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# Physics

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## Oculus&#39;s Luckey and Mitchell: What&#39;s the End Game for the Rift? (Q&amp;A, Part Two)

Original author:
Eric Johnson

Oculus VR’s Palmer Luckey, left, and Nate Mitchell, right. At center, AllThingsD’s Lauren Goode tries out the Oculus Rift at CES 2013.

This is the second part of our two-part Q&A with Palmer Luckey and Nate Mitchell, the co-founders of virtual-reality gaming company Oculus VR. In Part One, Luckey and Mitchell discussed controlling expectations, what they want from developers, and the challenges of trying to make games do something radically different.

AllThingsD: What do you guys think about Google Glass? They’ve got their dev kits out right now, too, and –

Palmer Luckey: — What’s Google Glass? [laughs]

No, seriously, they’re doing something sort of similar with getting this wearable computing device to developers. Does the early buzz about Glass worry you?

Luckey: No. They’re not a gaming device, and they’re not a VR device, and they’re not an immersive device, and they’re five times more expensive than us.

Nate Mitchell: It’s just a completely different product. Wearable computing is super-interesting, and we’d love to see more wearable computing projects in the market. At Oculus, especially, we’re excited about the possibilities of Google Glass. We’ve seen it, we’ve checked it out, it’s very cool. But if you bring them together –

Luckey: Our image size is like 15 times larger than theirs. It’s like the difference between looking at a watch screen and a 60-inch monitor. It’s just an enormous difference.

Mitchell: With the Rift, you’re in there. You’re totally immersed in the world. I think one of the things people keep bringing up (with Glass) is the awkward, the social aspect. For the Rift, you strap into this thing, and you’re gone.

Luckey: It’s about being inside the virtual world, not caring about the real one.

Mitchell: You could put your Glass on in the virtual space.

Luckey: We could do that! We could simulate Glass. … It’s not that hard. You just have a tiny heads-up display floating there. A really tiny one.

Mitchell: I like it.

“Okay, Rift, take a picture. Okay, Rift, record a video …”

Luckey: There’s actually Second Life mods like that. People sell heads-up displays that you can buy.

Mitchell: Really?

Luckey: And they put information in there like distance to waypoints and stuff.

Mitchell: Oh, that’s cool!

Luckey: Yeah, they overlay it on the screen when your character’s wearing it.

I never really “got” Second Life. Minecraft, I can wrap my head around quickly. But Second Life …

Luckey: It’s very difficult to get into. There’s a steep learning curve. The last time I went into Second Life was to buy bitcoins from a crazy guy who was selling them below market value, but you had to go into Second Life to meet with him.

Mitchell: The underbelly of the Internet.

Luckey: They’re actually working on Oculus Rift support, though. The kind of people who make games like Second Life definitely see the potential for virtual reality — being able to step into your virtual life.

And if you’re completely immersed in the game, I guess that wherever you’re playing, you need to trust whoever’s around you.

Mitchell: Absolutely. There’s already some sneaking up on people happening in the office. Someone’s developing, they’re testing the latest integration, and then Palmer comes up and puts his hands on their shoulders: “Heyyyy, Andrew! What’s going on?” There’s a trust factor.

Luckey: Have you seen the Guillotine Simulator? (video below) Some people are showing that without even telling the person what it is: “Here, check this out!” “Whoa, what’s going on?” And then — [guillotine sound effect]

Mitchell: One thing that that does lead into is, we’re exploring ways to just improve the usability of the device. When you put on the Rift, especially with the dev kit, you’re shut off from the outside world. What we’re looking at doing is how can we make it easy to pull it off. Right now, you have to slip it over your head like ski goggles. The dev kit was designed to be this functional tool, not the perfect play-for-10-hours device. With the consumer version, we’re going for that polished user experience.

What about motion sickness? Is it possible to overcome the current need for people to only play for a short period of time on their first go?

Luckey: The better we make the hardware, the easier it’ll be for people to just pick up and play. Right now, the hardware isn’t perfect. That’s one of the innate problems of VR: You’re trying to make something that tricks your brain into thinking it’s real. Your brain is very sensitive at telling you things are wrong. The better you can make it, the more realistic you can make it, the more easily your brain’s gonna accept the illusion and not be throwing warning bells.

