Purpose of theoretical physics - Was "What's wrong with loop QG" [Archive]

backdoorstudent

Oct17-04, 01:46 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\npeterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410150545.40567fb7@posting.google. com>...\n> Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0410121849250.11136-100000@feynman.harvard.edu>...\n> > This is the whole\n> > purpose of theoretical physics, to be reducing the number of independent\n> > ingredients that are necessary to describe an increasing body of\n> > observations!\n>\n> I would disagree. The whole purpose of theoretical physics is to come\n> up with models that better and better describe and predict behavior\n> of the real physical world. The discovery of the Standard Model was a\n> remarkable scientific advance. That it simultaneously greatly\n> reduced the number of free parameters in our theories and greatly\n> increased the accuracy of our experimental predictions is due to the\n> amazing fact that all of our experiments back then (and nearly\n> all of our experiments even now) can be almost exactly described by a\n> quantum field theory with 19 free parameters. The belief that all\n> of physics can be described by a theory having even fewer parameters\n> is a profound (and probably philosophically unjustifiable) faith in\n> the simplicity of the laws of physics.\n\nDon\'t you guys think that the purpose of theoretical physics is about\nmuch more than making predictions; it\'s about understanding them as\nwell? Shouldn\'t your theory tell you exactly how a result comes out\nrather than just be a recipe for their quantities?\n\nIsn\'t a physical theory (a good one, anyway) more than a black box\nwith mysterious knobs that, via tweaking, gives various outputs for\nvarious inputs? If a theory is only about prediction, i.e., knowing\nthe outcome but not understanding exactly why (or even how) the\noutcome exists, then it is not much more than accounting. Is it not\nmore engineering than science?\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>peterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410150545.40567fb7@posting.google.com>...
> Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0410121849250.11136-100000@feynman.harvard.edu>...
> > This is the whole
> > purpose of theoretical physics, to be reducing the number of independent
> > ingredients that are necessary to describe an increasing body of
> > observations!
>
> I would disagree. The whole purpose of theoretical physics is to come
> up with models that better and better describe and predict behavior
> of the real physical world. The discovery of the Standard Model was a
> remarkable scientific advance. That it simultaneously greatly
> reduced the number of free parameters in our theories and greatly
> increased the accuracy of our experimental predictions is due to the
> amazing fact that all of our experiments back then (and nearly
> all of our experiments even now) can be almost exactly described by a
> quantum field theory with 19 free parameters. The belief that all
> of physics can be described by a theory having even fewer parameters
> is a profound (and probably philosophically unjustifiable) faith in
> the simplicity of the laws of physics.

Don't you guys think that the purpose of theoretical physics is about
much more than making predictions; it's about understanding them as
well? Shouldn't your theory tell you exactly how a result comes out
rather than just be a recipe for their quantities?

Isn't a physical theory (a good one, anyway) more than a black box
with mysterious knobs that, via tweaking, gives various outputs for
various inputs? If a theory is only about prediction, i.e., knowing
the outcome but not understanding exactly why (or even how) the
outcome exists, then it is not much more than accounting. Is it not
more engineering than science?

