In 1890, the economist Alfred Marshall described something he could observe but not fully explain: when an industry concentrates in one place, "the mysteries of the trade become no mysteries; but are as it were in the air." Workers, ideas, and know-how leak between neighboring firms simply because people in the same trade talk to each other, move between employers, and watch what works. Marshall called it industrial atmosphere — and it is the actual mechanism behind why certain technology only gets built in certain places, not culture in some vague sense, but a specific, structural leakiness that some regions have and others don't.[1]
Route 128, the technology corridor ringing Boston, was the established center of American high tech before Silicon Valley had a name — as of 1965, it employed roughly three times as many technology workers as the Santa Clara Valley did. By 1975, Silicon Valley had caught up. From there, it never looked back. Same country, same era, same access to research universities and defense funding. What diverged was the structure underneath the technology, not the technology itself.[2]
Economist AnnaLee Saxenian spent more than a hundred interviews tracing the actual difference: Silicon Valley engineers moved constantly between employers and left to start their own companies, and that mobility was celebrated, not punished. On Route 128, the same move — leaving one firm for another, let alone for a startup — was rare and treated as disloyal; Route 128's companies stayed closed, vertically integrated, self-sufficient. Marshall's "atmosphere" needs people actually moving through it to carry knowledge from firm to firm. Silicon Valley had that circulation built in. Route 128 didn't.[3]
The reason isn't mysterious, and it isn't cultural in the soft sense — it's a specific, checkable law. California's Business and Professions Code Section 16600, on the books since 1872 and confirmed by the California Supreme Court as recently as 2008, makes noncompete agreements void: "every contract by which anyone is restrained from engaging in a lawful profession, trade, or business of any kind is to that extent void." Massachusetts enforces noncompetes. An engineer in Santa Clara County could leave for a rival or a garage startup with no legal exposure; an engineer on Route 128 usually couldn't. The law didn't just permit the job-hopping Saxenian documented — it's the specific reason the "atmosphere" Marshall described was legally allowed to circulate in one place and legally blocked in the other.[4]
This is the missing mechanism behind every anchor-and-orbit pattern this site has already documented — why an industry, once it takes root somewhere, tends to stay rooted for decades or a century, and why a rival region with comparable talent, funding, and technology often can't simply replicate it. The knowledge isn't written down anywhere a competitor could adopt it. It exists only in a live regional network of people who worked together, competed, and moved between each other's companies — and that network can only exist where the law, the culture, or both actually let people move.
The same mechanism, run in reverse and forward. How place shapes you makes the individual-level version of this claim — that certain formation only happens inside a lived window, not an adopted one. In January 1925, Three Men Founded an Airplane Company in Wichita, Kansas is the industrial-scale proof: a century of aerospace manufacturing that never dispersed, for exactly the reason named here. Job-Switching Isn't a Red Flag takes the same open-mobility mechanism down to the individual doing the switching.