Speed of universe’s expansion remains elusive

Unless you are a recent arrival from another universe, you’ve no doubt heard that this one is expanding. It’s getting bigger all the time. What’s more, its growth rate is accelerating. Every day, the universe expands a little bit faster than it did the day before.

Those day-to-day differences are negligible, though, for astronomers trying to measure the universe’s expansion rate. They want to know how fast it is expanding “today,” meaning the current epoch of cosmic history. That rate is important for understanding how the universe works, knowing what its ultimate fate will be and even what it is made of. After all, the prime mission of the Hubble Space Telescope when it was launched in 1990 was to help determine that expansion rate (known, not coincidentally, as the Hubble constant, named for the astronomer Edwin Hubble).
Since then evidence from Hubble (the telescope) and other research projects has established a reasonably precise answer for the Hubble constant: 73, in the units commonly used for this purpose. (It means that two independent astronomical bodies separated by 3.26 million light-years will appear to be moving away from each other at 73 kilometers per second.) Sure, there’s a margin of error, but not much. The latest analysis from one team, led by Nobel laureate Adam Riess, puts the Hubble constant in the range of 72–75, as reported in a paper posted online January 3. Considering that as late as the 1980s astronomers argued about whether the Hubble constant was closer to 40 or 90, that’s quite an improvement in precision.

But there’s a snag in this success. Current knowledge of the universe suggests a way to predict what the Hubble constant ought to be. And that prediction gives a probable range of only 66–68. The two methods don’t match.

“This is very surprising, I think, and very interesting,” Riess, of the Space Telescope Science Institute in Baltimore, said in a talk January 9 at a meeting of the American Astronomical Society.

It’s surprising because astrophysicists and cosmologists thought they had pretty much figured the universe out. It’s made up of a little bit of ordinary matter, a lot of some exotic “dark matter” of unknown identity, and even more of a mysterious energy permeating the vacuum of space, exerting gravitational repulsion. Remember that acceleration of the expansion rate? It implies the existence of such energy. Because nobody knows what it is, people call it “dark energy,” while suspecting that its real name is lambda, the Greek letter that stands for “cosmological constant.” (It’s called a constant because any part of space should possess the same amount of vacuum energy.) Dark energy contributes something like 70 percent of the total mass-energy content of the universe, various lines of evidence indicate.
If all that’s right, then it’s not all that hard to infer how fast the universe should be expanding today. You just take the recipe of matter, dark matter and dark energy and add some ghostly subatomic particles known as neutrinos. Then you carefully measure the temperature of deep space, where the only heat is the faint glow remaining from the Big Bang. That glow, the cosmic microwave background radiation, varies slightly in temperature from point to point. From the size of those variations, you can calculate how far the radiation from the Big Bang has been traveling to reach our telescopes. Combine that with the universe’s mass-energy recipe, and you can calculate how fast the universe is expanding. (You can, in fact, do this calculation at home with the proper mathematical utensils.)

An international team’s project using cosmic microwave background data inferred a Hubble constant of 67, substantially less than the 73 or 74 based on actually measuring the expansion (by analyzing how the light from distant supernova explosions has dimmed over time).

When this discrepancy first showed up a few years ago, many experts believed it was just a mirage that would fade with more precise measurement. But it hasn’t.

“This starts to get pretty serious,” Riess said at the astronomy meeting. “In both cases these are very mature measurements. This is not the first time around for either of these projects.”

One commonly proposed explanation contends that the supernova studies are measuring the local value of the Hubble constant. Perhaps we live in a bubble, with much less matter than average, skewing expansion measurements. In that case, the cosmic microwave background data might provide a better picture of the “global” expansion rate for the whole universe. But supernovas observed by the Hubble telescope extend far enough out to refute that possibility, Riess said.

“Even if you thought we lived in a void…, you still are basically stuck with the same problem.”

Consequently it seems most likely that something is wrong with the matter-energy recipe for the universe (technically, the cosmological standard model) used in making the expansion rate prediction. Maybe the vacuum energy driving cosmic acceleration is not a cosmological constant after all, but some other sort of field filling space. Such a field could vary in strength over time and throw off the calculations based on a constant vacuum energy. But Riess pointed out that the evidence is growing stronger and stronger that the vacuum energy is just the cosmological constant. “I would say there we have less and less wiggle room.”

Another possibility, appealing to many theorists, is the existence of a new particle, perhaps a fourth neutrino or some other relativistic (moving very rapidly) particle zipping around in the early universe.

“Relativistic particles — theorists have no trouble inventing new ones, ones that don’t violate anything else,” Riess said. “Many of them are quite giddy about the prospect of some evidence for that. So that would not be a long reach.”

