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  • Hey Vsauce Michael here

  • nyctophobia is the fear of the dark

  • but there's another fear that's more chilling

  • it's the fear that darkness will go away

  • optophobia the fear of opening your eyes

  • light travels at the fastest speed possible for a physical object

  • darkness is erased when light appears and returns

  • when light leaves the speed of dark

  • is the speed of light but there are other types and darkness

  • that can move faster than light speed for instance

  • a shadow

  • across a distance a shadow can become much larger than the object creating it

  • but still mimic its source moving in the same way for the same amount of time

  • so when a shadow is bigger than the object casting it, it moves a greater distance

  • when the object moves but in the same amount of time. Make a shadow large enough

  • and it can travel across the surface faster than light

  • if you hear on earth cast a shadow on to the moon

  • not an easy thing to do that pointed from say point a

  • on the moon's surface and then you moved your finger so that the shadow moved

  • to point B your finger would only move a few centimetres

  • in a fraction of a second but the shadowy cast on the moon

  • would move thousands of kilometers in the same amount of time

  • do it right and you're easily producing a shadow

  • that breaks the light barrier

  • but nothing's wrong here

  • the rule is that information can't travel faster than light

  • you can't cause something to happen somewhere else

  • faster than light could travel from you to that somewhere else

  • and our superluminal shadow is transferring

  • no information from point A to point B

  • sure point B is being cast into darkness

  • sooner than a light speed message from A could warn him it's coming

  • but darkness isn't traveling from point A to point B

  • it's traveling from you to point A and point B

  • at the speed of light what we tend to call a shadow

  • is really just a cross-section of a three-dimensional region

  • the darkness you are causing only changes shape

  • when newly unblocked light fills

  • the previous gap. That's all shadow is

  • a gap so in a way a shadow doesn't

  • travel at all that's an illusion caused by us thinking

  • that a shadow is a physical things when in reality

  • a shadow is just the lack of physical things

  • photons which chug along at speed limit

  • of the universe but that doesn't mean two shadows

  • can't kiss or at least

  • look like they are, watch as Guy brings two shadows

  • near each other, right before they actually make contact

  • the shadows seem to magically bulge toward one another

  • in a sort of smooch of darkness. What's going on is the

  • shadows blister effect and it has to do with the anatomy of a shadow

  • the region where an object completely blocks a light source is called

  • the Umbra it's the darkest part of the shadow in the most prototypical

  • part of the shadow where only a portion of the light source is

  • blocked we find the fainter penumbra but as two or more penumbra

  • approach and overlap the combined amount of light they block can be enough to

  • produce a perceivable difference

  • the shadow blister the Earth has a big

  • umbra, it's 1.4 million kilometers long

  • that's how far away you have to be from the earth for it to no longer have a

  • large enough apparent diameter

  • to block out all of the sun. Here on the surface of Earth we are nowhere near that

  • for away which is why night is so umbral

  • night is just the Earth's shadow falling on you

  • a you eclipse

  • sunsets are cool they're beautiful to look at but look the other way

  • and you can see the lumbering shadow of our planet

  • our atmosphere scatters shorter wavelengths of light

  • more than longer wavelengths which makes the sky

  • appear blue but in Earth's shadow there's less light to scatter and the sky

  • appears darker during twilight you can see

  • the demarcation while driving east from Denver to Kansas City

  • I got a particularly great view of it

  • this is Earth's approaching night making shadow

  • the beautiful pink band above it that's the belt of Venus

  • it's caused by the sky reflecting the the colors

  • of the sunset behind us. You've probably noticed that

  • light after the sunsets and disappears from view

  • there's still light in the sky scattered from the

  • no longer visible sun, this is what we call twilight

  • and there are many different stages of Twilight

  • if the sun is less than six degrees below the horizon it's technically

  • civil twilight you can still do plenty of stuff outdoors without the need for artificial lights

  • down to 12 degrees below the horizon we have

  • nautical twilight: artificial lights are more or less necessary that the sky

  • still scatters enough light to be bright enough for ships at sea

  • to navigate by seeing a contrast of the horizon between dark sea

  • and faintly lit sky. Down to 18 degrees

  • an astronomical twilight is occurring it looks like

  • night but the sky can still get darker until

  • astronomical Twilight ends not all night time astronomical observations can be made

  • below 18 degrees is technically

  • honestly, night. If you live at greater than 48.5 degrees north or south latitude

  • during the summer the sun never goes more than 18 degrees below the horizon

  • it's never technically night. Places like London only reach astronomical Twilight at the most

  • during these months. So if you live in one of these areas

  • and you want to avoid doing something during the summer just tell people

  • you'll do it tonight you'll buy yourself a few weeks

  • but thats slow darkness let's

  • cut to the chase because we are looking for fast darkness

  • when scissor blades snip the intersection point between both blades moves faster

  • than the blades themselves think of it this way

  • if you had a pair of scissors with believes that were a light year long

  • and it took one second to close them, the intersection point would've traveled an entire

  • light year, in not a year but...

