Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.mso.anu.edu.au/~charley/papers/9911294.ps Äàòà èçìåíåíèÿ: Mon Nov 15 17:00:00 1999 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 02:25:54 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: moon

astro­ph/9911294
16
Nov
1999
What is the Universe made of?
How old is it?
Charles H. Lineweaver
University of New South Wales
ABSTRACT
For the past 15 years most astronomers have assumed that 95% of the Universe was
in some mysterious form of cold dark matter. They also assumed that the cosmo­
logical
constant,\Omega \Lambda , was Einstein's biggest blunder and could be ignored. However,
recent measurements of the cosmic microwave background combined with other cos­
mological observations strongly suggest that 75% of the Universe is made of cosmo­
logical constant (vacuum energy), while only 20% is made of non­baryonic cold dark
matter. Normal baryonic matter, the stuff most physicists study, makes up about
5% of the Universe. If these results are correct, an unknown 75% of the Universe
has been identified. Estimates of the age of the Universe depend upon what it is
made of. Thus, our new inventory gives us a new age for the Universe: 13:4 \Sigma 1:6
Gyr.
``The history of cosmology shows us that in every age devout people believe
that they have at last discovered the true nature of the Universe.''
(E. Harrison in Cosmology: The Science of the Universe 1981)
1 Progress
A few decades ago cosmology was laughed at for being the only science with no data. Cosmology
was theory­rich but data­poor. It attracted armchair enthusiasts spouting speculations without
data to test them. It was the only science where the errors could be kept in the exponents --
where you could set the speed of light c = 1, not for dimensionless convenience, but because the
observations were so poor that it didn't matter. The night sky was calculated to be as bright as
the Sun and the Universe was younger than the Galaxy.
Times have changed. We have entered a new era of precision cosmology. Cosmologists are
being flooded with high quality measurements from an army of new instruments 1 . We are
observing the Universe at new frequencies, with higher sensitivity, higher spectral resolution and
higher spatial resolution. We have so much new data that state­of­the­art computers process and
store them with difficulty. Cosmology papers now include error bars -- often asymmetric and
sometimes even with a distinction made between statistical and systematic error bars. This is
progress.
1 COBE, ISO, IRAS, HIPPARCOS, HST, IUE, BeppoSax, UHURU, ROSAT, Chandra,
BATSE, VLA, ATCA, Arecibo, KAO, SOFIA, SCUBA, BIMA, KECK, VLT, CFHT, MMT,
UKIRT, AAT, CTIO, FLY's EYE, CSO, JCNT, NTT, KPNO, UKIRT, INT, JKT, WHT,
Magellan, GTC, LBT, MAX, Kamiokande, Super Kamiokande, HOMESTAKE, VIRGO,
LIGO, Gravity Probe­B, GINGA, ASTRO A,B,C,D, CERN, FERMILAB, STANFORD, DS1,
MILAGRO, Gran Sasso, SNO...
1

The standard hot big bang model describes the evolution of the Universe. It is the dominant
paradigm against which all new ideas are tested. It provides a consistent framework into which all
the relevant cosmological data seem to fit. Progress has been made in working out the details of
this hot big bang model -- for it is the details which provide new, unprecedentedly precise answers
to questions of mythical importance: What is the Universe made of? How old is the Universe?
time
to=13 Gyr
To=3 K
t=300,000 yr
T=3000 K
x
y
BIG BANG
SURFACEOF LAST SCATTERING
NOW
t=0
T=infinite
z=infinite
z=1000
A C
B
C' z=0
Figure 1. Our view of the Universe
In this spacetime diagram we are at the apex of our past light cone. All the photons we see
come to us along the surface of this cone. One spatial dimension has been suppressed. When
we look as far away as we can, we see the oldest observable photons -- the CMB -- coming from
the wavy circle in the surface of last scattering (A, B and C are on the circle). The opaque
surface of last scattering is the boundary between the current transparent universe and the
hotter, denser, opaque, ionized universe. The figure gives the time, temperature and redshift
of the big bang, the surface of last scattering and today. This is a comoving diagram, that
is, the expansion of the Universe is not shown. We see the object C on the surface of last
scattering as it was 13 Gyr ago. Today C has become C', but since the speed of light is not
infinite, we cannot see C' now.
2

