One of the most striking deviations of quantum mechanics from classical mechanics is that any measurement of a microscopic system involves the interaction with the measuring instruments. The interaction cannot be neglected and in fact leads to uncontrollable disturbance on the system. Let a measurement of an observable A yields the value a and is the eigenvalue of the operator A belonging to the eigenfunction φa. The individual measurements will deviate from the average value (〈a〉) computed over large number (N) of measurements. Denote the deviation of a from 〈a〉 as a˜. What would be the value of average deviation? We obtain 〈a˜〉 = 1 N ∑ (a− 〈a〉) = 0 . (8.1) This is because some of the values of a are below 〈a〉 while the others are above 〈a〉. Therefore, 〈a˜〉 is not useful for describing how much an individual value of an observable deviates from the expected or mean value. The mean-square deviation or variance (σ2), that is, the average of the squares of the deviations would be nonzero. The variance is given by σ2 = (∆a)2 = 1 N ∑ (a− 〈a〉)2 = 〈a2〉 − 〈a〉2 . (8.2) The square-root of mean-square deviation is called standard deviation or dispersion. This quantity could be taken as a measure of the spread in the measured values. When most of the values a are near 〈a〉 then the distribution of a peaks about 〈a〉 and in this case σ is small. If most of the values of a are found over a wide range about 〈a〉 then the distribution spreads over a wide range of a with a large value of σ. This spread, denoted as ∆A, in the measured values of A, is called the uncertainty in the measurement of A.One of the most striking deviations of quantum mechanics from classical mechanics is that any measurement of a microscopic system involves the interaction with the measuring instruments. The interaction cannot be neglected and in fact leads to uncontrollable disturbance on the system. Let a measurement of an observable A yields the value a and is the eigenvalue of the operator A belonging to the eigenfunction φa. The individual measurements will deviate from the average value (〈a〉) computed over large number (N) of measurements. Denote the deviation of a from 〈a〉 as a˜. What would be the value of average deviation? We obtain 〈a˜〉 = 1 N ∑ (a− 〈a〉) = 0 . (8.1) This is because some of the values of a are below 〈a〉 while the others are above 〈a〉. Therefore, 〈a˜〉 is not useful for describing how much an individual value of an observable deviates from the expected or mean value. The mean-square deviation or variance (σ2), that is, the average of the squares of the deviations would be nonzero. The variance is given by σ2 = (∆a)2 = 1 N ∑ (a− 〈a〉)2 = 〈a2〉 − 〈a〉2 . (8.2) The square-root of mean-square deviation is called standard deviation or dispersion. This quantity could be taken as a measure of the spread in the measured values. When most of the values a are near 〈a〉 then the distribution of a peaks about 〈a〉 and in this case σ is small. If most of the values of a are found over a wide range about 〈a〉 then the distribution spreads over a wide range of a with a large value of σ. This spread, denoted as ∆A, in the measured values of A, is called the uncertainty in the measurement of A.

