Dan Jones

A Boeing design concept for "Icon-II," a supersonic passenger jet. (Photo: Public Domain/WikiCommons)

On January 29th, some folks in New Jersey mistook loud rumbles and rattling windows for an earthquake. Turns out it was just a sonic boom—a thunder-like noise heard by earth-bound ears brought on by an aircraft flying overheard at supersonic speeds. The boom was a reminder to certain East Coast residents of the offshore Atlantic Test Range, a restricted airspace used for aircraft testing and training missions located in the Chesapeake Bay area off the coast of Maryland, Delaware, and Virginia.

Supersonic test flights take place here just about every day, but rarely do the sonic booms reach land. How, and who, is regulating supersonic flight? 

The first aircraft to break the sound barrier—flying faster than 660 miles per hour, or the speed of sound at cruising altitude (768 miles per hour at sea level)—was piloted by Chuck Yeager in 1947. The Concorde became the first civilian aircraft to do so in the 1970s, although by that time sonic booms had become a known nuisance in the U.S. Currently, overland supersonic flight is banned in the U.S. and Europe, though there are testing ranges, such as NASA’s Armstrong Flight Research Center in Edwards, California, where pilots are permitted to make supersonic flights over the desert.

A sonic boom, according to NASA, happens when the air reacts like a fluid to supersonic objects, and the force created by objects pushing aside air molecules as they travel through the air forms a shock wave, much like a boat breaking the water. Sonic booms come about when the cone of pressurized air from the shock wave is released, resonating like a clap of thunder. There’s no difference in sound inside the aircraft, since the whole shockwave system is moving along with the plane.

If we aren't hearing sonic booms regularly, that's because a lot of effort and coordination go into making sure the booms don’t disturb civilian ears. William Couch, Public Affairs Officer for the Naval Air Warfare Center Aircraft Division at Patuxent River, Maryland, oversees testing of Navy or Marine Corps aircraft and new systems in development. He explains the steps that his division takes to avoid unwanted booms: first, a flight plan is reviewed and approved by each squadron’s chief test engineer and the commanding officer to look at the direction and speed the aircraft will be traveling and whether it’ll have to turn. They might try changing its course so that it’s not pointed at land, if possible, and also look at the weather forecasts. Sound travels further when the air is higher density (cold and wet) and slower in lower density (warm and dry), since it takes more energy to get to the next molecule. 

Couch’s squadron has a noise management team in the case that a complaint comes up. They check to see how their plane flew and whether they could have adjusted its course or flown farther offshore, a discussion that takes place among senior leaders in the test wing. Sometimes when there’s a boom, NASA is even brought in to help the Department of Defense figure out whether an airplane could have caused certain damage. 

The shockwave pattern of a supersonic flight captured with Schlieren photography. (Photo: Public Domain/WikiCommons)

Peter Coen, project manager of Commercial Supersonic Technology at NASA’s Langley Research Center, says that NASA has computational tools that allow them to determine where the sonic boom is going to hit. They take information such as temperature, relatively humidity, and wind speed and put it into a computer code; if that shows they’re going to hit a housing area, they can adjust their flight track to minimize the exposure of people on the ground to the booms that they’re using for their research. They’re also working on a device that shows where the acoustic rays that create the boom are going to go once when they leave the airplane.

Right now, a pilot can’t anticipate the location of the boom left in her wake, but soon she’ll be able to adjust her flight plan to ensure that the boom or thump is heard by as few people on the ground as possible.

Regarding sonic booms, NASA and the military have very different priorities—and budgets. While supersonic flights take place every day in the Atlantic Test Range and other training zones, Coen’s team does only one or two test campaigns per year. Coen explains that the air force is trying to minimize their radar and heat signatures, making them less susceptible to weapons, but is not particularly interested in reducing sonic boom. (If you’re flying supersonic, by the time people hear the boom, the airplane’s already gone past.) For NASA, however, that’s the primary goal.

The Concorde taking flight in 1994. (Photo: Spaceaero2/WikiCommons CC BY-SA 3.0)

Some have raised concerns that the pressure waves brought on by the boom might trigger avalanches and earthquakes or even disrupt surgical procedures. However, according to NASA, these are not factors even with large booms like the recent one in New Jersey.

Only recently has interest in viable supersonic commercial flight been rekindled, with $2.3 million of funding going into NASA’s Commercial Supersonic Technology Project in June 2015. Reducing sonic booms is the biggest hurdle, but a low-boom supersonic jet is on the near horizon. NASA is busy with all kinds of tests involving both aircraft design and human noise tolerance; they’re currently working to make supersonic aircraft quieter, lighter, more efficient, and more economically feasible than the Concorde was while also trying to identify a loudness level that’s acceptable to both the Federal Aviation Administration and the public. They’re doing more supersonic research than at any other point in the last 10 years.

