Of Time and Space and Other Things

by Isaac Asimov

  Is this just speculation? To begin with, it was, but in late 1963 some observational data made it appear to be more than that.

  It involves a galaxy in Ursa Major which is called M82 because it is number 82 on a list of objects in the heavens prepared by the French astronomer Charles Messier about two hundred years ago.

  Messier was a comet-hunter and was always looking through his telescope and thinking he had found a comet and turning handsprings and then finding out that he had been fooled by some foggy object which was always there and was not a comet.

  Finally, he decided to map each of 101 annoying ob jects that were foggy but were not comets so that others would not be fooled as he was. It was that list of annoy ances that made his name immortal.

  The first on his list, Ml, is the Crab Nebula.. Over two dozen are globular clusters (spherical conglomerations of densely strewn stars), Ml 3 being the Great Hercules Clus ter, which is the largest known. Over thirty members of his list are galaxies, including the Andromeda Galaxy (M31) and the Whirlpool Galaxy (M51). Other famous objects on the list are the Orion Nebula (M42), the Ring Nebula (M57), and the Owl Nebula (M97).

  Anyway, M82 is a galaxy about 10,000,000 light-years from Earth which aroused interest when it proved to be a strong radio source. Astronomerp. turned the 200-inch telescope upon it and took pictures, through filters that blocked all light except that coming from hydrogen ions.

  There was reason to suppose that any disturbances that might exist would show up most clearly among the hydro gen ions.

  They did! A three-hour exposure revealed jets of bydro gen up to a thousand light-years long, bursting out of the galactic nucleus. The total mass of hydrogen being shot out was the equivalent of at least 5,000,000 average stars.

  From the rate at which the jets were traveling and the distance they had covered, the explosion must have taken place about 1,500,000 years before. (Of course, it takes light ten million years to reach us from M82, so that the explosion took place 11,500,000 years ago, Earth-time just at the beginning of the Pleistocene Epoch.)

  M82, then, is the case of an exploding galaxy. The energy expended is equivalent to that of five million super novas formed in rapid succession, like uranium atoms undergoing fission in an atomic bomb-though on a vastly greater scale, to be sure. I feel quite certain that if there had been any life anywhere in that galactic nucleus, there isn't any now.

  In fact, I suspect that even the outskirts of the galaxy may no longer be examples of prime real estate.

  Which brings up a horrible thought… Yes, you guessed it!

  What if the nucleus of our own dear Galaxy explodes?

  It very likely won't, of course (I don't want to cause fear and despondency among the Gentle Readers), for explod ing galaxies are probably as uncommon among galaxies as exploding stars are among stars. Still, if it's not going to happen, it is all the more comfortable then, as an intellec tual exercise, to wonder about the consequences of such an explosion.

  To begin with, we are not in the nucleus of our Galaxy but far in the outskirts and in distance there is a modicum of safety. This is especially so since between ourselves and the nucleus are vast clouds of dust that will effectively screen off any visible fireworks.

  Of course, the radio waves would come spewing out through dust and all, and this would probably ruin radio astronomy for millions of years by blanking out everything else. Worse still would be the cosmic radiation that might rise high enough to become fatal to life. In other words, we might be caught in the fallout of that galactic explo sion.

  Suppose, though, we put cosmic radiation to one side, since the extent of its formation is uncertain and since consideration of its presence would be depressing to the spirits. Let's also abolish the dust clouds with a wave of the speculative hand.

  Now we can see the nucleus. What does it look like without an explosion?

  Considering the nucleus to be 10,000 light-years in diameter and 30,000 light-years away from us, it would be visible as a roughly spherical area about 20' in dia meter. When entirely above the horizon it would make up a patch about %5 of the visible sky.

  Its total light would be about 30 times that given off by Venus at its brightest, but spread out over so large an area it would look comparatively dim. An area of the nucleus equal in size to the full Moon would have an average brightness only 1/200,000 of the full Moon.