You mentioned in one of your recent speeches that the Scout in Team Fortress 2 –

Luckey: — he’s running at like 40 miles per hour. But it’s not just, “Oh, I’m running fast.” It’s the physics of the whole thing. In real life, if you are driving at 40mph, you can’t instantly start moving backward. You can’t instantly start strafing sideways. You have inertia. And that’s something that, right now, games are not designed to have. You’re reacting in these impossible ways.

Mitchell: In that same vein, just as Palmer’s saying the hardware’s not perfect yet, a huge part of it is the content.

Luckey: You could make perfect hardware. Pretend we have the Matrix. Now you take someone and put them in a fighter jet and have them spinning in circles. That’s going to make someone sick no matter how good it is, because that actually does make people sick. If you make perfect hardware, and then you do things that make people sick in real life, you’re gonna make them sick in VR, too. Right now, there’s lots of things going on in games that don’t make people sick only because they’re looking at them on a screen. Or, in so many games, they’ll have cutscenes where they take control of the camera and shake it around. You don’t want to do that in VR because you’re not actually shaking around in real life.

You’re changing the experience that you have previously established within VR.

Mitchell: It breaks the immersion.

Luckey: And that’s why it’s so hard to instantly transfer. In the original version of Half Life 2, when you’d go into a new space for the first time, the whole game would just freeze for a second while it loads. It’s just a short freeze, but players were running along or driving along and all of a sudden, jjt! Now it looks like the whole world’s dragging along with you, and a lot of people feel very queasy when that happens.

Mitchell: It comes back to content. My talk at GDC was very specifically about how developing for VR is different from a 2-D monitor. All those things like cutscenes, storytelling, scale of the world — if the player is at four feet on the 2-D monitor and you put them in there, they immediately notice. They look down and they have the stereo cues: “I’m a midget!” So you make them taller, and now they don’t fit through doors. We really do believe that, at first, you’re going to see these ports of existing games, but the best “killer app” experiences are going to come from those made-for-VR games.

Luckey: And that’s not even to say it has to be new franchises. It doesn’t have to be a new type of game. But you want the content to be designed specifically for the hardware.

Mitchell: It’s just like the iPhone. The best games come from developers pairing hardware and software.

Oculus VR CEO Brendan Iribe testing out the Rift at D: Dive Into Media.

And that’s the 10,000-foot view: Does VR change game design in a fundamental way?

Mitchell: Yes. Fundamentally. Absolutely. I think, right now, there’s this great renaissance in the indie community. Indie developers are doing awesome things. If you look at games like The Walking Dead, you’ve got the mainstream genres here. You’re going to have a lot of these indie games start to feel more natural in virtual reality, because that’s almost, like, the intended experience.

Luckey: And not to invent a whole new genre on the fly, but you don’t see many first-person card games or something. There’s a lot of card game videogames, but there’s not many that are first-person because it wouldn’t make any sense to do.

Like a poker game where you could look around the table and read people’s reactions?

Mitchell: Exactly.

Luckey: And you could have all kinds of things integrated into it. I guess that would fit into the first-person-shooter genre, but not really, because you’re not moving and you’re not shooting. You’re just playing cards.

Mitchell: And if you look at the research that’s been done on virtual characters, it’s the type of thing where, if you smile at me in VR, even if you’re an NPC (non-playable character), I’m much more likely to smile back. Your brain is tricked into believing you’re there.

Luckey: There’s also fascinating research on confidence levels in VR, even tiny things. There was a study where a bunch of people performed tasks in real life, in a control group, and then performed them in VR. And the only difference is that one group in VR was about six inches taller than the other group. So, one was shorter than the NPC they were interacting with, one was taller. Universally, all of the “taller” people exhibited better negotiation with the NPCs. Then, they took them out (of the VR simulation) and they redid the (real-world) study, putting everyone back in another trial with a physical person. The people who’d been tall in VR and negotiated as a taller person did better when they went back into the real negotiation as well. It’s ridiculous.

Mitchell: That’s the sort of thing we’re super-excited about. That’s the dream.

And do you have a timeline for when –

Mitchell: When the dream comes to fruition?

Luckey: It’s a dream, man! Come on! [laughs]

Not when it comes to fruition. Are there milestones for specific accomplishments along the way?

Luckey: Sure, we have them, internally. [laughs]

Mitchell: We have a road map, but like we keep saying, a huge part of this is content. Without the content, it’s just a pair of ski goggles.

