Posts Tagged ‘Newton

Light can break Newton’s third law – by cheating

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by Michael Slezak
Isaac Newton just got cheated. Laser pulses have been made to accelerate themselves around loops of optical fibre, seeming to break the physicist’s law that every action must have an equal and opposite reaction. The work exploits a trick with light that only makes it appear to have mass, so it is a bit of a cheat, but it may one day lead to faster electronics and more reliable communications.

According to Newton’s third law of motion, when one billiard ball strikes another, the two balls should bounce away from each other. But if one of the billiard balls had a negative mass, then when the two balls collide they will accelerate in the same direction. This effect could be useful in a diametric drive, a speculative “engine” in which negative and positive mass interact to accelerate forever. NASA explored using the effect in the 1990s in a bid to make a diametric drive for better spacecraft propulsion. But there was a very big fly in the ointment: quantum mechanics states that matter cannot have a negative mass. Even antimatter, made of particles with the opposite charge and spin to their normal matter counterparts, has positive mass.

“Writing a negative mass in quantum field theory doesn’t make any difference,” says Archil Kobakhidze at the University of Sydney, Australia. The equations involve terms that are always squares of mass, so any negative mass will become positive anyway. “It has no observable meaning.”

Mass effect

Now Ulf Peschel at the University of Erlangen-Nuremberg in Germany and his colleagues have made a diametric drive using “effective mass”. As photons travel at the speed of light they have no rest mass. But if you shine pulses of light into some layered materials, such as crystals, some of the photons can be reflected backwards by one layer and then reflected forwards again by another. That delays part of the pulse, causing it to interfere with the rest of the pulse as it propagates more slowly through the material.

“It’s a bit like what happens with a stroboscope,” says Dragomir Neshev at the Australian National University in Canberra, who was not involved in the study. If you watch a spoked wheel turning under a strobe it can appear to move at a different speed or even backwards.

When a material slows the speed of the pulse proportional to its energy, it is behaving as if it has mass – called effective mass. Depending on the shape of the light waves and the structure of the crystal, light pulses can have a negative effective mass. But to get such a pulse to interact with one with a positive effective mass requires a crystal that is so long it would absorb the light before the two pulses could show a diametric drive effect.

To get around this, Peschel created a series of laser pulses in two loops of fibre-optic cable. The pulses get split between the loops at a contact point, and the light keeps moving around each loop in the same direction. The key is that one loop is slightly longer than the other, so light going around the longer loop is relatively delayed (see diagram, above right). When that pulse comes back around and splits at the contact point, it shares some of its photons with pulses in the other loop. After a few round trips, the pulses develop an interference pattern that gives them effective mass.

Clever loops

The team created pulses with positive and negative effective mass. When the opposing pulses interacted in the loops, they accelerated in the same direction, moving past the detectors a little bit sooner on each round trip.

“By having these loops you can loop it forever  – it’s equivalent to having enormously long crystals,” says Neshev, whose group has also tried to create a diametric drive. “It is nice physics and a very clever apparatus.”

Electrons in semiconductors can also have effective mass, so the loops could be used to speed them up and boost processing power in computers, says Peschel. And in some fibres the speed of a light pulse is equivalent to its wavelength, which means the loops could be used to control a fibre’s colour output. Neshev says the method could increase the bandwidth of optical communications or even help create bright displays like laser screens. But he cautions that it will not be easy to adapt the loops for practical purposes.

Journal reference: Nature Physics, DOI: 10.1038/NPHYS2777


Written by physicsgg

October 15, 2013 at 10:39 pm


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Isaac Newton and Erwin Schrödinger

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Today is Schrodinger‘s birthday (12 August 1887 – 4 January 1961)

Written by physicsgg

August 12, 2012 at 4:14 pm

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Newton saved the UK economy £10 million

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Making a mint for the Mint: Isaac Newton (Image: SSPL via Getty Images )

by Jacob Aron
Where’s a scientific genius when you need one? A statistical analysis suggests that Isaac Newton saved the UK economy the equivalent of millions of pounds by implementing measures tostandardise the country’s gold coins.

Although Newton is famous for his theory of gravity, he also spent the last 30 years of his life running the Royal Mint, where the country’s coins are manufactured. Ari Belenkiy, a mathematician at the British Columbia Institute of Technology in Vancouver, Canada, has now compared coins produced before and after Newton’s stint at the mint to study the effect of measures he introduced to prevent rich goldsmiths from exploiting a currency loophole.

The quality of coins produced by the Royal Mint is assessed each year at the Trial of the Pyx, a ceremony begun in the 13th century. As coins are minted, a few from each batch are placed in a small chest, or pyx, and later weighed to determine how far they stray from the required standard.

This was essential because if coins weighed more than their face value, canny goldsmiths would buy them from the Mint, melt them down, then sell them back to the Mint at a profit, a process known as culling. “Neither counterfeiting nor clipping was involved,” says Belenkiy. “The culling was a vocation of the rich!”

Belenkiy modelled the weight of the coins as a normal distribution, or bell curve. He then used a combination of records from the trials, Newton’s notes and mathematical reasoning to calculate the standard deviation of the distribution, revealing the effects of Newton’s improvements. His analysis suggests Newton reduced the standard deviation from 1.3 grains – roughly 85 milligrams – to 0.75 grains, or 49 milligrams.

Unfortunately, no historical accounts detail exactly how he achieved this, but Belenkiy suggests Newton may have applied his recently derived “cooling law” to slow the coins’ cooling and reduce variability. However he did it, Belenkiy calculates Newton’s improvements saved £41,510 during his time as Master of the Mint, which is roughly £3 million today. Belenkiy suggests this is an underestimate, however, as the four Masters who followed Newton also applied his techniques, saving twice as much again, which means Newton may have saved the UK around £10 million in today’s money.