Other assumptions built into the current cosmological standard model might also need to be revised. Dark matter, for example, is presumed to be very aloof from other forms of matter and energy. But if it interacted with radiation in the early universe, it could have an effect similar to that of relativistic particles, changing how the energy in the early universe is divided up among its components. Such a change in energy balance would alter how much the universe expands at early times, corrupting the calibrations needed to infer the current expansion rate.

It’s not the first time that determining the Hubble constant has provoked controversy. Edwin Hubble himself initially (in the 1930s) vastly overestimated the expansion rate. Using his rate, calculations indicated that the universe was much younger than the Earth, an obvious contradiction. Even by the 1990s, some Hubble constant estimates suggested an age for the universe of under 10 billion years, whereas many stars appeared to be several billion years older than that.

Hubble’s original error could be traced to lack of astronomical knowledge. His early overestimates turned out to be signals of a previously unknown distinction between different generations of stars, some younger and some older, Riess pointed out. That threw off distance estimates to some stars that Hubble used to estimate the expansion rate. Similarly, in the 1990s the expansion rate implied too young a universe because dark energy was not then known to exist and therefore was not taken into account when calculating the universe’s age.

So the current discrepancy, Riess suggested, might also be a signal of some astronomical unknown, whether a new particle, new interactions of matter and radiation, or a phenomenon even more surprising — something that would really astound a visitor from another universe.

Lakers vs. Warriors final score, results: Golden State forces Game 6 as Anthony Davis suffers head injury

Faced with a do-or-die situation in Game 5, the Warriors came up big.

A 121-106 win at Chase Center kept Golden State's season alive as they successfully avoided elimination at the hands of the Lakers. The series will now head back down to Los Angeles for Game 6, where LeBron James and Co. will have another chance to punch their ticket to the Western Conference Finals.

Stephen Curry led the way for the Warriors with 27 points and eight assists. Andrew Wiggins finished with 25 points and seven rebounds, while Draymond Green had one of his best games of the postseason with 20 points and 10 rebounds.

A bad night got even worse for LA when Anthony Davis was forced to leave the game late in the fourth quarter. He appeared to take a shot to the face from Golden State's Kevon Looney, and TNT's Chris Haynes reported that he was taken down the tunnel in a wheelchair. The Lakers now face an anxious wait to see whether he'll be good to go for a massive Game 6.

The Sporting News was tracking all the key moments as the Warriors defeated the Lakers in Game 5 of the Western Conference semifinals:

Lakers vs. Warriors score
Team Q1 Q2 Q3 Q4 Final
Lakers 28 31 23 24 106
Warriors 32 38 23 28 121
Lakers vs. Warriors live score, updates, highlights from Game 5
12:31 a.m. FINAL — The final buzzer rings out, and we're headed to a Game 6. Curry finishes with 27 points, Wiggins with 25 and Draymond Green with 20.

12:27 a.m. — Darvin Ham has raised the white flag and sent in his reserves. Golden State is going to get the win, and their season is going to continue. An excellent performance by the Warriors tonight with their backs against the wall.

12:24 a.m. — Both teams continue to trade blows, but with time ticking down, the Warriors look like they're going to cruise to a win here. Davis still hasn't returned to the court, and it sounds like he may be dealing with some dizziness and vision difficulties. He'll probably be sidelined for the rest of the game.

12:19 a.m. — Steph with a big shot! A triple from the corner extends the lead back to 14 points! It's Warriors 109, Lakers 95 as we enter the final minutes.

12:16 a.m. — Draymond gets the crowd on its feet with a nice jumper, but Austin Reaves answers at the other end with a three from way downtown! The Lakers have chipped away and the lead is now down to just nine points with 5:25 left.
12:14 a.m. — Davis is having to head down the tunnel and towards the locker room after that injury. TNT's Chris Haynes reported he looked a little shaky on his feet and needed some help to stay upright. Let's hope he's OK.

12:09 a.m. — Gary Payton II finishes with the hoop and harm over LeBron, and the crowd is loving it. To add insult to injury for the Lakers, Anthony Davis appeared to take an elbow to the face on the other end. He appears to be in significant discomfort, and he is forced to head to the bench.

12:03 a.m. — Any momentum the Lakers may have had has quickly vanished early in the fourth quarter. Curry drains a pull-up jumper with the shot clock winding down, then Wiggins converts on a running floater in the lane to stretch the lead back to 15 points. LA is running out of time here.
11:55 p.m. END OF THIRD QUARTER — The Lakers use a mini-run to cut into the lead slightly. LeBron converts on a layup with time winding down in the quarter, and we enter the final frame with Golden State up 93-82. James appeared to land on the foot of Wiggins on that last shot, and he was grimacing a little bit as he walked away. Something to keep an eye on.

