Thursday, August 20, 2015

gr caltech david The cornerstone of Einstein's theory, however, is the proposition that gravity is itself a fictitious force (or, rather, that it is indistinguishable from a fictitious force).

What is a "fictitious force"?

What is a "fictitious force"?
July 9, 2007


California Institute of Technology theoretical physicist and 2004 Nobel laureate David Politzer helps shed some light on these mysterious influences. The forces you feel in a moving car—those that push you back into your seat when the driver steps on the gas or throw you side to side when the car makes sharp turns—are everyday examples of fictitious forces. In general, these influences arise for no reason other than that the natural frame of reference for a given situation is itself accelerating. The term "fictitious force" has a precise meaning within Newtonian mechanics—in fact, it's always proportional to the mass of the object on which it acts. An elegant example of these types of apparent influences is the fictitious Coriolis force, which is responsible for the stately precession (or circular rotation) of a carefully suspended pendulum's plane of swing. If such a pendulum were suspended directly above the North Pole, it would appear to rotate 360 degrees every day. If you viewed this pendulum from a stationary point in outer space, however, it would appear to swing in a single, fixed plane while the Earth turned under it. From the outer space perspective, there is no sideways force (that is, perpendicular to the plane of swing) deflecting the sway of the pendulum. That is why the somewhat pejorative term "fictitious" is attached to this force. Likewise in the car, there simply is no real force pushing you back into your seat, your senses notwithstanding. Nevertheless, analyzing a situation in terms of fictitious forces may, in fact, be the most effective way to understand what is actually going on. Take a stirred cup of tea, a charming example of a consequence of the Coriolis force. If a few tea leaves are present in the cup, they end up in a pile at the center of the bottom surface (and not along the edge, as one might expect, as a result of the also fictitious centrifugal force). If you imagine yourself rotating around in sync with the stirred fluid, most of the fluid would appear to be at rest while the cup would be counter-rotating around you. That rotating cup drags some adjacent fluid along with it. Meanwhile, near the bottom, the Coriolis force on that dragged fluid pushes it toward the center of the cup, carrying the leaves along with it. With general relativity, Einstein managed to blur forever the distinction between real and fictitious forces. General relativity is his theory of gravity, and gravity is certainly the paradigmatic example of a "real" force. The cornerstone of Einstein's theory, however, is the proposition that gravity is itself a fictitious force (or, rather, that it is indistinguishable from a fictitious force). Now, some 90 years later, we have innumerable and daily confirmations that his theory appears to be correct.

What is a "fictitious force"?
July 9, 2007


California Institute of Technology theoretical physicist and 2004 Nobel laureate David Politzer helps shed some light on these mysterious influences. The forces you feel in a moving car—those that push you back into your seat when the driver steps on the gas or throw you side to side when the car makes sharp turns—are everyday examples of fictitious forces. In general, these influences arise for no reason other than that the natural frame of reference for a given situation is itself accelerating. The term "fictitious force" has a precise meaning within Newtonian mechanics—in fact, it's always proportional to the mass of the object on which it acts. An elegant example of these types of apparent influences is the fictitious Coriolis force, which is responsible for the stately precession (or circular rotation) of a carefully suspended pendulum's plane of swing. If such a pendulum were suspended directly above the North Pole, it would appear to rotate 360 degrees every day. If you viewed this pendulum from a stationary point in outer space, however, it would appear to swing in a single, fixed plane while the Earth turned under it. From the outer space perspective, there is no sideways force (that is, perpendicular to the plane of swing) deflecting the sway of the pendulum. That is why the somewhat pejorative term "fictitious" is attached to this force. Likewise in the car, there simply is no real force pushing you back into your seat, your senses notwithstanding. Nevertheless, analyzing a situation in terms of fictitious forces may, in fact, be the most effective way to understand what is actually going on. Take a stirred cup of tea, a charming example of a consequence of the Coriolis force. If a few tea leaves are present in the cup, they end up in a pile at the center of the bottom surface (and not along the edge, as one might expect, as a result of the also fictitious centrifugal force). If you imagine yourself rotating around in sync with the stirred fluid, most of the fluid would appear to be at rest while the cup would be counter-rotating around you. That rotating cup drags some adjacent fluid along with it. Meanwhile, near the bottom, the Coriolis force on that dragged fluid pushes it toward the center of the cup, carrying the leaves along with it. With general relativity, Einstein managed to blur forever the distinction between real and fictitious forces. General relativity is his theory of gravity, and gravity is certainly the paradigmatic example of a "real" force. The cornerstone of Einstein's theory, however, is the proposition that gravity is itself a fictitious force (or, rather, that it is indistinguishable from a fictitious force). Now, some 90 years later, we have innumerable and daily confirmations that his theory appears to be correct.

