Our world is full of light, and we depend upon it to power life on our planet. So it is appropriate to honor three scientists who invented new ways of using light rays to explore our world.
The 2018 Nobel Prize in physics was awarded to Arthur Ashkin, Gérard Mourou and Donna Strickland for developing tools made from light beams. Ashkin won half of the prize for his work on optical tweezers, which are beams of light that can actually manipulate tiny objects like cells or atoms, while Mourou and Strickland won the other half for creating technology that generates high-intensity, ultra-short laser pulses, which are used for eye surgeries, material sciences, studies of very fast processes and plasma physics, among others.
Alfred Nobel specified in his will that the physics prize should be awarded for “the most important discovery or invention within the field of physics,” so as a physicist I think he’d be pleased that this year’s award recognizes inventions made in the 1970s and 1980s that have led to practical applications that benefit mankind.
Donna Strickland is only the third woman to win the Nobel Prize in physics, out of 210 recipients, and the first since 1963. Marie Curie was the first, in 1903; she won another one in 1911 for chemistry. Maria Goeppert-Mayer was the second. Hopefully in the future the Nobel Prize committee can lower the average of 60 years between women laureates being named.
What are optical tweezers?
Using light to manipulate our world has become very important in science and medicine over the past several decades. This year’s physics Nobel recognizes the invention of tools that have facilitated advances in many fields. Optical tweezers use light to hold tiny objects in place or measure their movement. It may seem odd that light can actually hold something in place, but it has been well-known for more than a century that light can apply a force on physical objects through what is known as radiation pressure. In 1969, Arthur Ashkin used lasers to trap and accelerate micron sized objects such as tiny spheres and water droplets. This led to the invention of optical tweezers that use two or more focused laser beams aimed in opposite directions to attract a target particle or cell toward the center of the beams and hold it in place. Each time the particle moves away from the center, it encounters a force pushing it back toward the center.
Steven Chu, Claude Cohen-Tannoudji and William D. Phillips won the 1997 Nobel Prize in physics for development of laser cooling traps, known as optical traps, that hold atoms within a confined space. Askhin and Chu worked together at Bell Laboratories in the 1980s laying the foundation for work on optical traps. While Chu continued work with neutral atoms, Ashkin pursued larger, biological targets. In 1987, Ashkin used optical tweezers to examine an individual bacterium – without harming the microbe. Now optical tweezers are routinely used in studies of molecules and cells.
Ashkin earned his bachelor’s degree from Columbia University and his Ph.D. from Cornell. He started at Bell Laboratories in 1952 and retired in 1992. But he assembled a home laboratory to continue his scientific investigations. He has been awarded more than 45 patents.
Why are fast laser pulses important?
Gerard Mourou and Donna Strickland worked together at the University of Rochester, where they developed the technique called chirped pulse amplification for laser light. Strickland was a graduate student and Mourou was her thesis advisor in the mid-1980s. At the time, progress on creating brighter lasers had slowed. Stronger lasers tended to damage themselves. Strickland and Mourou invented a way to create more intense light, but in short pulses.
You are probably most familiar with laser pointers or barcode scanners, which are just some of the ways we use lasers in everyday life. But these are relatively low-intensity lasers. Many scientific applications need much stronger ones.
To solve this problem, Mourou and Strickland used lasers with very short (ultrashort) pulses – quick bursts of light separated in time. With chirped pulse amplification, the pulses are stretched in time, making them longer and less intense, and then the pulses are amplified up to a million times. When these pulses are compressed again (through reversing the process used to stretch), the pulses are much more intense than can be created without the chirped pulse amplification technique. As an analogy, consider a thick rubber band. When the band is stretched, the rubber becomes thinner. When it is released, it returns to its original thickness. Now imagine that there is a way to make the stretched rubber band thicker. When the band is released, it will end up thicker than than the original band. This is essentially what happens with the laser pulse.
There are a variety of ways the stretching and amplification can be done, but nearly all of the highest-power lasers in the world use some variation of this technique. Since the invention of chirped pulse amplification, the maximum intensity of new lasers has continued a dramatic rise.
