Age of the universe [Archive]

paragorn

May31-04, 04:21 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>Hello,\nI am sorry if this a stupid question but when the age of the Universe\nsince the Big Bang is given , what is the the reference frame used ?\nDoesn\'t that depend on the choice of the inertial reference frame? Or\nis it just that it is the earth reference frame?\nThanks and please be gentle :-)\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>Hello,
I am sorry if this a stupid question but when the age of the Universe
since the Big Bang is given , what is the the reference frame used ?
Doesn't that depend on the choice of the inertial reference frame? Or
is it just that it is the earth reference frame?
Thanks and please be gentle :-)

Urs Schreiber

Jun1-04, 04:42 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"paragorn" <paragorn18@hotmail.com> schrieb im Newsbeitrag\nnews:bf47ed82.0405301549.abdf60@posti ng.google.com...\n\n> I am sorry if this a stupid question but when the age of the Universe\n> since the Big Bang is given , what is the the reference frame used ?\n\nThe reference frame is the so-called "comoving" frame where the observer\'s\ntrajectory (in spacetime) is orthogonal to each spatial hypersurface.\n\nThe cosmological spacetime metric can be put in the form\n\nds^2 = -dt^2 + a^2(t) dOmega^2\n\nwhere dOmega^2 is the line element on a spatial slice of unit size and all\nthe time dependence of the "size of of the universe" is in the a^2(t)\nprefactor. Comoving observers are those that have fixed position with\nrespect to dOmega.\n\nFor instance if the spatial sections are flat (k=0) we have simply\n\nds^2 = -dt^2 + a^2(t)(dx^2 + dy^2 + dz^2)\n\nand comoving observers are those trajectories with 0 = dx = dy = dz.\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>"paragorn" <paragorn18@hotmail.com> schrieb im Newsbeitrag
news:bf47ed82.0405301549.abdf60@posting.google.com ...

> I am sorry if this a stupid question but when the age of the Universe
> since the Big Bang is given , what is the the reference frame used ?

The reference frame is the so-called "comoving" frame where the observer's
trajectory (in spacetime) is orthogonal to each spatial hypersurface.

The cosmological spacetime metric can be put in the form

ds^2 = -dt^2 + a^2(t) dOmega^2

where dOmega^2 is the line element on a spatial slice of unit size and all
the time dependence of the "size of of the universe" is in the a^2(t)
prefactor. Comoving observers are those that have fixed position with
respect to dOmega.

For instance if the spatial sections are flat (k=0) we have simply

ds^2 = -dt^2 + a^2(t)(dx^2 + dy^2 + dz^2)

and comoving observers are those trajectories with = dx = dy = dz.

Uncle Al

Jun1-04, 04:43 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>\nparagorn wrote:\n>\n> Hello,\n> I am sorry if this a stupid question but when the age of the Universe\n> since the Big Bang is given , what is the the reference frame used ?\n> Doesn\'t that depend on the choice of the inertial reference frame? Or\n> is it just that it is the earth reference frame?\n> Thanks and please be gentle :-)\n\nRead the original data.\n\nhttp://arXiv.org/abs/astro-ph/0310723\nWMAP + Sloane Digital Sky Survey\n\n--\nUncle Al\nhttp://www.mazepath.com/uncleal/qz.pdf\nhttp://www.mazepath.com/uncleal/eotvos.htm\n(The parity Eotvos experiment is queued)\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>paragorn wrote:
>
> Hello,
> I am sorry if this a stupid question but when the age of the Universe
> since the Big Bang is given , what is the the reference frame used ?
> Doesn't that depend on the choice of the inertial reference frame? Or
> is it just that it is the earth reference frame?
> Thanks and please be gentle :-)

Read the original data.

http://arXiv.org/abs/http://www.arxiv.org/abs/astro-ph/0310723
WMAP + Sloane Digital Sky Survey

--
Uncle Al
http://www.mazepath.com/uncleal/qz.pdf
http://www.mazepath.com/uncleal/eotvos.htm
(The parity Eotvos experiment is queued)

