DIRECTORY 339
Penrose has proposed a theory of a
cyclic cosmology, in which the heat
death (end state) of one universe
produces the conditions for the
Big Bang of another universe.
Penrose has also produced a
series of popular science books
in which he explains the physics
of the universe and suggests
novel explanations for the origins
of consciousness.
See also: Curves in spacetime
15 4 –55 ■ Hawking radiation 255SHIV S. KUMAR
1939–Indian-born astronomer Shiv S.
Kumar earned a doctorate in
astronomy at the University of
Michigan and has made his career
in the United States, working on
theoretical problems concerning
matters including the origin of the
solar system, the development of
life in the universe, and exoplanets.
In 1962, Kumar predicted the
existence of low-mass stars that
would be too small to sustain
nuclear fusion. Later named
brown dwarfs by Jill Tarter, their
existence was confirmed in 1995.
See also: Exoplanets 288–95BRANDON CARTER
1942–In 1974, Australian physicist
Brandon Carter formulated the
anthropic principle, which states
that the universe must necessarily
have certain characteristics for
humankind to exist. That is to say
that the physical properties of the
universe, such as the strength of
the fundamental forces, must fall
within very narrow limits for
sunlike stars capable of sustaininglife to develop. Since 1986, Carter
has been the director of research
at the Paris–Meudon Observatory.
He has also made contributions
to understanding the properties
of black holes.
See also: Life on other planets
228–35 ■ Hawking radiation 255JILL TARTER
1944–As director of the Center for SETI
Research in California, Jill Tarter
was a leading figure in the search
for extra-terrestrial life for more
than 30 years, lecturing widely on
the subject before her retirement in- In 1975, she coined the term
“brown dwarf” for the type of star,
discovered by Shiv S. Kumar, that
is not massive enough to sustain
nuclear fusion. Carl Sagan based
the protagonist in his novel and
film Contact on Tarter.
See also: Life on other planets
228–35
MAX TEGMARK
1967–Swedish cosmologist Max
Tegmark’s research at MIT has
focused on developing methods
to analyze the vast amounts of
data produced by surveys of the
cosmic microwave background.
Tegmark is a leading proponent
of the idea that the results of
quantum mechanics are best
explained by the existence of a
multiverse. He has developed the
mathematical universe hypothesis,
which proposes that the universe
is best understood as a purely
mathematical structure.
See also: Observing the CMB
280–85of radio sources. Deeply affected
by his experiences of war, Ryle
devoted his final years to the
promotion of the peaceful use
of science, warning against the
dangers of nuclear weapons and
power, and advocating research
into alternative energy.
See also: Radio astronomy 179 ■
Quasars and pulsars 236–39
HALTON ARP
1927–2013
A staff astronomer at the Mount
Wilson Observatory in California
for nearly 30 years, Halton Arp
gained a reputation as a skilled
observer. In 1966, he produced
his Atlas of Peculiar Galaxies,
which cataloged, for the first
time, hundreds of odd structures
that had been seen in nearby
galaxies. Today it is known that
many of these features are the
result of galaxies colliding. Later
in his career, Arp found himself
professionally marginalized when
he cast doubt on the Big Bang
theory. He contended that objects
with very different degrees of
redshift were close to one another
and not at vastly different distances.
See also: Beyond the Milky Way
172 –7 7
ROGER PENROSE
1931–
In the 1960s, British mathematician
and physicist Roger Penrose
figured out much of the complex
mathematics relating to the
curvature of spacetime around a
black hole. In collaboration with
Stephen Hawking, he showed how
matter within a black hole collapses
into a singularity. More recently,