Tuesday, October 13, 2020

Cosmological Inflation

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10^−36 seconds after the conjectured Big Bang singularity to some time between 10^−33 and 10^−32 seconds after the singularity. Following the inflationary period, the universe continued to expand, but at a slower rate. . . 

Inflation theory was developed in the late 1970s and early 80s, with notable contributions by several theoretical physicists, including Alexei Starobinsky at Landau Institute for Theoretical Physics, Alan Guth at Cornell University, and Andrei Linde at Lebedev Physical Institute. . . . It was developed further in the early 1980s. 
It explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe (see galaxy formation and evolution and structure formation). Many physicists also believe that inflation explains why the universe appears to be the same in all directions (isotropic), why the cosmic microwave background radiation is distributed evenly, why the universe is flat, and why no magnetic monopoles have been observed.

The detailed particle physics mechanism responsible for inflation is unknown. The basic inflationary paradigm is accepted by most physicists, as a number of inflation model predictions have been confirmed by observation; however, a substantial minority of scientists dissent from this position.The hypothetical field thought to be responsible for inflation is called the inflaton.
From Wikipedia.

I am skeptical of cosmological inflation theory for reasons similar to the reasons that Sabine Hossenfelder is skeptical of it. This group of theories is fundamentally a way to get from a particular set of initial conditions immediately after the Big Bang that is consistent with what we observe, to a different set of initial conditions that are just as arbitrary, a tiny fraction of a second earlier, with lots of intricate mathematical details that aren't easily distinguished from scores of alternative theories of the same genre.

The only reason to do this is that many scientists have presumptions, with no scientific basis, that don't match what we observe, about what the initial state of the universe must have looked like.

There also isn't a particularly credible calculation of what a non-inflationary baseline case to compare the predictions of a cosmological model to. Some scientists (educated layman's summary here) think that the baseline prediction of general relativity without inflation looks pretty much like what we see because ordinary gravitational evolution of the large scale structure of the universe should produces results like homogeneity that are often attributed to cosmological inflation.

I haven't invested much effort to really examining the issue with depth, however, because if we can get to initial conditions a fraction of a second after the Big Bang which would allegedly be produced by inflation and the earlier events are unknowable, this still seems like a very impressive accomplishment and knowing what happened in the very moment of creation isn't that important.


Graham Dungworth said...

The conventional Big Bang proceeds subsequent to an initial state of a hot thermalised bath of all standard model particles in thermodynamic equilibrium,at a temperature of >10^12 Kelvin and a circumference of ca. 4 light years (ly), expanding and cooling.

Inflation theories attempt to address various problems associated with the above general model namely the so called horizon, fine tuning, flatness, antimatter whereabouts, baryon number etc.

Whereas, the conventional BG records a high density state of ca. 1 ly radius,ca. > 4*10^9 that of liquid water here on Earth (STP)that expands and dilutes according to the inverse cube of radius and for which the temperature halves for each size doubling. The Inflaton field and its particles required a drastic solution to catch up timewise with BB initial conditions. Firstly, faster than speed of light expansion and secondly, inflation at constant density!

Roger Penrose has highlighted many of these problems and recently discussed his own conformal cosmology that recycles a new universe after a rather long wait ca. >10^100 year. Black Hole evaporation plays perhaps the most dominant role albeit after an eternity of elapsed time.

There are at least 3 mutually independent determinations of the age of the universe; The BB cooling curve/Hubble Constant measurement, everyone knows at ca. 14 *10^9 year, and similar ages from white dwarf cooling rate and cluster evaporation ages. Not just the whole universe but elements of our own galaxy were in place 9 billion years before our own solar system Sol and Terra Firma were in place. Sol Invictus, the oldest of our gods perhaps.So we can't bitch about its age and then endlessly discuss what happened before this event. St. Augustin famously derided those who did so "a special place in hell is reserved for those who do so".

