[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.35,0:00:04.37,Default,,0000,0000,0000,,Light is the connection\Nbetween us and the universe.
Dialogue: 0,0:00:04.63,0:00:06.91,Default,,0000,0000,0000,,Through light, we can\Nexperience distant stars
Dialogue: 0,0:00:06.91,0:00:10.07,Default,,0000,0000,0000,,and look back at the\Nbeginning of existence itself.
Dialogue: 0,0:00:10.28,0:00:11.38,Default,,0000,0000,0000,,But what is light?
Dialogue: 0,0:00:19.44,0:00:22.37,Default,,0000,0000,0000,,In a nutshell, light is the\Nsmallest quantity of energy
Dialogue: 0,0:00:22.37,0:00:26.73,Default,,0000,0000,0000,,that can be transported, a photon,\Nan elementary particle without a real size
Dialogue: 0,0:00:26.73,0:00:29.98,Default,,0000,0000,0000,,that can’t be split,\Nonly created or destroyed.
Dialogue: 0,0:00:30.26,0:00:32.71,Default,,0000,0000,0000,,LIght also has a wave-particle duality,
Dialogue: 0,0:00:32.71,0:00:35.67,Default,,0000,0000,0000,,being kind of a particle and\Na wave at the same time,
Dialogue: 0,0:00:35.67,0:00:37.11,Default,,0000,0000,0000,,although this is a lie.
Dialogue: 0,0:00:37.32,0:00:40.57,Default,,0000,0000,0000,,Also, when we say “light”,\Nwe actually mean visible light,
Dialogue: 0,0:00:40.57,0:00:43.48,Default,,0000,0000,0000,,which is a tiny part of\Nthe electromagnetic spectrum,
Dialogue: 0,0:00:43.48,0:00:46.07,Default,,0000,0000,0000,,energy in form of\Nelectromagnetic radiation.
Dialogue: 0,0:00:46.39,0:00:48.65,Default,,0000,0000,0000,,Electromagnetic radiation consists of
Dialogue: 0,0:00:48.65,0:00:51.26,Default,,0000,0000,0000,,an enormous range of\Nwavelengths and frequencies.
Dialogue: 0,0:00:51.47,0:00:55.15,Default,,0000,0000,0000,,Gamma rays have the smallest wavelengths,\Nbecause they are highest-energy photons.
Dialogue: 0,0:00:55.45,0:00:58.30,Default,,0000,0000,0000,,But most gamma rays are\Njust under 10 picometers,
Dialogue: 0,0:00:58.30,0:01:00.75,Default,,0000,0000,0000,,which is still way smaller\Nthan a hydrogen atom.
Dialogue: 0,0:01:01.26,0:01:04.19,Default,,0000,0000,0000,,For reference, a hydrogen atom\Ncompared to a cent
Dialogue: 0,0:01:04.19,0:01:06.96,Default,,0000,0000,0000,,is about as big as a cent\Ncompared to the Moon.
Dialogue: 0,0:01:07.41,0:01:09.44,Default,,0000,0000,0000,,Visible light is in\Nthe middle of the spectrum,
Dialogue: 0,0:01:09.44,0:01:13.00,Default,,0000,0000,0000,,in the range of about\N400 nanometers to 700 nanometers,
Dialogue: 0,0:01:13.00,0:01:14.60,Default,,0000,0000,0000,,about the size of bacteria.
Dialogue: 0,0:01:15.40,0:01:19.91,Default,,0000,0000,0000,,On the other end of the spectrum, radio\Nwaves can be up to 100 km in diameter,
Dialogue: 0,0:01:19.91,0:01:22.09,Default,,0000,0000,0000,,while the biggest\Nwavelengths we know exist
Dialogue: 0,0:01:22.09,0:01:26.31,Default,,0000,0000,0000,,can span from 10,000 km\Nto a baffling 100,000 km—
Dialogue: 0,0:01:26.31,0:01:27.74,Default,,0000,0000,0000,,way larger than Earth!
