Hi there.

I'm Diana, and I was just thinking, how cool is it that a random series of taps and swipes on your phone can end up sending a thoughtful message to your mom?

How does your phone do that?

Like, what exactly happens that a tiny, adorable cartoon shows up on your phone and is transmitted thousands of miles away and shows up on somebody else's?

It's like the future!

Today, I want to explore the physics of this simple act.

When you open up your text message app and you press that single emoji, what exactly is happening in your phone?

In other words, when you tap an emoji on your phone, your phone has to transmit that touch into an electrical signal.

So it has to sense exactly where you touched it.

A lot of smartphones today use a technology called mutual capacitance sensing because it's a lot more accurate and sensitive than other technologies.

It's also why your trackpad works.

The way this all fits together is pretty complicated.

Underneath the glass surface of your phone are tiny pieces of a conducting material called indium tin oxide.

There are two interlocked layers of these tiny conductors called electrodes, which are arranged in a diamond grid with each diamond spaced about 5 millimeters apart, totaling over 300 diamonds on most screens.

You can't see this grid, though, when you just look at your screen because it's mostly transparent, and they fill it in so it doesn't disrupt your Snapchat experience.

Your phone keeps these electrodes at a set voltage, which means that when you're not touching the screen, the phone has deposited a fixed number of electrons on one and taken some number of electrons away from the other, leaving one positively charged and one negatively charged electrode.

So each one will carry a specific amount of charge in equilibrium.

Now, when your finger touches the screen, you disrupt that equilibrium, because your finger has charges, too, usually equal numbers of positive and negative charges.

Unless you're getting out of a car and a dry day or you're currently being hit by lightning.

The electrons in your finger are attracted to the positive electrode, causing them to pile up on one side of your finger.

That charge imbalance causes the phone to deposit more electrons, changing the charge distribution on each electrode.

Each pair of electrodes then has a meter that keeps track of how many charges are on the two electrodes on that particular spot on the phone.

So when you begin to text, the number on this meter decreases.

Well, actually, this number goes down when you touch your screen with any material, but engineers have designed your phone to be sensitive to materials that are at least as disruptive as your finger.

So your stylus has to have at least two criteria.

Has to be at least as conductive as your finger and have sufficiently big surface area, which is why you can text with the back of a metal spoon or play "Pokemon Go" with a hot dog.

But you can't text with wool gloves, which aren't conductive enough, or with a metal safety pin, which doesn't have a big enough area.

So after all that, how does your phone know to project the emoji on your screen?

Is there an army of tiny, sentient ants in there going, heave-ho, the meter's gone done, turn on the pixels!

Metaphorically speaking, it's kind of like that.

Sort of.

Instead of a hyperintelligent ant colony, your phone has a computer chip.

Computer chips speak binary-- that's ones and zeros.

But what is physically going on?

This is my favorite part because it's where electrical hardware finally meets computer code.

The meters on your touch screen are connected to a complicated circuit made of resistors, capacitors, and transistors.

When the meter goes down enough, it triggers a current to the circuit.

The circuit manipulates that current into a new pattern, big and small pulses of electrical voltage.

Engineers refer to the high voltage as a one and the low voltage as a zero.

So those binary numbers are just a shorthand that mean high-low pulses of voltage.

It's really all just electronics.

And there's so much going on here with the transistors that I'm not going to get into it because engineers don't even think about each component individually.

They just regard them as a black box.

Just like a sociologists don't study human behavior by looking at each individual human cell.

But the key is that once the chip receives the digital signal from the touchscreen, its transistors then manipulate that into the poop emoji signal.

The emoji is expressed in a series of 32 pulses of voltage, or 32 bits.

11110000 10011111 10010010 10101001.

That's the poop emoji in binary.

I just didn't feel like memorizing it, but I encourage you to do so.

So then that binary goes out to the chip, which has its own binary-to-human language dictionary, known as Unicode.

Unicode assigns a unique combo of bits to each character-- Roman alphabet letters, 70,000 Chinese characters-- it even has binary for the thorn, a letter that only appears in Icelandic.

Unicode has space for billions of characters.

But even after encoding the world's languages, there are still vacancies.

But they take applications for new emoji every year, so get out those sketchbooks.

So now I'm going to simplify it a little bit, but basically the chip creates those 32 pulses, which get transmitted to another part of the chip.

Those 32 signals then trigger a bunch of transistors to do their thing and direct current to turn on the pixels on your text bar, and voila.

If this all sounds super complicated to you, that's because it is.

And I haven't even gotten to how your phone sends a text message, which is also really cool.

So in review, when you touch your phone screen, you change the charge distribution on your phone.

That signal gets sent over to your phone's computer chip, which, using a bunch of transistors, makes a series of 32 electrical signals, which trigger a different part of the chip to light up a series of pixels, which you see and interpret as the poop emoji.

And my favorite part-- this is all possible because of physics.

Your phone is changing its battery's stored chemical energy into perfectly organized light energy.

Can we just appreciate how much stuff your phone does in order to show you an emoji?

On that note, thank you so much for watching, and happy physicsing.

[music playing]