CRC Press eBooksDec 11, 20141 citation

Anti Heisenberg—Refutation Of Heisenberg’s Uncertainty Relation

Ilija Barukčić, Andrei Yu. Khrennikov, Gregg S. Jaeger +2 more

The quantum mechanical uncertainty principle for position and momentum plays an important role in many treatments on the (philosophical, physical and other) implications of quantum mechanics. Roughly speaking, the more precisely the momentum (position) of a (quantum mechanical) object is given, the less precisely can one say what its position (momentum) is. This quantum mechanical measurement problem is not just an interpretational difficulty, it raises broader issues as well. The measurement (of a property) of a (quantum mechanical) object determines the existence of the measured. In brief, the quantum mechanical uncertainty principle challenges some fundamental principles of Science and especially the principle of causality. In particular, an independently existing (external) objective reality is denied. As we shall see, that the quantum mechanical uncertainty principle for position and momentum is based on the assumption that 1⩽0, which is a logical contradiction.The quantum mechanical uncertainty principle for position and momentum plays an important role in many treatments on the (philosophical, physical and other) implications of quantum mechanics. Roughly speaking, the more precisely the momentum (position) of a (quantum mechanical) object is given, the less precisely can one say what its position (momentum) is. This quantum mechanical measurement problem is not just an interpretational difficulty, it raises broader issues as well. The measurement (of a property) of a (quantum mechanical) object determines the existence of the measured. In brief, the quantum mechanical uncertainty principle challenges some fundamental principles of Science and especially the principle of causality. In particular, an independently existing (external) objective reality is denied. As we shall see, that the quantum mechanical uncertainty principle for position and momentum is based on the assumption that 1⩽0, which is a logical contradiction.

AIP conference proceedingsJan 1, 20110 citations

Anti Heisenberg—Refutation Of Heisenberg’s Uncertainty Relation

Ilija Barukčić

AIP conference proceedingsJan 1, 201115 citations

Why Heisenberg's Uncertainity Principle Is Wrong! Proposed Device: Quantum-Limited Electron Imaging Camera (QLEIC-2050)