“It’s all about getting rid of the boom,” Coen says. “I want to have, one day, a headline that comes out in the paper that says, ‘Supersonic Aircraft Flies Over City; Nobody Notices.’”

The kids are all right.

We know this because every two years, the federal government asks thousands of teenagers dozens of questions about whether they are all right. Since 1991, it has sent something called the Youth Risk Behavior Surveillance Survey to more than 10,000 high school students every other year, to inquire about all sorts of bad behaviors that range from drug use to unprotected sex to fighting at school.

The overarching question this survey asks is basically: How much trouble are you getting into?

The answer, lately, has been, “Not that much at all” — especially when you compare today’s teens with their parents, who came of age in the early 1990s.

Most of the survey questions show that today’s teenagers are among the best-behaved on record. They smoke less, drink less, and have sex less than the previous generation. They are, comparatively, a mild-mannered bunch who will probably shoo away from your lawn quite respectfully (and probably wouldn’t dare set foot on your lawn to begin with!)

This is different from what adults typically expect. Polls show that we generally think teens’ behavior is getting worse. One 2013 study, for example, asked Americans whether the teen pregnancy rate had gone up, down, or stayed the same since 1990. Half of respondents said it was going up, and another 18 percent said it was the same. Only 18 percent got the right answer: Teen pregnancy has declined dramatically over the past three decades.

This isn’t just a story about teen pregnancy. Look, for example, at how today’s teenagers compare with the high school students of your day. Just tell us what year you were born.

“There is a good amount of positive stuff we find, where the trend is improving and current prevalence is pretty low,” says Stephanie Zaza, who directs the Centers for Disease Control and Prevention’s Division of Adolescent and School Health.

Today’s teenagers are not perfect, and there are some ways teen behavior has gotten worse. Obesity is higher now than it ever was, and high school students do eat fewer vegetables. There are new risks, like e-cigarettes, that the government is just beginning to try to measure.

But when you look at the long-term trends on really important issues that have been tracked for decades — things like illicit substances and sexual behaviors — you see a surprisingly positive portrait of teenagers today.

Sex

One of the most stunning public health trends in the United States — not just for adolescents but for Americans of any age — is the dramatic decline in teen births.

In 1995, 5.6 percent of teen girls in the United States gave birth. In 2014, the rate was 2.4 percent. While overall childbearing has declined a bit in recent years (particularly during the recession, as economic pressures likely delay planned pregnancies), the drop has been especially steep among teenagers.

"It's exciting and really unprecedented to see these types of declines on a health issue," says Ginny Ehrlich, chief executive of the Campaign to Prevent Teen and Unplanned Pregnancy. "Last year alone, the decline was 9 percent. Having spent a decade in child obesity prevention, where change happens much slower, this feels monumental."

Read: 4 reasons why America’s teen birth rate just hit an all-time low

There are lots of ideas about what caused this fast decline, which we’ve explored in depth in a separate story. But one especially important trend that turns up in the data is the fact that teenagers today just have less sex than those of 10 or 20 years ago.

Back in 1991, if you were a high school student and thought most your friends had had sex, you were probably right. In 1991, 54.1 percent of teenagers said they’d had sex at least once.

That’s not true anymore: In 2013, 46.8 percent of teenagers answered yes to the same question. Less sex, unsurprisingly, can help explain why teenagers are having fewer babies.

There’s also preliminary data showing that teens are better at using contraceptives. The percentage who use condoms has inched up, year after year. And teenagers appear to be gravitating toward types of birth control that are even better at preventing pregnancy. A separate data set shows that teens’ use of long-acting, reversible contraceptives has more than tripled since 2007.

Tobacco

Smoking used to be a symbol of teenage cool — think James Dean in a leather jacket, a cigarette casually dangling from his fingers.

Not anymore.

“Since 1996 and 1997, we’ve gotten 75 to 85 percent reductions in smoking, especially among 12th grade students,” says Lloyd Johnston, who helps run University of Michigan’s Monitoring the Future survey, which also tracks adolescent behavior. “That will have a huge effect on longevity and health of these cohorts, on whole generations of young people.”

The decline continues, year after year. Twenty years ago, 34.8 percent of students smoked. In 2013, that number dropped to 15.7 percent — an all-time low.

The decline in teen smoking mirrors a larger, nationwide drop in tobacco use. Interventions began in the mid-1960s, after the surgeon general first warned of cigarettes’ harmful effects. In 1969, the federal government added warning labels to cigarette packages and banned tobacco ads on television.

Arizona became the first state to ban smoking in certain public places in 1973 — the same year the government began requiring airplanes to offer nonsmoking sections. Throughout the 1970s and ‘80s, smoking bans in restaurants and planes started to become the norm.

