Britney Spears at the opening night of her tour at MGM National Harbor. (Kevin Mazur/BCU18/Getty Images)

The theoretical physicist and popular science author Carlo Rovelli opens his poetic new book, “The Order of Time,” by asserting a connection between temporality and the shaking of badonkadonks: “In Hindu mythology, the river of the cosmos is portrayed with the sacred image of Shiva dancing: his dance supports the coursing of the universe; it is itself the flowing of time.”

Has Britney Spears read this book? When the great American pop survivor launched her new concert tour at the Theater at MGM National Harbor on Thursday night, she danced with the unrelenting urgency of a ticking stopwatch. And this comes after a four-year, 248-gig residency in Las Vegas, which, unlike her historic head-shaving catharsis of 2007, seems to have transformed Spears in positive ways.

Or at least it seems to have transformed how we might think about her music from now on. That’s because Vegas is a place where an artist becomes a show — and while we expect artists to change the way we experience the world, a show simply gives us a break from it. The ticket prices get real high and the stakes get real low.

How low? On Thursday night, Spears essentially transplanted her Vegas extravaganza into a new casino — a generous song-and-dance affair with colorful songs and vigorous dancing, but without any discernible singing. The only time her headset microphone appeared to be functioning was between numbers when she offered breathless greetings to her flock. So as her band vamped along to prerecorded vocal tracks, Spears performed her hits — “Stronger,” “Toxic,” “Oops! . . . I Did It Again” — with the parts of her body that weren’t her lungs.


(Kevin Mazur/BCU18/Getty Images)

We’re talking ponytail to pinkie toe. This was 95 minutes of nonstop bouncing, jouncing, wiggling, jiggling, squiggling, speed-miming, ghost-humping, human-pyramiding, getting hoisted up by a team of backup dancers, getting carried around like Cleopatra, getting gently lowered back down to earth, rolling around on the floor, kicking the air, finger-wagging, fist-pumping, hair-whipping, strutting, thrusting, popping, locking, jazz-hands-on-Red-Bull — every instant crammed with movement from at least six major muscle groups.

It’s hard to remember Spears going this gonzo onstage back in her prime, and hearing these hits should have reminded you that, yes, it’s been nearly two decades since MTV transformed this humble Mouseketeer into the last Lolita of the 20th century. And like they always do, old songs begin to express new things. When a 16-year-old sings, “My loneliness is killing me,” we hear a specific kind of adolescent pain — excruciating, but fleeting. When a 36-year-old mouths along to those same words, it evokes an entirely different kind of wound.

Other songs changed meaning by changing shape. When the drumless intro of “Toxic” unfurled softly and slowly, like an opiate lullaby, you may have felt yourself getting dizzy on the only ballad of the night. But was the star of the show hearing any of it? During that little gap in the chorus where the surf guitar part usually goes, Spears quite literally passed the tenths of seconds by spinning in circles.

She made those lines — between manic and ecstatic, past and present — feel blurry all the way through the show’s big finish, “Till the World Ends,” a gorgeous wad of existential bubble gum that instructs us to “keep on dancing” until time stops flowing.

For a feel-good finale, it bristled with nervous energy — as if forever might not last as long as we had hoped.