# User talk:Boris Tsirelson

## [edit] Do we want this?

Look at Life/Signed Articles/John Whitfield. I'm not too crazy about this article, do we want it?--Paul Wormer 07:23, 9 December 2010 (CST)

- Specifically, I have no opinion. Generally, I do not bother if I'm not too crazy about an article, unless/until the article is going to approval. Approval is my red line. --Boris Tsirelson 09:46, 9 December 2010 (CST)

## [edit] Newlines

I have a LaTeX style with many newlines in math mode (which gives errors on Tendrl). It seems that your robot removes them now, is that true?--Paul Wormer 08:38, 9 December 2010 (CST)

- Yes, naturally. Surely it makes the source worse, but what can we do now otherwise? This is better that doing the same by hand, as before. If some day it will not be needed, one can restore the formulas from the very first version (before my robot intervention). --Boris Tsirelson 08:40, 9 December 2010 (CST)

## [edit] CZ credit

Why don't you want to give CZ more credit than is needed? You don't have a grudge against them, do you?--Paul Wormer 09:05, 9 December 2010 (CST)

- I never have a grudge against a set of people. I like some of them (individually) and dislike some of them (individually); but this is not the point. I only try to treat CZ in the same way as CZ treats WP. Why not? See for example CZ Talk:Non-Borel_set. Working here I want to increase the status of this site (and working on CZ or WP — of that site; I really do). Several lines article with "from CZ" at the end looks strange for me. --Boris Tsirelson 09:24, 9 December 2010 (CST)

- Let me explain that the (clumsy) text "NOTICE, please do not remove from top of page. I released this article to Citizendium. In particular, the identical text that appears there is of my sole authorship. Therefore, no credit for Citizendium content on the Tendrl applies" on Talk:Entanglement (physics) (and some other pages) is not invented by me. In no way! It is borrowed from CZ (mutatis mutandis). See for example CZ Talk:Taj_Mahal. It is generated by the CZ template:WPauthor. See also CZ template:WPauthor2 and CZ Template:WPimport. --Boris Tsirelson 01:08, 10 December 2010 (CST)

- And by the way, the text "Some content on this page may previously have appeared on Citizendium" is also not my invention. It appears (mutatis mutandis) on CZ if you check the "Content is from Wikipedia?" tick-box. --Boris Tsirelson 01:20, 10 December 2010 (CST)

## [edit] New plusses

Boris, I put + to physics articles starting with D and E. I noticed your Entanglement (physics), which is already present.--Paul Wormer 02:43, 10 December 2010 (CST)

- Nice; I'll do. --Boris Tsirelson 03:04, 10 December 2010 (CST)

- I did. "Catalysis" is now done; but "Divergence theorem" is not, due to "<math >" inside (too complicated for my robot).
- Once again, I find it rather ridiculous, officially importing such stubs as Electromagnetism, Electromagnetic induction, Erg (unit), Electric current. I'd better delete them. --Boris Tsirelson 04:37, 10 December 2010 (CST)

- I must confess that I checked most, but not all, articles. However, you must realise that some articles are intrinsically short. For instance, I wrote Erg (unit). There is not much to say about a unit, but its definition is sometimes difficult to find, so I think that it is useful to have it in an encyclopedia. In ordinary (paper) encyclopedias one also finds many short articles that are not far removed from dictionary articles. And why do you mind? Your robot is doing the work and short articles take small space.--Paul Wormer 04:56, 10 December 2010 (CST)

- OK, I agree about Erg. But Electromagnetism? It is a large part of physics. I'd prefer someone write a detailed article on it, from scratch (and without attribution to CZ). It is not a problem of robot or space, but a problem of degree of originality of this wiki. Just similarly, on CZ we prefer new articles from scratch to WP import. --Boris Tsirelson 05:15, 10 December 2010 (CST)
- Really, in the case of Erg a stub could be avoided, too. We could have a larger article "Energy units of measurement" and redirect Erg to it. --Boris Tsirelson 06:45, 10 December 2010 (CST)

## [edit] Plusses + types of encyclopedia

Hi Boris, I plussed F and G.

- It will wait a day.

With regard to the choice of many long articles versus a few short ones: this is an age-old discussion. Before internet was invented, we had in Holland two large competing encyclopedias (both about 20 volumes). One had the principle of many short articles (I own that one, and when I want to check something I put a chair in front of the bookshelf and go from volume to volume) and the other consists of long articles (and has a very long detailed index). Brittanica has both: the macropedia (a few long deep-delving articles) and the micropedia (many more superficial articles). I like both systems and in principle the computer allows both in one encyclopedia (WP has that).

- I do not object to short articles
*created*here. But I'd prefer to*import*a not-so-large number of good, and reasonably long, articles, as an "initial capital".

