Hello, Physics friends.

I'm Diana.

Physics experiment at home.

You do it.

I do it.

Let's do it.

I have a two-liter bottle that we drilled a circular hole in.

Took a little while to get it right.

And a green laser pointer.

I'm going to shine the laser beam through one side of the bottle and align it so it's going out the hole on the other side.

And you can see there's a beam shining straight through on my leg.

Now, I'm going to fill up the water bottle with water, and we're going to see what happens when I shine it in the same way.

Oh, no.

Is it working?

Really?

I wonder if it'll get better as that gets less turbulent?

Oh, yeah.

I mean, yeah.

Like that's-- well, you moved it.

There we go.

Whoa.

The light follows the water down the stream and no longer travels straight.

It's trapped.

It just works better when there's less water.

JAMIE: What is that?

Is it following the water?

CAMERA MAN: Yeah, yeah, because it keeps.

JAMIE: Oh, because it keeps bouncing off of the surfaces.

Oh, that's sick.

DIANA: Yeah, it's sick.

As Jamie noticed, the inside of the water is acting like a mirror, letting almost no light out as it follows the stream.

But light can escape water, which is why I can see this lime inside of a bowl of water.

But when I go below a certain angle-- it's so crazy.

It looks like there's-- JAMIE: You've got two limes in there?

DIANA: Yeah, it looks like it on here.

It looks like there's a floating lime.

Light is weird.

There's a point when light can't escape water, and we decided to try to find that angle with a laser beam.

JAMIE: Look.

DIANA: Oh, cool.

Dude!

JAMIE: Oh, sweet.

DIANA: The laser beam is coming up through the water until it hits the surface and reflects back down into the water.

JAMIE: At what point-- at what angle do you think it can escape?

DIANA: Good question, Jamie.

There's a certain angle where all the light reflects.

It's called the critical angle.

If we shine light steeper than it, some of the light starts to escape, and at a more glancing angle, all the light stays in in a phenomenon called total internal reflection.

JAMIE: Yeah, it just gets fainter and fainter.

DIANA: Oh, there we go.

JAMIE: Oh, so that's, like, about the angle right there.

And now it's all the way back in.

DIANA: Yeah, yeah, yeah.

Oh, OK. JAMIE: See?

That's right there where the critical angle is.

DIANA: This critical angle depends on the index of refraction of the materials, here, water and air, and it plays a hugely important role in our water experiment and as we'll see, in fiber optics.

In the stream, you can see light bouncing off the inside at a glancing angle.

It's not getting out because it's below the critical angle, and we can guide the light in a curved line.

Being able to control the direction of light is a big deal, especially in communication.

Think about this.

If I wanted to communicate with my parents in Hawaii from my home in San Diego, I could send them a postcard, which would get tossed in a truck and then put on a plane and then tossed in another truck and so on over a couple of days.

But light would take a hundredth of a second to travel that same distance, which is about the same amount of time it takes for sound to go from my mouth to someone else's ear in a regular conversation.

Side note-- it always confused me why Harry Potter sent mail using owls, which just goes to show you that our Muggle technology has long surpassed the wizarding world.

You can't even encrypt owl posts.

I digress.

So you can send information using light without controlling the direction.

All you need is a radio tower and everyone nearby can tune in and rock out to some Foo Fighters.

(SINGING) I'm lookin' for something to help me burn out right.

108 00:03:30,100 --> 00:03:31,750 Can't play the actual clip.

Copyright.

But if you wanted to live stream the Foo Fighters concert in 4K, you would need a tricked out, decked out radio tower on steroids.

But if you can confine and guide the light, like we did with the stream of water, you can make the signal go much farther.

This is how the various servers of the internet send information back and forth, except instead of using water streams, they use fibers made of extremely pure glass, sometimes as thin as the width of a human hair.

These are called optical fibers or fiber optics.

We're confining light here with a clear material.

It's cool.

Light travels about 2/3 the speed it would in the vacuum of space but still about 200,000 kilometers per second.

Now, I was thinking about communications one day, and I wondered, how do we send signals across, say, the Pacific Ocean?

Is that all wireless through satellites?

Surely we don't have fiber optic cables running across thousands of miles of open ocean.

But we do.

Engineers for telecom companies-- which to be honest, I haven't historically spent much time thinking about-- have linked the continents of the world by doing this incredible set of things.

They load up their ships with thousands of kilometers of fiber optic cable wound up in reels.

