The Big Crunch

[Deleted]

Current data and models point towards our universe becoming a De Sitter-universe:
http://en.wikipedia.org/wiki/De_Sitt...r_the_Universe

In the future, dark energy will drive expansion at an accelerating rate; distances will double every 20 billion years or so, into the indefinitely far future. It looks like the end will be in ``ice'', not ``fire''; the universe will expand forever in an increasingly cool ``Big Chill'' rather than recollapsing in a fiery ``Big Crunch''. On a smaller scale, what will happen to our galaxy and other galaxies as the universe chills out?
In the near future, stars will continue to form as they do now. However, with each generation of stars that form, more and more of the matter in the universe is locked away into stellar remnants (white dwarfs, neutron stars, and black holes). Eventually, all the gas will be used up, and no more stars will form.
10^12 (1 trillion) years after the Big Bang:
Stars die. No more fusion-powered stars, as the lowest-mass stars from the last generation of star formation dwindle away into white dwarfs. Galaxies will be filled with white dwarfs, neutron stars, and black holes, with no more brightly-shining stars.
10^27 (1000 trillion trillion) years after the Big Bang:
Galaxies ``dissolve''. Close encounters between stellar remnants within galaxies fling half of them out of the galaxy into intergalactic space. The remaining stars are swallowed by the galaxy's central supermassive black hole, swelling it to a gargantuan size (about 100 billion solar masses for a fair-sized galaxy like our own). Galaxies no longer exist - stellar remnants have been strewn throughout space.
10^31 (10 million trillion trillion) years after the Big Bang:
Supermassive black holes merge. After galaxies become unbound, flinging their stellar remnants into space, clusters of gargantuan black holes exist where clusters of galaxies used to be. The black holes, as they orbit through space, radiate ``gravitational waves''. These gravitational waves are ripples in space-time itself; just as ripples in water carry energy, so ripples in space-time carry energy away from the moving black holes, allowing them to spiral in toward the center of the cluster in which they live. Eventually, all the gargantuan black holes in the cluster will merge together to form a hyper-gargantuan black hole (about 1000 trillion solar masses for a fair-sized cluster like the Virgo Cluster).
10^45 (1 billion trillion trillion trillion) years after the Big Bang:
Protons and neutrons decay. Although we think of protons as being stable particles (unless they happen to meet up with an antiproton), they are actually subject to decay on extremely long time scales. The half-life of the proton is uncertain (because it is so long), but it's in the neighborhood of 10^45 years. After this time, protons (and their close relations, neutrons) decay into positrons, electrons, and photons. As a consequence, white dwarfs and neutron stars (and any planets, asteroids, and comets that are still around) will disintegrate into expanding clouds of electrons, positrons, and photons. For a long time after protons and neutrons decay, the universe will be fairly stable -- electrons, positrons, black holes, neutrinos, and photons will be spread throughout an ever-expanding universe.




(3) Eventually, black holes will evaporate into particles and antiparticles.
As Steven Hawking writes in his popular cosmology book, A Brief History of Time, ``Black holes ain't so black.'' According to classical physics, black holes can only absorb particles; they can't emit them. However, the laws of quantum mechanics state that black holes can emit particles and antiparticles. One of the fundamental laws of quantum mechanics is the Uncertainty Principle, which states that can't know precisely both the position and the velocity of a subatomic particle. In other words, there is a fundamental uncertainty built into the universe. On subatomic scales it is impossible to have complete knowledge of the universe. One of the attributes of the universe which is uncertain is the energy density of space. What we think of as ``empty'' space is actually filled with very tiny, very rapid fluctuations in energy, seething and bubbling on a subatomic length scale. If the energy is large enough, it is possible for a particle-antiparticle pair to form spontaneously at the location of the fluctuation. Under ordinary circumstances, the particle and antiparticle annihilate each other very shortly afterwards. However, consider what can happen if a particle-antiparticle pair spontaneously pops out of empty space very close to a black hole. In this case, it is possible for one member of the particle-antiparticle pair to fall into the event horizon, while the surviving ``widowed'' particle escapes in the opposite direction, carrying energy with it.
Bottom line: Thanks to the Uncertainty Principle, a black hole appears to be spitting out particles and antiparticles from its event horizon. Since these particles and antiparticles carry energy away from the black hole, the energy of the black hole decreases. Since energy is equivalent to mass, the mass of the black hole decreases. The time it takes for a black hole's mass to reach zero is very long. For a black hole initially equal in mass to the Sun, it takes about 10^65 years.
10^106 (10 billion trillion trillion trillion trillion trillion trillion trillion trillion) years after the Big Bang:
Supermassive black holes evaporate. After this mind-bogglingly long period of time, the hyper-gargantuan extra-massive black holes finally evaporate. The universe now contains electrons, positrons, photons, and neutrinos (none of which are subject to decay, as far as we know). The density of the universe is so staggeringly low that the electrons and positrons never have an opportunity to collide and annihilate.

