BBC NEws Story refuting HUP

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BBC NEws Story "refuting" HUP

http://www.bbc.co.uk/news/science-environment-19489385
Pioneering experiments have cast doubt on a founding idea of the branch of physics called quantum mechanics. The Heisenberg uncertainty principle is in part an embodiment of the idea that in the quantum world, the mere act of observing an event changes it. But the idea had never been put to the test, and a team writing in Physical Review Letters says "weak measurements" prove the rule was never quite right.
I did a double take when I read this, can someone please explain what it's all about?
 

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  • #2
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I took the important sentences from the full article:
The modern version of the uncertainty principle proved in our textbooks today, however, deals not with the precision of a measurement and the disturbance it introduces, but with the intrinsic uncertainty any quantum state must possess, regardless of what measurement (if any) is performed. These two readings of the uncertainty principle are typically taught side-by-side, although only the modern one is given rigorous proof. It has been shown that the original formulation is not only less general than the modern oneit is in fact mathematically incorrect...

Our work conclusively shows that, although correct for uncertainties in states, the form of Heisenberg's precision limit is incorrect if naively applied to measurement. Our work highlights an important fundamental difference between uncertainties in states and the limitations of measurement in quantum mechanics.
So, while the uncertainty coming from the disturbing influence of the measurement is smaller than Heisenberg's original formulation , the uncertainty principle itself remains valid (e.g. there is an intrinsic uncertainty any quantum system must possess).
 
  • #3
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hereafter "Uncertainity Relation"
 
  • #4
Demystifier
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It's about WEAK measurement, not ordinary measurement. Weak measurement determines only an AVERAGE value, not the actual value. For example, by weak measurement you can measure exactly average momentum at a given position, but not exact momentum at a given position. Therefore, HUP is not violated.

See also
https://www.physicsforums.com/blog.php?b=1225 [Broken]
https://www.physicsforums.com/blog.php?b=1226 [Broken]
https://www.physicsforums.com/blog.php?b=3077 [Broken]
 
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  • #5
Borek
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We already have threads on this, here and here.
 

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