For older generations, Pearl Harbor, the shooting of JFK, and the assassination of Martin Luther King stand out as milestones in public memory. These were moments when the collective conscious of an entire society stopped together in grief and fear for what would come next.

For many younger generations, that terrible distinction falls to 9/11, which, in hindsight, was more than just a terrorist attack. It was a turning in point in history. A clear line can be drawn from the events of Sept 11, 2001 to the deeply unsettled territory the world finds itself in today.

But lying underneath the entire trajectory that links 9/11 to our moment is a story not just of politics and culture, but of a single new kind of machine, a device the likes of which humanity has never seen before. On this 17th anniversary of 9/11, we would do well to step back and reflect on what that machine have become for us and were it might still lead.

While many of us will remember watching endless loops of the planes hitting the towers on CNN or some other TV news outlet, many people were also turning to the World Wide Web for updates. The network of linked computers called the internet wasn’t new in 2001, but it was growing rapidly. In many ways, 9/11 defined a moment when the internet came of age as a public space for shared news—whether mundane or world-shaking.

But at the time, we didn’t yet know how the internet would change society and culture.

Technologically, the foundational software principles—like the http and ftp protocols for establishing connections and transferring data—were all there. But the deeper potential for how networks of information-processing machines would become part of the fabric of human life was as yet unborn. That development would have to wait for a series of innovations.

The first of these were social networking software platforms—the pioneering MySpace, followed by Facebook. The development of wireless technologies was also crucial, allowing network connectivity to become free-floating. Finally the rise of the smartphone meant that connectivity would become temporally pervasive; we can now have all our machine networks with us 24/7—a ubiquitous facet of modern life. The results turned out to be different than most people expected, and that is where the line from 9/11 runs through into today.

Security, surveillance, and conspiracy theories

After 9/11, there was an immediate need to increase security to prevent another attack. The network’s technologies allowed for unprecedented levels of intelligence gathering which, without doubt, thwarted additional attacks.  But it also gave rise to the mass data collection and surveillance activities, which suddenly made the NSA a household word in the aftermath of the Edward Snowden leaks.

With the birth of social media, the network machine also gave us the ability to create world-wide conversations about everything from music to sports to our kids. But social divisions created in the aftermath of 9/11, particularly regarding the Iraq War and attitudes toward Muslims, were one powerful aspect in the easy balkanization—the echo chambers—which social media created. The network had the unintended consequence of separating us while also linking us together.

This combination of paranoia and the social silo-ing of opinion led directly to the strange “post-truth” world we live in today. Conspiracy theories about 9/11 being an inside job have been a mainstay of the shadowy part of internet conversations.   But that conspiracy-saturated vision of the world is no longer in the shadows. Today, conspiracy theories entirely devoid of any basis in the real world are a part of many people’s narrative about the world. Even a topic like climate change, which had nothing to do with 9/11, was touched by this new post-truth way of thinking via the infamous Climategate—a faux scandal driven by stolen network data (emails).

It’s hard to know where we will go from here. The vast machine called the network is one of the most remarkable achievements of human civilization. But with a single event, 9/11, that machine’s inherent capacities were taken in directions that might undermine the civilization that created it.

We are still watching this evolution unfold and, like that day 17 years ago, we are all watching together.

Frank is a professor of astrophysics at the University of Rochester.