Big Bang Vs Inflationary Big Bang

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Discussion Overview

The discussion centers on the comparison between the traditional Big Bang model and the inflationary Big Bang model, particularly focusing on the implications of fine-tuning and initial conditions in cosmology. Participants explore the motivations for adopting inflationary theory, its advantages, and the unresolved issues surrounding both models.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • Some participants suggest that the original Big Bang model implies a finely tuned Universe, leading to the development of the inflationary model to address these concerns.
  • Others argue that the flatness and horizon problems do not necessarily invalidate the original Big Bang model but rather indicate a need for fine-tuning.
  • One participant proposes that the Universe's apparent fine-tuning may not be unlikely if there are unknown physics mechanisms at play at the beginning of the Universe.
  • Another participant asserts that inflation serves as a dynamical mechanism that explains fine-tuning rather than requiring it, particularly in relation to the flatness problem.
  • Some contributions highlight that inflationary cosmology resolves several issues, such as the monopole problem and the origin of structure, which the original Big Bang model does not address.
  • A participant references a recent paper discussing inflation as a solution to the early Universe entropy problem and invites comments on its implications for established physicists.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and implications of fine-tuning in both models. While some acknowledge the advantages of inflationary cosmology, others maintain that the original Big Bang model is not necessarily invalidated. The discussion remains unresolved regarding the overall superiority of one model over the other.

Contextual Notes

Participants note that both models do not extend back to T=0, and there are ongoing debates about the interpretation of initial conditions and the role of fine-tuning in cosmological theories.

dm4b
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I was under the impression that originally the main impetus for inflationary Big Bang was that the original Big Bang model implied a finely tuned Universe, or highly unlikely starting conditions for the Universe.

In other words, the flatness and horizon problems, etc., don't necessarily indicate the original Big Bang has to be wrong. It just implies the Universe had to have a finely tuned beginning.

Well, perhaps the Universe really is fine tuned and our desire to avoid theories that seem to "predict" very unlikely starting conditions for the Universe has led us astray.

Since neither models go back to T=0, perhaps there was a mechanism that forced the Universe into what appears to be a finally tuned beginning. In other words, it isn't really a highly unlikely scenario - it only seems that way due to our lack of understanding of unknown physics that came into play at the very beginning.

So, I guess my questions is are there recent advances in cosmology that show additional advantages to the inflationary model and that exclude the original Big Bang model as impossible now.

Thanks.
 
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dm4b said:
I was under the impression that originally the main impetus for inflationary Big Bang was that the original Big Bang model implied a finely tuned Universe, or highly unlikely starting conditions for the Universe.

In other words, the flatness and horizon problems, etc., don't necessarily indicate the original Big Bang has to be wrong. It just implies the Universe had to have a finely tuned beginning.

Well, perhaps the Universe really is fine tuned and our desire to avoid theories that seem to "predict" very unlikely starting conditions for the Universe has led us astray.

Since neither models go back to T=0, perhaps there was a mechanism that forced the Universe into what appears to be a finally tuned beginning. In other words, it isn't really a highly unlikely scenario - it only seems that way due to our lack of understanding of unknown physics that came into play at the very beginning.

So, I guess my questions is are there recent advances in cosmology that show additional advantages to the inflationary model and that exclude the original Big Bang model as impossible now.

Thanks.

The dynamical mechanism to explain the fine tuning is precisely inflation though! It does deal with physics beyond the standard big bang scenario, namely something weird happening around the GUT scale.
 
Nabeshin said:
The dynamical mechanism to explain the fine tuning is precisely inflation though! It does deal with physics beyond the standard big bang scenario, namely something weird happening around the GUT scale.

I guess I was looking at that a bit differently.

For example, with the flatness problem you really do need fine tuning under the original Big Bang - specifically the Universe had to be very, very close to the critical density.

Under inflation, the observable Universe only appears flat in a way analogous to how the surface of the Earth appears flat to us. So, really, it explains away any need for fine tuning, rather than being a mechanism for it.
 
There was an interesting paper on initial conditions yesterday - Inflation as a Solution to the Early Universe Entropy Problem, http://arxiv.org/abs/1212.1087.
 
The fine tuning of Omega is definitely something resolved in inflationary big bang cosmology but not big bang (sans inflation) cosmology. But of course this isn't the only issue. Inflation solves the monopole problem, the horizon problem, the origin of structure problem and explains why the universe is so big and where the hot soup of particles comes from. So even if there was no observational evidence for inflation, which there is according to NASA WMAP team, then it would still have a lot going for it.
 
Chronos said:
There was an interesting paper on initial conditions yesterday - Inflation as a Solution to the Early Universe Entropy Problem, http://arxiv.org/abs/1212.1087.

Any comments on this paper? who think it'll satisfy the likes of Roger Penrose and Sean Caroll?
 

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