THOSE AD-HOC COSMOLOGICAL EPICYCLES
Sometimes observations are hard to explain. So you just have to tack on the best ad-hoc explanation that fits the facts, even if the explanation itself is lacking the nitty-gritty details. Astronomy went through such an exercise when anyone who was anyone said that the Earth was the centre of all things, and all things revolved around the Earth. That didn't end very well. I suspect that modern cosmology is in a similar situation that ultimately won't end well as far as the status-quo is concerned either.
Once upon a time humans thought and believed that the Earth was the centre of the cosmos and that all things revolved around the Earth. When it came to the Sun and the Moon, things worked out pretty smoothly. The Moon does go around the Earth and the Sun damn well appears to. The 'fixed' stars also appear to go around the Earth and provide no ammunition to suggest otherwise.
But the 'wandering stars', the planets, were different horses of other colours. Their motions, assumed to be going round the Earth, were difficult to reconcile with that stationary Earth in the middle. Nobody (at the time) was willing to abandon the Earth-centred cosmos, and so the motions of the planets had to be tweaked in order to get observation and theory to gel. Thus was invented the epicycle.
Planets were assumed to go through various loop-the-loops and other gyrations or acrobatics (collectively called epicycles) in order to conform to observation. But original epicycles had in turn to be provided with second generation epicycles as observations still didn't fit the 'facts', then third generation epicycles tacked on to the second generation tacked on to the original generation, until things go so out of hand and complicated that everything just collapsed in a heap. That resulted in a paradigm shift.
When the positions of the Earth and Sun were reversed, everything fell into place, theory matched observation (once ellipses were substituted for circles - the perfect circle was yet another once upon a time when humans were dictating to nature what nature should do requirement), and all those epicycles fell by the wayside.
We seem to face a similar situation today when it comes to modern cosmology. We have lots of observations that require ever increasing ad-hoc epicycles to account for them.
Many an observation has been made in the sciences, and then to explain a group of them, some sort of all encompassing explanation is given. That in turn results in various issues or problems and so to resolve them, another all encompassing explanation is given to explain that lot of them, and that in turn, well etc. etc. A clear case in point revolves around the standard model of cosmology.
Astronomers observe the universe - obviously. Certain observations in need of explanation have given rise to just such an explanation, albeit incomplete and rather unsatisfactory. That trilogy of observations is: 1) galactic red-shifts; 2) The cosmic microwave background radiation (CMBR); and 3) the ratio/abundance of hydrogen & helium.
The galactic red-shift observation boils down to the fact that nearly all galaxies are moving away from each other and the distances between them are in relation to their velocities such that galaxies moving at X velocity will be Y distance apart; galaxies that are 2X velocities will be 2Y distances apart and so on. Translated, it's what you would expect to see with respect to all the bits and pieces flying off on an exploding stick of dynamite. Thus we have an expanding Universe, and, by running the 'film' or the clock backwards, the Universe will have come to a 'point' roughly 13.7 billion years ago.
The detection of the Cosmic Microwave Background Radiation (a cosmic temperature detectable in part as static or hiss on your TV set when tuned between stations) was in accordance with theoretical predictions if the cosmos started out as an extremely hot explosion and slowly cooled down as the Universe expanded.
Lastly, when one observes and calculates the relative abundance of hydrogen and helium in the Universe, the two simplest of elements, that ratio is what you'd expect given known interactions part and parcel of particle physics under the extremes of temperature and pressure that would be expected in a high temperature explosion.
So, the Big Bang gets a heads up. Things are looking good. But, and there's always a 'but'!
There are immediately several issues with respect to this cosmic explosion termed the Big Bang. Firstly, it created time (no explanation or recipe given as to how); secondly it created space (no explanation or recipe given for that either); thirdly it created matter and energy (again, no explanation or recipe, given); fourthly the 'bang' wasn't 'big' since cosmologists choose to run the clock back as far as they can and thus cram the entire Universe back into a volume less than that of a pinhead; and lastly, no energy source for the 'bang' is given. In fact I've often read that apparently no energy source was actually necessary (because the Universe is energy neutral - it has as much positive energy as negative energy), which I find more than slightly odd.