At the same time, public health advocates pushed through higher cigarette taxes. The average inflation-adjusted price for a pack of cigarettes increased from $1.80 in 1995 to $4.15 in 2008.

“Teenagers tend to be a pretty price-sensitive group,” Johnston says. He believes the recent federal increase in tobacco taxes, which took effect as part of the 2009 stimulus package, helps explain the declines he’s seen in more recent years.

Alcohol and drugs

Twenty years ago, 80.4 percent of teenagers told researchers they had tried alcohol. Today that number stands at 66.2 percent.

At the same time, alcohol abuse has seen a similar decline: The number of teens who report binge drinking (five or more drinks in the same night) has fallen by a third over the past two decades.

With cigarettes, there is a clear story about public health campaigns and tobacco taxes that helps explain why smoking declined.

But alcohol is a bit more of a mystery. Alcohol taxes haven’t increased in the same way tobacco taxes have. While there have been specific public health campaigns — most notably, the formation of Mothers Against Drunk Driving in the 1980s — nothing begins to mirror the massive national push to end smoking.

I tried looking at other illicit substances, particularly marijuana but also other drugs, but there doesn’t seem to be a replacement effect going on either — marijuana taking the place of booze, for example.

“Generally, that’s not what we’ve seen,” says Johnston. “They’ve tended to co-vary together.”

Safety

There’s a hodgepodge of other ways teens are better behaved than their parents. They’re less likely to fight at school, for example, and more likely to wear a seat belt. They carry weapons to school less than the teens of generations past.

Seeing so many trends moving in the same direction suggests some bigger overarching explanation. Some have argued that the answer here is the decline in exposure to lead, which correlates well with some of the declines in teen crime and teen pregnancy. But at least one major recent study has questioned that relationship, suggesting it is based on faulty data.

And there are, of course, ways that kids these days are behaving more poorly. The YRBS survey finds that teens today eat fewer vegetables than the teens of yesteryear and have become just slightly less inclined to wear sunscreen.

“One new thing we worry about is texting or emailing while driving,” says the CDC’s Zaza. “We only asked about it for the first time in the last survey, and we had 41 percent say yes.”

Zaza would like to see numbers like this fall: to see fewer teens texting while driving or using indoor tanning beds. (The government started that in 2009, and so far numbers are moving in the right direction.) But she never expects that the numbers would make it all the way to zero. That’s just not how adolescence works.

“I think adolescence is a time of inherent risk taking,” Zaza says. “It’s a time when you’re separating from your parents, when you want to take some risks. That has to happen and is important.”

Paramount Pictures

We're at the start of what should be a big year for Star Trek. The franchise will celebrate its 50^th anniversary this fall, but 2016 also brings a new movie (Star Trek Beyond), the recovery of long-lost documents belonging to Gene Roddenberry, and the development of (finally!) a new series set to launch in January 2017.

It’s no secret that we here at Ars love (and sometimes hate) our Star Trek. With so much time having elapsed since the original series first aired—and with so much time spent watching/reading/thinking through it all—we felt it was about, well, time to thoroughly explore one of our favorite Trek staples: time travel.

Time travel, while perhaps one of the most interesting devices in the series, is also confusing, befuddling, and inconsistent. In the words of Captain Janeway, “the future is the past, the past is the future; it all gives me a headache.”

While we can’t get too deep into the purported mechanisms behind Trek time travel—they rely on things like “chronotons” whose nature real-world science has sadly yet to discover—it's still interesting to ponder time travel's effects. How does it affect the present? Is interference with the past a predestined part of history? Do alterations in the past get mixed into the current timeline?

Before examining the source material, it's important to acknowledge others have taken on these questions, notably Trek novelist Christopher L. Bennett. His detailed work ties together wide swaths of the Trek canon with real-world physics (and some extrapolations from real physics), all with the goal of developing an overarching theory of Trek time travel. The story of time travel in Trek wouldn’t be complete without discussion of his conclusions, but don't fret if you haven't finished all that pre-reading. We’ll take you through some of his conclusions as well.

As Janeway once put it, “Let's get started before my headache gets any worse.”

Consistent universe

Paramount Pictures

The “consistent universe” is a time travel idea present in plenty of science fiction—and occasionally in Trek—in which going back to the past doesn’t change the future. Instead, your attempts to change history were always part of the timeline. If you go back and try to kill Hitler, for example, your attempt might fail and you might realize that you had read about your own attempt in school as a child.

Perhaps the best example of this in Trek is The Next Generation (TNG) episode “Time’s Arrow,” in which the Enterprise is recalled to Earth upon a new archaeological discovery: Data’s head, buried for centuries in San Francisco. Immediately, Picard hopes to alter Data’s fate, but Data believes the outcome is inevitable.

"At some future date, I will be transported back to 19th century Earth, where I will die," is how Data puts it. "It has occurred. It will occur."