11:49 p.m. — With the third quarter winding down, the Warriors are showing no signs of letting up. Curry just blew right by three defenders for an easy layup, and once again Darvin Ham has used a timeout to try and spark something from his team.

11:41 p.m. — How about Draymond Green in this game? He's been sensational so far, racking up 18 points on 6 of 10 shooting from the field. He just converted on another layup to make it 85-70, Warriors.

11:32 p.m. — The Lakers are off to a terrible start in this half, and in the blink of an eye the Warriors have stretched their lead to 18 points! Wiggins caps off a 9-2 Golden State flurry with a one-handed putback slam and Darvin Ham takes a timeout to stop the bleeding. That could be a huge momentum swing in this game.
11:27 p.m. START OF SECOND HALF — And away we go in the third quarter. Can the Warriors hold off the Lakers to stay alive?

11:20 p.m. — Davis leads all scorers with 18 points at the half while Wiggins leads Golden State with 16. James has 17 and Curry has 12, including that buzzer-beater to make it an eleven-point game.

11:11 p.m. END OF FIRST HALF — Stephen Curry lights up Chase Center with a three to beat the buzzer! That's just his second trey of the night, but it sends the Warriors into the locker room with a 70-59 lead! They ended the half on a 16-5 run to take control of Game 5.
11:03 p.m. — We knew a run was coming from one of these teams, and this time it has come from the Warriors! Poole connects from deep, then Wiggins follows it up with a triple of his own. After a Lakers timeout, the home team leads 64-56 with less than two minutes left in the half.

10:56 p.m. — LeBron isn't cooling off, and he drives for a layup then knocks down a three moments later to tie things up at 50 apiece. Back and forth we go.

10:51 p.m. — Andrew Wiggins gets a bucket and a foul, then does it again less than 40 seconds later! That pair of three-point plays puts the Warriors back in the lead by five with seven minutes remaining in the first half.

10:45 p.m. — Now LeBron is starting to get going! He buries a pair of three-pointers to take his tally to 12 points on the night and give the Lakers the lead. After he sinks a pair of free throws, it's 41-40, LA.
10:37 p.m. END OF FIRST QUARTER — Whew, time to catch your breath! A Jordan Poole floater with six seconds left on the clock has made it 32-28 Warriors at the end of the first quarter. They could really use a good performance from him tonight. If the game continues like this, we're in for a treat.

10:35 p.m. — This game has been fast-paced and a lot of fun so far. Davis continues to fill it up and he's up to 13 points as we near the end of the first quarter. But 20-year-old Moses Moody has knocked down a pair of threes to keep Golden State's lead intact. They're up 30-26 with just over a minute left in the period.

10:27 p.m. — But here come the Lakers! Anthony Davis is getting himself involved, and his putback dunk cuts the Warriors' lead to just five points. He has nine points already in the early going.

10:20 p.m. — This has been one heck of a start by the Warriors. Gary Payton II drains a three, Draymond converts on another layup and then Stephen Curry opens his account for the night with a three from way downtown. The home team is out to a 17-5 lead less than five minutes into the game.
10:17 p.m. — Draymond Green is off to a fast start! He buries a three to get the Warriors on the board, and his layup through contact draws a foul and leads to a three-point play. Golden State leads 9-3 early.

10:12 p.m. — And there's the opening tip. We are underway in San Francisco.

10:07 p.m. — Knicks-Heat just wrapped up. meaning Warriors-Lakers is up next on TNT. Can Golden State do what New York did and stave off elimination at home in Game 5?

9:59 p.m. — Steph was doing Steph things in pregame warmups.
9:52 p.m. — No surprises from the Lakers with their starting lineup.
9:46 p.m. — For the second game in a row, Gary Payton II gets the start for Golden State.
What channel is Lakers vs. Warriors on?
Date: Wednesday, May 10
TV channel: TNT
Live streaming: Sling TV
Lakers vs. Warriors will air on TNT. Viewers can also stream the game on Sling TV.

Fans in the U.S. can watch the NBA Playoffs on Sling TV, which is now offering HALF OFF your first month! Stream Sling Orange for $20 in your first month to catch all the games on TNT, ESPN & ABC. For games on NBA TV, subscribe to Sling Orange & Sports Extra for $27.50 in your first month. Local regional blackout restrictions apply.

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What time is Lakers vs. Warriors tonight?
Date: Wednesday, May 10
Time: 10 p.m. ET | 7 p.m. PT
Lakers vs. Warriors will tip off around 10 p.m. ET (7 p.m. local time) on Wednesday, May 10. The game will be played at the Chase Center in San Francisco.

Lakers vs. Warriors odds
Golden State is a 7.5-point favorite heading into Game 5.

 Warriors    Lakers

Spread -7.5 +7.5
Moneyline -350 +260
For the full market, check out BetMGM.

