subatomic particle Apparently faster than Light ＞＜“

[max_kwok]

如果我冇理解錯
730km 係講緊 chord AB 唔係arc AB
所以條數唔係咁計

[WFPC2]

iheby發表於2011年 9月27日 2:01


(非常)粗略估算：

設地球為正球體，（最大）圓周 = 40,000 km，r 為地球半徑 = 40000 / (2π)，c 為光速
O 點為地心，中微子／光 由地表 A 點到 B 點，則 r = OA = OB


弧AB = 730 km

直線AB：考慮 三角 ΔOAB，以 cosine rule 得
2r²(1-cos θ) = AB²，θ = ∠AOB
另 rθ = 弧AB = 730 km，θ = 730 / r
直線AB ≒ 729.6 km

以當時被錄得時間比光速還早 60ns，中微子所走距離 = ( 730/c - 60ns ) v，v = 中微子速度
若中微子以光速前進，它走了 730 - 60ns(c) ≒ 729.982 km

729.6 km < 729.982 km < 730 km

結果不低於下限，中微子速度上仍有低於光速的下調空間。
中微子愈慢，它愈要採取較接近 直線AB 的路徑，才可以保持早到60ns
C.L. 的觀點仍屬合理。

=====
但不排除科學團隊其實早已把地球弧度納入計算

http://forum.hkas.org.hk/viewthread.php ... a=page%3D1

[WFPC2]

我個人想中微子是一種穿透力極強的粒子，它貫穿地球跟穿過真空
沒有多大分別，反而宇宙對光子來說並不是絕對暢通無阻，星際間
的氣體會對光子造成散射，吸收。另外真空的電磁量子漲落亦會扭
曲光子的路徑，因此造成中微子比光速快。

[Wah!!]

若沒記錯，真空光速是個定義值，不是測量值。

[WFPC2]

若沒記錯，真空光速是個定義值，不是測量值。

光速是測量值，但不管你以甚麼速度追趕光線，
你都是測得光速是c，這是光速不變定律。

[Wah!!]

http://zh.wikipedia.org/wiki/%E5%85%89%E9%80%9F

真空中的光速等於299,792,458米/秒（1,079,252,848.8千米/小時）。[2] 這個速度並不是一個測量值，而是一個定義。

[WFPC2]

Delete!

[WFPC2]

http://zh.wikipedia.org/wiki/%E5%85%89%E9%80%9F

真空中的光速等於299,792,458米/秒（1,079,252,848.8千米/小時）。[2] 這個速度並不是一個測量值，而是一個定義。

看英文版卻沒有此句，不知怎麼，總是覺得這句話的邏輯有點不妥。 [推眼鏡]
http://en.wikipedia.org/wiki/Speed_of_light
未經實驗所得的測量結果，我們怎樣知道光速的值?

[Wah!!]

In 1983, the metre was redefined in the International System of Units (SI) as the distance travelled by light in vacuum in 1⁄299,792,458 of a second. As a result, the numerical value of c in metres per second is now fixed exactly by the definition of the metre.[5]

[WFPC2]

這句只是表示光速c的精確值，相對論描述任何參照系的觀察者
都會測量到真空中的光速值是一個常數，每秒299,792,458 米。

[鄧登凳]

In 1983, the metre was redefined in the International System of Units (SI) as the distance travelled by light in vacuum in 1⁄299,792,458 of a second. As a result, the numerical value of c in metres per second is now fixed exactly by the definition of the metre.[5]

You are absolutely correct.

This is echoed by the Physics FAQ web maintained by the Mathematics department, University of California, Riverside.

At the 1983 Conference Generale des Poids et Mesures, the following SI (Systeme International) definition of the metre was adopted:

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.
This defines the speed of light in vacuum to be exactly 299,792,458 m/s. This provides a very short answer to the question "Is c constant": Yes, c is constant by definition!

(my colour highlight)

Because we now define distance by the speed of light, relativity effects have to be understood by time dilation rather than distance changes.

[WFPC2]

In 1983, the metre was redefined in the International System of Units (SI) as the distance travelled by light in vacuum in 1⁄299,792,458 of a second. As a result, the numerical value of c in metres per second is now fixed exactly by the definition of the metre.[5]

You are absolutely correct.

This is echoed by the Physics FAQ web maintained by the Mathematics department, University of California, Riverside.

At the 1983 Conference Generale des Poids et Mesures, the following SI (Systeme International) definition of the metre was adopted:

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.
This defines the speed of light in vacuum to be exactly 299,792,458 m/s. This provides a very short answer to the question "Is c constant": Yes, c is constant by definition!

(my colour highlight)

Because we now define distance by the speed of light, relativity effects have to be understood by time dilation rather than distance changes.

他們說光速是定義值，並不表示光速不是可測量的值。

Because we now define distance by the speed of light, relativity effects have to be understood by time dilation rather than distance changes.

This statement is definitely incorrect.

[Wah!!]

這句只是表示光速c的精確值，相對論描述任何參照系的觀察者
都會測量到真空中的光速值是一個常數，每秒299,792,458 米。

在1983年之前, 米是定義值, 所以要利用"米"來測量光速.

但是1983年之後, 按國際最新定義, 光速是定義值, 而"米"這個單位才是測量值.
一米等於光在真空中 1/299792458 秒內所走過的距離.

[WFPC2]

這句只是表示光速c的精確值，相對論描述任何參照系的觀察者
都會測量到真空中的光速值是一個常數，每秒299,792,458 米。

在1983年之前, 米是定義值, 所以要利用"米"來測量光速.

但是1983年之後, 按國際最新定義, 光速是定義值, 而"米"這個單位才是測量值.
一米等於光在真空中 1/299792458 秒內所走過的距離.

這是表示方式的不同，若測量到光速在 1/299792458 秒所走距離為1米，
，那麼光每秒就走299792458米的距離了。

[Wah!!]

不是表示方式的不同, 而是本質上的分別.
光速在1983年之前是測量出來的, 而1983年之後光速 299792458m/s 便是定義出來的一個值.
米這個單位, 亦由一個"標準米尺"的長度定義, 變成 "1/299792458光秒"