Monday 10 June 2019

Eugene Parker - the astrophysicist’s discoveries about the Sun led NASA to name a new solar mission after him

Born on 10 June 1927 in Houghton, Michigan, Eugene Parker is an astrophysicist who predicted the existence of the solar wind. Parker received a BS in physics from Michigan State University in 1948 and a PhD from Caltech in 1951. He then taught at the University of Utah, until accepting a position at the University of Chicago in 1955.


Parker began his investigation into the possibility of a solar wind because of the observations of comets and their tails, which always pointed away from the Sun. His mathematical calculations led to his proposing that a stream of high-energy charged particles originates in the Sun’s upper atmosphere and flows at supersonic speeds throughout the solar system and beyond.

The paper he submitted to the Astrophysical Journal was initially rejected. Parker appealed to the journal’s editor, Subrahmanyan Chandrasekhar, who overruled the reviewers and published the paper in 1958. Parker’s theory was validated four years later by measurements taken by the Mariner 2 probe on its way to Venus.

Sixty years later, NASA launched the Parker Solar Probe, the first NASA spacecraft to be named for a living person. Over his career, Parker studied other phenomena, such as cosmic rays and the magnetic fields of galaxies.


Such terms as the Parker instability, the Parker equation, and the Parker limit attest to his contributions to the field. In recognition of his work, he received numerous awards and honours, including the 1978 George Ellery Hale Prize, the 1989 National Medal of Science, the 1992 Royal Astronomical Society Gold Medal, the 1997 Bruce Medal, the 2003 Kyoto Prize, and the 2003 James Clerk Maxwell Prize.

Source - Physics Today

Thursday 2 May 2019

Electrolysis of Water - First Chemical Reaction using Electricity

May 2, 1800 - English chemist William Nicholoson along with Anthony Carlisle discovered electrolysis, the decomposition of water into hydrogen and oxygen by voltaic current. This was the first reaction to produce a chemical reaction by electricity.



The following is an interesting article about William Nicholoson published in Chemistry World, published by The Royal Society of Chemistry, on 1st August 2003.

Enterprise and electrolysis...

William Nicholson, born 250 years ago this year, founded a new journal and discovered electrolysis. Colin Russell elaborates.

This year is the 250th anniversary of the birth of a most remarkable Englishman. He was so diverse in his interests that to call him a ’chemist’ is rather too restricting (though some authors have done just that). Yet chemistry is lastingly in his debt, to say nothing of physics and engineering. Of all the discoveries he made, electrolysis is the most famous. They don’t come much more important than that. His name was William Nicholson and he lived from 1753 to 1815, the son of a London solicitor who practised in the Inner Temple.

The story of his life is briefly told. After education at a school in North Yorkshire, at the age of 16 Nicholson joined the East India Company, a private enterprise that virtually ran India in those days. He made several voyages in its service and then settled in India itself for a couple of years, returning to Europe in 1775. He was soon appointed commercial director for the pottery manufacturer Josiah Wedgwood in Amsterdam. This appointment did not last long, however, since Nicholson was tired of working for other people and was beginning to see the benefits of working for himself. With whatever fortune he had amassed from his overseas trading Nicholson returned to London and began to teach in a London mathematical school (possibly his own).

It was becoming clear, however, that school teaching was unlikely to satisfy Nicholson’s ambitions. He wanted to communicate, but on the grand scale. He had lots of ideas, a ready pen, enough money to invest in new ventures, and more than a smattering of the scientific ideas that were then fermenting in Europe and offering huge possibilities for exploitation and application. He would become what his contemporaries would call a ’projector’, though we might prefer the term ’entrepreneur’. To communicate science in new ways, to invent a host of interesting gadgets and scientific apparatus and to debate the hot scientific issues of the day, these were the objectives that spurred him on. Before long mathematics teaching was to fade into the background. He would write and publish.

