Physics

There Is Sound In Space, Thanks To Gravitational Waves

Merging black holes are one class of objects that creates gravitational waves of certain frequencies and amplitudes. Thanks to detectors like LIGO, we can 'hear' these sounds as they occur.

It’s long been said that there’s no sound in space, and that’s true, to a point. Conventional sound requires a medium to travel through, and is created when particles compress-and-rarify, making anything from a loud “bang” for a single pulse to a consistent tone for repeating patterns. In space, where there are so few particles that any such signals die away, even solar flares, supernovae, black hole mergers, and other cosmic catastrophes go silent before they’re ever heard. But there’s another type of compression-and-rarefaction that doesn’t require anything other than the fabric of space itself to travel through: gravitational waves. Thanks to the first positive detection results from LIGO, we’re hearing the Universe for the very first time.

Two merging black holes. The inspiral results in the black holes coming together, while gravitational waves carry the excess energy away. The background spacetime is distorted as a result.

Two merging black holes. The inspiral results in the black holes coming together, while gravitational waves carry the excess energy away. The background spacetime is distorted as a result.

Gravitational waves were something that needed to exist for our theory of gravity to be consistent, according to General Relativity. Unlike in Newton’s gravity, where any two masses orbiting one another would remain in that configuration forever, Einstein’s theory predicted that over long enough times, gravitational orbits would decay. For something like the Earth orbiting the Sun, you’d never live to experience it: it would take 10^150 years for Earth to spiral into the Sun. But for more extreme systems, like two neutron stars orbiting one another, we could actually see the orbits decaying over time. In order to conserve energy, Einstein’s theory of gravity predicted that energy must be carried away in the form of gravitational waves.

As two neutron stars orbit each other, Einstein's theory of general relativity predicts orbital decay, and the emission of gravitational radiation.

As two neutron stars orbit each other, Einstein’s theory of General Relativity predicts orbital decay, and the emission of gravitational radiation. The former has been observed very precisely for many years, as evidenced by how the points and the line (GR prediction) match up so very well.

These waves are maddeningly weak, and their effects on the objects in spacetime are stupendously tiny. But if you know how to listen for them — just as the components of a radio know how to listen for those long-frequency light waves — you can detect these signals and hear them just as you’d hear any other sound. With an amplitude and a frequency, they’re no different from any other wave. General Relativity makes explicit predictions for what these waves should sound like, with the largest wave-generating signals being the easiest ones to detect. The largest amplitude sounds all? It’s the inspiral and merging “chirp” of two black holes that spiral into one another.

In September of 2015, just days after advanced LIGO began collecting data for the first time, a large, unusual signal was spotted. It surprised everyone, because it would have carried so much energy in just a short, 200 millisecond burst, that it would have outshone all the stars in the observable Universe combined. Yet that signal turned out to be robust, and the energy from that burst came from two black holes — of 36 and 29 solar masses — merging into a single 62 solar mass one. Those missing three solar masses? They were converted into pure energy: gravitational waves rippling through the fabric of space. That was the first event LIGO ever detected.

The signal from LIGO of the first robust detection of gravitational waves. The waveform is not just a visualization; it's representative of what you'd actually hear if you listened properly.

The signal from LIGO of the first robust detection of gravitational waves. The waveform is not just a visualization; it’s representative of what you’d actually hear if you listened properly.

Now it’s over a year later, and LIGO is presently on its second run. Not only have other black hole-black hole mergers been detected, but the future of gravitational wave astronomy is bright, as new detectors will open up our ears to new types of sounds. Space interferometers, like LISA, will have longer baselines and will hear lower frequency sounds: sounds like neutron star mergers, feasting supermassive black holes, and mergers with highly unequal masses. Pulsar timing arrays can measure even lower frequencies, like orbits that take years to complete, such as the supermassive black hole pair: OJ 287. And combinations of new techniques will look for the oldest gravitational waves of all, the relic waves predicted by cosmic inflation, all the way back at the beginning of our Universe.

Gravitational waves generated by cosmic inflation are the farthest signal back in time humanity can conceive of potentially detecting. Collaborations like BICEP2 and NANOgrav may indirectly do this in the coming decades.

Gravitational waves generated by cosmic inflation are the farthest signal back in time humanity can conceive of potentially detecting. Collaborations like BICEP2 and NANOgrav may indirectly do this in the coming decades.

There’s so much to hear, and we’ve only just started listening for the first time. Thankfully, astrophysicist Janna Levin — author of the fantastic book, Black Hole Blues and Other Songs from Outer Space — is poised to give the public lecture at Perimeter Institute tonight, May 3rd, at 7 PM Eastern / 4 PM Pacific, and it will be live-streamed here and live-blogged by me in real time! Join us then for even more about this incredible topic, and I can’t wait to hear her talk.

 

The Universe is out there, waiting for you to discover it

Ethan SiegelEthan Siegel, Contributor

Merging black holes are one class of objects that creates gravitational waves of certain frequencies and amplitudes. Thanks to detectors like LIGO, we can 'hear' these sounds as they occur.

Merging black holes are one class of objects that creates gravitational waves of certain frequencies and amplitudes. Thanks to detectors like LIGO, we can ‘hear’ these sounds as they occur.

It’s long been said that there’s no sound in space, and that’s true, to a point. Conventional sound requires a medium to travel through, and is created when particles compress-and-rarify, making anything from a loud “bang” for a single pulse to a consistent tone for repeating patterns. In space, where there are so few particles that any such signals die away, even solar flares, supernovae, black hole mergers, and other cosmic catastrophes go silent before they’re ever heard. But there’s another type of compression-and-rarefaction that doesn’t require anything other than the fabric of space itself to travel through: gravitational waves. Thanks to the first positive detection results from LIGO, we’re hearing the Universe for the very first time.

Two merging black holes. The inspiral results in the black holes coming together, while gravitational waves carry the excess energy away. The background spacetime is distorted as a result.

Two merging black holes. The inspiral results in the black holes coming together, while gravitational waves carry the excess energy away. The background spacetime is distorted as a result.

Gravitational waves were something that needed to exist for our theory of gravity to be consistent, according to General Relativity. Unlike in Newton’s gravity, where any two masses orbiting one another would remain in that configuration forever, Einstein’s theory predicted that over long enough times, gravitational orbits would decay. For something like the Earth orbiting the Sun, you’d never live to experience it: it would take 10^150 years for Earth to spiral into the Sun. But for more extreme systems, like two neutron stars orbiting one another, we could actually see the orbits decaying over time. In order to conserve energy, Einstein’s theory of gravity predicted that energy must be carried away in the form of gravitational waves.

As two neutron stars orbit each other, Einstein's theory of general relativity predicts orbital decay, and the emission of gravitational radiation.

As two neutron stars orbit each other, Einstein’s theory of General Relativity predicts orbital decay, and the emission of gravitational radiation. The former has been observed very precisely for many years, as evidenced by how the points and the line (GR prediction) match up so very well.

These waves are maddeningly weak, and their effects on the objects in spacetime are stupendously tiny. But if you know how to listen for them — just as the components of a radio know how to listen for those long-frequency light waves — you can detect these signals and hear them just as you’d hear any other sound. With an amplitude and a frequency, they’re no different from any other wave. General Relativity makes explicit predictions for what these waves should sound like, with the largest wave-generating signals being the easiest ones to detect. The largest amplitude sounds all? It’s the inspiral and merging “chirp” of two black holes that spiral into one another.

