Catching the Gravitational Lens Express:
The Scientific Backstory to Mission to Methone
Les Johnson
The stars are our home. The Earth, our wonderful and special habitat, orbits the star named Sol at about 18 miles per second, yet most people don’t even give this amazing fact a second thought. The next logical step for human civilization is to spread to our moon, the asteroids and the other planets in the solar system. Finally, we are beginning to see that happen. Granted, those of us who recall Neil Armstrong walking on the Moon thought this would occur forty years ago, but we have made progress and it now appears that a sustainable space infrastructure is coming into place that may allow the progression to happen—at least to Mars.
Today, multiple new companies, such as SpaceX and Blue Origin, are challenging the status quo and driving down the cost of access to space in the process. Elon Musk of SpaceX makes no secret of his desire to send people to Mars in his lifetime. Jeff Bezos of Blue Origin has as one of his goals the development of space to help solve problems on Earth. More established rocket companies, such as Boeing, Lockheed Martin, and Orbital Sciences Corporation, are being reinvigorated as well. All are building rockets or spacecraft to carry people to, and through, space more affordably than ever before.
NASA will soon launch the long-awaited Space Launch System, a monster rocket capable of sending people back to the Moon and on to Mars. NASA is also beginning to develop the nuclear rockets that will be needed to make travel to and from Mars more affordable and faster. The Europeans, Japanese, Russians and Chinese are all making plans to send crews to the surface of the Moon. The global social and economic dynamic been has never before been so space-focused. The space renaissance of which we’ve dreamed might be taking shape.
Going beyond Mars will be much more difficult due to the vast distances involved and our lack of a space propulsion system capable of allowing us to travel hundreds of millions of miles in a reasonable amount of time. Rockets, even nuclear rockets, won’t allow us to get people to Jupiter and beyond in less than a decade—far too long. Physics tells us that there are ways we can shorten the travel time, but the technologies are nowhere near maturity, and likely won’t be for another fifty to one hundred years. Nuclear fusion, beamed energy, and antimatter propulsion may be possible, but they will take some time to develop.
Meanwhile, we have discovered thousands of planets circling other stars. Most of these exoplanets appear completely unsuitable for sustaining life as we know it, but many are in locations where life might just be able to exist. Their discovery has led to the obvious question, “How can we get there?” Unfortunately, the solar system beyond Mars is out of reach—let alone interstellar travel. At least for now.
These advancements and discoveries are prompting the broader society to consider the Big Questions so often asked by scientists and science fiction fans as they look out into space and wonder:
These are some of the questions I attempt to answer in my new Baen novel, Mission to Methone. Mission to Methone (M2M—hey, I work for NASA in my day job. Creating initialisms and acronyms is part of the job description!) is my personal vision of hope for a future where we have space development of the inner solar system, we have space solar power stations supplementing the electrical grid on Earth, we have asteroid mining, we have lunar bases and we have robust Mars exploration. (I want it all!) In M2M, an artifact from an alien civilization is found in our solar system, forcing humanity to grapple with some potentially unsettling answers to the Big Questions.
Can We Cheat Relativity and Travel at or Faster Than the Speed of Light?
One of the great issues facing physics today is the reconciliation of general relativity with quantum mechanics. Relativity says that nothing can travel at or beyond the speed of light because doing so would require infinite energy. (And who has that much energy lying around?) But wait, the other theory, quantum mechanics, says that some natural occurring events that involve particles moving from Point A to Point B happen instantaneously in a process called tunneling. If tunneling is truly instantaneous, then wouldn’t that be an example of faster than light travel? Perhaps. This question was first seriously addressed by Prince Louis de Broglie.
Prince Louis de Broglie lived in the latter part of the 19th century and into the early 20th and, yes, he was a prince. After serving in the French army during World War I, he engaged in his theoretical physics studies at Paris University. De Broglie made his mark in the field of quantum mechanics with the publication of his Ph.D. thesis, “Researches on the Quantum Theory,” in which he formulated modern wave mechanics. In layman’s terms, he theorized that physical particles like protons and electrons could be described as quantum mechanical waves—just as quantum mechanical wave theory had been accepted at the time for explaining the behavior of light.
His theory was confirmed in 1927 when the famous Davisson and Germer experiment confirmed that electrons could diffract like light, and therefore had wavelike properties. He was later awarded the Nobel Prize in physics for his work.
How does this relate to faster than light travel? It doesn’t, at least directly (yet), but it might!
