View Full Version : TIRED LIGHT
alistair
May20-04, 03:46 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>If photons get redshifted on their way to the Earth by transferring\nenergy to the dark energy of the cosmos their momenta would not be\nchanged and cause blurring because dark energy may not have momentum\nitself and so classical behaviour that would cause blurring would not\nnecessarily occur.\nRedshifted photons would still exhibit time dilation over large\ndistances.\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>If photons get redshifted on their way to the Earth by transferring
energy to the dark energy of the cosmos their momenta would not be
changed and cause blurring because dark energy may not have momentum
itself and so classical behaviour that would cause blurring would not
necessarily occur.
Redshifted photons would still exhibit time dilation over large
distances.
Phillip Helbig---remove CLOTHES to reply
May21-04, 02:46 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>\nIn article <861c1b21.0405191422.7310c0ac@posting.google.com>, \nalistair@goforit64.fsnet.co.uk (alistair) writes:\n\n> If photons get redshifted on their way to the Earth by transferring\n> energy to the dark energy of the cosmos their momenta would not be\n> changed and cause blurring because dark energy may not have momentum\n> itself and so classical behaviour that would cause blurring would not\n> necessarily occur.\n> Redshifted photons would still exhibit time dilation over large\n> distances.\n\nThere are (at least) two problems with the above. First, it is ad-hoc\nand too speculative. Second, the reason to believe that dark energy\nexists is based on observations interpreted within the "standard\ncosmological framework", which includes the cosmological redshift. If\nyou want to give up that framework, you can\'t use it to show that dark\nenergy exists.\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 <861c1b21.0405191422.7310c0ac@posting.google.com>,
alistair@goforit64.fsnet.co.uk (alistair) writes:
> If photons get redshifted on their way to the Earth by transferring
> energy to the dark energy of the cosmos their momenta would not be
> changed and cause blurring because dark energy may not have momentum
> itself and so classical behaviour that would cause blurring would not
> necessarily occur.
> Redshifted photons would still exhibit time dilation over large
> distances.
There are (at least) two problems with the above. First, it is ad-hoc
and too speculative. Second, the reason to believe that dark energy
exists is based on observations interpreted within the "standard
cosmological framework", which includes the cosmological redshift. If
you want to give up that framework, you can't use it to show that dark
energy exists.
alistair
May21-04, 10:14 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\nThere are (at least) two problems with the above. First, it is ad-hoc\n> and too speculative. Second, the reason to believe that dark energy\n> exists is based on observations interpreted within the "standard\n> cosmological framework", which includes the cosmological redshift. If\n> you want to give up that framework, you can\'t use it to show that dark\n> energy exists.\n\nI was not giving up the fact that redshift can be described by\nthe "standard cosmological framework." I am saying that the underlying\nreason why the redshift appears in the framework is because of dark\nenergy.\nThe idea might be speculative but I have not seen discussion of it\nelsewhere on this forum or anywhere else on the web so I thought it\nwas worth mentioning.\nSomeone else told me that the redshift would probably be higher if\nthe\nidea was right, but they didn\'t give details of why. Can someone tell\nme\nwhy the redshift would be higher? And if dark energy isn\'t uniformly\ndistributed at every point in space - if it was distributed like a\nuniform volume of atoms- could that reduce the redshift back to the\nexperimentally observed redshift?\nCan dark energy consist of individual quantized particle pairs of\nsome\nkind?\nApparently quintessence models have difficulty producing the supposed\nflatness of the dark energy distribution in a natural way.There is a\npaper on the arxiv that models dark energy as phenomenon with three\nmutually orthogonal Vectors to guarantee isotropy.Is dark energy a\nvector phenomenon?\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 (at least) two problems with the above. First, it is ad-hoc
> and too speculative. Second, the reason to believe that dark energy
> exists is based on observations interpreted within the "standard
> cosmological framework", which includes the cosmological redshift. If
> you want to give up that framework, you can't use it to show that dark
> energy exists.
I was not giving up the fact that redshift can be described by
the "standard cosmological framework." I am saying that the underlying
reason why the redshift appears in the framework is because of dark
energy.
The idea might be speculative but I have not seen discussion of it
elsewhere on this forum or anywhere else on the web so I thought it
was worth mentioning.
Someone else told me that the redshift would probably be higher if
the
idea was right, but they didn't give details of why. Can someone tell
me
why the redshift would be higher? And if dark energy isn't uniformly
distributed at every point in space - if it was distributed like a
uniform volume of atoms- could that reduce the redshift back to the
experimentally observed redshift?
Can dark energy consist of individual quantized particle pairs of
some
kind?
Apparently quintessence models have difficulty producing the supposed
flatness of the dark energy distribution in a natural way.There is a
paper on the arxiv that models dark energy as phenomenon with three
mutually orthogonal Vectors to guarantee isotropy.Is dark energy a
vector phenomenon?
Phillip Helbig---remove CLOTHES to reply
May24-04, 04:31 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>\nIn article <861c1b21.0405210711.60431171@posting.google.com>, \nalistair@goforit64.fsnet.co.uk (alistair) writes:\n\n> There are (at least) two problems with the above. First, it is ad-hoc\n> > and too speculative. Second, the reason to believe that dark energy\n> > exists is based on observations interpreted within the "standard\n> > cosmological framework", which includes the cosmological redshift. If\n> > you want to give up that framework, you can\'t use it to show that dark\n> > energy exists.\n>\n> I was not giving up the fact that redshift can be described by\n> the "standard cosmological framework." I am saying that the underlying\n> reason why the redshift appears in the framework is because of dark\n> energy.\n\nThis argument is circular. The strongest evidence---and perhaps the\nonly SINGLE evidence, as opposed to combinations of tests---for dark\nenergy comes from the m-z relation for supernovae. The cosmological\nparameters of the "concordance model" work out just fine---and they\nwouldn\'t if dark energy somehow "increased the redshift".\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 <861c1b21.0405210711.60431171@posting.google.com>,
alistair@goforit64.fsnet.co.uk (alistair) writes:
> There are (at least) two problems with the above. First, it is ad-hoc
> > and too speculative. Second, the reason to believe that dark energy
> > exists is based on observations interpreted within the "standard
> > cosmological framework", which includes the cosmological redshift. If
> > you want to give up that framework, you can't use it to show that dark
> > energy exists.
>
> I was not giving up the fact that redshift can be described by
> the "standard cosmological framework." I am saying that the underlying
> reason why the redshift appears in the framework is because of dark
> energy.
This argument is circular. The strongest evidence---and perhaps the
only SINGLE evidence, as opposed to combinations of tests---for dark
energy comes from the m-z relation for supernovae. The cosmological
parameters of the "concordance model" work out just fine---and they
wouldn't if dark energy somehow "increased the redshift".
alistair
May24-04, 10:33 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>\nhelbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote in message news:<c8n7da\\$52d\\$2@online.de>...\nThe cosmological\n> parameters of the "concordance model" work out just fine---and they\n> wouldn\'t if dark energy somehow "increased the redshift".\n\nIf the redshift is due to the expansion of the universe and we just\nsay that photons lose energy and when this happens more dark energy\nappears in the universe,how would dark energy stop the parameters of\nthe concordance model from working out?\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>helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote in message news:<c8n7da$52d$2@online.de>...
The cosmological
> parameters of the "concordance model" work out just fine---and they
> wouldn't if dark energy somehow "increased the redshift".
If the redshift is due to the expansion of the universe and we just
say that photons lose energy and when this happens more dark energy
appears in the universe,how would dark energy stop the parameters of
the concordance model from working out?