Lubos Motl

Jun1-04, 02:12 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>On Mon, 31 May 2004, paragorn wrote:\n\n> I am sorry if this a stupid question but when the age of the Universe\n> since the Big Bang is given , what is the the reference frame used ?\n\nDear paragorn, it is a good question. The time must be measured in a\n"preferred cosmic frame" which is roughly the frame associated with the\ncosmic microwave background, for example. It is the frame in which the CMB\nhas the same temperature in all directions. Yes, if you take the Earth,\nyour result won\'t change too much either. The cosmic microwave background\nradiation is very weak, but nevertheless its existence "spontaneously\nbreaks" the Lorentz invariance - the symmetry between the different\nobservers. Don\'t get me wrong, the actual laws of physics are symmetric\nand satisfy the rules of relativity - but the state of the Universe does\nnot. If we measured the time from the Big Bang along a curved,\naccelerating path in spacetime, we would get less than 14 billion years.\n__________________________________________ ____________________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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>On Mon, 31 May 2004, paragorn wrote:

> I am sorry if this a stupid question but when the age of the Universe
> since the Big Bang is given , what is the the reference frame used ?

Dear paragorn, it is a good question. The time must be measured in a
"preferred cosmic frame" which is roughly the frame associated with the
cosmic microwave background, for example. It is the frame in which the CMB
has the same temperature in all directions. Yes, if you take the Earth,
your result won't change too much either. The cosmic microwave background
radiation is very weak, but nevertheless its existence "spontaneously
breaks" the Lorentz invariance - the symmetry between the different
observers. Don't get me wrong, the actual laws of physics are symmetric
and satisfy the rules of relativity - but the state of the Universe does
not. If we measured the time from the Big Bang along a curved,
accelerating path in spacetime, we would get less than 14 billion years.
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Phil

Jun2-04, 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"paragorn" <paragorn18@hotmail.com> wrote in message\nnews:bf47ed82.0405301549.abdf60@posting.g oogle.com...\n> Hello,\n> I am sorry if this a stupid question but when the age of the Universe\n> since the Big Bang is given , what is the the reference frame used ?\n> Doesn\'t that depend on the choice of the inertial reference frame? Or\n> is it just that it is the earth reference frame?\n\nNo reference frame is needed to define what we mean by the age of the\nuniverse.\n\nThe age of the universe can be defined as the longest time-like worldline\nfrom\nthe Earth today, back to the big bang.\n\nWhen they come to measure it however, astronomers may make assumptions\nabout the universe such as homogeniety and the motion of the Earth relative\nto\nthe background raiation. These assumptions can themselves be checked by\nother\nobservations.\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>"paragorn" <paragorn18@hotmail.com> wrote in message
news:bf47ed82.0405301549.abdf60@posting.google.com ...
> Hello,
> I am sorry if this a stupid question but when the age of the Universe
> since the Big Bang is given , what is the the reference frame used ?
> Doesn't that depend on the choice of the inertial reference frame? Or
> is it just that it is the earth reference frame?

No reference frame is needed to define what we mean by the age of the
universe.

The age of the universe can be defined as the longest time-like worldline
from
the Earth today, back to the big bang.

When they come to measure it however, astronomers may make assumptions
about the universe such as homogeniety and the motion of the Earth relative
to
the background raiation. These assumptions can themselves be checked by
other
observations.

Tim S

Jun2-04, 01:28 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\non 31/05/2004 10:21 pm, paragorn at paragorn18@hotmail.com wrote:\n\n> Hello,\n> I am sorry if this a stupid question but when the age of the Universe\n> since the Big Bang is given , what is the the reference frame used ?\n> Doesn\'t that depend on the choice of the inertial reference frame? Or\n> is it just that it is the earth reference frame?\n> Thanks and please be gentle :-)\n>\n\nThere are no inertial reference frames in curved spacetime. However, the\nuniverse we live in happens to have (approximately) a nice frame called the\nco-moving frame. In a pure big bang model (a \'Friedmann-Robertson-Walker\'\nspacetime) comoving time is the time experienced by the uniformly expanding\nmatter. On a very large scale, this sort of model is an excellent\napproximation to the real world. On a smaller scale, it\'s not so good\n(because the matter isn\'t perfectly homogeneous or uniformly expanding) but\nit\'s mostly not too bad. Alternatively you can think of comoving time as the\ntime experienced in the rest frame of the cosmic microwave background\nradiation, as that is very close to uniform.\n\nTim\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>on 31/05/2004 10:21 pm, paragorn at paragorn18@hotmail.com wrote:

