by Michio Kaku
One can only speculate about the possible life-forms that might form under Europa’s ice. If they exist at all, they probably will be swimming creatures that use sonar, rather than light, for navigational purposes, so their view of the universe will be limited to living under the “sky” of ice.
LISA—BEFORE THE BIG BANG
Yet another space satellite that could create an upheaval in scientific knowledge is the Laser Interferometer Space Antenna (LISA) and its successors. These probes may be able to do the impossible: reveal what happened before the big bang.
Currently, we have been able to measure the rate at which the distant galaxies are moving away from us. (This is due to the Doppler shift, where light is distorted if the star moves toward or away from you.) This gives us the expansion rate of the universe. Then we “run the videotape backward,” and calculate when the original explosion took place. This is very similar to the way you can analyze the fiery debris emanating from an explosion to determine when the explosion took place. That is how we determined that the big bang took place 13.7 billion years ago. What is frustrating, however, is that the current space satellite, the WMAP (Wilkinson Microwave Anisotropy Probe), can peer back only to less than 400,000 years after the original explosion. Therefore, our satellites can tell us only that there was a bang, but cannot tell us why it banged, what banged, and what caused the bang.
That is why LISA is creating such excitement. LISA will measure an entirely new type of radiation: gravity waves from the instant of the big bang itself.
Every time a new form of radiation was harnessed, it changed our worldview. When optical telescopes were first used by Galileo to map the planets and stars, they opened up the science of astronomy. When radio telescopes were perfected soon after World War II, they revealed a universe of exploding stars and black holes. And now the third generation of telescopes, which can detect gravitational waves, may open up an even more breathtaking vista, the world of colliding black holes, higher dimensions, and even a multiverse.
Tentatively, the launch date is being set for between 2018 and 2020. LISA consists of three satellites that will form a gigantic triangle 3 million miles across, connected by three laser beams. It will be the largest space instrument ever sent into orbit. Any gravity wave from the big bang still reverberating around the universe will jiggle the satellites a bit. This disturbance will change the laser beams, and then sensors will record the frequency and characteristics of the disturbance. In this way, scientists should be able to get within a trillionth of a second after the original big bang. (According to Einstein, space-time is like a fabric that can be curved and stretched. If there is a big disturbance, like colliding black holes or the big bang, then ripples can form and travel on this fabric. These ripples, or gravity waves, are too small to detect using ordinary instruments, but LISA is sensitive and large enough to detect vibrations caused by these gravity waves.)
Not only will LISA be able to detect radiation from colliding black holes, it might also be able to peer into the pre–big bang era, which was once thought to be impossible.
At present, there are several theories of the pre–big bang era coming from string theory, which is my specialty. In one scenario, our universe is a huge bubble of some sort that is continually expanding. We live on the skin of this gigantic bubble (we are stuck on the bubble like flies on flypaper). But our bubble universe coexists in an ocean of other bubble universes, making up the multiverse of universes, like a bubble bath. Occasionally, these bubbles might collide (giving us what is called the big splat theory) or they may fission into smaller bubbles and then expand (giving us what is called eternal inflation). Each of these pre–big bang theories predicts how the universe should release gravity radiation moments after the initial explosion. LISA can then measure the gravity radiation emitted after the big bang and compare it with the various predictions of string theory. In this way, LISA might be able to rule out or in some of these theories.
But even if LISA is not sensitive enough to perform this delicate task, perhaps the next generation of detectors beyond LISA (such as the Big Bang Observer) may be up to the task.
If successful, these space probes may answer the question that has defied explanation for centuries: Where did the universe originally come from? So in the near term, unveiling the origin of the big bang may be a distinct possibility.
MANNED MISSIONS TO SPACE
While robotic missions will continue to open new vistas for space exploration, the manned missions will face much greater hurdles. This is because, compared to manned missions, robotic missions are cheap and versatile; can explore dangerous environments; don’t require costly life support; and most important, don’t have to come back.
Back in 1969, it seemed as if our astronauts were poised to explore the solar system. Neil Armstrong and Buzz Aldrin had just walked on the moon, and already people were dreaming about going to Mars and beyond. It seemed as if we were on the threshold of the stars. A new age was dawning for humanity.
Then the dream collapsed.
As science fiction writer Isaac Asimov has written, we scored the touchdown, took our football, and then went home. Today, the old Saturn booster rockets are idling in museums or rotting in junkyards. An entire generation of top rocket scientists was allowed to dissipate. The momentum of the space race slowly dissipated. Today, you can find reference to the famous moon walk only in dusty history books.
What happened? Many things, including the Vietnam War, the Watergate scandal, etc. But, when everything is boiled down, it reduces to just one word: cost.
We sometimes forget that space travel is expensive, very expensive. It costs $10,000 to put a pound of anything just into near-earth orbit. Imagine John Glenn made of solid gold, and you can grasp the cost of space travel. To reach the moon would require about $100,000 per pound. And to reach Mars would require about $1,000,000 per pound (roughly your weight in diamonds).
