Tag Archives: astronomy

Is our solar system the most unique in the universe?

Grappling with assumptions and knowledge bias

Say you are going to visit someone, but for thought-experiment reasons you know absolutely nothing about them, not even their name or gender or anything of the like. What can you confidently say about this person you don’t even know?

Well you can confidently say that they’re human, since I did specify that they were a “person,” and since there’s no evidence aliens exist on Earth. That means they eat food and breath air and all that other stuff. But besides the most vague generalities about human nature, you cannot confidently assert *anything* about them. If I forced you to guess about their qualities, you would only be able to guess the vaguest things that are almost universal among humans, like their physical traits (probably 2 arms and 2 legs) or human universalities (probably love their family, probably like food and traveling).

The only things you can confidently say about this person would be the *common and non-unique traits* that they probably share with all other humans. Because with so little to go on, it would be illogical to assume a set of very unique traits instead.

But then I tell you this person is an American. OK, you can now assume they almost certainly speak English (though it’s not totally certain, and they could always be a baby or a mute anyway). You can assume they know at least some of the cultural touchstones of Americanism (although again, they could be a baby), like they’ve heard the Star Spangled Banner, and they know what Star Wars and Marvel Movies are. They probably know that Hollywood is famous for movies, and that Texas is famous for oil.

But can you confidently say that they are a basketball player? Do you know if they enjoy Handel, Hershel, and Bach? Can you say anything about their politics wahtsoever?

If I then tell you they’re a climatologist, you get even more details. They’re likely on the left-side of the political spectrum. They’re almost certainly well-educated (a pre-requisite for climatology), and they’re far more likely to be an office worker than a manual laborer (although I guess *someone* has to install all those temperature stations).

Now let’s say that this person you’re going to meet is my friend Dave, who’s about 25 years old. Dave is a great basketball player, but he hates watching it because “the modern game is boring.” He likes jazz renditions of famous Baroque music. He plays Minecraft fanatically, although he’s never modded it. And he is a climatologist working at a local university, but he’s also deeply religious and prays before every meal.

The less you knew about Dave, the more generic he seemed. Just a person? There’s 8 billion of those. An American? They’re also common. Even a climatologist doesn’t seem unreasonably unique or special.

But when I gave you more details about his personality, he suddenly seemed fairly out of the ordinary: he’s both sporty and sciency, he’s young but also religious, he plays a popular game sure, but he also likes an incredibly eclectic style of music.

But is Dave *actually* unique? Or does his appearance of uniqueness come from *our knowledge* of him? I’d hazard than many of you can think of people in your lives with an even more unique set of traits, compared to the very few things I’ve told you about Dave. And when I was slowly describing Dave, before you knew how unique he was, you had to fill in the blanks with guesses based on common traits. This is true of anyone we don’t know well. People seem more common as we know less about them, more unique as we know more.

For every person we’ve ever met, we have a very limited set of knowledge about them, and we fill in whatever blanks exist with the “most likely” choices. That’s why even your parents or loved ones can still surprise you, as you may not have known that they did drugs in college, or ran a local newspaper, and you had just filled in those blanks with something else before they told you.

But that means that by definition, we default to assuming everyone around us has “common” and “ordinary” sets of traits. I’d hazard a guess that every person in the world has some set of traits that makes them extremely unique or out of the ordinary, even if these are things that you’d only know if you were close friends with them.

The office worker who reads about 2 books a week: that’s very out of the ordinary. The financial analyst who’s written a dozen murder mysteries: that’s very uncommon. The American who speaks fluent Korean: this is less common in America than having written a book. But if all you knew was “office worker,” “financial analyst,” or “American,” you’d think these people were more normal and less unique than my friend Dave up there, even if they end up being as or more unique than him when you know all their traits.

Extraordinary-ness is realized as we get more and more data about a person, as we find more and more things that are clearly *outliers* to the common trends. Because until we know those things, we naturally fill in the gaps in our knowledge with the “ordinary” placeholders, the “expected” values.

And the reason I’m talking about all that is that I’m almost certain this though process underlies claims about the uniqueness of our own sun and planet.

The Fermi Paradox and the Rare Earth Hypothesis

To shift gears slightly: many people have pondered about why Earth hasn’t been visited by aliens yet. If there are billions of stars in the Universe, and the Universe has existed for billions of years, then there should have been plenty of time for alien species to evolve, become technologically advanced, and start joyriding around the galaxy. As Enrico Fermi said: “where is everyone?”

