One afternoon last week, Stephen Goldsmith stood on Main Street and pointed up to the diminishing remains of the Crossroads Plaza. In 2011, this is where the brand new City Creek Center will stand, but all he saw were the exposed innards of Mervyn's department store, with its sagging fluorescent lights and its jumble of twisted metal.

Later this summer, the Key Bank building will come down, and then the ZCMI Center across the street — and later still, several buildings farther down Main.

So here are the choices, says Goldsmith, Salt Lake City's former planning director: We can wait four years until all the backhoes, jackhammers and temporary sidewalks are gone and downtown Salt Lake City is put back together again, or we can look at the whole messy process of the next four years as an opportunity.

On every torn up block, Goldsmith says, can be a museum without walls, a way to lure people downtown not just in spite of the mess but because of it.

A Temporary Museum of Permanent Change, as Goldsmith and two colleagues — photographer John Schaefer and graphic designer Gilberto Schaefer — call it.

The detritus from the old buildings? Why not look at it as teaching moments for students, posing questions like, "Where does steel come from?" and "Are we the only species that produces garbage?"

The temporary sidewalks? Why do they have to just be dull plywood tunnels? Why not turn them into display windows to show off the artifacts that construction workers uncover as they excavate? Why not display jewelry made from the debris?

The noisy bulldozers? "Violent operas of change," Goldsmith says. Blank storefronts waiting for Main Street to be revitalized? How about a Jumbotron where students can show off homemade videos?

Goldsmith and the two Schaefers have hundreds of ideas for the Temporary Museum of Permanent Change: gum ball machines that dispense poetry; billboards featuring ordinary Salt Lake residents ("Ask me about my downtown," the billboards will say, with a link to personal stories on the museum's Web site.); the World's First Day of Song next summer; the World's Largest Scrapbook.

The Temporary Museum of Permanent Change has received seed money from the Chamber of Commerce, the city and the Downtown Alliance. Now its founders are looking for private sponsors. In the meantime, they'll be at the Farmer's Market at Pioneer Park this Saturday, 9 a.m. to 1 p.m., to talk about the museum with anybody who saunters by.

Their PowerPoint presentation about the Temporary Museum of Permanent Change includes a picture of Main Street from the early 1950s, with its vibrant storefronts and its startling throngs of shoppers on the sidewalks.