All this, however, was covered up by the excitement and drama of competing with the Russians. Spectacular space stunts by brave astronauts hid the true cost of space travel from view, since nations were willing to pay dearly if their national honor was at stake. But even superpowers cannot sustain such costs over many decades.
Sadly, it has been over 300 years since Sir Isaac Newton first wrote down the laws of motion, and we are still dogged by a simple calculation. To hurl an object into near-earth orbit, you have to send it 18,000 miles per hour. And to send it into deep space, beyond the gravity field of the earth, you have to propel it 25,000 miles per hour. (And to reach this magic number of 25,000 miles per hour, we have to use Newton’s third law of motion: for every action, there is an equal and opposite reaction. This means that the rocket can go rapidly forward because it spews out hot gases in the opposite direction, in the same way that a balloon flies around a room when you inflate it and then let it go.) So it is a simple step from Newton’s laws to calculating the cost of space travel. There is no law of engineering or physics that prevents us from exploring the solar system; it’s a matter of cost.
Worse, the rocket must carry its own fuel, which adds to its weight. Airplanes partially get around this problem because they can scoop oxygen from the air outside and then burn it in their engines. But since there is no air in space, the rocket must carry its own tanks of oxygen and hydrogen.
Not only is this the reason space travel is so expensive, it is also the reason we don’t have jet packs and flying cars. Science fiction writers (not real scientists) glamorized the day when we would all put on jet packs and fly to work, or go on a Sunday day trip blasting off in our family flying car. Many people became disillusioned by futurists because these predictions never came to pass. (That is why we see a rash of articles and books with cynical titles like “Where’s My Jetpack?”) But a quick calculation shows the reason. Jet packs already exist; in fact, the Nazis used them briefly during World War II. But hydrogen peroxide, the common fuel used in jet packs, quickly runs out, so a typical flight in a
jet pack lasts only a few minutes. Also, flying cars that use helicopter blades burn up an enormous amount of fuel, making them far too costly for the average suburban commuter.
CANCELING THE MOON PROGRAM
Because of the enormous cost of space travel, currently the future of the manned exploration of space is in flux. Former president George W. Bush presented a clear but ambitious plan for the space program. First, the space shuttle would be retired in 2010 and replaced in 2015 by a new rocket system called Constellation. Second, astronauts would return to the moon by 2020, eventually setting up a permanent manned base there. Third, this would pave the way for an eventual manned mission to Mars.
However, the economics of space travel have changed significantly since then, especially because the great recession has drained funds for future space missions. The Augustine Commission report, given to President Barack Obama in 2009, concluded that the earlier plan was unsustainable given current funding levels. In 2010, President Obama endorsed the findings of the Augustine report, canceling the space shuttle and its replacement that was to set the groundwork for returning to the moon. In the near term, without the rockets to send our astronauts into space, NASA will be forced to rely on the Russians. In the meantime, this provides an opportunity for private companies to create the rockets necessary to continue the manned space program. In a sharp departure from the past, NASA will no longer be building the rockets for the manned space program. Proponents of the plan say it will usher in a new age of space travel, when private enterprise takes over. Critics say the plan will reduce NASA to “an agency to nowhere.”
LANDING ON AN ASTEROID
The Augustine report laid out what it called the flexible path, containing several modest objectives that did not require so much rocket fuel; for example, traveling to a nearby asteroid that happened to be floating by or traveling to the moons of Mars. Such an asteroid, it was pointed out, may not even be on our sky charts yet; it might be a wandering asteroid that might be discovered in the near future.
The problem, the Augustine report said, is that the rocket fuel for the landing and return mission from the moon, or especially from Mars, would be prohibitively expensive. But since asteroids and the moons of Mars have very low gravitational fields, these missions would not require so much rocket fuel. The Augustine report also mentioned the possibility of visiting the Lagrange points, which are the places in outer space where the gravitational pull of the earth and moon cancel each other out. (These points might serve as a cosmic dump, where ancient pieces of debris from the early solar system have collected, so by visiting them astronauts may find interesting rocks dating back to the formation of the earth-moon system.)
Landing on an asteroid would certainly be a low-cost mission, since asteroids have very weak gravitational fields. (This is also the reason asteroids are irregularly shaped, rather than round. In the universe, large objects—such as stars, planets, and moons—are all round because gravity pulls evenly. Any irregularity in the shape of a planet gradually disappears as gravity compresses the crust. But the gravity field of an asteroid is so weak that it cannot compress the asteroid into a sphere.)
One possibility is the asteroid Apophis, which will make an uncomfortably close pass in 2029. Apophis is about 1,000 feet across, the size of a large football stadium, and will come so close to the earth that it will actually pass beneath some of our satellites. Depending on how the orbit of the asteroid is distorted by this close pass, it may swing back to the earth in 2036, where there is a tiny chance (1 out of 100,000) that it might hit the earth. If this were to happen, it would hit with the force of 100,000 Hiroshima bombs, sufficient to destroy an area as large as France with firestorms, shock waves, and fiery debris. (By comparison, a much smaller object, probably the size of an apartment building, slammed into Tunguska, Siberia, in 1908, with the force of about 1,000 Hiroshima bombs, wiping out 1,000 square miles of forest and creating a shock wave felt thousands of miles away. It also created a strange glow seen over Asia and Europe, so that people in London could read the newspapers at night.)
