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 five 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 on 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.
It 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 down.
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 this 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 and 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 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 thor, 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 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.