Nicholson’s rate of publication was quite astounding. His first book, An introduction to natural philosophy, was published in 1781. Its two volumes soon made their mark as a competent exposition of the Newtonian ideas that had long dominated physics and were beginning to penetrate chemistry. The following year he published a new edition of Ralph’s Critical review of the public buildings, statues and ornaments in and about London and Westminster and also a translation from the French of a book by Ayder Ali Khan, New memoirs concerning the East Indies. By 1784 he had published his own book on marine navigation and in 1786 another on Parliamentary Acts preventing the export of wool.

By now Nicholson’s scientific competence was being recognised and in 1783 he was elected to one of the many informal London groupings of scientifically inclined people, the Chapter Coffee House Society. In due course he became its secretary. Meeting in Paternoster Row, the Society included the Irish chemist Richard Kirwan, Nicholson’s former employer Josiah Wedgwood, the engineer Matthew Boulton, the instrument maker Edward Nairne, and (as honorary member) Joseph Priestley. Several of these also belonged to the famous Lunar Society of Birmingham. Here he soon came face to face with the controversies then raging at the cutting edge of science, none more vigorously than in chemistry. Lavoisier, later to lose his head in the French Revolution, advocated a radical theory of the elements, with a new element called oxygen responsible for combustion. The notion that this involved an evolution of ’phlogiston’ was now discredited. Several leading opponents of the new theories attended the Coffee House. These were revolutionary times, politically and chemically.

As the 18th century drew to a close many were convinced that the key to chemical progress lay in a quantitative study of what were vaguely styled ’affinities’. Two French chemists who held that view were Antoine François de Fourcroy and Jean Antoine Chaptal. Nicholson, no mean linguist, proceeded to translate several of their works into English, adding comments of his own. He began with the second edition of Fourcroy’s Elements of natural history and chemistry (1788/9) and Chaptal’s Elements of chemistry (1791). He gave old trivial chemical names as well as the new systematic ones, though at that stage was less keen on the latter.

For chemistry, these were the dying days of the phlogiston theory of combustion, though supporters like Priestley had no idea that the end was so near. The alternative oxygen theory of Lavoisier could be challenged on many grounds and Nicholson found himself sitting precariously on the fence. On one hand he thought phlogiston was doubtful, and certainly rejected its alleged negative weight. On the other hand the theory did explain a lot. But when he introduced a translation of the French reply to Kirwan’s Essay on phlogiston (1789) Nicholson accused Lavoisier of ’an unwarrantable pretension to accuracy’. Elsewhere he challenged Lavoisier’s nomenclature. His suspicion of too much theory was thoroughly characteristic of the practical or ’Baconian’ approach to science then popular in England (after the philosopher Francis Bacon).

In that spirit Nicholson’s First principles of chemistry (1790) gave an impartial exposition of the doctrine of phlogiston alongside that of Lavoisier. His most famous book, A dictionary of chemistry, appeared in 1795. Although by now Nicholson was in favour of the new nomenclature he did not use it because he believed that the public ought to choose. This work was also remarkable in its use of some French chemical symbols, giving them a double page table with elements generally represented by marks within a circle, and compounds having square or triangular symbols. His definition of elements was thoroughly Baconian: ’simple substances relative to the present state of our knowledge, but in no other respect’. In other words the list of elements could change with time. This book was one of the formative works read by the young Humphry Davy and went through several editions.

Textbooks, however excellent, have their limitations. They cannot convey up-to-date information on current research. The great and the good could always publish their results in the austere Philosophical Transactions of the Royal Society, but lesser mortals were unable to do so and in any case the audience was inevitably restricted. So Nicholson the entrepreneur had a simple but brilliant idea: a popular science journal.

In April 1797 he founded the Journal of Natural Philosophy, Chemistry and the Arts, known ever after by its shorter name of Nicholson’s Journal (or just Nic. J.). Here was a vehicle for rapid publication where all aspiring authors could publish short papers, and where there were reports of scientific meetings at the Royal Society and elsewhere. Its authors included John Dalton, Thomas Thomson, Richard Phillips and others who were reluctant to publish in Philosophical Transactions. Over the years its ample pages included papers by Dalton on the atmosphere (1801) and on weather (1803) and discussions on them by Joseph Henry, John Gough and others. Even the great Berzelius sent him contributions from Sweden. Nor was Nicholson deterred from publishing over 60 papers of his own.