With regard to Tendrl: it seems to me that we first must make mileage (create content) to attract more people. I spent the last couple of days quite some time on drawings, I uploaded quite a few of my own drawings to Wiki Commons, and linked in a number (for instance pictures of Riemann and Pascal) that are not on CZ. --Paul Wormer 08:03, 10 December 2010 (CST)

- Nice. --Boris Tsirelson 08:45, 10 December 2010 (CST)

- Boris I plussed H and I. --Paul Wormer 07:00, 12 December 2010 (CST)

- I did. regretfully, "Ideal gas law" is overwritten. We have to understand which version is the best, and return to it if needed. --Boris Tsirelson 10:20, 12 December 2010 (CST)

[unindent] I plussed J and K.--Paul Wormer 10:40, 13 December 2010 (CST)

- I did. regretfully, "Johannes Diderik van der Waals/Works" was marked but "Johannes Diderik van der Waals" was not. --Boris Tsirelson 13:25, 13 December 2010 (CST)
- L and M are done.--Paul Wormer 03:34, 15 December 2010 (CST)
- N and O too. --Paul Wormer 02:46, 16 December 2010 (CST)
- P and Q checked. --Paul Wormer 10:37, 17 December 2010 (EST)
- Done. From now on, my robot does not spoil the source code of display equations. :-) --Boris Tsirelson 11:40, 18 December 2010 (EST)

- P and Q checked. --Paul Wormer 10:37, 17 December 2010 (EST)

- N and O too. --Paul Wormer 02:46, 16 December 2010 (CST)

- L and M are done.--Paul Wormer 03:34, 15 December 2010 (CST)

[unindent]

Good! R and S ready to go.--Paul Wormer 07:49, 19 December 2010 (EST)

- Done. Sulfur is lost, unfortunately. --Boris Tsirelson 17:28, 19 December 2010 (EST)
- T and U have been marked.--Paul Wormer 05:32, 21 December 2010 (EST)
- Done. I see, you have added Thylakoid; this did not help, since it is absent in the file exported from CZ (I do not know, why). --Boris Tsirelson 12:12, 21 December 2010 (EST)
- V and W checked. --Paul Wormer 10:08, 23 December 2010 (EST)

- Done. I see, you have added Thylakoid; this did not help, since it is absent in the file exported from CZ (I do not know, why). --Boris Tsirelson 12:12, 21 December 2010 (EST)

- T and U have been marked.--Paul Wormer 05:32, 21 December 2010 (EST)

[unindent] Checked X, Y, Z: three more articles. Shall we do math now? --Paul Wormer 10:09, 25 December 2010 (EST)

- Done; the end of physics is reached! :-)
- Not quite; now my robot needs a break; at least, it must learn to never overwrite existing articles. I also need a break for some meditation, what is happening. --Boris Tsirelson 14:23, 25 December 2010 (EST)

## [edit] Deletion

Could you delete November 25, 2010 ?--Paul Wormer 07:22, 11 December 2010 (CST)

- I am reluctant to do so without asking Fred Bauder. I do not know why he created it, but maybe he knows? --Boris Tsirelson 10:02, 11 December 2010 (CST)

## [edit] Can you do me a favour?

Boris, can you please send me a dummy e-mail via Special:EmailUser/Thomas Larsen? I just want to confirm that the mail configuration settings are functioning correctly now. I've just sent you an e-mail; can you let me know whether you received it?—Thomas Larsen (talk) 02:25, 19 December 2010 (EST)

- Yes, I got your email: "If you receive this e-mail, it means Knowino's e-mail configuration is probably correct." --Boris Tsirelson 02:31, 19 December 2010 (EST)
- And I've sent you an email. --Boris Tsirelson 02:33, 19 December 2010 (EST)

- Ah, and I received yours. Excellent! That means everything is (in theory) working properly.—Thomas Larsen (talk) 02:36, 19 December 2010 (EST)

- "In theory, there is no difference between theory and practice. But in practice, it is." :-) --Boris Tsirelson 02:39, 19 December 2010 (EST)

## [edit] Thanks!

Thanks for catching my OOOPS. I was in the process of editing and moving things over here. I'm glad you caught what I missed. These old eyes just don't work as well as they used too. LOL!Mary Ash 17:10, 19 December 2010 (EST)

- It was rather a joke; surely you would fix it anyway. Happy editing! --Boris Tsirelson 17:12, 19 December 2010 (EST)
- You are most welcome. Glad to see ya here! Mary Ash 20:24, 19 December 2010 (EST)

## [edit] Reviewing

Boris, the rules for reviewing are not very clear to me. Are they written up somewhere? --Paul Wormer 06:40, 20 December 2010 (EST)

- I do not know (indeed, I ask some questions on Village Inn). But what do you mean: technicalities, or conventions of Knowino? --Boris Tsirelson 06:44, 20 December 2010 (EST)

- Technicalities don't interest me, that's Thomas' job. The rules. For instance can I flag as "sighted" or "accurate" articles outside my field of expertise? If not, how do I know what is inside my field? --Paul Wormer 07:12, 20 December 2010 (EST)

