Nicholas Carr is the author of “The Shallows” and “The Glass Cage.” His new book, “Utopia Is Creepy,” will be published this year.

In the spring of 1997, the Library of Congress opened an ambitious exhibit featuring several hundred of the most historically significant items in its collection. One of the more striking of the artifacts was the “rough draught” of the Declaration of Independence. Over Thomas Jefferson’s original, neatly penned script ran edits by John Adams, Benjamin Franklin and other Founding Fathers. Words were crossed out, inserted and changed, the revisions providing a visual record of debate and compromise. A boon to historians, the four-page manuscript provides even the casual viewer with a keen sense of the drama of a nation being born.

Imagine if the Declaration were composed today. It would almost certainly be written on a computer screen rather than with ink and paper, and the edits would be made electronically, through email exchanges or a file shared on the Internet. If we were lucky, a modern-day Jefferson would turn on track-changes and print copies of the document as it progressed. We’d at least know who wrote what, even if the generic computer type lacked the expressiveness of handwriting. More likely, the digital file would come to be erased or rendered unreadable by changes in technical standards. We’d have the words, but the document itself would have little resonance.

Historian Abby Smith Rumsey was one of the curators of the Library of Congress exhibit, and that experience informs “When We Are No More,” her wide-ranging rumination on cultural memory. “A physical connection between the present and past is wondrously forged through the medium of time-stained paper,” she writes. But that “distinctive visceral connection” with history may be much diminished, if not lost, when our cultural heritage is stored in sterile databases rather than in actual objects. Rumsey’s book poses a vital question: As more and more of what we know, make and experience is recorded as vaporous bits in the cloud, what exactly will we leave behind for future generations?

We tend to think of memory as a purely mental phenomenon, something ethereal that goes on inside our minds. That’s a misperception. Scientists are discovering that our senses and even our emotions play important roles in recollection and remembrance. Memory seems to have emerged in animals as a way to navigate and make sense of the world, and the faculty remains tightly tied to the physical body and its material surroundings. Just taking a walk can help unlock memory’s archives, studies have shown.

"When We Are No More: How Digital Memory Is Shaping Our Future" by Abby Smith Rumsey (Bloomsbury)

Rumsey draws a powerful analogy to underscore memory’s materiality. The greatest memory system, she reminds us, is the universe itself. Nature embeds history in matter. When, in the early 19th century, scientists realized that they could read nature’s memory by closely examining the Earth and stars, we gained a much deeper understanding of the cosmos and our place in it. Geologists discovered that the strata in exposed rock tell the story of the planet’s development. Biologists found that fossilized plants and animals reveal secrets about the evolution of life. Astronomers realized that by looking through a telescope they could see not only across great distances but far back in time, gaining a glimpse of the origins of existence.

Through such discoveries, Rumsey argues, people both revealed and refined their “forensic imagination,” a subtle and creative way of thinking highly attuned to deciphering meaning from matter. We deploy that same imagination in understanding and appreciating our history and culture. The upshot is that the technologies a society uses to record, store and share information will play a crucial role in determining the richness, or sparseness, of its legacy. To put a new spin on Marshall McLuhan’s famous dictum, the medium is the memory.

Whether through cave paintings or Facebook posts, we humans have always been eager to record our experiences. But, as Rumsey makes clear, we’ve been far less zealous about safeguarding those records for posterity. In choosing among media technologies through the ages, people have tended to trade durability for transmissibility. It’s not hard to understand why. Intent on our immediate needs, we prefer those media that make communication easier and faster, rather than the ones that offer the greatest longevity. And so the lightweight scroll supplants the heavy clay tablet, the instantaneous email supplants the slow-moving letter. A cave painting may last for millennia, but a Facebook post will get you a lot more likes a lot more quickly.

We’re now in the midst of the most far-reaching shift in media ever, as we rush to replace all manner of physical media with digital alternatives. The benefits are compelling. We’ve gained instant access to a seemingly infinite store of information. But there are losses, too. “Digital memory is ubiquitous yet unimaginably fragile,” Rumsey reports, “limitless in scope yet inherently unstable.” All media are subject to decay, of course. Clay cracks, paper crumbles. What’s different now is that our cultural memory is embedded in a complex and ever-shifting system of technologies. Any change in the system can render the record unreadable. A book can sit on a shelf for hundreds of years and retain its legibility. All that’s required to decode it is a pair of eyes. A digital file is far more fussy. Dependent on computers for decoding, it can disappear or turn to gibberish whenever operating systems, software applications or document standards are revised.

All of us have experienced the evanescence of the digital. Web pages change by the day, leaving little or no trace of their earlier versions. Hyperlinks dead-end in 404 error pages, with their irritating “Not Found” notices. Internet services and social-media sites shut down, their data disappearing with them. And as for opening that file you saved on a floppy disk with an obsolete software program: Well, good luck. If we’re not careful, Rumsey warns, “the history of the twenty-first century will be riddled with large-scale blanks and silences.”

Rumsey is clear about the dangers of our “ephemeral digital landscape,” but she isn’t a doomsayer. She believes that we can protect our cultural legacy for our descendants, even if that legacy ends up mainly in the form of immaterial bits. But, she stresses, we’ll first need to overcome our complacency and start taking the long-term protection of valuable data seriously. We’ll need a reinvigorated system of libraries and archives, spanning the public, private and nonprofit sectors, that are adept at digital preservation. We’ll need thoughtful protocols for determining what data needs to be saved and what can be discarded. And we’ll need to ensure that control over culturally significant data doesn’t end up in the hands of a small group of commercial enterprises that focus on profit, not posterity.

Those are prudent suggestions. But, even as we continue down the path to a virtualized future, we shouldn’t lose sight of the enduring value of the material artifact. We should make sure that there’s always a place in the world for the eloquent object, the thing itself.