> Hello,
> I am sorry if this a stupid question but when the age of the Universe
> since the Big Bang is given , what is the the reference frame used ?
> Doesn't that depend on the choice of the inertial reference frame? Or
> is it just that it is the earth reference frame?
> Thanks and please be gentle :-)
>

There are no inertial reference frames in curved spacetime. However, the
universe we live in happens to have (approximately) a nice frame called the
co-moving frame. In a pure big bang model (a 'Friedmann-Robertson-Walker'
spacetime) comoving time is the time experienced by the uniformly expanding
matter. On a very large scale, this sort of model is an excellent
approximation to the real world. On a smaller scale, it's not so good
(because the matter isn't perfectly homogeneous or uniformly expanding) but
it's mostly not too bad. Alternatively you can think of comoving time as the
time experienced in the rest frame of the cosmic microwave background
radiation, as that is very close to uniform.

Tim

Serenus Zeitblom

Jun3-04, 09:34 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>\nLubos Motl <motl@feynman.harvard.edu> wrote in message\n> The cosmic microwave background\n> radiation is very weak, but nevertheless its existence "spontaneously\n> breaks" the Lorentz invariance - the symmetry between the different\n> observers. Don\'t get me wrong, the actual laws of physics are symmetric\n> and satisfy the rules of relativity - but the state of the Universe does\n> not.\n\nThis is a little misleading, because it might give readers the impression\nthat the laws of physics, including those of general relativity, are\nsymmetric under the Lorentz group. That is not the case, as can be\nverified by looking up the thread "Symmetries of general relativity"\nin this newsgroup last year. The question was finally settled by\nSteve Carlip, look for his entries in the thread.\n\n\n[Moderator\'s note: Notwithstanding disagreement about the best wording\neverybody agrees about the simple fact that the presence of the CMB allows us\nto determine velocities with respect to a special frame, namely the\nCMB\'s rest frame, and that this does not imply that there is any\npreferred frame in the laws of physics.\n-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>Lubos Motl <motl@feynman.harvard.edu> wrote in message
> The cosmic microwave background
> radiation is very weak, but nevertheless its existence "spontaneously
> breaks" the Lorentz invariance - the symmetry between the different
> observers. Don't get me wrong, the actual laws of physics are symmetric
> and satisfy the rules of relativity - but the state of the Universe does
> not.

This is a little misleading, because it might give readers the impression
that the laws of physics, including those of general relativity, are
symmetric under the Lorentz group. That is not the case, as can be
verified by looking up the thread "Symmetries of general relativity"
in this newsgroup last year. The question was finally settled by
Steve Carlip, look for his entries in the thread.

[Moderator's note: Notwithstanding disagreement about the best wording
everybody agrees about the simple fact that the presence of the CMB allows us
to determine velocities with respect to a special frame, namely the
CMB's rest frame, and that this does not imply that there is any
preferred frame in the laws of physics.
-usc]

