Tag Archives: Einstein

Gravitational waves discovered: top scientists respond

The Conversation

Keith Riles, University of Michigan; Alan Duffy, Swinburne University of Technology; Amanda Weltman, University of Cape Town; Daniel Kennefick, University of Arkansas; David Parkinson, The University of Queensland; Maria Womack, University of South Florida; Stephen Smartt, Queen’s University Belfast; Tamara Davis, The University of Queensland, and Tara Murphy, University of Sydney

One hundred years ago, Albert Einstein published his general theory of relativity, which described how gravity warps and distorts space-time.

While this theory triggered a revolution in our understanding of the universe, it made one prediction that even Einstein doubted could be confirmed: the existence of gravitational waves.

Today, a century later, we have that confirmation, with the detection of gravitational waves by the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) detectors.

Here we collect reactions and analysis from some of the leading astronomers and astrophysicists from around the world.


Keith Riles, University of Michigan

Keith Riles explains gravitational waves.

Einstein was skeptical that gravitational waves would ever be detected because the predicted waves were so weak. Einstein was right to wonder – the signal detected on September 14, 2015 by the aLIGO interferometers caused each arm of each L-shaped detector to change by only 2 billionths of a billionth of a meter, about 400 times smaller than the radius of a proton.

It may seem inconceivable to measure such tiny changes, especially with a giant apparatus like aLIGO. But the secret lies in the lasers (the real “L” in LIGO) that are projected down each arm.

Fittingly, Einstein himself indirectly helped make those lasers happen, first by explaining the photoelectric effect in terms of photons (for which he earned the Nobel Prize), and second, by creating (along with Bose) the theoretical foundation of lasers, which create coherent beams of photons, all with the same frequency and direction.

In the aLIGO arms there are nearly a trillion trillion photons per second impinging on the mirrors, all sensing the precise positions of the interferometer mirrors. It is this collective, coherent sensing that makes it possible to determine that one mirror has moved in one direction, while a mirror in the other arm has moved in a different direction. This distinctive, differential motion is what characterizes a gravitational wave, a momentary differential warp of space itself.

By normally operating aLIGO in a mode of nearly perfect cancellation of the light returning from the two arms (destructive interference), scientists can therefore detect the passage of a gravitational wave by looking for a momentary brightening of the output beam.

The particular pattern of brightening observed on September 14 agrees remarkably well with what Einstein’s General Theory of Relativity predicts for two massive black holes in the final moments of a death spiral. Fittingly, Einstein’s theory of photons has helped to verify Einstein’s theory of gravity, a century after its creation.


Amanda Weltman, University of Cape Town

The results are in and they are breathtaking. Almost exactly 100 years ago Einstein published “Die Feldgleichungen der Gravitation” in which he laid out a new theory of gravity, his General Theory of Relativity. Einstein not only improved on his predecessor, Newton, by explaining the unexpected orbit of the planet Mercury, but he went beyond and laid out a set of predictions that have shaken the very foundations of our understanding of the universe and our place in it. These predictions include the bending of light leading to lensed objects in the sky, the existence of black holes from which no light can escape as well as the entire framework for our modern understanding of cosmology.

NASA’s Hubble Space Telescope captured gravitational lensing of light, as predicted by Einstein.
NASA, ESA, K. Sharon (Tel Aviv University) and E. Ofek (Caltech), CC BY

Einstein’s predictions have so far all proven true, and today, the final prediction has been directly detected, that of gravitational waves, the tiniest ripples through space; the energy radiated away by two massive heavenly bodies spiralling into each other. This is the discovery of the century, and it is perhaps poetic that one of the places it is being announced is Pisa, the very place where, according to legend, 500 years ago, Galileo dropped two massive objects to test how matter reacts to gravity.

As we bathe in the glory of this moment it is appropriate to ask, what is next for astronomy and physics and who will bring about the next revolution? Today’s discovery will become tomorrow’s history. Advanced LIGO brings a new way of testing gravity, of explaining the universe, but it also brings about the end of an era of sorts. It is time for the next frontier, with the Square Kilometre Array project finally afoot across Africa and Australia, the global South and indeed Africa itself is poised to provide the next pulse of gravity research.


Stephen Smartt, Queen’s University Belfast

Not only is this remarkable discovery of gravitational waves an extraordinary breakthrough in physics, it is a very surprising glimpse of a massive black hole binary system, meaning two black holes that are merging together.

