What force holds an oxygen atom to another in O2? A] gravity B] electromagnetic force C] strong nuclear force D] weak nuclear force

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What force holds an oxygen atom to another in
O2?A gravityB electromagnetic forceC
strong nuclear forceD weak nuclear force
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The strong nuclear force occurs because of the
exchange of massive mesons between
protons/neutrons. We will discuss the
constituents of mesons protons neutrons
shortly.
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Through careful experimentation, you discover a
force of attraction between two people. It only
acts over a short range! There is no force if the
separation is gt 1 m. In keeping with physical
nomenclature, you call this force smell. There
are apparently two smells, nice and nasty.
Like attracts like. What is the mass of the
odoron, the quantum of the smell field?A
zeroB smaller than an electronC about as big
as a strongly flavored quarkD the same as a ton
of bricks
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The mass of the exchange particle is only one
possible limitation on range (through the
Heisenberg uncertainty.)The force will have a
short range if the energy required for long
range action exceeds the Heisenberg limit.
This is the case with quark-quark
interactions.Because the gluon carries color
charge, a gluon field emits more gluons. The
energy in all these gluons must be considered in
the Heisenberg limit in other words, there is an
effective mass that you get when you take into
account all the interaction energy.This is why
a) the color force is finite range and b)
color cannot be isolated.
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All observable hadrons are colorless. (Pulling a
red quark out of a proton would require so much
energy that you would make an anti-red and a red,
ending up with the proton and a meson.)
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Murray Gell-MannProfessor of Physics(now)
University of New Mexicoproposed Quarks in 1964
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Quarks (Baryons) Leptons Antiparticles
Top Bottom rows are different flavors Proton
decay is u d e ?e This conserves
lepton number baryon number And also keeps the
flavor difference constant in the
universe (adding one net particle of each
flavor.) Electrons, muons, taus are also said
to have different flavor. This is not conserved.
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Antiparticles
Whats the deal with antiparticles? Dirac wrote
down a relativistic version of the Schroedinger
Eqn. He found it had both positive and negative
energy solutions for e-. (Not surprising, since
it had to be second order in time!) Rather than
discard the negative energy solutions as
spurious, (as any sane or modest person would
do) he hypothesized that the negative energy
states were filled with unobservable electrons.
Moving an e- up out of this sea would leave a
hole of charge, that acts just like an
antielectron. Feynman showed that antiparticles
are just regular particles going backward in
time. This eliminates the need to postulate an
unobservable e- sea perhaps at the psychic
expense of worrying about backward time.
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The Big Bang The Expanding Universe
Distant galaxies are receding (Doppler shift of
spectral lines)
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The Big Bang The Expanding Universe
There is (probably) no center for expansion. To
have a center, you need a boundary.
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The Big Bang The Expanding Universe
If the universe is expanding, it must have been
denser and hotter in the past. We can sample
physics at higher temperatures (higher energies)
in accelerator experiments, and thus we can
extrapolate the current universe back to very
nearly its beginning.
lt380,000 years after the bang, the average energy
per particle is gt electronic binding energy.
There are no atoms, only ions, which scatter
light. The universe is opaque.
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A hundred seconds after the bang, the average
kinetic energy per particle is greater than
nuclear binding energy there are no nucleii A
microsecond after the bang, there is quark soup
no neutrons, or protons.
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Prof. Fields makes quark soup on Long Island.
What happened before the universe was quark soup
is mostly speculation. We dont have experiments
to test different ideas. We think the forces
should be unified.
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thought
We think we understand physics until here (or so)
You are here
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Gravitational Lensing Dark Matter
The bending of light by massive galaxies, And
the rotation rates of galaxies Both indicate A
LOT more mass than can be accounted for by stars
dust.
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Accelerating Expansion - Dark Energy
When we look carefully at the Doppler redshifts
of distant galaxies, they are smaller than Hubble
predicts. The expansion of the universe used to
be slower! Gravitational attraction should slow
the expansion down! Maybe the universe has stuff
in it pushing the expansion - dark energy Maybe
general relativity is wrong. Maybe there is
large-scale structure in the universe we are
unaware of.
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A few things we dont understand

• We havent been able to write a sensible
  complete theory combining General Relativity and
  QM
• Although the quantization of fields seems to work
  well (and makes verified predictions), it also
  predicts an infinite energy density (recall that
  even the ground state of a quantum system has
  some energy!)
• Although electrons appear to be pointlike
  particles, that would give them infinite self
  energy in their Coulomb field, and so infinite
  mass.
• We dont understand why charge is quantized, and
  mass isnt.
• We dont understand WHY there are three
  generations of matter.
• We dont understand the accelerating expansion of
  the universe
• We dont know what dark matter is.

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What is a perfect theory of everything?

• In physics, a perfect theory (IMO) shows how all
  physical laws and behaviors arise from the
  smallest set of postulates.
• In a perfect theory, we look at the small set of
  postulates and say, given that these are true,
  the universe could not be other than it is.
• (As an example, given that the spacetime has its
  geometry, Coulombs law, all of
  electromagnetism must follow!)
• There is a regression to smaller and smaller sets
  of postulates, and more basic (quasi-philosophical
  ) questions. For example, why does spacetime have
  Minkowski geometry? We dont know.

BUT WE CAN KNOW! The most incomprehensible thing
about the universe is that it is comprehensible!
- A Einstein
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