Universe before big bang
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Understanding the Universe Before the Big Bang
Quantum State and Loop Quantum Gravity
One of the primary questions about the universe before the Big Bang is whether it was in a classical state or a highly fluctuating quantum state. Research in loop quantum gravity suggests that the quantum evolution of a wavefunction extends through the Big Bang, indicating that it might be possible to observe the universe as it was before the Big Bang through future calculations and indirect observations1. However, the precise state of the universe remains uncertain due to inherent limitations in our current scientific understanding1.
CPT Symmetry and Neutrino Dark Matter
Another intriguing theory posits that the universe before the Big Bang is the CPT reflection of the universe after the Big Bang. This means that the universe and an anti-universe pair were created from nothing, maintaining CPT symmetry. This model provides a new perspective on the matter/anti-matter asymmetry and offers an explanation for the abundance of dark matter. It suggests that one of the heavy neutrinos in the standard model of particle physics is stable, matching the observed dark matter density2.
Harmonic Cosmology and Quantum Fluctuations
In the context of harmonic cosmology, quantum gravity could potentially remove classical space-time singularities, revealing the nature of the universe at the Big Bang. Studies show that quantum fluctuations before the Big Bang are generally unrelated to those after it, indicating that precise observations would be required to determine the pre-Big Bang quantum fluctuations of geometry3.
Ekpyrotic and Cyclic Cosmology
Ekpyrotic and cyclic cosmologies offer alternative models where the Big Bang is not the beginning of time but a collision of branes. Before the Big Bang, the universe undergoes an ekpyrotic phase, slowly contracting and resolving standard cosmological puzzles. This phase generates a nearly scale-invariant spectrum of cosmological perturbations and small-amplitude gravitational waves. The cyclic nature of this model suggests that the universe undergoes repeated phases of contraction and expansion4 5.
Pre-Big Bang Scenarios in String Cosmology
String cosmology introduces the concept of a pre-Big Bang phase characterized by accelerated evolution, which is the dual counterpart of the decelerating expansion era of standard cosmology. This scenario potentially avoids the initial singularity and provides significant inflation. Researchers are exploring ways to detect traces of the pre-Big Bang era through the properties of relic gravitons and their impact on the cosmic microwave background8.
Challenges and Limitations
Despite these theories, there are significant challenges in understanding the universe before the Big Bang. For instance, the pre-Big Bang scenario requires the universe to be extremely large and homogeneous from the very beginning, which poses difficulties in explaining the initial conditions and the homogeneity of the universe7. Additionally, the complexity of these models and the need for exceedingly precise observations make it difficult to draw definitive conclusions about the pre-Big Bang universe3.
Conclusion
The study of the universe before the Big Bang is a complex and evolving field, with various theories offering different perspectives. From loop quantum gravity and CPT symmetry to ekpyrotic and string cosmology models, each theory provides unique insights and challenges. While significant progress has been made, many questions remain unanswered, and future research and observations will be crucial in advancing our understanding of the universe's origins.
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Most relevant research papers on this topic
What happened before the Big Bang
The precise state of the Universe before the Big Bang remains unanswered, requiring assumptions and prejudices for understanding its pre-Big Bang state.
Highly CitedThe Big Bang, CPT, and neutrino dark matter
The universe before the Big Bang and the universe after the Big Bang can be viewed as a universe/anti-universe pair, with CPT selecting a preferred vacuum state for quantum fields, leading to a novel and economical explanation of the dark matter abundance.
Harmonic cosmology: how much can we know about a universe before the big bang?
Quantum fluctuations before the big bang are unrelated to those after the big bang, and determining pre-big bang geometry requires extremely precise observations.
Ekpyrotic and cyclic cosmology
Ekpyrotic and cyclic cosmologies suggest the big bang was not the beginning of time, and they propose a universe with a slow contraction before the big bang and a cyclic universe.
Highly CitedUniverse before Big Bang
The Ekpyrotic model proposes a pre-big bang universe with ghost condensates and a non-singular bounce, offering a distinct alternative to inflation theory for the birth of the universe.
Summary of session B4: early universe, pre-big bang, etc
The session B4 focused on the early universe and pre-big bang theories, with three invited talks by Vilenkin, Ashtekar, and Kodama highlighting the session's highlights.
Pre - big bang requires the universe to be exponentially large from the very beginning
The pre-big-bang scenario can only solve cosmological problems if the universe is extremely large and homogeneous from the beginning, and cannot replace usual inflation.
Pre-big-bang in string cosmology
String cosmology suggests a pre-big-bang phase of accelerated evolution, potentially avoiding initial singularity and providing large inflation, with potential tracks in relic gravitons and cosmic microwave background distortion.
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