Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100

were using Twitter and YouTube in their struggle to carry their message to the world.
    In the past, people said that the pen was mightier than the sword. In the future, it will be the chip that is mightier than the sword.
    One of the reasons the people of North Korea, a horribly impoverished nation, do not rebel is because they are denied all contact with the world, whose people, they believe, are also starving. In part, not realizing that they do not have to accept their fate, they endure incredible hardship.
    TYPE II CIVILIZATIONS
    By the time a society attains Type II status thousands of years into the future, it becomes immortal. Nothing known to science can destroy a Type II civilization. Since it will have long mastered the weather, ice ages can be avoided or altered. Meteors and comets can be also be deflected. Even if their sun goes supernova, the people will be able to flee to another star system, or perhaps prevent their star from exploding. (For example, if their sun turns into a red giant, they might be able swing asteroids around their planet in a slingshot effect in order to move their planet farther from the sun.)
    One way in which a Type II civilization may be able to exploit the entire energy output of a star is to create a gigantic sphere around it that absorbs all the sunlight of the star. This is called a Dyson sphere.
    A Type II civilization will probably be at peace with itself. Since spacetravel is so difficult, it will have remained a Type I civilization for centuries, plenty of time to iron out the divisions within their society. By the time a Type I civilization reaches Type II status, they will have colonized not just their entire solar system but also the nearby stars, perhaps out to several hundred light-years, but not much more. They will still be restricted by the speed of light.
    TYPE III CIVILIZATIONS
    By the time a civilization reaches Type III status, it will have explored most of the galaxy. The most convenient way to visit the hundreds of billions of planets is to send self-replicating robot probes throughout the galaxy. A von Neumann probe is a robot that has the ability to make unlimited copies of itself; it lands on a moon (since it is free of rust and erosion) and makes a factory out of lunar dirt, which creates thousands of copies of itself. Each copy rockets off to other distant star systems and makes thousands more copies. Starting with one such probe, we quickly create a sphere of trillions of these self-replicating probes expanding at near the speed of light, mapping out the entire Milky Way galaxy in just 100,000 years. Since the universe is 13.7 billion years old, there is plenty of time in which these civilizations may have risen (and fallen). (Such rapid, exponential growth is also the mechanism by which viruses spread in our body.)
    There is another possibility, however. By the time a civilization has reached Type III status, its people have enough energy resources to probe the “Planck energy,” or 10 19 billion electron volts, the energy at which space-time itself become unstable. (The Planck energy is a quadrillion times larger than the energy produced by our largest atom smasher, the Large Hadron Collider outside Geneva. It is the energy at which Einstein’s theory of gravity finally breaks down. At this energy, it is theorized that the fabric of space-time will finally tear, creating tiny portals that might lead to other universes, or other points in space-time.) Harnessing such vast energy would require colossal machines on an unimaginable scale, but if successful they might make possible shortcuts through the fabric of space and time, either by compressing space or by passing through wormholes. Assuming that they can overcome a number of stubborn theoretical and practical obstacles (such as harnessing sufficient positive and negativeenergy and removing instabilities), it is conceivable that they might be able to colonize the entire galaxy.
    This has prompted many people to speculate about why they have not visited us. Where are they? the critics ask.
    One possible answer is that perhaps they already have, but we are too primitive to notice. Self-replicating von Neumann probes would be the most practical way of exploring the galaxy, and they do not have to be huge. They might be just a few inches long, because of revolutionary advances in nanotechnology. They might be in plain view, but we don’t recognize them because we are looking for the wrong thing,