COOKING UP A COSMOS
Will our descendants create a universe in a laboratory?
YOU DON’T HAVE TO BE A MASTER CHEF TO MAKE meringue. Simply combine egg whites and sugar in a large bowl and beat vigorously until the mixture is light and fluffy. Spread in a pan and put in an oven preheated to 300 degrees F. Bake for 40 to 45 minutes and voile! Could it be just as easy to make a universe?
Since the big bang theory implies that the entire observed universe can evolve from a tiny speck, it’s tempting to ask whether a universe can in principle be created in a laboratory. Given what we know of the laws of physics, would it be possible for an extraordinarily advanced civilization to create new universes at will?
The first thing to think about is the list of necessary ingredients. Curiously, scientific theories continue to offer an enormous range of answers to the question of what the universe was made from. One of the most dramatic differences between the standard big bang theory (without inflation) and the inflationary universe theory is the answer that each gives to this fundamental question.
If the recipe for the standard big bang universe were written in a Cosmic Cookbook, how would it read? To begin the universe at an age of one second, the ingredient list would include 10[sup 89] photons, 10[sup 89] electrons, 10[sup 89] positrons, 10[sup 89] neutrinos, 10[sup 89] antineutrinos, 10[sup 79] protons, and 10[sup 79] neutrons. The ingredients should be stirred vigorously to produce a uniform batter, which should then be heated to a temperature of 10[sup 10] kelvins. After heating, the total mass/energy of the mix would be about 10[sup 65] grams, or 10[sup 32] solar masses. This number, by the way, is about 10 billion times larger than the total mass in the visible universe today. So, to produce a universe by the standard big-bang description, one must start with the energy of 10 billion universes! Since a chefs first task is to assemble the ingredients, this recipe looks formidable enough to discourage anybody.
The Cosmic Cookbook entry for an inflationary universe, on the other hand, looks as simple as meringue. In this case, the natural starting time would be the onset of inflation — just a fraction of a second after the Big Bang. In contrast to the standard big bang recipe, the inflationary version calls for only a single ingredient: a region of false vacuum (see The False Vacuum, page 56). And the region need not be very large. A patch of false vacuum 10-26 centimeter across might be all the recipe demands. While the mass required for the previous recipe was 1032 solar masses, the mass in this case is only an ounce: about the mass of a slice of bread. So, in the inflationary theory the universe evolves from essentially nothing at all, which is why I frequently refer to it as the ultimate free lunch.
Does this mean that the laws of physics truly enable us to create a new universe at will? If we tried to carry out this recipe, unfortunately, we would immediately encounter an annoying snag: Because a sphere of false vacuum 10[sup -26] centimeter across has a mass of one ounce, its density is a phenomenal 10[sup 80] grams per cubic centimeter. For comparison, the density of water is 1 gram per cubic centimeter, and even the density of an atomic nucleus is only 10[sup 15] grams per cubic centimeter. If the mass of the entire observed universe were compressed to false-vacuum density, it would fit in a volume smaller than an atom.
The mass density of a false vacuum is not only beyond the range of present technology, it is beyond the range of any conceivable technology. As a practical matter, therefore, I would not recommend buying stock in a company that intends to market do-it-yourself universe kits. Nevertheless, I will dismiss the gargantuan mass density of the false vacuum as a mere engineering problem, boldly assuming that some civilization in the distant, unforeseeable future will be capable of creating such densities. Is it possible, given what we know of the laws of physics, that someday our descendants might produce new universes by slicing pieces of false vacuum? On the darker side, does the physics of the false vacuum create the possibility of an ultimate doomsday machine? Is our universe imperiled by the threat that a super-advanced civilization in some remote galaxy might create a cancerous patch of false vacuum that would engulf us all?
The first step in trying to fabricate a laboratory universe is to create a patch of false vacuum. How exactly this can be achieved depends on the details of physics at extremely high levels of energy (more than a trillion times higher than modern particle accelerators), which at present we have no way of knowing. This part of the problem, therefore, will be left for our descendants to solve. At present, we can say that our current theories offer several possibilities. In many theories, the desired false vacuum can be created by heating a region of space to enormous temperatures (perhaps 10[sup 29] kelvins), and then rapidly cooling it. The region would then supercool into the false vacuum, exactly as we imagine that the early universe may have done.
Once a patch of false vacuum is created, its evolution does not depend on how it was created. The false vacuum is characterized by having a huge energy density and a huge but negative pressure. Through the equations of general relativity, these properties alone determine how space-time is distorted by a region of false vacuum.
Because the false vacuum creates a strong gravitational repulsion, we expect that the region of false vacuum will grow. However, if the false vacuum bubble wall is to move outward, there must be a force pushing it that way. The pressure outside the bubble is zero, and the pressure inside is negative. The pressure is therefore higher outside than inside, so the pressure difference will push inward on the bubble wall.
One might guess that the gravitational repulsion of the false vacuum would push outward on the bubble wall, so if this repulsion were strong enough, the bubble would start to grow. Not so, however, say the equations of general relativity. The gravitational repulsion causes the false vacuum to swell, but the repulsion does not extend beyond the false vacuum. Objects outside the bubble wall are attracted toward the bubble, and the gravitational force on the bubble wall is inward.