2 The CMB: cosmology's coolest new tool.
The cosmic microwave background (CMB) is the oldest fossil we have ever found. It is a bath
of photons coming from every direction. These photons are the afterglow of the big bang. Their
long journey toward us has lasted more than 99.99% of the age of the Universe and began when
the Universe was one thousand times smaller than it is today. The CMB was emitted by the hot
plasma of the Universe long before there were planets, stars or galaxies. The CMB is an isotropic
field of electromagnetic radiation -- the redshifted relic of the hot big bang.
One of the most recent and most important advances in astronomy has been the discovery
of hot and cold spots in the CMB based on data from the COBE satellite (Smoot et al. 1992).
This discovery has been hailed as ``Proof of the Big Bang'' and the ``Holy Grail of Cosmology'' and
elicited comments like: ``If you're religious it's like looking at the face of God'' (George Smoot) and
``It's the greatest discovery of the century, if not of all time'' (Stephen Hawking). As a graduate
student analyzing COBE data at the time, I knew we had discovered something fundamental but
its full import didn't sink in until one night after a telephone interview for BBC radio. I asked the
interviewer for a copy of the interview, and he told me that would be possible if I sent a request
to the religious affairs department.
The CMB comes from the surface of last scattering of the Universe. When you look into a
fog, you are looking at a surface of last scattering. It is a surface defined by all the molecules of
water which scattered a photon into your eye. On a foggy day you can see 100 meters, on really
foggy days you can see 10 meters. If the fog is so dense that you cannot see your hand then the
surface of last scattering is less than an arm's length away. Similarly, when you look at the surface
of the Sun you are seeing photons last scattered by the hot plasma of the photosphere. The early
Universe is as hot as the Sun and similarly the early Universe has a photosphere (the surface of
last scattering) beyond which (in time and space) we cannot see (Fig. 1). As its name implies, the
surface of last scattering is where the CMB photons were scattered for the last time before arriving
in our detectors. The `surface of last screaming' presented in Fig. 2 is a pedagogical analog.
Since the COBE discovery of hot and cold spots in the CMB, anisotropy detections have
been reported by more than a dozen groups with various instruments, at various frequencies
and in various patches and swathes of the microwave sky. Fig. 3 is a compilation of recent
measurements. The COBE measurements (on the left) are at large angular scales while most
recent measurements are trying to constrain the angular scale and amplitude of the dominant first
peak at ¸ 1=2 degree (the size of the full Moon). This dominant peak and the smaller amplitude
peaks at smaller angular scales are due to acoustic oscillations in the photon­baryon fluid in cold
dark matter (CDM) gravitational potential wells. The detailed features of these peaks in the power
spectrum are dependent on a large number of cosmological parameters including,
\Omega m the density of matter
(where\Omega m
=\Omega CDM
+\Omega b )
ffl\Omega CDM the density of cold dark matter
ffl\Omega b the density of normal baryonic matter
\Omega \Lambda the density of vacuum energy (cosmological constant)
h the Hubble constant (giving the rate of expansion of the Universe)
3

00
00
00
11
11
11 v sound
fa
Sur
ce
last
screaming
of
Figure 2. The Surface of Last Screaming.
Consider an infinite field full of people screaming. The circles are their heads. You are
screaming too. (Your head is the black dot.) Now suppose everyone stops screaming at the
same time. What will you hear? Sound travels at 330 m/s. One second after everyone stops
screaming you will be able to hear the screams from a `surface of last screaming' 330 meters
away from you in all directions. After 3 seconds the faint screaming will be coming from 1
km away...etc. No matter how long you wait, faint screaming will always be coming from
the surface of last screaming -- a surface that is receeding from you at the speed of sound
(`v sound '). The same can be said of any observer -- each is the center of a surface of last
screaming. In particular, observers on your surface of last screaming are currently hearing
you scream since you are on their surface of last scattering. The screams from the people
closer to you than the surface of last screaming have passed you by -- you hear nothing from
them (grey heads). When we observe the CMB in every direction we are seeing photons from
the surface of last scattering. We are seeing back to a time soon after the big bang when the
entire Universe was opaque (screaming). If the Universe were not expanding, the surface of
last scattering would be receding at the speed of light. The expansion of the Universe adds
an additional recession velocity and makes the surface of last scattering recede at ¸ 3 c.
4