- Again, I do not know. For now I just do it according to my taste. I've described my field(s) of expertise here. No, I do not flag as "accurate" articles outside my field of expertise. But sometimes I do it if most (but not all) article is within; see my remark to Line (geometry) (the last section is
*written*by me, but needs to be*approved*by an expert in general relativity). However I would not hesitate to flag as "sighted" something like that (beyond, but not far from my expertise). Precedents make rules... --Boris Tsirelson 07:20, 20 December 2010 (EST)

- Again, I do not know. For now I just do it according to my taste. I've described my field(s) of expertise here. No, I do not flag as "accurate" articles outside my field of expertise. But sometimes I do it if most (but not all) article is within; see my remark to Line (geometry) (the last section is

- The "sighted" flag means that the article is free of vandalism and that, after a cursory read, a reviewer found nothing wrong with it. I don't have issues with reviewers setting this flag on articles outside their respective fields of expertise, although the revision header at the top of the page should probably be changed to reflect the nature of this type of "review".

- The "accurate" flag means that an expert
*in the subject of the article*has reviewed the article and found no factual errors in the reviewed sections.

- The "accurate" flag means that an expert

- The "featured" flag means that the article has gone through a rigorous community selection process and deserves to be marked as one of Knowino's best articles for outstanding accuracy, balance, comprehensiveness, and readability. Any reviewer can set this flag on an article once it can be shown that community consensus is to do so.

- I hope that clarifies. Feel free to establish your own guidelines so that we can discuss them—after all, you folks will be using the system! :-) —Thomas Larsen (talk) 18:38, 20 December 2010 (EST)

- Yes, it clarifies. --Boris Tsirelson 01:05, 21 December 2010 (EST)

## [edit] Google search

Boris, it is convenient to have a Google search window below your Knowino search window (then Google can search Knowino for *any* string). Depending on your skin you create either
User:Boris_Tsirelson/monobook.js or User:Boris_Tsirelson/vector.js and you copy the little JavaScript program that I have under the corresponding name. For instance from: User:Paul_Wormer/monobook.js

--Paul Wormer 11:02, 25 December 2010 (EST)

- Thank you. I never dealt with these *.js files before. And now I do not feel a need in Google search here. Maybe somewhat later. --Boris Tsirelson 14:26, 25 December 2010 (EST)

## [edit] Orbital-angular momentum

Boris, although I'm not familiar with the undergraduate math curriculum in Israel, it seems to me that you as a mathematician must be able to read without any difficulties orbital-angular momentum. As I said before, it is based on a pedestrian approach: no manifolds, tangent bundles, integral curves, etc. --Paul Wormer 12:23, 29 December 2010 (EST)

- OK, I try; see Talk:Orbital-angular momentum#Remarks.

## [edit] From CZ

Are you planning to transfer more from CZ? If you don't I will transfer occasionally some of my own articles. If you do, I'll wait.--Paul Wormer 12:12, 11 January 2011 (EST)

- Yes, after browsing mathB and mathC I intend to transfer these:

Baccab formula Basel problem Basis (linear algebra) Bayes Theorem Benjamin Peirce Bijective function Binomial theorem Biology's next microscope: Mathematics Birthday paradox

Cantor's diagonal argument Cardinal number Carmichael number Cartesian coordinates Cartesian product Category theory Cauchy-Schwarz inequality Cauchy sequence Chain rule Characteristic subgroup Chinese remainder theorem Circle (mathematics) Closed set Cofactor (mathematics) Colin MacLaurin Commutative algebra Compactness axioms Compact space Complement (linear algebra) Complete metric space Completing the square Complex analysis Complex conjugation Congruent triangles Connected space Continuity Continuum hypothesis Contour plot Convolution (mathematics) Covariance Cubic equation Cyclotomic polynomial

Any comments? --Boris Tsirelson 15:22, 11 January 2011 (EST)

No comments.--Paul Wormer 01:46, 12 January 2011 (EST)

## [edit] Dual space

Boris, I need your advice in your two capacities: mathematician and (co)legislator of Knowino. I need an elementary article about the dual of a finite-dimensional vector space, and I'm willing to write it. However, we already have a fairly advanced article about it that does not fill my needs. What do you suggest: modify and augment the existing article, or rename it to "dual space (advanced)" and write "dual space (elementary)", or some other solution?--Paul Wormer 11:27, 21 January 2011 (EST)

- Well, I moved it to Dual space (functional analysis). Now you are welcome to create "Dual space" or maybe "Dual space (linear algebra)". In the future we'll think whether to join them or not. --Boris Tsirelson 10:32, 22 January 2011 (EST)

## [edit] Watchlist

Hey, I see you have a list of pages on your user-page. Did you know about the watchlist feature? You can add pages to your watchlist by clicking on the star icon near the search bar. If you want to add pages to your watchlist by hand, you can go to Special:Watchlist/raw.—Tom Larsen (talk) 04:19, 13 February 2011 (EST)

- Thanks. Surely I know (I am a wikipedian about 7 years). But for now I want also to have some other lists. By the way, I suspect that special pages are incorrect in counting and listing the pages. --Boris Tsirelson 05:17, 13 February 2011 (EST)

