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	<title>Steven Landsburg &#124; The Big Questions: Tackling the Problems of Philosophy with Ideas from Mathematics, Economics, and Physics &#187; Philosophy</title>
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	<description>The Big Questions &#124; Tackling the Problems of Philosophy with Ideas from Mathematics, Economics, and Physics</description>
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		<title>Basic Arithmetic:  On What There Is</title>
		<link>http://www.thebigquestions.com/2010/09/01/basic-arithmetic-on-what-there-is/</link>
		<comments>http://www.thebigquestions.com/2010/09/01/basic-arithmetic-on-what-there-is/#comments</comments>
		<pubDate>Wed, 01 Sep 2010 06:01:07 +0000</pubDate>
		<dc:creator>Steve Landsburg</dc:creator>
				<category><![CDATA[Math]]></category>
		<category><![CDATA[Ontology]]></category>
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		<guid isPermaLink="false">http://www.thebigquestions.com/?p=4519</guid>
		<description><![CDATA[This is an extremely elementary post about numbers.  (&#8221;Numbers&#8221; means the natural numbers 0,1,2 and so forth.)  It is a sort of sequel to my three recent posts on basic arithmetic, which are here, here and here.  But it can be read separately from those posts.  
Today&#8217;s question is:  Do [...]]]></description>
			<content:encoded><![CDATA[<p><a href="http://www.thebigquestions.com/wp-content/uploads/2009/12/complex.jpg"><img src="http://www.thebigquestions.com/wp-content/uploads/2009/12/complex.jpg" alt="complex" title="complex" width="150" height="116" class="alignleft size-full wp-image-1578" /></a>This is an extremely elementary post about numbers.  (&#8221;Numbers&#8221; means the natural numbers 0,1,2 and so forth.)  It is a sort of sequel to my three recent posts on basic arithmetic, which are <a href="http://www.thebigquestions.com/2010/08/17/basic-arithmetic/">here</a>, <a href="http://www.thebigquestions.com/2010/08/18/basic-arithmetic-part-ii/">here</a> and <a href="http://www.thebigquestions.com/2010/08/19/basic-arithmetic-part-iii-the-map-is-not-the-territory/">here</a>.  But it can be read separately from those posts.  </p>
<p>Today&#8217;s question is:  Do numbers exist?  The answer is:  Of course, and I don&#8217;t believe there&#8217;s much in the way of serious doubt about this.  You were familiar with numbers when you were five years old, and you&#8217;ve been discovering their properties ever since.   Extreme skepticism on this point is almost unheard of among mathematicians or philosophers, though it seems to be fairly common among denizens of the Internet who have gotten it into their head that extreme skepticism makes them look sophisticated.</p>
<p>Let me be clear that I am not (yet) asking in what <b>sense</b> the natural numbers exist &#8212; whether they have existed since the beginning of time, or whether they exist outside of time, or whether they exist only in our minds.  Those are questions that reasonable people disagree about (and that other reasonable people find more or less meaningless.)  We can &#8212; and will &#8212; come back to those questions in future posts.  For now, the only question:  Do the natural numbers exist?  And the answer is yes.  Or better yet &#8212; if you believe the answer is no, then there&#8217;s obviously no point in thinking about them, so why are you reading this post?</p>
<p><span id="more-4519"></span></p>
<p>&#8220;Existence&#8221; here is used in the ordinary everyday sense of the word, according to which rocks and trees exist, you and I exist, your hopes and dreams exist, and the idea of a unicorn exists.  Unicorns themselves do not exist and therefore it makes no sense to study their properties.  (Though you can have fun <i>inventing</i> some properties for them.)  By contrast, it makes perfect sense for geologists to study the properties of rocks, for botanists to study the properties of trees, for folklorists to study the properties of the idea of a unicorn, and for mathematicians to study the properties of the natural numbers.  </p>
<p>An extreme skeptic might deny the existence of rocks.  The only possible answers are:  a)  It&#8217;s hard to believe you&#8217;re serious, since you&#8217;ve been encountering rocks &#8212; just like you&#8217;ve been encountering numbers &#8212; your entire life.  b)  If you really <i>are</i> serious, I suppose your best strategy is to stop thinking about rocks, and leave them to those of us who find geology interesting.  And c) Do not fool yourself into believing that your position is anywhere close to any mainstream school of thought.   </p>
<p>Another extreme skeptic might deny the existence of numbers.  I&#8217;ll leave it to my readers to replace rocks with numbers in the above retorts.</p>
<p>What else might one say to an extreme skeptic?  Answer:  One might attempt to acquaint him with <a href="http://en.wikipedia.org/wiki/Completeness_theorem">Godel&#8217;s Completeness Theorem</a>.  (This is <b>not</b> the same as the far more famous <a href="http://www.thebigquestions.com/2009/11/25/godel-in-a-nutshell/">Godel&#8217;s <i>In</i>completeness Theorem</a>.)  Here is (part of) what the Completeness Theorem says:  First, without making any assumptions about existence, write down a list of axioms for the natural numbers.  For example, write down the <a href="http://en.wikipedia.org/wiki/Peano_axioms">Peano Axioms</a>.  Then the Completeness Theorem tells you that as long as those axioms are consistent, there must <b>be</b> some mathematical structure that obeys those axioms.  (Note that &#8220;be&#8221; is a synonym for &#8220;exist&#8221;.)  The smallest of those structures  (known as &#8220;models&#8221;) is our good old friend the natural numbers.</p>
<p>In other words, Godel&#8217;s Theorem tells you that <b>if</b> the Peano axioms are consistent, <b>then</b> the natural numbers must exist.  (Don&#8217;t confuse the map with the territory!  &#8220;Consistency&#8221; applies to the axioms; &#8220;existence&#8221; applies to the natural numbers themselves.)  </p>
<p>On the other hand, we can also argue in the opposite direction:   <b>If</b> the natural numbers exist, <b>then</b> the Peano axioms, being true statements about existing objects, must be consistent.  An accurate map of an existing territory cannot contradict itself.  </p>