Black holes are dark objects with a mass beyond what is possible for neutron stars, which are a type of very compact stars – about 10 km across and weighing up to two solar masses. To imagine this kind of density, think of the entire human population squeezed onto a tea spoon. Black holes are even more extreme than that. We’ve known about binary neutron stars for years and the first detection of gravitational waves were expected to be two neutron stars colliding.

What we know about black hole pairs so far comes from the study of the stars orbiting around them. These binary systems typically have black holes with masses five to 20 times that of the sun. But LIGO has seen two black holes with about 30 times the mass of the sun in a binary system that has finally merged. This is remarkable for several reasons. It is the first detection of two merging black holes, it is at a much greater distance than LIGO expected to find sources, and the total mass in the system is also much larger than expected.

This raises interesting questions about the stars that could have produced this system. We know massive stars die in supernovae, and most of these supernovae (probably at least 60%) produce neutron stars. The more massive stars have very large cores that collapse and are too massive to be stable neutron stars so they collapse all the way to black holes.

But a binary system with two black holes of around 30 solar masses is puzzling. We know of massive binary star systems in our own and nearby galaxies, and they have initial masses well in excess of 100 suns. But we see them losing mass through enormous radiation pressure and they are predicted, and often observed, to end their lives with masses much smaller – typically about ten times the sun.

If the LIGO object is a pair of 30 solar mass black holes, then the stars that formed it must have been at least as massive. Astronomers will be asking – how can massive stars end their lives so big and how can they create black holes so massive? As well as the gravitational wave discovery, this remarkable result will affect the rest of astronomy for some time.


Alan Duffy, Swinburne University

The detection of gravitational waves is the confirmation of Albert Einstein’s final prediction and ends a century-long search for something that even he believed would remain forever untested.

This discovery marks not the end, but rather the beginning, of an era in which we explore the universe around us with a fundamentally new sense. Touch, smell, sight and sound all use ripples in an electromagnetic field, which we call light, but now we can make use of ripples in the background field of space-time itself to “see” our surroundings. That is why this discovery is so exciting.

The Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) measured the tiny stretching of space-time by distant colliding black holes, giving them a unique view into the most extreme objects in general relativity.

The exact “ringing” of space-time as the ripples pass through the detector test this theory and our understanding of gravity in ways no other experiment can.

We can even probe the way galaxies grow and collide by trying to measure the gravitational waves from the even larger collisions of supermassive black holes as the galaxies they are contained in smash together.

Australia in particular is a leading nation in this search, using distant pulsars as the ruler at the Parkes telescope.

The LIGO detectors are sensitive to the minute ripples in space-time caused by the merging of two black holes.
University of Birmingham Gravitational Waves Group, Christopher Berry


Tara Murphy, University of Sydney

In addition to binary black holes, aLIGO will detect gravitational waves from other events such as the collision of neutron stars, which are the dense remnants left over when a massive stars collapse.

Astronomers think that two neutron stars colliding may trigger a gamma-ray burst, which we can detect with “regular” telescopes.

Simulation of neutron stars colliding. Credit: NASA

In Australia, we have been using the Murchison Widefield Array and the Australian Square Kilometre Array Pathfinder) to follow-up aLIGO candidates.

aLIGO is an incredibly sensitive instrument but it has very poor ability to determine where the gravitational waves are coming from. Our radio telescopes can scan large areas of sky extremely quickly, so can play a critical part in identifying the event.

This project has been like no other one I have worked on. When aLIGO identifies a candidate, it sends out a private alert to an international network of astronomers. We respond as quickly as possible with our telescopes, scanning the region the event is thought to have occurred in, to see if we can detect any electromagnetic radiation.

Everything is kept top secret – even the other people using our telescopes are not allowed to know where we are pointing them.

To make sure their complex processing pipeline was working correctly, someone in the aLIGO team inserted fake events into the process. Nobody on the team, or those of us doing follow-up, had any idea whether what we were responding to was real or one of these fake events.

We are truly in an era of big science. This incredible result has been the work of not only hundreds of aLIGO researchers and engineers, but hundreds more astronomers collaborating around the globe. We are eagerly awaiting the next aLIGO observing run, to see what else we can find.


Tamara Davis, University of Queensland

Rarely has a discovery been so eagerly anticipated.

When I was a university undergraduate, almost 20 years ago, I remember a physics lecturer telling us about the experiments trying to detect gravitational waves. It felt like the discovery was imminent, and it was one of the most exciting discoveries that could be made in physics.

Mass and energy warping the fabric of space is one of the pieces of general relativity that most captures the imagination. However, while it has enormous explanatory power, the reality of that curvature is hard to grasp or confirm.