## [edit] Candlewiki

If you check out [1], you'll see that the existing "Candlewiki" is basically dead: only a few changes have been made in the past 100 days, and all of them, as far as I can see, are spam. The site statistics page tells a similar story.—Tom Larsen (talk) 07:54, 20 February 2011 (EST)

- I see. --Boris Tsirelson 08:30, 20 February 2011 (EST)

## [edit] Proofwiki interwiki link?

Hello Boris! Would you like me to add "proofwiki:" as an interwiki link prefix? That way you could type "[[proofwiki:Foo]]" and a link would be created to the page "Foo" on Proofwiki. Cheers,—Tom Larsen (talk) 19:53, 27 March 2011 (EDT)

- Rather not. Trying their site I got discouraged. A lot of proofs of ridiculously trivial statements. And proofs of more interesting statements are often unfinished (and even stubby).
- I also tried Wikinfo; their mathematical articles are mostly (or even always?) copied from Wikipedia.
- --Boris Tsirelson 03:05, 28 March 2011 (EDT)
- However, what about interwiki links to WP and CZ? --Boris Tsirelson 10:37, 28 March 2011 (EDT)

- Fair enough.

- I've added "wp:", "citizendium:", and "cz:". ("wikipedia:" was already defined.)—Tom Larsen (talk) 13:02, 28 March 2011 (EDT)

- For example: wp:Foo, wikipedia:Foo, cz:Foo, citizendium:Foo.—Tom Larsen (talk) 13:02, 28 March 2011 (EDT)

- Nice. --Boris Tsirelson 14:19, 28 March 2011 (EDT)

## [edit] Template text

Boris, the CZauthor template speaks of *identical text*. This is a bit strong. Most of the times that I transfer an article from CZ to here, I haven't seen the CZ text for quite some time. Having a fresh look I see all sorts of things that I change. So, my Knowino texts are rarely ever identical with the CZ texts. Maybe it is better to say in the template something like: "this article originates from CZ" or a similar phrase. --Paul Wormer 03:20, 26 May 2011 (EDT)

- OK, do not hesitate to change the template. I did not invent the text, I just copied it from CZ. But maybe the "identical text" means: naturally, both articles (here and on CZ) are changing, but when you see a piece of identical text, be sure that it is of my sole authorship. --Boris Tsirelson 04:27, 26 May 2011 (EDT)

## [edit] Thanks for the Reviewer status

Hi Boris,

Thanks for the rapid upgrade up to Reviewer status. I'm reasonably familiar with how the flagged revs/pending changes system works from Wikipedia, Wikinews and Wikibooks and will try and use it carefully on Knowino. —Tom Morris (talk) 11:32, 30 May 2011 (EDT)

- You are quite welcome. Of course, our traditions are far from being well established for now. You can see an example of my "accurate" stamp at Plane (geometry) (at bottom, see Boris Tsirelson made the following notes reviewing this revision: Free of errors, to the best of my knowledge. Within my expertise, except for the section "Beyond mathematics".) My idea is: in contrast to CZ, we should not try to decide ourselves, who has enough expertise. If there is
*some*reason to treat a user as an expert, the rest is left to the reader; let him/her look at your page and decide, what to do with your opinion. --Boris Tsirelson 12:29, 30 May 2011 (EDT)

- Also, when importing our own articles from CZ, we usually add a credit note such as you can see on (say) Talk:Entanglement (physics). Is it clever or stupid? I do not know. --Boris Tsirelson 12:46, 30 May 2011 (EDT)

- Okay, done that. I've got a fair few more to import from Citizendium, and I've got stuff to import from Wikipedia as well. —Tom Morris (talk) 15:36, 30 May 2011 (EDT)

## [edit] White Argentine's credits

Moved to User talk:Pablo Zampini#White Argentine's credits and continued there.

## [edit] Your opinion on something...

Hi Boris. Some people say, *In an infinite universe, anything that could possibly happen will.* A more formal way of stating, is after an infinite number of trials, anything with non-zero probability will have a probability of one of happening at least once (indeed, of happening any number of times), and hence *almost surely* (but not surely) happen. Obviously that is true for some really simple examples, such as flipping a coin forever - every possibile finite bit sequence will occur in the result N times for a probability one and any positive N. But the question is... what about for our universe (or universes with similar laws to ours)? If the universe is infinite, wouldn't that imply all things (no matter how improbable) will occur an infinite number of times? Some reasonable (but unproven) cosmological models suggest the universe is temporally unbounded in the future.

One person I presented this idea to, had an interesting comeback - Polya's random walk constant for d=3. The suggestion is, there are points which the walk has a non-zero probability of reaching once, yet the probability of reaching there over an infinite period does not reach 1. His suggestion is that this is true for the laws of physics of our universe. I am not sure. But it got me thinking about some other types of 3-d lattice random walks, for which Polya's result would not hold. One line of thought is this: why isn't a 3-d random walk the same as three 1-d random walks, for which the level-crossing phenomena exists. Part of the answer is, movement in each dimension is connected with movement in the others, since a particle can only move in one direction at once. But if we allow movement in each dimension separately, so at each turn we have 1/3 of +1, 1/3 of -1, and 1/3 of 0? Would a Polya-style result still occur then? Thoughts? Zachary Martin 06:23, 8 June 2011 (EDT)

- Hi Martin. Let me answer in the inverse order. Polya's theorem states that the simple random walk is recurrent in dimensions 1 and 2, but transient in dimension 3 and higher. The same holds for arbitrary (not just simple) random walks under quite general conditions. Basically, it is required that the walk is driftless.

