The Physics of UFOs
How realistic is it for spacecraft to
travel interstellar distances to Earth?
by Michael K. Gainer
UFO reports have been evaluated in terms of the supposed reliability of eyewitness accounts and questionable photographic evidence. The constraints that interstellar distances, time and the conservation of energy impose on interstellar space travel for these supposed alien craft seem never to be considered by UFO proponents. Since they do provide descriptions of spacecraft of circular disks, cylinders and triangles that move strangely and rapidly and vary in size from 50 feet in diameter to 300 feet long, I undertake here to apply these constraints to the design of a hypothetical spacecraft in order to determine the feasibility of such craft and their use for interstellar travel. As a physicist and astronomer I think it important to consider not just the accounts of alien contact, but the physics of such a possibility as well.
The basic principles of physics are applicable independently of where in the galaxy a stellar system is located and will not change over time. Newton’s three laws of motion and the conservation of energy are descriptions of the manner in which different parts of a physical system interact. Consequently, a model based on an exploratory expedition leaving Earth would apply equally to all planetary systems in our galaxy. Any culture, no matter how advanced in technology, would face the same constraints imposed by physics.
For my model I have chosen a spacecraft with a crew of six that will leave its planet for a planet in the habitable zone of a star 10 light years away. It will be accelerated at a rate of 10 m/s2 (10 meters per second squared) to a velocity of 0.5 times the velocity of light (0.5c, where c is the velocity of light). The time for it to reach this velocity is given by this equation:
t = v/a = 1.5×108/10 = 3.06×107 s = 174 days
(a = acceleration in meters/second squared; v = velocity in meters/second;
s = time seconds)
This is remarkably short compared to the nonrelativistic time of 20 years for the trip to the destination star. I have chosen 0.5c to minimize the relativistic mass increase of the spacecraft and to minimize travel time. The acceleration rate is approximately equal to the gravity the crew would experience on an earth-like home planet.
The spacecraft would be constructed in orbit from components delivered by shuttles. It would include, in addition to engines and fuel, an internal power supply for all the operational systems as well as life support systems and sustenance for the crew. For a 20-year trip this would necessarily be a small nuclear reactor. A mechanism for rotating the crew’s quarters to provide artificial gravity would be essential. I have chosen a live crew rather than robots or androids because all of the alien encounter and abduction stories indicate their presence. A shuttle for transporting the crew to the surface of the destination planet would also have to be on board. Our current space shuttles have an unloaded mass of 105 kg. Consequently, considering all of the requirements, a mass of 107 kg is not unreasonable for our model. The kinetic energy of the spacecraft, defined as the energy any object has by virtue of its motion, at 0.5c is given by:
E = ½mv2 = 0.5×107×2.25×1016 = 1.13×1023 joules
(m is the mass of the spacecraft and v is the velocity equal to 0.5c).
This is the energy that must be supplied by engine thrust to reach 0.5c
The only source that can supply energy of this magnitude is thermonuclear fusion. The work energy (blast energy) of a one-megaton thermonuclear bomb is 4.2×1015 joules. This is the energy that would be available for thrust if it were to power the spacecraft. It is 100 times the energy released by the Hiroshima atomic bomb. Hereafter I shall refer to it as a megaton of energy. The energy required to accelerate the spacecraft to 0.5c is then
E = 1.13×1023/4.2×1015 = 2.7×107 megatons
This energy would be expended over the 174 days of acceleration and is equal to 1.8 megatons per second during acceleration. The process is different from the use of controlled nuclear fusion for power generation. In that process, millisecond thermal pulses of energy are immediately conducted away to produce steam for generators. For propulsion of the hypothetical spacecraft the blast energy would have to be converted, with near 100% efficiency, to a constrained unidirectional particle beam with thrust pulses of 1.8 megatons per second for 174 days. For a round trip to a star 10 light years distant this rate of energy expenditure would be needed for slowing down at the destination, leaving, and slowing down again when returning to the home planet after a 40 year expedition.