Journal reference: Journal of the Royal Statistical Society, DOI: 10.1111/j.1467-985X.2012.01037.x

Written by physicsgg

May 29, 2012 at 8:44 pm

Newton calculated that the world would end in 2060

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Read also: Peek into Isaac Newton’s theology papers

APOCALYPSE – Isaac Newton a prophétisé la fin du monde pour 2060

Une gravure de Sir Isaac Newton (AP Photo)

La controverse fait rage depuis des décennies : sir Isaac Newton, l’un des plus grands scientifiques de l’histoire, mort en 1727, était-il versé dans la théologie et le mysticisme ? Aux yeux de tous, Newton est celui qui a révolutionné la physique, les mathématiques et l’astronomie aux XVIIe et XVIIIe siècles, définissant notamment la loi de la gravité universelle et les trois lois du mouvement auxquelles il a donné son nom. Et pour beaucoup de nos contemporains, science et religion ne peuvent faire bon ménage.

“Contrairement à son image publique, la plupart des travaux de Newton n’étaient pas consacrés à la science mais davantage à la théologie, au mysticisme et à l’alchimie”, avance pourtant Haaretz. Le quotidien israélien en veut pour preuve les archives que vient de rendre publiques la Bibliothèque nationale d’Israël. Quelque sept mille cinq cents pages manuscrites d’archives, numérisées et mises en ligne en libre consultation dans le cadre du Projet Newton de l’université de Cambridge, qui dévoilent l’autre facette du grand scientifique britannique. Celle d’un influent théologien qui appliquait son approche scientifique à l’étude des textes sacrés, et notamment du mysticisme juif.

“De notre point de vue, il y a une contradiction entre les sciences naturelles et le rationalisme d’un côté, la théologie, le mysticisme et la foi de l’autre. Mais, dans son esprit, en tant que produit de son temps, comprendre les lois de la nature impliquait de comprendre comment le monde fonctionne”, explique Milka Levy-Rubin, commissaire de la collection de sciences humaines de la Bibliothèque nationale d’Israël.


Parmi les pages vieillies, une incroyable prédiction : la fin du monde aura lieu en 2060. Mais, quelle pomme a bien pu lui tomber sur la tête ? Cette conclusion, le physicien l’a tirée non pas au terme de savants calculs mathématiques, mais en lisant entre les lignes de la Bible et du Livre de Daniel de l’Ancien Testament. Newton est parti de la date symbolique du sacre de Charlemagne, en 800 ap. J.-C. Se référant au Livre de Daniel, qui selon lui prévoyait la fin du monde mille deux cent soixante ans plus tard, il a établi que la fin des temps serait 2060 (voir l’index des documents relatifs aux prophéties de Newton). Le décompte est lancé.

Les archives témoignent des heures passées par sir Isaac Newton dans les textes sacrés et les écrits mystiques. Tout aussi intéressantes sont les nombreuses tentatives qu’il a esquissées pour imaginer ce à quoi la fin des temps pourrait bien ressembler et les cartes qu’il a dessinées pour l’assister dans son calcul de l’apocalypse.


Extrait d'un écrit manuscrit de sir Isaac Newton (capture d'écran)

Pour la commissaire des collections, l’importance des écrits théologiques du physicien britannique vont au-delà de l’édification intellectuelle qu’ils révèlent. C’est donc un véritable trésor qui s’est retrouvé sur les étagères de la Bibliothèque nationale par “un mélange de chance et de coïncidence”, rapporte Haaretz.

Cent cinquante ans après sa mort, les descendants de sir Isaac Newton ont transféré ses manuscrits à l’université de Cambridge, où le physicien avait étudié. L’université n’a retenu que ses écrits scientifiques et a rendu les autres manuscrits à ses descendants. En 1936, ces manuscrits ont été proposé aux enchères chez Sotheby’s, à Londres. Mais, au même moment, son concurrent Christie’s organisait une vente d’art impressionniste, bien plus attendue.

Une aubaine pour les deux seuls acheteurs : le célèbre économiste John Maynard Keynes et le collectionneur et orientaliste juif Abraham Shalom Yehuda, qui se sont partagé la collection. A Keynes, les manuscrits d’alchimie et à Yehuda, les écrits théologiques. A la mort du collectionneur, en 1969, ces précieux documents ont été donnés à la Bibliothèque nationale d’Israël.

Written by physicsgg

February 18, 2012 at 7:15 am

Sir Isaac Newton’s handwritten notes now available online

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    • More than 4,000 pages of scientist’s works uploaded
    • Includes seminal Philosophiae Naturalis Principia Mathematica

Cambridge Digital Library

Groundbreaking: This annotated sketch of work on optics by Sir Isaac Newton is among 4,000 pages of his historic documents which have been put online by Cambridge University

Prized: Sir Isaac Newton's first edition copy of his Principia, widely regarded as one of the most significant works in the history of science

The college notebook - used by Newton between 1664 and 1665 - contains notes from his reading on mathematics and geometry, showing particularly the influence of John Wallis and René Descartes

The college notebook also shows evidence of Newton's own mathematical thinking including his study of infinite series and development of binomial theorem and the evolution of the differential calculus

Newton's English is recognisably different from our own, but his maths - building on work done by Rene Descartes - is exactly the same as what mathematicians use today. Here, he describes the curve of a mathematical function

Newton's 'Waste Book' contains much of the mathematician's work on calculus - which he began in 1664 while away from Cambridge due to the plague

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Written by physicsgg

December 12, 2011 at 1:46 pm