Re: Lost Mass in Chemical Reactions

mmeron_at_cars3.uchicago.edu
Date: 02/07/05 

Date: Mon, 07 Feb 2005 22:59:06 GMT

In article <ALKNd.27991$Yu.23578@fed1read01>, "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:net@nospam.com> writes:
>Dear mmeron:
>
><mmeron@cars3.uchicago.edu> wrote in message
>news:JSBNd.4$25.1329@news.uchicago.edu...
>> In article <mrdNd.15432$Yu.1883@fed1read01>, "N:dlzc D:aol T:com
>> \(dlzc\)" <N: dlzc1 D:cox T:net@nospam.com> writes:
>>>Dear Sbharris:
>>>
>>>"Sbharris[atsign]ix.netcom.com" <sbharris@ix.netcom.com> wrote in message
>>>news:1107645762.970063.35010@g14g2000cwa.googlegroups.com...
>>>>>>I also think that it is important to point out that in the case of an
>>>...
>>>> Because total energy is always conserved, total mass is, also. Due to
>>>> the fact that all energy has mass.
>>>
>>>The mass of the photon has been experimentally determined to have 10^-51
>>>kg
>>>of *rest* mass or less. This is how mass is currently defined, rest
>>>mass.
>>>Which mass does the photon have, if "all energy has mass"? Invariant,
>>>relativistic, gravitational, inertial, rest, what?
>>>
>> Well, here is a small problem for you. Asume an electron and a
>> positron annihilating, reaulting in the usual two photons. What is
>> the mass of said two photons?
>
>I believe it is an odd number of photons, since one photon "created" the
>initial pair (wherever that was), and spin is conserved.
>
One photon *cannot* create the original pair, that would violate
conservation of momentum/energy. It takes one photon interacting with
an additional particle to do pair creation. Thus, you cannot,
apriori, be sure what the spin of the pair is. Also, said electron
and positron do not have to have a common origin at all. So, again,
you know, apriori, nothhing of the spin. It is true, however, that
depending on the spin of the pair you may get either 2 or 3 photons.
The 2 photon decay is the most common.

>The mass would be measured to be m_e+ + m_e-, until the photons propagated
>beyond the "mass detector".
>
>How'd I do?

You're doing fine. So here is the thing, while a photon has zero mass,
photons (more than one) on the other hand, in general have a non-zero
mass.

Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"

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