Transcript PowerPoint Presentation - Extragalactic Astronomy

[4246] Physics 316
Extragalactic Astronomy &
Cosmology
Lecture 2
Jane Turner
Joint Center for Astrophysics
UMBC & NASA/GSFC
2003 Spring
Other Early Cosmologies (?)
It should be remembered that our knowledge of history
is solely dependent us on having written records
Also few (if any) of the original works survive,
so we must rely on later works (true & complete reporting ?)
Who knows what ideas have been lost...
One (radical) idea that was not developed (apparently ignored)
is due to Aristarchus (c280BCE - between Aristotle & Ptolemy)
a Heliocentric universe - the Earth orbiting the Sun (!)
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Recap
The following should be remembered:
Cosmology one of the oldest philosophies/sciences
Many ancient cosmologies grappled with some of the same deep
philosophical questions we still ponder with today.
The Greeks first (we think)
reasoned that Universe was formed by natural processes
which could be observed, understood/explained by mathematics
Developed the Empirical Scientific Method
Developed a geocentric system (Pythagoras of Samos, c.550BCE;
Aristotle,c.350BCE) culminating with that of Ptolemy,c.150
involving a complex arrangement of spheres & epicycles.
Reason and beauty/perfection were a strong influence of their
thoughts.
The universe was reasoned to be finite but eternal/unchanging
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Recap
Greeks thought Earth was stationary, if it were moving, wouldn’t we
feel a sense of motion (great winds, loose objects whizzing by us etc)
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Recap (cont)
Mathematics (ie. the Ptolemaic system) seen as a parameterization,
By c.1400, the Ptolemaic (geocentric) system had remained
essentially unchallenged as the cosmology for 1300 years
You should be familiar with
the concept of Parallax
the basics of how the Ptolemaic system works
(how epicycles, deferent etc account for retrograde
motion).
the concept of Ockham's Razor
Again, a detailed knowledge of names, dates and places is not required
However, you should be familiar with at least the names & approximate
dates of Atristotle (c.350BCE) and Ptolemy (c.150).
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Early Summary of Developments
Thales
(c.585BCE) universe run by natural processes
Pythagoras (c.530BCE) spherical Earth
Anaxagoras(c.430BCE) “Heaven” is knowable
Plato
(c.420BCE) Geocentric, planets-circular orbits,
stationary Earth
Democritus (c.400BCE) Universe is a mechanical system
Eudoxus (c.340BCE) Geocentric cosmo, 33 spheres,
stationary Earth
Aristotle (c.350BCE) Geocentric cosmo, 55 spheres,
stationary Earth
Aristarchus (c.280BCE) Heliocentric cosmo ! (ignored)
Hipparchus (c.125BCE) Distance of Moon (scale on the cosmos)
Ptolemy (c.150)
Geocentric cosmo, Epicycles
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Foundatn of Modern Cosmo
Topics:
The Earth moves from Center Stage
And Then the Apple Dropped…
Summary at the beginning of the C20th
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
State of the Universe, 1400
By 1400, the geocentric cosmology of Aristotle & Ptolemy
(based on concentric spheres, epicycles etc) had been
essentially unchallenged for well over a thousand years.
However the Greek Empire, under which the studies of
Aristotle,Ptolemy had flourished (+ Pythagoras, Plato,
Aristarchus, Hipparchus ... etc !) long-since collapsed (c.410).
An Islamic Renaissance (refinement of Ptolemic model, but
radical new ideas) had come and gone by c.1100.
However, in the 15th & 16th centuries, following the years of the
"Black Death" & centuries of strife, the start of the Renaissance
in W.Europe finally allowed scientific & technological progress.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Rumblings of Discontent
In c.1430, Nicholas de Cusa published
On Learned Ignorance
In which he suggested
the universe is infinite
(also Anaxagoras of Clazomenae (c.430BCE)
and in a poem by Lucreutis (c.100BCE)
but generally ignored),
the universe does not have a center,
the pattern of stars would look the
same at all locations.
all motion is relative,
& that the Earth might not be stationary
Homogeneity & Relativity
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Earth moves from Center Stage...
The suggestion by Nicholas de Cusa (c.1430) that
the Earth might not be stationary,
was supported by Leonardo da Vinci (c1490),
who amongst many (!) other things also suggested
the Earth moves (rather than the Sun).