Dialogue: 0,0:01:28.23,0:01:31.12,Default,,0000,0000,0000,,From a physics standpoint, all these\Ndifferent waves are the same—
Dialogue: 0,0:01:31.12,0:01:35.77,Default,,0000,0000,0000,,they all have the wave-particle duality\Nand travel at c, the speed of light,
Dialogue: 0,0:01:35.77,0:01:37.61,Default,,0000,0000,0000,,just at different frequencies.
Dialogue: 0,0:01:37.91,0:01:40.46,Default,,0000,0000,0000,,So what makes visible light special, then?
Dialogue: 0,0:01:40.60,0:01:42.41,Default,,0000,0000,0000,,Well… absolutely nothing.
Dialogue: 0,0:01:42.87,0:01:45.32,Default,,0000,0000,0000,,We just happen to have evolved\Neyes that are good at
Dialogue: 0,0:01:45.32,0:01:48.76,Default,,0000,0000,0000,,registering exactly this part\Nof the electromagnetic spectrum.
Dialogue: 0,0:01:49.12,0:01:51.78,Default,,0000,0000,0000,,This is not a complete\Ncoincidence, though;
Dialogue: 0,0:01:51.78,0:01:55.16,Default,,0000,0000,0000,,visible light is the only set of\Nelectromagnetic radiation
Dialogue: 0,0:01:55.16,0:01:56.92,Default,,0000,0000,0000,,that propagates well in water,
Dialogue: 0,0:01:56.92,0:02:00.98,Default,,0000,0000,0000,,which happens to be where most eyes\Nfirst evolved millions of years ago.
Dialogue: 0,0:02:01.51,0:02:04.81,Default,,0000,0000,0000,,That was a smart move, because\Nlight not only interacts with matter,
Dialogue: 0,0:02:04.81,0:02:07.23,Default,,0000,0000,0000,,it’s also altered by it and can be used
Dialogue: 0,0:02:07.23,0:02:09.46,Default,,0000,0000,0000,,to gather information\Nabout the world around us
Dialogue: 0,0:02:09.46,0:02:10.84,Default,,0000,0000,0000,,with almost no delay,
Dialogue: 0,0:02:10.84,0:02:14.10,Default,,0000,0000,0000,,which is arguably really\Nhelpful for survival.
Dialogue: 0,0:02:14.51,0:02:16.45,Default,,0000,0000,0000,,Okay, where does light come from?
Dialogue: 0,0:02:16.73,0:02:21.06,Default,,0000,0000,0000,,A vast range of electromagnetic waves\Nare created when atoms or molecules
Dialogue: 0,0:02:21.06,0:02:23.53,Default,,0000,0000,0000,,drop from a higher state of\Nenergy to a lower one.
Dialogue: 0,0:02:23.86,0:02:26.84,Default,,0000,0000,0000,,They lose energy and emit it\Nin the form of radiation.
Dialogue: 0,0:02:27.18,0:02:31.38,Default,,0000,0000,0000,,At the microscopic level, visible light is\Ncreated when an electron within an atom
Dialogue: 0,0:02:31.38,0:02:34.89,Default,,0000,0000,0000,,that is in an excited state drops\Nto a lower energy state
Dialogue: 0,0:02:34.89,0:02:36.98,Default,,0000,0000,0000,,and loses this excess energy.
Dialogue: 0,0:02:37.18,0:02:41.07,Default,,0000,0000,0000,,The same way, incoming light can elevate\Nan electron to a higher state of energy
Dialogue: 0,0:02:41.07,0:02:42.58,Default,,0000,0000,0000,,by being absorbed by it.
Dialogue: 0,0:02:42.100,0:02:45.48,Default,,0000,0000,0000,,Macroscopically, the moving charge\Nof the electron
Dialogue: 0,0:02:45.48,0:02:47.72,Default,,0000,0000,0000,,creates an oscillating magnetic field,
Dialogue: 0,0:02:47.72,0:02:50.83,Default,,0000,0000,0000,,which creates an oscillating electric\Nfield perpendicular to it.
