New Directions
or
Everything Your Know Is Rong
This logo denotes A102 appropriate
At the End of the 19th Century, a certain
scientific smugness was in the air
 Munich
physics professor Philipp von Jolly
advised his student Max Planck against
going into physics:

“…in this field, almost everything is already
discovered, and all that remains is to fill a few
holes.”
 Lord

Kelvin,1900:
“There is nothing new to be discovered in
physics now. All that remains is more and
more precise measurement.”
Albert Michelson, America’s
first Nobel Prize winner:

“The more important
fundamental laws and facts
of physical science have all
been discovered, and these
are now so firmly established
that the possibility of their
ever being supplanted in
consequence of new
discoveries is exceedingly
remote . . . Our future
discoveries must be looked
for in the sixth place of
decimals.”
 In
1899, the head of the United States
Patent Office, Charles Duell, allegedly
argued to close the Patent Office because
"everything that could have been invented,
has been invented.“

A


This could be apocryphal, but it illustrates the
mood
recurrent theme
Resurfaced at the end of the 20th century
Hubris, hubris, hubris
"Flight by machines heavier than air is impractical and insignificant, if not utterly impossible."
-- Simon Newcomb, Director, U.S. Naval Observatory, 1902
Clouds

There were a few unresolved issues, however
 1900: Lord Kelvin gave a lecture to the Royal
Institution of Great Britain titled “NineteenthCentury Clouds over the Dynamical Theory of
Heat and Light”
 He was talking about the null result of the
Michelson-Morley experiment and the problems
of blackbody radiation



Where was the ether?
Why are there discrete spectral lines?
Also, what the heck is Brownian Motion?
The Luminiferous Aether

Proposed by Aristotle
and again almost 2000
years later by
Descartes
 1881: Albert
Michaelson, along with
Edward Morley, set out
to find it
 The idea is this: if light
is a wave, then it must
travel through a
medium, like water
waves
 Therefore waves will
be different going with
the “current” than
across it
It’s still here!
Null Result
 Michaelson
and Morley found no evidence
of any aether
 Then how could light be a wave?

Recap:
• 1670: Huygens; light is a wave
• 1699: Newton; light is a stream of particles
• 1801: Thomas Young; light is a wave
 So
now what?
And then there’s Discrete Spectra

If light comes from
accelerated electrons
and light carries away
energy from the
electrons, why
doesn’t all matter
collapse as energy is
lost?
Resolutions circa 1910

Energy isn’t continuous but comes in discrete
packets called quanta



Light is neither a particle nor a wave but has the
qualities of both




The death of continuum physics and the birth of
quantum physics
Max Planck (a converted continuist); his “kludge” from
the Spectra PPT was a major instigator
And therefore requires no aether to propagate
Demonstrated by Einstein and later by Compton
Both denied ‘common sense’
Both required new ways of thinking
Einstein vs Newton
Newton’s Universe



Objects attract each other
with a force proportional
to their masses and
inversely proportional to
the square of the distance
between them
There is an absolute state
of rest
“Law” for almost 200
years, but with a cause
for gravity
Albert Einstein (1879-1955)
 Life/Career
 Achievements
 Important
Publications




1905 papers
1915 papers
1921 Nobel Prize
1935 EPR
Einstein’s Universe



General Theory of
Relativity, 1915
Mass curves space
*There is not absolute
state of rest

i.e. there is no perfect
place from which to view
the Universe

*All motion is relative,
but the speed of light is
fixed for everyone

BTW, Einstein explained
Brownian Motion in a 1905
paper
*Special Theory of Relativity, 1905
William Wallace Campbell





Director of Lick Observatory 19001930
Pioneer of the astronomical
spectroscopy; catalogued radial
speeds of stars.
Tried to confirm Einstein’s theory with
eclipse viewed in Kiev
Clouds!
Tries again in 1918 in WA


Bad gear, no confirmation
Goes to London to report negative
result
Sir Arthur Eddington

