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If God created the world, where was he before the Creation?…Know that the world is uncreated, as time itself is, without beginning and end.

—Mahaprana (India, ninth century)

AFTER THE BANG

Atomism postulates a universe composed of submicroscopic particles that possess the measurable quantities of mass, energy, and momentum that characterize the inertia we associate with matter. They kick back when you kick them. So far, we have focused on the nature of the particles themselves and the history of how our current understanding of their nature has come about. We have seen how the reductionism explicit in the atomic model was, and still is, widely unpopular with those whose philosophical and theological sentiments embrace a more holistic picture of a universe in which everything is closely connected to, and dependent on, everything else along with, perhaps, some outside power.

Atoms, by contrast, are only weakly connected to one another. They move around mostly independently in mostly empty space and interact only when they collide with one another, occasionally sticking together to form composite masses. Because we and the stuff around us are examples of such composite masses, we tend to think this is an important characteristic of matter. In fact, the universe is largely composed of particles in random motion that rarely interact. And there is no holism or outside power in atomism.

Only when the evidence became unassailable did the antiatomists finally admit, at least, that atoms serve as a good model for describing scientific observations and may even be “real.” Even now, however, the ancillary implications of atomism explicit in the philosophy of Democritus, Epicurus, and Lucretius are not palatable to many of those who otherwise accept the atomic model. Atomism, after all, is atheism.

The early atomists imagined a cosmos that was quite different from the conventional view that grew out of religious tradition. Most cultures have assumed a universe finite in size that came into existence at a finite time in the past by means of the purposeful act of a Creator, or perhaps some impersonal but still supernatural force. In the common theological view, not only matter and energy but also space and time themselves came into being at that pregnant moment.

Most who read this book will be familiar with the creation story in Genesis from the Hebrew Bible and Christian Old Testament. The Qur'an tells a similar tale. In 1927, a Belgian Catholic priest, Georges Lemaître (1894–1966), first proposed what was later dubbed the “big bang.”1 That is, he showed that Einstein's equations of general relativity implied an expanding universe that resembled an explosion.

Popes, theologians, and other religious figures seized on the big bang as providing scientific verification of a divine creation. In 1951, Pope Pius XII told the Pontifical Academy, “Creation took place in time, therefore there is a Creator, therefore God exists.”2 Lemaître, a good scientist as well as a priest, wisely advised the pope not make this statement “infallible.”

Even Einstein did not initially believe Lemaître, despite the fact that Lemaître had used Einstein's own equations to infer that the universe was expanding. Einstein still held to the almost-universal belief, found in Genesis and elsewhere, that the universe is composed of a “firmament” of more or less fixed stars that remain, on average, the same distance apart. His gravitational equation has a constant term in it that, when positive, results in a gravitational repulsion. He called this the cosmological constant and conjectured that it provided the repulsive gravitational force needed to balance the familiar gravitational attraction and keep the universe stable.

Although this is not widely known, Lemaître had data to back up his proposal. Unfortunately, his paper was in French and was not immediately translated into English.3 Independent confirmation, in English, came in 1929 when Edwin Hubble (1889–1953) in California determined from his and other's observations that the galaxies are, on average, moving away from us at speeds roughly proportional to their distances. That is, when you make a plot of the recessional speeds of galaxies versus their distances, what is called the Hubble plot, the data points scatter around a straight line. This was just what was to be expected if the galaxies were remnants of a giant explosion that occurred in the past, now estimated to be 13.75 billion years ago.4

Once the universe's expansion was confirmed, it became generally assumed that the cosmological constant is identically zero. Einstein called his inclusion of the constant in his theory his “greatest blunder.”5 However, it was certainly not the “fudge factor” that it is usually portrayed as in the literature. This is a derisive term applied to an arbitrary quantity added to an equation to make it agree with the data. The cosmological constant was already in Einstein's equation, and he had no theoretical reason to set it to zero.

