Time and the Space Traveler
TWO VIEWS
EUGEN SÄNGER
WILLIAM R. BREWSTER, JR.
NOT the least devastating effect of Hiroshima was the instantaneous transformation of E = mc2 from a remote bit of theoretical physics to a reality with terrifying implications for every human being. But the mass-energy relationship used for atomic fission is only one part of Dr. Einstein’s theories. For most non-scientists, much of the remainder is still so fantastic that we think of it, if at all, as a series of scientific allegories, as remote from ourselves as medieval arguments over how many angels could balance on the head of a pin.
Certainly Einstein’s theory that time and space shrink when measured within objects moving at great speed challenges our common sense. We know, or think we know, that an hour is an hour and a mile is a mile. Vet consider two facts. Laboratory experiments with particles moving at very high speed have already shown the shrinkage in time measurements that Einstein predicted, while according to press reports the Air Force has let two contracts for the study of photon (light particle) propulsion. A photon propulsion system would use the force of a beam of light emitted from the rear of a vehicle to propel the vehicle through space at a speed approaching that of light itself. The engineering problems are tremendous. Yet the principle is reported to have been successfully demonstrated in the laboratory.
Suppose man someday succeeds in building such a propulsion system. The two articles that follow consider the problems involved from two viewpoints. Dr. Eugen Sänger, Director of the Research Institute for Physics of Jet Propulsion, Stuttgart, Germany, discusses what Einstein’s shrinkage of time might mean in terms of human exploration across the great distances that separate our solar system from the nearest stars. William R. Brewster, Jr., and his colleagues of the Anesthesia Laboratory of the Harvard Medical School take issue with Dr. Sanger’s interpretation of Einstein’s theory and raise the question of what effect space travel might have on the physical structure of human beings. —THE EDITOR
REACHING FOR THE STARS
by EUGEN SANGER
TO ACHIEVE new living space for men will require an immense leap forward from interplanetary flight to interstellar flight that may bring us to other solar systems within our galaxy. Here, in these remote systems, many astrophysicists hope to find planets, and among them planets similar to our own earth.
Today interplanetary space flight is only at the very rudimentary stage of its technical development. This means that the investigation of such power-plant systems as the ion rockets and photon rockets is also in a very early stage.
Photon rockets are the ultimate development of jet propulsion. Their exhaust velocities attain the extreme physically possible limit, the velocity of light. At this point, flight speed in the technical sense becomes in effect limitless because of the relativistic phenomena that appear when the velocity of light is approached.
It is clear that rocket propulsion will play the decisive part in space flight. In view of the immense distances to be covered, fuel consumption will be the decisive factor in the ultimate choice among the different rocket systems.
In jet propulsion, we do not measure fuel consumption by such performance units as horsepower-hours, but by impulsion units, such as tonseconds. Ton-seconds (abbreviated “secton”) are the product of the thrust, in tons, of a jet power plant multiplied by the duration, in seconds, of this thrust.
A very modest fuel consumption — only 33 milligrams per secton — will enable space vehicles propelled by photon rockets to extend the duration of powered flight over years. Flight acceleration will be comparable to that produced by terrestrial gravity — that is, about 10 m/sec2. This means that on the one hand the crew will be able to live under the same gravity conditions that they are accustomed to on earth, and on the other hand the final velocities of the space vehicle, relative to earth, will come very close to the velocity of light.
Space vehicles of this kind can, therefore, aim for destinations outside our solar system — fixed stars within our galaxy or even stars of other galaxies. Thus we shall enter the age of interstellar or even intergalactic space flight.
For such space travels, we have to consider the special laws of the theory of relativity. These can create very peculiar situations, as can easily be shown by a practical example.
Let us suppose that such a vehicle starts from a space station near our earth toward a star about 1000 light-years away. For the better comfort of the passengers, the space vehicle would be accelerated only at a constant rate of 10 m/sec2 — that is, as measured by the instruments on board and according to the physiological effect on the travelers. During the flight the crew would keep the telescope sight of their navigating instruments aimed at their destination star. Due to the Doppler effect, the original color of the star — say yellow — will appear to the crew to change gradually to green, blue, violet, and so on as the speed of the spaceship increases. Finally, the radiation of the star will become invisible to human eyes in the ultraviolet range of the spectrum, so that from now on the vehicle can be kept on the right heading only by instruments. It is by means of this Doppler-effect shift that the crew will be able to tell after 1.4 years of flight that they are approaching their destination with a velocity 90 per cent of that of light.