Figure 3. Measurements of the CMB power spectrum.
The amplitudes of the hot and cold spots in the CMB depend on their angular size. Angular
size is noted in degrees on the top x axis. The y axis is the rms amplitude of the temperature
fluctuations. For example, the fluctuations at 1/2 degree are at 90 ¯K while the fluctuations
at 10 degrees are at 30 ¯K. This means that at the 1/2 degree angular scale, the hot spots are
3 times hotter and the cool spots are 3 times cooler than at the 10 degree scale. Each CMB
experiment is sensitive only to a limited range of angular scale. When the measurements at
various angular scales are put together they form the CMB power spectrum. The COBE­
DMR points at ` FWHM ¸ ? 7 o are primordial fluctuations corresponding to scales so big
they are `non­causal', i.e., they have physical sizes larger than the distance light could have
travelled between the big bang and their age at the time we see them (300,000 years after the
big bang). They are either the initial conditions of the Universe or were laid down during an
epoch of inflation ¸ 10 \Gamma35 seconds after the big bang. New sets of points are being added
every month or so. The three curves represent the three most popular models. ü 2 fits of this
data to such model curves yields the constraints in Fig. 5A.
5

My work over the past few years has been to extract values for these parameters by compar­
ing the most recent measurements of the CMB with parameter­dependent models (Lineweaver &
Barbosa 1998, Lineweaver 1998, 1999a). The three curves in Fig. 3 are examples of such mod­
els and represent the three most popular candidates for the best fit to reality. They are known
as standard­CDM, Open­CDM and
\LambdaCDM:(\Omega m
;\Omega \Lambda ) = (1:0; 0:0); (0:3; 0:0) and (0:3; 0:7)
respectively. The principal support for these models comes from theory, tradition and data, re­
spectively. The \LambdaCDM model fits the position and amplitude of the dominant first peak quite
well. The standard­CDM model has a peak amplitude much too low. The open­CDM model has
the peak at angular scales too small to fit the data and is strongly excluded by a fuller analysis
(see Fig. 5A).
3 What is the Universe made of?
If we know what the Universe is made of, we know how it will behave and how it has behaved --
we know its dynamics and shape and destiny -- whether it will expand forever or collapse in a big
crunch -- whether it is spatially finite or infinite -- whether it is 10 billion years old or 20. Many
of these issues can be reduced to the question: Where does our Universe lie in the
(\Omega m
;\Omega \Lambda )
plane? Observational constraints in this plane are then the crucial arbiters. Figure 4 can be used
to
translate\Omega m
and\Omega \Lambda constraints into the words most commonly used to describe the Universe.
In cosmology we keep track of the components of the Universe by their
densities:\Omega m
,\Omega CDM ,
\Omega b
,\Omega \Lambda . These are all dimensionless densities expressed in units of the critical density, 10 \Gamma29 g
cm \Gamma3 (9 orders of magnitude emptier than the best laboratory vacuums). If the Universe has the
critical density
(\Omega m = 1), then its current rate of expansion is analogous to the escape velocity,
that is, it will expand forever, asymptotically approaching no expansion as t ! 1 (just as the
velocity of an object with escape velocity asymptotically approaches 0). One can read from Fig.
4 that
an(\Omega m
;\Omega \Lambda ) = (1:0; 0:0) universe is flat, decelerating and will expand forever.
3.1 Much Ado About Nothing
One of the most surprising recent advances in cosmology is that 75% of the Universe seems to be
made out of nothing, i.e., the energy of the vacuum. I have assembled much of the observational
evidence for this in Fig. 5. Recent CMB anisotropy measurements favour the elongated triangle
in panel A of Fig. 5. This plot shows that
if\Omega \Lambda = 0
then\Omega m ¸ 0:3 is more than ¸ 4oe
from the best fit
and\Omega m ¸ 0:1 is more than ¸ 7oe away. The confidence levels in this diagram
are very rough but the message is clear:
if\Omega \Lambda = 0, then
low\Omega m models are strongly excluded
by the CMB data. No other data set can exclude this region with such high confidence. The
combination of CMB and supernovae constraints (Fig.5B) provides strong evidence
that\Omega \Lambda ? 0.
If
any\Omega \Lambda = 0 model can squeak by the new supernovae constraints it is the very
low\Omega m models.
However these models are the ones most strongly excluded by the CMB data. The constraints
shown in panels C, D and E support this result. Separately these data sets cannot determine
unambiguously what the destiny of the Universe will be. However, together they form a powerful
interlocking network of constraints yielding the most precise estimates
of\Omega m
and\Omega \Lambda . The result
is strong evidence and the best evidence to date that the Universe will expand forever, dominated
by a 75% contribution from the vacuum.
6

