(Roughly) Daily

Posts Tagged ‘gravity

“Men knew better than they realized, when they placed the abode of the gods beyond the reach of gravity”*…

In search of a theory of everything…

Twenty-five particles and four forces. That description — the Standard Model of particle physics — constitutes physicists’ best current explanation for everything. It’s neat and it’s simple, but no one is entirely happy with it. What irritates physicists most is that one of the forces — gravity — sticks out like a sore thumb on a four-fingered hand. Gravity is different.

Unlike the electromagnetic force and the strong and weak nuclear forces, gravity is not a quantum theory. This isn’t only aesthetically unpleasing, it’s also a mathematical headache. We know that particles have both quantum properties and gravitational fields, so the gravitational field should have quantum properties like the particles that cause it. But a theory of quantum gravity has been hard to come by.

In the 1960s, Richard Feynman and Bryce DeWitt set out to quantize gravity using the same techniques that had successfully transformed electromagnetism into the quantum theory called quantum electrodynamics. Unfortunately, when applied to gravity, the known techniques resulted in a theory that, when extrapolated to high energies, was plagued by an infinite number of infinities. This quantization of gravity was thought incurably sick, an approximation useful only when gravity is weak.

Since then, physicists have made several other attempts at quantizing gravity in the hope of finding a theory that would also work when gravity is strong. String theory, loop quantum gravity, causal dynamical triangulation and a few others have been aimed toward that goal. So far, none of these theories has experimental evidence speaking for it. Each has mathematical pros and cons, and no convergence seems in sight. But while these approaches were competing for attention, an old rival has caught up.

The theory called asymptotically (as-em-TOT-ick-lee) safe gravity was proposed in 1978 by Steven Weinberg. Weinberg, who would only a year later share the Nobel Prize with Sheldon Lee Glashow and Abdus Salam for unifying the electromagnetic and weak nuclear force, realized that the troubles with the naive quantization of gravity are not a death knell for the theory. Even though it looks like the theory breaks down when extrapolated to high energies, this breakdown might never come to pass. But to be able to tell just what happens, researchers had to wait for new mathematical methods that have only recently become available…

For decades, physicists have struggled to create a quantum theory of gravity. Now an approach that dates to the 1970s is attracting newfound attention: “Why an Old Theory of Everything Is Gaining New Life,” from @QuantaMagazine.

* Arthur C. Clarke, 2010: Odyssey Two

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As we unify, we might pause to remember Sir Arthur Stanley Eddington, OM, FRS; he died in this date in 1944.  An astrophysicist, mathematician, and philosopher of science known for his work on the motion, distribution, evolution and structure of stars, Eddington is probably best remembered for his relationship to Einstein:  he was, via a series of widely-published articles, the primary “explainer” of Einstein’s Theory of General Relativity to the English-speaking world; and he was, in 1919, the leader of the experimental team that used observations of a solar eclipse to confirm the theory.

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“Time is the longest distance between two places”*…

 

In quantum mechanics, time is universal and absolute; its steady ticks dictate the evolving entanglements between particles. But in general relativity (Albert Einstein’s theory of gravity), time is relative and dynamical, a dimension that’s inextricably interwoven with directions x, y and z into a four-dimensional “space-time” fabric. The fabric warps under the weight of matter, causing nearby stuff to fall toward it (this is gravity), and slowing the passage of time relative to clocks far away. Or hop in a rocket and use fuel rather than gravity to accelerate through space, and time dilates; you age less than someone who stayed at home.

Unifying quantum mechanics and general relativity requires reconciling their absolute and relative notions of time. Recently, a promising burst of research on quantum gravity has provided an outline of what the reconciliation might look like — as well as insights on the true nature of time…

The effort to unify quantum mechanics and general relativity means reconciling totally different notions of time; catch up on the state of play at “Quantum Gravity’s Time Problem.”

* Tennessee Williams, The Glass Menagerie

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As we set our watches, we might send carefully-calculated birthday greetings to Gabrielle-Émilie Le Tonnelier de Breteuil, Marquise du Châtelet, the French mathematician and physicist who is probably (if unfairly) better known as Voltaire’s mistress; she was born on this date in 1706.  Fascinated by the work of Newton and Leibniz, she dressed as a man to frequent the cafes where the scientific discussions of the time were held.  Her major work was a translation of Newton’s Principia, for which Voltaire wrote the preface; it was published a decade after her death, and was for many years the only translation of the Principia into French.

