A Window “Radically Different From All Previous Windows”

LIGO[Image: The corridors of LIGO, Louisiana, shaped like a “carpenter’s square”; via Google Earth].

It’s been really interesting for the last few weeks to watch as rumors and speculations about the first confirmed detection of gravitational waves have washed over the internet—primarily, at least from my perspective, because my wife, Nicola Twilley, who writes for The New Yorker, has been the only journalist given early access not just to the results but, more importantly, to the scientists behind the experiment, while writing an article that just went live over at The New Yorker.

It has been incredibly exciting to listen-in on partial conversations and snippets of overheard interviews in our home office here, as people like Kip Thorne, Rainer Weiss, and David Reitze, among a dozen others, all explained to her exactly how the gravitational waves were first detected and what it means for our future ability to study and understand the cosmos.

All this gloating as a proud husband aside, however, it’s a truly fascinating story and well worth mentioning here.

LIGO—the Laser Interferometer Gravitational-Wave Observatory—is a virtuoso act of precision construction: a pair of instruments, separated by thousands of miles, used to detect gravitational waves. They are shaped like “carpenter’s squares,” we read, and they stand in surreal, liminal landscapes: surrounded by water-logged swampland in Louisiana and “amid desert sagebrush, tumbleweed, and decommissioned reactors” in Hanford, Washington.

Ligo-Hanford [Image: LIGO, Hanford; via Google Earth].

Each consists of vast, seismically isolated corridors and finely calibrated super-mirrors between which lasers reflect in precise synchrony. These hallways are actually “so long—nearly two and a half miles—that they had to be raised a yard off the ground at each end, to keep them lying flat as Earth curved beneath them.”

To achieve the necessary precision of measurement, [Rainer Weiss, who first proposed the instrument’s construction] suggested using light as a ruler. He imagined putting a laser in the crook of the “L.” It would send a beam down the length of each tube, which a mirror at the other end would reflect back. The speed of light in a vacuum is constant, so as long as the tubes were cleared of air and other particles, the beams would recombine at the crook in synchrony—unless a gravitational wave happened to pass through. In that case, the distance between the mirrors and the laser would change slightly. Since one beam was now covering a shorter distance than its twin, they would no longer be in lockstep by the time they got back. The greater the mismatch, the stronger the wave. Such an instrument would need to be thousands of times more sensitive than any before it, and it would require delicate tuning, in order to extract a signal of vanishing weakness from the planet’s omnipresent din.

LIGO is the most sensitive instrument ever created by human beings, and its near-magical ability to pick up the tiniest tremor in the fabric of spacetime lends it a fantastical air that began to invade the team’s sleep. As Frederick Raab, director of the Hanford instrument, told Nicola, “When these people wake up in the middle of the night dreaming, they’re dreaming about the detector.”

Because of this hyper-sensitivity, its results need to be corrected against everything from minor earthquakes, windstorms, and passing truck traffic to “fluctuations in the power grid,” “distant lightning storms,” and even the howls of prowling wolves.

When the first positive signal came through, the team was actually worried it might not be a gravitational wave at all but “a very large lightning strike in Africa at about the same time.” (They checked; it wasn’t.)

Newton[Image: “Newton” (1795-c.1805) by William Blake, courtesy of the Tate].

The big deal amidst all this is that being able to study gravitational waves is very roughly analogous to the discovery of radio astronomy—where gravitational wave astronomy has the added benefit of opening up an entirely new spectrum of observation. Gravitational waves will let us “see” the fabric of spacetime in a way broadly similar to how we can “see” otherwise invisible radio emissions in deep space.

From The New Yorker:

Virtually all that is known about the universe has come to scientists by way of the electromagnetic spectrum. Four hundred years ago, Galileo began exploring the realm of visible light with his telescope. Since then, astronomers have pushed their instruments further. They have learned to see in radio waves and microwaves, in infrared and ultraviolet, in X-rays and gamma rays, revealing the birth of stars in the Carina Nebula and the eruption of geysers on Saturn’s eighth moon, pinpointing the center of the Milky Way and the locations of Earth-like planets around us. But more than ninety-five per cent of the universe remains imperceptible to traditional astronomy… “This is a completely new kind of telescope,” [David] Reitze said. “And that means we have an entirely new kind of astronomy to explore.”

Interestingly, in fact, my “seeing” metaphor, above, is misguided. As it happens, the gravitational waves studied by LIGO in its current state—ever-larger and more powerful new versions of the instrument are already being planned—“fall within the range of human hearing.”

If you want to hear spacetime, there is an embedded media player over at The New Yorker with a processed snippet of the “chirp” made by the incoming gravitational wave.

In any case, I’ve already gone on at great length, but the article ends with a truly fantastic quote from Kip Thorne. Thorne, of course, achieved minor celebrity last year when he consulted on the physics for Christopher Nolan’s relativistic time-travel film Interstellar, and he is not lacking for imagination.

Thorne compares LIGO to a window (and my inner H.P. Lovecraft reader shuddered at the ensuing metaphor):

“We are opening up a window on the universe so radically different from all previous windows that we are pretty ignorant about what’s going to come through,” Thorne said. “There are just bound to be big surprises.”

