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  • Where does all this stuff come from?

  • This rock?

  • That cow?

  • Your heart?

  • Not the things themselves, mind you, but what they're made of:

  • the atoms that are the fabric of all things.

  • To answer that question, we look to the law of conservation of mass.

  • This law says take an isolated system

  • defined by a boundary that matter and energy cannot cross.

  • Inside this system, mass, a.k.a. matter and energy,

  • can neither be created nor destroyed.

  • The universe, to the best of our knowledge,

  • is an isolated system.

  • But before we get to that, let's look at a much smaller and simpler one.

  • Here we have six carbon atoms, 12 hydrogen atoms,

  • and 18 oxygen atoms.

  • With a little energy, our molecules can really get moving.

  • These atoms can bond together to form familiar molecules.

  • Here's water,

  • and here's carbon dioxide.

  • We can't create or destroy mass.

  • We're stuck with what we've got, so what can we do?

  • Ah, they have a mind of their own.

  • Let's see. They've formed more carbon dioxide and water, six of each.

  • Add a little energy, and we can get them to reshuffle themselves to a simple sugar,

  • and some oxygen gas.

  • Our atoms are all accounted for: 6 carbon, 12 hydrogen, and 18 oxygen.

  • The energy we applied is now stored in the bonds between atoms.

  • We can rerelease that energy

  • by breaking that sugar back into water and carbon dioxide,

  • and still, same atoms.

  • Let's put a few of our atoms aside and try something a little more explosive.

  • This here is methane, most commonly associated with cow flatulence,

  • but also used for rocket fuel.

  • If we add some oxygen and a little bit of energy,

  • like you might get from a lit match,

  • it combusts into carbon dioxide, water and even more energy.

  • Notice our methane started with four hydrogen,

  • and at the end we still have four hydrogen captured in two water molecules.

  • For a grand finale, here's propane, another combustible gas.

  • We add oxygen, light it up, and boom.

  • More water and carbon dioxide.

  • This time we get three CO2s

  • because the propane molecule started with three carbon atoms,

  • and they have nowhere else to go.

  • There are many other reactions we can model with this small set of atoms,

  • and the law of conservation of mass always holds true.

  • Whatever matter and energy go into a chemical reaction

  • are present and accounted for when it's complete.

  • So if mass can't be created or destroyed,

  • where did these atoms come from in the first place?

  • Let's turn back the clock and see.

  • Further, further, further, too far.

  • Okay, there it is.

  • The Big Bang.

  • Our hydrogen formed from a high-energy soup of particles

  • in the three minutes that followed the birth of our universe.

  • Eventually, clusters of atoms accumulated and formed stars.

  • Within these stars, nuclear reactions fused light elements,

  • such as hydrogen and helium,

  • to form heavier elements, such as carbon and oxygen.

  • At first glance, these reactions may look like they're breaking the law

  • because they release an astounding amount of energy,

  • seemingly out of nowhere.

  • However, thanks to Einstein's famous equation,

  • we know that energy is equivalent to mass.

  • It turns out that the total mass of the starting atoms

  • is very slightly more than the mass of the products,

  • and that loss of mass perfectly corresponds to the gain in energy,

  • which radiates out from the star as light, heat and energetic particles.

  • Eventually, this star went supernova

  • and scattered its elements across space.

  • Long story short, they found each other and atoms from other supernovas,

  • formed the Earth,

  • and 4.6 billion years later got scooped up to play their parts

  • in our little isolated system.

  • But they're not nearly as interesting as the atoms that came together to form you,

  • or that cow,

  • or this rock.

  • And that is why, as Carl Sagan famously told us,

  • we are all made of star stuff.

Where does all this stuff come from?

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B1 US TED-Ed energy carbon hydrogen carbon dioxide dioxide

【TED-Ed】The law of conservation of mass - Todd Ramsey

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    稲葉白兎 posted on 2015/03/07
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