View Full Version : Ground state and QFT
<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>Does a QFT need to have a "groundstate".\nI know that a la Wightman, one of the\naxioms says it mus, but my question is\nmore questioning this "axiom". I.e.,\nwhy would one need this groundstate\nwhat happens without it? Why does it\npressumably exist in most basic known\nexamples of fields theories.\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>Does a QFT need to have a "groundstate".
I know that a la Wightman, one of the
axioms says it mus, but my question is
more questioning this "axiom". I.e.,
why would one need this groundstate
what happens without it? Why does it
pressumably exist in most basic known
examples of fields theories.
Arnold Neumaier
Dec4-04, 03:18 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>mandro wrote:\n> Does a QFT need to have a "groundstate".\n> I know that a la Wightman, one of the\n> axioms says it must,\n\nWightman axioms only describe a subset of field theories,\nthose with a mass gap. This excludes theories with a\nphoton or a graviton.\n\n\n> but my question is\n> more questioning this "axiom". I.e.,\n> why would one need this groundstate\n\nIt is the state without particles.\n\n\n> what happens without it?\n\nStrange things - read about the Unruh effect.\n\n\n> Why does it\n> pressumably exist in most basic known\n> examples of fields theories.\n\nBecause all current QFT is formulated in terms of vacuum expectations.\nWithout a vacuum no vacuum expectations.\n\nQuantum gravity is difficult because there the notion of\nvacuum seems ill-defined, and current QFT becomes inapplicable.\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>mandro wrote:
> Does a QFT need to have a "groundstate".
> I know that a la Wightman, one of the
> axioms says it must,
Wightman axioms only describe a subset of field theories,
those with a mass gap. This excludes theories with a
photon or a graviton.
> but my question is
> more questioning this "axiom". I.e.,
> why would one need this groundstate
It is the state without particles.
> what happens without it?
Strange things - read about the Unruh effect.
> Why does it
> pressumably exist in most basic known
> examples of fields theories.
Because all current QFT is formulated in terms of vacuum expectations.
Without a vacuum no vacuum expectations.
Quantum gravity is difficult because there the notion of
vacuum seems ill-defined, and current QFT becomes inapplicable.
Arnold Neumaier
<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> Wightman axioms only describe a subset of field theories,\n> those with a mass gap. This excludes theories with a\n> photon or a graviton.\n>\n\nI do not understand very well this issue of the\nmass gap.\n\n> It is the state without particles.\n\nSometimes such a state may not exist, while\na groundstate exists i.e., there may not\nbe a number operator(s) that commute with\nthe Hamiltonian. But I have no explicit\nconstructions which exhibit these properties\nso I\'m not sure.\n\n>\n>\n> > what happens without it?\n>\n> Strange things - read about the Unruh effect.\n\nI though the Unruh effect occurrs in a case\nwhere a groundstate exists i.e., standard quantum\nfield theory of a free field. I.e., take the ground\nstate of standard qft and analize it from the point\nof view of an accelerated detector.\n\n>\n> > Why does it\n> > pressumably exist in most basic known\n> > examples of fields theories.\n>\n> Because all current QFT is formulated in terms of vacuum\nexpectations.\n> Without a vacuum no vacuum expectations.\n>\n\nI think this statement is "after the fact"\nbut I may be wrong.\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>Wightman axioms only describe a subset of field theories,
> those with a mass gap. This excludes theories with a
> photon or a graviton.
>
I do not understand very well this issue of the
mass gap.
> It is the state without particles.
Sometimes such a state may not exist, while
a groundstate exists i.e., there may not
be a number operator(s) that commute with
the Hamiltonian. But I have no explicit
constructions which exhibit these properties
so I'm not sure.
>
>
> > what happens without it?
>
> Strange things - read about the Unruh effect.
I though the Unruh effect occurrs in a case
where a groundstate exists i.e., standard quantum
field theory of a free field. I.e., take the ground
state of standard qft and analize it from the point
of view of an accelerated detector.
>
> > Why does it
> > pressumably exist in most basic known
> > examples of fields theories.
>
> Because all current QFT is formulated in terms of vacuum
expectations.
> Without a vacuum no vacuum expectations.
>
I think this statement is "after the fact"
but I may be wrong.