In my own field of particle physics, chirped pulse amplification-based lasers are used to accelerate beams of particles, possibly providing a path to greater acceleration in a shorter distance. This could lead to lower-cost, high-energy accelerators that can push the bounds of particle physics – enabling us to detect evermore elusive particles and gain a better understanding of the universe.
But not all particle accelerators are behemoths like the Large Hadron Collider, which has a circumference of 17 miles. There are some 30,000 industrial particle accelerators worldwide that are used closer to home for material preparation, cancer treatment and medical research. Mourou and Strickland’s work may be used to shrink the size of these accelerators making them smaller and cheaper.
Ultrafast, high-intensity lasers are also now being used in eye surgery. It can be used to treat the cornea (surface of the eye) to improve vision in some patients. The chirped pulse amplification invention is also used in attosecond science for studying ultrafast processes. An attosecond is one million trillionth of a second. By having lasers that produce pulses every attosecond, we can get a snapshots of extremely fast processes such as atoms losing an electron (ionizing) and then recapturing it.
The Nobel Prize-winning work was the basis for Strickland’s Ph.D. thesis from the University of Rochester. Dr. Strickland is now an associate professor at the University of Waterloo in Canada. Mourou became the founding director of the Center for Ultrafast Optical Science at the University of Michigan in 1990. He later became director of the Laboratorie d’Optique de Applique in France.
The 2018 Nobel Prize in physics shines a light on the pioneering work of these three scientists. Over the past three decades, their inventions have created avenues of science and medical treatments that were previously unattainable. It is certain that we will continue to benefit from their work for a long time.
This was the dawn of multi-messenger astronomy: a new era in astronomy, where events in the universe are observed with more than just a single type of radiation. In this case, the messengers were gravitational waves and electromagnetic radiation.
What we’ve learned (so far)
From this single event, we learned an incredible amount. Last October, on the day the detection was made public, 84 scientific papers were published (or the preprints made available).
We learned that gravity and light travel at the same speed, neutron star mergers are a source of short gamma-ray bursts, and that kilonovae – the explosion from a neutron star merger – are where our gold comes from.
This rich science came from the fact that we were able to combine our observatories to witness this single event from multiple astronomical “windows”. The gravitational waves arrived first, followed 1.7 seconds later by gamma-rays. That is a pretty small delay, considering the waves had been travelling for 130 million years.
Over the next few weeks, visible light and radio waves began to be observed and then slowly faded.
It seemed like the news about gravitational waves was coming fast and furious, with the first detection announced in 2016, a Nobel prize in 2017, and the announcement of the binary neutron star merger just weeks after the Nobel prize.
Time for upgrades
On this first anniversary of the neutron star merger, the gravitational wave detectors are offline for upgrades. They actually went offline shortly after the detection and will come back online some time early in 2019.
The work of making gravitational wave detectors function requires extraordinary patience and dedication. These are exquisite experiments – it took more than 40 years of technological development by a community of more than a thousand scientists to get to the point of detecting the first signal.
Naturally, improving on this work is not easy. So what does it actually take?
We really do listen to gravitational waves, and our detectors act more like microphones than telescopes or cameras.
If you listen to the first ever gravitational wave signal (below) you can hear the wave-chirp itself, accompanied by a rumbling hiss (the audio is shifted to a higher frequency to make it easier to hear).
That hiss is noise in our detector. It’s what limits our ability to find gravitational waves, and it also limits our ability to infer properties about their sources.
It’s a bit like if you’re standing in the kitchen and you want listen to birds singing outside, but you can’t really hear them because the dishwasher is running too loudly.
To detect gravitational waves, we need to do more than just turn off the dishwasher. We need to build the quietest, best-isolated thing on Earth.
If we could eliminate the noise in our detectors entirely, the gravitational wave chirp would sound like this (again, the audio is shifted to a higher frequency to make it easier to hear):
Unfortunately, the laws of quantum mechanics and thermodynamics both prevent us from eliminating the noise entirely. Nonetheless, we strive to do the best that these fundamental limits permit. This involves, among many other extraordinary things, hanging our mirrors on glass threads .