In September of 2015, just days after advanced LIGO began collecting data for the first time, a large, unusual signal was spotted. It surprised everyone, because it would have carried so much energy in just a short, 200 millisecond burst, that it would have outshone all the stars in the observable Universe combined. Yet that signal turned out to be robust, and the energy from that burst came from two black holes — of 36 and 29 solar masses — merging into a single 62 solar mass one. Those missing three solar masses? They were converted into pure energy: gravitational waves rippling through the fabric of space. That was the first event LIGO ever detected.

The signal from LIGO of the first robust detection of gravitational waves. The waveform is not just a visualization; it's representative of what you'd actually hear if you listened properly.

The signal from LIGO of the first robust detection of gravitational waves. The waveform is not just a visualization; it’s representative of what you’d actually hear if you listened properly.

Now it’s over a year later, and LIGO is presently on its second run. Not only have other black hole-black hole mergers been detected, but the future of gravitational wave astronomy is bright, as new detectors will open up our ears to new types of sounds. Space interferometers, like LISA, will have longer baselines and will hear lower frequency sounds: sounds like neutron star mergers, feasting supermassive black holes, and mergers with highly unequal masses. Pulsar timing arrays can measure even lower frequencies, like orbits that take years to complete, such as the supermassive black hole pair: OJ 287. And combinations of new techniques will look for the oldest gravitational waves of all, the relic waves predicted by cosmic inflation, all the way back at the beginning of our Universe.

Gravitational waves generated by cosmic inflation are the farthest signal back in time humanity can conceive of potentially detecting. Collaborations like BICEP2 and NANOgrav may indirectly do this in the coming decades.

Gravitational waves generated by cosmic inflation are the farthest signal back in time humanity can conceive of potentially detecting. Collaborations like BICEP2 and NANOgrav may indirectly do this in the coming decades.

There’s so much to hear, and we’ve only just started listening for the first time. Thankfully, astrophysicist Janna Levin — author of the fantastic book, Black Hole Blues and Other Songs from Outer Space — is poised to give the public lecture at Perimeter Institute tonight, May 3rd, at 7 PM Eastern / 4 PM Pacific, and it will be live-streamed here and live-blogged by me in real time! Join us then for even more about this incredible topic, and I can’t wait to hear her talk.


The live blog will begin a few minutes prior to 4:00 PM Pacific; join us here and follow along!

The warping of spacetime, in the General Relativistic picture, by gravitational masses.

The warping of spacetime, in the General Relativistic picture, by gravitational masses.

3:50 PM: It’s ten minutes until showtime, and to celebrate, here are ten fun facts (or as many as we can get in) about gravity and gravitational waves.

1.) Instead of “action at a distance,” where an invisible force is exerted between masses, general relativity says that matter and energy warp the fabric of spacetime, and that warped spacetime is what manifests itself as gravitation.

2.) Instead of traveling at infinite speed, gravitation only travels at the speed of light.

3.) This is important, because it means that if any changes occur to a massive object’s position, configuration, motion, etc., the ensuing gravitational changes only propagate at the speed of light.

Computer simulation of two merging black holes producing gravitational waves.

Computer simulation of two merging black holes producing gravitational waves.

3:54 PM: 4.) This means that gravitational waves, for example, can only propagate at the speed of light. When we “detect” a gravitational wave, we’re detecting the signal from when that mass configuration changed.

5.) The first signal detected by LIGO occurred at a distance of approximately 1.3 billion light years. The Universe was about 10% younger than it is today when that merger occurred.

Ripples in spacetime are what gravitational waves are.

Ripples in spacetime are what gravitational waves are.

6.) If gravitation traveled at infinite speed, planetary orbits would be completely unstable. The fact that planets move in ellipses around the Sun mandates that if General Relativity is correct, the speed of gravity must equal the speed of light to an accuracy of about 1%.

3:57 PM: 7.) There are many, many more gravitational wave signals than what LIGO has seen so far; we’ve only detected the easiest signal there is to detect.

8.) What makes a signal “easy” to see is a combination of its amplitude, which is to say, how much it can deform a path-length, or a distance in space, as well as its frequency.

A simplified illustration of LIGO's laser interferometer system.

A simplified illustration of LIGO’s laser interferometer system.

9.) Because LIGO’s arms are only 4 kilometers long, and the mirrors reflect the light thousands of times (but no more), that means LIGO can only detect frequencies of 1 Hz or faster.

Earlier this year, LIGO announced the first-ever direct detection of gravitational waves. By building a gravitational wave observatory in space, we may be able to reach the sensitivities necessary to detect a deliberate alien signal.

Earlier this year, LIGO announced the first-ever direct detection of gravitational waves. By building a gravitational wave observatory in space, we may be able to reach the sensitivities necessary to detect a deliberate alien signal.

10.) For slower signals, we need longer lever-arms and greater sensitivities, and that will mean going to space. That’s the future of gravitational wave astronomy!

4:01 PM: We made it! Time to begin and introduce Janna Levin! (Pronounce “JAN-na”, not “YON-na”, if you were wondering.)

The inspiral and merger of the first pair of black holes ever directly observed.

The inspiral and merger of the first pair of black holes ever directly observed.

4:05 PM: Here’s the big announcement/shot: the first direct recording of the first gravitational wave. It took 100 years after Einstein first put forth general relativity, and she’s playing a recording! Make sure you go and listen! What does it mean to “hear” a sound in space, after all, and why is this a sound? That’s the purpose, she says, of her talk.

The galaxies Maffei 1 and Maffei 2, in the plane of the Milky Way, can only be revealed by seeing through the Milky Way's dust. Despite being some of the closest large galaxies of all, they were not discovered until the mid-20th century.

The galaxies Maffei 1 and Maffei 2, in the plane of the Milky Way, can only be revealed by seeing through the Milky Way’s dust. Despite being some of the closest large galaxies of all, they were not discovered until the mid-20th century.

4:08 PM: If you consider what’s out there in the Universe, we had no way of knowing any of this at the time of Galileo. We were thinking about sunspots, Saturn, etc., and were completely unable to conceive of the great cosmic scales or distances. Forget about “conceiving of other galaxies,” we hadn’t conceived of any of this!

 

4:10 PM: Janna is showing one of my favorite videos (that I recognize) from the Sloan Digital Sky Survey! They took a survey of 400,000 of the nearest galaxies and mapped them in three dimensions. This is what our (nearby) Universe looks like, and as you can see, it really is mostly empty space!

The (modern) Morgan–Keenan spectral classification system, with the temperature range of each star class shown above it, in kelvin.

The (modern) Morgan–Keenan spectral classification system, with the temperature range of each star class shown above it, in kelvin.

4:12 PM: She makes a really great point that she totally glosses over: only about 1-in-1000 stars will ever become a black hole. There are over 400 stars within 30 light years of us, and zero of them are O or B stars, and zero of them have become black holes. These bluest, most massive and shortest-lived stars are the only ones that will grow into black holes.

The identical behavior of a ball falling to the floor in an accelerated rocket (left) and on Earth (right) is a demonstration of Einstein's equivalence principle.

The identical behavior of a ball falling to the floor in an accelerated rocket (left) and on Earth (right) is a demonstration of Einstein’s equivalence principle.