Over the course of a fascinating episode involving time-traveling, neural energy-sucking aliens, and Samuel Clemens, we find that Data’s right. Luckily, it’s not the end for Data, as the future version of his head—the one that’s been buried for centuries—is reattached to his body and repaired.

This is a time loop; the decisions made by the Enterprise crew are caused by the discovery of Data’s head, and they in turn cause his head to be lost in the first place. Time loops, and thus inevitable fates like this one, are possible in a consistent universe because nothing can change what’s happened. If Picard and crew had succeeded in saving Data from his fate, his head never would have been found in the first place.

The Deep Space Nine (DS9) episode “Past Tense” also has elements of this approach. Captain Sisko and Dr. Bashir go back in time to the 21^st century and get stuck in a sealed-off district for homeless people. By the end of the episode, Sisko meets Gabriel Bell—the man who famously led riots that ended this kind of injustice—and sees him killed before Bell can lead those riots. As such, Sisko takes his place.

Witnessing the timeline shifting around their starship, the Defiant, the crew send rescue missions until they find Sisko and the timeline is restored.

Once Sisko and crew get back to the Defiant, Bashir goes into the ship’s historical database and finds a picture of Gabriel Bell... which turns out to be a picture of Sisko. The ship was shielded from changes to the timeline, which means that the picture of Sisko as Bell was in their database before the changes took place. Sisko had always been Bell.

Admittedly, the concepts of “changing the past” and witnessing an altered timeline conflict with the idea of the consistent universe. But the episode nonetheless has a consistent time loop that just happens to include the timeline changing back and forth.

Similarly, the TNG episode “Tapestry” has both a consistent effect and a changing timeline. Q gives Picard the chance to go back to his youth and make better choices. Once Picard realizes his error (getting into the fight with the Nausicaan and getting stabbed in the heart was somehow the best outcome for him), he’s given the opportunity to restore his original choices. This time, as he’s stabbed through the heart, he laughs. Interestingly, it had been mentioned in a previous episode, “Samaritan Snare,” that he had laughed when stabbed—indicating that his experience in the past had always been a part of Picard’s history.

The consistent universe is seen even more clearly in the original series (TOS). The episode “Assignment: Earth” has the Enterprise interfering in an alien secret agent’s mission to 20^th century Earth, with Kirk unsure whether the agent’s actions will destroy his timeline or secure it as the agent (Gary Seven) claims. In the pivotal moment, Kirk decides to trust Seven, allowing him to detonate a nuclear warhead before it impacts.

Seven, making his report to his alien superiors, concludes that the mission was completed despite the Enterprise’s interference in history. Spock, however, corrects him, saying that the Enterprise’s historical records show these events occurring exactly as they did, with a nuclear warhead exploding 104 miles above the surface. Thus, Spock explains, the “interference” is actually a part of the way things were supposed to happen.

There are a few other examples of consistent universe time travel in Trek, such as the Voyager (VOY) episode “Parallax,” in which the ship is lured into a singularity by a distress call which turns out to be Voyager’s own time-reflected distress call. Or DS9’s “Little Green Men,” which features Quark, Nog, and Rom crash-landing in 1947 to become the famous Roswell, New Mexico aliens. Their actions don’t seem to change the timeline as far as we can tell, and it’s probable that the Roswell incident had always taken place in the Trek universe (though, to be fair, we can’t be sure).

The consistent universe is an interesting device because we feel deep discomfort at not being able to change the course of events through our choices. If my attempt to kill Hitler is already part of history, there’s no way it can be undone.

In a physics sense, this is also the simplest time travel device. Time loops with simple particles are, in principle, totally consistent. In fact, there isn’t actually any difference between a time loop with these particles (a particle, moving in a loop, goes back in time to arrive at its starting point in time, becoming its past self) and a situation where a pair of particles, a particle and its antiparticle, are spontaneously created and annihilate soon after. Those are two equally valid ways of describing the same situation. In the second version, the antiparticle moving forwards in time is equivalent to the particle moving backwards in time.

But this situation no longer makes sense when you consider complex systems like human beings rather than individual particles. Imagine there’s a guy who comes out of a time portal, walks around in a circle, kicks a ball, and then enters the same portal from the other side. He travels back in time to when he emerged and does the same thing again.

The only trouble is even though he returns to the same time, he has changed from his experience. He remembers kicking the ball and might not feel like doing it the second time around. Additionally, the more times he does this, the more tired he’ll get. He’ll age. This situation worked fine with a particle, but it's not quite the same with a human.

After all, if I were to go back and try to kill Hitler, having read up on my attempt in the history books, what’s to stop me from trying something different the second time?

Luckily, the "consistent universe" isn't the only approach to time travel. In fact, it's not even Star Trek most common device. That honor is held by...

