Posted tagged ‘gravity’

Clinton, Canute, and a Certain Gravity.

May 6, 2008

Parts of the blogosphere is having (a) some fun with Senator Clinton’s sudden self-discovery as the scourge of experts or (b) a collective WTF at her continued attempt to reorganize the space time continuum in which we live into one that suits her better. (Not to mention this gem of a solution to high gas prices that apparently neither Clinton nor McCain considered.)

But the jump the shark moment — or perhaps the most recent leap in the 400 meter shark hurdle race — has to be this. Senator Clinton, perhaps recently bitten by a radioactive spider, has decided that she now has the mojo to break up OPEC.

Great idea! Why didn’t anyone think of that before?

Plenty of folks have already had their way with this one too. The most succinct that I have seen so far comes from Josh Marshall at Talking Points Memo. The basic take is, in essence, that Clinton is playing King Canute, without that monarch’s self awareness. (Or perhaps she’s Glendower in Henry IV: She can call spirits from the vasty deep, but with Hotspur we may reply, “Why, so can I, or so can any man; But will they come when you do call for them?”)

But to pick up on Josh’s take, I’m given to understand that the next target of the growing anti-elitist lobby will be the law of gravity. However, even were Senator Clinton to add her voice to the chorus of disdain for Isaac Newton, Albert Einstein and other such out of touch eggheads, this issue has in fact already been put on the table.

Ah well. It will all be over soon.

Image: J.W.M Turner, “The Sea at Egremont,” 1802. The work of art depicted in this image and the reproduction thereof are in the public domain worldwide. The reproduction is part of a collection of reproductions compiled by The Yorck Project. The compilation copyright is held by Zenodot Verlagsgesellschaft mbH and licensed under the GNU Free Documentation License.  Source:  Wikimedia Commons.

PZ’s Birthday — with Gravitas.

March 10, 2008

Belated happy birthday to the big squid on the block of science blogging — see Bora’s (who else’s?) catalogue of those around the blogosphere who responded in a more timely fashion to the Dear Cephalopod’s numerologically significant planetary rotation.

Not much to add to the universal cheer for PZ Myers continued presence on earth, except a quibble. (What did you expect? This is a blog, for Spagetti Monster’s sake).

PZ, in his acknowledgment of the outpouring of blogolove, noted that his accomplishment was pretty ordinary:

Now I do have to remind you all, though, that we’re all aging at exactly the same rate (unless you have access to a spaceship that travels at a significant fraction of the speed of light), and all I’ve got is a head start on many of you…

But alas, PZ here makes an error common to the non physicist or non-mud-grubbing pedant. (as my last physics course was some 34 years ago, guess which category into which I fall.) He nods towards the special relativistic side of time dilation, but, (horrors!) he ignores the gravitational impact on the passage of time.

The effect is a consequence of the way Albert Einstein’s general theory of relativity. (See here, or here. Fwiw, I wrote and directed the animations accompanying the second essay. They’re more than ten years old, but I still like them). General relativity states that strong gravitational fields make clocks run slower than clocks in a weaker field — as in fact they do. An observer at sea level will, if she happens to have an atomic clock handy, observe time as passing more slowly than will her colleague flying in an atomic-clock equipped airplane. (More precisely — the airborne clock will be observed to have run slightly fast compared to the clock on the ground when the plane lands.)

The effect is small in most circumstances (not near a black hole, though!) — but significant enough to matter a great deal to the Global Positioning System. (Click on Clifford Will to see the relevant essay.) Left uncorrected, the seemingly small time dilation effect (a clock on a satellite in geosynchronous orbit orbiting medium earth orbit altitude used by the GPS system (20,200 kilometers or 12,552  miles) ticks 45 microseconds/day faster than a clock on earth) would, even when accounting for special relativity, which pushes slows the speedy satellites’ clocks by 7 microseconds/day, produce navigation errors of more than 10 kilometers a day. Will writes that failing to account for the effect would render the system useless for navigation in just two minutes.

All of which is to say that PZ, professing reason at about 1,138 ft above sea level, (give or take the height of his office building), is aging slightly slower than any colleague he might want to chaff at the University of Colorado, Boulder, altitude 5,430, but just a smidgeon faster than your faithful blogger, writing this in Boston (ish), maybe a hundred feet above high tide.

Use those microseconds wisely, I say.

Update:  GPS satellite orbits corrected. Brain bubbles are my only excuse.  Thanks to commenter Tom below for catching the error.

Image: Guercino, “Et in Arcadia Ego” c. 1628. Source Wikimedia Commons.

Friday (Isaac) Newton blogging (Thursday edition): “The Coffee House” meeting

January 24, 2008

I don’t think I’ve got this precise to the day, but I can’t let the month pass without tipping my hat to Sir Christopher Wren, Robert Hooke, and the incomparable Edmund Halley. It was in January, 1684 that three men met for refreshment and conversation after one of the Royal Society’s weekly meetings.

