Unfortunately I haven't had time to sit down and keep up with the weekly episodes this week, as I caught a bad case of addiction to a new video game.

How do?

Since we're currently lacking native spoiler tags, I'd ask all of you to follow this scheme:
Post a top level comment with the title and episode number of the anime you want to talk about like this
**JoJo's Bizarre Adventure: Vento Aureo - Episode 1**
Then reply to those top level comments with your thoughts. This way people who haven't seen something yet or plan on binge watching once all the episodes are out can simply collapase the top level comment to not get spoiled ^.^

What do?

Simply post, discuss or joke about any currently airing anime you want. For Anime you've been watching that aren't currently airing refer to Cleb's weekly thread.

When do?

But what if the anime I want to talk about hasn't aired yet?

No problem, just post a comment here once the episode has aired, these threads aren't meant to last one single day.

Archive

Archives of these threads can be found at the unofficial wiki

Assume you have all the wealth necessary to do whatever. Money can buy all the things and grant you access to do your favourite things, but time is something is valuable and priceless. What would be worth your value to you because you simply enjoy it?

My friend and I are considering finishing a prototype of a Reddit app. We've already agreed to the following features on first release (if we keep going).

• Similar urls to current Reddit website (so you can change the URL to reddit.com and see the same page)
• voting, commenting, posting selftexts and links
• Directly uploading image posts may come later if it looks complicated
• Masstagger integrated.
• Dark theme (other options in later releases)
• Primary use case: desktop and mobile web.
• Performance first. Reddit's 1 minute load time on default mobile, missing/broken features on i.reddit.com/.compact, and a few tiny complaints on the desktop site are the primary reasons we are considering writing this app. Native is not in our collective skillsets or radar, so we're going to go the extra mile to make sure the app respects both your time and your battery where possible. We did do some research and found that Reddit has actually been negligent in this regard on mobile web, meanwhile we have years of experience in the subject.
• Mailbox (send/receive messages, orange icon on new message/comment reply/thread reply).
• No infinite scroll
• View source JSON of comments/posts.

What are some features/ideas that members of this community would really like in a Reddit app?

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!

I've tried using search (both by keyword and by tag) but I couldn't find anything about this. What's Tildes opinion about posting old news that haven't been discussed yet? I'm not talking about your regular news post from a newspaper that is already too late to be discussed about, I'm talking about things such as software releases or old blog posts that have never been posted but would be interesting to discuss about. How would one tag them? Where should we post them if allowed?

Edit: I'm sorry but I won't be here for discussing this tomorrow or during the weekend. I'm not staying at home, but I hope I can come back to some good responses next week.

Welcome to week 22! Here we've got this week's user-voted record: Survival by Bob Marley & The Wailers!

Taken from @koan's pitch:

Does Bob Marley have gold and platinum records? Definitely. Survival is not one of them, but in my opinion it is by far his greatest album -- hands down, no competition. Everybody has an opinion about Bob Marley, whether you've actually given him a shot or not. Reggae can be polarizing. Some love it, some think it's corny. But Survival is not corny. It's Marley's greatest roots reggae record.

While some Bob Marley songs might make you want to relax on a beach and sip cold cocktails, the songs on Survival make you want to get up and do something about shit. When I was absolutely stewing in dissatisfaction with my corporate job, listening to Survival on my commute in the morning inspired me to change my life. Be careful, because listening to it too much might turn you into a revolutionary.

If you're unfamiliar with reggae in general, or you think it's silly, give this record a chance. It might change your perspective about a very deep and varied genre of music.

Here's the place to discuss your thoughts on the record, your history with it or the artist, and basically talk about whatever you want to that goes along with Survival. Remember that this is intended to be a slow moving thing, feel free to take your time and comment at any point in the week!

If you'd like to stream or buy the album, it can be found on most platforms here.