As rocket propulsion continues to accelerate the ship, after the crew has measured the passage of 5.6 years they will find themselves speeding toward their destination with 99.999 per cent of light velocity. The light of the destination star will have meanwhile apparently changed its wave length from its original 5900 Angstrom units to 11 Angstrom units, thus becoming X radiation.
If the crew were now able to measure the distance between their vehicle and the destination star, they would find a value of about 5.5 lightyears instead of about 994 light-years, as you would ordinarily expect when you have traveled 5.6 light-years out of a total distance of 1000 lightyears.
This enormous discrepancy is due to the fact that the velocity of the vehicle relative to earth and to the destination star is now nearly that of light. As a result, the distance between earth and star is submitted to a relativistic change of length. It appears for the crew of the vehicle to be substantially diminished, in this case to less than a two-hundredth of its astronomic value.
Even without further acceleration our vehicle would reach its destination star after 5.5 years more — that is, after a total flight duration of only about 11 years.
But while the crew has spent some 11 years aboard, according to the accurate indication of their own chronometers, the human observers left behind on earth see more than 1000 years pass away according to their equally accurate watches. The two measurements of time have undergone a change in relation to each other, just as the two distance measurements, as figured on the earth and aboard the spaceship, have become different.
If the crew of the space vehicle were able to watch events on the surface of the destination star during their trip, at the start they would see conditions on the star as they existed 1000 years before. Then as the space vehicle accelerated, the history of the destination star in the previous 100O years would roll off before their eyes as in a speeded-up motion picture. When the crew arrived at the destination star after 11 years’ travel (according to their own measurement of time), they would consider things they find happening on the star as occurring in “present” time. Thus the crew would have observed the events of more than 1000 years within a period of only 11 years — that is, almost 100 times as fast as an inhabitant of the destination star itself would have observed them.
If the crew should stay for some time on the destination planet, they would observe events back on the earth happening in their proper rhythm but as they occurred about 1000 years earlier relative to the actual time of the crew. On the other hand, if the crew of the space vehicle should return to earth immediately after their arrival on the destination planet and should complete their return journey in exactly the same manner as their outward-bound trip, they would be another 11 years on the way, while another 1000 years would slip away on earth. Landing the space vehicle on earth after 22 years of travel, the crew would find that earth had become about 2000 years older.
Relativistic phenomena generally cause a lot of intellectual difficulties for the non-scientist. This is especially true of the concept of time on board a space vehicle that is traveling nearly at the speed of light — time that seems far longer to the observer on earth than to the traveler.
These intellectual difficulties are partially due to the fact that here we arc dealing with events far outside the range of our usual daily experience. We must get used to them in the same way that we have learned to accept other initially inconceivable things like radio, television, and human flight.
Partly, however, these difficulties are based on a substantial misconception that many people have: the idea that these apparent differences in time occur because something happens to slow up the instruments and the biological life rhythm of the crew. In reality neither the rate at which the crew ages nor the speed of the chronometers changes in the slightest. The extension of time is nothing else than an observation phenomenon just for the terrestrial observer. This phenomenon may be quite different for any other observer perceiving the same space vehicle from a point other than earth — say from a very fast-moving planet. If our crew never has a chance to communicate with their native planet during the flight, they will never become conscious of any extension of time but only perceive the shrinking of distances as a reality.
The mechanical reality of this relativistic extension of time was first measured in laboratory experiments almost 20 years ago by means of the so-called square Doppler effect. The outcome of these experiments, as well as of later measurements of cosmic-ray particles with velocity close to that of light, corresponded exactly to the Einstein theory. As a result, the special theory of relativity is today as firm a basis for interstellar space travel as Newtonian mechanics is for the earth satellite or for interplanetary travel.
There are two striking consequences.
