View Full Version : [SOLVED] what is "real"?
<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>There are people who post on this board saying wavefunctions or\nvirtual particles aren\'t "real" but are instead a mathematcal device.\nWell, you could say everything in every theory of physics is a\n"mathematical device". All of our theories were invented by humans,\nand are not the same thing as the real Universe. You could say all of\nor theories is just a mathematical construct to get the predictions to\nmatch up with observations, and all our theories are just convenient\nways of thiking about it, and all of our theories are obviously not\nthe real Universe, so how are wavefunctions or virtual particles less\n"real" than anything else in physics?\n\nDavid\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>There are people who post on this board saying wavefunctions or
virtual particles aren't "real" but are instead a mathematcal device.
Well, you could say everything in every theory of physics is a
"mathematical device". All of our theories were invented by humans,
and are not the same thing as the real Universe. You could say all of
or theories is just a mathematical construct to get the predictions to
match up with observations, and all our theories are just convenient
ways of thiking about it, and all of our theories are obviously not
the real Universe, so how are wavefunctions or virtual particles less
"real" than anything else in physics?
David
Hans Aberg
Apr24-04, 08:17 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>In article <53ca460a.0404230950.657b4da5@posting.google.com>, \nulmo@cheerful.com (Ulmo) wrote:\n\n>There are people who post on this board saying wavefunctions or\n>virtual particles aren\'t "real" but are instead a mathematcal device.\n>Well, you could say everything in every theory of physics is a\n>"mathematical device". All of our theories were invented by humans,\n>and are not the same thing as the real Universe. You could say all of\n>or theories is just a mathematical construct to get the predictions to\n>match up with observations, and all our theories are just convenient\n>ways of thiking about it, and all of our theories are obviously not\n>the real Universe, so how are wavefunctions or virtual particles less\n>"real" than anything else in physics?\n\nModern physics develops theories about relations between physically\nmeasurable quantities, that can be verified in the sense that they can\npredict observations and experiments. So from this point of view, all\nphysical fields, measurable or non-measurable, are all just brain\nconstructs used to describe some aspects of the physical reality that we\nlive in.\n\nBut QM, as already noted, makes a distinction between measurable physical\nquantities (time, length, mass, EM etc) and non-measurable QM fields\n(waves, Hilbert space vectors). According to the writing of QM, the\nmeasurable physical quantities can be measured within the limitations of\nthe Heisenberg uncertainty relations. The unmeasurable QM fields cannot be\ndirectly measured by physical experiments; these are only used in order to\ndescribe the relations between the physically measurable quantities (such\nas the Heisenberg uncertainty relations).\n\nThis works as follows: The state of a particle is described by a vector n\na Hilbert space. If one measures this particle say for its position, then\nthe position operator truncates this Hilbert space, one part give rise to\nthe physical measurement, and the other orthogonal part, the new state of\nthe particle. Thus, the measurement of the particle destroys its original\nstate (which causes the Heisenberg uncertainty principles). So there is no\npossibility to figure out is original state or its new state fully, but\nindirectly, from the measurements and QM theories, we can deduce some\nproperties of it. For example, one can deduce the electron orbits of an\natom this way, but not the phase (a complex number of norm 1) of the QM\nfields of the electrons.\n\nHans Aberg\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>In article <53ca460a.0404230950.657b4da5@posting.google.com>,
ulmo@cheerful.com (Ulmo) wrote:
>There are people who post on this board saying wavefunctions or
>virtual particles aren't "real" but are instead a mathematcal device.
>Well, you could say everything in every theory of physics is a
>"mathematical device". All of our theories were invented by humans,
>and are not the same thing as the real Universe. You could say all of
>or theories is just a mathematical construct to get the predictions to
>match up with observations, and all our theories are just convenient
>ways of thiking about it, and all of our theories are obviously not
>the real Universe, so how are wavefunctions or virtual particles less
>"real" than anything else in physics?
