Attaching politics to a topic they wish to squelch. That effectively “controversializes” the issue and divides public opinion so that no more than half of people will typically believe or pay attention to the offending information.

https://thehill.com/opinion/campaign/405807-a-news-consumers-guide-to-astroturf-sources

Preface

Different projects have different use cases that can ultimately result in common solutions not suiting your particular needs. Today I'm going to diverging a bit from my more abstract, generalized topics on code quality and instead focus on a specific project structure example that I encountered.

Background

For a while now, I've found myself being continually frustrated with the state of my project configuration management. I had a single configuration file that would contain all of the configuration options for the various tools I've been using--database, API credentials, etc.--and I kept running into the problem of wanting to test these tools locally while not inadvertently committing and pushing sensitive credentials upstream. For me, part of my security process is ensuring that sensitive access credentials never make it into the repository and to limit access to these credentials to only people who need to be able to access them.

Monolithic Files Cause Monolithic Pain

The first thing I realized was that having a single monolithic configuration file was just terrible practice. There are going to be common configuration options that I want to have in there with default values, such as local database configuration pointing to a database instance running on the same VM as the application. These should always be in the repo, otherwise any dev who spins up an instance of the VM will need to manually tread documentation and copy-paste the missing options into the configuration. This would be incredibly time-consuming, inefficient, and stupid.

I also use different tools which have different configuration options associated with them. Having to dig through a single file containing configuration options for all of these tools to find the ones I need to modify is cumbersome at best. On top of that, having those common configuration options living in the same place that sensitive access credentials do is just asking for a rogue git commit -A to violate the aforementioned security protocol.

Same Problem, Different Structure

My first approach to resolving this problem was breaking the configuration out into separate files, one for each distinct tool. In each file, a "skeleton" config was generated, i.e. each option was given a default empty value. The main config would then only contain config options that are common and shared across the application. To avoid having the sensitive credentials leaked, I then created rules in the .gitignore to exclude these files.

This is where I ran into problem #2. I learned that this just doesn't work. You can either have a file in your repo and have all changes to that file tracked, have the file in your repo and make a local-only change to prevent changes from being tracked, or leave the file out of the repo completely. In my use case, I wanted to be able to leave the file in the repo, treat it as ignored by everyone, and only commit changes to that file when there was a new configuration option I wanted added to it. Git doesn't support this use case whatsoever.

This problem turned out to be really common, but the solution suggested is to have two separate versions of your configuration--one for dev, and one for production--and to have a flag to switch between the two. Given the breaking up of my configuration, I would then need twice as many files to do this, and given my security practices, this would violate the no-upstream rule for sensitive credentials. Worse still, if I had several different kinds of environments with different configuration--local dev, staging, beta, production--then for m such environments and n configuration files, I would need to maintain n*m separate files for configuration alone. Finally, I would need to remember to include a prefix or postfix to each file name any time I needed to retrieve values from a new config file, which is itself an error-prone requirement. Overall, there would be a substantial increase in technical debt. In other words, this approach would not only not help, it would make matters worse!

Borrowing From Linux

After a lot of thought, an idea occurred to me: within Linux systems, there's an /etc/skel/ directory that contains common files that are copied into a new user's home directory when that user is created, e.g. .bashrc and .profile. You can make changes to these files and have them propagate to new users, or you can modify your own personal copy and leave all other new users unaffected. This sounds exactly like the kind of behavior I want to emulate!

Following their example, I took my $APPHOME/config/ directory and placed a skel/ subdirectory inside, which then contained all of the config files with the empty default values within. My .gitignore then looked something like this:

$APPHOME/config/*
!$APPHOME/config/main.php
!$APPHOME/config/skel/
!$APPHOME/config/skel/*
# This last one might not be necessary, but I don't care enough to test it without.

Finally, on deploying my local environment, I simply include a snippet in my script that enters the new skel/ directory and copies any files inside into config/, as long as it doesn't already exist:

cd $APPHOME/config/skel/
for filename in *; do
    if [ ! -f "$APPHOME/config/$filename" ]; then
        cp "$filename" "$APPHOME/config/$filename"
    fi
done

(Note: production environments have a slightly different deployment procedure, as local copies of these config files are saved within a shared directory for all releases to point to via symlink.)

All of these changes ensure that only config/main.php and the files contained within config/skel/ are whitelisted, while all others are ignored, i.e. our local copies that get stored within config/ won't be inadvertently committed and pushed upstream!

Final Thoughts

Common solutions to problems are typically common for a good reason. They're tested, proven, and predictable. But sometimes you find yourself running into cases where the common, well-accepted solution to the problem doesn't work for you. Standards exist to solve a certain class of problems, and sometimes your problem is just different enough for it to matter and for those standards to not apply. Standards are created to address most cases, but edge cases will always exist. In other words, standards are guidelines, not concrete rules.

Sometimes you need to stop thinking about the problem in terms of the standard approach to solving it, and instead break it down into its most abstract, basic form and look for parallels in other solved problems for inspiration. Odds are the problem you're trying to solve isn't as novel as you think it is, and that someone has probably already solved a similar problem before. Parallels, in my experience, are usually a pretty good indicator that you're on the right track.

More importantly, there's a delicate line to tread between needing to use a different approach to solving an edge case problem you have, and needing to restructure your project to eliminate the edge case and allow the standard solution to work. Being able to decide which is more appropriate can have long-lasting repercussions on your ability to manage technical debt.

I was looking for preferences on 120/140mm case fans. RGB is a want, but not at the expense of quality fans.

I'm pretty new to the topic and not super familiar with the technical side. So open to reading more in depth too.

Thanks!

Intro

Hello everyone,

Today we cover entropy and the heat death of the universe.

The previous chapters can be found here and here. While I recommend you read both, you should at least read the first part and skim the second.

A collection of all topics covered can be found here: https://tildes.net/~tildes/8al/.

Subject

Intro

Entropy describes how chaotic a system is. In thermodynamics, chaos is created from an irreversible process. We are all sort of familiar with this concept. A broken cup will not unshatter itself. As a consequence of how our universe works, (net) chaos can only increase. And this might have far reaching consequence, if we look at the effects of entropy on a cosmic scale.

Entropy

Entropy describes an amount of irreversible chaos.

But first, let's cover cycles super quickly. In thermodynamics, a very important concept is a "cycle". A cycle is a repeating process, that returns to its initial condition. For instance, when we ride a bike. We're turning our feet around the crank shaft. Repeatedly returning to the same position we started from. As we push on the pedal, some of our work is lost and turned into heat. Primarily due to friction from the wheels and from the different mechanical parts.

A cycle that wastes no energy is called a reversible cycle. That would mean 100% of the work in a cycle (even the work that is turned to heat) has to be returned in some way to its original state. The most famous example of this is the Carnot heat engine.[1] But in reality, the Carnot heat engine is nothing more than a theoretical engine. As we remember from before, we cannot turn 100% of heat back into work. So any heat engine, be it a car's motor, a refrigerator, a star, or the human body, will in some way contribute to this irreversible chaos.

Now what about entropy? If we look at entropy at the molecular level, it all becomes a bit abstract. But we can think of this concept with bigger building blocks than molecules, and still be close enough. Say you have a brick house with orderly layed bricks. This house would love to come crashing down. And lets imagine it does. When the house lays in ruins, it is not likely to suddenly "fall" into the shape of the house again. So if the house has collapsed, our system is in a higher state of chaos. Our entropy has increased. And unless we supply work to the system (and waste energy trough heat), we will not get the brick house back.

So now we understand, that on the grand scale of the universe, entropy will only increase.

The heat death of the universe

But what are the consequences of this? Imagine entropy going on for billions and billions of years. Everything in the universe slowly reaching a higher state of chaos. Everything that is orderly, turns into chaos. All high quality energy has turned into low quality energy. Everything has been wasted and turned into heat. Everything ripped apart until you are left with nothing to rip apart. At this point, there is no interactions between molecules any more. Everything has reached absolute zero temperature.

At this point, entropy is at its absolute maximum. And we have reached entropic equilibrium.

This is the heat death of the universe.

Afterword

Of course, the heat death of the universe is just one of the many theories about the end of the universe. It assumes that thermodynamics properly describes the universe, and that there are no hidden surprises.

Frankly told, it's the best bet we have with our current knowledge. But we still know so little. So I would not panic just yet. Alternatively, this is where we could continue with "an engineer's perspective on existensial nihilism". But I think that this is something better reserved for later, and better presented by someone else.

We have covered what I consider the absolute minimum of thermodynamics, that still gives us a basic understanding of thermodynamics. There are of course a lot of other topics we could cover, but thats it for now. I will potentially write an appendix later with some questions or things that have been asked.

But for now, that's it. Questions, feedback or otherwise?

Notes

[1] The Carnot heat cycle is a bit beyond the level of what we have discussed so far. It describes a system where heat is supplied and removed to have a piston expand and contract without any energy becoming waste heat.

Some people have mentioned they'd like to have some sort of weekly track-sharing thread, so let's have a little fun and find some good music in the process.

Everybody's got that playlist somewhere with all of your favorite earworms - the songs you put on repeat to the point where you annoy the hell out of everyone else in the room because you love them so much. Let's collect some of those earworms here and see what we can come up with.

