) A line is made up entirely of points.
    I'm sure you will not agree to the exact phrasing, but perhaps you could say it in your words.

    Cauchy sequences have a limit. But if we somehow defined the limit of an algorithm, then that would be infinitisticTonesInDeepFreeze

    I don't think there's a need to define the limit of an algorithm.

    our use of 'line' is only a figure of speech. It's not a line. It has nothing on it; it's a placeholder only - as YOU said. It's not a line in the sense of geometry or analytic geometry.TonesInDeepFreeze

    In my response yesterday I wanted to show you that the k-line is not just a placeholder. By moving up a dimension, it becomes clear that even the uncut line holds a lot of information. For example, if you draw a plot including the k-lines y=1 and y=2, the y=2 line will be above the k-line y=1 even if they do not have any points on them.

    And at no output does the cutting remotely resemble the continuum. First, at every output, there are only finitely many cuts and thus only finitely many rationals described. Second, there are no irrationals described. That is VERY different from the continuum that has both rational reals and irrational reals and altogether not just finitely many, but uncountably many, and proving a continuum.TonesInDeepFreeze

    You keep coming back to this point, which comes from a very number-centric view. I agree that a number system based on rational numbers cannot be continuous. I am not proposing that. I'm proposing an algorithm (e.g. program-based, equation-based) system. The restrictions on number systems do not apply to algorithm systems.

    Your "line", the k-line, has NOTHING on it, as YOU said. So 'continuous' is not even applicable. And there is no infinite set of cuts on the k-line that comes after all the rows. You just now admitted that.TonesInDeepFreeze

    Over and over you repeat the same point, as if I'm not understanding you. I understand what you're saying. I just thought my last response most concisely addressed this point, but I'm responding here because I actually value your input and you think I skip over points. In my view the equation (line) is fundamental. In the standard view the number (point) is fundamental. I say start with an equation (line) and then create numbers (points). The standard view is to start with infinite numbers (points) and then create the equation (line). You are wrong to say that the k-line has nothing on it. It has an equation (algorithm). And I wanted to go up a dimension to demonstrate this.

    Length is the absolute value of a difference. Even without irrationals, we have length with just rationals. Uncountability is not required to define length. Sheesh!TonesInDeepFreeze

    True. But in higher dimensions what about arc length.

    But even if it worked out, calculus needs more than just lengths. It seems you don't know what calculus is. Do you?TonesInDeepFreeze

    In my post yesterday, I tried to demonstrate to you that my thinking extends beyond length to include, for example, area.

    You keep wanting to have both only finite objects but also objects that exist only as provided as an end of an infinite process, while refusing in different forms to recognize that there is no such end hence no such objects.TonesInDeepFreeze

    At one point I was arguing this, but now everything that I'm working with is finite. The k-line fits entirely on the page (and so does the higher dimensional plot), there is no infinite tree, I'm not waiting infinite time for the k-algorithm to spit something out. What objects are you referring to?

    We don't need the k-line. It is extraneous to capturing the information we want. We can just say a row is the set of cuts.

    We don't need cuts. They are extraneous to capturing the information we want. We can just mention the fractions and their ordering.

    I think the reason you want all that is to give the illusion that it amounts to a kind of pseudo-"continuum". But it doesn't. Essentially it's a big red herring. Toss out the red herring and simplify as I showed you, which is basically what you proposed yesterday.
    TonesInDeepFreeze

    It is impossible to formalize a number system that completely describes a continuum without actual infinity. Such a system would be dead on arrival. I truly appreciate you drafting out some ideas, but I don't think that's the right way to go. I don't think that my algorithmic/interval/line approach is a red herring. Rather, I see it as the only viable path a finitist can go to make sense of calculus.

    So when you say that you’re unwilling to go to higher dimensions because I haven’t worked out the first dimension what I’m hearing is that you’re unwilling to deal with functions because I haven’t worked out the number system. And what I’m trying to show you is that you have it backwards. The algorithms (e.g. functions) come first and the numbers follow. I’m building an algorithm system, not a number system. If you’d consider my last message you might understand this.

    So in sum, I am responding to your main points, I’m just not spelling it out.
  • Real numbers and the Stern-Brocot tree
    I was asking whether you understand the post, which includes the various aspects of its explanations. Knowing your answer would let me know how much communication is taking place here.TonesInDeepFreeze

    I suppose you would like me to paraphrase so you can judge my comprehension. Fair enough. Earlier on in the discussion, I incorrectly claimed that the S-B paths converged to a limit. But all that there is in the tree are nodes and paths. Each node corresponds to a rational number. You used sqrt(2) but let me use phi for simplicity since it is RRL. The nodes along the phi path are 1, 2, 3/2, 5/3, … But none of the nodes along the path are the limit, the limit in fact is an irrational number. In this sense, the rational numbers are incomplete because the limit of some sequences of rational numbers are not rational numbers themselves. So then you asked, what object on the tree does this limit correspond to? Such an object must be a part of the system for it to be complete. Reals do not have this problem. The limit of every sequence of real numbers is also a real number.

    One way to rephrase this is to say that in the rationals there are some bounded sets for which there is no least upper bound. Essentially what this means is that if I were to have a set of rational numbers as described by the red coloring, there are many upper bounds (in blue) but there is no least upper bound (member of blue) because the number that we need is sqrt(2), which is not a rational number. Again, reals do not have this problem. "Every non-empty subset of X with an upper bound has a least upper bound in X."

    Dedekind_cut-_square_root_of_two.png

    I think this may be an important point to you because you are stressing the importance of completeness to calculus. If in my view the number system is incomplete, how is it possible to have the continuum needed to do much of calculus?

    I get to say, "Phi is the limit", because set theory proves there IS such a limit. You do not, because your framework PRECLUDES that infinitistic limit.TonesInDeepFreeze

    I understand this. I wasn't challenging this. What I'm suggesting is that by starting with uncountably infinite objects (corresponding to real numbers) you are effectively starting with the 'bottom of the tree'. And that agreeing to the former and not the latter is wanting your cake and having it too. I do not challenge the fact that one can prove a lot of things using a system built on infinite sets.