Arnold Neumaier
Dec10-04, 05:00 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>MM wrote:\n> Arnold Neumaier <Arnold.Neumaier@univie.ac.at> wrote in message news:<41B1DD93.6030101@univie.ac.at>...\n> mandro wrote:\n>\n> >> what happens [in QFT] without [a groundstate/vacuum]?\n>\n> Arnold Neumaier wrote:\n>\n> > Strange things - read about the Unruh effect.\n>\n> ??? I don\'t understand how the Unruh effect\n> is relevant in this context. I had understood\n> the Rindler vacuum of a uniformly accelerating\n> observer belongs to a representation which is\n> unitarily-inequivalent to that of an inertial\n> observer. But there is still a vacuum - just\n> a different vacuum from the original one. (?)\n\nWell, if the \'vacuum\' is observer-dependent, it cannot be a\nphysical state, hence not a graound state in any meaningful sense.\nObjective, physical objects must be observer independent,\nat least im my view of physics.\n\nBut this stuff is ill-understood, so there is little one can say\nwith definiteness.\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>MM wrote:
> Arnold Neumaier <Arnold.Neumaier@univie.ac.at> wrote in message news:<41B1DD93.6030101@univie.ac.at>...
> mandro wrote:
>
> >> what happens [in QFT] without [a groundstate/vacuum]?
>
> Arnold Neumaier wrote:
>
> > Strange things - read about the Unruh effect.
>
> ??? I don't understand how the Unruh effect
> is relevant in this context. I had understood
> the Rindler vacuum of a uniformly accelerating
> observer belongs to a representation which is
> unitarily-inequivalent to that of an inertial
> observer. But there is still a vacuum - just
> a different vacuum from the original one. (?)
Well, if the 'vacuum' is observer-dependent, it cannot be a
physical state, hence not a graound state in any meaningful sense.
Objective, physical objects must be observer independent,
at least im my view of physics.
But this stuff is ill-understood, so there is little one can say
with definiteness.
Arnold Neumaier
Arnold Neumaier
Dec10-04, 10:18 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>\npirillo wrote:\n>>Wightman axioms only describe a subset of field theories,\n>>those with a mass gap. This excludes theories with a\n>>photon or a graviton.\n>\n> I do not understand very well this issue of the\n> mass gap.\n\nIt says that there is an open interval ]0,m_0c^2[ such that,\nin the center of mass frame of any oberver, there are no stationary\nstates with energy in this interval. Thus it gives the vacuum state\na privileged, observer-independent and hence objective meaning.\n\n\n>>It is the state without particles.\n>\n> Sometimes such a state may not exist, while\n> a groundstate exists i.e., there may not\n> be a number operator(s) that commute with\n> the Hamiltonian.\n\nIn that case it is the state with zero 4-momentum.\nIn a good theory, it should be unique, since this is\nessentially equivalent with the cluster separation property.\n\n\n>>>what happens without it?\n>>\n>>Strange things - read about the Unruh effect.\n>\n>\n> I though the Unruh effect occurrs in a case\n> where a groundstate exists i.e., standard quantum\n> field theory of a free field.\n\nA free field has no Unruh effect since there are no interactions.\n\nI.e., take the ground\n> state of standard qft\n\nIn standard interacting qft, fields are not free.\n\n\n> and analyze it from the point of view of an accelerated detector.\n\nThis makes sense only in general relativity, and there standard\nfield theory is not really adequate; the concept of vacuum is gone\nsince there is no longer a provileged Minkowski structure whose\nmomentum vector could be used to define it. So the ground state\nconcept loses meaning. This is the only sense in which I can conceive\nof field theory without ground state.\n\n\n\n>>>Why does it\n>>>pressumably exist in most basic known\n>>>examples of fields theories.\n>>\n>>Because all current QFT is formulated in terms of vacuum expectations.\n>\n>>Without a vacuum no vacuum expectations.\n>\n> I think this statement is "after the fact"\n> but I may be wrong.\n\nThe facts are Nature, and we model what we see there in the best way\nwe understand. Thus all science is after the fact in this sense.\n\nThe only way people have been able to make sense of relativistic QFT\nis in terms of vacuum expectations. And it is a very natural way.\nIt is also related to the fact that we still do not have a good\nquantum gravity since there the lack of the concept of a ground state\nmakes things intractable, until a good substitute is found.\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>pirillo wrote:
>>Wightman axioms only describe a subset of field theories,
>>those with a mass gap. This excludes theories with a
>>photon or a graviton.
>
> I do not understand very well this issue of the
> mass gap.