Peter Shor

Oct20-04, 03:18 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nbackdoorstudent@yahoo.com (backdoorstudent) wrote in message news:<750f5e99.0410170611.1e149067@posting.google. com>...\n> peterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410150545.40567fb7@posting.google. com>...\n> > Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0410121849250.11136-100000@feynman.harvard.edu>...\n> > > This is the whole\n> > > purpose of theoretical physics, to be reducing the number of independent\n> > > ingredients that are necessary to describe an increasing body of\n> > > observations!\n> >\n> > I would disagree. The whole purpose of theoretical physics is to come\n> > up with models that better and better describe and predict behavior\n> > of the real physical world. The discovery of the Standard Model was a\n> > remarkable scientific advance. That it simultaneously greatly\n> > reduced the number of free parameters in our theories and greatly\n> > increased the accuracy of our experimental predictions is due to the\n> > amazing fact that all of our experiments back then (and nearly\n> > all of our experiments even now) can be almost exactly described by a\n> > quantum field theory with 19 free parameters. The belief that all\n> > of physics can be described by a theory having even fewer parameters\n> > is a profound (and probably philosophically unjustifiable) faith in\n> > the simplicity of the laws of physics.\n>\n> Don\'t you guys think that the purpose of theoretical physics is about\n> much more than making predictions; it\'s about understanding them as\n> well? Shouldn\'t your theory tell you exactly how a result comes out\n> rather than just be a recipe for their quantities?\n\nThat\'s part of what I meant when I said "describe and predict"; apparently\nI chose the wrong wording.\n\n> Isn\'t a physical theory (a good one, anyway) more than a black box\n> with mysterious knobs that, via tweaking, gives various outputs for\n> various inputs? If a theory is only about prediction, i.e., knowing\n> the outcome but not understanding exactly why (or even how) the\n> outcome exists, then it is not much more than accounting. Is it not\n> more engineering than science?\n\nBut how do you tell when a theory really gives understanding? There was\na lot of debate to this effect in the early days of quantum mechanics,\nwhich some physicists viewed as crazy rules for calculating probabilities\nthat yielded no new understanding. (Some people, but very few physicists,\nwill still argue this case). I think that this is one of these "I know it\nwhen I see it" quantitites. On the other hand, there is a philosophical\nview that the fewer knobs a theory has, the more understanding that can be\ncoaxed out of it. (And this argument feeds back into the discussion that\nspawned this thread.)\n\nPeter Shor\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>backdoorstudent@yahoo.com (backdoorstudent) wrote in message news:<750f5e99.0410170611.1e149067@posting.google.com>...
> peterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410150545.40567fb7@posting.google.com>...
> > Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0410121849250.11136-100000@feynman.harvard.edu>...
> > > This is the whole
> > > purpose of theoretical physics, to be reducing the number of independent
> > > ingredients that are necessary to describe an increasing body of
> > > observations!
> >
> > I would disagree. The whole purpose of theoretical physics is to come
> > up with models that better and better describe and predict behavior
> > of the real physical world. The discovery of the Standard Model was a
> > remarkable scientific advance. That it simultaneously greatly
> > reduced the number of free parameters in our theories and greatly
> > increased the accuracy of our experimental predictions is due to the
> > amazing fact that all of our experiments back then (and nearly
> > all of our experiments even now) can be almost exactly described by a
> > quantum field theory with 19 free parameters. The belief that all
> > of physics can be described by a theory having even fewer parameters
> > is a profound (and probably philosophically unjustifiable) faith in
> > the simplicity of the laws of physics.
>
> Don't you guys think that the purpose of theoretical physics is about
> much more than making predictions; it's about understanding them as
> well? Shouldn't your theory tell you exactly how a result comes out
> rather than just be a recipe for their quantities?

That's part of what I meant when I said "describe and predict"; apparently
I chose the wrong wording.

> Isn't a physical theory (a good one, anyway) more than a black box
> with mysterious knobs that, via tweaking, gives various outputs for
> various inputs? If a theory is only about prediction, i.e., knowing
> the outcome but not understanding exactly why (or even how) the
> outcome exists, then it is not much more than accounting. Is it not
> more engineering than science?

But how do you tell when a theory really gives understanding? There was
a lot of debate to this effect in the early days of quantum mechanics,
which some physicists viewed as crazy rules for calculating probabilities
that yielded no new understanding. (Some people, but very few physicists,
will still argue this case). I think that this is one of these "I know it
when I see it" quantitites. On the other hand, there is a philosophical
view that the fewer knobs a theory has, the more understanding that can be
coaxed out of it. (And this argument feeds back into the discussion that
spawned this thread.)

Peter Shor

backdoorstudent

Oct20-04, 10:48 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\npeterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410191323.5ef30875@posting.google. com>...\n> But how do you tell when a theory really gives understanding?\nWhen it\'s elements are clearly defined and you don\'t have to\narbitrarily pick and choose which mathematical artifacts to throw away\nin order to get it to correspond with anything.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>peterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410191323.5ef30875@posting.google.com>...
> But how do you tell when a theory really gives understanding?
When it's elements are clearly defined and you don't have to
arbitrarily pick and choose which mathematical artifacts to throw away
in order to get it to correspond with anything.

