by Michio Kaku
ESCAPE FROM APOCALYPSE
Given that the fate of the universe is likely to die a cold death in the distant future, what can we do about it? Can these cosmic forces be reversed?
There are at least three options.
The first is to do nothing and let the life cycle of the universe play out. As it gets colder and colder, intelligent beings will adjust and think slower and slower, according to physicist Freeman Dyson. Eventually, a simple thought may take millions of years, but these beings will never notice because all other beings will think slower as well. It would be possible to have intelligent conversations between these beings, even if it takes millions of years. So from this point of view, everything would seem normal.
Living in such a cold world may actually be quite interesting. Quantum leaps, which are extremely unlikely in a human life span, may begin to occur routinely. Wormholes may open up and close before our eyes. Bubble universes may pop into and out of existence. These beings may see them all the time because their brains operate so slowly.
However, this is only a temporary solution, because eventually molecular motion will become so slow that information cannot be transferred from one place to another. At this point all activity, including thinking, no matter how slow, will cease. One desperate hope is that the acceleration caused by dark energy will suddenly disappear all by itself before this happens. Since no one knows why the universe is accelerating, there is that possibility.
BECOMING TYPE IV
In the same vein, the second option is that we evolve into a Type IV civilization and learn to utilize energy beyond our own galaxy. I once gave a talk on cosmology and discussed the Kardashev scale. Afterward a ten-year-old boy came up to me and said I was wrong. There must be a Type IV civilization, beyond the usual Type I, II, III of the Kardashev classification. I corrected him and told him that there were only planets, stars, and galaxies in the universe and that hence a Type IV civilization is impossible. There was no energy source beyond the galaxy.
Later, I realized that perhaps I was too impatient with the boy.
Remember that each type of civilization is ten to one hundred billion times more powerful than the previous type. Since there are about one hundred billion galaxies in the visible universe, a Type IV civilization could harness the energy of the entire visible universe.
Perhaps the extragalactic energy source is dark energy, which is by far the largest source of matter/energy in the universe. How might a Type IV civilization manipulate dark energy and reverse the Big Rip?
Because, by definition, a Type IV civilization can harness extragalactic energy, they might manipulate some of the extra dimensions revealed by string theory and create a sphere in which dark energy reverses polarity, so that the cosmic expansion is reversed. Outside the sphere, the universe might still be expanding exponentially. But inside the sphere, the galaxies evolve normally. In this way, a Type IV civilization could survive even if the universe is dying all around it.
In some sense, it would act like a Dyson sphere. But although the purposes of the Dyson sphere would be to trap sunlight inside, the purpose of this sphere would be to trap dark energy, so that the expansion could be contained.
The final possibility is to create a wormhole through space and time. If the universe is dying, then one option might be to leave it and enter another, younger one.
The original picture given to us by Einstein is that the universe is a huge expanding bubble. We live on the skin of the bubble. The new picture given to us by string theory indicates that there are other bubbles out there, each one a solution of the string equations. In fact, there is a bubble bath of universes, creating a multiverse.
Many of these bubbles are microscopic and pop into existence in a mini Big Bang and then rapidly collapse. Most of them are of no consequence to us, since they live out their short lives in the vacuum of space. Stephen Hawking has called this constant churning of universes in the vacuum the “space-time foam.” So nothingness is not empty but is full of universes in constant motion. Strangely, this means that even within our bodies there are vibrations within the space-time foam, but they are so tiny that we are blissfully unaware of them.
The startling aspect of this theory is that if the Big Bang happened once, it can happen again and again. So a new picture emerges of baby universes budding from mother universes, and our universe is nothing but a tiny patch of a much larger multiverse.
(Occasionally, a tiny fraction of these bubbles do not vanish back into the vacuum but expand enormously due to dark energy. This is perhaps the origin of our own universe, or our universe may be the result of the collision of two bubbles or the fissioning of a bubble into smaller bubbles.)
As we saw in the last chapter, an advanced civilization might be able to build a gigantic particle accelerator the size of the asteroid belt that could open up a wormhole. If it is stabilized by negative energy, then it might provide an escape route to another universe. We’ve already discussed using the Casimir effect to create this negative energy. But another source of negative energy is these higher dimensions. They may serve two purposes: they may change the value of dark energy, thereby preventing the Big Rip, or they may create negative energy to help stabilize a wormhole.
Each bubble or universe in the multiverse has different laws of physics. Ideally, we want to enter a parallel universe where atoms are stable (so our bodies do not disintegrate when we enter it) but the amount of dark energy is much lower, so that it expands enough to cool down and allow habitable planets to form but not so much that it accelerates into an early Big Freeze.
