Things are getting lighter, lighter all the time -- more and more, items of value weigh less and less. This includes not only such obvious everyday paraphernalia as radios but software and hair-size fibers that can carry thousands of phone conversations simultaneously. All this is here and now but some items on the market or just around the corner suggest there is even less to come. PNS associate editor Walter Truett Anderson's most recent book is "Evolution Isn't What It Used To Be" (W.H. Freeman).

One of the strange, unexpected -- and still frequently overlooked -- features of today's economy is that all kinds of things are getting lighter. We still have heavy industry in the "postindustrial age," but a lot of the things it produces aren't really all that heavy. Federal Reserve Board Chairman Alan Greenspan recently pointed out that, although the value of goods and services produced in the United States has increased several times over in the past half-century, the actual weight of current output is probably only modestly higher than it was fifty years ago. This has inspired the term "weightless economy."

Part of this move can be attributed to the increasing importance of things that really don't weigh anything at all, such as services -- insurance, banking, consulting, etc. -- or weigh almost nothing, such as software, in which the value is the information and the floppy disk or CD is just packaging.

But tangible products are getting lighter as well: Transistors replaced vacuum tubes, and radios shrank from jukebox-sized to ones that fit into a shirt pocket or a set of earphones. Fiber-optic cables are replacing tons of copper wire in communications systems, and with far higher information-carrying capacity. The Economist recently noted that, in 1960, "a transatlantic telephone cable could carry only 138 conversations simultaneously. Now, a fiber-optic cable can carry 1,500 conversations. And very soon a fiber the diameter of a human hair will be able to transmit, in less than a second, the contents of every issue The Economist has ever printed in its 153-year history."

Advances in materials and engineering make it possible to construct buildings with less weight and bulk per square foot of floor space. Computers, the most spectacular downward growers of all, have gone from huge roomfuls of steel-housed electronics to palm-size.

The trend toward weightlessness has many advantages -- not only economic but ecological, because it tends to diminish consumption of energy and resources. It can also cause some problems, especially with organized labor. In the steel industry, for example, there have been labor-management conflicts over the so-called "mini-mills" that produce more output with fewer workers. The dispute between American Airlines and its pilots is mainly about the company's plan to use more small jets on low-volume routes. As the larger jets go -- say the pilots -- so do a lot of jobs.

For good or ill, the trend seems bound to continue. Researchers are working on a wide range of alloys and ceramics intended to be stronger, lighter and more flexible in everything from bridges to hand tools. Computer experts talk excitedly about the possibility of "quantum computing" in which a single atom might perform switching operations -- so huge amounts of data could be stored on the head of a pin.

Already here are micro - electro - mechanical systems (MEMS), small sensors on silicon chips which can detect changes in motion, light, heat and sound . They are widely used in devices such as automobile air bags and home blood-pressure testing kits. Several companies are hustling to develop and market various kinds of inexpensive chemical analysis instruments -- "laboratories on a chip" -- that might be used for anything from testing foods to detecting toxic gas on the battlefield.

We are clearly well into another wave of industrial revolution. We no longer carry in our minds quite the images of industry used fifty years ago both by those who celebrated its power and by those who condemned its ugliness.

As the nature of output changes, smokestacks are no longer appropriate symbols of modern industry. Some suggest the silicon chip is more suitable. Perhaps, if current technological trends continue, the real icon of wealth and productivity will be something you can't see at all.