Our mirrors weight 40kg each and are suspended from four of these glass threads, which are less than a half-millimetre in diameter and exquisitely crafted.
The threads are under enormous stress, and the slightest imperfection (or the slightest touch) can cause them to explode.
Just such an explosion happened earlier this year while installing a new mirror. Fortunately, the precious mirror fell into a cradle designed for just such a possibility, and was not damaged.
Nonetheless, the delicate, intricate work of creating the glass threads, attaching them to the mirror, hanging the mirror and then installing it all needed to be redone.
Improvements to the detector
This was a heartbreaking setback for the team, but the added delay was not entirely in vain. In parallel with remaking the glass threads and rehanging the new mirror, we made some other improvements to the detector, for which we otherwise would not have had enough time.
One of the goals of this upgrade period is to install something called a quantum squeezed light source into the gravitational wave detectors.
As mentioned earlier, quantum mechanics mandates a certain minimum amount of noise in any measurement. We can’t arbitrarily reduce this quantum noise, but we can move it around and change its shape by squeezing it.
This is a bit like sweeping dust under the rug. It’s not really gone, but it might not bother you so much anymore. The quantum squeezed light source does just this.
A gravitational wave detector is already a very complex system, and a squeezed light source is another complex system, so putting them together can be a challenge.
Despite the complexity of this challenge, when the squeezed light source was activated for the first time at the LIGO detector in Livingston, Louisiana, US, in February this year there was an immediate improvement in the quantum noise: the gravitational wave detector output got just a bit quieter.Much tuning remains to be done to get the detectors in optimal shape, but it is a real delight when something so complex goes well right from the start.
With these first detections, we have begun to explore the population of black holes in the universe, heard the merger of neutron stars, and
probably witnessed the birth of a new black hole.
With the upgrades under way, we will study these objects with better clarity, hopefully understand where they came from, and maybe even find something completely new and unexpected.
It’s 8pm on a Saturday night and you’re headed to the movies. The usher gives you and your friends 3D glasses and you’re super excited to see that new flick. You sit in the theatre, and somehow the images on the screen come out at you. A hand reaches forward and you flinch even though you know it’s not actually real. What you are seeing is a two dimensional event (a film), but experiencing its depth in 3D. Welcome to the Holographic Principle.
The Holographic Principle, initially presented by Gerard‘t Hooft, theorizes that we are in fact living on a two-dimensional surface and that the universe contains all the information necessary for our brains to interpret a three-dimensional existence. Sounds like science fiction right? Until you sit in a 3D movie, or use your computer.
Humans today have a unique perspective into the way the holographic principle functions because we exist in an age of enormous technological advancement. Take this article you’re reading right now, the words on this page don’t actually exist, but are a culmination of lines of code that come together and present themselves as words on a page. The hypothesis is that the Holographic Principle works in a similar manner.
The principle actually comes from the study of black holes. Stephen Hawking found that adding information to a black hole would cause the black hole to grow, but in surface area, not in volume. Initially, scientists thought that anything that entered a black hole would remain within it, but it would appear that it actually becomes encoded on its surface, or the “event horizon”.
Quantum physicists have taken this phenomenon and applied it to the universe as a hole. Physicists believe that the energy in our universe is encoded in its surface, and some believe that this means we are projections of that two-dimensional code. On a quantum level, this could make sense. Everything we see represented to us is the result of measurable mathematics. When we see colors we are actually seeing photons of electromagnetic radiation at certain wavelengths that we interpret as color. Our brains are built to take the items that we are presented with and deliver them to us logically. This begs the question, what is the nature of reality?
Philosophical heavyweights like Descartes and Kant theorize that the nature of existence is subjective. Everything that we experience enormously affects how we view every aspect of our physical reality, so we know that humans don’t see the world objectively. But what is there is no physical objectivity at all?
