Comments for physics musings http://phys.wordpress.com the tale of a physicist's comeback Thu, 01 Oct 2009 04:41:58 +0000 http://wordpress.com/ hourly 1 Comment on Geometrically speaking by Thomas Nickledock http://phys.wordpress.com/2006/07/06/geometrically-speaking/#comment-11375 Thomas Nickledock Thu, 01 Oct 2009 04:41:58 +0000 https://phys.wordpress.com/2006/07/06/geometrically-speaking/#comment-11375 I haven't digested the entire post yet, but I think it's very interesting. I would like to add a word of caution however, in that a proof by drawing can only be trusted if the entire symbology used in the drawing is well understood. (When viewed this way, traditional formulae are drawings too, in a sense.) As an example of the danger of accepting a proof-by-drawing where the symbology is not well-understood, when Euclid referred to a diagram to make his derivation of the Pythagorean theorem plausible, he missed an axiom that was necessary for the proof to work. I haven’t digested the entire post yet, but I think it’s very interesting. I would like to add a word of caution however, in that a proof by drawing can only be trusted if the entire symbology used in the drawing is well understood. (When viewed this way, traditional formulae are drawings too, in a sense.) As an example of the danger of accepting a proof-by-drawing where the symbology is not well-understood, when Euclid referred to a diagram to make his derivation of the Pythagorean theorem plausible, he missed an axiom that was necessary for the proof to work.

]]> Comment on Litmus test for QM interpretations by More on criteria for interpretations | Matt Leifer http://phys.wordpress.com/2006/06/29/litmus-test-for-qm-interpretations/#comment-11373 More on criteria for interpretations | Matt Leifer Sat, 22 Aug 2009 14:52:00 +0000 https://phys.wordpress.com/2006/06/29/litmus-test-for-qm-interpretations/#comment-11373 [...] popular blog post to date, thanks in no small part to a mention over at Uncertain Principles and a n u mber of other blogs. I know when I’m on to a good thing, so let’s stick with the [...] [...] popular blog post to date, thanks in no small part to a mention over at Uncertain Principles and a n u mber of other blogs. I know when I’m on to a good thing, so let’s stick with the [...]

]]> Comment on Bell’s inequality by Khalid http://phys.wordpress.com/bells-theorem/#comment-11372 Khalid Sun, 02 Aug 2009 21:58:15 +0000 https://phys.wordpress.com/bells-theorem/#comment-11372 Hi, Well, I think there is a problem at the hypothesis! How can each experimenter see the other "live" while performing their respective experiment, if even the light cannot reach one another before they have finished their experiments??? What form of communication signal their receivers will use to receive signals faster than the speed of light? Khalid Hi,

Well, I think there is a problem at the hypothesis!
How can each experimenter see the other “live” while performing their respective experiment, if even the light cannot reach one another before they have finished their experiments???
What form of communication signal their receivers will use to receive signals faster than the speed of light?

Khalid

]]> Comment on Portraits galore by sina http://phys.wordpress.com/2006/08/08/portraits-galore/#comment-11368 sina Tue, 07 Jul 2009 06:46:23 +0000 https://phys.wordpress.com/2006/08/08/portraits-galore/#comment-11368 murray gelman and feynman and one of them maybe fooladi our damn master murray gelman and feynman and one of them maybe fooladi our damn master

]]> Comment on Beliefs by Bending Light http://phys.wordpress.com/2006/09/08/beliefs/#comment-11330 Bending Light Thu, 21 May 2009 03:00:11 +0000 http://phys.wordpress.com/2006/09/08/beliefs/#comment-11330 I have learned that Science, Religion and Politics are three items that should never cross. What a great comic. I have learned that Science, Religion and Politics are three items that should never cross.

What a great comic.

]]> Comment on Bell’s inequality by Mike http://phys.wordpress.com/bells-theorem/#comment-11248 Mike Sat, 11 Apr 2009 18:02:09 +0000 https://phys.wordpress.com/bells-theorem/#comment-11248 I don't really call something that takes that long to explain "beautiful, elementary and ituitive"! Bell's Theorem (in its discrete binary form) is simply an inequality on set sizes: |Ac| + |Cb| >= |Ab| where sets A, B, C have complements a, b, c. The proof really is elementary Boolean algebra: The LHS is >= |Ac U Cb| (actually = because those sets are disjoint). Now intersect Ab with Ac U Cb to find that Ac U Cb contains Ab, whence the result. This models the physical situation by using simultaneous measurements on pairs of systems to deduce properties of single systems (the underlying sample set in the above) by appealing to EPR. Bob's your uncle :) I don’t really call something that takes that long to explain “beautiful, elementary and ituitive”!

Bell’s Theorem (in its discrete binary form) is simply an inequality on set sizes:

|Ac| + |Cb| >= |Ab|

where sets A, B, C have complements a, b, c.

The proof really is elementary Boolean algebra:

The LHS is >= |Ac U Cb| (actually = because those sets are disjoint). Now intersect Ab with Ac U Cb to find that Ac U Cb contains Ab, whence the result.

This models the physical situation by using simultaneous measurements on pairs of systems to deduce properties of single systems (the underlying sample set in the above) by appealing to EPR.