Lubo? Motl

Oct21-04, 02:47 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nPeter Shor wrote:\n\n> > I would disagree. The whole purpose of theoretical physics is to\n> > come up with models that better and better describe and predict behavior\n> > of the real physical world.\n\nWell, I would probably subscribe to this general description; my goal\nwas to define the words "better and better" a little bit better. ;-)\nMaybe I feiled.\n\n> > The discovery of the Standard Model was a\n> > remarkable scientific advance. That it simultaneously greatly\n> > reduced the number of free parameters in our theories and greatly\n> > increased the accuracy of our experimental predictions is due to the\n> > amazing fact that all of our experiments back then (and nearly\n> > all of our experiments even now) can be almost exactly described by a\n> > quantum field theory with 19 free parameters.\n\nI agree with this, too.\n\n> > The belief that all\n> > of physics can be described by a theory having even fewer parameters\n> > is a profound (and probably philosophically unjustifiable) faith in\n> > the simplicity of the laws of physics.\n\nIt\'s not just a matter of beliefs: it\'s an issue of choosing which\ntheories are more satisfying scientifically. You don\'t need QED to\ndescribe chemistry: you can work with an effective theory with\nhundreds of "elementary" particles called "atoms" which can interact\nthrough millions of interactions whose coefficients you may determine\nexperimentally. Of course that at the end, you can make such theories\nagree with whatever experimental data you have. Would you agree that\nthe Standard Model is a better theory than this "constructive physical\nchemistry"? If you do, how would you explain what is better about it?\n\nThere is no guarantee that the "final dream" of this reductionist\nprogram - a theory with no inputs - will become true. The Nature may\nneed some parameters at the end. However, this does not change the\nfact that among two theories able to agree with the observed\nphenomena, the less arbitrary theory (with less parameters and\nassumptions) is scientifically preferred. This preference is about the\nrules of science, and it is a different question that the question\n"how much Nature allows us to understand at the end".\n\nbackdoorstudent@yahoo.com (backdoorstudent) wrote in message news:<750f5e99.0410170611.1e149067@posting.google. com>...\n\n> Don\'t you guys think that the purpose of theoretical physics is about\n> much more than making predictions; it\'s about understanding them as\n> well? Shouldn\'t your theory tell you exactly how a result comes out\n> rather than just be a recipe for their quantities?\n\nThis is a good question, but unfortunately it is one on the border\nbetween physics and psychology (and philosophy). It\'s just hard to\ndefine "understanding" rigorously, but in such a way that it is not\njust the recipe. If one follows a recipe mechanically, she can feel\nthat she does not really understand what\'s going on. But that\'s just a\npsychological illusion. If the recipe allows her to predict any\nphenomenon she wants, she really "knows" what\'s going on.\n\nAnother question is whether one can make these calculations quickly,\nand without the use of a computer (or a paper). Of course, the less\ntools we need to make a prediction, the more we feel that we\n"understand" the subject. But in my opinion, this is a matter of\nsubjective feelings that can hardly be quantified, especially because\neach person views them differently. What can be quantified in reality\nis the ability to make the predictions and the agreement between these\npredictions and observations or experiments.\n\n> Isn\'t a physical theory (a good one, anyway) more than a black box\n> with mysterious knobs that, via tweaking, gives various outputs for\n> various inputs?\n\nThis question implicitly contains some incorrect bias in it. You must\nlet Nature to determine what the right theory is, and the right theory\nalso tells you whether there are knobs and whether a box is black or\nnot. ;-) What I want to say is that if you try to find a mechanistic,\neasy-to-imagine description of phenomena behind quantum mechanics, for\nexample, you will fail. The very well tested principles of quantum\nmechanics really tell us that the physical theory *is* a black box\nwith input being the initial conditions, and the output being the\npredicted probabilities of different outcomes. Any natural enough\nattempt to "illuminate" this black box - and imagine some little green\nmen in it - will lead you to an incorrect theory (that disagrees with\nexperiments directly or indirectly).\n\n> If a theory is only about prediction, i.e., knowing\n> the outcome but not understanding exactly why (or even how) the\n> outcome exists, then it is not much more than accounting.\n\nAs Feynman\'s dictum says, "shut up and calculate". Yours are\nphilosophical questions - and the calculation of the correct\npredictions is everything there objectively is. You may add a lot of\nsubjective stuff that helps you psychologically, it is a lot of fun,\nit is helpful, but it\'s strictly speaking not a part of science.\n\n> Is it not more engineering than science?\n\nWell, obviously, you use the word "engineering" as an insult. Well,\nwhat\'s the difference between a scientist and an engineer? The\nengineer usually tries to use various tricks and insights for much\nmore practical goals than an average scientists; and he focuses on the\nquestions that can have a practical impact. The scientist often asks\nquestions without such an impact, too. This allows the scientist to\nask much more general questions about the phenomena that are\nuninteresting for the engineer (and industry). Therefore, the\nscientist is led to much more precise theories and she understands\ntheir interior "better". But I don\'t think that the difference about\nthis better understanding goes beyond the "black box". The scientist\njust studies the black box finely, while the engineer focuses on the\nway how to combine a rough picture of the black box into complex\npatterns which are practically useful.\n\nBest wishes\nLubos\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>Peter Shor wrote:

