jfh (08/09/82)
I wish to respond to Bob Morris' comments (floyd.428). First,
however I want to say that the first sentence of my reply ("Surely you jest!!")
was unwarranted, and I apologize to him for it.
I have no quarrel with either the assertion that the center of mass
does not change during a supernova explosion (within limits of asymmetries),
or with relativistic mechanics. However, I believe that Morris has made some
erroneous assumptions.
"Again, during a supernova explosion, the change in
mass is zero, both instantaneously and long term."
Consider the fusion of four hydrogen atoms to form helium. (I know the
overall reaction is much more complicated than this makes it sound, but
please bear with me. This is an approximation for illustration only.)
The mass of a hydrogen atom is 1.00797 atomic mass units (amu), so four
of them comprise a total mass of 4.03188 amu. However, a helium atom
has a mass of only 4.0036 amu. (data from Handbook of Chemistry and Physics,
46th edition) This leaves a difference of 0.02828 amu, which is converted
to energy in accordance with Einstein's equation. Surely no one will
argue that the mass of four hydrogen atoms is equal to the mass of one
helium atom.
"Photons do just as good a job of causing gravitation
as anything else of the same mass."
This is the statement to which my original reply was directed. Photons have
no REST mass; hence the are able to move at the speed of light. I believe
that this is a requirement for any entity which can attain this velocity, since
it can be demonstrated that any massive body would require infinite energy
input to reach light speed. I certainly do not deny that photons possess
energy, and that this energy is equivalent to a certain mass.
However, while I acknowledge that energy and mass are equivalent, it
appears to me that Morris is claiming that energy and mass are the SAME.
It is not at all clear to me that this is a defensible position. Does a
body composed of a certain number and type of particles become more massive
if it is strongly heated (vibrational energy is presumably also equivalent
to mass)? The crux of the matter seems to reside in the (paraphrased)
question asked by Mike Knudson (ihnss.126), "Does energy exert gravity?"
Specifically, is it possible for photons to emit gravitons, or is this
property reserved to those particles with non-zero rest mass?
It is equally unclear that I have illuminated the situation at all.
One could presumably argue in the fusion example that as long as you were able
to contain all the energy in a closed system things haven't really changed.
Does the ability to emit gravitons "define" mass? Comments on these questions
or on my interpretation of the arguments are welcome. Although I saw the
announcement of net.physics a few minutes ago, I am also posting this to
net.space also, just in case.
Fran Heidlage
duke!phs!jfhrhm (08/09/82)
O.K. I will reply specifically to duke!phs!jfh
1. If four hydrogen atoms conspire somehow to form a helium atom, then
the mass of the helium is exactly that of the hydrogen atoms.
2. Mass and energy are the same.
3. Yes, the mass of a collection of particles increases if they are heated.
4. Energy exerts gravity.
Altogether, rest mass doesn't have much do with anything.
These positions may or may not be defensible, but I will let any physics
text do the defending for me. They are hardly disputed questions.gdw (08/09/82)
#R:phs:-64800:harpo:11700002:000:259 harpo!gdw Aug 9 09:59:00 1982 I'm lost! I thought 4 hydrogen atoms do have MORE mass than a helium atom. That is how hydrogen bombs work, isn't it? So perhaps those arguing the mass issue could be more specific; are we talking rest mass or "dialated" mass if the helium is more energetic?
knutsen@SRI-UNIX@sri-unix (08/09/82)
From: Andrew Knutsen <knutsen@SRI-UNIX> Actually I seem to recall even the energy of a gravitational field is supposed to exert gravity... this produces some hairy math in gravitational theory.
BollenG.ES@PARC-MAXC@sri-unix (08/09/82)
It's very difficult to discuss issues in quantum physics via pontification, and even more difficult when one neglects to define one's terms. I found Floyd's four-point message not only unnecessarily high and mighty, but equally difficult to understand. When fusion takes place, all of the constituent atoms must be in high kinetic states in order to get close enough together to fuse. The end products of the fusion must then also be in high energy states. The end products of this reaction are He, plus some very fast moving neutrinos. The neutrinos shoot off into oblivion, carrying some of the mass of the constituent 4 Hydrogen atoms, while the exited He sits and radiates photons until it gets down to its ground-state energy. So, the mass of the final product is equal to the sum-mass of the constituents minus the equivalent energy that leaves with the radiated photons, minus the relativistic mass of the neutrinos that are also produced in the fusion. It is neither accurate nor complete to simply say that the mass of the Helium is exactly the mass of the 4 Hydrogens. The above may add a bit of clarity to the first of floyd's four axioms, the other three seem to me to be even less meaningful than the first. So i won't comment unless queried..... but may i suggest that for a complete discussion of these and myriad other physical phenom's (as well as some very entertaining reading) that the physics text to look at would be Feynman's Lectures in Freshman Physics. Feynman was a Pontiff extraordinaire! Gregfish.
G:wing (08/10/82)
I would like to add another note to the other response to this set. (This should be titled Re: Re; Equivalence of Mass and Energy - (nf)) I thought it took only TWO deuterium or triterium (what ever) atoms to create one helium atom, with the extra neutrons flying off to make a fusion torch?
ech (08/10/82)
I find it amazing that this correspondence continues: not because of the exchange itself, but because of the amazing willingness of netnews correspondents to make "ex cathedra" statements based on little information and less understanding. There is simply no way for the interested but naive reader to separate the statements of those who understand what's going on from those who glibly state misinformation as fact. Naivete with regard to relativistic physics is, perhaps, something we can expect in the netnews community: only a small fraction are physicists. Indeed, were I a professional physicist I would be either outraged or fatally amused at some of the drivel we have seen recently; as a mere interested layman I feel a little of both. What I find frightening is the same kind of behavior within the computer science domain, where we might expect some measure of professional competence. The network has great potential for educating us all; we (the users) are a diverse lot: we have highly varied backgrounds and avocations, as demonstrated by the proliferation of non-cs interest groups. The net can be a fine resource, especially for the kind of queries we so often see for information about a specific topic. The net is also, in the words of one of my colleagues, "the world's largest graffitti wall." So, this is the plea: if you have genuine, reliable information, please contribute it to the net. If not, stop talking and start listening: you might learn something. =Ned Horvath=