Modern physics develops theories about relations between physically
measurable quantities, that can be verified in the sense that they can
predict observations and experiments. So from this point of view, all
physical fields, measurable or non-measurable, are all just brain
constructs used to describe some aspects of the physical reality that we
live in.
But QM, as already noted, makes a distinction between measurable physical
quantities (time, length, mass, EM etc) and non-measurable QM fields
(waves, Hilbert space vectors). According to the writing of QM, the
measurable physical quantities can be measured within the limitations of
the Heisenberg uncertainty relations. The unmeasurable QM fields cannot be
directly measured by physical experiments; these are only used in order to
describe the relations between the physically measurable quantities (such
as the Heisenberg uncertainty relations).
This works as follows: The state of a particle is described by a vector n
a Hilbert space. If one measures this particle say for its position, then
the position operator truncates this Hilbert space, one part give rise to
the physical measurement, and the other orthogonal part, the new state of
the particle. Thus, the measurement of the particle destroys its original
state (which causes the Heisenberg uncertainty principles). So there is no
possibility to figure out is original state or its new state fully, but
indirectly, from the measurements and QM theories, we can deduce some
properties of it. For example, one can deduce the electron orbits of an
atom this way, but not the phase (a complex number of norm 1) of the QM
fields of the electrons.
Hans Aberg
chronon
Apr27-04, 01:40 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>ulmo@cheerful.com (Ulmo) wrote in message news:<53ca460a.0404230950.657b4da5@posting.google. com>...\n\n>all of our theories are obviously not\n> the real Universe, so how are wavefunctions or virtual particles less\n> "real" than anything else in physics?\n\nOnce upon a time there was theory and there was reality. The realists\nbelieved that the theory described what was actually there, and the\nanti-realists believed otherwise. Then somehow, with the Copenhagen\nInterpretation, the anti-realism managed to get into the theory side\nof things. I think that this was the root of Einstein\'s complaint that\nquantum theory was incomplete. Unfortunately most people seemed to\nprefer philosophical musings, so Einstein was considered to have lost\nthis argument.\n\nStephen Lee\nwww.chronon.org\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>ulmo@cheerful.com (Ulmo) wrote in message news:<53ca460a.0404230950.657b4da5@posting.google.com>...
>all of our theories are obviously not
> the real Universe, so how are wavefunctions or virtual particles less
> "real" than anything else in physics?
Once upon a time there was theory and there was reality. The realists
believed that the theory described what was actually there, and the
anti-realists believed otherwise. Then somehow, with the Copenhagen
Interpretation, the anti-realism managed to get into the theory side
of things. I think that this was the root of Einstein's complaint that
quantum theory was incomplete. Unfortunately most people seemed to
prefer philosophical musings, so Einstein was considered to have lost
this argument.
Stephen Lee
www.chronon.org
Danny Ross Lunsford
Apr27-04, 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>Ulmo wrote:\n\n> There are people who post on this board saying wavefunctions or\n> virtual particles aren\'t "real" but are instead a mathematcal device.\n\nThis is not quite correctly stated, but OK. It would be better to say\nthat they are "auxiliary devices".\n\n> Well, you could say everything in every theory of physics is a\n> "mathematical device".\n\nNot really. There are key ideas that certain forms directly correspond\nto physically real things. So for example the x-coordinate is an\nauxiliary device, but the position vector is "real".\n\n> All of our theories were invented by humans,\n> and are not the same thing as the real Universe. You could say all of\n> or theories is just a mathematical construct to get the predictions to\n> match up with observations, and all our theories are just convenient\n> ways of thiking about it, and all of our theories are obviously not\n> the real Universe, so how are wavefunctions or virtual particles less\n> "real" than anything else in physics?\n\nYou would benefit from the book "Science and Hypothesis" by Poincare\'.\n\nVirtual particles have no individual identity. Only the complete sum of\nterms in the perturbation expansion (assuming it even converges)\nqualifies as a "real" thing. To use a mathematical example, one can\nwrite down a Fourier integral representing, say, the upper half of the\nunit circle. The circle is "real", but the periodic terms going into the\nsum are clearly component devices. In some sense, the "real" things\ncorrespond to what philosophers would call the "object of intention".\n\nThe wavefunction does deserve closer attention because there are still\nmisconceptions and controversies about the "metaphysical" content of\nquantum theory. In my experience only a few very special people have a\ncomprehensive overview of this topic - one can mention Bohm,\nFinkelstein, Jauch, and Gottfried. For every sensible statement there\nare 100 inchoate ones in the literature. One just has to learn how to\nsift. Remember the whole thing is a work in progress. Pluto has only\nmade 20 or so orbits since the days when we barked at the Moon, and only\n1 or 2 since we really began to get a grip on it.\n\n-drl\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>Ulmo wrote:
> There are people who post on this board saying wavefunctions or
> virtual particles aren't "real" but are instead a mathematcal device.
