On Roosevelt Island Wednesday, three beautiful, energy-efficient new edifices open their doors, joining the landscape of the greatest city in the world.

But its the astonishing work within that should give all New Yorkers a spine-tingling sense of optimism.

This is Cornell Tech, a playground for the brain, and its a wonder to behold.

It began in 2010, as a simple but radical idea. Mayor Mike Bloomberg, eager to diversify the citys economy and give Silicon Valley a run for its money, offered up land and modest financial assistance then invited the nations academic institutions to come forward with their proposals for creating a brand-new campus of higher learning that would draw top tech talent to the five boroughs.

That unleashed a torrent of blueprints to build genius magnets. A partnership between Cornell and Technion-Israel Institute of Technology won the contest and got right to work. Classes for a small number of students began in 2012, in space in Chelsea loaned by Google.

Now, after a remarkably speedy conception-to-completion timetable, the first piece of the permanent campus is done. Where once was old Goldwater Hospital, a faculty of 30 leaders in their fields is educating 300 grad students, growing each year for the foreseeable future with two more phases of the island campus yet to be built.

Here there will be a relentless push toward revolutionary thinking into using the internet, big data and other 21st century tools to transform the face of health care, business, education, law, architecture, media and cities themselves.

Computer science and engineering will be taught at the highest level, but never in artificial silos. Students, faculty and entrepreneurs will cross-pollinate, with an eye to improving real peoples lives.

Expect patents galore. And companies. Thirty-four have already spun off. One helps teachers of students with autism; another uses computer vision to find surfaces inside videos to host unobtrusive advertisements.

And, fingers crossed, with companies, jobs will blossom in a city that badly needs more high-quality, upwardly mobile opportunities. Cornells estimated economic windfall over the three decades will top $20 billion and 30,000 new positions.

Great thanks go to those who made it happen, starting with Bloomberg and his deputy mayor Robert Steel, and including Cornell Tech founding Dean Dan Huttenlocher and President Martha Pollack herself a leader in artificial intelligence.

Six years ago this week, we wrote: A top-flight genius-magnet would draw the best and the brightest from around the globe and serve as an incubator for innovative businesses and investment, here not elsewhere.

Salute the imagination and effort that made today possible. Encourage the work in progress. And brace for a city changed for good.