I believe this result is robust because of a series of conservative choices made in the analysis
and because it arises when the data sets are combined individually (as in panels B,C,D and E) or
combined together (as in F). Systematicerrors may compromiseone or the other of the observations
but are less likely to bias all of the observations in the same way.
The \LambdaCDM region of the
(\Omega m
;\Omega \Lambda ) plane fits the CMB, supernovae and other data sets
and should be viewed as the new standard model of cosmology. Standard CDM
with\Omega m = 1
and\Omega \Lambda = 0 is a simpler model, but circular planetary orbits are also simpler than ellipses.
The results presented in Fig. 5F (Lineweaver 1999a) quantify the main components of the new
standard \LambdaCDM model. They are depicted in Fig. 6 and are as follows:
Table of Contents of the Universe
ffl 75% Vacuum energy, cosmological
constant,\Omega \Lambda
The vacuum of modern physics is not empty. It is seething with virtual particles
coming in and out of existence. All this seething produces a vacuum energy (the zero
point energy of quantum field theory) which has a negative pressure. Unlike normal
mass which slows down the expansion of the Universe, vacuum energy speeds up the
expansion. It's a bit like discovering compressed springs everywhere in the vacuum of
space. These springs make the Universe expand. This mysterious stuff does not clump.
It is the Lorentz invariant structure of the vacuum and its existence is probably most
directly established by the Casimir effect and the Lamb
shift.\Omega \Lambda = 0:65 \Sigma 0:13
corresponding to 74 \Sigma 4% of the Universe.
ffl 20% Cold Dark Matter (CDM)
Non­baryonicand non­relativistic, CDM density fluctuations collapse gravitationally. It
clumps. Corresponding CDM potential wells (and hills) produce the hot and cold spots
in the CMB and are the principle seeds for the formation of the large scale structure
we see around us today (galaxies, great walls, voids etc). This non­baryonic stuff has
never been detected
directly.\Omega CDM = 0:19 \Sigma 0:09 corresponding to 21 \Sigma 7% of
the Universe. Leading candidates for it are axions or neutralinos (see Turner 1999).
ffl 5% Normal baryonic matter
This is the normal stuff that stars and ourselves are made of. We breathe it, eat it and
physicists study
it.\Omega b = 0:04 \Sigma 0:02, corresponding to 5 \Sigma 2% of the Universe. This
value comes from big bang nucleosynthesis calculations and deuterium measurements
in quasar spectra. In terms of elemental composition this normal baryonic matter is
75% hydrogen, 23% helium, and 2% all other elements. In terms of phase (see Fukugita
et al. 1998, Cen & Ostriker 1998), it is 80% diffuse hot ionized gas, 17% stars and 3%
neutral gas and dust.
The total density of the Universe
is\Omega total
=\Omega m
+\Omega \Lambda = 0:88 +0:07
\Gamma0:10 (Fig. 5F). The
percentages listed above are based
on\Omega total = 0:88
(not\Omega total = 1, most versions of inflation
have\Omega total = 1). The density from photons (from the CMB and from stars) is negligible:
0:006% of the Universe. I have left out one ingredient of the universe because we don't know
whether it is important or not -- neutrinos. We know their number density fairly accurately. It's
7