This is not quite correctly stated, but OK. It would be better to say
that they are "auxiliary devices".
> Well, you could say everything in every theory of physics is a
> "mathematical device".
Not really. There are key ideas that certain forms directly correspond
to physically real things. So for example the x-coordinate is an
auxiliary device, but the position vector is "real".
> All of our theories were invented by humans,
> and are not the same thing as the real Universe. You could say all of
> or theories is just a mathematical construct to get the predictions to
> match up with observations, and all our theories are just convenient
> ways of thiking about it, and all of our theories are obviously not
> the real Universe, so how are wavefunctions or virtual particles less
> "real" than anything else in physics?
You would benefit from the book "Science and Hypothesis" by Poincare'.
Virtual particles have no individual identity. Only the complete sum of
terms in the perturbation expansion (assuming it even converges)
qualifies as a "real" thing. To use a mathematical example, one can
write down a Fourier integral representing, say, the upper half of the
unit circle. The circle is "real", but the periodic terms going into the
sum are clearly component devices. In some sense, the "real" things
correspond to what philosophers would call the "object of intention".
The wavefunction does deserve closer attention because there are still
misconceptions and controversies about the "metaphysical" content of
quantum theory. In my experience only a few very special people have a
comprehensive overview of this topic - one can mention Bohm,
Finkelstein, Jauch, and Gottfried. For every sensible statement there
are 100 inchoate ones in the literature. One just has to learn how to
sift. Remember the whole thing is a work in progress. Pluto has only
made 20 or so orbits since the days when we barked at the Moon, and only
1 or 2 since we really began to get a grip on it.
-drl
Martin Lohmann
Apr27-04, 01:47 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>ulmo@cheerful.com (Ulmo) wrote in message news:<53ca460a.0404230950.657b4da5@posting.google. com>...\n> There are people who post on this board saying wavefunctions or\n> virtual particles aren\'t "real" but are instead a mathematcal device.\n> Well, you could say everything in every theory of physics is a\n> "mathematical device". All of our theories were invented by humans,\n> and are not the same thing as the real Universe. You could say all of\n> or theories is just a mathematical construct to get the predictions to\n> match up with observations, and all our theories are just convenient\n> ways of thiking about it, and all of our theories are obviously not\n> the real Universe, so how are wavefunctions or virtual particles less\n> "real" than anything else in physics?\n\nPhilosophically, you are surely right. The description of a thing will\nnever be the thing itself (of course, because it is only the\ndescription). But you should not forget, that physics is not only\nmathematics! Apart from its mathemtical device it has also a machinery\nwhich tells you how to INTERPRET the mathematics you have done.\nAlthough this interpretation has nothing to do with mathematics\n(because it is rather a set of axioms which can only be proven by\nexperiment), you might think of this interpretation as a map from your\nformula to the set of "physical terms" such as distance, or time\nintervals, i.e. as a map from mathematics to "reality". So it does\nmake sense to say that wavefunctions are not real, but only in the\nsense that "wavefunctions" are not in the domain of this\ninterpretation map.\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>ulmo@cheerful.com (Ulmo) wrote in message news:<53ca460a.0404230950.657b4da5@posting.google.com>...