A potential answer people have caught on is that intelligent life is unbelievably uncommon, and that Earth just happened to have a very very specific set of Astronomical circumstances that made life, and intelligent life, possible. Under this “Rare Earth Hypothesis,” life may evolve around only one in a quadrillion stars, there may only be a *single* life-bearing world in our galaxy: Earth.

Our planet and solar system do seem very rare. In the search for exoplanets, we rarely find ones with lots of gas giants so *far* away from their star, most gas giants appear way closer than ours do. Our sun also isn’t a binary star (like most sun-like stars are), and it has fewer flares and superflares.

But I would contend that, like my friend Dave above, we only notice our solar system’s “uniqueness” because we know so MUCH about our Sun and so LITTLE about exoplanets and their stars. We are *assuming regularity on all the variables we don’t have data for.*

Like, let’s take one of those stars that has a Jupiter-like gas giant orbiting close to the star. Maybe some of those Jupiters have large, rocky moons with complete atmospheres, and maybe these moons can support liquid water, which could support life. That’s probably uncommon, but is it more or less uncommon than our own system having its gas giants so far away?

Our planet has a very large moon, but are there exoplanets with rarer configurations, like an Earth sized planet with 4 or more smaller moons? Or an Earth sized planet with Saturn-like rings?

And our sun has unusually few flares, but is there a planet out there with an unusually strong magnetic field and an unusually thick water atmosphere, one that can easily protect its life-bearing planet from life-killing solar flares?

For this last example, let’s imagine that life has indeed evolved on such a world, intelligent life. They, like us, might think they’re the only life in the universe. They, like us, might think that their planet is unbelievably unique, and that their specific uniquenesses are what allowed their solar system to have life.

Maybe their solar system has a large gas giant orbitting close to the star, and the gas giant’s magnetic field, combine with their own planet’s uniqueness, serves to limit the damage of stellar flars coming to their planet. The gas giant could act like a kind of “shield,” sitting between their own planet and their star, too small to dim the star’s light, but with an incredibly strong magnetic field that blocks the force of any Coronal Mass Ejections (the technical name of large stellar flares).

These people might say “well of course life only evolved on *our* planet, how common is it to have a rocky terrestrial planet outside the orbit of a gas giant? We’ve never seen that in exoplanets. And our gas giant plus or magnetic field are unusually good at protecting us from solar flares. And since essentially all stars have large solar flares, then all planets but our own get blasted to death by Coronal Mass Ejections before intelligent life can evolve.”

But they wouldn’t be right, because we on Earth would still exist. And they’d be assuming every other star out there was “normal,” that there wasn’t a rocky planet *closer to its star* than a gas giant, orbiting an unusually quiet star. And since it would be so hard to get data on *our* star, they’d see our star and assume it was just another “ordinary” lifeless system (we’d have trouble knowing our own star had planets if we didn’t orbit it, it’s difficult to see by the most common measurement techniques)

See, I think Earth only seems *rare* because of how much we know about it. Just like Dave only seems *unique* because of how much I told you about him. If I’d just given you his more common traits (he’s 25, American, plays sports), he wouldn’t seem that unique or special at all.

The jar of marbles thought experiment

Imagine for instance that there’s a jar with 100 marbles in it, each numbered 1 to 100. You pull out number 8 and, aha! This is an exceptionally unique marble! No other marble has this specific number on it, and this marble is 1 in 100, isn’t that unique?

But in this jar, ALL the marbles are unique, they’re ALL 1 in 100. They’re just unique in different ways by having different numbers on them.

Or if you prefer, let’s say the jar of marbles has 999,900 marbles that are unlabeled, and 100 marbles numbered 1 to 100. Again you pull out marble number 8 and, aha, this time it’s even MORE unique! This time it’s a 1 in a MILLION marble! No other marble has this number!

But again, the numbered marbles are ALL 1 in a million, they have different numbers on them, different “things that make them unique,” but they are all still unique.

This marble thought experiment is how I think of the rare Earth hypothesis. Yes our Earth is rare, it’s got a number on it (life), and we think most other stars in the galaxy don’t have life, we assume most of them are unnumbered. But just because we’re 1 of a kind, with our own special number ENTIRELY DIFFERENT FROM ANYONE ELSE’S, doesn’t mean that another marble with another number doesn’t exist somewhere in the Galaxy, even somewhere close by.

We assume that life can only evolve if the marble has the number 8 on it, ie if a planet and solar system have our very unique set of traits (gas giant arrangement, large moon, quiet star, etc). But we don’t have telescopes powerful enough to *see the numbers* on any other marbles out in the galaxy, so we don’t know for sure if they have life or not. We assume that they are normal, that they have all the “common” traits stars have and that they don’t have anything special on them that would make them unique or life-bearing. But we don’t know.

