The 10 biggest science experiments on Earth

Sometimes science needs to go big. From telescopes spanning the globe to particle accelerators that would take over 24 hours to walk around, these experiments are among the largest ever conducted.

Gravitational wave hunting

Ripples in the gravitational field of the universe, known as gravitational waves, are remnants of massive galactic events such as black hole collisions and merging neutron stars. These waves may even record echoes of the Big Bang. To detect them, scientists need big equipment, such as the Laser Interferometer Gravitational-wave Observatory (LIGO).

LIGO consists of two large instruments, each with two 2.5-mile-long (4 kilometers) arms. The instruments are in Washington state and Louisiana, approximately 1,900 miles (3,000 km apart). The arms are laser interferometers, arranged in L shapes. A single laser beam is split in half, with each half sent down one of the arms. At the end of each arm is a set of mirrors, which bounce each half laser beam around a few hundred times and then back up the arms so they reunite.

By investigating the interference pattern — the way the peaks and troughs of the light waves combine — scientists can determine if a gravitational ripple happened during the experiment. If so, they can study it in detail. The larger the arms, the more sensitive the instrument, which is why LIGO boasts the longest laser interferometers ever built.

LIGO has detected all manner of mysterious galactic phenomena, from a merger between a neutron star and (probably) a superlight black hole to multiple collisions between neutron stars. (It has also detected a flock of ravens pecking on icicles at the Washington facility — an observation with fewer implications for the dynamics of the universe.)

Related: To hunt gravitational waves, scientists had to create the quietest spot on Earth

World's largest atom smasher

To study the very small, scientists sometimes have to use very big instruments. They don't come bigger than the Large Hadron Collider (LHC), the world's largest particle accelerator. Run by CERN, the European Organization for Nuclear Research, this 16.7-mile-diameter (27 km) ring is studded with four detectors, known as ATLAS, CMS, ALICE and LHCb. Befitting its location, the 7,700-ton (7,000 metric tons) ATLAS is the largest particle detector ever built. The instrument measures a wide range of subatomic particles created when scientists zap particle beams at one another at high speed, creating collisions that throw off elusive elementary particles like the Higgs boson.

The LHC boasts over 10,000 tons (9,000 metric tons) of iron in its magnetic systems and enough niobium-titanium cable to stretch to the sun and back over six times and then between Earth and the moon another few times. It's also the largest, coldest refrigerator on Earth, because the magnets must be kept at minus 456.25 degrees Fahrenheit (minus 271.25 degrees Celsius), slightly colder than outer space.

Miniature Amazon rainforests

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By pumping tons of carbon dioxide (CO2) into the atmosphere each year through the burning of fossil fuels, humanity is performing an extremely large-scale — and very uncontrolled — experiment. In the Amazon rainforest, researchers are trying to get a handle on the implications of those greenhouse gases in a large experiment of their own.

The project, called AmazonFACE, aims to amp up the carbon dioxide concentration in parts of the world's largest tropical forest basin to understand the impacts of elevated CO2 on the "lungs of the planet."

FACE stands for "Free-Air Carbon Dioxide Enrichment." The experiment consists of 12 observational arrays in six 98-foot-diameter (30 m) plots: three at ambient carbon dioxide concentrations and three at higher concentrations. The highest concentration — 615 parts per million — is predicted to be reached by the 2070s under a middle-of-the-road pathway to climate mitigation in which countries make slow and uneven progress toward sustainability.

Each plot contains around 400 plant species and many more specimens of fungus and soil microbes — a full ecosystem. As carbon dioxide increases, plants photosynthesize more quickly and release less water from their leaves, explained Beto Quesada, executive manager of the project and a researcher at the National Institute for Amazonian Research. This could help protect the forest from the impacts of climate change, which is expected to bring drought to the Amazon region.

But the balance between these two processes and the tipping point between a healthy forest and a collapsing ecosystem are unknown, said David Lapola, the project's scientific coordinator and a researcher at the Center for Meteorological and Climatic Research Applied to Agriculture of the University of Campinas (UNICAMP) in Brazil.

"We'll be trying to solve one of the biggest uncertainties with regard to the future of the Amazon forest in light of climate change," Lapola told Live Science.

The researchers will measure the impact of the extra CO2 on plant physiology, including whether plants in a carbon-rich atmosphere add temporary structures, like leaves, or more permanent features, such as wood. This is important to study because wood locks up carbon for centuries, whereas carbon used to grow leaves reenters the environment within a year or two. The experiment is expected to run for at least a decade.