However, postulating the Big Bang to explain the above trilogy of observations caused issues with another trilogy of observations. These observations centred on: 1) the horizon problem; 2) the flatness problem and 3) the monopole problem
The horizon problem - contact between two regions - is a problem in that if you look at exact opposite regions of the Universe; you tend to see pretty much the exact same thing, especially when it comes to temperature. So what? Well, in order for things to achieve equilibrium, your hot cup of coffee cooling off while the kitchen gets ever so slightly warmer until both coffee and room are the same temperature, requires that the two regions (coffee and room) be in relatively close proximity since the exchange can only happen at velocities equal to or less than the speed of light. If two opposite areas of the sky, looking deep into space, are the same temperature, it requires that these two regions were once close together, close enough for equilibrium at or less than the speed of light to have taken place in order to even conditions out. Unfortunately, the distances observed between opposite points in the sky are such that uniformity could not have been possible. They are now out of contact with each other - beyond each other's 'horizon' so any bits of non-uniformity between regions that eventuated way back when should have persisted - and when we look that deep into space we are looking way back when. We need some serious additional oomph to get uniformity between regions from way, way back then (i.e. - immediately post Big Bang) out to currently observed distances.
The flatness problem revolves around the observation that the Universe is fine tuned with respect to the density of matter and energy contained within, a density that has resulted in a just so 'flat' universe. Translated, a flat universe is one where Euclidian geometry holds sway (the three angles of a triangle add up to 180 degrees). Now if the density was greater, the Universe would be closed, like a sphere (i.e. - the Earth), where the angles of a triangle on the surface add up to more than 180 degrees. If the density were less, the Universe would be an open (i.e. - saddle-shaped) hyperbolic Universe where the angles of a triangle add up to less than 180 degrees. If you have a potentially wide range of possible densities, it's amazing that our Universe has that just-so flatness.
The monopole problem is that under the conditions of the Big Bang, one should have generated monopoles - magnets with either a north pole, or a south pole, but not both. Alas, no monopoles have ever been detected or observed. They appear to be rarer than hen's teeth.
Well, the way to circumnavigate those problems is to propose not just an original Big Bang explosion, but an additional super-ultra 'explosion' that speeded up the expansion of the Universe, ever so briefly, by a very, very, very large factor indeed. This secondary 'explosion' was termed Inflation. Inflation made the expansion rate of the Universe caused by the Big Bang to appear almost insignificant.
So how does an extreme, but brief, burst of expansion (i.e. - Inflation) solve the flatness, horizon and monopole issues?
The horizon problem is solved by inflation. While, initial pre-inflation Big Bang conditions would have provided for the required close enough contact to achieve uniformity, regions flying apart would soon acquire their own distinct 'personalities' and be far enough apart that equilibrium could never be restored between these regions, even at light speed. However, that additional serious bout of Inflation then rapidly expanded out that evenness, Inflation providing the extra oomph and freezing the uniformity in place to the distances we observe today.
The flatness problem is explained because an extremely rapid rate of Inflation would smooth out the Universe. If you're bacteria on the surface of an uninflated balloon, you'll see peaks and troughs - wrinkles. If that balloon is blown up thousands of times greater in extent, the surface will now appear flat - just like the surface of the Earth appears flat to us.
The monopole problem is solved because the volume of the Universe increased thousands of times over in nanoseconds such that monopoles were now dispersed over an incredibly large volume such that the odds one would be in our cosmic neighbourhood becomes vanishingly tiny.
The odd thing here is that I sometimes read that Inflation preceded the Big Bang, although it's usually an after-the-fact event. Obviously cosmologists haven't really a clue which came first - no, not the chicken or egg but the Big Bang or Inflation.
Okay, we've explained cosmological observations via the Big Bang and Inflation. Can we go on R&R now? No, not quite. For you see, yet another very nasty observation has surfaced that requires yet another ad hoc tack-on explanation that well, has no explanation.