In particular, let's go for the uplifting kind - feel good music. When the thread settles down I'll pull these all together in a nice playlist and share that here as a separate link submission.

Any time period, any genre, any style, popular, obscure, or even your own music, it's all good - just as long as it's positive energy and you can't stop spinning it. If you're on mobile, don't worry about making it into links, others can linkify it for you (and eventually, Tildes can do that automatically to make this all easier in the future). Share as many as you've got. If you've already got a playlist like this for yourself, you can share that too. ;)

Oh, and don't worry about nebulous 'standards' or if people will like it. If you like it, that's all that matters. Don't overthink it!

Edit: Almost forgot, feel free to make suggestions for the topics of upcoming share threads in the next few weeks!

I have poor vision and I rely heavily on a Firefox plugin called Stylus to make websites readable - in particular the trend for low contrast and small text. That includes Tildes.

I updated it to v1.5.0 and now the styles I set for Tlldes no longer work - most other sites still appear to work but I've not checked them exhaustively.

I immediately tried rolling back a release or two (1.4.23 and 1.4.22) but those versions no longer work for any site. I tried randomly downgrading to even older versions but the same result. I think I'm stuck with the latest version..

I notice in the browser console there are 2 errors reported on Tildes e.g. on this page I see:

Content Security Policy: The page's settings blocked the loading of a resource at inline ("script-src"). new_topic:1:1
Content Security Policy: The page's settings blocked the loading of a resource at inline ("style-src"). new_topic:1:1

Using the Firefox Developer tools Inspector - I see my style settings for Tildes injected by Styuls (after the body) but they do not work any more.

Since only Tildes so far is not working with my Stylus settings I guess there is also a recent change to Tildes that is causing Stylus to fail.

This is a rather serious issue for me as all the colour options in the setting are low contrast and cause eye strain which becomes painful without the Stylus settings.

Thanks for any help you can offer.

Introduction

I want to give an introduction on several physics topics at a level understandable to laypeople (high school level physics background). Making physics accessible to laypeople is a much discussed topic at universities. It can be very hard to translate the professional terms into a language understandable by people outside the field. So I will take this opportunity to challenge myself to (hopefully) create an understandable introduction to interesting topics in modern physics. To this end, I will take liberties in explaining things, and not always go for full scientific accuracy, while hopefully still getting the core concepts across. If a more in-depth explanation is wanted, please ask in the comments and I will do my best to answer.

Previous topics

Bookmarkable meta post with links to all previous topics

Today's topic

Today's topic is the dual nature of light and matter, the wave-particle duality. It is a central concept in quantum mechanics that - as is tradition - violates common sense. I will first discuss the duality for light and then, in the next post, for matter.

The dual nature of light

In what terms can we think of light so that its behaviour becomes understandable to us? As waves? Or as particles? There are arguments to be made for both. Let's look at what phenomena we can explain if we treat light as a wave.

The wave nature of light

Let's start with an analogy. Drop two stones in a pond, imagine what happens to the ripples in the pond when they meet each other. They will interact, when two troughs meet they amplify each other, forming a deeper trough. When two crests meet they do the same. When a crest and a trough meet they cancel out.

Now if we shine light through two small openings and observe the resulting pattern, we see it's just like ripples in a pond, forming an interference pattern. When looking at the pattern formed on a screen placed at some distance from the openings, we see a striped pattern Light can be described as an electromagnetic wave, with crests and troughs. It sure seems like light is wavey! The wave nature of light allows us to describe phenomena like refraction and diffraction.

The particle nature of light

When we shine light on some metals, they will start tossing out electrons. This is called the photoelectric effect. How can we understand this process? Well we know light is a wave, so we imagine that the wave crashes into the electron that is chilling out near the surface of the metal. Once the electron has absorbed enough of the light's energy it will be able to overcome the attractive forces between itself and the positively charged atom core (remember, an electron has negative charge and so is attracted to the atom cores). So a higher intensity of light should make the electron absorb the required amount of energy more quickly. Easy, done!

However, there's something very peculiar going on with the photoelectric effect. If we shine low frequency light on said metal, no matter how intense the light, not a single electron will emerge. Meanwhile if we shine very little high frequency light on the metal, no matter how low the intensity, the electron will emerge. But how can this be? A higher intensity of light should mean the electron is receiving more energy. Why does frequency enter into this?

It seems that the electron needs a single solid punch in order to escape the metal. In other words, it seems it needs to be hit by something like a microscopic billiard ball that will punch it out of the metal in one go. The way physicists understand this is by saying light is made up out of particles called photons, and that the energy a photon carries is linked to its frequency. So, now we can understand the photoelectric effect! When the frequency is high enough, the photons in the light beam all individually carry enough energy to convince an electron to leave the metal. When the frequency is too low, none of the photons individually can knock an electron out of the metal. So even if we fire a single photon, with high enough frequency, at the metal we will see one electron emerging. If we shine low frequency light with a super high intensity at the metal, not a single photon will emerge.

So there you have it! Light is made out of particles. Wait, what? You just told us it's made out of electromagnetic waves!

The wave-particle duality of light

So, maybe light is just particles and the wave are some sort of emerging behaviour? This was a popular idea, one that Einstein held for some time. Remember the experiment where we shone light through two small openings and saw interference (commonly known as the double slit experiment)? Let's just take a single photon and shoot it at the openings! Because light is particles we'll see the photon just goes through either opening - like a particle would. Then all the non-believers will have to admit light is made out of particles! However, when we do the experiment we see the photon interfere with itself, like it was a wave. Remember this picture which we said was due to wave interference of light? When a single photon goes through the openings, it will land somewhere on the screen, but it can only ever land in an area where the light waves wouldn't cancel out. If we shoot a bunch of photons through the openings one at a time, we will see that the photons create the same pattern as the one we said is due to wave interference!

Implications

So it would seem light acts like a particle in some cases, but it acts like a wave in some others. Let's take a step back and question these results. Why are we trying to fit light into either description? Just because it's convenient for us to think about things like waves and particles - we understand them intuitively. But really, there is no reason nature needs to behave in ways we find easy to understand. Why can't a photon be a bit wavey and a bit particley at the same time? Is it really that weird, or is it just our intuition being confused by this world we have no intuitive experience with? I would love to hear your opinions in the comments!

Observing photons

To add one final helping of crazy to this story; if we measure the photon's location right after it emerges from the slit we find that it doesn't interfere with itself and that it just went through a single slit. This links back to my previous post where I described superpositions in quantum mechanics. By observing the photon at the slits, we collapsed its superposition and it will behave as if it's really located at one spot, instead of being somehow spread out like a wave and interacting with itself. The self interaction is a result of its wavefunction interacting with itself, a concept that I will explain in the next post.

Conclusion

We learned that light cannot be described fully by treating it simply as a wave or simply as a bunch of particles. It seems to be a bit of both - but neither - at the same time. This forces us to abandon our intuition and accept that the quantum world is just fundamentally different from our every day life.

Next time

Next time we will talk about the dual nature of matter and try to unify the wave and particle descriptions through a concept known as the wavefunction.

Feedback

As usual, please let me know where I missed the mark. Also let me know if things are not clear to you, I will try to explain further in the comments!

Addendum

The photoelectric effect is actually what gave Einstein his Nobel prize! Although he is famous for his work on relativity theory he was very influential in the development of quantum mechanics too.

I've posted a few lengthy topics here outside of programming challenges, and I've noticed that the ones that seem to have spurred the most interest and generated some discussion were ones that were directly related to code quality. To avoid falling for confirmation bias, though, I thought I would ask directly.

Is there generally a greater interest in code quality discussions? If so, then what kind of things are you interested in seeing in those discussions? What do you prefer not to see? If not, then what kinds of programming-related discussions would you prefer to see more of? What about non-programming discussions?

Also, is there any interest in an informal series of topics much like the programming challenges or the a layperson's introduction to... series (i.e. decentralized and available for anyone to participate whenever)? Personally, I'd be interested in seeing more on the subject from others!

Intro

Hello everyone,

Today we cover equilibriums and phase changes. Through that we will get a basic understanding of how things like pressure, temperature, density, volume, etc. are related.

The previous chapter can be found here: https://tildes.net/~science/8ao/. I highly recommend that you read it before continuing.

A collection of all topics covered can be found here: https://tildes.net/~tildes/8al/.

Subject

Summarized

"Equilibrium" is fancy word for "balance". A system is in equilibrium when it is in balance with the surrounding systems. Any system will naturally attempt to be in equilibrim, and will adapt its physical properties to do so.

A phase change is the transition of matter from a state (solid, liquid, gas, or plasma) to a different state. This happens due to a change in internal energy, changing how a material is bonded.

Now that we have it summarised, lets dig a bit deeper.

Equilibrium

A system always tries to be in balance with its surrounding systems. We maybe don't think about this a lot, but we are all very familiar with this principle since we observe it every day.

If you have a cup of hot cocoa, it will cool down until it has reached ambient temperature. At this point, the cocoa is considered to be in "thermal equilibrium". If we fill a balloon with air, it will expand. It will do so until the air inside the balloon has the same pressure as the air outside the balloon. At this point, the balloon is considered to be in "barometric (pressure) equilibrium".