<p>So &#8212; We know that the natural numbers exist because we know the Peano axioms are consistent.  And we know that the Peano axioms are consistent because we know that the natural numbers exist.  Does that sound circular?  It&#8217;s not.  Here&#8217;s the point:  We have extremely good reasons for believing in the existence of the natural numbers (beginning with intuition, lifelong familiarity, and the fact that we seem to be able to discover their properties).  We have (partly) separate extremely good reasons for believing in the consistency of the Peano axioms (beginning with intuition and the fact that they&#8217;ve never yet led us to a contradiction).  The fact that our two beliefs <b>reinforce</b> each other &#8212; that if either is true, then so must be the other &#8212; should build up our confidence that the whole picture hangs together.</p>
<p>Now let&#8217;s get back to our extreme skeptic.  He denies the existence of the natural numbers.  We respond that Godel&#8217;s Completeness Theorem <b>proves</b> the existence of the natural numbers, as a consequence of the consistency of the Peano axioms.  He now has only two recourses (other than to concede defeat).  One is to deny the consistency of the Peano axioms, and the other is to deny the accuracy of Godel&#8217;s Completeness Theorem.  Let&#8217;s see how those strategies are likely to work out for him.</p>
<p>Should he doubt the consistency of the axioms?  The Peano Axioms lay out the rules of arithmetic that you&#8217;ve used your whole life; they say things like &#8220;Every number has exactly one immediate successor&#8221; and &#8220;x + (y+1) = (x+y) + 1&#8221;.  People (and to some extent animals) have been applying these axioms, explicitly or implicitly, since long before the dawn of history and no contradiction has ever arisen; moreover, for what it&#8217;s worth, the consistency of these simple axioms is instantly clear to most people&#8217;s intuitions.  If we were to jettison our belief that these axioms are consistent, then we&#8217;d pretty much have to give up all quantitative reasoning.</p>
<p>Well, then, should our skeptic doubt Godel&#8217;s Completeness Theorem?  The theorem is proved using elementary notions about sets &#8212; the idea that it&#8217;s possible to talk about sets of things and about membership in a set, that it&#8217;s possible to form the union of two sets, and so on.  This has nothing to do with the more esoteric subject of &#8220;axiomatic set theory&#8221;; instead, it uses only the most fundamental notions associated with forming collections of things.  (These notions, in fact, are prerequisite for axiomatic set theory and therefore cannot depend on it.)  Once again, if you were to abandon this sort of reasoning, you&#8217;d pretty much have to abandon reasoning altogether.</p>
<p>For anyone who accepts the simplest sorts of combinatorial reasoning, there is no longer an out.  The natural numbers are real.  Again, this says <b>nothing</b> about where they came from &#8212; be it Plato&#8217;s heaven, the minds of humans or the mind of God.  We&#8217;ll get back to that in the next installment of this occasional series.</p>
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		<slash:comments>57</slash:comments>
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		<title>Free Will versus Determinism:  The Web Comic</title>
		<link>http://www.thebigquestions.com/2010/03/16/free-will-versus-determinism-the-web-comic/</link>
		<comments>http://www.thebigquestions.com/2010/03/16/free-will-versus-determinism-the-web-comic/#comments</comments>
		<pubDate>Tue, 16 Mar 2010 07:01:06 +0000</pubDate>
		<dc:creator>Steve Landsburg</dc:creator>
				<category><![CDATA[Cool Stuff]]></category>
		<category><![CDATA[Philosophy]]></category>
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		<guid isPermaLink="false">http://www.thebigquestions.com/?p=2764</guid>
		<description><![CDATA[
Like everyone else I know, I am of course a longtime fan of the webcomic XKCD.  But somehow it took me until last week to become aware of the frequently brilliant competitor Luke Surl, of which the above is a delectable example.  What else out there am I missing?
Hat tip to Harry Brighouse [...]]]></description>
			<content:encoded><![CDATA[<p><a href="http://www.lukesurl.com/archives/1243"><img src="http://www.thebigquestions.com/wp-content/uploads/2010/03/lukesurl.jpg" alt="lukesurl" title="So 18 billion years of the universe have conspired for you to read this alt-text? Bit of a let down. There isn't even a joke." width="500" height="696" class="alignleft size-full wp-image-2765" /></a></p>
<p>Like everyone else I know, I am of course a longtime fan of the webcomic <a href="http://xkcd.com/">XKCD</a>.  But somehow it took me until last week to become aware of the frequently brilliant competitor <a href="http://www.lukesurl.com/">Luke Surl</a>, of which the above is a delectable example.  What else out there am I missing?</p>
<p>Hat tip to <a href="http://philosophy.wisc.edu/brighouse/">Harry Brighouse</a> of Crooked Timber.</p>
<p><center><font color=orange>Click <a href="http://www.thebigquestions.com/2010/03/16/free-will-versus-determinism-the-web-comic/">here</a> to comment or read others&#8217; comments.</font></center></p>
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		<slash:comments>13</slash:comments>
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		<title>Real Numbers</title>
		<link>http://www.thebigquestions.com/2010/01/13/real-numbers/</link>
		<comments>http://www.thebigquestions.com/2010/01/13/real-numbers/#comments</comments>
		<pubDate>Wed, 13 Jan 2010 07:01:09 +0000</pubDate>
		<dc:creator>Steve Landsburg</dc:creator>
				<category><![CDATA[Math]]></category>
		<category><![CDATA[Ontology]]></category>
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		<guid isPermaLink="false">http://www.thebigquestions.com/?p=1896</guid>
		<description><![CDATA[Yesterday we started a conversation about whether mathematics is invented or discovered.  Today I&#8217;ll give you my three best arguments for &#8220;discovered&#8221;.  And to focus the discussion, I&#8217;ll talk not about mathematics generally but about the natural numbers (0,1,2, and so forth) in particular. 
