每日科技报告 第18期 制造暗能量探测器

huashi3483

最近,斯坦福大学的Martin Perl和加州大学伯克利分校的Holger Mueller提出了在实验室检验暗能量的方法.文章中使用原子干涉这种方法.两个原子在非均匀的暗能量场中通过两条不同的路径,走过相同距离后干涉,因为两条路径上的暗能量场不同,所以原子的波函数会不同,可以通过两者波函数的干涉结果来检测暗物质.


       我们知道宇宙可见物质产生的都是引力,它们间相互吸引会导致宇宙慢慢聚团收缩,而实际上天文学观测到宇宙现在处于加速膨胀阶段,这便有了矛盾,现在主流观点是采用暗能量来解释宇宙膨胀,暗能量占宇宙全部物质的73%,密度为每立方米有10^-10焦耳,充满着宇宙,产生斥力,但暗能量至今没有观测到.

       最近,斯坦福大学的Martin Perl和加州大学伯克利分校的Holger Mueller提出了在实验室检验暗能量的方法.虽然10^-10焦耳的数量级很小,但是物理学家仍有能力测量,比如存在一电场,每米电压1伏特,那么这个电场的能量密度为10^-12焦耳每立方米,这要比暗能量的还小,但科学家可以轻松检测.

       问题是,电场和暗能量完全不同,电场你可以通过开关来检测能量的变化,关闭电源时可以认为电场能量为零,打开时测到的差值就是电场能量了.而暗能量你无法关闭,至少人类现有的科技无法做到操纵暗能量,这样的话就没法定标,没法比较测量.'

      仍有可能暗能量不是完全均匀的,可能会这儿密些,那儿稀些,这为我们提供了比较测量的途径.文章中使用原子干涉这种方法.如上图所示,两个原子在非均匀的暗能量场中通过两条不同的路径,走过相同距离后干涉,因为两条路径上的暗能量场不同,所以原子的波函数会不同,可以通过两者波函数的干涉结果来检测暗物质.这种双原子干涉的精度可以达到10^-17焦耳每立方米.

       这个实验令人兴奋,因为它用到了如今人类的最高水平技术.但实验有两个潜在的问题,一是我们对暗能量了解有限,它会不会影响原子的波函数仍不确定,二是在这么低的能量下,有可能存在未知的力干扰实验.但不管如何,我们期待实验结果,希望是另所有物理学家眉开眼笑的结果.

pwl1991317

怎么不是英文的。。。。。。。。。。。。。

huashi3483

How to Build a Dark Energy DetectorAll the evidence for dark energy comes from the observation of distant galaxies. Now physicists have worked out how to spot it in the lab.


The notion of dark energy is peculiar, even by cosmological standards.
Cosmologists have foisted the idea upon us to explain the apparent accelerating expansion of the Universe. They say that this acceleration is caused by energy that fills space at a density of 10^-10 joules per cubic metre.
What's strange about this idea is that as space expands, so too does the amount of energy. If you've spotted the flaw in this argument, you're not alone. Forgetting the law of conservation of energy is no small oversight.
What we need is another way of studying dark energy, ideally in a lab on Earth. Today, Martin Perl at Stanford University and Holger Mueller down the road at the University of California, Berkeley, suggest just such an experiment.
The dark energy density might sound small but Perl and Mueller point out that physicists routinely measure fields with much smaller energy densities. For example an electric field of 1 Volt per metre has an energy density of 10^-12 joules per cubic metre. That's easy to measure on Earth.
Of course there are some important differences between an electric field and the dark energy field that make measurements tricky. Not least of these is that you can't turn off dark energy. Another is that there is no known reference against which to measure it.
That leaves the possibility of a gradient in the dark energy field. If there is such a gradient, then it ought to be possible to measure its effect and the best way to do this is with atom interferometry, say Perl and Mueller.
Atom interferometry measures the phase change caused by the difference in two trajectories of an atom in space. So if a gradient in this field exists it should be possible to spot it by cancelling out the effects of all other forces. Perl and Mueller suggest screening out electromagnetic forces with conventional shields and using two atom interferometers to cancel out the the effect of gravitational forces.
That should allow measurements with unprecedented accuracy. Experiments with single atom interferometers have already measured the Earth's gravitational pull to an accuracy of 10^-9. The double interferometer technique should increase this to at least 10^-17.
That's a very exciting experiment which looks to be within reach with today's technology.
There are two potential flies in Perl and Mueller's ointment. The first is that the nature of dark energy is entirely unknown. If it exists and if there is a gradient, it is by no means certain that dark energy will exert a force on atoms at all. That will leave them the endless task of trying to place tighter and tighter limits on the size of a non-existent force.
The second is that some other unknown force will rear its head in this regime and swamp the measurements. If that happens, it's hard to imagine Perl and Mueller being too upset. That's the kind of discovery that ought to put a smile on any physicists face.
Ref:arxiv.org/abs/1001.4061: Exploring The Possibility Of Detecting Dark Energy In A Terrestrial Experiment Using Atom Interferometry

diguaaiqianqian

很好，我很喜欢，激起了我的兴趣

rockhuman

今年美赛考这个   昨晚有人来告诉我了。。。。。。。
嘘。。。。

rockhuman

请问坛主是从哪里找到那么好的文章的呢？

大笨象

呵呵.确实不错..

wuhao080910

似乎我们的论文与美国论文差距很大啊！

梦游枪手

飘过~~~~~~~~~~看不懂 呢

明心见性

呵呵.确实不错.......!!!!!!!!!!!!!!