Phillip Helbig---remove CLOTHES to reply
May25-04, 03:56 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\nIn article <861c1b21.0405240728.3d7c428a@posting.google.com>, \nalistair@goforit64.fsnet.co.uk (alistair) writes:\n\n> helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote in message news:<c8n7da\\$52d\\$2@online.de>...\n> The cosmological\n> > parameters of the "concordance model" work out just fine---and they\n> > wouldn\'t if dark energy somehow "increased the redshift".\n>\n> If the redshift is due to the expansion of the universe\n\nOK.\n\n> and we just\n> say that photons lose energy\n\nThey DO lose energy---which is inversely proportional to redshift---so\nwe don\'t have to "just say" it. (Of course, "just saying it" without\nany further evidence would be ad hoc.)\n\n> and when this happens more dark energy\n> appears in the universe,\n\nThis is completely ad hoc. You seem to be equating dark energy with\nredshift.\n\n> how would dark energy stop the parameters of\n> the concordance model from working out?\n\nMy point is the following: Redshift is due to expansion. Standard\ncosmological theory indicates that the expansion must be accelerating,\nwhich requires dark energy. So, we arrive at a value for dark energy\nwithout any strange explanation for the redshift, and this value is\nconsistent with other cosmological tests. So, if you then postulate\nthat dark energy somehow causes redshift, the above (convergence on the\nconcordance model) would not work.\n\nState what problem you are trying to solve, why you think dark energy\ncauses redshift and/or why you think this might be necessary and/or what\nis wrong with the conventional explanation.\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 <861c1b21.0405240728.3d7c428a@posting.google.com>,
alistair@goforit64.fsnet.co.uk (alistair) writes:
> helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote in message news:<c8n7da$52d$2@online.de>...
> The cosmological
> > parameters of the "concordance model" work out just fine---and they
> > wouldn't if dark energy somehow "increased the redshift".
>
> If the redshift is due to the expansion of the universe
OK.
> and we just
> say that photons lose energy
They DO lose energy---which is inversely proportional to redshift---so
we don't have to "just say" it. (Of course, "just saying it" without
any further evidence would be ad hoc.)
> and when this happens more dark energy
> appears in the universe,
This is completely ad hoc. You seem to be equating dark energy with
redshift.
> how would dark energy stop the parameters of
> the concordance model from working out?
My point is the following: Redshift is due to expansion. Standard
cosmological theory indicates that the expansion must be accelerating,
which requires dark energy. So, we arrive at a value for dark energy
without any strange explanation for the redshift, and this value is
consistent with other cosmological tests. So, if you then postulate
that dark energy somehow causes redshift, the above (convergence on the
concordance model) would not work.
State what problem you are trying to solve, why you think dark energy
causes redshift and/or why you think this might be necessary and/or what
is wrong with the conventional explanation.
greywolf42
May26-04, 05:12 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nPhillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>\nwrote in message news:c8up3d\\$p9h\\$1@online.de...\n>\n>\n> In article <861c1b21.0405240728.3d7c428a@posting.google.com>, \n> alistair@goforit64.fsnet.co.uk (alistair) writes:\n>\n> > helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to\nreply) wrote in message news:<c8n7da\\$52d\\$2@online.de>...\n> > The cosmological\n> > > parameters of the "concordance model" work out just fine---and they\n> > > wouldn\'t if dark energy somehow "increased the redshift".\n> >\n> > If the redshift is due to the expansion of the universe\n>\n> OK.\n>\n> > and we just\n> > say that photons lose energy\n>\n> They DO lose energy---which is inversely proportional to redshift---so\n> we don\'t have to "just say" it. (Of course, "just saying it" without\n> any further evidence would be ad hoc.)\n>\n> > and when this happens more dark energy\n> > appears in the universe,\n>\n> This is completely ad hoc. You seem to be equating dark energy with\n> redshift.\n>\n> > how would dark energy stop the parameters of\n> > the concordance model from working out?\n>\n> My point is the following: Redshift is due to expansion.\n\nThat is an ad hoc assumption. Redshift is observed. We assume that this is\ndue solely to recession velocity and/or expansion of space.\n\n> Standard\n> cosmological theory indicates that the expansion must be accelerating,\n> which requires dark energy.\n\nIt is not standard theory that indicates expansion must be accelerating. It\nis those inconvenient observations of supernovae that don\'t follow the\nstandard theory. Dark energy is merely another ad hoc addition to the ad\nhoc assumption of pure expansion.\n\n> So, we arrive at a value for dark energy\n> without any strange explanation for the redshift,\n\nDark energy *is* a very strange explanation for nonlinear redshifts.\n\n> and this value is\n> consistent with other cosmological tests.\n\nThat\'s because there are no other tests involved.\n\n> So, if you then postulate\n> that dark energy somehow causes redshift, the above (convergence on the\n> concordance model) would not work.\n\nIt is merely reversing the ad hoc assumption.\n\n> State what problem you are trying to solve, why you think dark energy\n> causes redshift and/or why you think this might be necessary and/or what\n> is wrong with the conventional explanation.\n\nThe conventional explanation (the current paradigm) is a pure ad hoc\naddition to theory. With no independent substance or prediction beyond\nsaving the theory.\n\n--\ngreywolf42\nubi dubium ibi libertas\n{remove planet for return e-mail}\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>Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>
wrote in message news:c8up3d$p9h$1@online.de...
>
>
> In article <861c1b21.0405240728.3d7c428a@posting.google.com>,
> alistair@goforit64.fsnet.co.uk (alistair) writes:
>
> > helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to
reply) wrote in message news:<c8n7da$52d$2@online.de>...
> > The cosmological
> > > parameters of the "concordance model" work out just fine---and they
> > > wouldn't if dark energy somehow "increased the redshift".
> >
> > If the redshift is due to the expansion of the universe
>
> OK.
>
> > and we just
> > say that photons lose energy
>
> They DO lose energy---which is inversely proportional to redshift---so
> we don't have to "just say" it. (Of course, "just saying it" without
> any further evidence would be ad hoc.)
>
> > and when this happens more dark energy
> > appears in the universe,
>
> This is completely ad hoc. You seem to be equating dark energy with
> redshift.
>
> > how would dark energy stop the parameters of
> > the concordance model from working out?
>
> My point is the following: Redshift is due to expansion.
That is an ad hoc assumption. Redshift is observed. We assume that this is
due solely to recession velocity and/or expansion of space.
> Standard
> cosmological theory indicates that the expansion must be accelerating,
> which requires dark energy.
It is not standard theory that indicates expansion must be accelerating. It
is those inconvenient observations of supernovae that don't follow the
standard theory. Dark energy is merely another ad hoc addition to the ad
hoc assumption of pure expansion.
> So, we arrive at a value for dark energy
> without any strange explanation for the redshift,
Dark energy *is* a very strange explanation for nonlinear redshifts.
> and this value is
> consistent with other cosmological tests.
That's because there are no other tests involved.
> So, if you then postulate
> that dark energy somehow causes redshift, the above (convergence on the
> concordance model) would not work.
It is merely reversing the ad hoc assumption.
> State what problem you are trying to solve, why you think dark energy
> causes redshift and/or why you think this might be necessary and/or what
> is wrong with the conventional explanation.
The conventional explanation (the current paradigm) is a pure ad hoc
addition to theory. With no independent substance or prediction beyond
saving the theory.
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
alistair
May27-04, 03:15 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>\nAlistair replies to greywolf:\n\nI don\'t agree that the expansion of the universe is ad hoc.\nThe Big Bang Nucleosynthesis theory which predicts the abundance of\nthe chemical elements is what convinces me that expansion has\nhappened.\nEven though half the lithium has not been accounted for, the\nprediction by BBN of the abundance of the other elements is\nremarkable.All I am contesting is this: what happens to the energy\nredshifted photons lose.Does it disappear by magic or does it become\ndark energy?\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>Alistair replies to greywolf:
I don't agree that the expansion of the universe is ad hoc.
The Big Bang Nucleosynthesis theory which predicts the abundance of
the chemical elements is what convinces me that expansion has
happened.
Even though half the lithium has not been accounted for, the
prediction by BBN of the abundance of the other elements is
remarkable.All I am contesting is this: what happens to the energy
redshifted photons lose.Does it disappear by magic or does it become
dark energy?
alistair
May29-04, 11:51 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>helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote in message news:<c8up3d\\$p9h\\$1@online.de>...\n> In article <861c1b21.0405240728.3d7c428a@posting.google.com>, \n> alistair@goforit64.fsnet.co.uk (alistair) writes:\n>\n> State what problem you are trying to solve, why you think dark energy\n> causes redshift and/or why you think this might be necessary and/or what\n> is wrong with the conventional explanation.\n\nConservation of energy. Where does the energy of redshifted photons go?\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>helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote in message news:<c8up3d$p9h$1@online.de>...
