How do scientists achieve greatness? They must possess knowledge, of course. But they also need curiosity and imagination. They must question why the universe works as it does. Then they must think creatively to discover the answers.

Albert Einstein possessed both imagination and curiosity. He was also a genius. He was one of the greatest scientists who ever lived. But Einstein was a humanitarian as well. Throughout his career, he was outspoken about the social and political issues of the day. He opposed war and encouraged others to act peacefully.

What made Einstein so great? He was able to ask questions about the universe that no one else had thought of before. He questioned existing theories and overturned some of them. He was also able to provide answers and prove why his theories were correct.
Einstein’s field was physics. Physics is the study of matter and energy. Matter is anything that has weight and takes up space, as a solid, liquid, or gas. Energy is the ability of something to do work.

A person who studies physics is called a physicist. Albert Einstein developed many theories about matter and energy. His ideas involved the study of light, heat, sound, electricity, motion, and force. Einstein’s theories were hard for many people to understand. Even other scientists had trouble with them at first. Yet Einstein was able to show the world how they worked. Scientific experiments proved that his new ideas were correct. Other scientists began to use Einstein’s theories to solve many of the problems they were working on.

You might think Einstein’s genius would have made him conceited. Yet the opposite is true. Einstein was very modest. He once said, “I have no special talents.
I am only passionately curious.” He remained curious his entire life. He said:

“The important thing is not to stop questioning.”

At age 16, Einstein wrote an essay. It explained why he wanted to study math and physics theories. He wrote,

“There is a certain independence in the scientific profession which greatly pleases me."

After finishing high school, Einstein studied at the Polytechnic in Zurich and later the Federal Institute of Technology. There he learned about many theories of past scientists. Some scientists thought that the world ran entirely on atoms. An atom is the basic building block of matter. Atoms are tiny and you cannot see them with the naked eye. At this time, scientists thought that atoms worked together like parts of a machine. Others believed that the world operated on fluids. Yet the theory that interested Einstein most was that of electromagnetism. It was developed by James Maxwell.

Albert Einstein when he was young

He believed that everything in the world operated on electric forces and magnetism.
At the Institute, Einstein met a physics student named Mileva Marić. Later, they married and had three children.

After finishing school, Einstein was unable to find work as a science teacher. He worked instead as an assistant at a patent office in Switzerland. Einstein was glad that his job was not too demanding. He spent all his free time reading physics books and discussing his new ideas with friends. He also continued his studies.

He received a Ph.D. degree in physics in 1905.

The year 1905 was an important one for Einstein. Besides getting his degree, he had several major articles, or papers, published in a German science magazine. Each paper contained original ideas, or theories, that Einstein had developed. The first paper dealt with photoelectric light—electric current produced by light. The second dealt with the movement of particles in a liquid or gas. The third paper gained Einstein the most attention. It was on his now-famous theory of relativity. Einstein gained much respect for his published work. Eventually, he was able to land a teaching job at a university.

Einstein’s paper on photoelectric light was published in March, 1905. It discussed the photoelectric effect. The effect takes place when a light beam causes metal atoms to release electrons. Atoms consist of a nucleus surrounded by electrons. The electrons are tiny particles that move around the nucleus. In a photoelectric machine, the electrons turn into electric current. The machine produces the current when light shines on it. In his paper, Einstein set forth a new theory on what caused the photoelectric effect. At the time, most physicists believed that light consisted of electromagnetic waves. But Einstein disagreed. He claimed that light exists of particles of energy called quanta. Scientific experiments supported him.

Einstein was greatly praised for his new theory. It opened up an important new field of physics called quantum mechanics. In 1921, Einstein won the Nobel Prize in physics for his work on the photoelectric effect.

In May, 1905, Einstein’s second paper was published. In it, he explained something that had been an unsolved mystery until then. Years earlier, in 1827, a biologist named Robert Brown had noticed something strange. He watched microscopic particles that were suspended in a liquid. They moved in an irregular way. At the time, no one could explain the “dancing” particles. Their movement became known as Brownian 'motion.

Einstein carefully analyzed the moving particles. He applied a well-known theory at the time about kinetic energy. Kinetic energy is energy of motion. An object which has motion possesses kinetic energy. This theory said that heat was caused by constantly-moving atoms. Einstein put tiny but visible particles in a liquid. As he predicted, they “danced” in an irregular way because the liquid’s invisible atoms kept hitting them. Einstein’s experiment's proved the kinetic energy theory. His experiments led to more research on the movement of atoms.

It eventually helped to prove that atoms do exist.

Einstein’s third paper was published in June, 1905. It dealt with electromagnetism and motion. For hundreds of years, physicists had known that still objects could be measured the same way as objects moving at a constant speed. A box on a docked ship behaves the same way as a box on a sailing ship.