For the last few months I’ve had to sit quietly and watch as colleagues followed up the potential gravitational wave signal. This is the one and only time in my scientific career that I wasn’t allowed to talk about a scientific discovery in progress.

But that’s because it is such a big discovery that we had to be absolutely sure about it before announcing it, lest we risk “crying wolf”.

Every last check had to be done, and of course, we didn’t know whether it was a real signal, or a signal injected by the experimenters to keep us on our toes, test the analysis and follow-up.

I work with a project called the Dark Energy Survey, and with our massive, wide-field, half-billion pixel camera on a four metre telescope in Chile, my colleagues took images trying to find the source of the gravitational waves.

The wide-field is important, because the gravitational wave detectors aren’t very good at pinpointing the exact location of the source.

Unfortunately if it was a black hole merger, we wouldn’t expect to see any visible light.

Now that we’re in the era of detecting gravitational waves, though, we’ll be able to try again with the next one.


Maria Womack, University of South Florida

This is a momentous change for astronomy. Gravitational-wave astronomy can now truly begin, opening a new window to the universe. Normal telescopes collect light at different wavelengths, such as Xray, ultraviolet, visible, infrared and radio, collectively referred to as electromagnetic radiation (EM). Gravitational waves are emitted from accelerating mass analogous to the way electromagnetic waves are emitted from accelerating charge; both are emitted from accelerating matter.

The most massive objects with the highest accelerations will be the first events detected. For example, Advanced LIGO, funded by the U.S. National Science Foundation, can detect binary black holes in tight, fast orbits. GWs carry away energy from the orbiting pair, which in turn causes the black holes to shrink their orbit and accelerate even more, until they merge in a violent event, which is now detectable on Earth as a whistling “chirp.”

An example signal from an inspired gravitational wave source.
A. Stuver/LIGO, CC BY-ND

The gravitational-wave sky is completely uncharted, and new maps will be drawn that will change how we think of the universe. GWs might be detected coming from cosmic strings, hypothetical defects in the curvature of space-time. They will also be used to study what makes some massive stars explode into supernovae, and how fast the universe is expanding. Moreover, GW and traditional telescopic observing techniques can be combined to explore important questions, such as whether the graviton, the presumed particle that transmits gravity, actually have mass? If massless, they will arrive at the same time as photons from a strong event. If gravitons have even a small mass, they will arrive second.


Daniel Kennefick, University of Arkansas

Almost 100 years ago, in February 1916, Einstein first mentioned gravitational waves in writing. Ironically it was to say that he thought they did not exist! Within a few months he changed his mind and by 1918 had published the basis of our modern theory of gravitational waves, adequate to describe them as they pass by the Earth. However his calculation does not apply to strongly gravitating systems like a binary black hole.

Albert Einstein was the original theorist who started the hunt for gravitational waves.

It was not until 1936 that Einstein returned to the problem, eventually publishing one of the earliest exact solutions describing gravitational waves. But his original sceptical attitude was carried forward by some of his former assistants into the postwar rebirth of General Relativity. In the 1950s, doubts were expressed as to whether gravitational waves could carry energy and whether binary star systems could even generate them.

One way to settle these disputes was to carry out painstaking calculations showing how the emission of gravitational waves affected the motion of the binary system. This proved a daunting challenge. Not only were the calculations long and tedious, but theorists found they needed a much more sophisticated understanding of the structure of space-time itself. Major breakthroughs included the detailed picture of the asymptotic structure of space-time, and the introduction of the concept of matched asymptotic expansions. Prior to breakthroughs such as these, many calculations got contradictory results. Some theorists even got answers that the binary system should gain, not lose, energy as a result of emitting gravitational waves!

While the work of the 1960s convinced theorists that binary star systems did emit gravitational waves, debate persisted as to whether Einstein’s 1918 formula, known as the quadrupole formula, correctly predicted the amount of energy they would radiate. This controversy lasted into the early 1980s and coincided with the discovery of the binary pulsar which was a real-life system whose orbit was decaying in line with the predictions of Einstein’s formula.

In the 1990s, with the beginnings of LIGO, theorists’ focus shifted to providing even more detailed corrections to formulas such as these. Researchers use descriptions of the expected signal as templates which facilitate the extraction of the signal from LIGO’s noisy data. Since no gravitational wave signals had ever been seen before, theorists found themselves unusually relevant to the detection project – only they could provide such data analysis templates.


David Parkinson, University of Queensland

Gravitational waves can be used to provide a direct probe of the very early universe. The further away we look, the further back in time we can see. But there is a limit to how far back we can see, as the universe was initially an opaque plasma, and remained so even as late as 300,000 years after the Big Bang.