If nothing in our universe exists in actual physical reality, and we do in fact exist in a hologram, is that hologram objective?
Physicists would say yes. Even though we interact with the world in a subjective manner, the Holographic Principle works on the objectivity of energy in the universe that is imprinted on its surface. If this is true, it means our perception of everything in the universe is completely unreliable, and if scientists eventually prove this theory, it would change the way we view the world forever.
Stephen Hawking, one of the most notable physicists of our generation, has passed away according to a family statement.
Hawking died peacefully on the morning of March 14th. Hawking was remembered by his children Lucy, Robert, and Tim in a family statement:
“We are deeply saddened that our beloved father passed away today. He was a great scientist and an extraordinary man whose work and legacy will live on for many years. His courage and persistence with his brilliance and humour inspired people across the world. He once said, ‘It would not be much of a universe if it wasn’t home to the people you love.’ We will miss him forever.”
Hawking held 13 honorary degrees, was a professor and PH.D graduate from the University of Cambridge, and once awarded the Presidential Medal of Freedom from Barack Obama in 2009.
He was diagnosed with Lou Gehrig’s disease (ALS) in 1963 and was told he had two years to live. He beat those odds by a long shot and went onto be one of the most prominent physicists of all time. He will forever be missed.
Hawking’s most recent project is Breakthrough Starshot, where he teamed up with Russian billionaire Yuri Milner to pledge 100 million dollars to interstellar travel. In the past year, Hawking became very vocal about moving up humanity’s deadline to leave Earth.
Ultimately, he never met his dream of going into space.
Reactions to Stephen Hawking’s Death
Stephen Hawking will not soon be forgotten. He’s likely to be remembered in history along side greats like Albert Einstein, and Isaac Newton.
Below, you can find a group of reactions from the scientific community honouring his legacy:
His passing has left an intellectual vacuum in his wake. But it's not empty. Think of it as a kind of vacuum energy permeating the fabric of spacetime that defies measure. Stephen Hawking, RIP 1942-2018. pic.twitter.com/nAanMySqkt
— Neil deGrasse Tyson (@neiltyson) March 14, 2018
Remembering Stephen Hawking, a renowned physicist and ambassador of science. His theories unlocked a universe of possibilities that we & the world are exploring. May you keep flying like superman in microgravity, as you said to astronauts on @Space_Station in 2014 pic.twitter.com/FeR4fd2zZ5
— NASA (@NASA) March 14, 2018
“Life would be tragic if it weren’t funny.” – Stephen Hawking
— ian bremmer (@ianbremmer) March 14, 2018
Light, which can travel as fast as 300,000 kms/sec in a vacuum, can apparently be stopped dead in its tracks.
Using “exceptional points”, scientists Tamar Goldzak, Alexei A. Mailybaev, and Nimrod Moiseyev, have proposed a theoretical way to slow light to a complete stop. The process involves trapping light inside crystals or ultracold clouds of atoms
A paper published in the Physical Review Letters outlines that previous theoretical attempts have seen light slow at an immense rate, but never to an absolute stop.
Almost twenty years ago, light was slowed down to less than 10−7 of its vacuum speed in a cloud of ultracold atoms of sodium. Upon a sudden turn-off of the coupling laser, a slow light pulse can be imprinted on cold atoms such that it can be read out and converted into a photon again. In this process, the light is stopped by absorbing it and storing its shape within the atomic ensemble. Alternatively, the light can be stopped at the band edge in photonic-crystal waveguides, where the group speed vanishes.
Light can also be released and accelerated buck to normal speed by reversing their gain/loss parameters. The entire process has been described as “driving a car into an icy two-lane tunnel, in which one slides around wildly, but from which one always comes out on the correct side of the road.”
Here, we extend the phenomenon of stopped light to the new field of parity-time (PT) symmetric systems. We show that zero group speed in PT symmetric optical waveguides can be achieved if the system is prepared at an exceptional point, where two optical modes coalesce. This effect can be tuned for optical pulses in a wide range of frequencies and bandwidths, as we demonstrate in a system of coupled waveguides with gain and loss.
