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- [Voiceover] So let's think
a little bit about waves.

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The classical notion of what a wave is,

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is it's a disturbance
traveling through a medium.

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Disturbance traveling through a medium.

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So what do we mean by disturbance and

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what do we mean by a medium?

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We could come up with some
fairly simple examples.

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Let's say that I have
a little puddle here.

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So that's my little puddle.

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And let's say I were to
drop a stone in that puddle.

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So this is my stone.

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It gets dropped in the puddle.

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We've all seen what happens.

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Right when it goes into the water,

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that pushes that water down,

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pushes the water around it out,

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then that water comes back up.

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Then you have this traveling disturbance.

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You have this traveling disturbance.

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These kind of rings that
start to radiate outward

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from where I actually dropped the pebble.

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You can actually see them move outwards.

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You can see the crests of
those waves move outwards.

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We're talking about a disturbance.

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Well this is that disturbance.

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The pond was completely flat,

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but then we agitate it.

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We pushed it down.

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It pushed the water outwards.

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Then that pushed the water
next to it up and down,

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up and down.

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It traveled outwards from the point

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of that initial disturbance.

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We have this disturbance
traveling through the medium.

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What's the medium here?

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The medium here is the water.

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The initial disturbance was the rock

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disturbing that water.

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But then that water disturbed
the water around it,

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which disturbed the water around it.

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That disturbance kept
traveling through the medium.

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We can give other examples of this.

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If I take a really long string
and hold it right there.

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That's my hand.

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The string is, let's just
say, attached to something.

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Let's say it's a really long string

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and right now there's some slack in it.

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It's attached to a wall.

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Let's say that I were to start
moving my hand up and down.

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So I move my hand up and down.

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What's going to happen?

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If I just did it once,

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what I'm gonna have is this lump of string

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move from the left to the right.

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So that's what it's
gonna look like at first.

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Then a few seconds later,
it's gonna look like this.

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It's gonna look something like this.

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You're gonna have this disturbance,

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which is this wave, this
lump that I just generated.

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It is going to move to the right.

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What's the medium?

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The medium in this case is the string.

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It is the string.

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What just happened there?

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When I jerk the string up,

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I'm disturbing those string
molecules right next to my hand.

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They're pulling on the
string molecules next to them

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pulling on the sting
molecules next to them.

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Then you have this traveling lump.

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Once again, these are
both examples of waves.

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Disturbances traveling through a medium.

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Now I can give other through a medium.

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I can give other examples.

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Sound waves.

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What causes sound waves?

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You have a bunch of air
particles all bouncing around

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at actually surprisingly fast speeds.

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But if you disturb them,

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if you cause something to, say, compress

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a bunch of air particles right here.

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These air particles get ultra-compressed.

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Some type of clap happens,

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so these get ultra-compressed.

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Then they're gonna bounce
on the ones next to them.

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Once again, you have this disturbance

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traveling through the medium.

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In this case, the medium is the air.

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The medium is the air.

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So, now that we've seen some

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classical notions of waves,

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let's think about something
a little bit more mysterious.

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That is the notion of light.

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Light definitely has wave like properties.

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Wave light can interfere with each other.

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We can do a whole other videos on light.

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If I were to take a barrier like that

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with two small slits in it.

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If I were to shine some light,

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one way to think about
it is these slits are

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the only place where the
disturbance gets through

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and then it would cause the light

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to propagate from each of them like that.

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Maybe I'm just drawing
the crests of the waves,

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but also come out from here.

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You can see where the two crests meet.

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They're going to constructively
enhance each other.

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They're going to constructively interfere.

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If you were to put some type
of a detector right over here,

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you would see the bright
points of the light

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and you would see the
dark points of the light.

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So light definitely behaves like a wave.

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I'm just showing you even one example of

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light behaving like a wave.

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But if it is a wave, that
means it needs to be or

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if we use our classical logic,

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you would say,

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well that means it's a disturbance

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traveling through a medium.

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But what is that medium?

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We have light coming from our sun.

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We call it sunlight.

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We have light coming,

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I keep wanting to make it a -

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actually our sun is white,

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we tend to draw it as a yellowish color,

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but that's just because of its -

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what happens is it goes
through the atmosphere.

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So you have the sun, you have the earth.

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This is not drawn to scale.

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Somehow that light is able to reach us

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over 93 million miles.

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What's it going through?

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Is it a disturbance
traveling through a medium?

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Well, for a long time, people said,

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well it must be.

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It has these wave-like properties.

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It seems to be traveling with a velocity,

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the speed of light.

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So there must be medium that
it is traveling through.

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People theorize what this medium is.

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They called it the luminiferous ether.

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Let me write that down
cause it's a fun word.

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It's a good name for a band.

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Luminiferous. Lumine, no
I'm not spelling it right.

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Luminiferous ether.

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It was this idea that maybe,
even in the vacuum of space,

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you have this substance.

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This luminiferous ether that
the light is traveling through.

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That it's somehow a disturbance

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in that luminiferous ether.

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Now, what we're gonna do in future videos,

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is we're gonna test that.

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We're gonna see if
that's actually the case

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because what's interesting
about if there is

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a luminiferous ether,

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we're not gonna be stationary relative to

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that luminiferous ether.

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In fact, we're orbiting around the sun.

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The sun is orbiting around
the center of the galaxy.

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There's no way that we're gonna be

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stationary relative to
that luminiferous ether.

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If we're not stationary relative to that

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luminiferous ether, we should be able to

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detect how light behaves.

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If it's going in the direction of ether

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or if it's going against the direction of

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the relative movement of
the ether relative to us.

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So anyway, I'll leave you there.

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This mystery of science.

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Waves, disturbance through a medium.

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We saw that with the water,

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with the air, with the string.

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But what about light?

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Is there a luminiferous ether?

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Put a question mark there.