    Of course, I'm sure you do not see set theory as starting from the bottom of the tree. And that's why I mused that maybe one day…
  • Real numbers and the Stern-Brocot tree
    @TonesInDeepFreeze

    To continue to clean up some of the language:
    • A point in the context of my view is a k-point
    • A line in the context of my view is a k-line
    • An interval in the context of my view is a k-interval
    • An algorithm which takes as input any natural number (corresponding to the row) and always outputs a k-interval (in finite time) is a k-algorithm
    • A function which takes as input rational number(s) and outputs rational number(s) is a k-function
    • A string of L's and R's (and underlines to represent repeats) is a k-string
    • A k-line which has no gaps is k-continuous.
    • ..and so on.

    Meanwhile, I've asked you three times now whether you understand this post:
    https://thephilosophyforum.com/discussion/comment/806060
    But you still say not a word about it.
    TonesInDeepFreeze

    Sorry, I thought I was answering this question indirectly but let me be more clear. The successive outputs of a k-algorithm do not converge to any object. Ever. The S-B algorithm does not terminate (or to someone who believes in actual infinity - there is no bottom of the S-B tree).

    Bringing in a concept of an initial object that is determined solely by -inf and +inf and then pseudo-intervals is extraneous.TonesInDeepFreeze

    The problem is that we've only been talking about numbers so far. The k-line becomes important when exploring higher dimensions. Consider the following k-functions:

    • y=3x^2+2
    • y=0
    • x=1
    • x=0

    These k-functions can be illustrated as k-lines as depicted in the k-graph below. Please do not concern yourself with the shape of these k-lines. All properties of these k-lines are invariant under any continuous deformation.

    jrjYNNj.png

    In this figure there are only four k-points: (0,0), (0,2), (1,5), and (1,0). Notice how these k-points emerge when the k-lines cut each other.

    The question is: What is the area between these k-lines?

    One can estimate the area by introducing more k-functions and using rectangles.
    HJqM5OZ.png

    So the area is approximately (5)(0.5)+(2.75)(0.5) = 3.875.
    I can continue adding more k-functions and summing the areas of smaller and smaller rectangles but this process will never be exhausted. I cannot provide an exact answer of the area between the four k-lines.

    However, because the above k-lines are k-continuous, I can using integration and provide you with the k-algorithm which can output a k-interval of arbitrarily narrow width. This k-algorithm can be described by the k-string RRRLR. Therefore the k-area between the k-lines is the k-string RRRLR.

    Of course, k-algorithms are just one type of algorithm. If people were to adopt my view I wouldn't expect them to transition to using the S-B algorithm. I could have used decimals to describe algorithms and the decimal which would describe the equivalent algorithm is 2.9.

    The reason why I say that my proposition is philosophical and not mathematical is because if you take away all of the k's you basically have standard calculus.

    Are my proposed algorithms that different from Cauchy sequences?
    — keystone
    Indeed they are! I EXPLAINED this.
    TonesInDeepFreeze

    I think it's a matter of perspective by what one means by 'that different'. What I believe though is that if this approach ever gets formalized it's going to use a lot of similar language as Cauchy sequences.

    Your use of 'line' is only a figure of speech. It's not a line. It has nothing on itTonesInDeepFreeze

    k-lines are associated with k-functions that describe their infinite potential.

    So what? It used infinitisitic methods. Set theory provided axioms to make those methods rigorously derived from axioms.TonesInDeepFreeze

    Maybe one day you will see set theory as the mathematics of the bottom of the S-B tree…the bottom which you (rightfully) claim doesn't exist. Perhaps it is you who wants to eat your cake and have it too.

    There is an algorithm, call it the 'k-S-B algorithm', that generates rows, starting with the base row, then to the next row that is row 0, ad infinitum. The k-S-B algorithm recursively exhausts all "turn decisions" of R and L.TonesInDeepFreeze

    No, I realized after contemplating about our debate on outputting something after an infinite loop that it wasn't necessary. k-algorithms only take natural numbers (corresponding to rows) as input and always output a k-interval in finite time.
  • Real numbers and the Stern-Brocot tree
    I really should not continue to reply when you so obnoxiously continue to apply the same fallacy, clothed differently, each time though I have explained it over and over and over and even asked you whether you understand, yet you don't reply even to that question itself.TonesInDeepFreeze

    I appreciate you continuing this discussion. I'm getting plenty of value out of this dialogue. I don't think your infinite loop programming example of me not listening was a fair representation as I believe I am learning (perhaps not fast enough).

    You STILL don't get it. You just keep putting new clothes on an old pig. Every time, you reformulate but you retain the essential fallacy.

    There is no single "vanishingly small pseudo-interval". There are only successively smaller pseudo-intervals on successive rows.
    TonesInDeepFreeze

    You're right. I shouldn't have used 'vanishingly small pseudo-interval'. That makes it sound like I'm talking about an object at the bottom of the tree. The only object is the line. There is no bottom of the tree.

    Let me rephrase a paragraph from my earlier post here:
    If asked, what number is a solution to 'phi^2-phi-1=0?' I would say that I cannot provide a number. But what I can provide is an algorithm (which inputs integer, ROW, and outputs pseudo-interval, PI) such that for any positive rational number, EPS, there is an input ROW which outputs a PI, whose potential cuts (rational number, m) would all yield |m^2-m-1| < EPS. This algorithm can be described as RRL and I call it the golden ratio.

    Except that I don't see that it improves the more simple approachTonesInDeepFreeze

    The idea behind this proposal is that the fundamental object is the line, not the point. This difference is significant.

    But it is the standard calculus depends on the completeness of the reals.TonesInDeepFreeze

    But doesn't that mean that standard calculus depends on there being no gaps on the line? That's what this suggests:
    https://en.wikipedia.org/wiki/Completeness_of_the_real_numbers

    There are no points on this line.
    — keystone
    [bold ORIGINAL]

    You seem to have no compunctions about insulting intelligence.
    TonesInDeepFreeze

    Infinite sets are so deeply embedded in your thinking that you're not even willing to imagine the possibility that points are not fundamental. Flip your thinking upside down just for a moment. In my proposal I start with a line and points get added as we progress down the rows. I'm starting with an unmarked 'stick', not a perfect precision 'ruler'. If I'm starting with a 'perfect precision ruler' on the top row then please tell me the coordinate of even a single specific point on that line [].