Visiting Apophis would not strain the NASA budget, since the asteroid is coming near earth anyway, but landing on the asteroid might pose a problem. Since it has a weak gravity field, one would actually dock with the asteroid, rather than land on it in the traditional sense. Also, the asteroid is probably spinning irregularly, so precise measurements have to be made before landing. It would be interesting to test to see how solid the asteroid is. Some believe that an asteroid may be a collection of rock loosely held together by a weak gravity field. Others believe that it may be solid. Determining the consistency of an asteroid may be important one day, if we have to use nuclear weapons to blow one up. An asteroid, instead of being pulverized into a fine powder, might instead break up into several large pieces. If so, then the danger from these pieces might be greater than the original threat. A better idea may be to nudge the asteroid out of the way before it comes close to earth.
LANDING ON A MOON OF MARS
Although the Augustine report did not support a manned mission to Mars, one intriguing possibility is to send astronauts to visit the moons of Mars, Phobos and Deimos. These moons are much smaller than earth’s moon and hence have a very low gravitational field. There are several advantages to landing on the moons of Mars, in addition to saving on cost.
1. First, these moons could be used as space stations. They would provide a cheap way of analyzing the planet from space without visiting it.
2. Second, they could eventually provide an easy way to access Mars. Phobos is less than 6,000 miles from the center of Mars, so a quick journey to the Red Planet can be made within a matter of hours.
3. These moons would probably have caves that could be used for a permanent manned base to protect against meteors and radiation. Phobos, in particular, has the huge Stickney crater on its side, indicating that the moon was probably hit by a huge meteor and almost blown apart. However, gravity slowly brought back the pieces and reassembled the moon. There are probably plenty of caves and gaps left over from this ancient collision.
BACK TO THE MOON
The Augustine report also mentioned a Moon First program, where we would go back to the moon, but only if more funding were available—at least $30 billion over ten years. Since that is unlikely, the moon program, in effect, is canceled, at least for the coming years.
The canceled moon mission was called the Constellation Program, which consisted of several major components. First was the booster rocket, the Ares, the first major U.S. booster rocket since the old Saturn rocket was mothballed back in the 1970s. On top of the Ares sat the Orion module, which could carry six astronauts to the space station or four astronauts to the moon. Then there was the Altair lander, which was supposed to actually land on the moon.
The old space shuttle, where the shuttle rocket was placed on the side of the booster rocket, had a number of design flaws, including the tendency of the rocket to shed pieces of foam. This had disastrous consequences for the Space Shuttle Columbia, which broke up on reentry in 2003, killing seven brave astronauts, because a piece of foam from the booster rocket hit the shuttle and made a hole in its wing during takeoff. Upon reentry, hot gases penetrated the hull of the Columbia, killing everyone inside and causing the ship to break up. In the Constellation, with the crew module placed directly on top of the booster rocket, this would no longer be a problem.
The Constellation program had been called “an Apollo program on steroids” by the press, since it looked very much like the moon rocket program of the 1970s. The Ares I booster was to be 325 feet tall, comparable to the 363-foot Saturn V rocket. It was supposed to carry the Orion module into space, replacing the old space shuttle. But for very heavy lifting, NASA was to use the Ares V rocket, which was 381 feet tall and capable of taking 207 tons of payload into space. The Ares V rocket would have been the backbone of any mission to the moon or Mars. (Although the Ares has been canceled, there is talk of perhaps salvaging some of
these components for future missions.)
PERMANENT MOON BASE
Although the Constellation Program was canceled by President Obama, he left open several options. The Orion module, which was to have taken our astronauts back to the moon, is now being considered as an escape pod for the International Space Station. At some point in the future, when the economy recovers, another administration may want to set its sights on the moon again, including a moon base.
The task of establishing a permanent presence on the moon faces many obstacles. The first is micrometeorites. Because the moon is airless, rocks from space frequently hit it. We can see this by viewing its surface, pockmarked by meteorite collisions, some dating back billions of years.
I got a personal look at this danger when I was a graduate student at the University of California at Berkeley. Moon rocks brought back from space in the early 1970s were creating a sensation in the scientific community. I was invited into a laboratory that was analyzing moon rock under a microscope. The rock I saw looked ordinary, since moon rock very closely resembles earth rock, but under the microscope I got quite a shock. I saw tiny meteor craters in the rock, and inside them I saw even tinier craters. Craters inside craters inside craters, something I had never seen before. I immediately realized that without an atmosphere, even the tiniest microscopic piece of dirt, hitting you at 40,000 miles per hour, could easily kill you or at least penetrate your space suit. (Scientists understand the enormous damage created by these micrometeorites because they can simulate these impacts, and they have created huge gun barrels in their labs that can fire metal pellets to study these meteor impacts.)