In a time of endless war and triumphant cynicism, I found myself the other day unexpectedly walking through the doors of perception. Yeah, those doors.

“You know the day destroys the night/Night divides the day/Tried to run/Tried to hide/ Break on through to the other side . . .”

The words, the music — the Doors, the voice of Jim Morrison — ignite not just the Summer of Love but a crazy something I don’t dare call hope, because those days of cultural and political revolution overdosed and imploded, didn’t they? War won. The Vietnam War dragged on, millions died (or thousands, if the only death toll that matters to you is that of U.S. soldiers), MLK and RFK were assassinated, the Cold War quietly morphed into the War on Terror and eventually the 911 attacks gave the military-industrialists the “new Pearl Harbor” they needed. Today’s military budget is securely bloated.

Knowing this, I was blindsided by the impact a remarkable exhibition I recently attended with my daughter had on me. And the star of the show was born in 1757.

The show, running through next March at Northwestern University’s Block Museum of Art, is called William Blake and the Age of Aquarius. Curated by art history professor Stephen Eisenman, it draws a link between the poetry, art and philosophy of Blake — an anti-authoritarian proponent of free thought and free love, a believer that every human being has a direct relationship with God — and many of the activists and artists of the ’60s, from Allen Ginsberg to Jim Morrison and Jimi Hendrix.

Blake spoke a complex truth. He embraced a far-flung, wildly loving philosophy of life: “If the doors of perception were cleansed everything would appear to man as it is, infinite. For man has closed himself up till he sees all things thro’ narrow chinks of his cavern.”

These words, from Blake’s poem “The Marriage of Heaven and Hell” (the title itself shows the convergence of forces he revered), gave Aldous Huxley the title of his book The Doors of Perception, about his experiences with mescaline. Then they gave Morrison the name of his rock band. And eventually they gave millions of young people, coming of age as a pointless war simmered and raged and Jim Crow stood its ground at the schoolhouse door, a glimpse at a world beyond the cruel and small-minded order that ruled the day.

This was not a simple world that flickered momentarily. This was not a tranquil, easy peace: “We chased our pleasures here/Dug our treasures there/But can you still recall/The time we cried/ Break on through to the other side . . .”

The cultural breakthrough was only partial. The political breakthrough still, often, feels to me like a complete dud. The Vietnam War went on for eight years beyond the 1967 Summer of Love; it finally became unfightable and ended in retreat and 16 years of proxy wars and “Vietnam Syndrome.” The American public was sick of war and the pointless sacrifice of young men and women. Then the powers that be ended the draft; and they saw in Saddam Hussein the perfect face of evil. In 2001, the towers went down.

And once again an extraordinary door of opportunity opened. But the country’s leaders had no wisdom beyond their own agenda of global hegemony.

Stephen Glain quotes Richard Clarke, counter-terrorism adviser for Bush 43, in his book State vs. Defense: The Battle to Define America’s Empire, recalling a cabinet meeting on Sept. 12, 2001, in which Defense Secretary Donald Rumsfeld said: “You know, we’ve got to do Iraq. There just aren’t enough targets in Afghanistan. . . . We need to bomb something else to prove that we’re, you know, big and strong and not going to be pushed around by these kind of attacks.”

As it turns out, I had come across that quote, in an excellent essay by Danny Sjursen, the day before I went to the William Blake/Age of Aquarius exhibit, and it had become seriously lodged in my consciousness — not as a surprise or a shock, just as a banal “of course.” The world was trembling, international compassion flowed, and the leaders of the world’s most powerful nation were plotting in utter ignorance a war that would make them look big and strong.

As the president soon put it, America’s mission was to “rid the world of evil.” They concocted what might as well be called the War To Promote Terror.

And the ’60s — the Summer of Love, the peace movement — is sandbagged by history’s cynicism, or so it has seemed until I saw the exhibit at Northwestern. Suddenly I felt the raw hope of those days come back to life: the outrage and the music and the possibility. The doors of perception reopened. And there was William Blake.

   O for a voice like thunder, and a tongue
   To drown the throat of war!
   When the senses
   Are shaken, and the soul is driven to madness,
   Who can stand?

Many people were standing. Politicians, even at the national level, dared to run on peace platforms and hippies stuck flowers in the barrels of guns. Oh, the cliché of that. Indeed, one of the pieces in the exhibit was a 1967 photo by Marc Riboud, taken during the march on the Pentagon that year, of a young woman confronting a soldier’s bayonet in her face with a flower. In the context of the exhibit, this wasn’t a cliché. It was courage.