Space Grain

[Image: A micrometeorite, photographed by Donald Brownlee, University of Washington].

A paper published last month in Geology reported “the discovery of significant numbers (500) of large micrometeorites (>100 μm) from rooftops in urban areas”—or “cosmic dust grains,” in the words of New Scientist, that have been “found on city rooftops for the first time.”

Although the samples were “collected primarily from roof gutters in Norway,” according to the original paper, their presence there “demonstrates that, contrary to current belief, micrometeorites can be collected from urban environments.” That is, the dust of ruined cosmic objects can be found intermixed with autumn leaves, cigarette butts, and brake pad dust, perhaps even accumulating on your bedroom window sill.

[Image: Gorgeous photograph of a micrometeorite by Matej Pašák].

Of course, it has long been possible to sample urban areas for micrometeorites, so this is not entirely new.

What’s fascinating, nonetheless, is that these micrometeorites are most likely to have arrived on Earth within the past six years, the study points out, but their size is notably larger than the average sample of micrometeorites from the recent geological record, indicating “variations in the extraterrestrial dust flux” on the scale of 800,000 years.

As New Scientist points out, this means that larger cosmic shifts can be deduced from the size and shape of these grains:

The differences [in size] may be linked to changes in the orbits of planets such as the Earth and Mars over millions of years, [researcher Matthew Genge] says. Resulting gravitational disturbances may have influenced the trajectory of the particles as they hurtled through space. This in turn would have an effect on the speed at which they slam into the Earth’s atmosphere and heat up.

“This find is important because if we are to look at fossil cosmic dust collected from ancient rocks to reconstruct a geological history of our solar system, then we need to understand how this dust is changed by the continuous pull of the planets,” Genge says.

Something’s changing in our local cosmic-dust environment, in other words, and evidence of this shift is slowly collecting on our roofs and sidewalks, accumulating in our gutters and sills.

(Conceptually related: War Sand).

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!