INFLATION
All these speculations at first seem preposterous, but the latest cosmological data from our satellites seem to support this picture. Even the skeptics are forced to admit that the multiverse idea is consistent with the theory called “inflation,” which is a supercharged version of the old Big Bang theory. In this scenario, just before the Big Bang, there was an explosion called inflation that created the universe in the first 10−33 seconds, much faster than the original theory. This idea, originally proposed by Alan Guth of MIT and Andrei Linde of Stanford, solved a number of cosmological mysteries. For example, the universe seems much flatter and more uniform than predicted by Einstein’s theory. But if the universe underwent a cosmic expansion, it would flatten out, much like inflating an enormous balloon. The surface of the inflated balloon seems flat because of its size.
Also, when we look in one direction of the universe and then look 180 degrees in the opposite direction, we see that the universe is pretty much the same no matter where we look. This requires some form of mixing between its different parts, but because light has a finite velocity, there is simply not enough time for information to travel across these vast distances. Hence, the universe should look lumpy and disorganized because there was not enough time to mix the matter. Inflation solves this by postulating that, at the beginning of time, the universe was a tiny patch of uniform matter. As inflation expanded this patch, it created what we see today. And because inflation is a quantum theory, there is a small but finite probability that it can happen again.
Although the inflation theory has had undeniable success in explaining the data, there is still a debate among cosmologists as to the underlying theory behind it. There is considerable evidence from our satellites that shows that the universe underwent a rapid inflation, but precisely what drove this inflation is not known. So far, the leading way to explain inflation theory is through string theory.
I once asked Dr. Guth if it might be possible to create a baby universe in the laboratory. He replied that he actually did the calculation. One would have to concentrate a fantastic amount of heat at one point. If the baby universe were to be formed inside a lab, it would explode violently in a Big Bang. However, it would explode in another dimension, so, from our point of view, the baby universe would vanish. However, we would still feel the shock wave of it being born, which would be equivalent to the explosion of many nuclear we
apons. So, he concluded, if we did create one, we would have to run quickly!
NIRVANA
The multiverse can also be viewed from the perspective of theology, where all religions fall into two categories: religions in which there was an instant of creation, and religions that are eternal. For example, the Judeo-Christian philosophy talks about a creation, a cosmic event when the universe was born. (Not surprisingly, the original calculations of the Big Bang were done by a Catholic priest and physicist, Georges Lemaître, who believed that Einstein’s theory was compatible with Genesis.) However, in Buddhism, there is no god at all. The universe is timeless, with no beginning or end. There is only Nirvana. These two philosophies seem totally in opposition to each other. Either the universe had a beginning or it didn’t.
But a melding of these two diametrically opposed philosophies is possible if we adopt the multiverse concept. In string theory, our universe did in fact have a cataclysmic origin, the Big Bang. But we live in a multiverse of bubble universes. These bubble universes, in turn, are floating in a much larger arena, a ten-dimensional hyperspace, which had no beginning.
So Genesis is happening all the time within the larger arena of Nirvana (hyperspace).
This then gives us a simple and elegant unification of the Judeo/Christian origin story with Buddhism. Our universe did in fact have a fiery beginning, but we coexist in a timeless Nirvana of parallel universes.
STAR MAKER
This takes us back to the work of Olaf Stapledon, who imagined that there is a Star Maker, a cosmic being that creates and discards entire universes. He is like a celestial painter, constantly conjuring up new universes, tinkering with their properties, and then moving on to the next one. Each universe has different laws of nature and different life-forms.
The Star Maker himself was outside these universes and could see all of them in their totality as he painted on the canvas of the multiverse. Stapledon writes, “Each cosmos…was itself gifted with its own peculiar time, in such a manner that the whole sequence of events with any single cosmos could be viewed by the Star Maker not only from within the cosmical time itself but also externally, from the time proper to his own life, with all the cosmical epochs co-existing together.”
This is very similar to the way in which string theorists view the multiverse. Each universe in the multiverse is a solution of the string equations, each with its own laws of physics, each with its own time scales and units of measurement. As Stapledon said, one must be outside of normal time, outside of all these universes, to see these bubbles all at once.
(This also is reminiscent of the way Saint Augustine viewed the nature of time. If God was all-powerful, then He could not be bound by earthly concerns. In other words, divine beings do not have to rush to meet deadlines or make appointments. In some sense, therefore, God must be outside of time. In the same way, the Star Maker and string theorists, gazing at the bubble bath of universes in the multiverse, are also outside of time.)
But if we have a bubble bath of possible universes, then which one is ours? This raises the question of whether our universe was designed by a higher being or not.
When we examine the forces of the universe, we find that it seems to be “tuned” just right to make intelligent life possible. For example, if the nuclear force were a bit stronger, the sun would have burned out millions of years ago. If it were a bit weaker, the sun would never have ignited in the first place. The same applies to gravity. If it were a bit stronger, we would have had a Big Crunch billions of years ago. If it were a bit weaker, we would have had a Big Freeze instead. In both cases, the nuclear and gravitational forces are “tuned” just right to make intelligent life on Earth possible. When we examine other forces and parameters, we find the same pattern.