This surface, from which the cosmic microwave background is emitted, represents the furthest back any measurement of electromagnetic radiation can directly investigate.

But this plasma is no impediment for gravitational waves, which will not be absorbed by any intervening matter, but come to us directly. Gravitational waves are predicted to be generated by a number of different mechanisms in the early universe.

For example, the theory of cosmic inflation, which suggests a period of accelerated expansion moments after the Big Bang, goes on to predict not just the creation of all structure that we see in the universe, but also a spectrum of primordial gravitational waves.

It is these primordial gravitational waves that the BICEP2 experiment believed it had detected in March 2014.

BICEP2 measured the polarisation pattern of the cosmic microwave background, and reported a strong detection of the imprint of primordial gravitational waves. These results turned out in fact to be contamination by galactic dust, and not primordial gravitational waves.

But there is every reason to believe that future experiments may be able detect these primordial gravitational waves, either directly or indirectly, and so provide a new and complementary way to understand the physics of the Big Bang.

The ConversationKeith Riles, Professor of Physics, University of Michigan; Alan Duffy, Research Fellow, Swinburne University of Technology; Amanda Weltman, SARChI in Physical Cosmology, Department of Mathematics and Applied Mathematics, University of Cape Town; Daniel Kennefick, Associate Professor of Physics, University of Arkansas; David Parkinson, Researcher in astrophysics, The University of Queensland; Maria Womack, Research Professor of Physics, University of South Florida; Stephen Smartt, Professor of Physics and Mathematics, Queen’s University Belfast; Tamara Davis, Professor, The University of Queensland, and Tara Murphy, Associate Professor and ARC Future Fellow, University of Sydney

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

 

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Timeline: the history of gravity

The Conversation

Geraint Lewis, University of Sydney

Our understanding of gravity has gone through a few permutations, from Newton’s equations through to Einstein’s general relativity. With today’s discovery of gravitational waves, we look back on how our grasp of gravity has evolved over the centuries.


1687: Newtonian gravity

Isaac Newton publishes Philosophiae Naturalis Principia Mathematica, giving a comprehensive account of gravity. This gave astronomers an accurate toolbox for predicting the motions of planets. But it was not without its problems, such as calculating the precise orbit of the planet Mercury.

All planets’ orbits precess – with the closest point of their orbit moving slightly with each revolution – due to the gravitational tugs from other planets.

Wes Mountain/The Conversation, CC BY-ND

The issue with Mercury’s orbit was that the amount of precession did not match what Newton’s theory predicted. It was only a small discrepancy, but big enough for astronomers to know it was there!

Wes Mountain/The Conversation, CC BY-ND

1859: Planet Vulcan

To explain Mercury’s odd behaviour, Urbain Le Verrier proposed the existence of an unseen planet called Vulcan, which orbited closer to the sun. He suggested that the gravity from Vulcan was influencing Mercury’s orbit. But repeated observations revealed no signs of Vulcan.

Wes Mountain/The Conversation, CC BY-ND

1905: Special relativity

Albert Einstein shakes up physics with his special theory of relativity. He then started incorporating gravity into his equations, which led to his next breakthrough.

1907: Einstein predicts gravitational redshift

What we now call gravitational redshift was first proposed by Einstein from his thoughts in the development of general relativity.

Wes Mountain/The Conversation, CC BY-ND

Einstein predicted that the wavelength of light coming from atoms in a strong gravitational field will lengthen as it escapes the gravitational force. The longer wavelength shifts the photon to the red end of the electromagnetic spectrum.

1915: General relativity

Albert Einstein publishes general theory of relativity. The first great success was its accurate prediction of Mercury’s orbit, including its previously inscrutable precession.

The theory also predicts the existence of black holes and gravitational waves, although Einstein himself often struggled to understand them.

Wes Mountain/The Conversation, CC BY-ND

1917: Einstein theorises stimulated emission

In 1917, Einstein publishes a paper on the quantum theory of radiation indicating stimulated emission was possible.

Einstein proposed that an excited atom could return to a lower energy state by releasing energy in the form of photons in a process called spontaneous emission.

In stimulated emission, an incoming photon interacts with the excited atom, causing it to move to a lower energy state, releasing photons that are in phase and have the same frequency and direction of travel as the incoming photon. This process allowed for the development of the laser (light amplification by stimulated emission of radiation).

1918: Prediction of frame dragging

Josef Lense and Hans Thirring theorise that the rotation of a massive object in space would “drag” spacetime around with it.