We have been aware that our Universe has been expanding for going on nearly a century now. Of course we are also aware, from a quite considerable earlier time that what goes up must come down. In other words, gravity grabs. The Universe has lots and lots of gravity, so presumably, what goes up (i.e. - the expansion rate) must come down (i.e. - the expansion rate must at least slow down, maybe even stop and reverse). Cosmologists were very interested in finding out exactly what the rate of deceleration was. How fast was the Universe's expansion rate decreasing? It's like you car might be going uphill, but at an ever slower and slower rate.
Okay, so, several teams of astronomers did the relevant observations and crunched the numbers and guess what - the Universe's expansion rate was accelerating, and gravity be damned. That's sort of like driving your car uphill and having it go faster and faster without you putting the pedal to the metal. Well, that surely was an unexpected result. So, they needed an explanation. The astronomers (team leaders anyway) got the Nobel Prize, but that was for the discovery, not for the explanation. You see, there wasn't any explanation. So, what do we want - an epicycle. When do we want it - now! What was the ad-hoc epicycle to be? It was called "Dark Energy", a sort of anti-gravity that was pushing the Universe apart faster and faster and faster. Trouble is, nobody then, or now, has the foggiest idea what Dark Energy is, yet in order to account for what this epicycle does, it must represent some roughly 70% of what makes the Universe up. That's a lot of epicycle that lacks any plausible explanation. Did someone mention rabbits and hats?
Now can we go home? Sorry, not yet.
There's yet another astronomical observation that in fact goes back to the first half of the 20th Century that has to deal with, at least initially, our own cosmic neck of the woods, the Milky Way Galaxy. Now you'd be well aware that in our solar system, Mr. Sun is the Big Cheese and keeps all of her planets in orbit via her gravity. However, gravity weakens as you get away from the source (the inverse square relationship) so it's not surprising that the farther a planet is outward bound from the Sun, giver the ever increasingly longer distance of its orbit around the Sun, the slower it orbits; the longer is its year. Now does that relationship apply to all the bits and pieces (i.e. - stars) that orbit around the centre of our galaxy? Well, in fact no. The outer stars whiz along just as quick-smart as the inner stars, so much so that the outer stars, given the amount of gravity the galaxy apparently has, should in fact escape altogether and head off into intergalactic space. The fact that they don't does mean the galaxy has a lot more gravity than apparently meets the astronomical eye. Oops, there's another epicycle coming on. This time the ad-hoc explanation is Dark Matter. It is dark because we can't see it. It is matter because it has (all that required additional) gravity. Of course, it makes up the majority of matter in our galaxy; of course nobody has a clue what it actually is, although the astronomical powers-that-be have been able to rule out a lot of what's dark, but common stuff like interstellar gas and dust, Black Holes, etc. So, for the here and now, Dark Matter is another epicycle, and what applies to our galaxy also has been observed for other galaxies.
The concept of epicycles was originally used in order to explain observations. That remains the case in modern cosmology, only the ad-hoc explanations themselves need explaining.
In conclusion, the state of cosmology and of our understanding of the Universe, its substance and structure, is pretty much at a crossroads where the state of our solar system was all those centuries ago. Once upon a time epicycles were heaped on epicycles in order to explain the solar system until everything fell to pieces. I suspect that history will repeat itself when it comes to the current state of cosmology. Explanations of observations are just too ad-hoc; too many things left unexplained by those ad-hoc epicycles. We've had the Copernican Revolution; it's time for the equivalent revolution in cosmology.
SUMMARY
Observation: Galactic Red-shifts
Observation: Cosmic Microwave Background Radiation (CMBR)
Observation: Ratio/Abundance Hydrogen & Helium
Ad-Hoc Epicycle: Big Bang (no energy source given)
Observation: Horizon Problem
Observation: Flatness Problem
Observation: Magnetic Monopoles
Ad-Hoc Epicycle: Inflation (many varieties, just like Heinz)
Observation: Accelerating Universe
Ad-Hoc Epicycle: Dark Energy (unexplained)
Observation: Galactic Rotations with Gravity Out of Sync
Ad-Hoc Epicycle: Dark Matter (unexplained)
