View Full Version : interpretations of gravity graviton versus spacetime curvature
<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>is GR"s spacetime curvature model an unnecessary fiction?\n\nin most quantum field theory, gravity is the result of elementary\nparticles exchanging virtual particles, whereas in classical GR,\ngravity is the manifestation of localspacetime.\n\nif string theory can describe gravitons and reproduce GR, can string\ntheory do away with spacetime curvature interpretation?\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>is GR"s spacetime curvature model an unnecessary fiction?
in most quantum field theory, gravity is the result of elementary
particles exchanging virtual particles, whereas in classical GR,
gravity is the manifestation of localspacetime.
if string theory can describe gravitons and reproduce GR, can string
theory do away with spacetime curvature interpretation?
chris h fleming
Sep12-04, 02:24 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>ensabah6@yahoo.com (Daniel) wrote in message news:<ba566c17.0409062350.5187113f@posting.google. com>...\n> is GR"s spacetime curvature model an unnecessary fiction?\n>\n> in most quantum field theory, gravity is the result of elementary\n> particles exchanging virtual particles, whereas in classical GR,\n> gravity is the manifestation of localspacetime.\n>\n> if string theory can describe gravitons and reproduce GR, can string\n> theory do away with spacetime curvature interpretation?\n\nThe Gravitational force is proportional to the mass of the particle\nfeeling the force. This suggests that Gravity is merely a frame effect\nand in GR it is. But without curvature then we would all be in\nfreefall together.\n\nI know nothing about string theory, but if the curvature model were to\nbe thrown away then you would have to explain the symmetry between\ninertial mass and gravitational mass. In GR there is only one kind of\nmass, as there is only one place to stick the mass variable.\n\nI do not see how this would be possible without making Gravity a frame\neffect (which would imply curvature), but I would be very pleased to\nbe proven 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>ensabah6@yahoo.com (Daniel) wrote in message news:<ba566c17.0409062350.5187113f@posting.google.com>...
> is GR"s spacetime curvature model an unnecessary fiction?
>
> in most quantum field theory, gravity is the result of elementary
> particles exchanging virtual particles, whereas in classical GR,
> gravity is the manifestation of localspacetime.
>
> if string theory can describe gravitons and reproduce GR, can string
> theory do away with spacetime curvature interpretation?
The Gravitational force is proportional to the mass of the particle
feeling the force. This suggests that Gravity is merely a frame effect
and in GR it is. But without curvature then we would all be in
freefall together.
I know nothing about string theory, but if the curvature model were to
be thrown away then you would have to explain the symmetry between
inertial mass and gravitational mass. In GR there is only one kind of
mass, as there is only one place to stick the mass variable.
I do not see how this would be possible without making Gravity a frame
effect (which would imply curvature), but I would be very pleased to
be proven wrong.
jgraber
Sep14-04, 12:07 PM
ensabah6@yahoo.com <mailto:ensabah6@yahoo.com>
(Daniel) wrote in message ..."news:<ba566c17.0409062350.5187113f@....google.com>...
> is GR"s spacetime curvature model an unnecessary fiction?
>
> in most quantum field theory, gravity is the result of elementary
> particles exchanging virtual particles, whereas in classical GR,
> gravity is the manifestation of localspacetime.
>
> if string theory can describe gravitons and reproduce GR, can string
> theory do away with spacetime curvature interpretation?
I will try to answer with an analogy:
Can you talk about gravity in English, French or German?
Answer: Of course.
Your first question is sort of like: Is talking about gravity in German unnecessary?
Answer: Of course, especially if English is your native language.
But your second question is like: Can talking about gravity in English do away with talking about gravity in German?
Answer: Of course not, not as long as there are still native German speakers around.
Think of curvature and gravitons as two different languages to describe gravity.
Strings is perhaps a third language or maybe a dialect of the graviton language, if you prefer.
