Cosmology is the study of the evolution of our Universe as a whole - from birth to death, or maybe birth to death to rebirth. Stellar objects and events, like nova and supernovae are in the cosmic scheme of things almost insignificant in comparison. It's like comparing the life and times of an individual insect to the life and times of Planet Earth. Still, there might be a lot to be gleamed from comparing the life and death of our Universe to the life and death of the stars within that Universe.
A cyclic universe - one with birth, death, rebirth, death, rebirth, death, etc. is a far more philosophically satisfying universe than a one-off born, live, and fade-away universe, which is what our Universe appears to be. A cyclic universe is probably more pleasing because such a concept more closely mirrors nearly all local reality - the cyclic four seasons endlessly repeating; day-night-day-night; New Moon - Full Moon - New Moon - Full Moon; evaporation - rainfall - evaporation - rainfall; the carbon cycle; the nitrogen cycle; you name it, it recycles. Okay, maybe you don't. You maybe are like our Universe - born, live yet doomed to fade-away. But the broader human species continues to recycle - birth, death, birth, death, etc. The names and the faces change, but the human cycle continues. Actually all of your stuff will recycle too. Part of you today might be part of a cockroach 100 years down the track! That aside, the Big Question is how can you generate a cyclic universe, one which eventually goes from initial Big Bang expansion to one which contracts into a Big Crunch then rebounds again? How do you generate that from a Big Bang universe that's apparently doomed to keep expanding, ever expanding, forever, and ever, amen?
The standard model of cosmology suggests that our Universe had a one-off moment of creation (the Big Bang) and will over trillions of years surrender to entropy (the evolution of a state of order to ultimate disorder) and die an eventual "heat death" (where the temperature - heat energy, the ultimate end product of all other forms of energy conversion - is exactly uniform throughout). So we go from Once Upon A Time/In the Beginning through to Cosmic Evolution through to The End. But that's the narrow view. What if there were many universes, and they could interact? Then there might not be an overall Once Upon A Time/In the Beginning and ultimately The End. The parallel analogy with supernovae explains all.
THE STORY OF THE SUPERNOVAE: We've all heard of supernovae, and while quite rare, there has been one visible to the naked eye recently that occurred in the Large Magellanic Cloud (SN 1987A), a nearby companion mini-galaxy to our own visible from the Southern Hemisphere. It was first witnessed on Planet Earth after the light flash travelled thousands upon thousands of years, traversing intergalactic and interstellar space, to arrive locally on the 23rd of February 1987. It was the first visible naked eye supernovae event since 1604 - rare indeed.
Their cosmic story and cosmic significance is fairly straight forward. Stars form out of interstellar gas, dust and perhaps larger debris. This mix of stuff slowly but surely contracts, all under the mutual attraction of their individual gravities that eventually brings it all together in a lump sum - if massive enough an embryo star forms. The intense pressures heat up the interior, and if the embryo star is indeed massive enough, the heat and pressure will be enough to cause the gas, etc. to start to fuse, usually starting with hydrogen fusing to helium and releasing [solar] energy in that conversion - nuclear fusion is what powers the stars.
Now interstellar gas and dust clouds are not all uniform in size. So, some stars fire up with the bare minimum of stuff, other stars fire up with a lot of stuff in their core bellies, but not too much. These are sort-of like Goldilocks stars; stars like our Sun. A few stars formed from such a thick region of gas and dust that they were 'born' obese.
How massive newborn stars are will determine their lifespan and their fate. The relationship tends to be that the thinner you are at birth, the longer you'll live. Very skinny stars are very frugal with their fuel. These misers have stellar life-spans perhaps measured in roughly a trillion or so years. When their fuel finally runs out, they just slowly, ever so slowly, fade away into a white dwarf then finally as a dark and cold black dwarf cinder. Average stars, like our Sun, are less thrifty, but even so manage a lifespan of roughly ten billion years. Average stars will go through a more complex evolution, but ultimately they too will settle down to a long retirement, cooling, ever cooling when the fuel is exhausted. They too will go out not with a bang but with a whimper.
However, some stars are born just plain fat! Some stars can also put on weight after-the-fact by stealing mass from a nearby companion star via their stronger gravity and close proximity. However the star gets fat, fat in a stellar sense (lots and lots of mass), the more massive a star is, the greater the temperatures and pressures in that star's core, and the faster nuclear fusion reactions go. Really massive stars live life in the fast lane; they live fast; they die young. And they don't go out with a whimper, but with a bang - sometimes endlessly hiccuping or burping or vomiting - novas; sometimes imploding due to massive gravity when their core fuel gets close to empty (leaving a bit of a void) which causes a massive rebound and a super-ultra-violent explosion called a supernovae. That really does spew their stellar guts back into the interstellar winds. While there are several different types of supernovae that have ultimately different origins, that's of no concern in this context. The important bit is that stuff gets spewed back into space and eventually recycled.
