Kiger Updated: Apr 15, It is difficult enough to imagine a time, roughly According to the Big Bang theory , one of the main contenders vying to explain how the universe came to be, all the matter in the cosmos -- all of space itself -- existed in a form smaller than a subatomic particle [source: Wall ].
Once you think about that, an even more difficult question arises: What existed just before the big bang occurred?
The question itself predates modern cosmology by at least 1, years. Fourth-century theologian St. Augustine wrestled with question of what existed before God created the universe. His conclusion was that the Biblical phrase "In the beginning" implied that God had made nothing previously. Moreover, Augustine argued that the world was not made by God at a certain time, but that time and the universe had been created simultaneously [source: Villanova University ].
In the early 20th century, Albert Einstein came to very similar conclusions with his theory of general relativity. Just consider the effect of mass on time. A planet's hefty mass warps time -- making time run a tiny bit slower for a human on Earth's surface than a satellite in orbit.
The difference is too small to notice, but time even runs more slowly for someone standing next to a large boulder than it does for a person standing alone in a field. Based upon Einstein's work, Belgian cosmologist Rev. According to Einstein's theory of relativity, time only came into being as that primordial singularity expanded toward its current size and shape.
Case closed? Far from it. This is one cosmological quandary that won't stay dead. Our Big Bang Universe is merely one such bubble among a possible infinity of other Big Bang universes in the ever-expanding inflationary vacuum! To start all this, a chunk of inflationary vacuum of only a kilogram was needed. Incredibly, the laws of quantum theory permit this to pop into existence out of nothing. The basic idea — that the Universe began hot and dense and has been expanding and cooling ever since — is incontrovertible.
But cosmologists have had to make tweaks to the theory, to account for certain observations. First, in the standard Big Bang model, galaxies grow by gravitationally pulling in matter. But if this were the only thing going on, it would take much longer than Second, the basic Big Bang predicts that the gravitational attraction between the galaxies acts like a web of elastic, slowing cosmic expansion.
A final tweak to the basic theory is needed to explain why the Universe has the same temperature everywhere. The former reigns supreme in the large-scale Universe, while the latter orchestrates the small-scale world of atoms and their constituents.
The problem with these ideas, Carroll said, is that there's no explanation for why or how an expanding universe would contract and return to a low-entropy state. Carroll and his colleague Jennifer Chen have their own pre-Big Bang vision. In , the physicists suggested that perhaps the universe as we know it is the offspring of a parent universe from which a bit of space-time has ripped off.
It's like a radioactive nucleus decaying, Carroll said: When a nucleus decays, it spits out an alpha or beta particle. The parent universe could do the same thing, except instead of particles, it spits out baby universes, perhaps infinitely.
These baby universes are "literally parallel universes ," Carroll said, and don't interact with or influence one another. If that all sounds rather trippy, it is — because scientists don't yet have a way to peer back to even the instant of the Big Bang, much less what came before it.
There's room to explore, though, Carroll said. The detection of gravitational waves from powerful galactic collisions in opens the possibility that these waves could be used to solve fundamental mysteries about the universes' expansion in that first crucial second.
Theoretical physicists also have work to do, Carroll said, like making more-precise predictions about how quantum forces like quantum gravity might work. He regarded the normalizable expansion history, which the path integral had merely helped uncover, as the solution to a more fundamental equation about the universe posed in the s by the physicists John Wheeler and Bryce DeWitt.
Wheeler and DeWitt — after mulling over the issue during a layover at Raleigh-Durham International — argued that the wave function of the universe, whatever it is, cannot depend on time, since there is no external clock by which to measure it. And thus the amount of energy in the universe, when you add up the positive and negative contributions of matter and gravity, must stay at zero forever. The no-boundary wave function satisfies the Wheeler-DeWitt equation for minisuperspace.
In the final years of his life, to better understand the wave function more generally, Hawking and his collaborators started applying holography — a blockbuster new approach that treats space-time as a hologram. Hawking sought a holographic description of a shuttlecock-shaped universe, in which the geometry of the entire past would project off of the present. But Turok sees this shift in emphasis as changing the rules.
In backing away from the path integral formulation, he says, proponents of the no-boundary idea have made it ill-defined. For the past year, Turok and his Perimeter Institute colleagues Latham Boyle and Kieran Finn have been developing a new cosmological model that has much in common with the no-boundary proposal.
But instead of one shuttlecock, it envisions two, arranged cork to cork in a sort of hourglass figure with time flowing in both directions. While the model is not yet developed enough to make predictions, its charm lies in the way its lobes realize CPT symmetry, a seemingly fundamental mirror in nature that simultaneously reflects matter and antimatter, left and right, and forward and backward in time.
Boyle, Finn and Turok take a stab at the singularity, but such an attempt is inherently speculative. Questions abound about how the various proposals intersect with anthropic reasoning and the infamous multiverse idea. The no-boundary wave function, for instance, favors empty universes, whereas significant matter and energy are needed to power hugeness and complexity. Hawking argued that the vast spread of possible universes permitted by the wave function must all be realized in some larger multiverse, within which only complex universes like ours will have inhabitants capable of making observations.
The recent debate concerns whether these complex, habitable universes will be smooth or wildly fluctuating. An advantage of the tunneling proposal is that it favors matter- and energy-filled universes like ours without resorting to anthropic reasoning — though universes that tunnel into existence may have other problems.
Or perhaps, instead of a South Pole-like non-beginning, the universe emerged from a singularity after all, demanding a different kind of wave function altogether. Either way, the pursuit will continue.
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