An English pacifist during WWI




Felt kinship with German
pacifist Einstein
Wanted to show science was
above politics
Also, first to propose a fusion-like
process for the Sun’s energy
Journeyed to island of Principe
off Africa for the best view of
1919 eclipse
 Results nebulous, but
Eddington wires London with
confirmation
Confirmed
 1922,
WWC goes to Australia for eclipse
viewing, confirms GT with 92 stars
Modern Testing
 Cassini
Spacecraft
sends back radio
signals from Saturn
 The curvature of
spacetime near the
Sun is tested
 Einstein is correct!
Gravitational Lensing
Microlensing
 Used



for:
Additional
magnification of
distant objects
Evidence of dark,
intervening objects
Space-time
curvature data
In other words:
 “Mass
tells space how to bend and space
tells matter how to move”
 GR predicts many things that were
heretical at the time


Stars, under certain conditions, can shrink to
nothing with infinite density
It is unlikely that the Universe is static
1914-1918: WWI


Karl Schwarzschild (18731916)
Child prodigy




Published a paper on orbits at
age 16
His son Martin also became a
famous Astrophysicist
Member of Prussian Academy
of Sciences up until the war
Joined the German army at
age 41

Submitted papers while serving in
Russia

1915: found a solution to GR that allowed stars to
collapse into zero volume and infinite density



Later named “Black Holes” by John Wheeler
KS was not the first mathematician to conceive of such things
Einstein verified the solution but didn’t like the
consequences
Massive Stars

If a giant star at the end
of its giant phase has >
1.4 Msun, it will collapse
suddenly and then
violently explode as its
materials rebound off a
superdense core
 There is about 1 SN
every century in our
galaxy, 1 every second in
the Universe
 In a few weeks they emit
more energy than the
Sun does in a century

However, if the giant
star has > 3 Msun at
the end of its giant
phase, the explosion
stalls due to the
overwhelming gravity,
and the star continues
to collapse to an
infinitely tiny point, or
singularity
 Space is so tightly
curved around it that
nothing can escape
To sum up GR (a little):

But he realized that his equations wouldn’t
permit this stability



Remember Poisson’s equation?
It says that the condition of no acceleration (e.g. no
gravitational force) can only exist in an empty
Universe
Introduced a cosmological constant, L (lambda),
into GR to counteract any acceleration that
would change his static model
The Steady State Model
 One
assumption that underlay the
discussion of the shape of the cosmos
was that the Universe was eternal and
unchanging
 SSM formally posed in 1948, but its
demise was already present in GR
 The idea was hard to bury, despite being a
source of paradox
Kepler’s *Paradox (AKA Olber’s Paradox)


If the Universe is eternal
and infinite, why is the
sky dark at night?
In Kepler’s words: “If [this]
is true, and if they are
suns having the same
nature as our sun, why do
not these suns
collectively outdistance
our sun in brilliance?”
*Ryden’s Law of Misonomy – Olber actually saw no paradox,
stating that the universe soaks up a little light from every star
Not So Steady

1692: Newton receives a letter from theologian
Richard Bentley


Newton replies that it would be static


Asks Newton how would the Universe change with
time if all matter was initially distributed perfectly
symmetrically
But perfect symmetry is as likely as “an infinite
number of needles standing on their tips on a mirror”
Bentley replies that isn’t that the same likelihood
as an infinite number of fixed stars?
Learning to Love L*
 Einstein
himself held that the Universe
was static and homogeneous with
spherical geometry


Remember, in 1915 when he produced GR, 5
years before The Great Debate, the scope of
the Universe was not known
He therefore looked at only stars in the MW
and saw that there was no obvious expansion
or contraction
*With a nod to Dr. Barbara Ryden
Alexander Friedman 1888-1925

Russian
Mathematician and
Cosmologist
 Like Schwarzschild
found a solution to
GR
 His 1922 solution
showed that GR
predicted an
expanding Universe
 1929 Hubble data
confirmed this
Edwin Hubble’s work, circa 1925

His observations helped settle the Great Debate
 But they also posed a new question:

Why is practically everything in the Universe moving
away from us?
Bigger and Bigger
Hubble’s data
suggests that the
Universe is
expanding
 Not only that, more
distant objects are
moving away faster
 Hubble determined
these distances
and velocities using
red shift

