【翻译】最强伽马射线爆发开启物理新视野
本帖最后由 森林里 于 2009-2-24 12:31 编辑美国航空航天局费米伽马射线太空望远镜的观测活动中表明，宇宙中可能并非所有形式的光都是以相同的速度传播。超高能伽马射线在时空的量子乱流中传播时，其速度可能会降低。如果在今后的观测中能够证实这一点，它将会撼动整个现代物理学基础，而且也许能够为追寻“万物至理”指出一条明路，进而统一20世纪物理学的两大支柱理论学说：爱因斯坦的广义相对论和量子力学。
http://media.skyandtelescope.com/images/GRB_jetart2_341px.jpg
这幅艺术想象图描绘的是在近处观察（我们可不建议这么做：））伽马射线爆发时的景象。爆发造成了两股喷流，喷流中的粒子以不低于99.9999%光速的速度传播。欧洲南方天文台供图
费米太空望远镜于2008年发射升空，它曾经称为“伽马射线大天区太空望远镜（GLAST）”。其主要目标就是研究宇宙中的极端现象——爆发中的恒星、宇宙喷流、湮灭粒子，以及其它那些我们根本不想发生在地球附近的现象。发射成功后不久，费米太空望远镜即开始收集伽马射线爆发（GRBs）的迹象，通常这种强烈的爆发是由濒死的恒星造成的。
2008年9月16日，费米望远镜发现了迄今为止最为强烈的伽马射线爆发。此次爆发发生在122亿年以前。不过令人疑惑的是，爆发产生的低能伽马射线竟然早于超高能伽马射线到达地球。众所周知，伽马射线能量越高，则波长越短。这些“费米大天区望远镜（LAT）”所侦测到的高能伽马射线的波长仅相当于原子核大小的千分之一。
http://media.skyandtelescope.com/images/GRB080916C_177px.jpg
美国航空航天局“雨燕”号卫星捕捉到的伽马射线余晖，产生于9月16日伽马射线爆发过后。
美国航空航天局/迅捷探测计划/施特藩·伊穆勒供图
根据量子力学理论以及经由无数实验室的验证，当“虚拟粒子”瞬间产生时，时空乱流的幅度是微乎其微的。而根据那些意图统一量子力学和广义相对论的学说判定，超短波长的伽马射线可以“触碰”乱流，致使其运行速度被拖慢。换句话说，如果这些学说完全切合实际情况的话，则高能伽马射线的传播速度要慢于光速。
这种效应非常捉摸不定，基本上不可能在实验室得以验证。不过根据费米望远镜项目科学家史蒂夫·里茨（美国航空航天局/戈达德宇宙飞行中心）的说法，伽马射线爆发提供了一个在太空进行实验的机会，因为伽马射线需要穿过广阔的星系空间，这是一段非常遥远的距离。爆发具有极大的能量，所以在极远的距离也可以观察到。事实上，9月16日观测到的爆发是迄今为止最为强烈的，所以费米望远镜很容易就发现了它。费米望远镜所具备的侦测超高能伽马射线能力，能够锁定太空中的坐标，非常适于进行这一实验。
在此次爆发中，观测到共计16.5秒的超高能伽马射线的时滞，这一结果与量子引力学的某些内容是一致的，同时这也是非常令人兴奋的学说进展。但在费米项目的科学家开香槟庆祝之前，他们必须排除其它一些解释的可能性。这就需要观测更多的伽马射线爆发目标。
总而言之，9月16日的爆发中所见到的时滞最直接的解释就是，造成爆发的某种机制也同时造成了超高能伽马射线对比低能伽马射线的几秒延迟。“我们对这些能量中喷发的射线了解还非常少，而费米望远镜正要告诉我们答案，”LAT项目首席科学家——斯坦福大学的彼得·米歇尔森这样说道，他的科研小组在2月19日出版的《科学快讯》中阐述了研究成果。
不过随着时间的推移，费米望远镜会不断发现更多的爆发点。如若费米望远镜能够发现高能伽马射线随着传播距离的增加而出现时滞，这就能压倒性地证明量子引力理论确实能够告诉我们一些事物最本初的性质。届时，费米项目的科学家们就不只是开香槟庆祝了；他们完全可以开始预订到斯德哥尔摩的往返机票。
“这次爆发给我们提出了一系列的疑问，”米歇尔森说，“在今后的几年内，我们或许会发现更理想的爆发样本，从而获取一些问题的答案。” 原文？ sorry, 忘记了~~不好意思~~
原文链接如下：
http://www.skyandtelescope.com/news/39867717.html
Most Powerful Gamma-Ray Burst May Point to New Physics
Observations from NASA’s Fermi Gamma-ray Space Telescope hint that all forms of light may not travel through space at the same speed. Very-high-energy gamma rays may be slowed down as they propagate through the quantum turbulence of space-time. If future observations bear this out, it will rock the foundations of modern physics, and perhaps point the way to a "theory of everything" that would help unify the twin pillars of 20th-century physics: Einstein’s general theory of relativity and quantum mechanics.
This artist’s concept depicts what a gamma-ray burst might look like if we could view it up close (this is not something we’d recommend). The explosion triggers two jets, whose particles travel no less than 99.9999 percent the speed of light.
European Southern Observatory
Fermi, formerly known as the Gamma-ray Large Area Space Telescope (GLAST), launched in June 2008. Its intended purpose is to the study the extreme universe — exploding stars, cosmic jets, annihilating particles, and other stuff that we don’t want happening near Earth. Soon after launch, Fermi started picking up gamma-ray bursts (GRBs), powerful explosions usually triggered by dying stars.