Go read the article in full!

Slingshots of the Oceanic

[Image: A diagram of the elaborate loops and ribbons of self-intersecting movement allowed by gravity-assisted travel, in this case heading toward a comet; original artist unknown].

Gravity-assisted space travel is when you use the gravitational pull of one planet or other celestial body as a fuel-efficient way to “slingshot” yourself toward another, more distant goal, someplace you could not have reached without assistance, either in terms of your velocity or even your basic direction.

You head toward one place to get to another—or “by indirections find directions out,” we might say.

These “gravity assists” can be pieced together to form almost a kind of invisible jungle gym, helping send probes into the outer solar system or even toward Mercury and the sun. As the Planetary Society explains:

Voyager 2 famously used gravity assists to visit Jupiter, Saturn, Uranus and Neptune in the late 1970s and 1980s. Cassini used two assists at Venus and one each at Earth and Jupiter in order to reach Saturn. New Horizons will arrive at Pluto in 2015 thanks to an assist at Jupiter. And Messenger used assists at Earth, Venus and three times at Mercury itself not to speed up, but to slow down enough to finally be captured by Mercury.

This can result in all sorts of insane weaving maneuvers, as objects can be made to loop stars, double back on themselves, veer off unpredictably, or even stop moving altogether, effectively parking themselves in space, as this GIF by David Shortt illustrates.

[Image: GIF by David Shortt, via The Planetary Society].

It’s like gravitational judo: using the speed and mass of your opponent as a counterbalance to perform something extraordinary yourself. Or perhaps it’s more like interplanetary spirography, where you could even loop-the-loop and slingshot your way between stars.

In any case, these types of assists can be made far more fuel-efficient—if not even possible in the first place—if you launch your journey at certain times rather than at others. In other words, you deliberately wait until the orbital cycles of Mars or Jupiter bring them near particular locations in space so that you can better use them to loop further outward toward, say, Neptune, a destination whose future position you will also have calculated in advance. If you want to use as little fuel and energy as possible, or even just to be as graceful as you can, you don’t just launch whenever you want and hope for the best.

The metaphoric potential of all this is obviously incredibly rich, but the real reason I’m writing this is because of a fascinating comment or two found in Brian Fagan’s book Beyond the Blue Horizon.

While discussing the human settlement of extremely remote islands in the South Pacific, what Fagan calls “remote Oceania,” he explains how ancient mariners relied on “seasonal winds” and celestial navigation to push “ever farther east” to the most extreme outer island edges of Polynesia. These seasonal winds formed part of what he calls “the Pacific’s waltz of atmosphere and ocean,” whereby known or predictable climatological events could be used to help propel people from one archipelago to another.

Here, Fagan writes that “[e]arly human settlement of the offshore Pacific revolved, in part, around enduring, large-scale meteorological phenomena that are still little understood. Ultimately, most of them depend on what one might call an elaborate, usually slow-moving waltz involving two partners—the atmosphere and the ocean.”

[Images: Polynesian “stick charts,” via The Nonist].

What fascinates me here is the idea that we can draw a rough analogy between Fagan’s “enduring, large-scale meteorological phenomena that are still little understood” and gravity-assisted space travel.

You can imagine, in other words, a well-organized group of extreme maritime navigators standing on the shores of a remote Pacific island chain, looking further out to sea together, knowing that there are distant land masses out there, implied by the winds and currents—but, more crucially, knowing that they will need a particular atmospheric event strong enough to take them there. They are thus timing their launch.

As people basically sat around waiting till the skies were right, Fagan’s “enduring, large-scale meteorological phenomena” would have produced amazing local mythologies of storms yet to come and other atmospheric folklore.

Like NASA scientists calculating the positions of Mars and Jupiter as they hoped to slingshot themselves beyond the black horizon of the solar system, these beach-going super-navigators would have known that the regional winds move in seven- or ten-year cycles, or even that a one-hundred year storm is required to bring them further out into the oceanic. They thus temporarily become land-based, settling there on a particular island chain and raising their children on tales of a journey yet to come. Navigators in waiting.

[Images: Polynesian “stick charts,” via The Nonist].

Imagine the diagrams or folklore that might have explained all this, like Arthur C. Clarke tales passed down family to family a thousand years ago on a windswept atoll—a science fiction not of interplanetary travel but a kind of anthropological Star Trek of outer-sea navigation.

Then the winds pick up, or strange Antarctic clouds begin to appear again for the first time in a generation, and everyone knows what it means: the signs are right and the skies are clicking back into place, and they start to build canoes, those little wooden space probes for pushing the limits of a maritime universe.

It’s just a different kind of slingshotting: not slingshotting yourself between planets using gravity, but slingshotting yourself from island chain to island chain, riding the long tail of predictable winds you know can’t last and that only appear once per generation. Those future storms will take you to distant archipelagoes where your descendants will have to wait another decade—or century or millennium—memorizing wind patterns and plotting their woven way through Fagan’s “slow-moving waltz” of rhythmic wind patterns and currents.