  It would be visible then as a patch of luminosity broad ening out of the Milky Way in the constellation of Sagit tarius, distinctly brighter than the Milky Way itself; bright est at the center, in fact, and fading off with distance from the center.

  But what if the nucleus of our Galaxy exploded? The explosion would take place, I feel certain, in the center of the nucleus, where the stars were thickest and the effect of one pre-supemova on its neighbors would be most marked. Let us suppose that 5,000,000 supernovas are formed, as in M82.

  If the nucleus has pre-supemovas separated by 5 light years in its central regions (as estimated earlier in the chapter, for galaxies capable of explosion), then 5,000,000 pre-supernovas would fit into a sphere about 850 light years in diameter. At a distance of 30,000 light-years, such a sphere would appear to have a diameter of 1.6', which is a little more than three times the apparent di ameter of the full Moon. We would therefore have an ex cellent view.

  Once the explosion started, supernova ought to follow supemova at an accelerating rate. It would be a chain reaction.

  If we were to look back on that vast explosion millions of years later, we could say (and be roughly correct) that the center of the nucleus had all exploded at once. But this is only roughly correct. If we actually watch the ex plosion in process, we will find it will take considerable time, thanks entirely to the fact that light takes considerable time to travel from one star to another.

  When a supernova explodes, it can't affect a neighbor ing presupemova (5 light-years away, remember) until the radiation of the first star reaches the second-and that would take 5 years. If the second star was on the far side of the first (with respect to ourselves), an additional 5 years would be lost while the light traveled back to the vicinity of the first. We would therefore see the second supernova 10 years later than the first.

  Since a supemova will not remain visible to the naked eye for more than a year or so even under the best condi tions (at the distance of the Galactic nucleus), the second supemova would not be visible until long after the first had faded off to invisibility.

  In short, the 5,000,000 supemovas, forming in a sphere 850 light-years in diameter, would be seen by us to appear over a stretch of time equal to roughly a thousand years.

  If the explosions started at the near edge of that sphere so that radiation had to travel away from us and return to set off other supernovas, the spread might easily be 1500 years.

  If it started at the far end and additional explosions took place as the light of the original explosion passed the pre supernovas en route to ourselves, the time-spread might be considerably less.

  On the whole, the chances are that the Galactic nucleus would begin to show individual twinkles. At first there might be only three or four twinkles a decade, but then, as the decades and centuries passed, there would be more and more until finally there.might be several hundred visible at one time. And finally, they would all go out and leave behind dimly glowing gaseous turbulence.

  How bright will the individual twinkles be? A single supemova can reach a maximum absolute magnitude of - 17. That means if it were at a distance of 10 parsecs (32.5 light-years) from ourselves, it would have an appar ent magnitude of -17, which is 1/10,000 the brightness of the Sun.

  At a distance of 30,000 light-years, the apparent magni tude of such a supemova would decline by l0 magnitudes.

  The apparent magnitude would now be -2, which is about the brightness of Jupiter at its brightest.

  This is quite a static statistic. At the distance of the nucleus, no ordinary star can be individually seen with the naked eye. The hun
dred billion stars of the nucleus just make up a luminous but featureless haze under ordinary conditions. For a single star, at that distance, to fire up to the apparent brightness of Jupiter is simply colossal. Such a supemova, in fact, burns with a tenth the light intensity of an entire non-exploding galaxy such as ours.

  Yet it is unlikely that every supemova forming will be a supemova of maximum brilliance. Let's be conservative and suppose that the supemovas will be, on the average, two magnitudes below the maximum. Each will then have a magnitude of 0, about that of the star Arcturus.

  Even so, the "twinkles" would be prominent indeed. If humanity were exposed to such a sight in the early stages of civilization, they would never make the mistake of think ing that the heavens were eternally fixed and unchangeable.

  Perhaps the absence of that particular misconception (which, in actual fact, mankind labored under until early modern times) might have accelerated the development of astronomy.

  However, we can't see the Galactic nucleus and that's that. Is there anything even faintly approaching such a multi-explosion that we can see?

