The Conventional Universe
We can see to the edge of all light. This is our light horizon, lying approximately fourteen billion light years away, in every direction. A short distance beyond it lies the Big Bang, which could be considered being the very edge of space, as anything further is contained within the depths of the Big Bang itself. The Big Bang was once right here, when it lay right here, long, long ago. Right now, that edge is still present, but no longer present right here anymore. Rather, although it still lies at the Big Bang, as always, that edge lies where the Big Bang is located right now, far, far away, in every three-dimensional direction, from here where it was once, then, long, long ago. (See "Riding a Beam of Light"" Article, two articles back.)
In the meantime, between then here long ago, and now there far away, approximately fourteen billion years have elapsed. Being the same Big Bang here then, as there now, puts the Big Bang at two very distant regions, and logically, at every point in between these two regions as well, during the entire course of the Big Bang's displacement from the one distance very near to us, here, then, to the other distance, very far from us, there, where the Big Bang lies now. All the while, the Big Bang has been happening, unceasingly, during the aforementioned approximately fourteen billion years, just as it constantly happens always, with each and every moment that passes, and, just as it will continue to happen, again, unceasingly, for eons of moments to come. As it constantly happens, one individual moment followed by another, the Big Bang constantly recedes from us in every direction at once, at nearly the speed of light.
Giving it a little thought, one realizes that our equally distant displacement in three spatial directions from the Big Bang now, is somewhat analogous to being at the center of a sphere in three dimensions, like, for example, at the center of the sphere of a soccer ball, with the Big Bang forming the surface of that sphere like the inflated skin of a soccer ball would - ignoring of course, temporarily, that the Big Bang is very small, while the skin of a soccer ball is very big compared to its tiny center. Taking this one step further by translating the Big Bang's approximately fourteen billion light year spatial displacement into elapsed years across time, we find ourselves here, now, at an equally distant displacement in a fourth temporal direction, from time's edge also, being approximately fourteen billion years removed from the Big Bang here then, and by implication, equivalently distant by any equal combined space and time displacement thereof. In other words, we seem to find ourselves, quite inescapably, in the center of what might be interpreted being a sphere in four directions, like a soccer ball with an additional dimension of depth. But, what does that mean? What would a four-dimensional soccer ball physically be? How would it differ from a three-dimensional one.
Most of us ordinarily spend our lives imagining shapes purely in three dimensions, or less, exclusively. So, how precisely does a round sphere manifest itself in the greater complexity that four dimensions allow, given that we are normally confined to thinking of a sphere in three dimensions alone and on the whole have no exposure at all to hyper-dimensional shapes of any kind? How do we imagine conceptually, the universe in the four dimensions that it really occupies, minimally, without reverting to the far simpler image of celestial bodies afloat in a an vast three-dimensional extent, nested within serially grander ones beyond our light horizon, ad infinitum "unto mysterium?" To answer, we must ask yet another question first, about exactness and precision. It is a very necessary question to ask, as it will answer the original question of how round in four dimensions manifests itself in our seemingly three-dimensional world.
The question we must ask is this: When we use the word universe, what is it exactly that we mean with our use of the term? We must ask this question of exact meaning, because the precise association that applies to the term "universe" may vary, according to just what we intend with our use of the word, and furthermore, may require specification stringent enough to fit rigorous scientific standards. The simple answer that the universe consists of space and time in every direction, along with all that fills it, although well enough as a general reference, may not be as precise a meaning as we might imagine it being, because it may not express the strictness that the rigors of science predicate. Trivial as it may seem, an accurate understanding of nature, as expressed in its physics, even in purely conceptual descriptions exclusive of math, requires an exact understanding with respect to an equally precise meaning for the term universe, or we are left with little more than the vague illusion of understanding in place of its actuality.
Now, in order to clarify in the precise terms of science just what is meant by the term universe, it is wise to start by considering the most recent evolution of the term, with respect to an important discovery available to us, that Einstein did not have available to him at the time he was using the word; although this important discovery seems to have only barely escaped his notice. Remarkably, it was he himself who identified the concept that ultimately led to this great discovery, as expressed in a value that he introduced into his equations, called the cosmological constant.
Apparently, Einstein added the cosmological constant to his relativity equations, setting its value appropriately so that these equations would yield a simple, static, 'flat' universe, which they would not have, without incorporating it, and further, fixing its value immutably. This was an image of the universe consistent with the widespread, conventional notions of Einstein's era. Then, the conventional picture of the universe was pretty simple. It included only our single galaxy alone, suspended eternally, in a flat otherwise empty space extending infinitely in every direction. Consistent with long-standing tradition, conventional notions left any questions of either origin or destiny, altogether beyond the realm of scientific inquiry. To the contrary, astronomical observations and scientific scrutiny of them would eventually demonstrate that long-standing tradition and common convention were not well founded at all in nature's far-better-established realities.
To his ultimate regret, by embracing the ease of the simplistic, convention of the day, to the extent of adjusting his equations accordingly, Einstein mistakenly failed to recognize, that is, failed to recognize before someone else did first, that a static universe was a universe that could simply never be. Upon review of Einstein's adjustment to his relativity equations, a man named Friedmann proposed that the then common notion of a finite, static universe, lying eternally in an infinite and flat, space, without any scientific consideration for finite temporal extent with respect to either origin or destiny, just like Einstein's specification of a cosmological constant that results in such a simple universe, required infinite precision, and, because of this, was plainly impossible. This left solely dynamic solutions as viable possibilities in nature, eliminating all hope of any unending permanence for the cosmos. According to Friedmann, space and time were no more flat and infinite than their measures were universally absolute for all (a direct contradiction to relativity). In a word, our universe HAD to be dynamic. And so it was, as subsequent scientific exploration would demonstrate, conclusively.
Not long after Friedmann proposed a dynamic universe as the only kind of universe possible, an astronomer named Edwin Hubble validated Friedmann's conclusions through his observations of what were then called nebulae. Using a star of known luminosity (brightness) as a "standard candle," Hubble determined that these nebulae were actually other galaxies, just like our own Milky Way is a galaxy. With this achievement, Hubble secured his name as legend in science, with what was among the greatest revelations ever made in astronomy. Hubble had discovered the existence of other galaxies besides our own. In so doing, he revealed the dynamic character of our universe, irrefutably.
What, exactly, it means for the universe to be dynamic is the subject of the next science article, and the two that follow it. It is not as simple a notion as it might, at first, seem to be.