They start burying the cable on land near the coastline at a place called a landing site in New Jersey, Florida, Oregon, Alaska, California, Hawaii you name it.

Then, a ship will use an underwater plow to dig a trench about a meter under the ocean floor.

It'll pull the fiber optic cable through that trench and then bury the cable.

When these cables need maintenance and repair, occasionally due to the wrath of angry sea creatures, they use underwater robots.

Talk about infrastructural feats of humanity.

Now, how does light traveling through a fiber become information?

Now, if we were living in the 1840s, you would send short flashes of light for dots and long flashes of light for dashes and someone at the other end would write it all down and translate, a Morse code of light, if you will.

We will.

But we live in a post-modern Muggle era.

So we have electronics and computer chips to do the flashing and blinking and translating for us.

OK, but the real question here is, how much longer does it actually take to send the postcard by mail versus a message on the internet?

I took to Twitter and I found a communications expert as you do.

I'm Nils Werner.

I'm a PhD student at the University of Erlangen Nuremberg.

I work at the audio department.

I asked Nils what happens when you send an image file and about how the information might not take the path you'd initially think, and he sent me back this amazing comprehensive email with references.

I was so happy when I got that.

How long will it take to send that postcard?

Like, you've got your image file, which compresses maybe about a megabyte.

How long is it going to take from when you click Send, until it gets received on the other end.

The biggest factor there is actually the connection at your home, because as we said, it's uploading stuff.

It's the slowest.

We talked briefly about why upload speed on your internet is typically slower than download speed, and it turns out, it's just out of necessity.

Most people are downloading video files and watching Netflix, and so internet service providers have given priority to downloading.

So it's only those of us that upload a lot to YouTube or stream on Twitch that get annoyed.

Back to it.

So that's the slowest bit.

And if we say we have five megabits of upload speed, let's say, it will take about two seconds to upload the postcard from your connection.

But after that, all the other links from each node to the next, even across the Atlantic or the Pacific, they're much, much, much, much faster.

So they don't play a big role anyways.

So the slowest part is your home.

10 times less than that for downloading on the other end, and then while it's traveling across the fiber optic network, it's fractions of a second, like hundredths of a second.

And so overall, your postcard takes, really just the time it takes to upload, so about two seconds plus a couple of fractions of a second more versus the four days it took to send by mail.

So now that we got the timing out of the way, there are so many other interesting things that are going on when you send your data over the internet.

Like your post card data gets split up into packets, and then those are sent from node to node across the network of the internet.

Number one, why is it encoded in packets?

And number two, do those packets all travel the same path?

So you're the exclusive user of the last bit of the connection to your home but you're sharing all the other connections with everybody else.

What they can do is they can transmit a lot more packets than you can transmit.

So they're basically mixing your tiny pockets with everybody else's tiny packets.

And so you're sharing the connection, one packet after another.

It sometimes happens, or it could happen, that your packets not all go down the same route because each individual node-- so you basically switch from one node to the next.

Each of them has to make the same decision where to send your packet next.

And if it just so happens that the next node is slow or not reachable or whatever, it just sends it down a different path.

So that's all the redundancy that's built into the internet basically.

So like the analogy with your postcard, sending it in a truck.

It's like you tear it up and put it in different tracks.

Yes, exactly.

And yeah, they're wildly different trucks and they could go in different speeds, different directions.

They could be different trucks as well.

So one could go over satellite.

The other one could go through a cable.

Oh, I didn't even think about that.

Yeah, this for me, was a fascinating look at how your data is sent, and there's even more, like how the data gets weaker as it goes through fiber optic cable.

So there's physical systems that boost the signal and have nothing to do with reading and resending your data.

Very cool stuff.

Thanks to Nils.

I think optical fiber might be an underrated technology.

I love my smartphone from the bottom of my heart, but let's face it, we're never going to be fully wireless.

Satellite communication is just too slow.

You have to beam the signal up to 35,000 kilometers and wait for it to come back down, and then there's the thing of installing them with rockets.

So when you make a Skype call halfway around the globe or you watch an awesome YouTube video, it's optical fiber that makes it possible.

So the messenger of the future is not going to be smoke signals or postcards or even electrons.

It's going to be fiber optics.

Thank you for watching this video.

And now, go forth into the world and enjoy the physics.

Thank you again for watching this video.

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I know you've wanted more math in your life.

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