However it was not until 1543 when
Nicholas Copernicus publishes his
Revolutionibus Orbium Coelestium
(The Revolution of the Celestial Spheres)
that this idea was put of a more rigorous
footing.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Heliocentric Cosmology
Copernicus suggested
the planets rotate (on circles)
around a central Sun
….with "slower" planets being
further from the Sun.
Heliocentric Cosmology
Copernicus also acknowledged
the Earth rotates on its axis
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
A “Good” (Simpler) Model
The heliocentric model of Copernicus obviously could be used
to make predictions, that could be compared to observations.
It was simpler than the model of Ptolemy that it replaced.
However,
it’s predictions were not any better than those of Ptolemy’s model
unless (much smaller) epicycles were added
to quote Alan W. Hirshfeld, in
"Parallax - The Race to Measure the Cosmos"
"Having donned the Artistolelian straightjacket of uniform
circular motion....Copernicus has each planet circle at constant
speed in a small epicycle whose center moves uniformly
around the Sun."
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Copernicus gets the credit, but..
to quote Alan W. Hirshfeld again, in
"Parallax - The Race to Measure the Cosmos”
"De Revolutionibus may have triggered the
so-called Copernican Revolution,
but it was not the revolution itself”
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The Cosmological Principles
Cosmological principles are the
assumptions which allow us to deduce
the whole of nature on the basis of the
observable to the unobservable. Not
surprisingly, any study of cosmological
principles must combine elements of
astronomy, physics and philosophy.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The Cosmological Principles
One of the most important aspects of
Copernicus’ work - took his
heliocentric model, went further and
made a model for the cosmos, by saying,
lets assume several things, then use
observations to test whether this is a
good model
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The Cosmological Principles
There are several flavours of Cosmological Principle, all of which
are essentially metaphysical in nature:
The Copernican Cosmological Principle
This is sometimes simply referred to as simply
“The Cosmological Principle”
The other cosmological principles are extensions of this
principle.
The Perfect Cosmological Principle
The Anthropic Cosmological Principle
This principle comes in two "flavours" Weak and Strong.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The Copernican Cosmo Principle
The Copernican Cosmological Principle is a logical
extension of the the Copernican theory that the Earth is
not the center of the universe.
Thus the Earth is not "special", thus the "laws of
nature" on (or around) Earth are not special.
It is essentially a philosophical
requirement/simplification necessary/assumed for all
modern cosmologies:
- our laws of physics are otherwise "irrelevant"
- "justified" by Ockham's Razor
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The CCP itself
The Copernican Cosmological Principle is that
On a large scale, the universe is both
homogeneous and isotropic (in 3-D space),
and has/will always be so.
Note that the statement "has/will always be so" refers to the
universe continuing to display the properties of homogeneity &
isotropy.
The CCP does not imply that any actual observable parameter
(e.g. the density of matter in the universe) will remain constant with
time. Indeed, the CCP allows the properties of the universe to
evolve with time, but states that at any given time the universe will
be both homogeneous and isotropic (in 3-D space).
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The CCP again
Another way of expressing
the Copernican Cosmological Principle is that ...
all observers (in inertial frames)
will see identical properties & laws - homogeneity
will NOT see any preferred direction - isotropy
We do not occupy a special
place in the universe
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Homogeneity/Isotropy
homogeneous - same properties everywhere
isotropic - no special direction, uniform in all dirns
homogeneous but
not isotropic
Jane Turner
isotropic but not
homogeneous
[4246] PHY 316 (2003 Spring)
The CCP - an analogy
A (small) sentient being living in the center of a "perfect" loaf of
bread…!
There may be obvious structure on small scales (air bubbles
etc), but on the large scale the loaf can be considered
uniform and isotropic
The laws of physics (e.g. which caused the dough to rise)
are the same throughout the loaf.
The loaf might still be rising - but (in this perfect loaf) this
happens
uniformly & following then same laws throughout the loaf
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The CCP Evidence for & against
The best support for the Copernican Cosmological Principle is
the Cosmic Microwave Background (CMB), which is isotropic
to 1 part in 105
The obvious observational evidence against the Copernican
Cosmological Principle seems to be the structure seen in the
universe on a variety of scales
(stars, galaxies, clusters, super-clusters..)
This is why the qualifier "On a large scale.." is required to be
added to the principle.