Luckey: And we don’t even know, necessarily, what a road map needs to look like. We’re getting this feedback, and if a lot of people need a certain feature — well, that means it’s going to take a little longer.

Mitchell: But we have a rough road map planned, and a lot of exciting stuff planned that I think you’ll see over the course of the next year.

And is there a timeline for when the first consumer version comes out?

Mitchell: It’s TBD. But what we can say is, Microsoft and Sony release their dev kits years in advance before they get up onstage and say, “The Xbox One is coming.” We went for the same strategy, just open and publicly.

Luckey: And we don’t want to wait many years before doing it.

Mitchell: Right. So, right now, we’re giving developers the chance to build content, but they’re also co-developing the consumer version of the Rift with us. Once everyone’s really happy with it, that’s when you’ll see us come to market.

Luckey: And not sooner. We don’t want to announce something and then push for that date, even though we know we can make it better.

And what about the company, Oculus VR? Is this dream you’re talking about something you have to realize on your own? Do you want to someday get acquired?

Luckey: Our No. 1 goal is doing it on our own. We’re not looking to get acquired, we’re not looking to flip the company or anything. I mean, partnering with someone? Sure, we’re totally open to discussions. We’re not, like, we want to do this with no help.

But you wouldn’t want to be absorbed into a bigger company that’s doing more than just VR.

Mitchell: The goal has been to build great consumer VR, specifically for gaming. We all believe VR is going to be one of the most important technologies of –

Luckey: — ever!

Mitchell: Basically.

Not to be too hyperbolic or anything.

Luckey: It’s hard not to be. It’s like every other technological advance could practically be moot if you could do all of it in the virtual world. Why would you even need to advance those things in the real world?

Mitchell: Sooo …

Luckey: [laughs]

Mitchell: With that in mind, we have to figure out how we get there. But right now, we’re doing it on our own.

Luckey: And we think we can deliver a good consumer VR experience without having to partner with anyone. We’re open to partnering, but we don’t think we have to. We’re not banking on it.

And how does being based in southern California compare to being closer to a more conventional tech hub like Silicon Valley?

Mitchell: Recruiting is a little harder for us. But overall, we’ve been able to attract incredible talent.

Luckey: And if you’re in Silicon Valley, it’s probably one of the easiest places to start a company in terms of hiring people. But VR is such a tiny field, it’s not like all of a sudden we’re going to go to Silicon Valley and there’s, like, thousands of VR experts. Now, if I’m a Web company or a mobile company –

Mitchell: — that’s where I’d want to be.

Luckey: But in this case, these people aren’t necessarily all up in Silicon Valley. We’ve hired a bunch of people from Texas and Virginia and all these other places. It’s a niche industry. We actually have the biggest concentration of people working in consumer VR right now. And a lot of the top talent we get, they don’t care where we are, as long as it’s not, like, Alaska. They just really want to work on virtual reality, and there’s no one else doing it like we are.

## “Temporal cloak” used to hide data transmitted at 12.7 Gbps

Original author:
John Timmer

In the past few years, there have been a regular series of announcements about devices that cloak something in space. These typically bend light around the cloak so that it comes out behind the object looking as if it had never shifted at all. In contrast, there's just been a single description of a temporal cloaking device, something that hides an event in time. The device works because in some media different frequencies of light move at different speeds. With the right combination of frequency shifts, it's possible to create and then re-seal a break in a light beam.

But that particular cloak could only create breaks in the light beam that lasted picoseconds. Basically, you couldn't hide all that much using it. Now, researchers have taken the same general approach and used it to hide signals in a beam of light sent through an optical fiber. When the cloak is in operation, the signals largely disappear. In this case the cloak can hide nearly half of the total bandwidth of the light, resulting in a hidden transmission rate of 12.7 Gigabits per second.

The work started with the Talbot effect in mind, in which a diffraction grating causes repeated images of the grating to appear at set distances away from it. The cloaking device relies on the converse of this. At other distances, the light intensity drops to zero. The key trick is to convert the Talbot effect from something that happens in space to something that happens in time.

## Q: What causes friction? (and some other friction questions)

Original author:
The Physicist

Physicist: Political conversations with family, for one.

“Friction” is a blanket term to cover all of the wide variety of effects that make it difficult for one surface to slide past another.