It says that there is an open interval ]0,m_{0c}^2[ such that,
in the center of mass frame of any oberver, there are no stationary
states with energy in this interval. Thus it gives the vacuum state
a privileged, observer-independent and hence objective meaning.
>>It is the state without particles.
>
> Sometimes such a state may not exist, while
> a groundstate exists i.e., there may not
> be a number operator(s) that commute with
> the Hamiltonian.
In that case it is the state with zero 4-momentum.
In a good theory, it should be unique, since this is
essentially equivalent with the cluster separation property.
>>>what happens without it?
>>
>>Strange things - read about the Unruh effect.
>
>
> I though the Unruh effect occurrs in a case
> where a groundstate exists i.e., standard quantum
> field theory of a free field.
A free field has no Unruh effect since there are no interactions.
I.e., take the ground
> state of standard qft
In standard interacting qft, fields are not free.
> and analyze it from the point of view of an accelerated detector.
This makes sense only in general relativity, and there standard
field theory is not really adequate; the concept of vacuum is gone
since there is no longer a provileged Minkowski structure whose
momentum vector could be used to define it. So the ground state
concept loses meaning. This is the only sense in which I can conceive
of field theory without ground state.
>>>Why does it
>>>pressumably exist in most basic known
>>>examples of fields theories.
>>
>>Because all current QFT is formulated in terms of vacuum expectations.
>
>>Without a vacuum no vacuum expectations.
>
> I think this statement is "after the fact"
> but I may be wrong.
The facts are Nature, and we model what we see there in the best way
we understand. Thus all science is after the fact in this sense.
The only way people have been able to make sense of relativistic QFT
is in terms of vacuum expectations. And it is a very natural way.
It is also related to the fact that we still do not have a good
quantum gravity since there the lack of the concept of a ground state
makes things intractable, until a good substitute is found.
Arnold Neumaier
Strong_Field
Dec12-04, 03:51 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>"Arnold Neumaier" <Arnold.Neumaier@univie.ac.at> wrote in message\nnews:41B87218.2090608@univie.ac.at...\n> MM wrote:\n> > Arnold Neumaier <Arnold.Neumaier@univie.ac.at> wrote in message\nnews:<41B1DD93.6030101@univie.ac.at>...\n > > mandro wrote:\n> >\n>\n> Well, if the \'vacuum\' is observer-dependent, it cannot be a\n> physical state, hence not a graound state in any meaningful sense.\n> Objective, physical objects must be observer independent,\n> at least im my view of physics.\n>\nHow can this be true? We know that light is not observer-indenpendent (a\nblind observer cannot observe light) but light has physical meaning. If\n*any* observer observes somethings then it has a physical meaning.\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>"Arnold Neumaier" <Arnold.Neumaier@univie.ac.at> wrote in message
news:41B87218.2090608@univie.ac.at...
> MM wrote:
> > Arnold Neumaier <Arnold.Neumaier@univie.ac.at> wrote in message
news:<41B1DD93.6030101@univie.ac.at>...
> > mandro wrote:
> >
>
> Well, if the 'vacuum' is observer-dependent, it cannot be a
> physical state, hence not a graound state in any meaningful sense.
> Objective, physical objects must be observer independent,
> at least im my view of physics.
>
How can this be true? We know that light is not observer-indenpendent (a
blind observer cannot observe light) but light has physical meaning. If
*any* observer observes somethings then it has a physical meaning.
Igor Khavkine
Dec13-04, 09:12 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>On Sun, 12 Dec 2004 09:51:45 +0000, Strong_Field wrote:\n\n> "Arnold Neumaier" <Arnold.Neumaier@univie.ac.at> wrote in message\n> news:41B87218.2090608@univie.ac.at...\n>> MM wrote:\n>> > Arnold Neumaier <Arnold.Neumaier@univie.ac.at> wrote in message\n> news:<41B1DD93.6030101@univie.ac.at>...\n>> > mandro wrote:\n>> >\n>> >\n>> Well, if the \'vacuum\' is observer-dependent, it cannot be a physical\n>> state, hence not a graound state in any meaningful sense. Objective,\n>> physical objects must be observer independent, at least im my view of\n>> physics.\n>>\n> How can this be true? We know that light is not observer-indenpendent (a\n> blind observer cannot observe light) but light has physical meaning. If\n> *any* observer observes somethings then it has a physical meaning.\n\nWhen physicists talk about something being observable, they mean\nobservable in principle. In principle, a blind man can still hold a\nphoto-detector that will tell him whether it detects some light or not.\n\nAlso, insisting on a human being present at the point of observation is\nanti-Copernican. The conventional view is that we are not at the center of\nthe universe and that physics should work regardless of the presence\nhumans.\n\nIgor\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>On Sun, 12 Dec 2004 09:51:45 +0000, Strong_Field wrote:
> "Arnold Neumaier" <Arnold.Neumaier@univie.ac.at> wrote in message
> news:41B87218.2090608@univie.ac.at...