Exploding stars, the novae but especially the supernovae return not only gas and dust and debris back to the interstellar medium, but enriched gas, dust and debris since the enormous temperatures and pressures cook up the heavier elements (elements more complex than helium), elements that are essential for life to ultimately grace the cosmos with its presence.
Gas and dust from one star's 'burp' intersect with gas and dust from another star's 'hick-up' and maybe intermingle with the 'spewing vomit' from a supernovae, all ultimately contracting again under mutual gravity to form a second, even third generation star and stellar planetary system. Our Sun is at least a third generation star and is made up of former spewed stuff, some of which is now heavier than just hydrogen and helium; ditto the Sun's family of planets, including Planet Earth. If it weren't for supernovae, we wouldn't be here. The late astronomer, Carl Sagan, said it best when he stated that we are indeed the end product of "star-stuff".
So the basic cosmic cycle is stars form from interstellar gas and dust; stars live; some stars spew their guts of gas and dust back out into interstellar space, providing the raw materials for the next generation of stars. You get creation - destruction - creation - destruction, over and over again, albeit at different times in different places.
THE PARALLEL COSMOLOGY ANALOGY: So what the hell does the above have to do with cosmology? There's lots of stars; only one Universe - or is that really the case?
One set of assumptions has to be made from the get-go. I postulate that the cosmos, all that is and ever will be, is infinite in both space and in time. This assumption is more philosophical than scientific. If you ever postulate a finite cosmos, a cosmos with a boundary, a fixed volume, you must, of necessity, deal with that maverick who asks, "Well, what exists beyond that boundary?" If you postulate a beginning and/or an end, that same maverick will annoy you with, "Well, what happened before that or after that?" It's just easier to wrap your head around a cosmos that is infinite; a cosmos that had no beginning and will have no end. Unfortunate, the standard model of cosmology postulates a beginning, and a fade-away ending and a finite amount of stuff and space to stuff it into.
We all know the standard scientific spiel to the creation of our Universe - no, not the Biblical Book of Genesis, but the Big Bang event. Well, already we have a parallel analogy - supernovae are mini big bang events.
Now the Big Bang and other associated real time events like an additional oomph of an in the beginning "inflation" have resulted in our Universe expanding, ever expanding. There's lots of observational evidence for the Big Bang and the expansion. So, lots of stuff has been vomited out into the cosmos from a unique point in time - 13.7 billion years ago. But if there was a finite Big Bang, then there must also have been a finite amount of space to stuff that vomit into. That violates my philosophical ideals of not only no boundary in time, but no bounds in space for our Universe to strut its stuff in.
Anyway, we have expansion of stuff spreading out through space. Well, that's a parallel analogy with the spewing out of gas and dust via stars going nova and supernovae. Now commonsense might suggest that the original oomph of the Big Bang would eventually run out of puff as the one-way attraction of gravity would slow the expansion down, and down, and down and eventually cause the expansion to come to a grinding halt - then reverse, as gravity would cause everything to contract once again back into the configuration from which the Big Bang arose from. In other words, the expected fate of our Universe was to be born from a Big Bang, live and evolve, and die in a Big Crunch.
Alas, life isn't that simple - Mother Nature is a baseball pitcher with a wicked curveball or knuckleball. Mother Nature's a real Hall-of-Fame bitch. A bunch of astronomical party-poopers discovered that the expansion of the Universe isn't slowing down; it bloody well accelerating! Thus, no Big Crunch is on the horizon in the far future, only a "Heat Death" as entropy ends up ruling the roost. So runs the standard spiel. So how are you going to eventually generate a second or third or one-hundredth generation universe out of that mess? But that's the limited view. Let's climb the cosmic mountain for the grander picture.
What comes now to the rescue is that there is more than one Big Bang (maxi nova or supernovae) universe; more than one expansion event, because, there's more than one universe, more than just our Universe, within that infinite (in space and time) cosmos referred to above.
And so, while from our limited point of view there is our Universe, and thus we assume the one-and-only-Universe, in fact there is more - much, much more. If you have a lot of universes in the infinite cosmos, all of which started off with a supernovae-like Big Bang, then, sooner or later, the spew of one (or more) will intersect with the spew of another (or more).
