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Physics/sub-atomic particles

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Question
Hi,

If the mass of the atom matches with the sum of mass of all the sub-atomic particles that have been discovered till now, does that mean we have completely identified all the sub-atomic particles that has mass.

Regards.

Answer
First, the mass of an atom does not equal the mass of all subatomic particles that have been discovered until now.  It is equal to the masses of all the particles which make it up, minus a correction for the binding energy of the atom (E=mc^2).  So that statement is wrong to start with.  Also, we know there's mass in the universe which exerts gravity, but which we have never observed.  We know there are things out there which are yet to be directly observed, or galaxies would rotate slower (for just one thing).

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Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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