by Paul Gilster | Jul 3, 2014 | Deep Sky Astronomy & Telescopes |
Growing up in the American Midwest, I used to haunt the library in Kirkwood, Missouri looking for books on astronomy. I had it in mind to read all of them and I pretty much did, looking with fascination at fuzzy images of distant objects I yearned to see close up. What did Saturn look like from Titan? What would it be like to be close enough to see the Crab Nebula fill the sky? Breathtakingly, what would it look like to be inside one of the great globular clusters?
Early on in Vernor Vinge’s A Fire Upon the Deep the character Ravna finds herself looking out a window at the entire Milky Way from a distance sufficient to view it whole:
She’d guessed right: tonight the Galaxy owned the sky… Without enhancement, the light was faint. Twenty thousand light-years is a long, long way. At first there was just a suggestion of mist, and an occasional star. As her eyes adapted, the mist took shape, curving arcs, some places brighter, some dimmer. A minute more and … there were knots in the mist … there were streaks of utter black that separated the curving arms … complexity on complexity, twisting toward the pale hub that was the Core. Maelstrom. Whirlpool. Frozen, still, across half the sky.
When I read that, all I could think was that I’d like to know what Chesley Bonestell would have done with the scene. The memory stuck with me, enough so that last weekend, I went digging through my collection of old magazines in search of a particular cover. We had been talking on Centauri Dreams about a Poul Anderson story called World Without Stars, and having been reminded of it by several readers, I kept thinking it was in a 1960s era Analog, and that Bonestell had indeed done a cover showing the Milky Way.
Soon I had magazines spread all over my office floor but couldn’t put my hands on the right one. The problem was that while I remembered (vaguely) the plot, about a crew that found itself tens of thousands of light years outside the galaxy on a mission to an isolated technical civilization, I had forgotten the original title. Finally I did the obvious and ran World Without Stars through the Internet Speculative Fiction Database, where I found the issue numbers. It turns out the story was serialized in Analog’s June and July, 1966 issues as The Ancient Gods, and my memory of a Chesley Bonestell cover was correct.
But serendipitous things happen when you collect old magazines. In leafing through the June issue, I came across a letter Poul Anderson had written to John Campbell, then in the latter part of his long run at the magazine — Campbell published it in Brass Tacks, his letter column, even though it was really just directed at the editor. Anderson talks about having been at Bonestell’s place and seeing the cover art for The Ancient Gods.
Did you notice in the Vinge paragraph above how dim the galaxy is depicted as being? Ravna thinks to herself that 20,000 light years is a long way out, and Anderson’s crew was to be a lot further out than that. Bonestell had been thinking all this over and had to find a way to work it into his painting. Thus Anderson to Campbell in the letter:
One point came up which may interest you. Though the galaxy would be a huge object in the sky, covering some 20? of arc, it would not be bright. In fact, I make its luminosity, as far as this planet is concerned, somewhere between 1% and 0.1% of the total sky-glow (stars, zodiacal light, and permanent aurora) on a clear moonless Earth night. Sure, there are a lot of stars there — but they’re an awfully long ways off!
If you look at the Bonestell cover, it does appear to be glowing more brightly than this, but Anderson says this is not a contradiction. His imagined planet’s natives, he points out, are adapted to the dim light of the red dwarf they orbit (no tidal lock here, evidently), and the galaxy in their night would appear luminous enough. Anderson adds: “To us, galaxies look brilliant in an astronomical photograph — but that picture involved a huge light-gathering mechanism plus hours of exposure. We could make the Milky Way look just as bright if we wanted to.”
Anyway, Bonestell had to come up with something that would be bright enough to be interesting while still suggesting the distances involved, and he certainly manages this. For the humans who have just landed on this remote world, the galaxy at 200,000 light years out is indeed a dim spectacle, as described in the story:
This evening the galaxy rose directly after sunset. In spite of its angular diameter, twenty-two degrees along the major axis, our unaided eyes saw it ghostly pale across seventy thousand parsecs. By day it would be invisible. Except for what supergiants we could see as tiny sparks within it, we had no stars at night, and little of that permanent aurora which gives the planets of more active suns a sky-glow.
And later:
Vast and beautiful, it had barely cleared the horizon, which made it seem yet more huge. I could just trace out the arms, curling from a lambent nucleus… yes, there was the coil whence man had come, though if I could see man by these photons he would still be a naked half-ape running the forests of the Earth…
Keep going further out and galaxies tend to all but disappear. Greg Laughlin noted this back in 2005 on his systemic site, where he discussed the beauty of objects like M104, the Sombrero Galaxy, which seen from a distance a bit further than Anderson’s 200,000 light years, would appear as “only a faintly ominous, faintly glowing flying saucer.” M31, the great Andromeda galaxy, is larger than the full Moon in the sky, but go out tonight and try to find it. Laughlin adds: “Our Galaxy, the Andromeda Galaxy, and the Sombrero Galaxy are all essentially just empty space. To zeroth, to first, to second approximation, a galaxy is nothing at all.”
More power, then, to long CCD time exposures and big mirrors, allowing us to see the things our eyes would perceive only dimly. Part of the thrill of those early library days was in looking at spectacular objects and trying to imagine them close up. But it was a thrill of equal measure to begin to learn about the wavelengths of light, about the gathering of photons, and the way we can tease out information about the universe with instruments designed to surmount our limitations.
by Paul Gilster | Jul 2, 2014 | Culture and Society |
The great Ukrainian mathematician Israil Moiseyevich Gelfand was famous for his weekly seminars in Moscow, where sudden switches in topics and impromptu presentations were the norm. Although his listeners had heard it many times, Gelfand liked to tell this story: In the early 20th Century, a man approaches a physicist at a party and says he can’t understand how the new wireless telegraphy works. How is it possible to send a signal without using wires?