What all of this jargon really means, is that exceptional points open up new possibilities for controlling waves, and that is very exciting. Professor Stefan Rotter (Institute for Theoretical Physics, TU Wien) compares this find to classical mathematics “just like complex numbers have brought us new possibilities in mathematics, complex exceptional points give us new ideas for the physics of waves. I am sure that we will soon hear a lot more about exceptional points in many different areas of physics”.
In the past exceptional points have been shown to exhibit strange characteristics when investigated. Lasers have been seen to switch on, even though energy is taken away from them, light is being emitted only in one particular direction, and waves which are strongly jumbled emerge from the muddle in an orderly, well-defined state. The future of exceptional point research is sure to have some wacky consequences.
This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!
What started the Big Bang? – Pippi, 8, Canberra.
This is one of the two questions I get asked a lot (the other one is: do aliens exist?) Both are very good questions! Pippi, the short answer is that we do not know what started the Big Bang. This is a big mystery.
The Big Bang is an idea about the history of the Universe, the history of space and time and matter (“stuff”) and energy. The Universe is about 13.8 billion years old and from observations we make using telescopes we can tell that the Universe was very small 13.8 billion years ago.
Observations also suggest that in the first fraction of a second, the Universe seemed to expand very quickly but then slow down. After a few hundred thousand years, the simplest type of atom formed: hydrogen. The hydrogen started to form stars and galaxies.
After billions of years the Earth (and us) formed from the atoms made inside stars – every atom in your body more complicated than hydrogen was made by a star at some point in the last 13.8 billion years. In all that time, the Universe has continued to expand. In fact, observations now tell us that the expansion of the Universe is getting faster.
The idea of the Big Bang agrees with all these observations. So scientists think the Big Bang is an idea that does a good job of describing the history of the Universe.
However, the idea is not perfect. We don’t know why the Universe expanded so quickly in the first second and then slowed down. We don’t know why the expansion of the Universe is speeding up now. We don’t know why we have a certain number of forces that control the Universe. And we don’t know what started the Big Bang!
Very large telescopes, like the Murchison Widefield Array can make observations that help us understand how the Universe evolved.
It took hundreds of years to build the idea of the Big Bang, and it may take a long time to improve it or find an idea that is better. Scientists have a lot of ideas about how the Big Bang started. But these ideas must agree with our observations of the Universe.
The future is very exciting for anyone who wants to help figure this out. The advanced technology we have means that we can build machines that smash particles (tiny little bits of stuff even smaller than an atom) together to show what happened right after the Big Bang. We can now build powerful new telescopes to observe the stars and galaxies in the Universe in a lot of detail. We will use these machines and telescopes to see which ideas about the Big Bang are right and which are wrong.
Sometimes new ideas take many years to be worked out. Sometimes new ideas pop into people’s heads very quickly. It is very exciting to have a new idea about the Universe. We will need lots of people who are good at puzzles to help us.
Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. They can:
Please tell us your name, age, and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.
According to astronomers, the Milky Way is a bit of a loner.
A new study presented at the american astronomical society and two subsequent papers published in the Astrophysical Journal detail evidence that our region of the universe has fewer planets, stars, galaxies, and matter than other regions.
The void that our galaxy lives is known as KBC and it’s the largest void we’ve ever found. KBC (named after discoverers Keenan, Barger, and Cowie), is seven times larger than the average galactic void, measuring 1 billion light-years.
The idea that we live in this void is a handy explanation for problems with the Hubble Constant. The Hubble Constant is the unit of measurement used to describe the expansion of the universe. It’s called the ‘constant’ because the rate of expansion should be the same at every point in the universe, but it isn’t – which suggests that there are varying gravitational forces all over the universe.
“No matter what technique you use, you should get the same value for the expansion rate of the universe today. Fortunately, living in a void helps resolve this tension.”
