Time travelers walk among us every day.

We know more than 3 million personally.

Don't believe it?

The mechanics of time travel say that it is entirely possible so long as you're desirous to witness the future.

Those 3 million? They all wanted exactly that, to see their futures.

And with our mechanical heart valves, they have.

People such as Allen Stendahl of Florida, who was barely 10 when rheumatic fever forced him to bed rest for three months. The fever damaged Stendhal's aortic valve, ultimately requiring surgery at 36. He's now more than doubled his age and through it all, his heart valve has carried him into a future that included marriage, children, a career and retirement.

And Sadie Rutenberg, born in Washington state with a congenital heart problem called complete atrioventricular canal defect in which the walls between her heart's left and right chambers did not form properly. A few years ago, she needed the smallest mechanical heart valve to save her life. It's designed for the tiniest patients, including newborns and babies 1-year-old and younger. Her future? Well, it's just getting started. And she's here for all of it.

And Ohio's Drew McCartt, who, by his own description, had always been, "go, go, go, go, go." But at 25, he was starting to slow and needed to have surgery to replace his leaky heart valve. Three decades later and counting, McCartt's mechanical valve is still there, still doing its job, still carrying him into what his future holds next. As the clock tick-tick-ticks forward, if you're really quiet, you can hear his valve working. Click-click. Click-click. Click-click.

Collectively, their stories account for more than a century of living that otherwise would not have happened. And that's just a handful of examples from among the more than 3 million lives that went on longer thanks to a mechanical valve being implanted.

So yes, time travelers walk among us, all around the globe.

They're here, living out their individual futures and the lives they want, futures they and their loved ones all hoped to see. And we're glad to witness them, too.