Transcript: Speculation about the possibility and implications of life in the universe dates back a long time. Over two thousand years ago, Plutarch wrote about the possibility of other worlds with their own races of men and beasts. By the eleventh century in Europe, the Catholic church had declared the idea of plurality of worlds, other worlds possibly with life on them, to be heretical, and in 1609, the mystic Giordano Bruno was burned at the stake in Rome for writing about life in the...

Transcript: However unlikely a successful outcome a priori, SETI is based on the premise that science is an empirical endeavor. Rather than philosophizing about the possibility or prospect of life in the universe, we should look. Rather than wondering if people are communicating with us from afar, we should listen. So the rebuttal to skeptics is that we must do the experiment. In this decision making, we have decided that photons are cheaper and faster than rockets, at least with current...

Transcript: It is very difficult to avoid anthropocentric thinking when considering the issue of life in the universe. Anthropocentric thinking means considering the subject in terms of human origins, human perceptions, human values, and human culture. When we think of science fiction, it’s often the case that aliens look something like us. They are bipedal, or they appear to be mammals or somewhat similar to us in some way. Life in the universe could be so strange as to be...

Transcript: One of the standard conceits of science fiction is that humans, when they develop the capability for starships and interstellar travel, will meet another set of civilizations with whom we can communicate and share our cultural values and our civilization histories. The truth is that the time scale issue makes such a very unlikely outcome. To illustrate this, consider the evolution of three prototypical Earths. Imagine that the evolution of life and complexity is somehow key to...

Transcript: One of the arguments that we are not alone in the universe and that there are other intelligent civilizations is based on what’s called the timescale consideration. Remember that there has been life of some kind on Earth for about four billion years. But only in the last couple of million years has the human species existed, and only in the past couple of hundred years has technology existed and the possibility for space travel. This is a tiny fraction in the history of the...

Transcript: The Fermi Paradox starts with the simple question, where are they? It’s based on the huge number of potential sites for life and the large amount of time in the history of the universe for intelligent civilizations that can travel in space to have developed. There is no answer to the Fermi paradox, but thinking about possible answers enlightens us into the role of the universe and life itself. Here are some possible solutions. We might be alone or so alone as to be isolated in...

Transcript: The idea of travel into space leads naturally to the concept of galactic civilizations. It’s been the history of humans on this planet to explore their evolutionary world, to radiate into every niche of the planet to try and understand it. We’ve only had space travel for fifty years, and it’s sobering to think that it’s thirty-five years since we’ve been back to the Moon. But in the long term, over hundreds or thousands of years, it’s likely that humans will live in space and...

Transcript: Johnny von Neumann, the father of modern computing, was thinking about the Fermi Paradox, the prospect that with life spread through the galaxy there must be intelligent civilizations that would presumably colonize the galaxy. He came up with the idea of what is called a von Neumann machine. If it sounds speculative, realize that it’s only a modest extrapolation of current technology. A von Neumann machine is a self replicating probe which travels from our solar system to...

Transcript: In the 1940s, Enrico Fermi, who was a Nobel Prize winning physicist and developer of the first working fission reactor, was sitting with his colleagues talking about philosophical issues when he asked the following question. “Where are they?” His premise was that it’s so likely that life must have developed elsewhere in the Milky Way, that the probability of their not being intelligent civilizations must be very low. Therefore, they must exist, but since they haven’t visited,...

Transcript: As an analogy for the Drake equation where independent probabilities combine to reduce an initially large number to a small number, consider the following hypothetical situation. Imagine the number of students in a large university, say, forty thousand. Now imagine what fraction of those students are women. It’ll be roughly fifty percent which brings you down to twenty thousand. Imagine the fraction of those that are econ majors. That's probably about one percent given the...

Transcript: Photons are the fastest thing there is. Light and other forms of electromagnetic communication travel at three hundred thousand kilometers per second, vastly out seeding the capabilities of any type of rocket that we know or can imagine. As an example of their swiftness, consider the distance covered in one year in various other forms of travel compared to the number of years needed to cover that same distance that photons travel in only one year. A human, with a speed of maybe...

Transcript: Science fiction writers have long dreamed of various ways of cheating the constraints of time and space. One popular device in science fiction and on TV is the idea of warp drive, travel at speeds faster than the speed of light. However, Einstein’s theory of relativity, a good physical theory of the universe, says that the speed of light is an absolute limit. It takes an infinite amount of energy to accelerate anything, even a microscopic particle, to the speed of light. ...

Transcript: As an example of the advantages of relativistic space travel, or travel close to the velocity of light, consider a hypothetical journey to a star that's five lightyears distant. Several hundred stars are this close or closer. At the limit of modern chemical rockets, a speed of five one-thousandths of a percent of the velocity of light, the roundtrip journey would take a hundred thousand years. At one-tenth the velocity of light, the limit of an ion engine or a solar sail, the...

