10 Science Experiments That Changed the World

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Stanley Milgram's 1960s obedience experiments qualify as some of the most famous and controversial science experiments. Milgram wanted to know how far ordinary people would go in delivering painful shocks to a peer, when commanded to do so by a scientific authority. This is his experiment:

1. Milgram recruited volunteers -- ordinary residents -- to deliver the shocks. He recruited actors to be the subjects who would receive the shocks. The final player was the authority figure, a scientist who would remain in the room for the study's duration.

2. The authority figure began each experiment by showing the unknowing volunteer how to use the mock shock machine. The machine allowed volunteers to deliver up to 450 volts, a shock labeled as highly dangerous.

3. Next, the scientist told the volunteers they were testing to see how shocks might improve word association recall. He instructed the volunteers to shock learners (actors) for wrong answers and to raise the voltage as the experiment progressed.

4. The learners cried out whenever they received a shock. At about 150 volts, they would demand to be freed. The scientist encouraged volunteers to continue delivering shocks no matter how agitated the learners became.

5. Some volunteers stopped at about 150 volts, but most kept going until they reached the maximum shock level of 450 volts.

Many people questioned the ethics of the experiments, but the results were fascinating. Milgram showed that average people will inflict a lot of pain on an undeserving victim simply because an authority commands them to do so.

• • Darvins flowers

Darwin used the data he collected about orchids and their insect pollinators to reinforce his theory of natural selection. He argued that cross-pollination produced orchids more fit to survive than orchids produced by self-pollination, a form of inbreeding that reduces genetic diversity and, ultimately, survivability of a species. And so three years after he first described natural selection in "On the Origin of Species," Darwin bolstered the modern framework of evolution with a few flower experiments.Read more

• Decoding DNA

Physicist Ernest Rutherford had already won a Nobel Prize in 1908 for his radioactivity work when he began some experiments that would reveal the structure of the atom. They relied on his previous research showing that radioactivity consisted of two types of rays -- alpha and beta rays. Rutherford and Hans Geiger had determined that alpha rays were streams of positively charged particles.

James Watson and Francis Crick get the credit for unlocking the mystery of DNA, but their discovery depended heavily on the work of others, like Alfred Hershey and Martha Chase, who, in 1952, conducted a now-famous experiment that identified DNA as the molecule responsible for heredity. Hershey and Chase worked with a type of virus known as a bacteriophage. Such a virus, made up of a protein coat surrounding a strand of DNA, infects a bacteria cell, programs the cell to make more viruses, then kills the cell to release the newly made viruses. The two knew this, but they didn't know which component -- protein or DNA -- was responsible until their ingenious "blender" experiment directed them to DNA's nucleic acids.After Hershey and Chase's experiment, scientists like Rosalind Franklin focused on DNA and rushed to decipher its molecular structure. Franklin used a technique called X-ray diffraction to study DNA. It involves shooting X-rays at aligned fibers of purified DNA. As the X-rays interact with the molecule, they are diffracted, or bent, off their original course. When allowed to strike a photographic plate, the diffracted X-rays form a pattern that's unique to the molecule being analyzed. Franklin's famous photo of DNA shows an X-shaped pattern that Watson and Crick knew was a signature of a helical (or spiral-shaped) molecule. They could also determine the width of the helix from looking at Franklin's image. The width suggested that two strands made up the molecule, leading to the double-helix shape we all take for granted today.

• • The first vaccination

• • • • • Did you know that Ivan Pavlov, the Russian-born physiologist and chemist responsible for the salivating-dogs experiment, wasn't interested in psychology or behavior? The research topics that interested him most were digestion and blood circulation. In fact, he was studying canine digestion when he discovered what we know today as classical conditioning.Read more

• • • • Edward Jenner, a British physician, set out to study smallpox and to develop a viable treatment. The genesis of his experiments was an observation that dairymaids living in his hometown often became infected with cowpox, a nonlethal disease similar to smallpox. Dairymaids who caught cowpox seemed to be protected from smallpox infection, so in 1796, Jenner decided to see if he could confer immunity to smallpox by infecting someone with cowpox on purpose. That someone was a young boy by the name of James Phipps. Jenner made cuts on Phipps' arms and then inserted some fluid from the cowpox sores of a local dairymaid named Sarah Nelmes. Phipps subsequently contracted cowpox and recovered. Forty-eight days later, Jenner exposed the boy to smallpox, only to find that the boy was immune.

