Friday, May 05, 2006

Myths in the making

Or the unmaking, perhaps. It was such a lovely story: a mysterious but very real force of attraction between objects caused by the peculiar tendency of empty space to spawn short-lived quantum particles has a maritime analogue in which ships are attracted because of the suppression of long-wavelength waves between them. That’s what was claimed ten years ago, and it became such a popular component of physics popularization that, when he failed to mention it in his book ‘Zero’ (Viking, 2000; which explored this aspect of the quantum physics of emptiness), Charles Seife was taken to task. But it seems that no such analogy really exists – or at least, that there is no evidence for it. The myth is unpicked here.

This vacuum force is called the Casimir effect, and was identified by Dutch physicist Hendrik Casimir in 1948 – though, being so weak and operating at such short distances, it wasn’t until the late 1990s that it was measured directly. It provides fertile hunting ground for speculative and sometimes plain cranky ideas about propulsion systems or energy sources that tap into this energy of the vacuum. (And it certainly seems that there is a lot of energy there – or at least, there ought to be, but something seems to cancel it out almost perfectly, which is why our universe can exist in its present form at all. Here’s a new idea for where all this vacuum energy has gone.)

So how did the false story of a naval analogy start? It was suggested in a paper in the American Journal of Physics by Sipko Boersma. Just as two closely spaced plates suppress the quantum fluctuations of the vacuum at wavelengths longer than the spacing between them, so Boersma proposed that two ships side by side suppress sea waves in a heavy swell. By the same token, Boersma suggests that a ship next to a steep cliff or wall is repelled, because the reflection of the ocean waves at the wall (without a phase shift, as occurs for electromagnetic waves) creates a kind of ‘virtual image’ of the ship within the wall, rolling perfectly out of phase – which reverses the sign of the force.

It sounds persuasive. But there doesn’t seem to be any evidence for such a force between real ships. The only real evidence that Boersma offered in his paper came from a nineteenth-century French naval manual by P. C. Caussée, where indeed a ‘certain attractive force’ was said to exist between ships moored close together. But Fabrizio Pinto has unearthed the old book, and he finds that the force was in fact said to operate only in perfectly calm (‘plat calme’, or flat calm) seas, not in wavy conditions. The engraving that Boersma showed from this manual was for a different set of circumstances, in a heavy swell (where the recommendation was simply to keep the ships apart so that their rigging doesn’t become entangled as they roll).

Regarding this discrepancy, Boersma says the following: “Caussée is not very exact. His mariners told him about ‘une certaine force attractive’ in calm weather and he made out of it an attraction on a flat sea… The reference to ‘Flat Calm’ is clearly an editing error; Caussée’s Album is not a scientific document. He should have referred his attraction to the drawing 14 ‘Calm with heavy swell’, or better still to the drawing 15 ‘Flat Calm’ but then modified with a long swell running. Having read my 1996 paper, one sees immediately what Caussée should have written.”

I’m not sure I follow this: it seems to mean not that Caussée made an ‘editing error’ but that he simply didn’t understand what he had been told about the circumstances in which the force operates. That might be so, but it requires that we take a lot on trust, and rewrite Caussée’s manual to suit a different conclusion. If Caussée was mistaken about this, should we trust him at all? And there doesn’t seem to be any other strong, independent evidence of such a force between ships.

But perhaps getting to the root of the confusion isn’t the point. The moral, I guess, is that it’s never a good idea to take such stories on trust – always check the source. Fabrizio says that scientists rarely do this; on the contrary, they embrace such stories as a part of the lore of their subject, and then react indignantly when they are challenged. “Because of the lamentable utter lack of philosophical knowledge background that afflicts many graduating students especially in the United States, sometimes these behaviors are closer to the tantrums of children who have learned too early of possible disturbing truths about Santa Claus”, he says. Well, that’s possible. Certainly, we would do well to place less trust in histories of science written by scientists, some of whom do not seem terribly interested in history as such but are more concerned simply to show how people stopped believing silly things and started believing good things (i.e. what we believe today). This Whiggish approach to history was abandoned by historians over half a century ago – strange that it still persists unchallenged among scientists. The ‘Copernican revolution’ is a favourite of physicists (it’s commonly believed that Copernicus got rid of epicycles, for instance), and popular retellings of the Galileo story are absurdly simplistic. (And while we’re at it, can we put an end to the notion that Giordano Bruno was burned at the stake because he believed in the heliocentric model? Or would that damage scientists’ martyr complex?) It may not matter so much that a popular idea about the Casimir effect seems after all to be groundless; it might be more important that this episode serves as a wake-up call not to be complacent about history.


uhfdf said...

歐美a免費線上看,熊貓貼圖區,ec成人,聊天室080,aaa片免費看短片,dodo豆豆聊天室,一對一電話視訊聊天,自拍圖片集,走光露點,123456免費電影,本土自拍,美女裸體寫真,影片轉檔程式,成人視訊聊天,貼圖俱樂部,辣妹自拍影片,自拍電影免費下載,電話辣妹視訊,情色自拍貼圖,卡通做愛影片下載,日本辣妹自拍全裸,美女裸體模特兒,showlive影音聊天網,日本美女寫真,色情網,台灣自拍貼圖,情色貼圖貼片,百分百成人圖片 ,情色網站,a片網站,ukiss聊天室,卡通成人網,3級女星寫真,080 苗栗人聊天室,成人情色小說,免費成人片觀賞,

傑克論壇,維納斯成人用品,免費漫畫,內衣廣告美女,免費成人影城,a漫,國中女孩寫真自拍照片,ut男同志聊天室,女優,網友自拍,aa片免費看影片,玩美女人短片試看片,草莓論壇,kiss911貼圖片區,免費電影,免費成人,歐美 性感 美女 桌布,視訊交友高雄網,工藤靜香寫真集,金瓶梅免費影片,成人圖片 ,女明星裸體寫真,台灣處女貼圖貼片區,成人小遊戲,布蘭妮貼圖片區,美女視訊聊天,免費情色卡通短片,免費av18禁影片,小高聊天室,小老鼠論壇,免費a長片線上看,真愛love777聊天室,聊天ukiss,情色自拍貼圖,寵物女孩自拍網,免費a片下載,日本情色寫真,美女內衣秀,色情網,

liwo said...


女優王國,免費無碼a片,0800a片區,免費線上遊戲,無名正妹牆,成人圖片,寫真美女,av1688影音娛樂網,dodo豆豆聊天室,網拍模特兒,成人文學,免費試看a片,a片免費看,成人情色小說,美腿絲襪,影片下載,美女a片,人體寫真模特兒,熊貓成人貼,kiss情色,美女遊戲區,104 貼圖區,線上看,aaa片免費看影片,天堂情色,躺伯虎聊天室,洪爺情色網,kiss情色網,貼影區,雄貓貼圖,080苗栗人聊天室,都都成人站,尋夢園聊天室,a片線上觀看,無碼影片,情慾自拍,免費成人片,影音城論壇,情色成人,最新免費線上遊戲,a383影音城,美腿,色情寫真,xxx383成人視訊,視訊交友90739,av女優影片,