***** This is an incomplete rough draft.. but it's the current state of it anyway (6/2018). Medium-length, maybe ~10 min read at moderate speed.
Related to the post about things we will discovering at in the coming years (here, on FB, from 9/2016), I wanted to write about a question I, and all cosmologists, get very often, quite naturally enough: what happened before 'the Big Bang'?
Now, sometimes the answer you'll hear is that time *started* at the Big Bang, which kind of really doesn't say very much, and is highly not in accord with our commonsense intuitions about how time flows in our normal everyday life -- I mean what does that *mean* anyway? Of
course, as I've written about in other postings, 'weird' non-intuitive things *do* happen in various domains of our Universe: such as QM (quantum mechanics) taking over at the very tiniest scales, time dilation and length contraction happening at very high velocities and near strong gravitational fields where GR (general relativity) must be used instead of Newtonian gravity, etc. So the fact that it
*seems* weird to us doesn't intrinsically rule out this answer as a sensible one.
However -- i think there is a simpler way to 'understand' as much as
we can for now the 'beginning', at least from my point of view, and
that is: that our entire current framework of physics breaks down very
close to 'the Big Bang', and we simply cannot understand time before
this point *currently*.
Now - what does *this* mean?
To try to understand this, let's step back and look at what cosmologists mean by the Big Bang picture of the Universe, which is actually simply this: that at some point, our Universe was in a very
hot, dense phase. And in fact, we can trace our Universe's expansion history *backwards* from the current moment and see all the galaxies streaming towards each other like a movie run in reverse until everything smushes together and there are only particles flying around in a superheated primordial soup -- a very early hot, dense phase.
Now when this movie runs in reverse, all the lengths between all objects shrink, and eventually, clearly, if they all shrink to exactly zero, the whole structure would collapse to a point -- an "infinitely dense" singularity. BUT -- say we don't let it get there, we stop the movie at a specific point, and to be conservative, let's say that point is 10^-10 sec after the time where things *would* have collapsed to a singular point, which i'll call the 'theoretical zero-time', or TZT (though we in fact believe we have a pretty good handle much farther back, to a point at least 10^-25 sec post-TZT, and possibly even 10^-35 sec post-TZT).
And let's call *that* (the 10^-10 point) the "theoretical breakdown time", or TBT. Now, back at that time, the TZT and TBT are hugely different because things are changing so rapidly, but beyond a few min after the TZT, the TZT and TBT look pretty much like the same instant for how the Universe evolved forward. (Much like just a few minutes makes a massive difference when a baby is first born, or in the first couple of minutes of its life, even though later in life gaps of a few minutes are typically not very significant and for most purposes we can approximate times like that as being the same.) But in a theoretical sense, *however* miniscule the TBT, there is a 'Universe' of difference between zero time and any nonzero (i.e. finite) TBT whatsoever. (One way to think of this is that infinity is a very strange concept when you probe more deeply into it, and on a 'logarithmic' scale, the space between any two finite times, small as they might be, can be stretched to an infinite length. [If this reminds anyone of Zeno's paradox, there is in fact some deep connection there] ).
Now, looking from a grand scale: yes, we believe we understand quite well from the TBT until our current time how things have worked on the largest scale, crazy enough as that sounds.
You might think -- what are you on, man, how do you have
*any* idea this picture is right, how can you trace something back
with so much certainty for 13.7 billion years???
And this would be quite a reasonable response except that -- we have
really *good* reasons that we know this is the right picture thus far.
[Just to throw out a few of them: our ability to see galaxies that from their redshifts are clearly over 13 billion years old, i.e. how they were just a few hundred million years post-TBT, our understanding
of the distribution of galaxies across the sky in 'large scale structure', and the earliest clear photon signature being the 'leftover light from the Big Bang', the Cosmic Microwave Background that is emitted at 380,000 years post-TBT (discussed in this nice 2017 KIPAC blogpost by Kyle Story). But my favorite, and perhaps the earliest confirmed and measured signature of our current framework, are the elemental abundances predicted by Big Bang Nucleosynthesis, or 'BBN' .]
