Science is all about asking questions and then running carefully controlled experiments to find the answers.

Most of the time, it doesn’t take too long to actually run those experiments — maybe a few years at most. But some experiments can take way longer, to the point where the original question is almost forgotten, and the researchers who originally asked the question are long gone.

From an electric bell that refuses to shut up to lead-sealed microbial time-capsules, here are some of the world’s longest-running experiments. Most mechanics will tell you that to keep your car running smoothly, you should change the battery every four years. But in a corner of the physics department in the University of Oxford, there is a battery that’s been running for 177 years.

And no one knows how it’s lasted that long. In 1840, Oxford physics professor Robert Walker bought a weird-looking contraption consisting of two long, sulfur-covered cylinders attached to two bells. A metal ball slowly vibrates back and forth between the bells, propelled by the charge propelled by the charge from the battery.

The type of battery it uses is called a dry pile, because unlike most modern batteries, the electrolyte, which is the stuff that actually allows electricity to flow, is a paste rather than a liquid. The bells were built only 40 years after the very first battery was invented, and the batteries powering the metal ball were only expected to last 4-5 years. So it’s pretty weird that this thing has lasted almost two centuries, and physicists would love to know more about how its batteries work.

But unfortunately, the cylinders are sealed, and the records of their manufacture were lost long ago. We do have some clues about these batteries. Other dry piles made at the time had layers and layers of metal discs stacked on top of each other, with sulfur sealing everything in.

The discs were usually coated with zinc sulfate on one side, and manganese dioxide on the other. These days, zinc sulfate is mostly used as a dietary supplement, but manganese dioxide is still used in modern dry-cell batteries. But something about the way this thing’s batteries were made has let them last a ridiculously long time.

The thing is, until we open up the cylinders, we won’t know for sure that’s what’s inside. And at this point, scientists don’t really want to crack it open and investigate — they’d rather see how long it keeps going first. Once it stops though, I imagine they’ll organize the autopsy pretty quickly.

Talk to a farmer, and they’ll probably tell you that one of their biggest challenges is weeds. Sometimes it seems like they’re fighting a never-ending battle against them. That’s because weeds have this annoying property where they can lie dormant, chilling out just under the surface.

They lull you into a false sense of security until you get complacent and then BAM! They’re all over the place again. There have been plenty of studies by agricultural scientists trying to find out how long weeds can hang around in the soil.

But the oldest, and longest-running, of these experiments can be found on the grounds of Michigan State University. There are 5 whiskey bottles, filled with sand, buried upside down in a top-secret location. And no, they aren’t the leftovers of some 19th century rave.

They’re the legacy of botanist William James Beal. He filled 20 of these bottles with seeds from 21 different species of weeds, plus moist sand. He buried them angled down so they wouldn’t fill up with water, and then planned to dig one up every five years and plant the seeds to see which survived.

At least, that was the plan. In 1919, there was an early frost and the bottle couldn’t be excavated without a jack-hammer, so they waited until 1920, and decided to extend the interval to ten years from then on. In 1990, instead of digging up a bottle, the researchers who’d taken over the project extended the interval again to 20 years.

The most recent one was opened in 2000, and there are five left. Which means the last bottle will be unearthed in 2100. When researchers planted the seeds from the bottle they dug up in 2000, seeds from only two of the original species sprouted into plants.

That’s pretty much what they expected, since the last time seeds from more than three species sprouted was in 1930. But they’re curious whether seeds from the hardiest species will keep sprouting when they dig up future bottles. By now, the point of the experiment has kind of flipped.

The researchers aren’t trying to figure out how to kill weeds — they want to know more about how seeds stay viable to help save plants that might be going extinct. Thousands of people all over the world have decided to sit and watch something that flows even slower than paint dries. All for the chance at witnessing the next big moment in a 90-year-old experiment.

It’s called The Pitch Drop Experiment. In 1927, Thomas Parnell, a physics professor at the University of Queensland in Australia, set up a demonstration to show that pitch, aka asphalt, actually flows. Even though it looks and acts like a solid.

And it turns out that it does flow … just, very slowly. The experiment consists of a large funnel filled with black pitch that slowly drips into a beaker. It took 8 years for the first drop to fall, and in the ninety years since, there have been 8 more drops.

