but the multiverse...!
by David Siegrist
Experts agree that natural laws have precise values and relationships to each other that in combination permit life to exist in the universe. This is referred to as cosmological “fine tuning” (see below). Theists say this must be the work of a supreme creator. Others may claim that science explains the world with no need for religion. Naturalists, who do not believe in anything supernatural, propose that there is a multiverse that explains the fine tuning. That is, they posit that an infinity of universes exist with multiple sets of natural laws, and that we are just the lucky winners in a cosmic lottery that does not require any omnipotent fine tuner. A leading exposition of this view is The Hidden Reality by Brian Greene.
Theorists cite several underlying scientific constructs to support the Multiverse’s existence, including eternal inflation and the string theory landscape. This paper is going to briefly describe eternal inflation, the string theory landscape, and the multiverse contention, and then discuss the implications for the fine-tuning argument.
Scientists believe that our universe came to be some 13.8 billion years ago in a hot Big Bang. It expanded and cooled, eventually forming matter, stars, and even planets like our own. Evidence for this includes the fact that distant galaxies are moving away from us in all directions. In addition, there is a cosmic background radiation (CBR) all around that represents remnants of the huge explosion. However, this background radiation seems too uniform for some, as though it were all touching at some point, although that appears to be impossible. Alan Guth developed the theory of inflation to account for this ‘excess uniformity,’ positing that the universe went through a rapid inflationary expansion quite early on, which had a smoothing effect on the CBR.
Most astrophysicists accept the general concept of inflation, and some tend to extend it further. They posit that our section of inflation collapsed, perhaps due to a quantum fluctuation. However, inflation itself continued indefinitely at an exponential rate, according to Andrei Linde – hence the concept of eternal inflation. It is moving along, and as areas of it decay, they form new pocket universes as energy is released in big bangs. These universes continue to expand, as ours did, but more slowly than inflation. So they may never bump into each other, because space-time itself is being created between them. In this manner, perhaps an infinity of universes may be created by the collapse of the original inflaton (a speculative field that is not otherwise observed).
Eternal inflation is a popular academic concept. However, it is more speculative and less accepted than the original construct. Moreover, although conceptually eternal inflation may spawn numerous universes, it does not cause such universes to have different physics until it is coupled with another theory.
String Theory Landscape
String Theory (ST) is a leading attempt to reconcile the two leading theories of the physical world, Quantum Mechanics (QM) and General Relativity (GR). QM and GR have enjoyed great empirical success. However, efforts to unify them have been frustrated thus far. ST is a leading candidate to do so. ST’s fundamental particles are tiny strings that can vibrate, stretch, and be open or closed in a loop. However, to make the underlying mathematics work, scientists need to posit the existence of ten dimensions. They then need to hide the extra six spatial dimensions by compacting them into tiny manifolds. And in these shimmering manifold appearances lie the explanations for all phenomena we observe, matter and space-time included. For instance, differing vibrations may manifest as force carriers with different properties, such as those found in the Standard Model (although matter “particles" may require supersymmetry).
There are many ways that the extra dimensions may be curled up, sometimes estimated as 10^500, a number far larger than the number of atoms in the observed universe, for instance. Detractors claim that so many possible solutions limit ST’s capability to predict anything. More recently, advocates have turned the objection into a possible advantage. They claim that each different pathway might bring a different physics solution to that particular instantiation of a universe, based on its underlying string configuration and energy.
Coupled with eternal inflation, this could mean that there is an almost infinite number of chances to draw a physics configuration for a universe out of the ST landscape. That way even an “unnatural” universe, such as our own, with its weak gravity and minute cosmological constant, would eventually come to be. Or so a standard multiverse construct holds.
Such theories have drawn critics as well as advocates. Amanda Gefter quotes Paul Steinhardt and Max Tegmark on their skepticism regarding inflation . Ethan Siegel quotes Stephen Hawking’s last paper on his interpretation that inflation may lead to just one universe. 