So run your finger down the conventional cooling temperature curve for the universe until it reaches a temperature of 2.725K associated with the cmb radiation and read off the age given from the Hubble flow rate at the present epoch ca. 70km/sec +/- ~10% per megaparsec(3.26 million ly).
The cosmic background radiation or cmb is associated with photon abundance in the universe. Every cubic metre of space has around 410 million photons but atoms, largely hydrogen atoms have one nuclear proton or baryon, very sparse in the cosmos, on average, namely ca. 4 baryons per cubic metre. The baryon/photon ration is incredibly tiny 1/10^9, ore ca. one billionth of its expected value based on the initial thermal bath! not only that - we only observe ca. 5% of what we expect for the ca. 4 baryon/m^3! Yet we anticipate the lepton number for the universe is zero. It's a book keeping device; lepton number should be zero as should the baryon number, but it's 1/10^9 in the inflaton/BB models.We can balance the books by associating the photon number with the abundance of neutrinos in the cmb. A thermal bath associates equi abundances of photons and neutrinos.

Graham Dungworth said...

Sadly lacking are experiments to test these theories. It's almost an established law that hydrogen H and helium He (2 protons and 2 neutrons) cannot be generated in stars. In some massive stars > 100 sol solar mass, a pair instability reaction generates leptons ie. electron positron pairs that cause stellar collapse, there's no feedback mechanism that can retard gravitational collapse. Core temperatures are never high enough to create proton antiproton pairs. Also for stellar masses > ca. 2 sol, either a ca. earth sized white dwarf or a neutron star( ca. 30 km radius) results or even a 3km black hole. These are now well known phenomena and Roger Penrose et al have earned a belated nobel Prize for this work and empirical back up.

There is a rare class of supermassive stars that create hypernovae. within this class of star >200 solar mass. Within this class is a rare type that leaves a H/He envelope after detonation. This remains a mystery as these lightest of elements should have burned away prior to detonation. Such stars are thought to have been common in the early universe as they have trace metallicities (ppm that of our own star.

Graham Dungworth said...

The Cern antigravity experiment according to Dragan Hadjukovic may be delays by 2-3 years after Feb 2021.

Supermassive stars may well generate baryons in the approach to 10^12 Kelvin. There is a rare class of hypernovae with trace metallicities that leave a H/He envelope in the location of the former gravitaing mass. A gravitating mass of cold photons neutrinos at 2.725 K will gravitate to a state of maximum entropy in a black hole. with an antigravity effect on particle antimatter pairs the detonation in the approach to the event horizon could blast all antimatter into a black hole. Half the mass of such a supermassive star , or normal matter would be blasted into our own universe. such a process , driven by neutrino degenerative pressure would be repeted up to 10^22 fold to account for the eventual abundance of all stars in ca. 10^11 galaxies. Neutrino degeneration pressure may resolve many of the problems associated with early cosmology, driven by scietific methodolgy.

Graham Dungworth said...

The problems raised by Sabine's comment some 3 years ago can't so easily be washed away or ignored. Hoyle, Peebles, Weinberg, Penrose and others expressed them as problems and sought to state them in a manner that could be solved. The second law equates thermodynamic equilibrium with causal contact and that's not possible for the hot BG, unless one considers almost infinite density at the Planck length. For the antimatter problem it may prove interesting to bud it off into a coeval antimatter universe or to profer a cyclic universe that alternates matter and antimatter cycles eg. the recent models of Penrose et al or Hadjukovic over time periods equated with metaphysics.

Is it science if it can't be tested? The fact is scientists debate it endlessly.

If the ca. 1 milli electron volt electron neurtrino rest mass is vindicated then it will prove more likely that these excess cold photons are equated with the lepton number and not that of the baryon. Also, if matter antimatter is found to antigravitate then a sufficiently hypermassive star >200-250 solar will upon gravitation of an initial early cosmological state, initial conditions of solely photons and neutrinos, initially devoid of charged leptons and baryons, will lead to charged leptogenesis and then baryogenesis immediately prior to detonation as a hypernova, 50% of the mass energy directed into an "anti matter blackhole" and the remnant 50% mass energy of what we call left handed chiral normal matter,directed into our side of the universe, a consequence of neutrino degeneracy pressure.

We have data on these rare hypermassive hypernova and await the crucial Cern antigravity experiment and determination of neutrino rest mass.. It's galling that it has been delayed beyond Feb. 2021
as a consequence of covid 19.

andrew said...

"if matter antimatter is found to antigravitate"

This is all but conclusively ruled out.