4:15 PM: When you consider “where did Einstein’s theory come from,” Janna makes a great point: the idea of the equivalence principle. If you have gravity, you might consider that you feel “heavy” in your chair, for example. But this reaction that you have is the exact same reaction you’d feel if you were accelerating, rather than gravitating. It’s not the gravity that you feel, it’s the effects of the matter around you!

4:17 PM: The band OKGO did a video flying in the vomit comet. Janna can’t show the whole thing, with audio, for copyright reasons, and highly recommends it. Luckily for you, thanks to the internet… here it is! Enjoy at your leisure!

To travel once around Earth's orbit in a path around the Sun is a journey of 940 million kilometers.

To travel once around Earth’s orbit in a path around the Sun is a journey of 940 million kilometers.

4:19 PM: There’s another huge revelation for gravity: the way we understand how things work comes from watching how things fall. The Moon is “falling” around the Earth; Newton realized that. But the Earth is falling around the Sun; the Sun is “falling” around the galaxy; and atoms “fall” here on Earth. But the same rule applies to them all, so long as they’re all in free-fall. Amazing!

Black holes are something the Universe wasn't born with, but has grown to acquire over time. They now dominate the Universe's entropy.

Black holes are something the Universe wasn’t born with, but has grown to acquire over time. They now dominate the Universe’s entropy.

4:21 PM: Here’s a fun revelation: stop thinking of a black hole as collapsed, crushed matter, even though that might be how it originated. Instead, think about it as simply a region of empty space with strong gravitational properties. In fact, if all you did was assign “mass” to this region of space, that would perfectly define a Schwarzschild (non-charged, non-rotating) black hole.

The supermassive black hole (Sgr A*) at the center of our galaxy is shrouded in a dusty, gaseous environment. X-rays and infrared observations can partially see through it, but radio waves might finally be able to resolve it directly.

The supermassive black hole (Sgr A*) at the center of our galaxy is shrouded in a dusty, gaseous environment. X-rays and infrared observations can partially see through it, but radio waves might finally be able to resolve it directly.

4:23 PM: If you were to fall into a black hole the mass of the Sun, you’d have about a microsecond, from crossing the event horizon (according to Janna) until you were crushed to death at the singularity. This is consistent with what I once calculated, where, for the black hole at the center of the Milky Way, we’d have about 10 seconds. Since the Milky Way’s black hole is 4,000,000 times as massive as our Sun, the math kind of works out!

Joseph Weber with his early-stage gravitational wave detector, known as a Weber bar.

Joseph Weber with his early-stage gravitational wave detector, known as a Weber bar.

4:26 PM: How would you detect a gravitational wave? Honestly, it would be like being on the surface of the ocean; you’d bob up and down along the surface of space, and there was a big argument in the community as to whether these waves were real or not. It wasn’t until Joe Weber came along and decided to try and measure these gravitational waves, using a phenomenal device — an aluminum bar — that would vibrate if a rippling wave “plucked” the bar very slightly.

Weber saw many such signals that he identified with gravitational waves, but these, unfortunately, were never reproduced or verified. He was, for all of his cleverness, not a very careful experimenter.

4:29 PM: There’s a good question from Jon Groubert on twitter: “I have a question about something she said – there is something inside a black hole, isn’t there? Like a heavy neutron star.” There should be a singularity, which is either point-like (for a non-rotating singularity) or a one-dimensional ring (for a rotating one), but not condensed, collapsed, three-dimensional matter.

Why not?

Because in order to remain as a structure, a force needs to propagate and be transmitted between particles. But particles can only transmit forces at the speed of light. But nothing, not even light, can move “outward” towards the exit of a black hole; everything moves towards the singularity. And so nothing can hold itself up, and everything collapses into the singularity. Sad, but the physics makes this inevitable.

From left to right: the two LIGO detectors (in Hanford and Livingston, US) and the Virgo detector (Cascina, Italie).

From left to right: the two LIGO detectors (in Hanford and Livingston, US) and the Virgo detector (Cascina, Italie).

4:32 PM: After Weber’s failures (and fall from fame), the idea of LIGO came along by Rai Weiss in the 1970s. It took more than 40 years for LIGO to come to fruition (and over 1,000 people to make it happen), but the most fantastic thing was that it was experimentally possible. By making two very long lever-arms, you could see the effect of a passing gravitational wave.

 

 

4:34 PM: This is my favorite video illustrating what a gravitational wave does. It moves space itself (and everything in it) back and forth by a tiny amount. If you have a laser interferometer set up (like LIGO), it can detect these vibrations. But if you were close enough and your ears were sensitive enough, you could feel this motion in your eardrum!

4:35 PM: I’ve got some really good headphones, Perimeter, but unfortunately I can’t hear the different gravitational wave model signals that Janna is playing!

The LIGO Hanford Observatory for detecting gravitational waves in Washington State, USA.

The LIGO Hanford Observatory for detecting gravitational waves in Washington State, USA.

4:38 PM: It’s funny to think that this is the world’s most advanced vacuum, inside the LIGO detectors. Yet birds, rats, mice, etc., are all under there, and they chew their way into almost the vacuum chamber that the light travels through. But if the vacuum had been broken (it’s been constant since 1998), the experiment would have been over. In Louisiana, hunters shot at the LIGO tunnels. It’s horrifying how sensitive and expensive this equipment is, but yet how fragile it all is, too.

4:41 PM: Janna is doing a really great job telling this story in a suspenseful but very human way. We only saw the final few orbits of two orbiting black holes, drastically slowed down in the above movie. They were only a few hundred kilometers apart, those final four orbits took 200 millisecond, and that’s the entirety of the signal that LIGO saw.

 

4:43 PM: If you’re having trouble listening/hearing the events in the talk, listen to this video (above), in both natural pitch and increased pitch. The smaller black holes (roughly 8 and 13 solar masses) from December 26, 2015, are both quieter and higher pitched than the larger ones (29 and 36 solar masses) from September 14th in the same year.

4:46 PM: Just a little correction: Janna says this was the most powerful event ever detected since the Big Bang. And that’s only technically true, because of the limits of our detection.

When we get any black hole mergers, approximately 10% of the mass of the least massive black hole in a merger pair gets converted into pure energy via Einstein’s E = mc2. 29 solar masses is a lot, but there are going to be black holes of hundreds of millions or even billions of solar masses that have merged together. And we have proof.

The most massive black hole binary signal ever seen: OJ 287.

The most massive black hole binary signal ever seen: OJ 287.

4:49 PM: This is OJ 287, where a 150 million solar mass black hole orbits an ~18 billion solar mass black hole. It takes 11 years for a complete orbit to occur, and General Relativity predicts a precession of 270 degrees per orbit here, compared to 43 arc seconds per century for Mercury.

4:51 PM: Janna did an incredible job ending on time here; I’ve never seen an hour talk actually end after 50 minutes at a Perimeter public lecture. Wow!

The Earth as viewed from a composite of NASA satellite images from space in the early 2000s.

The Earth as viewed from a composite of NASA satellite images from space in the early 2000s.

4:52 PM: What would happen if Earth got sucked up into a black hole? (Q&A question from Max.) Although Janna’s giving a great answer, I’d like to point out that, from a gravitational wave point of view, Earth would be shredded apart, and we’d get a “smeared out” wave signal, that would be a much noisier, static-y signal. Once Earth got swallowed, the event horizon would grow just a tiny bit, as an extra three millionths of a solar mass increased the black hole’s radius by just that tiny, corresponding amount.

