Calculating the end of our universe.

originally posted by: Develo
a reply to: johnb

Black holes only swallow what is inside their event horizon.

Everything else is simply orbiting around them or out of their reach.


Also how do you know the universe isn't infinite in size? No one knows.

But they are not all static, some of them move around like meteors.

originally posted by: PhoenixOD

originally posted by: Develo
a reply to: johnb

Black holes only swallow what is inside their event horizon.

Everything else is simply orbiting around them or out of their reach.


Also how do you know the universe isn't infinite in size? No one knows.

But they are not all static, some of them move around like meteors.

And still, they don't swallow everything in sight.

Black holes do attract matter, exactly like stars do. No less, no more.

I'm not getting the connection of where the mathematics of a black hole could be interpreted to predict the end of existence.

originally posted by: johnb
Could this be done by working out the density of black holes, how fast they are growing, moving etc

I would have thought we could work out a reasonable approximation by using the number of known black holes their average mass and how often they occur in mapped space and extrapolating outwards from there?

Thoughts from the physicists?

Who cares how the Universe will end? Our own solar system will end way before that, and even that is billions of years away.

We have real problems affecting the world RIGHT NOW that need the attention of science. Theoretical physics is a luxury field we should not be spending money on at a time when we are facing so many other issues science should be addressing.

originally posted by: babybunnies
Who cares how the Universe will end? Our own solar system will end way before that, and even that is billions of years away.

We have real problems affecting the world RIGHT NOW that need the attention of science. Theoretical physics is a luxury field we should not be spending money on at a time when we are facing so many other issues science should be addressing.

Everything is theoretical, until proven.

It was theory that gave us flight, among many other technological advancements. The next major advancements will come from theory.

I believe in an eternal self-sustaining Universe via some sort of cyclic mechanism. By belief I mean I would bet money on it. I'm not qualified to be an authority on this matter [punny?] in any way though hehe.

originally posted by: Develo
a reply to: johnb

Why do you think black holes have anything to do with the end of the universe? Black holes are completely marginal compared to the other forces ruling our universe.

The current hypothesis is that the universe will keep expanding forever, hence it has no end, only a slow heath death.

we cannot know if the heat death thing is real because we have no way of knowing that future creation events will not occur. it could be that once the space density reaches an arbitrary threshold the quantum vacuum potential may react by "spontaneously" collapsing or exploding. we also do not know for sure white holes are merely mathematical artifacts of the solutions of relativity. It could be that they are real things really creating or exporting matter into our universe in which case at some point their output in energy and matter may exceed the losses due to thermodynamic entropy. also we do not know for sure that hawking processes do not result in recombination at some point. if it does then all of the black holes including stellar, galactic and galactic cluster black holes would be regenerating the universe. we also are not cognizant of the 95 percent of the universe that does not consist of normal matter and energy and what processes involve them other than probably gravity.

imagine if you will red dwarfs whose lifespan can exceed the age of the universe many times over... these are expanding farther and farther away from each other. if there were to be plural creation events the new matter and energy would not destroy the red dwarfs entirely. just the ones unfortunate enough to be near the creation event. and even those might survive for billions of years after the new big bang because the wave fronts would take whatever amount of time it would take light to travel from the epicenter to the red dwarf (which is still in motion.) in fact massive particles (protons, electrons, neutrons, helium nuclei, lithium nuclei) would take longer than light to reach the red dwarf location.

this pre-supposes a violent creation. it may be that the expansion of space itself generates quantities of matter or photons by separating them before they can recombine or some mechanism like that. it could be that gentle creation happens all the time and we do not notice it because in any given volume (where we can measure) only miniscule amounts are generated locally. globally however it could be massive amounts when you add it up.

we probably do not know enough to justify our assumptions; their chief justification being we need assumptions in order to figure things out or to form a frame work for investigation.

Where to start?

If the Universe is not going to expand forever, then at some time in the future it will stop expanding; the likely hood is that it would then begin to contract; eventually to the point of a "Big Crunch". Perhaps followed by another "Big Bang", who knows. So maybe that's what you mean by black holes swallowing all the matter in the universe. The big "however" is that most folks don't think the Universe will ever stop expanding.

If the Universe continues to expand forever, then everything is getting farther and farther away from everything else all the time. Sure there are objects at all levels (stars, galaxies, clusters, and so on) on collision trajectories, but while that is happening space itself is getting bigger. As space expands, the rate of separation of objects increases, eventually beyond the speed of light. Things that are within "eyesight" of each other will, one day, no longer be. The night sky from from Earth (and every other planet in every other galaxy) will gradually get dimmer and dimmer as the objects (galaxies, stars) get so far away that their light cannot never reach us.

the universe will expand forever. But one of the constraints will shrink. That gets pretty complicated. so here is an article on the difference between the particle horizon, cosmic event horizon and the hubble sphere:

phys.org...

the upshot: there are parts of this universe that particles can never get to even if we waited an infinite amount of time. thus if there was another big bang it could not destroy the whole universe because parts of the universe are receding at superluminal speeds. nothing can ever catch up to it. and we will never be able to see any of the portion of it already too far gone for it's photons to ever catch up with us from it's local perspective.

a reply to: Develo

i wasn't suggesting they do. AS they are moving they roam the universe swallowing everything within their event horizon

originally posted by: PhoenixOD
a reply to: Develo

i wasn't suggesting they do. AS they are moving they roam the universe swallowing everything within their event horizon

The event horizon of a black hole is still very small. Black holes are collapsed stars. Their gravitational pull isn't that much greater.

Are stars swallowing everything in sight as they move along?

Really black holes are just another kind of stars despite all the imagery associated to them.

originally posted by: Develo
The event horizon of a black hole is still very small.

That depends on how massive the black hole is.

If the black hole has the mass of the moon, the event horizon is less than a millimeter across, so that's pretty small.

However there's some math you might not expect going on with more massive black holes. As they get more and more massive, the size of the event horizon does NOT grow in direct proportion to the mass, it grows much more than that as mass increases. One black hole we have discovered has a event horizon about four times larger than the orbit of Neptune which is a record, but I think there are several more discovered with an event horizon about the same diameter as Neptune's orbit. That's a big event horizon, and it's no ordinary star. It can not only eat stars, but entire solar systems, earning the nickname "solar system swallower". But yes a black hole of three solar masses is no big deal, I agree with that much. These supermassive black holes are so much more than that though.

The Solar System Swallower

Gebhardt says the black hole's event horizon—the edge from within nothing can escape, not even light—is four times as large as the orbit of Neptune, the outermost planet in our solar system.

Supermassive black holes like the one in galaxy M87 probably grow not only by feeding on infalling gas and stars but also by mergers of smaller black holes.