The ever-changing timeline

CBS

This is the stark opposite of the consistent universe. Interactions with the past are not “part of the way things were supposed to happen,” so they can undermine the way things have happened. With an ever-changing timeline, a time traveler might return from the past to find that his present is no longer the one he remembers.

The classic example of this comes in the TOS episode “The City on the Edge of Forever,” often hailed as the best episode in all Trek. Dr. McCoy uses a sentient time portal known as the Guardian of Forever, which can lead to any period in history, and he travels back to 1930. His actions change the timeline such that the Enterprise never existed.

Oddly, though, Kirk and the rest of the landing party still exist on the planet’s surface. (This might be explained because the temporal distortions surrounding the planet shielded them from being erased with the rest of their timeline.)

The crux of the episode is that Edith Keeler, a social worker with grand ideas of a peaceful future—the very type future that Star Trek embodies—must die, ironically, for that future to come about. McCoy’s interference saved her, but that's the change that erased the original timeline. Once Kirk and Spock restored her death to history, the Enterprise, along with the rest of the Federation, reappears.

This form of time travel was exemplified in the movie Star Trek: First Contact. Like “City on the Edge,” First Contact has the Enterprise crew shielded from the erasure of the timeline around them, allowing them to witness an Earth long since assimilated by the Borg. They then to go back in time to stop the assimilation.

A truly fascinating look into time travel in the Trek universe comes in Voyager’s “Year of Hell, ” which showcases a different version of the changing timeline. In this episode, a Krenim man named Annorax has created a weapon ship that can erase whatever it fires at from history. The ship itself is shielded from the changes it causes to the timeline, but the rest of the universe is vulnerable.

But Annorax finds that changing history is a lot dicier than expected. Erase an asteroid and you've undone every interaction that asteroid has ever had; in the new timeline, this will have unintended consequences. Annorax suffered for this, as his meddling with history inadvertently erased his wife from existence. But like Captain Ahab, he can't stop his quest for the perfect timeline.

The threat only ends when Voyager manages to erase the weapon ship from history, and in the resulting timeline none of its temporal attacks occurred. As a result, everything erased from the timeline is restored, including Annorax's wife.

The episode showcases how tightly woven history is and how even timelines can depend on each other. Apparently, altering the timeline which altered the timeline also affects the timelines it affected.

Another example of this is Star Trek: Enterprise's "

The idea of a changing timeline is in some ways more counterintuitive than the consistent universe. It's exactly the kind of time travel that can lead to paradoxes. After all, if changing the past can really change everything after it, then someone could kill his grandfather and erase himself from existence. Which, of course, would prevent himself from killing his grandfather.

For some reason, this is never a problem in Trek. In episodes where the timeline changes, there always seems to be a definite outcome. But maybe there's more to this idea than is immediately apparent. After all, just because the timeline's changing doesn't mean there can't be a consistent universe... after a fashion.

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Sub Title: Under Pressure

Josh Valcarcel/WIRED

Early last year, an editor asked me to review and rank home carbonators—those countertop machines that turn chilly water into lovely seltzer. Research quickly revealed an industry in chaos. Some brands were plagued with deservedly horrible reviews or simply didn’t sell. One, with a tendency to explode, was recalled. SodaStream made carbonators that some people liked and had politics that some didn’t. It got so complex, I needed a spreadsheet to keep track of it all.

I soon wrote back to the editor, advising against doing a story.

I’ve owned a SodaStream Fountain Jet for several years and have found it to be a reliable machine for carbonating water. Say, an 8 out of 10 on the WIRED scale. With large, exchangeable CO2 canisters, it’s more environmentally friendly than buying plastic bottles of store-bought fizzy water, or the tiny, individual-use chargers like those used with old-school seltzer bottles and whipping siphons.

My beef is that it only carbonates water. Carbonate anything else and you’ll not only void your warranty, you’ll understand exactly why. Try to pull a bottle of, say, orange juice from the machine and it will instantly fill with foam and launch sticky juice into the guts of the machine, an unholy mess that can only be avoided by waiting (and waiting) for the foam to die down.

For bartenders and cocktail aficionados, carbonating more than water is an exciting prospect. It means everything can be carbonated, not just the soda water poured into the drink. It also adds a pleasing nip of acidity and—busy bartenders love this—it can all done ahead of time.

Due to all this, bartenders like Jeffrey Morgenthaler in Portland, Oregon, used a Twist ‘n’ Sparkle (the one with a tendency to explode), long after it was recalled simply because there wasn’t a better option out there. People learned the clumsy process of sloooooooowly venting pressure out of their SodaStream bit by bit to keep the foaming to a minimum. It was a mess, and it was slow, but it worked. The drinks were good.

