inertial mass and gravitational mass [Archive]

alistair

Jun28-04, 12:10 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\n\nA photon has gravitational mass because it is deflected by the Sun.\nInertial mass is supposed to be the same as gravitational mass.\nSo why can\'t a photon have inertial mass too?\nBecause special relativity says that it has zero rest mass?\nOr are there other reasons?\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>A photon has gravitational mass because it is deflected by the Sun.
Inertial mass is supposed to be the same as gravitational mass.
So why can't a photon have inertial mass too?
Because special relativity says that it has zero rest mass?
Or are there other reasons?

Pmb

Jun30-04, 05:37 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:861c1b21.0406251152.475cb627@posting .google.com...\n>\n>\n>\n>\n> A photon has gravitational mass because it is deflected by the Sun.\n> Inertial mass is supposed to be the same as gravitational mass.\n> So why can\'t a photon have inertial mass too?\n\nPhotons do have inertial mass, where "inertial mass" is defined as m = p/v\n\nPmb\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:861c1b21.0406251152.475cb627@posting.google.c om...
>
>
>
>
> A photon has gravitational mass because it is deflected by the Sun.
> Inertial mass is supposed to be the same as gravitational mass.
> So why can't a photon have inertial mass too?

Photons do have inertial mass, where "inertial mass" is defined as m = p/v

Pmb

Michael Varney

Jul2-04, 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>\n\n"Pmb" <someone@somewhere.com> wrote in message\nnews:B-ednb9QE4hSG33dRVn-gw@comcast.com...\n> "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\n> news:861c1b21.0406251152.475cb627@posting.google.c om...\n> >\n> >\n> >\n> >\n> > A photon has gravitational mass because it is deflected by the Sun.\n> > Inertial mass is supposed to be the same as gravitational mass.\n> > So why can\'t a photon have inertial mass too?\n>\n> Photons do have inertial mass, where "inertial mass" is defined as m = p/v\n\nTo clarify what PMB is saying:\n\nA single photon does not have inertial mass.\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>"Pmb" <someone@somewhere.com> wrote in message
news:B-ednb9QE4hSG33dRVn-gw@comcast.com...
> "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
> news:861c1b21.0406251152.475cb627@posting.google.c om...
> >
> >
> >
> >
> > A photon has gravitational mass because it is deflected by the Sun.
> > Inertial mass is supposed to be the same as gravitational mass.
> > So why can't a photon have inertial mass too?
>
> Photons do have inertial mass, where "inertial mass" is defined as m = p/v

To clarify what PMB is saying:

A single photon does not have inertial mass.

Eduardo Rodríguez

Jul2-04, 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>\n\n> A photon has gravitational mass because it is deflected by the Sun.\n> Inertial mass is supposed to be the same as gravitational mass.\n> So why can\'t a photon have inertial mass too?\n> Because special relativity says that it has zero rest mass?\n> Or are there other reasons?\n\nA photon has zero mass (inertial and/or gravitational) but nonzero momentum;\naccording to the relativistic relation E^2 = p^2c^2 + m^2c^4, it has energy\nE = pc and thus can even curve spacetime around it! On the other hand,\nmassless particles in General Relativity move along null geodesics, so\nthere\'s no need for the photon to have a nonzero mass in order to follow a\npath which looks "curved" from our three-dimensional perspective.\n\nPhotons are massless (insofar as one can answer "why") because the\nelectromagnetic field is a U(1) gauge field and gauge invariance forces it\nto be massless, even in the quantum theory. Other non-abelian gauge fields\nacquire masses in the quantum theory thorugh "spontaneous symmetry\nbreaking", but I don\'t feel comfortable enough with this idea to be able to\nsay any further.\n\nI\'d be glad to hear more comments about these matters!\n\nEduardo\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>A photon has gravitational mass because it is deflected by the Sun.
> Inertial mass is supposed to be the same as gravitational mass.
> So why can't a photon have inertial mass too?
> Because special relativity says that it has zero rest mass?
> Or are there other reasons?

A photon has zero mass (inertial and/or gravitational) but nonzero momentum;
according to the relativistic relation E^2 = p^{2c}^2 + m^{2c}^4, it has energy
E = pc and thus can even curve spacetime around it! On the other hand,
massless particles in General Relativity move along null geodesics, so
there's no need for the photon to have a nonzero mass in order to follow a
path which looks "curved" from our three-dimensional perspective.

Photons are massless (insofar as one can answer "why") because the
electromagnetic field is a U(1) gauge field and gauge invariance forces it
to be massless, even in the quantum theory. Other non-abelian gauge fields
acquire masses in the quantum theory thorugh "spontaneous symmetry
breaking", but I don't feel comfortable enough with this idea to be able to
say any further.

I'd be glad to hear more comments about these matters!

Eduardo

mathman

Jul2-04, 04:32 AM

Photons have zero rest mass. The inertial and gravitational masses (equal) are determined by its energy.