Gravity and Our Earliest Beginnings

The our in the title should more accurately be the universe’s earliest beginnings because we are relatively newcomers to the scene. Everyone has heard that everything we see today--all matter, energy, space and time--sprang into existence some 13 billion years ago. The event was referred to as the Big Bang by a British scientist who was ridiculing the idea, and the name has stuck. Although difficult for us to fathom, the evidence for the Big Bang is very solid. Who says nature has to be mindful of human sensibilities and logic. The Big Bang was an unbelievably high temperature, high energy event that began from a single point and rapidly expanded. As the initial energy ballooned outward creating more and more space, it slowly cooled. Matter began to crystallize out as simple atoms of primarily the gases hydrogen, and helium. Matter can be thought of as frozen energy, and the two are equivalent and interchangeable as Einstein has shown. Notably in this early universe, there was little of the stuff of which we or our Earth are made. These elements had to be cooked in stars much later in time.

Most popular accounts of the Big Bang rarely mention that certain other things were also created at this time. Namely, the rules of the game. These took the form of four forces that were to shape and control the newly formed universe for the rest of time. Scientists refer to them as gravity, electromagnetism, the strong and weak nuclear forces. These forces determine everything that happens in our physical world. Why they exist and act as they do is not clear--they just are. Although all are active in our universe, only two are normally encountered by we humans. They are gravity and electromagnetism.

Gravity holds our feet to the Earth, gives things weight, causes rain to fall, powers the cycle of tides, pulls the stuff of planets and stars toward their centers to form spheres, and holds planets in orbit around the Sun. Gravity rules on the large scale when massive bodies like planets stars, and galaxies are involved. Electromagnetism, on the other hand, rules on the small scale. It is the electrical force that binds atoms and molecules together to form all the natural and man made things we know including our own bodies. This force is responsible for all the properties of things such as their shape, solidity, texture, and color. Of the four forces, gravity is the weakest. The fact that we walk erect against the Earth’s gravity pulling us down testifies to the fact that the electromagnetic force is much, much stronger.

Nevertheless, if it were not for the influence of gravity in the post Big Bang era, our universe would consist of nothing more than a homogenous mixture of essentially hydrogen and helium expanding probably forever. No stars, no planets, no people would have ever come about. Luckily, at least for us, the universe did not remain homogenous. Instead, regions developed that were cooler and more dense. These regions would attract more matter through their greater gravitational pull, increasing the density even more. Over eons of time the universe began to break up into ever growing individual clouds of hydrogen. As they became increasingly more massive, their gravity began to pull the clouds into a spherical shape. Their internal temperatures began to rise due to the compression of the gas by gravity. When their core temperatures reached some millions of degrees, a nuclear fusion of hydrogen into helium was ignited with the release of tremendous amounts of radiant energy in all forms including visible light. The first stars were born! This set off a new era in the expanding universe that resulted in the creation of all the other chemical elements through the birth, evolution and death of stars, and the subsequent birth of new stars from the ashes of the old. The coalescing of these elements formed planets orbiting many stars, and at least around one third generation star, the Sun, life forms began, evolved, and culminated in humans that figured all this out.

Canned Sunlight

The concept of energy has always fascinated me, and this web log will discuss aspects of it often. Everyone realizes that the ultimate source of energy for most of mankind’s activities on Earth is our Sun. The exceptions are nuclear energy and hydrothermal energy which results from radioactivity deep within the Earth. A friend of mine who has no knowledge of science or any interest in it, made a comment while sitting before my fireplace "those flames are ancient sunlight being released from the wood." I found it a remarkable observation coming from him, and, of course, he was absolutely right. All our fossil fuels, coal, wood, petroleum, and natural gas, result from solar energy stored in now fossilized ancient plants. These plants used solar energy to combine the simple ingredients of carbon dioxide from the air and water from the soil into more complex hydrocarbon molecules that make up our fossil fuels. Energy must be used to create more organized things (hydrocarbons), and is released again when these organized things are broken down again by combustion. This is nature’s way, and we call it the law of conservation of energy.

Getting back to the Sun. Why is it hot and where did the energy which it so freely radiates come from? If you are science savvy, your immediate answer might be the nuclear fusion in the Sun’s core. Yes, there is a controlled hydrogen bomb like explosion going on continuously in the Sun’s center. Atoms of hydrogen are fused into those of helium with the release of lots of energy. In fact, this nuclear fusion actually keeps the Sun cool. The Sun, like all stars, condensed out of an immense, diffuse cloud of cool gas. As the cloud collapsed toward its center under the pull of its own gravity, the potential energy of the gas is converted into increasing velocity of its atoms resulting in higher and higher temperatures. Eventually, the core temperature becomes hot enough to kindle thermonuclear reactions. Now, the radiation pressure from nuclear burning balances the force of gravity and stops the Sun from contracting further--preventing it from getting any hotter. So the initial gravitational collapse of the Sun is what makes it hot.