INFLATION

When Einstein's gravitational equation, including a positive cosmological constant, is applied to a universe empty of matter, it predicts an exponentially expanding universe. Here, the term matter includes familiar objects with mass as well as electromagnetic radiation, which we have seen is a form of matter (photons). In the 1980s, several physicists independently proposed that during a tiny interval of time (10–35 second or so) after the universe first appeared, it underwent a rapid, exponential expansion called inflation.6

The expansion observed in the data by Lemaître and Hubble was far from exponential. Rather it appeared to be linear. That is, when the recessional speeds of galaxies were plotted against their distances, they appeared to be scattered around a straight line. This is exactly what you would expect in an explosion when the pieces go flying off independently of one another. The faster pieces will go farther.

This picture, however, was inconsistent with other observable facts. First, the universe appears very homogeneous and isotropic, as if it has reached some kind of equilibrium. But the farthest galaxies on opposite sides of the universe traveling near the speed of light relative to one another could never have been in causal contact in the linear scenario. That is, in the linear scenario, the universe did not have time to equilibrate. This was called the horizon problem.

Second, the measured average density of matter in the universe seems to be precisely equal to the critical density at which the universe is geometrically flat. That is, although general relativity describes space-time in terms of non-Euclidean geometries, the data indicate, on average, a Euclidean universe. This was called the flatness problem because Euclidean space, such as a plane, is flat, while non-Euclidean space, such as the surface of a sphere, is curved. A flat universe is very unlikely in the linear scenario.

Furthermore, Grand Unification Theories (GUTs) implied that the universe is filled with magnetic monopoles (see chapter 6) produced in the early universe. Yet, after intense searches, none have been found. This was called the monopole problem.

Inflation solved all three problems. During the inflationary phase, the universe expanded so enormously that the galaxies in all directions and at all distances came from the same original region of space. This solved the horizon problem. To see how the flatness problem was solved, think of the surface of a balloon blown up to huge size. A small patch on the surface of the balloon will be very flat. Our universe is like that patch. Note that other patches exist on the rest of the surface. The full surface of the balloon represents the universe that, in the inflationary scenario, must exist outside our light horizon. The light horizon defines the distance within which light can have reached us in 13.7 billion years. One estimate is that 10100 as many galaxies exist there, beyond our reach, as the 100 billion or so within our horizon.

As for magnetic monopoles, because they were produced only in the early universe, inflation spread them over the entire universe, including the enormous part now beyond our horizon. The chance of finding one is negligible. That doesn't mean we should stop looking. If some are found, inflation might be in trouble.

Inflation also solves another problem. It provides a mechanism for the formation of galaxies. Observations by a series of increasingly more sophisticated space-born instruments, notably the Cosmic Background Explorer (COBE)7 and the Wilkinson Microwave Anisotropy Probe (WMAP),8 have provided incredibly precise measurements of the cosmic background radiation. This is a thermalized gas of the very low-energy photons left over from the big bang that fills the universe. These photons have been cooled to 2.7 degrees Kelvin by the universe's expansion and are in the microwave region of the electromagnetic spectrum.

While highly uniform and isotropic, observations reveal a small fluctuation of one part in one hundred thousand. Cosmological models that combine inflation and the (almost) linear big bang nicely account for just the right amount of matter clumping to form the first galaxies around 13 billion years ago.

I don't want to sweep under the rug problems with the inflationary model, which has a number of prominent opponents. However, their objections are theoretical and philosophical rather than observational. No noninflationary model exists that answers as many questions and fits all the data as well as inflation.

