诛仙副本里死了怎么办:新技术令我们可以观察到布朗运动

公元前60年，诗人卢克莱修描绘了暗室里的灰尘运动，推测了原子的存在。1827年，英国植物学罗伯特·布朗利用显微镜观察悬浮于水中的花粉，发现了用他名字命名的布朗运动。1905年，爱因斯坦完整揭示了布朗运动的原因——花粉粒子在水分子撞击下受力不均导致的瞬间失衡。爱因斯坦计算得出，粒子减速的时间极短，几乎难以察觉，当时的技术不可能测量。现在，研究人员的探测设备（分辨率0.2埃，瞬时分辨率10ns）已经足够快到能跟踪运动的粒子。

2D random walkChristopher Dombrowski

New tech shows Einstein wrong: we can watch Brownian motion

The seemingly random movement of Brownian motion just got a little more classical. Scientists have been able to image the ultrafast motions of a trapped particle, revealing the underlining trajectories causing Brownian motion. This is the first time inertial Brownian motion of a particle in a fluid have been measured.

In 60 BC, the poet Lucretius described the motions of dust in a dark room and speculated on the existence of atoms. In 1827, Robert Brown described the random motions of pollen in water, the motion which now bears his name. It took until 1905 for Einstein to fully describe how Brownian motion arises from instantaneous imbalances in the forces from collisions with water molecules.

At its heart, Brownian motion is still described by classical Newtonian physics, even if we cannot define a classical velocity and can only measure mean square displacement. Einstein said, "It is therefore impossible... to ascertain the root mean square velocity by observation" because the timescales of the instantaneous velocity are vanishingly short. Einstein calculated that the time for a particle to decelerate significantly is about ~100ns, impossibly fast to measure at the time.

But that was then. Now researchers have been able to probe time scales an order of magnitude faster. By holding a micron-sized sphere in a optical trap and measuring the scattered light with a high speed position detector (75MHz), a team was able to measure the motion of the spheres with a resolution of 0.2 angstroms and a temporal resolution of ~10ns. At these resolutions, they were able to track the inertial Brownian motion of the sphere.