What about the very earliest moments of the Universe—those times well less than the first second of existence when all the forces of Nature are thought to have been merged into a single, grand-unified force that controlled everything? Going back even closer to the origin of all things, our quest to unify all the known forces combines aspects of very big scales and the small scales—the subjects of cosmology and particle physics. These efforts—including some of the most exotic work at the frontiers of science—have led to tentative advances toward a controversial “theory of everything.”
What follows in this section is informed speculation, based on extensions of much better known phenomena on intermediate scales, akin to what we routinely witness in space, time, and energy. The closest time to the big bang that astronomers can observationally study physical phenomena directly is ~300,000 years after the bang; this again is when the cosmic background radiation was launched and it does contain hints and clues regarding events in the earlier Universe. And the closest that physicists can experimentally study those earlier events is about 10-10 second after the bang; these are laboratory simulations, done in quick bursts at the big accelerators, that approximate the violence of the very young Universe impressively close in time to the bang, but currently no closer. Scientific descriptions of events earlier than a trillionth of the first second of time are only reverse extrapolations—regarded by scientists as better than religious dogma, philosophical musing, or science fiction, but how much better is frankly unknown.
Force Unification During the last quarter of the twentieth century, the electromagnetic force binding atoms and molecules and the weak nuclear force governing the decay of radioactive matter were merged into a single theory asserting them to be different manifestations of one and the same force—the "electroweak" force. As implied by Figure 1.22, crucial parts of this theory have been confirmed at the world's most powerful accelerators at CERN and Fermi Lab, and concerted efforts are now under way to extend this unified theory to include the strong nuclear force that binds elementary particles within nuclei. Furthermore, although scientists are unsure at this time how, in turn, to incorporate into this comprehensive theory the fourth known force (gravity), we have reason to suspect that Einstein's dream is nearing—to understand all the forces of Nature as different aspects of a single, fundamental force.
The intellectual synthesis of the macrodomain of cosmology (for gravity is a demonstrably long-range force) and the microdomain of particle physics (pertaining to the tiniest scales) is but a small part of the grand scenario of cosmic evolution. Yet it’s an important part, for the newly emerging interdisciplinary specialty of "particle cosmology" could well provide great insight into a much earlier period of the Universe, namely, the time interval often colloquially labeled chaos—a temporal domain resembling the terra incognita parts bordering old maps of antiquity.
In brief, descriptive terms, this is the way the newly understood electroweak force operates. In submicroscopic (quantum) physics, forces between two elementary particles are exerted, or mediated, by the exchange of a generic particle, called a boson; in effect, the two particles can be imagined to be playing a rapid game of catch using a boson as a ball. In ordinary electromagnetism familiar to us on Earth, the boson is the usual photon, and for the strong nuclear force that boson is a gluon; both types of bosons always travel at the velocity of light. The new electroweak theory includes four such bosons: the photon as well as three other subatomic particles having the innocuous names W+, W-, and Z0. At temperatures less than ~1015 K—the thermal range of all events on Earth and in the stars today—these four bosons split into two families: the photon that expresses the usual electromagnetic force and the other three that carry the weak force. But at temperatures greater than ~1015 K, these bosons work together in such a way as to make indistinguishable the weak and electromagnetic forces.
Thus, by experimentally probing the behavior of this new force, we gain insight into not only the essence of Nature's building blocks but also some of the earliest periods of the Universe, especially the hadron period around 10-10 second after the bang. Paralleling the well-known phrase, "observing out in space is equivalent to probing back in time," that we must always keep in mind macroscopically, we now have another, equally important phrase that pertains microscopically: "the higher the temperature, the better the probe of the early Universe."
This is where (or when) the experimental confirmations of theoretical ideas currently end, for humankind has not been able to build large enough accelerators capable of generating even higher energies typifying greater densities and temperatures prevalent at times closer to the big bang than 10-10 second. Even so, it’s remarkable that science can manage to do as well as it does—to take that last demanding step in the scientific method and to test events that might have occurred ideas much less than the first second of absolute existence.