Just like when we talk about energy, there is a relationship when we talk about equilibriums. We have something we call (you may remember this from basic chemistry) an "ideal gas". An ideal gas is a good way of looking at this principle. Since the temperature, volume and pressure have a direct relationship.

Pressure-volume-temperature diagram for ideal gases.

In the diagram above we can see that if we change one of the three variables, then one (or both) of the other two variables has to change too. For instance, if we heat some air in a canister, the air will try to expand. But being unable to change in volume, it will instead increase pressure. [1]

Phase changes

Any material has a set of phases. The ones we'll discuss are the solid, liquid and gaseous phases. Unless we control the material's environment very carefully, materials will always follow this order when energy is added. Solid becomes liquid, liquid becomes gas, and vice versa. For instance water; ice (solid) becomes water (liquid), water becomes steam (gas). So each of these transformations is a phase change.

So when water is solid (ice), the molecules are in a grid. The molecules do not move around much, maybe a little bit where they stand. But they all still stand in a grid.

When the water gets heated up, the molecules will start to move. Molecules have a natural attraction to each other due to subatomic forces like the van der Waals force. So the molecules will no longer stay in a grid, but they will still keep each other close due to this attraction. So a material that sticks together but freely moves around is called a liquid.

Once the material overcomes this natural attraction, the molecules can go anywhere they want. And that's when we get a gas. Or steam, in the case of water. All of this applies even for materials we don't usually imagine would melt or evaporate, for instance steel.

Here is a visual representation of the three states.

Now comes the fun part. Ice is water that is at 0 degrees Celcius or below. Liquid water is water that is 0 degrees and above. But wait! Does that mean that water can be both solid and liquid at the same temperature? Yes, indeed. A material requires a certain amount of internal energy to become liquid. That is why internal energy and temperature is often used interchangeably, but is not exactly the same.

The water molecules in ice will use the supplied energy to get excited and start moving around. This continues until the solid-liquid water reaches a point where all molecules move around. At that point it has completely become a liquid. While water is in solid-liquid state, the amount of internal energy dictates how much is liquid and how much is solid. The exact same thing happens with water at 100 degrees. It can be steam or liquid, but not fully either until it reaches a certain amount of internal energy.

Here is a diagram of this process.

Another fun tidbit that makes water special: Water has a lower density as a solid than it has as a liquid, when both are at 0 degrees Celcius. This means that per unit of volume ice weighs less than (liquid) water. Therefore ice floats on top of water. This is the only material that behaves in this way. And thats extremely important to our existince, since it helps regulate heat in the ocean.

Steam engines (and implication)

We have learned a few new things today. But there is one really important wrinkle to all of this. A system always will try to be in balance. And this we can exploit. Pressure is a type of "pushing". So thats a type of work! And an increase in thermal energy can lead to an increase in temperature. We remember that from the ideal gas. So if we cleverly organize our system, we can create work from heat! This is the basis behind most heat engines (simplified a ton). We supply thermal energy to some gas or fluid, and extract work from this gas or fluid.

A classical example is the steam engine. We have water inside a closed system. When we heat up the water, it will turn into steam. And this steam will want to be much less dense than water. As a consequence, the pressure inside the water tank increases drastically. We release a small amount of this steam into a closed piston.

Here is an animation of this in action.

The piston suddenly gets a high pressure level. As we remember, it will want to be in equilibrium with its surroundings. Currently the pressure inside the piston is much higher than outside the piston. As we remember from the ideal gas law, a higher volume will mean a lower pressure. So the piston will be moved, as the steam expands to reach a pressure balance. The movement from the piston will drive something, like a wheel. The steam is removed from the expanded piston, and the piston will return to its closed position.[2] Then the process is repeated again and again, to have the piston continously move something.

All that from a bit of water in a tank and some supplied heat.

Whats next?

Next time we will talk about another important property. Entropy! In the previous topic I had a lot of questions regarding the quality of energy types, and what specifies heat from work on an intrinsic level. Entropy is the big answer to this. From that we will also cover the heat death of the universe, which would be a good introduction to "a laypersons introduction to nihilism" if we have any philosophers here.

Note

[1] For solid and fluid materials (as well as non-ideal gassess) this becomes a lot more complicated. If we ever do a "layperson's intro to fluid mechanics" we will cover it then.
[2] This described design is very inefficient and very simplified. Usually the piston is made so steam is supplied in turns supplied to either side of the piston. Then the work will both removed the steam that already performed work as well as move the piston. That way you can have continous movement in both directions.

See for instance this image.

I'd love to hear about how you create your favorite works. Of anything. How did you write your best music? How did you create your favorite character in a story you wrote? Anything of the sort.

I'd love to hear all the different processes people have. It's really quite an interesting topic of discussion, for me.

Personally, I grab a cup of coffee and listen to instrumental music (mostly avant-garde jazz [Coltrane, Washington, etc]) while creating the world of the story I'm writing. There's something very productive-feeling about being wired on caffeine while also having a constant noise in your ears. It's how I compose some of my better characters and settings.

Due to my constant writer's block phenomenon, sometimes I'll smoke some pot to get past it. It's almost like phasing through a wall you can't jump over. There's something lifting about it.

Deimos and I were discussing the use of "ask" topic tags this week, and we agreed it might be a good idea to get a consensus on these.

At the moment, Tilders are using four "ask" tags on topics:

• ask

• ask.survey

• ask.recommendations

• ask.help

(There may be more "ask" tags created in the future, but these four are what we're all using at the moment.)

Anything that's a question gets tagged with "ask". Some specific types of question will then get tagged with "ask.survey" or "ask.recommendations" or "ask.help", depending in the type of question being asked.

• "ask.survey" is for questions about preferences and favourites. "What's your favourite horror movie?" "What's the best place you ever visited?" "What's your favourite type of holiday?" The asker is collecting data about people's likes and dislikes (even if they're not going to publish the results in a report later!).

• "ask.recommendations" is for questions asking for recommendations. "What's a good browser to use?" "What book should I read next?" "Which brand of phone should I buy?" The asker is looking for people to recommend things to them.

However, Deimos and I wondered about "ask.help". One interpretation we came up with was that "ask.help" is for questions looking for a specific answer, where it should generally be possible for people to think "yes, this is the right answer to the question". This would include questions seeking help learning about an academic topic, such as happens in /r/AskScience and /r/AskHistorians over on Reddit. Another interpretation we came up with was that "ask.help" is for questions looking for guidance on doing something, like a "how to" type question. This would be more like the types of questions in /r/Help and like the Help menus in software and the F1 key - helping people get things done.

What do you think about the "ask" tags? In particular, what should the "ask.help" tag be used for? In general, are the existing "ask" tags okay? Do we need more "ask" tags? Do we need different "ask" tags?

Introduction

I want to give an introduction on several physics topics at a level understandable to laypeople (high school level physics background). Making physics accessible to laypeople is a much discussed topic at universities. It can be very hard to translate the professional terms into a language understandable by people outside the field. So I will take this opportunity to challenge myself to (hopefully) create an understandable introduction to interesting topics in modern physics. To this end, I will take liberties in explaining things, and not always go for full scientific accuracy, while hopefully still getting the core concepts across. If a more in-depth explanation is wanted, please ask in the comments and I will do my best to answer.

Previous topics

Bookmarkable meta post with links to all previous topics

Today's topic

Today's topic will be light emitting diodes, better known as LEDs. As the name suggests, we'll have to discuss light and diodes. We will find out why LEDs can only emit a single colour and why they don't get hot like other sources of light. Let's start by discussing diodes, in case you are already familiar with diodes note that I will limit the discussion to semiconductor (p-n with a direct bandgap) diodes as that's the type that's used in LEDs.

What's a diode?

A diode is an electronic component that, ideally, only lets electric current through in one direction. In other words it's a good resistor when the current flows in one direction and a really good conductor when the current flows in the other direction. Let's look a bit closer at how diodes function.

Semiconductors

Diodes are made out of two different semiconducting materials. In everyday life we tend to classify materials as either conducting (metals being the prime example) or non-conducting (wood, plastics, rubber). Conductance is the flow of electrons through a material, a conducting material has a lot of electrons that can move freely through a material while an insulator has none. Semiconducting materials fall in between these two categories. They do conduct but not a lot, so in other words they have a few electrons that can move freely.

N-type semiconductors

We are able to change a semiconductor's conductivity by adding tiny amounts of other materials, this is called doping. As an example, we can take silicon (the stuff that the device you're reading this on is made out of) which is the most well-known semiconductor. Pure silicon will form a crystal structure where each silicon atom has 4 neighbours, and each atom will share 1 electron with each neighbour. Now we add a little bit of a material that can share 5 electrons with its neighbours (how generous!). What will happen? Four of its shareable electrons are busy being shared with neighbours and won't leave the vicinity of the atom, but the fifth can't be shared and is now free to move around the material! So this means we added more freely flowing electron and that the conductivity of the semiconductor increases. An illustration of this process is provided here, Si is chemistry-talk for silicon and P is chemistry-talk for phosphorus, a material with 5 shareable electrons. This kind of doping is called n-type doping because we added more electrons, which have a negative charge, that can freely move.

