Leading Harvard physicist has a radical new theory for why humans exist

Stephanie Mitchell/Harvard Staff Photographer Lisa Randall.

Where do we come from? There are many right answers to this question, and the one you get often depends on who you ask.

For example, 

• an astrophysicist might say that the chemical components of our bodies were first forged in the nuclear fires of stars.
• On the other hand, an evolutionary biologist might look at the similarities between our DNA and that of other primates' and conclude we evolved from apes.
• Lisa Randall, a theoretical physicist at Harvard University, has a different, and novel answer, which she describes in her latest book, "Dark Matter and the Dinosaurs."

Randall has written other popular science books, including the New York Times bestseller "Warped Passages: Unraveling the Mysteries of the Universe's Hidden Dimensions." Her studies at Harvard explore theoretical particle physics and cosmology.

In her latest book, she posits that the extinction of the dinosaurs — necessary for the emergence of humans — is linked to dark matter. Dark matter is the mysterious, invisible matter that astronomers estimate makes up 85% of all matter in our universe.

One species' extinction is another's head start

Thomson Reuters

Paleontologists largely agree that about 66 million years ago a giant, 9-mile-long celestial body — likely a comet — struck Earth. The impact wiped out 75% of species across the planet, including most of the dinosaurs.

Among the survivors were small primates. Over the next 66 million years these primates diversified, grew larger, learned to walk on two legs, and developed large brains, which they eventually used to invent pizza delivery.

So what caused that giant space rock to collide with our planet in the first place and give primates a chance to thrive?

It could just be chance — or luck, depending on your perspective — but Randall would disagree with both of these ideas.

Business Insider

In her book, Randall describes a dark, pancake-shaped patty of densely packed dark matter within our galaxy that could be responsible for our emergence as a species.

Dark matter has never been directly detected. However, there is enough evidence for its immense gravitational influence on our universe that the vast majority of the scientific community agrees that dark matter is a form of mysterious matter that we can neither see or touch, but that nevertheless must permeate the cosmos.

Generally, dark matter tends to be concentrated in large halos around galaxies like giant bubbles. But Randall thinks that there could also be a so-called dark disc amid the stars, planets, and gas clouds in our galaxy.

Beware the dark disc

If there is dark matter in Randall's hypothetical disc, then it stands to reason that the disc has a powerful gravitational influence on the objects around it — including our solar system.

But our solar system is not always near the disc, which is the crux of Randall's theory.

As the solar system revolves around the center of the Milky Way — the same way Earth revolves around the sun — it moves up and down, or oscillates, through the plane of our galaxy. And the rate of this oscillation is very intriguing.

Below is an illustration of our solar system's oscillation, where the orange dot in the lower left rectangle is our sun and the black line at the center is the dark disc:

APS/Alan Stonebraker

A team of astronomers made a rough estimate of this oscillation rate near the turn of this century, calculating that our solar system passes through the plane of the Milky Way about once every 32 million years, which means if there's a dark disc, we pass through that at the same rate.

Interestingly, there's evidence to suggest that mass extinctions in Earth's past happened within this time frame, or about once every 25 to 35 million years.

It's this similarity between the mass-extinction rate and the rate of our solar system's oscillation through the galaxy that made Randall and her Harvard colleague Matthew Reece first suggest the link in a scientific paper published in the journal Physical Review Letters last year, and that Randall explores more in her book.

Randall hypothesizes that when we're passing through the dark disc, the gravity from the dark matter within influences the outer region of our solar system, called the Oort cloud.

The Oort cloud, illustrated below just right of center, sits between roughly 1,000 to 100,000 Astronomical Units (90 billion to 9 trillion miles) from the sun and is thought to contain billions of icy objects at least 12 miles wide.

Uploaded by WolfmanSF to Wikipedia

If something 12 miles wide hit Earth today, it would mean the end of life as we know it. And Randall thinks that's exactly what happened to the dinosaurs 66 million years ago that opened the door for widespread primate evolution.

Prove it

NASA Goddard Spaceflight Center Dark matter is illustrated here as the fog between galaxies.

While it's impossible to wind back the clock, proving the existence of the dark disc would greatly advance Randall's theory.

She's tried to do so by looking at the speed and direction of stars in our galaxy. If stars moved in ways that couldn't be explained by the amount of ordinary, visible matter around them, then it could suggest the presence of the dark disc.

