The Extreme Cosmology thread

[Naomasa298]

Been doing quite a lot of research on cosmology, mostly just out of interest rather than writing, so thought I'd start a thread on it, maybe it will help inspire some SF writers.

First up, I guess it's more or less as extreme as possible in our current universe, black holes.

They range in size between microscopic and billions of solar masses, but there's a curious gap between "regular" black holes (sub-100 solar masses) and intermediate-sized ones (up to a few hundred thousand solar masses). Millions and billions of solar masses, fine, we know where to find them, at the centre of galaxies. But the IMBHs, we've only found a few hundred candidates.

Spinning black holes drag spacetime around them (frame dragging). That means, close to the event horizon, it is impossible to stay still with respect to infinity. In other words, even if you don't have any motion, you are dragged around by the motion of space - it is impossible to, for example, remain stationary with respect to a distant star. To do so, you'd need to travel at more than the speed of light, which is obviously impossible. But in your local frame of reference, you're not moving it all - you're in the same place relative to the black hole and other objects being dragged around with you. The bending of space is also why you can see both sides of the black hole at the same time - that halo you see above and below it is the accretion disk behind the it, not a halo that surrounds it on all sides. The same thing is true to a lesser extent with neutron stars - you'd be able to see around 60% of its surface from any given vantage point.

As you fell into a black hole, assuming you weren't somehow spaghettified, you'd see all the light in the universe gradually being reduced to a single, blue point. An instant would pass for you, while millions of years passed in the outside universe. You'd see the universe aging in moments. From the outside, you never appear to cross the event horizon. You get gradually closer and closer, while never quite hitting it. Your image will redshift, and eventually fade.

A load of random factoids, which you can feel free to ignore.

And once inside, because space is curved, you can never leave it. There is no pathway to the outside - all roads led to the singularity, which is not just a point in space, but also a point in time, your inevitable future.

And the freaky thing is, if the entire mass of the universe was compressed into a black hole, the size of the Schwarzschild (who the hell came up with that spelling?) radius, the size of the event horizon, would be approximately the size of the universe as we know it. So maybe our universe is a black hole in a larger reality - but we can never know that.

 

[Naomasa298]

Here's a thought for you, if you've read the philosophy thread.

In a universe where either time or space are infinite, anything with a non-zero possibility of happening, must happen, sometime, somewhere. Infinity makes that inevitable. So somewhere, somewhen, there is a universe where all your dreams have come true. You're just the poor SOB who is stuck in the bit where it hasn't.

 

[Heartlet Happer]

Well, that does not compute. The masses/radii of universe vs equivalent black hole. If milky way mass turns into black hole, it will be less than 1 light year. 5 orders of magnitude less than galaxy. And milky way on average is denser than universe on average.

What seems to be the major point of grand design, is that distances and numbers are so abysmal, that one may suspect the single purpose of keeping the cosmic distances large. I suspect that distances are made large to keep sentients away from each other, for their own good.

Or, perhaps, the designer meant for everyone who decides to travel, to be humbled and completely voided of any thought of aggression, conquest or domination. The only reward which awaits us light years away is appreciation of knowing that someone else is out there.

 

[Naomasa298]

Well, that does not compute. The masses/radii of universe vs equivalent black hole. If milky way mass turns into black hole, it will be less than 1 light year. 5 orders of magnitude less than galaxy. And milky way on average is denser than universe on average.

It would be. But if you took all baryonic matter, including dark matter, a rough estimate puts the Schwarzschild radius at about 5 times the radius of the universe, which is roughly the same order of magnitude. I mean, I haven't done the calculations, and I haven't done astrophysics beyond one basic university module, but you could work it out. The Schwarzschild radius calculation isn't *that* complex, you could just plug in the numbers.

The density of a black hole, when calculated according to its Schwarzschild radius means that it actually gets less dense as the radius increases.

Schwarzschild radius - Wikipedia

en.wikipedia.org

Have fun.