> In article <861c1b21.0405240728.3d7c428a@posting.google.com>,
> alistair@goforit64.fsnet.co.uk (alistair) writes:
>
> State what problem you are trying to solve, why you think dark energy
> causes redshift and/or why you think this might be necessary and/or what
> is wrong with the conventional explanation.
Conservation of energy. Where does the energy of redshifted photons go?
Mark Palenik
May31-04, 06:26 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\nnews:861c1b21.0405250456.1496b69e@posting .google.com...\n> helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply)\nwrote in message news:<c8up3d\\$p9h\\$1@online.de>...\n> > In article <861c1b21.0405240728.3d7c428a@posting.google.com>, \n> > alistair@goforit64.fsnet.co.uk (alistair) writes:\n> >\n> > State what problem you are trying to solve, why you think dark energy\n> > causes redshift and/or why you think this might be necessary and/or what\n> > is wrong with the conventional explanation.\n>\n> Conservation of energy. Where does the energy of redshifted photons go?\n>\n\nThat\'s sort of like asking where the kinetic energy of a car goes when your\nriding in it.\n\n\n[Moderator\'s note: No, it is quite different. Energy in GR is only locally conserved in\ngeneral and in particular in cosmology, where there is no timelike Killing vector field,\nit is not conserved globally. So as the universe expands the energy stored in radiation does\nindeed decrease without "going anywhere". -usc]\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>"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
news:861c1b21.0405250456.1496b69e@posting.google.c om...
> helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply)
wrote in message news:<c8up3d$p9h$1@online.de>...
> > In article <861c1b21.0405240728.3d7c428a@posting.google.com>,
> > alistair@goforit64.fsnet.co.uk (alistair) writes:
> >
> > State what problem you are trying to solve, why you think dark energy
> > causes redshift and/or why you think this might be necessary and/or what
> > is wrong with the conventional explanation.
>
> Conservation of energy. Where does the energy of redshifted photons go?
>
That's sort of like asking where the kinetic energy of a car goes when your
riding in it.
[Moderator's note: No, it is quite different. Energy in GR is only locally conserved in
general and in particular in cosmology, where there is no timelike Killing vector field,
it is not conserved globally. So as the universe expands the energy stored in radiation does
indeed decrease without "going anywhere". -usc]
Phillip Helbig---remove CLOTHES to reply
May31-04, 06:26 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nIn article <861c1b21.0405250456.1496b69e@posting.google.com>, \nalistair@goforit64.fsnet.co.uk (alistair) writes:\n\n> helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to\n> reply) wrote in message news:<c8up3d\\$p9h\\$1@online.de>...\n> > In article <861c1b21.0405240728.3d7c428a@posting.google.com>, \n> > alistair@goforit64.fsnet.co.uk (alistair) writes:\n> >\n> > State what problem you are trying to solve, why you think dark energy\n> > causes redshift and/or why you think this might be necessary and/or what\n> > is wrong with the conventional explanation.\n>\n> Conservation of energy. Where does the energy of redshifted photons go?\n\nNowhere. Energy is not conserved in cosmology. As is always the case\nwith confusing stuff in cosmology, this is covered well in Edward\nHarrison\'s COSMOLOGY textbook.\n\nIn General Relativity in general, energy is not as well-defined a\nquantity as it is in most of the rest of physics.\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 <861c1b21.0405250456.1496b69e@posting.google.com>,
alistair@goforit64.fsnet.co.uk (alistair) writes:
> helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to
> reply) wrote in message news:<c8up3d$p9h$1@online.de>...
> > In article <861c1b21.0405240728.3d7c428a@posting.google.com>,
> > alistair@goforit64.fsnet.co.uk (alistair) writes:
> >
> > State what problem you are trying to solve, why you think dark energy
> > causes redshift and/or why you think this might be necessary and/or what
> > is wrong with the conventional explanation.
>
> Conservation of energy. Where does the energy of redshifted photons go?
Nowhere. Energy is not conserved in cosmology. As is always the case
with confusing stuff in cosmology, this is covered well in Edward
Harrison's COSMOLOGY textbook.
In General Relativity in general, energy is not as well-defined a
quantity as it is in most of the rest of physics.
greywolf42
May31-04, 04:20 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>alistair <alistair@goforit64.fsnet.co.uk> wrote in message\nnews:861c1b21.0405250456.1496b69e@posting .google.com...\n> helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply)\nwrote in message news:<c8up3d\\$p9h\\$1@online.de>...\n> > In article <861c1b21.0405240728.3d7c428a@posting.google.com>, \n> > alistair@goforit64.fsnet.co.uk (alistair) writes:\n> >\n> > State what problem you are trying to solve, why you think dark energy\n> > causes redshift and/or why you think this might be necessary and/or what\n> > is wrong with the conventional explanation.\n>\n> Conservation of energy. Where does the energy of redshifted photons go?\n\nIt is lost to the aether, or the spacetime continuum, or to the zero-point\nenergy, or to strings or to whatever physical entity you consider supports\nthe field.\n\n"Conservation of energy" says nothing about whether assumptions about the\nperfection of EM waves hold over scales tens of orders of magnitude in\ndistance and time greater than we can test in the lab.\n\n--\ngreywolf42\nubi dubium ibi libertas\n{remove planet for return e-mail}\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>alistair <alistair@goforit64.fsnet.co.uk> wrote in message
news:861c1b21.0405250456.1496b69e@posting.google.c om...
> helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply)
wrote in message news:<c8up3d$p9h$1@online.de>...
> > In article <861c1b21.0405240728.3d7c428a@posting.google.com>,
> > alistair@goforit64.fsnet.co.uk (alistair) writes:
> >
> > State what problem you are trying to solve, why you think dark energy
> > causes redshift and/or why you think this might be necessary and/or what
> > is wrong with the conventional explanation.
>
> Conservation of energy. Where does the energy of redshifted photons go?
It is lost to the aether, or the spacetime continuum, or to the zero-point
energy, or to strings or to whatever physical entity you consider supports
the field.
"Conservation of energy" says nothing about whether assumptions about the
perfection of EM waves hold over scales tens of orders of magnitude in
distance and time greater than we can test in the lab.
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
alistair
May31-04, 04:22 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>PHILIP HELBIG:\n" energy doesn\'t have to be conserved in cosmology on large\nscales(summary!)\n\nALISTAIR writes:\n\nI\'ve seen somewhere else on this forum people debating whether or not\nit is possible to speak of an average energy for a stress energy\ntensor and whether or not temperature is proportional to energy in\nGeneral Relativity.It seems to me that no-one knows anything for sure\nabout energy in a relativistic context.\nGR is undoubtedly an accurate theory backed by experiment. But given\nthe amount of debate I have seen about energy in GR and given that the\nconcept of energy is fundamental to GR, I doubt that anyone really\nunderstands why GR works!\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>PHILIP HELBIG:
" energy doesn't have to be conserved in cosmology on large
scales(summary!)
ALISTAIR writes:
I've seen somewhere else on this forum people debating whether or not
it is possible to speak of an average energy for a stress energy
tensor and whether or not temperature is proportional to energy in
General Relativity.It seems to me that no-one knows anything for sure
about energy in a relativistic context.
GR is undoubtedly an accurate theory backed by experiment. But given
the amount of debate I have seen about energy in GR and given that the
concept of energy is fundamental to GR, I doubt that anyone really
understands why GR works!
greywolf42
Jun4-04, 02:47 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>Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>\nwrote in message news:c9ai4c\\$cu\\$1@online.de...\n>\n> In article <861c1b21.0405250456.1496b69e@posting.google.com>, \n> alistair@goforit64.fsnet.co.uk (alistair) writes:\n>\n> > helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to\n> > reply) wrote in message news:<c8up3d\\$p9h\\$1@online.de>...\n> > > In article <861c1b21.0405240728.3d7c428a@posting.google.com>, \n> > > alistair@goforit64.fsnet.co.uk (alistair) writes:\n> > >\n> > > State what problem you are trying to solve, why you think dark energy\n> > > causes redshift and/or why you think this might be necessary and/or\n> > > what is wrong with the conventional explanation.\n> >\n> > Conservation of energy. Where does the energy of redshifted photons go?\n>\n> Nowhere. Energy is not conserved in cosmology. As is always the case\n> with confusing stuff in cosmology, this is covered well in Edward\n> Harrison\'s COSMOLOGY textbook.\n\nThat pretty well sums up most objections to the standard big-bang cosmology.\nBut that \'vagueness\' is a property of the big-bang. Not cosmology in\ngeneral.\n\n> In General Relativity in general, energy is not as well-defined a\n> quantity as it is in most of the rest of physics.\n\nI believe you might get Tom Van Flandern to agree to this, but not Steve\nCarlip.\n\nIn what way to you see energy poorly defined in GR?\n\n--\ngreywolf42\nubi dubium ibi libertas\n{remove planet for return e-mail}\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>Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>
wrote in message news:c9ai4c$cu$1@online.de...