Cosmic Inflation To appreciate the nature of matter at temperatures exceeding 1015 K, and thereby explore indirectly times even closer to the big bang, physicists are now researching a more general theory that merges the electroweak and strong nuclear forces (but not yet gravity). Several versions of this so-called grand-unified theory, dubbed GUT for short, have been proposed, though testing capable of determining which, if any, of these theories is correct has really only begun. Like the other known forces, this grand-unified “superforce” is expected to be mediated by a boson elementary particle—for want of better name, the X boson. It is, according to these unifying theories, the very massive (and thus very energetic) X bosons that are expected to play a vital role in the first instants of time.
Imagine a time equal to 10-39 second, when the temperature approximated 1030 K. At that moment, only one type of force other than gravity operated—namely, the grand unified force just noted. According to the theory of such a superforce, the matter of the Universe must have then exerted a huge pressure that pushed outward in all directions. (In classical terms, pressure is the product of density and temperature, so if, in the early Universe, each of these quantities was large, then the pressure must have been unbelievably high.) The Universe would have responded to this ultra-pressure by expanding and dropping its temperature. As time advanced from 10-39 to 10-35 second, say, the Universe grew another couple of orders of magnitude and the temperature fell to about 1028 K.
According to most grand-unified theories, this temperature—1028 K—is special, for at this value a dramatic change occurred in the expansion of the Universe. In short, when matter was cooler than this temperature, the X bosons could no longer be produced; at times after 10-35 second, the energy needed to create such particles was too dispersed owing to the diminishing temperature. So as the temperature fell below 1028 K, the disappearance of the X bosons is thought to have caused a surge of energy roughly like that released as latent heat when water freezes (an event that often contributes to the bursting of closed containers.) After all, energy no longer concentrated enough to yield X bosons was nonetheless available to enhance the general expansion of the Universe—in fact, to cause it to expand violently, or "burst," for a short duration just after the demise of the bosons.
The youthful Universe, though incredibly hot at the time, was quite definitely cooling and in this way experienced a series of such "freezings" while passing progressively toward cooler states of being. Perhaps the most impressive of all such transitions, the rapid decay of the X bosons caused a tremendous acceleration in the rate of expansion. This period of exponentially fast expansion has been popularly termed "inflation." Each tiny patch of space doubled in size at least 100 times, such inflation enlarging a volume a trillionth that of a proton to that of an acorn—a huge difference. In well less than the blink of an eye represented by a mere 10-35 second, the Universe inflated some 1050 times, smoothing out (by stretching) any irregularities existing at the outset, much as crinkles on a balloon vanish as it’s inflated. Hence the reason why the Universe seems so accurately described by flat, Euclidean geometry, despite all the curving and warping of spacetime near massive objects. We apparently now see only a tiny part of the whole Universe, which seems flat to us, much as an ant on the surface of that rapidly expanding balloon would see less and less of it, all the while the enlarged surface seemingly grew flatter.
At the conclusion of the inflationary phase at about 10-35 second, the X bosons had disappeared forever, and with them the grand-unified force. In its place were the electroweak and strong nuclear forces that operate around us in the more familiar, lower-temperature Universe of today. Physicists describe such an event as “broken symmetry,” with the strong and electroweak forces, previously one and the same force, having then become separate entities. With these new forces in control (along with gravity), the Universe resumed its more leisurely expansion. Later, ~10-10 second, when the cosmic temperature had decreased to ~1015 K, a second symmetry breaking occurred, enabling the electroweak force to reveal its more familiar electromagnetic and weak nature that guides almost everything we currently know about on Earth and in the stars.