July 9, 2007


California Institute of Technology theoretical physicist and 2004 Nobel laureate David Politzer helps shed some light on these mysterious influences. The forces you feel in a moving car—those that push you back into your seat when the driver steps on the gas or throw you side to side when the car makes sharp turns—are everyday examples of fictitious forces. In general, these influences arise for no reason other than that the natural frame of reference for a given situation is itself accelerating. The term "fictitious force" has a precise meaning within Newtonian mechanics—in fact, it's always proportional to the mass of the object on which it acts. An elegant example of these types of apparent influences is the fictitious Coriolis force, which is responsible for the stately precession (or circular rotation) of a carefully suspended pendulum's plane of swing. If such a pendulum were suspended directly above the North Pole, it would appear to rotate 360 degrees every day. If you viewed this pendulum from a stationary point in outer space, however, it would appear to swing in a single, fixed plane while the Earth turned under it. From the outer space perspective, there is no sideways force (that is, perpendicular to the plane of swing) deflecting the sway of the pendulum. That is why the somewhat pejorative term "fictitious" is attached to this force. Likewise in the car, there simply is no real force pushing you back into your seat, your senses notwithstanding. Nevertheless, analyzing a situation in terms of fictitious forces may, in fact, be the most effective way to understand what is actually going on. Take a stirred cup of tea, a charming example of a consequence of the Coriolis force. If a few tea leaves are present in the cup, they end up in a pile at the center of the bottom surface (and not along the edge, as one might expect, as a result of the also fictitious centrifugal force). If you imagine yourself rotating around in sync with the stirred fluid, most of the fluid would appear to be at rest while the cup would be counter-rotating around you. That rotating cup drags some adjacent fluid along with it. Meanwhile, near the bottom, the Coriolis force on that dragged fluid pushes it toward the center of the cup, carrying the leaves along with it. With general relativity, Einstein managed to blur forever the distinction between real and fictitious forces. General relativity is his theory of gravity, and gravity is certainly the paradigmatic example of a "real" force. The cornerstone of Einstein's theory, however, is the proposition that gravity is itself a fictitious force (or, rather, that it is indistinguishable from a fictitious force). Now, some 90 years later, we have innumerable and daily confirmations that his theory appears to be correct.




当然我没有贬低老师没有创造力的意思，只是说他技术熟练而已。


六根胡须：


这个话题我是第一次听说，我有点想法如下：
首先我们遇到的是温度如何定义的事情。先考虑一个静止的体积为V的箱子里面有温度为T的气体。那么T此时的统计意义是很明确的，它决定了能量本征态的相对权重:exp(-E/T)。
现在我们做相对箱子的运动。（设C=1）之前的每一种态的协变4动量是（-E,0,0,0），在新的参考系中每个态的能量就会增加相同的倍数\gamma，但分布概率是不会变的，为了保持温度的统计意义，T必须变为T*\gamma。尽管如此，我还是觉得温度就是一个标量。运动系下的所谓温度，就好像运动系下的所谓引力质量是差不多的概念吧。如果把静止质量视为标量的话，那温度就是个标量

Posted by at

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)