I believe the natural numbers exist, quite independently of [...]]]></description>
			<content:encoded><![CDATA[<p><a href="http://www.thebigquestions.com/wp-content/uploads/2010/01/numbers.jpg"><img src="http://www.thebigquestions.com/wp-content/uploads/2010/01/numbers-150x150.jpg" alt="numbers" title="numbers" width="150" height="150" class="alignleft size-thumbnail wp-image-1903" /></a>Yesterday we started a <a href="http://www.thebigquestions.com/2010/01/12/jellyfish-math/">conversation</a> about whether mathematics is invented or discovered.  Today I&#8217;ll give you my three best arguments for &#8220;discovered&#8221;.  And to focus the discussion, I&#8217;ll talk not about mathematics generally but about the natural numbers (0,1,2, and so forth) in particular. </p>
<p>I believe the natural numbers exist, quite independently of whether anyone&#8217;s around to think of them.  Here&#8217;s why:  First, we perceive them directly.  Second, we know non-trivial facts about them.  Third, they can explain the Universe.  In more detail:</p>
<p><span id="more-1896"></span></p>
<p><b>1.  We perceive them directly.</b>   I believe that flowers, rainbows and headaches exist because I perceive them directly.  I believe that the natural numbers exist for exactly the same reason.  Almost anyone who has ever thought hard about higher arithmetic will tell you the same thing.  Yesterday I quoted the Fields Medalist <a href="http://en.wikipedia.org/wiki/Alain_connes">Alain Connes</a> saying that when mathematicians contemplate arithmetic, &#8220;we run up against a reality every bit as uncontestable as physical reality&#8221;.  Today I&#8217;ll quote <a href="http://en.wikipedia.org/wiki/Kurt_godel">Kurt Godel</a>, the greatest logician of all time:</p>
<blockquote><p>
Despite their remoteness from sense experience, we do have something like a perception of the objects of set theory, as is seen from the fact that the axioms force themselves on us as being true.  I don&#8217;t see any reason why we should have less confidence in this kind of perception, i.e. in mathematical intuition, than in sense perception.</p>
</blockquote>
<p><b>2. We know non-trivial facts about them.</b>  In 1637, <a href="http://en.wikipedia.org/wiki/Fermat">Pierre de Fermat</a> wondered whether you can find four positive numbers x, y, z and n, with n at least 3, that satisfy the equation<br />
<center>x<sup>n</sup>+y<sup>n</sup>=z<sup>n</sup></center><br />
After 350 years, the question was settled by <a href="http://en.wikipedia.org/wiki/Gerhard_frey">Gerhard Frey</a>, <a href="http://en.wikipedia.org/wiki/Ken_Ribet">Ken Ribet</a> and <a href="http://en.wikipedia.org/wiki/Andrew_wiles">Andrew Wiles</a> in one of the most spectacular mathematical achievements of the twentieth century.  The answer, as Fermat had believed, is no.</p>
<p>That&#8217;s certainly a meaningful statment:  It means that no matter what four numbers you write down, we can predict with certainty that as long as they&#8217;re positive, and as long as n is at least 3, the equation I&#8217;ve just written down will never be true.  But unlike the axioms that Godel was referring to, it&#8217;s hardly self-evident and it does not force itself on us as being true; that&#8217;s part of why it took 350 years to prove.  </p>
<p>So how do we know that Fermat&#8217;s Last Theorem (i.e. the statement that the equation has no solutions) is true?  The answer is <b>not</b> that it follows step by step from some list of self-evident axioms about the natural numbers.   As far as I am aware, nobody has the foggiest idea whether Fermat&#8217;s Last Theorem follows from any set of reasonably self-evident axioms about arithmetic, such as the <b>Peano axioms</b> that I wrote about <a href="http://www.thebigquestions.com/2009/12/17/non-simple-arithmetic/">here</a>.  Instead, we know that Fermat&#8217;s Last Theorem is true via informal (but, to almost all mathematicians, completely convincing) arguments that are <b>not</b> about manipulating axioms but instead are about the properties of <b>numbers themselves</b>.</p>
<p>(It&#8217;s a virtual certainty that these informal arguments could be formalized in <b>some</b> language, but&#8212;again as far as I know&#8212;it&#8217;s quite unknown whether they could be formalized in the usual language of arithmetic.)</p>
<p>So I agree with Godel that the self-evident nature of the axioms is evidence that the natural numbers are real, but I also believe, quite separately, that the <b>non</b>-self-evident nature of statements like Fermat&#8217;s Last Theorem is additional evidence.  Here we have a statement that is <b>true</b>, but it&#8217;s truth is not derived from axioms about arithmetic.  Instead it&#8217;s true because it&#8217;s a correct statement <b>about</b> something.  That &#8220;something&#8221; is the system of natural numbers.</p>
<p><b>3.  They explain the Universe.</b>  This argument is surely more speculative than the others, but I cannot imagine any way to explain the existence of the Universe without the prior existence of the natural numbers.  (This is more or less the same reason some people give for believing in God.)  It seems to me that the most compelling question in philosophy is why anything exists at all.  Any satisfactory answer has to start with something that <b>must</b> exist.  The natural numbers fill that role admirably.  In <a href="http://www.amazon.com/Big-Questions-Philosophy-Mathematics-Economics/dp/143914821X/ref=nosim/?tag=moseissase-20"><em>The Big Questions</em></a>, I&#8217;ve sketched a story about how, once you&#8217;ve got some mathematical objects, the Universe can sort of bootstrap itself in existence from there; this is similar in spirit to the story advanced by the noted cosmologist <a href="http://en.wikipedia.org/wiki/Max_Tegmark">Max Tegmark</a> in his essay on <a href="http://arxiv.org/abs/0704.0646">The Mathematical Universe</a> (cited in yesterday&#8217;s comments by Al V.)</p>
<p>Now admittedly, my inability to find any alternative explanation for the Universe does not prove that this explanation is correct.  For that matter, my hunger for an explanation doesn&#8217;t mean there has to be one.  Maybe the Universe just <b>is</b>.  But when you&#8217;re facing a huge riddle and you can only think of one possible solution, you&#8217;ve got to at least contemplate the possibility that you&#8217;re on to something.</p>
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		<title>Jellyfish Math</title>
		<link>http://www.thebigquestions.com/2010/01/12/jellyfish-math/</link>
