We live in a universe of extremes, from vast distances, huge galaxy clusters and extreme energies to extremely tiny atomic and subatomic particles and infinitesimal energies. Living things, too, range from the huge to the microscopic, from the ages old to the ephemeral, from the powerful to the powerless in almost infinite forms and extreme complexity. Let’s take a tour of the wonders of our reality. Since the subject is so broad and complex, I will attempt to give you an appreciation of its wonders without bogging you down in any more details than necessary. Since some of the “facts” are still debated, I will stick to the status quo explanations for our tour.
Tour of the Universe
The universe is composed of vast stretches of empty space sparsely dotted with galaxies. Each galaxy is composed of billions to a trillion stars, some of which have planets, as well as copious amounts of interstellar dust and gases. Galaxies assume several forms such as elliptical, irregular and spiral discs with central masses and/or barred centers. Andromeda, our closest neighbor is a spiral galaxy composed of a trillion stars. Our own galaxy is a barred spiral galaxy, perhaps as large as Andromeda.
There are hundreds of billions of galaxies arrayed in clusters such as our Local Group, the Virgo Super Cluster or the Great Wall, a super cluster that is the largest known structure in the universe. Clusters surround huge, dark voids where no galaxies are apparent. The standard model is of an ever expanding universe that started with a gigantic “explosion”, known as the Big Bang, that created all of the matter, energy and space in the universe and even time itself about 13.7 billion years ago. The universe has been expanding ever since.
How big is it? Suffice it to say it is really, really, mind-bogglingly BIG! So big that no one can really wrap their mind around it. No one really knows how far it extends or whether there is an end to it, but currently the farthest object detected is a small galaxy thought to be at least 13.2 billion light years distant, just 500 million years after the beginning of the universe, according to the Big Bang theory. A light year is the distance light travels in a year in a vacuum, so the number of light years is the distance and also the time it took for the light to travel to us. At 9.46 million billion km (5.88 million billion miles) per light year, the observed distance to the farthest object would be 125 million billion billion km (78 million billion billion miles).
When the farthest galaxy was detected, we saw it as it was 13.2 billion years ago, and if the responsible object is receding at a constant rate, it would now be farther away by how far it could travel in 13.2 billion years. The apparent speed is an ever increasing rate the farther back in time (and distance) you go. This is a bit of an enigma since the universe is supposed to really be expanding at a constant rate. This acceleration into the distant past is attributed to the very space between the galaxies expanding and thus exaggerating the apparent, but not real, speed of recession the farther out we go. Since the observable universe is assumed to be uniform in all directions, the diameter would be greater than 26.4 billion light years (radius of 13.2 times 2). With each advance in telescope technology, the observable universe has “grown” by significant amounts. Beyond that, there is the unobservable universe.
To give some perspective on size and distance, while our Milky Way Galaxy, with perhaps a trillion stars, is a mere 100,000 light years in diameter, it is 2.5 million light years or 25 times the diameter of the Milky Way to the nearest spiral galaxy, Andromeda. By comparison, the average distance from earth to the sun is approximately 93 million miles or 8.3 light minutes. How about this for comparison? The distance from New York to Los Angeles is about 3000 miles (4830 km), or 0.016 light seconds (16 light milliseconds). Sorry for the tedious details, but it is the only way to illustrate the size of the observable universe, which may be a mere fraction of the total size.
Let’s see if we can put some perspective on these distances by an analogy. If we represent the Milky Way Galaxy by 1 cm (0.4 inch), the distance to Andromeda would be 25 cm (10 inches). The diameter of the local group of galaxies would be 1 meter (100 cm or 39.4 inches). The diameter of the Virgo Super Cluster of galaxies would be 11 meters (1100 cm or 43 feet) and the distance to the farthest object detected would be 1.32 kilometers (0.81 miles), i.e. 13.2 million cm. The entire solar system, including the supposed very distant Oort Cloud of comets, is less than 1/100,000th of the diameter of the Milky Way Galaxy, so in this example, the diameter of the solar system would be represented by about 10 microns, (micrometers), or about twice the size of an average large bacterium, (assuming that the galaxy is represented by 1 cm).
If we try to carry this down to the relative size of the earth or of humans, the analogy breaks down into confusingly tiny numbers, so let’s use a different analogy. If we let the solar system, with a diameter of 7.5 trillion km, be represented by 1000 km, then the diameter of the earth would be 1.7 microns, about the size of a small bacterium. (That’s 0.0017th or 1.7 ten thousandths of the solar system diameter.) Again, the analogy breaks down when we compare the height of humans to the diameter of the earth since the average height (170 cm) is 1.3 ten millionths the diameter of the earth (12750 km).
Since the sun comprises over 99% of the mass of the solar system and Jupiter and Saturn account for 90% of the remainder, an alien spaceship approaching the solar system, might describe it as a star with four (gas giant) planets and debris, with the earth as part of the debris. Similarly, an alien looking at the earth from space would consider the entire biomass, including man, as a relatively minor feature compared to the size of the earth or its oceans or continents. I hope this helps to put in perspective the size of the universe and the relative size of our galaxy, our solar system, our planet and us in it. Notice that I did not say the significance. Size and significance are two different things.