First, it is possible in principle for individuals to cover any astronomic distance of the universe within their limited lifetime. Traveling speeds can increase without limit, if they are calculated by comparing the astronomic distances as they are measured on earth and the times as they are measured on board a spaceship. A photon particle with the velocity of light could thus travel infinitely fast. As a result, human beings will be able to reach remote stars, thousands of lightyears away, within their own lifetime. It will not be necessary to man spacecraft with miniature communities that perpetuate themselves through generation after generation of new individuals that arc born, grow up, and die flashing across space until at last far descendants of the original crew reach the destination.
Second, the fuel consumption which is needed for these immense velocities is, relatively, remarkably low. Even so, the absolute value of this fuel consumption is still high. For instance, the initial gross weight of a spaceship able to approach 99.999 per cent of light velocity would have to be 447 times its final weight at its landing point. Nevertheless, this ratio appears to be technologically feasible as astronautical engineering develops.
Far more uncertain, on the other hand, are the technical details of how the photon power plants will be achieved. Today we can only speculate that the photon jet will probably appear to the crew as ultraviolet rays and will be generated by hot metallic vapors. This part of the power plant will be analogous to present-day mercury vapor lamps, but the metallic vapors — or, better, metallic plasmas — may have temperatures of as much as 150,000 degrees Kelvin temperature.
These bright metallic plasmas would form an integral part of the power plant and would be heated by the energy produced by the propellants. This energy in its turn is liberated by more or less complete transformation of matter into energy. This is already done with increasing perfection by today’s nuclear techniques.
Man’s eternal reaching for the stars may yet succeed. The infinite universe will open to us, open to its ultimate boundaries.
THE PARADOX OF MOTION
by WILLIAM R. BREWSTER, JR.
LAWS pertaining to life processes in space must be developed in anticipation of the time when we will possess sufficient knowledge of the laws of the universe to predict both the course of man’s travel in interstellar space and the effect of an alteration of the environment on his biological structure and function. At present we do not understand completely the laws of life or the laws determining the behavior of a particle, body, or energy quantum in space. There is hope, however, that a more thorough understanding of electromagnetic and gravitational influence upon orbital bodies might result in a better knowledge of energy transfer in the minute universe of the living molecule.
What influence will be exerted on the rate of energy transfer in the human body when it is subjected to uniform motion relative to the earth? The answer is none whatsoever. Not only sciencefiction writers who are eager to entice the public with the bizarre, but many teachers of college physics, have stated that men who travel away from the earth at a given high velocity relative to the velocity of the earth will experience physical shortening in the direction of motion and a slowing of their life processes, causing them to return to the earth at a less advanced stage of life than they would have been in had they stayed home.
The fallacy of this notion is found on reconsidering Einstein’s two basic principles in his special theory of relativity: 1) The velocity of light is constant to all observers regardless of its source. 2) An observer cannot detect uniform motion of his own system.
Concerning the latter first: One can measure his velocity only in relation to another object. The earth-bound brother considers himself at rest (and we remember to exclude all consideration of acceleration and gravity, confining our description to uniform motion only). He sees the brother in the spaceship whizzing past. He observes that his brother’s dimensions are contracted, according to the FitzGerald-Lorentz contraction equations. He observes his brother’s clock to be running slow, and his brother’s heart beats, like the clock, are observed to be slow.
But the value of the (v) — velocity — is not absolute; it is relative, and Einstein says that the two frames of reference may be interchanged and the calculation that was true for one system of reference will hold true for the other. So the brother in the spaceship, since he is moving uniformly and therefore cannot detect his own motion, may assume his ship to be at rest. He sees the earth whiz past. The objects on earth are observed by him to be contracted, according to the above equation; his brother’s clock is observed to be slow, and his brother’s heart is observed to be beating with the rate of a hibernating animal. But that brother did not “go” anywhere. So we see that when two moving systems are considered, space brother is slowed and shortened in earth brother’s observation, while earth brother is slowed and shortened according to space brother’s observation.
If space brother’s life had slowed in comparison to its previous rate (or to what it would be were he still on earth), then he, from his spaceship, must observe earth brother as getting older faster than himself, his clock running faster, and his dimensions proportionately larger. To believe this is to defy the structure that Einstein has built. The value of (v) must apply to either system, depending on which one is chosen for the frame of reference. If the advocates of the Sleeping Beauty twin apply the FitzGerald-Lorentz contraction law to the space brother, they are right when the earth is used as the frame of reference, as long as they apply the same law to the earth brother using the spaceship as the frame of reference. While he is traveling through space, and is being considered on earth as hibernating, he is calculating that those on earth are hibernating and he is the one who is getting older. When he arrives home, he and his brother will have a most engaging discussion over which one is the older!