		<comments>http://www.thebigquestions.com/2010/01/12/jellyfish-math/#comments</comments>
		<pubDate>Tue, 12 Jan 2010 07:01:14 +0000</pubDate>
		<dc:creator>Steve Landsburg</dc:creator>
				<category><![CDATA[Books]]></category>
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		<guid isPermaLink="false">http://www.thebigquestions.com/?p=1861</guid>
		<description><![CDATA[
Is mathematics invented or discovered?  In my experience, applied scientists often think of mathematics as a human invention, while actual mathematicians (with a few notable exceptions) feel sure that mathematics was always there to be discovered. (Of course, it&#8217;s sometimes hard to tell how much of this is genuine disagreement and how much is [...]]]></description>
			<content:encoded><![CDATA[<p><a href="http://www.amazon.com/God-Mathematician-Mario-Livio/dp/0743294068/ref=nosim/?tag=moseissase-20"><img src="http://www.thebigquestions.com/wp-content/uploads/2010/01/livio1.jpg" alt="livio" title="livio" width="130" height="200" class="alignleft size-full wp-image-1873" /></a><br />
Is mathematics invented or discovered?  In my experience, applied scientists often think of mathematics as a human invention, while actual mathematicians (with a few notable exceptions) feel sure that mathematics was always there to be discovered. (Of course, it&#8217;s sometimes hard to tell how much of this is genuine disagreement and how much is a language barrier.)  </p>
<p>I&#8217;ve just finished reading an excellent book by <a href="http://en.wikipedia.org/wiki/Mario_Livio">Mario Livio</a> which is entirely about the invention/discovery question, though he&#8217;s chosen the (somewhat unfortunate) title <a href="http://www.amazon.com/God-Mathematician-Mario-Livio/dp/0743294068/ref=nosim/?tag=moseissase-20">Is God a Mathematician?</a>  Much of the book is a lively romp through mathematical history, with a well chosen mix of biography and exposition.  Although he parts company with them in the last chapter, Livio gives a more than fair hearing to the many great mathematicians who have insisted that they are discoverers, from <a href="http://en.wikipedia.org/wiki/Pythagoras">Pythagoras</a> through <a href="http://en.wikipedia.org/wiki/Galileo">Galileo</a>, <a href="http://en.wikipedia.org/wiki/G.H._Hardy">G.H. Hardy</a>, <a href="http://en.wikipedia.org/wiki/Goedel">Kurt Godel</a>, and the contemporary Fields Medalist <a href="http://en.wikipedia.org/wiki/Connes">Alain Connes</a> (among others).   Here, for example is Connes:</p>
<p><span id="more-1861"></span></p>
<blockquote><p>
Take prime numbers, for example, which as far as I&#8217;m concerned, constitute a more stable reality than the physical reality that surrounds us.  The working mathematician can be likened to an explorer who sets out to discover the world&#8230;We run up against a reality every bit as uncontestable as physical reality.
</p></blockquote>
<p>Readers of <a href="http://www.amazon.com/Big-Questions-Philosophy-Mathematics-Economics/dp/143914821X/ref=nosim/?tag=moseissase-20"><em>The Big Questions</em></a> will know that I am entirely in Connes&#8217;s camp on this issue, for reason I&#8217;ll blog about later in the week.  And as I&#8217;ve said, it seems that most mathematicians sit in this camp.  But there are notable dissenters, including the great <a href="http://en.wikipedia.org/wiki/Michael_atiyah">Sir Michael Atiyah</a>, another Fields Medalist who I might well have included in my <a href="http://www.thebigquestions.com/2010/01/06/the-world-wide-wall/">gallery of heroes</a>.  Despite my great admiration for Atiyah, I believe he&#8217;s wrong on this issue.  But more fundamentally, I believe his primary argument proves <b>exactly the opposite</b> of what he thinks it does.  Here is that argument (slightly condensed):</p>
<blockquote>
<p>Any mathematician must sympathize with Connes.  We all feel that the integers really exist in some abstract sense and the Platonic view is extremely seductive.  But can we really defend it? It might seem that counting is really a primordial notion.  But let us imagine that intelligence had resided, not in mankind, but in some vast solitary and isolated jellyfish, buried deep in the Pacific Ocean.  It would have no experience of individual objects, only of the surrounding water.  Motion, temperature and pressure would provide its basic sensory data.  In such a pure continuum the discrete would not arise and there would be nothing to count.</p>
</blockquote>
<p>Here Atiyah has envisioned a world where the natural numbers get neither invented <b>nor</b> discovered.  I&#8217;m not sure why that&#8217;s supposed to prove they don&#8217;t exist.  On the contrary, it seems to me that quite unbeknownst to Atiyah&#8217;s Jellyfish, the earth would still have exactly one moon and exactly two magnetic poles, and two would still be twice one.  Two would still be a prime number, and 1729 would still be the smallest number that is the sum of two cubes in two different ways.  </p>
<p>Indeed, all these things were true back in the days when the world <b>was</b> populated by creatures who were unaware of them.  It doesn&#8217;t matter for the argument whether those creatures are highly intelligent in other ways.  In that sense, Atiyah&#8217;s Jellyfish is more like a Red Herring.</p>
<p>Or to put this another way:  Atiyah says that an intelligent creature might be unaware that one plus one makes two.  Sure&#8212;so might any creature.  To me, this indicates that 1+1=2 is not an invention; it&#8217;s simply a truth.  Can anyone explain why Atiyah thinks his story proves otherwise?</p>
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		<title>Non-Simple Arithmetic</title>
		<link>http://www.thebigquestions.com/2009/12/17/non-simple-arithmetic/</link>
		<comments>http://www.thebigquestions.com/2009/12/17/non-simple-arithmetic/#comments</comments>
		<pubDate>Thu, 17 Dec 2009 07:01:04 +0000</pubDate>
		<dc:creator>Steve Landsburg</dc:creator>
				<category><![CDATA[Logic]]></category>
		<category><![CDATA[Math]]></category>
		<category><![CDATA[Ontology]]></category>
		<category><![CDATA[Philosophy]]></category>

		<guid isPermaLink="false">http://www.thebigquestions.com/?p=1556</guid>
		<description><![CDATA[The Intelligent Design folk tell you that complexity requires a designer.
The Richard Dawkins crowd tell you that complexity must evolve from simplicity.
I claim they&#8217;re both wrong, because the natural numbers, together with the operations of arithmetic, are fantastically complex, but were neither created nor evolved. 