String Theory and Multiverse Skepticism
There is some disagreement among scientists whether string theory is an actual scientific theory, since it doesn’t seem to be able to make predictions or be observed, let alone tested. Sean Carroll and others have advocated that the requirements for scientific claims need to be loosened, including allowing for abduction, “inference to the best explanation.”. .  Critics might point out that once one allows arguments from abduction, someone claiming that “God did it” as an explanation for fine-tuning, may prove more compelling than explaining ten dimensions and inflatons.
In addition, the concept of the multiverse cannot be taken to mean that the mystery of existence has been solved. "That is simply not true," Paul Davies says. “…All theories of the multiverse assume quantum physics to provide the element of spontaneity, to make the bangs happen. They assume pre-existing space and time. They assume … a whole host of pre-existing conditions."  And those pre-existing conditions would, of course, themselves require explanations. “Having all possible universes is not an explanation, because by invoking everything, you explain nothing," Davies adds.
What if String Theory is True?
If some form of string theory turns out to be true, it would be hard to know it, because strings are so fantastically small. However, I believe they would still not offer a potentially limitless number of solutions to the laws of physics. For instance, there are very significant consistency and stability issues that need to be worked out for individual paths of strings. In addition, only high-energy solutions may be viable.
Even if there were a great number of potential string solutions remaining, it might still be a very unlikely event that a world would come from them that would support life, especially life that could make the universe self-aware, as ours is. Since string theory is intended to reconcile quantum mechanics and general relativity, its solutions should tend to be at least somewhat related to phenomena we have already seen, such as those described by the Standard Model. Furthermore, multiverse theories may invoke QM for initiation and seeding large-scale structure in their constructs.
Each universe’s “rules” would need to be incredibly coherent to support complexity as ours does. For example, our universe started with extremely low entropy. Increasing entropy is a way that structure is created in our world, according to the Second Law of Thermodynamics. Roger Penrose calculated that the likelihood of that low amount of entropy at the beginning is 10^-123 .
In addition, critical aspects of our existence are all intimately related. The strength of the four forces in our world, along with the masses of particles of matter, the speed of light, and several other key factors, including the Cosmological Constant and the Fine Structure Constant, are all precisely related. Their relationships are fine-tuned, sometimes to the 50th decimal place. Without those exact relationships, for instance, the Big Bang might have turned quickly into the Big Collapse, or conversely into the Big Rip of runaway expansion.
In another example of fine tuning, the universe might have no carbon or hydrogen, or be all hydrogen. Luke Barnes has highlighted the fact that for interesting chemistry to be possible, the weight ratio of up quarks to down quarks (the components of protons and neutrons) must have a precise ratio that is astronomically minuscule in possibility space.
It is therefore unsurprising that Einstein claimed that there may be only one way to reconcile all the interdependencies in natural laws and constants to enable the world we know to exist. In fact, string theory might even be considered a somewhat elegant way for a superior being to manage to fine-tune all those critical parameters just to get one or a few solutions that in the end would support the development of intelligent life.
The concepts of eternal inflation, string theory, and the multiverse are intriguing and stimulating. One or more might be true. However, they are also extremely speculative for reasons I have begun to describe. Further, they are largely non-falsifiable. Therefore they don’t qualify as “normal science,” which has observable phenomena, supports predictions, and is testable. So it appears overreaching to claim that “science” vouchsafes the multiverse and obviates the need for any cosmological fine-tuner. Rather, it is more like informed speculation, which is fine if it is done self-consciously and labeled as such. To believe that this fantastically improbable world came together merely through chance is a real act of (misplaced) faith.
 George F. R. Ellis. “Does the Multiverse Exist?” Scientific American. August 2011 https://www.scientificamerican.com/article/does-the-multiverse-really-exist/ Accessed June 22, 2108
 “String Theory Meets Loop Quantum Gravity”. By Sabine Hossenfelde Quanta Magazine https://www.quantamagazine.org/string-theory-meets-loop-quantum-gravity-20160112/ Jan 12, 2016
 Amanda Gefter “What Kind of Bang Was the Big Bang?” 29 June 2012 New Scientist. “We thought that inflation predicted a smooth, flat universe,” says Paul Steinhardt of Princeton University, a pioneer of inflation who has become a vocal detractor. “Instead, it predicts every possibility an infinite number of times. We’re back to square one.” Max Tegmark agrees: “Inflation has destroyed itself. It logically self-destructed.”
