Archive: September, 2020

Ten years ago I gave a talk at An Event Apart all about interaction design. It was called Paranormal Interactivity. You can watch the video, listen to the audio or read the transcript if you like.

I think it holds up pretty well. There’s one interaction pattern in particular that I think has stood the test of time. In the talk, I introduce this pattern as something you can see in action on Huffduffer:

I was thinking about how to tell the user that something’s happened without distracting them from their task, and I thought beyond the web. I thought about places that provide feedback mechanisms on screens, and I thought of video games.

So we all know Super Mario, right? And if you think about when you’re collecting coins in Super Mario, it doesn’t stop the game and pop up an alert dialogue and say, “You have just collected ten points, OK, Cancel”, right? It just does it. It does it in the background, but it does provide you with a feedback mechanism.

The feedback you get in Super Mario is about the number of points you’ve just gained. When you collect an item that gives you more points, the number of points you’ve gained appears where the item was …and then drifts upwards as it disappears. It’s unobtrusive enough that it won’t distract you from the gameplay you’re concentrating on but it gives you the reassurance that, yes, you have just gained points.

I think this a neat little feedback mechanism that we can borrow for subtle Ajax interactions on the web. These are actions that don’t change much of the content. The user needs to be able to potentially do lots of these actions on a single page without waiting for feedback every time.

On Huffduffer, for example, you might be looking at a listing of people that you can choose to follow or unfollow. The mechanism for doing that is a button per person. You might potentially be clicking lots of those buttons in quick succession. You want to know that each action has taken effect but you don’t want to be interrupted from your following/unfollowing spree.

You get some feedback in any case: the button changes. Maybe the text updates from “follow” to “unfollow” accompanied by a change in colour (this is what you’ll see on Twitter). The Super Mario style feedback is in addition to that, rather than instead of.

I’ve made a Codepen so you can see a reduced test case of the Super Mario feedback in action.

See the Pen Unobtrusive feedback by Jeremy Keith (@adactio) on CodePen.

Here’s the code available as a gist.

It’s a function that takes two arguments: the element that the feedback originates from (pass in a DOM node reference for this), and the contents of the feedback (this can be a string of text or it can be HTML …or SVG). When you call the function with those two arguments, this is what happens:

1. The JavaScript generates a span element and puts the feedback contents inside it.
2. Then it positions that element right over the element that the feedback originates from.
3. Then there’s a CSS transform. The feedback gets a translateY applied so it drifts upward. At the same time it gets its opacity reduced from 1 to 0 so it’s fading away.
4. Finally there’s a transitionend event that fires when the animation is over. Once that event fires, the generated span is destroyed.

When I first used this pattern on Huffduffer, I’m pretty sure I was using jQuery. A few years later I rewrote it in vanilla JavaScript. That was four years ago so I wonder if the code could be improved. Have a go if you fancy it.

Still, even if the code could benefit from an update, I’m pleased that the underlying pattern still holds true. I used it recently on The Session and it’s working a treat for a new Ajax interaction there (bookmarking or unbookbarking an item).

If you end up using this unobtrusive feedback pattern anyway, please let me know—I’d love to see more examples of it in the wild.

I was helping a client with a bit of a performance audit this week. I really, really enjoy this work. It’s such a nice opportunity to get my hands in the soil of a website, so to speak, and suggest changes that will have a measurable effect on the user’s experience.

Not only is web performance a user experience issue, it may well be the user experience issue. Page speed has a proven demonstrable direct effect on user experience (and revenue and customer satisfaction and whatever other metrics you’re using).

It struck me that there’s a continuum of performance challenges. On one end of the continuum, you’ve got technical issues. These can be solved with technical solutions. On the other end of the continuum, you’ve got human issues. These can be solved with discussions, agreement, empathy, and conversations (often dreaded or awkward).

I think that, as developers, we tend to gravitate towards the technical issues. That’s our safe space. But I suspect that bigger gains can be reaped by tackling the uncomfortable human issues.

This week, for example, I uncovered three performance issues. One was definitely technical. One was definitely human. One was halfway between.

The technical issue was with web fonts. It’s a lot of fun to dive into this aspect of web performance because quite often there’s some low-hanging fruit: a relatively simple technical fix that will boost the performance (or perceived performance) of a website. That might be through resource hints (using link rel=“preload” in the HTML) or adjusting the font loading (using font-display in the CSS) or even nerdier stuff like subsetting.

