11 Modern Cosmology
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concerned that the model requires fine tuning to explain the universe, as we
know it. By varying parameters in the model, any conceivable universe can
be explained. Steinhardt goes further and adds that inflation would produce
not just one universe, but a multiverse containing all possible universes with
all possible properties. There is no way to verify, or falsify, such a theory,
which Wolfgang Pauli might well say is “not even wrong” (see Chap. 10).
Steinhardt’s (and Pauli’s) rejection of non-testable theories is not a philosophical viewpoint shared by all physicists. Many take a different view, i.e.
that a theory can simply provide an explanation that relates observations to
underlying physical principles.
Steinhardt and collaborators have proposed that instead of inflation, the
universe is cyclic in nature, and our universe has arisen from the remains of
an earlier collapsed universe. This approach is not without its own difficulties, running afoul of the Second Law of Thermodynamics, which requires
that entropy (or disorder) increase inexorably. A baby universe is in a lowentropy ordered state, and an old universe is in a much higher entropy state.
A recycled universe would begin its life in an unacceptably high entropy state.
Roger Penrose and others have made suggestions on how to overcome this
problem by modifying some of the laws of physics.
In this section, we have probed into some of the controversy that underlies
the physics of the early universe. We conclude by noting that the inflation
theory, as we described it in Chap. 10, remains the most popular of the
contending theories among astronomers and cosmologists. It is perhaps also
worth giving ourselves the wry reminder that the most popular cosmological
theory of the 1950s was the Steady State Theory, long since defunct. In the
long run, popularity in science counts for very little.
11.3 The Strange Case of the Missing Mass
In the 1930s, from studies of the orbital speed of galaxies in clusters, and stars
within galaxies, including the Milky Way, it was discovered that the velocities of objects gravitationally bound to each other were higher than expected
[2, 3]. The observed velocities were explained by assuming that more mass
existed in the galaxy, or the galaxy cluster, than was actually observed. We
have noted already in Chap. 3 that interstellar dust is a feature of our galaxy.
Matter is also present in the remnants of dead stars, planets and asteroids,
none of which are visible from their radiation. However the sum total of all
such obscure matter is estimated to contain less mass than the visible stars. In
order to explain the anomalous orbital velocities, it would appear that there
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concerned that the model requires fine tuning to explain the universe, as we
know it. By varying parameters in the model, any conceivable universe can
be explained. Steinhardt goes further and adds that inflation would produce
not just one universe, but a multiverse containing all possible universes with
all possible properties. There is no way to verify, or falsify, such a theory,
which Wolfgang Pauli might well say is “not even wrong” (see Chap. 10).
Steinhardt’s (and Pauli’s) rejection of non-testable theories is not a philosophical viewpoint shared by all physicists. Many take a different view, i.e.
that a theory can simply provide an explanation that relates observations to
underlying physical principles.
Steinhardt and collaborators have proposed that instead of inflation, the
universe is cyclic in nature, and our universe has arisen from the remains of
an earlier collapsed universe. This approach is not without its own difficulties, running afoul of the Second Law of Thermodynamics, which requires
that entropy (or disorder) increase inexorably. A baby universe is in a lowentropy ordered state, and an old universe is in a much higher entropy state.
A recycled universe would begin its life in an unacceptably high entropy state.
Roger Penrose and others have made suggestions on how to overcome this
problem by modifying some of the laws of physics.
In this section, we have probed into some of the controversy that underlies
the physics of the early universe. We conclude by noting that the inflation
theory, as we described it in Chap. 10, remains the most popular of the
contending theories among astronomers and cosmologists. It is perhaps also
worth giving ourselves the wry reminder that the most popular cosmological
theory of the 1950s was the Steady State Theory, long since defunct. In the
long run, popularity in science counts for very little.
11.3 The Strange Case of the Missing Mass
In the 1930s, from studies of the orbital speed of galaxies in clusters, and stars
within galaxies, including the Milky Way, it was discovered that the velocities of objects gravitationally bound to each other were higher than expected
[2, 3]. The observed velocities were explained by assuming that more mass
existed in the galaxy, or the galaxy cluster, than was actually observed. We
have noted already in Chap. 3 that interstellar dust is a feature of our galaxy.
Matter is also present in the remnants of dead stars, planets and asteroids,
none of which are visible from their radiation. However the sum total of all
such obscure matter is estimated to contain less mass than the visible stars. In
order to explain the anomalous orbital velocities, it would appear that there