Now - let us go back to what TZT means, and why i keep using that term vs. the more common "Big Bang" -- and that's because when we say "Big Bang Model" we only mean that *everything* everywhere was in a hot dense expansive phase. What happens if we try to trace farther back than the TBT is that our current equations *break down*. They just can't be solved in that domain, and we really have *no* idea before that time. An analogy might be that you can't solve equations of
fluids in outer space which is empty, or use Newton's equations around black holes where strong gravity takes over, or use wave equations for macroscopic objects in the Universe, etc. It just makes no *sense* to try to apply the eq's in those domains.
You might ask if that bothers me, or other physicists, and I would say
of course, at some level, this limit on our ability to know things
does, but -- that doesn't mean we *can't* ever understand it. It
means that right now, we don't get it, and have to be ok with that.
To extrapolate further, to try to think we can know more theoretically
without experimental verification is, to me, closer to philosophizing
which while nearly inevitable given the expansive and wide-ranging
nature of the human brain, has no real scientific grounding as most
working scientists understand that term. It's fine to do if someone
is interested in engaging in it -- it just doesn't interest *me* or
most cosmologists nearly as much as actually making the slow steady
progress in shining light into the darkness based on experimental
testing that is the fundamental hallmark of what science as an
endeavor separate from our particular species on this Earth *is*.
To me -- it is truly *ok* to be humble in the face of the immensity of the University, the vast expanse of time and space that we with our brief, mayfly-like lives on this little planet, can only ever make
finite stabs at in our time.
This is not at all to diminish the grandeur and profundity of all we
*have* discovered over time -- it continues to amaze *me* how well it
all fits together, everytime i look at the edifice of physical science
that we humans have built over the centuries, and particularly, in the
last one.
But -- there are an infinite number of digits after the decimal point
of any measurement. And if we can measure to several, we do pretty
well. In fact, in a couple of instances, we can match to some 15
digits (!!!) in physics. That's stunning -- and yet, 15, or 20, or
100, or a million or a *gazillion* is in fact 'essentially zero' when
compared with infinity. Infinity is just a concept that we humans
cannot i believe ever fully 'get'. We just work with it, as best we
can.
So - I'm ok with where our current framework breaks down, and I am
just continually humbled that in fact we *can* still make progress
going forward with learning more, going farther back, farther out,
farther in.
Btw loosely related to this is the question of how 'big' the Universe is -- another reason we can't really get to the TZT currently is that our current picture doesn't have the Big Bang happening at any particular point in space, and thus the distances between all objects can never shrink to identically zero. They can get arbitrarily *small*, but as long as they are finite, the entire Universe can still be infinite in extent, and still the same everywhere because the product of any small finite number, however miniscule, and infinity, is still infinity. However -- we can only see to the observable edge, as far as light has been able to travel in the time since the TBT, and that's it.
---------------------------------- Appendix:
---- Btw, to picture how the expansion works (or contraction, when run in reverse mode), people have different analogies, but i usually picture the structure of space as a 3-dimensional tinkertoy grid, with the lines extending out infinitely in all 6 Cartesian directions from a given vertex (i.e. +/- x, +/- y, +/- z). Now, what we mean by the expansion of space is that the actual *legs* of the tinkertoy structure are each growing, at the same rate. And if we sit on *one* particular vertex -- which could represent e.g. our Galaxy -- *every* other vertex (where e.g. another galaxy might sit) is moving away from us, with a velocity in direct linear proportion (in this analogy) to its distance from us, the central vertex (and, of course, our particular vertex is not special -- the same would be true if we switched our perspective to sitting on *another* one of the vertices, and watched what happened with the other vertices in relation to us).
---- BBN is the period from a few sec post-TZT to about a half hour after it -- and it is when nearly *ALL* the helium in our Universe is created. Along with the deuterium, and lithium, as well. These are all isotopes of the first 3 elements of the periodic table, the simplest 3 nuclei that can be made. And it happens because this 'hot soup' phase has temperatures fairly about like those at the center of modern stars, and what do we know stars do there? Well, that's the place where the protons are energetic enough to overcome their normal electrical repulsion, and they smush together (in a couple of different steps) to make: helium. This is exactly what happened in that first half hour of the Universe.
So -- we actually have a pretty good handle on that first half hour post-TZT.