This is called the Principle of Relativity.

Years later, however, scientist James Maxwell developed a new theory. He said that light would not follow the Principle of Relativity. He felt that motion would affect the velocity, or speed, of light. Unfortunately, Maxwell was unable to prove his theory. All his experiments failed to show that the speed of light could ever vary.

Einstein believed that the Principle of Relativity applied to everything even light. In his paper, he wrote that constant motion does not affect the speed of light.

It seemed to most people that Maxwell’s theory contradicted the Principle of Relativity. Yet Einstein showed that the two really did not clash. Einstein did it by rethinking the concept of time. He called his new theory the special theory of relativity. It involved a new way of analyzing time and space. He was able to explain his theory so that other scientists understood and accepted it.

In September, 1905, Einstein expanded upon his theory of relativity. He said if an object gives off a certain amount of energy, then the mass of the object will decrease accordingly. Mass is the amount of matter that an object contains. Einstein expressed his new idea in a now-famous formula: E = mc^2. E stands for energy; m stands for mass; and c stands for the speed of light. Squared means multiplied by itself.

In plain English, Einstein’s formula meant this: Energy could be changed into mass, and mass could be changed into energy. At first, not all scientists thought that Einstein’s formula was true. However, over the years, it was proven to be correct. In 1933, scientists took a photograph that actually showed energy being changed into mass. In the photograph, an invisible particle of light carried energy that changed into mass. Two tiny particles were created from the energy.

Later, the reverse was also seen. Scientists broke apart an atom. The total mass of the individual pieces was less than the mass of the original atom. Where did the missing did the missing mass go? It turned into energy!

Over time, Einstein’s discovery had a great impact on the world. It led to a worldwide increase in energy production. That included electric energy made in nuclear power plants.

By 1909, Einstein was quite famous in the scientific world. He became a professor of physics in Switzerland. Later he taught at the German University in Austria-Hungary.
In 1914, Einstein moved to Germany. There he headed a physics research center. He continued to develop new physics theories. Among them was his general theory of relativity. Einstein believed that gravity affected time. He found that the strong pull of gravity on a clock made the clock run slower.

He claimed that gravity affected light as well. He said his theory could be proven by watching the sun’s gravity bend light rays. In 1919, scientists watched a solar eclipse. They saw that the sun’s gravity did indeed bend starlight. Einstein’s theory was true! In time, it led to the discovery of black holes. Those are parts of space where gravity is so strong that nothing—not even light—can escape it.

Einstein’s work and career were successful. However, his marriage was not. He and his wife Mileva divorced in 1919. That same year, Einstein married his cousin, Elsa. Einstein faced other difficulties. He lived in Germany, where the Nazi Party was growing. Anti-Jewish feelings were spreading across the nation. Einstein, who was Jewish, became the target of many verbal attacks. He was a public figure who sometimes received death threats. He began to feel unsafe in Germany. He left for a while and visited many other countries in Europe, Asia, and South America.

Eventually, Einstein returned to Germany. But when the Nazis took power there in 1933, Einstein decided to leave for good. He moved to the United States. He became a physics professor at the Institute for Advanced Study in Princeton, New Jersey. Later he became an American citizen. By the late 1930 s, Einstein was even more worried about the threat of Nazism. In August, 1939, he wrote a letter to President Franklin Roosevelt. In his letter he warned that German scientists might be trying to build an atomic bomb.

When World War II broke out the next month, Roosevelt took action. He ordered a top secret project code-named the Manhattan Project to build an atomic bomb. By 1945, the project was completed. The United States had produced the first atomic bomb. It was used that year to bring an end to World War II. During the project Einstein became very concerned about the use of atomic energy.

After the war, Einstein was even more concerned about the use of atomic energy. He saw how much destruction the first bomb had caused. He worried that other nations might build and use more atomic bombs. He worked to limit and control the use of atomic energy. He spoke on the radio and published many articles. He urged nations with nuclear weapons to destroy them.

Atomic bomb in Hiroshima 1945

Throughout his life, Einstein pursued his love of physics. In his final years, he continued to search for theories that would explain more about the universe. The theories he developed are used today and have changed our understanding of the universe.
Einstein wrote many books that explain his theories. He also wrote books on his personal and political beliefs. Although his efforts helped develop the atomic bomb, he believed in a ban on nuclear weapons. He spoke out against racism and took a stance on political issues. He lectured throughout America, Europe, and Asia. He received many awards from universities and organizations around the world. Despite his fame, Einstein remained a modest person. He said:

“I do not care for money...I do not crave praise. The only thing that gives me pleasure... is the appreciation of my fellow workers.”