    Changed from standard analysis? No, your proposal is radically different from standard analysis, from the start: Standard analysis uses infinite sets, you disclaim infinite sets. Standard analysis has a continuum; you don't. Standard analysis has uncountably many reals. With you, it's not clear how many comp-reals there are, since there are denumerably many real-ithms but you disclaim that there are denumerable sets (but maybe you could argue that there is not a set of all real-ithms but instead a program that itself generates real-ithms).TonesInDeepFreeze

    Are my proposed algorithms that different from Cauchy sequences?
    Is my proposed line that different from the real number line?
    Is my proposed line not continuous?
    Standard analysis achieves length by having uncountably many points. Is length not also achieved by having pseudo-intervals?
    Of course I'm proposing something different, but we must remember that calculus came before set theory. I'm only proposing a different foundational underpinning. If you don't think that's philosophy then sure.

    Then, define '<', '+' and '*' on real-ithms, and you'd be on our way to something.

    In other words, for arbitrary real-ithms G and R:
    G < R <-> [fill in definiens]
    G+R = [fill in definiens]
    G*R = [fill in definiens]
    TonesInDeepFreeze

    This is sound advice. I need to research this. I appreciate you advising me on next steps.

    You want only finite objects, but you also want real numbersTonesInDeepFreeze

    I don't want all real numbers, only the computable ones when they're needed. And to calculate the area between y=1, y=0, x=0 and x=1, I don't need to there to exist infinite points. As long as I know that there are no gaps across the lines then I can calculate the area just fine. Would anyone claim to explicitly make use of infinite points in their calculation?
  • Real numbers and the Stern-Brocot tree
    By contrast, in a language with lazy semantics such as Haskell, terms can be used and passed around in partially evaluated form. This means that real numbers can exist in the sense of partially-evaluated "infinite lists" consisting of an evaluated prefix and an unevaluated tail. These lazy languages allow runtime conditions to decide what rational value is used in place of a term of real-number type, which is allowed to vary during the course of computation and which corresponds more closely to the notion of "potential infinity".sime

    Actually, the algorithm used to perform arithmetic on the Stern-Brocot tree was originally written in Haskell (I rewrote it in Python) and it does just this!

    https://www.sciencedirect.com/science/article/pii/S1570866706000311#:~:text=The%20Stern%E2%80%93Brocot%20tree%20is,rope%20between%20zero%20and%20infinity'.
  • Real numbers and the Stern-Brocot tree
    @TonesInDeepFreeze

    You raise some good criticisms. I have reformulated my proposal to address them.

    The object that I want to talk about moving forward is not the actually infinite S-B tree (which you're right, I don't believe in), but instead the blue line as illustrated below.

    LKAAht9.png

    Don't think of this figure as depicting an infinite collection of blue lines, but instead as a single line, and each row describes a finite set of cuts which can be performed on the line. Although I'm not talking about the S-B tree, the cuts are closely linked with the S-B tree, which I'll call the S-B algorithm moving forward to avoid any confusion on my philosophy).

    This line is not the real number line (which is composed of uncountably infinite points). On the very top row we have segment [] as described by the interval (-inf,+inf). There are no points on this line. I recognize that intervals across continua are typically associated with the infinite set of points between them so I'm not using the term 'interval' as it is typically used. To avoid any confusion, moving forward, in this context I will use pseudo-interval instead of interval.

    In row 0, the line is cut into two segments:
    (1) segment L corresponding to the pseudo-interval (-inf,0)
    (2) segment R corresponding to the pseudo-interval (0,+inf)

    With each cut, a point is introduced on the line corresponding to a rational number. This point is not an actual object, but instead only demarks the space between adjacent line segments.

    With each successive row, the line is cut more and more times.

    If asked, what number is a solution to 'phi^2-phi-1=0?' I would say that I cannot provide a number. But what I can provide is the pseudo-interval within which it lies at any row. For example,

    Row 0: R
    Row 1: RR
    Row 2: RRL
    Row 3: RRLR
    Row 4: RRLRL
    Row 5: RRLRLR
    Etc.

    We can proceed arbitrarily far down the tree, continually shrinking the pseudo-interval within which the solution lies. However, since there is no bottom of the tree, perfect precision cannot be achieved (i.e. the pseudo-interval can never be reduced to a single number, and the line cannot be reduced to a point). The solution to this problem is therefore not a number, but instead a vanishingly small pseudo-interval.

    One might say that the sequence of pseudo-intervals describing phi is (R,RR,RRL,RRLR,RRLR,RRLRL,RRLRLR,…) but this sequence is infinite and so I do not believe it exists. What exists is the potentially infinite algorithm to generate successive cuts to narrow the pseudo-interval. In this case, the algorithm can be succinctly captured by the string: RRL. Similarly, the algorithms corresponding to 1 are RLR and RRL. Infinite S-B strings are algorithms. Reals are algorithms.

    The claim that there are only countably many algorithms/programs does not imply that this view has gaps in the line. The line is there in full from the start. It simply means that it is impossible for any computer to hone in on some sections of the line.

    It is my suspicion that this view is so closely tied with Cauchy sequences that maybe few new proofs are needed. Perhaps only a proof to shown that Cauchy sequences are actually talking about this. All that's really changed is the philosophy - but even that hasn't changed as much as one might think. For example, when explaining integrals, we use ever shrinking rectangles - this is not unlike the ever shrinking pseudo-intervals used here.

    P.S. I've moved on from talking about the output of an unending program, but I do agree that any program you can write can in principle be stated as a Turing machine.
  • Real numbers and the Stern-Brocot tree
    Do you consider this a valid function?
    — keystone

    I haven't the foggiest.
    TonesInDeepFreeze

    def endless_loop()
    	while True:
    	    print("Looping indefinitely...")
    	Return 1
    

    I do plan to respond to all of your comments (it may take some time for me to collect my thoughts) but please allow me to dwell on this point some more as your response will help me compose a response to your earlier comments. In case you 'haven't the foggiest' simply because you're not familiar with Python, what this function is designed to do is loop indefinitely (printing the string 'Looping indefinitely...' with each iteration) and at the end return (i.e. output) 1.

    This function follows all of the required Python syntax and so it can be interpreted and run. It is a valid program.

    What I want is your view on whether it makes any sense to say what this function returns. I want to distinguish between the design of the code and the execution. The code can never be executed to completion so it can never actually return 1. However, as described above the code is designed to return 1.

    I would phrase this by saying that the output of the function is potentially 1, but it is never actually 1.

    What do you think?
  • Real numbers and the Stern-Brocot tree
    There you go again, invoking an infinitistic object (the real number line) that you claim doesn't exist.TonesInDeepFreeze

    So that I can respond it will be helpful if you clarify your position on programs by answering these questions I asked in my earlier message to you.