1919: First observation of gravitational lensing

Gravitational lensing is the bending of light around massive objects, such as a black hole, allowing us to view objects that lie behind it. During a total solar eclipse in May 1919, stars near the sun were observed slightly out of position. This indicated that light was bending due to the sun’s mass.

Wes Mountain/The Conversation, CC BY-ND

1925: First measurement of gravitational redshift

Walter Sydney Adams examined light emitted from the surface of massive stars and detected a redshift, as Einstein predicted.

1937: Prediction of a galactic gravitational lensing

Swiss astronomer Fritz Zwicky proposed that an entire galaxy could act as a gravitational lens.

1959: Gravitational redshift verified

The theory was conclusively tested by Robert Pound and Glen Rebka by measuring the relative redshift of two sources at the top and bottom of Harvard University’s Jefferson Laboratory tower. The experiment accurately measured the tiny change in energies as photons travelled between the top and the bottom.

Wes Mountain/The Conversation, CC BY-ND

1960: Laser invented using stimulated emission

Theodore H. Maiman, a physicist at Hughes Research Laboratories in California, builds the first laser.

1960s: First evidence for black holes

The 1960s was the beginning of the renaissance of general relativity, and saw the discovery of galaxies that were powered by the immense pull of black holes in their centres.

There is now evidence of massive black holes in the hearts of all large galaxies, as well as there being smaller black holes roaming between the stars.

1966: First observation of gravitational time delays

American astrophysicist Irwin Shapiro proposed that if general relativity is valid, then radio waves will be slowed down by the sun’s gravity as they bounce around the solar system.

Wes Mountain/The Conversation, CC BY-ND

The effect was observed between 1966-7 by bouncing radar beams off the surface of Venus and measuring the time taken for the signals to return to Earth. The delay measured agreed with Einstein’s theory.

We now use time-delays on cosmological scales, looking at the time differences in flashes and flares between gravitationally lensed images to measure the expansion of the universe.

1969: False detection of gravitational waves

American physicist Joseph Weber (a bit of a rebel) claimed the first experimental detection of gravitational waves. His experimental results were never reproduced.

Wes Mountain/The Conversation, CC BY-ND

1974: Indirect evidence for gravitational waves

Joseph Taylor and Russell Hulse discover a new type of pulsar: a binary pulsar. Measurements of the orbital decay of the pulsars showed they lost energy matching the amounts predicted by general relativity. They receive the 1993 Nobel Prize for Physics for this discovery.

Wes Mountain/The Conversation, CC BY-ND

1979: First observation of a galactic gravitational lens

The first extragalactic gravitational lens was discovered, when observers Dennis Walsh, Bob Carswell and Ray Weymann saw two identical quasi-stellar objects, or “quasars”. It turned out to be one quasar that appears as two separate images.

Since the 1980s, gravitational lensing has become a powerful probe of the distribution of mass in the universe.

1979: LIGO receives funding

US National Science Foundation funds construction of the Laser Interferometer Gravitational-Wave Observatory (LIGO).

1987: Another false alarm for gravitational waves

A false alarm on direct detection from Joseph Weber (again) with claimed signal from the supernova SN 1987A using his torsion bar experiments, which consisted of large aluminium bars designed to vibrate when a large gravitational wave passed through it.

1994: LIGO construction begins

It took a long time, but the construction of LIGO finally began in Hanford, Washington, and Livingston, Louisiana.

 

2002: LIGO starts first search

In August 2002, LIGO starts searching for evidence of gravitational waves.

2004: Frame dragging probe

NASA launches Gravity Probe B to measure the spacetime curvature near the Earth. The probe contained gyroscopes that rotated slightly over time due to the underlying spacetime. The effect is stronger around a rotating object which “drags” spacetime around with it.

Wes Mountain/The Conversation, CC BY-ND

The gyroscopes in Gravity Probe B rotated by an amount consistent with Einstein’s theory of general relativity.

Wes Mountain/The Conversation, CC BY-ND

2005: LIGO hunt ends

After five searches, the first phase of LIGO ends with no detection of gravitational waves. The sensors then undergo an interim refit to improve sensitivity, called Enhanced LIGO.

2009: Enhanced LIGO

An upgraded version called Enhanced LIGO starts new hunt for gravitational waves.

2010: Enhanced LIGO hunt ends

Enhanced LIGO fails to detect and gravitational waves. A major upgrade, called Advanced LIGO begins.

2014: Advanced LIGO upgrade completed

The new Advanced LIGO has finished installation and testing and is nearly ready to begin a new search.

