Starship Asterisk*

Detailed computer simulations have found that a cosmic contraction can generate features of the universe that we observe today.

Credit: Lucy Reading-Ikkanda/Quanta Magazine

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The standard story of the birth of the cosmos goes something like this: Nearly 14 billion years ago, a tremendous amount of energy materialized as if from nowhere.

In a brief moment of rapid expansion, that burst of energy inflated the cosmos like a balloon. The expansion straightened out any large-scale curvature, leading to a geometry that we now describe as flat. Matter also thoroughly mixed together, so that now the cosmos appears largely (though not perfectly) featureless. Here and there, clumps of particles have created galaxies and stars, but these are just minuscule specks on an otherwise unblemished cosmic canvas.

That theory, which textbooks call inflation, matches all observations to date and is preferred by most cosmologists. But it has conceptual implications that some find disturbing. In most regions of space-time, the rapid expansion would never stop. As a consequence, inflation can’t help but produce a multiverse — a technicolor existence with an infinite variety of pocket universes, one of which we call home. To critics, inflation predicts everything, which means it ultimately predicts nothing. “Inflation doesn’t work as it was intended to work,” said Paul Steinhardt, an architect of inflation who has become one of its most prominent critics.

In recent years, Steinhardt and others have been developing a different story of how our universe came to be. They have revived the idea of a cyclical universe: one that periodically grows and contracts. They hope to replicate the universe that we see — flat and smooth — without the baggage that comes with a bang.

To that end, Steinhardt and his collaborators recently teamed up with researchers who specialize in computational models of gravity. They analyzed how a collapsing universe would change its own structure, and they ultimately discovered that contraction can beat inflation at its own game. No matter how bizarre and twisted the universe looked before it contracted, the collapse would efficiently erase a wide range of primordial wrinkles. ...

Over the last year and a half, a fresh view of the cyclic, or “ekpyrotic,” universe has emerged from a collaboration between Steinhardt, Anna Ijjas, and others — one that achieves renewal without collapse.

• Physics Letters B 795:666 (10 Aug 2019) DOI: 10.1016/j.physletb.2019.06.056
• arXiv.org > gr-qc > arXiv:1904.08022 > 16 Apr 2019

• arXiv.org > gr-qc > arXiv:2006.01172 > 01 Jun 2020

• arXiv.org > gr-qc > arXiv:2006.04999 > 09 Jun 2020 (v1), 08 Jul 2020 (v2)

Marsdmitri wrote: ↑Sun Nov 22, 2020 5:31 am It is correct, that Dark matter has 10 different types? And you have to use it in your mathematical models.
Or I forgot something?

1. Very small neutron stars, young pulsars, quark stars.

2. Black holes and jets from electrons.

3. Red dwarfes (the smallest and coolest kind of star), any planets.

4. Any dust like: cement, Carbon, Fe3O (cementite https://en.wikipedia.org/wiki/Cementite), ice in the space with the temperature about 3-5 Kelvin. Boze condensate. Clouds of O2 (oxygen) and H2(Hydrogen), He, and isotopes (isotopes of boron (5B), isotopes of lithium 3Li, 6Li, 4Li and so on). And other very cold gas in space.

5. Chondrites, small asteroids, comets.

6. Clasters from dust. New materials, like dust of carbon, graphene, very heavy metals like gold, platinum, uranium and so on with very small temperature of surface.

7. Clouds from Oxygen with temperature 9,5 million Celsius with dust from heavy metals like Wolfram, Fe, Uranium, gas Radon and so on. The filament from these matter connect black holes or centers of all Galaxies.

8. Clouds from neutrino.

9. Organic materials (lyzine(https://en.wikipedia.org/wiki/Lysine), Benzene (https://en.wikipedia.org/wiki/Benzene), methanol, hydrogen cyanide, tholins, ammonia, acetylene, ethane and so on.

10. Something else. Nobody knows what it is. New particles like new type of neutrino maybe. Quark with zero electric charge and so on. It is exotic.
We can not see all these things in our telescope. But it is exist.

BDanielMayfield wrote: ↑Fri Aug 14, 2020 6:41 pm But doesn't the accelerating expansion of the universe rule out cyclical cosmologies?

