**Einstein Eq.:**

**Equation-of-state**

**Hubble constant**

or

**Hubble time**

**Hubble distance**

**Age of the Universe**

**Luminosity distance:**

**BH Lifetime **

**Critical Density**

** Fluct. amp.**

**Cosmic Microwave Background:**

**Cosmic Neutrino Background:**

**Matter-Radiation Equality:**

**Planck Mass**(=”“)

**Megaparsec**

**The GeV**

**Cosmic destiny**

**the Big Crunch**. In other words, if there is enough matter in the Universe eventually gravitational forces will stop its expansion. At the point of maximum expansion, gravity will cause the universe to reverse its direction and it will begin to collapse under its own weight. This phase of the Universe’s life is known as the “Big Crunch”. The alternative is that the Universe, without new creation of matter, will freeze to something close to the absolute zero. This scenario is called the

**Big Freeze/the Big Chill**or the

**thermal death**of the Universe.

**cyclic cosmology**or the

**Phoenix Universe**(even sometimes you know it as oscillating cosmology, but this name is something that does not imply a total collapse or a permanent positively accelerate Univers). In this way the Universe would last forever but would continually go through these phases of expansion and contraction, Big Bang and Big Crunch and so on…

*collapses into a future singularity*, similar to a supermassive black hole. It is the

**Big Crunch**.

*expands forever*, it freezes or cools until a temperature close to the absolute zero. It is the

**Big Freeze/Big Chill/thermal death**of the Universe.

**cyclic cosmology**scenario or the

**Phoenix Universe**. It begins with a Big Bang, it recollapses with a Big Crunch, then another Big Bang reignites a new Universe, it follows another Big Crunch, and so on…

future what the Universe may look like in very distant eras.

**stelliferous or Star-Filled era**. The state of the Universe is filled with stars and galaxies and planets. This era ends when all the stars have exhausted their fuel and have died leaving behind only remnants of their brilliance.

**Degenerate era**. The universe will be composed of dead planets, brown dwarfs, white dwarfs, neutron stars, black holes, and some theoretical forms of dark matter in that time. This era ends with the disintegration of all protons (supposing the GUT idea is right), which compose the nuclei of all atoms. Then the universe will enter then into the Black Hole era. Black holes will be the only gravitationally important objects remaining in the universe. Black holes do not last forever if our understanding of them is right. They will eventually evaporate, radiating away into nothingness. After that all that will remain is radiation and particles which have an infinite lifetime such as electrons, positrons, and neutrinos. From this point on it is impossible to fathom what will happen as we have reached the limits of our knowledge.

If Ω<1, the geometry of space is open, or negatively curved like the surface of a saddle. The angles of a triangle sum to less than 180 degrees, and lines that do not meet are never equidistant; they have a point of least distance and otherwise grow apart. The geometry of such a universe is hyperbolic. But even in the absence of dark energy, a negatively curved universe expands forever, with gravity having little effect in slowing the rate of expansion. With dark energy, the expansion not only continues but accelerates, which seems to be our current condition after some 13.6 billion years of existence.

**Big Rip**, in which the dark energy inspired acceleration eventually becomes so strong that it completely overwhelms the effects of the gravitational, electromagnetic and weak binding forces. On the other hand, a negative cosmological constant, which would correspond to a negative energy density and positive pressure, would cause even an open universe to recollapse to a Big Crunch. This has been ruled out by recent observations. But there are aspects of all of this that remain problematic.

**flat universe**(a contemporary update of the flat Earth idea extended to the whole Universe!)…If the average density of the universe equals the critical density so that Ω=1, then the geometry of the universe is flat:

**as in Euclidean geometry**, the sum of the angles of a triangle is 180 degrees and parallel lines continuously maintain the same distance. Absent of dark energy, a flat universe expands forever but at a continually decelerating rate, with expansion asymptotically approaching a fixed rate. With dark energy, the expansion rate of the universe initially slows down, due to the effect of gravity, but eventually increases. The ultimate fate of the universe is the same as an open universe. That is, there is a Big Rip in the future of the Universe or the Universe becomes disconnected from every place. In a dark energy dominated future of the Universe, we will not see clusters, galaxies or even stars, they will be taken away beyond our horizon. Astronomy will become boring in some Gyrs!!!

**density of the universe and the dominating fluid.**The preponderance of evidence to date, based on measurements of the rate of expansion and the mass density, favors a universe that will continue to expand indefinitely, resulting in the

*“big*

*freeze”*scenario.