4:55 PM: What a fun talk, a great and snappy Q&A session, and a great experience overall. Enjoy it again and again, because the video of the talk is now embedded as a permalink. And thanks for tuning in!

Ceramic Pottery Reveals an Ancient Geomagnetic Field Spike

The magnetic field surrounding Earth is constantly fluctuating in strength.

Credit: NASA’s Scientific Visualization Studio

More than 2,500 years ago in the ancient Near East, the Earth’s geomagnetic field was going gangbusters. During the late eighth century B.C., a new study finds, the magnetic field that surrounds the planet was temporarily 2.5 times stronger than it is today.

Researchers know about these fluctuations thanks to the bureaucracy of Judah, an ancient kingdom situated around what is now Jerusalem. Pottery jugs from between the eighth and second centuries B.C. bear administrative stamps that changed with the political situation. Unbeknown to the people firing these jugs, the act of heating locked information about the Earth’s geomagnetic field into minerals present in the clay. Because the stamps provide precise information about when the pots were fired, the study allows a detailed look at geomagnetic changes over 600 years.

“This was the system of the king in Jerusalem to be able to collect tax efficiently,” study author Erez Ben-Yosef, an archaeologist at Tel Aviv University, said of the stamps. “We are actually benefiting from a good bureaucratic system, the ancient IRS.” [7 Ways the Earth Changes in the Blink of an Eye]

The Earth is surrounded by a magnetic field that arises from the motion of iron in the liquid outer core. Direct observation of the field has been possible for only about 180 years, Ben-Yosef told Live Science. In that time, the field has weakened by about 10 percent, he said. Some researchers think the field might be in the process of flipping, so that magnetic north becomes magnetic south and vice versa.

The new study reveals much faster changes in intensity. There was a spike in intensity during the late eighth century B.C., culminating in a rapid decline after about 732 B.C., Ben-Yosef and his colleagues reported today (Feb. 13) in the journal Proceedings of the National Academy of the Sciences. In a mere 31 years beginning in the year 732 B.C., there was a 27 percent decrease in the strength of the magnetic field, the researchers found. From the sixth century B.C. to the second century B.C., the field was generally stable, with a slight gradual decline.

“Our research shows that the field is very fluctuating,” Ben-Yosef said. “It fluctuates quite rapidly, so there is nothing to worry about,” as far as the current decline, he said. (This doesn’t mean that the magnetic field isn’t going to flip in the near future; the new study looked at only strength of the field, not directionality. The findings do suggest that there’s no reason to worry that a 10 percent decline in the field strength over more than a century is abnormal, Ben-Yosef said.)

At least in the Levant, that is. All of the pottery in the study came from this region, which encompasses what is now Syria, Jordan, Israel, Palestine, Lebanon and nearby areas. That means researchers can’t be sure whether the same fluctuations were happening elsewhere. Because the scientists also don’t know for sure the precise locations within the Levant where the pottery was fired, they can’t say anything about the direction of the geomagnetic field at the time, only its strength. [Photos: Ancient Burial and Metal Tool from Southern Levant]

The clays in ceramic pots contain ferromagnetic minerals, or minerals containing iron. When the clays are heated, the electrons in these minerals align according to the Earth’s magnetic field — imagine a series of iron filings lining up in arcs around a bar magnet. Once cooled, the magnetic patterns are locked in for good. The same process occurs when lava cools, so researchers can also detect changes in the magnetic field by studying volcanic rocks.

A stamped pottery handle from the Israel settlement called Ramat Rahel. The magnetic minerals used in the pottery were sealed in during heating and are revealing the history of Earth's magnetic field.

A stamped pottery handle from the Israel settlement called Ramat Rahel. The magnetic minerals used in the pottery were sealed in during heating and are revealing the history of Earth’s magnetic field.

Credit: Courtesy of Oded Lipschits

Understanding the ancient magnetic field has implications for many fields of research, Ben-Yosef said. Archaeologists would like to develop a new system so they could look at the magnetic properties of heated materials and date them according to what the magnetic field was doing at the time. Earth scientists want to better understand the deep structures in the core that create the magnetic field. Atmospheric scientists want to understand the interactions of the magnetic field with cosmic radiation. Biologists are interested in cosmic radiation, too: Because the magnetic field protects the planet from damaging cosmic rays, Earth owes its flourishing life to the existence of the geomagnetic field.

“This is related to various different phenomena, from biology, Earth sciences, geophysics, atmospheric sciences and archaeology,” Ben-Yosef said.

The researchers are now trying to expand their study of this time period to see if the fluctuations they observed were a regional phenomenon, or more widespread.

Physicists Forge Impossible Molecule That Chemists Failed To Make

 

There’s a bunch of physicists out there that are feeling a little bit pleased with themselves right now, and no wonder – they may have just made all of chemistry redundant. Okay, that’s not really true, but they’ve certainly beat chemistry researchers at their own game.

You see, a team of IBM physicists have managed to forge a new type of molecule, named “triangulene”, that chemistry researchers have been long hoping to synthesize themselves. This suggests that physical processes can be used to make molecules that are essentially impossible to make any other way.

This particular molecule is, unsurprisingly, triangular shaped. Triangular-shaped molecules are fairly rare due to a phenomenon known as “ring strain.” The tight angles of their molecular bonds mean that they are unstable and highly reactive, and don’t last long in a wide range of environments.

Triangulene has been hypothesized to exist by chemistry acolytes for several years now, as a single-atom layer of carbon with the triangular shape being formed from smaller hexagon forms – but no conventional chemical process seemed to be able to create a stable version of it.

Enter IBM, who decided to use a device that could manipulate atoms on an electron scale. First, as reported in the journal Nature Nanotechnology, they nabbed a precursor molecule from chemists in the UK. This molecule looks a lot like triangulene, but it came with two additional hydrogen atoms.

A sketch of triangulene imposed onto the image of the real deal. IBM Research

They placed this precursor on a range of copper and insulating plates, and used a combination of carbon monoxide and gold to probe the molecule – on the smallest of scales – using a unique atomic imaging device.

This device had previously been used to look at weird molecules like olympicene, one that’s shaped like the official logo of the Olympics. Although the images are blurry, individual atomic bonds can be seen.

The device uses changing voltages to “poke” around the molecule by interacting directly with its electrons. The interaction allows the researchers to view its intricate structure, but the team wondered if they could also use it to actually change the chemistry of the molecule itself.

Using some precisely-aimed, set-voltage “bolts,” they managed to remove the two additional hydrogen atoms, and the precursor molecule transformed into the fabled triangulene. It lasted for four days before reverting back to a more stable form – long enough to prove its existence.

“Triangulene is the first molecule that we’ve made that chemists have tried hard, and failed, to make already,” Leo Gross, who led the IBM team at the firm’s laboratories in Zurich, told Nature.

Far from just trouncing cutting-edge chemistry, the team noted that the two free electrons left over from the physical manipulation could “spin” in two separate directions. This is a key feature of molecules used in quantum computing, in that this type of molecule could have one segment of it representing a “0” and the other a “1”.

By being able to represent both states at the same time, more digital information could be stored on a system made of these molecules than ever before. That, of course, explains why IBM is so interested in the forging of triangulene.

So they didn’t just score a victory over chemistry, but one for the future of quantum computing. That’s pretty damn impressive.