      • Proofpozitive of the atomic nucleus

      • Physicist Ernest Rutherford had already won a Nobel Prizein 1908 for his radioactivity work when he began some experiments that would reveal the structure of the atom. They relied on his previous research showing that radioactivity consisted of two types of rays -- alpha and beta rays. Rutherford and Hans Geiger had determined that alpha rays were streams of positively charged particles.Read more

• • • • X-ray Vision

      • We spoke of Rosalind Franklin's X-ray diffraction studies earlier, but her work owed much to Dorothy Crowfoot Hodgkin, one of only three women ever to win the Nobel Prize in chemistry. In 1945, Hodgkin was considered the world's foremost practitioner of X-ray diffraction techniques, so it's not surprising that she eventually revealed the structure of one of medicine's most important chemicals -- penicillin. Alexander Fleming had discovered the bacteria-killing substance in 1928, but scientists struggled to purify the chemical in order to develop an effective treatment. By mapping out the 3-D arrangement of penicillin's atoms, Hodgkin opened new avenues for creating and developing semisynthetic derivatives of penicillin, revolutionizing how doctors fought infections.Read more

        • Primordial soup

      • U.S. chemists Harold C. Urey and Stanley Miller set out to test the Oparin-Haldane hypothesis in 1953. They reproduced the early atmosphere of Earth by creating a carefully controlled, closed system. The ocean was a warmed flask of water. As water vapor rose from the water and collected in another chamber, Urey and Miller introduced hydrogen, methane and ammonia to simulate the oxygen-free atmosphere. Then they discharged sparks, representing lightning, into the mixture of gases. Finally, a condenser cooled the gases into a liquid they collected for analysis.

      • After a week, Urey and Miller had astonishing results: Organic compounds were abundant in the cooled liquid. Most notably, Miller found several amino acids, including glycine, alanine and glutamic acid. Amino acids are the building blocks of proteins, which themselves are the key ingredients of both cellular structures and cellular enzymes responsible for important chemical reactions. Urey and Miller concluded that organic molecules could form in an oxygen-free atmosphere and that the simplest of living things might not be far behind.

• • • • Making light

      • When the 19th century dawned, light

      •  

      • remained a mystery that inspired several

      •  fascinating experiments, most notably

      •  Thomas Young's "double-slit

      •  experiment" that told us light behaved as

      •  a wave, not as a particle. But we still

      •  didn't know how fast it traveled.

      • In 1878, physics instructor A.A. Michelson devised an experiment to calculate the speed of light and prove that it was a finite, measurable quantity. Here's what he did:

• • • 1. First, he placed two mirrors far apart on a seawall near campus, aligning them so that light striking one mirror would reflect back and strike the second. He measured the distance between the two mirrors and found they were 1,986.23 feet (605.4029 meters) apart.

      2. Next, Michelson used a steam-powered blower to spin one of the mirrors at 256 revolutions per second. The other mirror remained stationary.

      3. Using a lens, he focused a beam of light onto the stationary mirror. When the light struck the stationary mirror, it bounced back toward the rotating mirror, where Michelson had placed an observation screen. Because the second mirror was moving, the returning light beam was deflected slightly.

      4. When Michelson measured the deflection, he found it to be 5.236 inches (133 millimeters).

      5. Using this data, Michelson calculated the speed of light to be 186,380 miles per second (299,949.53 kilometers per second).

• • • • The accepted value for the speed of light today is 186,282.397 miles per second. Michelson's measurement was amazingly accurate. More important, scientists had a more accurate picture of light and a foundation upon which to build the theories of quantum mechanics and r

• • • • • Revealing radiation

• • • • The year 1897 was momentous for Marie Curie. Her first child with husband Pierre was born and, a few weeks later, she went looking for a subject for a doctoral thesis. She eventually decided to study the "uranium rays," first described by Henri Becquerel. Becquerel had discovered these rays accidentally when he left uranium salts in a dark room and returned to find that they had exposed a photographic plate. Marie Curie chose to study these mysterious rays and to determine if other elements gave off similar emissions.Read more