There could be a number 9 marble right next door to us, a planet orbiting a star with its own collection of unique traits completely different from ours, but thinking just as we do that they are the only life-bearing system in the entire galaxy, because our star doesn’t have their star’s unique traits.

And they’d be wrong. And we’d be wrong too. Just something to think about: we should be more humble when trying to argue from “uniqueness.”

Anyway I still want to post part 2 of my fusion power post, so stay tuned for that very soon.

Stars with a Story

I wanted to tell a short story about a star I found interesting. It’s nothing like I’ve blogged about before, but I haven’t blogged in a long time and I need to write SOMETHING.

At the heart of the Crab Nebula is a little star that I will call Crabby. Its real name is PSR B0531+21, but no one’s going to remember that name so Crabby it is. Crabby is a star that exploded in 1054 AD, and the Crab Nebula is the remnants of that explosion.

What’s so special about Crabby is that we know *exactly* when it exploded, because Chinese astronomers recorded it. For almost every other supernova remnant in the galaxy we don’t have that kind of information, it’s hard to tell whether something exploded a million years ago or a *billion* years ago because we’re viewing it from so far away. So knowing the exact *year* that Crabby exploded is like knowing someone’s time of birth down to the millisecond. It gives us incredible precision that we normally don’t get in astronomy.

And that precision has let scientists come up with some wacky theories, such as the theory that Crabby is a “strange star.”

Now what’s a strange star exactly? Isn’t it a little rude to call a star “strange” in the first place? Well it requires a little bit of quantum mechanics to explain this, but read on because I promise it’s worth the read.

See, when a star normally collapses, the force of gravity becomes so great that it compactifies the matter within to a ridiculous extent. The core of a collapsing star is usually made of heavy elements like iron, and the collapse forces those atoms as close together as physically possible. There’s a simple rule in quantum mechanics: two things can’t occupy the same exact space, and this rule leads to an absolute limit of density: the density where atoms can’t get any closer together or they’d literally overlap.

Here on earth atoms aren’t usually that close together. Liquids and gases of course let atoms slosh about, but even solids on earth usually have their atoms arranged in intricate patterns with a little bit of space in between each atom. White dwarfs crush this down into the absolute limit of density, around a ton or more per cubit centimeter.

So white dwarfs like this are ultra compact objects with ultra compact structures. But gravity can do even better than a white dwarf.

See the strength of gravity depends on mass: more mass, more gravity. So what happens in the cases of a VERY massive white dwarf? Their high mass means they want to crush things down even denser, but we’ve already reached the limits of atomic density, so where else can we go?

Well remember that atoms themselves are mostly made up of empty space, there’s a lot of emptiness between the nucleus and the electrons, for example. Atoms themselves can be crushed down into just their neutrons, with each proton absorbing an electron to become a neutron. When we crush down atoms in this way, we remove all that empty space they contain, and that lets us crush the whole star down to *even greater levels of density*.

At this level we have a “neutron star,” a star so crushingly dense that it’s the size of a city with the mass of the sun. Our friend Crabby is theorized to be a neutron star. But it might possibly be even more special.

Some have theorized that Crabby is a bit too cold for its age, and how could it have lost all that heat? The answer may bring us to the fringes of theoretical physics.

See just like atoms can be crushed down into neutrons, neutrons can be crushed down further. Neutrons are made up of 3 quarks: 2 down quarks and 1 up quark. But those quarks are much smaller than the neutron itself, and between them is mostly empty space. So once again, if the gravity of the star is strong enough, a neutron star can be “crushed down,” until its neutrons are crushed into quarks.

The whole star itself can’t be crushed like this, or else it would get so small that it would become a black hole. But the core of a massive neutron star may be so dense that its neutrons are indeed crushed into quarks, releasing all that empty space within the neutrons, and leaving a quark-rich soup that resembles the instant after the big bang. We have no firm evidence of this happening, but if it happens, then such a star would be called a quark star.

And then some massive quark stars might have a final trick up their sleeves. Remember that rule from earlier, about how 2 things can’t occupy the same space? That rule is what holds each of these type of stars from crushing down too far. White dwarfs can’t let their atoms occupy the same space, it’s only when the force of gravity is *large enough to crush atoms* that a white dwarf gets crushed down into a neutron star.

Similarly, neutron stars can’t let their neutrons occupy the same space, and that’s what keeps them from crushing down further. But when gravity is strong enough to *crush neutrons*, then parts of the neutron star might devolve into a quark star.

