XKCD: It's more than a comic

OK, let's say that the Stellar Era of the Universe lasts for 1 trillion years. At 15 billion years, we are 1.5%, or 1.5 stellar cycles (for a star the size of the Sun) into this Era. That's why I'm saying the Universe is young. It will look like it is now for a much longer time than it's been looking like this. Even if we consider that in the later parts of this Era star creation rate will be much lower than it is now.

Edit: Another perspective. When it comes to astronomical scales, there are always millions and billions: number of stars in a galaxy, number of galaxies etc. If we consider the life span of the Sun as 1 Unit (larger stars may last only a few hundredth units, while smaller ones can last thousands), the age of the Universe of 1.5 Units is not much.

Edited by petersohn on Jan 15th 2019 at 2:45:06 PM

The universe is under no obligation to make sense to us.

Eh, it won't look exactly like this. After all the high and medium-mass stars burn out, and galaxies have exhausted their supplies of interstellar hydrogen gas to create new ones, the universe will be much dimmer than it is now, with only white and red dwarfs providing appreciable light.

Galaxies in local groups will merge due to mutual gravitational attraction, forming unstructured mega-galaxies and kicking off new rounds of star formation, but that will pass relatively quickly. Cosmic expansion will push these clusters apart until they are beyond each others' cosmic horizons, and each will be a little island of fading light amid a vast darkness.

There is a little bit of light out there, literally. Red dwarfs get hotter as they age, increasing their brightness until their surface temperatures are even hotter than our sun is now. The last civilizations may cling to life on terraformed planets (or even megastructures) in close orbit around these, having moved there from their home stars eons in the past. Red dwarfs don't explode on death, either, but just stop fusing once they've turned all their hydrogen into helium. At that point they become white dwarfs and cool gradually.

Over even more time, gravitational perturbations will scatter stars and planets out of their home galaxies, as material continually falls into the supermassive black holes at their centers. The occasional flare-up of these monsters' accretion disks will provide flashes of illumination, as will the gravitational mergers of neutron stars. Civilizations may siphon energy from rotating black holes by throwing matter into them. White dwarfs and neutron stars may also be temporary energy sources until they've radiated all their heat away.

^note What happens after that depends on quantum mechanics. If protons decay, then all matter that isn't in black holes will eventually dissolve into quarks. If not, then all planetary and stellar remnants will decay into iron through quantum tunneling over a much longer period of time. A third possibility is that quantum tunneling will randomly cause tiny bits of degenerate matter to collapse into black holes, and that all matter will fall victim to this fate. All of these effects will release a tiny amount of energy but not enough to be usable.

The very last gasps of energy in the universe will be the Hawking radiation emitted from black holes, with the largest taking up to a googol years to finally decay. Then that'll be it.

Try hundreds of billions of stars in a galaxy and trillions of galaxies. But yeah. Our Sun is a third-generation star, born from collapsing gas that is itself the remnant of the supernova of a much bigger star.

Edited by Fighteer on Jan 15th 2019 at 9:03:14 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

Why would it all decay into iron?

Optimism is a duty.

Iron is the most stable chemical element. Fusing lighter elements into iron releases energy, but iron fusion requires more energy than you get out of it. This is what causes supernovas in massive stars, FYI. ^note Increasing pressure and temperature in their cores causes increasingly frantic and energetic rounds of fusion, until iron, whose fusion consumes energy rather than producing it. The core no longer has the energy needed to hold itself up against gravitational collapse and KABOOM. Over truly enormous time periods, all elements lighter than iron will spontaneously undergo nuclear fusion due to quantum tunneling as their nuclei jostle around into lower energy states. We're talking incomprehensibly long here: 10^150 years or more.

In turn, all elements heavier than iron are slightly unstable: over long enough periods of time they will undergo nuclear fission and decay into iron, again releasing energy. Fission is also a quantum tunneling event: it occurs when neutrons escape their bonds by jumping across the energy barrier created by the weak nuclear force. (Fusion, by contrast, is protons tunneling into the nucleus across that same barrier.)

Spontaneous quantum tunneling always moves particles into lower energy states, so it is impossible (i.e., it is a reversal of entropy) for iron to naturally undergo fission or fusion.

Edited by Fighteer on Jan 15th 2019 at 2:12:42 PM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

We should call it the iron age of the cosmos, then.

Optimism is a duty.

Assuming that's what actually happens. We aren't sure yet, because the deciding factor is whether proton decay is a real thing. We haven't observed it in laboratory settings, and theory puts its half-life at a minimum of 1.67 x 10^34 years, with a three order of magnitude uncertainty factor.

That may sound like a big uncertainty range, but even 10^31 years is 21 orders of magnitude longer than our universe has existed.

The numbers are just too large to comprehend on these scales.

Edited by Fighteer on Jan 15th 2019 at 2:27:53 PM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

So the heat death of the Universe is a real thing after all. Given that it keeps expanding, at least. Otherwise, it will collapse into a giant black hole and hit reset button.

The universe is under no obligation to make sense to us.

Or that ultra-advanced supercomputer we build figures out how to do it. ;)

Princess Aurora is underrated, pass it on.

