To make it worth the hassle, they would have to stake their claim on a large black hole. Because, you guessed it, size matters. A lot of time is required for the large ones to evaporate enough energy to make harvesting the energy worthwhile, something along the line of about 1057 x 13.8 billion years. The lifetime of a black hole is the cube of its mass (m3).7 And these large suckers have a lot of mass.
Fear not. When a civilization approaches the late stage of type I status, the idea of having a lifespan is quaint. Time might be on their side for these types of energy projects.
HOW ARE BLACK HOLES DETECTED?
Black holes exist mathematically, but science demands evidence. They can't be seen optically (here it comes) because they are black and so is space. Their existence and size can still be detected by indirect means. You can use the known mass of objects you can directly detect to estimate the mass of a black hole by how it affects those known stellar objects.
Another method is to measure the X-rays emitted by heated material as it falls into the black hole. A third way comes from another prediction of general relativity called gravitational lensing, the amount that background light is warped by massive objects. The more massive the stellar object, the more the light is curved.
WORMHOLES (AGAIN)
Let's pair up what we know about quantum mechanics with our knowledge of black holes. Only instead of entangled particles, I want you to think of entangled black holes. The quantum state of one black hole is in sync with the quantum state of a second black hole. If instruments measure the quantum state of the first black hole, guess what? You know about the second one because everything that is entangled on the quantum level is in the same state.
Now consider the possibility that a singularity isn't a point but really is a hole, a wormhole that connects two black holes. Each black hole resides in a different place and perhaps even in different times. The black holes are physically connected, and the entanglement causes a wormhole because of entanglement's effect on the geometry of spacetime.
Recently, more and more physicists have been looking at the effects of quantum entanglement on spacetime. A few even believe that quantum entanglement itself might create spacetime.8
CAN BLACK HOLES BE USED FOR TIME TRAVEL?
In principle, yes. However, it means stretching the physics of general relativity to the limit, which is okay at least for good science fiction. Here are a few ways it could be done.
1.Go for a spin
Fig. 7.2. Illustration of a spinning black hole. (NASA/JPL-Caltech.)
The first way requires a rotating black hole. According to general relativity, a spinning black hole twists the surrounding fabric of spacetime. This phenomena is known as frame-dragging. I hope you still have that two-dimensional sheet we used in chapter 1 pulled taut with a big ball lying on it. Now spin the ball. It pulls the sheet along for the ride.
The same holds true for objects spinning in our three-spatial-dimensional spacetime sheet. Scientists have tested this for the earth using gyroscopes aboard NASA's Gravity Probe B satellite.9 The frame drag of forty-two milliarcseconds of angle over the course of a year is consistent with the prediction from general relativity. This isn't a big number, but space around Earth is dragged.
The technology doesn't yet exist for a satellite to test a black hole for twisting spacetime. That doesn't stop scientists from thinking up more practical ways to conduct that test. They came up with the idea to study stuff circling the ingeniously named H1743-322 black hole through the X-rays emitted from iron ions embedded in that circling matter.10 The X-rays grow or shrink depending on how the ions move relative to an observer. The frame-dragging effect is about one hundred trillion times as strong as the one found near Earth.
Now all you need to do is have your pilot fly your ship into the spin cycle as everyone holds on. You and your crew have just entered a different time frame.
2.Care for a donut?
Another possibility for time travel that uses a rotating black hole is a ring singularity (think donut). This type of singularity is called a Kerr singularity, named after mathematician Roy Kerr who solved Einstein's field equations of general relativity for a rotating black hole.11
And now we mix some science fiction with the Kerr singularity. You start by creating a starship with enough density to survive the gravity gradient and maintain its shape as it passes through the event horizon. Step one completed: spaghettification avoided. Now all that is left is to dive through the center of the ring and emerge in a different time.
3.Time dilation (general relativity) because sometimes you just have to go with the classics
Another way to time travel is to camp out in a starship near the edge of the event horizon and take advantage of the time dilation. Remember that as gravity increases, time flows slower for those in the starship relative to their companions on a settlement very far away. An example of this can be found in the television series Andromeda where a starship uses this method to travel three hundred years into the future.
PARTING COMMENTS
Black holes are where the physics of both quantum mechanics and general relativity break down. Black holes are gravity wells pressing so deeply into the fabric of spacetime that light and electromagnetism can't climb out. They exist and hold galaxies together, but they can't be completely defined by general relativity or quantum mechanics. They don't last forever. For the record, black holes don't actually suck you in. Instead, you fall into them.
CHAPTER 7 BONUS MATERIALS
BONUS 1: A MASSIVE MYSTERY
Supermassive black holes are believed to start out small. They gradually grow by taking in matter and by merging with other black holes. Astronomers have detected the existence of these big guys in the early years of the universe, back when it was a youngster of less than a billion years old.