These new molecules could be a vital component of future quantum computers. Jurik Peter/Shutterstock

If you want to be a modern day alchemist, then, forget Breaking Bad – have a look at Cosmos instead.

Your Electricity Company Fears This Man

your-electricity-company-fears-this-man

As we documented in a previous article, electricity is the key to unleash world democracy and freedom,

“It’s well known that many wars are fought over resources, many times oil and other energy bases. Electricity is arguably the most essential staple for human survival; because with enough electricity, water can literally be extracted from thin air, which can then be used to plant and water crops.

With enough electricity, nearly all of humanity’s needs can be met.

Centralized energy, like most of us have now, is inherently dangerous to a free society. It can fluctuate, prices can be raised, and grids can be shut down or get damaged by natural disasters. The move toward localized production of electricity, then, is a move towards freedom, security, and democracy. Autonomous energy production is the precursor to an autonomous free society. The secondary effect of increased use of renewable energy is, of course, cleaner air and less pollution. We have all the reasons in the world to support this exciting new development.”

Our previous article pointed out the strides that some countries are taking to make the move toward solar and other sustainable energies. Now, an even more exciting development has been made in the most unlikely of places: an obscure home work shop in Virginia known privately as the “box full of creative chaos”.

Doug Coulter of Floyd, Virginia, lives in the woods in what he calls a “libertarian communism”community where he spends much of his life inventing and innovation in his home work shop.

What Doug has developed can be a game changer when it comes to providing the world’s electricity. He claims that,

“If this works, I’m about to anger several trillion dollar a year businesses.”

These businesses include gas and electric utilities and Big Oil companies.

Doug claims to be on the verge of cracking what has stumped scientists for decades: nuclear fusion. Doug runs an open source forum for scientists and engineers, where he got much of the research needed to crack this priceless problem. He says that once his nuclear fusion reactor is complete, it too will be open source so that anyone living anywhere will have access to the technology. Watch this video to see what he is up to:

 

Astronomers have spotted a black hole so ravenous, it’s pushing the limits of physics

The Universe’s hungriest black hole.

 

Astronomers have discovered a giant black hole that’s so hungry, it’s been gorging on a star for more than a decade – more than 10 times longer than any stellar meal detected before.

Not only is this by far the largest meal a black hole has been seen consuming, but the feast has been going on so long that scientists aren’t quite sure how it’s been sustained without bending the laws of physics. And the answer could tell us how black holes in the early days of the Universe grew more massive than we’ve been able to explain.

When a star gets too close to a black hole, the black hole’s immense gravitational force can rip the star apart – an event known as a tidal disruption event (TDE).

We’ve seen plenty of these TDE’s in the past, thanks to the distinct X-ray flare they produce. After the black hole destroys a star, it flings some of its contents into space at high speeds, and devours the rest, growing larger and blasting out a super hot flare of X-ray radiation in the process.

But most TDEs are short-lived affairs, which is why the new observation is so surprising.

“We have witnessed a star’s spectacular and prolonged demise,” said lead researcher Dacheng Lin from the University of New Hampshire in Durham.

“Dozens of tidal disruption events have been detected since the 1990s, but none that remained bright for nearly as long as this one.”

In fact, that feast has been going on for so long, it’s pushing the limits of physics – the star being consumed has consistently surpassed something called the Eddington limit, which is the maximum luminosity a star can achieve before it’s no longer stable.

The idea is that if a star is pushing out enough radiation to get this bright, then gravity should barely be able to hold it together. And for that reason we’ve never really been able to understand how supermassive black holes at the centre of many galaxies, including our Milky Way, grew as big as they are.

This record-breaking hungry black hole is nicknamed XJ1500+0154, and exists at the core of a small galaxy about 1.8 billion light-years away.

It was spotted by a trio of satellites – NASA’s Chandra X-ray observatory and Swift satellite, as well as the European Space Agency’s XMM-Newton.

The satellites were hunting for TDEs when they stumbled across the incredibly bright flare emitted by XJ1500+0154 back in 2005.

They’ve been observing it ever since, and although it appears the meal is now winding up, the team’s evidence suggests that the black hole was consuming the star’s material for well over 10 years.

That means this is either the most massive star we’ve ever seen get caught up in a TDE, or it’s the first time we’ve seen a smaller star get completely torn apart.

“For most of the time we’ve been looking at this object, it has been growing rapidly,” said one of the researchers, James Guillochon from the Harvard-Smithsonian Centre for Astrophysics.

“This tells us something unusual – like a star twice as heavy as our Sun – is being fed into the black hole.”

The fact that we now have early evidence that black holes can eat something so massive – and grow so ginormous as a result – opens up a while new world of possibilities when it comes to black holes.

We need to keep in mind that the research has only been published on the pre-print site arXiv.org for the physics community to pore over before it’s submitted to a peer-reviewed journal, so we need to wait for independent validation of the results before we get too carried away.

Importantly, if confirmed, this observation could help explain how supermassive black holes were able to get about a billion times more massive than our Sun in the early days of the Universe – something researchers have struggled to explain.

“This event shows that black holes really can grow at extraordinarily high rates,” said team member Stefanie Komossa of China’s QianNan Normal University for Nationalities.

“This may help understand how precocious black holes came to be.”

The team predicts that XJ1500+0154’s feeding supply should be greatly reduced in the next decade, causing the black hole to fade in X-ray brightness and disappear from the satellites’ view.

Whether or not that happens remains to be seen, but astronomers will be watching the black hole closely.

You can read the full paper here.

Lab-created Metallic Hydrogen, If Legit, Could Revolutionize Physics

science, hydrogen

Harvard researchers announced they have been able to compress liquid hydrogen into a metal. HARVARD UNIVERSITY/YOUTUBE

Back in 1935, physicists Eugene Wigner and Hillard Bell Huntington of Princeton University predicted that if subjected to sufficiently intense pressure, hydrogen would become a solid metal. For the past several decades, scientists in a few elite labs around the world have been trying to accomplish just that, bombarding hydrogen with lasers and electrical pulses, and trying to squeeze it between diamonds.

It’s not just curiosity that drives them. If metallic hydrogen could be manufactured and remain stable at room temperatures, it might be an amazingly useful material. For one thing, scientists believe that it would be a superconductor, capable of allowing electrons to flow through it without any energy loss. And when heated, it would release a huge amount of energy, giving it the potential to be a game-changing propellant for rockets.

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The periodic table is an invaluable tool for scientists across the planet — but how does it work? In this episode, Allison and Robert explore the creation of the periodic table. Tune in to learn more about the history and structure of the periodic table.

But one downside to metallic hydrogen? Nobody’s been able to actually produce it — that is, apparently, until now. Harvard University researchers believe that they have created metallic hydrogen for the first time in the laboratory. In an article published in the journal Science, natural science professor Isaac Silvera and research fellow Ranga Dias describe compressing hydrogen at low temperatures between specially treated synthetic diamond anvils, and observing it transition through stages — from transparent to black, and eventually to a substance that reflects light. “The properties are those of an atomic metal,” they conclude.

Corresponding author Silvera didn’t respond to an email, but in a Harvard YouTube video, he says: “We have made a new material. It’s a material that never has existed on Earth before.”

 

Others also see the discovery as momentous.