**The Big Freeze, The Big Chill or Heat Death**

*it could also occur*in a closed universe. This scenario is currently the most commonly accepted theory within the scientific community. A related scenario is Heat death, which states that the universe goes to a state of maximum entropy in which everything is evenly distributed, and there are no gradients — which are needed to sustain information processing, one form of which is life. The Heat Death scenario is compatible with any of the three spatial models, but requires that the universe reach an eventual temperature minimum.

**The Big Rip: Finite Lifespan**

*The end state of the universe is a future singularity*, as the dark energy density and expansion rate becomes infinite. While on the surface this makes sense, it too is problematic. But the Big Rip, or some variants dubbed as Little Rips or even no Big Rip at all are possible cases with a phantom energy future.

**The Big Crunch**

**oscillatory**

**universe.**Let me point out the oscillatory universe can be understood as well as a Universe in which there are several phases of positive acceleration (“inflation like” bounces) and negative acceleration (crunch like in which there is no total collapse into a future singularity). Anyway, the terminology is a bit fuzzy with respect to the name oscillatory universe, cyclic universe or Phoenix Universe. The universe could then consist of an infinite sequence of finite universes, each finite universe ending with a Big Crunch that is also the Big Bang of the next universe (after some timeless periods sometimes called

**aeons**). Theoretically, the oscillating universe could not be reconciled with the second law of thermodynamics: entropy would build up from oscillation to oscillation and cause heat death.

static surfboard.

**Big Bounce**

**The False vacuum and the Big Decay scenario**

**false vacuum**, it could tunnel into a lower energy state. This is called the vacuum metastability event. This has the potential to fundamentally alter our universe; in more audacious scenarios even the various physical constants could have different values, severely affecting the foundations of matter, energy, and spacetime. Our current knowledge of the Standard Model seems to point out that we live in a false vacuum, a long-lived metastable phase of matter and energy. Only further studies of the Higgs sector and the hidden (dark) sector of the Standard Model will tell if it is so or there are new particles that stabilize the vacuum.

**Cosmic uncertainty **

**and our Great Destiny/Cosmic Doom**

*we know almost*

*nothing of the real physics of the dark energy*.

**If the theory of inflation is true**, the

**universe went through an episode dominated by a different form of dark energy**

*in the first moments of the Big Bang;*but

*inflation ended*,

**indicating an equation of**

**state much more complicated than those assumed so far for present-day dark**

**energy**.

**It is possible that the dark energy equation of state could change again***resulting in an event that would have consequences which are extremely difficult*

*to parametrize or predict.*It is also possible the universe may never have an end and continue in its present state forever.

**Choosing among these rival scenarios is done by ‘weighing’ the universe**, and it is not easy at all. For example,

*measuring the relative contributions of matter, radiation, dark matter*

*and dark energy to the critical density*. More concretely,

*competing scenarios are*

*evaluated against data on galaxy clustering and distant supernovae*,

*and on the*

*anisotropies in the Cosmic Microwave Background.*

**Classical options:**Big Crunch, ethernal expansion with or without Big Freeze, Phoenix Universe, each of them depending on the geometry and the total density omega.

**Modern options:**Big Crunch, Big Freeze, Thermal Death, Big Rip, Little Rip, oscillating universes, bouncing universes, the false vacuum scenario with a Big Decay (quantum tunneling through a massive desintegration event), and the Multiverse/Polyverse scenario.

**More ideas: inflation, holography, string theory and all that**

*two-dimensional information*structure “painted” on the

*cosmological horizon*, such that the three dimensions we observe are only an effective description at macroscopic scales and at low energies.

cosmological horizon has a finite area and grows with time. However, there are some interesting proposals by Padmanabhan.

Meanwhile, back at the ranch, Andrei Linde, Alan Guth, Ted Harrison, and Ernest Sternglass argued that inflationary cosmology strongly suggests the presence of a Multiverse, and that it would be practical even with today’s knowledge for intelligent beings to generate and transmit de novo information into a distinct universe. Alan Guth has speculated that a civilization at the top of the Kardashev scale might create fine-tuned universes in a continuation of the evolutionary drive to exist, grow, and multiply.

**the Selfish**

**Biocosm Hypothesis**, and by

*the proposal that the existence of the fundamental*

*physical constants may be subject to a Darwinian evolution of Universes*.

*the Holographic Principle suggests that traditional physical quantities may*

*possibly themselves be describable in terms of exchanges of information*, which in turn raises questions about the applicability of older cosmological models. Of course, the holographic idea could be an illusion telling us that there is a new thermodynamics and statistical mechanics (based on non-extensive entropy) in which we should study these issues. But it is a current area of research. :).

**“Endings”**with an initial commentary to go with Alex Reynolds’ “Origin” By David Rountree, that you can find in the internet. I have updated it and removed the author personal views to include mine.

**See you in my next chaosmic post!**