In this case, the issue was with the file format of the font itself. By switching to woff2, there were significant file size savings. And the great thing is that @font-face rules allow you to specify multiple file formats so you can still support older browsers that can’t handle woff2. A win all ‘round!

The performance issue that was right in the middle of the technical/human continuum was with images. At first glance it looked like a similar issue to the fonts. Some images were being served in the wrong formats. When I say “wrong”, I guess I mean inappropriate. A photographic image, for example, is probably going to best served as a JPG rather than a PNG.

But unlike the fonts, the images weren’t in the direct control of the developers. These images were coming from a Content Management System. And while there’s a certain amount of processing you can do on the server, a human still makes the decision about what file format they’re uploading.

I’ve seen this happen at Clearleft. We launched an event site with lean performant code, but then someone uploaded an image that’s megabytes in size. The solution in that case wasn’t technical. We realised there was a knowledge gap around image file formats—which, let’s face it, is kind of a techy topic that most normal people shouldn’t be expected to know.

But it was extremely gratifying to see that people were genuinely interested in knowing a bit more about choosing the right format for the right image. I was able to provide a few rules of thumb and point to free software for converting images. It empowered those people to feel more confident using the Content Management System.

It was a similar situation with the client site I was looking at this week. Nobody is uploading oversized images in order to deliberately make the site slower. They probably don’t realise the difference that image formats can make. By having a discussion and giving them some pointers, they’ll have more knowledge and the site will be faster. Another win all ‘round!

At the other end of continuum was an issue that wasn’t technical. From a technical point of view, there was just one teeny weeny little script. But that little script is Google Tag Manager which then calls many, many other scripts that are not so teeny weeny. Third party scripts …the bane of web performance!

In retrospect, it seems unbelievable that third-party JavaScript is even possible. I mean, putting arbitrary code—that can then inject even more arbitrary code—onto your website? That seems like a security nightmare!

Remember when I did a countdown of the top four web performance challenges? At the number one spot is other people’s JavaScript.

Now one technical solution would be to remove the Google Tag Manager script. But that’s probably not very practical—you’ll probably just piss off some other department. That said, if you can’t find out which department was responsible for adding the Google Tag Manager script in the first place, it might we well be an option to remove it and then wait and see who complains. If no one notices it’s gone, job done!

More realistically, there’s someone who’s added that Google Tag Manager script for their own valid reasons. You’ll need to talk to them and understand their needs.

Again, as with images uploaded in a Content Management System, they may not be aware of the performance problems caused by third-party scripts. You could try throwing numbers at them, but I think you get better results by telling the story of performance.

Use tools like Request Map Generator to help them visualise the impact that third-party scripts are having. Talk to them. More importantly, listen to them. Find out why those scripts are being requested. What are the outcomes they’re working towards? Can you offer an alternative way of providing the data they need?

I think many of us developers are intimidated or apprehensive about approaching people to have those conversations. But it’s necessary. And in its own way, it can be as rewarding as tinkering with code. If the end result is a faster website, then the work is definitely worth doing—whether it’s technical work or people work.

Personally, I just really enjoy working on anything that will end up improving a website’s performance, and by extension, the user experience. If you fancy working with me on your site, you should get in touch with Clearleft.

Safari is the only browser on iOS devices.

I don’t mean it’s the only browser that ships with iOS devices. I mean it’s the only browser that can be installed on iOS devices.

You can install something called Chrome. You can install something called Firefox. Those aren’t different web browsers. Under the hood they’re using Safari’s rendering engine. They have to. The app store doesn’t allow other browsers to be listed. The apps called Chrome and Firefox are little more than skinned versions of Safari.

If you’re a web developer, there are two possible reactions to hearing this. One is “Duh! Everyone knows that!”. The other is “What‽ I never knew that!”

If you fall into the first category, I’m guessing you’ve been a web developer for a while. The fact that Safari is the only browser on iOS devices is something you’ve known for years, and something you assume everyone else knows. It’s common knowledge, right?

But if you’re relatively new to web development—heck, if you’ve been doing web development for half a decade—you might fall into the second category. After all, why would anyone tell you that Safari is the only browser on iOS? It’s common knowledge, right?

So that’s the situation. Safari is the only browser that can run on iOS. The obvious follow-on question is: why?

Apple at this point will respond with something about safety and security, which are certainly important priorities. So let me rephrase the question: why on iOS?

