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Natural Science Forum / Physics / General Physics / February 2007Measuring position and velocity of particles
In a discussion of Heisenberg's Uncertainty Principle I read that we must shine light on a particle to measure its position and velocity. How does this work exactly? Does the particle cast a shadow on a wall detector? Or is its position inferred some other way? > In a discussion of Heisenberg's Uncertainty Principle I read that we > must shine light on a particle to measure its position and velocity. > How does this work exactly? Does the particle cast a shadow on a wall > detector? Or is its position inferred some other way? nope, it is position and momentum. google for it. > > In a discussion of Heisenberg's Uncertainty Principle I read that we > > must shine light on a particle to measure its position and velocity. [quoted text clipped - 4 lines] > > google for it. Momentum is just mass times velocity, so measuring momentum amounts to measuring velocity and vice versa. > > "Scott H" <zinites_p...@yahoo.com> wrote in message > [quoted text clipped - 11 lines] > Momentum is just mass times velocity, so measuring momentum amounts to > measuring velocity and vice versa. That is true for measuring slow-moving (compared with c), massive objects. This is NOT the momentum for a photon, for example, and so the uncertainty in momentum of a photon does NOT amount to an uncertainty in the velocity of the photon. > > "Scott H" <zinites_p...@yahoo.com> wrote in message > [quoted text clipped - 11 lines] > Momentum is just mass times velocity, so measuring momentum amounts to > measuring velocity and vice versa. Not in general. That's only true for inertial momentum. There can be other forms. > In a discussion of Heisenberg's Uncertainty Principle I read that we > must shine light on a particle to measure its position and velocity. Not true. However, any attempt to measure position and velocity of a particle must involve disturbing both with your measuring technique, at least a little. We can't measure without the particle interacting with our measuring equipment. > How does this work exactly? You misunderstood. Perhaps it was a hypothetical measuring technique that involved bouncing photons (not necessarily visible light) off the particle. But there are many possible techniques. It was probably just a general discussion about how measuring involves disturbing. - Randy >> In a discussion of Heisenberg's Uncertainty Principle I read that we >> must shine light on a particle to measure its position and velocity. [quoted text clipped - 15 lines] > It was probably just a general discussion about > how measuring involves disturbing. HUP says you cannot measure both momentum and position precisely (but you can measure either one as precisely as you like). Dp * Dx ~ h. http://www.aip.org/history/heisenberg/ > In a discussion of Heisenberg's Uncertainty Principle I read that we > must shine light on a particle to measure its position and velocity. > How does this work exactly? Does the particle cast a shadow on a wall > detector? Or is its position inferred some other way? It's not complicated. When you look at a ball to measure its position, it is illuminated. When you take a strobe photo of it, it is illuminated. This light is intercepted by your eye or by a camera CCD. The global statement is that the exchange of light between the ball and a detector represents an *interaction* between the ball and the detector. There is absolutely no way for a detector to *detect* an object without some sort of interaction like this. The interesting thing is that this interaction, the exchange of light for example, also passes the things that light carries: momentum, energy, spin, etc. This means that there is a *transfer* of these properties from the ball to the detector, and that in turn means that the momentum, energy, spin (etc.) of the ball is different after the interaction than what it was before. There is simply no way to detect an object without affecting the properties of this object. The very act of *seeing* an object involves changing something about that object. This is what the uncertainty principle conveys in more precise terms. PD >> In a discussion of Heisenberg's Uncertainty Principle I read that we >> must shine light on a particle to measure its position and velocity. [quoted text clipped - 23 lines] > > PD The 'light transmitted' distant UNIVERSE [observed] in and by the lens of a telescope. The very light itself. "There is absolutely no way for a detector to *detect* an object without some sort of interaction..." "There is simply no way to detect an object without affecting the properties of this object." "The very act of *seeing* an object involves changing something about that object." Light waves, as they expand in space and up through time away from the point of propagation in space and time (no longer affiliated with the source of propagation) merge with other light waves also expanding, thus gaining more and ever more periphery of space and time, thus submerging (contracting) points of propagation by way of all that accelerating accumulation of periphery, now being a vastly expanded universe of vastly contracted points, strikes and enters into the material mass [universe] of the telescope's lens suddenly to thereto interact, transfer, and receive transference, regarding "properties." An exchange that will, in sheer magnitude, enormously exceed all accumulated prior [countless] exchanges. You bear repeating once more for those too many today who have the retentive capacity of a two year old. "There is absolutely no way for a detector to *detect* an object without some sort of interaction..." "There is simply no way to detect an object without affecting the properties of this object." "The very act of *seeing* an object involves changing something about that object." Something else that seems to me is all but totally unrealized by astronomers, cosmologists, and most physicists too (if not all). Buried very, very, deep inside the causing event, and the simultaneous event of light propagation, is the Planck horizon. Inherent to both the message and the messenger, any continuous submergence (contraction) of a point of propagation within light waves, within the waves' innumerable points, via continuous mergers and accumulations of message (universe) periphery, should be contraction toward some graduating entanglement of the vastly, vastly, contracted message itself with that horizon-property of the messenger itself. It is my thought that the farthest horizon searched for in the message from farthest out itself, and the horizon-property possessed by the messenger itself, happen to be one and the same horizon. So which way is it being approached? In which entity? In the magnification of the message? Or in the magnification of the messenger so tightly entangled with -- so tightly imposed upon -- the message? This is the one kind of messenger that is all but completely -- indivisibly and dominatingly -- merged with the message. GLB |
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