>> MM wrote:
>> > Arnold Neumaier <Arnold.Neumaier@univie.ac.at> wrote in message
> news:<41B1DD93.6030101@univie.ac.at>...
>> > mandro wrote:
>> >
>> >
>> Well, if the 'vacuum' is observer-dependent, it cannot be a physical
>> state, hence not a graound state in any meaningful sense. Objective,
>> physical objects must be observer independent, at least im my view of
>> physics.
>>
> How can this be true? We know that light is not observer-indenpendent (a
> blind observer cannot observe light) but light has physical meaning. If
> *any* observer observes somethings then it has a physical meaning.
When physicists talk about something being observable, they mean
observable in principle. In principle, a blind man can still hold a
photo-detector that will tell him whether it detects some light or not.
Also, insisting on a human being present at the point of observation is
anti-Copernican. The conventional view is that we are not at the center of
the universe and that physics should work regardless of the presence
humans.
Igor
Arnold Neumaier
Dec13-04, 10:05 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>isolation of man from nature,\nexcessive rapidity of social change and the break-down of natural\nsmall-scale communities such as the extended family, the village or\nthe tribe.\n\n48. It is well known that crowding increases stress and aggression.\nThe degree of crowding that exists today and the isolation of man from\nnature are consequences of technological progress. All pre-industrial\nsocieties were predominantly rural. The industrial Revolution vastly\nincreased the size of cities and the proportion of the population that\nlives in them, and modern agricultural technology has made it possible\nfor the Earth to support a far denser population than it ever did\nbefore. (Also, technology exacerbates the effects of crowding because\nit puts increased disruptive powers in people\'s hands. For example, a\nvariety of noise-making devices: power mowers, radios, motorcycles,\netc. If the use of these devices is unrestricted, people who want\npeace and quiet are frustrated by the noise. If their use is\nrestricted, people who use the devices are frustrated by the\nregulations... But if these machines had never been invented there\nwould have been no conflict and no frustration generated by them.)\n\n49. For primitive societies the natural world (which usually changes\nonly slowly) provided a stable framework and therefore a sense of\nsecurity. In the modern world it is human society that dominates\nnature rather than the other way around, and modern society changes\nvery rapidly owing to technological change. Thus there is no stable\nframework.\n\n50. The conservatives are fools: They whine about the decay of\ntraditional values, yet they enthusiastically support technological\nprogress and economic growth. Apparently it never occurs to them that\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>isolation of man from nature,
excessive rapidity of social change and the break-down of natural
small-scale communities such as the extended family, the village or
the tribe.
48. It is well known that crowding increases stress and aggression.
The degree of crowding that exists today and the isolation of man from
nature are consequences of technological progress. All pre-industrial
societies were predominantly rural. The industrial Revolution vastly
increased the size of cities and the proportion of the population that
lives in them, and modern agricultural technology has made it possible
for the Earth to support a far denser population than it ever did
before. (Also, technology exacerbates the effects of crowding because
it puts increased disruptive powers in people's hands. For example, a
variety of noise-making devices: power mowers, radios, motorcycles,
etc. If the use of these devices is unrestricted, people who want
peace and quiet are frustrated by the noise. If their use is
restricted, people who use the devices are frustrated by the
regulations... But if these machines had never been invented there
would have been no conflict and no frustration generated by them.)
49. For primitive societies the natural world (which usually changes
only slowly) provided a stable framework and therefore a sense of
security. In the modern world it is human society that dominates
nature rather than the other way around, and modern society changes
very rapidly owing to technological change. Thus there is no stable
framework.