A fourth language is shrinkature, the bit about shrinking rods and slowing clocks you usually hear in connection with special relativity. But long ago, Poincare' proved that you can also express GR in terms of flat space and shrinkature instead of curvature, especially locally. There is still some debate about whether this correspondence can be made global, particularly in case the topology of space is nontrivial.
Curvature and shrinkature are usually used only to describe classical effects, not quantum ones. Graviton and String language is usually also used to describe quantum effects as well and so talk about a larger range of topics. (But note that no *gravitational* quantum effects have yet been observed.)
(Another aside: quantum mechanics in curved spacetime is very hard, even without gravitation. It is argued whether any satisfactory such theory has yet been written down.)
That said, why do physicists still like to talk about gravitation in curvature language, other than the historic reason that this is how Einstein first expressed GR? (Also in German, by the way, which has not stopped us from talking about it in English now.)
One answer is that curvature is a very restrictive language, and nature seems to respect these restrictions. (Curvature leads naturally to the universality of free fall for instance. Some experiments to test String theory, which has scalar fields as well as curvature, look for violations of this law.) Also, all the cosmology stuff (now finally getting strong observational support) seems easier to do in curvature language.
So even if Strings or something else turns out to be correct, physicists will still probably use the curvature language.
However, if something important is discovered that is hard or impossible to describe in the language of curvature, that will be very important. (Of course, some people say that all of quantum mechanics meets this requirement, and that's what this whole quantum gravity mess is all about.)
I hope this answers your question in a way you can understand. You don't have to talk about (or think about) gravity in terms of curvature if you don't want to, but if you want to understand a lot of previous work, you will at least have to learn how to "read" and understand the language of curvature.
Also anyone who proposes or supports an alternate language must show that they can reproduce the successes of the curvature language with equal ease and clarity if they want others to adopt their alternate language. Strings for instance, is not usually said to be easier than GR, but rather justified on its inclusion of quantum mechanics and (so far unverified) additional predictions. In fact String theorists sometimes use the metric "curvature" language of GR. So the String language can be thought of as an extension of the curvature language as well as (or instead of) a replacement for it. Think of the pair of pants diagram for example.
Hope this helps.
Best, Jim Graber
Hello Jim,
I like your explanation
In regards to Poincare, I assume that such a rise form the supersymmetry would have been of value in the sphere? I mean most certainly we see torodial features here as J Pierre offers his pictures to us from his site. Your statement about gravity association seemed puzzling to me. For I understood the beginning of this universe to have supergravity?
Without Poincare pointing us in this direction, should your statement read different? Forgive the intrusion.
Mark Palenik
Sep14-04, 12:15 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>\n\n\n"Daniel" <ensabah6@yahoo.com> wrote in message\nnews:ba566c17.0409062350.5187113f@posting .google.com...\n> is GR"s spacetime curvature model an unnecessary fiction?\n>\n> in most quantum field theory, gravity is the result of elementary\n> particles exchanging virtual particles, whereas in classical GR,\n> gravity is the manifestation of localspacetime.\n>\n> if string theory can describe gravitons and reproduce GR, can string\n> theory do away with spacetime curvature interpretation?\n>\n\nIsn\'t a large portion of string theory devoted to describing forces as\ncurvature of space in a sort of kaluza-kline-esque way?\n\nThat fact that string theory is supposed to be able to reproduce GR in a\nclassical limit, and supposedly predicts a metric means that if string\ntheory is right, we can\'t do away with GR.\n\nAnyway, gravitons are supposed to be the quantization of gravitational\nwaves, which are "ripples" in spacetime. Just because these waes are\nquantized into particles doesn\'t make them any less waves through spacetime\nthan the idea of photons prevents light from being electromagnetic\nradiation.\n\nAlthough I don\'t really know anything at all about quantum field theory, my\nguess is that virtual gravitons, which would be responsible for transmitting\nthe gravitational force, can be described as a series of perturbations to\nflat spacetime that, when summed up, look something like GR on a large\nscale.\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>"Daniel" <ensabah6@yahoo.com> wrote in message
news:ba566c17.0409062350.5187113f@posting.google.c om...