In 1803 Nicholson’s Journal reprinted an anonymously produced leaflet announcing a new metal ’palladium’. This was available at a Soho shop at about six times the price of gold. The announcement aroused much interest, and also much scepticism. A few months later the same journal carried an anonymous letter offering £20 to anyone who could produce palladium artificially - in the presence of three chemical witnesses to be nominated by the editor. Clearly Nicholson felt himself on the verge of a journalistic scoop. But no one seems to have come forward, and the mystery donor remained unknown (except that both anonymous contributions had the same handwriting).

Then, six months later, a paper was read to the Royal Society concluding that the ’palladium’ offered for sale last year was present in very small amounts in the crude ore of platina, and appeared to be an element. The author was W. H. Wollaston, who in February 1805 wrote to Nicholson admitting authorship of the anonymous communication to his journal. He wished to claim priority over others working on platina, though without disclosing his identity too soon. Since he could not publish anonymously in Philosophical Transactions he had reported to Nicholson’s Journal.

The journal was so successful that within a year a rival had been started by Tilloch, the Philosophical Magazine. For various reasons it was even more successful than Nicholson’s venture and began to overtake it. A second rival arrived in 1813 with Thomson’s Annals of Philosophy, in which year Nicholson gave up his editorship and the journal was discontinued.

However life for Nicholson was not all spent at the writing desk. In 1799 he opened a school in Soho for 20 pupils, and offered weekly lectures in chemistry. He also became a patent agent in Red Lion Square, and worked as an inventor. He devised a new hydrometer, worked on industrial machinery and even acted as a water engineer for the Portsea Island Waterworks Company.

His most important gadget was in the field of electrostatics. To detect a static electric charge in the 18th century Galvani had used frogs’ legs that twitched on receiving a charge. An electroscope with diverging gold leaves was more reliable, and had been improved by the so-called electric ’doubler’, a device invented by Abraham Bennet for roughly doubling the charge. Nicholson invented an improved doubler and this was applied by the Italian physics professor Allesandro Volta in his crucial experiments on charges induced by bimetallic contact. This gave far better results than frogs’ legs which by 1796 were off his menu. Nicholson’s doubler was also used by Bennet himself to detect charges on liquids like wines as they evaporated, which were opposite to those of their vapours. In the case of water he found the charges could be reversed by the simple process of spitting into it.

Meanwhile something far more important was afoot and was to change the whole fabric of physical science. The electrical effects obtained by placing two different metals in contact had led to the momentous invention of Volta’s Pile, consisting of copper and zinc (or other metals) sandwiched between pads of moist material with many such units on top of each other. The effect was, for the first time in history, a method for obtaining a continuous electric current. This first electric battery was described in a letter from Volta dated 20 March 1800 to the President of the Royal Society, Sir Joseph Banks ’On the electricity excited by the mere contact of conducting substances of different kinds’.

On receipt of the letter Banks was also excited. It had to pass through France, which was then at war with Britain, and Volta seems to have expected problems of communication. Possibly for that reason he sent his note in two parts. While waiting for the second part Banks showed the first few pages to Anthony Carlisle, a London surgeon. He began trying to repeat Volta’s experiments immediately. Humphry Davy said Volta’s work was ’an alarm bell to experimenters all over Europe’ and Carlisle was the first to prove him right.

At this point enter a friend of Carlisle, William Nicholson. Together they replicated Volta’s experiments, using Nicholson’s doubler to show charges on the upper and lower plates. This meant that they had to connect them to the electroscope, and it was not easy to maintain a good contact. To overcome this little problem they added a drop of water to the uppermost disc and inserted the wire in that. They were surprised to note the appearance of a gas, soon shown to be hydrogen. They then took a small tube filled with water from the New River (an artificial channel completed in 1613 to bring water from Hertfordshire to the City) and inserted wires from the Voltaic pile at each end. To their astonishment the other suspected constituent of water, oxygen, did not appear at the same place but at the other wire ’at a distance of almost two inches’. They had discovered electrolysis.