Lakers vs. Warriors schedule
Here is the complete schedule for the second-round series between Los Angeles and Golden State:

Date Game Time (ET) TV channel
May 2 Lakers 117, Warriors 112 10 p.m. TNT
May 4 Warriors 127, Lakers 100 9 p.m. ESPN
May 6 Lakers 127, Warriors 97 8:30 p.m. ABC
May 8 Lakers 104, Warriors 101 10 p.m. TNT
May 10 Game 5 10 p.m. TNT
May 12 Game 6* TBD ESPN
May 14 Game 7* TBD ABC

Mysterious high-energy particles could come from black hole jets

It’s three for the price of one. A trio of mysterious high-energy particles could all have the same source: active black holes embedded in galaxy clusters, researchers suggest January 22 in Nature Physics.

Scientists have been unable to figure out the origins of the three types of particles — gamma rays that give a background glow to the universe, cosmic neutrinos and ultrahigh energy cosmic rays. Each carries a huge amount of energy, from about a billion electron volts for a gamma ray to 100 billion billion electron volts for some cosmic rays.
Strangely, each particle type seems to contribute the same total amount of energy to the universe as the other two. That’s a clue that all three may be powered by the same engine, says physicist Kohta Murase of Penn State.

“We can explain the data of these three messengers with one single picture,” Murase says.

First, a black hole accelerates charged particles to extreme energies in a powerful jet (SN: 9/16/17, p. 16). These jets “are one of the most promising candidate sources of ultrahigh energy cosmic rays,” Murase says. The most energetic cosmic rays escape the jet and immediately plow through a sea of magnetized gas within the galaxy cluster.

Some rays escape the gas as well and zip towards Earth. But less energetic rays are trapped in the cluster for up to a billion years. There, they interact with the gas and create high-energy neutrinos that then escape the cluster.
Meanwhile, the cosmic rays that escaped travel through intergalactic space and interact with photons to produce the glow of gamma rays.

Murase and astrophysicist Ke Fang of the University of Maryland in College Park found that computer simulations of this scenario lined up with observations of how many cosmic rays, neutrinos and gamma rays reached Earth.

“It’s a nice piece of unification of many ideas,” says physicist Francis Halzen of the IceCube Neutrino Observatory in Antarctica, where the highest energy neutrinos have been observed.

There are other possible sources for the particles — for one, IceCube has already traced an especially high-energy neutrino to a single active black hole that may not be in a cluster (SN Online: 4/7/16). The observatory could eventually trace neutrinos back to galaxy clusters. “That’s the ultimate test,” Halzen says. “This could be tomorrow, could be God knows when.”

Here’s the key ingredient that lets a centipede’s bite take down prey

Knocking out an animal 15 times your size — no problem. A newly identified toxin in the venom of a tropical centipede helps the arthropod to overpower giant prey in about 30 seconds.

Insight into how this venom overwhelms lab mice could lead to an antidote for people who suffer excruciatingly painful, reportedly even fatal, centipede bites, an international research team reports the week of January 22 in Proceedings of the National Academy of Sciences.

In Hawaii, centipede bites account for about 400 emergency room visits a year, according to data from 2004 to 2008. The main threat there is Scolopendra subspinipes, an agile species almost as long as a human hand.
The subspecies S. subspinipes mutilans starred in studies at the Kunming Institute of Zoology in China and collaborating labs. Researchers there found a small peptide, now named “spooky toxin,” largely responsible for venom misery.

This toxin blocks a molecular channel that normally lets potassium flow through cell membranes. A huge amount of the biochemistry of staying alive involves potassium, so clogging some of what are called KCNQ channels caused mayhem in mice: slow and gasping breath, high blood pressure, frizzling nerve dysfunctions and so on. Administering the epilepsy drug retigabine opened the potassium channels and counteracted much of the toxin’s effects, raising hopes of a treatment for these bites.

New technique could help spot snooping drones

Now there’s a way to tell if a drone is spying on someone.

Researchers have devised a method to tell what a drone is recording — without having to decrypt the video data that the device streams to the pilot’s smartphone. This technique, described January 9 at arXiv.org, could help military bases detect unwanted surveillance and civilians protect their privacy as more commercial drones take to the skies.

“People have already worked on detecting [the presence of] drones, but no one had solved the problem of, ‘Is the drone actually recording something in my direction?’” says Ahmad Javaid, a cybersecurity researcher at the University of Toledo in Ohio, who was not involved in the work.
Ben Nassi, a software engineer at Ben-Gurion University of the Negev in Israel, and colleagues realized that changing the appearance of objects in a drone’s field of view influences the stream of encrypted data the drone sends to its smartphone controller. That’s because the more pixels that change from one video frame to the next, the more data bits the drone sends per second. So rapidly switching the appearance of a person or house and seeing whether those alterations correspond to higher drone-to-phone Wi-Fi traffic can reveal whether a drone is snooping.