“This paper is likely to be one of the most important ones in physics for several decades. It solves (experimentally) a major outstanding problem,” says Jeffrey M. McMahon, an assistant professor of physics at Washington State University not involved in the research, via email. “This is especially the case if metallic hydrogen exhibits the remarkable properties expected.” He says that metallic hydrogen could turn out to be “potentially the most powerful rocket fuel known.”

To create the substance, Silvera and Dias began by compressing liquid hydrogen — the element liquefies when cooled to minus 423 degrees Fahrenheit (minus 253 degrees Celsius) — in an anvil made from two synthetic diamonds. Then they turned a steel screw to exert more and more pressure upon the liquid hydrogen.

At a pressure of about 2 million times that of Earth’s atmosphere, the hydrogen was transparent. But once they doubled the force to 4 million atmospheres — more intense than the pressure inside Earth’s core — the hydrogen turned opaque and black. Tightening the screw even further, the hydrogen sample reflected about 90 percent of the light that was shined upon it.

The researchers used diamond anvils to compress molecular hydrogen. R. DIAS AND I.F. SILVERA/HARVARD UNIVERSITY

The Harvard scientists’ finding comes more than 80 years after metallic hydrogen was first imagined. “It has taken so long because the pressure at which it becomes metallic is higher than was originally thought by Wigner and Huntingdon,” explains University of Illinois professor David M. Ceperley, an expert in condensed matter physics, via email. “At pressures about 300 [atmospheres], diamonds become very susceptible to cracking, especially when hydrogen is present. Many other experimentalists are surprised that Dias and Silvera were able to go up to the pressures they report successfully.”

Ceperley cautions that the discovery will need to be validated by additional research. “Even the Harvard group has not repeated it yet,” he says. “They need to verify that what is in their cell is pure hydrogen and that the gasket material did not get dissolved in there making it metallic. They need to measure other properties than just optical reflectivity.”

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But in a recent article in the journal Nature, some scientists expressed skepticism about the discovery, saying that they wanted to see additional proof that metallic mercury actually had been produced. Rivera told The New York Times he plans to perform additional measurements on the hydrogen, using a process called Raman scattering, which uses laser light. He also plans to take the sample to the U.S. government’s Argonne National Laboratory in Illinois, where it will be probed with X-rays.

Ceperley also isn’t convinced that metallic hydrogen will necessarily turn into a game-changing rocket fuel. He doesn’t think it will remain stable once the pressure upon it is released, the way that a diamond does. Instead, he expects that it will revert to a molecular form that’s stable only at low pressure.  “I think the most likely application,” he says, “is to teach us how to make better superconductors out of hydrogen-containing compounds. Clearly pure metallic hydrogen by itself will be at too high a pressure to be useful.”

NOW THAT’S INTERESTING

According to the 2005 scientific textbook “Structure-Property Relations in Nonferrous Metals,” while metallic hydrogen would be an exotic material on Earth, it’s likely to be abundant within the interiors of Jupiter-sized gas planets in other solar systems; the authors write that it might even be “the most common metal in the universe as a whole.”

Physicists address loophole in tests of Bell’s inequality using 600-year-old starlight

Physicists address loophole in tests of Bell’s inequality using 600-year-old starlight

Physicists from MIT, the University of Vienna, and elsewhere have presented a strong demonstration of quantum entanglement even when vulnerability to the freedom-of-choice loophole is significantly restricted. Credit: Christine Daniloff/MIT

Quantum entanglement may appear to be closer to science fiction than anything in our physical reality. But according to the laws of quantum mechanics—a branch of physics that describes the world at the scale of atoms and subatomic particles—quantum entanglement, which Einstein once skeptically viewed as “spooky action at a distance,” is, in fact, real.

Imagine two specks of dust at opposite ends of the universe, separated by several billion light years. Quantum theory predicts that, regardless of the vast distance separating them, these two particles can be entangled. That is, any measurement made on one will instantaneously convey information about the outcome of a future measurement on its partner. In that case, the outcomes of measurements on each member of the pair can become highly correlated.

If, instead, the universe behaves as Einstein imagined it should—with particles having their own, definite properties prior to measurement, and with local causes only capable of yielding local effects—then there should be an upper limit to the degree to which measurements on each member of the pair of particles could be correlated. Physicist John Bell quantified that upper limit, now known as “Bell’s inequality,” more than 50 years ago.

In numerous previous experiments, physicists have observed correlations between particles in excess of the limit set by Bell’s inequality, which suggests that they are indeed entangled, just as predicted by . But each such test has been subject to various “loopholes,” scenarios that might account for the observed correlations even if the world were not governed by .

Now, physicists from MIT, the University of Vienna, and elsewhere have addressed a loophole in tests of Bell’s inequality, known as the freedom-of-choice loophole, and have presented a strong demonstration of even when the vulnerability to this loophole is significantly restricted.

“The real estate left over for the skeptics of quantum mechanics has shrunk considerably,” says David Kaiser, the Germeshausen Professor of the History of Science and professor of physics at MIT. “We haven’t gotten rid of it, but we’ve shrunk it down by 16 orders of magnitude.”

A research team including Kaiser; Alan Guth, the Victor F. Weisskopf Professor of Physics at MIT; Andrew Friedman, an MIT research associate; and colleagues from
the University of Vienna and elsewhere has published its results today in the journal Physical Review Letters.

Closing the door on quantum alternatives

The freedom-of-choice loophole refers to the idea that experimenters have total freedom in choosing their experimental setup, from the types of particles to entangle, to the measurements they choose to make on those particles. But what if there were some other factors or hidden variables correlated with the experimental setup, making the results appear to be quantumly entangled, when in fact they were the result of some nonquantum mechanism?

Physicists have attempted to address this loophole with extremely controlled experiments, in which they produce a pair of entangled photons from a single source, then send the photons to two different detectors and measure properties of each photon to determine their degree of correlation, or entanglement. To rule out the possibility that hidden variables may have influenced the results, researchers have used random number generators at each detector to decide what property of each photon to measure, in the split second between when the photon leaves the source and arrives at the detector.

But there is a chance, however slight, that hidden variables, or nonquantum influences, may affect a random number generator before it relays its split-second decision to the photon detector.

“At the heart of quantum entanglement is the high degree of correlations in the outcomes of measurements on these pairs [of particles],” Kaiser says. “But what if a skeptic or critic insisted these correlations weren’t due to these particles acting in a fully quantum mechanical way? We want to address whether there is any other way that those correlations could have snuck in without our having noticed.”

“Stars aligned”

In 2014, Kaiser, Friedman, and their colleague Jason Gallicchio (now a professor at Harvey Mudd College) proposed an experiment to use ancient photons from astronomical sources such as stars or quasars as “cosmic setting generators,” rather than on Earth, to determine the measurements to be made on each entangled photon. Such cosmic light would be arriving at Earth from objects that are very far away—anywhere from dozens to billions of light years away. Thus, if some hidden variables were to interfere with the randomness of the choice of measurements, they would have had to have set those changes in motion before the time the light left the cosmic source, long before the experiment on Earth was conducted.

In this new paper, the researchers have demonstrated their idea experimentally for the first time. The team, including Professor Anton Zeilinger and his group at the

University of Vienna and the Austrian Academy of Sciences, set up a source to produce highly entangled pairs of photons on the roof of a university laboratory in Vienna. In each experimental run, they shot the entangled photons out in opposite directions, toward detectors located in buildings several city blocks away—the Austrian National Bank and a second university building.

