Monday, December 14, 2009
Sunday, November 29, 2009
霍金在《时间简史》中,详细解释事件光锥如下:
“如果有一个光脉冲从一特定的空间的点在一特定的时刻发出,在时间的进程中,它就会以光球面的形式发散开来,而光球面的形状和大小与源的速度无关。在百万分之一秒后,光就散开成一个半径为
类似地,从一个事件散开的光在四维的空间——时间里形成了一个三维的圆锥,这个圆锥称为事件的未来光锥。以同样的方法可以画出另一个称之为过去光锥的圆锥,它表示所有可以用一光脉冲传播到该事件的集合。” (黑体是我加的。)
因为这段话是如此地重要,是我直斥霍金科学地撒播荒诞的主要依据,我把后面几句他的英文原文抄录在这里:(黑体是我加的。)
“Similarly, the light spreading out from an event forms a (three-dimensional) cone in (the four-dimensional) space-time. This cone is called the future light cone of the event. In the same way we can draw another cone, called the past light cone, which is the set of events from which a pulse of light is able to reach the given event Figure 2:4.”
英文原文比中文译文更清楚地显示了
“以同样的方法可以画出另一个称之为过去光锥的圆锥,它是许多事件的集合,从这个事件集合一条光脉冲能够到达一给定事件。”
但不管怎么译法,在这几句话里,霍金都说得很明白:未来光锥是一“事件散开的光”在四维的空间——时间里形成的一个三维的圆锥,怎么就能变成了事件集合呢?请读者自己去霍金或者爱因斯坦的著作里找一找,“事件散开的光”怎么就能变成了“事件”本身呢?经过了任何证明吗?还是就这么含含糊糊地说着说着就把上一句说的“事件散开的光”,在下一句里用一个莫须有的“同样的方法”糊弄成了“事件”本身呢?如果是这样,世界上还有比这更不严肃的“科学”推理吗?用这样的所谓“科学”名正言顺地围剿我们的传统文化,是我们可以接受的吗?
我在这里公开请求
我的这些文字是很尖酸刻薄。可是,想起我自己和我这一代人,从小起在做人的道理上被教导得傻不拉叽,读书后在科学的道理上又被这些权威糊弄得昏天黑地,心里怎能没有气?
记得小时候读一本《科学家谈21世纪》,里面讲到如果我们能比光跑得快,就能追上过去追上历史。自那时起就念念不忘,常常就着这话题作儿时的幻想少年的梦。长大后思路开阔了一点,人生阅历多了一点,偶尔再就着这话题想起来,就见到无数的破绽,把它当作不值一谈的少年梦付之秋风。不料今天还要来严肃地讨论它。
我发现了吴先生这段文章里的有个不大不小的问题:他误解了Hawking原文中某一层的意思!首先,“到达一给定事件”应译作“到达这一给定事件”。其次,发出光脉冲的不是事件集合,而是那个事件集里的每个事件,换言之,那个定语从句修饰的是events,而不是set of events。这样就比较容易理解这段话的意思了:光必须有光源,这里姑且把每个光源称为事件。光锥本身是虚的(只有光,没有事件实体),但它的来源是事件实体。
我怀疑Hawking的表述只是不够精准,他可能想说:In the same way we can draw another cone, called the past light cone, which is the product of a set of events from which a pulse of light is able to reach the given event.
他“可能”并不想说,光锥本身是事件!
即便如此,吴先生的质疑依然有效:这个给定事件的未来光锥散发出去形成光球面,这个光球面不是事件,更不是事件集合,但它的过去光锥源头却是事件集合?
这里牵涉到时间维度。事件A的过去光锥不是事件A散发的,而是发生在过去的事件B、C、D、E、F、G的各自光锥射向事件A形成的,因为事件A处于过去这些事件的各自光锥的结合点。
但这里的问题是:往事的“光”,对未来的事件有影响吗?在绝对意义上来说,不可能没有影响。但这是什么性质的影响?假如真的有大爆炸,那么那个事件的过去光锥是什么来源?
我要弄本A Brief History of Time,再读一遍。第一次读没有下功夫。
Wednesday, November 25, 2009
After an agonisingly verbose, but understandably indispensable (thus graciously suffered by the audience), drone of opening speeches by a few dignitaries, the show begins, not to the rousing gongs and drums that typically usher in a traditional Wushu performance, but to the blasting decibels of a pick-n-mix concoction of Chinese folk music plus revolutionary Peking opera plus Cantopop plus disco beat and what-not.
The emcees (one gorgeous-looking female and one slightly shy but nonetheless presentable male) speak in English and French alternately, but the guy's voice fails to rise above the ambience-critical music throughout the show. Luckily for me, he is the one who speaks French. Obviously, at some subconscious level, the organiser believes the melodies, albeit less than melodious most of the time, are more integral to the show than some feeble commentaries, especially if they are delivered in French.
The emcees introduce the lineup. Impressive! Thirteen national and world champions and the rest, silver medalists. Each performs a short routine of what he or she is best at, as a silent/nonverbal self-introduction. The guy with the lance is a little unfortunate: The shaft breaks in two during that short routine. "I hope he has a spare one", I think to myself. Later, it turns out that he does have a spare one, but the ornamental tassel below the spearhead looks half-shorn, presumably because there isn't enough time for him to fasten all the strands of the tassel in place.
The first proper performance is a warm-up routine. One expression comes to my mind: gravity-defying. When Jet Li's films were introduced to the West, that was the word that the Western media often used to describe his feats. So very apt.