Dialogue: 0,0:02:51.08,0:02:53.53,Default,,0000,0000,0000,,These two fields move\Nthemselves through space,
Dialogue: 0,0:02:53.53,0:02:55.97,Default,,0000,0000,0000,,transferring energy from\None place to another,
Dialogue: 0,0:02:55.97,0:02:59.30,Default,,0000,0000,0000,,carrying information about its\Nplace of creation with it.
Dialogue: 0,0:02:59.54,0:03:03.48,Default,,0000,0000,0000,,Why, of all the things in the universe, is\Nlight the fastest thing there is?
Dialogue: 0,0:03:03.91,0:03:05.04,Default,,0000,0000,0000,,Let’s change the question:
Dialogue: 0,0:03:05.04,0:03:08.08,Default,,0000,0000,0000,,what is the fastest way to travel\Nthrough space in the universe?
Dialogue: 0,0:03:08.31,0:03:16.16,Default,,0000,0000,0000,,It’s c, exactly 299,792,458 m/s\Nin a vacuum,
Dialogue: 0,0:03:16.16,0:03:18.62,Default,,0000,0000,0000,,one billion kilometers per hour.
Dialogue: 0,0:03:18.62,0:03:22.66,Default,,0000,0000,0000,,Electromagnetic radiation just\Nhappens to move this fast.
Dialogue: 0,0:03:22.66,0:03:27.81,Default,,0000,0000,0000,,Any particle that has no mass travels at\Nc, without acceleration or any in-between.
Dialogue: 0,0:03:28.15,0:03:29.84,Default,,0000,0000,0000,,The light that’s being\Nreleased from a candle
Dialogue: 0,0:03:29.84,0:03:32.35,Default,,0000,0000,0000,,does not speed up until\Nit reaches lightspeed;
Dialogue: 0,0:03:32.35,0:03:35.64,Default,,0000,0000,0000,,at the very instant of its creation,\Nits speed is c.
Dialogue: 0,0:03:36.04,0:03:39.56,Default,,0000,0000,0000,,So why is c, or the\Nspeed of light, finite, then?
Dialogue: 0,0:03:39.73,0:03:41.31,Default,,0000,0000,0000,,Well… nobody knows.
Dialogue: 0,0:03:41.46,0:03:43.40,Default,,0000,0000,0000,,Our universe is just built this way.
Dialogue: 0,0:03:43.40,0:03:45.01,Default,,0000,0000,0000,,We don’t have a smart answer here.
Dialogue: 0,0:03:45.32,0:03:47.11,Default,,0000,0000,0000,,So light is a part of a spectrum,
Dialogue: 0,0:03:47.11,0:03:49.95,Default,,0000,0000,0000,,an elementary particle that\Nalso behaves like a wave,
Dialogue: 0,0:03:49.95,0:03:52.19,Default,,0000,0000,0000,,propelled by two perpendicular fields
Dialogue: 0,0:03:52.19,0:03:54.65,Default,,0000,0000,0000,,traveling at the speed\Nlimit of the universe.
Dialogue: 0,0:03:55.12,0:03:57.68,Default,,0000,0000,0000,,Okay, that’s nice and all, but what\Nabout all the crazy stuff about
Dialogue: 0,0:03:57.68,0:04:00.02,Default,,0000,0000,0000,,traveling at the speed of light and time,
Dialogue: 0,0:04:00.02,0:04:02.93,Default,,0000,0000,0000,,the twin paradox, quantum stuff,\Nthings like that?
Dialogue: 0,0:04:03.41,0:04:05.39,Default,,0000,0000,0000,,We have to save them for another video.
Dialogue: 0,0:04:05.80,0:04:08.56,Default,,0000,0000,0000,,For now, let’s just be happy that we\Nevolved eyes that pick up
Dialogue: 0,0:04:08.56,0:04:10.98,Default,,0000,0000,0000,,waves of information\Npermeating the universe,
Dialogue: 0,0:04:10.98,0:04:15.34,Default,,0000,0000,0000,,making us see things that help us to put\Nour existence into perspective.