- Thus, your case (1/3, 1/3, 1/3) is not different.

- Also the 3-dim walk combined from three independent 1-dim simple random walks is transient. No paradox here. The first coordinate vanishes infinite number of times (but these instants are rare). The second coordinate also vanishes infinite number of times. The two independent infinite sets (of instants) have an infinite intersection (but its points are even more rare). However, the intersection of three such sets appears to be finite, and has a chance to be empty.

- For technical details see for example Chapter 3 "Random walks" in book: Durrett, Richard (1996), "Probability: theory and examples" (Second ed.)

- About the universe... this is not a math, of course, and I can voice only a vague impression. Such ideas were in fashion before the 20 century (and maybe at its beginning, still). Nowadays physicists say: we do not investigate reality, we investigate models (that resemble reality to a reasonable extent...) True, some cosmological models are temporally unbounded in the future. Also true, the Euclidean space contains infinitely many points in every ball. Etc, etc. But we should not forget: models are just similar to reality in some (practically important) aspects.

- I recall the book "Veiled Reality: An Analysis of Present-Day Quantum Mechanical Concepts" by Bernard D'espagnat; it is finished by something like that: after centuries of physics our understanding of reality (beyond mere practical aspects) consists of only few claims, and even these are mere negative.

- For cosmology, "infinite in time" means rather "probably much longer than 10
^{10}years". On the other hand, flipping only 1000 coins, we have 2^{1000}possible outcomes. The latter number is huge in comparison with the former. (See also Theory (mathematics)#Sharp or fuzzy; real or ideal.)

- --Boris Tsirelson 11:38, 8 June 2011 (EDT)

Hmm... I suppose my approach is this:

- I am interested in the idea of the universe being recurrent, of time being ultimately circular, as e.g. expressed by Nietzsche in
*Thus Spake Zarathustra* - Although my primary reasons for believing this idea are not to do with physics, I am interested in whether physics (particularly mathematical physics) would lend support or not to this idea
- I agree with you, that we can't really know anything about the long-term future of the universe, for sufficiently large values of long-term
- We can start with models, that are partially accurate (but not completely accurate) descriptions of reality, but simplified enough that reasoning about them is tractable
- I think it is an interesting question, taking reasonable mathematical models of reality, to ask what their behaviour over extremely long time periods (e.g. over say Graham's number years)
- Of course, we can't infer much about the real world from the behaviour of those models in such extreme conditions, since the models are only meant as approximations, and it is quite likely that under such extreme inputs the models are no longer valid, and of course we cannot test any of this experimentally
- But, if one starts from a position of knowing nothing about the question, then knowing the behaviour of these models leads you to know a little bit more than you did before. In Bayesian terms, we might say we start with confidence 0.5, and discovering the behaviour of these models may push our confidence a bit nearer in the direction of 0 or 1, even if only by a tiny amount

Within those broad outlines, there have been two particular approaches I have been exploring:

- Drawing on statistical mechanics - particles move randomly. Suppose we want the particles to evolve into some specific configuration X (in the recurrent case, X is identical to their current configuration). What is the probability they will eventually do so, given infinite time? Might it be 1 for all or many such configurations? This is how the discussion about random walks started. Related to this question is whether the universe as a whole exhibits ergodicity, and whether the Poincaré recurrence theorem theorem holds for it
- Drawing on quantum physics - since every particle is described by a wave-function, which extends to the end of the universe, with an unimaginably miniscule yet non-zero probability any particle could suddenly jump to anywhere else in the universe (the distance, among other things, will determine how unimaginably miniscule this probability actually is). Since this could happen to many particles simulatenously, there is a finite non-zero probability that the universe as a whole (assuming it is finite), or any sized subvolume of it, could instantaneously rearrange itself into an arbitrary state. This could include a recurrent state (a state it has had previously). Even though the probability of such an event is unimaginably miniscule, if it is non-zero, if the universe exists forever might it not end up with a probability of 1?
- Been exploring arguments based on the Bekenstein bound. Suppose the universe is spatially infinite, and contains an infinite quantity of matter, but otherwise obeys known laws of physics, and is reasonably uniform. There is some lower and upper bound on the size and energy content of Earth-like planets. By the Bekenstein bound, there is an upper bound of the information an Earth-like planet can contain, or (equivalently) on the number of distintinguishable states it could exist in. Let's call the number of such states N. Thus, at most N distinct planets could exist at any one time. Since we would expect such a universe to contain an infinite number of planets, and hence an infinite number of Earth-like planets, it implies that there are only a finite number of distinct planets in the universe, but the universe contains an infinite number of identical simultaneous copies of each of them. So, the universe would right now contain an infinite number of identical copies of you, all exactly alike. So, this is an argument for spatial recurrence; I'm wondering if I could construct a similar argument for temporal recurrence.