>
> In article <861c1b21.0405250456.1496b69e@posting.google.com>,
> alistair@goforit64.fsnet.co.uk (alistair) writes:
>
> > helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to
> > reply) wrote in message news:<c8up3d$p9h$1@online.de>...
> > > In article <861c1b21.0405240728.3d7c428a@posting.google.com>,
> > > alistair@goforit64.fsnet.co.uk (alistair) writes:
> > >
> > > State what problem you are trying to solve, why you think dark energy
> > > causes redshift and/or why you think this might be necessary and/or
> > > what is wrong with the conventional explanation.
> >
> > Conservation of energy. Where does the energy of redshifted photons go?
>
> Nowhere. Energy is not conserved in cosmology. As is always the case
> with confusing stuff in cosmology, this is covered well in Edward
> Harrison's COSMOLOGY textbook.
That pretty well sums up most objections to the standard big-bang cosmology.
But that 'vagueness' is a property of the big-bang. Not cosmology in
general.
> In General Relativity in general, energy is not as well-defined a
> quantity as it is in most of the rest of physics.
I believe you might get Tom Van Flandern to agree to this, but not Steve
Carlip.
In what way to you see energy poorly defined in GR?
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
carlip@no-physics-spam.ucdavis.edu
Jun6-04, 04:26 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>greywolf42 <mingstb@marssim-ss.com> wrote:\n> Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>\n> wrote in message news:c9ai4c\\$cu\\$1@online.de...\n\n[...]\n> > In General Relativity in general, energy is not as well-defined a\n> > quantity as it is in most of the rest of physics.\n\n> I believe you might get Tom Van Flandern to agree to this, but not\n> Steve Carlip.\n\nOn the contrary, I certainly agree with the statement. In particular,\na local energy density is well-defined in GR only for spacetimes that\nadmit a timelike Killing vector. These are exceedingly rare, and\ncertainly don\'t describe the real spacetime we live in.\n\nThere are various proposed definitions of ``quasilocal energy\'\' in GR,\nsome of which are quite useful. But they don\'t all agree, and no one\nhas a convincing argument that one or another of them is ``right.\'\'\nThere are also good approximate definitions of the energy of small\nperturbations on a fixed background. These can be very useful, for\nexample in the description of gravitational radiation, but they apply\nonly in a narrow set of circumstances, and only as approximations.\nFinally, in an asymptotically flat spacetime (or in a few other cases\nin which the structure of spacetime at infinity is fixed), there are\ngood definitions of total energy, basically because there is at least\nan asymptotic timelike Killing vector. But these definitions clearly\nfails in a cosmological setting.\n\nThe basic problem is that in order to have a useful definition of a\nconserved energy, you clearly have to include gravitational potential\nenergy -- otherwise you already fail in the Newtonian limit. But by\nthe principle of equivalence, the gravitational field at any given\npoint P can always be transformed to zero by a suitable coordinate\ntransformation (going to a freely falling frame). You presumably\ndon\'t want to say that the gravitational field\'s energy at point P\nis nonzero even though there\'s no gravitational field there; so you\nhave to allow the possibility of transforming the gravitational energy\nto zero at P. But this means the gravitational energy can\'t be part\nof a tensor. That\'s because if a tensor is zero at P in one coordinate\nsystem, then it\'s zero in all coordinate systems; but since P was any\narbitrary point, this would make the energy zero everywhere.\n\nThe upshot is that gravitational energy cannot be described by a\ntensor. That means it must either depend on a choice of coordinates,\nor else it must not be local (you can transform the gravitational\nfield away at a point, but not in a finite region, so if the energy\nis nonlocal the argument I\'ve given fails). If there\'s a timelike\nKilling vector, that picks out a ``preferred\'\' time coordinate, which\ncan be used to define an energy. If the spacetime is asymptotically\nflat, there\'s a preferred set of coordinates at infinity. If you\'re\nlooking at a small perturbation around a fixed background, you can\nuse the background to define a frame. And if you drop locality,\nas I said, there are a number of ``quasilocal\'\' possibilities for\ndefining energy in a small but finite region.\n\nAs far as I know, no one has yet systematically studied the role of\nvarious quasilocal energies in cosmology. The other possibilities\nclearly don\'t apply in a cosmological setting.\n\nSteve Carlip\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>greywolf42 <mingstb@marssim-ss.com> wrote:
> Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>
> wrote in message news:c9ai4c$cu$1@online.de...
[...]
> > In General Relativity in general, energy is not as well-defined a
> > quantity as it is in most of the rest of physics.
> I believe you might get Tom Van Flandern to agree to this, but not
> Steve Carlip.
On the contrary, I certainly agree with the statement. In particular,
a local energy density is well-defined in GR only for spacetimes that
admit a timelike Killing vector. These are exceedingly rare, and
certainly don't describe the real spacetime we live in.
There are various proposed definitions of ``quasilocal energy'' in GR,
some of which are quite useful. But they don't all agree, and no one
has a convincing argument that one or another of them is ``right.''
There are also good approximate definitions of the energy of small
perturbations on a fixed background. These can be very useful, for
example in the description of gravitational radiation, but they apply
only in a narrow set of circumstances, and only as approximations.
Finally, in an asymptotically flat spacetime (or in a few other cases
in which the structure of spacetime at infinity is fixed), there are
good definitions of total energy, basically because there is at least
an asymptotic timelike Killing vector. But these definitions clearly
fails in a cosmological setting.
The basic problem is that in order to have a useful definition of a
conserved energy, you clearly have to include gravitational potential
energy -- otherwise you already fail in the Newtonian limit. But by
the principle of equivalence, the gravitational field at any given
point P can always be transformed to zero by a suitable coordinate
transformation (going to a freely falling frame). You presumably
don't want to say that the gravitational field's energy at point P
is nonzero even though there's no gravitational field there; so you
have to allow the possibility of transforming the gravitational energy
to zero at P. But this means the gravitational energy can't be part
of a tensor. That's because if a tensor is zero at P in one coordinate
system, then it's zero in all coordinate systems; but since P was any
arbitrary point, this would make the energy zero everywhere.
The upshot is that gravitational energy cannot be described by a
tensor. That means it must either depend on a choice of coordinates,
or else it must not be local (you can transform the gravitational
field away at a point, but not in a finite region, so if the energy
is nonlocal the argument I've given fails). If there's a timelike
Killing vector, that picks out a ``preferred'' time coordinate, which
can be used to define an energy. If the spacetime is asymptotically
flat, there's a preferred set of coordinates at infinity. If you're
looking at a small perturbation around a fixed background, you can
use the background to define a frame. And if you drop locality,
as I said, there are a number of ``quasilocal'' possibilities for
defining energy in a small but finite region.
As far as I know, no one has yet systematically studied the role of
various quasilocal energies in cosmology. The other possibilities
clearly don't apply in a cosmological setting.
Steve Carlip
Phillip Helbig---remove CLOTHES to reply
Jun7-04, 04:54 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>\nIn article <10bpmpcca0r6g88@corp.supernews.com>, "greywolf42"\n<mingstb@marssim-ss.com> writes:\n\n> > In General Relativity in general, energy is not as well-defined a\n> > quantity as it is in most of the rest of physics.\n>\n> I believe you might get Tom Van Flandern to agree to this, but not Steve\n> Carlip.\n>\n> In what way to you see energy poorly defined in GR?\n\nCatch up on the newsgroup. This has been discussed here quite often,\nalso recently. No need to compose a repetitive post to repeat the\ndiscussion.\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 <10bpmpcca0r6g88@corp.supernews.com>, "greywolf42"
<mingstb@marssim-ss.com> writes:
> > In General Relativity in general, energy is not as well-defined a
> > quantity as it is in most of the rest of physics.
