ssuming the Big Bang is a valid theory of the
creation of Earth and the Universe, then where did the original mass
come from, that formed everything that we see today?
First of all, note that mass and energy are equivalent. So, the
total mass of the Universe need not be conserved even though the total
energy (taking into account the energy that is equivalent of the mass
in the Universe) is
conserved. Mass and energy are related by the famous equation E=mc2.
Hence if there is enough energy, photons can create matter-antimatter
pairs. This is called pair production and is responsible for the mass
in the Universe.
As to where everything came from, there is no conclusive
opinion. One idea was that the Universe was created from vacuum. This
is because according to quantum theory, the apparently quiescent vacuum
is not really empty at
all. For example, it is possible for an electron and a positron (a
matter antimatter pair) to materialize from the vacuum, exist for a
brief flash of time and then disappear into nothingness. Such vacuum
fluctuations cannot be observed directly as they typically last for
only about 10-21 seconds and the separation between the electron and positron is typically no longer than 10-10 cm. However, through indirect measurements,
physicists are convinced that these fluctuations are real.
Hence, any object in principle might materialize briefly in the vacuum.
The probability for an object to materialize decreases dramatically
with the mass and complexity of the object. In 1973, Edward Tyron
proposed that the Universe is a result of a vacuum fluctuation. The
main difficulty of
this proposal is that the probability that a 13.7 billion year old
Universe could arise from this mechanism is extremely small. In
addition, physicists would question Tyron’s starting point: if the
Universe was born from empty space, then where did the empty space come
from? (Note that
from the point of view of general relativity, empty space is
unambiguously something, since space is not a passive background, but
instead a flexible medium that can bend, twist and flex.)
In 1982, Alexander Vilenkin proposed an extension of Tyron’s
idea and suggested that the Universe was created by quantum processes
starting from "literally nothing", meaning not only the absence of
matter, but the absence of space and time as well. Vilenkin took the
idea of quantum tunneling and proposed that the Universe started in the
totally empty geometry and then made a quantum tunneling transition to
a non-empty state (subatomic in size), which through inflation (the
Universe expands exponentially fast for a brief period of time which
causes its size to increase dramatically) came to its current size.
Another idea is from Stephen Hawking and James Hartle. Hawking
proposed a description of the Universe in its entirety, viewed as a
self-contained entity, with no reference to anything that might have
come before it. The
description is timeless, in the sense that one set of equations
delineates the Universe for all time. As one looks to earlier and
earlier times, one finds that the model Universe is not eternal, but
there is no creation
event either. Instead, at times of the order of 10-43
seconds, the approximation of a classical description of space and time
breaks down completely, with the whole picture dissolving into quantum
ambiguity. In Hawking’s words, the Universe "would neither be created
nor destroyed. It would just BE."
So, the origin of mass in the Universe and the Universe itself
is quite speculative at this point. If you are interested, you can read
Alan Guth’s book "The Inflationary Universe", page 271-276. You can
also read Hawking’s "A brief history of time: From the Big Bang to
black holes" page 136.
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in the Astronomy Department
at Cornell University.
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