Let me list some of the achievements of WMAP, which quantitatively define the universe far better than ever before:9

THE STUFF OF THE UNIVERSE

In this book, we have worked our way from the speculations of the ancient Greek philosophers on the nature of matter to our current understanding in terms of the elementary particles of the standard model. We saw that physicists who work at particle colliders deal with hundreds of varieties of tiny objects that they describe with three generations of quarks, leptons, and gauge bosons (see table 11.1). For most scientists, the situation is even simpler; everything they deal with can be accounted for by four particles: the u and d quarks, the electron, and the photon. They deal with only matter on Earth. Astronomers, cosmologists, and particle physicists have to deal with the matter in a whole universe. What do they find?

Let us begin with the matter that composes the stars and planets. That turns out to be the same simple stuff, chemical elements made of the same quarks and electrons, as we see on Earth. Not terribly interesting to the cosmologist, but that's not all there is. In fact, the luminous matter in stars comprises only 0.5 percent of the mass of the universe.

In the 1930s, astronomers noticed that the orbital speeds of stars at the edge of the Milky Way do not have the values that they should have according to Newton's law of gravity and the observed distribution of visible matter in the galaxy. In fact, their orbits are best described as if they are moving through invisible matter of more or less uniform density and extending well beyond the luminous stars in our galaxy. In the years since, other observations in the Milky Way and beyond have indicated that about 23 percent of the mass of the universe is comprised of this invisible form of matter dubbed dark matter.

Besides the measurements of stellar motions, a number of other types of observations have confirmed the existence of dark matter.10 One of the most convincing and exotic is gravitational lensing. Galaxy clusters are dense groups of hundreds of galaxies held together by gravity. Light from objects behind a cluster can be bent by this strong gravity. A lensing effect sometimes occurs, resulting in multiple images of the source in our telescopes. Measurements on such images enable the mass of the clusters to be estimated. These turn out to be much higher than the mass estimated from the emitted light.

As we saw above, WMAP has also confirmed the existence of dark matter and has provided the best estimate of its contribution to the mass of the universe.

WHAT IS THE DARK MATTER?

Let us ask, what should be the properties of whatever entities comprise dark matter? First of all, they must interact very weakly with normal matter, or else they would have been detected by now. For the same reason, they must be electrically neutral. Second, they are likely to be massive in order to produce their large gravitational effects, although it's possible that they are very light and there are just many of them.

A variety of cosmological evidence implies that dark matter cannot be composed of the same elementary particles that have been identified as the ingredients of all the matter we observe on Earth, including the most exotic particles that have so far been produced in colliding-beam experiments or observed in cosmic rays. This matter is referred to as baryonic because most of its mass is in the heavier particles such as the proton and neutron, which are classified as baryons.

The evidence for the dark matter not being baryonic requires some explanation. It is important to one of the themes of this book, which is to demonstrate the great extent of our current knowledge of the nature of the matter in our universe.

We have covered in great detail the highly successful standard model of elementary particles and forces. In the last few decades, data from Earth- and space-based telescopes covering the full electromagnetic spectrum, from radio to gamma rays, have enabled cosmologists to develop a standard model (with variations) of their own to describe this wealth of data.

The standard model of cosmology includes a quantitative description of the synthesis of the nuclei of the light chemical elements hydrogen, helium, and lithium in the early big bang. The two isotopes of hydrogen, 1H1 and 1H2, and of helium, 2He3 and 2He4, are included (see chapter 8 for notation). The abundances of these nuclei are very sensitive to the baryon density of the universe, which is estimated to be about 5 percent of the observed density of all matter, including 4.5 percent nonluminous baryonic matter. Thus, 95 percent of the matter of the universe is nonbaryonic. As mentioned, the dark matter is about 23 percent while the rest is dark energy, which will be covered in the next section.

The favorite candidates for the dark matter are WIMPs, weakly interacting massive particles.11 Several theories for new physics at energies beyond about 1 TeV, where electroweak symmetry is no longer broken, in particular supersymmetry (see chapter 11), predict a new, stable WIMP at a mass of about 100 GeV. The favorite SUSY candidate is the neutralino, a combination of the spartners of the photon, Z boson, and neutral Higgs boson. SUSY also predicts several Higgs bosons, including some that are charged, not to mention the higgsino, the spartner of the Higgs.