P-type semiconductors

We can do the same thing by adding a material that's a bit stingy and is only willing to share 3 electrons, for example boron. Think for a moment what will happen in this case. One of the silicon atoms neighbouring a boron atom will want to share an electron, but the boron atom is already sharing all of its atoms. This attracts other electrons that are nearby, one of them will move in to allow the boron atom to share a fourth electron. However, this will create the same problem elsewhere in our material. Which will also get compensated, but this just creates the same problem once more in yet another location. So what we now have is a hole, a place where an electron should be but isn't, that is moving around the crystal. So in effect we created a freely moving positive charged hole. We call this type of doping p-type. Here's an illustration with B the boron atoms.

Creating a diode

So what would happen if we took a n-type semiconductor and a p-type semiconductor and pushed them against one another? Suddenly the extra free-flowing electrons of the n-type semiconductor have a purpose; to fill the holes in the p-type. So these electrons rush over and fill the holes nearest to the junction between the two semiconductors. However, as they do this a charge imbalance is created. Suddenly the region of p-type semiconductor that is near the junction has an abundance of electrons relative to the positive charges of the atom cores. A net negative charge is created in the p-type semiconductor. Similarly, the swift exit of the electrons from the n-type semiconductor means the charge of the cores there isn't compensated, so the region of the n-type semiconductor near the junction is now positively charged. This creates a barrier, the remaining free electrons of the n-type cannot reach the far-away holes of the p-type because they have to get through the big net negative charge of the p-type near the junction. Illustration here. We have now created a diode!

How diodes work

Think for a moment what will happen if we send current* (which is just a bunch of electrons moving) from the p-type towards the n-type. The incoming electrons will face the negative charge barrier of the p-type and be unable to continue. This means there is no current. In other words the diode has a high resistance. Now let's flip things around and send electrons through the other way. Now they will come across the positive charge barrier of the n-type semiconductor and be attracted to the barrier instead. The electrons' negative charge compensates the net positive charge of the barrier on the n-type and it will vanish. This destroys the equilibrium situation of the barrier. The p-type holes are no longer repelled by the positive barrier of the n-type (as it no longer exists) and move closer to the junction, this means the entire barrier will fade and current can move through. We now have a conductor.

OK, but I don't see what this has to do with light

Now let's find out how we can create light using this method. When current is applied to a diode what happens is that one side of the diode is at a higher energy than the other side. This is what motivates the electrons to move, they want to go from high energy to low energy. If the p-type semiconductor is at a higher energy than the n-type the electron will, upon crossing the junction between the two types, go from a high energy level to a lower one. This difference in energy must be compensated because (as @ducks mentioned in his thermodynamics post) energy cannot be destroyed. So where does the energy go? It gets turned into light!

The energy difference between the p-type and n-type is fixed, meaning a fixed amount of energy is released each time an electron crosses the junction. This means the light is of a single colour (colour is how we perceive the wavelength of light, which is determined by the energy of the light wave). Furthermore, none of the energy is lost so there is no energy being turned into heat, in other words the LED does not get warm.

Conclusion

So now we know why the LED is so power-efficient; it does not turn any energy into heat, it all goes into light. We now also know why they only emit a single colour, because the energy released when an electron crosses the junction is fixed.

Next time

I think next time I will try to tackle the concept of wave functions in quantum mechanics.

Feedback

As usual, please let me know where I missed the mark. Also let me know if things are not clear to you, I will try to explain further in the comments!

Addendum

*) Yes, current flow is defined to be opposite to the flow of the electrons, but I don't want to confuse readers with annoying definitions.

Intro

Hello everyone,

@wanda-seldon has been giving us an introduction to quantum physics. For now, she will be given a short break to prepare new stuff. In the meantime I will be covering some classical mechanics, more specifically thermodynamics. In part 1, we need to work our way through some of the more dry concepts, so we can understand and appreciate the horrifying implications of the fun parts. So I promise, this will be the most verbose one.

Some of you may have briefly seen a version of this posted, that was due to me misunderstanding the schedule with @wanda-seldon. If you saw that one, I will mention I rewrote nearly all of it to be more readable.

Now, on today's agenda: The basics of heat, work and energy and how it's all related.

Previous posts can be found here: https://tildes.net/~science/8al/meta_post_for_a_laypersons_introduction_to_series

Important note

If @wanda-seldon in her posts mention "energy", it's most likely in the context of energy operators, which is a concept in quantum physics. I'm not going to pretend I understand them, so I will not be explaining the difference. We will cover what energy is in classical mechanics. So keep that in mind if you read something from either of us.

Subject

Summarized

What is heat? Using a lot of fancy words we can describe it as follows. Heat is an energy that is transferred between systems by thermal interaction. And what is work? Work is an energy that is applied in a way that performs... work. The combined energy in a system is called internal energy. This type of energy can be transformed or applied to other systems.

These are a lot of new words, so lets break that down a bit.

Systems

A system is just a catch-all term for something that can be defined with a boundary of sorts. Be it mass, volume, shape, container, position, etc. A canister, your tea mug, the steam inside a boiler, your body, a cloud, a room, earth, etc. They are all systems because you can in some way define what is within the boundary, and what is beyond the boundary.

In theory, you could define every single nucleid in the universe as an unique system. But that would be counter-intuitive. In thermodynamics we tend to lump things into a system, and treat it as one thing. As opposed to Quantum stuff that looks at the smallest quantity. Calculating every single water molecule in my coffee would be pure insanity. So we just treat my mug as the boundary, and the tea inside the mug as the system. And just so it's mentioned, systems can contain systems, for instance a tea mug inside a room.

Energy

Energy is some quantifiable property that comes in either the form of heat, work. It can be transferred to other systems, or change between the different energy types. An example of transfer is my coffee cooling down because it's in a cold room. That means heat has been transferred from one system (my mug) to another system (the room). Alternatively you could say my hot coffee mug is warming up the room, or that the room is cooling down my coffee. Thermodynamics is a LOT about perspective. An example of transforming energy types is when we rub our hands together. That way we convert work (rubbing) into heat. It's really not more complicated than that. An interaction in this case is just a system having an effect on a different system. So a thermal interaction means it's an interaction due to heat (like in the mug example).

This brings us to an extremely important point. So important, it's considered "law". The first law of thermodynamics even. Energy cannot be destroyed, it can only change forms.

Your battery charge is never really lost. Neither is the heat of your mug of coffee. It just changed form or went somewhere else. The combined energy of all types that is residing inside a system is called internal energy.

Heat and work

Let's say we have a system, like a room. And all windows and doors are closed, so no energy can leave. In this system, you have a running table fan connected to a power line, getting energy from outside the system. The table fan is making you feel cool. Is the fan cooling down the room, heating up the room, or doing nothing? Think about it for a moment.

http://imgbox.com/CKtQLLOQ

The first thought of many would be to think that this fan would cool the room down, it sure makes you feel cooler! But it's actually heating up the room. As we remember, internal energy is the energy inside a system (room, in this case). The fan is getting energy from outside, and uses this energy to perform work. The fan accelerates the air inside the room, and this accelerated air will evaporate some of your sweat, so you feel cool. But as we remember, energy cannot be destroyed. So we are importing energy into the system, increasing the internal energy. Some of the work from the fan is also directly converted to heat, since the motor of the fan will get hot.

So if we are not getting rid of any of this excess energy, we are increasing the internal energy. And therefore actively increasing the temperature of the room.

http://imgbox.com/SAtqk7YG

To use a more tangible example: Simplified, this phenomena is why green house gases are bad. Lets define earth as a system. Earth gets a lot of energy from the sun. And a lot of this energy will be reflected and sent back to space. Green house gases will reflect back some of this energy trying to leave earth. So instead of having a roughly equal amount of energy enter the system (from the sun, from us doing stuff, etc) that leaves out in space, we have an increasing amount of energy on earth. This, as a consequence, increases temperature.

Implications

Now, what are the maybe not so obvious implications of this?

Waste heat, from supplied energy or inefficient work is a constant headache in engineering. If we cannot remove enough heat, we will actively heat up objects until they are destroyed. Thats why good cooling systems are important in cars, computers, etc.

Whats next?

Now this was not so bad. In the future we will cover phase changes, equilibriums, entropy, the heat death of the universe and briefly touch upon engines. So thats most likely two more parts after this. After that @wanda-seldon will take over again.

I plan on doing one main part per week, but if something is asked that warrants a small topic I might do smaller ones inbetween.

Feedback

Something unclear? Got questions? Got feedback? Or requests of topics to cover? Leave a comment.

What's this?

This post contains all entries of the "a layperson's introduction to" series. I will keep this thread up to date and sorted. This means this post is an excellent opportunity to try out the bookmarking feature!

Physics

Quantum Physics

Basics of quantum physics

Material Science

Classical physics

Thermodynamics

Computer Science

Artificial Intelligence

I am a bit lazy, and I also seem to like the default 3 day filter on the activity feed... but, sometimes a person less lazy than I responds to a topic of mine which is older that 3 days. These are usually good responses. These folks clearly played with the time filter. Other users are missing out on these responses.

I agree that a 3 day filter may be the ideal filter at the normal activity level of Tildes at large, at this point. But Tildes is still really fluctuating in activity, as may other sites based on the codebase. This may be an even bigger issue in specific groups.

Would there be any workable and beneficial way to make the default time filter a function of recent activity? This may apply to the main feed, and each group feed. This would help in site/group times of low activity, and might scale to the much higher activity of the future.. does this make any sense at all?