Waiting till the rest of Volta’s letter had arrived and been presented to the Royal Society, Nicholson and Carlisle decided to publish their results, and where better than in Nicholson’s Journal? This humble periodical was the means for conveying to the world a discovery that led to a new science: electrochemistry. Quickly it published many other results in this field, including descriptions of the Voltaic pile with DIY instructions for making one, and early papers on the subject by Humphry Davy.

Not all readers were convinced that actual decomposition had taken place, especially those who had doubts about the new chemistry. Hydrogen and oxygen might be compounds of water with (respectively) positive and negative electricity, they thought. But it did not take long for doubters to be convinced, and Lavoisier’s chemistry received an additional boost. Within a few years electrolysis had been used by Davy to isolate sodium, potassium, calcium, strontium, barium, magnesium and lithium. Chemistry would never be the same again.

In three ways Nicholson was at the centre of this scientific revolution at the dawn of the 19th century. He seems to have been a more able experimenter than his surgical friend, and he actually suggested the crucial experiment with New River water; his improved ’doubler’ was an essential tool in their investigations; and it was his journal that carried almost all the new work on the infant science of electrochemistry. Yet such were the vicissitudes of fortune felt by many ’projectors’ at that time that Nicholson saw little material gain from all his efforts. Like Boyle’s chemical mentor George Starkey he even spent some time in a debtor’s prison. Two years after the collapse of his journal he succumbed to a long illness at Bloomsbury on 21 May 1815. The Gentleman’s Magazine observed ’he lived in trouble, and died poor’. He shared that fate with another scientific contemporary, the 9th Earl of Dundonald, and like him left a science immeasurably enriched by his work.

Sources -
  1. Pacific Science Center
  2. Wikipedia
  3. Chemistry World (https://www.chemistryworld.com/news/enterprise-and-electrolysis/3001445.article)

Tuesday 23 April 2019

David Thouless obituary by J Michael Kosterlitz (An obituary of a Nobel laureate by a Nobel laureate)