Testing the GUTs Can we test this unified-force proposal, including its implied and spectacular inflationary phase change? The answer is a qualified yes, for we can do so only indirectly. Even the biggest accelerators on Earth are barely able to create, and only for the briefest of instants, conditions approximating 1015 K sufficient to confirm the electroweak theory. By contrast, the grand unified theories become operative at much higher temperatures, in fact greater than 1028 K, which physicists will likely never be able to simulate on Earth. To boost subatomic particles to the immense energies needed to test the grand-unified theories would require a particle accelerator spanning the distance between Earth and the Alpha Centauri star system ~4 light-years away—a truly cosmic machine that would require for each second of operation an altogether unreasonable expenditure of power needed to drive the annual U.S. gross national product! So, while the physical conditions in specialized laboratories have successfully reproduced the lepton period (~10-6 s) and parts of the earlier hadron period (~10-10 s), scientists have concluded that the earliest chaos period is likely to remain forevermore “too hot to handle.”
One especially attractive aspect of the grand-unified theories is that they seem able to account for the observed excess of matter over antimatter, and thus potentially solve that dilemma noted earlier in this PARTICLE EPOCH. It so happens that the decay of the X bosons at times earlier than 10-35 second lacks symmetry; their decay is expected to have created slightly greater numbers of protons than antiprotons (or electrons than positrons). Specifically, calculations imply that for every billion antiprotons (or positrons), a billion and one (i.e., 109 + 1) protons (or electrons) were created. The billion matched pairs subsequently annihilated each other, leaving a residue of ordinary matter from which everything—including ourselves—emerged. If this imbalance is true—another example of broken symmetry—then the matter extant today is just a tiny fraction of that formed originally.
This prediction can be tested in a straightforward way, for if protons can be created they can also be destroyed. Protons might not be the immortal building blocks once thought, and the grand-unified theories can be used to estimate the proton’s average life expectancy. That lifetime turns out to be 1032 years—a hundred quadrillion quadrillion years—which is much, much greater than the age of the Universe! This extremely long lifetime guarantees that, although all matter might ultimately be destined to disappear, the probability of decay in any given time span is exceedingly small. Nonetheless, given that we now realize Nature is largely governed by statistical physics, and not the classical physics of old, any one proton is in danger of decaying at any one moment. In fact, since water is an abundant source of protons, theory predicts that roughly one proton should decay per year in each ton of water. Alternatively expressed, a typical human body is expected to lose only about a single proton in an entire human lifetime. Experiments are now in progress attempting to detect such events in huge water tanks stored in deep underground mines at several places on Earth (thus shielding them from spurious effects triggered by cosmic rays reaching Earth's surface from outer space). Furthermore, a statistical measurement of a proton's lifetime should enable us to discriminate among a variety of grand-unified theories, further refining our "approximations of reality." Alas, the simplest of these theories has apparently been ruled out as no proton decays have been detected in the last decade in several tons of water. Perhaps protons, like diamonds, are forever, and it’s Nature that’s not so simple. Some physicists take the lack of proton-decay detections as a bad sign, for the history of science has taught us that, more often than not, theoretical complications usually indicate that we are on the wrong track.
An intriguing cosmological implication of the inflationary concept is that, if correct, it must have put the Universe into a state precariously balanced between infinite expansion and ultimate collapse. Recall from earlier in this PARTICLE EPOCH that for this to happen, the correct model is one for which its density equals precisely the critical density—namely, the case for which its accumulated gravitational effect exactly offsets its rate of expansion, and the resulting geometry is flat. Since astronomers have observationally demonstrated that the density of normal, baryonic matter is only a few percent of this critical density, we surmise that more than 95% of the Universe is made not of normal matter but of some unorthodox, dark-matter form such as massive neutrinos and exotic particles (black holes won’t do it, as they are made of normal matter), or of some entirely new kind of (dark) energy not yet known in physics.
