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  • I'd like you all to close your eyes, please ...

  • and imagine yourself sitting in the middle of a large, open field

  • with the sun setting on your right.

  • And as the sun sets,

  • imagine that tonight you don't just see the stars appear,

  • but you're able to hear the stars appear

  • with the brightest stars being the loudest notes

  • and the hotter, bluer stars producing the higher-pitched notes.

  • (Music)

  • And since each constellation is made up of different types of stars,

  • they'll each produce their own unique melody,

  • such as Aries, the ram.

  • (Music)

  • Or Orion, the hunter.

  • (Music)

  • Or even Taurus, the bull.

  • (Music)

  • We live in a musical universe,

  • and we can use that to experience it from a new perspective,

  • and to share that perspective with a wider range of people.

  • Let me show you what I mean.

  • (Music ends)

  • Now, when I tell people I'm an astrophysicist,

  • they're usually pretty impressed.

  • And then I say I'm also a musician -- they're like, "Yeah, we know."

  • (Laughter)

  • So everyone seems to know

  • that there's this deep connection between music and astronomy.

  • And it's actually a very old idea;

  • it goes back over 2,000 years to Pythagoras.

  • You might remember Pythagoras from such theorems

  • as the Pythagorean theorem --

  • (Laughter)

  • And he said:

  • "There is geometry in the humming of the strings,

  • there is music in the spacing of the spheres."

  • And so he literally thought

  • that the motions of the planets along the celestial sphere

  • created harmonious music.

  • And if you asked him, "Why don't we hear anything?"

  • he'd say you can't hear it

  • because you don't know what it's like to not hear it;

  • you don't know what true silence is.

  • It's like how you have to wait for your power to go out

  • to hear how annoying your refrigerator was.

  • Maybe you buy that,

  • but not everybody else was buying it, including such names as Aristotle.

  • (Laughter)

  • Exact words.

  • (Laughter)

  • So I'll paraphrase his exact words.

  • He said it's a nice idea,

  • but if something as large and vast as the heavens themselves

  • were moving and making sounds,

  • it wouldn't just be audible,

  • it would be earth-shatteringly loud.

  • We exist, therefore there is no music of the spheres.

  • He also thought that the brain's only purpose was to cool down the blood,

  • so there's that ...

  • (Laughter)

  • But I'd like to show you that in some way they were actually both right.

  • And we're going to start by understanding what makes music musical.

  • It may sound like a silly question,

  • but have you ever wondered why it is

  • that certain notes, when played together, sound relatively pleasing or consonant,

  • such as these two --

  • (Music)

  • while others are a lot more tense or dissonant,

  • such as these two.

  • (Music)

  • Right?

  • Why is that? Why are there notes at all?

  • Why can you be in or out of tune?

  • Well, the answer to that question

  • was actually solved by Pythagoras himself.

  • Take a look at the string on the far left.

  • If you bow that string,

  • it will produce a note as it oscillates very fast back and forth.

  • (Musical note)

  • But now if you cut the string in half, you'll get two strings,

  • each oscillating twice as fast.

  • And that will produce a related note.

  • Or three times as fast,

  • or four times --

  • (Musical notes)

  • And so the secret to musical harmony really is simple ratios:

  • the simpler the ratio,

  • the more pleasing or consonant those two notes will sound together.

  • And the more complex the ratio, the more dissonant they will sound.

  • And it's this interplay between tension and release,

  • or consonance and dissonance,

  • that makes what we call music.

  • (Music)

  • (Music ends)

  • (Applause)

  • Thank you.

  • (Applause)

  • But there's more.

  • (Laughter)

  • So the two features of music we like to think of as pitch and rhythms,

  • they're actually two versions of the same thing,

  • and I can show you.

  • (Slow rhythm)

  • That's a rhythm right?

  • Watch what happens when we speed it up.

  • (Rhythm gets gradually faster)

  • (High pitch)

  • (Lowering pitch)

  • (Slow Rhythm)

  • So once a rhythm starts happening more than about 20 times per second,

  • your brain flips.

  • It stops hearing it as a rhythm and starts hearing it as a pitch.

  • So what does this have to do with astronomy?

  • Well, that's when we get to the TRAPPIST-1 system.

  • This is an exoplanetary system discovered last February of 2017,

  • and it got everyone excited

  • because it is seven Earth-sized planets all orbiting a very near red dwarf star.

  • And we think that three of the planets

  • have the right temperature for liquid water.

  • It's also so close that in the next few years,

  • we should be able to detect elements in their atmospheres

  • such as oxygen and methane -- potential signs of life.

  • But one thing about the TRAPPIST system is that it is tiny.

  • So here we have the orbits of the inner rocky planets

  • in our solar system:

  • Mercury, Venus, Earth and Mars,

  • and all seven Earth-sized planets of TRAPPIST-1

  • are tucked well inside the orbit of Mercury.

  • I have to expand this by 25 times

  • for you to see the orbits of the TRAPPIST-1 planets.