Would it be better to make the default time filter a function of activity, instead of a arbitrary setting which an admin selected?

Edit: the list box label might default to a dynamic “recent”, or similar, and then still have the other options of “last 1 hour, last 12 hours,” etc...

EDIT: With the help of @ducks the post now has illustrations to clear up the experimental set-up.

Introduction

I want to give an introduction on several physics topics at a level understandable to laypeople (high school level physics background). Making physics accessible to laypeople is a much discussed topic at universities. It can be very hard to translate the professional terms into a language understandable by people outside the field. So I will take this opportunity to challenge myself to (hopefully) create an understandable introduction to interesting topics in modern physics. To this end, I will take liberties in explaining things, and not always go for full scientific accuracy, while hopefully still getting the core concepts across. If a more in-depth explanation is wanted, please ask in the comments and I will do my best to answer.

Previous topics

Spintronics
Quantum Oscillations
Quantisation and spin, part 1

Today's topic

Today's topic will be a continuation of the topics discussed in my last post. So if you haven't, please read part 1 first (see link above). We will be sending particles through two Stern-Gerlach apparatuses and then we'll put the particles through three of them. We will discuss our observations and draw some very interesting conclusions from it on the quantum nature of our universe. Not bad for a single experiment that can be performed easily!

Rotating the Stern-Gerlach apparatus

We will start simple and rotate the set-up of the last post 90 degrees so that the magnets face left and right instead of up and down. Now let's think for a moment what we expect would happen if we sent silver atoms through this setup. Logically, there should not be in any difference in outcome if we rotate our experiment 90 degrees (neglecting gravity, whose strength is very low compared to the strength of the magnets). This is a core concept of physics, there are no "privileged" frames of reference in which the results would be more correct. So it is reasonable to assume that the atoms would split left and right in the same way they split up and down last time. This is indeed what happens when we perform the experiment. Great!

Two Stern-Gerlach apparatuses

Let's continue our discussion by chaining two Stern-Gerlach apparatuses together. The first apparatus will be oriented up-down, the second one left-right. We will be sending silver atoms with unknown spin through the first apparatus. As we learned in the previous post, this will cause them to separate into spin-up and spin-down states. Now we take only the spin-up silver atoms and send them into the second apparatus, which is rotated 90 degrees compared to the first one. Let's think for a moment what we expect would happen. It would be reasonable to assume that spin-left and spin-right would both appear 50% of the time, even if the silver atoms all have spin-up too. We don't really have a reason to assume a particle cannot both have spin up and spin right, or spin up and spin left. And indeed, once again we find a 50% split between spin-left and spin-right at the end of our second apparatus. Illustration here.

Three Stern-Gerlach apparatuses and a massive violation of common sense

So it would seem silver atoms have spin up or down as a property, and spin left or spin right as another property. Makes sense to me. To be sure, we take all the silver atoms that went up at the end of the first apparatus and right at the end of the second apparatus and send them through a third apparatus which is oriented up-down (so the same way as the first). Surely, all these atoms are spin-up so they will all come out up top again. We test this and find... a 50-50 split between up and down. Wait, what?

Remember that in the previous post I briefly mentioned that if you take two apparatuses who are both up-down oriented and send only the spin-up atoms through the second one they all come out up top again. So why now suddenly do they decide to split 50-50 again? We have to conclude that being forced to choose spin-left or spin-right causes the atoms to forget if they were spin-up or spin-down.

This result forces us to fundamentally reconsider how we describe the universe. We have to introduce the concepts of superposition and wave function collapse to be able to explain these results.

Superpositions, collapse and the meaning of observing in quantum physics

The way physicists make sense of the kind of behaviour described above is by saying the particles start out in a superposition; before the first experiment they are 50% in the up-state and 50% in the down-state at the same time. We can write this as 50%[spin up]+50%[spin down], and we call this a wave function. Once we send the particles through the first Stern-Gerlach apparatus each one will be forced to choose to exhibit spin-up or spin-down behaviour. At this point they are said to undergo (wave function) collapse; they are now in either the 100%[spin up] or 100%[spin down] state. This is the meaning of observing in quantum mechanics, once we interact with a property of an atom (or any particle, or even a cat) that is in a superposition this superposition is forced to collapse into a single definite state, in this case the property spin is in a superposition and upon observing is forced to collapse to spin up or spin down.

However, once we send our particles through the second apparatus, they are forced to collapse into 100%[spin left] or 100%[spin right]. As we saw above, this somehow also makes them go back into the 50%[spin up]+50%[spin down] state. The particles cannot collapse into both a definite [spin up] or [spin down] state and a definite [spin left] or [spin right] state. Knowing one precludes knowing the other. An illustration can be seen here.

This has far reaching consequences for how knowable our universe it. Even if we can perfectly describe the universe and everything in it, we still cannot know such simple things as whether a silver atom will go left or right in a magnetic field - if we know it would go up or down. It's not just that we aren't good enough at measuring, it's fundamentally unknowable. Our universe is inherently random.

Conclusion

In these two posts we have broken the laws of classical physics and were forced to create a whole new theory to describe how our universe works. We found out our universe is unknowable and inherently random. Even if we could know all the information of the state our universe is in right now, we still would not be able to track perfectly how our universe would evolve, due to the inherent chance that is baked into it.

Next time

Well that was quite mind-blowing. Next time I might discuss fermions vs bosons, two types of particles that classify all (normal) matter in the universe and that have wildly different properties. But first @ducks will take over this series for a few posts and talk about classical physics and engineering.

Feedback

As always, please feel free to ask for clarification and give me feedback on which parts of the post could me made clearer. Feel free to discuss the implications for humanity to exist in a universe that is inherently random and unknowable.

Addendum

Observant readers might argue that in this particular case we could just as well have described spin as a simple property that will align itself to the magnets. However, we find the same type of behaviour happens with angles other than 90 degrees. Say the second apparatus is at an angle phi to the first apparatus, then the chance of the particles deflecting one way is cos^2(phi/2)[up] and sin^2(phi/2)[down]. So even if there's only a 1 degree difference between the two apparatuses, there's still a chance that the spin will come out 89 degrees rotated rather than 1 degree rotated.

feels like we should probably have one of these in here since it doesn't appear we've had one of these as a community in ~creative in awhile--if ever.

i've spent the better portion of my day today working on a census form for the kryfona kingdom, which is one of the many countries in my fairly large worldbuilding effort. the first page actually came out really well, i think, so that was time well spent. i've considered making a post about some of its more intricate detail since i think some people on here might enjoy that, but for now i've opted to just make this general thread since i dunno how well it'd go as a discussion topic. maybe if y'all think it's worthy of one? idk.

anyways, what creative things have you been working on recently?

I have not been paying close attention lately, but I swear that it was possible to highlight some text in my notifications and/or topic’s comment thread views, so that I can paste it into a quote in my reply.

Anyone else have an iOS device that they can try this on?

Hey Tildes, I got a job directly supervising a small team of 4 software developers. I'm very excited at the prospect and would like to put my best foot forward. To that end, I would like to have a discussion around a few topics. Feel free to expand the scope if you believe the conversation would be beneficial. I'm sure I won't be the last person to be in this position. I've done research, read, and watched videos regarding several of these questions; however, since Tilde prioritizes high-quality discussion, I thought it would be a fun opportunity to chat with others about these topics.

• As a member of a software development team, what are things that your supervisor has done that has had the greatest (a) positive and (b) negative impact?
• Supervisors, when you joined your new team, what was your methodology for reviewing the team, projects, and processes? What was the scenarios behind your review and the outcome? What would you do differently?

Sometimes one may knowingly add a comment that should be tagged as one of those, and sometimes I see people say (me included) things like "BTW this should be tagged <as such>." Maybe allowing a user to tag their own comment proactively with these three tags would be useful?

Edit: My main focus is the offtopic tag because I think that it's not necessarily bad or low-quality. Partially off-topic content can be very interesting and useful. Maybe I'm misunderstanding the use of that tag, was it intended for completely off-topic stuff in the first place?

Edit 2: I've opened an issue on Tildes Gitlab for this.

Introduction

I want to give an introduction on several physics topics at a level understandable to laypeople (high school level physics background). Making physics accessible to laypeople is a much discussed topic at universities. It can be very hard to translate the professional terms into a language understandable by people outside the field. So I will take this opportunity to challenge myself to (hopefully) create an understandable introduction to interesting topics in modern physics. To this end, I will take liberties in explaining things, and not always go for full scientific accuracy, while hopefully still getting the core concepts across. If a more in-depth explanation is wanted, please ask in the comments and I will do my best to answer.

Previous topics

Spintronics
Quantum Oscillations

Today's topic

Today's topic will be quantisation, explained through the results of the Stern-Gerlach experiment which was first performed in 1922. This topic treats a much more fundamental concept of quantum physics than my previous topics.

What is the Stern-Gerlach experiment?

In 1922 physicists Stern and Gerlach set up an experiment where they shot silver atoms through a magnetic field, the results of this experiment gave conclusive support for the concept of quantisation. I will now first explain the experiment and then, using the results, explain what quantisation is. If you would rather watch a video on the experiment, wikipedia provided one here, it can be watched without sound. Note that I will dive a bit deeper into the results than this video does.