Searches for dark matter are underway in both collider and deep underground laboratories.12 It can be anticipated that the LHC will either confirm supersymmetry or dispose of it. Since it has already produced a 125 GeV Higgs, a WIMP of about the same mass is well within its capability. Physicists were surprised and delighted that the Higgs candidate appeared in only two years of running. They expected that SUSY would be seen first, and this did not happen. In fact, as mentioned in the previous chapter, doubts are beginning to surface on the validity of SUSY. Hopefully the issue will be settled before the LHC shutdown in 2013. If not, it certainly will be settled after the shutdown, since the machine energy will be doubled.

Other non-SUSY candidates for the dark matter include sterile neutrinos. Sterile neutrinos could constitute both the ingredient of dark matter and a pointer to new physics.13 As mentioned earlier, it was demonstrated in 1998 that neutrinos have mass. Massless particles with spin have the feature of always spinning either in the same direction as their motion, like a right-handed screw, or opposite. Neutrinos are observed to have left-handed “helicity,” that is, to spin opposite to their direction. Antineutrinos are right-handed, like a normal screw.

However, when a particle has mass, it travels at less than the speed of light, and you can always find a reference frame with either helicity. It follows that neutrinos must have a small right-handed component while antineutrinos have a small left-handed part. Since these components are not observed, they may possibly be “sterile,” meaning, they interact mainly gravitationally. In that case, they are good candidates for dark matter.

Interest in sterile neutrinos has been piqued by several hints in neutrino experiments and astronomical observations.14 None are sufficiently significant, however, to claim a discovery.

Sterile neutrinos would have to have a mass of a few keV (1 keV = 1,000 eV), much heavier than normal neutrinos but still much lighter than electrons, to constitute the dark matter. The main decay mode of a sterile neutrino is into two normal neutrinos and an antineutrino, which is not very detectable, to say the least. However, the decay into one normal neutrino and an x-ray photon is detectable in the diffuse cosmic x-ray background, at least in principle. To constitute the dark matter, the average lifetime of the sterile neutrino must be more than a billion years.15

Another long-considered candidate is a hypothetical particle called the axion. This particle would help solve some technical problems with quantum chromodynamics. Laboratory measurements constrain its mass to about 10–4 eV.16

DARK ENERGY

We have seen that the recessional speeds of galaxies have indicated a simple linear relationship between distance and speed in the Hubble plot. While speeds are easy to measure from the redshifts of spectral lines, measurements of distances are much more difficult and, until recently, were very crude. In the late 1990s, two independent projects were able to improve the accuracy of distance measurements to galaxies. Using ground-based telescopes, astronomers studied exploding Type 1a supernovas inside galaxies. Such supernovas provide excellent “standard candles” because of the consistency of their peak luminosities. Type 1a supernovas result from the explosion of white dwarf stars, which occur only in a narrow range of stellar mass.

Both groups expected to find evidence for the plot of distance versus speed to start turning down at great distances as gravity acts to slow the expansion. Instead, they got the surprise of their lives (and the Nobel Prize to boot): the curve turned up instead of down.17 They found that, using the Type 1a supernovae as standard candles, galaxies at a given redshift (higher recessional speed) were farther away than expected, indicating that the universe is undergoing an acceleration of its expansion rate. The universe is falling up!18

Since then, this result has been amply confirmed by the Hubble Space Telescope and other observations. The expansion of the universe is speeding up. Furthermore, whatever is responsible for this acceleration is the main ingredient of the universe, its energy density constituting 73 percent of the mass/energy density of the universe. This ingredient is called dark energy to distinguish it from dark matter, although both are fundamentally material in nature.