greywolf42

Jun4-04, 07:52 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>\nSerenus Zeitblom <serenuszeitblomphd@yahoo.com> wrote in message\nnews:c7fd6c7a.0406030518.47c377a0@posting .google.com...\n>\n> Lubos Motl <motl@feynman.harvard.edu> wrote in message\n> > The cosmic microwave background\n> > radiation is very weak, but nevertheless its existence "spontaneously\n> > breaks" the Lorentz invariance - the symmetry between the different\n> > observers. Don\'t get me wrong, the actual laws of physics are symmetric\n> > and satisfy the rules of relativity - but the state of the Universe does\n> > not.\n>\n> This is a little misleading, because it might give readers the impression\n> that the laws of physics, including those of general relativity, are\n> symmetric under the Lorentz group. That is not the case, as can be\n> verified by looking up the thread "Symmetries of general relativity"\n> in this newsgroup last year. The question was finally settled by\n> Steve Carlip, look for his entries in the thread.\n>\n>\n> [Moderator\'s note: Notwithstanding disagreement about the best wording\n> everybody agrees about the simple fact that the presence of the CMB allows\nus\n> to determine velocities with respect to a special frame, namely the\n> CMB\'s rest frame, and that this does not imply that there is any\n> preferred frame in the laws of physics.\n> -usc]\n\nNote on Moderator\'s note.\n\nIt does not imply it according to GR. It does imply it if you are using\nalmost any other theory of gravity. But that \'special\' frame is required by\naether theories and LET. Trying to make a distinction between a \'special\'\nframe and a \'preferred\' frame is just a word game.\n\n\n[Moderator\'s note: Too clarify, the difference between "special" and "preferred"\nin the context of that note was precisely as in the following sentence:\n"My office is a special location in space (because my ability to earn money\ndepends on my distance to that special location) but - nevertheless - the location\nof my office is by no means a location preferred by the laws of nature."\nMaybe there are words better suited than "special" and "preferred" to express the\nfact that the properties of special solutions of a theory need not be identical to\nthe properties of the theory itself, but that\'s the whole point.\n-usc]\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>Serenus Zeitblom <serenuszeitblomphd@yahoo.com> wrote in message
news:c7fd6c7a.0406030518.47c377a0@posting.google.c om...
>
> Lubos Motl <motl@feynman.harvard.edu> wrote in message
> > The cosmic microwave background
> > radiation is very weak, but nevertheless its existence "spontaneously
> > breaks" the Lorentz invariance - the symmetry between the different
> > observers. Don't get me wrong, the actual laws of physics are symmetric
> > and satisfy the rules of relativity - but the state of the Universe does
> > not.
>
> This is a little misleading, because it might give readers the impression
> that the laws of physics, including those of general relativity, are
> symmetric under the Lorentz group. That is not the case, as can be
> verified by looking up the thread "Symmetries of general relativity"
> in this newsgroup last year. The question was finally settled by
> Steve Carlip, look for his entries in the thread.
>
>
> [Moderator's note: Notwithstanding disagreement about the best wording
> everybody agrees about the simple fact that the presence of the CMB allows
us
> to determine velocities with respect to a special frame, namely the
> CMB's rest frame, and that this does not imply that there is any
> preferred frame in the laws of physics.
> -usc]

Note on Moderator's note.

It does not imply it according to GR. It does imply it if you are using
almost any other theory of gravity. But that 'special' frame is required by
aether theories and LET. Trying to make a distinction between a 'special'
frame and a 'preferred' frame is just a word game.

[Moderator's note: Too clarify, the difference between "special" and "preferred"
in the context of that note was precisely as in the following sentence:
"My office is a special location in space (because my ability to earn money
depends on my distance to that special location) but - nevertheless - the location
of my office is by no means a location preferred by the laws of nature."
Maybe there are words better suited than "special" and "preferred" to express the
fact that the properties of special solutions of a theory need not be identical to
the properties of the theory itself, but that's the whole point.
-usc]

--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}

greywolf42

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>\n\ngreywolf42 <mingstb@marssim-ss.com> wrote in message\nnews:10buk3qculh9b46@corp.supernews.com.. .\n>\n> Serenus Zeitblom <serenuszeitblomphd@yahoo.com> wrote in message\n> news:c7fd6c7a.0406030518.47c377a0@posting.google.c om...\n\n{snip}\n\n> > [Moderator\'s note: Notwithstanding disagreement about the best wording\n> > everybody agrees about the simple fact that the presence of the CMB\n> > allows us to determine velocities with respect to a special frame,\nnamely\n> > the CMB\'s rest frame, and that this does not imply that there is any\n> > preferred frame in the laws of physics.\n> > -usc]\n>\n> Note on Moderator\'s note.\n>\n> It does not imply it according to GR. It does imply it if you are using\n> almost any other theory of gravity. But that \'special\' frame is required\n> by aether theories and LET. Trying to make a distinction between a\n> \'special\' frame and a \'preferred\' frame is just a word game.\n>\n> [Moderator\'s note: Too clarify, the difference between "special" and\n> "preferred" in the context of that note was precisely as in the\n> following sentence: "My office is a special location in space\n> (because my ability to earn money depends on my distance to that\n> special location) but - nevertheless - the location of my office is\n> by no means a location preferred by the laws of nature."\n> Maybe there are words better suited than "special" and "preferred" to\n> express the fact that the properties of special solutions of a theory\n> need not be identical to the properties of the theory itself, but\n> that\'s the whole point.\n> -usc]\n\nNote to moderators note:\n\n{Perhaps it would be better if the moderator participated directly in the\ndiscussion as a poster, if he has something to dispute.}\n\nThe presence of the CMB frame in an aether theory is not merely a personal\npreference -- it is a requirement of the theory.\n\nYour attempt to claim that the use of the word \'special\' indicates nothing\nmore than a personal preference is merely a strawman argument. (And a\ncontinuation of the word game.) This discussion is entirely about the \'laws\nof nature\', not about personal preferences.\n\n--\ngreywolf42\nubi dubium ibi libertas\n{remove planet for return e-mail}\n\n\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>greywolf42 <mingstb@marssim-ss.com> wrote in message
news:10buk3qculh9b46@corp.supernews.com...
>
> Serenus Zeitblom <serenuszeitblomphd@yahoo.com> wrote in message
> news:c7fd6c7a.0406030518.47c377a0@posting.google.c om...