  • a second. No laws are being broken here because such a snip

  • would be physically impossible as I've mentioned before

  • rigid objects don't move instantaneously all over

  • when a push force is applied to them

  • Instead that force moves via electromagnetic forces from one atom

  • to the next and so on down the line a compression wave

  • that travels at the speed of sound through the material

  • but what if we ignored that problem by allowing the blades to simply be separately

  • already in motion well their point at intersection

  • can still travel faster than light because it's not a physical thing

  • It's just a geometric point and it carries

  • no more information than you could already gather

  • by witnessing the approaching blades

  • but don't count out that geometric point of intersection just yet it's the key to

  • another type of darkness that can move faster than light

  • when waves collide their crests can fuse into larger crests

  • their troughs into larger troughs this is constructed interference

  • but crests colliding with troughs cancel out

  • destructive interference if these waves or light

  • the result is darkness and in certain circumstances

  • darkness created this way can travel like the intersection between two lines

  • faster than light. Imagine these concentric circles as waves of light

  • the lines are wave crests and the gaps in between

  • are troughs when they meet the points where they Intersect

  • flee up and down faster than the waves travel

  • especially in the middle which in the case of light waves makes them

  • faster than light. The superluminal speeds of these dark patches can be seen really clearly

  • if we make the wave crests of one source black

  • as well as the background overlapping regions where red

  • peeks through represent destructive interference

  • darkness and you can see how especially in the middle

  • this darkness races up and down faster than the waves

  • In 1995 a man named McArthur Wheeler

  • robbed a bank in Pittsburgh, he was caught

  • because his only disguise was lemon juice

  • he covered his face with it. He knew that lemon juice could be used as an invisible ink

  • when writing on paper revealed by heating and he knew so little about

  • why that worked and he knew so little about how cameras worked

  • that he assumed with extreme confidence that lemon juice

  • could make him invisible to

  • seriously Wheeler is an extreme example

  • and was the inspiration for the dunning-kruger effect

  • novacist people unskilled in particular disciplines

  • will often overestimate their knowledge and abilities

  • in said disciplines because they don't even know

  • how little they know, how much more there is to learn

  • on the flip side experts in particular field will often

  • underestimate their knowledge have less confidence in their abilities

  • or think that everyone else has the same level of knowledge that they do

  • What drives the dunning-kruger effect

  • is the fact that often the more you learn about something the more you realise

  • just how rich and complex and over whelming and full of as of yet unanswered questions it really is

  • George Bernard Shaw once famously toasted Albert Einstein by saying

  • science is always wrong

  • it never solves a problem without creating 10 more

  • eisenstein didn't exactly disagree he used

  • geometry to illustrate how ignorance grows faster than knowledge saying

  • as our circle of knowledge expands so does the circumference

  • of darkness surrounding it learning

  • studying, shedding light on a field inquiry also reveals just how

  • in the dark we continue to be how many shadowy things there are left

  • for us to illuminate. The diameter of white

  • never exceeds the shadowy circumference

  • but what's the speed of that kind dark the speed of the growth

  • of the number of things we know we are in the dark about

  • what's the speed of ignorance?

  • if we define ignorance as the difference between questions we know to ask

  • and answers we have, the field of agnotology

  • the study of ignorance suggests that the amount of

  • things we know we are in the dark about is growing faster

  • than the amount the things we have shed light on

  • is it a coincidence that the phrase in the dark originated during of all ages

  • the age of enlightenment? When Levinbook put a scraping

  • from his tooth under a collection of magnifying lenses he built

  • he saw for the first time in human history

  • little moving creatures... microorganisms

  • he called them animalcules. The discovery shed light on why

  • food spoiled life didn't spontaneously come from old meat

  • it was already there we just couldn't see it

  • but the discovery also showed us that we were in the dark

  • about an entirely new realm of biology

  • as Philippe Bourdeau has poetically put it enlightenment leads to benightedness

  • science entails nescience

  • what's really cool about the expanding size of our nescience circumference

  • is what Stewart Firestein the chair of biological sciences at Columbia University has said about it

  • it is there that science begins

  • where the facts run out just beyond them

  • he says it is a mistake to bob around in the circle of facts

  • instead of riding the wave to the great expanse

  • lying outside the circle

  • If science is a road trip facts are the photos

  • we take along the way the fuel that drives it forward

  • is ignorance. Facts... more like

  • fax, part of the past not the way forward

  • when it comes to understanding our world

  • knowing why is obsolesce by asking why

  • knowing facts makes you bright but the

  • equally quick sometimes quicker and most rewarding prize

  • is the dark

  • and admitting that you don't know everything but that you would like to know some of it

  • and as always thanks for watching

Hey Vsauce Michael here

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B1 US shadow darkness twilight faster speed dark

What Is The Speed of Dark?

  • 208 13
    Tu Howard posted on 2014/09/27
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