> > I would disagree. The whole purpose of theoretical physics is to
> > come up with models that better and better describe and predict behavior
> > of the real physical world.

Well, I would probably subscribe to this general description; my goal
was to define the words "better and better" a little bit better. ;-)
Maybe I feiled.

> > The discovery of the Standard Model was a
> > remarkable scientific advance. That it simultaneously greatly
> > reduced the number of free parameters in our theories and greatly
> > increased the accuracy of our experimental predictions is due to the
> > amazing fact that all of our experiments back then (and nearly
> > all of our experiments even now) can be almost exactly described by a
> > quantum field theory with 19 free parameters.

I agree with this, too.

> > The belief that all
> > of physics can be described by a theory having even fewer parameters
> > is a profound (and probably philosophically unjustifiable) faith in
> > the simplicity of the laws of physics.

It's not just a matter of beliefs: it's an issue of choosing which
theories are more satisfying scientifically. You don't need QED to
describe chemistry: you can work with an effective theory with
hundreds of "elementary" particles called "atoms" which can interact
through millions of interactions whose coefficients you may determine
experimentally. Of course that at the end, you can make such theories
agree with whatever experimental data you have. Would you agree that
the Standard Model is a better theory than this "constructive physical
chemistry"? If you do, how would you explain what is better about it?

There is no guarantee that the "final dream" of this reductionist
program - a theory with no inputs - will become true. The Nature may
need some parameters at the end. However, this does not change the
fact that among two theories able to agree with the observed
phenomena, the less arbitrary theory (with less parameters and
assumptions) is scientifically preferred. This preference is about the
rules of science, and it is a different question that the question
"how much Nature allows us to understand at the end".

backdoorstudent@yahoo.com (backdoorstudent) wrote in message news:<750f5e99.0410170611.1e149067@posting.google.com>...

> Don't you guys think that the purpose of theoretical physics is about
> much more than making predictions; it's about understanding them as
> well? Shouldn't your theory tell you exactly how a result comes out
> rather than just be a recipe for their quantities?

This is a good question, but unfortunately it is one on the border
between physics and psychology (and philosophy). It's just hard to
define "understanding" rigorously, but in such a way that it is not
just the recipe. If one follows a recipe mechanically, she can feel
that she does not really understand what's going on. But that's just a
psychological illusion. If the recipe allows her to predict any
phenomenon she wants, she really "knows" what's going on.

Another question is whether one can make these calculations quickly,
and without the use of a computer (or a paper). Of course, the less
tools we need to make a prediction, the more we feel that we
"understand" the subject. But in my opinion, this is a matter of
subjective feelings that can hardly be quantified, especially because
each person views them differently. What can be quantified in reality
is the ability to make the predictions and the agreement between these
predictions and observations or experiments.

