10C's : C9, C10
C9
Evolution of Stars and the Universe
[See lectures, class web pages, HWs &
solutions, & TB1, as specified below (all figures referred to are from
TB1) .]
Our Star
** Brief history of the Sun
** How it shines; Fig. 15-7.
*** Professor Hans Bethe
of Cornell U got the Nobel Prize in 1967 for his contribution to the understanding
of star energy
** "Tug of war" between gravitational pull and nuclear
fusion energy push out ---- gravitational/fusion pressure balance or equilibrium.
*** See Fig. 15.8.
** Fusion vs fission, Fig. 15.5;
** Layers of the Sun, Fig. 15.4;
** Studying Sun by Doppler effect: Fig. 15.9
The cosmic distance ladder ( Fig. 20.21.)
** Step 0, up to 10^-4 ly (the solar system):
trigonomitry (e.g. Erotasthenes) and/or radar ranging;
** Step 1, up to 10^2 ly (near by stars): parallax
(see Fig. 16.3);
** Step 2, up to 10^5 ly (Milky Way): Main-Sequence
fitting (using the H-R diagram; see Fig.16.10, and Fig. 20.11).
** Step 3, up to 10^7 ly (near by galaxies): Cepheids
variables (using their brightness/period relation established in the galaxies
whose distances were well establised in the previous steps);
** Step 4, up to 10^10 ly (galaxy clusters);
** Step 5, up to R_ob, the radius of the observable
universe. (Remember to review the definition of obserbable U.)
The age of the universe (cosmic age) is nothing but (approximately
equal to) the inverse of the Hubble constant,
T_U = 1/H_0 =
1.4 x 10^ 10 yr.
(See, section 20.4 of TB1.)
Gravitational lensing: Figs. 22.9, 22.10, and dark matter (e.g.
MACHOS, Fig,.22.12)
Fate of the universe: Figs. 22.17, 22.18.
Eras of the universe: Fig. 23.2. Of particular importance
is the form the now cosmic microwave background (CMB). See its Planck
distribution shown in Fig. 23.7.
C10
Theory of Everything (TOE)
(This is what the whole TB2 tries to elaborate. The following characterizations
are given by Chau and she will elaborate them in future classes.)
* This is a hope. We do not know whether there is such a
thing as the Theory of Every Theory. We can probably characterize the
attempt better by "the pursuit of the next unification." Chances are that
nature has infinite richness, and human beings are privileged to be allowed
to find layer after layer of their understanding. The next layers that
scientists are searching for answers to are the following.
* Quantum gravity: a harmonious unification between the laws
for the large -- gravity, and the laws for the microscopic -- quantum
physics. The ingredients of the theory are, as already listed in C7:
** Particles with mass and/or energy
** Force particles: gravitons
** Force particles mediate gravitational force
among through masses and energy.
* Unified description of all four fundamental forces
** Strong and the electroweak have not been
successfully unified. Attempts have been continuingly made. Such a
unified theory will be call GUT (Grand Unified Theory). (Chapter 7 of TB2;
in particular p.175-178; and see the index in TB2.)
** While looking for a full solution
for quantum gravity, scientists are looking for its unification with
GUT.
* The full understanding of the evolution of the universe
:
** The understanding of the "beginning" of
the universe. There is a singularity in the "beginning" of the universe
in current theories. Maybe, there is no such a thing as "the beginning"
of the universe.
** The fate of the universe. The current puzzle
is that the expansion of the universe seems to be accelerating.
* The M-theory (the theory-to-be that unifies five apparently
different string theories), one of the most popular current theories,
has partial successes on the above mentioned topics, as eloquently indicated
by TB2.
** It uses supersymmetry, yet to be experimentally
verified.
** It uses extra dimensions, first proposed by
Klein and Kaluza in the early 20th century. Such extra dimensions are
yet to be verified experimentally.
******** This page is updated 2/14/05. ****************