  There's one conceivable possibility. Here and there, in our Galaxy, are to be found globular clusters. It is estimated there are about 200 of these per galaxy. (About a hundred of our own clusters have been observed, and the other hundred are probably obscured by the dust clouds.)

  These globular clusters are like detached bits of galactic nuclei, 100 light-years or so in diameter and containing from 100,000 to 10,000,000 stars-symmctricary scat tered about the galactic center.

  The largest known globular cluster is the Great Hercules Cluster, M13, but it is not the closest. The nearest globular cluster is Omega Centauri, which is 22,000 light-years from us and is clearly visible to the naked eye as an object of the fifth magnitude. It is only a point of light to the naked eye, however, for at that distance even a diameter of 100 light years covers an area of only about 1.5 minutes of arc in diameter.

  Now let us say that Omega Centauri contained 10,000 pre-supemovas and that every one of these exploded at their earliest opportunity. There would be fewer twinkles altogether, but they would appear over a shorter time in terval and would be, individually, twice as bright.

  It would be a perfectly ideal explosion, for it would be unobscured by dust clouds; it would be small enough to be quite safe; and large enough to be sufficiently spectacular for anyone.

  And yet, now that I've worked up my sense of excite ment over the spectacle, I must admit that the chances of viewing an explosion in Omega Centauri are just about nil.

  And even if it happened, Omega Centauri is not visible in New England and I would have to travel quite a bit south ward if I expected to see it high in the sky in full glory and I don't like to travel.

  Hmm… Oh well, anyone for a neighborhood fire?

  Part II

  Of Other Things

  11. Forget It!

  The other day I was looking through a new textbook on biology (Biological Science: An Inquiry into Life, written by a number of contributing authors and published by Har court, Brace amp; World, Inc. in 1963). 1 found it fascinating.

  Unfortunately, though, I read the Foreword first (yes, I'm one of that kind) and was instantly plunged into the deepest gloom. Let me quote from;the first two paragraphs:

  "With each new generation our fund of scientific knowl edge increases fivefold… At the current rate of s.cien tific advance, there is about four times as much'significant biological knowledge today as in 1930, and about sixteen times as much as in 1900. By the year 2000, at this rate of increase, there will be a hundred times as much biology to dcover' in the introductory course as at the beginning of the century."

  Imagine how this affects me. I am a professional "keeper upper" with science and in my more manic, ebullient, and carefree moments, I even think I succeed fairly well.

  Then I read something like the above-quoted passage and the world falls about my ears. I don't keep up with science. Worse, I can't keep tip with it. Still worse, I'm falling farther behind every day.

  And finally, when I'm all through sorrowing for myself, I devote a few moments to worrying about the world generally. What is going to become of Homo sapiens?

  We're going to smarten ourselves to death. After a while, we will all die of pernicious education, with our brain cells crammed to indigestion with facts and concepts, and with blasts of information exploding out of our ears.

  But then, as luck would have it, the very day after I read the Foreword to Biological Science I came across an old, old book entitled Pike's Arithmetic. At least that is the name on the spine. On the title page it spreads itself a bit better, for in those days titles were titles. It goes "A New and Complete System of Arithmetic Composed for the Use of the Citizens of the United States," by Nicolas Pike, A.M.

  It was first published in 1785, but the copy I have is only the "Second Edition, Enlarged," published in 1797.

  It is a large book of over 500 pages, crammed full of small print and with no relief whatever in the way of illustrations or diagrams. It is a solid slab of arithmetic except for small sections at the very end that introduce algebra and geometry.

  I was amazed. I have two children in grade school (and once I was in grade school myself), and I know what arith metic books are like these days. They are nowhere near as large. They can't possibly have even one-fifth the wordage of Pike.

  Can it be that we are leaving anything out?

  So I went through Pike and, you know, we are leaving something out. And there's nothing wrong with that. The trouble is we're not leaving enough out.