There a some chemical bonds (glue is an extreme example), there are electrical effects (like van der waals), and then there are effects from simple physical barriers.  A pair of rough surfaces will have more friction than a pair of smooth surfaces, because the “peaks” of one surface can fall into the “valleys” of the other, meaning that to keep moving either something needs to break, or the surfaces would need to push apart briefly.

This can be used in hand-wavy arguments for why friction is proportional to the normal force pressing surfaces together.  It’s not terribly intuitive why, but it turns out that the minimum amount of force, Ff, needed to push surfaces past each other (needed to overcome the “friction force”) is proportional to the force, N, pressing those surfaces together.  In fact this is how the coefficient of friction, μ, is defined: Ff = μN.

The force required to push this bump “up hill” is proportional to the normal force.  This is more or less the justification behind where the friction equation comes from.

The rougher the surfaces the more often “hills” will have to push over each other, and the steeper those hills will be.  For most practical purposes friction is caused by the physical roughness of the surfaces involved.  However, even if you make a surface perfectly smooth there’s still some friction.  If that weren’t the case, then very smooth things would feel kinda oily (some do actually).

Sheets of glass tend to be very nearly perfectly smooth (down to the level of molecules), and most of the friction to be found with glass comes from the subtle electrostatic properties of the glass and the surface that’s in contact with it.  But why is that friction force also proportional to the normal force?  Well… everything’s approximately linear over small enough forces/distances/times.  That’s how physics is done!

That may sound like an excuse, but that’s only because it is.

Q: It intuitively feels like the friction force should be directly proportional to the surface area between materials, yet this is never considered in any practical analysis or application.  What’s going on here?

A: The total lack of consideration of surface area is an artifact of the way friction is usually considered.  Greater surface area does mean greater friction, but it also means that the normal force is more spread out, and less force is going through any particular region of the surface.  These effects happen to balance out.

If you have one pillar the total friction is μN. If you have two pillars each supports half of the weight, and thus exert half the normal force, so the total friction is μN/2 + μN/2 = μN.

Pillars are just a cute way of talking about surface area in a controlled way.  The same argument applies to surfaces in general.

Q: If polishing surfaces decreases friction, then why does polishing metal surfaces make them fuse together?

A: Polishing two metal surfaces until they can fuse has to do with giving them both more opportunities to fuse (more of their surfaces can directly contact each other without “peaks and valleys” to deal with), and polishing also helps remove impurities and oxidized material.  For example, if you want to weld two old pieces of iron together you need to get all of the rust off first.  Pure iron can be welded together, but iron oxide (rust) can’t.  Gold is an extreme example of this.  Cleaned and polished gold doesn’t even need to be heated, you can just slap two pieces together and they’ll fuse together.

Inertia welders also need smooth surfaces so that the friction from point to point will be constant (you really don’t want anything to catch suddenly, or everyone nearby is in trouble).  This isn’t important to the question; it’s just that inertia welders are awesome.

Q: Why does friction convert kinetic energy into heat?

A: The very short answer is “entropy”.  Friction involves, at the lowest level, a bunch of atoms interacting and bumping into each other.  Unless that bumping somehow perfectly reverses itself, then one atom will bump into the next, which will bump into the next, which will bump into the next, etc.

And that’s essentially what heat is.  So the movement of one surface over another causes the atoms in each to get knocked about jiggle.  That loss of energy to heat is what causes the surfaces to slow down and stop.

## Q: Is fire a plasma? What is plasma?

Original author:
The Physicist

Physicist: Generally speaking, by the time a gas is hot enough to be seen, it’s a plasma.

The big difference between regular gas and plasma is that in a plasma a fair fraction of the atoms are ionized.  That is, the gas is so hot, and the atoms are slamming around so hard, that some of the electrons are given enough energy to (temporarily) escape their host atoms.  The most important effect of this is that a plasma gains some electrical properties that a non-ionized gas doesn’t have; it becomes conductive and it responds to electrical and magnetic fields.  In fact, this is a great test for whether or not something is a plasma.

For example, our Sun (or any star) is a miasma of incandescent plasma.  One way to see this is to notice that the solar flares that leap from its surface are directed along the Sun’s (generally twisted up and spotty) magnetic fields.