Toward Creation What about even earlier phases of this, the earliest of all periods (“chaos”), at times prior to 10-35 second? Can we probe, even theoretically, any closer to the start of all things at the celebrated “t = 0” when literally everything began? Efforts are currently hampered because doing so requires the gravitational force to be incorporated into the correct grand-unified theory. Yet, no one has managed to develop such a self-consistent, super-grand-unified theory (or "super-GUT"), as this is tantamount to inventing a quantum theory of gravity—a towering intellectual achievement that would ostensibly merge Heisenberg's uncertainty principle (that guides submicroscopic phenomena) and Einstein's relativity theory (that describes macroscopic scales). Whoever does achieve this holy grail of physics will surely get a free and celebrated trip to Stockholm, courtesy of the Nobel committee.
Our current knowledge of the strong gravitational force implies that such quantum effects very likely become important whenever the Universe is even more energetic than we’ve yet contemplated. Specifically, at a time earlier than 10-43 second (known as the "Planck time," after Max Planck, one of the creators of quantum theory), when the temperature exceeded 1032 K, the four known basic forces are thought to have been one—a truly fundamental force operating at energies prevalent during the earliest parts of the chaos period. There and then, with all the matter in the Universe conjectured to have been unimaginably compacted and a trillion trillion times hotter than the core of a hydrogen-bomb explosion, the curvature of (Einsteinian) spacetime and the dimension of (Heisenbergian) uncertainty both equal 10-33 cm (the "Planck length"), inside which relativity theory is no longer an adequate description of Nature. Only at lesser energies (i.e., at times after 10-43 second) would the more familiar four forces begin to manifest themselves distinctly, though in reality all four are merely different aspects of the single, fundamental, super-grand force that ruled at or near the big bang.
In a potentially related advance, attempts to understand force unification have driven theorists toward the fascinating concept of “supersymmetry.” This extends the idea of symmetry among forces to that among particles. Accordingly, all elementary particles are reasoned to have so-called supersymmetric partners—exotic particles (sometimes called “sparticles”) that exist alongside their normal counterparts readily observed in the everyday world of our human senses. Of particular interest to astronomers, these particles would have been produced in great abundance in the early aftermath of the big bang and should still be around today. Since they are thought to be relatively massive (at least a hundred times that of a proton), these supersymmetric relics are among the leading candidates for dark matter within and beyond the galaxies. However, none of these suspected particles has yet been experimentally detected, so the theory’s validity remains uncertain.
Ironically, with the physicists unable to build equipment on Earth sufficiently energetic to reproduce cosmic chaos, and thus perhaps to recreate in the lab some of the bizarre elementary particles likely created in the very early Universe, it’s the astronomers who, by studying the macrorealm, are beginning to provide tests, albeit indirect ones, of the grand unification of the microrealm. This is another example of how interdisciplinary efforts are so richly rewarding, in this case the newly emerging subject of particle cosmology bringing together the very largest and very smallest scales in Nature.
In another possibly important development noted earlier, some physicists have recently become enamored of a radical idea originally proposed several decades ago. Variously called “string theory,” "superstrings," or mysteriously “M-theory,” this idea aspires to unite all the laws of physics into a single mathematical framework, perhaps even to discover one equation that can explain all things—the so-called theory of everything! New and provocative terms—such as strings, curls, and membranes—derive from the notion that the ultimate building blocks of Nature might not be point-like particles at all, but tiny, vibrating, extended objects. If this novel view is correct, it means that the protons and neutrons in all matter, from our bodies to the farthest star, are fundamentally made of strings or superstrings shaped like loops. Alas, no one has ever seen, or has much prospect of seeing, such strings since they are predicted to be more than a billion billion times smaller than a proton—in fact, 10-33 cm, again the Planck length. Depending on the mode of vibration, separate particles of matter can be made from such subatomic strings, much the way violin strings can resonate with different frequencies, each one creating a separate tune of the musical scale. Disconcertingly, the theory of superstrings works only if the Universe began with (usually) 11 dimensions of spacetime, 7 of which (somehow) collapsed or otherwise became "hidden" near the time of the big bang. To some physicists, such a revolutionary idea borders on science fiction (or even the supernatural), whereas for others it possesses breathtaking mathematical elegance and perhaps the best hope of avoiding a whole host of thorny problems on the road to quantum gravity. In any case, caution is warranted as the history of science and even today's science journals are littered with mathematically beautiful theories that seemingly have no basis in physical reality. Although the theory of superstrings is now causing great excitement in the physics community, to date no experimental or observational evidence supports it.