Blunder

With Hubble’s discovery Einstein removed L and
called the constant his “greatest blunder”

“Much later, when I was discussing cosmological
problems with Einstein, he remarked that the
introduction of the cosmological term was the biggest
blunder of his life”. -- George Gamow, My World Line, 1970
he was right: L is back in
modern cosmology
 Ironically,
• If only he had stuck by his guns!
Georges Lemaître 1894-1966

Belgian Roman
Catholic Priest and (!)
Cosmologist
 1927 submitted a
paper that
independently arrived
at Friedman’s solution


Primordial atom
Einstein read both
and, at the time,
dismissed them
Expansion of the Universe
A

tricky idea
What is not happening:
• Objects are getting bigger
• The space in atoms is increasing

Proper motion is not part of the expansion
 Expansion
means that space is stretching,
like polka dots on the surface of an
inflating balloon with conditions
 Regardless
of how, Hubble showed, and
Einstein agreed, that the Universe was
indeed expanding
 This implies:



The Universe is not static
The Universe is not infinitely old
The Universe had a beginning
 However,
at first, Hubble’s equation was
good but his measurements were off,
causing the Universe to be too young at 2
Gyr.
And this explains it all, right? 



Called the Robertson-Walker metric (AKA FLRW)
Shows how space and time scale with expansion
For the curious:

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Distance: s
Cosmological scale factor: a
Time: t
Curvature: k
Radial distance: r
Azimuth angle Q
Altitude angle: f
In a way, it’s like measuring distances on the surface of the Earth


It’s not that
everything in
the Universe is
expanding in a
big box, it’s that
the box itself is
expanding
How it expands
is the subject of
Cosmology


The so-called
Big Bang is
just a part of
the subject
(details to
follow later)
Still there were doubters

Sir Frederick Hoyle
1915-2001
 Respected
Astrophysicist

Postulated stellar
nucleosynthesis

Proponent of Steady
State Theory
 Dismissed Friedman’s
idea of a “Big Bang”

Cited 2 Gyr cosmos
SSM

Hoyle and his camp agreed that the Universe
was expanding
 But to avoid a “beginning” he had the Universe
constantly creating matter between the galaxies
Karl Jansky 1905-1950

1931: discovered radio waves
emanating from the Milky Way

A clue!
George Gamow



With colleagues *Ralph Alpher and
Robert Hermann pictured the early
Universe as a nuclear oven in which
light elements were cooked, backing up
the Big Bang theory
They posed that the earliest
temperatures would be staggeringly
high ~ 100 billion K
During the late 1940s and early 1950s
they made predictions that the cosmos
would have cooled like a blackbody
radiator to a temperature ranging from
5K to 50K

Evident as microwave radiation
•
Hoyle actually backed them up on this
while maintaining his SSM!
*GG’s grad
student, the
mathematician of
the group
Blackbody Radiation
Hot objects (T > 0K) emits a spread of “heat’
radiation
 Peak occurs ~ 1mm

CMB

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
Cosmic Microwave Background
First observed in 1940 by Andrew McKellar
Cyanogen excitation (0 -> 1) corresponds to 2.4K
These data were not recognized for what they were at
the time, or even in an important paper in 1950
Hissssssssssss


1965: Arno Penzias and
Robert Wilson, worked for Bell
Labs in NJ
Used an ultra-sensitive
microwave receiving system to
study radio emissions from the
Milky Way



Found an unexpected
background of radio noise
They consulted with Princeton
physicist Robert H. Dicke who
had predicted that if the Big
Bang theory was correct, a
background radiation at 3degree Kelvin would exist
This and better Hubble
measurements in 1949 verified
BB
Wilson explaining the noise
Cr.mpg
Another View

Wilkinson Microwave
Anisotropy Probe


The red regions are where
CMB photons, losing
energy as they climb out of
a gravitational potential, are
red-shifted


Colleague of Robert Dicke
And the reverse, of course
1967 calculations by Sachs
and Wolfe predicted this at
structures ~1o of arc

More on that in another ppt
The Future depends on L