Nassi’s team tested this idea by covering a house window with a smart film that could switch between transparent and nearly opaque, and aiming a drone with a video camera at the window from 40 meters away. Every two seconds, the researchers either flickered the smart film back and forth or left it transparent. They pointed a radio frequency scanner at the drone to intercept its outgoing Wi-Fi signals and found that its traffic spiked whenever the smart film flickered.

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For people without such radio equipment, it’s also possible to intercept Wi-Fi signals with a laptop or computer with a wireless card, says Simon Birnbach, a computer scientist at the University of Oxford not involved in the work.

In another test, a drone recorded someone wearing a strand of LED lights from about 20 meters’ distance. At five-second intervals, the person either flipped the LED lights on and off, or left them off. The drone camera’s data stream peaked whenever the LED lights flickered.

This strategy to discern a drone camera’s target is “a very cool idea,” says Thomas Ristenpart, a computer scientist at Cornell University not involved in the work. But the researchers need to test whether the method works in a wider range of settings and find ways to alter a drone’s view without cumbersome equipment, he says. “I don’t think anyone is going to want to wear a [light-up] shirt on the off chance a drone may fly by.”

Javaid agrees that this prototype system must be made more user-friendly to achieve widespread use. For home security, he imagines a small device stuck to a window that flashes a light and intercepts a drone’s Wi-Fi signals whenever it detects one nearby. The device could alert the homeowner if a drone is found scoping out the house.

Still, identifying a nosy drone may not always be enough to know who’s flying it. “It’s sort of the equivalent of knowing that an unmarked van pulled up and waited outside of your house,” says Drew Davidson, a computer scientist at Tala Security, Inc. in Dallas, who was not involved in the study. “Better to know than not, but not exactly enough for the police to find a suspect.”

Stars with too much lithium may have stolen it

Something is giving small, pristine stars extra lithium. A dozen newly discovered stars contain more of the element than astronomers can explain.

Some of the newfound stars are earlier in their life cycles than stars previously found with too much lithium, researchers report in the Jan. 10 Astrophysical Journal Letters. Finding young lithium-rich stars could help explain where the extra material comes from without having to tinker with well-accepted stellar evolution rules.

The first stars in the Milky Way formed from the hydrogen, helium and small amounts of lithium that were produced in the Big Bang, so most of this ancient cohort have low lithium levels at the surface (SN: 11/14/15, p. 12). As the stars age, they usually lose even more.
Mysteriously, some aging stars have unusually high amounts of lithium. About a dozen red giant stars — the end-of-life stage for a sunlike star — have been spotted over the last few decades with extra lithium at their surfaces. It’s not enough lithium to explain a different cosmic conundrum, in which the universe overall seems to have a lot less lithium than it should (SN: 10/18/14, p. 15). But it’s enough to confuse astronomers. Red giants usually dredge up material that is light on lithium from their cores, making their surfaces look even more depleted in the element.

Finding lithium-enriched red giants “is not expected from standard models of low-mass star evolution, which is usually regarded as a relatively well-established field in astrophysics,” says astronomer Wako Aoki of the National Astronomical Observatory of Japan in Tokyo. A red giant with lots of lithium must have had a huge amount of lithium in its former life, or imply a tweak is needed to some fundamental rule of stellar evolution.

Aoki and his colleagues used the Subaru Telescope in Hawaii to find the 12 new lithium-rich stars, all about 0.8 times the mass of the sun. Five of the stars seem to be relatively early in their life cycles — a little older than regular sunlike stars but a little younger than red giants.
That suggests lithium-rich stars somehow picked up the extra lithium early in their lives, though it’s not clear from where. The stars could have stolen material from companion stars, or eaten unfortunate planets (SN: 5/19/01, p. 310). But there are reasons to think they did neither — for one thing, they don’t have an excess of any other elements.

“This is a mystery,” Aoki says.

Further complicating the picture is the possibility that the five youngish stars could be red giants after all, thanks to uncertainties in the measurements of their sizes, says astronomer Evan Kirby of Caltech. Future surveys should check stars that are definitely in the same stage of life as the sun.

Still, the new results are “tantalizing,” Kirby says. “It’s a puzzle that’s been around for almost 40 years now, and so far there’s no explanation that has satisfying observational support.”

Your phone is like a spy in your pocket

Consider everything your smartphone has done for you today. Counted your steps? Deposited a check? Transcribed notes? Navigated you somewhere new?

Smartphones make for such versatile pocket assistants because they’re equipped with a suite of sensors, including some we may never think — or even know — about, sensing, for example, light, humidity, pressure and temperature.

