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霍金輻射的實驗性測量

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Stephen Hawking proposed in 1974 that black holes evaporate. In essence, vacuum fluctuations near a black hole's horizon produce particle–antiparticle pairs. One of each pair falls into the hole while the other escapes. Since the escaping particle has energy, the black hole must lose energy.

1974年,史帝芬霍金提出了黑洞縮減的見解。本質上,靠近黑洞視界的真空波動產生粒子-反粒子對。每對中的一個粒子陷入黑洞中,而另一個粒子脫離。由於脫離的粒子具有能量,因此黑洞勢必喪失能量。

 

A blackbody temperature inversely proportional to the black hole's mass can be assigned to the process, yet the temperature is so low—on the order of 100 nK for a solar mass—that the radiation is difficult to observe directly.

霍金幅射(Hawking radiation)是由於量子效應,被斷言由黑洞發出之具有黑體光譜(black body spectrum)的熱輻射。黑體溫度與黑洞質量成反比,能被歸因於上述過程。不過溫度很低(就一個太陽質量而言,大約是100nK),以至於不易直接觀測這種輻射。(nKnanoKelvin十億分之一絕對溫度)

 

But William Unruh (University of British Columbia) demonstrated an analogy between the behaviors of waves near the black hole and sound waves in moving fluids.

不過,加拿大英屬哥倫比亞大學的William Unruh論證了,靠近黑洞之波動與活動流體中之聲波,兩者變化間的相似性。

 

Now, physicists Silke Weinfurtner, Matthew Penrice, and Unruh and engineers Edmund Tedford and Gregory Lawrence at UBC have used another analogous system, surface waves, to study the Hawking process.

目前(20113),該大學的物理學家Silke WeinfurtnerMatthew PenriceUnruh,及工程師Edmund TedfordGregory Lawrence,業已利用另一種類似體系─表面波,來研究霍金輻射過程。

 

They put a streamlined object shaped like an airplane wing into a channel of flowing water to create a region of high-velocity flow. Long-wavelength surface waves created downstream could propagate upstream toward that region but were blocked by the obstacle and converted into short-wavelength waves.

他們將狀若飛機機翼的流線型物體置入流水道中,來產生高速水流區域。下游產生的長波長表面波會朝上游上述區域傳播,不過遭到此障礙物阻擾,結果轉變成短波長的波動。

 

The figure shows the converted waves (bottom) and the interference between them and the incoming wave (top). The obstacle behaves like a so-called white hole, which, as a time-reversed black hole, lets no radiation in but does let radiation escape.

原文圖示了經轉變的波(下圖)及這些波與到來波之間的干擾(上圖)。此障礙物起了如同(作為時間反轉的黑洞)使輻射脫離卻無法進入之所謂白洞的作用。(白洞是物質及光無法從外部進入,卻能從內部脫離的一種假設性區域。)

 
(圖援用自原文)

 

The conversion is the analogue of stimulated emission, and the team's measurements of the amplitudes of the converted waves matched the expected thermal distribution.

上述轉變類似受激放射的情況,結果該團隊有關經轉變之波動幅度的測量,與預期的熱散佈相一致。

 

Moreover, despite the system's nonlinearities, turbulence, and viscosity, and along with prior numerical work by various groups, the new results demonstrate the generic nature of Hawking radiation.

此外,儘管該體系的諸多非線性、紊流及黏性(viscosity),不過連同先前不同團隊的數值研究,該項新研究結果證實了霍金幅射的一般性質。

 

 

原文網址:http://physicstoday.scitation.org/doi/10.1063/1.3604511

翻譯:許東榮

台長: peregrine
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