Since some effects in the microscopic world do not require causes, it is possible that there was no cause to start off the Big Bang! And things can get even weirder. It is also possible that time did not exist before the Big Bang. The North Pole is the most northern point on Earth, and so there is nowhere north of it. Some scientists suggest our Universe is the recycled result of another Universe dying and collapsing in on itself. This collapsing Universe would meet back to a singularity before bouncing back out, causing the Big Bang and starting off a brand new universe.
In that case, gravity would not only need to stop the Universe from stretching, but bring everything within it back to one single point. Or maybe our Universe is at the other end of a black hole called a white hole.
The relic signatures imprinted on our Universe from an inflationary state before the hot Big Bang give us a unique way to test our cosmic history. The particular properties of the Universe that are imprinted upon it from the earliest stages provide a window into the physical processes that took place at those times. Not only do they tell us that we cannot extrapolate the Big Bang all the way back to a singularity, but they tell us about the state that existed prior to and set up the hot Big Bang: a period of cosmic inflation.
During inflation, there was a tremendous amount of energy inherent to space itself, causing the Universe to expand both rapidly and relentlessly: at an exponential rate. This period of inflation occurred prior to the hot Big Bang, set up the initial conditions that our Universe began with, and left a series of unique imprints that we searched for and discovered after the theory had already predicted them.
By any metric, inflation is a tremendous success. The quantum fluctuations that occur during inflation get stretched across the Universe, and when This leads, over time, to the large-scale structure in the Universe today, as well as the fluctuations in temperature observed in the CMB. These new predictions are essential for demonstrating the validity of a fine-tuning mechanism, and have validated inflation as our new, leading theory of how our Big Bang got its start. But this severely alters our conceptions of how the Universe began.
Earlier, I presented you a graph of how the size or scale of the Universe evolved with time. The graph displayed the differences between how the Universe would expand if it were dominated by matter in red , radiation in blue , or space itself such as during inflation, in yellow at early times.
However, I wasn't completely honest with you in displaying that graph. You see, I omitted something in the earlier graph, because I truncated it at a positive, finite time. In other words, I stopped the graph before we reached a size of zero.
That would have been where the original idea of the Big Bang occurred. But in an inflationary Universe, you only asymptote to a size of zero; you never reach it. But in an inflationary scenario yellow , we never reach a singularity, where space goes to a singular state; instead, it can only get arbitrarily small in the past, while time continues to go backwards forever.
The Hawking-Hartle no-boundary condition challenges the longevity of this state, as does the Borde-Guth-Vilenkin theorem, but neither one is a sure thing. Like many great discoveries in science, this leads to a slew of delightful new questions, including:.
The different ways dark energy could evolve into the future. Remaining constant or increasing in Under either of those two scenarios, time may be cyclical, while if neither comes true, time could either be finite or infinite in duration to the past.
Observationally, we don't know the answer to any of these questions. The Universe, as far as we can observe it, only contains information from the final 10 seconds or so of inflation. Anything that occurred prior to that — which includes anything that would tell us how-or-if inflation began and what its duration was — gets wiped out, as far as what's observable to us, by the nature of inflation itself.
Theoretically, we don't fare much better. The Borde-Guth-Vilenkin theorem tells us that all points in the Universe, if you extrapolate back far enough, will merge together, and that inflation cannot describe a complete spacetime. But that doesn't necessarily mean an inflating state couldn't have lasted forever; it could just as easily imply that our current rules of physics are incapable of describing these earliest stages accurately. 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. In the decades following Einstein's death, the advent of quantum physics and a host of new theories resurrected questions about the pre-big bang universe. Keep reading to learn about some of them. One of the earliest string theory notions is the "ekpyrotic" universe, which comes from the Greek word for "conflagration," or fire.
In this scenario, what we know as the Big Bang was sparked by something else happening before it — the Big Bang was not a beginning, but one part of a larger process. Extending the ekpyrotic concept has led to a theory, again motivated by string theory, called cyclic cosmology.
I suppose that, technically, the idea of the universe continually repeating itself is thousands of years old and predates physics, but string theory gave the idea firm mathematical grounding. The cyclic universe goes about exactly as you might imagine, continually bouncing between big bangs and big crunches, potentially for eternity back in time and for eternity into the future. As cool as this sounds, early versions of the cyclic model had difficulty matching observations — which is a major deal when you're trying to do science and not just telling stories around the campfire.
The main hurdle was agreeing with our observations of the cosmic microwave background, the fossil light leftover from when the universe was only , years old. While we can't see directly past that wall of light, if you start theoretically tinkering with the physics of the infant cosmos, you affect that afterglow light pattern. But the ekpyrotic torch has been kept lit over the years, and a paper published in January to the arXiv database has explored the wrinkles in the mathematics and uncovered some previously missed opportunities.
The physicists, Robert Brandenberger and Ziwei Wang of McGill University in Canada, found that in the moment of the "bounce," when our universe shrinks to an incredibly small point and returns to a Big Bang state, it's possible to line everything up to get the proper observationally tested result.
In other words, the complicated and, admittedly, poorly understood physics of this critical epoch may indeed allow for a radically revised view of our time and place in the cosmos.
But to fully test this model, we'll have to wait for a new generation of cosmology experiments, so let's wait to break out the ekpyrotic champagne. Paul M. Originally published on Live Science. Join our Space Forums to keep talking space on the latest missions, night sky and more!
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