The researchers also set up telescopes at both detector sites and trained them on stars, the closest of which is about 600 light years away, which they had previously determined would send sufficient photons, or starlight, in their direction.

“On those nights, the stars aligned,” Friedman says. “And with bright stars like these, the number of photons coming in can be like a firehose. So we have these very fast detectors that can register detections of cosmic photons on subnanosecond timescales.”

“Out of whack” with Einstein

In the few microseconds before an entangled photon arrived at a detector, the researchers used each telescope to rapidly measure a property of an incoming stellar photon—in this case, whether its wavelength was redder or bluer than a particular reference wavelength. They then used this random property of the stellar photon, generated 600 years ago by its star, to determine what property of the incoming entangled photons to measure. In this case, red stellar photons signaled a detector to measure an entangled photon’s polarization in a particular direction. A blue stellar photon would set the device to measure the polarization of the entangled particle along a different direction.

The team conducted two experiments, with each experimental run lasting only three minutes. In each case, the researchers measured about 100,000 pairs of . They found that the polarization measurements of the photon pairs were highly correlated, well in excess of the bound set by Bell’s inequality, in a way that is most easily explained by quantum mechanics.

“We find answers consistent with quantum mechanics to an enormously strong degree, and enormously out of whack with an Einstein-like prediction,” Kaiser says.

The results represent improvements by 16 orders of magnitude over previous efforts to address the freedom-of-choice loophole.

“All previous experiments could have been subject to this weird loophole to account for the results microseconds before each experiment, versus our 600 years,” Kaiser says. “So it’s a difference of a millionth of a second versus 600 years’ worth of seconds—16 orders of magnitude.”

“This experiment pushes back the latest time at which the conspiracy could have started,” Guth adds. “We’re saying, in order for some crazy mechanism to simulate
quantum mechanics in our experiment, that mechanism had to have been in place 600 years ago to plan for our doing the experiment here today, and to have sent photons of just the right messages to end up reproducing the results of quantum mechanics. So it’s very far-fetched.”

There is also a second, equally far-fetched possibility, says Michael Hall, a senior research fellow at Griffith University in Brisbane, Australia.

“When photons from the distant stars reach the devices that determine the measurement settings, it is possible that these devices act in some way to change the colors of the photons, in a way that is correlated with the laser producing the entanglement,” says Hall, who was not involved in the work. “This would only require a 10-microsecond-old conspiracy between the devices and the laser. However, the idea that photons don’t show their ‘true colors’ when detected would overturn all observational astronomy and basic electromagnetism.”

Explore further: Quantum physics mimics spooky action into the past

More information: Cosmic Bell Test: Measurement Settings from Milky Way Stars. arxiv.org/abs/1611.06985v2

Read more at: https://phys.org/news/2017-02-physicists-loophole-bell-inequality-year-old.html#jCp

Material can turn sunlight, heat and movement into electricity—all at once

sunny

Credit: Marina Shemesh/public domain

Many forms of energy surround you: sunlight, the heat in your room and even your own movements. All that energy—normally wasted—can potentially help power your portable and wearable gadgets, from biometric sensors to smart watches. Now, researchers from the University of Oulu in Finland have found that a mineral with the perovskite crystal structure has the right properties to extract energy from multiple sources at the same time.

Perovskites are a family of minerals, many of which have shown promise for harvesting one or two types of at a time—but not simultaneously. One family member may be good for solar cells, with the right properties for efficiently converting solar energy into electricity. Meanwhile, another is adept at harnessing energy from changes in temperature and pressure, which can arise from motion, making them so-called pyroelectric and piezoelectric materials, respectively.

Sometimes, however, just one type of energy isn’t enough. A given form of energy isn’t always available—maybe it’s cloudy or you’re in a meeting and can’t get up to move around. Other researchers have developed devices that can harness multiple forms of energy, but they require multiple materials, adding bulk to what’s supposed to be a small and portable device.

This week in Applied Physics Letters Yang Bai and his colleagues at the University of Oulu explain their research on a specific type of perovskite called KBNNO, which may be able to harness many forms of energy. Like all perovskites, KBNNO is a ferroelectric material, filled with tiny electric dipoles analogous to tiny compass needles in a magnet.

When like KBNNO undergo changes in temperature, their dipoles misalign, which induces an electric current. Electric charge also accumulates according to the direction the dipoles point. Deforming the material causes certain regions to attract or repel charges, again generating a current.

Previous researchers have studied KBNNO’s photovoltaic and general ferroelectric properties, but they did so at temperatures a couple hundred degrees below freezing, and they didn’t focus on properties related to temperature or pressure. The new study represents the first time anyone has evaluated all of these properties at once above room temperature, Bai said.

The experiments showed that while KBNNO is reasonably good at generating electricity from heat and pressure, it isn’t quite as good as other perovskites. Perhaps the most promising finding, however, is that the researchers can modify the composition of KBNNO to improve its pyroelectric and piezoelectric properties. “It is possible that all these can be tuned to a maximum point,” said Bai, who, with his colleagues, is already exploring such an improved material by preparing KBNNO with sodium.

Within the next year, Bai said, he hopes to build a prototype multi-energy-harvesting device. The fabrication process is straightforward, so commercialization could come in just a few years once researchers identify the best material.

“This will push the development of the Internet of Things and smart cities, where power-consuming sensors and devices can be energy sustainable,” he said.

This kind of material would likely supplement the batteries on your devices, improving energy efficiency and reducing how often you need to recharge. One day, Bai said, multi-energy harvesting may mean you won’t have to plug in your gadgets anymore. Batteries for small devices may even become obsolete.

Explore further: Stability challenge in perovskite solar cell technology

More information: Yang Bai et al, Ferroelectric, pyroelectric, and piezoelectric properties of a photovoltaic perovskite oxide, Applied Physics Letters (2017). DOI: 10.1063/1.4974735

Read more at: https://phys.org/news/2017-02-material-sunlight-movement-electricityall.html#jCp

Measuring time without a clock

Measuring time without a clock

Credit: Ecole Polytechnique Federale de Lausanne

EPFL scientists have been able to measure the ultrashort time delay in electron photoemission without using a clock. The discovery has important implications for fundamental research and cutting-edge technology.

When light shines on certain materials, it causes them to emit . This is called “” and it was discovered by Albert Einstein in 1905, winning him the Nobel Prize. But only in the last few years, with advancements in laser technology, have scientists been able to approach the incredibly short timescales of photoemission. Researchers at EPFL have now determined a delay of one billionth of one billionth of a second in photoemission by measuring the spin of photoemitted electrons without the need of . The discovery is published in Physical Review Letters.

Photoemission

Photoemission has proven to be an important phenomenon, forming a platform for cutting-edge spectroscopy techniques that allow scientists to study the properties of electrons in a solid. One such property is spin, an intrinsic quantum property of particles that makes them look like as if they were rotating around their axis. The degree to which this axis is aligned towards a particular direction is referred to as , which is what gives some materials, like iron, magnetic properties.

Although there has been great progress in using photoemission and spin polarization of photo-emitted electrons, the time scale in which this entire process takes places have not been explored in great detail. The common assumption is that, once light reaches the material, electrons are instantaneously excited and emitted. But more recent studies using advanced laser technology have challenged this, showing that there is actually a time delay on the scale of attoseconds.