 Ethan Siegel. “I Am An Astrophysicist. Here's What Stephen Hawking's Final Paper Was Actually About.” Forbes. March 21 2018. “Hawking and his co-author contend that the exit from inflation doesn't give you something eternally inflating into the future, with disconnected pockets where hot Big Bangs occur, but rather that the exit is finite and smooth. In other words, it gives you a single Universe, not a series of disconnected Universes embedded in a larger multiverse.”
 Sean Carroll. “Beyond Falsiﬁability: Normal Science in a Multiverse”. California Institute of Technology, Pasadena, CA 91125, U.S.A. January 17, 2018 “I argue that the way we evaluate multiverse models is… on the basis of abduction, Bayesian inference, and empirical success. There is no scientiﬁcally respectable way to do cosmology without taking into account diﬀerent possibilities for what the universe might be like outside our horizon. Multiverse theories are utterly conventionally scientiﬁc, even if evaluating them can be diﬃcult in practice.”
 Paul Davies quoted in Robert Lawrence Kuhn, “Confronting the Multiverse: What Infinite Universes Would Mean,” in Closer to Truth, December 2015. https://www.space.com/31465-is-our-universe-just-one-of-many-in-a-multiverse.html Accessed June 22, 2018.
 Iosif Bena and Mariana Grana. “String Cosmology and the Landscape”. Comptes Rendus Physique 18 2017) 200-206.
 Laura Mersini-Houghton. “Selection of the Initial Conditions from the Landscape Multiverse.” Perimeter Institute. Jul 14, 2011. http://pirsa.org/11070024 Accessed 6-22-18.
 Roger Penrose cited in Robert Spitzer, New Proofs for the Existence of God, Eerdsman Publishing, Grand Rapids, MI. 2010. Pp 57-59.
 Paul Davies. Accidental Universe, 1982. Cited in Robert Spitzer, New Proofs for the Existence of God, Eerdsman Publishing, Grand Rapids, MI. 2010, pp. 59-62. For example, “take the Fine Structure Constant denoted by the Greek letter α, alpha. Were α to change by 4%, stellar fusion would not produce carbon, so that carbon-based life would be impossible. If α were greater than 0.1, stellar fusion would be impossible and no place in the universe would be warm enough for life as we know it. α is in turn related to a number of things that would not seem intuitive, including the value of the electron’s negative charge, π ; the reduced Planck constant ħ = h/2π; the speed of light; the permittivity and permeability of free space; and others. Α is a key factor in quantum electrodynamics and the electroweak theory, among others.”
 Barr, S. M. & Khan, A., 2007, PhRvD, 76, 045002 cited by Luke Barnes, “The Fine-Tuning of the Universe for Intelligent Life “ Publications of the Astronomical Society of Australia, 2012, 29, 529–564 http://dx.doi.org/10.1071/AS12015.
 Robbert Dijkgraaf. “There Are No Laws of Physics. There’s Only the Landscape.” Quanta Magazine https://www.quantamagazine.org/there-are-no-laws-of-physics-theres-only-the-landscape-20180604/ June 4, 2018
David Siegrist discusses science and religion periodically at the National Presbyterian Church Wrestlers’ Class. He has a Ph.D. in Biodefense from George Mason University. His research had to do with evaluation of statistical anomaly detection for early warning of outbreaks of disease. He is currently employed by the MITRE Corporation. (The author’s affiliation with the MITRE Corporation is provided for identification purposes only, and is not intended to convey or imply MITRE’s concurrence with, or support for, the positions, opinions, or viewpoints expressed by the author).