>
> I believe you might get Tom Van Flandern to agree to this, but not Steve
> Carlip.
>
> In what way to you see energy poorly defined in GR?
Catch up on the newsgroup. This has been discussed here quite often,
also recently. No need to compose a repetitive post to repeat the
discussion.
greywolf42
Jun8-04, 02:23 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<carlip@no-physics-spam.ucdavis.edu> wrote in message\nnews:c9tajo\\$d6h\\$2@woodrow.ucdavis.edu ...\n> greywolf42 <mingstb@marssim-ss.com> wrote:\n> > Phillip Helbig---remove CLOTHES to reply\n<helbig@astro.multiCLOTHESvax.de>\n> > wrote in message news:c9ai4c\\$cu\\$1@online.de...\n>\n> [...]\n> > > In General Relativity in general, energy is not as well-defined a\n> > > quantity as it is in most of the rest of physics.\n>\n> > I believe you might get Tom Van Flandern to agree to this, but not\n> > Steve Carlip.\n>\n> On the contrary, I certainly agree with the statement.\n\nWell, I was wrong, then.\n\n> In particular,\n> a local energy density is well-defined in GR only for spacetimes that\n> admit a timelike Killing vector. These are exceedingly rare, and\n> certainly don\'t describe the real spacetime we live in.\n\nHow does this square with your position on Noether\'s theorem and orbital\nenergy conservation?\n\n> There are various proposed definitions of ``quasilocal energy\'\' in GR,\n> some of which are quite useful. But they don\'t all agree, and no one\n> has a convincing argument that one or another of them is ``right.\'\'\n> There are also good approximate definitions of the energy of small\n> perturbations on a fixed background. These can be very useful, for\n> example in the description of gravitational radiation, but they apply\n> only in a narrow set of circumstances, and only as approximations.\n> Finally, in an asymptotically flat spacetime (or in a few other cases\n> in which the structure of spacetime at infinity is fixed), there are\n> good definitions of total energy, basically because there is at least\n> an asymptotic timelike Killing vector. But these definitions clearly\n> fails in a cosmological setting.\n\nTo what specific failure are you referring? Whitehead\'s flat-spacetime\nstill hasn\'t been cosmologically disproved.\n\n> The basic problem is that in order to have a useful definition of a\n> conserved energy, you clearly have to include gravitational potential\n> energy -- otherwise you already fail in the Newtonian limit. But by\n> the principle of equivalence, the gravitational field at any given\n> point P can always be transformed to zero by a suitable coordinate\n> transformation (going to a freely falling frame). You presumably\n> don\'t want to say that the gravitational field\'s energy at point P\n> is nonzero even though there\'s no gravitational field there; so you\n> have to allow the possibility of transforming the gravitational energy\n> to zero at P. But this means the gravitational energy can\'t be part\n> of a tensor. That\'s because if a tensor is zero at P in one coordinate\n> system, then it\'s zero in all coordinate systems; but since P was any\n> arbitrary point, this would make the energy zero everywhere.\n>\n> The upshot is that gravitational energy cannot be described by a\n> tensor. That means it must either depend on a choice of coordinates,\n> or else it must not be local (you can transform the gravitational\n> field away at a point, but not in a finite region, so if the energy\n> is nonlocal the argument I\'ve given fails). If there\'s a timelike\n> Killing vector, that picks out a ``preferred\'\' time coordinate, which\n> can be used to define an energy. If the spacetime is asymptotically\n> flat, there\'s a preferred set of coordinates at infinity. If you\'re\n> looking at a small perturbation around a fixed background, you can\n> use the background to define a frame. And if you drop locality,\n> as I said, there are a number of ``quasilocal\'\' possibilities for\n> defining energy in a small but finite region.\n>\n> As far as I know, no one has yet systematically studied the role of\n> various quasilocal energies in cosmology. The other possibilities\n> clearly don\'t apply in a cosmological setting.\n\nIf GR cosmology can\'t \'keep track\' of all energy, then the argument that was\nused \'against\' tired light theories (that one must know where all the energy\nis going) is spurious.\n\n--\ngreywolf42\nubi dubium ibi libertas\n{remove planet for return e-mail}\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><carlip@no-physics-spam.ucdavis.edu> wrote in message
news:c9tajo$d6h$2@woodrow.ucdavis.edu...
> greywolf42 <mingstb@marssim-ss.com> wrote:
> > Phillip Helbig---remove CLOTHES to reply
<helbig@astro.multiCLOTHESvax.de>
> > wrote in message news:c9ai4c$cu$1@online.de...
>
> [...]
> > > In General Relativity in general, energy is not as well-defined a
> > > quantity as it is in most of the rest of physics.
>
> > I believe you might get Tom Van Flandern to agree to this, but not
> > Steve Carlip.
>
> On the contrary, I certainly agree with the statement.
Well, I was wrong, then.
> In particular,
> a local energy density is well-defined in GR only for spacetimes that
> admit a timelike Killing vector. These are exceedingly rare, and
> certainly don't describe the real spacetime we live in.
How does this square with your position on Noether's theorem and orbital
energy conservation?
> There are various proposed definitions of ``quasilocal energy'' in GR,
> some of which are quite useful. But they don't all agree, and no one
> has a convincing argument that one or another of them is ``right.''
> There are also good approximate definitions of the energy of small
> perturbations on a fixed background. These can be very useful, for
> example in the description of gravitational radiation, but they apply
> only in a narrow set of circumstances, and only as approximations.
> Finally, in an asymptotically flat spacetime (or in a few other cases
> in which the structure of spacetime at infinity is fixed), there are
> good definitions of total energy, basically because there is at least
> an asymptotic timelike Killing vector. But these definitions clearly
> fails in a cosmological setting.
To what specific failure are you referring? Whitehead's flat-spacetime
still hasn't been cosmologically disproved.
> The basic problem is that in order to have a useful definition of a
> conserved energy, you clearly have to include gravitational potential
> energy -- otherwise you already fail in the Newtonian limit. But by
> the principle of equivalence, the gravitational field at any given
> point P can always be transformed to zero by a suitable coordinate
> transformation (going to a freely falling frame). You presumably
> don't want to say that the gravitational field's energy at point P
> is nonzero even though there's no gravitational field there; so you
> have to allow the possibility of transforming the gravitational energy
> to zero at P. But this means the gravitational energy can't be part
> of a tensor. That's because if a tensor is zero at P in one coordinate
> system, then it's zero in all coordinate systems; but since P was any
> arbitrary point, this would make the energy zero everywhere.
>
> The upshot is that gravitational energy cannot be described by a
> tensor. That means it must either depend on a choice of coordinates,
> or else it must not be local (you can transform the gravitational
> field away at a point, but not in a finite region, so if the energy
> is nonlocal the argument I've given fails). If there's a timelike
> Killing vector, that picks out a ``preferred'' time coordinate, which
> can be used to define an energy. If the spacetime is asymptotically
> flat, there's a preferred set of coordinates at infinity. If you're
> looking at a small perturbation around a fixed background, you can
> use the background to define a frame. And if you drop locality,
> as I said, there are a number of ``quasilocal'' possibilities for
> defining energy in a small but finite region.
>
> As far as I know, no one has yet systematically studied the role of
> various quasilocal energies in cosmology. The other possibilities
> clearly don't apply in a cosmological setting.
If GR cosmology can't 'keep track' of all energy, then the argument that was
used 'against' tired light theories (that one must know where all the energy
is going) is spurious.