While surprising, the result was not totally unanticipated or completely mysterious. As we saw above, Einstein's cosmological constant, if positive, will produce a gravitational repulsion.19 Further observations so far are consistent with the interpretation that the cosmological constant, which is equivalent to an energy density, is the source of dark energy. However, other possibilities for the source of the cosmic acceleration20 are actively under consideration because, as we will see next, the cosmological constant option has a serious difficulty.

Alternatively, a gas can have negative pressure and gravitational repulsion under the right conditions. A field of particles might exist throughout the universe, somewhat like the Higgs field, that has negative pressure and produces gravitational repulsion and the acceleration of the expansion of the universe.

THE COSMOLOGICAL CONSTANT PROBLEM

In 1989, Steven Weinberg published a paper showing that a huge discrepancy existed between the observed upper limit on the cosmological constant and the value calculated from elementary particle physics.21 The cosmological constant is equivalent to a field of constant energy density filling the vacuum of space. Recall from chapter 9 that quantum fields have a zero-point energy that corresponds to a state in which no quanta of the field are present. This can be interpreted as the energy density of the vacuum.

The calculation of that energy density is very straightforward.22 Assuming only photons or other bosons, the result is 120 orders of magnitude higher than what is observed. This is the number you usually see in the literature. However, recall that fermions have a negative zero-point energy and when they are included, the discrepancy is lower. Nevertheless, the difference is still at least 51 orders of magnitude, so the problem remains a problem. This calculation is often characterized as the worst in physics history!

Weinberg and others have considered various ways out. However, we can think of at least one reason why the calculation has to be wrong, other than the obvious fact that it is so grossly inconsistent with the data. The energy-density estimate is made by summing up all the quantum states throughout a sphere within the universe. However, the number of states in such a sphere cannot be greater than that of a black hole of the same size. And it can be shown that the number of states of a black hole is proportional to its surface area, not its volume. When the calculation is redone summing over the states on the surface of the sphere, the resulting energy density is very close to the density of the universe.23 Because the density of the dark energy is 73 percent of the total, this is good agreement indeed.

However, I may have oversimplified the situation, since this solution to the cosmological constant problem is far from achieving a consensus. In any case, a number of other solutions have been proposed, and we just have to await one that satisfies the experts.

BEFORE THE BANG

The theologians who waxed so enthusiastic about the big bang were well aware that the cosmological model bore little, if any, resemblance to the creation story in Genesis or that of any other religious tradition for that matter. The key point for them was that science was providing evidence that a beginning did in fact occur, that there was a moment in the past when the universe appeared out of nothing: creation ex nihilo.24

Furthermore, as shown in 1970 by Stephen Hawking and Roger Penrose, Einstein's general theory of relativity implies that the universe at its first moment of existence was a singularity, that is, an infinitesimal point in space of infinite energy density.25 This meant that not only was matter created at that moment, but so were space and time. As we saw in chapter 2, Augustine addressed the question of what God was doing in all that time before he created the universe by saying that God created time along with the universe.

A finite, created universe conflicts with the teachings of the atomists that the universe is eternal and boundless. In chapter 1, Epicurus was quoted as saying, “The universe is without limit.” The big bang seemed to refute atheist atomism.

However, there was a fly in the ointment. General relativity is not a quantum theory and so does not apply to a region of space less than 1.616 × 10–35 meter in diameter, called the Planck length, named for the physicist Max Planck who, as we saw in chapter 7, initiated the quantum revolution. Applying the Heisenberg uncertainty principle of quantum mechanics, it can be shown that it is fundamentally impossible to define a smaller distance or to make any measurements inside a region of that size.26 Basically, we can have no information about what is inside a sphere with a diameter equal to the Planck length. It is a region of maximal chaos.

The uncertainty principle also mandates that no time interval shorter than 5.391 × 10–43 second, called the Planck time, can be measured. Thus, our cosmological equations, derived from general relativity, can apply only for times greater than the Planck time and only for distances greater than the Planck length. Although their singularity proof was correct for the assumptions made, both Hawking and Penrose long ago agreed that it does not apply once quantum mechanics was taken into account,27 a fact most theologians, including William Lane Craig, have conveniently ignored. In short, the origin of our universe was not a singularity and need not have been the beginning of time.