Figure 4. Describing the Universe.
The language used to describe the Universe, e.g. `infinite/finite', `open/flat/closed', `accel­
erating/decelerating' and `a universe which will expand forever/end in a big crunch', can be
confusing. However the boundaries between these various types of universe can be simply
represented in the
(\Omega m
;\Omega \Lambda ) plane. For example, spatially open universes (3­D analog of the
surface of a saddle, negative curvature) are in the lower left while spatially closed universes (3­
D analog of the surface of a sphere, positive curvature) are in the upper right. Flat Euclidean
universes are on the diagonal line between them. Flat and open models are spatially infinite;
closed models are finite. Notice that one can have finite universes which expand forever and
can be either accelerating or decelerating. One can also have infinite universes which collapse
into a big crunch
(if\Omega \Lambda ! 0). A detail that is slightly ambiguous:
if\Omega \Lambda = 0
then\Omega m Ÿ 1
universes expand forever
while\Omega m ? 1 universes crunch. Observational constraints in this
(\Omega m
;\Omega \Lambda ) plane are given in Fig. 5; they favour accelerating, slightly open, but nearly flat
universes
with\Omega m ú 0:3
and\Omega \Lambda ú 0:7.
8

Figure 5. Observational constraints in the
(\Omega m
;\Omega \Lambda ) plane.
These 6 panels show the regions of the
(\Omega \Lambda
;\Omega m ) plane preferred by the data. The CMB
constraint is in the top left panel (A). Other constraints are from type Ia supernovae (B),
galaxy cluster mass­to­light ratios (C), galaxy cluster evolution (D) and double lobed radio
sources (E) and all combined (F). The thickest contours in each panel are from combining
each constraint with the CMB constraint from A. The combined constraints (F)
yield\Omega \Lambda =
0:65 \Sigma 0:13
and\Omega m = 0:23 \Sigma 0:08 and
thus\Omega total = 0:88 +0:07
\Gamma0:10 . \LambdaCDM models in
the upper left are consistent with all the data sets. The CMB excludes the lower left region
of the
(\Omega m
;\Omega \Lambda ) plane while each of the other constraints excludes the lower right. In A,
the contours labeled `10' through `14' (Gyr) are the iso­age contours for a Hubble constant
h = 0:68; the 13 and 14 Gyr contours are repeated in all panels. The contours within the
CMB 68% CL are the best­fitting H values. See Lineweaver (1998,1999a) for details.
9

W L
H
other elements
~2%
He
W b
W CDM
stars
neutral gas
matter
baryonic
normal
vacuum energy
cold dark
matter
ionized
gas
~3%
Figure 6. What is the Universe made of?
\Omega \Lambda (75%) is now controlling the dynamics of the Universe, causing the Universe to accelerate.
\Omega CDM (20%) acts in the opposite sense, trying to decelerate the Universe (slow down the
rate of expansion) but it can't compete
with\Omega \Lambda (see Fig.
8).\Omega b (5%) is a pawn, pushed and
pulled around by the gravitational potentials due to spatial variations in the density of CDM.
Most physicists study the 5% of the Universe made up of normal baryonic matter. Taking a
closer look at the baryonic matter, 98% of it is either hydrogen or helium and 80% of it is in
difficult to detect ionized gas. See the Table of Contents of the Universe (p. 7) for details.
10

