What are the Four Fundamental Forces of Nature?
Comprehensive Final Exam Learning Objectives (All previous Objectives including the ones below) • Describe the general structure of the Milky Way Galaxy. • Where is the Sun located within our Galaxy? • How do halo stars differ from disk stars? • What is the galaxy made of? • What creates the 21cm radio emission and why is it important? • What are emission, reflection and absorption nebulae? • Briefly describe the Galaxys star-gas-star cycle. • How does observing in different wavelengths allow us to study different parts of the interstellar medium and find out what is happening in • different regions of the Galaxy? • How do stellar orbits in the disk differ from those in the halo? • Why are spiral arms bright and why do they maintain their shape? • How do we determine Galactic mass from stellar orbits? • What is the significance of a rotation curve that is flat at large distances from the Galactic center? • What lies in the center of our Galaxy? • What is the evidence for the existence
Since the early 20th century, physicists have recognized four fundamental forces, or interactions, which encompass all known phenomena in nature. Three out of four have been characterized rigorously and mathematically by the Standard Model, formulated in the early 1970s. The four forces are the strong nuclear force (also known as the color force), the weak nuclear force (mediates beta decay), the electromagnetic force, and gravity. At very high energies, the weak nuclear force and the electromagnetic force unite (start behaving interchangeably), while at still higher forces, it is believed that the strong force unites with the electroweak, and finally, the strong-electroweak force unites with gravity. It is believed that all four fundamental forces were united an instant after the Big Bang, in the earliest stages of the universe’s formation. The strong nuclear force holds together protons and neutrons in the atomic nucleus. More specifically, it is mediated by the exchange of gluons be
As you sit in front of your computer reading this article, you may be unaware of the many forces acting upon you. A force is defined as a push or pull that changes an object’s state of motion or causes the object to deform. Newton defined a force as anything that caused an object to accelerate — F = ma, where F is force, m is mass and a is acceleration. The familiar force of gravity pulls you down into your seat, toward the Earth’s center. You feel it as your weight. Why don’t you fall through your seat? Well, another force, electromagnetism, holds the atoms of your seat together, preventing your atoms from intruding on those of your seat. Electromagnetic interactions in your computer monitor are also responsible for generating light that allows you to read the screen. Gravity and electromagnetism are just two of the four fundamental forces of nature, specifical
