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are space craft from a distant star, or the future, or some other dimension. The trouble is, nearly all of this population of believers think the inhabitants of the UFOs merely have a more advanced technology than we do. This does nothing to make belief in UFOs respectable among scientists. There is good reason to think that interstellar travel cannot use any known space technology. There is only interstellar exodus, by means of the solar-sailed Ark. Lawrence Krauss, a well respected neutrino physicist, has taken the Starship Enterprise apart, piece by piece, done the calculations and shown that there isn't one single thing that Star Trek got right, unless it is the Prime Directive. See his book THE PHYSICS OF STAR TREK. As one example, he has calculated that it would take all the energy the sun has produced and ever will produce just to achieve Warp One. Thus, FTL (Faster Than Light) travel is impractical. Teleportation is not FTL because it has no velocity. A teleported object does not travel through space-time. It takes a shortcut, through other spatial dimensions. Star systems capable of evolving complex life are not very common, though there may be a great many with bacteria. Only certain kinds of stars will do. Our own star is a metal rich, middle aged G2 singlet. We have the only such star within a radius of at least thirty light-years. The planets circling multiple star systems would not have stable orbits. Only a narrow range of K2 to G2 (orange dwarf to yellow dwarf) stars will live long enough for intelligence to evolve and at the same time be warm enough to produce a comfort zone for a planet, where some liquid water will always be present. The hotter the star, the shorter is its life. Somewhere in the middle, we find the possibility of intelligent life. Only stars older than 4.5 billion years are likely to harbor intelligent humanoids, since it takes 4 to 5 billion years for intelligence to evolve. A planet which remains as tectonically active as the Earth, after 4.5 billion years, is unlikely unless the system formed out of a dust cloud high in heavy metals, including radioactive metals. Tau Ceti and Epsilon Eridani are possible target stars. They are about 10 or 11 light-years away. However, they are too young, too small, too low in metals, and both appear to be part of multiple star systems. See http://www.solstation.com/stars.htm for information about our immediate neighborhood. Links disappear, so if there is anyone or anything you want to know more about, just Google it. Chances are the information is on the Web somewhere. Planets with our Earth-Moon combination are rare. Without a large single Moon, our Earth would not maintain its stable angle of tilt. It could wobble as much as 90 degrees, and could sometimes lie over on its side, like Uranus. Our Moon was created by a collision with a Mars sized object very much like Earth, in that it had a metal core. The first collision was a glancing blow that gave our Earth-Moon combination its present angular momentum. Some of Earth's mantle splashed out to form the Moon, while the Earth got the metal core of the smaller planet on the second collision that captured the errant planetoid. Without this event, we would neither have such a large metal core (half the radius), nor would we have 24-hour days. By contrast, Venus has no metal core, and hardly any angular momentum. It slowly rotates backwards. Plate tectonics ceased long ago on both Venus and Mars. They are dead planets, incapable of supporting complex life. Planets will
suffer many collisions in the formative stage of planetary development. It is pure chance if there is a final big collision at just the right angle to produce something like the Earth-Moon combination. This is the thesis of a book called RARE EARTH. Thus, planets suitable for humanoid development are rare and the combinations of perfect star and perfect planet-moon are likely to be few and far apart, probably thousands of light years. There is no known technology that can traverse thousands of light-years in anything less than millions of years. The fastest possible rocket would expel an ionized propellant. This rocket could conceivably reach 1/10th the speed of light. The limiting factor on this kind of rocket (impulse power to Trekkies) is a law of vanishing returns, not Einstein's speed limit. To go faster requires more propellant and that increases initial mass, making the spaceship accelerate more sluggishly. At about one-tenth the speed of light, simply adding more propellant does not increase the velocity one can reach. There is no known power source to reach 0.1 C. For one thing, all known power sources have mass that must be subtracted from the propellant. Existing interplanetary probes might some day travel one light day in about ten years. Our Solar System is one-half a light day in diameter. A light day per decade is two or three times faster than any existing probes. A light year in distance would thus take roughly 3650 years in time. Since the nearest star system is 4.3 light-years away, it would take 15695 years to get to the Alpha Centauri system, roughly 16,000 years. In this multiple star system, star A is a G2, about 1.5 times the mass of the Sun. It probably won’t last 5 billion years. Another star is 40 AU (Astronomical Units) away from A. Planets around A might not have stable orbits. The unit of AU is the average distance from the Earth to the Sun. 40 AU is also the radius of the Solar system, if we ignore the Oort Cloud. A solar sailed Ark would be a better alternative than rockets since it could provide acceleration to leave home and deceleration when it approached its target star. The G forces involved would be enormous, 14 to 17 G. A blastocyst is the only form of a human being which can withstand such forces. A blastocyst is just a fertilized egg that has formed a hollow ball with a little pile of stem cells inside. Unlike a fetus, a blastocyst can be made in a test tube, and it can be frozen and thawed out years later and still be viable. The first and last generation on an Ark journey would thus