5 Things We Know About Gravitational Waves—And 2 That Are a Mystery

An illustration showing the merger of two black holes and the gravitational waves that ripple outward as the black holes spiral toward each other.
An illustration showing the merger of two black holes and the gravitational waves that ripple outward as the black holes spiral toward each other.
LIGO/T. Pyle

Gravitational waves, first detected in fall 2015 and then again a few months later, are making headlines this week following the detection of a third pair of colliding black holes. This particular duo is located a whopping 3 billion light years from Earth, making it the most distant source of gravitational waves discovered so far.

The signal from this latest black hole merger tripped the detectors at the twin LIGO facilities on January 4 of this year (the acronym stands for Laser Interferometer Gravitational-wave Observatory). The newly created black hole—the result of this latest cosmic collision—weighs in at about 49 times the mass of the Sun, putting it in-between the two earlier black hole collisions that LIGO recorded, in terms of size. There’s now ample evidence that black holes can weigh more than 20 solar masses—a finding that challenges the traditional understanding of black hole formation. “These are objects we didn’t know existed before LIGO detected them,” David Shoemaker, an MIT physicist and spokesperson for the LIGO collaboration, said in a statement.

Gravitational waves are shaping up to be the hot new astronomical tool of the 21st century, offering glimpses into the universe’s darkest corners and providing insights into the workings of the cosmos that we can’t get by any other means. Here, then, are five things we know about these cosmic ripples, and a couple more things that we haven’t quite figured out yet:

1. THEY'D HAVE MADE EINSTEIN SMILE.

We knew, or at least strongly suspected, that gravitational waves existed long before their discovery in 2015. They were predicted by Einstein’s theory of gravity, known as general relativity, published just over 100 years ago. The first black hole mergers observed by LIGO produced tell-tale cosmic signatures that meshed perfectly with what Einstein’s theory predicted. But the black hole collision announced this week may yield yet another feather for Einstein’s cap. It involves something called “dispersion.” When waves of different wavelengths pass through a physical medium—like light passing through glass, for example—the rays of light diverge (this is the how a prism creates a rainbow). But Einstein’s theory says gravitational waves ought to be immune to this sort of dispersion—and this is exactly what the observations suggest, with this latest black hole merger providing the strongest confirmation so far. (This Einstein fellow was pretty bright!)

2. THEY'RE RIPPLES IN THE FABRIC OF SPACE-TIME.

According to Einstein’s theory, whenever a massive object is accelerated, it creates ripples in space-time. Typically, these cosmic disturbances are too small to notice; but when the objects are massive enough—a pair of colliding black holes, for example—then the signal may be large enough to trigger a “blip” at the LIGO detectors, the pair of gravitational wave laboratories located in Louisiana and in Washington state. Even with colliding black holes, however, the ripples are mind-bogglingly small: When a gravitational wave passes by, each 2.5-mile-long arm of the L-shaped LIGO detectors gets stretched and squeezed by a distance equivalent to just 1/1000th of the width of a proton.

3. THEY LET US "LISTEN" TO THE UNIVERSE.

At least in a figurative sense, gravitational waves let us “listen in” on some of the universe’s most violent happenings. In fact, the way that gravitational waves work is closely analogous to sound waves or water waves. In each case, you have a disturbance in a particular medium that causes waves to spread outward, in ever-increasing circles. (Sound waves are a disturbance in the air; water waves are a disturbance in water—and in the case of gravitational waves, it’s a disturbance in the fabric of space itself.) To “hear” gravitational waves, you just have to convert the signals received by LIGO into sound waves. So what do we actually hear? In the case of colliding black holes, it’s something like a cosmic “chirp”—a kind of whooping sound that progresses quickly from low pitch to high.

4. THEY'VE SHOWN US THAT YOU REALLY DON'T WANT TO GET TOO CLOSE TO A PAIR OF COLLIDING BLACK HOLES.

Thanks to gravitational waves, we’re learning a lot about that most mysterious of objects, the black hole. When two black holes collide, they form an even bigger black hole—but not quite as large as you’d expect from simply adding up the masses of the two original black holes. That’s because some of the mass gets converted into energy, via Einstein’s famous equation, E=mc2. The magnitude of the explosion is truly staggering.

As astronomer Duncan Brown told Mental Floss last June: “When a nuclear bomb explodes, you’re converting about a gram of matter—about the weight of a thumb-tack—into energy. Here, you’re converting the equivalent of the mass of the Sun into energy, in a tiny fraction of a second.” The blast could produce more energy than all the stars in the universe—for a split-second.