  On page 19, for instance, Pike devotes half a page to a listing of numbers as expressed in Roman numerals, ex tending the list to numbers as high as five hundred thou sand.

  Now Arabic numerals reached Europe in the High Middle Ages, and once they came on the scene the Roman numerals were completely outmoded. They lost all pos sible use, so infinitely superior was the new Arabic nota tion. Until then who knows how many reams of paper were required to explain methods for calculating with Roman numerals. Afterward the same calculations could be performed with a hundredth of the explanation. No knowledge was lost only inefficient rules.

  And yet five hundred years after the deserved death of the Roman numerals, Pike still included them and ex pected his readers to be able to translate them into Arabic numerals and vice versa even though he gave no instruc tions for how to manipulate them. In fact, nearly two hun 138 dred years after Pike, the Roman numerals are still being taught. My little daughter is learning them now.

  But why? Where's the need? To be sure, you will find Roman numerals on cornerstones and gravestones, on clockfaces and on some public buildings and documents, but it isn't used for any need at all. It is used for show, for status, for antique flavor, for a craving for some kind of phony classicism.

  I dare say there are some sentimental fellows who feel that knowledge of the Roman numerals is a kind of gate way to history and culture; that scrapping them would be like knocking over what is left of the Parthenon, but I have no patience with such mawkishness. We might as well suggest that everyone who learns to drive a car be required to spend some time at the wheel of a Model-T Ford so he could get the flavor of early cardom.

  Roman numerals? Forget iti-And make room instead for new and valuable material.

  But do we dare forget things? Why not? We've forgot ten much; more than you imagine. Our troubles stem not from the fact that we've forgotten, but that we remember too well; we don't forget enough.

  A great deal of Pike's book consists of material we have imperfectly forgotten. That is why the modern arithmetic book is shorter than Pike. And if we could but perfectly forget, the modern arithmetic book could grow still shorter.

  For instance, Pike devotes many pages to tables-pre sumably important tables that he thought the reader ought to be familiar with. His fifth table is labeled "cloth meas ure.29 Did you know that 2% inches make a "nail"? Well, they do. And 16 nails make a ya
rd; while 12 nails make an ell.

  No, wait a while. Those 12 nails (27 inches) make a Flemish ell. It takes 20 nails (45 inches) to make an English ell, and 24 nails (54 inches) to make a French ell. Then, 16 nails plus 1% inches (371/5 inches) make a Scotch ell.

  Now if you're going to be in the business world and import and export cloth, you're going to have to know all those ells-unless you can figure some way of getting the ell out of business.

  Furthermore, almost every piece of goods is measured in its own units. You speak of a firkin of butter, a punch of prunes, a fother of lead, a stone of butcher's meat, and so on. Each of these quantities weighs a certain number of pounds (avoirdupois pounds, but there are also troy pounds and apothecary pounds and so on), and Pike carefully gives all the equivalents.

  Do you want to measure distances? Well, how about this: 7 92/100 inches make I link; 25 links make I pole; 4 poles make I chain; 10 chains make I furlong; and 8 furlongs make I mile.

  Or do you want to measure ale or beer-a very com mon line of work in Colonial tim6s. You have to know the language, of course. Here it is: 2 pints make a quart and 4 quarts make a gallon. Well, we still know that much anyway.

  In Colonial times, however, a mere gallon of beer or ale was but a starter. That was for infants. You had to know how to speak of man-sized quantities. Well, 8 gallons make a firkin-that is, it makes "a firkin,of ale in Lon don." It takes, however, 9 gallons to make "a firkin of beer in London." The intermediate quantity, 81/2 gallons, is marked down as "a firkin of ale or beer"-presumably outside of the environs of London where the provincial citizens were less finicky in distinguishing between the two.

  But we go on: 2 firkins (I suppose the intermediate kind, but I'm not sure) make a kilderkin and 2 kilderkins make a barrel. Then ll/z barrels make I hogshead; 2 bar rels make a puncheon; and 3 barrels make a butt.