50. The conservatives are fools: They whine about the decay of
traditional values, yet they enthusiastically support technological
progress and economic growth. Apparently it never occurs to them that
Strong_Field
Dec13-04, 10:57 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>position\nof power it tends to invade every private corner and force every\nthought into a leftist mold. In part this is because of the\nquasi-religious character of leftism; everything contrary to leftists\nbeliefs represents Sin. More importantly, leftism is a totalitarian\nforce because of the leftists\' drive for power. The leftist seeks to\nsatisfy his need for power through identification with a social\nmovement and he tries to go through the power process by helping to\npursue and attain the goals of the movement (see paragraph 83). But no\nmatter how far the movement has gone in attaining its goals the\nleftist is never satisfied, because his activism is a surrogate\nactivity (see paragraph 41). That is, the leftist\'s real motive is not\nto attain the ostensible goals of leftism; in reality he is motivated\nby the sense of power he gets from struggling for and then reaching a\nsocial goal.[35]\n\nConsequently the leftist is never satisfied with the goals he has\nalready attained; his need for the power process leads him always to\npursue some new goal. The leftist wants equal opportunities for\nminorities. When that is attained he insists on statistical equality\nof achievement by minorities. And as long as anyone harbors in some\ncorner of his mind a negative attitude toward some minority, the\nleftist has to re-educated him. And ethnic minorities are not enough;\nno one can be allowed to have a negative attitude toward homosexuals,\ndisabled people, fat people, old people, ugly people, and on and on\nand on. It\'s not enough that the public should be informed about the\nhazards of smoking; a warning has to be stamped on every package of\ncigarettes. Then cigarette advertising has to be restricted if not\nbanned. The activists will never be satisfied until tobacco is\noutlawed, and after that it\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>position
of power it tends to invade every private corner and force every
thought into a leftist mold. In part this is because of the
quasi-religious character of leftism; everything contrary to leftists
beliefs represents Sin. More importantly, leftism is a totalitarian
force because of the leftists' drive for power. The leftist seeks to
satisfy his need for power through identification with a social
movement and he tries to go through the power process by helping to
pursue and attain the goals of the movement (see paragraph 83). But no
matter how far the movement has gone in attaining its goals the
leftist is never satisfied, because his activism is a surrogate
activity (see paragraph 41). That is, the leftist's real motive is not
to attain the ostensible goals of leftism; in reality he is motivated
by the sense of power he gets from struggling for and then reaching a
social goal.[35]
Consequently the leftist is never satisfied with the goals he has
already attained; his need for the power process leads him always to
pursue some new goal. The leftist wants equal opportunities for
minorities. When that is attained he insists on statistical equality
of achievement by minorities. And as long as anyone harbors in some
corner of his mind a negative attitude toward some minority, the
leftist has to re-educated him. And ethnic minorities are not enough;
no one can be allowed to have a negative attitude toward homosexuals,
disabled people, fat people, old people, ugly people, and on and on
and on. It's not enough that the public should be informed about the
hazards of smoking; a warning has to be stamped on every package of
cigarettes. Then cigarette advertising has to be restricted if not
banned. The activists will never be satisfied until tobacco is
outlawed, and after that it
Frank Hellmann (Certhas -at- gmail -dot- com)
Dec14-04, 10:18 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>\nNope Observer independent has a rather specific meaning. It says\n(roughly) that if two observers in different physical states observe\nthe same phenomenon it must reduce to a common fundamental event,\nindependently of the state of observers, meaning that no contradiction\nbetween the relations between events can be derived from observations\nof different observers.\nIf we limit ourselfs to classes of observers related by Lorentz\ntransformations, we get the non accelerated observers of Special\nRelativity, and observer independence is manifest in the formal\ninvariance of physical laws under transformation into the\n"observational system".\nIn GR where we consider all possible observers but not any two of them\nare equivalent, which makes things rather more subtle.\n\nUnfortunately observer independence and symmetry are often thrown in to\nargue for the invariance under coordinate transformations, this in\nitself is missing the assumption that each coordinate system\ncorresponds to an observational mode in some sense.\nIf I model the observation completely in the mathematical framework,\nthen I can always subject any theory to any mathematical transformation\nwithout changing it.\nIt\'s not immidiately clear to me if this is significant for covariant\nQuantum Mechanics.\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>Nope Observer independent has a rather specific meaning. It says
(roughly) that if two observers in different physical states observe
the same phenomenon it must reduce to a common fundamental event,
independently of the state of observers, meaning that no contradiction
between the relations between events can be derived from observations
of different observers.
If we limit ourselfs to classes of observers related by Lorentz
transformations, we get the non accelerated observers of Special
Relativity, and observer independence is manifest in the formal
invariance of physical laws under transformation into the
"observational system".
In GR where we consider all possible observers but not any two of them
are equivalent, which makes things rather more subtle.