5. THEY MIGHT BE POWERFUL ENOUGH TO KICK A BLACK HOLE OUT OF A GALAXY.

This spring, astronomers discovered a “rogue” black hole moving speedily away from a distant galaxy known as 3C186, located some 8 billion light years from Earth. The black hole is believed to weigh as much as 1 billion Suns—which means it must have received quite a kick, to set it in motion (its speed was determined to be around 5 million miles per hour, or a bit less than 1 percent of the speed of light). Astronomers have suggested that the necessary energy may have come from gravitational waves produced by a pair of very heavy black holes that collided near the galaxy’s center.

But there’s still plenty we’d like to know about gravitational waves—and about the objects they let us probe. For example …

6. WE DON'T KNOW IF GRAVITATIONAL WAVES CONTRIBUTE TO "DARK MATTER."

Most of the mass of the universe—about 85 percent—is stuff we can’t see; astronomers call this unseen material “dark matter.” Exactly what this dark stuff is has been the subject of intense debate for decades. The leading theory is that dark matter is made up of exotic particles created soon after the big bang. But some physicists have speculated that so-called “primordial black holes”—black holes created in the first second of the universe’s existence—might make up a significant fraction of the mysterious dark matter. The theorists who back this idea say that it could help to explain the unusually high masses of the black hole binary systems that LIGO has detected so far.

7. WE DON'T KNOW IF THEY ARE EVIDENCE OF DIMENSIONS BEYOND THE ONES WE PERCEIVE.

Particle physicists and cosmologists have long speculated about the existence of “extra dimensions” beyond the four we experience (three for space and one for time). It was hoped that experiments at the Large Hadron Collider would offer hints of these dimensions, but no such evidence has turned up so far. Some physicists, however, suggest that gravitational waves might provide a clue. They speculate that gravity could freely spread out over all of the dimensions, perhaps explaining why gravity is such a weak force (it’s by far the weakest of the four known forces in nature). Further, they say that the existence of extra dimensions would leave their mark on the gravitational waves that we measure here on Earth. So, stay tuned: It’s only been a bit more than a year since we first detected gravitational waves; no doubt they have much more to tell us about our universe.

Being Surrounded By Greenery Can Be Good for Your Heart

iStock.com/Givaga
iStock.com/Givaga

Living in a place with a little greenery is good for your health in more ways than one. Recent research has found that people perceive their health status as significantly better if they live around trees, and for good reason—in addition to helping you chill out, exposure to lots of green vegetation may be good for your cardiovascular health, as Cardiovascular Business reports.

A new study in the Journal of the American Heart Association suggests that living in green areas is correlated with certain biomarkers for cardiovascular health. Scientists analyzed blood and urine samples from 408 people at a cardiology clinic, then compared the results to satellite-derived data on the levels of greenery around those patients’ homes (using 820-foot and half-mile radiuses).

Adjusting for age, sex, race, smoking status, “neighborhood deprivation” and other factors known to be linked heart disease rates, the researchers found that living in a green area was correlated with several markers of a healthy heart. Blood and urine samples from those participants who lived in green neighborhoods showed lower levels of sympathetic activation—the body’s automatic fight-or-flight response, which raises the heart rate and is involved in heart failure. Those participants also had reduced oxidative stress—an imbalance between free radicals and antioxidants in the body, which can cause tissue damage and is linked to chronic disease. And they had higher angiogenic capacity, which refers to the body’s ability to form new blood vessels.

All this suggests that being around trees is somehow linked to having a healthier heart, though these are just biomarkers, not rates of heart disease or major cardiac events. But while scientists have yet to prove directly that being around trees causes your heart to be healthier, it’s not the first study to suggest a link. In 2015, a study of American women found that rates of heart disease went up in certain areas after a beetle invasion killed off a significant number of trees. Other studies have suggested that being around trees can reduce stress, which in itself may affect your risk of heart disease. Luckily, whether it qualifies as heart medicine or not, spending more time hanging out under trees couldn’t hurt.

[h/t Cardiovascular Business]

14 Facts About Feet

iStock/pepifoto
iStock/pepifoto

The foot is one of the most overworked, under-appreciated parts of the human body. Think about it: In a single day, the average person takes 8000 to 10,000 steps. That works out to be four trips around the world over a lifetime, putting a lot of wear and tear on your intricate foot bones. The foot may be humble, but its design is essential to how we walk upright, and hoofing it on two feet is a defining feature of humanity. Here are some fun—and a few funky—facts about the human foot.

1. FOOT BONES MAKE UP ABOUT A QUARTER OF ALL THE BONES IN OUR BODIES.

There are 26 foot bones in each of your feet—one less than in each hand. When we’re born, those foot bones are mostly cartilage. They only completely harden around age 21.

2. HUMANS HAVE WORN SHOES FOR A VERY LONG TIME.

When did humans begin wearing shoes, anyway? About 40,000 years ago, according to research from Washington University in St. Louis that analyzed foot bones from Neanderthals and early humans. Older specimens had thicker, stronger toes, likely from gripping the ground as they walked barefoot. That’s around the same time that the archaeological record shows a burst of artistic and technological advancements among early humans, including the first stone tools, which may have aided in the production of shoes. The oldest preserved shoe, incidentally, is 5500 years old and was found in an Armenian cave, buried in sheep dung.