So, anyway, that is where my mind is going. Zachary Martin 03:21, 10 June 2011 (EDT)

- OK, given all these reservations (especially this: "we can't infer much about the real world from the behaviour of those models in such extreme conditions, and we cannot test any of this experimentally"), I have no objections.
- Here is an analogy. The sum of the first 20 terms of the Taylor series for sine gives a good approximation around the origin, and shows alternating maxima and minima. However, one must be careful using it when discussing "the problem of" boundedness of the sine on the whole line. --Boris Tsirelson 03:39, 10 June 2011 (EDT)
- "So, the universe would right now contain an infinite number of identical copies of you, all exactly alike." --- OK, even if so, the question remains, how fast the instant similarity will disappear in time. --Boris Tsirelson 04:14, 10 June 2011 (EDT)
- Well, thinking some more about this. If the universe contains an infinity of Earths (by which I mean Earth-like-planet), but there are only finitely many possible distinct Earths, that means that there must be an infinite number of copies of at least one Earth, but not necessarily of every Earth. This applies on a moment-by-moment basis, so it may not be the same Earth in every moment that has the infinite number of copies. (Although I think, supposing that all of them posess an infinite number of copies in every moment is simpler.) Zachary Martin 06:37, 10 June 2011 (EDT)

- One more thought... Thinking this way I also claim existence of (infinitely many) copies of you such that during all "your" life, "your" kettle freezes each time you try to boil it. I could also add: "...but "you" feel the water hot when in fact it is cold" etc etc. --Boris Tsirelson 04:49, 10 June 2011 (EDT)
- And what about a being that transmogrifies from "you" to "me" each summer, and back each winter? :-) --Boris Tsirelson 05:33, 10 June 2011 (EDT)
- Oh yes... actually, I don't actually believe in an infinite universe. I personally think the universe is spatiotemporally finite. Some of my arguments about the consequences of infinity are a bit of a
*reductio ad absurdum*against infinity. Actually, you could even call me an ultrafinitist, of sorts... Zachary Martin 06:39, 10 June 2011 (EDT)- Aha! I am also very suspicious about straightforward applicability of mathematical infinities to anything real. --Boris Tsirelson 07:36, 10 June 2011 (EDT)
- I would say, I am sympathetic to the ultrafinitist position, that only 'manageable' numbers actually 'exist'. I think mathematics exists in human minds, there are numbers too big to fit in a human mind. There is some finite number, which will be the largest number any human will ever think of (and I just did a Berry paradox). Any larger number definitely does not exist (and many smaller). So this in a sense makes me an ultrafinitist. I think quantity can be subdivided into: the hypofinite (quantities which are finite, and not "too large for humans"); the hyperfinite (that which is finite, yet so large no human will ever refer it individually); the infinite. The finite can be subdivided into two parts, a finite hypofinite prefix, and the infinite hyperfinite remainder. So to me, only hypofinite numbers exist; hyperfinite and infinite ones don't. That said, I understand some ultrafinitists have suggested that, if infinity does not exist, mathematics must be reimplemented without it. I don't agree. I'm happy for mathematicians to keep their infinity of infinities of infinities (anyone want a Mahlo cardinal?), I'll just insist they aren't "real" in the sense that hypofinite numbers are real. But I don't think one needs to worry about this when one does mathematics, just when one wants to philosophise. Zachary Martin 07:57, 10 June 2011 (EDT)
- Agreed. --Boris Tsirelson 08:07, 10 June 2011 (EDT)

- I would say, I am sympathetic to the ultrafinitist position, that only 'manageable' numbers actually 'exist'. I think mathematics exists in human minds, there are numbers too big to fit in a human mind. There is some finite number, which will be the largest number any human will ever think of (and I just did a Berry paradox). Any larger number definitely does not exist (and many smaller). So this in a sense makes me an ultrafinitist. I think quantity can be subdivided into: the hypofinite (quantities which are finite, and not "too large for humans"); the hyperfinite (that which is finite, yet so large no human will ever refer it individually); the infinite. The finite can be subdivided into two parts, a finite hypofinite prefix, and the infinite hyperfinite remainder. So to me, only hypofinite numbers exist; hyperfinite and infinite ones don't. That said, I understand some ultrafinitists have suggested that, if infinity does not exist, mathematics must be reimplemented without it. I don't agree. I'm happy for mathematicians to keep their infinity of infinities of infinities (anyone want a Mahlo cardinal?), I'll just insist they aren't "real" in the sense that hypofinite numbers are real. But I don't think one needs to worry about this when one does mathematics, just when one wants to philosophise. Zachary Martin 07:57, 10 June 2011 (EDT)

- Aha! I am also very suspicious about straightforward applicability of mathematical infinities to anything real. --Boris Tsirelson 07:36, 10 June 2011 (EDT)

- Oh yes... actually, I don't actually believe in an infinite universe. I personally think the universe is spatiotemporally finite. Some of my arguments about the consequences of infinity are a bit of a

## [edit] Academic boycott of Israel

Hi Boris. I saw on your homepage some links about attempts to boycott Israel in the academic area. Being an Israeli academic, have you been personally affected by that?