likely be blastocysts. A solar-sailed Ark would not get there any faster. It would still take millions of years to reach other humanoid civilizations, if we assume they are thousands of light-years apart. An "Ark" is a self-contained ecological system, capable of renewing itself generation after generation, each of which would be born on the Ark, reproduce, live to a ripe old age, and die. The inhabitants might all be blastocysts for long periods of time. A primitive culture like ours could build such an Ark within this millennium. By traveling at a lower speed, we wouldn't have to worry so much about interstellar dust grains exploding into the hull with the force of an H-bomb, although shields would still be necessary. It wouldn't really matter how long it took to cross interstellar space. It would eventually get there. It could carry nuclear generators to create electricity. It would not have to carry much propellant, just enough for maneuvering. It has the
virtue that the same method used to propel it also stops it at the other end of the journey. For interstellar takeoff, it would maneuver as close to the sun as possible, point itself in the right direction, and unfurl an enormous solar sail. After gaining escape velocity, furl the sail and spin up the ring shaped ark to provide artificial gravity. It would then coast. At the end of the trip the reverse process would be used for deceleration, many thousands or millions of years later. This is the only technology of space travel proposed so far that might actually work, but only as a form of exodus. When I think of "travel”, I think of trips that might take a few hours, days or possibly even a few years. Anything longer than that would be a one-way trip, where one is not likely to come back. Another way of saying the same thing is that interstellar travel by technology is impossible. Some of the people who leave messages in the guest book on my interstellar web site present an argument from analogy. They say, "Look how far we have progressed in technology in the last 200 years. Surely, in another 200 years we will have developed technology we can't even imagine." Maybe. On the other hand, technology may have run its course. I have often thought it would be interesting to go back in time (something I believe to be impossible) and talk to Thomas Jefferson. In philosophy and science, history and art, we would be in the same mental world and that would not be true if I visited Luther or Augustine or Plato. As I looked around his palatial mansion, I am sure I would find it remarkable that every single item had been hand made by a craftsman, often designed by Jefferson himself. Every gadget or item of furniture would be unique, without any interchangeable parts. Technology goes for long periods of time with little or no change. Neither people nor ideas could travel any faster in Jefferson's time than in Ancient Roman times or in the times of the Sumerians and the pyramid building Egyptians. Both people and ideas could travel about 9 knots, or 10 mph. No more. That is the speed of a fast sailing sloop, or the average speed of a pony express, with remounts. Any student of Toynbee must realize one can never extrapolate the past into the future. The one thing we can be sure about the future is that it will have surprising and unpredictable changes in direction for our civilization. The areas that have seen the most active change in the past few changes might cease to change. Change might pass to metaphysics or the arts. We can now communicate worldwide at the speed of light, and we can travel at the speed of sound. Will we be communicating any faster in 200 years? Of course not. That would violate a fundamental law of physics. Will we be traveling any faster than the speed of sound? Through the air? Not if we value the ozone layer. I propose a return to the bicycle and the train since this would provide much faster commuter times than we now have with cars (only 5 mph at rush hour in Boston or LA). In many ways, technology reached apogee in the last quarter of the 20th Century, when we decided not to build an SSC (Superconducting Super Collider), decided not to build the SST (Super Sonic Transport) and decided not to send any more people to the moon. Computers and communications are reaching apogee now, with the World Wide Web. There are a lot of computer users (me for one) who think the capabilities of their present systems are quite sufficient and would prefer to avoid upgrade or change, though it may be impossible to avoid.
Is there any possibility that physics could discover some way of jumping light years? While it is impossible to predict future discoveries, we can at least look at the problem areas in physics and its remaining questions, puzzles and paradoxes. String theory turns out to be relevant to interstellar travel. So does dark matter. In the appendix, you will find my take on the current state of physics, in a chapter called “Physics Without Paradox.” There is nothing there to make us change our minds about the impossibility of "The Star Ship Enterprise." I put it at the end because it presupposes some knowledge of science, and there are a few very simple equations and important numbers. Still, you will need to read parts of it to understand my theory of the mind in terms of dark matter, de Broglie waves, and the warping of geodesics. It is because scientists know that space travel by technology is impossible that they are so skeptical of UFOs. This also explains SETI (Search for Extra-Terrestrial Intelligence). SETI is really the search for very stupid ETs. Why would any intelligent species set up a powerful radio or laser beacon, saying to the universe, “Here I am, a nice, water-fat planet with lots of oxygen and dry land -- come and get me!” Such a beacon might draw species like us, brutal, greedy, violent and reductionist, with no knowledge of the sciences of civilization, or of the mind and spirit. Unevolved, in other words. Even a primitive and unevolved species could traverse the cosmic spaces slowly with a Solar-sailed Ark, even though it might take millions of years to arrive at the destination.