Why can I install Chrome or Firefox or Edge on my Macbook running macOS? If there are safety or security reasons for preventing me from installing those browsers on my iOS device, why don’t those same concerns apply to my macOS device?

At one time, the mobile operating system—iOS—was quite different to the desktop operating system—OS X. Over time the gap has narrowed. At this point, the operating systems are converging. That makes sense. An iPhone, an iPad, and a Macbook aren’t all that different apart from the form factor. It makes sense that computing devices from the same company would share an underlying operating system.

As this convergence continues, the browser question is going to have to be decided in one direction or the other. As it is, Apple’s laptops and desktops strongly encourage you to install software from their app store, though it is still possible to install software by other means. Perhaps they’ll decide that their laptops and desktops should only be able to install software from their app store—a decision they could justify with safety and security concerns.

Imagine that situation. You buy a computer. It comes with one web browser pre-installed. You can’t install a different web browser on your computer.

You wouldn’t stand for it! I mean, Microsoft got fined for anti-competitive behaviour when they pre-bundled their web browser with Windows back in the 90s. You could still install other browsers, but just the act of pre-bundling was seen as an abuse of power. Imagine if Windows never allowed you to install Netscape Navigator?

And yet that’s exactly the situation in 2020.

You buy a computing device from Apple. It might be a Macbook. It might be an iPad. It might be an iPhone. But you can only install your choice of web browser on one of those devices. For now.

It is contradictory. It is hypocritical. It is indefensible.

Cennydd asked for recommendations on Twitter a little while back:

Can anyone recommend an outlining app for macOS? I’m falling out with OmniOutliner. Not Notion, please.

This was my response:

The only outlining tool that makes sense for my brain is https://kinopio.club/

It’s more like a virtual crazy wall than a virtual Dewey decimal system.

I’ve written before about how I prepare a conference talk. The first step involves a sheet of A3 paper:

I used to do this mind-mapping step by opening a text file and dumping my thoughts into it. I told myself that they were in no particular order, but because a text file reads left to right and top to bottom, they are in an order, whether I intended it or not. By using a big sheet of paper, I can genuinely get things down in a disconnected way (and later, I can literally start drawing connections).

Kinopio is like a digital version of that A3 sheet of paper. It doesn’t force any kind of hierarchy on your raw ingredients. You can clump things together, join them up, break them apart, or just dump everything down in one go. That very much suits my approach to preparing something like a talk (or a book). The act of organising all the parts into a single narrative timeline is an important challenge, but it’s one that I like to defer to later. The first task is braindumping.

When I was preparing my talk for An Event Apart Online, I used Kinopio.club to get stuff out of my head. Here’s the initial brain dump. Here are the final slides. You can kind of see the general gist of the slidedeck in the initial brain dump, but I really like that I didn’t have to put anything into a sequential outline.

In some ways, Kinopio is like an anti-outlining tool. It’s scrappy and messy—which is exactly why it works so well for the early part of the process. If I use a tool that feels too high-fidelity too early on, I get a kind of impedence mismatch between the state of the project and the polish of the artifact.

I like that Kinopio feels quite personal. Unlike Google Docs or other more polished tools, the documents you make with this aren’t really for sharing. Still, I thought I’d share my scribblings anyway.

After writing about a declarative Web Share API here yesterday I thought I’d better share the idea (see what I did there?).

I opened an issue on the Github repo for the spec.

(I hope that’s the right place for this proposal. I know that in the past ideas were kicked around on the Discourse site for Web platform Incubator Community Group but I can’t stand Discourse. It literally requires JavaScript to render anything to the screen even though the entire content is text. If it turns out that that is the place I should’ve posted, I guess I’ll hold my nose and do it using the most over-engineered reinvention of the browser I’ve ever seen. But I believe that the plan is for WICG to migrate proposals to Github anyway.)

I also realised that, as the JavaScript Web Share API already exists, I can use it to polyfill my suggestion for:

<button type="share">

The polyfill also demonstrates how feature detection could work. Here’s the code.

This polyfill takes an Inception approach to feature detection. There are three nested levels:

1. This browser supports button type="share". Great! Don’t do anything. Otherwise proceed to level two.
2. This browser supports the JavaScript Web Share API. Use that API to share the current page URL and title. Otherwise proceed to level three.
3. Use a mailto: link to prefill an email with the page title as the subject and the URL in the body. Ya basic!