    Consider the follow Python function:
    keystone
    def endless_loop()
    	while True:
    	    print("Looping indefinitely...")
    	Return 1
    

    Do you consider this a valid function? It certainly obeys Python syntax rules and can be interpreted by a computer program. Does it make sense to say that it is designed to return 1 even though it never actually could?
  • Real numbers and the Stern-Brocot tree
    @TonesInDeepFreeze

    I just realized I incorrectly described the black lines in the S-B tree image. They do not correspond to paths from 0/1 to all the rational numbers. They link any node to its two parent nodes. Doh! It was a while ago when I made that figure...
  • Real numbers and the Stern-Brocot tree
    Consider the follow Python function:

    def endless_loop()
    	while True:
    	    print("Looping indefinitely...")
    	Return 1
    

    Do you consider this a valid function? It certainly obeys Python syntax rules and can be interpreted by a computer program. Does it make sense to say that it is designed to return 1 even though it never actually could? I see in your recent post that you can see the basic idea of reals being programs so perhaps these questions don't need answering.

    THE EXTENDED S-B TREE

    Moving forward, let's use this extended version of the S-B tree so that all real numbers are covered.
    fbE6f4o.png


    • At every row we have a blue line corresponding to the real number line.
    • The white nodes indicate that the blue lines corresponds to the open interval (-inf,+inf).
    • One can travel from the 0/1 node to any rational node in the tree by a unique sequence of left and right turns as described by S-B strings. Some examples of S-B strings are RL (1/2) and LL (-2/1).
    • There are two ways to interpret infinite journeys: (1) as completed processes, whereby they correspond to the entire path travelled and (2) as incomplete unending processes. I prefer the latter but until it becomes an issue, let's use journey ambiguously without saying whether it is completed or not.
    • Row infinity does not exist. From now on, when I say 'approaching row infinity' it will be an informal placeholder corresponding to an unending journey down the tree.
    • I have an issue with infinite sets but I see value in the concept of equivalence classes. Instead of discussing what an equivalence class might mean in the absence of infinite sets, please grant me slack to use this concept loosely. While each node only contains the reduced form of a rational number, it actually correspond to an equivalence class of integer pairs.
    • As we progress down the tree, nodes are placed directly on top of their corresponding point on the real number line. For example, the node corresponding to 2/3 lies directly on top of the point corresponding to 2/3. Although the nodes are illustrated as large circles, let's imagine that they are actually points. So while the blue line gets hidden from the illustration as the nodes become more numerous, let's imagine that the real number line is still present in its entirety at every row.

    Who all are the people that constitute the "we" who say the tree doesn't exist but there is a program held in their mind?TonesInDeepFreeze

    When I imagine the Stern-Brocot tree, I visualize the first few rows of the tree and then internally mutter 'and so on as governed by the rules for constructing it'. That 'and so on' is not a formal program, but it refers to an algorithm which we can fit into our finite brains and be comprehended.

    AGAIN, you can't just take a sequence and say that there is a limit; it's not enough to say that the terms of the sequence get closer to each the next - you have to PROVE that there is an object such that the terms get arbitrarily close to it.TonesInDeepFreeze

    With the real number line now embedded in the tree, hopefully it is reasonable to say that as we approach row infinity, the journey corresponding to RRL converges to the point corresponding to the golden ratio.

    So when I say "exist", without opining on philosophical notions, I mean at least there is an existence theorem.TonesInDeepFreeze

    Given this, I'll stop using 'exists' since my view of existence extends beyond mathematics. I know you don't like it when I make up new terms, but hopefully you'll give me slack here as I'm trying not to hijack 'exists'. Instead, I'll use 'actualized' for what I mean. In my view, an object is actualized if it is present in the memory of a 'computer'. I am actualized because I am present in the 'computer of the universe'. I'm thinking of a purple cow so that purple cow is actualized because it is present in the 'computer of my mind'. This statement is actualized as I type because it is present in the memory of my laptop. When a memory of an object is flushed, it becomes 'potentialized'.

    But we have to keep in mind that this covers only the computable reals. So we'd have to explain how to formalize calculus with only the computable reals.TonesInDeepFreeze

    The infinite decimal corresponding to pi is forever potentialized.
    Leibniz's formula for pi/4 is currently actualized because it is present in my mind.
    If I understand correctly, non-computable reals cannot be present in the memory of any computer so they are forever potentialized.

    Let's say we color the necessarily potentialized points on the real number line red and all possible actualized points green. Given that the computable reals are countable, they have measure 0 so the real number line is entirely red. But we still have the line and can perform calculus as usual. I don't understand why we would need to adjust anything in our formalization of calculus.
  • Real numbers and the Stern-Brocot tree
    @TonesInDeepFreeze

    As always, I appreciate your detailed responses.

    I believe in what I'm saying but IF it's untrue then you're right - according to Merriam-Webster, my statements would be considered lies. I don't want to argue with you about my intentions. I was wrong to claim that you came up with the path definition. I will not claim something is 'inconsistent' unless I can prove that both a statement and its negations are theorems of the mathematics of concern. Sorry. Overall, I've been sloppy with my communication. I intend to be more clear. I ask that we set aside my earlier comments in this thread and I'll start afresh to better capture my position as I respond to your last set of messages. I'll need some time to digest all of your comments and formulate my response.
  • Real numbers and the Stern-Brocot tree
    I want to characterize all paths on the S-B tree by their destination. Infinite paths do not actually have destinations but neither does 1/x have a value at x=infinity. After all, x never is infinity and there is no row infinity on the S-B tree. But there is value in saying that 1/x approaches 0 as x approaches infinity. Similarly, there is value in saying that the path RL approaches 1 as we descend the tree and approach 'row infinity'. In both of these examples, infinity is a useful fiction. But it's important to acknowledge that it is a fiction, however you want to phrase it.

    Now, given that paths (as described by infinite sequences of rational numbers) are analogous to Cauchy sequences, it doesn't seem like a big jump to say that the limit of a SB path is analogous to the limit of a Cauchy sequence, or in other words, that the limit of infinite SB paths are nodes corresponding to real numbers. But these nodes only exist at row infinity (which is a fiction) and so they too are useful fictions. Of course, it's obvious that they're fictions since, once again, infinite paths do not end at any node (in a similar way that Cauchy sequences do not end at any rational number).