David Thouless, working with Michael Kosterlitz, overturned a theory that had held sway for at least 30 years. 
David Thouless, who has died aged 84, won half of the 2016 Nobel prize in physics, the other half being shared by Duncan Haldane and me. David and I solved an interesting theoretical problem by introducing some new ideas with important implications, and so unknowingly created a new field in the discipline.
Our main innovation came from topology: the mathematical study of the properties preserved when objects are twisted, stretched or crumpled, properties that change only step by step. From 1972 to 1974 we sought a theoretical explanation of a phase transition, a change of state such as water turning into steam and back to water again. The one we examined was from a high-temperature disordered phase, a gas, to a low-temperature partially ordered one, a liquid, in an arrangement operating in two dimensions – a thin film or layer of something not supported by anything else. Previously it had been thought for very good reasons that such a phase transition could not happen in two dimensions, but only in three or more.
David and I managed to overturn that at least 30-year-old theory. We demonstrated that superconductivity, an electrical current flowing with no resistance, could occur at low temperatures in a very thin film. This opened up a hitherto unknown way of doing physics, revolutionised knowledge about phase transitions and later led to understanding topological insulators, which in turn may be used for developments including quantum computers, operating at a much higher level of complexity than conventional ones.
We took up the challenge of a conflict between theory and observation, and were the ideal pair to do so. David was a physical and mathematical genius who knew and understood all the conventional wisdom that said a transition could not exist, but had a very flexible mind that was always prepared to discard conventional wisdom if necessary. On the other hand, I was an energetic postdoctoral researcher looking for any interesting problem in any branch of physics. David talked about concepts that were all completely new to me, and left my head spinning.
After refining the calculations that I took back to him, he decided that we should write them up for publication. The resulting couple of articles in the Journal of Physics C: Solid State Physics did not engender much interest for some years, but in 1978 theory and experiment came together, and in the early 1980s David undertook further research with Haldane.
By the time the Nobel for the three of us came, four decades after the start of the work, David’s mind was affected by dementia. However, he was well enough to enjoy every moment of the Nobel week in Stockholm that we experienced together. I hear that he subsequently enjoyed leafing through the album of photos and mementos assembled by his family.
Born in Bearsden, a northern suburb of Glasgow, David was the son of Robert Thouless, a psychologist and academic, and his wife, Priscilla (nee Gorton), a teacher. At the age of four David taught himself to read, write and count to large numbers. His education started at St Faith’s school for girls in Cambridge, where he was taught with pupils who were two years older. He then attended a boys’ prep school and Winchester college.
From there he went to Trinity Hall, Cambridge, and, following his bachelor’s degree in mathematics, gained a PhD in theoretical physics under Hans Bethe at Cornell University, in Ithaca, New York (1958). After a year at the Lawrence Radiation Laboratory in Berkeley, California, he returned to Britain as a research fellow at Birmingham University (1959-61), working under Rudolf Peierls.
At Churchill College, Cambridge (1961-65), David was director of studies in physics and a university lecturer. He then went to Birmingham University as professor (1965-78), Yale (1979-80), and the University of Washington (1980-2003) in Seattle.
As well as being a giant of theoretical physics, David was a deeply religious and very moral person. He never let others down and always kept all promises, regardless of how inconvenient they might be.
An initial accidental encounter with him in Cambridge in 1962 had left me very impressed with his grasp of advanced mathematics. I got to know him properly at Birmingham in 1970, and began to appreciate the loneliness of a man who did not understand that he was much cleverer than most people he found himself talking to.
David wrote two books on quantum subjects, and with me a chapter in the collection 40 Years of Berezinskii-Kosterlitz-Thouless Theory (2013). He was elected a fellow of the Royal Society (1979) and a member of the US National Academy of Sciences (1995), and awarded the Wolf Prize in Physics (1990) and the Dirac Medal (1993).
In 1958 he married Margaret Scrase, who went on to become a professor of pathobiology. She survives him, along with two sons, Michael and Christopher, and a daughter, Helen.
Source - The Guardian

Wednesday 3 April 2019

Scientists Working on a Periodic Table for Ecology

An adult male Green Basilisk lizard hangs out in a tree in the rainforest of Costa Rica. A team of ecologists has been working to summarise and simplify the idea of niche to eventually predict how different ecosystems will evolve as a result of climate change.

In 1867, Russian chemist Dmitri Mendeleev was writing a chemistry textbook, but it wasn't going well. At the time, only 56 elements were known to exist, but Mendeleev was having a tough time figuring out how to organize them in a way that would demonstrate their relationships to each other. But then, as legend has it, he had a dream which showed him not only how to organize the known elements by atomic weight and chemical reactivity, but also allowed him to predict other elements that had yet to be discovered.

Mendeleev accomplished in this single night's sleep what scientists from pretty much every discipline would kill for: a straightforward, predictive way to organize and depict complicated information. For ecologists, for instance, this might be a model that could distill the enormous complexity of how an organism functions within the ecological community in which it lives.

Scientists have been intrigued by the idea since the early 1970s, when Robert MacArthur, an evolutionary ecologist, had the idea of ordering organisms similarly to chemistry’s periodic table, in which elements are organized by the combination of certain chemical properties, the configuration of their electrons and their atomic number (number of protons).

So in 2015, a group of ecologists published a paper in the journal Ecology Letters in order to take a stab at what had long been discussed but had never been attempted: creating a periodic table for ecological niches, similar to the periodic table for elements in chemistry, which would essentially represent the complex roles different species play within a community. This could include how they reproduce, what they do for food and shelter, how they protect themselves, how they interact with their living and nonliving neighbors, and so on.

The approach of producing periodic tables of niches is a way to organize species according to sets of functional traits that have known influences for ecological performance. It is an approach that allows us to make an abstract concept approachable for empirical study.

