Did h-bar change? What happened to h-bar?

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Discussion Overview

The discussion revolves around the representation of the uncertainty principle in different physics textbooks, specifically the use of "h/4pi" versus "h/2pi" and the implications of these variations on the understanding of quantum uncertainty.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants note a discrepancy in the representation of the uncertainty principle, with newer texts stating "greater than or equal to h/4pi" while older texts indicate "greater than or equal to hbar/2."
  • One participant mentions that both versions appear to be in use, referencing an external source that discusses the uncertainty principle.
  • Another participant clarifies that hbar is defined as h/2pi, suggesting that the confusion may stem from different definitions or interpretations.
  • Several participants emphasize that the choice of representation may depend on the context or definition used, with one stating that precise definitions lead to the hbar/2 formulation.
  • There is a humorous acknowledgment of the uncertainty principle's implications, with a quote from Griffiths suggesting a cautious approach when discussing it.
  • One participant mentions checking multiple quantum textbooks, finding a mix of representations, and concludes that the specific factor may not be critically important.

Areas of Agreement / Disagreement

Participants express differing views on the correct representation of the uncertainty principle, with no consensus reached on which formulation is preferable or more accurate.

Contextual Notes

Participants highlight that the variations in the representation may depend on definitions and contexts used in different texts, indicating a lack of a universally accepted standard.

Chi Meson
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What happened to "h-bar"?

Imagine my surprise when I'm looking through the new formula sheets for the new IB Physics curriculum, and I see the uncertainty principle as "equal to or greater than h/4pi."

Over 4pi? When did that happen? I thought I was going crazy. My textbooks all say "over 2pi," and they are publications from 1999 and 2000 (not too old). Only this new text edition (sent as a sample) that was published in 2004 shows the 4pi.

I guess this means we are twice as certain about things than we previously thought.
 
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Am I missing something? hbar=h/2pi
 
dlgoff said:
Am I missing something? hbar=h/2pi
Yeah, you're missing the first post:biggrin:

HUP has forever been stated as "greater than or equal to h-bar."

Now I find that it's "greater than or equal to h/4pi."

So what happened to h-bar, was it too uncertain?
 
I checked half a dozen of my quantum books, including Messiah written in 1958 and Griffiths written recently, and they all say hbar/2.

It's a matter of definition. Hand-wavy arguments often establish hbar, but if a precise definition of RMS deviation is used, then it's alway hbar/2. Messiah gives both.

Usually, factors of two don't matter that much; the important things are that there is a lower bound on the the product of the uncertainties, and that this lower bound is quantum in nature because it's on the order of hbar.

According to Griffiths (in his elementary particles book),"When you hear a physicist invoke the uncertainty principle, keep a hand on your wallet."
 
George Jones said:
According to Griffiths (in his elementary particles book),"When you hear a physicist invoke the uncertainty principle, keep a hand on your wallet."

heh heh.

I have just checked back to my old college texts, and they also give h/4pi.

I guess it isn't that important.
 

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