> is GR"s spacetime curvature model an unnecessary fiction?
>
> in most quantum field theory, gravity is the result of elementary
> particles exchanging virtual particles, whereas in classical GR,
> gravity is the manifestation of localspacetime.
>
> if string theory can describe gravitons and reproduce GR, can string
> theory do away with spacetime curvature interpretation?
>
Isn't a large portion of string theory devoted to describing forces as
curvature of space in a sort of kaluza-kline-esque way?
That fact that string theory is supposed to be able to reproduce GR in a
classical limit, and supposedly predicts a metric means that if string
theory is right, we can't do away with GR.
Anyway, gravitons are supposed to be the quantization of gravitational
waves, which are "ripples" in spacetime. Just because these waes are
quantized into particles doesn't make them any less waves through spacetime
than the idea of photons prevents light from being electromagnetic
radiation.
Although I don't really know anything at all about quantum field theory, my
guess is that virtual gravitons, which would be responsible for transmitting
the gravitational force, can be described as a series of perturbations to
flat spacetime that, when summed up, look something like GR on a large
scale.
<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>chris_h_fleming@yahoo.com (chris h fleming) wrote in message news:<8dd8e508.0409101908.5122d4@posting.google.co m>...\n> ensabah6@yahoo.com (Daniel) wrote in message news:<ba566c17.0409062350.5187113f@posting.google. com>...\n> > is GR"s spacetime curvature model an unnecessary fiction?\n> >\n> > in most quantum field theory, gravity is the result of elementary\n> > particles exchanging virtual particles, whereas in classical GR,\n> > gravity is the manifestation of localspacetime.\n> >\n> > if string theory can describe gravitons and reproduce GR, can string\n> > theory do away with spacetime curvature interpretation?\n>\n> The Gravitational force is proportional to the mass of the particle\n> feeling the force. This suggests that Gravity is merely a frame effect\n> and in GR it is. But without curvature then we would all be in\n> freefall together.\n>\n> I know nothing about string theory, but if the curvature model were to\n> be thrown away then you would have to explain the symmetry between\n> inertial mass and gravitational mass. In GR there is only one kind of\n> mass, as there is only one place to stick the mass variable.\n>\n> I do not see how this would be possible without making Gravity a frame\n> effect (which would imply curvature), but I would be very pleased to\n> be proven wrong.\n\nit\'s my understanding that unlike conventional quantum field theories,\nstring theory can reproduce GR through the exchange of virtual\nparticles, the graviton, through FLAT Minkowski space.\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>chris_h_fleming@yahoo.com (chris h fleming) wrote in message news:<8dd8e508.0409101908.5122d4@posting.google.com>...
> ensabah6@yahoo.com (Daniel) wrote in message news:<ba566c17.0409062350.5187113f@posting.google.com>...
> > is GR"s spacetime curvature model an unnecessary fiction?
> >
> > in most quantum field theory, gravity is the result of elementary
> > particles exchanging virtual particles, whereas in classical GR,
> > gravity is the manifestation of localspacetime.
> >
> > if string theory can describe gravitons and reproduce GR, can string
> > theory do away with spacetime curvature interpretation?
>
> The Gravitational force is proportional to the mass of the particle
> feeling the force. This suggests that Gravity is merely a frame effect
> and in GR it is. But without curvature then we would all be in
> freefall together.
>
> I know nothing about string theory, but if the curvature model were to
> be thrown away then you would have to explain the symmetry between
> inertial mass and gravitational mass. In GR there is only one kind of
> mass, as there is only one place to stick the mass variable.
>
> I do not see how this would be possible without making Gravity a frame
> effect (which would imply curvature), but I would be very pleased to
> be proven wrong.
it's my understanding that unlike conventional quantum field theories,
string theory can reproduce GR through the exchange of virtual
particles, the graviton, through FLAT Minkowski space.
