Modern physics

Modern physics generally refers to developments in the science of physics made after the beginning of the twentieth century. Prior to this period, work in the scientific field was known as classical physics. Classical physics is the study of matter and energy on an everyday scale of observation. It is concerned with the works of physicists such as Isaac Newton and James Clerk Maxwell, as well as others. Modern physics deals with the study of matter and energy at very high speeds or on very large or small scales. The two main branches of modern physics are considered to be quantum physics and relativity. Quantum physics is based on the work of many scientists and examines matter on the atomic and subatomic levels. Relativity grew from the work of physicist Albert Einstein; it studies the effects of gravity and the speed of light on time and space.

Background

The ancient Greeks were among the first of the world's cultures to study the natural world in a scientific manner. The term physics is derived from phusis, the Greek word for "nature." Rather than relying on religious explanations, Greek philosophers tried to answer questions using reasoning and logic. While many of their results may have been incorrect, the process of scientific reasoning they introduced would go on to influence future generations.

By the sixteenth and seventeenth centuries, scientists began to break from the centuries-old beliefs on how the natural world worked and developed new theories based on scientific experimentation and observation. The most influential scientific figure of the period was British physicist Isaac Newton. Newton developed many groundbreaking theories on light, mathematics, and gravity. His most famous work was his three laws of motion that he published in 1687. The laws dealt with the physics of moving objects and how outside forces interact and influence that movement. Newton's work was so influential that the classical physics he helped develop is sometimes called Newtonian physics.

Other milestones in classical physics included Scottish physicist James Clerk Maxwell's work with electromagnetic radiation—a form of energy caused by the interaction of electric and magnetic fields. Thermodynamics is a field of study dealing with heat energy, temperature, and conductivity. Acoustics is a type of physics that studies the properties of sound, while optics is the study of light.

Overview

By the nineteenth century, scientists had determined that the chemical elements that make up matter were composed of particles called atoms. In the 1890s, further discoveries revealed that atoms were made up of even smaller particles. While investigating the properties of matter and energy on the subatomic level, German physicist Max Planck discovered that the theories set forth by classical physics did not work very well. For years, scientists had believed that energy flowed evenly in the form of a wave. Planck's work found that energy also acted as a particle, moving in individual packets he called quanta—the plural form of the Latin quantum, meaning "how much" or "how great."

Quantum physics is an often complicated field that is defined more by probabilities than scientific certainty. Among its main findings is that matter and energy display properties of both waves and particles. For example, light—which is a form of electromagnetic energy—is made up of particles known as photons. Photons move in waves that can change frequency depending on the energy level of the photon.

Quantum physics also allowed scientists to explore the seemingly strange world of subatomic particles. The electrons, protons, and neutrons that make up atoms are themselves made up of smaller, more mysterious particles. Some of these particles can exist in more than one physical location at the same time; they can also move from one place to another without traveling through the space in between. These phenomena, however, can only be seen indirectly. If scientists actually try to observe the particles, the effect ends in what scientists call wave function collapse. These discoveries had led some physicists to speculate in the existence of parallel universes or alternate realities.

In 1905, German-born physicist Albert Einstein published a paper that supported the theory that light traveled as small packets of energy. It was another paper, however, that would make him one of the most famous scientists of the twentieth century. Einstein's theory on the effects of immense speed and gravity on space and time revolutionized science.

His theory of special relativity holds that the speed of light travels through space at a constant 186,000 miles per second (300,000 kilometers per second). Nothing can ever travel faster than the speed of light. For people traveling along with the light, the laws of physics would appear normal. Einstein theorized that time and space were not constants but changed depending on the motion of the observer. For example, time would appear to slow down for people traveling at speeds close to light. To observers in a stationary position, time would move at its normal pace. He illustrated this by imagining a set of twins. One twin stayed on Earth, while the other traveled near light speed. The Earth-bound twin would age at a normal rate, while the spacefaring twin would return having aged more slowly.

This theory led Einstein to develop the idea that physical space is made up of the normal three dimensions—width, length, and depth—and a fourth dimension, time. Special relativity also showed that mass and energy are related. Einstein demonstrated this with his famous equation E=mc², where energy (E) is equal to mass (m) times the speed of light (c) squared.

Einstein's theory made him instantly famous, but he was bothered by some inconsistencies in his work. His work was correct, but it did not take into account what would happen if an object was accelerating or experienced a strong gravitational field. He worked on these problems for a decade, and in 1915, he published his general theory of relativity. The theory stated that large gravitational objects would produce a distortion in the fabric of space-time, like an indent in a mattress if a bowling ball were placed on it. Massive accelerating objects, such as stars and black holes, would cause ripples in the fabric of space-time that would spread away from the source like waves on a pond. Large gravity sources could also bend light if it passed too close—a phenomenon known as gravitational lensing.

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