> Isn't a physical theory (a good one, anyway) more than a black box
> with mysterious knobs that, via tweaking, gives various outputs for
> various inputs?

This question implicitly contains some incorrect bias in it. You must
let Nature to determine what the right theory is, and the right theory
also tells you whether there are knobs and whether a box is black or
not. ;-) What I want to say is that if you try to find a mechanistic,
easy-to-imagine description of phenomena behind quantum mechanics, for
example, you will fail. The very well tested principles of quantum
mechanics really tell us that the physical theory *is* a black box
with input being the initial conditions, and the output being the
predicted probabilities of different outcomes. Any natural enough
attempt to "illuminate" this black box - and imagine some little green
men in it - will lead you to an incorrect theory (that disagrees with
experiments directly or indirectly).

> If a theory is only about prediction, i.e., knowing
> the outcome but not understanding exactly why (or even how) the
> outcome exists, then it is not much more than accounting.

As Feynman's dictum says, "shut up and calculate". Yours are
philosophical questions - and the calculation of the correct
predictions is everything there objectively is. You may add a lot of
subjective stuff that helps you psychologically, it is a lot of fun,
it is helpful, but it's strictly speaking not a part of science.

> Is it not more engineering than science?

Well, obviously, you use the word "engineering" as an insult. Well,
what's the difference between a scientist and an engineer? The
engineer usually tries to use various tricks and insights for much
more practical goals than an average scientists; and he focuses on the
questions that can have a practical impact. The scientist often asks
questions without such an impact, too. This allows the scientist to
ask much more general questions about the phenomena that are
uninteresting for the engineer (and industry). Therefore, the
scientist is led to much more precise theories and she understands
their interior "better". But I don't think that the difference about
this better understanding goes beyond the "black box". The scientist
just studies the black box finely, while the engineer focuses on the
way how to combine a rough picture of the black box into complex
patterns which are practically useful.