Transcript: Visionaries have imagined leapfrogging over current or even planned technologies to the forms of rocket propulsion that can reach relativistic speeds, rocket speeds close to that of light. One form of energy release is matter-antimatter annihilation. Antimatter is rare on Earth. It naturally doesn't occur, but it can be created in the lab and potentially in a rocket engine. Matter-antimatter annihilation liberates the entire mc2 of trapped energy in matter with an efficiency...

Transcript: Conventional rocket systems, even those that rely on nuclear energy, tend to rely on the principle of burning a certain amount of fuel, accelerating the rocket initially, and then having it coast to its destination. Other ideas for propulsions systems, some of which have been tested or prototyped but none of which have been put into large scale operation, involve steadier or more gradual acceleration towards the distant target. In an ion engine, a tiny amount of fuel is used...

Transcript: Rocket scientists have long been aware that fusion or fission are more efficient energy sources than chemical energy for rockets, and so there has been much experimentation but no totally viable design that’s currently used for any propulsion system. Of course, the environmental climate is such that people are not too happy about having nuclear reactors in space. The energy source is however much more efficient. Gaining energy from E = mc2, even with less than one percent...

Transcript: The difficulty of space travel to the stars with conventional rockets is illustrated by the best examples of our technologies so far. The Saturn V rocket, the largest ever built, that took the astronauts to the Moon burnt a mixture of kerosene and liquid oxygen, but it took a rocket the size of a fourteen story building to launch a small, cramped payload with three astronauts to the Moon. Four manmade spacecraft have left the solar system: Pioneer 10 and 11 and Voyager 1 and 2. ...

Transcript: The fundamental limitation of space travel for our civilization is connected with the vastness of space and the difficulty of finding efficient energy sources for raising a payload out of the Earth’s gravity and into interstellar space. The entire history of the space age, only about fifty years, is that of chemical rockets. The Saturn V is nothing much more than a large firecracker. Chemical fuel has been used for almost every space age advance, including getting to the Moon,...

Transcript: Large brains and the possibility for communication occurred after a relatively long time of evolution of life on Earth, only after about four billion years of natural selection. It’s interesting to note that for many species on Earth, there is a strict linear ratio between body size and brain size. It’s called the encephalization ratio. It indicates that although humans are unusual in the complexity and sophistication of their brain function, they are not extraordinary in terms...

Transcript: The fastest way to communicate through space is with electromagnetic waves traveling at three hundred thousand kilometers per second. But space is vast, and so if civilizations in the Milky Way are rare, then communication becomes a real issue. Civilizations, if sufficiently rare, can be isolated in time and space. In terms of the Drake equation, if the average civilization lasts less than a few thousand years, then on average the distance to the next nearest civilization is a...

Transcript: Even though there’s no way to decide logically or with available evidence whether the optimistic or pessimistic views of outcomes from the Drake equation is valid, we can follow the implications of the lifetime of civilizations. Under the optimistic assumptions for SETI, the number of intelligent, communicable civilizations is roughly equal to the lifetime of the civilization in years. Civilizations scattered through the Milky Way galaxy become isolated in time and space. They...

Transcript: Astronomers who are pessimistic about the prospect of intelligent, communicable civilizations in the Milky Way tend to take low values for the factors in the Drake equation. For example, they assume that not every solar star has habitable planets, and that the number of habitable planets per typical solar system is less than one, also that life does not evolve on every habitable planet, and that even if life exists, it does not always end up as intelligent or with the capability...

Transcript: Astronomers who are optimistic about the prospect of intelligent civilizations in the universe tend to take high values for the numbers in the Drake equation. For example, assuming that the fraction of stars with planets is close to a hundred percent, that there is at least one habitable planet per star, and that when a habitable planet exists not only does life develop but intelligent life develops eventually, then intelligent life with technology will naturally want to...

Transcript: The final factor in the Drake equation is a time given in years, the average lifetime of a civilization in the intelligent and communicable state. In other words, we are interested not just in the creation and existence of civilizations but their duration, and not just the duration of a civilization of intelligent creatures but their duration in a state where they can communicate in space. Human civilizations are about ten thousand years old, but we’ve only had the technology...

Transcript: The sixth factor in the Drake equation is the fraction of planets that have intelligent life where technology develops, in particular the technology that allows for communication through space or for space travel. As with the previous few factors, we are completely uncertain as to how to estimate this number. Again, we have only ourselves to go on. We know that in one case, on Earth, intelligence did lead to technology and the ability to explore space and receive and send...