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 of 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, here on Earth, cast a shadow onto
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
shadow it 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 thing, 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 penumbras 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 kilometres long. That's how far away you'd 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 far 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 colours of the sunset behind us. You've probably noticed that right after the sun sets, 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 but 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 that's 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
blades 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
constructive interference. But crests colliding with troughs cancel
out. Destructive interference if these waves
are 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 too. Seriously. Wheeler is an extreme example and was the inspiration for the Dunning-Kruger effect Novices, 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 overwhelming 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 ten more." Einstein 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 of
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
light 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 Leeuwenhoek 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 Stuart 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.
“Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.” ― Terry Pratchett, Reaper Man
My favorite quote
Ugh, I wish the title didn't infer we were going to realize the speed of dark. Halfway through and I felt relief knowing this channel is still credible.
What's the speed of push?
Imagination > Knowledge
Did this remind anyone else of the shadows on the cliff in Infinite Jest?
Have you ever seen Never Ending Story 2? They say right there that the speed of darkness is twice as fast as the speed of light.
Neil deGrasse Tyson talking about the speed of dark. https://www.youtube.com/watch?v=h_FFjYSkkpA
That shadow thing moving faster than light sounds wrong to me.
This might be hard to explain why.
This is just my thought. Does anyone else agree?