Jerzy Karczmarczuk
Sep15-04, 03:45 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>\njgraber wrote:\n\n> ... (But note that no *gravitational* quantum effects have\n> yet been observed.)\n> (Another aside: quantum mechanics in curved spacetime is very hard,\n> even without gravitation. It is argued whether any satisfactory such\n> theory has yet been written down.)=20\n\nWell, the gravitational red shift has been measured through the\nM=F6ssbauer effect, which is quantum. (Now, don\'t tell me that it\nwasn\'t what you had in mind, and add some smileys here if you\nwish...).\n\nJerzy Karczmarczuk\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>jgraber wrote:
> ... (But note that no *gravitational* quantum effects have
> yet been observed.)
> (Another aside: quantum mechanics in curved spacetime is very hard,
> even without gravitation. It is argued whether any satisfactory such
> theory has yet been written down.)=20
Well, the gravitational red shift has been measured through the
M=F6ssbauer effect, which is quantum. (Now, don't tell me that it
wasn't what you had in mind, and add some smileys here if you
wish...).
Jerzy Karczmarczuk
Kefka G
Sep16-04, 07:09 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>Mark Palenik wrote:\n\n>Isn\'t a large portion of string theory devoted to describing forces as\n>\n>curvature of space in a sort of kaluza-kline-esque way?\n>\n\nI\'m not a string theory expert by any means, but from what I\'ve gleaned, this\nis not the way it describes forces. The flavor of a Kaluza-Klein approach is\nas follows (forgive me, this is too simplistic to be totally accurate - there\nare several nice expositions online):\n\n1) Start with GR in n+1 spacetime dimensions\n2) Curl up n-3 of these dimensions into some compact manifold\n3) Look at the first Fourier mode of the field in the compact dimensions\n(loosely: neglect all derivatives in any of those directions)\n4) The isometry group of the compact manifold becomes the gauge group of the\n3+1 Kaluza-Klein theory\n\nBut in string theory, the extra dimensions are compactified on Calabi-Yau\nmanifolds, which (if I remember correctly) admit no isometry groups, and hence\nthere really are no corresponding K-K theories since the main point of K-K\ntheory is (isometry-->gauge). Those manifolds are chosen so as to preserve the\nconsistency of the theory and effect a 3+1 interpretation, NOT to obtain the\nforces in 3+1-D. In fact, (correct me if I\'m wrong, please) I think that the\nusual forces come out of the dynamics of the string in open dimensions, and the\nK-K step is even more classical than it was originally intended - it\'s\nanalagous to the way that Maxwell\'s theory in 4+1-D looks a lot like the 3+1-D\ntheory if we compactify one dimension classically. (Even this step is somewhat\nquestionable, though - 4+1 compactified on a circle is not exactly the same as\n3+1, for a whole host of reasons which I won\'t go into since this is a gravity\nthread; for one, 4+1 Maxwell is not even renormalizable classically, so\nsomething hinky is going on)\n\nOr I could be wrong - I temporarily gave up learning string theory well before\nI understood it all. It\'s quite possible that it\'s not that simple at all.\nMaybe someone with a bit of expertise can clarify?\n\nMark:\n>Although I don\'t really know anything at all about quantum field theory, my\n>\n>guess is that virtual gravitons, which would be responsible for transmitting\n>\n>the gravitational force, can be described as a series of perturbations to\n>\n>flat spacetime that, when summed up, look something like GR on a large\n>\n>scale.\n\nThis is essentially the "Feynman" approach (originally due to Deser, I think)\nwhere Einstein\'s equations are derived from a massless spin-2 theory that is\nmade consistent by letting it act as its own source - the resulting theory is\n(classically) identical to Einstein\'s as long as there\'s no topological funny\nbusiness (not surprising, as it is a perturbative theory and odd topologies\ncertainly can\'t be described as perturbations of flat space). Even the changes\nin the propagation speed of light, time dilation, etc. come out of looking at\nit this way. I think this, in fact, is exactly how GR comes out as the low\nenergy limit to string theory, since there is a massless spin-2 mode of the\nstring.\n\nBut it\'s worth repeating that one of the primary objections most gravity folk\nhave to string theory is that it is background dependent, i.e. it starts off\nwith flat spacetime of some given topology and lets gravity work like a regular\nold force on that, rather than letting gravity alter the spacetime itself.\nI\'ve heard rumblings that string theory allows the background dependence to\n"fade away" by allowing space-tearing transitions, etc., but I can\'t really\nunderstand how that can happen when from the get-go it is formulated as a field\ntheory on the background...if the background spacetime is not a dynamical\nvariable of the theory, then how can it possibly change? I don\'t know, so I\nmust be misinterpreting part of the theory. Maybe in a non-perturbative\nformulation (does one even exist?) the background is dynamical? Someone want\nto help straighten this out?\n\n-Eric\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>Mark Palenik wrote:
>Isn't a large portion of string theory devoted to describing forces as
>
>curvature of space in a sort of kaluza-kline-esque way?
