Cosmic inflation and singularity

[sshai45]

"Cosmic inflation" and singularity

Hi.

I saw this on Wikipedia:
http://en.wikipedia.org/wiki/Chronology_of_the_universe#Planck_epoch

In inflationary cosmology, times before the end of inflation (roughly 10−32 second after the Big Bang) do not follow the traditional big bang timeline. The universe before the end of inflation was a very cold near-vacuum and persisted for much longer than 10−32 seconds. Times from the end of inflation are based on the big bang time of the non-inflationary big bang model, not on the actual age of the universe at that time, which cannot be determined in inflationary cosmology. Therefore, inflationary cosmology lacks a traditional Planck epoch—though similar conditions may have prevailed in a pre-inflationary era of the universe.

Later:

Inflation ended when the inflaton field decays into ordinary particles in a process called "reheating", at which point ordinary Big Bang expansion began. The time of reheating is usually quoted as a time "after the Big Bang". This refers to the time that would have passed in traditional (non-inflationary) cosmology between the Big Bang singularity and the universe dropping to the same temperature that was produced by reheating, even though, in inflationary cosmology, the traditional Big Bang did not occur.

If there was no "traditional Big Bang" with inflationary cosmology, would this remove the singularity at the beginning of the universe? If so, then what is all the hubbub about using quantum gravity and so forth to resolve this "singularity"? Hasn't "inflation" theory been a mainstream component of the standard picture of cosmology for a while now? If not, does that mean the singularity still existed, just further back in time? Note that in that previous quote it says with regard to the Planck epoch that "similar conditions may have prevailed in a pre-inflationary era of the universe" -- could this be it, or something 'close' to the supposed singularity that needs "resolving"? However, it only says "may" -- could it be that they didn't, and there was no singularity ever ever, and so it's resolved right there, just like that?

 

[bapowell]

It is expected that even inflationary spacetimes are not past-eternal, i.e. there is still an initial singularity to contend with. See: http://arxiv.org/abs/grqc/0110012

 

[sshai45]

It is expected that even inflationary spacetimes are not past-eternal, i.e. there is still an initial singularity to contend with. See: http://arxiv.org/abs/grqc/0110012

So then there'd ultimately be a "real Big Bang" some unknown time interval before the point marked "end of inflation"? How far back could it be, anyways?

 

[bapowell]

Sure, or if not a real big bang, some other sort of quantum cosmological genesis event. I don't know how far back it could be...my suspicion is "quite far".

 

[sardar]

Thank you for your question. Let's start by defining what we mean by "singularity" in the context of cosmology. A singularity refers to a point in time where the laws of physics break down and our current understanding of the universe cannot explain what happened. In the traditional Big Bang model, the singularity occurs at the beginning of the universe, when it is believed that all matter and energy were condensed into a single point of infinite density and temperature.

However, with the theory of cosmic inflation, this singularity is no longer necessary. Inflation proposes that the universe underwent a rapid expansion in the first fractions of a second, stretching out the fabric of space-time and smoothing out any irregularities. This means that the universe was not condensed into a single point, and therefore there is no need for a singularity.

So to answer your question, if the universe did not undergo a traditional Big Bang, then there is no singularity at the beginning of the universe. The idea of using quantum gravity to resolve the singularity comes from the traditional Big Bang model, where the laws of physics break down at the singularity. However, with inflation, this is no longer a problem.

Inflation theory has been a mainstream component of the standard model of cosmology for a while now, and it has been supported by various observations such as the cosmic microwave background radiation. The "pre-inflationary era" mentioned in the quote refers to the period before inflation, where conditions may have been similar to those at the Planck epoch. However, this is still a topic of ongoing research and is not yet fully understood.

In conclusion, the theory of cosmic inflation does remove the need for a singularity at the beginning of the universe. It is a well-supported theory in the scientific community and has helped to explain many mysteries of the universe. You are correct in thinking that the singularity has been resolved with inflation theory, and it is no longer a major concern in cosmology.