> There are people who post on this board saying wavefunctions or
> virtual particles aren't "real" but are instead a mathematcal device.
> Well, you could say everything in every theory of physics is a
> "mathematical device". All of our theories were invented by humans,
> and are not the same thing as the real Universe. You could say all of
> or theories is just a mathematical construct to get the predictions to
> match up with observations, and all our theories are just convenient
> ways of thiking about it, and all of our theories are obviously not
> the real Universe, so how are wavefunctions or virtual particles less
> "real" than anything else in physics?
Philosophically, you are surely right. The description of a thing will
never be the thing itself (of course, because it is only the
description). But you should not forget, that physics is not only
mathematics! Apart from its mathemtical device it has also a machinery
which tells you how to INTERPRET the mathematics you have done.
Although this interpretation has nothing to do with mathematics
(because it is rather a set of axioms which can only be proven by
experiment), you might think of this interpretation as a map from your
formula to the set of "physical terms" such as distance, or time
intervals, i.e. as a map from mathematics to "reality". So it does
make sense to say that wavefunctions are not real, but only in the
sense that "wavefunctions" are not in the domain of this
interpretation map.
greywolf42
Apr27-04, 02:05 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>Ulmo <ulmo@cheerful.com> wrote in message\nnews:53ca460a.0404230950.657b4da5@posting .google.com...\n> There are people who post on this board saying wavefunctions or\n> virtual particles aren\'t "real" but are instead a mathematcal device.\n\n> Well, you could say everything in every theory of physics is a\n> "mathematical device".\n\nIf you said that, you would be egregiously in error.\n\n> All of our theories were invented by humans,\n\nThe source of a theory has nothing to do with the epistomelogical basis of a\nconcept. Or the physical existence of an external entity to which we\nascribe a name.\n\n> and are not the same thing as the real Universe.\n\nNeither is a measurement of length the same a length. But your statement is\nempty of content.\n\n> You could say all of\n> or theories is just a mathematical construct to get the predictions to\n> match up with observations,\n\nBut this is not a true statement. It is true that many of the priests of\nacademia currently try to sell this religion. However such a view has\nnothing whatsoever in common with the scientific method.\n\n> and all our theories are just convenient\n> ways of thiking about it, and all of our theories are obviously not\n> the real Universe, so how are wavefunctions or virtual particles less\n> "real" than anything else in physics?\n\nBecause -- unlike *real* entities in the *real* universe -- they have no\nphysical existence outside of the arcane scribbles on paper made by priests.\n\nShall we discuss the uncorporeal dragon? (See Sagan\'s "The Demon-Haunted\nWorld, Science as a Candle in the Dark")\n\n[Moderator\'s note: No, we shall not. Let\'s stick to physics. -TB]\n\n--\ngreywolf42\nubi dubium ibi libertas\n{remove planet for return e-mail}\n\n\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>Ulmo <ulmo@cheerful.com> wrote in message
news:53ca460a.0404230950.657b4da5@posting.google.c om...
> There are people who post on this board saying wavefunctions or
> virtual particles aren't "real" but are instead a mathematcal device.
> Well, you could say everything in every theory of physics is a
> "mathematical device".
If you said that, you would be egregiously in error.
> All of our theories were invented by humans,
The source of a theory has nothing to do with the epistomelogical basis of a
concept. Or the physical existence of an external entity to which we
ascribe a name.
> and are not the same thing as the real Universe.
Neither is a measurement of length the same a length. But your statement is
empty of content.
> You could say all of
> or theories is just a mathematical construct to get the predictions to
> match up with observations,
But this is not a true statement. It is true that many of the priests of
academia currently try to sell this religion. However such a view has
nothing whatsoever in common with the scientific method.
> and all our theories are just convenient
> ways of thiking about it, and all of our theories are obviously not
> the real Universe, so how are wavefunctions or virtual particles less
> "real" than anything else in physics?
Because -- unlike *real* entities in the *real* universe -- they have no
physical existence outside of the arcane scribbles on paper made by priests.