the uncertainty in their mass which is responsible for our ignorance. Much effort is being put into
measuring the mass(es) of neutrinos. Potentially they could contribute more than all the baryons
and probably as much as all the stars. A good guess might
be\Omega š = 0:05 +0:10
\Gamma0:047 where the upper
limit comes from the tendency of relativisitc particles to escape from small scale structures, i.e.,
if neutrinos formed more than 15% of the Universe, we could see much less small scale structure.
The lower limit comes from the recent Super Kamiokande detection of a small but positive mass
difference between two neutrino species (Fukuda et al. 1998). They could be negligible at 0:3%
of the Universe or they could be ¸ 15% of the Universe (Turner 1999). A ¸ 10% contribution
would
make\Omega total ¸ 1 as preferred by inflation and would reduce the contribution
of\Omega \Lambda from
75% to 65%.
The values quoted above for the composition of the Universe are not universally accepted. A
vocal minority of \Lambda­phobic cosmologists and particle theorists believe that
any\Omega \Lambda ? 0 result
has got to be wrong. Their reasoning goes something like this. Theory predicts
that\Omega \Lambda ¸ ? 10 52 .
Since it is obviously not this
value,\Omega \Lambda must be zero based on supersymmetric cancellation of the
contributions to the vacuum energy from bosons and fermions. See Cohn (1998, Section II) for a
more judicious discussion.
4 How old is the Universe?
In the big bang model, the age of the Universe, t o , is a function of three parameters:
h,\Omega m and
\Omega \Lambda . The dimensionless Hubble's constant, h, tells us how fast the Universe is expanding. The
matter
density\Omega m slows the expansion while the vacuum
energy\Omega \Lambda speeds up the expansion.
Until recently, large uncertainties in the measurements of
h,\Omega m
and\Omega \Lambda made efforts to determine
t o
(h;\Omega m
;\Omega \Lambda ) unreliable. Theoretical preferences were, and still are, often used to remedy these
observational uncertainties. One assumed the standard model
(\Omega m =
1,\Omega \Lambda = 0), dating the
age of the Universe to t o = 6:52=h billion years old. However for large, or even moderate h
estimates ( ¸ ? 0:65) these simplifying assumptions resulted in an age crisis in which the universe
was younger than our Galaxy (t o ú 10 Gyr ! t Gal ú 12 Gyr).
With a new inventory of the Universe described in the previous section and a new more precise
value for the Hubble constant (e.g. Mould et al. 2000), a new more precise age for the Universe
can be calculated. This was the focus of an article I recently published in Science entitled ``A
Younger Age for the Universe''. The result I obtained was more than a billion years younger than
other recent results (see Fig. 7).
5 What could be wrong?
Doubts about some of the observation used here are discussed in Dekel et al. (1998). The contri­
bution of neutrinos (or another form of hot dark matter)
to\Omega m remains a wild card. It is possible
that supernovae are not as uniformly bright as we believe. It is possible that the well­motivated as­
sumptions used in the CMB analysis (gaussian adiabatic fluctuations, structure formation through
gravitational instability) are mistaken. A mild conspiracy of unknown systematic errors could sub­
stantially change the constraints in Fig. 5F.
There has been some speculation recently that the evidence
for\Omega \Lambda is really evidence for some
11

Figure 7. How old is the Universe?
A compilation of recent age estimates for the Universe and for the oldest objects in our Galaxy.
Estimates of the age of the Universe are based on estimates
of\Omega m
,\Omega \Lambda and h. Galactic age
estimates are direct in the sense that they do not depend on cosmology. Averages of the
estimates of the age of the Galactic halo and Galactic disk are shaded grey. The absence of
any single age estimate more than ¸ 2oe from the average adds plausibility to the possibly
overdemocratic procedure of computing the variance­weighted averages. The age of the Sun
is accurately known and is included for reference. The largest dot at 13:4 \Sigma 1:6 Ga (billion
years) is the main result of the Lineweaver (1999a) paper. This age range is shaded grey on
the x­axis of the Fig. 8. Comfortingly, the Universe is older than the objects in it. This has
not always been the case in cosmology and its absence has been a leading cause of cosmology
bashing.
12

