Analog Science Fiction & Fact Magazine
"The Alternate View" columns of John G. Cramer

Banishing the "Inflaton" from the Early Universe

by John G. Cramer

Alternate View Column AV-236

Keywords: early universe, inflation, inflaton field, Big Bang, exponential expansion, FTL, gravitational waves

Published in the May-June-2025 issue of Analog Science Fiction & Fact Magazine;
This column was written and submitted 01/07/2025 and is copyrighted ©2025 by John G. Cramer.
All rights reserved. No part may be reproduced in any form without the explicit permission of the author.

In the late 1940s, building on the ideas of Georges Lemaître and Alexander Friedmann and on Edwin Hubble's 1929 discovery that the universe is expanding, George Gamow and his students at George Washington University developed the Big Bang Model, which describes the initial stages of our universe and its evolution. It depicts a nearly infinitesimal spatial region that violently explodes, resulting in an outward momentum that opens up space-time and drives the Hubble-observed expansion of the universe.

Their Big Bang Model was initially ignored (and even ridiculed) by mainstream physics. However, in 1965 Arno Penzias and Robert W. Wilson of Bell Labs announced their accidental discovery of the 2.7° cosmic microwave background (CMB) radiation. Gamow's model had predicted that such radiation should be produced in an early phase of the Big Bang as the very hot medium permeating the universe transitioned from an opaque plasma of charged electrons and protons to transparent hydrogen gas, as electrically neutral hydrogen atoms formed and the free electric charges disappeared.

Suddenly, Gamow's under-appreciated Big Bang Model became an observationally verified fact. It rapidly replaced the reigning and widely accepted Steady State Model of Hoyle, Bondi, and Gold as the new standard model of cosmology. The Big Bang Model has since revolutionized astrophysics, leading to increased understanding of the early universe and explaining the primordial abundances of hydrogen, helium, and lithium. Unfortunately, George Gamow died of liver failure at age 64 in 1968, only three years after his Big Bang work had been spotlighted by the CMB discovery.

In the 1970s cosmologists came to realize that their new Big Bang Model, for all its powerful insights, did not explain everything about the evolution of the universe. A few serious problems seemed to be built into the description. These were characterized as the cosmological problems of Matter/Antimatter, Horizon, Flatness, Homogeneity, Isotropy, and Primordial Monopoles. (See AV-02 in the September-1984 Analog for details.)

In 1979, in an effort to address these problems, Alan Guth of Harvard University modified the Big Bang Model by introducing his "inflationary scenario", which assumes that in the very early stages of the Big Bang, for reasons he did not explain, the universe began to expand at an exponentially increasing rate under the influence of some ultra-strong repulsive force, with its radius growing much faster than the speed of light. After a brief time this rapid inflation subsided. The universe then continued to expand, but at the present more modest pace observed by Hubble.

We note that at the time of Guth's work the long term expansion rate of the universe was expected to slowly decrease from the cumulative pull of gravity, However, more recent evidence shows that this is not the case. Observations of the red shift and luminosity of Type 1A supernovas, announced in 1998, indicate that the universe's rate of expansion is actually increasing. To accommodate this result, the Standard Model of Cosmology now includes a positive cosmological constant L, signaling the presence of dark energy that increases the expansion rate of the universe in later times as it evolves.

A serious problem with the current Standard Model of Cosmology (called LCDM for Cold Dark Matter with inflation) is that the initial inflation of the universe, an important part of the model, had been "put in by hand" by Guth, with no credible explanation of why it occurred or why it stopped. The inflation concept has since been given a paste-up theoretical basis by adding a strong scalar "inflaton" field, also put in by hand, that was briefly present just after the Big Bang, producing the strong repulsive force that caused the ultra-rapid expansion. In other words, the mysterious inflaton field was there and then gone, for reasons unknown.

To put in context possible explanations of inflation, let's consider a few of the simpler mathematical models of the universe. In 1917, during his early work in applying general relativity (GR) to cosmology, Albert Einstein assumed that our universe was static, i. e., neither expanding nor contracting. That assumption, standard at the time, was not compatible with the version of GR that Einstein was using, so he introduced the cosmological constant L, which quantifies the amount of energy resident in the vacuum itself. For non-obvious reasons, if energy in the universe takes the form of mass or radiation, it produces an attractive gravitational force, but if it is present in the vacuum itself, it produces a repulsive "dark energy" force.

Einstein's static universe assumption creates constraints, leading to a GR solution called the Einstein Universe. It contains a significant matter density r (producing a gravitational pull to contract the universe), delicately balanced by a positive cosmological constant L (producing a repulsive force to expand the universe). This balance keeps the Einstein Universe static in size. We now understand that the Einstein Universe is a not good approximation to the state of our actual universe, because it does not accommodate the observed Hubble expansion.

Also in about 1917, the Dutch physicist/mathematician Willem de Sitter proposed an alternative GR solution to describe the universe. This de Sitter Universe contained no matter density of consequence, was spatially flat (no curvature), had a positive cosmological constant L>0, and was expanding. As it turns out (and contrary to Einstein's assumption), our universe is indeed expanding. Cosmologists find that the de Sitter Universe is a good approximation to the expected state of the universe in the far future, after the matter density had been diluted to near zero and expansion continues.

Later, in 1932, Einstein and de Sitter joined forces, and together they proposed the Einstein-de Sitter Universe, which is flat (no overall space curvature), has a null cosmological constant L=0, and is expanding with time t such that the universe's scale factor (~radius) increases as t^2/3. Cosmologists find that this is a good approximation to the state of the intermediate universe, well after the Big Bang but before dark energy begins to drive acceleration of the expansion.