In order to make it seem ridiculous for man to think himself worthy of the attention of any creator-god the earth is often described as an unremarkable planet orbiting a rather ordinary star that is located far out on one of the spiral arms of an ordinary galaxy that is but one in billions. This is a specious argument because it is based on our presuming to know how a creator-god would logically think and behave. HDTKT? Beats me! However, it is conceivable that any being that can create such ordered complexity could be capable of anything, including contact with us.
Does the size and complexity of the universe mean we are but one example of billions of similar “earths” with abundant, perhaps intelligent, life and are therefore not unique? Maybe; maybe not. Does this mean the earth and life as we know it are insignificant or inconsequential or are but a happy accident? The answer to that depends on whether you are a materialist atheist or not. This argument for man’s insignificance is often used by those who would claim the universe has produced life completely at random without the need for a Creator or Designer, but it is a specious argument as stated above. It is merely an opinion, and it certainly is not science.
The rarity or abundance of life in the universe can be interpreted either as an affirmation of atheism or an affirmation of theism. It proves nothing but only reveals the belief system of the originator. For the atheist and the theist alike it is a theological argument. Rarity can mean “special” or not; abundance of life elsewhere can mean we are “ordinary” and the result of chance, or not. It all depends on your philosophical perspective. Science says nothing either way.
We exist. What is IS, whether it was designed by a creator God or came from a hairball coughed up by a giant Cat, or was sneezed from the snout of the great green Arcelsiezier or just appeared from nothing in a giant explosion unaided by anything. All of these scenarios are equally unfounded, unbelievable, fantastic and weird. They are philosophy or pure speculation, and certainly are not science. But I digress. Back to our tour.
Mass and Volume
How much matter is there in the universe? The sizes of the galaxies pale in comparison to the vast distances between them. At least astronomers think the space between galaxies is emptier than the best vacuum we can produce on earth. The universe is mostly empty space, so that averaging all the matter estimated to be in the galaxies and intergalactic space, it results in an average density of 1 hydrogen atom in 4 cubic meters of space, roughly a 1.6 meter or 5 foot cube. Doing the math based on the diameter of the hydrogen atom (2.2×10-10 or 0.00000000022 meters), there is roughly 7 x 1029 or 700,000 trillion, trillion times as much space as matter. That’s practically and effectively empty! Only gravity, which organizes the matter into galaxies, clusters, stars, etc., makes any of it more than just sparsely scattered gas and dust in the vast vacuum of space.
One figure given for the estimated total number of atoms in the observable universe is 1 x 1090. That’s 1 with 90 zeros after it or a million trillion trillion trillion trillion trillion trillion atoms, a truly inconceivable number. At 1 atom per 4 cubic meters, that would be 4 x 1090 cubic meters in the observable universe. The detectable matter in the universe, by number of detectable particles, is approximately 90% Hydrogen, 9% Helium and the balance is all the other elements combined.
It is thought that as much as 90% of the matter and energy in the universe are undetectable “Dark Matter” and “Dark Energy,” which are totally undetectable so far. The fact that the speed of rotation of stars around the center of galaxies does not decline at greater distances from the center as much as expected by theoretical calculations seems to indicate a massive Dark Matter halo; and there is evidence of an accelerating expansion of the universe that may be caused by Dark Energy. Dark matter is thought to slow the expansion of the universe through gravity. Dark energy is thought to promote expansion.
What is Dark Matter? No one knows but two types are hypothesized: MACHOs or Massive Compact Halo Objects probably composed of ordinary matter such as small black holes, failed stars called brown dwarfs or solid chunks of heavy elements, and WIMPs, Weakly Interacting Massive Particles of unknown composition, though none have been detected – and thus are “dark.” Since WIMPs are thought to interact only through gravity, they could not be ordinary matter and are called “exotic.”
Unobserved/ undetectable matter need not be exotic, just cold solid ordinary matter that we can’t see. The clouds of dust and gas in our galaxy, of which there is quite a lot, is only detectable because stars within them make them glow or by reflection of the light from nearby stars or by obviously blocking our view of stars and glowing gas and dust behind them. Outside our galaxy in intergalactic space, these means of detection are almost nonexistent, so most of the vast amounts of dust and other solid objects that could be there would be undetectable except for blocking or dimming the light from distant galaxies. Hmm, clusters of galaxies around vast dark voids… it makes one wonder.
 “A Galaxy when Galaxies Were Young”, by Jessica Kloss, Sky and Telescope, January 27, 2011
 Million billion = quadrillion = 1 followed by 15 zeros.
 Million billion billion = a 1 followed by 24 zeros.
 This is a simplification; there is a theory that this rate is accelerating.
 Attribution is uncertain for this illustration. I read it about 30 years ago. It could be Isaac Asimov.
 HDTKT – How Do They Know That
 Douglass Adams, Hitchhiker’s Guide to the Galaxy, 1979