form of stranger dark energy (dubbed `quintessence') that we have been incorrectly interpreting
as\Omega \Lambda . Several workers have tested this idea. The evidence so far indicates that the cosmological
constant interpretation fits the data as well as or better than an explanation based on more
mysteriousdark energy (Perlmutter et al. 1999a, Garnavich et al. 1998, Perlmutter et al. 1999b).
6 The Future
As the quality and quantity of cosmological data improve, the questions: What is the Universe
made of? How old is the Universe? will get increasingly precise answers from an ever­tightening
network of constraints. An army of instruments is coming on line. Better CMB detectors are being
built; long duration balloons will fly; sensitive new high resolution interferometers will soon be on
line and we all have high expectations for the two CMB satellites MAP and Planck. In the near
future, new CMB measurements will reduce the error bars in Fig. 5 by a factor of ¸ 5 and/or...
if some inconsistency is found, force us to change our basic understanding of the Universe. Maybe
inflation is wrong, maybe CDM doesn't exist or we live in an eternally inflating multiverse.
The biggest prize of all may be somethingunexpected. We know that our model of the Universe
is incomplete at the largest scales and that it breaks down as we get closer and closer to the big
bang. It seems very probable that our model is wrong in some unexpectedly fundamental way. It
may contain some crucial conceptual blunder (as has happened so many times in the past). Some
unexpected quirk in the data may point us in a new direction and revolutionize our view of the
Universe on the largest scales. Surely this is the golden age of cosmology.
What does this all mean for the physicists in the street? We should devote more effort to
studying nothing -- the vacuum. We should improve on measurements of the Casimir effect.
Maybe one of us will invent a heat engine based not on a phase transition of water but on a
phase transition of the vacuum. In the past, on the few occasions where general relativity and
quantum theory intersected
(\Omega \Lambda is a quantum term in a classical equation) exciting new things
have emerged: Hawking radiation, entropy calcuations of black holes and maybe soon a theoretical
calculation
of\Omega \Lambda which will lead to a plausible theory of quantum gravity.
ACKNOWLEDGMENTS I am supported at UNSW by a Vice Chancellor's Research Fellowship.
I acknowledge the editorial support of Kathleen Ragan, author of ``Fearless Girls: Heroines in
Folktales from Around the World''
13

Figure 8. Destiny of the Universe.
The size of the Universe, in units of its current size, as a function of time. The age of the
five models can be read from the x axis as the time between `NOW' and the intersection of
the model with the x axis. The main age result from Lineweaver 1999a, t o = 13:4 \Sigma 1:6
Gyr, is labeled t o and is shaded grey on the x axis. Models
containing\Omega \Lambda curve upwards
( ¨
R ? 0) and are currently accelerating. The empty universe has ¨
R = 0 (dotted line) and
is `coasting'. The expansion of matter dominated universes is slowing down ( ¨
R ! 0). The
(\Omega \Lambda
;\Omega m ) = (0:3; 0:7) model is favoured by the data. Over the past few billion years and
on into the future, the rate of expansion of this model increases. This acceleration means that
we are in a period of slow inflation.
14

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Perlmutter, S. et al. 1999a, Ap.J., 517, 565
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Smoot, G.S. et al. 1992, Ap.J., 396, L1
Turner, M.S. in press, available at http://xxx.lanl.gov/abs/astro­ph/9904051
7 Bio
PHOTO
Charles Lineweaver is a Vice Chancellor's Research Fellow at the University of New South Wales.
He studied undergraduate physics at Ludwig Maximillian Universit¨at, Germany and at Kyoto
University, Japan. He obtained his PhD in Physics from the University of California at Berkeley.
After a postdoctoral fellowship at Strasbourg, France he came to UNSW in 1997. He also has an
undergraduate degree in history and a masters degree in English. He has lived or travelled in 58
countries, speaks four languages and has played semi­professional soccer. He is co­convener with
John Webb of a popular new UNSW course on bioastronomy: ``Are We Alone?''.
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