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THE AGE OF THE
UNIVERSE
Arturo Villarreal III
Math89s
February 22, 2016
“Since the beginning of time,” is a hackneyed phrase, attached with some arbitrary
subject, that looks to exaggerate any issue its paired with. Although the use of the phrase
highlights an individual’s vague grasp on the depth of time and use of uninspired hyperbole, one
could find it surprising that even the most sophisticated engineering marvels and greatest
scholars that have roamed the science realm were dubious about the age of the universe up until
the early 21st century.
The measurement uncertainty in the 1900s, known as the cosmic age problem, perplexed
astronomers and speculated an unclear age for the Universe. In the early 20th century, the
theoretical developments of the Friedmann equations supplemented with Edwin Hubble’s
discovery of an expanding universe made it intuitive to trace this expansion backwards in time to
a universe that had almost zero size at a finite time. Early measurements of the expansion rate
of the universe, known as the Hubble parameter H0, were around 550km/s/MPC. These units of
measurement read: kilometers/second/megaparsec, meaning for every megaparsec (3 million
light years) you go out the universe is expanding 550km/sec faster. This parameter approximated
the age of the universe to be around 1.8 billion years which conflicted with geological claims of
the day that had Earth at over 2 billion years old. The focus on solving the cosmic age problem
shifted following the discovery of two errors in Hubble’s extragalactic distance scale during the
1950s. The first discovery can be credited to Walter Baade who discovered there were two
classes of Cepheid variable star (a star varying in both diameter and temperature that brightens
and dims periodically). This doubled the Hubble time as previous samples had encompassed
different classes of Cepheid variable star nearby and in other galaxies. (Hubble time tH is the age
of the universe had its expansion been linear, or is simply the reciprocal of the Hubble
parameter.) The second error, discovered by Allan Sandage, dealt with galaxies beyond the local
group. Since Hubble’s instruments were unable to observe Cepheids beyond the local group, he
resorted to using the brightest stars as distance indicators. However, many of these stars were
actually clusters containing an immense amount of stars causing an underestimation of distances
for these more distant galaxies. Taking this into account, Sandage was able to recalculate the
Hubble parameter and settled with the value: 75km/s/MPC. However, new developments in the
theory of stellar evolution in the 1960s enabled age estimates for global clusters. These clusters
estimated the universe to be around 15 billion years old. A solution that satisfied the cosmic age
problem seemed to have emerged. However, in the late 1970s to the early 1990s, new estimates
of the Hubble parameter gave greater values to the age of the universe. The age problem was
eventually resolved in 2003 following a string of 8 year projects. First off, the Hubble space
telescope measured the Hubble parameter at 72km/s/MPC with 10 percent uncertainty.
Secondly, measurements of parallax by the Hipparcos spacecraft in 1995 revised globular cluster
distances upwards by 5-10%. Finally, the observations by the Wilkinson Microwave Anisotropy
Probe (WMAP) led to the acceptance of dark energy and the establishment of the Lambda-CDM
model as the standard model of cosmology. The presence of dark energy implies that the
universe was expanding more slowly at around half its present age than today, which makes the
universe older for a given value of the Hubble parameter. The precision of the more recent
measurements from the Planck spacecraft have very accurately established the age of the
universe to be 13.82 billion years with only 0.3 percent uncertainty. (Anderson 83-84) How could
humans, who struggle predicting an accurate 7-day weather forecast, measure the age of our
existence with such a degree of accuracy? Nevertheless, it’s worth inquiring how such an amazing
feat now stands in the hall of great human accomplishments.
The launch of the Wilkinson Microwave Anisotropy Probe on June 30, 2001 inched
mankind closer to answering many longstanding questions about the universe’s age,
composition, and development. The spacecraft maneuvered to the Sun-Earth L2 Lagrangian point
(position in an orbital configuration of two large bodies) where it was to conduct its first CMB
observation. By studying the oldest light in the universe, the WMAP sought to measure the
temperature differences in the Cosmic Microwave Background radiation in order to map the
afterglow of the earliest moments of the universe. (NASA 1). This light lost energy as the universe
expanded over 13.7 billion years, so WMAP recorded the light as microwaves. By making accurate
measurements of microwave patterns and observing in five frequencies, the WMAP produced a
full sky map of the Cosmic Microwave Background. Measured in Kelvins, the red regions were
about 0.0002 kelvin hotter than the cold regions. WMAP’s additional angular resolution allowed
scientist to infer a great deal of additional information about conditions in the early universe.
(NASA 3) The WMAP observed in five frequencies in order to permit the measurement and
subtraction of foreground contamination such as the Milky Way and extra-galactic sources. The
spacecraft’s location also maximized its data accuracy by minimizing the amount of
contaminating terrestrial, solar, and lunar emissions registered. (NASA 2) Each WMAP
observation of the full sky required a six-month period known as the Six-Month Exposure.
This orbit diagram above shows the process by which WMAP collects data from the full
sky over the six-month exposure. Because WMAP must always face away from the sun, it can not
view all portions of the sky until it rotates around the sun at the same rate as the Earth. To view
the entire sky, without looking to the Sun, the WMAP traced a path around L2 in a Lissajous orbit
(a special type of orbit). WMAP measured the entire sky every six months, and completed its first,
full-sky observation in April 2002; its prime two years of mission operations in the L2 orbit were
completed by September 2003. (NASA 2) In addition to producing high-quality full-sky maps of
the CMB, WMAP observations also alluded to a theory that accounted for the earliest moments
of the universe. Known as "inflation," the theory claims that the universe grew by more than a
trillion trillion-fold in less than a trillionth of a trillionth of a second. Tiny fluctuations were
generated during this expansion that eventually grew to form galaxies. Given all the information
that has been provided, the question still begs to be answered: “How does a full sky map of the
Cosmic Microwave background point to the age of the universe?” The premise to this answer lies
on the temperature fluctuations in the CMB. These cosmic temperature fluctuations are
speculated to trace fluctuations in the density of matter as they were imprinted in the early
universe. This being the case, they reveal a great deal about the early universe plus the origin of
galaxies and large scale structure in the universe. (NASA 3). By detecting polarized protons,
WMAP was able to reveal the ionization history of the universe. Since ionized gas can interact
with CMB photons, WMAP observations allowed for the detection of objects that occurred much
earlier than quasars. This information allowed astronomers to infer that the first objects with the
ability to ionize gas formed at around 400 million years following the Big Bang. (NASA 4)
The Wilkinson Microwave Anisotropy Probe is derelict as of October 2010 with its final
official data release taking place in 2012. Although its project has been succeeded by the much
more advanced Planck spacecraft, its worth noting that the data gathered during its time was the
greatest infromation leap to date. Measuring the age of the universe at a precision better than
1%, the WMAP and its mission will stand as some of the greatest feat ever accomplished by
mankind.
Bibliography
The Cosmic Compendium: The Ultimate Fate of the Universe
By Rupert W Anderson
WMAP – From the archives
https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11008 (NASA 1)
WMAP Facts
http://map.gsfc.nasa.gov/news/facts.html (NASA 2)
Fluctuations in the Cosmic Microwave Background
http://map.gsfc.nasa.gov/universe/bb_cosmo_fluct.html (NASA 3)
When did the first Cosmic Structures form?
http://map.gsfc.nasa.gov/universe/rel_firstobjs.html (NASA 4)
(Anderson)