Unfortunately observer independence and symmetry are often thrown in to
argue for the invariance under coordinate transformations, this in
itself is missing the assumption that each coordinate system
corresponds to an observational mode in some sense.
If I model the observation completely in the mathematical framework,
then I can always subject any theory to any mathematical transformation
without changing it.
It's not immidiately clear to me if this is significant for covariant
Quantum Mechanics.
mikem@despammed.com
Dec14-04, 10:19 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\nArnold Neumaier wrote:\n\n> [...] if the \'vacuum\' is observer-dependent, it cannot be a\n> physical state, hence not a graound state in any meaningful\n> sense. Objective, physical objects must be observer\n> independent, at least im my view of physics.\n\nThis is tied up with the question of whether unitarily-inequivalent\nrepresentations are physically different objectively. Let\'s\nlook an easier example of this. In your paper with Ulf\nLeonhardt (quant-ph/0306123) and also Leonhardt\'s earlier tutorial\npaper (quant-ph/0305007), it is shown how to model\nactive optical elements by mixing creation and annihilation\noperators via Bogoliubov transformations. Such mixing\nresults in a representation of the out-modes which is\nunitarily-inequivalent to that of the in-modes. I.e: the\nout-fields live in a Fock space which is orthogonal\nto that of the in-fields. Therefore a lab observer is dealing\nwith two different vacua, both of which are physically\nreal for him/her (but presumably indistinguishable\nphysically?).\n\nIt seems to me that a physically-objective\nvacuum state need not necessarily be\nobserver-independent. Rather there only\nneeds to be a transformation law relating\nthe inequivalent vacua.\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>Arnold Neumaier wrote:
> [...] if the 'vacuum' is observer-dependent, it cannot be a
> physical state, hence not a graound state in any meaningful
> sense. Objective, physical objects must be observer
> independent, at least im my view of physics.
This is tied up with the question of whether unitarily-inequivalent
representations are physically different objectively. Let's
look an easier example of this. In your paper with Ulf
Leonhardt (http://www.arxiv.org/abs/quant-ph/0306123) and also Leonhardt's earlier tutorial
paper (http://www.arxiv.org/abs/quant-ph/0305007), it is shown how to model
active optical elements by mixing creation and annihilation
operators via Bogoliubov transformations. Such mixing
results in a representation of the out-modes which is
unitarily-inequivalent to that of the in-modes. I.e: the
out-fields live in a Fock space which is orthogonal
to that of the in-fields. Therefore a lab observer is dealing
with two different vacua, both of which are physically
real for him/her (but presumably indistinguishable
physically?).
It seems to me that a physically-objective
vacuum state need not necessarily be
observer-independent. Rather there only
needs to be a transformation law relating
the inequivalent vacua.
Strong_Field
Dec16-04, 08:06 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>"Igor Khavkine" <k_igor_k@lycos.com> wrote in message\n>\n> When physicists talk about something being observable, they mean\n> observable in principle. In principle, a blind man can still hold a\n> photo-detector that will tell him whether it detects some light or not.\n>\n> Also, insisting on a human being present at the point of observation is\n> anti-Copernican. The conventional view is that we are not at the center of\n> the universe and that physics should work regardless of the presence\n> humans.\n\nI think you are right. I was thinking stick figures as in popular\naccounts of general relativity in an elevator making observations. But\nthis is the popular and pictorial definition of nature. Physicists only\nthink in terms of mathematical description of nature. Is there an agreed\nupon technical definition of “observer?”\n\nIn any case, my reply was to the statement that if an observable is\nobserver-dependent it “cannot be a physical state.”\n\nLet’s eliminate all human observers. We imagine two\n“observers” in your sense, A and B. A is sensitive to light and\nB is not. In this experiment A observes light and B does not. This makes\nlight observer-dependent. But it does not make light a non-physical\nentity. In other words the physical nature of light is independent of an\nobserver’s inability to observe it. Or as you put it, “physics\nshould work regardless of the presence of humans,” [and observers].\n(brackets my emphasis.)\n\nIf just one observer observes a quantity then that quantity must be\nphysical. Obviously here we are not getting into philosophical questions\nwhere the observed quantity is an artifact of the observational device.