The idea is that, as long as you include the 20 lines of polyfill code, you could start using button type="share" in your pages today.

I’ve made a test page on Codepen. I’m just using plain text in the button but you could use a nice image or SVG or combination. You can use the Codepen test page to observe two of the three possible behaviours browsers could exhibit:

1. A browser supports button type="share". Currently that’s none because I literally made this shit up yesterday.
2. A browser supports the JavaScript Web Share API. This is Safari on Mac, Edge on Windows, Safari on iOS, and Chrome, Samsung Internet, and Firefox on Android.
3. A browser supports neither button type="share" nor the existing JavaScript Web Share API. This is Firefox and Chrome on desktop (and Edge if you’re on a Mac).

See the Pen Polyfill for button type=”share" by Jeremy Keith (@adactio) on CodePen.

The polyfill doesn’t support Internet Explorer 11 or lower because it uses the DOM closest() method. Feel free to fork and rewrite if you need to support old IE.

I’ve written about the Web Share API before. It’s a handy little bit of JavaScript that—if supported—brings up a system-level way of sharing a page. Seeing as it probably won’t be long before we won’t be able to see full URLs in browsers anymore, it’s going to fall on us as site owners to provide this kind of fundamental access.

Right now the Web Share API exists entirely in JavaScript. There are quite a few browser APIs like that, and it always feels like a bit of a shame to me. Ideally there should be a JavaScript API and a declarative option, even if the declarative option isn’t as powerful.

Take form validation. To cover the most common use cases, you probably only need to use declarative markup like input type="email" or the required attribute. But if your use case gets a bit more complicated, you can reach for the Constraint Validation API in JavaScript.

I like that pattern. I wish it were an option for JavaScript-only APIs. Take the Geolocation API, for example. Right now it’s only available through JavaScript. But what if there were an input type="geolocation" ? It wouldn’t cover all use cases, but it wouldn’t have to. For the simple case of getting someone’s location (like getting someone’s email or telephone number), it would do. For anything more complex than that, that’s what the JavaScript API is for.

I was reminded of this recently when Ada Rose Cannon tweeted:

It really feels like there should be a semantic version of the share API, like a mailto: link

I think she’s absolutely right. The Web Share API has one primary use case: let the user share the current page. If that use case could be met in a declarative way, then it would have a lower barrier to entry. And for anyone who needs to do something more complicated, that’s what the JavaScript API is for.

But Pete LePage asked:

How would you feature detect for it?

Good question. With the JavaScript API you can do feature detection—if the API isn’t supported you can either bail or provide your own implementation.

There a few different ways of extending HTML that allow you to provide a fallback for non-supporting browsers.

You could mint a new element with a content model that says “Browsers, if you do support this element, ignore everything inside the opening and closing tags.” That’s the way that the canvas element works. It’s the same for audio and video—they ignore everything inside them that isn’t a source element. So developers can provide a fallback within the opening and closing tags.

But forging a new element would be overkill for something like the Web Share API (or Geolocation). There are more subtle ways of extending HTML that I’ve already alluded to.

Making a new element is a lot of work. Making a new attribute could also be a lot of work. But making a new attribute value might hit the sweet spot. That’s why I suggested something like input type="geolocation" for the declarative version of the Geolocation API. There’s prior art here; this is how we got input types for email, url, tel, color, date, etc. The key piece of behaviour is that non-supporting browsers will treat any value they don’t understand as “text”.

I don’t think there should be input type="share". The action of sharing isn’t an input. But I do think we could find an existing HTML element with an attribute that currently accepts a list of possible values. Adding one more value to that list feels like an inexpensive move.

Here’s what I suggested:

<button type=”share” value=”title,text”>

For non-supporting browsers, it’s a regular button and needs polyfilling, no different to the situation with the JavaScript API. But if supported, no JS needed?

The type attribute of the button element currently accepts three possible values: “submit”, “reset”, or “button”. If you give it any other value, it will behave as though you gave it a type of “submit” or “button” (depending on whether it’s in a form or not) …just like an unknown type value on an input element will behave like “text”.

If a browser supports button type="share”, then when the user clicks on it, the browser can go “Right, I’m handing over to the operating system now.”

There’s still the question of how to pass data to the operating system on what gets shared. Currently the JavaScript API allows you to share any combination of URL, text, and description.

