Flanked by two powerful European nations, the English Channel has long been one of the world’s most important maritime passages.
Yet for most of its history, the channel’s rocky shores and stormy weather made crossing a dangerous prospect.
Engineers of the early 1800's proposed numerous plans for spanning the 33 kilometer gap.
Their designs included artificial islands linked by bridges, submerged tubes suspended from floating platforms, and an underwater passage more than twice the length of any existing tunnel.
By the end of the century, this last proposal had captured European imagination.
The invention of the tunnel boring machine and the discovery of a stable layer of chalk marl below the seabed made this fantastic tunnel more feasible.
But the project’s most urgent obstacles were ones no engineer could solve.
At the time, Britons viewed their geographic isolation as a strategic advantage, and fears about French invasion shut down plans for the tunnel.
The rise of aerial warfare rendered these worries obsolete, but new economic concerns arose to replace them.
Finally, 100 years after the initial excavation, the two countries reached an agreement— the tunnel would proceed with private funding.
In 1985, a group of French and British companies invested the modern equivalent of 14 billion pounds, making the tunnel the most expensive infrastructure project to date.
The design called for three separate tunnels— one for trains to France, one for trains to England, and one service tunnel between them.
Alongside crossover chambers, emergency passages, and air ducts, this amounted to over 200 kilometers of tunnels.
In 1988, workers began excavating from both sides, planning to meet in the middle.
Early surveys of the French coast revealed the site was full of fault lines.
These small cracks let water seep into the rock, so engineers had to develop waterproof boring machines.
The British anticipated drier conditions, and forged ahead with regular borers.
But only months into the work, water flooded in through undetected fissures.
To drill in this wet chalk, the British had to use grout to seal the cracks created in the borer’s wake, and even work ahead of the main borer to reinforce the chalk about to be drilled.
With these obstacles behind them, both teams began drilling at full speed.
Boring machines weighing up to 1,300 tons drilled at nearly 3.5 meters per hour.
As they dug, they installed lining rings to stabilize the tunnel behind them, making way for support wagons following each machine.
Even at top speed, work had to proceed carefully.
The chalk layer followed a winding path between unstable rock and clay, punctured by over 100 boring holes made by previous surveyors.
Furthermore, both teams had to constantly check their coordinates to ensure they were on track to meet within 2 centimeters of each other.
To maintain this delicate trajectory, the borers employed satellite positioning systems, as well as paleontologists who used excavated fossils to confirm they were at the right depth.
During construction, the project employed over 13,000 people and cost the lives of ten workers.
But after two and a half years of tunneling, the two sides finally made contact.
British worker Graham Fagg emerged on the French side, becoming the first human to cross the channel by land since the Ice Age.
There was still work to be done— from installing crossover chambers and pumping stations, to laying over a hundred miles of tracks, cables, and sensors.
But on May 6, 1994, an opening ceremony marked the tunnel’s completion.
Full public service began 16 months later, with trains for passengers and rail shuttles for cars and trucks.
Today, the Channel Tunnel services over 20 million passengers a year, transporting riders across the channel in just 35 minutes.
Unfortunately, not everyone has the privilege of making this trip legally.
Thousands of refugees have tried to enter Britain through the tunnel in sometimes fatal attempts.
These tragedies have transformed the tunnel’s southern entrance into an ongoing site of conflict.
Hopefully, the structure’s history can serve as a reminder that humanity is at their best when breaking down barriers.
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.
And so, in the last few billion years, they've actually lost their tuning, quite a bit more than TRAPPIST has, and so what we're going to do is go back in time and imagine what they would've sounded like just as they were forming.
(Music) (Music ends) (Applause) Thank you.
Now, you may be wondering: How far does this go?
How much music actually is out there?
And that's what I was wondering last fall when I was working at U of T's planetarium, and I was contacted by an artist named Robyn Rennie and her daughter Erin.
Robyn loves the night sky, but she hasn't been able to fully see it for 13 years because of vision loss.
And so they wondered if there was anything I could do.
So I collected all the sounds I could think of from the universe and packaged them into what became "Our Musical Universe."
This is a sound-based planetarium show exploring the rhythm and harmony of the cosmos.
And Robyn was so moved by this presentation that when she went home, she painted this gorgeous representation of her experience.
And then I defaced it by putting Jupiter on it for the poster.
(Laughter) So ...
in this show, I take people of all vision levels and bring them on an audio tour of the universe, from the night sky all the way out to the edge of the observable universe.
But even this is just the start of a musical odyssey to experience the universe with new eyes and with new ears, and I hope you'll join me.
Thank you.
(Applause)