Any theory purporting to penetrate even closer to the very beginning of time is currently hardly more than conjecture. Given our limited knowledge of physics at the highest conceivable energies, it makes little scientific sense to talk about times earlier than 10-43 second. Time intervals smaller than this are not yet part of the lexicon of science, and notions of space and time earlier than this border on the meaningless.
That said, many researchers suspect that once a proper theory of quantum gravity is in hand, our understanding might automatically include a natural description of the original creation event itself. It’s even conceivable that the primal energy emerged at zero time from essentially nothing, uncannily in accord with the structureless singularity described by the time-honored poetic expression, “…without form and void, with darkness upon the face of the deep….” Even in a perfect vacuum—a region of space containing neither matter nor energy—particle-antiparticle pairs (such as an electron and its antiparticle opposite, the positron) constantly appear and disappear in a time span too short to observe. Although it would seem impossible that a particle could materialize from nothing—not even from energy—it so happens that no laws of physics are violated because the particle is annihilated by its corresponding antiparticle before either one can be detected. Furthermore, for such events not to happen would violate quantum physics, which cites, via Heisenberg’s principle again, the impossibility of determining exactly the energy content of a system at every moment in time. Hence, natural, quantum fluctuations of energy must occur in empty space, even when the average energy present is zero.
In this way, the Universe may well have been creatio ex nihilo by means of an energy change that lasted for an unimaginably short duration—a "self-creating Universe" that erupted into existence spontaneously, the result of a random quantum fluctuation! The net energy was then, is now, and forever shall be zero; all of gravity and its myriad negative, attractive, potential energies conceivably balanced perfectly all other known positive energies (including heat, light, mass, and so on), making our vast Universe seem like “something for nothing.” If so, then the Universe could have originated from a quantum fluctuation large enough that energy, matter, time, and space all instantaneously sprang into being. Could this be the solution to the time-honored philosophical query, "Why is there something rather than nothing?"—the answer being, ostensibly, that the probability is greater that "something" rather than "nothing" will happen. This sort of “statistical” birth of the Universe from a kind of nothingness has been sacrilegiously dubbed “the ultimate free lunch”—an extreme manifestation of the long-standing quip that Nature abhors a vacuum.
Qualification That some of these latter ideas are speculative is putting it mildly. Skeptics would say that they are not real science at all, for they violate one of the central tenets of the modern scientific method: Many of these concepts are virtually impossible to test experimentally. But they do illustrate how the world of science has itself changed at the start of the new millennium, as its scope now encompasses, for the first time, a model for the very origin of the origin. Might this be the beginning of a meaningful merger of science and religion into a truly profound interdiscipline, or might it signal renewed warfare between these two great institutions, as science treads on sacred turf where it’s not quite gone before?
Should this quantum scenario, or some revised version of it, prove to be a correct description of the birth of the Universe, then our Galaxy, our Sun, our Earth, and ourselves are a direct consequence of a series of random events, albeit ones obeying physical law, that occurred during an unimaginably short period of time some 14 billion years ago. Even if not a valid understanding of the ultimate creation event itself, such submicroscopic fluctuations in density, enhanced by inflation and thereafter guided by expansion, might well have eventually grown into today’s large-scale, macroscopic structures encountered throughout the remaining epochs of this Web site. Clearly, the development of a quantum-gravitational description of events at literally the origin of time, none of which attempts has thus far met with much consensus, is the foremost challenge in the subject of physics today.