2015: False alarm #3 for gravitational waves

The indirect signature of gravitational waves in the early universe was claimed by the BICEP2 experiment, looking at the cosmic microwave background. But it looks like this was dust in our own galaxy spoofing the signal.

2015: LIGO upgraded again

Advanced LIGO starts a new hunt for gravitational waves with four times the sensitivity of the original LIGO. In September, it detects a signal that looks likely to be from the collision between two black holes.

2016: Gravitational wave detection confirmed

After rigorous checks, the Advanced LIGO team announce the detection of gravitational waves.

Wes Mountain/The Conversation, CC BY-ND

The ConversationGeraint Lewis, Professor of Astrophysics, University of Sydney

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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The art and beauty of general relativity

The Conversation

Margaret Wertheim, University of Melbourne

One hundred years ago this month, an obscure German physicist named Albert Einstein presented to the Prussian Academy of Science his General Theory of Relativity. Nothing prior had prepared scientists for such a radical re-envisioning of the foundations of reality.

Encoded in a set of neat compact equations was the idea that our universe is constructed from a sort of magical mesh, now known as “spacetime”. According to the theory, the structure of this mesh would be revealed in the bending of light around distant stars.

To everyone at the time, this seemed implausible, for physicists had long known that light travels in straight lines. Yet in 1919 observations of a solar eclipse revealed that on a cosmic scale light does bend, and overnight Einstein became a superstar.

Einstein is said to have reacted nonchalantly to the news that his theory had been verified. When asked how he’d have reacted if it hadn’t been, he replied: “I would have felt sorry for the dear Lord. The theory is correct.”

What made him so secure in this judgement was the extreme elegance of his equations: how could something so beautiful not be right?

The quantum theorist Paul Dirac would latter sum up this attitude to physics when he borrowed from poet John Keats, declaring that, vis-à-vis our mathematical descriptions of nature, “beauty is truth, and truth beauty”.

Art of science

A quest for beauty has been a part of the tradition of physics throughout its history. And in this sense, general relativity is the culmination of a specific set of aesthetic concerns. Symmetry, harmony, a sense of unity and wholeness, these are some of the ideals general relativity formalises. Where quantum theory is a jumpy jazzy mash-up, general relativity is a stately waltz.

As we celebrate its centenary, we can applaud the theory not only as a visionary piece of science but also as an artistic triumph.

What do we mean by the word “art”?

Lots of answers have been proposed to this question and many more will be given. A provocative response comes from the poet-painter Merrily Harpur, who has noted that “the duty of artists everywhere is to enchant the conceptual landscape”. Rather than identifying art with any material methods or practices, Harpur allies it with a sociological outcome. Artists, she says, contribute something bewitching to our mental experience.

It may not be the duty of scientists to enchant our conceptual landscape, yet that is one of the goals science can achieve; and no scientific idea has been more enrapturing than Einstein’s. Though he advised there’d never be more than 12 people who’d understand his theory, as with many conceptual artworks, you don’t have to understand all of relativity to be moved by it.

There is a beauty in spacetime. NASA, CC BY-NC

In essence the theory gives us a new understanding of gravity, one that is preternaturally strange. According to general relativity, planets and stars sit within, or withon, a kind of cosmic fabric – spacetime – which is often illustrated by an analogy to a trampoline.

Imagine a bowling ball sitting on a trampoline; it makes a depression on the surface. Relativity says this is what a planet or star does to the web of spacetime. Only you have to think of the surface as having four dimensions rather than two.

Now applying the concept of spacetime to the whole cosmos, and taking into account the gravitational affect of all the stars and galaxies within it, physicists can use Einstein’s equations to determine the structure of the universe itself. It gives us a blueprint of our cosmic architecture.

Synthesis

Einstein began his contemplations with what he called gedunken (or thought) experiments; “what if?” scenarios that opened out his thinking in wildly new directions. He praised the value of such intellective play in his famous comment that “imagination is more important than knowledge”.

The quote continues with an adage many artists might endorse: “Knowledge is finite, imagination encircles the world.”

But imagination alone wouldn’t have produced a set of equations whose accuracy has now been verified to many orders of magnitude, and which today keeps GPS satellites accurate. Thus Einstein also drew upon another wellspring of creative power: mathematics.

As it happened, mathematicians had been developing formidable techniques for describing non-Euclidean surfaces, and Einstein realised he could apply these tools to physical space. Using Riemannian geometry, he developed a description of the world in which spacetime becomes a dynamic membrane, bending, curving and flexing like a vast organism.

