Origin of Everything: Hot Bang or Ageless Universe?
The primary message of this article is that as of 1955, there were two
equally probable theories for the origin of the Universe – the
steady-state theory and the evolutionary Universe theory (later known as
Big Bang theory). At the time, the observational evidence was
insufficient to decide between the two theories.
In the 1950s there were two theories regarding the nature of the
universe: the Steady State and the Big Bang. At that time, there was
not sufficient observational evidence to clearly favor or disprove
either of them.
The British astronomer Fred Hoyle was the champion of the Steady
State theory. He, Tommy Gold, and Hermann Bondi developed this theory
after seeing the movie Dead of Night, which ends the way it
begins. Hoyle thought that the universe could be unchanging but dynamic.
So as the universe expands, matter is created to fill the space. It
would require only 1 hydrogen atom per cubic meter every 300,000 years
(comparable to "a few hundred atoms per year per galaxy"). Hoyle
developed the "Perfect Cosmological Principle", which states that the
universe is the same at any place and at any time.
The "Evolutionary" model for the universe (a.k.a. "Big Bang") was
built on theoretical work in the 1920s and 1930s. In the 1940s, George
Gamow was trying to solve the problem of the origin of the chemical
elements. He determined that most elements could not form in the
early universe - the right conditions of temperature and density would
not last long enough. With Alpher, he showed that hydrogen and
helium would form (and in the right proportions), but nothing heavier.
(Later astronomers figured out how heavier elements could be made in
the dense hot core of stars.). In doing this, Gamow developed many of
the fundamental ideas about the early "evolutionary" universe. He
developed the relation between temperature and mass density,
recognized that atoms (not just nuclei) would form only after the
universe had cooled sufficiently, and developed the theory of early
galaxy formation. In 1949 Alpher and Herman redid these calculations,
and in doing so predicted a "relic primordial radiation" with a
temperature of about 5 K. They didn't think this would be detectable,
and indeed instruments at the time could only detect a background
radiation of only 20 K.
Both theories made predictions. Some are described in the table below
| Issue |
Steady State |
Big Bang |
| Density of the Universe |
The density is constant |
The density changes, but do known physical laws apply at
early time of very high density? |
| Age of the Universe |
Ageless |
In 1955, Big Bang gave an age less than known age of solar
system |
| Rate of Expansion |
Expansion is constant |
Expansion should slow |
| Ages of Galaxies |
Old and young Galaxies should be mixed in space |
Galaxies age with time |
| Background Microwave Radiation |
There should be none |
It should exist, with a temperature of about 5 K |
In the 1950s, the evidence was mixed. A number of observations seemed
to favor the Big Bang, but it was not definitive. The fact that the
age derived for the Big Bang was less than the known age of the Solar
System was a major problem. However, there was no conclusive evidence
for one theory or the other.
Interestingly, the presence of the Steady State as a competing theory
provided the impetus to make the observations to test the theories.
Side Notes:
-
Interestingly, one of Thomas Bondi's major contributions to astronomy came with
the discovery of pulsars in 1967. He was the first to explain them as
rotating neutron stars, which turned out to be correct.
-
As a bit of joke, Gamow asked Hans Bethe if his name could be included
on the paper Gamow was writing with Alpher. Bethe, who had not
participated at all in the research, agreed. So the initial paper on
the Big Bang was authored by Alpher, Bethe and Gamow, reminiscent of
the first three letters of the Greek alphabet.
-
Alpher was Gamow's graduate student, and only after many years did he
get full credit for working out Gamow's ideas, and predicting the
cosmic microwave background. In the mid-1950's Alpher and Herman's
theories were challenged by supporters of the Steady State. Alpher and
Herman were nearly forgotten when Penzias and Wilson discovered the
cosmic microwave background in 1965 (although Penzias mentioned their
work in his Nobel lecture in 1978). Alpher received honors starting in
the 1970's culminating with the National Medal of Science (the highest
scientific honor in the US) two weeks before he died in 2007.
Other resources
The following web pages have more detailed information:
-
Arno
Penzias' Nobel Prize Lecture describes the development of the Big
Bang theory and how astronomers wrestled with the problem of the
origin of the chemical elements.
-
Big Bang or Steady State? - an article from the American Institute
of Physics describing the issues surrounding these two theories.
|