I&#8217;ve made this argument multiple times, in The Big Questions, [...]]]></description>
			<content:encoded><![CDATA[<p><img src="http://www.thebigquestions.com/wp-content/uploads/2009/12/complex.jpg" alt="complex" title="complex" width="150" height="116" class="alignleft size-full wp-image-1578" />The Intelligent Design folk tell you that complexity requires a designer.</p>
<p>The Richard Dawkins crowd tell you that complexity must evolve from simplicity.</p>
<p>I claim they&#8217;re both wrong, because the natural numbers, together with the operations of arithmetic, are fantastically complex, but were neither created nor evolved. </p>
<p>I&#8217;ve made this argument multiple times, in <a href="http://www.amazon.com/Big-Questions-Philosophy-Mathematics-Economics/dp/143914821X/ref=nosim/?tag=moseissase-20"><em>The Big Questions</em></a>, on this blog, and elsewhere.  Today, I aim to explain a little more deeply why I say that the natural numbers are fantastically complex.</p>
<p><span id="more-1556"></span></p>
<p>Here&#8217;s one way to think about simplicity versus complexity:  Simple things have short descriptions; complex things have only long descriptions.  A string of a million zeros is very simple because I can describe it in six words:  &#8220;A string of a million zeros&#8221;.  A string of a million random numbers is complex, because it takes a long time to describe all of the content.</p>
<p>Now what about the system of natural numbers?  To first appearances, there&#8217;s a very simple description:  Start with 0, then add 1, then add 1 again, keep doing this forever, and those are the natural numbers.  Unfortunately, &#8220;keep doing this forever&#8221; is a little vague, and the complexity comes in when you try to make that precise.</p>
<p>So if you were setting out to give a complete description of the natural numbers, where would you start?  Probably here:  </p>
<ul>
<li>We have a number called zero, and then every number has a successor.</li>
</ul>
<p> But that description fits a lot of things besides the natural numbers; it also fits, for example, the integers (the integers, unlike the natural numbers, include negatives).  Here&#8217;s an attempt to fix that:</p>
<ul>
<li>We have a number called zero, and then every number has a successor, <b>and</b> zero is not the successor of any number.</li>
</ul>
<p>Better, but still no good; this fails to rule out a system where 1 follows 0, 2 follows 1, 3 follows 2, and 1 follows 3, like this:<br />
<a href="http://www.thebigquestions.com/wp-content/uploads/2009/12/three.gif"><img src="http://www.thebigquestions.com/wp-content/uploads/2009/12/three.gif" alt="three" title="three" width="237" height="77" class="aligncenter size-full wp-image-1558" /></a><br />
To fix <b>that</b>, we have to add a clause specifying that no two numbers (such as 0 and 3) have the <b>same</b> successor.   But even now, we&#8217;ve only just begun.</p>
<p>We still haven&#8217;t ruled out the possibility of infinite gaps between numbers.  For all we can tell from our description so far, the number system might look like this:<br />
<a href="http://www.thebigquestions.com/wp-content/uploads/2009/12/infinite.gif"><img src="http://www.thebigquestions.com/wp-content/uploads/2009/12/infinite-300x19.gif" alt="infinite" title="infinite" width="300" height="19" class="aligncenter size-medium wp-image-1560" /></a><br />
with <b>infinitely</b> many numbers in between 3 and that very large number N.  How can we rule <b>that</b> out?</p>
<p>This one is not so easy.  We&#8217;d like to say that all gaps between numbers are finite.  But how do we define &#8220;finite&#8221;? Usually we say a number is finite if it&#8217;s part of the set of natural numbers.  Or to put this another way:  We&#8217;d like to say that no matter where you start (say at N), you can&#8217;t count backward forever; eventually you&#8217;ve got to hit a stopping point.  But what does it mean to count backwards forever?  It means counting back more than a natural number of steps.  There&#8217;s that circularity again.</p>
<p>What we really really need, it turns out, is to add a clause like this to our description:</p>
<ul>
<li>Every non-empty subset of the natural numbers has a smallest element.</li>
</ul>
<p>This will solve our problem, because it implies, for example, that the set of numbers you can reach by counting backwards from N has a smallest element&#8212;eliminating the possibility of that infinite gap.</p>
<p>But this assumption, stated in this way, opens a can of worms that almost nobody wants to open.  Here&#8217;s why:  For the first time, we&#8217;ve been forced to talk about <b>sets</b> of natural numbers, as opposed to natural numbers themselves&#8212;and even to talk about all those sets at once.  In technical jargon, we&#8217;ve left the world of first-order logic and entered the world of second-order logic.  But that&#8217;s a very strange world indeed.  In ordinary (first-order) logic, we have a small number of rules of inference that allow us to proceed, for example, from &#8220;Socrates is a man&#8221; and &#8220;All men are mortal&#8221; to &#8220;Socrates is mortal&#8221;.  But in second-order logic, not only are the rules of inference not finite; they cannot even be printed out (even in an infinite amount of time) by any computer.  That&#8217;s why the great logician <a href="http://en.wikipedia.org/wiki/W._V._Quine">Willard van Ormand Quine</a> insisted that second order logic is not logic, and why mathematicians usually prefer to avoid it.  </p>
<p>All is not lost, though.  Instead of adding one second-order axiom, we can add infinitely many first-order axioms, viz:</p>
<ul>
<li>The set of odd numbers has a smallest element.</li>
<li>The set of numbers greater than 7 has a smallest element.</li>
<li>The set of numbers that can be reached by counting backward from 100 has a smallest element.</li>
</ul>
<p>And so on.</p>
<p>Okay, our description of the natural numbers just got infinitely long, but at least it&#8217;s infinitely long in a simple sort of way.  We&#8217;ve added an infinite number of axioms, but they all fit the same simple pattern&#8212;a pattern that you could easily train your computer to recognize.</p>
<p>Unfortunately, though, we still have a long way to go to get to a full description of arithmetic.  First, we have to add rules for addition and multiplication.  (If we don&#8217;t do this, then we won&#8217;t be able to talk about interesting subjects like prime numbers.)  Now we&#8217;ll want to add even more axioms.  But now we come up against the content of Godel&#8217;s incompleteness theorem:  NO description suffices.  No matter what axioms you add, your description will always fail to distinguish the natural numbers from any of an infinite number of other structures.    (Those other structures are usually called &#8220;non-standard models of arithmetic&#8221;).  </p>
