by Michio Kaku
At present, however, because of the complexity of the mathematics of string theory, physicists have not been able to apply it to these questions. This is a mathematical problem, not an experimental one, so perhaps one day an enterprising physicist will be able to definitively calculate the properties of wormholes and hyperspace. Instead of idly speculating about faster-than-light travel, a physicist using string theory has the ability to determine whether this might be possible. But we will have to wait until the theory is sufficiently understood to make this determination.
END OF THE DIASPORA?
So there is a possibility that a Type III civilization may be able to use a quantum theory of gravity to achieve faster-than-light-speed spaceships.
But what are the implications of this for humanity?
Earlier, we noted that a Type II civilization, bound by the speed of light, may establish space colonies that eventually branch off, creating many distinct genetic lineages which may eventually lose all contact with the mother planet.
The question remains, What happens when a Type III civilization masters the Planck energy and begins to make contact with these branches of humanity?
History may repeat itself. For example, the Great Diaspora ended with the coming of the airplane and modern technology, giving us a rapid international transportation network. Today, we can take a short plane trip over continents that once took our ancestors tens of thousands of years to cross.
In the same way, when we make the transition from a Type II civilization to a Type III civilization, we will, by definition, have enough power to explore the Planck energy, the point at which space-time becomes unstable.
If we assume that this makes faster-than-light travel possible, it means that a Type III civilization might be able to unify the various Type II colonies that have spread out across the galaxy. Given our common human heritage, it may make possible the creation of a new galactic civilization, as envisioned by Asimov.
As we have seen earlier, the amount of genetic divergence that humanity may experience over several tens of thousands of years in the future is roughly the same as the divergence that has already occurred since the Great Diaspora. The key point is that we have maintained our humanity throughout. A young child, born in one culture, can easily grow up and mature in another totally different culture, even if the two cultures may be separated by a vast cultural chasm.
This also means that Type III archeologists, curious about ancient human migrations, may try to retrace the ancient migration routes of various branches of Type II civilizations across the galaxy. Galactic archeologists may look for signs of various ancient Type II civilizations.
In the Foundation saga, our heroes are in search of the ancestral planet that gave birth to the Galactic Empire, whose name and location were lost in the chaos of galactic prehistory. Given that the human population numbers in the trillions, with millions of inhabited planets, this seems like a hopeless task. But by exploring the most ancient planets in the galaxy, they find ruins of the earliest planetary colonies. They see how planets were abandoned because of wars, disease, and other calamities.
Likewise, a Type III civilization may emerge from a Type II civilization and try to retrace the various branches that were explored centuries earlier by sub-light-speed spaceships. In the same way that our current civilization is enriched by the presence of so many different types of cultures, each with a different history and perspective, a Type III civilization may be enriched by interacting with the many divergent civilizations that emerged during a Type II civilization.
So the creation of faster-than-light spaceships may make the dream of Asimov come true, unifying humanity into one galactic civilization.
As Sir Martin Rees has said, “If humans avoid self-destruction, the post-human era beckons. Life from Earth could spread through the entire galaxy, evolving into a teeming complexity far beyond what we can even conceive. If so, our tiny planet—this pale blue dot floating in space—could be the most important place in the entire Galaxy. The first interstellar voyagers from Earth would have a mission that would resonate through the entire Galaxy and beyond.”
But eventually any advanced civilization will have to face the ultimate challenge to their existence, which is the end of the universe itself. We have to ask the question, Can an advanced civilization, with all its vast technology, evade the death of everything there is? Perhaps the only hope for intelligent life is to evolve into a Type IV civilization.
Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
—ROBERT FROST, 1920
Eternity is an awful long time—especially towards the end.
—WOODY ALLEN
14 LEAVING THE UNIVERSE
The Earth is dying.
In the movie Interstellar, a strange blight has hit the planet, causing crops to fail and agriculture to collapse. People are starving. Civilization is slowly crumbling as it faces a devastating famine.
Matthew McConaughey plays a former NASA astronaut who is given a dangerous mission. Earlier, a wormhole mysteriously opened up near Saturn. It is a gateway that will transport anyone who enters it to a distant part of the galaxy, where there might be new inhabitable worlds. Desperate to save humanity, he volunteers to enter the wormhole and search for a new home for humanity among the stars.
Meanwhile, back on Earth, scientists are desperately trying to find the secret of the wormhole. Who made it? And why did it appear just as humanity was about to perish?
Slowly, the truth dawns on the scientists. The technology to make this wormhole is millions of years more advanced than ours. The beings who made it are actually our descendants. The creators are so advanced that they live in hyperspace, beyond our familiar universe. They have built a gateway to the past, to send advanced technology to save their ancestors (us). By saving humanity, they will actually save themselves. According to Kip Thorne, who in addition to being a physicist was one of the producers of the film, the inspiration for the physics behind the movie comes from string theory.
If we survive, one day we will face a similar crisis, except this time, the universe is dying.
