The
Big Bounce is a theorized scientific model related to the formation of the known
UniverseThe Universe comprises everything that physically exists, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them...
. It derives from the
cyclic modelA cyclic model is any of several cosmological models in which the universe follows infinite, self-sustaining cycles .-Overview:...
or
oscillatory universeThe oscillating universe theory is a cosmological model investigated briefly by Albert Einstein in 1930 and critiqued by Richard Tolman in 1934, in which the universe undergoes a series of oscillations, each beginning with a big bang and ending with a big crunch...
interpretation of the
Big BangThe Big Bang is the cosmological model of the initial conditions and subsequent development of the Universe that is supported by the most comprehensive and accurate explanations from current scientific evidence and observation...
where the first cosmological event was the result of the collapse of a previous universe.
According to some oscillatory universe theorists, the Big Bang was merely the beginning of a
period of expansionThe metric expansion of space is the averaged increase of metric distance between distant objects in the universe with time. It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space...
that followed a period of contraction.
The
Big Bounce is a theorized scientific model related to the formation of the known
UniverseThe Universe comprises everything that physically exists, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them...
. It derives from the
cyclic modelA cyclic model is any of several cosmological models in which the universe follows infinite, self-sustaining cycles .-Overview:...
or
oscillatory universeThe oscillating universe theory is a cosmological model investigated briefly by Albert Einstein in 1930 and critiqued by Richard Tolman in 1934, in which the universe undergoes a series of oscillations, each beginning with a big bang and ending with a big crunch...
interpretation of the
Big BangThe Big Bang is the cosmological model of the initial conditions and subsequent development of the Universe that is supported by the most comprehensive and accurate explanations from current scientific evidence and observation...
where the first cosmological event was the result of the collapse of a previous universe.
Expansion and Contraction
According to some oscillatory universe theorists, the Big Bang was merely the beginning of a
period of expansionThe metric expansion of space is the averaged increase of metric distance between distant objects in the universe with time. It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space...
that followed a period of contraction. In this view, one could talk of a
Big CrunchIn physical cosmology, the Big Crunch is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately ending as a black hole singularity.- Overview :...
followed by a
Big Bang, or more simply, a
Big Bounce. This suggests that we might be living in the first of all universes, but are equally likely to be living in the 2 billionth universe (or any of an infinite other sequential universes).
The main idea behind the quantum theory of a Big Bounce is that, as density approaches infinity, the behavior of the
quantum foamQuantum foam, also referred to as spacetime foam, is a concept in quantum mechanics, devised by John Wheeler in 1955. The foam is supposedly the foundations of the fabric of the universe, but it can also be used as a qualitative description of subatomic spacetime turbulence at extremely small...
changes. All the so-called fundamental physical constants, including the speed of light in a vacuum, were not so constant during the Big Crunch, especially in the interval stretching 10
−43 seconds before and after the point of inflection. (One unit of
Planck timeIn physics, the Planck time, , is the unit of time in the system of natural units known as Planck units. It is the time required for light to travel, in a vacuum, a distance of 1 Planck length...
is about 10
−43 seconds.)
If the fundamental physical constants were determined in a quantum-mechanical manner during the Big Crunch, then their apparently inexplicable values in this universe would not be so surprising, it being understood here that a
universe is that which exists between a Big Bang and its Big Crunch.
Recent developments in the theory
Martin BojowaldMartin Bojowald is a German physicist who now works at the of the Pennsylvania State University, USA. In 2005 he joined the permanent staff of the IGC, after spending several years at the in Potsdam, Germany...
, an assistant professor of physics at
Pennsylvania State UniversityThe Pennsylvania State University is a state-related, land-grant, space grant public research university located in the University Park area and within State College and College Township in Pennsylvania, United States...
, published a study in July 2007 detailing work somewhat related to
loop quantum gravityLoop quantum gravity , also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity...
that claimed to mathematically solve the time before the Big Bang, which would give new weight to the oscillatory universe and Big Bounce theories.
One of the main problems with the Big Bang theory is that at the moment of the Big Bang, there is a singularity of zero volume and infinite energy. This is normally interpreted as the end of the physics as we know it; in this case, of the theory of
general relativityGeneral relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics. It unifies special relativity and Newton's law of universal gravitation, and describes gravity as a...