Thus, a lot of expanding regions of individual universes will intersect, eventually. That intersect region will, under combined gravities, start to slow things down. That region will slowly, but surely, start to contract. That contraction will eventually collapse into a Big Crunch. It seems something cyclic has happened. Lots of Big Bangs have generated a Big Crunch - actually a lot of Big Crunches when you look at the total 3-D picture. Big Bang A's expansion might intersect with Big Bang expansions B, C, and D in one direction, say left. Big Bang A's expansion might intersect with Big Bang expansions E, F and G in the opposite direction. Big Bang A's expansion might intersect with Big Bang expansions H, I, J and K in the up direction; Big Bang A's expansion might intersect with the L, and M Big Bangs in the downward direction, and so on and so forth. The Big Crunches (resulting in the Mother of all Black Holes) will be symmetrical, turning inside out into newly vomiting Big Bangs, or White Holes.
And so the endlessly cycling of stellar nova/supernova (expansion) to intersecting clouds of interstellar gas/dust (contractions) thus forming new stellar objects, some of which will in turn vomit up their quota of interstellar gas/dust has a parallel though many orders of magnitude on up the line. Endlessly cycling Big Bang expansions intersect to form high gravity regions which contract (in Big Crunches) to form new regions where conditions are ripe for a new Big Bang event. And so we have an overall cyclic cosmos or Multiverse (because there is more than one universe). There's not just one expanding universe slowing down and contracting to ultimate reform that one expanding universe again, but a whole potpourri of universes that are all just expanding, intersecting and contracting, comings and goings at different times and places - night and day; Full Moon to New Moon; evaporation to rainfall; etc.
In fact, if you think about it, the idea that there are many expanding and contracting universes is but the next logical step in what was already proven to be a natural progression. Once upon a time Terra Firma (Earth) was the centre of the Universe. Now we know better. Then the Sun and solar system were elevated to that centre. Now we know better because there are lots of suns and planets that have eliminated our uniqueness. Once upon a time our galaxy was considered to be the be-all-and-end-all of the Universe. Today we know better. There are billions and billions of other galaxies out there and our galaxy occupies no special place in space or time and has no special appearance. So, I suggest that our Universe is now not the centre of the universe (or cosmos to avoid confusion). We have a Multiverse! And we have a cyclic Multiverse that should satisfy that philosophical idealistic need referred to at the start.
Now it could already be the case that part of our expanding Universe has recently (even as in multi-millions of years ago) intersected part of another expanding universe. However, we wouldn't be aware of that because it's going to take billions of years for the visuals and the gravitational effects to reach us from such vast distances.
There is at least one interesting consequence inherent in this cyclic Multiverse. Even if there is only a finite amount of mass and energy in this infinite volume (and that doesn't have to be the case since you can fit an infinite amount of mass and energy into an infinite volume), that finite mass and energy has been recycled an infinite number of times in the unending past and will be recycled an infinite number of times in the unending future. The upshot of that is that anything and everything that can happen, everything that is not forbidden by the laws, principles and relationships inherent in nature, has happened an infinite number of times and will happen again an infinite number of times. Translated, you have and will exist again, and again, and again in all possible permutations. Although the 'you' that is reading this in the 'now' will fade away (that sounds nicer than kicking-the-bucket), take comfort in that another 'you', somewhere and somewhen else, will carry on carrying on the 'you' tradition.
JOHN'S COSMOLOGY - SUPERNOVAE ANALOGY IN SUMMARY FORM
1) Contraction of a universe - 1) Contraction of interstellar gas/dust
2) Big Crunch (Black Hole) - 2) Massive star forms
3) Transition to - 3) Stellar life span
4) Big Bang (White Hole) - 4) Supernovae
5) Expanding Universe - 5) Expulsion of gas/dust
6) Intersection with another expanding universe - 6) Interaction with other gas/dust
7) Gravity rules - 7) Gravity rules
8) Contraction of new universe - 8) Contraction of interstellar gas/dust
POINT AND COUNTERPOINT: Now your standard run-of-the-mill, everyday professor of cosmology at your local leading university will tell you if you show her this scenario that it is all total nonsense and I should be consigned to the pseudoscientific rubbish bin. The Big Bang event was a one-off; it was unique; a one-of-a-kind; a fluke; just one of those interesting things that happen for no apparent reason at all. The Big Bang event created time and space, therefore time and space cannot be infinite.
