The Big Bang is, without doubt, one of the greatest achievements of human civilization. So why then are so many scientists waiting so expectantly for its immanent demise?
Most folks think of the Big Bang as a description of the Universe's creation but that was never really the case. The Big Bang was always a theory of after creation. It describes what happens after the Bang and it does so in exquisite detail. In Big Bang theory you begin with a super-hot, super-dense fireball that contains all Space, all Time, all Matter and all Energy. There is no "outside" the fireball because Big Bang Theory takes all those "alls" seriously. The super-hot super-dense fireball is all existence. Big Bang theorists just assume it's existence and then they just let it go.
What they get is expansion. The whole shebang expands and cools and evolves. After 13.7 billion years the original fireball of space-time and subatomic particles coalesces into galaxies, stars, planets and, (in at least one case), people. It is a magnificent story that has been confirmed many times by mountains of data. The Big Bang is a spectacular success.
Except for the beginning... I spent the last two years tracking the history of cosmology for a new book and from that work its clear to me how much the beginning in the Big Bang was always a problem.
When the Big Bang was first proposed no one was happy with the idea of the Universe just starting, like God popping open a bottle of champagne. How could everything just start, suddenly, from nothing? Even the name "Big Bang" was meant as an insult. It was hurled at the theory by a rival cosmologist (Fred Hoyle) whose rival idea did not demand all of creation just pop into existence. But as mountains of data piled up showing that the Universe must have once been hotter and denser than it is today most scientists sucked up their misgivings and assumed that someone, at some point would figure out what Time = 0 really meant.
But no one ever did. Until, maybe, now.
The problem with the Big Bang's beginning was that the further you push back in time, the hotter and denser the Universe gets until Space-Time itself becomes so compressed that Einstein glorious description of it -- called General Relativity -- rolls on to its back and wiggles its legs like a stinkbug juiced on RAID. Infinities begin popping up in the theory in a way that tells scientists the theory no longer applies. At that point what should happen is scientists switching over to a different theory -- a quantum description of Space-Time.
Quantum Mechanics describes nature at the smallest scales like electrons, protons and quarks. In the Universe's very beginning even Space-Time should become quantized, appearing as a frothy foam of reality. But the problem is no one has ever developed a full working theory of "atoms of space-time" -- formally called a theory of Quantum Gravity. Without knowing how to merge Einstein's General Theory of Relativity with Quantum Mechanics, scientists cannot describe the beginning. They could not describe the Universe in its natal state (i.e. the first trillion, trillion, trillion, trillion-th of a second).
Now, however, contenders to the Quantum Gravity throne have appeared and they are offering alternatives to the Big Bang, its question of before. The question is will the price for these answers be too high.
String Theory is the most popular and well known of the Quantum Gravity wannabees. String Theory tells us that matter is not made of point-like particles but is, instead, composed of tiny vibrating threads (or even sheets) of energy. Though incomplete, String Theory has been pointing towards an impressive unity between all the forces and particles we know of exist including gravity. But achieving this unity has come with a high price. String Theory demands that the Universe have 7 "extra-dimensions" that we can not see because they curl up on themselves like tiny straws. Many scientists were not happy with the appearance of these unseen dimensions in a new theory
Worse still, in 2005 String Theorists found that their theory did not predict 1 universe (i.e. ours); it predicted the existence of a near infinity of them. In this way String Theorists now speak of a multiverse -- Universe of Universes -- in which all we see is just one bubble in an ocean of possibilities. In a multiverse no single Big Bang is ever required as these "bubble" Universes are forever being born.
If these ideas sound like science fiction you are in good company. For many scientists the hidden dimensions of String Theory and unseen Universes of the Multiverse are too far fetched and to far from any observational data to be taken as anything more than mathematical possibilities. Advocates of these ideas point to the impressive success in leading scientists to new theoretical possibilities and ask for patience saying only time and experiments (which may be decades in the future) will tell.
In the meantime other ideas for quantum gravity and cosmology are also in the works. Loop-Quantum Gravity, for example, takes the "atoms of space-time" concept seriously. It advocates have provided the theoretical outlines for directly quantizing Space-Time into discreet packets of pure geometry. The exploration of these space-time atoms has even allowed Loop Quantum Gravity to make cosmological predictions. An Oscillating Universe in which a Big Crunch follows each Big Bang becomes theoretically possible with the machinery of Loop Quantum Gravity.
As of this writing there is no way to tell which set of ideas will form the next experimentally confirmed cosmology. String Theory, Multiverses and Atoms of Space-Time all remain possibilities alongside a host of even more mind-bending conceptions.
One thing is clear however. While we have a supremely accurate theory of what happened after our Universe started in its super-hot, super-dense childhood, we are still in the dark about its birth. But after more than a half century of work scientists are, perhaps, finally ready to go before and beyond the Big Bang.