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What are the fundamental quantities, as far as we can tell, that really tell us something about the structure of nature? One would be the speed of light. Everything that is massless travels at the speed of light- at this speed, whatever it is. If you have any mass at all, you cannot travel, you cannot accelerate to this speed. Another one would be the strenght of the gravitional force. What is the force between two objects of a particular mass? Or in Einstein's theory, how does a particular amount of matter or energy distort the fabric of the universe? The number that tells you about that us Newton's gravitational constant, which was first measured back in the 1780's or 1790's. And then there's Plank's constant itself.

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What are the fundamental quantities / as far as we can tell / that really tell us something about the structure of nature? // One would be the speed of light. / Everything that is massless travels at the speed of light, / at this speed, whatever it is. // If you have any mass at all, / you cannot travel, / you cannot accelerate to this speed. // Another one would be the strength of the gravitational force. / What is the force between two objects of a particular mass? / Or in Einstein's theory, / how does a particular amount of matter or energy distort the fabric of the universe? // The number that tells you about that is Newton's gravitational constant, / which was first measured back in the 1780's, 1790's. // And then there's Planck's constant itself. //

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In 1900, Max Planck made a revolutionary proposal. You could say, for example, that there's a fundamental limit on how accurately we can know the position of a particle and the momentum of a particle. You can't know them both with absolute precision. There's a fundamental limit, and it's around about Planck's constant. Planck first introduced it in the context of the frequency or the wavelength of light emitted from hot objects. Photons- what's the energy of a photon? A packet of light: it's Planck's constant multiplied by the frequency. So those three things- speed of light, strength of gravity, and Planck's constant- allow you to define some distances, a particular distance called the Planck length.

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In 1900, Max Planck made a revolutionary proposal. // You could say, for example, / that there's a fundamental limit on how accurately we can know the position of a particle / and the momentum of a particle. / You can't know them both with absolute precision. // There's a fundamental limit, / and it's around about Planck's constant. // Planck first introduced it in the context of the frequency / or the wavelength of light emitted from hot objects. // Photons- what's the energy of a photon? / A packet of light: / It's Planck's constant multiplied by the frequency. // So those three things- speed of light, / strength of gravity, / and Planck's constant- allow you to define some distances, / a particular distance called the Planck length. //