Because smartphones have become essential companions, those sensors probably stayed close by throughout your day: the car cup holder, your desk, the dinner table and nightstand. If you’re like the vast majority of American smartphone users, the phone’s screen may have been black, but the device was probably on the whole time.

“Sensors are finding their ways into every corner of our lives,” says Maryam Mehrnezhad, a computer scientist at Newcastle University in England. That’s a good thing when phones are using their observational dexterity to do our bidding. But the plethora of highly personal information that smartphones are privy to also makes them powerful potential spies.
Online app store Google Play has already discovered apps abusing sensor access. Google recently booted 20 apps from Android phones and its app store because the apps could — without the user’s knowledge — record with the microphone, monitor a phone’s location, take photos, and then extract the data. Stolen photos and sound bites pose obvious privacy invasions. But even seemingly innocuous sensor data can potentially broadcast sensitive information. A smartphone’s movement may reveal what users are typing or disclose their whereabouts. Even barometer readings that subtly shift with increased altitude could give away which floor of a building you’re standing on, suggests Ahmed Al-Haiqi, a security researcher at the National Energy University in Kajang, Malaysia.

These sneaky intrusions may not be happening in real life yet, but concerned researchers in academia and industry are working to head off eventual invasions. Some scientists have designed invasive apps and tested them on volunteers to shine a light on what smartphones can reveal about their owners. Other researchers are building new smartphone security systems to help protect users from myriad real and hypothetical privacy invasions, from stolen PIN codes to stalking.

Message revealed
Motion detectors within smartphones, like the accelerometer and the rotation-sensing gyroscope, could be prime tools for surreptitious data collection. They’re not permission protected — the phone’s user doesn’t have to give a newly installed app permission to access those sensors. So motion detectors are fair game for any app downloaded onto a device, and “lots of vastly different aspects of the environment are imprinted on those signals,” says Mani Srivastava, an engineer at UCLA.

For instance, touching different regions of a screen makes the phone tilt and shift just a tiny bit, but in ways that the phone’s motion sensors pick up, Mehrnezhad and colleagues demonstrated in a study reported online April 2017 in the International Journal of Information Security. These sensors’ data may “look like nonsense” to the human eye, says Al-Haiqi, but sophisticated computer programs can discern patterns in the mess and match segments of motion data to taps on various areas of the screen.

For the most part, these computer programs are machine-learning algorithms, Al-Haiqi says. Researchers train them to recognize keystrokes by feeding the programs a bunch of motion sensor data labeled with the key tap that produces particular movement. A pair of researchers built TouchLogger, an app that collects orientation sensor data and uses the data to deduce taps on smartphones’ number keyboards. In a test on HTC phones, reported in 2011 in San Francisco at the USENIX Workshop on Hot Topics in Security, TouchLogger discerned more than 70 percent of key taps correctly.

Since then, a spate of similar studies have come out, with scientists writing code to infer keystrokes on number and letter keyboards on different kinds of phones. In 2016 in Pervasive and Mobile Computing, Al-Haiqi and colleagues reviewed these studies and concluded that only a snoop’s imagination limits the ways motion data could be translated into key taps. Those keystrokes could divulge everything from the password entered on a banking app to the contents of an e-mail or text message.

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A more recent application used a whole fleet of smartphone sensors — including the gyroscope, accelerometer, light sensor and magnetism-measuring magnetometer — to guess PINs. The app analyzed a phone’s movement and how, during typing, the user’s finger blocked the light sensor. When tested on a pool of 50 PIN numbers, the app could discern keystrokes with 99.5 percent accuracy, the researchers reported on the Cryptology ePrint Archive in December.

Other researchers have paired motion data with mic recordings, which can pick up the soft sound of a fingertip tapping a screen. One group designed a malicious app that could masquerade as a simple note-taking tool. When the user tapped on the app’s keyboard, the app covertly recorded both the key input and the simultaneous microphone and gyroscope readings to learn the sound and feel of each keystroke.

The app could even listen in the background when the user entered sensitive info on other apps. When tested on Samsung and HTC phones, the app, presented in the Proceedings of the 2014 ACM Conference on Security and Privacy in Wireless and Mobile Networks, inferred the keystrokes of 100 four-digit PINs with 94 percent accuracy.

Al-Haiqi points out, however, that success rates are mostly from tests of keystroke-deciphering techniques in controlled settings — assuming that users hold their phones a certain way or sit down while typing. How these info-extracting programs fare in a wider range of circumstances remains to be seen. But the answer to whether motion and other sensors would open the door for new privacy invasions is “an obvious yes,” he says.

Motion sensors can also help map a person’s travels, like a subway or bus ride. A trip produces an undercurrent of motion data that’s discernible from shorter-lived, jerkier movements like a phone being pulled from a pocket. Researchers designed an app, described in 2017 in IEEE Transactions on Information Forensics and Security, to extract the data signatures of various subway routes from accelerometer readings.