Understanding our place in these voids is integral to learning about the large scale structure of our universe. Our universe is described as “Swiss cheese-like in the sense that it is composed of “normal matter” in the form of voids and filaments. The filaments are made up of superclusters and clusters of galaxies, which in turn are composed of stars, gas, dust and planets. Dark matter and dark energy, which cannot yet be directly observed, are believed to comprise approximately 95 percent of the contents of the universe.”
The latest findings show quite evidently that our galaxy lives in a much larger than average sized void which importantly highlights the differential rates at which our universe is expanding. It’s an important find that will aid astronomers in deciphering the structure of our cosmos.
(Reuters) – Scientists have for a third time detected ripples in space from black holes that crashed together billions of light years from Earth, a discovery that confirms a new technique for observing cataclysmic events in the universe, research published on Thursday shows.
Such vibrations, known as gravitational waves, were predicted by Albert Einstein more than 100 years ago and were detected for the first time in September 2015. They are triggered by massive celestial objects that crash and merge, setting off ripples through space and across time.
The latest detection occurred on Jan. 4, 2017. Twin lasers in Louisiana and Washington picked up the faint vibrations of two black holes that were 20 and 30 times more massive than the sun, respectively, before they spiraled toward each other and merged into a larger black hole.
The discovery marks a turning point in the nascent field of gravitational-wave astronomy, which scientists are developing to learn more about how the universe formed. The first detection of gravitational waves created a scientific sensation.
“We’re really moving from novelty to a new observational science,” said Massachusetts Institute of Technology astrophysicist David Shoemaker.
A team of more than 1,000 scientists published their findings in this week’s issue of Physical Review Letters.
Like the previous two detections, the gravitational waves discovered in January slightly jiggled the L-shaped, 2.5 mile-long (4 km) laser beams that comprise the heart of the Laser Interferometer Gravitational-Wave Observatory, or LIGO.
By matching the shape of the waves with computer models, scientists confirmed the collision took place about 3 billion light years from Earth, twice as far as previous detections.
Black holes are regions so dense with matter that not even photons of light can escape their gravitational pull.
Analysis shows the pair likely were spinning in different directions before merging, a clue that they formed separately in a dense cluster of stars, sank to the core of the cluster and then paired up, Georgia Institute of Technology physicist Laura Cadonati told reporters during a conference call.
A second gravitational wave observatory in Italy is scheduled to begin operations this summer and will enhance LIGO’s ongoing studies. Scientists eventually expect to be able to find black holes merging about once a day.
They also are on the hunt for other objects, including colliding neutron stars, which are the dense remnants of collapsed stars so packed with matter that a single teaspoon would weigh 10 million tons on Earth.
(Reporting by Irene Klotz in Cape Canaveral, Fla.; Editing by Colleen Jenkins)
The first direct detection of gravitational waves, a phenomenon predicted by Einstein’s 1915 general theory of relativity, was reported by scientists in 2016.
Armed with this “discovery of the century”, physicists around the world have been planning new and better detectors of gravitational waves.
Physicist Professor Chunnong Zhao and his recent PhD students Haixing Miao and Yiqiu Ma are members of an international team that has created a particularly exciting new design for gravitational wave detectors.
The new design is a real breakthrough because it can measure signals below a limit that was previously believed to be an insurmountable barrier. Physicists call this limit the standard quantum limit. It is set by the quantum uncertainty principle.
The new design, published in Nature magazine this week, shows that this may not be a barrier any longer.
Using this and other new approaches may allow scientists to monitor black hole collisions and “spacequakes” across the whole of the visible universe.
How gravitational wave detectors work
Gravitational waves are not vibrations travelling through space, but rather vibrations of space itself. They have already told us about an unexpectedly large population of black holes. We hope that further study of gravitational waves will help us to better understand our universe.
But the technologies of gravitational wave detectors are likely to have enormous significance beyond this aspect of science, because in themselves they are teaching us how to measure unbelievably tiny amounts of energy.
Gravitational wave detectors use laser light to pick up tiny vibrations of space created when black holes collide. The collisions create vast gravitational explosions. They are the biggest explosions known in the universe, converting mass directly into vibrations of pure space.