. This is why one expects quantum effects to become important and avoid the singularity.
However, research in
loop quantum cosmologyLoop quantum cosmology is a finite, symmetry reduced model of loop quantum gravity, theorizing that our universe expands and then eventually contracts over and over, rebirthing for eternity...
purported to show that a previously existing
universeThe Universe comprises everything that physically exists, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them...
collapsed, not to the point of singularity, but to a point before that where the quantum effects of gravity become so strongly repulsive that the universe rebounds back out, forming a new branch. Throughout this collapse and bounce, the evolution is unitary.
Bojowald also claims that some properties of the universe that collapsed to form ours can also be determined. Some properties of the prior universe are not determinable however due to some kind of uncertainty principle.
This work is still in its early stages and very speculative. Some extensions by further scientists have been published in
Physical Review Letters.
Peter LyndsPeter Lynds is a New Zealander who first drew sudden attention in 2003 with the publication of a physics paper about time, mechanics and Zeno's paradoxes....
has recently put forward a new cosmology model in which time is cyclic. In his theory our Universe will eventually stop expanding and then contract. Before becoming a singularity, as one would expect from Hawking's black hole theory, the Universe would bounce just before it became a singularity. Lynds feels that a singularity would violate the second law of thermodynamics and this stops the Universe from being bounded by singularities. The Big Crunch would be avoided with a new Big Bang. Lynds feels the exact history of the Universe would be repeated in each cycle. Some critics feel that while the Universe may be cyclic, the histories would all be variants.
Objections
One of the main objections to the Big Bounce view is the evidence that has been accumulating that our universe is destined for a Big Freeze or
heat deathThe heat death is a possible final state of the universe, in which it has "run down" to a state of no thermodynamic free energy to sustain motion or life. In physical terms, it has reached maximum entropy...
rather than a Big Crunch (see
Accelerating universeThe accelerating universe is the observation that the universe appears to be expanding at an increasing rate. In 1998 observations of Type Ia supernovae suggested that the expansion of the universe is accelerating since around redshift of z~0.5....
). However, this evidence does not exclude the possibility that our Big Bang was preceded by the very last Big Crunch, at least the very last one in our vicinity.
Another main objection is that a Big Bounce would reverse entropy by resetting the state of the universe, violating the
second law of thermodynamicsThe second law of thermodynamics is an expression of the universal principle of entropy, stating that the entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium, and that the entropy change dS of a system undergoing any...
. Also, the collapse into a singularity would destroy most of the information in the previous universe.
Furthermore, it remains a possibility that a better understanding of
quantum foamQuantum foam, also referred to as spacetime foam, is a concept in quantum mechanics, devised by John Wheeler in 1955. The foam is supposedly the foundations of the fabric of the universe, but it can also be used as a qualitative description of subatomic spacetime turbulence at extremely small...
may result in a re-interpretation of the evidence regarding the fate of our universe.
See also
- Abhay Ashtekar
Abhay Ashtekar is an Indian physicist. He is the Eberly Professor of Physics and the Director of the Institute for Gravitational Physics and Geometry at Pennsylvania State University. As the creator of Ashtekar variables, he is one of the founders of loop quantum gravity and its subfield loop...
- Anthropic principle
In physics and cosmology, the anthropic principle is the collective name for several ways of asserting that physical and chemical theories, especially astrophysics and cosmology, need to take into account that there is life on Earth, and that one form of that life, Homo sapiens, has attained...
- Martin Bojowald
Martin Bojowald is a German physicist who now works at the of the Pennsylvania State University, USA. In 2005 he joined the permanent staff of the IGC, after spending several years at the in Potsdam, Germany...
- Loop quantum gravity
Loop quantum gravity , also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity...
- Supernova
A supernova is a stellar explosion. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this short interval, a supernova can radiate as much energy as the Sun could emit over...
- John Archibald Wheeler
John Archibald Wheeler was an eminent American theoretical physicist. One of the later collaborators of Albert Einstein, he tried to achieve Einstein's vision of a unified field theory...
External links