Think of a time axis as extending without limit from time t = 0. If you use the operational definition of time as what you read on a clock, rather than giving it some unmeasurable metaphysical meaning, the minimum definable time interval is the Planck time. Thus, the time parameter, t, will not be a continuous variable but will be discrete in steps equal to the Planck time. That is, according to quantum mechanics, time is quantized in units equal to the Planck time: t = 0, 1, 2, 3,…and so on.

Because the Planck time is so small by ordinary standards, we can generally get away with treating t as a continuous variable—even in most quantum mechanical applications. However, we cannot assume temporal continuity as we move closer to the origin of our universe. In fact, to properly describe what happens, we need to use a theory in which quantum mechanics and general relativity are combined. Despite decades of effort, no such theory, usually referred to as quantum gravity, has yet to be successfully formulated.28 I am not sure what such a theory will accomplish anyway, since we already have established that we cannot measure anything at distance intervals less than the Planck length and at time intervals less than the Planck time.

In any case, if we stick to intervals greater than the Planck time, we are probably on safe ground to at least draw some general conclusions based on our best existing knowledge. Note that we can also count time steps in the opposite direction: t = –1, –2, –3,…and so on. Nothing in the cosmological equations derived from general relativity prevent them from being applied for t < 0. That is, we cannot rule out another universe on the opposite side of our time axis.

In one scenario, which I have discussed in previous books and has been worked out mathematically, our universe appears from an earlier one by a process known as quantum tunneling.29 For our purposes here, suffice it to say that nothing in our current knowledge of physics and cosmology requires us to conclude that the beginning of our universe was the beginning of space, time, and everything else that is.

THE MATTER-ANTIMATTER PUZZLE

Besides the nature of dark matter and dark energy, another important puzzle about the universe that remains to be solved is its large excess of matter over antimatter. If the universe began, as cosmology and physics suggest, in perfect symmetry, then why is there such a large asymmetry between matter and antimatter? For every billion protons and electrons found in the universe, there are only one antiproton and one antielectron (positron), along with a few produced in high-energy cosmic-ray collisions.

In 1967, the great Russian physicist and political dissident Andrei Sakharov suggested a solution.30 He proposed that baryon-number conservation and CP symmetry are violated, leading to matter-antimatter asymmetry. Recall from chapter 10 that the violation of CP symmetry was observed in 1964. In chapter 11 we saw that the decay of protons, which violates baryon-number conservation, is predicted by some Grand Unified Theories. Despite intense searches, proton decay and the violation of baryon-number conservation so far have not been observed.

Nevertheless, we still have a reasonable expectation that the violation of baryon-number and lepton-number conservation will eventually be discovered and we will be able to explain the matter-antimatter asymmetry in the universe.

THE ETERNAL MULTIVERSE

As we saw previously, while the big bang was the beginning of our universe, it was not necessarily the beginning of all that is. Modern inflationary cosmology strongly suggests that other universes besides our own exist in what is called the multiverse.31 Because we have no observational evidence (yet) for other universes, I will not indulge in speculations about them, except to say that such speculations are based on well-established science and their ultimate empirical confirmation is not out of the realm of possibility. In any case, allow me to simply use the term multiverse to refer to all that is, even of it should turn out that our universe is all there is.

Still, I must address a question that more closely relates to the cosmological view of the atomists, which is whether a multiverse (all that is) can be eternal. While the ancient atomists accepted the fact that everything made of atoms eventually decays, the atoms themselves were eternal and continued to make worlds anew. Although I have covered this question in earlier books,32 I need to review it here because of its direct relevance to atomism. I can do this in a few words.