 

[Heartlet Happer]

Cosmologically speaking, it is numbers, that make the mind wander.

For solar punk optimistic sci-fi purposes, the numbers should help, instead of being an obstacle. Say, there is billions of habitable planets with no claims, they are just destinations, and there are billions of empty starships parked in asteroid belt. All combined with scarcity of individual humans willing to travel. And humanity on Earth is completely unaware of that demand. The aliens responsible for project are lazy and dysfunctional for reasons of being too tired and scarce.

The story begins one morning with a spam mail envelope in ..

 

[Homer Potvin]

I have my astronomy textbooks open on my desk next to my laptop. Last thing I was looking at was... lemme see... dust lanes in nebulas and how they affect emission vs absorption lines in their hydrogen spectra. Spent roughly an hour to reading about it in various sources to write one paragraph of dialogue, which I just ended up deleting.

I think the think fiction gets wrong about black holes is that they are no more destructive than any other garden variety object of stellar mass. They don't go galivanting around the cosmos sucking up matter like shop vac. And innocent astronauts don't accidently stumble across them and "fall in." I mean, I suppose they could, but you can get much closer to a blackhole than a star, which would fry your ass long before you reached an insurmountable escape speed. Some of them do toss off dangerous emission bursts from the accretion process, namely gamma rays, but you get the point.

 

[Naomasa298]

I think the think fiction gets wrong about black holes is that they are no more destructive than any other garden variety object of stellar mass. They don't go galivanting around the cosmos sucking up matter like shop vac. And innocent astronauts don't accidently stumble across them and "fall in." I mean, I suppose they could, but you can get much closer to a blackhole than a star, which would fry your ass long before you reached an insurmountable escape speed. Some of them do toss off dangerous emission bursts from the accretion process, namely gamma rays, but you get the point.

I'm fairly sure you won't find a tesseract at the centre of Saggitarius A* either. Or Sandra Bullock, come to that.

That's when sci-fi collapses into fantasy for me.

 

[Madman Starryteller]

My kinda thread.

It's been theorized that the last advanced civilisations in the universe will build their homes around black holes. Ideas I've incorporated into my own stories where there are black hole cities.

They may use different processes to extract energy from the motions of the black holes. Such as the Penrose process.

Space is big and mysterious.

 

[Naomasa298]

My kinda thread.

It's been theorized that the last advanced civilisations in the universe will build their homes around black holes. Ideas I've incorporated into my own stories where there are black hole cities.

They may use different processes to extract energy from the motions of the black holes. Such as the Penrose process.

Space is big and mysterious.

Yeah, once you start dealing with exotic physics, intuitive logic breaks down. You just have to decide on how much your readers will tolerate. Once they start questioning the physical viability of sandworms, that's why you gotta tell them they're reading the wrong story.

 

[Madman Starryteller]

Here's a thought for you, if you've read the philosophy thread.

In a universe where either time or space are infinite, anything with a non-zero possibility of happening, must happen, sometime, somewhere. Infinity makes that inevitable. So somewhere, somewhen, there is a universe where all your dreams have come true. You're just the poor SOB who is stuck in the bit where it hasn't.

If this is the truth of things, then there's also the opposite. A universe where all your worst nightmares are real.

For that very reason, I'm a firm believer in the nearly infinite, limited and finite, multiverse. But such a universe would guarantee that what we experience now, we have already experienced before, because time is endless. So maybe that too is a nightmare in and of itself.

 

[Heartlet Happer]

Talking of the infinity of space. In the mostly accepted theory, the Big Bang occurred in limited volume. There was time when universe was measured in millimeters, meters and so on. Then somehow later we speak of it as an infinite. It does not compute.

 

[Madman Starryteller]

Talking of the infinity of space. In the mostly accepted theory, the Big Bang occurred in limited volume. There was time when universe was measured in millimeters, meters and so on. Then somehow later we speak of it as an infinite. It does not compute.

