Future of Universe: Big Freeze, Big Rip, Big Crunch, Big Bounce?

[TheDemx27]

http://en.wikipedia.org/wiki/Future_of_an_expanding_universe
*Shudders at the size and scale of the universe of things. Existential crises incoming for the umpteenth time.*

 

[bahamagreen]

http://en.wikipedia.org/wiki/Future_of_an_expanding_universe
*Shudders at the size and scale of the universe of things. Existential crises incoming for the umpteenth time.*

Gotta love wikipedia, after 10^100 years, "What happens after this is speculative." :)

 

[Torbjorn_L]

If we assume the limit of detectability is the current CMB temperature, then our universe would have to expand by a factor of over 1000 before all galaxies not gravitationally-bound to us are redshifted to undetectability. A super-rough back-of-the-envelope calculation leads me to think that this will take on the order of a hundred billion years.

And so most life would be gone. Granted, new red/white dwarfs will be produced for quite a while yet. But star production has dropped a factor 100 on average AFAIK (running out of gas, literary), so that is at the tail end of natural emergent life.

As for the rest of cosmology, it will be knowable for a while after that, just more difficult. The galaxy SMBH will throw the random high speed star out of the galaxy, and those suffice to observe dark energy as I understand it. Hence predicting the else curious CMB spectral peak portions.

"What happens after this is speculative."

Ah, another symmetry (by analogy). Cosmology has speculative physics before and after the known parts.

 

[Clayjay]

There isn't enough of it, compared to the rate of expansion, for the dark matter to halt the expansion.

i am just trying to make sense of this so allow me to round numbers - On a cosmic scale the universe is about 70% dark energy and 30% gravitational energy (power). Of all the gravity 85% is dark matter and 15% is light matter (baryons). The local group is gravitationally bound and so are all galaxy groups. All galaxies groups exist within dark matter and dark matter is gravitational bound.

Where could dark energy expand space? It seems to me the perfect environment for expressing dark energy is in the very huge cosmic special voids. The internal distance or diameter of the voids run around between 50 -150 million light years while the distance across filaments is around 5-10 million light years.

I am not saying I am right but I am expressing my simple logic that counters the idea of dark energy acting on any gravitationally bound matter, even dark matter clouds that envelop baryonic matter. As far as dark or baryonic matter is concerned dark energy does not exist.

 

[Chalnoth]

The bit about gravitational energy is entirely incorrect. It's about 30% matter (currently). Gravitational energy is a somewhat nebulous concept which would be extremely misleading to use in this context, because dark energy influences the expansion history through gravity as well. It's just that different kinds of matter have different impact on the expansion rate.

Dark energy also doesn't "expand space". The expansion is already there. Dark energy just prevents the expansion rate from falling too low. It acts, in effect, as a repulsive force. Basically, it changes gravity in the Newtonian limit from:
F = -{G m_1 m_2 \over r^2}
to:
F = -{G m_1 m_2 \over r^2} + {1 \over 3}\Lambda r

This has an impact everywhere in the universe. But the value of \Lambda is so small that it's unmeasurable on scales shorter than billions of light years.

Finally, the the density ratios today really don't tell you much of anything about our universe (except for the ratio of normal matter to dark matter: that's pretty stable over time). The problem is that the density ratios are a function of time. A billion years ago, matter would have been a larger portion of the total energy density. 12 billion years ago dark energy was a negligible component of the total energy density.

In order to get a handle on what the makeup of the universe means, you have to look at each component individually. The dark energy remains roughly constant over time. As the square of the expansion rate is proportional to the density, this means that the current ~70km/s/Mpc expansion rate will slowly decrease to ~60km/s/Mpc in the far future. As long as the dark energy is constant, it will remain at that rate indefinitely. The matter density, meanwhile, will decrease over time until nothing but empty space remains.

 

[Clayjay]

The bit about gravitational energy is entirely incorrect. It's about 30% matter (currently). Gravitational energy is a somewhat nebulous concept which would be extremely misleading to use in this context, because dark energy influences the expansion history through gravity as well. It's just that different kinds of matter have different impact on the expansion rate.

It looks to me we are both correct in the context we used. The universe is roughly 70% dark energy and 30% gravity or matter. The universal gravitational constant coverts the terms. The whole universe is 100% divided into 70% dark energy plus 25% dark matter and 5% ordinary matter. Of the 30% that is 100% gravity 83.33% of the gravity is attributed to dark matter and 16.66% to ordinary matter. It was my responsibility to communicate clearly but I didn't. I will try to improve. Thank you for your help.