"It is an ecosystem-scale experiment," Quesada said, "but it's much more than that. It goes to the social, economical and environmental impacts that the loss of the rainforest will have."

A truly massive carbon capture facility

According to the Intergovernmental Panel on Climate Change , humanity doesn't just need to stop releasing carbon dioxide into the atmosphere to avoid raising the global temperature more than 1.5 C (2.7 F) above preindustrial levels. We also have to pull carbon back out of the air.

By 2050, 6 to 10 gigatons of carbon equivalent need to be removed to avoid hitting the warming threshold set by the Paris Agreement. There are many options for carbon sequestration, such as capturing industrial waste streams and burying biomass. But the first-ever commercial-scale marine carbon-capture facility is aiming to remove carbon right from the ocean.

The ocean naturally takes up carbon from the atmosphere, but it can't absorb it fast enough to make a climatic difference on the scale of a human life span. The carbon-capture company Equatic is aiming to accelerate that timeline.

"Equatic's commercial plant takes five minutes to remove one tonne of carbon by pumping seawater in, running an electrical current through, and then contacting the seawater with a stream of air from the atmosphere," Edward Sanders, Equatic's chief operating officer, told Live Science in an email. "An equivalent area of open ocean takes 12 months to remove that one tonne of carbon."

The chemical process that removes the carbon from the seawater also creates hydrogen, a chemical that's for many industries and can be burned as fuel to power 40% of the energy costs of the carbon-capture process. The carbon is then sequestered as bicarbonate, the same material found in seashells, which will keep the carbon out of the atmosphere for up to 10,000 years. This bicarbonate can be put back in the sea or be used in fertilizers. It can also serve as a building material in coastal restoration, Sanders said.

Similar experiments have been done on a pilot scale, but Equatic's facility in Quebec will aim to sequester 120,700 tons (109,500 metric tons) of carbon per year starting in 2027. It will be the first commercial-scale attempt to make a dent in the greenhouse gas overload in the atmosphere via the oceans.

A world of babies

How do babies learn language? When do they understand gestures? Are they hardwired to imitate adults? All of these questions are tough to answer, because babies are challenging research subjects, prone to crying and unexpected naps.

The difficulty of recruiting busy, exhausted parents and their often-uncooperative infants to do research studies led to the birth of ManyBabies. This global collaboration of researchers from over 50 nations pools smaller-scale studies of infant development into large sample sizes — often thousands of babies.

The research collaboration has found that infants really do prefer baby talk to adult-style speech, suggesting that the natural tendency to coo about a baby's toesie-woesies is an evolutionary adaptation that helps them learn language. Researchers are now studying how babies develop an understanding of other people's beliefs — a skill known as theory of mind — and trying to figure out when they learn to apply abstract rules to situations. They're also developing new methods, such as eye-tracking technology and noninvasive brain imaging techniques, to find out what infants are learning.

A city-size chunk of Antarctic ice

Neutrinos are often called "ghost particles" because the nearly massless particles barely interact as they pass through matter. Because they rarely perturb other matter, they're difficult to detect. But finding neutrinos from distant cosmic sources can be a way to observe and analyze high-energy environments such as pulsars, supernovas and black holes.

"We need a very big target, such as a billion tons of material, to have a fighting chance to — once in a while — catch some of them," said Albrecht Karle, a professor of physics at the University of Wisconsin-Madison.

Those billions of tons of material come from a cubic kilome ter of ice at the South Pole. Karle is the associate director of science and instrumentation at the IceCube Neutrino Observatory, which is remarkable in both its size and remoteness. IceCube consists of a series of optical detectors on strings, running through holes drilled 4,800 to 8,000 feet (1,450 to 2,450 meters) into the Antarctic ice.

When a neutrino interacts with the ice, it creates other particles that emit tiny flashes of light. The sensors detect this light and can measure its wavelength to reveal the flavor of neutrino and its source. (That's why a transparent medium, such as ice, is important, Karle told Live Science — the material needs to be clear for the light to be detectable.)

IceCube data has allowed scientists to make the first map of the Milky Way using matter, not just light. The observatory has also revealed strange, high-energy cosmic rays with no easy explanation. And Karle and his colleagues have plans to go even bigger. They're currently drafting a plan for IceCube Gen-2, which would expand the current observatory to eight times its current size, with a 200-square-mile (500 square kilometers) radio detector array to amplify incoming neutrinos. This would massively increase the sensitivity of the detector and allow better classification of the neutrinos that pass through it, Karle said.