Back in early 2015, one of the foundering brands on my spreadsheet was the iSoda carbonator. Now rebranded as the DrinkMate, it looks and acts quite a bit like a SodaStream. Rather amazingly, the DrinkMate uses SodaStream’s CO2 tanks, which you swap out at participating retailers. This is understandable, as it lets a small company like iDrink (DrinkMate’s manufacturer) skip figuring this part out, but at SodaStream’s standard—and somewhat pricey—$15 for the 30 liter refill, it’s a shame.

For bartenders and cocktail aficionados, carbonating more than water is an exciting prospect.

The key difference is a collar, which iDrink calls the “fizz infuser,” that is on top of the bottle and comes right off with the bottle when you slide it out of the machine after carbonating. Many things happen at this point in the carbonation process, particularly one that differentiates the DrinkMate from its competition, so let’s pause here for a brief Moment of Science.

Carbonating is the act of cramming carbon dioxide (CO2) into a liquid, supersaturating it by using pressure. The colder the liquid, the better this works.

Like fans streaming out of a stadium after a buzzer beater, when you initially open a pressurized container of carbonated liquid, the contents rush to come to equilibrium with the world around them. This effect is much more pronounced when it’s something other than water in the bottle. Stuff like juices, wines, cocktails, or beer wreaks foamy havoc inside—and outside—a SodaStream if you open it quickly.

Try to remove a SodaStream bottle filled with, say, carbonated wine and you can very easily paint the walls, the ceiling, the inside of the machine, and yourself with it. You can get around this by finessing it off, controlling the pressure release by letting little bursts of air out, then waiting for the foam to subside, and doing it over and over again until you can coax it off without the foam overflowing. It’s slow and inelegant, but it usually gets the job done.

This is where the beauty of DrinkMate kicks in: that collar/fizz infuser has both a slow and fast release valve, allowing what’s inside to work its way back to equilibrium in an orderly manner. To go back to the stadium example, a fast release (SodaStream’s only option) is like someone yelling “Fire!” while everyone stampedes toward the doors. DrinkMate’s slow release, on the other hand, is like everyone filing toward the exits in an orderly fashion.

Once you’ve poured carbonated liquid into a glass, bubbles form around what’s called nucleation sites—imperfections in the glass or a bit of microscopic dust in the liquid—that, say, leave an enticing trail of bubbles in a glass of Champagne. A rough-surfaced ice cube will cause more intense bubbling. Mentos, with all their micro-craters, create chaos in Coke or any other carbonated drink.

I ran tests, starting with 500 milliliters of Ryan’s Honey Crisp Cider. It’s cloudy, which means it’s full of potential nucleation sites, and sweet, so it’s got a ready-to-foam viscosity. In the SodaStream, I repeatedly pressed and released the carbonation button, building pressure in short bursts, and by the time the pressure release valve made that awful noise it makes to let you know it’s done, there was already a foamy mess inside. I waited a few minutes to let the foam subside and pulled the bottle outward for a moment to let out a puff of pressure and closed it again because foam had shot to the top. I repeated the process several times over several minutes before I could finally open it.

(I should reiterate here, that SodaStream clearly professes that all it does is carbonate water. Flavored drinks are made by adding a syrup into the already-carbonated water.)

That said, I carbonated the cider in the DrinkMate and after its much-more pleasing pressure release sound, pulled the bottle from the machine, flipped up the slow-release valve on the collar and, a few seconds later, the fast release. At every step, I winced, preparing for foamy disaster. None came. For the cider, my notes simply read “No problem.”

No problem!

I set up a side-by-side comparison of carbonated cocktails à la Jeffrey Morgenthaler and made a carbonated Americano, a bitter beauty featuring Campari and sweet vermouth that can easily become your go-to drink in any season. I played it cautious with the SodaStream and it still came out looking like the side view of the trifle dessert I made for fancy New Year’s Eve dinners as a kid. The DrinkMate needed less than two minutes to depressurize and while, yes, it took two minutes, it was controllable. It was fun.

My wife swung through my test kitchen made a carbonated afternoon drink with cider, water and lemon juice. Easy peasy.

Results for re-carbonating the contents of flat tallboys of PBR were mixed, for both the SodaStream and the DrinkMate. Further testing from other beers would be necessary, but at least for flat PBR, it just wasn’t worth it. My GrowlTap growler carbonator would live to see another day in my kitchen. Both the SodaStream and the DrinkMate did a nice job turning white wine into something fizzy and festive, giving a cheap bottle of chenin blanc an added bit of acidic tang from the carbonic acid.

Over all, is it worth it, particularly when the entry-level SodaStream Fountain Jet lists for $20 less than the $120 DrinkMate? If you’re thinking about carbonating anything other than water, the answer is an effervescent yes.

Food writer Joe Ray (@joe_diner) is a Lowell Thomas Travel Journalist of The Year, a restaurant critic, and author of “Sea and Smoke” with chef Blaine Wetzel.