A solar flare as seen in the x-ray spectrum.  The material of the flare, being a plasma, is affected and directed by the Sun’s magnetic field.  Normally this brings it back into the surface (which is for the best).

We also see the conductance of plasma in “toys” like a Jacob’s Ladder.  Spark gaps have the weird property that the higher the current, the more ionized the air in the gap, and the lower the resistance (more plasma = more conductive).  There are even scary machines built using this principle.  Basically, in order for a material to be conductive there need to be charges in it that are free to move around.  In metals those charges are shared by atoms; electrons can move from one atom to the next.  But in a plasma the material itself is free charges.  Conductive almost by definition.

A Jacob’s Ladder.  The electricity has an easier time flowing through the long thread of highly-conductive plasma than it does flowing through the tiny gap of poorly-conducting air.

As it happens, fire passes all these tests with flying colors.  Fire is a genuine plasma.  Maybe not the best plasma, or the most ionized plasma, but it does alright.

The free charges inside of the flame are pushed and pulled by the electric field between these plates, and as those charged particles move they drag the rest of the flame with them.

Even small and relatively cool fires, like candle flames, respond strongly to electric fields and are even pretty conductive.  There’s a beautiful video here that demonstrates this a lot better than this post does.

The candle picture is from here, and the Jacob’s ladder picture is from here.

## Q: Since all particles display wave-like characteristics, does that imply that one could use destructive wave interference to destroy or at least drastically change a particle?

Physicist: The wave-like property of particles allows you to do a lot of cute things with particles that would otherwise seem impossible, but making a particle disappear isn’t one of them.  You can use destructive interference to make it very unlikely to find a particle in particular places, which is exactly what’s happening in the double slit experiment, and is also the basis behind how “diffraction gratings” work.

The wave nature of things (in this case light) can be used to get it to go places it normally wouldn’t (right), or not go places it normally would (left).  By using two slits you can interfere the light waves to cause the light to never show up in places where it would when passing through one slit (dark bands in in the lower left).

But in order to destroy a particle using destructive interference you’d need to ensure that there was nowhere left with any constructive interference.  In the pictures above there are dark regions, but also light regions.  Turns out there are some very solid mathematical principles and physical laws that don’t allow waves to behave that way (not just waves in particle physics, but waves in general), not the least of which is the conservation of energy.  So, say you’ve got some kind of waves bouncing around (light waves, sound waves, particle fields, whatever), and you want to make new waves to cancel them out.  You can certainly do that, but only in small regions.

How noise canceling headphones work.  Rather than destroying sound around them, they cancel out the sound on one side that’s coming from the other.  But ultimately they’re just speakers that make the environment louder overall.

The new waves add energy to the overall system, so no matter how hard you try to cancel things out, you’ll always end up adding energy somewhere, it’s just a question of where.  Noise canceling headphones are a beautiful example.  They actively produce sound in such a way that they destructively interfere with sound waves coming from nearby, in the anti-headward direction.  Although they create quiet in the ears, they create noise everywhere else.  There’s no getting around it.

Say you’ve got a bunch of noise bouncing about.  Noise canceling techniques can create a quite region, but end up generating more total noise outside of that region.

Similarly, you could try to kill off particles by creating new waves in the particles field (each kind of particle has a corresponding field, for example light particles are called “photons” and they have the electromagnetic field) that cancel out the particle.  You can totally create a particle “dead zone”, assuming you know exactly what the particle’s wave form is.  Headphones need this as well; you can’t just get rid of sound, you first need to know exactly what the sound is first.  However, anything you try will end up adding more particles , and won’t destroy the particle you’re worried about anyway, just redirect it.

There are a few ways to destroy a particle.  You can chuck it out (which is as good as destroying it, for most practical purposes), or you can annihilate it.  But annihilation is a bit of a cheat; you just put a particle in a chamber with its anti-particle and let nature take its course.  But that doesn’t use waves and interference (in the way we normally think of waves), they just combine, disappear, and leave behind a burst of energy.  But not in a cool, wavey interferey, kind of way.

The pictures at the top of this post are from here and here.

## How to: Instantly turn water into snow

Chalk this up under "Blogs You Ought to be Following". The Tumblr Fuck Yeah Fluid Dynamics is a great place to find succinct, clear explanations of the forces that make things flow. In particular, they're fantastic at posting explanations behind things you see in YouTube videos, both viral and obscure.