In classical physics, if an electron of a certain energy is trapped in an electric field, then it is considered to be in a potential well. (Think of it as being dropped in a hole. If the hole isn’t very deep, you can jump or climb out. Your “energy level” is large enough to escape the hole. If the hole is too deep for you to jump out, then you are trapped within it.) Unless the electron has enough energy to escape, it will remain in the potential well forever. This is shown in Figure 1.
Figure 1. In classical physics, electrons cannot cross a potential barrier unless they have enough energy to do so. Image courtesy the author.
In reality, electrons can be placed in a deep potential well from which they should never be able to escape and yet do so anyway—sometimes. Sometimes the electron will remain inside and sometimes not. And, if you study enough electrons in potential wells, then you would see that there is some probability of its escaping over a specific period of time. This can only be explained if you think of the electron as a wave. In wave mechanics, the location of a particle is described in terms of probabilities and waves, which can be shown graphically in Figure 2. If you think of the electron’s location as being somewhere under the curve, and the curve can extend beyond the potential barrier, then there is a small chance the electron will relocate itself outside of the potential well and on the other side of the energy barrier. Thinking back to the hole you jumped into above, it would be as if you, from one moment to the next, simply appeared standing on the ground next to the hole rather than remaining inside it. That’s quantum tunneling.
Figure 2. In quantum physics, an electron behaves like a wave and has a small probability of escaping the potential barrier even if its energy is too low. Image courtesy the author.
Tunneling on a microscopic scale is real and is the reason that many modern electronic devices work. Examples include computer flash drives, scanning tunnel microscopes, and diodes. It is also the key process in radioactive decay.
The problem with a macroscopic object, say a human being, tunneling is scale. The matter wave of macroscopic objects are inversely related to their mass. In practical terms, this means the probability of you or I tunneling or relocating to another location in the universe is EXTREMELY small, but not zero. (What would be the likelihood of randomly tossing one hundred pennies and having them all come up heads? Very small, but not zero!) The probability of macroscopic tunneling is so small, however, that the likelihood of it happening in the lifetime of the universe is very close to zero. But that’s in nature. What if someone or something figures out how to externally relocate a macroscopic object’s matter wave to the destination of their choosing? By forcing the small, but finite probability of the object relocating to be equal to 1, the object would jump out of the hole and go where it was directed to go. (Which, itself is probably not accurate. It would simply go from point A to point B because that’s where it is supposed to be, probabilistically. Just like in our natural world it appears to remain at Point A because that’s where the probability of its being is highest.)
The speed of tunneling is another topic. In M2M, I assumed that tunneling across large distances is limited by relativity to be no faster than the speed of light. There is some evidence that the effect may, in fact, be instantaneous—but I’m not ready to assert that this phenomenon violates Professor Einstein’s rules. Not until there is sufficient, credible evidence to do so.
I also speculate that interstellar tunneling is facilitated by an interesting property of very large masses, like black holes and stars, called gravity lensing.
Light is constrained to move within the fabric of physical reality known as space-time. In the absence of a massive object, light behaves in the relativistic universe in which we live just as it would in a non-relativistic (i.e. Euclidean) universe by moving in a straight line. But when a massive object is interposed between us and whatever is emitting the light, something curious happens—the light appears to be bent around that object. The space-time around the massive object is bent, and the light which is constrained to move through space-time, bends with it.
The result is something similar to what happens when light is refracted in everyday glasses worn by nearsighted people. When light is bent, it can come to a focus. The effect was first measured in 1919 when astronomers Arthur Eddington and Frank Watson Dyson observed stars that appeared near the sun during a total solar eclipse. Similar observations were made across the globe and, sure enough, the light from stars passing close to the Sun (VERY close to the Sun and therefore only visible during an eclipse) was found to be bent by the Sun’s mass. They made these observations before they could be readily explained by Einstein’s Theory of General Relativity—which came much later. Since then, the effect has been observed on a galactic scale with massive galaxies bending the light from more distant galaxies, enabling them to be seen by our telescopes.
It turns out that the Sun’s gravitational lens has a focal line at about 550 Astronomical Units (AU). One AU is the distance from the Earth to the Sun, or approximately 93 million miles. It is for this reason that the alien races exploring other star systems place their de Broglie transfer stations at these locations. (Other stars have masses different than our Sun and their gravity lens locations are therefore different.) By using this lensing effect, one can theoretically use much less energy to send any sort of radiation or quanta (light, radio, and, presumably, matter waves) than would be required without the lensing. According to physicist Dr. Claudio Maccone, a radio with a power of only a few tens of watts could use this lensing effect to send detectable signals to Alpha Centauri!
Are We Along in the Universe?