Because both pressure and gravity pull inward on the bubble wall, a bubble that is started from rest will start to contract. With nothing to halt the contraction, it will collapse to a black hole. While a black hole is interesting, it would certainly be viewed as a disappointment by our would-be universe creator.
Suppose, however, that the bubble was not started from rest, but instead was given an outward push. If the initial outward velocity is large enough, then the bubble will follow the sequence shown in the figure on the facing page. As the bubble grows, the indentation will become deeper, as shown at the top. The indentation will continue to deepen, developing a neck, or wormhole, as shown in the middle. Once the wormhole develops, a dramatic change takes place — the bubble has turned inside out. Now the region of false vacuum can grow larger and larger without encroaching on the original space. It creates new space as it expands, resembling an inflating balloon. The climax of the evolution is shown at the bottom: The region of false vacuum, with a region of true vacuum attached, disconnects from the parent space, forming a new, completely isolated closed universe. It will then continue to enlarge, going through the usual evolution of an inflationary universe. A new universe has been created, and the parent universe is unharmed — universe creation is not a doomsday machine. From the point of view of the parent universe, the umbilical cord of the child universe is indistinguishable from a black hole. The umbilical connection in the child universe would similarly look like a black hole.
If we assume that the false vacuum driving the inflation has a mass density of about 10[sup 80] grams per cubic centimeter, then the time that it takes the child universe to disconnect is roughly 10[sup -37] second. After this time there will be no contact between the parent universe and child. A false-vacuum-bubble universe creator would watch helplessly as his new universe slipped inexorably through the wormhole and severed all contact. Once the new universe has separated, the black hole that remains in the parent universe would evaporate. It would disappear in roughly 10[sup -23] second, releasing the energy equivalent of a 500-kiloton nuclear explosion. While the parent universe would be in no danger of annihilation, the safety of the experimenters would require precautions similar to those used in hydrogen bomb tests.
The story of inflationary universe creation sounds complete at this point, but there is an important and surprising twist: It is not clear whether it is possible, even in principle, to attain the expansion velocity needed for the false vacuum bubble to evolve into a new universe.
One hope for evading this problem involves a peculiar consequence of quantum theory, the process of quantum tunneling. A quantum system can make a discontinuous transition from one configuration to another, even when the system would not normally have enough energy to exist in the intermediate configurations. This quantum leap is the origin of a frequently used metaphor (and a successful American television series), and it also plays a crucial role in the decay of the false vacuum.
But calculations show that each time a false vacuum bubble is set into expansion, the probability that it will tunnel to become a new universe is extraordinarily small. To write out the number in decimal notation would require a decimal point, followed by approximately 10[sup 13] zeros, followed by a one. So even if some super-advanced civilization develops the capacity to produce and manipulate regions of false vacuum, they would still require a fantastic amount of patience to produce a new universe.
It may be premature, however, for us to bemoan the difficulties that our super-advanced descendants will face. Calculations show that the probability becomes higher as the mass density of the false vacuum increases. If there exists a false-vacuum state associated with the unification of gravity and the other three forces of nature, then the mass density would be about 10[sup 93] grams per cubic centimeter. For this density, the answer to our probability calculation would be approximately one — a new universe would be created with just about every attempt.
While advanced civilizations can conceivably create multiple universes, inflation itself can have the same effect. Most versions of the inflationary universe theory imply that the false vacuum does not decay all at once, but instead decays a fragment at a time. Each fragment produces a universe, while the bulk of the false vacuum continues eternally to double and redouble in size. Each doubling in size might occur in as little as 10[sup -37] second. Because the time needed for the development of a super-advanced civilization is measured in billions of years or more, there appears to be no chance that laboratory production of universes could compete with the natural process of eternal inflation.
On the other hand, a child universe created in a laboratory by a super-advanced civilization would set into motion its own progression of eternal inflation. Could the super-advanced civilization find a way to enhance its efficiency? We may have to wait a few billion years to find out.
THE FALSE VACUUM
The false vacuum is a peculiar form of matter predicted to exist by modern theories of elementary particles. If inflationary cosmology is correct, it was the driving force behind the Big Bang. The false vacuum has an extraordinarily high density, perhaps 10[sup 80] grams per cubic centimeter, and also a pressure that is extraordinarily large, but negative — it acts like a suction. The huge negative pressure turns gravity on its head, producing a repulsive gravitational force that can launch a region of false vacuum into explosive expansion.
Why does the false vacuum have such a peculiar name? While the word vacuum is often defined as a state devoid of matter, this definition is not precise enough for physicists, since it is not clear exactly what matter means. The physicist defines vacuum as the state with the lowest possible density of energy. The false vacuum is not really a vacuum, but its energy density can be lowered only by a very slow process, called the decay of the false vacuum. So, while the false vacuum is waiting to decay, it behaves as if its energy density cannot be lowered — as if it were a temporary vacuum.
COOKING UP A COSMOS