Initially I was thinking that the value attribute could be used to store this data in some kind of key/value pairing, but the more I think about it, the more I think that this aspect should remain the exclusive domain of the JavaScript API. The declarative version could grab the current URL and the value of the page’s title element and pass those along to the operating system. If you need anything more complex than that, use the JavaScript API.

So what I’m proposing is:

<button type="share">

That’s it.

But how would you test for browser support? The same way as you can currently test for supported input types. Make use of the fact that an element’s attribute value and an element’s property value (which 99% of the time are the same), will be different if the attribute value isn’t supported:

var testButton = document.createElement("button");
testButton.setAttribute("type","share");
if (testButton.type != "share") {
// polyfill
}

So that’s my modest proposal. Extend the list of possible values for the type attribute on the button element to include “share” (or something like that). In supporting browsers, it triggers a very bare-bones handover to the OS (the current URL and the current page title). In non-supporting browsers, it behaves like a button currently behaves.

Jessica and I went to cinema yesterday.

Normally this wouldn’t be a big deal, but in our current circumstances, it was something of a momentous decision that involved a lot of risk assessment and weighing of the odds. We’ve been out and about a few times, but always to outdoor locations: the beach, a park, or a pub’s beer garden. For the first time, we were evaluating whether or not to enter an indoor environment, which given what we now know about the transmission of COVID-19, is certainly riskier than being outdoors.

But this was a cinema, so in theory, nobody should be talking (or singing or shouting), and everyone would be wearing masks and keeping their distance. Time was also on our side. We were considering a Monday afternoon showing—definitely not primetime. Looking at the website for the (wonderful) Duke of York’s cinema, we could see which seats were already taken. Less than an hour before the start time for the film, there were just a handful of seats occupied. A cinema that can seat a triple-digit number of people was going to be seating a single digit number of viewers.

We got tickets for the front row. Personally, I love sitting in the front row, especially in the Duke of York’s where there’s still plenty of room between the front row and the screen. But I know that it’s generally considered an undesirable spot by most people. Sure enough, the closest people to us were many rows back. Everyone was wearing masks and we kept them on for the duration of the film.

The film was Tenet). We weren’t about to enter an enclosed space for just any ol’ film. It would have to be pretty special—a new Star Wars film, or Denis Villeneuve’s Dune …or a new Christopher Nolan film. We knew it would look good on the big screen. We also knew it was likely to be spoiled for us if we didn’t see it soon enough.

At this point I am sounding the spoiler horn. If you have not seen Tenet yet, abandon ship at this point.

…

I really enjoyed this film. I understand the criticism that has been levelled at it—too cold, too clinical, too confusing—but I still enjoyed it immensely. I do think you need to be able to enjoy feeling confused if this is going to be a pleasurable experience. The payoff is that there’s an equally enjoyable feeling when things start slotting into place.

The closest film in Christopher Nolan’s back catalogue to Tenet is Inception in terms of twistiness and what it asks of the audience. But in some ways, Tenet is like an inverted version of Inception. In Inception, the ideas and the plot are genuinely complex, but Nolan does a great job in making them understandable—quite a feat! In Tenet, the central conceit and even the overall plot is, in hindsight, relatively straightforward. But Nolan has made it seem more twisty and convuluted than it really is. The ten minute battle at the end, for example, is filled with hard-to-follow twists and turns, but in actuality, it literally doesn’t matter.

The pitch for the mood of this film is that it’s in the spy genre, in the same way that Inception is in the heist genre. Though there’s an argument to be made that Tenet is more of a heist movie than Inception. But in terms of tone, yeah, it’s going for James Bond.

Even at the very end of the credits, when the title of the film rolled into view, it reminded me of the Bond films that would tease “The end of (this film). But James Bond will return in (next film).” Wouldn’t it have been wonderful if the very end of Tenet’s credits finished with “The end of Tenet. But the protagonist will return in …Tenet.”

The pleasure I got from Tenet was not the same kind of pleasure I get from watching a Bond film, which is a simpler, more basic kind of enjoyment. The pleasure I got from Tenet was more like the kind of enjoyment I get from reading smart sci-fi, the kind that posits a “what if?” scenario and isn’t afraid to push your mind in all kinds of uncomfortable directions to contemplate the ramifications.

Like I said, the central conceit—objects or people travelling backwards through time (from our perspective)—isn’t actually all that complex, but the fun comes from all the compounding knock-on effects that build on that one premise.