Best wishes
Lubos

Paul Draper

Oct21-04, 02:47 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nbackdoorstudent@yahoo.com (backdoorstudent) wrote in message news:<750f5e99.0410170611.1e149067@posting.google. com>...\n> peterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410150545.40567fb7@posting.google. com>...\n> > Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0410121849250.11136-100000@feynman.harvard.edu>...\n> > > This is the whole\n> > > purpose of theoretical physics, to be reducing the number of independent\n> > > ingredients that are necessary to describe an increasing body of\n> > > observations!\n> >\n> > I would disagree. The whole purpose of theoretical physics is to come\n> > up with models that better and better describe and predict behavior\n> > of the real physical world. The discovery of the Standard Model was a\n> > remarkable scientific advance. That it simultaneously greatly\n> > reduced the number of free parameters in our theories and greatly\n> > increased the accuracy of our experimental predictions is due to the\n> > amazing fact that all of our experiments back then (and nearly\n> > all of our experiments even now) can be almost exactly described by a\n> > quantum field theory with 19 free parameters. The belief that all\n> > of physics can be described by a theory having even fewer parameters\n> > is a profound (and probably philosophically unjustifiable) faith in\n> > the simplicity of the laws of physics.\n>\n> Don\'t you guys think that the purpose of theoretical physics is about\n> much more than making predictions; it\'s about understanding them as\n> well? Shouldn\'t your theory tell you exactly how a result comes out\n> rather than just be a recipe for their quantities?\n>\n> Isn\'t a physical theory (a good one, anyway) more than a black box\n> with mysterious knobs that, via tweaking, gives various outputs for\n> various inputs? If a theory is only about prediction, i.e., knowing\n> the outcome but not understanding exactly why (or even how) the\n> outcome exists, then it is not much more than accounting. Is it not\n> more engineering than science?\n\nThe problem is, you can always ask again, "But why?" I don\'t believe\nwe\'ll ever get to the point where the ultimately reduced laws of\nphysics will be self-evident, as in, "It couldn\'t possible be any\nother way."\n\nIndeed, if Lenny Susskind has a long-lasting legacy, the\nlongest-lasting will be the realization that at some level our own\nlittle "bubble universe" is an accident of an infinite number of\npossible universes, and ours just happens to be the one that features\nthe laws of physics as we see them. (The anthropic principle.) This\nmeans something deeper: that it\'s pointless to ask why our laws of\nphysics are what they are -- they just happen to be that in our\nuniverse.\n\nQM makes the same deep philosophical leap, that nature is at some\nlevel *inherently* random and probabilistic, and that it makes no\nsense to ask what\'s going on at a deeper level to kick things around\nand give the appearance of randomness. The key phrase is "makes no\nsense to". It\'s not a practical note. It\'s not an abdication of the\nsearch for what\'s really going on underneath. It\'s a claim that there\nIS nothing really going on underneath.\n\nActually, most of the blather that goes on in the other s.p.\nnewsgroups, especially s.p.p. and s.p.r, has to do with a gut-level\nrejection of that proposition, and a claim that there MUST be an\nintuitively appealing accounting of what\'s really going on underneath.\nThe problem is that "intuitively appealing" is in the eye of the\nbeholder. The rejection of absolute time in favor of the postulates of\nspecial relativity are anathema to some. The idea that a vacuum can\nhave a dielectric constant is repellent to others. In the end, the\nONLY satisfactory arbiter of the validity of the (often unfounded)\nassumptions built into a theory is the success and breadth of the\ntheory in predicting experimentally verifiable behavior.\n\nPD\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>backdoorstudent@yahoo.com (backdoorstudent) wrote in message news:<750f5e99.0410170611.1e149067@posting.google.com>...
> peterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410150545.40567fb7@posting.google.com>...
> > Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0410121849250.11136-100000@feynman.harvard.edu>...
> > > This is the whole
> > > purpose of theoretical physics, to be reducing the number of independent
> > > ingredients that are necessary to describe an increasing body of
> > > observations!
> >
> > I would disagree. The whole purpose of theoretical physics is to come
> > up with models that better and better describe and predict behavior
> > of the real physical world. The discovery of the Standard Model was a
> > remarkable scientific advance. That it simultaneously greatly
> > reduced the number of free parameters in our theories and greatly
> > increased the accuracy of our experimental predictions is due to the
> > amazing fact that all of our experiments back then (and nearly
> > all of our experiments even now) can be almost exactly described by a
> > quantum field theory with 19 free parameters. The belief that all
> > of physics can be described by a theory having even fewer parameters
> > is a profound (and probably philosophically unjustifiable) faith in
> > the simplicity of the laws of physics.
>
> Don't you guys think that the purpose of theoretical physics is about
> much more than making predictions; it's about understanding them as
> well? Shouldn't your theory tell you exactly how a result comes out
> rather than just be a recipe for their quantities?
>
> Isn't a physical theory (a good one, anyway) more than a black box
> with mysterious knobs that, via tweaking, gives various outputs for
> various inputs? If a theory is only about prediction, i.e., knowing
> the outcome but not understanding exactly why (or even how) the
> outcome exists, then it is not much more than accounting. Is it not
> more engineering than science?

The problem is, you can always ask again, "But why?" I don't believe
we'll ever get to the point where the ultimately reduced laws of
physics will be self-evident, as in, "It couldn't possible be any
other way."

Indeed, if Lenny Susskind has a long-lasting legacy, the
longest-lasting will be the realization that at some level our own
little "bubble universe" is an accident of an infinite number of
possible universes, and ours just happens to be the one that features
the laws of physics as we see them. (The anthropic principle.) This
means something deeper: that it's pointless to ask why our laws of
physics are what they are -- they just happen to be that in our
universe.

QM makes the same deep philosophical leap, that nature is at some
level *inherently* random and probabilistic, and that it makes no
sense to ask what's going on at a deeper level to kick things around
and give the appearance of randomness. The key phrase is "makes no
sense to". It's not a practical note. It's not an abdication of the
search for what's really going on underneath. It's a claim that there
IS nothing really going on underneath.