In experiments with Samsung smartphones on the subway in Nanjing, China, this tracking app picked out which segments of the subway system a user was riding with at least 59, 81 and 88 percent accuracy — improving as the stretches expanded from three to five to seven stations long. Someone who can trace a user’s subway movements might figure out where the traveler lives and works, what shops or bars the person frequents, a daily schedule, or even — if the app is tracking multiple people — who the user meets at various places.
Accelerometer data can also plot driving routes, as described at the 2012 IEEE International Conference on Communication Systems and Networks in Bangalore, India. Other sensors can be used to track people in more confined spaces: One team synced a smartphone mic and portable speaker to create an on-the-fly sonar system to map movements throughout a house. The team reported the work in the September 2017 Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies.

“Fortunately there is not anything like [these sensor spying techniques] in real life that we’ve seen yet,” says Selcuk Uluagac, an electrical and computer engineer at Florida International University in Miami. “But this doesn’t mean there isn’t a clear danger out there that we should be protecting ourselves against.”

That’s because the kinds of algorithms that researchers have employed to comb sensor data are getting more advanced and user-friendly all the time, Mehrnezhad says. It’s not just people with Ph.D.s who can design the kinds of privacy invasions that researchers are trying to raise awareness about. Even app developers who don’t understand the inner workings of machine-learning algorithms can easily get this kind of code online to build sensor-sniffing programs.

What’s more, smartphone sensors don’t just provide snooping opportunities for individual cybercrooks who peddle info-stealing software. Legitimate apps often harvest info, such as search engine and app download history, to sell to advertising companies and other third parties. Those third parties could use the information to learn about aspects of a user’s life that the person doesn’t necessarily want to share.

Take a health insurance company. “You may not like them to know if you are a lazy person or you are an active person,” Mehrnezhad says. “Through these motion sensors, which are reporting the amount of activity you’re doing every day, they could easily identify what type of user you are.”

Sensor safeguards
Since it’s only getting easier for an untrusted third party to make private inferences from sensor data, researchers are devising ways to give people more control over what information apps can siphon off of their devices. Some safeguards could appear as standalone apps, whereas others are tools that could be built into future operating system updates.

Uluagac and colleagues proposed a system called 6thSense, which monitors a phone’s sensor activity and alerts its owner to unusual behavior, in Vancouver at the August 2017 USENIX Security Symposium. The user trains this system to recognize the phone’s normal sensor behavior during everyday tasks like calling, Web browsing and driving. Then, 6thSense continually checks the phone’s sensor activity against these learned behaviors.

If someday the program spots something unusual — like the motion sensors reaping data when a user is just sitting and texting — 6thSense alerts the user. Then the user can check if a recently downloaded app is responsible for this suspicious activity and delete the app from the phone.

Uluagac’s team recently tested a prototype of the system: Fifty users trained Samsung smartphones with 6thSense to recognize their typical sensor activity. When the researchers fed the 6thSense system examples of benign data from daily activities mixed in with segments of malicious sensor operations, 6thSense picked out the problematic bits with over 96 percent accuracy.
For people who want more active control over their data, Supriyo Chakraborty, a privacy and security researcher at IBM in Yorktown Heights, N.Y., and colleagues devised DEEProtect, a system that blunts apps’ abilities to draw conclusions about certain user activity from sensor data. People could use DEEProtect, described in a paper posted online at arXiv.org in February 2017, to specify preferences about what apps should be allowed to do with sensor data. For example, someone may want an app to transcribe speech but not identify the speaker.

DEEProtect intercepts whatever raw sensor data an app tries to access and strips that data down to only the features needed to make user-approved inferences. For speech-to-text translation, the phone typically needs sound frequencies and the probabilities of particular words following each other in a sentence.

But sound frequencies could also help a spying app deduce a speaker’s identity. So DEEProtect distorts the dataset before releasing it to the app, leaving information on word orders alone, since that has little or no bearing on speaker identity. Users can control how much DEEProtect changes the data; more distortion begets more privacy but also degrades app functions.

In another approach, Giuseppe Petracca, a computer scientist and engineer at Penn State, and colleagues are trying to protect users from accidentally granting sensor access to deceitful apps, with a security system called AWare.

Apps have to get user permission upon first installation or first use to access certain sensors like the mic and camera. But people can be cavalier about granting those blanket authorizations, Uluagac says. “People blindly give permission to say, ‘Hey, you can use the camera, you can use the microphone.’ But they don’t really know how the apps are using these sensors.”

Instead of asking permission when a new app is installed, AWare would request user permission for an app to access a certain sensor the first time a user provided a certain input, like pressing a camera button. On top of that, the AWare system memorizes the state of the phone when the user grants that initial permission — the exact appearance of the screen, sensors requested and other information. That way, AWare can tell users if the app later attempts to trick them into granting unintended permissions.