Shall we discuss the uncorporeal dragon? (See Sagan's "The Demon-Haunted
World, Science as a Candle in the Dark")
[Moderator's note: No, we shall not. Let's stick to physics. -TB]
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
<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>ulmo@cheerful.com (Ulmo) wrote in message news:<53ca460a.0404230950.657b4da5@posting.google. com>...\n> There are people who post on this board saying wavefunctions or\n> virtual particles aren\'t "real" but are instead a mathematcal device.\n> Well, you could say everything in every theory of physics is a\n> "mathematical device". All of our theories were invented by humans,\n> and are not the same thing as the real Universe. You could say all of\n> or theories is just a mathematical construct to get the predictions to\n> match up with observations, and all our theories are just convenient\n> ways of thiking about it, and all of our theories are obviously not\n> the real Universe, so how are wavefunctions or virtual particles less\n> "real" than anything else in physics?\n>\n> David\n\nInteresting question. My take on all this is that we are not modeling\n"reality" so much as putting together a map. And let us be reminded\nof the classical notion of never confusing the map with the actual\nterritory. Actually, I think sometimes we\'re making maps of maps.\nIt\'s all like a black box where all we can be absolutely sure of is\nwhat goes in and what comes out.\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>ulmo@cheerful.com (Ulmo) wrote in message news:<53ca460a.0404230950.657b4da5@posting.google.com>...
> There are people who post on this board saying wavefunctions or
> virtual particles aren't "real" but are instead a mathematcal device.
> Well, you could say everything in every theory of physics is a
> "mathematical device". All of our theories were invented by humans,
> and are not the same thing as the real Universe. You could say all of
> or theories is just a mathematical construct to get the predictions to
> match up with observations, and all our theories are just convenient
> ways of thiking about it, and all of our theories are obviously not
> the real Universe, so how are wavefunctions or virtual particles less
> "real" than anything else in physics?
>
> David
Interesting question. My take on all this is that we are not modeling
"reality" so much as putting together a map. And let us be reminded
of the classical notion of never confusing the map with the actual
territory. Actually, I think sometimes we're making maps of maps.
It's all like a black box where all we can be absolutely sure of is
what goes in and what comes out.
Arnold Neumaier
Apr28-04, 01:46 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>Ulmo wrote:\n> There are people who post on this board saying wavefunctions or\n> virtual particles aren\'t "real" but are instead a mathematcal device.\n> Well, you could say everything in every theory of physics is a\n> "mathematical device". All of our theories were invented by humans,\n> and are not the same thing as the real Universe. You could say all of\n> or theories is just a mathematical construct to get the predictions to\n> match up with observations, and all our theories are just convenient\n> ways of thiking about it, and all of our theories are obviously not\n> the real Universe, so how are wavefunctions or virtual particles less\n> "real" than anything else in physics?\n\nOf course, all language is only an approximation to reality,\nwhich simply is. But to do science we need to classify the aspects\nof reality that appear to have more permanence, and consider them\nas real. Nevertheless, all concepts, including \'real\' have a fuzziness\nabout them, unless they are phrased in terms of rigorous mathematical\nmodels (in which case they don\'t apply to reality itself but only to\na model of reality).\n\nIn the informal way I use the notion, \'real\' in theoretical physics\nmeans a concept or object that\n- is independent of the computational scheme used to\nextract information from a theory,\n- has a reasonably well-defined and consistent formal basis\n- does not give rise to misleading intuition.\nThis does not give a clear definition of real, of course.\nBut it makes charge distributions and inputs and outputs of\n(theoretical models of) scattering experiments something real,\nwhile making bare particles and virtual particles artifacts of\nthe approximation scheme.\n\n\nArnold Neumaier\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>Ulmo wrote:
> There are people who post on this board saying wavefunctions or
> virtual particles aren't "real" but are instead a mathematcal device.