<p>When I say that &#8220;NO description suffices&#8221;, you might reasonably ask what counts as a description.  Here&#8217;s what counts:  A description is some (possibly infinite) list of axioms that some computer program is capable of recognizing.   So if, for example, you try to describe arithmetic by listing every true statement about it, I will cry foul, because no computer program is capable of recognizing every true statement about arithmetic.  (This is not just an observation about the state of the art in computer programming.  It is a theorem about all <b>possible</b> computer programs.)</p>
<p>That&#8217;s the sense in which arithmetic is fantastically complex.  Not only do the natural numbers have no finite description; they have no description that is recognizable by any computer.   If &#8220;simple&#8221; means &#8220;capable of a short description&#8221;, then the natural numbers are about as far from simple as you can get.  Not only do they have no short description, they don&#8217;t even have an <b>infinite</b> description.  </p>
<p>Other mathematical structures are simpler.  Euclidean geometry, for example, can be fully described by a first-order theory, and there <b>is</b> a computer program that can distinguish true from false statements in that theory.  </p>
<p>Likewise for the (first-order) theory of the real numbers.  There are axioms for the real numbers that suffice to prove all true first-order statements about the real numbers, and there is a computer program that can distinguish the true statements from the false.  In that sense, the real numbers are far simpler than the natural numbers.   (There are still non-standard models of the real numbers, but through a first-order lens, they are indistinguishable from the real thing.)</p>
<p>(You might be tempted to think that because the natural numbers sit inside the real numbers, they must be simpler.  But of course any sequence of arbitrary complexity sits inside the very simple sequence 010101010101&#8230;.., if you can pick and choose what to keep and what to throw away.  Complexity can reside quite comfortably inside simplicity.)</p>
<p>Did that help?</p>
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		<title>Life, the Universes and Everything</title>
		<link>http://www.thebigquestions.com/2009/12/02/life-the-universes-and-everything/</link>
		<comments>http://www.thebigquestions.com/2009/12/02/life-the-universes-and-everything/#comments</comments>
		<pubDate>Wed, 02 Dec 2009 07:01:03 +0000</pubDate>
		<dc:creator>Steve Landsburg</dc:creator>
				<category><![CDATA[Ontology]]></category>
		<category><![CDATA[Philosophy]]></category>
		<category><![CDATA[Physics]]></category>
		<category><![CDATA[Religion]]></category>

		<guid isPermaLink="false">http://www.thebigquestions.com/?p=1186</guid>
		<description><![CDATA[As I mentioned the other day, I&#8217;ve recently (at the direction of my old friend Deirdre McCloskey) been reading some of the work of John Polkinghorne, the physicist-turned-theologian who seems to write about a book a week attempting to reconcile his twin faiths in orthodox science and orthodox Christianity.
Although Belief in God in an Age [...]]]></description>
			<content:encoded><![CDATA[<p>As I <a href="http://www.thebigquestions.com/2009/11/30/lament-of-deirdre/http://www.thebigquestions.com/2009/11/30/lament-of-deirdre/">mentioned</a> the other day, I&#8217;ve recently (at the direction of my old friend Deirdre McCloskey) been reading some of the work of <a href="http://en.wikipedia.org/wiki/Polkinghorne">John Polkinghorne</a>, the physicist-turned-theologian who seems to write about a book a week attempting to reconcile his twin faiths in orthodox science and orthodox Christianity.</p>
<p>Although <a href="http://www.amazon.com/Belief-Science-Polkinghorne-F-R-S-K-B-E/dp/0300099495/ref=nosim/?tag=moseissase-20">Belief in God in an Age of Science</a> is a very short book, it is too long to review in a single blog post.  Fortunately, though, much of the non-lunatic content is concentrated in roughly the first ten pages, so I&#8217;ll comment here only on those.</p>
<p>Polkinghorne begins in awe.  He is awestruck by the extent to which our Universe seems to have been fine-tuned to support life; this is the subject matter of the much-discussed <a href="http://en.wikipedia.org/wiki/Anthropic_principle">anthropic cosmological principle</a>.  To take just one example (which Polkinghorne does not mention):  The very existence of elements other than hydrogen and helium depends on the fact that it&#8217;s possible, in the interior of a star, to smoosh three helum atoms together and make a carbon atom; everything else is built from there.  But it&#8217;s not enough to <i>make</i> that carbon atom; you&#8217;ve also got to make it stick together long enough for a series of other complicated reactions to occur.  Ordinarily, that doesn&#8217;t happen, but now and then it does.  And the reason it happens even occasionally is that the carbon atom happens to have an energy level of exactly 7.82 million electron volts.   In  fact, this energy level was predicted (by <a href="http://en.wikipedia.org/wiki/Fred_Hoyle">Fred Hoyle</a> and <a href="http://en.wikipedia.org/wiki/Edwin_Salpeter">Edwin Salpeter</a>) before it was observed, precisely on the basis that without this energy level, there could be no stable carbon, no higher elements, and no you or me.  </p>
<p><span id="more-1186"></span></p>
<p>That energy level is only one of many (apparent) cosmic coincidences that make us possible; change any of the fundamental physical constants (like, say, the strength of gravity) by a little bit in either direction, and the Universe would, as far as we can tell, become completely inhospitable to life.  So one does tend to feel that there&#8217;s something here that needs explaining. </p>
<p>Some have attempted to dismiss the issue by turning the direction of causality on its head:  Here we are, so of course the laws of physics must allow for our existence.  Case closed.  <a href="http://en.wikipedia.org/wiki/Douglas_adams">Douglas Adams</a>, for example, offers this brief and brilliant parable:</p>
<blockquote>
<p>Imagine a puddle waking up one morning and thinking, ‘This is an interesting world I find myself in, an interesting hole I find myself in, fits me rather neatly, doesn’t it? In fact it fits me staggeringly well, must have been made to have me in it!’</p>
</blockquote>
<p>But I have some sympathy for Professor Polkinghorne&#8217;s refusal to accept this dismissal.  Instead, he takes his stand with the philosopher <a href="http://en.wikipedia.org/wiki/John_A._Leslie">John Leslie</a>:</p>
<blockquote>
<p>The fine tuning is evidence, genuine evidence, of the following fact:  that God is real, and/or there are many and varied universes.</p>
</blockquote>
<p>I agree with that (with the proviso that evidence is not proof).  I agree with it to exactly the same extent that I agree with this:</p>
<blockquote>
<p>The fine tuning is evidence, genuine evidence of the following fact:  Either invisible pink bunny rabbits, created at the time of the Big Bang, fine tuned the physical constants in order to make the Universe hospitable to lettuce, and/or there are many and varied universes.</p>