The video above — in which a nice Siberian guy tosses boiling water off his balcony and creates a cloud of snow — has been making the rounds recently. Here's how Fuck Yeah Fluid Dynamics explains it:

Several effects are going on here. The first thing to understand is how heat is transferred between objects or fluids of differing temperatures. The rate at which heat is transferred depends on the temperature difference between the air and the water; the larger that temperature difference is the faster heat is transferred. However, as that temperature difference decreases, so does the rate of heat transfer. So even though hot water will initially lose heat very quickly to its surroundings, water that is initially cold will still reach equilibrium with the cold air faster. Therefore, all things being equal, hot water does not freeze faster than cold water, as one might suspect from the video.

The key to the hot water’s fast-freeze here is not just the large temperature difference, though. It’s the fact that the water is being tossed ...

## Kickstarter Projects: MaK (VergeGameStudios)

Remember MaK? The developers called it a 'physics sandbox with tethers, rockets, engines, balloons, explosives, teleportation, relative gravity and potentially unlimited room for creativity.' There's more than a whiff of Super Mario space Galaxy wrapped in up in it as well. If you've ever wanted a whimsical Minecraft set in space, this may be it.

As you might have guessed from the title, they're also in need of some financial help. MaK currently has a Kickstarter project up that is looking to achieve \$230, 000 in funding. If you feel like contributing, here's the appropriate link.

## Q: Is it possible for an artificial black hole to be created, or something that has the same effects? If so, how small could it be made?

Physicist: Not with any current, or remotely feasible technology.  The method in use by the universe today; get several Suns worth of mass into a big pile and wait, is a pretty effective way to create black holes.

In theory, all you need to do to create an artificial black hole (a “black faux”?) is to get a large amount of energy and matter into a very small volume.  The easiest method would probably be to use some kind of massive, super-duper-accelerators.  The problem is that black holes are dense, and the smaller and less massive they are the denser they need to be.

A black hole with the mass of the Earth would be so small you could lose it pretty easy.  Except for all the gravity.

But there are limits to how dense matter can get on its own.  The density of an atomic nucleus, where essentially all of the matter of an atom is concentrated, is about the highest density attainable by matter: about 1018 kg/m3, or about a thousand, million, million times denser than water.  This density is also the approximate density of neutron stars (which are basically giant atomic nuclei).

When a star runs out of fuel and collapses, this is the densest that it can get.  If a star has less than about 3 times as much mass as our Sun, then when it gets to this density it stops, and then hangs out forever.  If a star has more than 3 solar masses, then as it collapses, on it’s way to neutron-star-density, it becomes a black hole (a black hole with more mass needs less density).

The long-winded point is; in order to create a black hole smaller than 3 Suns (which would be what you’re looking for it you want to keep it around), it’s not a question of crushing stuff.  Instead you’d need to use energy, and the easiest way to get a bunch of energy into one place is to use kinetic energy.

There’s some disagreement about the minimum size that a black hole can be.  Without resorting to fairly exotic, “lot’s of extra dimensions” physics, the minimum size should be somewhere around $2\times 10^{-21}$ grams.  That seems small, but it’s very difficult (probably impossible) to get even that much mass/energy into a small enough region.  A black hole with this mass would be about 10-47 m across, which is way, way, way smaller than a single electron (about 10-15 m).  But unfortunately, a particle can’t be expected to concentrate energy in a region smaller than the particle itself.  So using whatever “ammo” you can get into a particle accelerator, you find that the energy requirements are a little steeper.

To merely say that you’d need to accelerate particles to nearly the speed of light doesn’t convey the stupefying magnitude of the amount of energy you’d need to get a collision capable of creating a black hole.  A pair of protons would need to have a “gamma” (a useful way to talk about ludicrously large speeds) of about 1040, or a pair of lead nuclei would need to have a gamma of about 1037, when they collide in order for a black hole to form.  This corresponds to the total energy of all the mass in a small mountain range.  For comparison, a nuclear weapon only releases the energy of several grams of matter.

CERN, or any other accelerator ever likely to be created, falls short in the sense that a salted slug in the ironman falls short.

There’s nothing else in the universe the behaves like a black hole.  They are deeply weird in a lot of ways.  But, a couple of the properties normally restricted to black holes can be simulated with other things.  There are “artificial black holes” created in laboratories to study Hawking radiation, but you’d never recognize them.  The experimental set up involves tubes of water, or laser beams, and lots of computers.  No gravity, no weird timespace stuff, nothin’.  If you were in the lab, you’d never know that black holes were being studied.