The question them becomes a question of scale (now large is
"large" ?), and whether the observed structures on large scales
are indeed representative of the universe on these scales (or
are "perturbations" which "happen” to be visible to us).
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 3
The Perfect Cosmo Principle
The Perfect Cosmological Principle is an extension
of the Copernican Cosmological Principle and is that
not only
on a large scale, the universe is both
homogeneous and isotropic (in 3-D space), and
has/will always be so
but also that
it is also true for all times
This principle is a fundamental assumption of the
Steady-State Cosmological Theory:
the universe should present a similar aspect when
viewed from any point in space AND time.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The PCP - an analogy
A (small) sentient being living in the center of a "perfect" loaf of
bread…!
There may be obvious structure on small scales (air bubbles etc),
but on the large scale the loaf can be considered
uniform and isotropic
The laws of physics (e.g. which caused the dough to rise)
are the same throughout the loaf.
However (contrary to the case for the CCP loaf) the loaf has always (&
will always) exist with the same characteristics as a function of time.
So if the loaf appears still be rising, (which in this perfect loaf) this
happens uniformly & following the same laws throughout the loaf),
then the density of the loaf must remain constant, thus bread-particles
must spontaneously appear to compensate for the expansion.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Recap
We are up to 1400
We briefly mentioned the ideas of Nicholas de Cusa
Homogeneity & Relativity
We discussed the Heliocentric system of Nicholas Copernicus
We then discussed the Copernican Cosmological Principle
On a large scale, the universe is both
homogeneous and isotropic (in 3-D space)
and the Perfect Cosmological Principle
On a large scale, the universe is both
homogeneous and isotropic (in space AND time)
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The Anthropic Cosmo Principle
The Anthropic Cosmological Principle is an extension of the
Copernican Cosmological Principle and is that not only
on a large scale, the universe is both homogeneous and
isotropic (in 3-D space), and has/will always be so
but also that
by our very being here, we are viewing "our universe"
at a "privileged" location in spacetime
The rationale behind the first part is as for the CCP. The
implication is that
the same laws of physics hold throughout the universe.
The rationale behind the second part is as an explanation as to
why the laws of physics (& the universe itself) are the way
they are (at least as seen by us).
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The Weak ACP
The Weak Anthropic Cosmological Principle states that
the conditions necessary for the development of sentient
beings (capable of asking the question why is the universe
the way it is ?) will only exist in a universe where the laws
of physics are the way they are as they are experienced by
us.
i.e. sentient beings can only evolve and exist in a universe
-that "happens" to have a density close to that observed
(by us),
-that "happens" to be about as old as ours,
-where the charge of an electron "happens" to have the
value
observed (by us).
... etc.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 4
The Weak ACP - an analogy
Back to our sentient being in the center of a "perfect" loaf of bread
As before, on the large scale the loaf is uniform and isotropic
The laws of physics are the same throughout the loaf.
However (as an extension to the CCP loaf) the sentient being
reasons that out of all the possible loaves (universes)
(ingredients, proportions, open temperatures, baking times etc),
they exist in the loaf/universe they do since the
conditions were just right
to bake such a loaf.
Had they not been
(no yeast added, baking time not long enough etc),
then it would not have been possible for them to reach the level
they have (if they could even exist at all).
This is the Weak flavor of the ACP
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The Strong ACP
The Strong Anthropic Cosmological Principle takes
the
Weak ACP one step further to state that
there could be many different universes (or regions in a
single universe) where the laws of physics are different
There are yet more flavors of the Strong ACP dealing with
whether or not sentient beings might be able to have
evolved in these other "universes".
But such metaphysical questions are beyond the scope of
the current course
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The Strong ACP - yet more loaves
In the Strong flavor of the ACP, the sentient beings go on
to allow for the
possibility of the existence of other loaves
having been in the oven (or other ovens),
with different mixtures of ingredients etc.
Whether the conditions may have been right for other
sentient beings to evolve in (a very small number of) these
other loaves (most likely in a form v.different to themselves)
is a matter of debate.
However (most of) the sentient beings see
no possiblity of loaf-to-loaf travel in any case...
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
The ACPs - just games in logic ?!
Not really !
There appear to have to have been a large number of
“coincidences” for life (as we know it) to exist..