> Well, you could say everything in every theory of physics is a
> "mathematical device". All of our theories were invented by humans,
> and are not the same thing as the real Universe. You could say all of
> or theories is just a mathematical construct to get the predictions to
> match up with observations, and all our theories are just convenient
> ways of thiking about it, and all of our theories are obviously not
> the real Universe, so how are wavefunctions or virtual particles less
> "real" than anything else in physics?
Of course, all language is only an approximation to reality,
which simply is. But to do science we need to classify the aspects
of reality that appear to have more permanence, and consider them
as real. Nevertheless, all concepts, including 'real' have a fuzziness
about them, unless they are phrased in terms of rigorous mathematical
models (in which case they don't apply to reality itself but only to
a model of reality).
In the informal way I use the notion, 'real' in theoretical physics
means a concept or object that
- is independent of the computational scheme used to
extract information from a theory,
- has a reasonably well-defined and consistent formal basis
- does not give rise to misleading intuition.
This does not give a clear definition of real, of course.
But it makes charge distributions and inputs and outputs of
(theoretical models of) scattering experiments something real,
while making bare particles and virtual particles artifacts of
the approximation scheme.
Arnold Neumaier
alistair
Apr28-04, 09:30 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\nI think you\'ll find that most people define real as anything that\nyou can make a prediction about that can be verified accurately by\nexperiment.But then we must define accurate - this is why gravity\nprobe b for example is currently in space testing general relativity\nbecause people want theory to match experiment to more decimal places\nto convince them that something is real.Quantum field theory gives\nexperimentally backed predictions to 11 decimal places but you\'ll\nstill find peole who don\'t think it\'s right - I\'m one of them.\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>I think you'll find that most people define real as anything that
you can make a prediction about that can be verified accurately by
experiment.But then we must define accurate - this is why gravity
probe b for example is currently in space testing general relativity
because people want theory to match experiment to more decimal places
to convince them that something is real.Quantum field theory gives
experimentally backed predictions to 11 decimal places but you'll
still find peole who don't think it's right - I'm one of them.
Arnold Neumaier
Apr28-04, 01:28 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>Danny Ross Lunsford wrote:\n> Ulmo wrote:\n>\n>> There are people who post on this board saying wavefunctions or\n>> virtual particles aren\'t "real" but are instead a mathematcal device.\n>\n> This is not quite correctly stated, but OK. It would be better to say\n> that they are "auxiliary devices".\n>\n>> Well, you could say everything in every theory of physics is a\n>> "mathematical device".\n>\n>\n> Not really. There are key ideas that certain forms directly correspond\n> to physically real things. So for example the x-coordinate is an\n> auxiliary device, but the position vector is "real".\n\nHmm ... since the origin of the ordinate system is also an auxiliary\ndevice, only the difference of two vectors (as elements in an abstract\nvector space) is real in this sense.\n\n\nArnold Neumaier\n\n\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>Danny Ross Lunsford wrote:
> Ulmo wrote:
>
>> There are people who post on this board saying wavefunctions or
>> virtual particles aren't "real" but are instead a mathematcal device.
>
> This is not quite correctly stated, but OK. It would be better to say
> that they are "auxiliary devices".
>
>> Well, you could say everything in every theory of physics is a
>> "mathematical device".
>
>
> Not really. There are key ideas that certain forms directly correspond
> to physically real things. So for example the x-coordinate is an
> auxiliary device, but the position vector is "real".
Hmm ... since the origin of the ordinate system is also an auxiliary
device, only the difference of two vectors (as elements in an abstract
vector space) is real in this sense.
Arnold Neumaier
wavelength
Apr28-04, 02:16 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>Hiyas :),\n\nWhats real ? ONLY what can be observed that is what can be seen by\nexperiment ( as far as Natural Philosophy is concerned ). ANYTHING else, is\na abstraction of the mind.\n\nBest\n\n:)\n\n[Moderator\'s note: This discussion is getting awfully general. If it\ncan\'t be tied back to specific issues in physics, let\'s drop it.\n-TB]\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>Hiyas :),
Whats real ? ONLY what can be observed that is what can be seen by
experiment ( as far as Natural Philosophy is concerned ). ANYTHING else, is
a abstraction of the mind.
