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  • Light, is the connection between us and the universe.

  • Through light, we could experience distant stars and look back at the beginning of existence itself.

  • But, what is light?

  • In a nutshell, light, is the smallest quantity of energy that can be transported.

  • A photon, an elementary particle without a real size that can't be split, only created or destroyed.

  • Light also has a wave-particle duality, being kind of a particle and a wave at the same time (although this is a lie).

  • Also when we say light, we actually mean visible light which is a tiny part of the electromagnetic spectrum: Energy in form of electromagnetic radiation.

  • Electromagnetic radiation consist of an enormous range of wavelengths and frequencies.

  • Gamma rays have the smallest wave lengths because they are the highest energy photons.

  • But most gamma rays are just under ten picometers, which is still way smaller than a hydrogen atom.

  • For reference, a hydrogen atom compared to a cent is about as big as a cent compared to the Moon.

  • Visible light is in the middle of the spectrum in a range of about 400 nanometers to 700 nanometers: about the size of a bacteria.

  • On the other end of the spectrum, radio waves can be up to 100 kilometers in diameter.

  • While the biggest wave lengths we know exist can span from 10,000 kilometers to a baffling 100,000 kilometers, way larger than Earth.

  • From a physics stand point, all these different waves are the same.

  • They all have the wave-particle duality and travel at 'c', the speed of light, just at different frequencies.

  • So what makes visible light special, then?

  • Well... Absolutly nothing.

  • We just happen to have evolved eyes, that are good at registering exactly this part of the electromagnetic spectrum.

  • This is not a complete coincidence though.

  • Visible light is the only set of electromagnetic radiation that propagates when in water, which happens to be where most eyes first evolved, millions of years ago.

  • That was a smart move, because light not only interacts with matter, it's also altered by it and can be used to gather information about the world around us, with almost no delay.

  • Which is arguably really helpful for survival.

  • Okay, where does light come from?

  • A vast range of electromagnetic waves are created when atoms or molecules drop from a higher state of energy to a lower one.

  • They lose energy and emit it in the form of radiation.

  • At the microscopic level, visible light is created when an electron within an atom that is in an excited state drops to a lower energy state and loses this excess energy.

  • The same way, incoming light can elevate an electron to a higher state of energy by being absorbed by it.

  • Macroscopically, the moving charge of the electron creates an oscillating magnetic field, which creates an oscillating electric field perpendicular to it.

  • These two fields move themselves through space, transferring energy from one place to another, carrying information about its place of creation with it.

  • Why of all the things in the universe is light the fastest thing there is?

  • Let's change the question: What is the fastest way to travel through space in the universe?

  • It's c, exactly two hundred ninety-nine million, seven hundred ninety-two thousand, four hundred and fifty-eight metres per second in a vacuum, one billion kilometres per hour.

  • Electromagnetic radiation just happens to move this fast.

  • Any particle that has no mass travels at c, without acceleration or any in between.

  • The light that has been released from a candle does not speed up until it reaches light speed, at the very instant of its creation, its speed is c.

  • So why is c, the speed of light, finite then?

  • Well, nobody knows.

  • Our universe is just built this way.

  • We don't have the smart answer here.

  • So light is part of a spectrum, an elementary particle that also behaves like a wave, propelled by two perpendicular fields, travelling at the speed limit of the universe.

  • Okay, that's nice and all, but what about the crazy stuff about travelling at the speed of light, and time, the twin paradox, quantum stuff, and things like that?

  • We have to save them for another video.

  • For now, let's just be happy that we've evolved eyes that pick up waves of information permeating the universe.

  • Making us see things and put our existence into perspective.

Light, is the connection between us and the universe.

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