\n\nThe point I am making is that physicists study the mathematical nature,\nnot the pictorial nature.\n\n\n\no--------o\n\n| O |\n\n| /|\\ |\n\n| | |\n\n| / \\ |\n\no--------o\n\nX\n\n\n\nX is a pictorial observer. He violates the Copernican principle.\n\n\n\n\n\no--------o\n\n| |\n\n| . |\n\n| |\n\n| |\n\no--------o\n\nY\n\n\n\nY is a mathematical observer. Y doesn’t have human *and* material\nattributes. So your “photo-detector” is still a pictorial item, physicists\ncan only talk about point observers.\n\nMore specifically:\n\n\n\nTheorem: Objective [and] physical\n\nobjects [are] observer independent,\n\ntherefore,\n\no---------------------------------o\n\n| vacuum |\n\n| | |\n\n| | |\n\n| v |\n\nP | observer dependent |\n\n| :: |\n\n| :: |\n\n| VV |\n\n| it cannot be a physical state |\n\no---------------------------------o\n\n\n\n\n\nDefinition: Observer dependent\n\no-----------------------------------o\n\n| Observer dependent |\n\n| /\\ |\n\n| / \\ |\n\nQ | / \\ |\n\n| / \\ |\n\n| A registers B registers |\n\n| “true” “null” |\n\no-----------------------------------o\n\n\n\n\n\nDefinition: Observer independent\n\no----------------------------------o\n\n| Observer independent |\n\n| /\\ |\n\n| / \\ |\n\nR | / \\ |\n\n| / \\ |\n\n| A registers B registers |\n\n| “true” “true” |\n\no----------------------------------o\n\n\n\n(Q) means that the values A and B do not agree.\n\n\n\n(R) means that A and B agree. (R) is never possible because each observer\nmust report its result to a third observer who must agree to the results.\n\nFor instance, for two experimentally minded flies the glass window is a\nphysical thing because by repeatedly colliding with it, they prove by\nexperiment that glass is physical. But if you ask a passing photon,\nthere is no such thing as a glass thing obstructing its passage. Glass\ndoes not exist for the photon as an obstacle. Do we say glass window is\nnot a physical presence because it is observer dependent? “Observer\nindependent” is another name for “absolute frame.”\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>"Igor Khavkine" <k_{igor_k}@lycos.com> wrote in message
>
> When physicists talk about something being observable, they mean
> observable in principle. In principle, a blind man can still hold a
> photo-detector that will tell him whether it detects some light or not.
>
> Also, insisting on a human being present at the point of observation is
> anti-Copernican. The conventional view is that we are not at the center of
> the universe and that physics should work regardless of the presence
> humans.
I think you are right. I was thinking stick figures as in popular
accounts of general relativity in an elevator making observations. But
this is the popular and pictorial definition of nature. Physicists only
think in terms of mathematical description of nature. Is there an agreed
upon technical definition of “observer?”
In any case, my reply was to the statement that if an observable is
observer-dependent it “cannot be a physical state.”
Let’s eliminate all human observers. We imagine two
“observers” in your sense, A and B. A is sensitive to light and
B is not. In this experiment A observes light and B does not. This makes
light observer-dependent. But it does not make light a non-physical
entity. In other words the physical nature of light is independent of an
observer’s inability to observe it. Or as you put it, “physics
should work regardless of the presence of humans,” [and observers].
(brackets my emphasis.)
If just one observer observes a quantity then that quantity must be
physical. Obviously here we are not getting into philosophical questions
where the observed quantity is an artifact of the observational device.
The point I am making is that physicists study the mathematical nature,
not the pictorial nature.
o--------o
| O |
| /|\ || | || / \ |
o--------o
X
X is a pictorial observer. He violates the Copernican principle.
o--------o
| |
| . |
| || |
o--------o
Y
Y is a mathematical observer. Y doesn’t have human *and* material
attributes. So your “photo-detector” is still a pictorial item, physicists
can only talk about point observers.
More specifically:
Theorem: Objective [and] physical
objects [are] observer independent,
therefore,
o---------------------------------o
| vacuum |
| | || | |
| v |
P | observer dependent |
| :: |
| :: |
| VV |
| it cannot be a physical state |
o---------------------------------o
Definition: Observer dependent
o-----------------------------------o
| Observer dependent |
| /\ || / \ |
Q | / \ || / \ |
| A registers B registers |
| “true” “null” |
o-----------------------------------o
Definition: Observer independent
o----------------------------------o
| Observer independent |
| /\ || / \ |
R | / \ || / \ |
| A registers B registers |
| “true” “true” |
o----------------------------------o
(Q) means that the values A and B do not agree.