Where the Newtonian cosmos was a static featureless void, the Einsteinian universe is a landscape, constantly in flux, riven by titanic forces and populated by monsters. Among them: pulsars shooting out giant jets of x-rays and light-eating black holes, where inside the maw of an “event horizon”, the fabric of spacetime is ripped apart.

One mark of an important artist is the degree to which he or she stimulates other creative thinkers. General relativity has been woven into the DNA of science fiction, giving us the warp drives of Star Trek, the wormhole in Carl Sagan’s Contact, and countless other narrative marvels. Novels, plays, and a Philip Glass symphony have riffed on its themes.

At a time when there is increasing desire to bridge the worlds of art and science, general relativity reminds us there is artistry in science.

Creative leaps here are driven both by playful speculation and by the ludic powers of logic. As the 19th century mathematician John Playfair remarked in response to the bizzarities of non-Euclidean geometry, “we become aware how much further reason may sometimes go than imagination may dare to follow”.

In general relativity, reason and imagination combine to synthesise a whole that neither alone could achieve.

The ConversationMargaret Wertheim, Vice-Chancellor’s Fellow in Science Communication, University of Melbourne

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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Why is Einstein’s general relativity such a popular target for cranks?

The Conversation

Michael J. I. Brown, Monash University

Scientists maybe celebrating the 100th anniversary of Albert Einstein’s general theory of relativity, but there was also a death in 1915. It was one of the many deaths of simple and intuitive physics that has happened over the past four centuries.

Today the concepts and mathematics of physics are often removed from everyday experience. Consequently, cutting edge physics is largely the domain of professional physicists, with years of university education.

But there are people who hanker for a simpler physics, toiling away on their own cosmologies. Rightly or wrongly, these people are often labelled cranks, but their endeavours tell us much misconceptions about science, its history and what it should be.

I regularly browse open access website arxiv.org to look for the latest astrophysics research. Real astrophysics, that is. But if I want to take a look at what pseudoscientists are up to, I can browse vixra.org. That’s right, “arxiv” backwards. The vixra.org website was founded by “scientists who find they are unable to submit their articles to arXiv.org” because that website’s owners filter material they “consider inappropriate”.

There are more than 1,800 articles on vixra.org discussing relativity and cosmology, and many don’t like relativity at all. Perhaps one reason why cranks particularly dislike relativity is because it is so unlike our everyday experiences.

Einstein predicted that the passage of time is not absolute, and can slow for speeding objects and near very massive bodies such as planets, stars and black holes. Over the past century, this bizarre predication has been measured with planes, satellites, and speeding muons.

But the varying passage of time is nothing like our everyday experience, which isn’t surprising as we don’t swing by black holes on our way to the shops. Everyday experience is often central to cranky ideas, with the most extreme example being flat earthers.

Thus many crank theories postulate that time is absolute, because that matches everyday experience. Of course, these crank theories are overlooking experimental data, or at least most of it.

History and linearity

One of the most curious aspects of pseudoscience is an oddly linear approach to science. To be fair, this can result from an overly literal approach to popular histories of science, which emphasise pioneering work over replication.

A pivotal moment in relativity’s history is Albert Michelson and Edward Morley’s demonstration that the speed of light didn’t depend on its direction of travel nor the motion of the Earth.

Of course, since 1887 the Michelson-Morley experiment has been confirmed many times. Modern measurements have a precision orders of magnitude better than the original 1887 Michelson-Morley experiment, but these don’t feature prominently in popular histories of science.

Interestingly many pseudoscientists are fixated on the original Michelson-Morley experiment, and how it could be in error. This fixation assumes science is so linear that the downfall a 19th century experiment will rewrite 21st century physics. This overlooks how key theories are tested (and retested) with a myriad of experiments with greater precision and different methodologies.

Another consequence of the pseudoscientific approach to history is that debunked results from decades past are often used by buttress pseudoscientific ideas. For example, many pseudoscientists claim Dayton Miller detected “aether drift” in the 1930s. But Miller probably underestimated his errors, as far more precise studies in subsequent decades did not confirm his findings.

Unfortunately this linear and selective approach to science isn’t limited to relativity. It turns up in cranky theories ranging from evolution to climate.

Climate scientist Michael E Mann is still dealing with cranky accusations about his seminal 1998 paper on the Earth’s temperature history, despite the fact it has been superseded by more recent studies that achieve comparable results. Indeed, it devoured so much of Mann’s time he has literally written a book about his experience.

What about the maths?

