Early universe size after the big bang
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Early Universe Size: Big Bang and Initial Expansion
The size of the universe immediately after the Big Bang is a complex topic, with estimates depending on the specific moment in time and the theoretical framework used. In the earliest moments, known as the Planck era (up to about 10^-43 seconds after the Big Bang), our understanding is limited and highly speculative, as this period requires a theory of quantum gravity, such as string theory, which is not yet fully developed or confirmed .
Size Estimates After the Big Bang
Several models attempt to estimate the universe's size as it transitioned from the quantum-dominated Planck era to more classical behavior. According to the Quantum Big Bang theory, when the universe entered the classical Friedmann-Robertson-Walker (FRW) phase, its size was about 0.2 centimeters in radius . This estimate is based on calculations of primordial matter density contrast and does not require the assumption of an early inflationary phase.
Other theoretical models, such as Liu’s Cosmological Model, suggest that at its "nascence," the universe had a radius of approximately 4.84 × 10^11 meters (about 484 million kilometers), though this is based on alternative assumptions and is not widely accepted in mainstream cosmology Liu2016Liu2022.
Observable Universe vs. Total Universe
It is important to distinguish between the observable universe and the total universe. The observable universe is currently about 93 billion light-years in diameter, but this is much larger than the universe's size immediately after the Big Bang. The actual universe could be vastly larger than what we can observe, as suggested by models considering the gravitational influence of the Big Bang and the possibility of a cosmological wave complex, which implies a universe much greater in size than the observable part .
Role of Inflation
The inflationary model proposes that a fraction of a second after the Big Bang, the universe underwent a period of extremely rapid expansion, increasing its size by many orders of magnitude in a tiny fraction of a second. This would mean that the universe, which may have started at subatomic scales, expanded to macroscopic or even astronomical sizes almost instantly . However, some alternative models, like the Quantum Big Bang theory, argue that such an inflationary phase may not be necessary to explain the observed properties of the universe .
Conclusion
The size of the universe immediately after the Big Bang depends on the specific time considered and the theoretical model applied. Estimates range from subatomic scales to several centimeters or even larger, depending on the framework. While the observable universe today is vast, the initial size after the Big Bang was much smaller, with rapid expansion (possibly due to inflation) quickly increasing its scale. The true total size of the universe, however, may be far beyond what we can currently observe or measure Louis2021Ram2008Nilsen2022+3 MORE.
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