>
I'm not a string theory expert by any means, but from what I've gleaned, this
is not the way it describes forces. The flavor of a Kaluza-Klein approach is
as follows (forgive me, this is too simplistic to be totally accurate - there
are several nice expositions online):
1) Start with GR in n+1 spacetime dimensions
2) Curl up n-3 of these dimensions into some compact manifold
3) Look at the first Fourier mode of the field in the compact dimensions
(loosely: neglect all derivatives in any of those directions)
4) The isometry group of the compact manifold becomes the gauge group of the
3+1 Kaluza-Klein theory
But in string theory, the extra dimensions are compactified on Calabi-Yau
manifolds, which (if I remember correctly) admit no isometry groups, and hence
there really are no corresponding K-K theories since the main point of K-K
theory is (isometry-->gauge). Those manifolds are chosen so as to preserve the
consistency of the theory and effect a 3+1 interpretation, NOT to obtain the
forces in 3+1-D. In fact, (correct me if I'm wrong, please) I think that the
usual forces come out of the dynamics of the string in open dimensions, and the
K-K step is even more classical than it was originally intended - it's
analagous to the way that Maxwell's theory in 4+1-D looks a lot like the 3+1-D
theory if we compactify one dimension classically. (Even this step is somewhat
questionable, though - 4+1 compactified on a circle is not exactly the same as
3+1, for a whole host of reasons which I won't go into since this is a gravity
thread; for one, 4+1 Maxwell is not even renormalizable classically, so
something hinky is going on)
Or I could be wrong - I temporarily gave up learning string theory well before
I understood it all. It's quite possible that it's not that simple at all.
Maybe someone with a bit of expertise can clarify?
Mark:
>Although I don't really know anything at all about quantum field theory, my
>
>guess is that virtual gravitons, which would be responsible for transmitting
>
>the gravitational force, can be described as a series of perturbations to
>
>flat spacetime that, when summed up, look something like GR on a large
>
>scale.
This is essentially the "Feynman" approach (originally due to Deser, I think)
where Einstein's equations are derived from a massless spin-2 theory that is
made consistent by letting it act as its own source - the resulting theory is
(classically) identical to Einstein's as long as there's no topological funny
business (not surprising, as it is a perturbative theory and odd topologies
certainly can't be described as perturbations of flat space). Even the changes
in the propagation speed of light, time dilation, etc. come out of looking at
it this way. I think this, in fact, is exactly how GR comes out as the low
energy limit to string theory, since there is a massless spin-2 mode of the
string.
But it's worth repeating that one of the primary objections most gravity folk
have to string theory is that it is background dependent, i.e. it starts off
with flat spacetime of some given topology and lets gravity work like a regular
old force on that, rather than letting gravity alter the spacetime itself.
I've heard rumblings that string theory allows the background dependence to
"fade away" by allowing space-tearing transitions, etc., but I can't really
understand how that can happen when from the get-go it is formulated as a field
theory on the background...if the background spacetime is not a dynamical
variable of the theory, then how can it possibly change? I don't know, so I
must be misinterpreting part of the theory. Maybe in a non-perturbative
formulation (does one even exist?) the background is dynamical? Someone want
to help straighten this out?