Actually, most of the blather that goes on in the other s.p.
newsgroups, especially s.p.p. and s.p.r, has to do with a gut-level
rejection of that proposition, and a claim that there MUST be an
intuitively appealing accounting of what's really going on underneath.
The problem is that "intuitively appealing" is in the eye of the
beholder. The rejection of absolute time in favor of the postulates of
special relativity are anathema to some. The idea that a vacuum can
have a dielectric constant is repellent to others. In the end, the
ONLY satisfactory arbiter of the validity of the (often unfounded)
assumptions built into a theory is the success and breadth of the
theory in predicting experimentally verifiable behavior.

PD

robert j. kolker

Oct25-04, 08:10 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\n\n\nbackdoorstudent wrote:\n\n> Don\'t you guys think that the purpose of theoretical physics is about\n> much more than making predictions; it\'s about understanding them as\n> well? Shouldn\'t your theory tell you exactly how a result comes out\n> rather than just be a recipe for their quantities?\n\nAny understanding of the world is by way of the constructs and\nhypotheses utilized by a theory. No one has ever seen an atom or a\nmolecule with his naked eye or a simple magnifier. What we understand\nabout atoms and molecules is -inferential- and the inferences are\nmediated by a theory, model or some underlying hypotheses (that is a\nfancy word for guess). So we end up understanding our theories, in the\nsense we can intuitively anticipate the kind of interpretations that can\nbe derived by laborious mathematical efforts. Our understand (better our\nintuition) is an oft-successful shortening of linear logical derivation.\n\n\n>\n> Isn\'t a physical theory (a good one, anyway) more than a black box\n> with mysterious knobs that, via tweaking, gives various outputs for\n> various inputs? If a theory is only about prediction, i.e., knowing\n> the outcome but not understanding exactly why (or even how) the\n> outcome exists, then it is not much more than accounting. Is it not\n> more engineering than science?\n\nTheory may be more than a black box to the person who comprehends it,\nbut the -world- is the ultimate semi-opaque box. We only get hints and\nglimpses of what is going on at the smallest and largest scales.\nBasically, we directly know the dots and our theories connect them.\n\nBob Kolker\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>backdoorstudent wrote:

> Don't you guys think that the purpose of theoretical physics is about
> much more than making predictions; it's about understanding them as
> well? Shouldn't your theory tell you exactly how a result comes out
> rather than just be a recipe for their quantities?

Any understanding of the world is by way of the constructs and
hypotheses utilized by a theory. No one has ever seen an atom or a
molecule with his naked eye or a simple magnifier. What we understand
about atoms and molecules is -inferential- and the inferences are
mediated by a theory, model or some underlying hypotheses (that is a
fancy word for guess). So we end up understanding our theories, in the
sense we can intuitively anticipate the kind of interpretations that can
be derived by laborious mathematical efforts. Our understand (better our
intuition) is an oft-successful shortening of linear logical derivation.

>
> Isn't a physical theory (a good one, anyway) more than a black box
> with mysterious knobs that, via tweaking, gives various outputs for
> various inputs? If a theory is only about prediction, i.e., knowing
> the outcome but not understanding exactly why (or even how) the
> outcome exists, then it is not much more than accounting. Is it not
> more engineering than science?

Theory may be more than a black box to the person who comprehends it,
but the -world- is the ultimate semi-opaque box. We only get hints and
glimpses of what is going on at the smallest and largest scales.
Basically, we directly know the dots and our theories connect them.