Our Solar System contains eight planets, five dwarf planets, numerous moons and thousands of asteroids. We know that at least one planet contains life (Earth) and another might have supported life at one time (Mars). There are also at least three moons, Europa, Titan and Enceladus that may have conditions suitable for life. And this is just within our own Solar System.
Thanks to the Kepler Space Telescope, we now know that there are thousands of nearby stars with planetary systems, some of which are known to have planets in the “habitable zone,” which means they may have conditions suitable for life as we know it. Based on the statistics from Kepler, it appears that almost all stars have planetary systems, with an estimated 2.5 planets per system.
Our galaxy, the Milky Way, contains between one-hundred billion and three-hundred billion stars. That translates to estimated two-hundred-fifty billion planets. Recent estimates place the number of galaxies in the universe at nearly one trillion. If the stars in these galaxies are similar to our own, and we have every reason to believe they are, then there are about 2,500,000,000,000,000,000,000,000 planets in the universe. Does anyone seriously believe we are alone? Though I doubt we humans are being or have been visited by extraterrestrials (see my essay, “The Aliens Are Not Among Us,” on the Baen website for my rationale), I don’t believe it is impossible for that to happen or for it to have happened in the past. In fact, when I think about these numbers, it is nearly impossible for me to believe that we are alone in the universe.
And then there is the observational evidence for the existence of ET. There is none. Despite decades of radio searches and thousands, if not hundreds of thousands, of astronomers (professional and amateur) gazing at the stars, there is no sign of another civilization like our own out there anywhere or any time. Surely, the argument goes, if other technological civilizations exist, then their presence would eventually become obvious—as ours is on track to being as we move out to explore our Solar System and develop toward becoming an interplanetary species. We’ve only been in the game, that is, we’ve only been a technological civilization for a few hundred years out of the four and a half billion years of Earth’s history. Within the next thousand years, it is likely that anyone nearby in the galaxy will know we exist by our energy emissions alone. If another civilization developed technology before us, which is likely given the sheer numbers involved, then their presence should be obvious to us.
But again, there is no evidence of anyone else out there. This is called the Fermi Paradox, named after Enrico Fermi, the physicist who is credited with raising this question. Why not? Why have we not seen signs of ET among the stars? I don’t pretend to know if we are truly alone or if the universe is teaming with as-yet undetected life, but that will not stop me from speculating.
Physicist Stephen Hawking warned that “Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they could reach." That’s enough to cause one to pause and think, regardless of the reality of his concern. We know how humans behave toward each other; why would we expect ET to behave differently? That is a scary thought.
Finally, we have some amazing places to explore within our own solar system. One of them, Saturn’s moon, Methone, is so odd that I believe we should go there sooner rather than later.
Why Methone?
Orbiting Saturn between the much larger moons Mimas and Enceladus lies the almost three mile-long, egg-shaped Methone. Methone (pronounced “mi-thoh-nee”) is so small that it remained undetected until NASA’s Cassini spacecraft discovered it in 2004. Like the planets and many of their moons, Methone owes its name to Greek or Roman mythologies—in this case, Greek. Methone was one of the Alkyonides, the seven beautiful daughters of the Giant Alkyoneus—an opponent of Heracles. Methone figures prominently in M2M.
Cassini passed relatively close to it in 2012, passing just 1800 miles away where it took some spectacular photographs (Figure 3). As you can see, Methone looks like a nearly-perfect egg.
Figure 3 Methone, one of Saturn's moons, as seen by the NASA Cassini spacecraft. Image courtesy of NASA.
There are no visible craters and it is believed that the moon is made from or at least covered by ice. Based upon Cassini’s observations, scientists have determined that Methone has a density one third that of water, making it less dense than any other moon or asteroid in the Solar System. You can see why imagination might run wild and turn it into a spaceship rather than a moon.
While we embrace the space revolution that appears to be happening, we should keep our sights set on the ultimate goals of preserving the Earth, establishing the human species on other planets in our solar system and, eventually, on planets orbiting distant stars. As science advances, we will almost certainly find a way to reconcile relativity with quantum mechanics or come up with a new theory that does. In a hundred years, or perhaps a thousand, we’ll figure out how to travel fast enough to reach those other stars. Maybe we will just tunnel our way there—who knows? On a galactic scale, a thousand, even ten thousand years, rounds to nothing when compared to the billions of years that preceded us.
If we might be able to reach the stars in one to ten thousand years in a galaxy that is billions of years old, then why hasn’t anyone else? Shouldn’t they, whoever they are, be here already? They aren’t, and that is worrisome. Perhaps we should take Stephen Hawking’s advice, keep quiet, advance our technologies, and dream . . .