The physicist tells him it is simple. “To understand wireless telegraphy, you must first understand how the wired telegraph system works. Imagine a dog with its head in London and its tail in Paris. You yank the tail in Paris and the head in London barks. That is wired telegraphy. Wireless telegraphy is the same thing except without the dog.”
It always got Gelfand a laugh, but he liked to use the story for a deeper purpose. According to Edward Frenkel, who in his youth attended and presented at some of Gelfand’s seminars, Gelfand would use the tale whenever he thought a problem needed a more radical solution than anyone had proposed. “What I am trying to say,” he invariably added, “is that we need to do it without the dog.” Read Frenkel’s charming Love & Math: The Heart of Hidden Reality (Basic Books, 2013) for a look at Soviet-era mathematicians and the world they worked in.
I’m thinking that if there was ever a man who worked without the dog, it was Fritz Zwicky (1898-1974). The name of the Bulgarian-born physicist who spent his career in the United States inevitably came up in the light of our discussions on moving entire stars. This was a man with a deeply independent mind whose six-volume catalog of 30,000 galaxies, based on the Palomar Observatory Sky Survey, remains a touchstone in the study of galaxy clusters. But he was also a thorn in the side of many astronomers, routinely disparaging their work and their characters.
If a combative colleague — he coined the term ‘spherical bastards’ to describe his fellow astronomers, who he said were bastards from any angle you chose to observe them — Zwicky was kind to students, university administrators and people outside his profession. He was a man who liked to think big. Zwicky broached the subject of what we might call ‘stellar propulsion’ in a May, 1948 lecture at Oxford University, where he said there was a possibility of:
“…accelerating…[the Sun] to higher speeds, for instance 1000 km/s directed toward Alpha Centauri A in whose neighborhood our descendants then might arrive a thousand years hence. [This one-way trip] could be realized through the action of nuclear fusion jets, using the matter constituting the Sun and the planets as nuclear propellants.”
Zwicky’s lecture was published later that year in The Observatory (68:121-143). In a June, 1961 article in Engineering and Science called “The March Into Inner and Outer Space,” he followed up on the idea, although as before only in broad terms shorn of detail. In Zwicky’s view, a journey to the stars should not necessarily demand leaving the Earth behind. Instead, accelerate the Sun, letting it pull the planets along with it, and you maintain your own environment on the most comfortable of all generation ships. As to how to do it:
In order to exert the necessary thrust on the sun, nuclear fusion reactions could be ignited locally in the sun’s material, causing the ejection of enormously high-speed jets. The necessary nuclear fusion can probably best be ignited through the use of ultrafast particles being shot at the sun. To date there are at least two promising prospects for producing particles of colloidal size with velocities of a thousand kilometers per second or more. Such particles, when impinging on solids, liquids, or dense gases, will generate temperatures of one hundred million degrees Kelvin or higher-quite sufficient to ignite nuclear fusion. The two possibilities for nuclear fusion ignition which I have in mind do not make use of any ideas related to plasmas, and to their constriction and acceleration in electric and magnetic fields.
Zwicky would amplify his stellar propulsion ideas in his book Discovery, Invention, Research through the Morphological Approach (Macmillan, 1969), where he described how these directed exhaust jets would accelerate the Sun to a velocity sufficient to reach Alpha Centauri in about fifty human generations. Left for the reader’s imagination is the question of how a moving Solar System would decelerate once it arrived in the vicinity of the Alpha Centauri stars, presumably to join them to form a new triple (or quadruple, counting Proxima Centauri) star system.
We’ve seen how Leonid Shkadov conceived of wrapping a thruster around a star in such a way as to create propulsive forces, an idea now explored in the Greg Benford and Larry Niven novels Bowl of Heaven and Shipstar. But it’s clear that a star journey via a propulsive Sun is yet another idea that Zwicky had early, although he never went ahead to work out all the ramifications. In addition to manipulating the Sun’s own fusion, Zwicky’s Engineering and Science article described other broad concepts: The benefits of taming fusion for power and rocket propulsion, the need for a human presence in nearby space, particularly the Moon, and the possibility of using what he called ‘terrajet engines’ to burrow into the interior of the Earth.
In tribute to Zwicky, it’s necessary to mention several of his insights, including the notion that cosmic rays are produced in the explosion of massive stars which he began, in 1931 lectures, to describe as ‘supernovae,’ as opposed to the more common and less powerful novae. Working with Mount Wilson Observatory astronomer Walter Baade, he went on to extrapolate the creation of neutron stars that were dense as atomic nuclei but only a few kilometers in diameter, an idea that was met with skepticism.
The Palomar Observatory Sky Survey grew out of Zwicky’s work, and Zwicky himself discovered 122 supernovae. But his work hardly ended with exploding stars. Investigating the Coma cluster of galaxies, he worked out that the mass of the cluster was far too little to produce the gravitational forces needed to keep the cluster together. Unseen matter — and he coined the term ‘dark matter’ — must be making up the difference in mass. How to investigate the idea? Zwicky suggested gravitational lensing, now a common technique but a novel solution in his day.
In his dark matter work in particular, Zwicky can be said to have done what Israil Moiseyevich Gelfand urged. He learned how to do it without the dog, to take an enormous conceptual leap into an answer that later observation would prove suggestive and worthy of intense follow-up. He was a stormy genius, an irritated, irritating treasure of a man.