Judge me for my own merits, or lack of them, but do not look upon me as a mere appendage to this great general or that great scholar, this star that shines at the court of France or that famed author. I am in my own right a whole person, responsible to myself alone for all that I am, all that I say, all that I do. it may be that there are metaphysicians and philosophers whose learning is greater than mine, although I have not met them. Yet, they are but frail humans, too, and have their faults; so, when I add the sum total of my graces, I confess I am inferior to no one.
– Mme du Châtelet to Frederick the Great of Prussia

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Written by (Roughly) Daily

December 17, 2016 at 1:01 am

Obsessed with his weight…

German scale-maker Kern has been in the weighing business since 1844.  To demonstrate the precision of the scientific instruments in which it now specializes, Kern has launched The Gnome Experiment.

If Earth was a perfect sphere of uniform density, then gravity would be consistent. But it’s not, which means gravity varies wherever you go. So can we chart those discrepancies using just a basic-range Kern scale?

Method

We’re shipping our Gnome Kit from scientist to scientist around the world. Join the experiment and you’ll receive:

1x Kern EWB 2.4 Scale
Pre-calibrated according to local gravity at Kern HQ, Balingen, Germany.

1x Kern Gnome
The perfect test-subject for two good reasons: Gnomes are already accustomed to travelling the world. They also originate from our homeland, Germany.

1x Lab gloves & 1 x Air duster
Important because dust or grease will reduce the accuracy of the results.

Readers can check up on results-to-date…

… and can sign up to participate, here.

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As we pack our bags to move south,* we might send earthy birthday greetings to civil engineer and geodesist John Fillmore Hayford; he was born on this date in 1868.  Hayford, the father of the modern science of geodesy, made the first precise determination of the ellipsoidal shape and size of the earth.

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* an object weighs about 0.5% more at the poles than at the Equator.

Written by (Roughly) Daily

May 19, 2012 at 1:01 am

A Matter of Some Gravity…

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I’ve been noticing gravity since I was very young.
-Cameron Diaz

Isaac Newton first proposed a universal law of gravitation, where every massive body in the universe was attracted to every other one. This simple law proved extremely powerful, able to explain the orbits of planets and the reason the apocryphal apple fell on his head. However, Newton was never able to explain why gravity worked or what exactly it was. Two hundred plus years later, Albert Einstein was able to offer a more complete description of gravity—one where Newton’s laws are a limited case. According to Einstein, gravity was due to the warpage of spacetime by mass and energy; all objects followed straight paths, just on curved spaces.

With the advent of quantum theory over the past 100 years, scientists have been able to develop an elegant mathematical framework capable of uniting three of the four fundamental forces that are thought to exist in the universe. The fourth, gravity, still remains the fly in the ointment, and has resisted unification to this point. Early last year, Dutch theoretical physicist Erik Verlinde published a manuscript to the arXiv that purports to explain why science cannot reconcile all four fundamental forces. According to him, it is simple: “gravity doesn’t exist.”

Read the full story (SPOILER ALERT: it relates to Leonard Susskind‘s “holographic principle,” suggesting in effect that gravity isn’t a fundamental force, but an “entropic” result of information imbalances between the bodies/regions in question) in Ars Technica (recapping Physical Review D, 2011. DOI: 10.1103/PhysRevD.83.021502).

As we sit more confidently beneath apple trees, we might wish a polymathic Happy Birthday to the painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor, anatomist, geologist, cartographer, botanist and writer– the archetypical Renaissance Man– Leonardo da Vinci; he was born on this date in 1452.

Self-portrait in Red Chalk (source)

G Whiz…

In Rio, at the 2016 Olympics, the same jump will get an athlete >1 cm higher than that jump at the London Olympics in 2012…

From the ever-illuminating xkcd.

As we rethink our choice of venue, we might wish a humorously absurd Happy Birthday to Terry Jones, author, screenwriter, director, actor, television host– and most famously, founding member of Monty Python.  He was born on this date in 1942.  Among his many awards, “9622 Terryjones,” an asteroid in the main belt between Mars and Jupiter, was named in his honor.

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Written by (Roughly) Daily

February 1, 2011 at 1:01 am

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