Andy Young
If there is one thing that will turn me against a science-fiction story in the twinkling of an eyelash, it is the mention of "the absolute zero of outer space". I guess this must be my pettiest peeve in science-fiction. I can take hyperspace and faster-than-light travel without a murmur, partly because I don't expect every author to have a good knowledge of relativistic mechanics, and partly because I accept it in the realm of science-fantasy -- temporarily suspending disbelief as is necessary with dragons and witches. But contradictory' it not only goes against a vast body of esoteric laboratory experimentation, it is opposed to the simplest sort of physical experience. The most rudimentary reflection is necessary to show that the idea is an absurdity, and a little more sophisticated thought confirms this.
It was just a few months ago that someone was commenting in a fanzine (Wendigo 9) on the relative effects of hot and cold air and water on the sensation of temperature. It's plain enough that cold water feels colder than cold air, and the reason is just that water is denser than air so there are more cold water molecules sitting next to your warm hide to carry away heat (in cold water) than there are cold air molecules to cool you in cold air. Now it would certainly be consistent with common experience to assume that a cold vacuum (if there is such a thing) would feel still less cold than cold air. Nobody seems to have thought of this.
Still looking from the simple everyday view and not bringing in atoms and quantum mechanics, it is a truism taught in most high-school science courses that the only way heat can be transferred through a vacuum is by radiation. How do you think all that heat gets here from the sun, hey? Radiation. Now it is also pretty common knowledge that hot bodies radiate more than cold ones, and that every object warmer than absolute zero radiates at least a little heat. If you have any sort of solid object that either rotates fast enough or is small enough to have a reasonably uniform temperature sitting out in space, it will eventually come to a temperature where it radiates heat at the same rate it received it. At the Earth's distance from the sun, this equilibrium temperature is near the freezing point of water. (Freshly fallen meteorites are about the temperature of ice.) Pretty warm compared to Absolute Zero, hmmm? Even way out in interstellar space the energy received from starlight is enough to keep a lump of rock or metal several degrees above absolute zero.
The point I wish to make is that empty space just does not have the property of temperature. That attribute belongs exclusively to matter, not space. Since Space is neither cold not hot, it can't cool or heat a spaceship. Let's keep radiative equilibrium in mind, please.
But there is a further interesting point to be made: matter doesn't always have a temperature either! In the simplest theory of heat, thermodynamics, temperature is defined only in an equilibrium condition. More advanced theories such as statistical mechanics show that we cannot measure a unique temperature unless conditions are very nearly in equilibrium; if things are changing rapidly or if the gas molecules have not collided with each other often enough after a change to spread out the thermal energy among them, a piece of matter may not have a temperature at all.
This condition is met with sometimes in astronomy, particularly in the stars. There are various ways of measuring the "temperature" of a star, and they usually give different results. For the sun we have temperatures ranging from about 4200°K on up. I find an excitation temperature of 4500°K, effective temperature 5785°K, color temperatures from 5800° to 7500°, and brightness temperatures from 5910° to 6480°. Hot, isn't it?
You can even have two things in close contact and still have them permanently at different temperatures; oddly enough, this can happen out there where the ol' Absolute Zero thing is supposed to crop up. For example, you can have a cloud of gas and dust in which the dust grains have a temperature a few degrees above absolute zero and the gas has a temperature of a hundred degrees above absolute zero. How come? Well, the dust grains can cool off until they come into radiative equilibrium with starlight, but the gas atoms can only cool off by striking the cool dust particles. Because the gas and dust are so dilute, the gas atoms pick up energy from the starlight fairly easily but only rarely get a chance to unload it on the dust. So the gas is always hotter than the dust.
On the other hand, there are regions around certain hot stars in which the gas is heated (by ultraviolet light from the star) to several thousand degrees' but the gas still stays fairly cold. I have heard that someone once wrote a science-fiction story about a spaceship that was sent into a red giant star; these objects are less dense than the best laboratory vacuum so the only heating the ship would get would be by radiation. It may be possible to send a cold spaceship into a fairly hot star for a short while without heating the ship up very much, though I wouldn't want to spend my life inside any star.
An interesting sidelight on the matter of the absolute zero of you-know-where is the time it takes for an object to cool off by radiation. A copper sphere one foot in diameter, if coated with a perfectly black coating, will cool by radiation into empty space in six minutes and twenty seconds at room temperature. But as it cools, the rate of cooling decreases; it will take nineteen and a half days to reach -196°C (77° above absolute zero) and one year and twenty-two days to cool from there to -235°C (20° Absolute) at which point it takes seven and a half days to cool one degree. But this is all assuming the sphere to be perfectly black; actually it will cool much slower than this and a polished copper sphere will take about a hundred times as long to cool because it is a poor radiator. This should discourage Hugo Gernsback and his eager-beaver followers who have recently proposed and patented devices which would use Absolute Zero of Outer Space to make electrical equipment superconductive. It takes decades for an object of any size to cool in outer space, even down to 20° above absolute zero; and superconductivity does not show up until still lower temperatures are reached, as low as two or three degrees above zero in many cases. I can see Hugo & Co. sitting around for years waiting for their little robot to cool off and start working; finally they all die off, and their grandchildren collect the royalties. If the thing hasn't been destroyed by a meteor by that time.
Foosh on the Absolute Zero of O.S. Like I say, it leaves me cold.
--- Andy Young
Data entry by Judy Bemis
Hard copy provided by Geri Sullivan
Data entry by Judy Bemis
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