We don't know with absolute certainty that the universe will expand forever, but it is the most likely current hypothesis. There are proposed ideas for how it might collapse again, but none of them are sufficiently supported by observational evidence.

The idea of it all being one giant singularity should it recollapse is also a little questionable, since it would imply that the early universe should also have been a singularity. Yet, we know it wasn't. This gets complicated, but at a very basic level, the formation of an event horizon requires that there be a preferred direction of gravitational attraction: that is, there needs to be more mass-energy in one place than in others. If everything is equally dense in all directions, then gravity is pulling equally in all directions, and thus no black hole.

Indications are that the early universe was homogeneous for all intents and purposes, and expanding so quickly that local eddies and disturbances didn't have time to collapse into black holes (but see "primordial black holes" for a hypothesis about how that might not hold in all cases). A reverse of that expansion — a Big Crunch — would share those same properties.

There's another issue: if the universe is perfectly geometrically flat, and therefore infinite, no matter how much it collapses it'll never be anything other than infinite. (Never mind that, if the universe is geometrically flat, it wouldn't collapse under its own gravity regardless, since as I said above there's no preferred direction for things to fall towards.) That's a whole other fun concept to get into one's head, and we won't dive too deep here.

Edited by Fighteer on Jan 16th 2019 at 9:28:24 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

XKCD #2099: Missal of Silos

That would suck if fuzzy pattern matching put an ancient historical document on someone's nuclear counterstrike target list.

Edited by Fighteer on Jan 17th 2019 at 9:58:15 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

Well obviously that oldest written document is a threat to humanity in the case of nuclear war. Can't afford to risk sparing it.

Huh, for whatever reason I also thought Cheyenne Mountain was in Wyoming.

Probably because because Cheyenne is the capital of Wyoming.

#2100: Models of the Atom

Where's Dalton? Wasn't there a Dalton's Atomic Theory I remember learning about?

So the difference between Bohr and Chadwick is that Bohr proposes that the nucleus is a small solid ball with positive charge?

Also I'm surprised that Bohr is predated by a model that doesn't have the orbits in the same plane. They usually layer in Bohr (really Chadwick I guess), then Rutherford (or Rutherford with nuclear particles), then the Quantum Model as you get higher into physics education.

"Surrounded by math" is a pretty good way to describe electron orbitals, actually.

Fresh-eyed movie blog

Our current model of what atoms actually "look like" is weird enough that you might as well attempt to appreciate it while on drugs.

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

The plum pudding model was a real atomic model.

Optimism is a duty.

Well with that revelation, if you tell me that the nunchuck model is untrue, I will be forced to stop believing in science.

I don't think I want to live in a world in which the nunchuck model does not exist.

I feel sorry for future kids in chemistry class that have to build the "small hard ball surrounded by math" model. Doesn't seem nearly as fun. The quantum model may also be a tad difficult to replicate with wire and styrofoam.

I remember in my chemistry class we did projects for each of the models, including the ones that had been disproven. And then our teacher explained both what was wrong with these models and why scientists made those mistakes.

Most of my science teachers were pretty awesome. It wasn't until I took an out of class college prep course that I encountered the "read dully from the book for an hour" type of teacher.

Well, I wouldn't call them mistakes, per se. These old models were based on available data, and were only disproven when further discoveries were made. Whether or not a model is accurate depends on whether or not you have all possible information about what you're modelling, and you can never be sure you really have all the pieces of the puzzle or not. The latest model might be the right one, but it very likely isn't.

Optimism is a duty.

My chemistry teacher did something similar, spending the entire first class teaching us about phlogiston (the old theory about how fire works). All the smart-asses in class kept trying to say that fire was really caused by oxygen, but since this was the first class they didn't actually know how to prove that yet. It was especially frustrating when he demonstrated a fire going out when covered by a glass bowl and asked us why. We spent like 5 minutes with all the students trying to talk about oxygen until finally I got frustrated and said "the air is saturated with phlogiston."

I thought that was a pretty interesting way to start a science class. "Here's the old theory, now try to prove it wrong." Were people in the past dumb for believing this? No, they just didn't have all the same data we have now.

Obviously the next class was an experiment to disprove phlogiston.

Edited by Clarste on Jan 19th 2019 at 4:44:11 AM

"Mistakes" was a poor choice of words on my part. My teachers basically did that, though not with anything as cool as fire and phlogiston.

I just had an otherwise cool sixth grade science teacher who responded to me challenging his assertion that the moon doesn't rotate (it rotates at pretty much the same speed it orbits Earth) by setting up a class activity where one kid stood in the center of the room as the Earth and another kid walked around the room as the moon, and said that since the moon was always facing the Earth, that demonstrated that it doesn't rotate. I was too flustered to articulate why that was still wrong.

Fresh-eyed movie blog

I guess the moon example is a bit confusing because it turns around the Earth as it rotates, making it difficult to pick a frame of reference from which the rotation is obvious.

I suspect what the teacher meant was that the moon was not turning as seen from Earth, and confusing that with the moon not rotating at all.

Optimism is a duty.