The mystery is that although the first stars were huge (one hundred times the mass of our sun) and burned for only a few million years, their explosions should have created black holes of about the same mass as the original star. And yet, some of the supermassive black holes weigh in at least ten billion solar masses.12
BONUS 2: THE INFORMATION PARADOX
It is generally accepted that, if you have information about a system such as particle states and their quantum probabilities, you should be able at any time to determine its state at any other time. In other words, the quantum probability wave that describes the states must be conserved. This conservation holds in quantum mechanics and general relativity until a black hole is introduced.
As we've seen, these critters have the habit of gobbling up everything in their paths, including quantum information. That means the quantum wave is incomplete. Back in chapter 2, I described how a probability wave holds all possible states of a particle until it is observed. At that moment, the wave collapses and its state can be measured. All the future possibilities of a particle were included in the wave function.
After a black hole has destroyed at least part of that wave, we can no longer know everything about the particle. This contradicts general relativity, which has time dilation preserving the system information. This contradiction is known as the information paradox. A theoretical solution will be provided in chapter 20. It questions what we know of reality.
Evolution is cleverer than you are.
—Leslie Orgel, evolutionary biologist
This chapter is dedicated to the opportunism that has built life on Earth. Whether the cause was natural selection, random mutations, selfish genes, dark energy, or chemical reactions doesn't matter. Things have changed over time, and the things we see now didn't exist in the past. The reason is evolution.
Evolution affects everything in the macro universe from life to stars to black holes. As long as time has a direction, evolution occurs. There is no escaping it. For organic life on Earth, evolution is the backbone on which life sciences are built. It is the name given to the slow process (in human terms) of inheritable changes in populations over time.
Evolution can be confusing and even controversial because it is sometimes referred to as fact and other times as theory. It is both. A fact describes a phenomenon while a theory attempts to explain it. This is no different than our discussion on gravity. You can see that gravity exists (a fact) by simply dropping this book. The theoretical explanation for gravity is the curvature of spacetime. This theory might not be complete because we know it doesn't jibe perfectly with quantum mechanics. Nevertheless, gravity exists.
Evolution is no different. The fact of evolution is backed up by a lot of evidence such as DNA mapping and the fossil record. Evolution theory is used to explain the how. Charles Darwin believed the how of evolution to be natural selection, where a variation that provides a survival advantage in a population is passed down through the generations.
His theory was predicated on the Malthusian principle of population growth. Reverend Thomas Robert Malthus argued in his book An Essay on the Principle of Population that populations grew exponentially, but the ability to feed the increasing population grew at a lower geometric rate.1 The human population, he claimed, grows at a faster rate than its food supply.
Darwin had much the same idea about species. Since they produce more offspring than the number that can be supported in a given environment, some members of the population will be better suited to survive in that environment and more likely to mate.
With natural selection, those members more likely to survive are more likely to reproduce. Natural selection also weeds out individuals with unfavorable traits, called survival of the fittest. Survival of the fittest does not mean survival of the smartest, or that higher intelligence is the outcome of evolution. All that matters is the passing on of genes. In Kurt Vonnegut's novel Galapagos, humans in a distant future have evolved into sea creatures that laugh at farts.2
How these variations arise in a population was a mystery to Darwin. Today we know they are caused by random changes in DNA. More specifically, evolution is a function of genetic mutation, a mistake (alteration) in a DNA sequence created when a cell copies itself for cell division. Occasionally the mistake gives the organism a survival advantage.
Surviving (obviously) enhances the likelihood of meeting a mate and reproducing, which passes the mutation to the next generation. As I said at the beginning of this chapter, it is all about opportunism, selfish genes passing themselves down to future generations. This same process eliminates bad mutations from the gene pool.
Some people confuse adaptation with evolution. This is easy to do because they are related. A member of a species who adapts to a hostile environment is more likely to find a mate than members who weren't able to adapt…and died. Adaption is a short-term phenomenon where the survivor is still a member of the original species; the species itself hasn't changed. Evolution is a much longer process where physical changes begin at the genetic level and take generations to produce species more suited to an environment. Adaption is about the short-run survival of an individual member while evolution is the long-run survival of the entire species.
Evolution to the rescue: Between 1996 and 2016, about 80 percent of Tasmanian devils were wiped out from a contagious cancer called devil facial tumor disease (DFTD). The small number of survivors had a genetic variant that helped them survive the disease long enough to reproduce. They evolved themselves out of extinction.3
THE HUMAN STORY
You are both a hominin and a hominid. Congratulations. These terms differ in a subtle way that can cause confusion. A hominin is any subspecies of early humans more closely related to humans than chimpanzees. Hominids include all hominins plus all modern and extinct apes, gorillas, chimps, and orangutans. You are also human, part of the homo genus. In fact, your species is the last of its kind.
Our story reveals how evolution is a steady process but not necessarily a straight-line progression. Darwin's book, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, expressed his belief in branching evolution from a common ancestor. He was correct. There are many branches in our family tree. Most were pruned away because they couldn't adapt to changing environmental conditions.