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
greywolf42
Jun12-04, 07:15 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>Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>\nwrote in message news:c9qjub\\$7hm\\$1@online.de...\n>\n> In article <10bpmpcca0r6g88@corp.supernews.com>, "greywolf42"\n> <mingstb@marssim-ss.com> writes:\n>\n> > > In General Relativity in general, energy is not as well-defined a\n> > > quantity as it is in most of the rest of physics.\n> >\n> > I believe you might get Tom Van Flandern to agree to this, but not Steve\n> > Carlip.\n> >\n> > In what way to you see energy poorly defined in GR?\n>\n> Catch up on the newsgroup. This has been discussed here quite often,\n> also recently. No need to compose a repetitive post to repeat the\n> discussion.\n\nA link would be nice, or a quick summary. However, your post is not\nresponsive to the question at hand. You have snipped the substantive\ncontext:\n==============\n> > Conservation of energy. Where does the energy of redshifted photons go?\n>\n> Nowhere. Energy is not conserved in cosmology. As is always the case\n> with confusing stuff in cosmology, this is covered well in Edward\n> Harrison\'s COSMOLOGY textbook.\n\nThat pretty well sums up most objections to the standard big-bang cosmology.\nBut that \'vagueness\' is a property of the big-bang. Not cosmology in\ngeneral.\n==============\n\nQuite simply, the argument was made that \'tired light\' was a valid theory\n*only if* one could account for all energy.\n\nIf one believes that GR cannot account for all energy at all times, then\nthis argument is completely spurious.\n\n--\ngreywolf42\nubi dubium ibi libertas\n{remove planet for return e-mail}\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>Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>
wrote in message news:c9qjub$7hm$1@online.de...
>
> In article <10bpmpcca0r6g88@corp.supernews.com>, "greywolf42"
> <mingstb@marssim-ss.com> writes:
>
> > > In General Relativity in general, energy is not as well-defined a
> > > quantity as it is in most of the rest of physics.
> >
> > I believe you might get Tom Van Flandern to agree to this, but not Steve
> > Carlip.
> >
> > In what way to you see energy poorly defined in GR?
>
> Catch up on the newsgroup. This has been discussed here quite often,
> also recently. No need to compose a repetitive post to repeat the
> discussion.
A link would be nice, or a quick summary. However, your post is not
responsive to the question at hand. You have snipped the substantive
context:
==============
> > Conservation of energy. Where does the energy of redshifted photons go?
>
> Nowhere. Energy is not conserved in cosmology. As is always the case
> with confusing stuff in cosmology, this is covered well in Edward
> Harrison's COSMOLOGY textbook.
That pretty well sums up most objections to the standard big-bang cosmology.
But that 'vagueness' is a property of the big-bang. Not cosmology in
general.
==============
Quite simply, the argument was made that 'tired light' was a valid theory
*only if* one could account for all energy.
If one believes that GR cannot account for all energy at all times, then
this argument is completely spurious.
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
Phillip Helbig---remove CLOTHES to reply
Jun16-04, 03:43 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 <10cbpeksalhsma0@corp.supernews.com>, "greywolf42"\n<mingstb@marssim-ss.com> writes:\n\n> Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>\n> wrote in message news:c9qjub\\$7hm\\$1@online.de...\n> >\n> > In article <10bpmpcca0r6g88@corp.supernews.com>, "greywolf42"\n> > <mingstb@marssim-ss.com> writes:\n> >\n> > > > In General Relativity in general, energy is not as well-defined a\n> > > > quantity as it is in most of the rest of physics.\n> > >\n> > > I believe you might get Tom Van Flandern to agree to this, but not Steve\n> > > Carlip.\n> > >\n> > > In what way to you see energy poorly defined in GR?\n> >\n> > Catch up on the newsgroup. This has been discussed here quite often,\n> > also recently. No need to compose a repetitive post to repeat the\n> > discussion.\n>\n> A link would be nice, or a quick summary.\n\nSteve Carlip has since responded with an excellent summary.\n\n> However, your post is not\n> responsive to the question at hand. You have snipped the substantive\n> context:\n> ==============\n> > > Conservation of energy. Where does the energy of redshifted photons go?\n> >\n> > Nowhere. Energy is not conserved in cosmology. As is always the case\n> > with confusing stuff in cosmology, this is covered well in Edward\n> > Harrison\'s COSMOLOGY textbook.\n>\n> That pretty well sums up most objections to the standard big-bang cosmology.\n> But that \'vagueness\' is a property of the big-bang. Not cosmology in\n> general.\n> ==============\n>\n> Quite simply, the argument was made that \'tired light\' was a valid theory\n> *only if* one could account for all energy.\n>\n> If one believes that GR cannot account for all energy at all times, then\n> this argument is completely spurious.\n\nSo loss of energy can\'t be used as an argument against tired light if GR\nhas the same problem. OK. However, in most tired-light theories, the\nenergy is NOT lost as it is in GR, so this was never a strong argument\nagainst tired-light theories anyway. If we put tired light and GR on\nthe same footing with respect to energy loss, the other criticisms of\ntired-light, mainly that they are ad-hoc, remain. Also, if one gives up\nGR as an explanation for redshift, any alternative theory has to explain\na lot of other things besides the cosmological redshift. For example,\nthe period increase in the binary pulsar. One can\'t say "just like GR\neverywhere but in cosmology" as a starting point for an alternative\ntheory.\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>In article <10cbpeksalhsma0@corp.supernews.com>, "greywolf42"
<mingstb@marssim-ss.com> writes:
> Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>
> wrote in message news:c9qjub$7hm$1@online.de...
> >
> > In article <10bpmpcca0r6g88@corp.supernews.com>, "greywolf42"
> > <mingstb@marssim-ss.com> writes:
> >
> > > > In General Relativity in general, energy is not as well-defined a
> > > > quantity as it is in most of the rest of physics.
> > >
> > > I believe you might get Tom Van Flandern to agree to this, but not Steve
> > > Carlip.
> > >
> > > In what way to you see energy poorly defined in GR?
> >
> > Catch up on the newsgroup. This has been discussed here quite often,
> > also recently. No need to compose a repetitive post to repeat the
> > discussion.
>
> A link would be nice, or a quick summary.
Steve Carlip has since responded with an excellent summary.
> However, your post is not
> responsive to the question at hand. You have snipped the substantive
> context:
> ==============
> > > Conservation of energy. Where does the energy of redshifted photons go?
> >
> > Nowhere. Energy is not conserved in cosmology. As is always the case
> > with confusing stuff in cosmology, this is covered well in Edward
> > Harrison's COSMOLOGY textbook.
>
> That pretty well sums up most objections to the standard big-bang cosmology.
> But that 'vagueness' is a property of the big-bang. Not cosmology in
> general.
> ==============
>
> Quite simply, the argument was made that 'tired light' was a valid theory
> *only if* one could account for all energy.
>
> If one believes that GR cannot account for all energy at all times, then
> this argument is completely spurious.
So loss of energy can't be used as an argument against tired light if GR
has the same problem. OK. However, in most tired-light theories, the
energy is NOT lost as it is in GR, so this was never a strong argument
against tired-light theories anyway. If we put tired light and GR on
the same footing with respect to energy loss, the other criticisms of
tired-light, mainly that they are ad-hoc, remain. Also, if one gives up
GR as an explanation for redshift, any alternative theory has to explain
a lot of other things besides the cosmological redshift. For example,
the period increase in the binary pulsar. One can't say "just like GR
everywhere but in cosmology" as a starting point for an alternative
theory.
