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Dark matter killed the dinosaurs, says a noted cosmologist

Harvard's theoretical physicist Lisa Randall links the extinction of the dinosaurs to the mysterious "dark matter".

Dark matter killed the dinosaurs, says a noted cosmologist
Small magnetic cloud with one half of a model of its dark matter (center). Credits: Dark matter, R. Caputo et al. 2016; background, Axel Mellinger, Central Michigan University


What killed the dinosaurs is a classic science mystery whose prevailing current solution is that a giant asteroid crashed in the Yucatan Peninsula in Mexico about 66 million years ago. It caused all manner of calamities, from tsunamis and volcanic eruptions to blocking out the sky with debris for a few years, bringing about a cold darkness on Earth that proved to be the demise of the dinosaurs.

Physicist Lisa Randall, who teaches at Harvard University, doesn’t necessarily dispute this turn of events. But she thinks the celestial object that did the dinosaurs in was possibly sent on its way by dark matter - an enigmatic and theoretical material that scientists theorize makes up about 27% of the known universe. Randall’s book “Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe” lays out her case.

What Randall proposes is that a part of dark matter (perhaps 5%) can experience a force similar to electromagnetism, which she calls “dark light”. By interacting with dark light, this portion of dark matter could have formed an invisible disk that overlapped with the visible disk of spiral arms in the Milky Way galaxy. And what’s more - this dark disk , which is thin and extremely dense, interfered with the orbit of a comet on the outer reaches of our solar system, in an area known as the Oort Cloud. This resulted in the comet ultimately colliding with Earth, bringing to extinction to its dinosaurs.

Other scientists have generally reacted to this hypothesis with curiosity, especially considering Randall’s track record in the field, saying the idea may be credible but lacks supporting evidence. Randall thinks that we could eventually locate such a disk and that the catapulting of the comets happens with some regularity so we might be in for it once again at some point.

You can read Lisa Randall and Matthew Reece’s study on the subject of dark matter triggering comet impacts here, in Physical Review Letters.

For more, check out Lisa Randall’s talk upon the release of her book on dark matter and dinosaurs: 

Cover Photo: 

PER NASA: The Small Magellanic Cloud (SMC), at center, is the second-largest satellite galaxy orbiting our own. This image superimposes a photograph of the SMC with one half of a model of its dark matter (right of center). Lighter colors indicate greater density and show a strong concentration toward the galaxy's center. Ninety-five percent of the dark matter is contained within a circle tracing the outer edge of the model shown. In six years of data, Fermi finds no indication of gamma rays from the SMC's dark matter. Credits: Dark matter, R. Caputo et al. 2016; background, Axel Mellinger, Central Michigan University

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Exactly why or even how quantum tunneling happens is unknown: Do particles just pop over to the other side instantaneously in the same way entangled particles interact? Or do they progressively tunnel through? Previous research has been conflicting.

That quantum tunneling occurs has not been a matter of debate since it was discovered in the 1920s. When IBM famously wrote their name on a nickel substrate using 35 xenon atoms, they used a scanning tunneling microscope to see what they were doing. And tunnel diodes are fast-switching semiconductors that derive their negative resistance from quantum tunneling.

Nonetheless, "Quantum tunneling is one of the most puzzling of quantum phenomena," says Aephraim Steinberg of the Quantum Information Science Program at Canadian Institute for Advanced Research in Toronto to Live Science. Speaking with Scientific American he explains, "It's as though the particle dug a tunnel under the hill and appeared on the other."

Steinberg is a co-author of a study just published in the journal Nature that presents a series of clever experiments that allowed researchers to measure the amount of time it takes tunneling particles to find their way through a barrier. "And it is fantastic that we're now able to actually study it in this way."

Frozen rubidium atoms

Image source: Viktoriia Debopre/Shutterstock/Big Think

One of the difficulties in ascertaining the time it takes for tunneling to occur is knowing precisely when it's begun and when it's finished. The authors of the new study solved this by devising a system based on particles' precession.

Subatomic particles all have magnetic qualities, and they spin, or "precess," like a top when they encounter an external magnetic field. With this in mind, the authors of the study decided to construct a barrier with a magnetic field, causing any particles passing through it to precess as they did so. They wouldn't precess before entering the field or after, so by observing and timing the duration of the particles' precession, the researchers could definitively identify the length of time it took them to tunnel through the barrier.

To construct their barrier, the scientists cooled about 8,000 rubidium atoms to a billionth of a degree above absolute zero. In this state, they form a Bose-Einstein condensate, AKA the fifth-known form of matter. When in this state, atoms slow down and can be clumped together rather than flying around independently at high speeds. (We've written before about a Bose-Einstein experiment in space.)

Using a laser, the researchers pusehd about 2,000 rubidium atoms together in a barrier about 1.3 micrometers thick, endowing it with a pseudo-magnetic field. Compared to a single rubidium atom, this is a very thick wall, comparable to a half a mile deep if you yourself were a foot thick.

With the wall prepared, a second laser nudged individual rubidium atoms toward it. Most of the atoms simply bounced off the barrier, but about 3% of them went right through as hoped. Precise measurement of their precession produced the result: It took them 0.61 milliseconds to get through.

Reactions to the study

Scientists not involved in the research find its results compelling.

"This is a beautiful experiment," according to Igor Litvinyuk of Griffith University in Australia. "Just to do it is a heroic effort." Drew Alton of Augustana University, in South Dakota tells Live Science, "The experiment is a breathtaking technical achievement."

What makes the researchers' results so exceptional is their unambiguity. Says Chad Orzel at Union College in New York, "Their experiment is ingeniously constructed to make it difficult to interpret as anything other than what they say." He calls the research, "one of the best examples you'll see of a thought experiment made real." Litvinyuk agrees: "I see no holes in this."

As for the researchers themselves, enhancements to their experimental apparatus are underway to help them learn more. "We're working on a new measurement where we make the barrier thicker," Steinberg said. In addition, there's also the interesting question of whether or not that 0.61-millisecond trip occurs at a steady rate: "It will be very interesting to see if the atoms' speed is constant or not."

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