What happened before the Big Bang?
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THE accepted wisdom in modern cosmology is that the universe was born some 14 billion years ago with a Big Bang, in what was an incredibly dense and hot state, and has been expanding and cooling ever since. In this scenario, everything starts with the Big Bang, and it is meaningless to ask what came before the moment of creation.
Yet, for a few years, some maverick cosmologists have been asking that very question. Some physicists are uncomfortable with the notion that everything — including time itself — started with the Big Bang. The equations of modern physics break down at the moment of creation — physicists term this “a singularity”.
“No one is happy with the Big Bang singularity, since mathematically it is difficult to deal with,” says Martin Bojowald, a theorist at Penn State University, who started wondering about seven years ago if there was a way to know what preceded the Big Bang.
Bojowald works on loop quantum gravity — a theory that seeks to unify the principles of general relativity and quantum mechanics. In loop quantum gravity, space-time is made of tiny interconnected loops, each about a 100-millionth of one billion-billion-billionth metre across (that is 10-35 metres across), which together form a smooth fabric much like a shirt’s fabric is smooth even though it is woven from separate threads.
Bojowald realised that if he had to make precise statements about what one can predict and expect in a quantum model of the early universe, he needed a model that he could solve exactly analytically. To enable himself to this, he made a few simplifications, treating the universe as a fluctuating quantum system. In effect, he created a toy model of the early universe that allowed him to make precise statements about the limits of predictability.
He assumed that the physical properties of this toy quantum universe were the same in all directions, and that it contained a sort of matter that did not interact with itself. He allowed for gravity but he did not include radiation. His universe evolved according to Einstein’s equation of general relativity.
In his model, the Big Bang singularity was replaced by a “bounce” — it was the point at which the quantum fluctuation was the smallest. With time and evolution of the universe, the fluctuations would grow. The beauty of the model was that the physical properties would evolve through the bounce; in effect, he could work back from our existing universe to the state that preceded it.
Bojowald finds that most of the information about what came before the Big Bang gets irretrievably lost through the Big Bang transition — although it’s possible to know something of what came before. In a perpetually cyclical scenario, where the universe exists forever, going through a Big Bang and then an expanding phase, followed by a contracting phase, and then another Big Bang, no two universes are ever the same because of this information loss — which he terms “cosmic forgetfulness”.
Paul Steinhardt, a Princeton University cosmologist who has also investigated pre-Big Bang scenarios, says Bojowald’s model is right in principle. “It’s important to lose some information, but not everything,” he says, so that the universes have unique properties and are not just an eternal recurring cycle.
Thomas Thiemann, another theorist who works on quantum gravity, commended Bojowald on his approach, saying that although some assumptions may turn out to be too simple, this was “the cleanest derivation of a pre big bang scenario that any physical theory has delivered so far, much cleaner than in string theory-inspired
models.”
Bojowald says his model is still simple, and he will try to introduce more realism over time. For example, he is adding inhomogeneities to make it more like the universe we see.
(The author lives is based in New York and can be contacted at saswatodas@gmail.com)
Yet, for a few years, some maverick cosmologists have been asking that very question. Some physicists are uncomfortable with the notion that everything — including time itself — started with the Big Bang. The equations of modern physics break down at the moment of creation — physicists term this “a singularity”.
“No one is happy with the Big Bang singularity, since mathematically it is difficult to deal with,” says Martin Bojowald, a theorist at Penn State University, who started wondering about seven years ago if there was a way to know what preceded the Big Bang.
Bojowald works on loop quantum gravity — a theory that seeks to unify the principles of general relativity and quantum mechanics. In loop quantum gravity, space-time is made of tiny interconnected loops, each about a 100-millionth of one billion-billion-billionth metre across (that is 10-35 metres across), which together form a smooth fabric much like a shirt’s fabric is smooth even though it is woven from separate threads.
Bojowald realised that if he had to make precise statements about what one can predict and expect in a quantum model of the early universe, he needed a model that he could solve exactly analytically. To enable himself to this, he made a few simplifications, treating the universe as a fluctuating quantum system. In effect, he created a toy model of the early universe that allowed him to make precise statements about the limits of predictability.
He assumed that the physical properties of this toy quantum universe were the same in all directions, and that it contained a sort of matter that did not interact with itself. He allowed for gravity but he did not include radiation. His universe evolved according to Einstein’s equation of general relativity.
In his model, the Big Bang singularity was replaced by a “bounce” — it was the point at which the quantum fluctuation was the smallest. With time and evolution of the universe, the fluctuations would grow. The beauty of the model was that the physical properties would evolve through the bounce; in effect, he could work back from our existing universe to the state that preceded it.
Bojowald finds that most of the information about what came before the Big Bang gets irretrievably lost through the Big Bang transition — although it’s possible to know something of what came before. In a perpetually cyclical scenario, where the universe exists forever, going through a Big Bang and then an expanding phase, followed by a contracting phase, and then another Big Bang, no two universes are ever the same because of this information loss — which he terms “cosmic forgetfulness”.
Paul Steinhardt, a Princeton University cosmologist who has also investigated pre-Big Bang scenarios, says Bojowald’s model is right in principle. “It’s important to lose some information, but not everything,” he says, so that the universes have unique properties and are not just an eternal recurring cycle.
Thomas Thiemann, another theorist who works on quantum gravity, commended Bojowald on his approach, saying that although some assumptions may turn out to be too simple, this was “the cleanest derivation of a pre big bang scenario that any physical theory has delivered so far, much cleaner than in string theory-inspired
models.”
Bojowald says his model is still simple, and he will try to introduce more realism over time. For example, he is adding inhomogeneities to make it more like the universe we see.
(The author lives is based in New York and can be contacted at saswatodas@gmail.com)
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