(R) means that A and B agree. (R) is never possible because each observer
must report its result to a third observer who must agree to the results.
For instance, for two experimentally minded flies the glass window is a
physical thing because by repeatedly colliding with it, they prove by
experiment that glass is physical. But if you ask a passing photon,
there is no such thing as a glass thing obstructing its passage. Glass
does not exist for the photon as an obstacle. Do we say glass window is
not a physical presence because it is observer dependent? “Observer
independent” is another name for “absolute frame.”
Arnold Neumaier
Dec17-04, 07:49 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>mikem@despammed.com wrote:\n> Arnold Neumaier wrote:\n>\n>>[...] if the \'vacuum\' is observer-dependent, it cannot be a\n>>physical state, hence not a graound state in any meaningful\n>>sense. Objective, physical objects must be observer\n>>independent, at least im my view of physics.\n>\n> This is tied up with the question of whether unitarily-inequivalent\n> representations are physically different objectively. Let\'s\n> look an easier example of this. In your paper with Ulf\n> Leonhardt (quant-ph/0306123) and also Leonhardt\'s earlier tutorial\n> paper (quant-ph/0305007), it is shown how to model\n> active optical elements by mixing creation and annihilation\n> operators via Bogoliubov transformations. Such mixing\n> results in a representation of the out-modes which is\n> unitarily-inequivalent to that of the in-modes. I.e: the\n> out-fields live in a Fock space which is orthogonal\n> to that of the in-fields. Therefore a lab observer is dealing\n> with two different vacua, both of which are physically\n> real for him/her (but presumably indistinguishable\n> physically?).\n\nThis is for finitely many modes only; hence there is only one Hilbert\nspace and all representations are equivalent. The physical vacuum is the\ndark state without light, and all observers see it in the same way. The\nBogoliubov transformations are used in optics not to create alternative\nvacuum states but to describe the transformation behavior of an optical\ndevice. This is just a way to describe how the S-matrix transforms\nn-particle states.\n\nBut in QFT, a respectable vacuum must be fixed by the S-matrix.\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>mikem@despammed.com wrote:
> Arnold Neumaier wrote:
>
>>[...] if the 'vacuum' is observer-dependent, it cannot be a
>>physical state, hence not a graound state in any meaningful
>>sense. Objective, physical objects must be observer
>>independent, at least im my view of physics.
>
> This is tied up with the question of whether unitarily-inequivalent
> representations are physically different objectively. Let's
> look an easier example of this. In your paper with Ulf
> Leonhardt (http://www.arxiv.org/abs/quant-ph/0306123) and also Leonhardt's earlier tutorial
> paper (http://www.arxiv.org/abs/quant-ph/0305007), it is shown how to model
> active optical elements by mixing creation and annihilation
> operators via Bogoliubov transformations. Such mixing
> results in a representation of the out-modes which is
> unitarily-inequivalent to that of the in-modes. I.e: the
> out-fields live in a Fock space which is orthogonal
> to that of the in-fields. Therefore a lab observer is dealing
> with two different vacua, both of which are physically
> real for him/her (but presumably indistinguishable
> physically?).
This is for finitely many modes only; hence there is only one Hilbert
space and all representations are equivalent. The physical vacuum is the
dark state without light, and all observers see it in the same way. The
Bogoliubov transformations are used in optics not to create alternative
vacuum states but to describe the transformation behavior of an optical
device. This is just a way to describe how the S-matrix transforms
n-particle states.
But in QFT, a respectable vacuum must be fixed by the S-matrix.
Arnold Neumaier
Arnold Neumaier
Dec17-04, 07:49 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>Arnold Neumaier wrote:\n> mandro wrote:\n>\n>>why would one need this groundstate\n>\n> It is the state without particles.\n>\n>>what happens without it?\n>\n> Strange things - read about the Unruh effect.\n\n\nApart from problems in curved space, one can also say something\nin flat space. The charge 1 sector of QED contains no ground state.\nI don\'t understand this well, but you can probably get more information\nunder \'infraparticle\' from scholar.google.com\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>Arnold Neumaier wrote:
> mandro wrote:
>
>>why would one need this groundstate
>
> It is the state without particles.
>
>>what happens without it?
>
> Strange things - read about the Unruh effect.
Apart from problems in curved space, one can also say something
in flat space. The charge 1 sector of QED contains no ground state.
I don't understand this well, but you can probably get more information
under 'infraparticle' from scholar.google.com
Arnold Neumaier
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