But in a quark star, the neutrons are crushed into 2 down quarks and 1 up quark each. Now here’s the funny thing about that quantum rule I told you about: two things can’t occupy the same space right? Well that’s only true *if they’re the same type of thing*. Two neutrons can’t occupy the same space because they’re both neutrons. Same with 2 down quarks, they can’t occupy the same space either. But a down quark and an up quark? They can occupy the same space no problem.

So the neutrons are crushed into 2 down quarks and 1 up quark right? 1 down and 1 up quark can occupy roughly the same space, they can take up 1 “unit” of space together. But that second down quark? It needs to find a *different* space for itself to occupy.

But let’s bring gravity back into the picture: we’ve already seen how it can crush atoms down to neutrons, and neutrons down to quarks, can it crush these quarks even further? Well not directly, quarks are “fundamental particles,” there’s nothing they could crush down into. But there is an *indirect* form of crushing that could happen…

Remember that 1 down and 1 up quark can share the same space but that second down quark has to find a new space. If we could change that second down quark into something else, we could free up that space so gravity could crush further, but how?

Well while all the “regular” matter of our universe, stars, planets, bloggers, is all made of just up and down quarks, there’s more quarks then just them hiding in the fringes of particle physics.

The strange quark is another type of quark, different from up and down. It’s decidedly strange indeed, since it doesn’t exist anywhere in the universe except for fractions of a second at very high energies. But that’s not important, what *is* important is that *it’s another type of quark,” and just like how up and down quarks can share the same space because they’re different from each other, a strange quark *can also share that space* because it’s different from both up and down quarks.

So at the very highest limits of density, when neutrons themselves are crushed and when their quarks are crushed further, the sheer force of gravity might force those quarks to take drastic action. Half of the down quarks from the neutrons might convert into strange quarks, so that they can take up less space with the other quarks and crush the star yet further.

If this is the case, and these strange quarks do exist at the hearts of massive neutron stars, then this may the *only* place they exist for any significant length of time. Usually strange quarks decay because they’re so unstable, but at the crushing densities here, strange quarks are forced to *exist* because it’s the only way to crush down far enough under gravity. Despite being unstable, strange quarks here *can’t* decay, because gravity is forcing them to stay strange.

Now this is all very theoretical, but it begs the question: do strange stars even exist?

Maybe

And it begs another question: is Crabby a strange star?

Maybe maybe

Like I said if the neutrons are crushed into quarks and eventually strange quarks, it will only happen at the very center of the neutron star, a place we can’t observe and can only speculate about. But there is tantalizing evidence: we know exactly how old Crabby is thanks to those Chinese astronomers who recorded its explosion, and our evidence shows it to be a fair bit colder than we’d expect for a neutron star of its age, why could that be?

It’s been suggested that when neutrons are crushed into quarks and then strange quarks, that bursts of neutrinos are created which carry away much of the star’s heat into the cosmos. It *may be* that such a thing happened to Crabby, which is why it’s so cold.

This theory wouldn’t even be possible if we didn’t know how old Crabby is, if it were just another neutron star we would always have questions about if it’s actually just an older star that has had time to cool down, rather than being a young star that is unusually cold. And we owe it all to the astronomers from the past who first saw Crabby in their night sky, nearly one thousand years ago.

Sorry for no posts, I was watching the eclipse

Sorry I haven’t posted in a while, I drove halfway across the continent to see the eclipse. And then after it was finished I immediately drove the other halfway back home. After more than 24 hours of driving, I was beat, and this week was kind of a wash for me after that.

But the eclipse itself was beautiful and I encourage everyone to look for images of it online. NASA had an entire party for the eclipse, I don’t know if they did that for 2017 but maybe with how popular the 2017 eclipse was, they felt they needed to.

There was also some real science being done during this eclipse. Telescopes trained on the sun to look at its corona in great detail as the moon passed in front. A longstanding humorous story in the scientific community comes from an eclipse observed not long after Albert Einstein published his theory of general relativity. The theory predicted that light should bend when passing by massive objects. So scientists used a solar eclipse to visualize stars that were hiding near the sun. As predicted by Einstein, their light appeared to be “bent” because it had passed so close to the sun to get to us.

The newspapers published this with a somewhat hilarious line:

Stars not where they seemed or were calculated to be, but nobody need worry.

New York Times

The “but nobody need worry” always gets to me.

Regardless, eclipses are fun both for scientists and non-scientists alike. I hope if you missed this one, you’ll get to see one soon!