No Universe without the BB:

[beecee]

I came across the following article.....comments appreciated.......

https://phys.org/news/2017-06-universe-big.html

No Universe without Big Bang June 15, 2017

According to Einstein's theory of relativity, the curvature of spacetime was infinite at the big bang. In fact, at this point all mathematical tools fail, and the theory breaks down. However, there remained the notion that perhaps the beginning of the universe could be treated in a simpler manner, and that the infinities of the big bang might be avoided. This has indeed been the hope expressed since the 1980s by the well-known cosmologists James Hartle and Stephen Hawking with their "no-boundary proposal", and by Alexander Vilenkin with his "tunnelling proposal". Now scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam and at the Perimeter Institute in Canada have been able to use better mathematical methods to show that these ideas cannot work. The big bang, in its complicated glory, retains all its mystery.

Read more at: https://phys.org/news/2017-06-universe-big.html#jCp

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.95.103508

ABSTRACT

"We argue that the Lorentzian path integral is a better starting point for quantum cosmology than its Euclidean counterpart. In particular, we revisit the minisuperspace calculation of the Feynman path integral for quantum gravity with a positive cosmological constant. Instead of rotating to Euclidean time, we deform the contour of integration over metrics into the complex plane, exploiting Picard-Lefschetz theory to transform the path integral from a conditionally convergent integral into an absolutely convergent one. We show that this procedure unambiguously determines which semiclassical saddle point solutions are relevant to the quantum mechanical amplitude. Imposing “no-boundary” initial conditions, i.e., restricting attention to regular, complex metrics with no initial boundary, we find that the dominant saddle contributes a semiclassical exponential factor which is precisely the inverse of the famous Hartle-Hawking result".

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I was once told by an Astronomer that any future QGT will most likely still encompass the BB/Inflationary model that is generally supported today.

By the same token, Newtonian gravity is still mostly used in space endeavours within our solar system, being accurate enough to achieve the desired results, albeit less accurate then GR.

The first sentence of the article has me somewhat bemused. "According to Einstein's theory of relativity, the curvature of spacetime was infinite at the big bang"

As an amateur, my Astronomer friend, along with a GR theorist, pumped into me the fact that the BB was an evolution of space and time, [spacetime] from the first 10-43 seconds after the event. Personally I always encompass the evolution of spacetime with spacetime, as we know it. I also like the "Superforce" scenario as put by Paul Davis in his book of the same name......that is that all the four forces were at the precise moment of the BB, united as per the holy grail of astronomy the sort after "Theory of Everything" or TOE.

Questions: Is the BB as secure and as certain as the article says? Personally, as an amateur, I would agree understanding that a scientific theory is never certain, and always open for modification etc, but also obviously scientific theories do grow in certainty over time and as they continue to match observational and experimental results... eg: The theory of evolution, and GR. Will a future QGT entail the BB model as I was told a few years ago?

I am not that well informed at this time re string theory and its many derivitives, including LQG, but do any of them support the "Superforce" concept and TOE?

How will the recent discovery of gravitational waves help in this regard?

Any other comments on the article and paper also encouraged.

 

Edited June 15, 2017 by beecee

[Mordred]

Good questions, as there is other readers as well. I will probably add what you may already know (judging from other posts I've read of yours). The BB model itself in current form of LCDM only truly covers from a hot dense state. Starting from [latex]10^{-45}[/latex] second forward.

 

It by itself doesn't attempt to describe how the universe began but rather from that hot dense state. Prior to that we run into mathematical singularity problems.

 

The model above is one where the singularity issue is avoided by the tunnelling described above. Mathematically it is a universe beginning model but like other universe beginning models (not LCDM, BB).

 

LQC for example has a bounce previous universe collapse then bounce. In effect their is 3 classes of models that try to answer the beginning. Universe from nothing, cyclic and bounce. The paper above being a cyclic if I recall.

 

So no LCDM is still secure, the model above works with LCDM including the homogeneous and isotropic mass distribution.

 

Gravity waves can be helpful in one way other than confirming GR.

 

We have a limit as to how far we can see via the electromagnetic spectrum. That limit being the surface of last scattering. (CMB) prior to that mean free path of photons becomes less than [latex]10^{-32}[/latex] metres. Due to free electrons, protons and neutrons.

 

This is called the dark ages in cosmology, Theoretically the only two ways of detection beyond this that I am aware of is detecting the Neutrino background and Detecting GW waves that originate prior to the dark ages. So via those GW waves we could theoretically see further assuming we have the funds to build sensitive enough detectors.

Edited June 15, 2017 by Mordred

[StringJunky]

 

How will the recent discovery of gravitational waves help in this regard?

IIRC GWs might help scientists 'see' further back in time when the universe was opaque to photons.

Edited June 15, 2017 by StringJunky

[Mordred]

Stringy and I x posted.

[beecee]

 

 

Good questions, as there is other readers as well. I will probably add what you may already know (judging from other posts I've read of yours). The BB model itself in current form of LCDM only truly covers from a hot dense state. Starting from [latex]10^{-45}[/latex] second forward.

It by itself doesn't attempt to describe how the universe began but rather from that hot dense state. Prior to that we run into mathematical singularity problems.

The model above is one where the singularity issue is avoided by the tunnelling described above. Mathematically it is a universe beginning model but like other universe beginning models (not LCDM, BB).

LQC for example has a bounce previous universe collapse then bounce. In effect their is 3 classes of models that try to answer the beginning. Universe from nothing, cyclic and bounce. The paper above being a cyclic if I recall.

So no LCDM is still secure, the model above works with LCDM including the homogeneous and isotropic mass distribution.

Gravity waves can be helpful in one way other than confirming GR.

We have a limit as to how far we can see via the electromagnetic spectrum. That limit being the surface of last scattering. (CMB) prior to that mean free path of photons becomes less than [latex]10^{-32}[/latex] metres. Due to free electrons, protons and neutrons.

This is called the dark ages in cosmology, Theoretically the only two ways of detection beyond this that I am aware of is detecting the Neutrino background and Detecting GW waves that originate prior to the dark ages. So via those GW waves we could theoretically see further assuming we have the funds to build sensitive enough detectors.

Gravitational waves from the BB itself! That would be great!

From previous links I have given, as an amateur I see the "universe from nothing" or the "ultimate free lunch" as easier to understand then any infinite quantities, but that's just a subjective opinion at this time.

BTW, the astronomer that "took me under his wing" so to speak, was a fella called Geraint Lewis from Sydney University.

[petrushka.googol]

AFAIK an inflationary epoch requires a triggering event, which of course, is the BB. The Universe is undefined prior to the Planck time. That is all scientists are able to conjecture as of now, at least.