The experiment consists of two magnets, put on top of each other with a gap in the middle. The top magnet has its north pole facing the gap, the bottom magnet has its south pole facing the gap. See this illustration. Now we can shoot things through the gap. What do we expect would happen? Let's first shoot through simple bar magnets. Depending on how its poles are oriented, it will either bend downwards, upwards or not at all. If the bar magnet's north pole is facing the top magnet, it will be pushed downwards (because then north is facing north). If the bar magnet's south pole is facing the top magnet, it will instead be pushed upwards. If the bar magnet's poles are at a 90 degree angle to the two magnets it will fly straight through, without bending. Lastly, if the bar magnet's poles are at any other angle, say 45 degrees, it will still bend but less so. If we send through a lot of magnets, all with a random orientation, and measure how much they got deflected at the other side of the set-up we expect to see a line, see 4 in the illustration.

Now we'll send through atoms, Stern and Gerlach chose silver atoms because they were easy to generate back in 1922 and because they have so-called spin, which we will get back to shortly. We send these silver atoms through in the same way we sent through the bar magnets; lots of them and all of them with a random orientation. Now what will happen? As it turns out all the atoms will either end up being deflected all the way up or all the way down, with nothing in between. 50% will be bent upwards, 50% downwards. So silver atoms seem to respond as if they were bar magnets that either bend maximally up or maximally down. In the illustration this is labeled 5.

If we were to take only the silver atoms that bent upwards and sent them through the experiment again, all of them would bend upwards again. They seem to remember if they previously went up or down rather than just deciding on the spot each time if they go up or down. What model can we think of that would explain this behaviour? The silver atoms must have some property that will make them decide to bend up or down. Let's call this property spin, and say that if the silver atoms chose to bend up they have spin up, if they chose to bend down they have spin down. It seems that these are the only two values spin can have, because we see them bend either maximally up or maximally down. So we can say the spin is quantised; it has two discrete values, up or down, and nothing in between.

Conclusion

We have found a property of atoms (and indeed other particles like electrons have spin too) that is quantised. This goes against classical physics where properties are continuous. This shows one of the ways in which physics at the smallest scales is fundamentally different from the physics of everyday life.

Next time

Next time we will investigate what happens when we rotate the angle of the magnets used in the experiment. This will lead us to discover other fundamental aspects of physics and nature, quantum superpositions and the inherent randomness of nature.

EDIT: part 2 is now up here.

Feedback

As discussed in the last post, I am trying something different for this post. Talking about more fundamental quantum physics that was discovered 100 years ago rather than modern physics. Did you like it? Let me know in the comments!

Yesterday @talklittle posted the topic Halloween game sales are live. What are your Horror/Halloween-themed recommendations?. There have been some good recommendations and whatnot. If you like horror games and weren't aware of the ongoing sales, go check out the comments for some recommendations.

Being the meta-killjoy that I am, I started this sidebar about the top comment. tl;dr: I don't think this type of content engenders Tildes's discussion forward community.

Fell free to read the whole thread of comments for some civil discussion on the matter, but I do want to open this up to all of Tildes: should this type of comment be policed on Tildes?

Also: do you think this type of comment is good? Do you agree with me that it's retroactive to Tildes's goals? Am I just a big killjoy? Given that the comment I'm calling into question is the top comment of that topic, I'm probably David in this arena but I want to hear it from everyone else.

I've been thinking about my experience on Tildes with news and articles. It's mostly been seeing high quality content and discussion that I'm happy with. However for the sake of this, I want to discuss avoiding something negative.

Lately I've noticed news and articles with headlines that I feel are biasing in nature and potentially inflammatory.

I would guess that we're all pretty familiar with this method in general. At some point when a forum/aggregate becomes large enough it provides an profitable opportunity for third parties to distribute content. Or an individual is pursuing their fulfillment of a personal ideal.

I have a few suggestion to handle the issues productively.

News sources that put a higher priority on traffic versus their reputation tend to do so consistently. It would be valuable for users to be required to tag the parent domain when posting external links to allow users to discern sources case by case using tags.

Blocking something a news source versus <inciting-phrase> has the benefit of allowing higher quality sources mentioning the same topic to have an impact on the user. That's potentially very valuable in encouraging informed perspective.

Linking news and articles for commercial or personally motivated reasons is posted on subs that have a marginal relation. E.g. Posting a story on Mike Pence denouncing all white men working in agriculture in an agriculture sub. The connection can certainly be made but I don't think that's a good way of organizing that information. I think it would be more productive to post that in a news or news/political thread. Having the ability to choose when we see and engage with that type of content is important. It benefits the individual and encourages healthy and engaged communities.

Blocking users ( I wasn't sure if this existed ) Alternatively, a system for linked content reputation per user. But I think that's a bad solution overall.
I meant filtering users content and comments as a preference for users. I'm not talking about site wide.

I'm curious if other Tilde users agree with my issues or suggestions.

We have the "Exemplary" label for comments, which identifies comments as particularly good, and even boosts their ranking within threads.

Now that we've had this for a while, I keep finding myself want to do the same for topics. I'll read an article and want to give it an extra boost because it's better than average.

I'm ready for an equivalent to the "Exemplary" label for topics.

At the moment, there are two types of topics that can be posted on Tildes:

• Link topics, which consist of a title and a URL.

• Text topics, which consist of a title and text.

These two types of topic are supported by having three input fields for new topics: Title; Link; Text.

I propose that we combine these two topic types into just one topic type. The submission page for all topics will include only two fields: a title field and a general all-purpose text box. The submitter will type a title for their post, and then put anything else into the general all-purpose box.

If the submitter is posting off-site content, they can put the link to that content in the all-purpose box. If they want to provide a summary of the off-site content, they can write the summary in the all-purpose box, with the link.

If the submitter is posting their own original content (no link), they can type their text into the all-purpose box.

The single all-purpose box includes everything that is currently split between the Link and Text boxes. When the topic is posted, everything entered in that all-purpose box is displayed in the main body of the post.

At the moment, summaries of off-site content are usually being posted as comments under the main topic, as a result of a change made a few months ago. These comments merely clutter up the thread. If these summaries were in the post itself, that clutter would be reduced.

One topic type, one streamlined submission page, one place for all topic content.

Introduction and motivation

In an effort to get more content on Tildes, I want to try and give an introduction on several 'hot topics' in condensed matter physics at a level understandable to laypeople (high school level physics background). Making physics accessible to laypeople is a much discussed topic at universities. It can be very hard to translate the professional terms into a language understandable by people outside the field. So I will take this opportunity to challenge myself to (hopefully) create an understandable introduction to interesting topics in modern physics. To this end, I will take liberties in explaining things, and not always go for full scientific accuracy, while hopefully still getting the core concepts across. If a more in-depth explanation is wanted, please ask in the comments and I will do my best to answer.

Previous topics

Spintronics

Why has it been 100 days since the last post?

I had a different topic planned as a second post, however it turned out I had to explain a lot more concepts that I anticipated so that it would no longer fit this format. Then I got busy. Now I finally found a topic I think I can do justice in this format.

Today's topic

Today's topic will be quantum oscillations.

What are quantum oscillations?

Quantum oscillations are periodic fluctuations in some materials' properties when it is exposed to a strong magnet. As the name suggests, this effect arises from quantum physics. Nevertheless, I think it's relatively easy to give a feel on how it works. In the rest of this post I will focus on one kind of quantum oscillation, the oscillation of a material's resistance (with the very fancy name Shubnikov-de Haas oscillations), because electrical resistance is a concept most people are familiar with. However, there are many other material properties that fluctuate similarly.

What do quantum oscillations look like?

Let's start from the basics, electrical resistance. Electrical resistance tells you how hard it is for an electrical current to flow through a material. Related to this is conductance, which instead tells you how easy it is for a current to flow through a material (so it is the inverse of the resistance). Now, something funny happens to some metals' conductance when you expose them to a strong magnet.

Let's think for a moment on what we expect would happen. Would the conductivity be affected by the magnet? Perhaps a stronger magnet would increase the conductivity, or reduce it. What we most certainly wouldn't expect to happen is for the conductivity to go up and down as we increase the strength of the magnet we aimed at the material. Yet, this is exactly what happens. In this picture we see the conductivity (expressed on the vertical axis) plotted against the magnetic field (expressed on the horizontal axis). The conductivity is going up and down like crazy!

Why is this happening?

One of quantum physics core principle is quantisation (who'd have thought). And as it turns out, this quantisation is at the core of this behaviour. For the purpose of this post, quantisation can be thought of as energies at which the electrons are allowed to have.

Normally, when electrons are in a metal, there are no real restrictions on what energy they are allowed to have. Some electrons will not have a lot of energy and won't move, other electrons will have a lot of energy and be able to move freely around the metal.

However, when metals are put in a strong magnetic field the energies of the low energy electrons are allowed to have changes drastically. The electrons are only allowed to be at certain energies, with a wide gaps in between these energies. Crucially, the exact values of these energies change with the strength of the magnet.

This means that at some magnet strengths, the allowed low-energy energies will nicely line up with the energies the free-flowing electrons have. This means some of those electrons will interfere with the free flowing electrons, making it harder for them to flow freely*. This interference in electron flow means less conductance! Then, when we change the magnetic field so that the energies are no longer aligned, the free flowing electrons no longer get caught and will be able to move freely, so that the conductivity goes up again. This pattern becomes more pronounced as the magnetic field strength increases.