{snip}

> > [Moderator's note: Notwithstanding disagreement about the best wording
> > everybody agrees about the simple fact that the presence of the CMB
> > allows us to determine velocities with respect to a special frame,
namely
> > the CMB's rest frame, and that this does not imply that there is any
> > preferred frame in the laws of physics.
> > -usc]
>
> Note on Moderator's note.
>
> It does not imply it according to GR. It does imply it if you are using
> almost any other theory of gravity. But that 'special' frame is required
> by aether theories and LET. Trying to make a distinction between a
> 'special' frame and a 'preferred' frame is just a word game.
>
> [Moderator's note: Too clarify, the difference between "special" and
> "preferred" in the context of that note was precisely as in the
> following sentence: "My office is a special location in space
> (because my ability to earn money depends on my distance to that
> special location) but - nevertheless - the location of my office is
> by no means a location preferred by the laws of nature."
> Maybe there are words better suited than "special" and "preferred" to
> express the fact that the properties of special solutions of a theory
> need not be identical to the properties of the theory itself, but
> that's the whole point.
> -usc]

Note to moderators note:

{Perhaps it would be better if the moderator participated directly in the
discussion as a poster, if he has something to dispute.}

The presence of the CMB frame in an aether theory is not merely a personal
preference -- it is a requirement of the theory.

Your attempt to claim that the use of the word 'special' indicates nothing
more than a personal preference is merely a strawman argument. (And a
continuation of the word game.) This discussion is entirely about the 'laws
of nature', not about personal preferences.

--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}

Italo Vecchi

Jun12-04, 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>"greywolf42" <mingstb@marssim-ss.com> wrote in message news:<10c1jsonljs4d7f@corp.supernews.com>...\n\n> The presence of the CMB frame in an aether theory is not merely a personal\n> preference -- it is a requirement of the theory.\n>\n> Your attempt to claim that the use of the word \'special\' indicates nothing\n> more than a personal preference is merely a strawman argument. (And a\n> continuation of the word game.) This discussion is entirely about the \'laws\n> of nature\', not about personal preferences.\n\nI would think twice before attributing the choice of a reference frame\nto "nature" (whatever that means) rather than to an observer. The\nhistory of science suggests that claims about absolute reference\nframes tend to reflect the observer\'s inability to appreciate the\nrelativity of his/her perspective.\n\n\nIV\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 in message news:<10c1jsonljs4d7f@corp.supernews.com>...

> The presence of the CMB frame in an aether theory is not merely a personal
> preference -- it is a requirement of the theory.
>
> Your attempt to claim that the use of the word 'special' indicates nothing
> more than a personal preference is merely a strawman argument. (And a
> continuation of the word game.) This discussion is entirely about the 'laws
> of nature', not about personal preferences.

I would think twice before attributing the choice of a reference frame
to "nature" (whatever that means) rather than to an observer. The
history of science suggests that claims about absolute reference
frames tend to reflect the observer's inability to appreciate the
relativity of his/her perspective.