Dark energy also doesn't "expand space". The expansion is already there. Dark energy just prevents the expansion rate from falling too low. It acts, in effect, as a repulsive force.

"The expansion or already there" is a useful reasonable perspective. However Big Bang logic starts with a singularity that contained 100% of space-time. There was no space before space-time and the statement "expansion already there" is unsupported by Big Bang theory. All points in space today where one point in the beginning. True - that BB was a point in time and not space. True - there was no space before time. Logically time is primary or a prioriand space a posteriori. Inmy view, the concept of space-time is unified and looses meaning if therms are separated.

In order to get a handle on what the makeup of the universe means, you have to look at each component individually.

Does the context-logic of your statements have a unified principle in it? I think there is miscommunication galore here because of the diametric frameworks of classical and quantum cosmology. Classical physics is built on deductive logic while quantum mechanics uses inductive logic. Classical physics and Quantum mechanics have different ways of knowing things.

In my opinion it is a common misperception that cosmology is a branch astrometry. It seems to me that science is a branch cosmology. In prehistorical time cosmology had magical answers and legends. Through the Greek’s “Natural Philosophy” magical thinking was removed and replaced with logic. Logic can be viewed as having two branches, deductive and inductive logic. Classical physics is a result of deductive logic, where as quantum mechanics is a result of inductive logic. I experienced this divergence during my advanced physics studies as classical physics failed at the atomic level where the phonon or quantum level physics account for the data. Classical physics and quantum physics are both logically self-consistent but at the atomic level the logic methodology flips from deductive to inductive. A difference I think that is worth knowing for a cosmologist.

 

[Chalnoth]

It looks to me we are both correct in the context we used. The universe is roughly 70% dark energy and 30% gravity or matter. The universal gravitational constant coverts the terms. The whole universe is 100% divided into 70% dark energy plus 25% dark matter and 5% ordinary matter. Of the 30% that is 100% gravity 83.33% of the gravity is attributed to dark matter and 16.66% to ordinary matter. It was my responsibility to communicate clearly but I didn't. I will try to improve. Thank you for your help.

These aren't percents of gravity. That doesn't really make sense. These are percents of the current average energy density of the universe.

"The expansion or already there" is a useful reasonable perspective. However Big Bang logic starts with a singularity that contained 100% of space-time. There was no space before space-time and the statement "expansion already there" is unsupported by Big Bang theory. All points in space today where one point in the beginning. True - that BB was a point in time and not space. True - there was no space before time. Logically time is primary or a prioriand space a posteriori. Inmy view, the concept of space-time is unified and looses meaning if therms are separated.

As the singularity is an artifact in the equations that never occurred, this paragraph makes no sense. Big bang logic doesn't start with a singularity at all. It starts with the concept of a homogeneous, isotropic universe.

It's very useful to get out of the paradigm of the universe as a narrative, with each part building on the next. The problem with that paradigm is that our image of the earliest times is the most uncertain, so that if we relied upon models that were narratives, we'd never be able to get at the truth.

Scientific theories are not narratives. They are not stories where some early event leads to some later event. They are attempts to explain the structure and behavior of our universe.

Does the context-logic of your statements have a unified principle in it? I think there is miscommunication galore here because of the diametric frameworks of classical and quantum cosmology. Classical physics is built on deductive logic while quantum mechanics uses inductive logic. Classical physics and Quantum mechanics have different ways of knowing things.

In my opinion it is a common misperception that cosmology is a branch astrometry. It seems to me that science is a branch cosmology. In prehistorical time cosmology had magical answers and legends. Through the Greek’s “Natural Philosophy” magical thinking was removed and replaced with logic. Logic can be viewed as having two branches, deductive and inductive logic. Classical physics is a result of deductive logic, where as quantum mechanics is a result of inductive logic. I experienced this divergence during my advanced physics studies as classical physics failed at the atomic level where the phonon or quantum level physics account for the data. Classical physics and quantum physics are both logically self-consistent but at the atomic level the logic methodology flips from deductive to inductive. A difference I think that is worth knowing for a cosmologist.

Whaaa?? Um, no. All of science combines both inductive and deductive logic. Classical physics and quantum mechanics certainly do not have different ways of knowing things. Quantum mechanics is the physics which is needed to describe the behavior of the universe on small scales or cold temperatures.

 

[PeterDonis]

Big Bang logic starts with a singularity that contained 100% of space-time.

"Spacetime" is not the universe at one instant. It contains the entire history of the entire universe. So even if the initial singularity were part of spacetime (which it isn't, as Chalnoth pointed out), it would only be a very small part; it would not be 100% of it.