Jim Jastrzebski
Jun17-04, 06:16 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><carlip@no-physics-spam.ucdavis.edu> wrote in message\nnews:c9tajo\\$d6h\\$2@woodrow.ucdavis.edu ...\n> greywolf42 <mingstb@marssim-ss.com> wrote:\n> > Phillip Helbig---remove CLOTHES to reply\n<helbig@astro.multiCLOTHESvax.de>\n> > wrote in message news:c9ai4c\\$cu\\$1@online.de...\n>\n> [...]\n> > > In General Relativity in general, energy is not as well-defined a\n> > > quantity as it is in most of the rest of physics.\n>\n> > I believe you might get Tom Van Flandern to agree to this, but not\n> > Steve Carlip.\n>\n> On the contrary, I certainly agree with the statement. In particular,\n> a local energy density is well-defined in GR only for spacetimes that\n> admit a timelike Killing vector. These are exceedingly rare, and\n> certainly don\'t describe the real spacetime we live in.\n>\n> There are various proposed definitions of ``quasilocal energy\'\' in GR,\n> some of which are quite useful. But they don\'t all agree, and no one\n> has a convincing argument that one or another of them is ``right.\'\'\n> There are also good approximate definitions of the energy of small\n> perturbations on a fixed background. These can be very useful, for\n> example in the description of gravitational radiation, but they apply\n> only in a narrow set of circumstances, and only as approximations.\n> Finally, in an asymptotically flat spacetime (or in a few other cases\n> in which the structure of spacetime at infinity is fixed), there are\n> good definitions of total energy, basically because there is at least\n> an asymptotic timelike Killing vector. But these definitions clearly\n> fails in a cosmological setting.\n>\n> The basic problem is that in order to have a useful definition of a\n> conserved energy, you clearly have to include gravitational potential\n> energy -- otherwise you already fail in the Newtonian limit. But by\n> the principle of equivalence, the gravitational field at any given\n> point P can always be transformed to zero by a suitable coordinate\n> transformation (going to a freely falling frame). You presumably\n> don\'t want to say that the gravitational field\'s energy at point P\n> is nonzero even though there\'s no gravitational field there; so you\n> have to allow the possibility of transforming the gravitational energy\n> to zero at P. But this means the gravitational energy can\'t be part\n> of a tensor. That\'s because if a tensor is zero at P in one coordinate\n> system, then it\'s zero in all coordinate systems; but since P was any\n> arbitrary point, this would make the energy zero everywhere.\n>\n> The upshot is that gravitational energy cannot be described by a\n> tensor. That means it must either depend on a choice of coordinates,\n> or else it must not be local (you can transform the gravitational\n> field away at a point, but not in a finite region, so if the energy\n> is nonlocal the argument I\'ve given fails). If there\'s a timelike\n> Killing vector, that picks out a ``preferred\'\' time coordinate, which\n> can be used to define an energy. If the spacetime is asymptotically\n> flat, there\'s a preferred set of coordinates at infinity. If you\'re\n> looking at a small perturbation around a fixed background, you can\n> use the background to define a frame. And if you drop locality,\n> as I said, there are a number of ``quasilocal\'\' possibilities for\n> defining energy in a small but finite region.\n>\n> As far as I know, no one has yet systematically studied the role of\n> various quasilocal energies in cosmology. The other possibilities\n> clearly don\'t apply in a cosmological setting.\n\nTo avoid all those problems it might seem advisable to forget the\nwhole notion of "gravitational potential energy", which in fact is a\nNewtonian concept following from another Newtonian concept,\n"universal gravitational attraction", of which our "gravitational\npotential energy" is just an integral. So since the "universal\ngravitational attraction" is exactly null in Einsteinian world, it\nseems wise to make the associated with it "gravitational potential\nenergy" also null, and in the process get rid of all the above\nheadaches.\n\nIt requires only to find a proper reservoir of energy that would\nabsorb or deliver the kinetic energy of various massive objects,\nmoving in general with variable velocities despite no forces\nacting on them. Finding such a reservoir of energy, possibly\nperfectly localized, shouldn\'t be of course too difficult for any\ncompetent physicist. I could even volunteer for the job myself\nhowever I\'m sure there are much brighter people than me, who\ncan do it much better.\n\n-- Jim\n\n> Steve Carlip\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><carlip@no-physics-spam.ucdavis.edu> wrote in message
news:c9tajo$d6h$2@woodrow.ucdavis.edu...
> greywolf42 <mingstb@marssim-ss.com> wrote:
> > Phillip Helbig---remove CLOTHES to reply
<helbig@astro.multiCLOTHESvax.de>
> > wrote in message news:c9ai4c$cu$1@online.de...
>
> [...]
> > > In General Relativity in general, energy is not as well-defined a
> > > quantity as it is in most of the rest of physics.
>
> > I believe you might get Tom Van Flandern to agree to this, but not
> > Steve Carlip.
>
> On the contrary, I certainly agree with the statement. In particular,
> a local energy density is well-defined in GR only for spacetimes that
> admit a timelike Killing vector. These are exceedingly rare, and
> certainly don't describe the real spacetime we live in.
>
> There are various proposed definitions of ``quasilocal energy'' in GR,
> some of which are quite useful. But they don't all agree, and no one
> has a convincing argument that one or another of them is ``right.''
> There are also good approximate definitions of the energy of small
> perturbations on a fixed background. These can be very useful, for
> example in the description of gravitational radiation, but they apply
> only in a narrow set of circumstances, and only as approximations.
> Finally, in an asymptotically flat spacetime (or in a few other cases
> in which the structure of spacetime at infinity is fixed), there are
> good definitions of total energy, basically because there is at least
> an asymptotic timelike Killing vector. But these definitions clearly
> fails in a cosmological setting.
>
> The basic problem is that in order to have a useful definition of a
> conserved energy, you clearly have to include gravitational potential
> energy -- otherwise you already fail in the Newtonian limit. But by
> the principle of equivalence, the gravitational field at any given
> point P can always be transformed to zero by a suitable coordinate
> transformation (going to a freely falling frame). You presumably
> don't want to say that the gravitational field's energy at point P
> is nonzero even though there's no gravitational field there; so you
> have to allow the possibility of transforming the gravitational energy
> to zero at P. But this means the gravitational energy can't be part
> of a tensor. That's because if a tensor is zero at P in one coordinate
> system, then it's zero in all coordinate systems; but since P was any
> arbitrary point, this would make the energy zero everywhere.
>
> The upshot is that gravitational energy cannot be described by a
> tensor. That means it must either depend on a choice of coordinates,
> or else it must not be local (you can transform the gravitational
> field away at a point, but not in a finite region, so if the energy
> is nonlocal the argument I've given fails). If there's a timelike
> Killing vector, that picks out a ``preferred'' time coordinate, which
> can be used to define an energy. If the spacetime is asymptotically
> flat, there's a preferred set of coordinates at infinity. If you're
> looking at a small perturbation around a fixed background, you can
> use the background to define a frame. And if you drop locality,
> as I said, there are a number of ``quasilocal'' possibilities for
> defining energy in a small but finite region.
>
> As far as I know, no one has yet systematically studied the role of
> various quasilocal energies in cosmology. The other possibilities
> clearly don't apply in a cosmological setting.
To avoid all those problems it might seem advisable to forget the
whole notion of "gravitational potential energy", which in fact is a
Newtonian concept following from another Newtonian concept,
"universal gravitational attraction", of which our "gravitational
potential energy" is just an integral. So since the "universal
gravitational attraction" is exactly null in Einsteinian world, it
seems wise to make the associated with it "gravitational potential
energy" also null, and in the process get rid of all the above
headaches.
It requires only to find a proper reservoir of energy that would
absorb or deliver the kinetic energy of various massive objects,
moving in general with variable velocities despite no forces
acting on them. Finding such a reservoir of energy, possibly
perfectly localized, shouldn't be of course too difficult for any
competent physicist. I could even volunteer for the job myself
however I'm sure there are much brighter people than me, who
can do it much better.
