The Big Bang – the First “Cosmic Event”
The universe is expanding. We know this because we can measure the rate at which all major structures in the universe are moving away from one another. It is a well studied and easily measured property of our universe (see Astronomers, Edwin Hubble). By going back in time, astronomers and physicists can identify a theoretical sequence of events leading to today’s universe. Most astronomers and physicists see the Big Bang theory as the logical beginning based on observations to date. By observing, measuring, and analyzing data collected over the past hundreds of years, scientists have developed a logical sequence of events leading backwards to the beginning of the universe. This is pretty heady stuff…from the knowledge of the past hundreds of years we think we know how it all began nearly 14,000 million years ago! It is definitely a theory only, but there are lots of experimental evidence to support the theories leading to it.
The beginning of the universe is now generally accepted as described by the Big Bang Theory. What is the Big Bang? Current science considers the Big Bang to be the beginning ….the First Moment… when all the substance of the universe consisted only of sub-atomic and atomic particles……and lots of energy, at a temperature of trillions of degrees! All the material of today’s universe evolved from a single point of pure energy! Think of it….no material, no stable matter. Nothing to put your hands on! Just elementary particles and an energy field! …a huge energy field….and at a very high temperature. It is hard to imagine such a time and place! From that moment, all we know of today evolved in accordance with the physical laws we know of or have theorized. It is important also to note that the Big Bang Theory requires an infinite density and temperature, which is consistent with Einstein’s General Theory of Relativity.
Cooling of the Universe began immediately after the Big Bang, as it expanded. The initial temperature was trillions of degrees. As the universe expanded to its present size this temperature dropped, until today when it is -270°C .
The chart to the right shows the timeline for the Big Bang Theory, currently held by today’s astrophysicists and scientists. The chart shows 3 phases for the formation of the universe. The first phase occurs within nanoseconds of the Big Bang, when all matter was in the form of sub-atomic particles and energy.
The second phase covers the next 300,000 years when the universe expanded/inflated. During this period there was no light and the extremely high temperatures from the beginning dropped as the inflation progressed.
At the beginning of the third phase the temperature had dropped sufficiently so that atoms could form and therefore light was possible. From this point the universe began to form the structures we know of today….stars, planets, galaxies, etc.
You are probably wondering right about now….”How the hell do they know that?” Good question. The answer lies in the experiments that these scientists have performed. The tools they use are big, expensive, and exotic….Particle Colliders. In order to test what happens in very hot, very dense environments, the scientists must create very hot, very dense environments. That is what the Particle Colliders do. The workhorse to date has been the Relativistic Heavy Ion Collider (RHIC). With this instrument, conditions approaching those that are thought to exist about 2 microseconds (μsec) after the Big Bang are created. Yes…at atomic nuclei levels, pressures as high as 15×1030 PSIG and temperatures of several trillions of degrees have been attained. The particles which exist at these conditions can be created and their properties measured. How to go further back in time to that Big Bang? Build bigger and better Colliders. The new Large Hadron Collider (LHC), located in France and Switzerland, is just the instrument. It is expected to reach densities several times larger than the RHIC and temperatures in excess of 10 trillion degrees. If successful this will allow scientists to investigate the conditions existing just 0.3 of a μsec after the Big Bang! Yes…this is definitely exotic science!
However, some physicists have recently developed the concept that there was a time before the Big Bang. This concept involves the idea that there was a universe before this one that had collapsed in on itself, to the point where the entire universe occupied a single, finite point in time and space at which point a “big bang” occurred. This alternate theory may be thought of as the Big Bounce. In this scenario the previous universe imploded to a point of finite density, at a given point in time and space, and then explodes to begin the expansion all over. The underlying basis for this concept is that a single point of infinite density (as required by the Big Bang Theory) is not possible, even though Einstein’s General Theory of Relativity requires it. Contrary to the General Theory of Relativity, recent theories of quantum theory of gravity provide for a limit to the density of energy and matter. This limit would then require the present universe to have begun with a finite beginning. The relevant question then is “how did this energy and matter get to that point?”. One possible answer would suggest some sort of process for the accumulation of material, such as a collapse of a previous universe. So expect more theories and adjustments to define this initial state for the Big Bang.
In any event, the universe we know of began with a bang…..and it proceeded to expand and continues to this day. There is a fine point of the Big Bang theory regarding the expansion of the universe…..from the first moment, the universe expanded…it did not expand into something, rather the universe itself simply expanded. There was no edge to the universe as it expanded, nor was there a central point from which the expansion began. The universe simply was the universe and it expanded itself. Yes, this concept is a bit mind-bending because it requires one to visualize a space not only empty (in the truest sense of the word) but also a place which is not a place…..irrelevant! I don’t know about you, but I’ve got a little problem getting my mind around that concept….
So the Big Bang occurred…as some very smart people tell us. Within the first 20 minutes, ¼ of the matter in the universe was converted to helium nuclei. Why helium and not hydrogen?
It was simply too hot for an electron to stick to a single proton, or any proton-neutron nuclei. But the formation of Helium was perfectly suited for this environment! In rapid succession, as the universe cooled slightly in the first few minutes, a proton and a neutron formed, then 2 protrons and a neutrons, then finally 2 protrons and 2 neutrons….a helium nucleus. But electrons could not attach to these nuclei because they had so much energy (high temperature). However, after some 300,000 years the universe cooled sufficiently for this helium nucleus to attract an electron and the first hydrogen atom was formed.
This is predicted by nuclear physics and confirmed by observations – even today ¼ of the universe is helium. The universe expanded and cooled for the next hundreds of thousands of years and not much changed. After half a million years or so, the temperature had dropped to 3,000°K and this allowed hydrogen molecules to form… the stuff stars are made of. This opened the door for the existence of molecules as stable matter and allowed the formation of stars and galaxies. And the formation of stars provided, for the first time, the means to produce elements heavier than hydrogen and helium, through the process of nuclear fusion.