</blockquote>
<p>Or, more succinctly:</p>
<blockquote>
<p>The fine tuning is evidence, genuine evidence of the following fact:  There are many and varied universes.</p>
</blockquote>
<p>Polkinghorne wants to reject this second horn of Leslie&#8217;s dilemma, but he manages to do so, I think, only by taking too crabbed a view of what those many and varied Universes might be.  First, we have the parallel worlds promised to us by the many-worlds interpretation of quantum theory; Polkinghorne is absolutely right to say these can&#8217;t be the worlds we&#8217;re looking for, because they all obey the same basic laws of nature.  Higher on what Polkinghorne calls the &#8220;scale of bold speculation&#8221; we have suggestions from quantum cosmology that Universes are bubbling up all the time as quantum fluctuations in some universal substrate.  But again, Polkinghorne is right to say that this only pushes the mystery back a bit&#8212;why do those fluctuations obey laws that have even a chance of producing a habitable Universe?  Where do the laws come from?  </p>
<p>This is the point where Polkinghorne gives up and falls back on God.  But it seems to me that he has given up just one level of abstraction too soon.  A Universe is fundamentally a <i>mathematical</i> object&#8212;it&#8217;s an abstract pattern that might or might not contain subpatterns that might or might not be sufficiently complex in just the right away to achieve an awareness of their surroundings, and might or might perceive those surroundings as physical objects.  And <b>of course</b> there are many Universes, because there are many mathematical patterns, including, as just one of a dazzling infinity of examples, the Universe in which we live.</p>
<p>That, in any event, is the best explanation I can come up with, and it&#8217;s an explanation that feels completely right to me (which admittedly proves nothing).  In <a href="http://www.amazon.com/Big-Questions-Philosophy-Mathematics-Economics/dp/143914821X/ref=nosim/?tag=moseissase-20"><em>The Big Questions</em></a>, I&#8217;ve elaborated on what I mean by all this, how it can be true, and why it is entirely consistent with mainstream physics and the stated views of many mainstream physicists.  </p>
<p>Now, Professor Polkinghorne might or might not buy this vision, but my point is that <b>he never even contemplates it</b>.  He makes the leap to theism by considering and rejecting all of the weakest alternatives, but ignoring the only one that makes sense.  This oversight is all the more remarkable because Polkinghorne devotes his closing pages to a rousing defense of the independent reality of mathematical objects, in clear and convincing language that had me wishing I&#8217;d written these pages myself.   </p>
<p>The rest of the book is far worse.  I might come back to that in a later post.</p>
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		<title>Giving Thanks</title>
		<link>http://www.thebigquestions.com/2009/11/26/giving-thanks/</link>
		<comments>http://www.thebigquestions.com/2009/11/26/giving-thanks/#comments</comments>
		<pubDate>Thu, 26 Nov 2009 07:01:49 +0000</pubDate>
		<dc:creator>Steve Landsburg</dc:creator>
				<category><![CDATA[Philosophy]]></category>
		<category><![CDATA[Policy]]></category>
		<category><![CDATA[Progress]]></category>

		<guid isPermaLink="false">http://www.thebigquestions.com/?p=1076</guid>
		<description><![CDATA[After the philosopher Daniel Dennett was rushed to the hospital for lifesaving surgery to replace a damaged aorta, he had an epiphany:

I saw with greater clarity than ever before in my life that when I say &#8220;Thank goodness!&#8221; this is not merely a euphemism for &#8220;Thank God!&#8221; (We atheists don&#8217;t believe that there is any [...]]]></description>
			<content:encoded><![CDATA[<p>After the philosopher <a href="http://en.wikipedia.org/wiki/Daniel_Dennett">Daniel Dennett</a> was rushed to the hospital for lifesaving surgery to replace a damaged aorta, he had <a href="http://www.edge.org/3rd_culture/dennett06/dennett06_index.html">an epiphany:</a></p>
<blockquote>
<p>I saw with greater clarity than ever before in my life that when I say &#8220;Thank goodness!&#8221; this is not merely a euphemism for &#8220;Thank God!&#8221; (We atheists don&#8217;t believe that there is any God to thank.) I really do mean <i>thank goodness!</i> There is a lot of goodness in this world, and more goodness every day, and this fantastic human-made fabric of excellence  is genuinely responsible for the fact that I am alive today. It is a worthy recipient of the gratitude I feel today, and I want to celebrate that fact here and now. </p>
<p><span id="more-1076"></span></p>
<p>To whom, then, do I owe a debt of gratitude? To the cardiologist who has kept me alive and ticking for years, and who swiftly and confidently rejected the original diagnosis of nothing worse than pneumonia. To the surgeons, neurologists, anesthesiologists, and the perfusionist, who kept my systems going for many hours under daunting circumstances. To the dozen or so physician assistants, and to nurses and physical therapists and x-ray technicians and a small army of phlebotomists so deft that you hardly know they are drawing your blood, and the people who brought the meals, kept my room clean, did the mountains of laundry generated by such a messy case, wheel-chaired me to x-ray, and so forth. These people came from Uganda, Kenya, Liberia, Haiti, the Philippines, Croatia, Russia, China, Korea,  India—and the United States, of course—and I have never seen more impressive mutual respect, as they helped each other out and checked each other&#8217;s work. But for all their teamwork, this local gang could not have done their jobs without the huge background of contributions from others. I remember with gratitude my late friend and Tufts colleague, physicist Allan Cormack, who shared the Nobel Prize for his invention of the c-t scanner. Allan—you have posthumously saved yet another life, but who&#8217;s counting? The world is better for the work you did. Thank goodness. Then there is the whole system of medicine, both the science and the technology, without which the best-intentioned efforts of individuals would be roughly useless. So I am grateful to the editorial boards and referees, past and present, of <i>Science, Nature, Journal of the American Medical Association, Lancet</i>, and all the other institutions of science and medicine that keep churning  out improvements, detecting and correcting flaws.</p>
</blockquote>
<p>Indeed.  And because the supply of thankfulness is not fixed, it will not depreciate the value of Professor Dennett&#8217;s sentiment to add a word of thanks not just for <i>goodness</i> but for <i>greed</i>&#8212;the greed that inspired generations of inventors and investors, laborers and capitalists, doctors and nurses, technicians and scientists to envision and perfect such a thing as an artificial aorta, to educate themselves in the healing professions, and to show up for work every day.  For the most part, they did it to make a buck.</p>