    As we agreed earlier, nodes are analogous to points. The issue then is that in the S-B tree, we only have nodes corresponding to the rational numbers. The nodes corresponding to the real numbers are fictional. Comparatively, with the real number line, we do not distinguish between the rational and irrational points on the real number line. They are of the same essence. This disagreement between the S-B tree and the real number line is what I'm trying to highlight.

    You need to stop using the word 'inconsistency' with your own private meanings.TonesInDeepFreeze

    Granted, the branches of the S-B tree never actually intersect, but if we're trying to illustrate the real line as the limiting row of the tree, one approach we might be able to use is projective geometry. With this approach, the parallel lines of 0/1 and 1/0 (and all the branches in between) meet at a single node at infinity. So in a sense, maybe one can say that at infinity (if it were not a fiction) all of the real numbers would be equal. Or analogously, going back to the 1/x example, at x = infinity we have a singularity. Perhaps all numbers being equal is more in line with a standard notion of inconsistency. However, this is all 'handwavy'. For example, what if 0/1 and 1/0 were instead diverging lines? Anyway, until I can support arguments like this with something more concrete, I'll refrain from using the term inconsistency.

    stern-brocot.png

    "Just remember it's not a lie if you believe it".
    Look up 'lie' in Merriam-Webster.
    TonesInDeepFreeze

    Lie - to make an untrue statement with intent to deceive.
    Perhaps cranks are deluded, but our intentions are pure.

    Choose a definition and stick with it.
    First you said the reals are the paths. Now you say they are nodes.
    TonesInDeepFreeze

    I think it is a virtue to be able to adjust one's view upon new evidence. I wanted to treat the real numbers as unending journeys along a path but you were inclined to treat them as the paths themselves. While I went along with this for a while I realized that it doesn't align with my views regarding infinity. As such, I have adjusted my view to something that seems more agreeable to both of us - limits. We can both speak of limits while in our heads, you are imagining an actually infinite object (path) and I am imaging a potentially infinite process (journey).

    Your insouciance in not making definitions and sticking to them invites confusion and is annoying.TonesInDeepFreeze

    Sorry, I can see how this can frustrate someone.

    If you want to have the things that are going to serve as the limits, then you need to prove they exist.TonesInDeepFreeze

    In the 1/x analogy above, does one have to prove that infinity is a 'thing' to talk about x approaching it?

    To be clear, since you write ambiguously "create the entire tree". Yes, there is a program such that, for any n, the program will generate up to and including the nth row and stop. But there is no program that generates all rows and stops. I take it that you agree.TonesInDeepFreeze

    There is a difference between writing a program and executing it. I can write a program that generates all rows and stops. However, I cannot execute it. The program is no less of a program just because the output doesn't exist. The output is a fiction. The execution of the program is a potentially infinite process, the output of the program is an actually infinite object.

    But, again, it entails that those limits are THEMSEVLES objects - existing.TonesInDeepFreeze

    Analogously, the output of the program doesn't have to exist for us to use it to describe the program and its execution. The [fictitious] output is used to describe the program/execution (not the other way around).

    But does the tree exist for you or not? Please don't answer with yet more wiffle waffle undefined terminology. Please just say whether it exists or not.TonesInDeepFreeze

    FOR ME - The program to create the tree exists, and it can be written with finite characters. But the program cannot be executed to completion (it doesn't halt - i.e. it is potentially infinite) so the output of the program does not exist. There is no actually infinite object corresponding to the S-B tree. Nobody has ever seen the actually infinite object with their minds eye. What we see with our minds eye is the program.

    But let's say the object of study is the program itself. Okay, but then pray tell how do you extract from that study of the program real analysis for the mathematics for the sciences?TonesInDeepFreeze

    I believe that reformulating calculus using limits did just that. In my view, calculus doesn't need any reformulation. Consider that I can write a program to perform Newton's method but if I'm hunting for an irrational solution it will never halt. The Cauchy sequence of intermediate rational 'approximations' describes the program/execution, not the solution. There is no solution.

    Actually, this is a huge bait and switch by you. You said that the real numbers are to be the paths in the tree. But now you don't want to have the existence of those paths, so you switch to saying "study the program". I was game for talking about the initial proposal, but now you've switched to something undefined to the point of nebulousness.TonesInDeepFreeze

    This is not a bait and switch. Infinity is inseparably tied with calculus. If one denies infinite objects one has to then accept infinite processes otherwise calculus doesn't get off the ground. And the simplest way to talk about processes is to treat them as programs being executed. It is unreasonable for you to disallow programs from the discussion, especially given that computer science is so closely tied with mathematics.

    EDIT: You're not disallowing programs from the discussion so my last paragraph should be retracted. Instead, perhaps I should have acknowledged that my ideas and method of communication are evolving. However, I wouldn't call this a bait and switch since I'm not trying to trick you.
  • Real numbers and the Stern-Brocot tree
    Thanks for providing a detailed and thoughtful response.

    I'm accepting whatever coherent proposal YOU are making.TonesInDeepFreeze

    Let me re-share this image of the S-B tree (https://imgur.com/vWBO6U9) because it shows how I see the connection between the S-B tree and the real number line. The nodes are projected down and at the limit we have nodes for all real numbers forming the continuous real number line in totality. Granted, the limit is not a part of the tree, after all, there are no nodes for irrational numbers in the tree. However, the limit can still be a property of the tree just as an irrational number can be a property of a Cauchy sequence. So from the perspective of the Stern-Brocot tree, the real line is like a mirage. It's not actually a part of the tree, but it's a valid property of the tree nonetheless. With this view, the objects of concern are the nodes (not the paths). But since some paths are not actually linked with nodes, I proposed we say that they converge to virtual nodes. Or in other words, the real number line is composed of points and virtual points.

    While it may be convenient to think in terms of paths, there is no analogous pictorial connection between paths and the real number line. I also think paths are more like the Cauchy sequences themselves while the nodes are more like the limits of Cauchy sequences.

    Now, you claim there is an inconsistency there. So PROVE that there is an inconsistency there. Otherwise, you are making the claim utterly without basis; you are fabricating, which is to say you are lying.TonesInDeepFreeze

    With my view now outlined above, I am arguing that it is inconsistent to say that the real number line is composed entirely of actual points. That would only be possible if there was a row infinity in the tree, which we agree that there is not. Instead, the real number line can only exist at the limit and must be composed of both points and virtual points.

    lie41.jpeg

    I mention that to explain why I personally don't like to say "the paths are in the tree" but rather "the paths are of the tree".TonesInDeepFreeze

    Might we also be allowed to say that the limit is of the tree?