A lesser source than thermonuclear fusion would be inadequate to provide the required energy for traveling at 0.5c. A lower velocity would mean travel times of hundreds to thousands of years. A lower acceleration rate would greatly increase the time to reach the desired velocity. For example, an acceleration of 0.5 m/s2 would require 1.9 years to reach 0.1c. The required energy would be a one megaton pulse per minute. The travel time would be 200 years for a round trip to a stellar system 10 light years away. There is no possible material construction that can constrain and direct the thermal and blast energy of the nuclear fusion rate required for interstellar travel. Consequently, I conclude that alien spacecraft cannot exist.
How then do we account for alien sightings? One personal example extrapolated to many others is illuminating. One evening as dusk was fading I had just opened my small backyard observatory for some night viewing through my 5-inch telescope when I saw in the sky with my naked eye, about 30º above the horizon toward Pittsburgh in the west, a very bright star. It resembled the appearance of the planet Venus. But Venus was not visible at that time. It was stationary so I thought it might be a supernova. I looked at it through the telescope and what I saw was a weather balloon with an instrument package dangling from it. It was at just the right position to produce a bright reflection from the recently set Sun. As I watched it rise into the stratosphere it suddenly burst and presented a beautiful sight of hundreds of shards spreading spherically. It resembled a bright globular star cluster. If I had not been looking through a telescope I would have seen a bright stationary object in the sky that suddenly faded from view. It would have been what some UFO reports have described as a bright light that suddenly disappeared as if it were a spacecraft accelerating at an amazing speed. On another occasion I saw, from my house in the foothills of the Allegheny mountains, strange lights moving vertically and horizontally in irregular paths in the eastern sky above the ridge a few miles away. The next day I drove out to that area and discovered that lights were attached to large cranes involved in a strip mining operation at the top of the ridge.
When UFOs are reported they should be evaluated with the attitude that alien spacecraft cannot exist. This is not closed mindedness. It is facing the reality of the constraints that time, stellar distances, and available energy place on interstellar space travel. We must also face the reality that human travel beyond the limits of the solar system is not possible. Any communication with sentient beings beyond the solar system can only take place through electromagnetic signal transmission and reception, so the SETI searches remain our best bet for contact.
About Michael K. Gainer
Dr. Michael K. Gainer is Emeritus Professor of Physics and former chair of the Department of Physics at St. Vincent College in Latrobe, PA. At St. Vincent he taught astronomy and advanced undergraduate physics courses for physics majors. He is the author of Real Astronomy for Small Telescopes, published by Springer in the Patrick Moore Practical Astronomy Series in 2006. Prior to his academic career he was a member of the scientific staff at the U.S. Army Ballistics Research Laboratory at Aberdeen, MD. There he conducted research on hyper velocity metal deformation in high intensity shock waves.
Another Physics of UFOs
Peter Huston’s rebuttal to Gainer
In his article on “The Physics of UFOs” in Skeptic Vol. 17, No. 3, Michael K. Gainer, a physicist, seeks to determine if it is possible to construct an interstellar spacecraft that fits the description of reported UFOs.
Although I have several problems with some of the minor assumptions he makes in the article, for the moment let’s focus on his key arguments. Gainer assumes such a craft should be capable of making a 10 light year round trip to a new destination and back to its home system in approximately 20 (Earth) years time each way. Although he never explicitly states it, he also assumes that the laws of physics as currently understood will not be violated. (i.e. no “hyper-warp-jump-faster-than-light-drives”). Fair enough. He states that the spacecraft should be accelerated at a rate of 10 meters per second squared and that, at this rate of acceleration, it will require 174 (Earth) days to reach half the speed of light. This would take a great deal of power, therefore he states: “the only source that can supply energy of this magnitude is thermonuclear nuclear fusion.” He then explains that the energy from the thermonuclear fusion would have to be directed rearward as “a constrained unidirectional particle beam,” then concludes: “There is no possible material construction that can constrain and direct the thermal and blast energy of the nuclear fusion rate required for interstellar travel. Consequently, I conclude that alien spacecraft cannot exist.”
In other words, if I understand correctly, what Gainer is saying is that an interstellar spacecraft must use thermonuclear power as its power source and because there is no possible material that could contain and direct thermonuclear power into a propulsion beam, interstellar spaceflight is impossible. To a non-physicist such as myself, the obvious questions are “Why is such a material impossible?” and “Why is thermonuclear power the only feasible power source?”