In the film, and in interviews about the film, everyone is at pains to point out that this isn’t time travel. But that’s not true. In fact, I would argue that Tenet is one of the few examples of genuine time travel. What I mean is that most so-called time-travel stories are actually more like time teleportation. People jump from one place in time to another instaneously. There are only a few examples I can think of where people genuinely travel.

The grandaddy of all time travel stories, The Time Machine by H.G. Wells, is one example. There are vivid descriptions of the world outside the machine playing out in fast-forward. But even here, there’s an implication that from outside the machine, the world cannot perceive the time machine (which would, from that perspective, look slowed down to the point of seeming completely still).

The most internally-consistent time-travel story is Primer. I suspect that the Venn diagram of people who didn’t like Tenet and people who wouldn’t like Primer is a circle. Again, it’s a film where the enjoyment comes from feeling confused, but where your attention will be rewarded and your intelligence won’t be insulted.

In Primer, the protagonists literally travel in time. If you want to go five hours into the past, you have to spend five hours in the box (the time machine).

In Tenet, the time machine is a turnstile. If you want to travel five hours into the past, you need only enter the turnstile for a moment, but then you have to spend the next five hours travelling backwards (which, from your perspective, looks like being in a world where cause and effect are reversed). After five hours, you go in and out of a turnstile again, and voila!—you’ve time travelled five hours into the past.

Crucially, if you decide to travel five hours into the past, then you have always done so. And in the five hours prior to your decision, a version of you (apparently moving backwards) would be visible to the world. There is never a version of events where you aren’t travelling backwards in time. There is no “first loop”.

That brings us to the fundamental split in categories of time travel (or time jump) stories: many worlds vs. single timeline.

In a many-worlds story, the past can be changed. Well, technically, you spawn a different universe in which events unfold differently, but from your perspective, the effect would be as though you had altered the past.

The best example of the many-worlds category in recent years is William Gibson’s The Peripheral. It genuinely reinvents the genre of time travel. First of all, no thing travels through time. In The Peripheral only information can time travel. But given telepresence technology, that’s enough. The Peripheral is time travel for the remote worker (once again, William Gibson proves to be eerily prescient). But the moment that any information travels backwards in time, the timeline splits into a new “stub”. So the many-worlds nature of its reality is front and centre. But that doesn’t stop the characters engaging in classic time travel behaviour—using knowledge of the future to exert control over the past.

Time travel stories are always played with a stacked deck of information. The future has power over the past because of the asymmetric nature of information distribution—there’s more information in the future than in the past. Whether it’s through sports results, the stock market or technological expertise, the future can exploit the past.

Information is at the heart of the power games in Tenet too, but there’s a twist. The repeated mantra here is “ignorance is ammunition.” That flies in the face of most time travel stories where knowledge—information from the future—is vital to winning the game.

It turns out that information from the future is vital to winning the game in Tenet too, but the reason why ignorance is ammunition comes down to the fact that Tenet is not a many-worlds story. It is very much a single timeline.

Having a single timeline makes for time travel stories that are like Greek tragedies. You can try travelling into the past to change the present but in doing so you will instead cause the very thing you set out to prevent.

The meat’n’bones of a single timeline time travel story—and this is at the heart of Tenet—is the question of free will.

The most succint (and disturbing) single-timeline time-travel story that I’ve read is by Ted Chiang in his recent book Exhalation. It’s called What’s Expected Of Us. It was originally published as a single page in Nature magazine. In that single page is a distillation of the metaphysical crisis that even a limited amount of time travel would unleash in a single-timeline world…

There’s a box, the Predictor. It’s very basic, like Claude Shannon’s Ultimate Machine. It has a button and a light. The button activates the light. But this machine, like an inverted object in Tenet, is moving through time differently to us. In this case, it’s very specific and localised. The machine is just a few seconds in the future relative to us. Cause and effect seem to be reversed. With a normal machine, you press the button and then the light flashes. But with the predictor, the light flashes and then you press the button. You can try to fool it but you won’t succeed. If the light flashes, you will press the button no matter how much you tell yourself that you won’t (likewise if you try to press the button before the light flashes, you won’t succeed). That’s it. In one succinct experiment with time, it is demonstrated that free will doesn’t exist.

Tenet has a similarly simple object to explain inversion. It’s a bullet. In an exposition scene we’re shown how it travels backwards in time. The protagonist holds his hand above the bullet, expecting it to jump into his hand as has just been demonstrated to him. He is told “you have to drop it.” He makes the decision to “drop” the bullet …and the bullet flies up into his hand.

