Chapter 9
Before the Big Bang
E. R. Siegel
Abstract The Big Bang has been typically identified as the beginning of the
Universe: t ¼ 0 if you extrapolate back our expanding Universe to a state of
arbitrarily high temperatures and densities. While you can naively do exactly that
in an expanding Universe under the rules of General Relativity, those conditions lead
to observable effects that run contrary to what we see. Instead, the Universe is better
described by cutting off the matter-and-radiation dominated Universe at some early
time, patching on an inflationary epoch where space is expanding exponentially and
dominated by some sort of vacuum energy. This is not mere theory nearly 40 years
on, but is supported by a vast suite of observable evidence. The case for this
conclusion, even in the absence of B-mode polarization in the CMB, is laid out here.
9.1 Introduction
There is, perhaps, no greater question in all of cosmology than the one concerning
the origin of the Universe. When Albert Einstein first put forth his General Theory of
Relativity, it was quickly recognized that the only static solutions containing matter
required an inordinate amount of fine tuning and were inherently unstable. One of
the earliest sets of solutions discovered were of isotropic, homogeneous Universes
filled either with a cosmological constant or with a mix of matter, radiation, and
spatial curvature. In both cases, it was found that the Universe cannot be static, but,
depending on the initial conditions, will either expand or contract over time.
The revelation that, unlike in Newtonian physics, Einstein’s equations admitted
an evolving Universe solution, meant that spacetime was not necessarily static over
time. In fact, the Universe could be full of many different types of matter and energy
and still expand or contract. This was a big deal, because not only was our Universe
full of stars, but galaxies as well. Making use of Leavitt’s Law, Edwin Hubble
became the first to measure the distance to a galaxy other than our own, by
discovering Cepheid variables in the great Andromeda nebula, M31. Leavitt’s Law
E. R. Siegel (*)
Lewis & Clark College, Portland, OR, USA
© Springer Nature Switzerland AG 2021
B. G. Sidharth et al. (eds.), Fundamental Physics and Physics Education Research,
https://doi.org/10.1007/978-3-030-52923-9_9
85
Before the Big Bang
E. R. Siegel
Abstract The Big Bang has been typically identified as the beginning of the
Universe: t ¼ 0 if you extrapolate back our expanding Universe to a state of
arbitrarily high temperatures and densities. While you can naively do exactly that
in an expanding Universe under the rules of General Relativity, those conditions lead
to observable effects that run contrary to what we see. Instead, the Universe is better
described by cutting off the matter-and-radiation dominated Universe at some early
time, patching on an inflationary epoch where space is expanding exponentially and
dominated by some sort of vacuum energy. This is not mere theory nearly 40 years
on, but is supported by a vast suite of observable evidence. The case for this
conclusion, even in the absence of B-mode polarization in the CMB, is laid out here.
9.1 Introduction
There is, perhaps, no greater question in all of cosmology than the one concerning
the origin of the Universe. When Albert Einstein first put forth his General Theory of
Relativity, it was quickly recognized that the only static solutions containing matter
required an inordinate amount of fine tuning and were inherently unstable. One of
the earliest sets of solutions discovered were of isotropic, homogeneous Universes
filled either with a cosmological constant or with a mix of matter, radiation, and
spatial curvature. In both cases, it was found that the Universe cannot be static, but,
depending on the initial conditions, will either expand or contract over time.
The revelation that, unlike in Newtonian physics, Einstein’s equations admitted
an evolving Universe solution, meant that spacetime was not necessarily static over
time. In fact, the Universe could be full of many different types of matter and energy
and still expand or contract. This was a big deal, because not only was our Universe
full of stars, but galaxies as well. Making use of Leavitt’s Law, Edwin Hubble
became the first to measure the distance to a galaxy other than our own, by
discovering Cepheid variables in the great Andromeda nebula, M31. Leavitt’s Law
E. R. Siegel (*)
Lewis & Clark College, Portland, OR, USA
© Springer Nature Switzerland AG 2021
B. G. Sidharth et al. (eds.), Fundamental Physics and Physics Education Research,
https://doi.org/10.1007/978-3-030-52923-9_9
85