What is it good for?

These oscillations were first noticed in bismuth by Shubnikov and de Haas in the year 1930. It was direct evidence for the quantum mechanics underlying nature. These days quantum oscillations are a popular method to extract information on a metals, alloys and semimetals' properties. These techniques have been used to, for example, further our understanding of high temperature superconductivity.

Sources

D Shoenberg - Magnetic Oscillations in Metals (1984)

*more technically: the probability of scattering is proportional to the number of states into which the electron can be scattered, which is given by the number of available states near the energy surface of the material.

Preface

In a previous topic, I'd covered the subject of a few small lessons regarding code quality. Especially important was the impact on technical debt, which can bog down developer productivity, and the need to pay down on that debt. Today I would like to touch on a practical example that I'd encountered in a production environment.

Background

Before we can discuss the refactor itself, it's important to be on the same page regarding the technologies being used. In my case, I work with PHP utilizing a proprietary back-end framework and MongoDB as our database.

PHP is a server-side scripting language. Like many scripting languages, it's loosely typed. This has some benefits and drawbacks.

MongoDB is a document-oriented database. By default it's schema-less, allowing you to make any changes at will without an update to schema. This can blend pretty well with the loose typing of PHP. Each document is represented using a JSON-like structure and is stored in something called a "collection". For those of you accustomed to using relational database, a "collection" is analogous to a table, each document is a row, and each field in the document is a column. A typical query in the MongoDB shell would look something like this:

db.users.findOne({
    username: "Emerald_Knight"
});

The framework itself has some framework-specific objects that are held in global references. This makes them easily accessible, but naturally littering your code with a bunch of globals is both error-prone and an eyesore.

Unexpected Spaghetti

In my code base are a number of different objects that are designed to handle basic CRUD-like operations on their associated database entries. Some of these objects hold references to other objects, so naturally there is some data validation that occurs to ensure that the references are both valid and authorized. Pretty typical stuff.

What I noticed, however, is that the collection names for these database entries were littered throughout my code. This isn't necessarily a bad thing, except there were some use cases that came to mind: what if it turned out that my naming for one or more of these collections wasn't ideal? What if I wanted to change a collection name for the sake of easier management on the database end? What if I have a tendency to forget the name of a database collection and constantly have to look it up? What if I make a typo of all things? On top of that, the framework's database object was stored in a global variable.

These seemingly minor sources of technical debt end up adding up over time and could cause some serious problems in the worst case. I've had breaking bugs make their way passed QA in the past, after all.

Exchanging Spaghetti for Some Light Lasagna

The problem could be characterized simply: there were scoping problems and too many references to what were essentially magic strings. The solution, then, was to move the database object reference from global to local scope within the application code and to eliminate the problem of magic strings. Additionally, it's a good idea to avoid polluting the namespace with an over-reliance on constants, and using those constants for database calls can also become unsightly and difficult to follow as those constants could end up being generally disconnected from the objects they're associated with.

There turned out to be a nice, object-oriented, very PHP-like solution to this problem: a so-called "magic method" named "__call". This method is invoked whenever an "inaccessible" method is called on the object. Using this method, a database command executed on a non-database object could pass the command to the database object itself. If this logic were placed within an abstract class, the collection could then be specified simply as a configuration option in the inheriting class.

This is what such a solution could look like:

<?php

abstract class MyBaseObject {

    protected $db = null;
    protected $collection_name = null;

    public function __construct() {
        global $db;
        
        $this->db = $db;
    }

    public function __call($method_name, $args) {
        if(method_exists($this->db, $method_name)) {
            return $this->executeDatabaseCommand($method_name, $args);
        }

        throw new Exception(__CLASS__ . ': Method "' . $method_name . '" does not exist.');
    }

    public function executeDatabaseCommand($command, $args) {
        $collection = $this->collection_name;
        $db_collection = $this->db->$collection;

        return call_user_func_array(array($db_collection, $command), $args);
    }
}

class UserManager extends MyBaseObject {
    protected $collection_name = 'users';

    public function __construct() {
        parent::__construct();
    }
}

$user_manager = new UserManager();
$my_user = $user_manager->findOne(array('username'=>'Emerald_Knight'));

?>

This solution utilizes a single parent object which transforms a global database object reference into a local one, eliminating the scope issue. The collection name is specified as a class property of the inheriting object and only used in a single place in the parent object, eliminating the magic string and namespace polluting issues. Any time you perform queries on users, you do so by using the UserManager class, which guarantees that you will always know that your queries are being performed on the objects that you intend. And finally, if the collection name for an object class ever needs to be updated, it's a simple matter of modifying the single instance of the class property $collection_name, rather than tracking down some disconnected constant.

Limitations

This, of course, doesn't solve all of the existing problems. After all, executing the database queries for one object directly from another is still pretty bad practice, violating the principle of separation of concerns. Instead, those queries should generally be encapsulated within object methods and the objects themselves given primary responsibility in handling associated data. It's also incredibly easy to inadvertently override a database method, e.g. defining a findOne() method on UserManager, so there's still some mindfulness required on the part of the programmer.

Still, given the previous alternative, this is a pretty major improvement, especially for an initial refactor.

Final Thoughts

As always, technical debt is both necessary and inevitable. After all, in exchange for not taking the excess time and considering structuring my code this way in the beginning, I had greater initial velocity to get the project off of the ground. What's important is continually reviewing your code as you're building on top of it so that you can identify bottlenecks as they begin to strain your efficiency, and getting those bottlenecks out of the way.

In other words, even though technical debt is often necessary and is certainly inevitable, it's important to pay down on some of that debt once it starts getting expensive!

• ABC: Same-sex penguin couple at Sea Life Sydney Aquarium become parents

• SBS: Sydney's very own gay penguins have welcomed their first baby

• Sydney Morning Herald: Love birds: Sydney's same-sex penguin couple welcomes baby chick

• Daily Telegraph: Same-sex penguins Sphen and Magic foster baby chick

This is a follow-up to this previous topic posted here a couple of weeks ago: Same-Sex Penguin Couple Fosters An Egg In Sydney

Some of you may have heard that Google+ will be shutting down in August, 2019. Though much criticised (including by me), the site offered some compelling dynamics, and I've reflected a lot on those.

I'm involved in the effort to find new homes for Plussers and Communities, which has become something of an excuse to explore and redefine what "online" and "social" media are ("PlexodusWiki").

Part of this involves some frankly embarrassing attempts to try to define what social media is, and what its properties are (both topics reflected heavily in the recent-changes section of the wiki above).

Tildes is ... among the potential target sites (there are a few Plussers, some of whom I really appreciated knowing and hearing from there), here, though the site dynamics make discovering and following them hard. This site is evolving its own culture and dynamics, parts of which I'm becoming aware of.

I've been online for well over 30 years, and discovered my first online communities via Unix talk, email, FTP, and Usenet, as well as (no kidding) a computerised university library catalogue system. Unsurprisingly: if you provide a way, especially for bright and precocious minds to interact with one another, they will. I've watched several evolutions of Internet and Web, now increasing App-based platforms. There are differences, but also similarities and patterns emerging. Lessons from previous eras of television, radio, telephony, telegraphy, print, writing, oral traditions, and more, can be applied.

I've got far more questions than answers and thought I'd put a few out here:

• What does online or social media mean to you? Is it all user-generated content platforms? Web only? Apps? Email or chat? Wikis? GitHub, GitLab, and StackExchange?

• Is social networking as exemplified by Facebook or Twitter net good or bad? Why? If bad, how might you fix it? Or is it time to simply retreat?

• What properties or characteristics would you use to specify, define, or distinguish social or online media?

• What emergent properties -- site dynamics, if you will -- are positive or negative? What are those based on?

• What are the positive and negative aspects of scale?

• What risks would you consider in self-hosting either your own or a group's online presence?

• What is/was the best online community experience you've had? What characterised it? How did it form? How did it fail (if it did)?

• What elements would comprise your ideal online experience?

• What would you nuke from orbit, after takeoff, just to be sure?

• Are you or your group seeking new options or platforms? What process / considerations do you have?

I could keep going and will regret not adding other questions, but this is a good start. Feel free to suggest other dimensions, though some focus on what I've prompted with would be appreciated.

This is a sort of continuation of a previous topic I posted. This weekend I will be wiping and reinstalling my computer and encrypting all of my drives in the process. In doing so, I will have to choose secure passphrases. As such, I have some questions about how best to do this:

1. I have three drives that will be encrypted. Is it okay to have the same passphrase for all of them, or should I have different ones for each?

2. In looking up info on this topic, I came across this article which recommends something called a Diceware wordlist. The premise is that you roll dice which match to a list of 7000+ words. You then string six or more of these words together which become your passphrase. Is this a sound way to generate one?

3. Rather than using the Diceware wordlist, couldn't I roll my own password of the same type using six "random" words of my choosing? I feel like that would be easier to remember, but am I weakening security in doing so?

4. If the Diceware method is to be trusted, does that mean I do not need to pepper my passphrase with digits, mixed case, and special characters? Or should I add these anyway?