This is a brilliant bit of sleight of hand (if you’ll excuse the choice of words) on Nolan’s part. It seems to imply that free will really matters. Only by deciding to “drop” the bullet does the bullet then fly upward. But here’s the thing: the protagonist had no choice but to decide to drop the bullet. We know that he had no choice because the bullet flew up into his hand. The bullet was always going to fly up into his hand. There is no timeline where the bullet doesn’t fly up into his hand, which means there is no timeline where the protagonist doesn’t decide to “drop” the bullet. The decision is real, but it is inevitable.

The lesson in this scene is the exact opposite of what it appears. It appears to show that agency and decision-making matter. The opposite is true. Free will cannot, in any meaningful sense, exist in this world.

This means that there was never really any threat. People from the future cannot change the past (or wipe it out) because it would’ve happened already. At one point, the protagonist voices this conjecture. “Doesn’t the fact that we’re here now mean that they don’t succeed?” Neil deflects the question, not because of uncertainty (we realise later) but because of certainty. It’s absolutely true that the people in the future can’t succeed because they haven’t succeeded. But the protagonist—at this point in the story—isn’t ready to truly internalise this. He needs to still believe that he is acting with free will. As that Ted Chiang story puts it:

It’s essential that you behave as if your decisions matter, even though you know that they don’t.

That’s true for the audience watching the film. If we were to understand too early that everything will work out fine, then there would be no tension in the film.

As ever with Nolan’s films, they are themselves metaphors for films. The first time you watch Tenet, ignorance is your ammuntion. You believe there is a threat. By the end of the film you have more information. Now if you re-watch the film, you will experience it differently, armed with your prior knowledge. But the film itself hasn’t changed. It’s the same linear flow of sequential scenes being projected. Everything plays out exactly the same. It’s you who have been changed. The first time you watch the film, you are like the protagonist at the start of the movie. The second time you watch it, you are like the protagonist at the end of the movie. You see the bigger picture. You understand the inevitability.

The character of Neil has had more time to come to terms with a universe without free will. What the protagonist begins to understand at the end of the film is what Neil has known for a while. He has seen this film. He knows how it ends. It ends with his death. He knows that it must end that way. At the end of the film we see him go to meet his death. Does he make the decision to do this? Yes …but he was always going to make the decision to do this. Just as the protagonist was always going to decide to “drop” the bullet, Neil was always going to decide to go to his death. It looks like a choice. But Neil understands at this point that the choice is pre-ordained. He will go to his death because he has gone to his death.

At the end, the protagonist—and the audience—understands. Everything played out exactly as it had to. The people in the future were hoping that reality allowed for many worlds, where the past could be changed. Luckily for us, reality turns out to be a single timeline. But the price we pay is that we come to understand, truly understand, that we have no free will. This is the kind of knowledge we wish we didn’t have. Ignorance was our ammunition and by the end of the film, it is spent.

Nolan has one other piece of misdirection up his sleeve. He implies that the central question at the heart of this time-travel story is the grandfather paradox. Our descendents in the future are literally trying to kill their grandparents (us). But if they succeed, then they can never come into existence.

But that’s not the paradox that plays out in Tenet. The central paradox is the bootstrap paradox, named for the Heinlein short story, By His Bootstraps. Information in this film is transmitted forwards and backwards through time, without ever being created. Take the phrase “Tenet”. In subjective time, the protagonist first hears of this phrase—and this organisation—when he is at the start of his journey. But the people who tell him this received the information via a subjectively older version of the protagonist who has travelled to the past. The protagonist starts the Tenet organistion (and phrase) in the future because the organisation (and phrase) existed in the past. So where did the phrase come from?

This paradox—the bootstrap paradox—remains after the grandfather paradox has been dealt with. The grandfather paradox was a distraction. The bootstrap paradox can’t be resolved, no matter how many times you watch the same film.

So Tenet has three instances of misdirection in its narrative:

• Inversion isn’t time travel (it absolutely is).
• Decisions matter (they don’t; there is no free will).
• The grandfather paradox is the central question (it’s not; the bootstrap paradox is the central question).

I’m looking forward to seeing Tenet again. Though it can never be the same as that first time. Ignorance can never again be my ammunition.

I’m very glad that Jessica and I decided to go to the cinema to see Tenet. But who am I kidding? Did we ever really have a choice?