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They call him “Dr. WAI,” short for “Where Am I.” A well-educated 29-year-old man without any history of disease or trauma, it took him four tries to produce a semi-accurate map of the house he had lived in for 15 years.¹ Another patient, Jennifer, from San Francisco, always feels like she is facing north, regardless of which direction she is actually facing. Judy Bentley had her memory of her physical surroundings suddenly vanish one day in high school. She suddenly had no idea what was beyond the classroom door.

These are just some of the subjects that have been identified by a field that was kicked off with what might be called patient one, whom we’ll call Alice.² In 2007, Alice approached the neuroscientist Giuseppe Iaria with a peculiar and vexing problem: She had extraordinary difficulty finding her way around. Sometimes she would even get lost in her own house. She had to rely on standardized routes, going from door to door along a carefully memorized path. To get to work she knew when to get off the bus, and how to walk from memorized landmark to memorized landmark until she reached her office building.

But if Alice strayed even slightly she would be hopelessly lost, and the only solution was to call her father to pick her up. She didn’t have any trouble seeing—she could recognize landmarks and other objects as well as anybody. Her intelligence was perfectly normal, and she was an avid reader. While she had developed a coping strategy, she was afraid it was about to fail: Her company wanted to relocate her, and she was terrified by the prospect of having to learn her way around a new environment.

Homing in: A distorted home map drawn by a subject with DTD is shown on the left. The actual map is on the right. Neuropsychologia

Iaria, who hails from the University of Calgary, was immediately fascinated. He had spent years studying human navigation and its underlying brain systems, and knew of many subjects who had problems navigating. But all of them had some sort of brain damage, most commonly resulting from a stroke. Alice was the first person he encountered who had severe navigation problems without any apparent brain damage.

When Iaria tested Alice, he found that she fell into the normal range on a wide variety of cognitive tasks. Her brain showed no structural abnormalities, and there was no obvious problem with her upbringing that might have caused her to fail to learn how to navigate normally. She was completely unable to draw a useful map herself, though, or to form maps in her mind. The only plausible explanation, it seemed, lay somewhere in her genes. Iaria coined the term “Developmental Topographic Disorientation” (DTD) for her problem—and for other cases like her, who soon turned up in substantial numbers.

Here, out of the blue, was a new and relatively common condition that had the potential to reveal something new about how we know that we are where we are.

Let’s suppose that you are hiking in the mountains. You have a map (an ordinary paper map) and a compass (an ordinary magnetic compass); and you are trying to get to the peak of Mount Possible.  There are several strategies you could use:

1. If you can see the peak from where you are standing, and see the intervening terrain, you can formulate a route based on what you see. This is “visual navigation.”
2. If you are on a trail, and there is a sign in front of you saying, “Mt. Possible  0.4 mi,” you can simply follow the trail without bothering with the map. This is “route-based navigation.”
3. If neither of those approaches are viable, you have to locate yourself on the map, use the compass to orient the map properly, locate Mt. Possible on the map, and use the map to work out a route getting you from your present location to Mt. Possible. This is “map-based navigation.”

People such as Alice generally have no problem with visual navigation or route-based navigation. Their difficulty is specifically with map-based navigation. But map-based navigation is a rather complex operation, and there are several ways it can go wrong. Some (not all) possible causes of difficulty include inability to form a good map of the environment; inability to locate yourself on your map; failure to orient yourself with respect to your map; and inability to use the map to work out a route connecting two points. Each of these failure modes probably correlates with a different type of brain dysfunction, and a different part of the brain.

Here, out of the blue, was a new and relatively common condition.

If the problem is in making a map, then the hippocampus is probably involved. Neurons in the hippocampus become active when an animal passes through specific places in the environment. These “place responses” combine information from the senses and elsewhere in the brain, particularly from the entorhinal cortex, which is located near the hippocampus and implements a spatial coordinate system.

If the problem is one of alignment, then the problem may lie with the “head direction” system, which is essentially an inertial compass located inside the brain. The hippocampus and entorhinal cortex work in close harmony with a set of brain structures implementing this system. Unlike a magnetic compass, the head direction system does not encode “true north” in any meaningful sense; instead it is more like a gyrocompass in that it uses inertial properties to maintain a consistent direction code in spite of movements and changes in orientation.

But the brain structure most frequently implicated in people suffering from damage-induced topographic disorientation is the retrosplenial cortex. This area lies near the center of the brain, and is strongly connected to the hippocampus and the other navigation-related areas. The retrosplenial cortex is not needed to have an accurate cognitive map or sense of direction, but it seems somehow to be crucial, in a way we don’t yet understand, for the ability to properly use the map and compass to formulate a route to a goal.

