The Layman's Guide to the Solar System, part I: Formation.

As you may already know, our solar system contains eight planets, all orbiting the Sun; however, something less commonly considered is that they show a surprising amount of order. They all orbit in the same direction (which is also the direction the Sun rotates), and all more or less sit in the same plane in space. The four inner planets are small and rocky, while the four outer ones are giant, icy and have large gaseous envelopes.

Most of these are facts that are covered in school – but one question remains untouched: why? Why do none of the planets orbit in the other direction? Why do all of the orbits neatly line up, rather than being oriented at random? Why are none of the gas giants closer to the Sun, and why are none of the terrestrial ones further away? All of this has to do with how the planets formed in the first place.

In the beginning...
Our solar system started as a spinning cloud of dust and gas. As the cloud began to collapse under gravity, it span faster, due to conservation of angular momentum. This spinning caused it to collapse into a disk. This is because the existing angular momentum stops the cloud collapsing inwards, but there's nothing stopping it collapsing onto the plane of rotation. Imagine spinning holding a ball on a string – it's easy to move it up or down, but harder to pull it towards you.

Click for an enlarged view

Much of the mass in the cloud was concentrated at the centre of the disk, where collisions between particles caused them to heat up. Once the temperature hit about 10 million degrees kelvin, the collisions between gas particles became sufficiently energetic for nuclear fusion¹ to begin. Thus the Sun was born. This “spinning disk” origin explains why all the planets orbit in the same direction and the same plane.

What happens next?
So far we have a spinning disk of hot gas and dust, and a star in the centre. Over time the gas cooled and molecules began to condense into small solid grains. These then collided to form larger clusters, which eventually formed clumps of rock. Once the rocks got large enough, they attracted each other via gravity and formed the planets. This process is known as accretion.

Terrestrial planets and gas giants
Close to the Sun, only the heavier elements could condense into solid particles, which meant that the planets took a long time to form, as there wasn't much matter around. By this time most of the light gas in the disk (hydrogen and helium) had escaped, which is why the inner planets lack large hydrogen/helium envelopes.

On the other hand, far from the Sun, the temperature was low enough that ices (mostly water, ammonia and methane) could form on the grains (the distance from the Sun at which this happens is known as the frost line ). This made the grains much more massive, allowing the planets to form relatively quickly². As a result, the outer planets were large enough early enough to gravitationally attract and hold a large amount of gas, which is why they have an icy core and a gas envelope.

One interesting caveat is that large, gaseous planets have been observed close to their parent stars, within the frost line. They are thought to have formed in the outer disk and then migrated inwards later on.

Wrapping up
At this point, our initial questions about the solar system have been answered: the planets all orbit in the same manner due to the “spinning disk” origin, and the large icy planets are further out because it was too hot closer to the sun. The next episode will taking a closer look at the workings of the Sun, and stars in general.

¹Fusion in layman's terms: Two atoms smash together so violently that they fuse to form a new, heavier atom, releasing energy in the process. This is how stars “burn”. (More on this in part II! :D)
²“Quickly” in this case means in the order of 10 million years.

Kepler's anomalous discovery: an infographic

I created this a while ago when the story was big in the news, but at the time I just posted it on social media for the benefit of my friends. I feel it fits with the theme of the blog, so should probably be available here. Simply click to open it in a new tab, then click again to enlarge it.

Still can't sleep: a look at communication

An introduction of sorts
You may be wondering why a blog about what I find to be interesting topics has boredom in the title. I often have insomnia, and, around 11, if I'm not already asleep my brain tends to fire up and won't stop thinking. It gets very tedious, but I do occasionally come up with something interesting. The posts on this blog are the result of those times, hence 11pmBoredom.

The second reason my blog exists is that I want to practice writing: being able to effectively communicate ideas is an invaluable skill, one which writing this post has shown me I need to improve.

This isn't down to some intrinsic lack of ability (whatever you may believe about astrophysicists), but the simple fact that I rarely do it. If you don't practice something, you can't expect to be any good at it. In terms of content, there'll be will  layman's explanations of interesting physics, along with a mixture of my random thoughts (like today's, which we rather ironically still haven't got to despite being 173 words in).

Sound like the worst thing ever? Too bad, you can't stop me...

Effective communication
I recently began reading "The rough guide to Economics" by Andrew Mell and Oliver Walker. So far, it's quite well written. Concepts are clearly explained with appropriate analogies and it's accurately pitched at a reader with no prior knowledge.

