Neologisms and Polonium 210 have something in common. Both have a half life of less than six months.

In the case of Polonium 210 it’s the radioactivity that declines. In the case of a new and useful word, it’s adherence to the original definition. Just as radioactive substances eventually decay into inert, dull elements like lead, so neologisms decay into inert, dull meanings.

This is the sad fate of the term, “disruptive technology.” Coined by Clayton Christensen in his groundbreaking The Innovator’s Dilemma to describe tools and techniques that disrupt and ultimately redefine marketplaces, it has deteriorated, now referring to any new technology that might achieve marketplace success.

It’s a shame, because the concept is endangered along with the term. Take wireless LANs — potentially disruptive in the original sense.

A disruptive technology isn’t, at first, a useful replacement for the older technology from which it emerged. Christensen’s original case study looked at disk technologies: Winchester drives couldn’t replace mainframe DASD (IBMese for disk); 5¼ inch hard drives couldn’t replace Winchesters, and so on. Instead, each needed new markets and uses to incubate and improve.

Christensen’s insight was that disruptive technologies never do overtake their predecessors. What they do instead is overtake the needs of their predecessor’s marketplace. 5¼ inch hard drives, for example, never exceeded Winchester drives in capacity or performance but did eventually overtake the needs of the minicomputer marketplace that Winchester drives dominated. When they did, Winchester drives ceased to have any marketplace at all.

Which brings us back to wireless LANs. Commodity 100 Mbps Ethernet outperforms the most optimistic performance improvement possible for wireless LANs — the 2,000 percent performance increase modem technology achieved. It’s simple: If wireless LANs reach, for example, 1 Gbps, just add 99 more wires and you’ve achieved cheap parity (actually, much more than parity since wired Ethernet bandwidth is switched while wireless bandwidth is shared).

So wireless LANs have to incubate where wired LANs can’t go: Airports, coffee shops, and homes. Then, there’s a self-serving favorite of mine — your facility, to connect consultants without jeopardizing security, by hooking cheap wireless hubs to a VLAN channel outside your firewall.

Incubated in niches like these, wireless LAN technology will improve. To be truly disruptive, though, it will have to overtake the needs of the wireless marketplace. I have my doubts.

But don’t let that stop you from the VLAN use. I’d really like something faster than a modem connection.

Please?