(you will NOT be tested on these)
for those interested, see...
http://userweb.nashville.com/~al.schroeder/anthcoi.htm
Examples…
THE BERYLLIUM BOTTLENECK IN THE MAKING OF ELEMENTS
NEUTRINOES, THE WEAK INTERACTION, AND SUPERNOVAS
ELECTRON/PROTON MASS RATIO
ELECTRON-PROTON CHARGE BALANCE
ELECTRON/NEUTRON MASS RATIO
NEUTRON/PROTON MASS DIFFERENTIAL
ELECTRON EXCITATION AND STELLAR TYPES
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Tycho Brahe (c.1570))
Also famous for having lost his nose in a swordfight
Tycho Brahe (c.1570)
did accept that the (other) Planets
move around the Sun
but did not accept that the Earth & Stars
move around the Sun
Why ?
… Falling bodies fall towards the Earth
... The lack of Stellar Parallax
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
What was his problem ?)
Falling Bodies fall towards the Earth
Indeed if you throw something vertically upwards,
it falls vertically downwards (to the same spot)
Tycho Brahe reasoned this surely meant
the Earth was the center of the universe
Tycho Brahe was unable to detect (by naked-eye) Stellar Parallax
and reasoned that in a Copernican system this would require
the Stars to be so far away they would have to be
"unreasonably" large/bright.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Tycho Brahe the observer
Tycho Brahe was primarily an observer & made observations that
strengthened the rejection of the cosmology of Aristotle & Ptolemy
a Supernova
position did not change (so it was not a comet or meteor),
- lack of Parallax must be in one of the outer spheres
brightness changed - outer sphere of star does change!
a Comet
position did not change significantly throughout the night.
- lack of Parallax, must lay beyond the orbit of the Venus
positions of Mars twice-daily
which implied its orbit intersects that of the Sun.
- apparent crossing/smashing of the “crystalline spheres”
“there are no solid spheres "holding" the celestial bodies”
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Tycho Brahe - his contribution
So, even though Tycho Brahe’s
(geocentric) cosmological model was wrong…
… his observations did play a major role in the final
rejection
of the notions of Aristotle/Ptolemy that
the celestial bodies are carried by crystalline spheres,
with everything beyond the Moon eternal & unchanging.
In addition Tycho Brahe also actually published his data !
In particular his twice-daily measurements of the position of Mars
provided Johannes Kepler with a crucial database a few years later.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Johannes Kepler - Laws 1 & 2
In 1609 Johaness Kepler publishes
Astronomia Nova (New Astronomy)
1st two laws:
Planets move in ellipses with the Sun at one focus
(not the perfect circular orbits previously assumed)
Planets "sweep out" equal "areas" in equal times
during their motion around the Sun
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Johannes Kepler - Law 3
In 1619 Johaness Kepler publishes
Harmonices Mundi (Harmonies of the World)
3rd law:
The period P (of a Planet's orbit) squared is
proportional to the (average) distance R cubed
P2 = K x R3
(where K is a constant)
Cosmology finally escapes the
"Artistolelian straightjacket of uniform circular motion”
Kepler’s laws are "parameterizations" of motion (rather than how/why …)
e.g. the physics "hidden" in the constant of proportionality K was not understood
but for the 1st time, laws provide the ability to measure the
relative size of the Solar System.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Sun at the center - still somewhat “radical”
Following the publication of Revolutionibus Orbium Coelestium
by Nicholas Copernicus (1543), a heliocentric solar system
slowly slipped into the scientific mainstream.
Many still considered the Copernican system radical ...
Others took the ideas even further.
Thomas Digges (1572) - universe is infinite (in space) and
populated by innumerable suns & worlds.
Giordane Bruno (1584) - universe is infinite in both time & space
and contains many worlds
with intelligent beings.
Jane Turner
[4246] PHY 316 (2003 Spring)
Lecture 2
Kepler
Orbits and Keplers Laws
2
P  R 
   

 yr   AU 
3
For the Earth, we know
that:
P=1 year
R=150 million km (1
Astronomical Unit, A.U.)
ht
Jane Turner
[4246] PHY 316 (2003 Spring)
Kepler
Orbits and Keplers Laws
ht
Jane Turner
[4246] PHY 316 (2003 Spring)
Homework
Read Chapters 1+2 of Hawley &
Holcomb
Answer chapter 2, question 10 (should
take ~10 mins), email response to
[email protected]
work through web-tutorial
www.aw.com/astronomyplace #1
“Scales of the Universe”
Jane Turner
[4246] PHY 316 (2003 Spring)