Why, then, does this FitzGerald-Lorentz contraction appear to produce a paradox? Einstein’s other basic assumption is that the velocity of light is constant. That is, light waves must traverse 2.998 x 105 km/sec from every frame of reference no matter how it moves relative to another body. Though the number of km/sec is constant, the value of the km and the sec is flexible and cannot be determined except in terms of a given frame of reference. In the same way, the man whose heart, beats 72 times a minute will continue to count 72 in each minute by his clock regardless of how he moves relative to another body, since there is no way to detect uniform motion of one’s own system.
If earth brother determines the heart rate of space brother to be, say, 40/min., he is counting 40 beats to his own earth minute, which is now different from his traveling brother’s minute. Space brother will still count 72 beats for each minute on his own watch, but the length of the minute in the spaceship can never be synchronized with the minute on earth. The tick of the clock and the beats of the heart on one moving system occur farther apart in distance to the observer who is aware of their motion and, since Einstein has shown us that space is a function of time, the time interval is longer to that observer. The FitzGerald-Lorentz contraction, then, fills the purpose of adjusting the geometry of space and time to each moving system, reconciling the observed discrepancies in measurement between two moving bodies.
Therefore, I propose that the energy transfer process which we call life can be considered constant within a frame of reference which is moving relatively to another body at any uniform velocity. This consideration, however, is a hypothetical one, since the Einstein theory is concerned with uniform motion only and not with the effects of acceleration, gravity, and inertia.
In dealing with the effect of uniform velocity upon the living system, we see immediately that the process of life and its characteristics will not be altered as a function of uniform velocity per se. This consideration alone, however interesting, still leaves untouched many formidable problems: the nature of life, its properties, and the conditions required for its existence.
Recent work in many laboratories has demonstrated that life in description is not as vague as it might seem. In structure, it is the grouping of thousands of different kinds of ions and molecules. In function, this structure is able to capture, store, transfer, and utilize the energy of quanta of light photons to maintain the internal energy of its system at average levels where free energy may be dissipated as work. This dissipation of free energy and the incidental performance of work are responsible for varied processes, such as the contraction of heart muscle, the moving of ions by the kidney, and nerve impulse transmission. The living system is essentially an “open” thermodynamic system in which the cells are capable of exchanging energy with outside sources. More information is needed concerning the rate at which energy is stored and expended. Biological optima of temperature and pressure play a key role in this respect and clearly determine the rate of performance of work.
We know from the data of divers that an increase in pressure of one atmosphere is tolerated for only a few hours. Data from man and laboratory animals indicate that there is limited survival when the atmospheric pressure is reduced by one half. Survival is limited to a few weeks with or without an increased oxygen concentration in the atmosphere.
There exists the possibility that life on earth has built-in constants which must be maintained for at least optimal performance, if not survival. These constants include a gravitational field, an electromagnetic field, and the energy of the photon. Evidence of these constants may well be seen in the spin of orbital electrons, the activated states of orbital electrons, the selection of the living organism of molecules which specifically rotate a plane of polarized light to the left, and the alpha helix structure of fibrous proteins. Evidence is accumulating to suggest that the biosphere has its own specificity for spin and moment which may well be critical.
The photons emanating from the sun, both in their frequency and incident intensity, are responsible for the existence of life on earth. We have read much concerning the constancy of the velocity of photons, little about their influence as a flux upon the field of forces about earth. How greatly will the dissipated flux energy affect a body moving through the resistance of a photon flux? What fields of forces will result? What will determine the energy imparted to a body moving through a flux and to the occupants or inhabitants of this body? An answer to these questions may well be essential in our search for conditions necessary to survival of life in “space.”
What will happen to man, who has evolved on earth, when his surrounding fields are altered? What will happen to the various living energy systems, vectored to contend with earth’s phenomena? Is there a minimum field necessary for man’s existence? If so, we must design a space vehicle that will be consistent with man’s need for the constants required for survival.