Here is a flash history of how we got from Earth's start to hominins traipsing about to humans messing about on Twitter:
4.5 billion years ago (BYA), Earth forms.4
2 BYA, oxygen on Earth increases significantly.
650 million years ago (MYA), multicellular life begins in the oceans.
440 MYA, life climbs onto land.
250 MYA, dinosaurs appear.
65 MYA, dinosaurs go extinct.
4 to 3 MYA, Australopithecus afarensis stood on its hind legs and walked. This hominin is the common ancestor to both the genus Australopithecus and the genus Homo. You might have heard about the A. afarensis celebrity known as Lucy.5
2.5 to 3 MYA, the climate changes, forcing Australopithecus to move out of the forests and into open territory. They adapted to new food and new predators. The genus Homo begins.
Something to ponder: if the climate had not changed then, Australopithecus might still be around today.
3 to 1.5 MYA, Homo naledi buried their dead. Homo habilis mastered stone technology. H. naledi were Australopithecus sized but had some of the modern Homo features (bigger skull size). They might be the earliest of Homo species.
1.9 MYA, a chinless Homo erectus started a fire. The movie One Million Years BC (originally released in 1940 with the famous remake produced in 1966) shows how dinosaurs and humans chased each other around. Do you want to know if this is fiction? I'll tell you.
Both the historical and fossil records tell quite a different story about what was really going on at this time. In one million BCE, H. erectus were picking up stones and definitely did not look anything like Loana the Fair One of the Shell tribe, as played by Raquel Welch. Also, there weren't any dinosaurs.
Perhaps the title contains a typo and the writers of the movie really meant 100,000 BCE when humans were working their way through the Stone Age. The problem, again, is that there weren't any dinosaurs during that time either, so I suspect One Million Years BC wasn't produced in a documentarian style.
The movie 10,000 BC (2008) is a little closer to accuracy, but somehow the Nile Valley of 2,000 BCE makes an appearance along with ice-age Egyptians who wield steel and ride domesticated horses.6 So I'm guessing this movie didn't rely much on the historic record.
780,000 to 125,000 years ago in Africa, Homo heidelbergensis split into at least two groups. One stayed in Africa while the other migrated to parts of Europe and Asia. Individuals who hunkered down in Europe evolved into Homo neanderthalensis (aka Neanderthals), while those who planted their flag in Asia evolved into Denisovans (status pending, but probably in the Homo genus). The branch of H. heidelbergensis that stayed in Africa eventually evolved into Homo sapiens.
75,000 to 50,000 years ago, the largest migration of H. sapiens left Africa. There is a theory that our species almost did not make it beyond this point. About seventy-four thousand years ago, a volcano in Indonesia caused a volcanic winter that lasted six to ten years.7 This gray weather was followed by a thousand-year-long cooling. This might have reduced the human population to ten thousand to thirty thousand individuals. It is called the Toba catastrophe. The good news is we haven't gone extinct, at least not yet. That is a topic for another chapter.
Now back to our history. The largest migration of humans out of Africa happened between fifty thousand to seventy-five thousand years ago, possibly because of climate changes. All non-Africans alive today descended from this group. There is early evidence of humans hiking about, but we didn't descend from them. Those early migration humans all died out. Scientists aren't sure what happened. Perhaps the massive migration overwhelmed the smaller earlier migrations physically and genetically. Whatever happened, only bits of their DNA made it down to us today.
25,000 to 40,000 years ago, H. neanderthalensis dies out.
10,000 to 20,000 years ago, the Homo floresiensis branch dies out and Homo sapiens sapiens is the last species of the genus Homo standing. That's you. H. floresiensis gets the dubious nickname of “hobbit” from J. R. R. Tolkien's diminutive protagonist. These historical hobbits were about half the size of H. sapiens. They were hanging out on the island of Flores in Southeast Asia when modern humans wandered across Europe. Did humans meet them and start an oral story tradition about dwarfs? Possibly.
Anyway, this branch of the family tree is a mystery. One theory is that they are a descendant of some early H. erectus that settled on the island about one million years ago. They then evolved smaller bodies to accommodate limited island resources. In evolutionary terms, this is tricky because they would have had to shrink in the span of a mere 300,000 years.
FOSSILS ARE SO YESTERDAY (LITERALLY)
Scientists no longer need only fossils to reconstruct human evolution history. Today they also rely on genetics. During the Stone Age, all these different hominins conducted a lot of fraternizing. The DNA results are in, and there is no hiding paternity (and maternity). Between 1.5 percent and 4 percent of Neanderthal DNA can be found in today's non-African genomes. Between 1.9 percent and 3.4 percent of modern Melanesians genes come from the Denisovans.8
There is also some genetic evidence that Neanderthals and Denisovans might also have thrown some adult private dating parties. In addition, there is evidence that Neanderthals and Denisovans mated with other archaic humans about 120,000 years ago. Apparently they couldn't wait for modern humans to come along.
Blockbuster Science Page 10