One day in the far future, the universe will go cold and dark; stars will cease to shine as the universe is plunged into a Big Freeze. All life will cease to exist when the universe itself dies, eventually reaching near absolute zero in temperature.
But the question is, Are there any loopholes? Can we avoid this cosmic doom? Can we, like Matthew McConaughey, find salvation in hyperspace?
In order to understand how the universe might die, it is important to analyze the predictions of the far future given to us by Einstein’s theory of gravity and then analyze the startling new revelations that have been made in the last decade.
According to these equations, there are three possibilities for the ultimate fate of the universe.
BIG CRUNCH, BIG FREEZE, OR BIG RIP
The first is the Big Crunch, when the expansion of the universe slows down, stops, and reverses itself. In this scenario, the galaxies in the heavens will eventually halt and begin to contract. Temperatures will rise dramatically as the distant stars come closer and closer. Eventually, all the stars coalesce into a primordial superheated mass. In some scenarios, there might even be a Big Bounce and the Big Bang could start all over again.
The second is the Big Freeze, when the growth of the universe continues unabated. The second law of thermodynamics states that total entropy always increases, so eventually, the universe will grow cold as matter and heat become more diffuse. The stars will cease to shine, the night sky would become totally black, and temperatures would plunge to near absolute zero, when even molecules cease almost all their motion.
For decades, astronomers have been trying to determine which scenario determines the fate of our universe. This is done by calculating its average density. If the universe is dense enough, then there is e
nough matter and gravity to attract the distant galaxies and reverse the expansion, so that the Big Crunch becomes a realistic possibility. If the universe lacks sufficient mass, then there is not enough gravity to reverse the expansion and the universe goes into a Big Freeze. The critical density separating these two scenarios is roughly six hydrogen atoms per cubic meter.
But in 2011, the Nobel Prize in physics was given to Saul Perlmutter, Adam Riess, and Brian Schmidt for a discovery that overturned decades of cherished belief. They found that the universe, instead of slowing down in its expansion, was actually speeding up. The universe is 13.8 billion years old, but about 5 billion years ago, it began to accelerate exponentially. Today, the universe is expanding in a runaway fashion. Scientific American claimed, “The astrophysical community was stunned to learn that the universe was driving itself apart.” These astronomers came to this astounding conclusion by analyzing supernova explosions in distant galaxies to determine the rate at which the universe expanded billions of years ago. (One type of supernova explosion, called Type Ia, has a fixed luminosity, so we can accurately measure its distance using its brightness. If one has a headlamp of known luminosity it’s easy to tell how far away it is, but if you don’t know its brightness it’s difficult to tell its distance. A headlamp of known brightness is a “standard candle.” A Type Ia supernova acts as a standard candle, so it’s easy to tell its distance.) When analyzing these supernovae, scientists found that they were moving away from us, just as expected. But to their shock, they found that closer supernovae appeared to be moving away more rapidly than they should, indicating the rate of expansion was accelerating.
So in addition to the Big Freeze and Big Crunch, a third alternative began to emerge from the data, the Big Rip, which is like the Big Freeze on steroids. It is a vastly accelerated time frame for the life cycle of the universe.
In the Big Rip, the distant galaxies eventually move away from us so fast that they exceed the speed of light and disappear from view. (This does not violate special relativity, because it is space that is expanding faster than light. Material objects cannot move faster than light, but empty space can stretch and expand at any speed.) This means that the night sky will become black, because light from the distant galaxies is moving away so quickly it can’t reach us.
Eventually, this exponential expansion becomes so great that not only is the galaxy torn apart, the solar system is ripped apart, and the very atoms making up our bodies are also torn apart. Matter as we know it cannot exist in the final stages of the Big Rip.
Scientific American writes, “Galaxies would be destroyed, the solar system would unbind and eventually all the planets would burst asunder as the rapid expansion of space rips apart its very atoms. Finally, our universe would end in an explosion, a singularity of literally infinite energy.”
Bertrand Russell, the great British philosopher and mathematician, once wrote:
All the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system, and [the] whole temple of man’s achievement must inevitably be buried beneath the debris of a universe in ruins…Only within the scaffolding of these truths, only on the firm foundation of unyielding despair, can the soul’s habitation henceforth be safely built.
Russell wrote about “a universe in ruins” and “unyielding despair” in response to predictions by physicists of the Earth’s eventual demise. But he did not foresee the coming of the space program. He did not foresee that advances in technology might allow us to escape the death of our planet.
But although we might one day avoid the death of the sun with our spaceships, how will we avoid the death of the universe itself?
FIRE OR ICE?
The ancients, in some sense, anticipated many of these violent scenarios.
Every religion, it seems, has some mythology to explain the birth and death of the universe.