Dark Energy is overwhelming (I was going to write trumps, but that word has been ruined for normal usage) the attractive gravitational pull of all the rest of the material in the universe.

Natalie Wolchover of Quanta Magazine wrote:

A provocative paper published today in the journal Nature Astronomy argues that the universe may curve around and close in on itself like a sphere, rather than lying flat like a sheet of paper as the standard theory of cosmology predicts. The authors reanalyzed a major cosmological data set and concluded that the data favors a closed universe with 99% certainty — even as other evidence suggests the universe is flat.

The data in question — the Planck space telescope’s observations of ancient light called the cosmic microwave background (CMB) — “clearly points towards a closed model,” said Alessandro Melchiorri of Sapienza University of Rome. He co-authored the new paper with Eleonora di Valentino of the University of Manchester and Joseph Silk, principally of the University of Oxford. In their view, the discordance between the CMB data, which suggests the universe is closed, and other data pointing to flatness represents a “cosmological crisis” that calls for “drastic rethinking.”

Camille M. Carlisle of Sky & Telescope wrote:
Similarly, the wiggly power spectrum graph (shown above) may have some problems over large patches of the sky. While the agreement between observation and theory is extraordinary at small angular scales, temperature fluctuations in the CMB at the largest scales don’t behave as well. The team can’t maneuver the graph to fit these points without losing the beautiful fit elsewhere.

Marsdmitri wrote: ↑Sun Nov 22, 2020 5:31 am It is correct, that Dark matter has 10 different types? And you have to use it in your mathematical models.

BDanielMayfield wrote: ↑Sun Nov 22, 2020 12:39 pm The intellectual waters are deeper than we are tall here, but still we try to tread along. I could certainly be wrong, but Ann, you might be conflating two different things here: Universal shape and universal destiny, space and time. The universe's shape can be closed, flat or open while it's destiny can be finite or infinite, terminal or unbounded. It could be that spatially the universe might be closed (which we compare to the surface of a sphere on which a line extended out in any direction from any point comes back upon itself) and still have an infinite future (due to unending expansion).

Since my opinion is irrelevant as to which of these possibilities it is I'll keep it to myself, except to agree that the Big Crunch is a huge bummer.

Ethan Siegel wrote:

... it would be unfair to say that the Cosmic Microwave Background demonstrated that the Universe was unambiguously flat, since the patterns of temperature fluctuations that it revealed had multiple possible solutions. The Universe could be expanding somewhat faster or slower at the expense of adjusting some of the parameters; a Universe that was slightly either closed (and overdense) or open (and underdense) were still permitted. There is wiggle-room with the CMB alone...

Gravitational lensing is a cumulative effect of having matter in between your observation point and the source you're measuring: in this case, the Cosmic Microwave Background itself. The identification of a stronger-than-expected lensing signal, one possible interpretation of the Planck data, suggests that there's more matter density than previously expected. If there's more matter than other indicators suggest, perhaps that means the Universe is closed and overdense, and there's a slight amount of (positive) spatial curvature.

The authors note — importantly but controversially — that a number of other anomalies might fit in perfectly with this. A closed and overdense Universe could explain why the temperature fluctuations on the largest angular scales (corresponding to scales of ~30 million light-years or so) are lower than expected...

Given that the Cosmic Microwave Background prefers a value of about 67 km/s/Mpc, while distance ladder methods prefer 73 km/s/Mpc, it's reasonable to hope that playing with this extra wiggle-room might help solve a large number of problems. When the authors run their analysis, they find that the best fit to all the data involves a slightly overdense Universe with positive curvature at the 4.4% level, achieving about a 3-sigma statistical significance favoring this value...

(However,) the best constraints on spatial curvature no longer come from Cosmic Microwave Background experiments, but from a different source: measurements of baryon acoustic oscillations. By mapping the large-scale structure of the Universe and determining how galaxies clump, cluster, and correlate on large scales, we've been able to constrain the curvature of the Universe to ~0.4% precision. When we use that data, we find that the Universe is perfectly spatially flat, and that a curvature of ~4.4% is ruled out at greater than 10-sigma significance, something the authors themselves acknowledge.