However, as they repeatedly leap into the air and do one somersault after another, I begin to worry: Won't they burn out at this rate? I mean – this is only the first routine. Save your energy, kids!
But I am proven wrong, subsequently. They are bursting with bountiful energy, each jumping higher than the previous person and showing not the slightest fatigue.
Highlights include:
(5) Swordplay by Shen Guangmei, silver medalist at the 11th National Games. Comment: She flows.
(6) Broadsword routine by Zhang Bo, gold medalist at the National Wushu Championship. Comment: Speed backed up by a lot of power.
(9) Double broadswords (wielded by Zhang Li, gold medalist at the 10th National Games) against two lances (in the hands of Ji Taijing, silver medalist at the 11th National Games, and Shen Guangmei, ditto). Comment: Zhang Li would be super efficient in the kitchen with double cleavers. Just imagine two spears darting at you at all angles, like woodpeckers, and you have to fend them off with two pieces of flat metal and eventually snatch away their weapons and chop them in half (hypothetically, I hasten to add)!
(10) Group performance, southern style, by Zhou Jing (gold medalist at the 9th World Wushu Championships and the 7th Asian Wushu Championships) et al. Comment: Yummy! Zhou performs the first form of Wing Chun/Yongchun, at dazzling speed, to make it look more powerful and more entertaining. He also spars with each of his three teammates, using predominantly the Hong style techniques, not Wing Chun. Regrettably, the final stroke is invariably a kick, which is more characteristic of the northern style.
(11) Taiji by Dong Qing (20 years old, gold medalist at the 1st World Junior Wushu Championship and the 2nd Asian Junior Wushu Championship, one of the Taiji performers at the Opening Ceremony of the Beijing Olympics) et al. Comment: Solid training, with inspirational flair. A thorough joy to watch!
There is no intermission, but according to the programme, (1)-(11) is the cluster of competitive styles (competitive in the sense of being performed at national games and international championships). It is followed by a cluster of "traditional" styles. The most impressive among this lot is Xingyiquan (Form-and-Mind Boxing) performed by Zhou Jing, yes, the southern-style guy. Xingyi is one of the three "internal" schools of martial arts, the other two being Taiji and Bagua. Unlike the latter two, Xingyi doesn't readily lend itself to "performance" on stage. But Zhou does a very decent job by demonstrating the essential Xingyi moves while letting the audience sense the power that surges within.
This 30-year-old guy is truly amazing, as he then surprises the audience with a somewhat comical rendition of sparring performance: Hammer versus cudgel, with him brandishing a long-handled hammer and his hopeless opponent taking him on with a pole. And he is not even puffed out when he, quite literally, "nails" his hapless mate in the end!
It is an evening of jolly good fun. Triple thumbs-up to the young performers. I want to shout bravo or encore, but (a) I sit too far away from the stage and I am aware that the emcee, with the help of the PA system, can't even beat the music; and (b) I sit among a group of ladies, so the sheepish side in me gets the better of my other side, whatever that other side is!
QED
Friday, November 13, 2009
Friday, October 16, 2009
TELEPORTATION
The theory: Going from here to somewhere else without passing through anywhere in between.
The science fiction: Beam me up, Scotty.
In practice: Take two particles of light and entangle them - now you can teleport quantum information - such as what their spin is - from one to the other, instantaneously.
The layman's explanation: Photons, particles of light, have a property called "spin". This can be up, down, or a mixture of the two. Alice has a photon, and she wants Bob to have one with the same spin. She can't send him hers because the Post Office is on strike, and she can't measure her spin and phone him, because the measurement can change the spin.
Fortunately, the last time she met Bob she gave him one photon from an entangled pair, and kept the other. "Entangled" means that the two photons were prepared so that their states were related in a special way. Alice lets her photon interact with her other photon from the entangled pair. This instantly teleports information about the spin to Bob's half. However, he can't "read" that information until a message arrives by more conventional means. A quick call on Alice's mobile, telling him some measurements she has made, now puts his entangled photon into the desired state.
Quantum "teleportation" destroys the original state and can't be used to send messages faster than light. It doesn't actually teleport matter - just quantum information.
Coming to a store near you?: In 1998, the quantum optics group at Caltech used "squeezed light" to teleport the state of a photon in a laboratory. It's now been done with atoms, too. In 2004 Austrian physicists teleported the state of a photon across the Danube river. Within another century it will be an amoeba. But be warned: when you are teleported, your body will be ripped to shreds and rebuilt at the other end.
Sunday, October 04, 2009
Wednesday, September 16, 2009
Thursday, July 30, 2009
Monday, July 27, 2009
Saturday, July 25, 2009
Thursday, July 16, 2009
Sunday, June 21, 2009
Friday, June 12, 2009
Thursday, June 11, 2009
Tuesday, June 09, 2009
Sunday, May 24, 2009
Tuesday, May 19, 2009
Friday, May 01, 2009
Thursday, April 30, 2009
Wednesday, April 15, 2009
Friday, April 10, 2009
偶然
徐志摩
我是天空里的一片云,
偶尔投影在你的波心--
你不必讶异,
更无须欢喜--
在转瞬间消灭了踪影。
你我相逢在黑夜的海上,
你有你的,我有我的,方向;
你记得也好,
最好你忘掉
在这交会时互放的光亮!
By Chance
Hsu Chih-mo
By chance, mirrored in your heart's limpid water --
I don't mean to alarm,
Nor to charm --
When you look again, I'm gone like a goner.
Our paths cross in the night, in the deep,
You follow your course, I to mine keep;
Remember it you may,
Nay, you would do better to move away