For instance, Petracca and colleagues imagine a crafty data-stealing app that asks for camera access when the user first pushes a camera button, but then also tries to access the mic when the user later pushes that same button. The AWare system, also presented at the 2017 USENIX Security Symposium, would realize the mic access wasn’t part of the initial deal, and would ask the user again if he or she would like to grant this additional permission.

Petracca and colleagues found that people using Nexus smartphones equipped with AWare avoided unwanted authorizations about 93 percent of the time, compared with 9 percent among people using smartphones with typical first-use or install-time permission policies.

The price of privacy
The Android security team at Google is also trying to mitigate the privacy risks posed by app sensor data collection. Android security engineer Rene Mayrhofer and colleagues are keeping tabs on the latest security studies coming out of academia, Mayrhofer says.

But just because someone has built and successfully tested a prototype of a new smartphone security system doesn’t mean it will show up in future operating system updates. Android hasn’t incorporated proposed sensor safeguards because the security team is still looking for a protocol that strikes the right balance between restricting access for nefarious apps and not stunting the functions of trustworthy programs, Mayrhofer explains.

“The whole [app] ecosystem is so big, and there are so many different apps out there that have a totally legitimate purpose,” he adds. Any kind of new security system that curbs apps’ sensor access presents “a real risk of breaking” legitimate apps.

Tech companies may also be reluctant to adopt additional security measures because these extra protections can come at the cost of user friendliness, like AWare’s additional permissions pop-ups. There’s an inherent trade-off between security and convenience, UCLA’s Srivastava says. “You’re never going to have this magical sensor shield [that] gives you this perfect balance of privacy and utility.”

But as sensors get more pervasive and powerful, and algorithms for analyzing the data become more astute, even smartphone vendors may eventually concede that the current sensor protections aren’t cutting it. “It’s like cat and mouse,” Al-Haiqi says. “Attacks will improve, solutions will improve. Attacks will improve, solutions will improve.”

The game will continue, Chakraborty agrees. “I don’t think we’ll get to a place where we can declare a winner and go home.”

New device can transmit underwater sound to air

Don’t expect to play a game of Marco Polo by shouting from beneath the pool’s surface. No one will hear you because, normally, only about 0.1 percent of sound is transmitted from water to the air. But a new type of device might one day help.

Researchers have designed a new metamaterial — a type of material that behaves in ways conventional materials can’t — that increases sound transmission to 30 percent. The metamaterial could have applications for more than poolside play. A future version might be used to detect noisy marine life or listen in on sonar use, say applied physicist Oliver Wright of Hokkaido University in Sapporo, Japan, and a team at Yonsei University in Seoul, South Korea, who describe the metamaterial in a paper accepted to Physical Review Letters.
Currently, detection of underwater sounds happens with hydrophones, which have to be underwater. But what if you wanted to listen in from the surface?

Enter the new device. It’s a small cylinder with a weighted rubber membrane stretched across a metal frame that floats atop the water surface. When underwater sound waves hit the device, its frame and membrane vibrate at finely tuned frequencies to help sound transmit into the air.

“A ‘hard’ surface like a table or water reflects almost 100 percent of sound,” says Wright. “We want to try to mitigate that by introducing an intermediary structure.”
Both water and air resist the flow of sound, a property known as acoustic impedance. Because of its density, water’s acoustic impedance is 3,600 times that of air. The greater the mismatch, the more sound is reflected at a boundary.
Adding a layer of material one-fourth the thickness of an incoming wave’s wavelength can reduce the amount of reflection. This is the principle at work behind anti-reflective coatings applied to lenses of cameras and glasses. While optical light has a wavelength in the hundreds of nanometers, necessitating a thin coating only a few atoms thick, audible sound waves can be meters long.

Even though it’s only one-hundredth the thickness of the sound’s wavelength, instead of the conventional one-fourth, the metamaterial still transmits sound.

“It’s a tour de force of experimental demonstration,” says Oleg Godin, a physicist at the Naval Postgraduate School in Monterey, Calif., who was not involved with the research. “But I’m less impressed by the suggestions and implications about its uses. It’s wishful thinking.”

One major problem that the researchers would have to overcome is the device’s inability to transmit sound that hits the surface an angle. In the lab, the device is tested in a tube — effectively a one-direction environment. But on the vast surface of a lake or ocean, the device would be limited to transmitting sounds from the small area directly below it. Additionally, the metamaterial is limited to transmitting a narrow band of frequencies. Noise outside that range reflects off the water’s surface as usual.

Still, the scientists are optimistic about the next steps, and even propose that a sheet of these devices could work in concert.