But - and you'll read that non-observation (since there was no one around including any lady cosmologists to observe at the Big Bang's ground zero) in any standard book on the subject - it's nonsense, a scientific fabrication if you really stop and think about it. You cannot create something, anything, without having the space already available to create it into. That applies to the creation of our Universe as much as it applies to creating widgets in a factory! To claim otherwise is to suggest all of ultimate creation was kick-started in no space at all! How absurd is that! Consider the reverse: how can you cram everything into nothing?
Now if the Big Bang event did not, could not, create space way back then, then space is not undergoing continuous creation today contrary to the standard spiel. Translated, space is not expanding into some non-space region of non-existence. Expanding space either means that space is getting thinner and thinner (less dense) like an expanding balloon skin stretching (and that's nonsense - how can space decrease in density?), or new space is being created out of nothing to fill the void as space expands. You can't create something out of pure nothing; not then (at the Big Bang); not now. That's a violation of all the basic conservation laws that are the bedrock of physics.
So, the obvious alternative is that what's expanding is the stuff vomited out by the Big Bang event into pre-existing space and the vomit just keeps thinning out as it expands throughout an ever wider volume of that pre-existing space. Now fortunately for me, and unfortunately for those cosmology professors, there's no actual observational test or experiment that can be done to distinguish between the two possibilities and settle the matter. If there were such observational evidence that proved that space itself was expanding (and thus being continuously created even as I type this) that evidence would be given in the textbooks. But it's not there. All you get is just the standard scenario: "the Big Bang created space; space is expanding and therefore space is still being created today". The unwritten sentence is "just take my word for it" because I can't back it up with any evidence, far less proof. The only evidence is that something is expanding. That something could equally be Big Bang stuff spewing out into pre-existing space like an exploding firecracker will spew its contents outward bound and ever expanding.
It's the unanswered question that remains in fact unasked in the standard textbooks - what exactly is our Universe's expanding space expanding into? What is our expanding space shoving out of the way as it expands, ever expands? It can't be pre-existing space according to the standard model since the Big Bang event created all of space; the entirety of space in the beginning 13.7 billion years ago. Perhaps space is pushing into a theoretical higher dimension (whatever that really means), but that would be an ad hoc pull of the rabbit out of the proverbial hat where nobody advocating that could provide any evidence that either the rabbit or the hat exists at all. Besides, all those extra dimensions predicted by the purely mathematical and hypothetical string theory (if string theory is to work) are compactified; curled up into super-ultra microscopic foetal positions; they are tiny. They aren't the sort of higher dimension you can expand a universe of space into. So it's back to the drawing board for our standard lady (and gentlemen) cosmologists.
The other bit, the creation of time, is equally absurd. The Big Bang was an event. It was an effect. If causality has any meaning at all, and it's one of the foundations upon which all of science rests on, then an effect has a cause. Causes must precede effects when cause and effect are intimately related (there are of course lots of causes and lots of effects that have no connection). Therefore, whatever caused the Big Bang event (or effect), must of necessity have happened before (preceded) the Big Bang event. Therefore, there must have been an already existing time prior to the Big Bang event and therefore the Big Bang event did not, could not, create time. Since there was a before the Big Bang, since cause always precedes effect, then again time could not have been created - time has always been, is, and always will be.
Fortunately for me, and unfortunately for those professors of cosmology ramming down the standard 'creation of time and space' scenario to their students, all equations (that which usually substitutes for lack of ways and means to do actual observations) that try to describe the Big Bang event; ground zero when space allegedly equals zero and time allegedly also equals zero, totally break down. So the standard 'create time and space' model is pure extrapolation (running the film backwards from today's data) and ultimately a best guess. So while I've no doubt the Big Bang scenario is correct in the broad-brush generalities, there is a lot of observational evidence that something really big happened 13.7 billion years ago that kick-started our Universe off on its evolutional path, when it comes to some of the nitty-gritty details, like that 'create time and space' detail, well I just think that is plain wrong - pure and simple.
So why is that 'Big Bang created time and space' the only accepted scenario? It is beyond me, except it probably has a lot to do, not with science, but the sociology and the office politics of science - peer pressure. Science, like the church and other formal institutions does not approve of mavericks that go against the grain. So if you want a Ph D., a job, research funding, a career with promotions, publications, etc. you don't rock the boat. Science, and that includes cosmology, for all its self-correcting ways and means and methods and ideals is still, ultimately, a human endeavour. As such, you tow the party line; go with the flow; parrot to your students what your professors parroted to you.
Now there are a few bold cosmologists who do acknowledge that the Big Bang event still has some kinks to be ironed out and that there was a "before the Big Bang". That's not to say they would endorse my scenario. They probably wouldn't in a pink fit!