    (I suggest that it might be better to make the rational reals the finite sequences of nodes and the irrational numbers the infinite sequences of nodesTonesInDeepFreeze

    Can we say that the rational/irrational numbers are the limits of their corresponding paths.

    And that does not entail that I did that as something similar to a "No true Scotsman" ploy (as I surmise you were suggesting).TonesInDeepFreeze

    I followed my statement with "I don't believe it, but if that level of complexity/formality is required to discuss infinity then so be it." In other words, you made the conversation too complex for me. Whether it was too complex for the topic is not for me to decide.

    so there is no path to 2/4, so 2/4 is not a rational number. So what is it?TonesInDeepFreeze

    I suppose you can use the S-B tree to compute 2 divided by 4 and you'd get the rational 1/2. But I see your point.

    But you are also trying to impugn the standard theory, which you have objected to for being infinitistic. But the S-B approach is no less infinitistic.TonesInDeepFreeze

    One can write a finite (but complete) computer program to create the entire S-B tree. My point is simply that that program cannot actually be executed to completion. As such, the object of study should not be the complete output of the program (which cannot be generated) but instead the program itself whose execution is potentially infinite.

    So while I don't believe in 'the set of all natural number', I don't mind a computer program that prints all natural numbers. And when 'we' work with infinite sets, 'we' don't actually work with the infinite sets themselves, 'we' work with the 'algorithms' used to generate them. If my view were to be proven true, standard theory wouldn't fall apart. It would just be a philosophical shift from actually infinite objects to potentially infinite algorithms/programs. For example, in set theory, it could be as small as moving from saying 'there exists a set' to 'construct a set'.
  • Real numbers and the Stern-Brocot tree
    If you propose the tree as a basis for the real numbers, then you have to provide such a definition.TonesInDeepFreeze

    Fair enough. The author of the paper proved the algorithm to work specifically for the rationals (not reals). I imagine the proof is much more difficult (impossible?) to extend to reals. You're right, I don't have the knowledge to produce a formal definition, let alone prove it. My take was based on my experience coding and utilizing the alorithm.

    of course such a sequence does not converge to sqrt(2), since sqrt(2) is a sequence and not a node.TonesInDeepFreeze

    (RL) converges to the node corresponding to 1. RL (phi) does not converge to any node.

    what I did in the other threads was to generously give you increasingly detailed explanationsTonesInDeepFreeze

    You brought the conversation to a level of complexity/formality that I wasn't comfortable with so the conversation ended. I don't believe it, but if that level of complexity/formality is required to discuss infinity then so be it.

    What I don't like, because it's a lie, is your claim that the existence of the real line contradicts the existence of the S-B tree.TonesInDeepFreeze
    You are evading my point.TonesInDeepFreeze

    Let's table this for a moment as I better understand your interpretation of real numbers on the SB tree.

    I have no problem with saying that set of real numbers is the set of paths in the S-B treeTonesInDeepFreeze

    Do you think the real number RL (phi) is the path itself or the limit of the path?

    And, since all complete ordered fields are isomorphic with one another, the one based on the S-B tree would be isomorphic with the others too.TonesInDeepFreeze

    I agree with this. The reason why I prefer the S-B tree view is that it's more understandable to amateurs like myself. What I want to reiterate is that I'm not trying to abandon the reals or the existence of continua like the real line. Instead, I'm trying to understand what the real line is from the perspective of the S-B tree.

    The set of paths in the S-B tree is not part of the S-B tree.TonesInDeepFreeze

    I understand that there are no sets in the tree, but the paths do exist in the tree, right? The tree is composed of both the paths and the nodes, right?
  • Real numbers and the Stern-Brocot tree
    Exactly. Meanwhile, with the other common definitions, we do define addition and multiplication of real numbers and that is not blocked by the fact that computations do not accept infinite sequences as inputs.TonesInDeepFreeze

    All I said was that the computation when the inputs were infinite strings wouldn't complete. The SB algorithm can certainly accept infinite strings as inputs though, it would just absorb the digits little by little and emit output digits little by little, never actually completing the output. In other words, I wasn't presenting a limitation of the algorithm, I was conveying my disbelief in supertasks. I would relate this to computing the digits of pi. The pi generating algorithm works, it would just never actually output all digits of pi.

    sqrt(2) is a real number. A real number doesn't converge. A sequence converges.TonesInDeepFreeze

    As we've informally agreed, irrationals (e.g. sqrt(2)) are unending paths on the SB tree. In an informal sense, it is reasonable to say that paths converge. The paths LR and RL both converge to the node 1. When I mentioned sqrt(2) not converging to a point, I was referring to the path sqrt(2) not converging to any node (in that sense). Would you rather I use another term than converge?

    The difference between
    And it's even WORSE in this thread, because in the other threads, the discussion was about thought experiments, which are informal analogies about mathematics, while in this thread, we are talking about an exact mathematical object.TonesInDeepFreeze

    The difference here is that we have a mathematical object (SB tree) which is very simple but yet still (it appears to) sufficiently captures to topic of concern. But unlike with our other thread, you cannot defend your position by making your arguments more and more complex. I, on the other hand, am defending my position by making my augments more and more simple. I suppose one way for you to end this would be by explaining why the SB tree (and my argument) oversimplifies the issue. If you don't like my description of the real number line as it relates to the SB tree, can you propose a better description using the SB tree?

    For example, the square root of 2 does not remind me of a mirage. It is not problematic that it is the limit of a sequence of rationals but is not one of the entries in that sequence.TonesInDeepFreeze

    It does not bother me that there are (unending) paths on the SB tree having no destination node. I also think there's value in saying that such a path is approaching a 'virtual' node. Calculus demonstrates the utility of such a belief. But I wouldn't accept that virtual nodes and actual nodes are the same thing. I think when we say rationals and irrationals are both numbers, we are essentially doing that.
  • Real numbers and the Stern-Brocot tree
    I can only take your word for it that you've satisfactorily worked out that arithmetic. Don't forget that you have to manage not just finite sequences but infinite ones too.TonesInDeepFreeze

    Aside from never being able to complete the computation involving infinite strings, there is a scenario where the algorithm may appear to hang. This is where it would continue to absorb more input digits without generating more output digits. A decimal analogy might be when subtracting 0.9 from 1.0 where (depending on your approach) you might get stuck in the step of continually looking ahead for a non-zero digit to borrow from.