It takes huge amounts of energy to make space bend and ripple. Our detectors – exquisitely perfect devices that use big heavy mirrors with scarily powerful lasers – must measure space stretching by a mere billionth of a billionth of a metre over the four kilometre scale of our detectors. These measurements already represent the smallest amount of energy ever measured.
But for gravitational wave astronomers this is not good enough. They need even more sensitivity to be able to hear many more predicted gravitational “sounds”, including the sound of the moment the universe was created in the big bang.
This is where the new design comes in.
A spooky idea from Einstein
The novel concept is founded on original work from Albert Einstein.
In 1935 Albert Einstein and co-workers Boris Podolsky and Nathan Rosen tried to depose the theory of quantum mechanics by showing that it predicted absurd correlations between widely spaced particles.
Einstein proved that if quantum theory was correct, then pairs of widely spaced objects could be entangled like two flies tangled up in a spider’s web. Weirdly, the entanglement did not diminish, however far apart you allowed the objects to move.
Einstein called entanglement “spooky action at a distance”. He was sure that his discovery would do away with the theory of quantum mechanics once and for all, but this was not to be.
Since the 1980s physicists have demonstrated time and again that quantum entanglement is real. However much he hated it, Einstein’s prediction was right and to his chagrin, quantum theory was correct. Things at a distance could be entangled.
Today physicists have got used to the “spookiness”, and the theory of entanglement has been harnessed for the sending of secret codes that cannot be intercepted.
Around the world, organisations such as Google and IBM and academic laboratories are trying to create quantum computers that depend on entanglement.
And now Zhao and colleagues want to use the concept of entanglement to create the new gravitational wave detector’s design.
A new way to measure gravitational waves
The exciting aspect of the new detector design is that it is actually just a new way of operating existing detectors. It simply uses the detector twice.
One time, photons in the detector are altered by the gravitational wave so as to pick up the waves. The second time, the detector is used to change the quantum entanglement in such a way that the noise due to quantum uncertainty is not detected.
The only thing that is detected is the motion of the distant mirrors caused by the gravitational wave. The quantum noise from the uncertainty principle does not appear in the measurement.
To make it work, you have to start with entangled photons that are created by a device called a quantum squeezer. This technology was pioneered for gravitational wave astronomy at Australian National University, and is now an established technique.
Like many of the best ideas, the new idea is a very simple one, but one that took enormous insight to recognise. You inject a miniscule amount of squeezed light from a quantum squeezer, and use it twice!
Around the world physicists are getting ready to test the new theory and find the best way of implementing it in their detectors. One of these is the GEO gravitational wave detector at Hannover in Germany, which has been a test bed for many of the new technologies that allowed last year’s momentous discovery of gravitational waves.
Dark matter is a mysterious substance composing most of the material universe, now widely thought to be some form of massive exotic particle. An intriguing alternative view is that dark matter is made of black holes formed during the first second of our universe’s existence, known as primordial black holes. Now a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, suggests that this interpretation aligns with our knowledge of cosmic infrared and X-ray background glows and may explain the unexpectedly high masses of merging black holes detected last year.
“This study is an effort to bring together a broad set of ideas and observations to test how well they fit, and the fit is surprisingly good,” said Alexander Kashlinsky, an astrophysicist at NASA Goddard. “If this is correct, then all galaxies, including our own, are embedded within a vast sphere of black holes each about 30 times the sun’s mass.”
In 2005, Kashlinsky led a team of astronomers using NASA’s Spitzer Space Telescope to explore the background glow of infrared light in one part of the sky. The researchers reported excessive patchiness in the glow and concluded it was likely caused by the aggregate light of the first sources to illuminate the universe more than 13 billion years ago. Follow-up studies confirmed that this cosmic infrared background (CIB) showed similar unexpected structure in other parts of the sky.