IV

greywolf42

Jun14-04, 03:14 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>Italo Vecchi <vecchi@weirdtech.com> wrote in message\nnews:61789046.0406070954.6c6bcf66@posting .google.com...\n> "greywolf42" <mingstb@marssim-ss.com> wrote in message\nnews:<10c1jsonljs4d7f@corp.supernews.com> ...\n>\n> > The presence of the CMB frame in an aether theory is not merely a\npersonal\n> > preference -- it is a requirement of the theory.\n> >\n> > Your attempt to claim that the use of the word \'special\' indicates\nnothing\n> > more than a personal preference is merely a strawman argument. (And a\n> > continuation of the word game.) This discussion is entirely about the\n\'laws\n> > of nature\', not about personal preferences.\n>\n> I would think twice before attributing the choice of a reference frame\n> to "nature" (whatever that means) rather than to an observer.\n\n??? I made no such attribution. Nature makes no choices. \'Twas the\nmoderator\'s note that asserted that \'special\' implied a personal choice.\n\n> The\n> history of science suggests that claims about absolute reference\n> frames tend to reflect the observer\'s inability to appreciate the\n> relativity of his/her perspective.\n\nI agree. But then I don\'t know of anyone -- other than Relativists creating\nstrawmen -- who seem to use the concept of absolute reference frames.\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>Italo Vecchi <vecchi@weirdtech.com> wrote in message
news:61789046.0406070954.6c6bcf66@posting.google.c om...
> "greywolf42" <mingstb@marssim-ss.com> wrote in message
news:<10c1jsonljs4d7f@corp.supernews.com>...
>
> > The presence of the CMB frame in an aether theory is not merely a
personal
> > preference -- it is a requirement of the theory.
> >
> > Your attempt to claim that the use of the word 'special' indicates
nothing
> > more than a personal preference is merely a strawman argument. (And a
> > continuation of the word game.) This discussion is entirely about the
'laws
> > of nature', not about personal preferences.
>
> I would think twice before attributing the choice of a reference frame
> to "nature" (whatever that means) rather than to an observer.

??? I made no such attribution. Nature makes no choices. 'Twas the
moderator's note that asserted that 'special' implied a personal choice.

> The
> history of science suggests that claims about absolute reference
> frames tend to reflect the observer's inability to appreciate the
> relativity of his/her perspective.

I agree. But then I don't know of anyone -- other than Relativists creating
strawmen -- who seem to use the concept of absolute reference frames.

--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}

Kirk Gregory Czuhai

Jun17-04, 06:13 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>Tim S <Tim@timsilverman.demon.co.uk> wrote in message news:<BCE27EEC.AE15%Tim@timsilverman.demon.co.uk>. ..\n> on 31/05/2004 10:21 pm, paragorn at paragorn18@hotmail.com wrote:\n>\n> > Hello,\n> > I am sorry if this a stupid question but when the age of the Universe\n> > since the Big Bang is given , what is the the reference frame used ?\n> > Doesn\'t that depend on the choice of the inertial reference frame? Or\n> > is it just that it is the earth reference frame?\n> > Thanks and please be gentle :-)\n> >\n>\n> There are no inertial reference frames in curved spacetime. However, the\n> universe we live in happens to have (approximately) a nice frame called the\n> co-moving frame. In a pure big bang model (a \'Friedmann-Robertson-Walker\'\n> spacetime) comoving time is the time experienced by the uniformly expanding\n> matter. On a very large scale, this sort of model is an excellent\n> approximation to the real world. On a smaller scale, it\'s not so good\n> (because the matter isn\'t perfectly homogeneous or uniformly expanding) but\n> it\'s mostly not too bad. Alternatively you can think of comoving time as the\n> time experienced in the rest frame of the cosmic microwave background\n> radiation, as that is very close to uniform.\n>\n> Tim\n\ni suppose the lifetime of a supernova or any star could be used as an\nestimate for the "lower limit" of the lifetime of the universe but so\ncould my life time!\n\nIs it not true that the measurements leading to the calculation of\nHubble\'s constant is still the best estimate that leads to the\nestimate for the lifetime of the universe? This of course requires\nassumptions about the the spacetime and carries an uncertainty. But\nrecently i read in the popular press that the universe was estimated\nto be "150 billion light-years in \'diameter\'".\n\n75 billion light-years makes one wonder what one needs a 14 billion\nlight year estimate for?\n\npeace and love,\n\n(kirk) kirk gregory czuhai\nhttp://www.altelco.net/~lovekgc/lovebridge.htm\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>Tim S <Tim@timsilverman.demon.co.uk> wrote in message news:<BCE27EEC.AE15%Tim@timsilverman.demon.co.uk>...
> on 31/05/2004 10:21 pm, paragorn at paragorn18@hotmail.com wrote:
>
> > Hello,
> > I am sorry if this a stupid question but when the age of the Universe
> > since the Big Bang is given , what is the the reference frame used ?
> > Doesn't that depend on the choice of the inertial reference frame? Or
> > is it just that it is the earth reference frame?
> > Thanks and please be gentle :-)
> >
>
> There are no inertial reference frames in curved spacetime. However, the
> universe we live in happens to have (approximately) a nice frame called the
> co-moving frame. In a pure big bang model (a 'Friedmann-Robertson-Walker'
> spacetime) comoving time is the time experienced by the uniformly expanding
> matter. On a very large scale, this sort of model is an excellent
> approximation to the real world. On a smaller scale, it's not so good
> (because the matter isn't perfectly homogeneous or uniformly expanding) but
> it's mostly not too bad. Alternatively you can think of comoving time as the
> time experienced in the rest frame of the cosmic microwave background
> radiation, as that is very close to uniform.
>
> Tim