To answer these questions and check Gainer’s claim, I consulted with Carl Frederick, a retired physics professor and hard science fiction writer who regularly contributes to the magazine Analog Science Fiction/Science Fact. (A publication that, until recently, was edited by Stanley Schmidt, a Ph.D. physicist. For the record, no one claims that all stories in Analog are scientifically sound in all ways, (i.e. time travel stories), but part of the “game” of being an Analog contributor is to know exactly when, how and why one is breaking scientific laws and to only do it with a good reason.) A few of his criticisms and comments were as follows.
First, to assume that something is impossible because current technology, as opposed to the known laws of physics, doesn’t allow it is “silly.” Other points were that there is a great deal of research being done into controlled fusion and that might considerably change the way in which a thermonuclear spacecraft engine might work. Furthermore, as there are now indications that quantum physics might allow a spacecraft to draw energy from the vacuum as it travels, the thermonuclear engines might not be the only source of fuel. Additionally, Frederick said that the Gainer assumed that nuclear fusion is the best form of energy. He disagreed saying that particle / anti-particle annihilation was a better alternative. Finally, he said, there’s no reason one couldn’t go slower and use less fuel, if you, for instance, freeze the crew.
As for me, the non-physicist, although I really could not address the main points of the article, I had many quibbles about the minor assumptions in the article. For example, he assumes that a spacecraft would require energy in equal amounts to accelerate to its destination, decelerate when arriving, accelerate on its way home, and decelerate as it approaches home. Why? Couldn’t it use solar sails catching photons and the gravitational forces of planets and other astronomical objects to help slow itself? And, why do so many people assume that a spacecraft would need to make a return trip? I have little doubt that there are plenty of would-be astronauts who would gladly take a one way trip to another star system never to return home again. Indeed, surveys have found that there are astronauts who would take a one-way trip to Mars.
There are other points I question, many of which hint that Gainer is assuming we only can use modern technology (e.g., he states his UFO would be built in orbit by shuttles.) At least one other point ignores the modern UFO mythology entirely: Gainer assumes his ship needs a shuttle to land and return to the ship. Why? Particularly since UFOs are reported to land and then float away gently into the sky. Personally, I like the idea of taking the small UFO Gainer describes and putting it inside a giant “mother ship” that contains a crew of thousands or more and is a permanent home to generations of beings all living a more or less urban life style as they float between systems. It’s just one of dozens or more of alternatives to the scenario he, first, envisions, and then, secondly, uses to claim interstellar spacecraft are impossible. Perhaps such a race could even have “seeded” space using robotic craft to cache fuel here and there. (Note: I’m speculating. I do not believe anything in UFOlogy seriously indicates alien visitation.)
Gainer’s article is the sort that led to my burn out from skepticism. It contains questionable assumptions at several points and then over-reaches from the logical conclusions to make the point the author wishes. For example: “When UFOs are reported they should be evaluated with the attitude that alien spacecraft cannot exist.” This may be the author’s belief, but, based on what I saw, it is a faith-based belief, not grounded in proven fact. And, as skeptics, isn’t it simply enough to say “When UFOs are reported they should be evaluated with the attitude that none have ever been proven to be alien spacecraft”? We are supposed to be the people who read, question and think—not the ones who blindly repeat assertions that fit our pre-conceived notions.
I think we, as skeptics, need to be more careful of such statements and false conclusions. They only hurt us in the end.
About Peter Huston
In the 1990s, Peter Huston was a frequent contributor and book reviewer to skeptical publications, president and vice-president of the Inquiring Skeptics of Upper New York, and author of the books, Scams from the Great Beyond and More Scams of the Great Beyond. Today he teaches Chinese students in a college prep program at a major university in the Boston area. He holds a master’s degrees in Asian Studies with a focus on Chinese history and the history of Western science in China from Cornell and a second master’s in teaching English to Speakers of Other Languages from the University at Albany. His interests include science, history, martial arts, aikido and self defense,languages, cooking, miniature wargaming, large event security and EMS and ambulances. He’s excited to currently be rewriting the completed first draft of a novel that takes a surreal look at the decline of Schenectady, New York.