<p>We can be thankful too for the system that channels all that potentially destructive greed into life-sustaining brilliance.  But we might temper our gratitude just a bit with a moment of wistful regret for the lives lost because of unnecessary imperfections in that system.  As a society, we spend far too little on basic research in health care, largely because breakthroughs are under-rewarded.  For one thing, our reliance on third-party payers (with the attendant loss of control over our own health care choices) makes us willing to pay handsomely even for relatively ineffective treatments, which diminishes the incentive for innovators to make treatments more effective.   (This compelling observation comes from <a href="http://www.journals.uchicago.edu/doi/abs/10.1086/508033">a paper</a> by the economists <a href="http://en.wikipedia.org/wiki/Kevin_M._Murphy">Kevin Murphy</a> and <a href="http://www.chicagobooth.edu/faculty/bio.aspx?person_id=12825845760">Robert Topel</a>; I&#8217;ll be blogging on their work in more detail in the near future.)  </p>
<p>For the sake of future Daniel Dennetts, I hope our legislators have the goodness and wisdom to devise a health care reform package that strengthens the incentive structure instead of weakening it still further.   When they fail, as they probably will, there will be plenty of time for outrage.  Meanwhile, things could be far far worse, and there&#8217;s much to be grateful for on this Thanksgiving day.</p>
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		<title>Principia Mathematica:  The Comic Book</title>
		<link>http://www.thebigquestions.com/2009/10/30/principia-mathematica-the-comic-book/</link>
		<comments>http://www.thebigquestions.com/2009/10/30/principia-mathematica-the-comic-book/#comments</comments>
		<pubDate>Fri, 30 Oct 2009 06:05:10 +0000</pubDate>
		<dc:creator>Steve Landsburg</dc:creator>
				<category><![CDATA[Books]]></category>
		<category><![CDATA[Heroes]]></category>
		<category><![CDATA[Philosophy]]></category>

		<guid isPermaLink="false">http://www.thebigquestions.com/?p=333</guid>
		<description><![CDATA[Logicomix is&#8212;I am not making this up&#8212;a graphic novel (that is, what we used to call a comic book) about Bertrand Russell and the writing of Principia Mathematica.  Implausibly enough, it succeeds, making rather gripping drama out of the twentieth century crisis in the foundations of mathematics.  The technical issues are portrayed clearly [...]]]></description>
			<content:encoded><![CDATA[<p><a href="http://www.amazon.com/Logicomix-Search-Truth-Apostolos-Doxiadis/dp/1596914521/ref=nosim/?tag=moseissase-20">Logicomix</a> is&#8212;I am not making this up&#8212;a graphic novel (that is, what we used to call a comic book) about <a href="http://en.wikipedia.org/wiki/Bertrand_russell">Bertrand Russell</a> and the writing of <a href="http://en.wikipedia.org/wiki/Principia_Mathematica">Principia Mathematica</a>.  Implausibly enough, it succeeds, making rather gripping drama out of the twentieth century crisis in the foundations of mathematics.  The technical issues are portrayed clearly and accurately (a novice reader could learn a lot from this book) but never coldly; this is above all a saga about human obsession.  I even like the device where the authors themselves appear as characters, trying to figure out how best to present this stuff.  It works.</p>
<p>But there&#8217;s one part I find almost impossible to believe is accurate; maybe a reader can set me straight.  The novel begins in 1939 and proceeds by flashback.  In 1939 we see Russell, a lifelong pacifist confronted by the Nazi horror, being shaken to the core by the realization that his beloved Logic does not contain the answers to all of life&#8217;s problems.  Can there be even a shred of truth to this?  Surely the man who devoted his youth and over 300 printed pages to proving that 1+1=2 must always have been well aware that formal logic has its limitations as a practical guide to life.<br />
<span id="more-333"></span></p>
<p>In the novel, Russell comes to his epiphany&#8212;or at least expresses it&#8212;during a lecture in September, 1939 to an audience of pacifists at &#8220;an American university&#8221;.  (The September date is important; that&#8217;s when the British declared war on Germany.)  Was there ever such a talk?  Russell spent the early summer of 1939 on an American lecture tour, but according to his <a href="http://www.amazon.com/Autobiography-Bertrand-Russell/dp/041522862Xref=nosim/?tag=moseissase-20">autobiography</a> there were only two memorable moments on that tour:  First, the discovery that the professors at Louisiana State University all thought well of Huey Long because he had raised their salaries, and second, ten minutes of peace lying in the grass at the top of the dykes along the Mississippi.  By September, Russell had begun his first year of teaching at UCLA, where he was preoccupied with preparing classes and presumably hard at work on his <a href="http://www.amazon.com/Inquiry-Meaning-Truth-Bertrand-Russell/dp/0851247377">Inquiry into Meaning and Truth</a>.  </p>
<p>Russell was indeed a lifelong optimist, but he had never, to my knowledge, held the infantile view&#8212;attributed to him iin this novel&#8212;that the methods of formal logic could solve all the world&#8217;s problems.</p>
<p>Indeed he says pretty much the opposite in the postscript to his autobiography, written 30 years after the onset of World War II:</p>
<blockquote><p>
The serious part of my life ever since boyhood has been devoted to two different objects, which for a long time remained separate and have only in recent years united into a single whole.  I wanted, on the one hand, to find out whether anything could be known; and on the other hand, to do whatever might be possible toward creating a happier world.
</p></blockquote>
<p>And then, reflecting on the battles of his mental life:</p>
<blockquote><p>
I set out with a more or less religious belief in a Platonic eternal world, in which mathematics shone with a beauty like that of the last Cantos of the <i>Paradiso</i>.  I came to the conclusion that the eternal world is trivial, and that mathematics is only the art of saying the same thing in different words.  I set out with a belief that love, free and courageous, could conquer the world without fighting.  I came to support a bitter and terrible war.
</p></blockquote>
<p>As I read that, he&#8217;s maintaining a clear dichotomy between the world of formal logic on the one hand and the world of love and war on the other.</p>
<p>So I think that in this one respect, <a href="http://www.amazon.com/Logicomix-Search-Truth-Apostolos-Doxiadis/dp/1596914521/ref=nosim/?tag=moseissase-20">Logicomix</a> gives us very much a comic book version of Lord Russell.  But again&#8212;perhaps some reader knows more about this than I do.</p>
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