A globe-spanning psychology study

The COVID-19 pandemic was its own global experiment, albeit one with a massive number of uncontrolled variables. Psychologists took advantage of this shared global experience with some of the largest psych studies of all time.

One, with almost 50,000 participants, found that people with a stronger national identity responded more cooperatively with public health efforts. Across 67 countries, people with a stronger feeling of identification with their nation were more likely than those with a weaker sense to stay put during quarantine, to support public health policies, and to say they engaged in social distancing and stricter physical hygiene after the onset of the pandemic. National identity is about a sense of collective belonging and mutual cooperation, the authors noted. This is different from beliefs about national superiority, which is a belief that one's country is better than others.

"These results are consistent with the social psychological literature on the benefits of identifying with one's social groups," the authors wrote. "They also underscore a potential benefit of [national identity], which might be salient during a national or global health crisis."

Another major COVID-era study, with nearly 27,000 participants, found that messages emphasizing autonomy encouraged adherence to social distancing recommendations. The study tested different social distancing messaging strategies across 89 countries and found that those that focused on personal autonomy and the value of thoughtful choices were more effective than messages that emphasized shame and pressure.

A centuries-long plant experiment

Small in size but big in duration, Michigan State University botanist William James Beal's seed viability experiment has been running continuously since 1879. The goal of this experiment is to find out how long seeds of different plants can lie dormant before sprouting. To find out, Beal buried bottles of seeds from 23 different plants 3 feet
(0.9 m) deep in an undisturbed (and secret) location so they could not sprout. He started unearthing bottles in five-year increments — a gap that was eventually stretched to every 10 years.

Incredibly, the experiment is still running — and now, researchers are stretching the gap between bottle openings to 20 years, because seeds just keep sprouting. The last bottles were opened in 2021, and the next set will get their time to shine in 2040. The findings have implications for plant evolution and seed germination and might be useful for understanding the process of habitat restoration and seed banking, or saving seeds for potential use in the distant future.

The plan is to keep the experiment running until 2100, according to Michigan State. Will that be enough time to find the maximum age any of their seeds can sit before sprouting? Probably not; plants have sprouted from seeds up to 2,000 years old.

China's monstrously huge radio telescope

China's Five-hundred-meter Aperture Spherical Telescope (FAST) array is the world's largest single-dish radio telescope, at 1,640 feet in diameter. Holding up the dish are 328-foot (100 m) steel towers and 6,670 cables. Now, a new phase of construction is adding 24 131-foot (40 m) movable radio telescopes to the facility.

The array sits in a natural depression called Dawodang in the rugged topography of China's Guizhou province. This shields it from electromagnetic interference from human sources and increases its sensitivity to cosmic radio signals. The goal, according to the Chinese Academy of Sciences (CAS), is to use the telescope's sensitivity to conduct large-scale surveys of the universe.

FAST started operating at full capacity in 2020 and has already discovered more than 200 pulsars, which are rotating neutron stars that emit regular pulses of electromagnetic radiation. These include the pulsar PSR J0318+0253, which, at 4,000 light-years away and with a rotation period of less than 10 milliseconds, is one of the faintest radio millisecond pulsars ever found, according to CAS.

A telescope network that spans most of the world

What could you see with a telescope the size of the world? Well, the black hole at the heart of the Milky Way, for one thing.

The Event Horizon Telescope (EHT) is a network of radio telescopes stretching from Greenland to the South Pole (north to south) and from Spain to Hawaii (east to west). The exact number of observatories in the EHT shifts with time (it was 11 as of 2021), and new telescopes will be added in the future — including one planned for the Canary Islands.

These observatories work together to detect faint radio signals associated with black holes. This collaboration generated the first-ever view of a black hole, including the contours of the event horizon, the boundary through which no light or matter can escape. Scientists have also seen the mesmerizing swirl of the black hole at the center of our own galaxy and observed giant electromagnetic jets shooting from the supermassive black hole at the heart of the galaxy Perseus A. Recently, they peered into the heart of a quasar, a superluminous galactic core powered by a massive black hole.

The EHT needs to be large because it relies on the ability to observe the universe continuously over eight- to 14-hour stretches from several angles, according to the Black Hole Partnerships for International Research and Education, a collaboration that develops the algorithms used by the telescope. These algorithms also rely on Earth's rotation to overlap observations, allowing researchers to combine images from numerous telescopes. Only then can they peer into some of the biggest, yet hardest-to-see phenomena in the universe.