But that's a very tall order. There are about 100 billion stars in the Milky Way, and hunting dark matter is notoriously tricky.

We have a dozen or so functioning detectors underground, on Earth's surface, and in space — and none of them has yet managed to sniff out a dark-matter particle. If they do, it would be a significant step toward supporting Randall's hypothesis.

In her concluding remarks, Randall writes:

"In some global sense, we are all descendants of Chicxulub [the town where the dinosaur-killing meteor impacted]. It's a part of our history that we should want to understand. If true, the additional wrinkle presented in this book would mean that not only was dark matter responsible for irrevocably changing our world, but also that some of it played a crucial role in allowing our existence." 

ORIGINAL: Business Insider 

By Jessica Orwig

14.11.2015

Here’s What Really Killed the Dinosaurs

Portrait of a killer: volcanoes were no friend to the dinos
Sebastian Crespo Photography; Getty Images/Flickr RF

It wasn't just an asteroid

At the start of the 1980s, the question of what forced dinosaurs and huge numbers of other creatures to become extinct 65 million years ago was still a mystery. By the decade’s end, that mystery was solved: a comet or asteroid had slammed into Earth, throwing so much sun-blocking dust into the air that the planet plunged into a deep-freeze. The discovery of a massive impact crater off the coast of Mexico, of just the right age, pretty much sealed the deal in most scientists’ minds.

But a second global-scale catastrophe was happening at much the same time: a series of ongoing volcanic eruptions that dwarf anything humans have ever seen. They were so unimaginably powerful that they left nearly 200,000 square miles (518,000 sq. km) of what’s now India buried in volcanic basalt up to a mile and a half thick. And the gases and particulate matter spewed out by those eruptions, argue at least some scientists, could have played a big role in the dinosaurs’ doom as well.

How big a role, however, depends on exactly when the eruptions began and how long they lasted, and a new report in Science goes a long way toward answering that question. “We can now say with confidence,” says Blair Schoene, a Princeton geologist and lead author of the paper, “that the eruptions started 250,000 years before the extinction event, and lasted for a total of 750,000 years.” And that, he says, strengthens the idea that the eruptions could have contributed to the mass extinction of multiple species.

Schoene and his co-authors don’t claim volcanoes alone wiped out the dinosaurs; only that they changed the climate enough to put ecosystems under stress, setting them up for the final blow. “We don’t know the exact mechanism,” he admits. Volcanoes emit carbon dioxide, which could have triggered an intense burst of global warming, but they also emit sulfur dioxide, which could have caused global cooling. “What we do know,” Schoene says, “is that earlier mass extinctions were caused by volcanic eruptions alone.” The new dates, he and his co-authors believe, will help scientists understand what role these volcanoes played in the dinosaurs’ demise.

If there was such a role, that is, and despite this new analysis, plenty of paleontologists still doubt it seriously. The dating of the eruptions, based on widely accepted uranium-lead measurement techniques, is not an issue, says Brian Huber, of the Smithsonian Institution. “That part of the science is great,” he says. “It moves things forward.”

But the link between eruptions and the disappearance of species, he thinks, is invalid. “The case of the mass extinctions being caused by an impact is overwhelming,” says Huber. “One of the wonderful things about these arguments is that they’ve forced us to look really carefully at the fossil evidence, on land and at sea. We’ve accumulated a really detailed data set.”

And those data, Huber says, make it clear that the extinction rate for the 250,000 years leading up to the asteroid impact wasn’t especially large. Then, at the time of the impact: whammo. The idea that volcanoes played a significant role in this extinction event keeps coming up every so often, and in Huber’s view, “the argument has gotten very tiresome. I no longer feel the need to put any energy into it. It’s from a minority arguing against overwhelming evidence.”

For onlookers, that might seem harsh—not to mention overconfident. Sometimes a vocal scientific minority turns out to be right in its challenge to the scientific mainstream, as when Alfred Wegener argued, to much ridicule, that continents move around the Earth. And sometimes it’s dead wrong—Sir Fred Hoyle’s futile campaign against the Big Bang theory, for example.

In both cases, however, it was the accumulation of evidence that ultimately vindicated one argument and torpedoed the other. So far, the volcanic impact people have most of the torpedoes on their side.

ORIGINAL: Time

Michael D. Lemonick @MLemonick 

Dec. 11, 2014