Several philosophies have emerged to address the problem of the narrow range of these fundamental laws that could allow life.
The first is the Copernican principle, which simply states that there is nothing special about the Earth. So the Earth is just a piece of cosmic dust wandering aimlessly through the cosmos. It is just a coincidence that the forces of nature are “tuned” just right.
The second is the anthropic principle, which states that our very existence places enormous constraints on what kinds of universes can exist. A weak form of this principle simply says that the laws of nature should be such that life is possible, since we exist and are contemplating those laws. Any universe is just as good as any other, but only our universe has intelligent beings who can ponder and write about this. But a much stronger version states that it is so unlikely that intelligent life exists that perhaps the universe is compelled in some way to allow intelligent life to exist, that perhaps the universe was designed for it to be so.
The Copernican principle says that our universe is not special, while the anthropic principle says that it is. Strangely, while both principles are diametrically opposite of each other, they are both compatible with the universe as we know it.
(When I was in second grade, I clearly remember my teacher explaining this idea to me. She said that God so loved the Earth that He put it just the right distance from the sun. If it was too close, the oceans would boil. If it was too far, the oceans would freeze. So God chose the Earth to be just right from the sun. This was the first time I had ever heard a scientific principle explained in this way.)
The way to resolve this problem without invoking religion is the existence of exoplanets, most of which are too close or too far from the sun to support life. We are here today because of luck. It was luck that we live in the Goldilocks zone around the sun.
Likewise, the explanation for why the universe seems to be fine-tuned to allow for life as we know it is because of luck, because there are billions of parallel universes that are not fine-tuned for life, that are completely lifeless. We are the lucky ones who can live to tell about it. So the universe is not necessarily designed by a superior being. We are here to discuss the question because we live in a universe compatible with life.
But there is another way to look at this problem. This is the philosophy that I prefer and the one that I am working on at present. In this approach, there are many universes in the multiverse, but most are not stable and will eventually decay down to a more stable universe. Many other universes might have existed in the past, but they didn’t last and were subsumed into ours. In this picture, our universe survives because it is one of the most stable.
So my point of view combines both the Copernican and anthropic principle. I believe that our universe is not special, as in the Copernican principle, except for two features: that it is very stable and that it is compatible with life as we know it. So instead of having an infinite number of parallel universes floating in the Nirvana of hyperspace, most of them are unstable, and perhaps only a handful of them survive to create life like ours.
The final word on string theory has yet to be written. Once the full theory is solved, we can compare it with the amount of dark matter in the universe and the parameters describing subatomic particles, which may settle the question of whether the theory is correct or not. If it is correct, string theory may also explain the mystery of dark energy, which physicists believe is the engine that may one day destroy the universe. And if we are fortunate enough to evolve into a Type IV civilization, capable of harnessing extragalactic power, then string theory may explain how the death of the universe itself may be avoided.
Perhaps some enterprising young mind, reading this book, will be inspired to complete the last chapter in the history of string theory and answer the question of whether the death of the universe can be reversed.
THE LAST QUESTION
Isaac Asimov once said that of all the short stories he had written, his favorite was “The Last Question,” which gave a startling new vision of life trillions of years into the future and explained how humanity might confront the end of the universe.
In that story, people have asked over the aeons whether the universe must necessarily die or wh
ether it was possible to reverse the expansion and prevent the universe from freezing over. When asked, “Can entropy ever be reversed?” the master computer replies each time, “There is insufficient data for a meaningful answer.”
Finally, in the far future trillions of years from now, humanity has outgrown the confines of matter itself. Humans have evolved into pure energy beings that can transport themselves across the galaxy. Without the shackles of matter, they can visit the far reaches of the galaxy as pure consciousness. Their physical bodies are immortal but stored in some distant, forgotten solar system, so that their minds are free to roam. But each time they ask the fateful question, “Can entropy be reversed?” they get the same response: “There is insufficient data for a meaningful answer.”
Finally, the master computer is so powerful that it cannot be placed on any planet and is housed in hyperspace. The trillions of minds that make up humanity fuse with it. As the universe enters its final death throes, the computer finally solves the problem of reversing entropy. Just as the universe dies, the master computer declares “Let there be light!” And there was light.
So ultimately, the future of humanity is to evolve into a god that can create an entirely new universe and begin again. This was a masterful work of fiction. But let us now analyze this short story from the point of modern physics.
As we mentioned in the last chapter, we might be able to laser-port our consciousness at the speed of light within the next century or so. Eventually, laser porting may become a vast intergalactic superhighway, carrying billions of minds racing across the galaxy. So Asimov’s vision of beings of pure energy exploring the galaxy is not such a far-fetched idea.