The underlying causes of DTD probably include some or all of these possibilities. Some people, such as the initial patient, Alice, seem to form cognitive maps that are severely distorted: This suggests a dysfunction in the entorhinal cortex or parietal cortex, the areas that are involved in grasping spatial relationships. For others, the difficulty centers on orientation, suggesting a dysfunction involving the head direction system. Judy Bentley, one of Iaria’s patients, finds her sense of direction to flip unpredictably between four settings, and each time it flips she has to learn a new set of relationships. Sharon Roseman also frequently loses her sense of direction, but she has learned that if she closes her eyes and spins around, upon opening her eyes it usually comes back. And Jennifer, the San Franciscan patient, always feels like she is facing the same direction, even as she turns from side to side.

The few systematic experimental studies of DTD that have been done implicate certain structures and functions of the brain, but are not conclusive. Two years ago Iaria and several colleagues found reduced interactions between the hippocampus and prefrontal cortex in nine women suffering from DTD, compared to control subjects. That’s interesting, but there are reasons to suspect it might be a consequence of DTD rather than a cause: To put it crudely, the hippocampus makes maps and the prefrontal cortex makes plans—reduced interactions suggest that the plans people make are less influenced by their maps. This may simply be a result of people having learned that their maps are unreliable.

The odds are high that some of the readers of this article suffer from DTD, and don’t know it.

In a 2014 paper, a group of investigators from Princeton and Carnegie Mellon University did a thorough study of brain activity in a woman with DTD who was asked only to view spatial scenes on a computer screen, not to actually navigate.³When her brain activity patterns were compared with those of control subjects, no differences were seen for the hippocampus, but clear differences appeared for the retrosplenial cortex—the same brain area most often affected in topographic disorientation caused by brain damage. The subject showed reduced effects of familiarity on her retrosplenial responses, and reduced functional connectivity between the retrosplenial cortex and the “parahippocampal place area,” a portion of the temporal lobe involved in encoding memory for scenes. Thus it is possible that the retrosplenial cortex will turn out to be as critical for DTD as it is for brain-damage-caused topographic disorientation—at least in some cases.

Over the long term, perhaps the most important information DTD might give us will be a better understanding of the genes involved in spatial cognition. There is anecdotal evidence that DTD is often inherited—Iaria promises to publish a paper soon that will back up that claim—and if it is possible to identify a small number of genetic variants that distinguish people with DTD from others, we will have an excellent start. It might not work: The number of genes expressed specifically in the brain is huge, and there is no telling how many are involved in spatial cognition. Unless multiple people with DTD show mutations of the same genes, it will be difficult to make progress. But it is certainly worth trying. The results would not only be useful for understanding DTD, they would also potentially be useful for understanding the normal range of variation in spatial abilities. Where large mutations cause severe problems, smaller differences in gene expression are likely to cause more moderate differences in behavior.

A particularly intriguing point, in relation to the genetics of DTD, is that it seems to show up much more often in women than men: Iaria’s initial group of 120 subjects included 102 women and 18 men.⁴ This doesn’t amount to proof, because most of Iaria’s DTD cases were self-reported, and women could simply be more open about this problem than men. To properly establish a relationship would require a randomly selected sample of people. Even so, the difference is large enough that it can be expected to hold up, especially given that studies have shown that, on average, men are a little bit better than women at map-based navigation.⁵ Thus at least some of the genes in question are likely to show sexually dimorphic patterns of expression.

Over the last five years, several hundred cases of DTD have been identified. It might actually not be uncommon: An informal survey that Iaria carried out among students at the University of Calgary found that as many as 2 percent of them might meet the criteria for the disorder. The odds are high that some of the readers of this article suffer from DTD, and don’t know it. Iaria plans to have an online test available for the public this July. It may very well be worth taking. As for Alice, she ended up not being relocated, and continued to find her way to her old job one landmark at a time.

William Skaggs is a neuroscientist and science writer, whose research has focused on the role of hippocampus in spatial cognition and memory.

References

1. Bianchini, F., et al. Where am I? A new case of developmental topographical disorientation. Journal of Neuropsychology 8, 107-124 (2014).

2. Iaria, G., Bogod, N., Fox, C.J., & Barton, J.J. Developmental topographical disorientation: Case one. Neuropsychologia 47, 30-40 (2009).

3. Kim, J.G., Aminoff, E.M., Kastner, S., & Behrmann, M. A neural basis for developmental topographic disorientation. The Journal of Neuroscience 35, 12954-12969 (2015).

4. Iaria, G., & Barton, J.J. Developmental topographical disorientation: A newly discovered cognitive disorder. Experimental Brain Research 206, 189-196 (2010).

5. Andersen, N.E., Dahmani, L., Konishi, K., & Bohbot, V.D. Eye tracking, strategies, and sex differences in virtual navigation. Neurobiology of Learning and Memory 97, 81-89 (2012).

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February 09 2016