William Lane Craig and other theistic philosophers and theologians have argued that an eternal multiverse is mathematically impossible.33 Simply put, they claim that if the multiverse is infinitely old, then it would have taken an infinite time to reach the present. That is, we would never reach “now.”

My rebuttal is equally simple. An eternal multiverse did not begin an infinite time ago. It had no beginning. It always was. No matter how far you go back in time—100 billion years, 100 trillion years—the time to the present is finite. An eternal multiverse is perfectly possible, mathematically and scientifically.

SOMETHING ABOUT NOTHING

I am often confronted with a rhetorical question from theists that they are convinced settles the argument about the existence of a supernatural creation: “How can something come from nothing?” Well-known cosmologist and popular author Larry Krauss attempted to provide an answer in a 2012 book, A Universe from Nothing: Why There Is Something Rather Than Nothing.34

Krauss describes how our universe could have arisen naturally from a preexisting, structureless void he calls “nothing.” He bases his argument on quantum physics, along with now well-established results from elementary particle physics and cosmology. In an afterword, prominent atheist Richard Dawkins exults, “Even the last remaining trump card of the theologian, ‘Why is there something rather than nothing?’ shrivels up before your eyes as you read these pages.”

Philosopher and physicist David Albert is unimpressed. In a review in the New York Times he asks, “Where, for starters, are the laws of quantum mechanics themselves supposed to have come from?”35 Krauss admits he does not know, but he suggests they may arise randomly, in which case some universe like ours would have arisen without cause. In my 2006 book The Comprehensible Cosmos, I show how the primary laws of physics, notably the great conservation principles, arise naturally from the symmetries of the void and the spontaneous breaking of those symmetries.36 We have already seen how symmetries provide the foundation of the standard model of particles and fields.

In any case, Albert asserts that it doesn't matter what the laws of physics are. He insists they “have no bearing whatsoever on questions of where the elementary stuff came from, or of why the world should have consisted of the particular elementary stuff it does, as opposed to something else, or to nothing at all.”37

Albert is not satisfied that Krauss has answered the fundamental question: Why is there something rather than nothing, or, put differently, why is there being rather than nonbeing? Again, there is a simple retort: Why should nothing, no matter how defined, be the default state of existence rather than something? The theist has the burden of showing how there could have been nothing. And one could ask the theist: Why is there God rather than nothing? Once they assert that there is a God (as opposed to nothing), they can't turn around and ask a cosmologist why there is a universe (as opposed to nothing). They claim God is a necessary entity. But then, why can't a godless multiverse be a necessary entity?

Krauss says that the reason there is something rather than nothing is that the quantum vacuum state is unstable. Here he refers to the statement made by Nobel-laureate physicist Frank Wilczek in a 1980 article in Scientific American, “Nothing is unstable.”38

Krauss's theological and philosophical critics claim that what he discusses is not really “nothing.” Krauss dismisses this criticism and says that the “nothing” of his critics is some “vague and ill-defined” and “intellectually bankrupt” notion of “nonbeing.” Albert retorts, “Krauss is dead wrong and his religious and philosophical critics are absolutely right.”

Clearly, no academic consensus exists on how to define “nothing.” It may be impossible. To define “nothing” you have to give it some defining property. But, then, if it has a property, then it is not nothing!

Krauss shows that our universe could have arisen naturally without violating any known laws of physics. While this has been well known for a quarter century or more,39 Krauss brings the discussion up to date.

The “nothing” that Krauss mainly talks about throughout his book is, in fact, precisely definable. It should perhaps be better termed as a “void,” which is what you get when you apply quantum theory to space-time itself. It's about as nothing as nothing can be. This void can be described mathematically. It has an explicit wave function. This void is the quantum gravity equivalent of the quantum vacuum in quantum field theory.

So the real issue is not where our particular universe came from but where the multiverse came from. This question has an easy answer. As we saw above, the multiverse is most likely eternal. Repeating myself, since it always was, it didn't have to come from anything.