Time without a clock

The lab of Hugo Dil at EPFL, with colleagues in Germany, showed that during photoemission, the spin polarization of emitted electrons can be related to the attosecond time delays of photoemission. More importantly, they have shown this without the need for any experimental time resolution or measurement—essentially, without the need for a clock. To do this, the scientists used a type of photoemission spectroscopy (SARPES) to measure the spin of electrons photo-emitted from a crystal of copper.

“With lasers you can directly measure the between different processes, but it is difficult to determine when a process starts – time zero,” says Mauro Fanciulli, a PhD student of Dil’s group and first author on the paper. “But in our experiment we measure time indirectly, so we don’t have that problem – we could access one of the shortest timescales ever measured. The two techniques [spin and lasers], are complementary, and together they can yield a whole new realm of information.”

The information about the timescale of photoemission is included in the wavefunction of the emitted electrons. This is a quantum description of the probability of where any given electron can be found at any given time. By using SAPRES, the scientists were able to measure the spin of the electrons, which in turn allowed them to access their wavefunction properties.

“The work is a proof of principle that can trigger further fundamental and applied research,” says Hugo Dil. “It deals with the fundamental nature of time itself and will help understand the details of the photoemission process, but it can also be used in photoemission spectroscopy on materials of interest.” Some of these materials include graphene and high-temperature superconductors, which Dil and his colleagues will be studying next.

Read more at: https://phys.org/news/2017-02-clock.html#jCp

Never-before-seen topological solitons experimentally realized in liquid crystals

topological soliton

A polarizing optical micrograph of the twistion, a type of topological soliton, observed in chiral nematic liquid crystals. Credit: Ackerman and Smalyukh. Published by the American Physical Society

Read more at: https://phys.org/news/2017-02-never-before-seen-topological-solitons-experimentally-liquid.html#jCp

(Phys.org)—Physicists have discovered that dozens of 3-D knotted structures called “topological solitons,” which have remained experimentally elusive for hundreds of years, can be created and frozen for long periods of time in liquid crystals like those used in electronic displays. Until now, topological solitons have been realized only in a few experiments, and for such a short time that it has been impossible to study them in any detail.

The new results may change all that, as they provide a way to produce a wide diversity of long-lasting topological solitons that can be studied with microscopes and, perhaps one day, play a role in novel optical and electrical applications.

The researchers, Paul J. Ackerman and Ivan I. Smalyukh at the University of Colorado, Boulder, have published a paper on the experimental realization of topological solitons in a recent issue of Physical Review X.

“Our work establishes experimental and numerical approaches for detailed studies of 3-D topological solitons, with the great advantage of enabling a direct comparison between experimental and theoretical results and with a potential impact on many branches of physics and the mathematical field of topology,” Smalyukh told Phys.org. “Our work not only experimentally demonstrates 3-D topological solitons that mathematicians and theoretical physicists envisaged previously, but also reveals a series of solitonic structures that have not been anticipated.”

 

https://phys.org/news/2017-02-never-before-seen-topological-solitons-experimentally-liquid.html

 

Knotted background

Interest in topological solitons dates back to the early 1800s, when the mathematician Carl Friedrich Gauss suggested that the lines of magnetic and electric fields form 3-D knots that might behave like particles. Later, Lord Kelvin and others considered knotted vortices as an early model of the atom, in which the knots’ properties could explain the chemical properties of the different elements.

Currently, many models in physics and cosmology involve topological solitons—for instance, models of condensed matter systems, elementary particles, magnetic monopoles, and magnetic particles called skyrmions that play a role in the emerging field of spintronics.

What exactly are topological solitons? If you take two or more circular rings, link them together to make a chain, then distort the rings by twisting and pulling on them as if they were made of putty, and finally embed the entire structure into a background surface, the result would look like a topological soliton. Describing these objects in more precise detail requires defining them as four-dimensional objects called “three-spheres,” and then converting these four-dimensional objects into three-dimensional objects using a mathematical technique called Hopf mapping. It’s these 3-D objects, called “preimages,” that are the linked rings shown in visual representations.

One of the reasons why topological solitons are so difficult to experimentally realize is that they correspond to a physical system’s lowest energy state in order to be stable. For this reason, they have been demonstrated only as transient structures in liquid crystals. It’s also possible that topological solitons may exist in another medium, chiral ferromagnets, but a lack of experimental imaging techniques prevents researchers from observing them.

topological solitons

An assortment of topological solitons, depicted by computer simulations, illustrations of Hopf maps, and polarizing optical micrographs. Credit: Ackerman and Smalyukh. Published by the American Physical Society

Freezing knots

In the new study, the researchers developed a method to “freeze” topological solitons in a solid film of chiral through a polymerization process involving low levels of ultraviolet light, along with heating and cooling. To enable the experiment to be broadly accessible, the researchers used commercially available liquid crystals, to which they added chiral dopants. Using optical tweezers to generate and manipulate patterns in the pre-frozen liquid crystals, the researchers could also control the types of topological solitons being made.

After the topological solitons are frozen into the liquid crystals, the researchers can study them using an optical microscope—specifically, a three-photon excitation fluorescence polarizing microscope, which produces an optical signal that can be used to construct 3-D images of the solitons.

In the second part of their study, the researchers showed how this data could then be used to make numerical simulations corresponding to the highly complex physical structures. This process is based on analyzing the energetically favorable twisting patterns that minimize the liquid crystals’ elastic free energy. Essentially, this process of converting the experimental structures (preimages) to numerical models is analogous to the mathematical Hopf mapping of 3-D objects (preimages) to four dimensions.

Potential applications

The ability to generate long-lasting topological solitons also opens the doors to potential applications. One idea is to take advantage of the fact that different topological solitons have distinct optical properties, which could be used in optical devices that shift the phase of light, as well as in pixels for optical displays. In addition, if the topological solitons identified here in liquid crystals also exist in solid ferromagnets, the researchers expect that they could potentially revolutionize the field of skyrmionics, in which skyrmions could be used to construct magnetic devices, such as data storage and logic.

topological solitons

Linking diagrams and graphs of some 3D topological solitons. Credit: Ackerman and Smalyukh. Published by the American Physical Society

“The large variety of localized long-term stable topological solitons, combined with the unique electro-optic properties of the host medium, will inevitably lead to technological applications, such as electro-optic devices and bistable information displays,” Ackerman said. “A broad spectrum of new opportunities also emerge on the fundamental side, where our research group will work to establish how different topological solitons can transform one to another and also how the solitons with large Hopf index values can be experimentally realized.”

Overall, one of the biggest advantages of the new method is that it provides a much more comprehensive, detailed analysis of topological soliton preimages than other construction methods. As a result, the new method uncovers small details in the topology that could easily be missed otherwise, such as subtle differences between very similar structures that could have been mistaken to be the same structure. The results show that topological solitons are more complex and diverse than previous evidence could show, and indicate that many more of these structures are still waiting to be discovered.

“An infinitely large number of topological solitons may potentially exist, especially when considering different physical systems,” Smalyukh said.

Explore further: Towards new IT devices with stable and transformable solitons

More information: Paul J. Ackerman and Ivan I. Smalyukh. “Diversity of Knot Solitons in Liquid Crystals Manifested by Linking of Preimages in Torons and Hopfions.” Physical Review X. DOI: 10.1103/PhysRevX.7.011006

Read more at: https://phys.org/news/2017-02-never-before-seen-topological-solitons-experimentally-liquid.html#jCp

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