3. THE BIG TOE USED TO BE A KIND OF FOOT THUMB.

This grasping toe helped our predecessors climb trees and, when young, grip onto their mothers. Thanks to modern science, if you lose your thumb, you can now replace it with a toe: toe-to-thumb transplants are a surprisingly common procedure these days.

4. FOOT BONES HOLD BIG CLUES ABOUT THE EVOLUTION OF BIPEDALISM.

Scientists are studying Homo naledi, a specimen discovered in a South African cave in 2013 that many researchers believe is a new human relative. H. naledi had very human-like feet, but with somewhat curved toe bones that suggest it climbed trees. It could be that H. naledi was beginning to experiment with walking. 

5. THERE WAS A FOOT CHEESE EXHIBITION IN IRELAND.

Warm, sweaty feet make a perfect home for bacteria, which feed on our dead skin cells and produce gases and acids that emit those arresting foot odors. They're apparently also good at cultivating cheese. An exhibition in Dublin in 2013 displayed a variety of cheeses made with bacteria samples obtained from real people’s feet, armpits, and belly buttons. Delicious. (No one actually ate any of the cheeses.)

6. FEET ARE ONE OF THE MOST TICKLISH PARTS OF THE BODY.

There’s a good reason for that: Humans have nearly 8000 nerves in our feet and a large number of nerve endings near the skin. Having ticklish feet can be a good sign: Reduced sensitivity can be an indicator of peripheral neuropathy (numbness in the feet caused by nerve damage). 

7. FOOT NUMBNESS CAN CAUSE BIG PROBLEMS FOR DIABETICS.

Complications of diabetes include poor circulation and foot numbness that can lead to serious skin ulcers, which sometimes require amputation of toes or feet. In 2010 alone, 73,000 lower-limb amputations were performed on diabetics.

8. FOOT SIZES AND WIDTHS IN THE U.S. AND UK ARE INCREASING.

Feet are spreading to support extra weight as our populations pack on the pounds. According to a 2014 study by the College of Podiatry in the UK, the average foot has increased two sizes since the 1970s. As people have grown taller and heavier, feet respond by growing. It appears many people are still in denial about their expanding feet: Though retailers are starting to respond by making larger and roomier shoes, half of women and a third of men reported they buy poorly fitting shoes. Podiatrists say ill-fitting shoes are to blame for a significant portion of foot problems, especially among women.

9. MANY GLAMOROUS CELEBRITIES HAVE BIG FEET.

From the bound feet of female Chinese elites to Cinderella and Barbie, freakishly small feet are often celebrated as more feminine. But plenty of glamorous women both past and present have had larger than average feet, among them Jacqueline Kennedy, Oprah Winfrey, Uma Thurman, and Audrey Hepburn (size 10, 11, 11, and 10.5, respectively).

10. WOMEN HAVE FOUR TIMES AS MANY FOOT PROBLEMS AS MEN.

That painful fact is often attributed to wearing heels. Ironically, Western women started wearing heels to effect a more masculine look: European men adopted the look from Persian warriors in the 17th century, and women soon followed suit.

11. THE AVERAGE PERSON WALKS ABOUT 100,000 MILES IN A LIFETIME. 

That’s a lot of stress on our feet. It’s not surprising, then, that lower back pain, headaches, indigestion, and spine misalignment are often related to foot problems. Some runners blow way past this mark: They've logged at least 100,000 in running miles alone. One committed runner, Herb Fred, has run a whopping 247,142 miles.

12. FOOT SIZE HAS ZERO TO DO WITH PENIS SIZE.

In a study published in 2015, researchers synthesized data from 17 previous studies that included the penis measurements of more than 15,000 men from around the world. The results: There is little evidence that penis size is linked to height, body mass, or shoe size.

13. THERE'S A REASON GRANDPA'S TOENAILS LOOK LIKE THAT.

Ever heard someone describing their toenails as “horse hooves”? As we get older, our toenails tend to thicken, making them hard to trim. This happens because toenails grow more slowly as we age, causing the nail cells to accumulate. Stubbing toes, bad shoes, and dropping things on your feet can also cause thickening, as can fungal infections and peripheral arterial disease, which narrows arteries and reduces the blood flow to limbs.

14. THERE'S A GUINNESS WORLD RECORD FOR MOST FEET AND ARMPITS SNIFFED.

Odds are you don’t have any job-related tasks nearly as revolting as this one: In the 15 years that Madeline Albrecht worked for an Ohio lab that tests Dr. Scholl products, she sniffed more than 5600 feet and untold numbers of armpits. Albrecht currently holds the Guinness World Record for—yes, this is a category—the number of feet and armpits sniffed.

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