Bob’s your uncle :)

]]> Comment on New physics, old computing by navaburo http://phys.wordpress.com/2006/04/21/new-physics-old-computing/#comment-11092 navaburo Sun, 22 Feb 2009 06:48:43 +0000 http://phys.wordpress.com/2006/04/21/new-physics-old-computing/#comment-11092 Fortran is used extensively (and if I am not mistaken, exclusively) at my uni for physics simulations. Personally I have written physics simulations in C and in Scheme, and I must say the C implementation has much more impressive speed and graphics (since I have not found (or, admittedly, even looked for) SDL bindings for Scheme) however the Scheme code is actually structured, readable, and largly reusable, as a result of the language. I know I could have made my C code readable, structured, and reusable, but I didn't. I also have learned more about the underlying mathematics by programming in Scheme. And I have time to get coffee while waiting for simulations to run! Fortran is used extensively (and if I am not mistaken, exclusively) at my uni for physics simulations.

Personally I have written physics simulations in C and in Scheme, and I must say the C implementation has much more impressive speed and graphics (since I have not found (or, admittedly, even looked for) SDL bindings for Scheme) however the Scheme code is actually structured, readable, and largly reusable, as a result of the language. I know I could have made my C code readable, structured, and reusable, but I didn’t. I also have learned more about the underlying mathematics by programming in Scheme. And I have time to get coffee while waiting for simulations to run!

]]> Comment on Taking issue with String Theory by Shamal Jayakody http://phys.wordpress.com/2006/10/07/taking-issue-with-string-theory/#comment-11084 Shamal Jayakody Fri, 20 Feb 2009 22:12:40 +0000 http://phys.wordpress.com/2006/10/07/taking-issue-with-string-theory/#comment-11084 String theory is of interest to many physicists because it requires new mathematical and physical ideas to mesh together its very different mathematical formulations. One of the most inclusive of these is the 11-dimensional M-theory, and in the M-theory way of thinking, string theory requires space time to have eleven dimensions,[as opposed to the usual three space and one time. The original string theories from the 1980s describe special cases of M-theory where the eleventh dimension is a very small circle or a line, and if these formulations are considered as fundamental, then string theory requires ten dimensions. But the theory also describes universes like ours, with four observable space time dimensions, as well as universes with up to 10 flat space dimensions, and also cases where the position in some of the dimensions is not described by a real number, but by completely different type of mathematical quantity. So the notion of space-time dimension is not a fixed thing in string theory: it is best thought of as different in different circumstances. String theory is of interest to many physicists because it requires new mathematical and physical ideas to mesh together its very different mathematical formulations. One of the most inclusive of these is the 11-dimensional M-theory, and in the M-theory way of thinking, string theory requires space time to have eleven dimensions,[as opposed to the usual three space and one time. The original string theories from the 1980s describe special cases of M-theory where the eleventh dimension is a very small circle or a line, and if these formulations are considered as fundamental, then string theory requires ten dimensions. But the theory also describes universes like ours, with four observable space time dimensions, as well as universes with up to 10 flat space dimensions, and also cases where the position in some of the dimensions is not described by a real number, but by completely different type of mathematical quantity. So the notion of space-time dimension is not a fixed thing in string theory: it is best thought of as different in different circumstances.

]]> Comment on You’re never too old by Subway Philosophy http://phys.wordpress.com/2006/04/05/youre-never-too-old/#comment-10936 Subway Philosophy Mon, 01 Dec 2008 06:36:46 +0000 http://phys.wordpress.com/2006/04/05/youre-never-too-old/#comment-10936 I don't know anything about physics, but I do love your writing. I get lost in it, and re-re-read and google and wikipedia, and fail miserably. Regardless, congratulations on getting back on the horse most people will never know how to get on. I don’t know anything about physics, but I do love your writing. I get lost in it, and re-re-read and google and wikipedia, and fail miserably. Regardless, congratulations on getting back on the horse most people will never know how to get on.

]]> Comment on New physics, old computing by zur http://phys.wordpress.com/2006/04/21/new-physics-old-computing/#comment-10867 zur Sat, 11 Oct 2008 14:46:38 +0000 http://phys.wordpress.com/2006/04/21/new-physics-old-computing/#comment-10867 Efficiency matters a lot with these kind of programs ... It can matter a lot that your simulation finishes in one night, and not in four days. Or not in one month, if you'd dare to use some absolutely unsuitable high level scripting language to write the program. Fortran 90 is not obsolete. It have its serious disadvantages as a general purpose language, but it is much better suited for writing numerical stuff than C. It is also easier to learn. People being stuck with Fortran 77 (or even Fortran 66!), and not willing to learn something new or document their code is of course another matter. I hate it when people say how superior their 40 year old unmaintainable horror of unstructured Fortran code is ... Efficiency matters a lot with these kind of programs … It can matter a lot that your simulation finishes in one night, and not in four days. Or not in one month, if you’d dare to use some absolutely unsuitable high level scripting language to write the program.

Fortran 90 is not obsolete. It have its serious disadvantages as a general purpose language, but it is much better suited for writing numerical stuff than C. It is also easier to learn.

People being stuck with Fortran 77 (or even Fortran 66!), and not willing to learn something new or document their code is of course another matter. I hate it when people say how superior their 40 year old unmaintainable horror of unstructured Fortran code is …

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