Instead of looking at all the possible demands a species might make on its living situation — acceptable ranges of nutrients like nitrogen and phosphorous, temperature, moisture, soil type (and one species might have hundreds of requirements) — the authors chose just a few essential properties to capture the idea of a niche: diet, habitat, life history, metabolism and defense mechanisms.

The Lizard Model

The research team published a study in November 2017 in The American Naturalist as a way to begin the task of putting this idea to work on ... the world's lizards. They compiled as much data as they could on 134 lizard species, from 24 of the 38 lizard families living on four of Earth's continents today. Then they took their five essential properties of niche, listing between seven and 15 variables for each, and then began crunching the numbers.

Through creating models of their data, they found what they might have expected to find: that lizards are like many other organisms — they evolve to interact with their habitats, forage for food, and observe active and inactive times each day, no matter where they live. For instance, lizards that fill a certain niche in South America have similar traits to lizards that fill similar niches in Australia, Africa or America, even though they're not very closely related, evolutionarily speaking.

Because we can see similarities between lizards that occupy similar niches in completely different places, summarizing and simplifying the idea of niche in this way might eventually help researchers to predict how different ecosystems will evolve as a result of climate change.

Simplifying the Structure

The researchers have used this lizard study to confirm that it may just be possible to simplify the idea of niche from hundreds of dimensions to just five. So, while we don't have an ecological periodic table just yet, perhaps it's not too far off.

Source - HowStuffWorks.com

2018 global CO2 growth 4th highest on record


According to National Oceanic and Atmospheric Administration (NOAA) data, global growth in atmospheric carbon dioxide (CO2) in 2018 was the 4th-highest in 60 years of record-keeping.

By the end of 2018, NOAA’s atmospheric observatory at Mauna Loa, Hawaii, recorded the fourth-highest annual growth in the concentration of atmospheric carbon dioxide (CO2) in 60 years of record-keeping. Carbon dioxide grew by 2.87 parts per million (ppm) at the mountaintop observatory during 2018, jumping from an average of 407.05 ppm on January 1, 2018, to 409.92 on January 1, 2019, according to a new analysis of air samples collected by NOAA’s Global Monitoring Division (GMD).

That means three of the four highest annual increases have occurred in the past four years.

A chart showing the steadily increasing concentrations of carbon dioxide in the atmosphere (in parts per million) observed at NOAA’s Mauna Loa Observatory over the course of 60 years. Measurements of the greenhouse gas began in 1959.

NOAA captures and analyses air samples from a network of observatories and collecting stations around the world. Situated close to the top of Hawaii’s Mauna Loa volcano, NOAA’s Mauna Loa Observatory samples “background” samples of Northern Hemisphere air. Mauna Loa is the oldest in the network and has the longest record of CO2 measurements.

The increase observed in 2018 ranks behind only 2016’s record jump of 3.01 ppm, 2015’s near-record increase of 2.98 ppm and 1998’s growth of 2.93 ppm/yr in the modern record. The record dates to March 1958 when David Keeling of the Scripps Institution of Oceanography started measuring atmospheric CO2 in what’s known as the Keeling Curve.

Globally averaged CO2 levels increased by a similar amount to what was observed on Mauna Loa during 2018.

Carbon dioxide is by far the most important of the five primary greenhouse gases – carbon dioxide, methane, nitrous oxide, carbon monoxide and ozone – both in total amount and the rate of increase. When the first Mauna Loa samples were analyzed in 1958, CO2 had already risen 35 ppm from the pre-industrial level of 280 ppm. In the past 60 years, CO2 has increased by an additional 95 ppm to 410 ppm today.

In the last two decades, the rate of increase has been roughly 100 times faster than previous natural increases, such as those that occurred at the end of the last ice age 11,000-17,000 years ago. Today’s rise of CO2 is dominated by human activities. It’s not from natural causes.

About NOAA greenhouse gas monitoring
NOAA tracks five primary greenhouse gases (CO2, CH4, CO, N2O, and SF6) that warm the planet by trapping heat from Earth’s surface that would otherwise escape into space, including two chlorofluorocarbons controlled by the Montreal Protocol that damage Earth’s ozone layer. All five gases account for about 96 percent of the atmosphere’s increased heat-trapping capacity since 1750, another climate indicator tracked by NOAA.