  • It's actually much more similar in size to our planet Jupiter and its moons,

  • even though it's seven Earth-size planets orbiting a star.

  • Another reason this got everyone excited was artist renderings like this.

  • You got some liquid water, some ice, maybe some land,

  • maybe you can go for a dive in this amazing orange sunset.

  • It got everyone excited,

  • and then a few months later, some other papers came out

  • that said, actually, it probably looks more like this.

  • (Laughter)

  • So there were signs

  • that some of the surfaces might actually be molten lava

  • and that there were very damaging X-rays coming from the central star --

  • X-rays that will sterilize the surface of life and even strip off atmospheres.

  • Luckily, just a few months ago in 2018,

  • some new papers came out with more refined measurements,

  • and they found actually it does look something like that.

  • (Laughter)

  • So we now know that several of them have huge supplies of water --

  • global oceans --

  • and several of them have thick atmospheres,

  • so it's the right place to look for potential life.

  • But there's something even more exciting about this system,

  • especially for me.

  • And that's that TRAPPIST-1 is a resonant chain.

  • And so that means for every two orbits of the outer planet,

  • the next one in orbits three times,

  • and the next one in four,

  • and then six, nine, 15 and 24.

  • So you see a lot of very simple ratios among the orbits of these planets.

  • Clearly, if you speed up their motion, you can get rhythms, right?

  • One beat, say, for every time a planet goes around.

  • But now we know if you speed that motion up even more,

  • you'll actually produce musical pitches,

  • and in this case alone,

  • those pitches will work together,

  • making harmonious, even human-like harmony.

  • So let's hear TRAPPIST-1.

  • The first thing you'll hear will be a note for every orbit of each planet,

  • and just keep in mind,

  • this music is coming from the system itself.

  • I'm not creating the pitches or rhythms,

  • I'm just bringing them into the human hearing range.

  • And after all seven planets have entered,

  • you're going to see --

  • well, you're going to hear a drum for every time two planets align.

  • That's when they kind of get close to each other

  • and give each other a gravitational tug.

  • (Tone)

  • (Two tones)

  • (Three tones)

  • (Four tones)

  • (Five tones)

  • (Six tones)

  • (Seven tones)

  • (Drum beats)

  • (Music ends)

  • And that's the sound of the star itself -- its light converted into sound.

  • So you may wonder how this is even possible.

  • And it's good to think of the analogy of an orchestra.

  • When everyone gets together to start playing in an orchestra,

  • they can't just dive into it, right?

  • They have to all get in tune;

  • they have to make sure

  • their instruments resonate with their neighbors' instruments,

  • and something very similar happened to TRAPPIST-1 early in its existence.

  • When the planets were first forming,

  • they were orbiting within a disc of gas,

  • and while inside that disc,

  • they can actually slide around

  • and adjust their orbits to their neighbors

  • until they're perfectly in tune.

  • And it's a good thing they did because this system is so compact --

  • a lot of mass in a tight space --

  • if every aspect of their orbits wasn't very finely tuned,

  • they would very quickly disrupt each other's orbits,

  • destroying the whole system.

  • So it's really music that is keeping this system alive --

  • and any of its potential inhabitants.

  • But what does our solar system sound like?

  • I hate to be the one to show you this, but it's not pretty.

  • (Laughter)

  • So for one thing,

  • our solar system is on a much, much larger scale,

  • and so to hear all eight planets,

  • we have to start with Neptune near the bottom of our hearing range,

  • and then Mercury's going to be all the way up

  • near the very top of our hearing range.

  • But also, since our planets are not very compact --

  • they're very spread out --

  • they didn't have to adjust their orbits to each other,

  • so they're kind of just all playing their own random note at random times.

  • So, I'm sorry, but here it is.

  • (Tone)

  • That's Neptune.

  • (Two tones)

  • Uranus.

  • (Three tones)

  • Saturn.

  • (Four tones)

  • Jupiter.

  • And then tucked in, that's Mars.

  • (Five tones)

  • (Six tones)

  • Earth.

  • (Seven tones)

  • Venus.

  • (Eight tones)

  • And that's Mercury --

  • OK, OK, I'll stop.

  • (Laughter)

  • So this was actually Kepler's dream.

  • Johannes Kepler is the person

  • that figured out the laws of planetary motion.

  • He was completely fascinated by this idea

  • that there's a connection between music, astronomy and geometry.

  • And so he actually spent an entire book

  • just searching for any kind of musical harmony amongst the solar system's planets

  • and it was really, really hard.

  • It would have been much easier had he lived on TRAPPIST-1,

  • or for that matter ...

  • K2-138.

  • This is a new system discovered in January of 2018

  • with five planets,

  • and just like TRAPPIST,

  • early on in their existence, they were all finely tuned.

  • They were actually tuned

  • into a tuning structure proposed by Pythagoras himself,

  • over 2,000 years before.

  • But the system's actually named after Kepler,

  • discovered by the Kepler space telescope.