There are many different theories. Some say this is the only universe in existence, others that there are multiple universes like our own out there. Hence finite and infinite.

Some theories suggest that this universe will suffer a cold death, that all the stars will evaporate and be eaten by black holes, who in turn will also evaporate over such a long time that it can't be reasonably thought of.

Then there are other theories that suggest that this universe will contract at some point and another big bang will occur.

So many theories, and all are equally plausible to me. Who is to say for sure what the truth is with such enormous time frames and such?

 

[Homer Potvin]

Talking of the infinity of space. In the mostly accepted theory, the Big Bang occurred in limited volume. There was time when universe was measured in millimeters, meters and so on. Then somehow later we speak of it as an infinite. It does not compute.

Basically we're all nuts in the same fruitcake expanding in all directions away from each other, as the analogy from one of my professors went. That's why the cosmic microwave background, the "echo" of the big bang, is detectable at the same rate in all directions at the same time without variation. It's along the 21cm radio line, I think, and what causes static on radios and televisions, back when those things existed.

 

[Naomasa298]

Some theories suggest that this universe will suffer a cold death, that all the stars will evaporate and be eaten by black holes, who in turn will also evaporate over such a long time that it can't be reasonably thought of.

That's the heat death of the universe, but very recent research has suggested that dark energy is changing over time, and in fact, we may be heading to a Big Crunch after all.

 

[Naomasa298]

If this is the truth of things, then there's also the opposite. A universe where all your worst nightmares are real.

That's correct.

And yes, repeating all this shit over again ad infinitum does sound like hell to me.

 

[Naomasa298]

Talking of the infinity of space. In the mostly accepted theory, the Big Bang occurred in limited volume. There was time when universe was measured in millimeters, meters and so on. Then somehow later we speak of it as an infinite. It does not compute.

We simply have no way of telling what was there before the Big Bang, if such a concept does, in fact, exist. It may have been nothing, but it may have been, for example, a De Sitter universe, one in which there is no matter, but in which time *does* in fact, pass, and our universe is expanding into that previously existing De Sitter space.

As for "infinite" itself, it depends what you mean by that. As, in, you could travel forever in one direction and never reach a boundary? Well, that could be true in a closed, finite universe too, like travelling across the surface of a sphere. You'd never reach a boundary there either.

 

[Naomasa298]

In 2015, the first merger of two black holes was observed. Designated GW150914, the merger was between a 36 and 29 mass black hole, and for a fraction of a second, it released 50 (fifty) times more energy (in the form of gravitational waves) than the light output of the entire universe.

 

[Homer Potvin]

in which time *does* in fact, pass,

The best explanation I heard about this--time not existing before the Bang Bang--is that in the absence of energy, matter, and molecular motion, there is nothing for time to measure. Ergo, it didn't exist until after. That particular cosmologist defined time as a simple measuring tool, no different than a yard stick, and he kept making time references substituting inches for time units to illustrate the concept. I wish I could remember a few of them because it was very cool and made a lot of sense. One was sort of like, "Time can have no affect on things any more than inches can."

 

[Naomasa298]

The best explanation I heard about this--time not existing before the Bang Bang--is that in the absence of energy, matter, and molecular motion, there is nothing for time to measure. Ergo, it didn't exist until after. That particular cosmologist defined time as a simple measuring tool, no different than a yard stick, and he kept making time references substituting inches for time units to illustrate the concept. I wish I could remember a few of them because it was very cool and made a lot of sense. One was sort of like, "Time can have no affect on things any more than inches can."

That's right, but in a De Sitter universe, although there is no motion, there is a changing metric - the expansion of space. My understanding is a bit fuzzy, but as I understand it, a De Sitter universe has unchanging Hubble constant, so the universe's expansion isn't accelerating. So because there's a measurable, changing metric, time is actually passing, there just aren't any objects or particles on which that change can be measured, only the scale of space. I mean, that's just one possible state before the Big Bang, not the only one.