During the birth of physics, one could gain insights with relatively simple (and beautiful) mathematics. My favourite example is Johannes Kepler’s charting of the orbit of Mars via triangulation.

In the 17th century, Johannes Kepler used elegantly simple mathematics to chart the motion of Mars. Johannes Kepler / University of Sydney

Over subsequent centuries, the mathematics required for new physical insights has become more complex, as illustrated by Newton’s use of calculus and Einstein’s use of tensors. This level of mathematics is rarely in the domain of the enthusiastic but untrained amateur? So what do they do?

One option is to hark back to an earlier era. For example, trying to disprove general relativity by using the assumptions of special relativity or even Newtonian physics (again, despite the experiments to the contrary). Occasionally even numerology makes an appearance.

Another option is arguments by analogy. Analogies are useful when explaining science to a broad audience, but they aren’t the be-all and end-all of science.

In pseudoscience, the analogy is taken to the point of absurdity, with sprawling articles (or blog posts) weighed down with laboured analogies rather than meaningful analyses.

Desiring simplicity but getting complexity

Perhaps the most fascinating aspect of pseudoscientific theories is they hark for simplicity, but really just displace complexity.

A desire for naively simple science can produce bizarrely complex conclusions, like the moon landing hoax conspiracy theories. NASA/flickr

Ardents of the most simplistic pseudoscientific theories often project complexity onto the motives of professional scientists. How else can one explain scientists ignoring their brilliant theories? Claims of hoaxes and scams are commonplace. Although, to be honest, even I laughed out loud the first time I saw someone describe dark matter was a “modelling scam”.

Again, this isn’t limited to those who don’t believe in relativity. Simple misunderstandings about photography, lighting and perspective are the launch pad for moon landing conspiracy theories. Naively simple approaches to science can lead to complex conspiracy theories.

Changing intuition

Some have suggested that pseudoscience is becoming more popular and the internet certainly aids the transmission of nonsense. But when I look at history I wonder if pseudoscience will decay.

In the 19th century, Samuel Rowbotham promoted Flat Earthism to large audiences via lectures that combined wit and fierce debating skills. Perhaps in the 19th century a spherical world orbiting a sun millions of kilometres away didn’t seem intuitive.

But today we can fly around the globe, navigate with GPS and Skype friends in different timezones. Today, a spherical Earth is far more intuitive than it once was, and Flat Earthism is the exemplar of absurd beliefs.

Could history repeat with relativity? Already GPS utilises general relativity to achieve its amazing precision. A key plot device in the movie Interstellar was relativistic time dilation.

Perhaps with time, a greater exposure to general relativity will make it more intuitive. And if this happens, a key motivation of crank theories will be diminished.

Will general relativity become more widely understood via popular media, such as the movie Interstellar?


Michael will be on hand for an Author Q&A between 4 and 5pm AEDT on Tuesday, November 24, 2015. Post your questions in the comments section below.

The ConversationMichael J. I. Brown, Associate professor, Monash University

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

 

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Einstein and Chaplin on universality

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Einstein on problems

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Common sense fallacy

by Tim Harding

The American writer H L Mencken once said “There is always a well-known solution to every human problem — neat, plausible, and wrong.” He was referring to ‘common sense’, which can be superficially plausible and sometimes right, but often wrong.

The Common Sense Fallacy (or ‘Appeal to Common Sense’) is somewhat related to the Argument from Popularity and/or  the Argument from Tradition. However, it differs from these fallacies by not necessarily relying on popularity or tradition.

Instead, common sense relies on the vague notion of ‘obviousness’, which means something like ‘what we perceive from personal experience’ or ‘what we should know without having had to learn.’ In other words, common sense is not necessarily supported by evidence or reasoning. As such, beliefs based on common sense are unreliable.  The fallacy lies in giving too much weight to common sense in drawing conclusions, at the expense of evidence and reasoning.

In some ways, scientific methods have been developed to avoid the errors that can result from common sense. For instance, common sense used to tell us that the Earth is flat and that the Sun revolves around the Earth – because that is the way things appear to us without scientific investigation.  Another example of ‘common sense’ is that the world appears to have been designed, so therefore there must have been a designer.

Einstein’s theories of relativity were initially resisted, even by the scientific community, because they defied common sense.  They seemed to belong more in the realm of science fiction than reality, until they were later verified by scientific observations.  Our modern Global Positioning System (GPS) now uses Einstein’s relativity theories.  This initial resistance may have led Einstein to later say that ”Common sense is nothing more than a deposit of prejudices laid down by the mind before you reach eighteen” .

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Einstein on insanity


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Einstein on explanations


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