They may have done so to put a little rigor into an evening that could have been truly scattered. Neal Stephenson caught the flavor of early Royal Society meetings perfectly in the first volume of his Baroque Cycle. His account is taken from life: if you look at the early volume’s of the Society’s pleadings (JSTOR has ’em all online, if you have access to that resource) you’ll find articles like “An Accompt of the improvement of Optick Glasses” and Robert Hooke’s own telescopic observation “A Spot in one of the Belts of Jupiter” jostling for space with “An Account of a very odd Monstrous Calf” or “Of an Hungarian Bolus of the same Effect with the Bolus Armenus.” (All of these from meetings in 1665.)

So it may well have been either boredom with yet more deformed animals, or exhilaration at some deep observational challenge that got three of the real intellects in the Society going that January night.Wren asked the question that got the fireworks going. How, he asked, did the force of gravity vary as the distance between objects changed? Could it be an inverse square relationship, as he and others had speculated, but failed to demonstrate? (I.e. — did the force of gravitational attraction between two bodies vary inversely with the square of the distance between them?)

This was, of course, the fundamental cosmological problem of the day. The geometry of the solar system was basically understood — laid out by Johannes Kepler and his three descriptive laws of the planets’ orbital motion. But how the planets held to the paths they traced — that no one knew, though Wren and his listeners recognized that the ill-understood phenomenon of gravity must have something to do with problem.

Wren himself and Halley too both confessed they could not demonstrate that an inverse square law actually held in the real world, but Hooke claimed that he had already completed a proof of the idea. Pressed to reveal it, he declined, declaring he would hold it back for a time so that “others triing and failing, might know how to value it.”

To coax out the truth, Wren offered a prize — a book worth 40 shillings (a week’s stipend for Newton at that moment, as it happened) — to Hooke (or anyone else) if he could actually do what he claimed he could within two months. Nothing came.

Then, in August, Edmund Halley made his way to Cambridge for his famous chat with Isaac Newton. In the middle of the conversation, seemingly as an aside, he asked Newton, “what he thought the Curve would be that would be described by the Planets supposing the force of attraction towards the Sun to be reciprocal to the square of their distance from it?”

An ellipse, Newton answered, without pause for thought.

How did he know?

“I have calculated it.”

Newton probably had, unlike the similarly confident Hooke, though he didn’t produce the calculation on the spot. In November, though, he sent Halley a more in depth analysis of the problem, a nine page manuscript “on the motion of bodies in orbit.” Halley immediately recognized that this wasn’t merely the resolution of a bet, but the outline of a whole new science. He urged — almost demanded — that Newton fill out the account…

…and hence, with considerable labor yet to come and a great debt owed to Halley as the project’s midwife, was born Newton’s Principia — and with it, much of what we think of as modern science.

I do not usually toast with coffee, preferring stronger stuff. But it is time to titrate some caffeine into my system, so, in remembrance of that argument in the coffee house, I will shortly lift my mug of Peet’s brew — not to Isaac Newton, this time, deserving of his honors as he certainly is — but to those other three men, who at the crucial moment asked the crucial question, which ultimately found its way to the right man.

So, in this three hundred and twenty first fourth January since Sir Christopher Wren offered his prize, here’s to Wren, Robert Hooke, and above all, to Edmund Halley.

PS: in case anyone was wondering, the name of this blog is indeed an homage to Newton, the subject of my forthcoming book. (Jan-Feb, 2009, at last count.)

Update: arithmetical error corrected above, proving that I shouldn’t do mental arithmetic while in a state of mild caffeine withdrawal. Dependency is an ugly thing.

Image: Robert Hooke’s microscope from Micrographia, 1665. Source: Wikipedia Commons.

Saturday Feynman blogging

January 19, 2008

Chad Orzel over at Uncertain Principles has an “I can’t believe I hadn’t read this yet” review of Richard Feynman’s QED. He liked it, with a caveat that comes Feynman’s way a lot.

The presentation here is so elegant and seamless that it’s a little hard to imagine someone who isn’t Feynman using this book as the basis to explain the theory to someone else. If you already know a little bit about it, this can illuminate some other aspects, and provide some tricks that you could combine with pre-existing knowledge to make a good presentation, but the book alone conveys more of a sense of understanding than actual understanding.

Orzel goes on to say that he means this as high praise, and I think it is. To unpack that a little: what Feynman does give his readers is a sense of how a great scientist thinks through a very complicated idea, in language that any willing reader can grasp. It’s exhilarating

But that said, there is another book that I think is simply wonderful, better even than QED.  Check out the way too intimidatingly titled The Character of Physical Law. In it, Feynman uses the history and inner life of Newton’s law of gravitation to delve into the deep connection between mathematics and physics.

Character was a revelation to me when I first read it.  It hits the sweet spot:  Newton’s gravitation is not particularly mathematically intimidating — and Feynman deliberately chose to keep his focus there, instead of on the mathematically intense modern theory of gravity, General Relativity.

That keeps  this book from falling into the criticism Orzel makes of QED:  the reader can follow the details of argument without too much trouble.  With that hurdle removed, Feynman gave his hearers (first) and readers (now)   the satisfaction followin both the thinking and the thought embodied in Newton’s gravity.  It’s a great read.