- I am welcome in some institutions and conferences in Austria, Canada, Finland, France, Germany, Greece, India, Italy, Japan, UK, USA. Still, it may happen that someone did not invite me for political reasons; I have no way to detect such cases.

Personally, I try to be fair, but if I am honest my own sympathies are often more on the Palestinian than the Israeli side.

- Anyway, political debates are unwelcome on Knowino.
- It was not my intention to start a political debate with you on the topic :) I don't think that would benefit either of us. Simply what I was trying to say, was that even though on the broader questions here I probably have a rather different perspective from you, I wanted to express my agreement with you on this particular issue. Also, if Knowino aims to be a generalist encyclopedia, inevitably it is going to cover topics (e.g. recent history of the Middle East) which are going to be very controversial, and are inevitably going to produce heated political debates. So I'm not sure how political debates can be avoided, unless one decides certain topics are off limits to articles, in which case one is not aiming at being a generalist encyclopedia any more. Zachary Martin 19:56, 11 June 2011 (EDT)

- Anyway, political debates are unwelcome on Knowino.

That said, I don't support any academic boycotts of Israel. It is a pity that the world is full of heated political conflicts; but it is a good thing that a lot of areas, e.g. academic disciplines with no direct relation to the conflict, can be kept separate from that. (Obviously, some disciplines, like history or politics or law, will be inevitably relevant to these sort of conflicts; but no need to get mathematics or chemistry involved.) Trying to bring the conflict into those areas too, both harms those disciplines, and harms the world in general. The conflict is already wide-ranging, we don't need to make it even bigger, and politicise things that don't need to be politicised. Zachary Martin 18:32, 10 June 2011 (EDT)

- Yes. Also Knowino is among such things. --Boris Tsirelson 12:07, 11 June 2011 (EDT)

## [edit] Figures

Boris, I see that you didn't transfer yet the figures of sine. I also saw that law of sines has one wrong figure and lacks 3 figures. Don't you know how to transfer drawings, or don't you want to do it, or are you postponing it for some reason?--Paul Wormer 11:48, 12 June 2011 (EDT)

- Paul, you astonish me. Did you forget that (not long ago) I've asked you to transfer yourself your figures whose copyright status on CZ is formally undefined? Once again, "I do not find the words "public domain" on cz:File:Def sine cosine.png". This is about "Sine". About "Law of sines", I did not look at it yet. --Boris Tsirelson 13:12, 12 June 2011 (EDT)
- I misunderstood your earlier message. I thought that you only wanted me to change the license. I did not understand that you wanted me to transfer the drawings as well. Lately I have been using CC by the sea, see angle (geometry), although I don't understand why my releasing to the public domain of my drawings gives them an undefined status.--Paul Wormer 13:49, 12 June 2011 (EDT)
- Just because you forgot to write "Public domain". It must be written, explicitly. Otherwise it is not formally stated. --Boris Tsirelson 13:55, 12 June 2011 (EDT)

- I misunderstood your earlier message. I thought that you only wanted me to change the license. I did not understand that you wanted me to transfer the drawings as well. Lately I have been using CC by the sea, see angle (geometry), although I don't understand why my releasing to the public domain of my drawings gives them an undefined status.--Paul Wormer 13:49, 12 June 2011 (EDT)

## [edit] SI

Boris, SI links through to WP instead of to the Knowino article International System of Units. Oddly enough I don't know how to fix this. Do you? --Paul Wormer 04:49, 20 June 2011 (EDT)

- I fixed it by a hack, not via an "official" route. I edited an arbitrary article and changed the URL in the browser address field. It seems to me that there must be easier ways.--Paul Wormer 05:23, 20 June 2011 (EDT)

- Oops, it is my error, this redirect; I did not note our article.
- One way to come to a redirect page is, via User:Boris Tsirelson#Redirects to Wikipedia.
- But if a redirect to WP is not made by me, then it probably is not linked there, and then I see no way simpler than using either my trick (mimicking the syntax used by me there) or your trick. --Boris Tsirelson 07:04, 20 June 2011 (EDT)
- NO, no, an "official" route is Special:ListRedirects. Enjoy... --Boris Tsirelson 07:13, 20 June 2011 (EDT)
- Thank you.--Paul Wormer 08:17, 20 June 2011 (EDT) PS Don't forget to adapt SI in User:Boris Tsirelson#Redirects to Wikipedia.