On September 16, 2008, Fermi picked up the most powerful GRB observed to date. The burst took place 12.2 billion years ago. Intriguingly, the highest-energy gamma rays from this GRB arrived later than the low-energy gamma rays. The higher a gamma ray’s energy, the shorter its wavelength. These high-energy gamma rays, detected by Fermi’s Large Area Telescope (LAT), have wavelengths one-thousandth the size of an atomic nucleus.
NASA’s Swift satellite picked up the X-ray afterglow of the September 16th gamma-ray burst.
NASA / Swift / Stefan Immler
As predicted by quantum mechanics, and as verified by countless laboratory experiments, space-time becomes turbulent at very tiny scales, as "virtual particles" pop into existence for fleeting moments. According to some theories that attempt to unify quantum mechanics with general relativity, very-short-wavelength gamma rays will "feel" this turbulence, which would retard their velocity. In other words, if these theories accurately describe nature, high-energy gamma rays travel slightly slower than the speed of light.
This effect would be so subtle it would be nearly impossible to measure in a laboratory experiment. But as Fermi project scientist Steve Ritz (NASA/Goddard Space Flight Center) notes, GRBs give us a chance to conduct the experiment in space by letting gamma rays run a very long race across the vast distances of intergalactic space. These explosions are so powerful they can be seen to immense distances. In fact, the September 16th burst is the most powerful observed to date, and was easily detected by Fermi. With Fermi’s ability to detect very-high-energy gamma rays, and pin down their sky coordinates, it is uniquely suited to carry out this experiment.
The 16.5-second delay for the highest-energy gamma ray observed in this burst is consistent with some of these theories of quantum gravity, which is an exciting development. But before Fermi’s scientists uncork their champagne bottles, they must rule out alternative explanations. And this will require observations of many more GRBs.
After all, the most straightforward interpretation of the time delay seen in the September 16th burst is that the mechanism that produced the burst created the highest-energy gamma rays a few seconds later than their lower-energy counterparts. "Burst emissions at these energies are still poorly understood, and Fermi is giving us the tools to figure them out," says LAT lead scientist Peter Michelson of Stanford University, whose team reports its results in the February 19th Science Express.
But over the next few years, Fermi will detect more and more bursts. If Fermi sees a time lag for high-energy gamma rays that becomes larger with increasing distance, this would present compelling evidence that these theories of quantum gravity are indeed telling us something profound about nature at its most fundamental scales. At that time, Fermi scientists may do more than just uncork the champagne; they can start reserving themselves a round-trip ticket to Stockholm.
"This one burst raises all sorts of questions," says Michelson. "In a few years, we'll have a fairly good sample of bursts, and we may have some answers." 森林里兄开始发威了~~~
也在这里跟个贴吧，再有一个月进行第一次评奖。
http://www.astronomy.com.cn/bbs/thread-102837-1-1.html 森林里兄开始发威了~~~
也在这里跟个贴吧，再有一个月进行第一次评奖。
http://www.astronomy.com.cn/bbs/thread-102837-1-1.html
positron 发表于 2009-2-23 12:30 http://www.astronomy.com.cn/bbs/images/common/back.gif
马上去跟~~呵呵
不过我是不定期的，因为要上班。闲的时候就会翻一些。 如果光速不是恒定的，类星体的红移现象会不会有其他解释？ 证实的话铁定诺贝尔啊。。。 7# 愚石
这个文章说的光速和相对论说的光速是两码事。
这里的光子是超高能光子，能够激发微观真空，所以“看起来像是速度减慢”。一般意义上的光子是没有能力激发微观真空的。
至于具体微观过程是怎样的，文章含糊其词，估计这个科普作者自己都没弄明白，所以我们就不必深究了。
一个类似的、比较有趣的问题是GZK疑难，也是关于高能光子和背景场的相互作用的，有兴趣的朋友就去wiki吧。 楼主的翻译没搞错吗？我们无数的实验表明虽然在介质中，粒子运动的速度可以超过正常情况下光在该介质中的速度，但是真空中光速恒定是毫无疑问的。
我认为，与其相信在穿越了122亿光年距离后，两种γ射线间有了16.5秒的到达间距，远远不如相信这两种爆发的本身时间间隔就是16.5秒来得合适，也非常容易理解。
现在物理界也够燥的，为了出名什么都想呢。 如果是一次超新星爆发或类似爆发的话，高能γ射线本来就是在最后阶段才产生的，我倒是认为这个间距能够很好的说明恒星核心在最后阶段的变化有多快。 在我们所熟悉的低能小尺度范围内, 光速c的常数性是经受了很高精确度的实验检验的. 但是在很高能量, 以及像这种穿越了宇宙学尺度得到的积累效应是否体现出和现行理论的偏离却是未知数而且是值得研究的. 有些量子引力理论预言了光速随着能量的变化, 高能光子跑得比低能光子慢, 或者等效地说光子存在一个正比于能量(或者能量平方, 或者更高次方等)的"质量"项, 有一种形象的理解就是时空中存在量子泡沫, 低能光子看来这些泡沫尺度太小(可以和其波长比较)根本不足以影响它们, 而高能光子则会体验到在量子泡沫里面穿行, 等效行走路程变长, 因而看起来速度变慢.
近期有不少利用TeV gamma射线研究这个问题的, 有的还发表在Phys.Rev.Lett.上. 例如
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000101000017170402000001&idtype=cvips&gifs=yes ::yun2::实在是佩服各位的理论基础及能力~~~我已经晕了~~
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