This Physics Breakthrough Looks Impossible

0:00 Okay, so here are two different ways of describing reality.

0:04 Imagine a silly movie where you have two cops.

0:07 One, you have the slow cop that works by the book.

0:12 This guy is rigidly organized, loves structure.

0:15 Scientists call this the Finite Element Method.

0:18 He likes to take something solid, slice it up into tiny little blocks,

0:23 and compute how these blocks interact with each other.

0:27 This guy is great at a simple case, one perpetrator, like simulating solids.

0:32 But taking care of a chaotic riot?

0:35 Like splashing water, or crumbling sand?

0:38 This guy just can’t keep up.

0:41 Not a chance.

0:42 He says, yes, we can take care of that, but first, a little paperwork.

0:47 By the time the paperwork is done, it’s too late.

0:52 So what do we do?

0:54 Of course, we do what every silly cop movie does: we hire another cop.

0:59 This cop is fast, and used to be a criminal.

1:04 Now this guy is crazy, okay?

1:06 He is the loose cannon.

1:09 Doesn’t care about paperwork,

1:10 probably even shoots a nice little hole through it, okay?

1:15 He is fast, amazing at taking care of a crazy riot like this, fluids and sand?

1:22 No problems.

1:23 We call this the Material Point Method.

1:26 However, if you ask him to hold everything together nicely, he falls apart.

1:32 See how it completely ignored the interaction between the two?

1:36 Fine geometry+ chaos equals pandemonium.

1:39 Can’t be done by this guy.

1:42 Now we have a huge problem.

1:45 These guys would be the perfect duo.

1:49 Yes!

1:49 Wait, no.

1:50 No, because these guys hate each other.

1:54 So in video games, when things try to interact, we get clipping,

1:58 where solid objects just ghost through each other

2:02 or explode into infinity because the math breaks.

2:06 Now this research work finally gives us a way

2:08 to get these two guys to work together.

2:11 Remember this?

2:12 Well, hold on to your papers Fellow Scholars,

2:15 because it suddenly looks like this!

2:19 Finally, chaotic interactions and keeping geometry intact at the same time!

2:26 Woo-hoo!

2:27 Now, let’s take a bunch of sand with about 5.5 million particles,

2:32 and wrap it up nicely with a piece of cloth.

2:36 This is the perfect gift….for someone you hate with a passion.

2:41 Okay, so what happens?

2:42 The fast cop takes care of the sand particles,

2:46 and the slow cop defines the cloth.

2:49 And, no cheating, no crazy clipping, just two cops working together in harmony.

2:56 Absolutely loving this.

2:58 Now this is crazy, because normally, these two officers really hate each other.

3:03 Zero chance of working together.

3:06 And yet, this work somehow pulls off the impossible.

3:10 How?

3:11 I’ll tell you in a moment.

3:13 And I’ll note that no AI is required here, only human brilliance.

3:17 That would be great because we can

3:20 even drop a snowball onto these elastic mushrooms,

3:24 have a wheel imprint itself into granular soil.

3:29 Absolutely incredible.

3:30 Just think about every video game and animation movie doing this!

3:36 Wow.

3:36 And once again, two worlds collide.

3:39 They simulate a rolling pin flattening dough.

3:42 It deforms permanently, while the pin stays rigid.

3:46 And I absolutely love this massive landslide.

3:49 Normally, you can simulate the sand particles,

3:53 but not the interaction with something elastic.

3:56 Now check this out!

3:58 Oh my.

3:59 The trees are waving,

4:02 and the interaction leaves these little streaks in the sand at the same time.

4:08 It is an absolute miracle that we can do this.

4:12 Okay, this used to be impossible.

4:14 But not anymore- so how on Earth did they do that?

4:18 Dear Fellow Scholars, this is Two Minute Papers with Dr.

4:22 Károly Zsolnai-Fehér.

4:22 Well, the key idea in this paper is

4:26 creating a shared bulletin board for the two cops.

4:29 This allows two fundamentally opposed simulation methods

4:33 to exchange forces without ever directly touching.

4:37 And the result is crash-proof physics.

4:41 How?

4:41 Think of it as a way of communicating between the two cops.

4:46 The by the book guy, the Finite Element Method is slow and methodical.

4:51 He needs time to fill out his reports.

4:54 The fast cop, the material point method is fast and reactive.

4:59 He makes split-second decisions.

5:01 If they tried to talk at the same time, it would be chaos.

5:06 So the researchers created a schedule.

5:09 The slow officer takes a big, slow step.

5:12 Now, here is the key.

5:14 Now inside that one big step, the fast cop takes many tiny, fast steps.

5:20 They occasionally update each other only when necessary.

5:24 Here, they effectively agree to disagree on time, but agree on force.

5:31 Genius.

5:31 We can actually look at how this works.

5:34 Check out this beautiful simulation view.

5:37 This is like a thermal camera showing which officer is sweating.

5:42 The blue areas are calm- zero interaction, low computational cost.

5:47 Blue means peace.

5:48 Blue means the two cops don’t have to argue, and we can save a ton of compute.

5:55 Why?

5:56 Because everyone is doing what they are good at.

5:59 But wait, look at the red area!

6:02 What’s going on here?

6:04 An argument, that’s what’s happening!

6:06 So what happens then?

6:07 Well, here, the slow cop says to the fast cop, hey, wait a second.

6:13 Let’s stop and sync up.

6:15 You give away a little speed here and get more stability.

6:20 Okay, now let’s put this all together and analyze this scene.

6:25 Look at this.

6:26 We have highly viscous honey, controlled by the fast cop,

6:30 pouring onto a piece of cloth.

6:33 This is the slow officer.

6:35 Normally, this is a crime scene waiting to happen.

6:39 Why?

6:39 Because the cloth is only maybe half a millimeter thick.

6:44 But wait, we know what happens with that!

6:49 Oh yes, clipping.

6:50 Usually, the honey particles would just ignore the thin

6:54 barrier and ghost right through it like it doesn’t exist.

6:58 But here, the slow cop holds the line!

7:02 There is communication!

7:03 Look, the cloth actually buckles under the weight of the honey.

7:08 The honey folds over itself, and starts doing my favorite: coiling.

7:13 Oh my, loving it.

7:15 And it kinda sticks to the fabric.

7:19 An absolutely insane simulation.

7:22 To make these two officers respect a fraction

7:25 of a millimeter boundary without exploding is a mathematical miracle.

7:30 Not only that, but this is also excellent life advice.

7:34 We have two cops here that are good at different things.

7:38 Neither of them can do everything.

7:40 And you should also stop trying to be good at everything.

7:45 Partner with someone who is strong where you are weak.

7:48 This is also what I do with my wife Felícia.

7:52 She is strong exactly at areas where I am weak.

7:55 That’s why we’ve been able to run this channel for more than a 1,000 videos now.

8:00 Let’s be honest, I am the loose cannon here,

8:03 and I need someone that makes sure the Papers

8:06 lab does not work like a mental asylum.

8:10 And it works beautifully.

8:11 She gave me this nice white jacket and my lunch slides in under the door.

8:17 What’s not to like?

8:19 Now, all this means we can finally

8:23 simulate movie-quality destruction in one unified system.

8:26 What a time to be alive!

8:28 Now, on a more serious note,

8:31 this is an absolutely beautifully written research paper.

8:34 I see absolutely nobody talking about this.

8:37 I kind of understand,

8:38 I mean it is a really advanced work in physics simulations.

8:42 But I am worried that if I don’t talk about it here, no one else talks about it.

8:48 And this thing is a treasure.

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9:00 to run simulations and anything else on.

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