-Eric
chris h fleming
Sep19-04, 06:55 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>\nensabah6@yahoo.com (Daniel) wrote in message news:<ba566c17.0409122254.546f108@posting.google.c om>...\n> chris_h_fleming@yahoo.com (chris h fleming) wrote in message news:<8dd8e508.0409101908.5122d4@posting.google.co m>...\n> > ensabah6@yahoo.com (Daniel) wrote in message news:<ba566c17.0409062350.5187113f@posting.google. com>...\n> > > is GR"s spacetime curvature model an unnecessary fiction?\n> > >\n> > > in most quantum field theory, gravity is the result of elementary\n> > > particles exchanging virtual particles, whereas in classical GR,\n> > > gravity is the manifestation of localspacetime.\n> > >\n> > > if string theory can describe gravitons and reproduce GR, can string\n> > > theory do away with spacetime curvature interpretation?\n> >\n> > The Gravitational force is proportional to the mass of the particle\n> > feeling the force. This suggests that Gravity is merely a frame effect\n> > and in GR it is. But without curvature then we would all be in\n> > freefall together.\n> >\n> > I know nothing about string theory, but if the curvature model were to\n> > be thrown away then you would have to explain the symmetry between\n> > inertial mass and gravitational mass. In GR there is only one kind of\n> > mass, as there is only one place to stick the mass variable.\n> >\n> > I do not see how this would be possible without making Gravity a frame\n> > effect (which would imply curvature), but I would be very pleased to\n> > be proven wrong.\n>\n> it\'s my understanding that unlike conventional quantum field theories,\n> string theory can reproduce GR through the exchange of virtual\n> particles, the graviton, through FLAT Minkowski space.\n\nIs this anything like when you try to make a tensor theory of gravity\nontop of a flat spacetime but it turns out that the flat spacetime you\nbuild on isn\'t really physical and you are really just doing GR in a\nvery convoluted manner?\n\nOr is it only perturbative as (classically) we only see these spin-2\nmassless gravitational waves as perturbations on a flat spacetime or\nvery few other metrics?\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>ensabah6@yahoo.com (Daniel) wrote in message news:<ba566c17.0409122254.546f108@posting.google.com>...
> chris_h_fleming@yahoo.com (chris h fleming) wrote in message news:<8dd8e508.0409101908.5122d4@posting.google.com>...
> > ensabah6@yahoo.com (Daniel) wrote in message news:<ba566c17.0409062350.5187113f@posting.google.com>...
> > > is GR"s spacetime curvature model an unnecessary fiction?
> > >
> > > in most quantum field theory, gravity is the result of elementary
> > > particles exchanging virtual particles, whereas in classical GR,
> > > gravity is the manifestation of localspacetime.
> > >
> > > if string theory can describe gravitons and reproduce GR, can string
> > > theory do away with spacetime curvature interpretation?
> >
> > The Gravitational force is proportional to the mass of the particle
> > feeling the force. This suggests that Gravity is merely a frame effect
> > and in GR it is. But without curvature then we would all be in
> > freefall together.
> >
> > I know nothing about string theory, but if the curvature model were to
> > be thrown away then you would have to explain the symmetry between
> > inertial mass and gravitational mass. In GR there is only one kind of
> > mass, as there is only one place to stick the mass variable.
> >
> > I do not see how this would be possible without making Gravity a frame
> > effect (which would imply curvature), but I would be very pleased to
> > be proven wrong.
>
> it's my understanding that unlike conventional quantum field theories,
> string theory can reproduce GR through the exchange of virtual
> particles, the graviton, through FLAT Minkowski space.
Is this anything like when you try to make a tensor theory of gravity
ontop of a flat spacetime but it turns out that the flat spacetime you
build on isn't really physical and you are really just doing GR in a
very convoluted manner?
Or is it only perturbative as (classically) we only see these spin-2
massless gravitational waves as perturbations on a flat spacetime or
very few other metrics?
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