Based on these drops, researchers found that pitch has a viscosity 30 billion times greater than water — meaning, it flows about 30 billion times more slowly than water does. In the 1980s, scientists at the university debated taking down the experiment, since they figured it had served its purpose. But then, two things happened.

First, they realized that no one had ever actually seen the drop fall. They’d just found another drop in the beaker the next morning. And second, the pitch started acting… weird.

The drops had been falling at a semi-consistent rate up until this point, but the 8th drop took a lot longer to fall than the previous ones. It fell in 2000, but a really badly timed blackout meant the cameras set up to record the drop failed. The 9th drop fell in 2014, and was caught on camera.

But now, it seems like the pitch is flowing faster, and scientists aren’t sure exactly why. So the experiment is still going, and researchers hope the pitch’s behavior will give us insights into other super-high viscosity materials like plastics and silicone. According to the Centers for Disease Control, cardiovascular disease is the leading cause of death in the United States, claiming over 600,000 people a year.

And scientists back in the 1940s wanted to know more about how to prevent it. In 1948, about 5,000 people in Framingham, Massachusetts volunteered to be a part of a massive, long-term study. Researchers picked healthy adults that showed no signs of heart disease and started monitoring their lifestyle and physical health.

The study linked cholesterol, high blood pressure, and other factors like smoking to heart disease and stroke. And it’s still going, even though there are very few of the original participants left. In the 1970s, the adult children of the first subjects were enrolled and, more recently, a third generation was added to the study.

And as the study continues, it’s helping us learn more about the role of genetics in heart disease. Evolution happens very slowly. It can take generations for a single change to spread through a population.

And it can be hard to study exactly how those changes spread. When you’re dealing with nature, you can’t just re-wind the clock and see if the same adaptations will happen again. Which is why, in 1988, American biologist Richard Lenski decided to grow 12 cultures of E. coli bacteria.

The thing about bacteria is that they don’t live very long. So over the nearly 30 years that Lenski’s team has been growing these cultures, they’ve cycled through tens of thousands of generations. And the group has had a front-row seat the way the populations have changed under different conditions.

Since it’s a laboratory experiment, they can grow multiple cultures at the same time and see if they do the same thing. Over time, the E. coli have gotten bigger, started mutating more often, and gotten better at digesting the sugar in the solution they’re grown in. And around 33,000 generations in, one strain evolved a more complex mutation that allows it to digest citrate, a compound in the solution, in a way that E. coli aren’t normally able to do.

From our point of view, this experiment has only been running since 1988 — which, compared with some of the other experiments I just mentioned, basically makes it a tiny baby experiment. But from the E. coli’s perspective, they’ve been growing and evolving over 60,000 generations. Which sort of makes it the longest-running experiment in history, right?

Technically, this one isn’t a long-term study … yet. Microbiologists have been studying life in tough places on our planet for decades, and they’ve learned that some microbes have a special ability: When conditions get too extreme, they can survive, dormant and dried out, while they wait for things to improve. Then they just wake up and go about their lives.

They might be able to survive this way for thousands of years, but we’re still not totally sure how they do it. So a group of researchers from around the globe have set up what they’re calling the 500-year microbiology experiment. They’ve dried out and preserved microbes in two sets of 800 glass vials different boxes.

One box is lead-lined to protect the microbes against radiation, and the other’s just using glass to keep them isolated. It’s a little bit like the seed experiment, but with less sand, and microbes instead of weeds. For now, every other year, they’re opening up three vials from each box to rehydrate them and see if they’ve survived, and to analyze their DNA for damage.

Starting in 2038, they’ll only open new vials every 25 years, which means that assuming the microbes survive that long and there’s no zombie apocalypse, the experiment will finish up in 2514! Researchers are hoping the results of these experiments will help us understand the extremes of life: how long can some of the simplest organisms survive being preserved and then reanimated? Knowing more about life in the most extreme conditions on Earth will also help us learn more about where life could have evolved on other planets.

But there’s another side to this experiment, too: the vials of preserved microbes are a sort of time-capsule. Researchers investigating them in the 26th century will have a unique snapshot of microbial communities from 500 years ago. It’ll be interesting to see what’s changed and how they’ve evolved.

Not that we’re going to get to see those changes, though. Lucky future scientists. We’ll all be dead.

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