The new ideas about inflation that we want to describe here are the work of Italian and Spanish cosmologists Bertacca, Jimenez, Matarrese, and Ricciardone (BJMR). They propose that intense scalar gravitation-based perturbations that formed just after the Big Bang produced the inflation. This scenario offers the advantage that it does not conjure up any arbitrary scalar inflaton field. The inflation occurs in a de Sitter universe in which strong gravitational waves naturally arise from quantum vacuum oscillations, and the needed scalar perturbations driving inflation are second-order effects of the intense gravitational waves. Later, when the universe transitions from a state dominated by gravitational waves to one dominated by radiation, the expansion rate diminishes to the familiar Hubble level, providing a natural explanation of why the inflation begins and ends, just as Guth hypothesized.

Why were the post-Big-Bang gravitational waves so intense that their second-order effects could produce exponential expansion of the universe? The BMJR model invokes quantum "power spectrum" effects, essentially a consequence of Heisenberg's uncertainty principle. Because the early post-Big-Bang universe was confined to such a near-infinitesimal size, the momentum wave functions describing this highly localized system must be very broad, including extremely large and energetic momentum components that would never be present in later eras. This leads to very large quantum fluctuations in the super-hot medium, which produce intense gravitational waves. These generate nonlinearities that cause deviations from the smooth Gaussian statistical behavior that characterizes most of the universe's later expansion. Thus, non-Gaussian statistics is a prediction of the BMJR model. However, as the universe expands, the large fluctuations and their consequences die off, ultimately terminating the brief period of exponential expansion that we call inflation.

That's the BJMR cosmic inflation scenario. Does it work? I'm not in a position to provide an independent opinion. However, it does seem plausible, and it provides concise model-free explanations of why inflation occurred in the early universe and why it stopped.

The other question about this work is whether or not it is capable of making predictions that can be tested by observation with existing or planned projects and instrumentation. The BJMR authors do not directly address this question, but they implicitly promise to take it up in later publications.

As I see it, there are at least two observational possibilities that might support or falsify the BJMR scenario:
(1) The assumed super-intense gravitational waves invoked in the BJMR calculations should leave behind artifacts that could be detected. Specifically, the searches for B-mode linear polarization in the cosmic microwave background (see AV-174 in the October-2014 Analog) will reach a new level of precision when the Japanese LiteBIRD satellite is launched in about 2032, and this could reveal evidence for the presence of super-intense gravitational waves and inflation just after the Big Bang.
(2) Evidence for the non-Gaussian statistical behavior predicted by the BJMR calculations might show up in analyzing the high-L (large angular momentum) components of variations in the cosmic microwave background. It is not clear whether this is possible with available Planck Mission data from 2009, but improved measurements of the cosmic microwave background are in the works. For example, CMB-S4 is a next-generation ground-based experiment supported by then US Department of Energy and the National Science Foundation that is aimed to begin full operation in the early 2030s and will use twelve telescopes at the South Pole and in the Chilean Atacama desert equipped with 500,000 cryogenically-cooled superconducting detectors to provide extensive new data on the cosmic microwave background.

In summary, a major problem with our understanding of the early universe may have been resolved, and the mysterious inflaton field may soon be given a decent burial. Unfortunately, information from both LiteBIRD and CMB-S4 will not be available until at least the early 2030s. However, ongoing analysis of data from CMB projects like PLANCK and BICEP3 might provide evidence sooner. Watch this AV Column for further developments.

John G. Cramer's 2016 nonfiction book describing his transactional interpretation of quantum mechanics, The Quantum Handshake - Entanglement, Nonlocality, and Transactions, (Springer, January-2016) is available online as a hardcover or eBook at:
http://www.springer.com/gp/book/9783319246406 or https://www.amazon.com/dp/3319246402 .

SF Novels: John's 1^st hard SF novel Twistor is available online at: https://www.amazon.com/Twistor-John-Cramer/dp/048680450X. His 2^nd and 3^rd novels, Einstein's Bridge and its new sequel Fermi's Question, are now available as eBooks from Baen Books at: https://www.baen.com/einstein-s-bridge.html and https://www.baen.com/fermi-s-question.html .

Alternate View Columns Online: Electronic reprints of 236 or more of "The Alternate View" columns written by John G. Cramer and previously published in Analog are currently available online at: http://www.npl.washington.edu/av .

References:

D. Bertacca, R. Jimenez, S Matarrese, and A. Ricciardone, "Inflation without an Inflaton," arXiv:2412.14265v1 [astro-ph.CO] 18 Dec 2024.

A. H. Guth, "The Inflationary Universe: A Possible Solution to the Horizon and Flatness Problems," Phys. Rev. D 23, 347 (1981); doi:10.1103/PhysRevD.23.347.

A. D. Linde, "A New Inflationary Universe Scenario: A Possible Solution of the Horizon, Flatness, Homogeneity, Isotropy and Primordial Monopole Problems," Adv. Ser. Astrophys. Cosmol. 3, 149-153 (1987); doi:10.1016/0370-2693(82)91219-9.

See https://litebird.isas.jaxa.jp for a description of the LiteBIRD Mission.

K. Abazajian, et al, (The CMB-S4 Collaboration), "CMB-S4: Forecasting Constraints on Primordial Gravitational Waves," Astrophys. J. 926, 54, (2022); https://arxiv.org/abs/2008.12619 .

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This page was created by John G. Cramer on 01/07/2025.