i suppose the lifetime of a supernova or any star could be used as an
estimate for the "lower limit" of the lifetime of the universe but so
could my life time!

Is it not true that the measurements leading to the calculation of
Hubble's constant is still the best estimate that leads to the
estimate for the lifetime of the universe? This of course requires
assumptions about the the spacetime and carries an uncertainty. But
recently i read in the popular press that the universe was estimated
to be "150 billion light-years in 'diameter'".

75 billion light-years makes one wonder what one needs a 14 billion
light year estimate for?

peace and love,

(kirk) kirk gregory czuhai
http://www.altelco.net/~lovekgc/lovebridge.htm

Ulmo

Jun22-04, 01:03 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>lovekgc@altelco.net (Kirk Gregory Czuhai) wrote in message news:<68c18740.0406142339.43fa6483@posting.google. com>...\n> But\n> recently i read in the popular press that the universe was estimated\n> to be "150 billion light-years in \'diameter\'".\n>\n> 75 billion light-years makes one wonder what one needs a 14 billion\n> light year estimate for?\n>\n\nI\'m guessing that this is a reference to theories that we live in a\nclosed finite volume universe, which if this is the case, couldn\'t\nhave a radius less than 75 billion years, and appear as spatially flat\nas it does. Of course, when people say "universe", they are usually\nreferring to the "observable universe", which of course has a radius\nof 13.7 billion light years.\n\nDavid\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>lovekgc@altelco.net (Kirk Gregory Czuhai) wrote in message news:<68c18740.0406142339.43fa6483@posting.google.com>...
> But
> recently i read in the popular press that the universe was estimated
> to be "150 billion light-years in 'diameter'".
>
> 75 billion light-years makes one wonder what one needs a 14 billion
> light year estimate for?
>

I'm guessing that this is a reference to theories that we live in a
closed finite volume universe, which if this is the case, couldn't
have a radius less than 75 billion years, and appear as spatially flat
as it does. Of course, when people say "universe", they are usually
referring to the "observable universe", which of course has a radius
of 13.7 billion light years.