Source: http://www.astronomy.ohio-state.edu/...0/notes42.html

[Deleted]

Current data and models point towards our universe becoming a De Sitter-universe:
http://en.wikipedia.org/wiki/De_Sitt...r_the_Universe

Source: http://www.astronomy.ohio-state.edu/...0/notes42.html

Well, that sums it up quite neatly doesn't it?

[PACOX]

Yeah.

If we're going to discuss theories that have no current proof backing them up, then we might as well say that the Universe will instantly turn into cottage cheese at some random point in the future. Makes just as much sense, if you're going with "we just don't know enough."

Because not being an expert means you can't discuss something?

[Nihilan]

iirc red shift observations implies that all stuff in the universe is accelerating away from each other

Andromeda and the Milky Way are on a collision course for one another. Somewhere out there is something that was massive enough to sling our galaxies at one another. A galactic cluster, a mega black hole, etc, etc. Damn space, you scurry.

The sky is falling people! We only have about 4-5 billion years left before our precious Milky way crashes through Andromeda and they begin to slowly spiral and meld over the following billion or so years.



This is how close Andromeda actually is to us. This is what it would look like right now if it were possible to see it without interference from pollution and the atmosphere.

[poser765]

What difference does it make? None. What is happening has no impact on us or our billionth generations in terms we can do anything to change it. It is possible the universe will keep expanding....forever. Or there may be other factors involved we cannot even begin to fathom. Such as stuff appears to be expanding from each other only because of our limited knowledge of the shape of the universe. We assume it exists in a defined space. See anyone can throw out some bullshit.

Dude, part of the human condition is the desire to explain or at least understand our environment. That includes the larger workings of the universe. We simply want to know for knowing's sake.

Why did the man climb the mountain? Because it was there.

[Garnier Fructis]

Andromeda and the Milky Way are on a collision course for one another. Somewhere out there is something that was massive enough to sling our galaxies at one another. A galactic cluster, a mega black hole, etc, etc. Damn space, you scurry.

The sky is falling people! We only have about 4-5 billion years left before our precious Milky way crashes through Andromeda and they begin to slowly spiral and meld over the following billion or so years.

I think I remember hearing from an astrophysics prof. that there is so much space between stars that it's pretty rare for stars to collide even while the galaxies are merging.

[poser765]

I think I remember hearing from an astrophysics prof. that there is so much space between stars that it's pretty rare for stars to collide even while the galaxies are merging.

I'm no expert, but I don't think the big issue with colliding galaxies isn't in the form of stars literally hitting each other.

I think the bigger mess would come from the turmoil that would be caused by all the gravity spheres interposing with each other. think of planetary orbits being effected, locations and vectors of larger objects being changed, etc.

[Nihilan]

I think I remember hearing from an astrophysics prof. that there is so much space between stars that it's pretty rare for stars to collide even while the galaxies are merging.

Yeah, relatively few stars would actually collide, but the effect on orbital mechanics would be catastrophic. Entire star systems stripped of their planets, or flung out into intergalactic space. Eventually everything would settle down. There would also be a huge burst of star formation as well.

[Pull My Finger]

I thought this would be about the stat squish. Boring!

[Nihilan]

Just imagine what the night sky from earth will look like three billion years from now. Andromeda will literally fill half the sky. Its core will be easily visible during the day. Though it is unlikely that humanity will be there to admire the view.

(Assuming our sun hasn't swollen into a red giant by then, in which case earth will either be gone, or a lifeless oven.)

[zorkuus]

Andromeda and the Milky Way are on a collision course for one another. Somewhere out there is something that was massive enough to sling our galaxies at one another.

Eh... gravity? Our galaxies are close enough that gravity can still overcome the expansion of the universe.