Source - EarthSky.org

Wednesday 20 March 2019

Einstein's Theory of General Relativity

March 20, 1916 - Albert Einstein's Theory of General Relativity was published as an academic paper in Annalen der Physik.

Einstein's Theory of General Relativity

In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time.

Einstein then spent 10 years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity.

Einstein's theory of general relativity predicted that the space-time around Earth would be not only warped but also twisted by the planet's rotation. Gravity Probe B showed this to be correct.

Gravity
Two objects exert a force of attraction on one another known as "gravity." Sir Isaac Newton quantified the gravity between two objects when he formulated his three laws of motion. The force tugging between two bodies depends on how massive each one is and how far apart the two lie. Even as the center of the Earth is pulling you toward it (keeping you firmly lodged on the ground), your center of mass is pulling back at the Earth. But the more massive body barely feels the tug from you, while with your much smaller mass you find yourself firmly rooted thanks to that same force. Yet Newton's laws assume that gravity is an innate force of an object that can act over a distance.

Albert Einstein, in his theory of special relativity, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.

As he worked out the equations for his general theory of relativity, Einstein realized that massive objects caused a distortion in space-time. Imagine setting a large body in the center of a trampoline. The body would press down into the fabric, causing it to dimple. A marble rolled around the edge would spiral inward toward the body, pulled in much the same way that the gravity of a planet pulls at rocks in space.

Experimental evidence

Although instruments can neither see nor measure space-time, several of the phenomena predicted by its warping have been confirmed.

Gravitational lensing - Light around a massive object, such as a black hole, is bent, causing it to act as a lens for the things that lie behind it. Astronomers routinely use this method to study stars and galaxies behind massive objects.

Einstein's Cross, a quasar in the Pegasus constellation, is an excellent example of gravitational lensing. The quasar is about 8 billion light-years from Earth, and sits behind a galaxy that is 400 million light-years away. Four images of the quasar appear around the galaxy because the intense gravity of the galaxy bends the light coming from the quasar.

Einstein's Cross is an example of gravitational lensing

Gravitational lensing can allow scientists to see some pretty cool things, but until recently, what they spotted around the lens has remained fairly static. However, since the light traveling around the lens takes a different path, each traveling over a different amount of time, scientists were able to observe a supernova occur four different times as it was magnified by a massive galaxy.

In another interesting observation, NASA's Kepler telescope spotted a dead star, known as a white dwarf, orbiting a red dwarf in a binary system. Although the white dwarf is more massive, it has a far smaller radius than its companion.

Changes in the orbit of Mercury - The orbit of Mercury is shifting very gradually over time, due to the curvature of space-time around the massive sun. In a few billion years, it could even collide with Earth.

Frame-dragging of space-time around rotating bodies - The spin of a heavy object, such as Earth, should twist and distort the space-time around it. Imagine the Earth as if it were immersed in honey. As the planet rotates, the honey around it would swirl, and it's the same with space and time.

In 2004, NASA launched the Gravity Probe B (GP-B). The precisely calibrated satellite caused the axes of gyroscopes inside to drift very slightly over time, a result that coincided with Einstein's theory. GP-B confirmed two of the most profound predictions of Einstein's universe, having far-reaching implications across astrophysics research.

Gravitational red-shift - The electromagnetic radiation of an object is stretched out slightly inside a gravitational field. Think of the sound waves that emanate from a siren on an emergency vehicle; as the vehicle moves toward an observer, sound waves are compressed, but as it moves away, they are stretched out, or red-shifted. Known as the Doppler Effect, the same phenomena occurs with waves of light at all frequencies.

In 1959, two physicists, Robert Pound and Glen Rebka, shot gamma-rays of radioactive iron up the side of a tower at Harvard University and found them to be minutely less than their natural frequency due to distortions caused by gravity.