My main issue and the inspiration for this post is the regular reference to upcoming parts of the book. In the first 16 pages there are no fewer than three summaries of the book's contents. There's the contents page itself, a short round-up in the preface and yet another, more verbose one at the end of the first chapter. On top of this, explanations throughout the book are regularly interrupted or concluded by telling the reader when the topic is next going to arise. As an example:
"[Explanation of utility maximisation]. In this book, the use of utility maximisation is most evident in chapter 3 which shows how it gives rise to a theory of consumer demand, and chapter 8, which uses it to analyse "strategic" decision making..." (the emboldening is reflective of the actual type).

This would be wonderful were it the kind of book you want to be able to flick through to find relevant information (i.e. a textbook), but it isn't. It's the kind of book you want to read cover to cover and emerge feeling like you've been taught something about the subject at hand. Efficiency is particularly important when it's an introduction to something as broad as economics and is only 344 pages long.

My current train of thought is thus: for effective communication, sentences should be doing at least one of two things:

1. Imparting new, pertinent information to the reader or listener.
2. Clarifying previously imparted information (for example, describing a previous idea in a new way so as to enhance comprehension: "Economists call the benefit derived from the last unit of something marginal benefit, and the cost of the last unit of something marginal cost. [Helpful analogy using Robinson Crusoe].)

If a sentence isn't achieving either of these, it's bloat and can be eliminated. The knowledge that in six chapters I'm going to come across strategic decision making does not add to my current understanding of utility management, it just wastes my time. 

I would be inclined to assume these increasingly annoying titbits are included as a "hook" to keep the reader interested, though this implies such a stunning lack of faith in the material itself, the quality of its presentation and the attention span of the reader that I'm not sure I want to run with this hypothesis. If the content is interesting to the reader (which we shall assume to be true in this case since they have bought the book), explaining it clearly and concisely should be enough to maintain the reader's attention. A more likely theory is that the book is trying to be both a beginner's guide and a useful reference for those with some prior experience, and it's ended up a sort of frustratingly structured hybrid.

As somebody who enjoys attaching numbers and logic to everything, I'm going to try to pseudo-quantify what makes explicative text engaging to read. To do this, we're going to have to make some starting definitions (part of which will be repeating the previous point in a more structured manner). 

Definitions

1. A block is an arbitrary snippet of text. I have been using "sentence" up until now, but I'd like this argument to be more general.
2. Information density is the amount of new and pertinent information in a given block, in comparison to its length.
3. Blocks can be binned into three types:
   1. Blocks imparting new, pertinent information to the reader or listener.
   2. Blocks clarifying previously imparted information
   3. Bloat, or anything that isn't i or ii (this is a rather strong assumption).

The first thing to note is that type i blocks increase information density as they actively introduce new ideas. Conversely, types ii and iii decrease it.

The argument is then that maintaining an appropriate level of information density is key to keeping your audience engaged. Too high and the reader or listener is overwhelmed with new information, too low and they will be quickly bored or frustrated. Both result in us losing their attention. I'll give you two blocks of similar length about the planets of the solar system to illustrate the two extremes.

Example 1 (high density)

Our solar system contains four terrestrial (rocky) planets (Mercury, Venus, Earth and Mars) and, beyond the asteroid belt, four larger gas giants (Jupiter, Saturn, Uranus and Neptune) on wider orbits.

Let's unpack what's contained in the 30 words above.

• The solar system contains 8 planets
• These are split into 4 rocky ones and 4 larger more gaseous ones
• The 4 rocky ones are Mercury, Venus, Earth and Mars
• The 4 gas giants are Jupiter, Saturn, Uranus and Neptune
• The rocky ones are closer to the centre while the gas giants are further out
• The two groups are separated by the asteroid belt.

Example 2 (low density)

There are a total of 8 planets in our solar system, mostly named after various Greek deities. Mercury, Venus, Earth, Mars and Jupiter were discovered first by ancient Babylonian astronomers...

This block contains much less pertinent information (note - pertinent is the key word here. It still contains lots of information, but about the history of the planets' discoveries, which is not what we're after in this case.):

• The solar system contains 8 planets
• 5 of them are Mercury, Venus, Earth, Mars and Jupiter

As with most things, moderation seems to be the best way forward. The high density example could do with being split up a bit, and the low density one needs some serious trimming. This argument can be applied to everything from individual words to entire sections of a text. The take-home message seems to be firstly that we should be aware of and aim for appropriate levels of information density when attempting to convey ideas. Secondly, we should reach the desired level by combining type i and ii blocks rather than resorting to bloat. This is by no means the only important point when it comes to effective communication, but it's certainly something to bear in mind as either extreme can easily mar what is otherwise excellent text.

Wrapping up
So, has writing this improved my communicative skills? Honestly, I'm not sure. Practice is only useful if it is used to improve - repeatedly making the same mistakes helps nobody. With this in mind, if you've gotten this far, please feel free to leave a comment or send me a message telling me how I can do this better. It'll mean a lot :)
-Benji

Coming soon! "A layman's guide to the Solar System".