    For example, the square root of 2 does not remind me of a mirage. It is not problematic that it is the limit of a sequence of rationals but is not one of the entries in that sequence. But some people just can't grok the idea of the entries of a sequence getting arbitrarily close to a point but that point is not itself an entry in the sequence.TonesInDeepFreeze

    From the Stern-Brocot perspective, what is a point if not a node on the tree? Sqrt(2) does not converge towards any node on the tree. However, it appears to converge to a node that exists at 'row infinity'. Of course, there is no 'row infinity' which is why I relate it to a mirage. There is an inconsistency in claiming that both (1) the real number line exists and (2) 'row infinity' does not exist. You can't have it both ways. The real number line is an incredibly useful mirage.
  • Real numbers and the Stern-Brocot tree

    It's clear you're providing useful comments but you've mentioned multiple topics/terms which I'm not familiar with. I've got some homework to do! Thanks.
  • Real numbers and the Stern-Brocot tree
    I'm not talking about that tree in that context. I was talking about the three competing definitions of 'is a real number' and how easy or difficult it is to define the operations for real numbers based on those definitions.TonesInDeepFreeze

    Accepted. I suppose I changed the topic a little, hoping to show how arithmetic with real decimals (which troublesomely starts from the right of the string) is less manageable than arithmetic with real SB strings (which conveniently starts from the left of the string).

    so if 'is a real number' would be defined as just one particular Cauchy sequence of rationals, then which of the infinitely many should it be?TonesInDeepFreeze

    The SB tree might offer something here since it appears that each real number has a single path which can correspond to a sequence of rationals [as you hinted].

    'is a path on the left side of the SB tree' as a fourth competing definiens? It would be of 'is a real number between 0 and 1 inclusive'.TonesInDeepFreeze

    Can you rephrase this? I'm not sure what you're asking.

    And are you sure that every irrational number is one of the denumerable paths? And that the sequence of nodes of every denumerable path converges to an irrational number?TonesInDeepFreeze

    My intuition says yes, but I wouldn't know how to prove it. I think it's clear that every decimal number can be captured by a SB string (of L's and R's) but that is no proof.

    Aren't there denumerable paths that stay constant on a single rational number?TonesInDeepFreeze

    Every path (whether finite or infinite) leads to a different number. Finite paths lead to rational numbers. Infinite paths lead to irrational numbers. Or I think you'd be more comfortable saying that infinite paths that don't end in R or L lead to irrational numbers. I think of the limit of the tree as the real number line as depicted here:

    https://imgur.com/vWBO6U9

    But as we agreed, there is no bottom of the tree. This limit exists somewhat like an ever distant mirage.

    But 2=1.9. If your method entails that that is not the case, then I doubt that your method actually provides a complete ordered field.TonesInDeepFreeze

    I agree that RLR (1.9) converges to 2 (R). So in the conventional sense of equality they are equal. However there is no row of the tree where the two paths intersect. If equality corresponds to intersecting paths, then in this stricter sense of equality I argue that they are not equal. I believe there is value in both uses of equality. The former is useful for practical purposes (e.g. working with calculus) while the later is useful for philosophical purposes (e.g. calculus, which is inseparably tied to real numbers, is the mathematics of the journeys (paths), not of the destinations (nodes)). If we move our focus away from arriving at a destination (which is a mirage after all) then we lose our attachment to actual infinity. Potential infinity will suffice.

    That's a strawman. He didn't say that all discourse has to be at the level of a mathematics journal.TonesInDeepFreeze

    Fair enough. I think I got defensive because I interpreted it as 'get educated and then talk' when his comment may have simply been something like 'if you want to take this to the next level you need to formalize your ideas'.

    Here's what you need to provide for your SB proposal: rigorous definition...We also don't yet have a rigorous (not just ostensive) definitions of the SB tree, 'R' and 'L'. But I don't doubt that there are ones, though complicated they probably are, so we could at least provisionally work with the ostensive definitions we know. Also, you might want to consider taking reals not as paths but as sequences of nodes on paths. Perhaps it's easier to talk about sequences of nodes rather than sequences of edges, or at least it's more familiar.TonesInDeepFreeze

    I agree that for this to be taken seriously I must present a rigorous definition. However, at this time I'm not equipped to do it. I like the idea of paths/journeys because it corresponds to a process. But yes, I like the idea of describing a path/journey by the intermediate stops along the way (i.e. sequence of nodes).

    Anyway, I am interested in the idea of SB used for defining the reals, as another poster has proposed, but I'd like to see that notion developed beyond mere handwaving.TonesInDeepFreeze

    Cool. Yeah, I would too.

    EDIT: When I mentioned a rational path intersecting an irrational path, I meant that rational dashed line never intersects with an irrational solid line, similar to image below.

    https://upload.wikimedia.org/wikipedia/commons/3/37/SternBrocotTree.svg
  • Real numbers and the Stern-Brocot tree
    He may have devised the continued fraction expansion of the equationjgill

    That's certainly a beautiful definition of the golden ratio.
  • Real numbers and the Stern-Brocot tree
    @Count Timothy von Icarus

    I appreciate your responses but Tones captured my concerns in a more eloquent way than I could have put it so I'll refrain from repeating his points.
  • Real numbers and the Stern-Brocot tree
    Who are you trying to convince here? Philosophers who consider definitions optional?jgill

    This is a chat forum, not a journal. We should be allowed to spitball here.
  • Real numbers and the Stern-Brocot tree
    every real has a decimal representation, it is not common to define 'is a real number' that way.TonesInDeepFreeze

    If you're talking about a number like sqrt(2) then I agree. However, for indescribable real numbers, I imagine that it would be less work to exhibit a single infinite string of digits than to exhibit an equivalence class of Cauchy sequences. Of course, 'less' can be confusing when talking about infinite work.

    Also, I don't know how easy are the definitions of addition and multiplication compared with the definitions of those operations with equivalence classes of Cauchy sequences or Dedekind cuts.TonesInDeepFreeze

    As for arithmetic on the Stern-Brocot tree, the algorithm is relatively simple (but computationally expensive - I rewrote it in Python if you want to play with it) (https://www.sciencedirect.com/science/article/pii/S1570866706000311#:~:text=The%20Stern%E2%80%93Brocot%20tree%20is,usual%20ordering%20of%20the%20rationals.). You can take any pair of strings (composed of L's and R's) and perform arithmetic on them, whereby it gradually consumes the strings working from the left to the right. As for infinite strings, you can interrupt it at any point to get a partial answer, whereby the longer you wait, the more characters you'll have in the output string.