## [edit] Sine again

I added the section sine#Series expansion. I don't see the importance of later sections in the sine article, but since I am not a mathematician, I don't want to be Wikipedia-ish and delete them. However, you *are* a mathematician, so could you have a look and either discard sections you find unnecessary, or add a few sentences making clearer what their use is? Thank you. --Paul Wormer 11:37, 20 June 2011 (EDT)

- OK, I just moved them to the talk page. Maybe a part of this content will some day find its place in another, more appropriate article. Have you a better (than Kiselev) textbook to cite? --Boris Tsirelson 14:20, 20 June 2011 (EDT)
- No I don't have a better book to cite than Kiselev. My highschool textbooks were all in Dutch, and I doubt that any of them are still in use. Pedagogues have changed the practice of teaching math at least five times since I left school. I believe that this is also true in the US. I had, of course, never heard of Kiselev before I looked at sine. Googling the book I'm surprised about its impact. Did you use it as a Russian kid? --Paul Wormer 01:29, 21 June 2011 (EDT)
- Probably I did, but I do not remember. --Boris Tsirelson 01:48, 21 June 2011 (EDT)

- No I don't have a better book to cite than Kiselev. My highschool textbooks were all in Dutch, and I doubt that any of them are still in use. Pedagogues have changed the practice of teaching math at least five times since I left school. I believe that this is also true in the US. I had, of course, never heard of Kiselev before I looked at sine. Googling the book I'm surprised about its impact. Did you use it as a Russian kid? --Paul Wormer 01:29, 21 June 2011 (EDT)

## [edit] Symmetric / permutation group

It is easy to merge the two articles. Shall I do it? I don't mind whether it is permutation group with symmetric group as redirect, or vice versa. Do you have a preference?--Paul Wormer 03:57, 3 August 2011 (EDT)

- Yes, please do. No, I have no preference, too. --Boris Tsirelson 04:41, 3 August 2011 (EDT)

## [edit] Algebra

I see that you linked Algebra to WP. Don't you want to copy the CZ article? If not, why?--Paul Wormer 04:01, 3 August 2011 (EDT)

- I did not copy it, since it was copied from WP to CZ in 2007, and basically not changed on CZ. The observed now distinctions between WP and CZ articles are due to progress on WP, not CZ. --Boris Tsirelson 04:39, 3 August 2011 (EDT)

## [edit] Gauss-Legendre

Did you copy http://en.citizendium.org/wiki/GauLegExample/code from CZ? If so, under which name?--Paul Wormer 08:33, 8 August 2011 (EDT)

- No, I did not. (I do not remember copying any code hereto.) --Boris Tsirelson 11:00, 8 August 2011 (EDT)
- When I copy it, whereto? --Paul Wormer 11:51, 8 August 2011 (EDT)
- But, where do you like to put a link to it? If on "Gauss-Legendre" then it may be "Gauss-Legendre/Code". Generally, we have separate namespaces for Bibliography and Links (only). Everything else should be subpages: "X/Y". --Boris Tsirelson 11:57, 8 August 2011 (EDT)

- When I copy it, whereto? --Paul Wormer 11:51, 8 August 2011 (EDT)

## [edit] Mathematics sub-categories

In my editing of the Catgories, I have been aiming at the following sub-categories for Mathematics:

Arithmetic - Algebra - Trigonometry - Geometry - Curves and Plane Figures - Analysis - Statistics - Mathematicians

For the moment, I have been placing "Curves and Plane Figures" under Geometry rather than in a separate sub-category. Any comments or suggestions of yours as to these divisions would be appreciated.

Also, is there any difference between "Algebraic geometry" and "Analytical geometry"?

JFPerry 11:28, 12 November 2011 (EST)

- Why "Curves and Plane Figures" rather than just "Geometry"?
- "Probability" (or "Probability theory") could be also used (it relates to statistics like biology to medicine...)
- Yes, Algebraic geometry is quite a serious domain, more-or-less equally spaced from algebra and geometry, while Analytical geometry is now a matter to teach/learn and use, but (almost) no more to research, and it is geometry, not algebra, I think so (but these boundaries can be somewhat controversial). --Boris Tsirelson 11:42, 12 November 2011 (EST)

## [edit] Article "Statistics theory"

I cannot rename (or move - same thing, I think) pages. But I believe you can. So if you think *Statistics theory* would be better entitled *Statistical theory*, by all means rename it. There is one other page which desperately needs renaming: Page. U.S. Ambassador to the Netherlands.

BTW, I created a short (stub) article (Bicycle) essentially for the purpose of creating the *Inventions* category. I hope that's okay. The *Inventions* category will contain articles like Pencil, Paper clip, Cotton gin, Steam engine, etc.

JFPerry 19:52, 16 November 2011 (EST)

- About "Statistics theory" I am not sure; maybe there is a reason to call it this way.
- About "Ambassador": already moved by Paul.
- About "Bicycle": OK, why not. I do not like stubs
*imported*hereto (from CZ or whatever), but stubs*written*here is another matter. - --Boris Tsirelson 01:41, 17 November 2011 (EST)

## [edit] Spambots

Boris, a helpful hint: delete the spam when blocking the spammer. I deleted the "entry" and added "Spam" to the deletion reason list. Thanks!--Fred Anderson 19:17, 17 January 2012 (EST)

- Thanks.—Tom Larsen (talk) 20:45, 17 January 2012 (EST)