In Norse mythology, the Twilight of the Gods is called Ragnarok, the day of reckoning, when the world is blanketed in unending snow and ice and the heavens freeze over. The world witnesses the final battle between the frost giants and the Norse gods of Asgard. In Christian mythology, we have Armageddon, when the forces of good and evil clash for the last time. The Four Horsemen of the Apocalypse appear, foretelling the Final Judgment. In Hindu mythology, there is no final end of days at all. Instead, there is an unending series of cycles, each lasting about eight billion years.
But after thousands of years of speculation and wonder, science is beginning to understand how our world will evolve and eventually die.
For the Earth, the future lies in fire. In five or so billion years we will have the last nice day on our home planet, then the sun will exhaust its hydrogen fuel and expand into a red giant star. Eventually the sun will set the sky on fire. The oceans will boil and the mountains will melt. The Earth will be engulfed by the sun, and will orbit like a burnt-out cinder within its fiery atmosphere. There is a biblical reference that says, from ashes to ashes, dust to dust. Physicists say, from stardust we came, to stardust we will return.
The sun itself will suffer a different fate. After the red giant phase, it will eventually exhaust all its nuclear fuel, shrink, and go cold. It will become a small white dwarf star, about the size of the Earth, and eventually die as a dark dwarf star, a piece of nuclear waste drifting in the galaxy.
Unlike our sun the Milky Way galaxy will die in fire. About four billion years from now, it will collide with Andromeda, the nearest spiral galaxy. Andromeda is roughly twice the size of the Milky Way, so it will be a hostile takeover. Computer simulations of the collision show that the two galaxies will enter a death dance as they orbit around each other. Andromeda will rip off many of the arms of the Milky Way, dismembering it. The black holes at the center of both galaxies will orbit around each other and finally collide, merging into a bigger black hole, and a new galaxy will emerge from the collision, a giant elliptical galaxy.
In each of these scenarios, it is important to realize that rebirth is also part of this cosmic cycle. Planets, stars, and galaxies get recycled. Our sun, for example, is probably a third-generation star. Each time a star explodes, the dust and gas it spews into space reseed the next generation of stars.
Science also gives us an understanding of the life of the entire universe. Until recently, astronomers thought they understood its history and ultimate fate trillions of years into the future. They had speculated that it is evolving slowly in five epochs:
1. In the first epoch, the first billion years after the Big Bang, the universe was filled with hot opaque clouds of ionic molecules, too hot for electrons and protons to condense into atoms.
2. In the second epoch, a billion years after the Big Bang, the universe cooled down enough so that atoms, stars, and galaxies could emerge from the chaos. Empty space suddenly became crystal clear, and stars lit up the universe for the first time. We are living in this era now.
3. In the third epoch, about one hundred billion years after the Big Bang, the stars will have exhausted most of their nuclear fuel. The universe will consist mainly of small red dwarf stars, which burn so slowly that they can shine for trillions of years.
4. In the fourth epoch, trillions of years after the Big Bang, all the stars will finally burn out and the universe will go completely black. Only dead neutron stars and black holes remain.
5. In the fifth epoch, even black holes begin to evaporate and disintegrate, so the universe becomes a sea of nuclear waste and drifting subatomic particles.
With the discovery of the accelerating universe, this entire scenario might be compressed into billions of years. The Big Rip upsets the entire applecart.
DARK ENERGY
What is causing this sudden change in our understanding of the ultimate fate of the universe?
According to Einstein’s theory of relativity, there are two sources of energy that drive the evolution of the universe. The first is the curvature of space-time, which cre
ates the familiar gravity fields surrounding the stars and galaxies. This curvature is what keeps our feet on the ground. This is the energy source most studied by astrophysicists.
But there is also a second source of power, which is usually ignored. It is the energy of nothingness, the energy of the vacuum, called dark energy (not to be confused with dark matter). The very emptiness of space contains energy.
The most recent calculations show that this dark energy acts like antigravity and it is pushing the universe apart. The more the universe expands, the more dark energy there is, which causes it to expand even faster.
At present, the best data indicate that about 69 percent of the matter/energy (since matter and energy are interchangeable) in the universe is contained in dark energy. (By contrast, dark matter makes up about 26 percent, atoms of hydrogen and helium make up about 5 percent, and higher elements, which make up the Earth and our own bodies, only make up a tiny 0.5 percent.) So dark energy, which is pushing the galaxies away from us, is clearly the dominant force in the universe, much larger than the energy contained in the curvature of space-time.
One of the central problems in all of cosmology is therefore to understand the origin of dark energy. Where does it come from? Will it ultimately destroy the universe?
Usually, when we simply combine relativity and the quantum theory in a crude shotgun marriage, we can get a prediction for dark energy, but the resulting prediction is off by a factor of 10120, which is the largest mismatch in the history of science. Nowhere do we find a discrepancy this large. It indicates that something is terribly wrong with our understanding of the universe. So the unified field theory, instead of being a scientific curiosity, becomes essential to understanding how everything works. The solution to this question will tell us the fate of the universe and all intelligent creatures in it.