5. I'm also considering changing over passwords on a lot of my online accounts based on this method. I like the idea of using a single passphrase as a root, but how do you modify it so that it is different for each account? Would I do something like [dicewarewords]tildes, [dicewarewords]spotify, [dicewarewords]ubuntuforums, etc.? I feel like it would be too on-the-nose, and it would make it easy to guess my other passwords if one were compromised. On the other hand, I don't like the idea of using a password manager to generate a random string for me. I'd like to still be able to login even without my password manager.

6. For people that have used something like this, how do you then deal with password restrictions on sites? I know that no matter how great I set things up I'm still going to have to make exceptions for sites that that either require or forbid numbers, mixed case, or special characters, have character limits, or make me change my password frequently.

I have posted a few topics on tildes so far, and someone edited the tags on it. I looked at that person's profile but couldn't see any indication that they were a mod. I am aware of the coming 'trysf' system, but I think it hasn't been implemented yet. My question: how does one edit tags? Is this a certain account age required?

Having seen the topic about lost games, I recalled my experiences with trying to find a game from my childhood that I just couldn't dig up no matter how hard I tried. A few years ago someone managed to help me figure out what that game was, but I'd given up all hope of ever finding out before then. For the record, that game happened to be Legend of Legaia, a pretty fantastic RPG, in my opinion.

I'm pretty sure I'm not the only one to experience this kind of frustration, so I thought it could be nice to try to help each other rediscover old games that would otherwise be lost to us only because we couldn't divine the title from our memories and couldn't google the answer forth.

Link to the announcement -- Do read it, it's a short email.

I'm posting this here because I think it generated some good discussion over on HN, which unfortunately got .. flamewary. (Is that irony?)

I've myself created and moderated several large-ish communities over the years and my views on codes of conduct are mixed. I'm always trying to make an envi. They themselves can range quite a bit, with 'opponents' to CoCs often picking the worst offenders in terms of overreach as examples. To me, it's always felt like the software engineering world is rediscovering... forum guidelines?

This is a politically-charged topic now, where almost all discussion on CoCs being centered on black&white "if you oppose them then you're basically alt-right". This makes the topic of CoCs an interesting example, IMO, of how we ("we" as in "the internet") give loudspeakers to the most extremist voices, silencing nuance.

Reminds me of a post by @deadaluspark here discussing the effect that this increasing divide has on us.

Well anyway, I brought up the announcement in question because Stallman (someone who tends to usually be pretty radical and have clear cut opinions) positively surprised me. This seemed to resonate with people, especially the parts about replacing sticks with carrots. It felt pretty good to see someone ignore (probably by virtue of being shielded from it) the politically-charged side of the topic and simply focus on trying to improve communication. Sounds cliché, but I feel that this approach has gotten very rare the past 4-5 years, and its higher frequency on Tildes is part of why I've been enjoying reading the comments here so much.

I was recently reading a reddit post about a 15 year old speaking out about climate change. In the comments there was a depressing amount of people dismissing her thoughts, opinions, and arguments simply because of age (and possibly because of the topic, but most stated reasons were age). In my own opinion I think young people should have just as much consideration given to their arguments as older people, if not more. They are the ones that are going to live in the world the older generations are leaving behind, and they want to make it a good place to live in. Admittedly, I am biased towards giving her a stage. I myself am still pretty young, especially here on Tildes. Maybe I only view it this way because of that. It's hard to tell, which is why I want some other viewpoints. Do you think younger people should be given consideration, despite their age?

I'm a big fan of "discussion threads" over on reddit, if you're unfamiliar they're essentially threads a subreddit will pin every day or week where you can post things that don't deserve a full post or are slightly frivolous or off topic. To give an example, a while back I wanted to make a post with some thoughts on Coleridge's "Ode to Dejection", but after typing it out didn't think there was enough to warrant making a thread over it. I didn't feel like doing a more extensive analysis or trying to artificially broaden the scope (ie, doing something like "what's a poem you like?" as an excuse for sharing my thoughts), so I just trashed it.

I like discussion threads because they help save "small" content like that as well as helping to build a sense of community and are just generally quite comfy.

However, I recognize that there can be some downsides:

• May end up being "low quality" in the minds of certain users. I know this is somewhat contentious, since the site culture is still being established, I personally don't want Tildes to be that serious but I know some people do.

• Normal group activity could drop if people opt to use the discussion thread instead of making a post. This is doubly bad because the site is small.

I wished to set aside some threads to read on my Kindle. I use the Kindle Chrome extension for that, but on Tildes it only captures the main topic, not the comments. I tried saving the page locally but the Kindle app still didn't work. My only option on Chrome seems to be printing to PDF, but that's a subpar solution. I was able to convert the offline page to mobi using Calibre, though, but this is not very practical and the result was not that good.

maybe I should have written conversion friendly, because printing to paper/PDF is working fine

I'm interested in patterns and culture. I think it's a fascinating topic from many perspectives. Mathematically there are many tools for pattern analysis and formation, but at the same time philosophically our minds try to make things fit into patterns generally (maybe because it requires more energy to remember a whole thing than a set of rules that describe the thing). A mathematical example of cases where order arises from pure disorder (or maximum entropy) would be Ramsey theory.

I'd like to discuss the cultural influence on our pattern analysis/synthesis, but also explore a bit what is a pattern, whether everything is a pattern or nothing is a pattern, whether patterns are interesting in themselves or not, etc.

I was wondering if anyone has recommendations for readings in this area, or if anyone has an opinion on it. I know of many works regarding a single pattern (for example the different theories of linguistics, the different theories of music, the different theories of cooking... you get the idea) but I've never seen a meta-perspective on why are we so interested on patterns and whether our approach actually makes sense.

Thanks!

Prompted by the comment just left by @Adams on the first post, I thought I'd make a topic for the next episode!

So what did people think? For those of you who weren't particularly into the first episode, did this one work better for you? (If not, no hard feelings, I'm just curious why/why not~)

I'll stick my thoughts in a comment again.

Designing, coding, moderating, promoting and doing all the business admin on Tildes must be fairly thankless. But without all this effort we'd not be able to enjoy discussions with each other & share all this interesting content. I don't feel that much appreciation is really shown on here (except maybe miss-voting on all Deimos' comments).

But it is a little awkward, spurious thanks all over the place would just be noise. I thought I'd make a topic especially for people to say thanks in. I'm really enjoying Tildes content and discussion. Plus I'm a big believer in the goals of Tildes as laid out in the docs.

So I'd like to say a big thank you to Deimos and other useful contributors! Thanks for making the site we have to use today and dreaming of the hopefully better possible site we'll see in the future.

I'm also hoping to start a discussion on what enthusiastic Tildes users can do to most usefully help make Tildes good now and better in the future.

A list of stuff we can do:

• Obviously posting lots of good content and interesting discussions. Voting honestly and using comment labels judiciously.

• You can donate and currently we can see Tildes Patreon is at $375 a month. Deimos posted some more figures recently.

• We all regularly get invite codes and bringing in more people who can get excited (and maybe also help) is obviously good.

• The issue tracker and bug reports are all public so you can make suggestions, vote or comment on existing ones and perhaps more usefully see if you can work out how to reproduce reported bugs.

• As of a bit over two months ago Tildes is open source. This means you can track down bugs from the issue tracker or even contribute code for new features.

RFC:

So are other people liking Tildes? What is it you like? Are you excited enough to want to help out?

Also is there anything useful users can do I've missed? In these already mentioned areas what's actually most useful to do? Are some things of negative use? Could Deimos change his process to make more use of community help? Is there anything Deimos could delegate that people would be willing to volunteer on? Gitlab Walmart greeter would be cool but is anyone willing to do it?

They could be user submitted and the admins/mods could choose a poll to display every week.

I think it would fit well in the sidebar with the percentage of overall votes being shown once your vote is cast.

I think small things like that help build a sense of community and helps keep people engaged. The topic of the polls could be as lighthearted or serious as the mods decide, though i'd personally like a mix of both.

Thanks to whoever fixed the tags, i'm still not entirely sure how to tag topics appropriately.

Tags are tricky-- should they be plural? How granular should they be? How generic should they be?

I think something that could help solve this problem is autocomplete suggestions while typing out tags. As I've been looking at posts and retagging, I've realized a lot are placed in single-post tags. Sure, this is bound to happen, especially on a new site, but autocompleting tags as you type them should help encourage users to tag with the correct one, like academic studies vs academic study.

The main con I can see with such a system would be overtagging. Since tags should actually apply to the topic at hand directly, seeing these tag suggestions could encourage people to use less applicable tags rather than think of them themselves.

Thoughts?

I was watching my favorite weekly space show on YouTube, TMRO, and I learned about Astro Live Experiences (ALE.) They will soon launch two test satellites which will be able to provide a burst of 30-40 man made shooting stars at a prearranged time and place, for a fee.

Japanese company ALE is the first "space entertainment" company of which I am aware. The only event in the same ballpark was New Zealand based RocketLab's Humanity Star which caused a large amount of controversy. ALE's initial technology will allow a 200km radius of earth to see their multi-color shooting star show. According to the interview on TMRO, in the long term, they are planning to allow image rendering and even artificial aurora.

This type of business seems inevitable as we advance into space. I can see some benefits and some downsides to this technology. What do you all think of this?

^{Maybe this topic belongs in ~misc}