Bob Kolker

Malcolm

Oct25-04, 08:10 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\n\nbackdoorstudent@yahoo.com (backdoorstudent) wrote in message news:<750f5e99.0410200645.7c4c4ccd@posting.google. com>...\n> peterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410191323.5ef30875@posting.google. com>...\n> > But how do you tell when a theory really gives understanding?\n> When it\'s elements are clearly defined and you don\'t have to\n> arbitrarily pick and choose which mathematical artifacts to throw away\n> in order to get it to correspond with anything.\n\nRoger Penrose belives that mathematics exists in an ideal world of\nperfect Platonic forms. As mathematics is then used to describe the\nreal world there is a close link between physical reality and Plato\'s\nworld. He develops this idea in some detail in his latest book "The\nRoad to Reality", which tries to bring the full canon of mathematical\nphysics to the attention of the general reader. The following page has\nlinks to many reviews of this book and interviews with Penrose:\n\nhttp://www.321books.co.uk/reviews/the-road-to-reality-by-roger-penrose.htm\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>backdoorstudent@yahoo.com (backdoorstudent) wrote in message news:<750f5e99.0410200645.7c4c4ccd@posting.google.com>...
> peterwshor@aol.com (Peter Shor) wrote in message news:<9b2e17b4.0410191323.5ef30875@posting.google.com>...
> > But how do you tell when a theory really gives understanding?
> When it's elements are clearly defined and you don't have to
> arbitrarily pick and choose which mathematical artifacts to throw away
> in order to get it to correspond with anything.

Roger Penrose belives that mathematics exists in an ideal world of
perfect Platonic forms. As mathematics is then used to describe the
real world there is a close link between physical reality and Plato's
world. He develops this idea in some detail in his latest book "The
Road to Reality", which tries to bring the full canon of mathematical
physics to the attention of the general reader. The following page has
links to many reviews of this book and interviews with Penrose:

http://www.321books.co.uk/reviews/the-road-to-reality-by-roger-penrose.htm

David Golden

Nov3-04, 10:02 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>backdoorstudent wrote:\n\n>\n> Isn\'t a physical theory (a good one, anyway) more than a black box\n> with mysterious knobs that, via tweaking, gives various outputs for\n> various inputs? If a theory is only about prediction, i.e., knowing\n> the outcome but not understanding exactly why (or even how) the\n> outcome exists, then it is not much more than accounting. Is it not\n> more engineering than science?\n\nIMHO, that\'s a bit iffy re engineering. Just being able to predict an\noutput given a known input in engineering isn\'t exactly useless, but\nit\'s not the be-all and end-all: Engineering is mostly about _making\nstuff happen_. So you often need to be able to work out how to produce\na _particular_ outcome by working back from the desired effect to a\ncausable-by-you cause, preferably by means shorter than the awful*\n"calculate outputs for all possible inputs, see if one of the outputs\nis the desired effect" algorithm.\n\nPerhaps this hasn\'t mattered much until recently, since older physical\ntheories (ones still mostly used by engineers**) could typically be\nfairly trivially run backwards, but I think it\'s a point worth making.\n\nAnyway, my EUR0.02 with an engineering hat on.\n\nBest Regards,\n\nDave G.\n\n\n* but selling lots of computer clusters right now...\n\n** it\'s not just that the math is easier or they\'re adequate for the\nlimited domain, it\'s that the theories are more clearly, um,\nprior-dictive, not just pre-dictive.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>backdoorstudent wrote:

>
> Isn't a physical theory (a good one, anyway) more than a black box
> with mysterious knobs that, via tweaking, gives various outputs for
> various inputs? If a theory is only about prediction, i.e., knowing
> the outcome but not understanding exactly why (or even how) the
> outcome exists, then it is not much more than accounting. Is it not
> more engineering than science?

IMHO, that's a bit iffy re engineering. Just being able to predict an
output given a known input in engineering isn't exactly useless, but
it's not the be-all and end-all: Engineering is mostly about _making
stuff happen_. So you often need to be able to work out how to produce
a _particular_ outcome by working back from the desired effect to a
causable-by-you cause, preferably by means shorter than the awful*
"calculate outputs for all possible inputs, see if one of the outputs
is the desired effect" algorithm.

Perhaps this hasn't mattered much until recently, since older physical
theories (ones still mostly used by engineers**) could typically be
fairly trivially run backwards, but I think it's a point worth making.

Anyway, my EUR0.02 with an engineering hat on.

Best Regards,

Dave G.

* but selling lots of computer clusters right now...

** it's not just that the math is easier or they're adequate for the
limited domain, it's that the theories are more clearly, um,
prior-dictive, not just pre-dictive.