Gravitational waves - Violent events, such as the collision of two black holes, are thought to be able to create ripples in space-time known as gravitational waves.

In 2016, the Laser Interferometer Gravitational Wave Observatory (LIGO) announced that it found evidence of these tell-tale indicators. In 2014, scientists announced that they had detected gravitational waves left over from the Big Bang using the Background Imaging of Cosmic Extragalactic Polarization (BICEP2) telescope in Antarctica. It is thought that such waves are embedded in the cosmic microwave background. However, further research revealed that their data was contaminated by dust in the line of sight.

Aerial photo of LIGO Livingston, Louisiana, showing all of one 4 kilometer long arm and part of the other (off to the right). The visible arms are concrete structures that protect the vacuum tubes from the elements.

India is also going to join the hunt for Gravitational Waves by building a gravitational-wave detector that will work in concert with the two detectors currently operating in the United States and a third detector set to come online in Italy. The project could come online as soon as 2023.


Sources -
1. Space.com
2. Wikipedia
3. Pacific Science Center

Thursday 31 January 2019

Can moons have moons?

A new study shows that Earth’s moon should, theoretically, be able to have its own moon. Why doesn’t it?

Size comparison of the major moons in our solar system 

Most of the planets in our solar system have orbiting moons, and even some asteroids have their own moons. But do any moons have moons? Is it possible? Could there be so-called submoons?

It’s a simple enough question. If most other objects in the solar system can have moons, why not moons themselves? Researchers decided to try to answer this question of a 4 year old. Their results have now been published in a new peer-reviewed paper in the February 2019 issue of the Monthly Notices of the Royal Astronomical Society.

Planets orbit stars and moons orbit planets, so it is natural to ask if smaller moons could orbit larger ones. So far at least, no submoons have been found orbiting any of the moons considered most likely to support them – Jupiter’s moon Callisto, Saturn’s moons Titan and Iapetus and Earth’s own moon.

The lack of known submoons in our solar system, even orbiting around moons that could theoretically support such objects, can offer us clues about how our own and neighboring planets formed, about which there are still many outstanding questions.

Earth’s moon should theoretically be able to have its own moon. Why doesn’t it?

Researchers found that only large moons on wide orbits from their host planets would be capable of hosting submoons. Usually, any submoons orbiting smaller moons closer to their planet would have their orbits destabilized by tidal forces. Jupiter’s large moon Callisto, Saturn’s large moon Titan, another Saturn moon called Iapetus and Earth’s moon could all theoretically have submoons, so why don’t they?

There may be other sources of submoon instability, such as the non-uniform concentration of mass in Earth’s moon’s crust.

Part of the answer might also have to do with how the primary moons formed in the first place. Earth’s moon is thought to have been born out of a collision between Earth and another body about the size of Mars – and that collision may have helped life on Earth to get started. But some other moons, like those orbiting Jupiter and Saturn, originated from the same cloud of gas and dust that the planets themselves formed from.

Even asteroids can have moons, such as 2004 BL86. It is about 325 meters in diameter, and its moon is tiny, only 70 meters wide.

It may be that in many or even most cases, there are multiple factors that make the orbits of submoons inherently unstable. Knowing whether that is true or not may have to wait for discoveries of moons orbiting distant exoplanets. Moons themselves are much harder to detect and only one promising candidate has been found so far – a possible exomoon orbiting the Jupiter-sized exoplanet Kepler-1625b. That possible moon – about the size of Neptune – is large enough and far enough from its planet that submoons should be possible as well. Astronomers will need to verify that primary moon first – if it does exist – before looking for any submoons.

Even though Earth’s moon doesn’t have a submoon now, it may in the future, according to the researchers – an artificial one, perhaps NASA’s planned Lunar Gateway. The Lunar Gateway would help to establish humanity’s presence in deep space.

The possibility of moons having their own moons is a fascinating one, even though we haven’t found any examples yet. This new research from Carnegie Science shows that it is indeed possible, but only under the right circumstances.

Download the research paper here.

Adapted from EarthSky.org