## Q: Since the real-world does all kinds of crazy calculations in no time, can we use physics to calculate stuff?

The original question was: I’ve heard somewhere that they’re also trying to build computers using molecules, like DNA. In general would it work to try and simulate a factoring algorithm using real world things, and then let the physics of the interactions stand-in for the computer calculation? Since the real-world does all kinds of crazy calculations in no time.

Physicist: The amount of time that goes into, say, calculating how two electrons bounce off of each other is very humbling.  It’s terribly frustrating that the universe has no hang ups about doing it so fast.

In some sense, basic physical laws are the basis of how all calculations are done.  It’s just that modern computers are “Turing machines“, a very small set of all the possible kinds of computational devices.  Basically, if your calculating machine consists of the manipulation of symbols (which in turn can always be reduced to the manipulation of 1′s and 0′s), then you’re talking about Turing machines.  In the earlier epoch of computer science there was a strong case for analog computers over digital computers.  Analog computers use the properties of circuit elements like capacitors, inductors, or even just the layout of wiring, to do mathematical operations.  In their heyday they were faster than digital computers.  However, they’re difficult to design, not nearly as versatile, and they’re no longer faster.

Nordsieck's Differential Analyzer was an analog computer used for solving differential equations.

Any physical phenomena that represents information in definite, discrete states is doing the same thing a digital computer does, it’s just a question of speed.  To see other kinds of computation it’s necessary to move into non-digital kinds of information.  One beautiful example is the gravity powered square root finder.

Newtonian physics used to find the square root of numbers. Put a marble next to a number, N, (white dots) on the slope, and the marble will land on the ground at a distance proportional to √N.

When you put a marble on a ramp the horizontal distance it will travel before hitting the ground is proportional to the square root of how far up the ramp it started.  Another mechanical calculator, the planimeter, can find the area of any shape just by tracing along the edge.  Admittedly, a computer could do both calculations a heck of a lot faster, but they’re still descent enough examples.

Despite the power of digital computers, it doesn’t take much looking around to find problems that can’t be efficiently done on them, but that can be done using more “natural” devices.  For example, solutions to “harmonic functions with Dirichlet boundary conditions” (soap films) can be fiendishly difficult to calculate in general.  The huge range of possible shapes that the solutions can take mean that often even the most reasonable computer program (capable of running in any reasonable time) will fail to find all the solutions.

Part of Richard Courant's face demonstrating a fancy math calculation using soapy water and wires.

So, rather than burning through miles of chalkboards and a swimming pools of coffee, you can bend wires to fit the boundary conditions, dip them in soapy water, and see what you get.  One of the advantages, not generally mentioned in the literature, is that playing with bubbles is fun.

Today we’re seeing the advent of a new type of computer, the quantum computer, which is kinda-digital/kinda-analog.  Using quantum mechanical properties like super-position and entanglement, quantum computers can (or would, if we can get them off the ground) solve problems that would take even very powerful normal computers a tremendously long time to solve, like integer factorization.  “Long time” here means that the heat death of the universe becomes a concern.  Long time.

Aside from actual computers, you can think of the universe itself, in a… sideways, philosophical sense, as doing simulations of itself that we can use to understand it.  For example, one of the more common questions we get are along the lines of “how do scientists calculate the probability/energy of such-and-such chemical/nuclear reaction”.  There are certainly methods to do the calculations (have Schrödinger equation, will travel), but really, if you want to get it right (and often save time), the best way to do the calculation is to let nature do it.  That is, the best way to calculate atomic spectra, or how hot fire is, or how stable an isotope is, or whatever, is to go to the lab and just measure it.

Even cooler, a lot of optimization problems can be solved by looking at the biological world.  Evolution is, ideally, a process of optimization (though not always).   During the early development of sonar and radar there were (still are) a number of questions about what kind of “ping” would return the greatest amount of information about the target.  After a hell of a lot of effort it was found that the researchers had managed to re-create the sonar ping of several bat species.  Bats are still studied as the results of what the universe has already “calculated” about optimal sonar techniques.

You can usually find a solution through direct computation, but sometimes looking around works just as well.