-- Jim
> Steve Carlip
carlip@no-physics-spam.ucdavis.edu
Jun21-04, 02:51 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>\ngreywolf42 <mingstb@marssim-ss.com> wrote:\n\n> <carlip@no-physics-spam.ucdavis.edu> wrote in message\n> news:c9tajo\\$d6h\\$2@woodrow.ucdavis.edu...\n\n[...]\n> > In particular,\n> > a local energy density is well-defined in GR only for spacetimes that\n> > admit a timelike Killing vector. These are exceedingly rare, and\n> > certainly don\'t describe the real spacetime we live in.\n\n> How does this square with your position on Noether\'s theorem and orbital\n> energy conservation?\n\nIt squares because of the part of my post you quoted below:\n\n[...]\n> > There are also good approximate definitions of the energy of small\n> > perturbations on a fixed background. These can be very useful, for\n> > example in the description of gravitational radiation, but they apply\n> > only in a narrow set of circumstances, and only as approximations.\n> > Finally, in an asymptotically flat spacetime (or in a few other cases\n> > in which the structure of spacetime at infinity is fixed), there are\n> > good definitions of total energy, basically because there is at least\n> > an asymptotic timelike Killing vector.\n\nFor binary systems losing energy through the emission of gravitational\nradiation, one can describe the radiation quite accurately as a small\nperturbation on a fixed background. Furthermore, such systems can be\ntreated as asymptotically flat to a good approximation, since one can\nget far enough away that the spacetime curvature goes to very nearly\nzero before running into problems from other stars or from large-scale\ncosmological effects.\n\nThere was a famous paper by Ehlers, Rosenblum, Goldberg, and Havas,\nAstrophysical Journal 208 (1976) L77, pointing out that one had to be\ncareful to use a consistent set of approximations to use the weak\nfield definition of energy conservation, and arguing that work up to\nthat time was not good enough. This led to a resurgence in work on\nsystematizing the approximation methods, and to careful calculations\nof direct radiation reaction effects that bypassed the need to use\nenergy conservation considerations. (To no one\'s great surprise,\nthe pre-1976 calculations turned out to be right, but the further\nwork paved the way for more exact computations of wave forms that\ndetectors like LIGO will need for searches.)\n\n> > But these definitions clearly fails in a cosmological setting.\n\n> To what specific failure are you referring? Whitehead\'s flat-spacetime\n> still hasn\'t been cosmologically disproved.\n\nI was referring to the definitions of energy in general relativity\nthat you just quoted. Since Whitehead\'s theory is not GR, I don\'t\nunderstand the relevance of your comment.\n\nSteve Carlip\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>greywolf42 <mingstb@marssim-ss.com> wrote:
> <carlip@no-physics-spam.ucdavis.edu> wrote in message
> news:c9tajo$d6h$2@woodrow.ucdavis.edu...
[...]
> > In particular,
> > a local energy density is well-defined in GR only for spacetimes that
> > admit a timelike Killing vector. These are exceedingly rare, and
> > certainly don't describe the real spacetime we live in.
> How does this square with your position on Noether's theorem and orbital
> energy conservation?
It squares because of the part of my post you quoted below:
[...]
> > There are also good approximate definitions of the energy of small
> > perturbations on a fixed background. These can be very useful, for
> > example in the description of gravitational radiation, but they apply
> > only in a narrow set of circumstances, and only as approximations.
> > Finally, in an asymptotically flat spacetime (or in a few other cases
> > in which the structure of spacetime at infinity is fixed), there are
> > good definitions of total energy, basically because there is at least
> > an asymptotic timelike Killing vector.
For binary systems losing energy through the emission of gravitational
radiation, one can describe the radiation quite accurately as a small
perturbation on a fixed background. Furthermore, such systems can be
treated as asymptotically flat to a good approximation, since one can
get far enough away that the spacetime curvature goes to very nearly
zero before running into problems from other stars or from large-scale
cosmological effects.
There was a famous paper by Ehlers, Rosenblum, Goldberg, and Havas,
Astrophysical Journal 208 (1976) L77, pointing out that one had to be
careful to use a consistent set of approximations to use the weak
field definition of energy conservation, and arguing that work up to
that time was not good enough. This led to a resurgence in work on
systematizing the approximation methods, and to careful calculations
of direct radiation reaction effects that bypassed the need to use
energy conservation considerations. (To no one's great surprise,
the pre-1976 calculations turned out to be right, but the further
work paved the way for more exact computations of wave forms that
detectors like LIGO will need for searches.)
> > But these definitions clearly fails in a cosmological setting.
> To what specific failure are you referring? Whitehead's flat-spacetime
> still hasn't been cosmologically disproved.
I was referring to the definitions of energy in general relativity
that you just quoted. Since Whitehead's theory is not GR, I don't
understand the relevance of your comment.
Steve Carlip
alistair
Jun27-04, 05:55 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>"Jim Jastrzebski" <nospam@nospam.com> wrote in message news:<caskl5>\n\n>To avoid all those problems it might seem advisable to forget the\n> whole notion of "gravitational potential energy", which in fact is a\n> Newtonian concept following from another Newtonian concept,\n> "universal gravitational attraction", of which our "gravitational\n> potential energy" is just an integral.\n\n\nAlistair writes:\n\nIf Professor Milgrom is right about Modified Newtonian Dynamics then\nsince force no longer would equal mass x acceleration,the force of\ngravity would not equal Gm1 m2 / r^2 and the gravitational potential\nenergy which is the integral of force with respect to distance, would\nbe different from\n- G m1 m2 / r .Perhaps it would be useful in this thread to discuss\ngravitational potential energy in the context of Modified Newtonian\nDynamics.\n\n\n> Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>\n> > wrote in message news:c9ai4c\\$cu\\$1@online.de...\n>\n> [...]\n> > > In General Relativity in general, energy is not as well-defined a\n> > > quantity as it is in most of the rest of physics.\n\n\nAlistair writes:\nDoes it follow that if energy is not well defined we should say it is\nnot conserved.Surely we should ask: why isn\'t energy well defined in\nGR when it is\nin most of the rest of physics - is there something fundamentally\nwrong with GR?\n\n\nSteve Carlip said:\n\n> a local energy density is well-defined in GR only for spacetimes that\n> admit a timelike Killing vector. These are exceedingly rare, and\n> certainly don\'t describe the real spacetime we live in.\n\nAlistair writes:\n\nThe space-time we live in has a well-defined energy density - 10^52 kg\nin 10^78 m^3.\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>"Jim Jastrzebski" <nospam@nospam.com> wrote in message news:<caskl5>
>To avoid all those problems it might seem advisable to forget the
> whole notion of "gravitational potential energy", which in fact is a
> Newtonian concept following from another Newtonian concept,
> "universal gravitational attraction", of which our "gravitational
> potential energy" is just an integral.
Alistair writes:
If Professor Milgrom is right about Modified Newtonian Dynamics then
since force no longer would equal mass x acceleration,the force of
gravity would not equal Gm1 m2 / r^2 and the gravitational potential
energy which is the integral of force with respect to distance, would
be different from
- G m1 m2 / r .Perhaps it would be useful in this thread to discuss
gravitational potential energy in the context of Modified Newtonian
Dynamics.
> Phillip Helbig---remove CLOTHES to reply <helbig@astro.multiCLOTHESvax.de>
> > wrote in message news:c9ai4c$cu$1@online.de...
>
> [...]
> > > In General Relativity in general, energy is not as well-defined a
> > > quantity as it is in most of the rest of physics.
Alistair writes:
Does it follow that if energy is not well defined we should say it is
not conserved.Surely we should ask: why isn't energy well defined in
GR when it is
in most of the rest of physics - is there something fundamentally
wrong with GR?
Steve Carlip said:
> a local energy density is well-defined in GR only for spacetimes that
> admit a timelike Killing vector. These are exceedingly rare, and
> certainly don't describe the real spacetime we live in.
Alistair writes:
The space-time we live in has a well-defined energy density - 10^52 kg
in 10^78 m^3.
carlip@no-physics-spam.ucdavis.edu
Jun29-04, 05:50 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>alistair <alistair@goforit64.fsnet.co.uk> wrote:\n\n[...]\n> Steve Carlip said:\n\n> > a local energy density is well-defined in GR only for spacetimes that\n> > admit a timelike Killing vector. These are exceedingly rare, and\n> > certainly don\'t describe the real spacetime we live in.\n\n> The space-time we live in has a well-defined energy density - 10^52 kg\n> in 10^78 m^3.\n\nNo, it doesn\'t. The number you quote is an estimate of the *nongravitational*\nenergy density. It does not include gravitational potential energy, is not\nconserved, and doesn\'t make sense as a total energy even in the Newtonian\nlimit.\n\nSteve Carlip\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>alistair <alistair@goforit64.fsnet.co.uk> wrote:
[...]
> Steve Carlip said:
> > a local energy density is well-defined in GR only for spacetimes that
> > admit a timelike Killing vector. These are exceedingly rare, and
> > certainly don't describe the real spacetime we live in.
> The space-time we live in has a well-defined energy density - 10^52 kg
> in 10^78 m^3.
No, it doesn't. The number you quote is an estimate of the *nongravitational*
energy density. It does not include gravitational potential energy, is not
conserved, and doesn't make sense as a total energy even in the Newtonian
limit.
Steve Carlip
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