David

ebunn@lfa221051.richmond.edu

Jun27-04, 05:59 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 <68c18740.0406142339.43fa6483@posting.google.com>, \nKirk Gregory Czuhai <lovekgc@altelco.net> wrote:\n\n>Is it not true that the measurements leading to the calculation of\n>Hubble\'s constant is still the best estimate that leads to the\n>estimate for the lifetime of the universe? This of course requires\n>assumptions about the the spacetime and carries an uncertainty.\n\nAs you say, without knowing about the spacetime geometry (including\nnot just whether space is flat today but also how the expansion rate\nchanged in the past), you can\'t get an estimate of the age of the\nUniverse, even if you know the Hubble constant perfectly. (Instead of\nsaying that we need to know the spacetime geometry, people usually say\nwe need to know the densities of matter and the cosmological constant\n/ dark energy. As long as general relativity is right and the\nUniverse is described by the Friedmann equation, these are\nequivalent.)\n\nThe high-precision estimates you often hear nowadays for the age of\nthe Universe come from a combination of data:\n\n- The microwave background power spectrum from WMAP and other\nexperiments, which implies a spatially flat Universe and also allows\nestimates of the matter and dark energy densities and of the Hubble\nconstant.\n\n- Observations of high-redshift supernovae, which complement the\nmicrowave background observations to pinpoint the dark matter and\ndark energy densities more accurately.\n\n- Direct measurements of the Hubble constant.\n\nSurprisingly, I think that the last one is actually the *least*\nimportant today in determining the age of the Universe. That is, even\nif you throw away the direct measurements of H, you can still get H\naccurately enough from the CMB alone to give a good determination of\nthe age. On the other hand, if you throw away the matter and energy\ndensities from the other two sources, you can\'t get a good age\nestimate at all.\n\nOf course, the most important part is that the estimates that you get\nare all consistent with each other: the value of H from direct\nmeasurements is consistent with the WMAP power spectrum, for instance.\nIt didn\'t have to turn out that way.\n\n\n>But\n>recently i read in the popular press that the universe was estimated\n>to be "150 billion light-years in \'diameter\'".\n\nIf I could have one wish (well, one Usenet-related wish), it would be\nthat people would never again mention something that they\'d read "in\nthe press" without saying where and precisely what they\'d read.\n\nIf you really read something that said that, then you read something\nwrong. (This wouldn\'t be at all surprising, of course. Wrong\nstatements in science journalism are not exactly scarce.) There is no\nrational basis for saying that the Universe has been estimated to be\n150 billion light-years in diameter. With a bit of extra theoretical\nassumption, one could justifiably claim that the Universe must be *at\nleast* this big (for instance, if inflation is right, that is almost\ncertainly a safe bet). But there\'s no evidence at all against the\npossibility that the Universe is, say, 500 quintillion light-years in\ndiameter.\n\n-Ted\n\n--\n[E-mail me at name@domain.edu, as opposed to name@machine.domain.edu.]\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 <68c18740.0406142339.43fa6483@posting.google.com>,
Kirk Gregory Czuhai <lovekgc@altelco.net> wrote:

>Is it not true that the measurements leading to the calculation of
>Hubble's constant is still the best estimate that leads to the
>estimate for the lifetime of the universe? This of course requires
>assumptions about the the spacetime and carries an uncertainty.

As you say, without knowing about the spacetime geometry (including
not just whether space is flat today but also how the expansion rate
changed in the past), you can't get an estimate of the age of the
Universe, even if you know the Hubble constant perfectly. (Instead of
saying that we need to know the spacetime geometry, people usually say
we need to know the densities of matter and the cosmological constant
/ dark energy. As long as general relativity is right and the
Universe is described by the Friedmann equation, these are
equivalent.)

The high-precision estimates you often hear nowadays for the age of
the Universe come from a combination of data:

- The microwave background power spectrum from WMAP and other
experiments, which implies a spatially flat Universe and also allows
estimates of the matter and dark energy densities and of the Hubble
constant.

- Observations of high-redshift supernovae, which complement the
microwave background observations to pinpoint the dark matter and
dark energy densities more accurately.

- Direct measurements of the Hubble constant.

Surprisingly, I think that the last one is actually the *least*
important today in determining the age of the Universe. That is, even
if you throw away the direct measurements of H, you can still get H
accurately enough from the CMB alone to give a good determination of
the age. On the other hand, if you throw away the matter and energy
densities from the other two sources, you can't get a good age
estimate at all.

Of course, the most important part is that the estimates that you get
are all consistent with each other: the value of H from direct
measurements is consistent with the WMAP power spectrum, for instance.
It didn't have to turn out that way.

>But
>recently i read in the popular press that the universe was estimated
>to be "150 billion light-years in 'diameter'".

If I could have one wish (well, one Usenet-related wish), it would be
that people would never again mention something that they'd read "in
the press" without saying where and precisely what they'd read.

If you really read something that said that, then you read something
wrong. (This wouldn't be at all surprising, of course. Wrong
statements in science journalism are not exactly scarce.) There is no
rational basis for saying that the Universe has been estimated to be
150 billion light-years in diameter. With a bit of extra theoretical
assumption, one could justifiably claim that the Universe must be *at
least* this big (for instance, if inflation is right, that is almost
certainly a safe bet). But there's no evidence at all against the
possibility that the Universe is, say, 500 quintillion light-years in
diameter.

-Ted

--
[E-mail me at name@domain.edu, as opposed to name@machine.domain.edu.]