In 2013, another study compared how the cosmic X-ray background (CXB) detected by NASA’s Chandra X-ray Observatory compared to the CIB in the same area of the sky. The first stars emitted mainly optical and ultraviolet light, which today is stretched into the infrared by the expansion of space, so they should not contribute significantly to the CXB.
Yet the irregular glow of low-energy X-rays in the CXB matched the patchiness of the CIB quite well. The only object we know of that can be sufficiently luminous across this wide an energy range is a black hole. The research team concluded that primordial black holes must have been abundant among the earliest stars, making up at least about one out of every five of the sources contributing to the CIB.
The nature of dark matter remains one of the most important unresolved issues in astrophysics. Scientists currently favor theoretical models that explain dark matter as an exotic massive particle, but so far searches have failed to turn up evidence these hypothetical particles actually exist. NASA is currently investigating this issue as part of its Alpha Magnetic Spectrometer and Fermi Gamma-ray Space Telescope missions.
“These studies are providing increasingly sensitive results, slowly shrinking the box of parameters where dark matter particles can hide,” Kashlinsky said. “The failure to find them has led to renewed interest in studying how well primordial black holes — black holes formed in the universe’s first fraction of a second — could work as dark matter.”
Physicists have outlined several ways in which the hot, rapidly expanding universe could produce primordial black holes in the first thousandths of a second after the Big Bang. The older the universe is when these mechanisms take hold, the larger the black holes can be. And because the window for creating them lasts only a tiny fraction of the first second, scientists expect primordial black holes would exhibit a narrow range of masses.
On Sept. 14, gravitational waves produced by a pair of merging black holes 1.3 billion light-years away were captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves as well as the first direct detection of black holes. The signal provided LIGO scientists with information about the masses of the individual black holes, which were 29 and 36 times the sun’s mass, plus or minus about four solar masses. These values were both unexpectedly large and surprisingly similar.
“Depending on the mechanism at work, primordial black holes could have properties very similar to what LIGO detected,” Kashlinsky explained. “If we assume this is the case, that LIGO caught a merger of black holes formed in the early universe, we can look at the consequences this has on our understanding of how the cosmos ultimately evolved.”
In his new paper, published May 24 in The Astrophysical Journal Letters, Kashlinsky analyzes what might have happened if dark matter consisted of a population of black holes similar to those detected by LIGO. The black holes distort the distribution of mass in the early universe, adding a small fluctuation that has consequences hundreds of millions of years later, when the first stars begin to form.
For much of the universe’s first 500 million years, normal matter remained too hot to coalesce into the first stars. Dark matter was unaffected by the high temperature because, whatever its nature, it primarily interacts through gravity. Aggregating by mutual attraction, dark matter first collapsed into clumps called minihaloes, which provided a gravitational seed enabling normal matter to accumulate. Hot gas collapsed toward the minihaloes, resulting in pockets of gas dense enough to further collapse on their own into the first stars. Kashlinsky shows that if black holes play the part of dark matter, this process occurs more rapidly and easily produces the lumpiness of the CIB detected in Spitzer data even if only a small fraction of minihaloes manage to produce stars.
As cosmic gas fell into the minihaloes, their constituent black holes would naturally capture some of it too. Matter falling toward a black hole heats up and ultimately produces X-rays. Together, infrared light from the first stars and X-rays from gas falling into dark matter black holes can account for the observed agreement between the patchiness of the CIB and the CXB.
Occasionally, some primordial black holes will pass close enough to be gravitationally captured into binary systems. The black holes in each of these binaries will, over eons, emit gravitational radiation, lose orbital energy and spiral inward, ultimately merging into a larger black hole like the event LIGO observed.
“Future LIGO observing runs will tell us much more about the universe’s population of black holes, and it won’t be long before we’ll know if the scenario I outline is either supported or ruled out,” Kashlinsky said.
Kashlinsky leads science team centered at Goddard that is participating in the European Space Agency’s Euclid mission, which is currently scheduled to launch in 2020. The project, named LIBRAE, will enable the observatory to probe source populations in the CIB with high precision and determine what portion was produced by black holes.
Originally published at NASA