    No, the paths are not real numbers. First, a path is a sequence of edges, not a sequence of nodes. Second, a sequence of nodes is not a real number. Rather the limit of the sequence is a real number.TonesInDeepFreeze

    Feeding the aforementioned algorithm the string RL, it will treat it exactly as the golden ratio. If RL looks like the golden ratio and it behaves like the golden ratio, why do you not say that it is the golden ratio? I think we both agree that RL corresponds to a specific path on the Stern-Brocot tree, not a node. If the algorithm treats RL as the golden ratio, then it seems reasonable to say that the golden ratio (and all real numbers) are paths on the Stern-Brocot tree. I like this view because it clearly distinguishes between rational and real numbers. Rationals are the nodes with finite characters (e.g. R=2). Reals are the paths with infinite characters (e.g. RLR=1.9). And since nodes and paths are distinct objects, we don't feel inclined to say that 2=1.9).

    A description is a linguistic object. A description is not a real number.TonesInDeepFreeze

    I am good with how you distinguished between the two.
  • Real numbers and the Stern-Brocot tree
    To answer that question, we would need a mathematical definition of 'describe'.

    Meanwhile, GR [Phi], like any real number, is the limit of a Cauchy sequence of rationals.
    TonesInDeepFreeze

    I suppose I should use is instead of describe.

    Real numbers are not sequences. Real numbers are equivalence classes of Cauchy sequences of rationals. And a real number is the limit of a Cauchy sequence of rationals.TonesInDeepFreeze

    "Other common definitions of real numbers include equivalence classes of Cauchy sequences (of rational numbers), Dedekind cuts, and infinite decimal representations. All these definitions satisfy the axiomatic definition and are thus equivalent." https://en.wikipedia.org/wiki/Real_number Do you agree with this? If so, let's please focus on the infinite decimal representation as I want to compare it with the infinite Stern-Brocot sequence.

    So, you can't just magically add Phi as a node to this tree.TonesInDeepFreeze

    I agree that you can't just add a node to the tree. My impression is that finite SB strings describe 'destinations' (numbers) and infinite SB strings describe 'journeys' (unending processes with no destination). My issue is that I don't see how decimals are any different. Why can't we say that (non-repeating) infinite decimals are journeys that are described by unending processes (e.g. limits) and not 'destinations' (numbers)?

    We could simplify by taking the complete infinite binary tree....But there is no irrational number represented by a node in that tree. Period.TonesInDeepFreeze

    Your tree works too, but I find the right-left string useful for my argument instead of just using the numbers at the nodes. While irrationals do not correspond to any node in your tree, they do describe a paths on that tree (from the top all the way down), no?

    What is your definition of 'completely described'?TonesInDeepFreeze

    Loosely speaking, I mean that the definition is not an approximation but instead a perfect description. Or perhaps, I should simply say that the complete description of the number is the number.
  • Real numbers and the Stern-Brocot tree
    I don't think an infinite series can encode an irrational number while remaining itself rationalCount Timothy von Icarus

    Are you suggesting that there's no way to completely describe an irrational number? Why does the infinite series have to remain rational?

    I'm saying a decimal number is just an encoding of a pattern/abstraction, it isn't identical with it.Count Timothy von Icarus

    Oh...so would you argue that '2' and the numerical property held by a pair of apples is not identical?
  • Real numbers and the Stern-Brocot tree
    Pi is the ratio of circumference to diameter of a circle. The Golden Ratio can be defined as the ratio of a particular line segment to another - you can look it up on Wikipedia. Other irrationals, have at it.jgill

    Pi and the golden ratio are special in that sense. You can't do that with almost all other irrational numbers (unless you say that one of the line segments is the unit line, in which case irrational number, x, is defined as the ratio x/1....not particularly satisfying).

    Since these expansions are non-ending they do not completely describe the mathematical entities they represent.jgill

    Almost all other irrational numbers require non-ending descriptions, such as Cauchy sequences. Do you take the view that Cauchy sequences cannot completely define an irrational number? Or do you take the view that the vast majority of irrational numbers cannot be completely described?
  • Real numbers and the Stern-Brocot tree
    Since these expansions are non-ending they do not completely describe the mathematical entities they represent.jgill

    How do you finitely and completely describe these mathematical entities (irrational numbers)?
  • Real numbers and the Stern-Brocot tree
    the Golden Ratio is irrational. As such, how are we going to describe it with the positive rationals? There is no "last" set of turns that can describe the GR, since there will always be more to describe.Count Timothy von Icarus

    Do you think a Cauchy sequence of positive rationals can be used to describe the Golden Ratio? If so, whats the fundamental difference here?

    However, if we could fully describe one irrational with the rationals than it stands to reason that we should be able to do this with others through a different series of turns. However, that can't be the case given the aforementioned.Count Timothy von Icarus

    On the Stern-Brocot tree, might irrationals be all the infinite strings which do not end in R_repeated or L_repeated?

    It is not an abstract object, but rather a property of abstract objects, ratios being necessarily relational.Count Timothy von Icarus

    Do you think some irrational numbers have conditional existence while others do not? Or are you making a claim about numbers in general requiring abstract objects to exist?

    The complete series of decimals or turns wouldn't be the ratio though, even if such a series was finitely possible.Count Timothy von Icarus

    Am I understanding correctly that you believe there is no decimal representation of the Golden Ratio? If that's the case, do you believe there are 2 solutions to the equation x^2-x-1=0? Are you saying something subtle here, such as there are 2 solutions but we can't represent them in decimal form?
  • Real numbers and the Stern-Brocot tree
    How would you use infinite decimal digits to define the GR?jgill

    Wikipedia says that the decimal representation of the Golden Ratio is 1.618033988749894...
    https://en.wikipedia.org/wiki/Golden_ratio

    Do you disagree with this?
  • The "parable" of Hilbert's Hotel (NOT the paradox)


    Hilbert's Hotel is a paradox because, in spite of being completely full, it can continue to make room for more guests without dislodging any of the current guests. If it made room for more guests by kicking out existing guests the magic is lost and nobody would care about the paradox. It wouldn't be a paradox.