Best
:)
[Moderator's note: This discussion is getting awfully general. If it
can't be tied back to specific issues in physics, let's drop it.
-TB]
Frank Hellmann
Apr28-04, 02:27 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>Well everybody has a different conception on what is "real", some\npeople mean measurable, others observable. For one extreme look at the\noriginal EPR paper.\n\nI personally find the following way of thinking about it effective:\n\nAssume a physical theory, if that theory, if fed into an infintely\nstrong computer (InfiComp) would produce a reality that is, at least\nin the aspects that the physical theory is supposed to model, similar\nto our experienced reality, then it is a real theory.\nFor example GR is a completely real theory.\nIf parts of the theory need to be removed ad hoc before we arrive at\nour experienced reality then these parts are "non real".\nQuantum Mechanics and the wave function are examples here. Some sort\nof ad hoc is always needed, picking out the decoherent history,\ninserting the probabilities, collapsing the wave function.\nIn EPR terms: The state vector does not correspond to an element of\nphysical reality.\nNow QFT is actually a tricky one. I personally would tend to call the\nvirtual particles in QFT real, even though they can not been directly\nmeassured. This is consistent with my definition above, since they are\nnot explained away but instead summed over. So on the one hand they\nnever appear in the physical reality, yet they are always present, and\nare not removed ad hoc.\nInitially the way those virtual particles were dealt with was to\npretty much ignore them since their contributions were divergent, so\nthe "virtuality" of these particles might be historical.\nFurthermore they are not elements of the physical Fock space, in this\nsense they are not removed ad hoc, but dissapear by internal reasons\nof the theory before reality emerges in our InfiComp. They are thus\ndefinately more real then the wave function for example, but less real\nthen the particles in Newtonian Mechanics (which are about as real as\nit get\'s really...)\n\nOne could conceivably work with a concept of minimal reality, Occam\nstyle. The minimal reality is the simulation you can run in your\ncomputer that uses the least entities while producing the same\nresults.\nVirtual particles are definately not minimal real.\nHowever, neither is the metric in GR probably.\n\nFun with words,\nFrank Hellmann.\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>Well everybody has a different conception on what is "real", some
people mean measurable, others observable. For one extreme look at the
original EPR paper.
I personally find the following way of thinking about it effective:
Assume a physical theory, if that theory, if fed into an infintely
strong computer (InfiComp) would produce a reality that is, at least
in the aspects that the physical theory is supposed to model, similar
to our experienced reality, then it is a real theory.
For example GR is a completely real theory.
If parts of the theory need to be removed ad hoc before we arrive at
our experienced reality then these parts are "non real".
Quantum Mechanics and the wave function are examples here. Some sort
of ad hoc is always needed, picking out the decoherent history,
inserting the probabilities, collapsing the wave function.
In EPR terms: The state vector does not correspond to an element of
physical reality.
Now QFT is actually a tricky one. I personally would tend to call the
virtual particles in QFT real, even though they can not been directly
meassured. This is consistent with my definition above, since they are
not explained away but instead summed over. So on the one hand they
never appear in the physical reality, yet they are always present, and
are not removed ad hoc.
Initially the way those virtual particles were dealt with was to
pretty much ignore them since their contributions were divergent, so
the "virtuality" of these particles might be historical.
Furthermore they are not elements of the physical Fock space, in this
sense they are not removed ad hoc, but dissapear by internal reasons
of the theory before reality emerges in our InfiComp. They are thus
definately more real then the wave function for example, but less real
then the particles in Newtonian Mechanics (which are about as real as
it get's really...)
One could conceivably work with a concept of minimal reality, Occam
style. The minimal reality is the simulation you can run in your
computer that uses the least entities while producing the same
results.
Virtual particles are definately not minimal real.
However, neither is the metric in GR probably.
Fun with words,
Frank Hellmann.
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