Sardar Dilbag Singh Khalsa

The uncertainty principle is commonly regarded as a fundamental limitation ofquantum mechanics, often attributed directly to Heisenberg’s 1927 analysis.In this work, we revisit the original formulation of the principle and carefullydistinguish Heisenberg’s measurement–disturbance argument from the latermathematical uncertainty relations derived by Kennard, Robertson, andSchrödinger. We show that the standard variance-based formulation relies onthe prior introduction of fluctuation operators and ensemble averages, therebypresupposing statistical indeterminacy rather than deriving it from firstprinciples. From a physical perspective, Heisenberg’s argument is shown toreflect constraints imposed by invasive measurement techniques rather than auniversal prohibition on simultaneous knowledge of conjugate variables.Motivated by this distinction, we propose a conjecture that, in the absence ofmeasurement-induced energy transfer, the simultaneous determination ofposition and momentum may, in principle, be achievable. Our analysis suggeststhat quantum uncertainty, as traditionally formulated, encodes limitations ofcurrent observational methods rather than an intrinsic property of nature. \section{Heisenberg’s original observation and formulation (1927)} In his seminal 1927 paper \emph{Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik} \cite{Heisenberg1927}, Werner Heisenberg sought to clarify the physical meaning of quantum mechanics rather than to establish a rigorous mathematical theorem. His analysis was based on thought experiments concerning the act of measurement, most notably the $\gamma$ -ray microscope. Heisenberg argued that any attempt to localize a particle within a spatial region $\Delta x$ requires radiation of wavelength comparable to $\Delta x$ , which inevitably transfers an uncontrollable momentum $\Delta p$ to the particle. As a consequence of this measurement-induced disturbance, he proposed that the product of the inaccuracies in position and momentum measurements satisfies a relation of the order\begin{equation}\Delta x\, \Delta p \sim h .\end{equation}Here, $\Delta x$ and $\Delta p$ denote operational measurement imprecisions arising from the interaction between the measuring apparatus and the system, rather than statistical variances of quantum observables. Heisenberg did not introduce operators, Hilbert space, or probability distributions, nor did he provide a formal inequality with a precise lower bound. The argument was explicitly heuristic and qualitative, emphasizing limitations imposed by the measurement process itself. Consequently, the original uncertainty principle was formulated as a statement about measurement disturbance and experimental resolution, not as a universal mathematical constraint on quantum states. \section{Standard mathematical proof of the position--momentum uncertainty relation} \subsection{Setup and definitions} Let $\mathcal{H}$ be a Hilbert space and let $|\psi\rangle \in \mathcal{H}$ be anormalized state, $\langle \psi | \psi \rangle = 1$ . Let $A$ and $B$ beself-adjoint operators (observables) on a common dense domain containing $|\psi\rangle$ , such that all expressions below are well-defined. Define expectation values\cite{Kennard1927,Robertson1929,Schrodinger1930,Ballentine1998,Sakurai1994}\begin{equation}\langle A \rangle := \langle \psi | A | \psi \rangle,\qquad\langle B \rangle := \langle \psi | B | \psi \rangle .\end{equation}Define the fluctuation (centered) operators\begin{equation}\Delta A := A - \langle A \rangle, \qquad \Delta B := B - \langle B \rangle .\end{equation}The variances are\begin{equation}\sigma_A^2 := \langle (\Delta A)^2 \rangle = \langle \psi | (\Delta A)^2 | \psi \rangle,\qquad\sigma_B^2 := \langle (\Delta B)^2 \rangle = \langle \psi | (\Delta B)^2 | \psi \rangle.\end{equation} \subsection{Key inequality: Cauchy--Schwarz in Hilbert space} Define vectors\begin{equation}|\phi\rangle := \Delta A |\psi\rangle, \qquad |\chi\rangle := \Delta B |\psi\rangle .\end{equation}By the Cauchy--Schwarz inequality,\begin{equation}\langle \phi|\phi\rangle \, \langle \chi|\chi\rangle \ge |\langle \phi|\chi\rangle|^2 .\end{equation}Compute each factor:\begin{equation}\langle \phi|\phi\rangle= \langle \psi| (\Delta A)^\dagger (\Delta A) |\psi\rangle= \langle \psi| (\Delta A)^2 |\psi\rangle= \sigma_A^2,\end{equation}and similarly $\langle \chi|\chi\rangle = \sigma_B^2$ . Therefore\begin{equation}\sigma_A^2 \sigma_B^2 \ge \left| \langle \psi| \Delta A \Delta B |\psi\rangle \right|^2= |\langle \Delta A \Delta B \rangle|^2 .\label{eq:cs_step}\end{equation} \subsection{Robertson--Schr\"odinger decomposition} Decompose $\Delta A \Delta B$ into commutator and anticommutator parts:\begin{equation}\Delta A \Delta B=\frac{1}{2}\bigl[\Delta A,\Delta B\bigr]+\frac{1}{2}\bigl\{\Delta A,\Delta B\bigr\},\end{equation}where $[X,Y]=XY-YX$ and $\{X,Y\}=XY+YX$ . Taking expectation values gives\begin{equation}\langle \Delta A \Delta B \rangle=\frac{1}{2}\langle [\Delta A,\Delta B]\rangle+\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle .\label{eq:decomp_exp}\end{equation} Now note the following facts for self-adjoint $A,B$ :\begin{itemize}\item The operator $[\Delta A,\Delta B]$ is anti-self-adjoint, hence $\langle [\Delta A,\Delta B]\rangle$ is purely imaginary.\item The operator $\{\Delta A,\Delta B\}$ is self-adjoint, hence $\langle \{\Delta A,\Delta B\}\rangle$ is real.\end{itemize}Therefore the two terms in \eqref{eq:decomp_exp} are orthogonal in the complex plane(real vs.\ imaginary), and we may write\begin{equation}|\langle \Delta A \Delta B \rangle|^2=\left(\frac{1}{2}|\langle [\Delta A,\Delta B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2 .\label{eq:RS_identity}\end{equation} Substituting \eqref{eq:RS_identity} into \eqref{eq:cs_step} yields theSchr\"odinger uncertainty relation:\begin{equation}\boxed{\sigma_A^2 \sigma_B^2 \ge\left(\frac{1}{2}|\langle [\Delta A,\Delta B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2}.\label{eq:schrodinger}\end{equation} Since constants commute with everything,\begin{equation}[\Delta A,\Delta B] = [A-\langle A\rangle,\; B-\langle B\rangle] = [A,B].\end{equation}Hence \eqref{eq:schrodinger} can be written as\begin{equation}\boxed{\sigma_A^2 \sigma_B^2 \ge\left(\frac{1}{2}|\langle [A,B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2}.\end{equation} \subsection{Robertson inequality (weaker but widely quoted)} Dropping the nonnegative anticommutator term gives Robertson's inequality:\begin{equation}\boxed{\sigma_A \sigma_B \ge \frac{1}{2}|\langle [A,B]\rangle|}.\label{eq:robertson}\end{equation} \subsection{Specialization to position and momentum} Take $A=x$ and $B=p$ (one spatial dimension), with canonical commutation relation\begin{equation}[x,p] = i\hbar.\end{equation}Therefore,\begin{equation}|\langle [x,p]\rangle|= |\langle i\hbar \rangle|= \hbar,\end{equation}and \eqref{eq:robertson} yields the standard position--momentum uncertainty relation\begin{equation}\boxed{\sigma_x \sigma_p \ge \frac{\hbar}{2}.}\end{equation} \subsection{Condition for equality (minimum-uncertainty states)} Equality in Cauchy--Schwarz holds iff the vectors are linearly dependent:\begin{equation}\Delta A|\psi\rangle = \lambda \, \Delta B|\psi\rangle\quad \text{for some complex } \lambda.\end{equation}For $A=x$ and $B=p$ , this condition leads (in the $x$ -representation) to afirst-order differential equation whose normalized solutions are Gaussianwave packets. Hence Gaussian states saturate $\sigma_x \sigma_p = \hbar/2$ . \subsection{Definition of fluctuation operators and their role in the uncertainty relation} In the mathematical formulation of quantum uncertainty developed after Heisenberg’s original 1927 heuristic proposal, the quantities entering the uncertainty relation were redefined in statistical terms. In particular, in his 1929 paper, Robertson introduced the operators. \noindent\textbf{Critical observation.}The introduction of the fluctuation operators \begin{center}\fcolorbox{red}{white}{ $\Delta A = A - \langle A \rangle,\qquad\Delta B = B - \langle B \rangle$ }\end{center} \textbf{constitutes a nontrivial mathematicalassumption rather than a derived physical necessity. In the Robertson--Schrödinger formalism, the uncertainty of observables is defined \emph{a priori} in terms ofstatistical deviations from expectation values, thereby presupposing the verynotion of indeterminacy that the uncertainty principle is intended to justify.In other words, the operators $\Delta A$ and $\Delta B$ encode uncertainty byconstruction, since their variances measure ensemble spread relative to a mean.The subsequent derivation of a lower bound on $\sigma_A \sigma_B$ thereforeestablishes a constraint on these predefined statistical quantities, rather than demonstrating that physical observables must be uncertain from first principles.Consequently, the uncertainty relation obtained in this manner is logicallyconditional upon the initial choice of variance-based definitions and does not,by itself, prove the existence of intrinsic measurement indeterminacy or disturbance in individual quantum events.} \textit{They actully assumed and defined the spread and uncertainity initial in both the quantities and proved the uncertainity principle.} where $A$ and $B$ are self-adjoint operators representing observables and $\langle A \rangle = \langle \psi | A | \psi \rangle$ denotes the expectationvalue in a normalized quantum state $|\psi\rangle$ \cite{Robertson1929}.These operators describe deviations of observables from their mean valuesand are introduced in direct analogy with classical statistical fluctuations.The corresponding variances, $\sigma_A^2 = \langle (\Delta A)^2 \rangle$ and $\sigma_B^2 = \langle (\Delta B)^2 \rangle$ ,measure the statistical spread of measurement outcomes over an ensembleof identically prepared systemsThe uncertainty principle is commonly regarded as a fundamental limitation ofquantum mechanics, often attributed directly to Heisenberg’s 1927 analysis.In this work, we revisit the original formulation of the principle and carefullydistinguish Heisenberg’s measurement–disturbance argument from the latermathematical uncertainty relations derived by Kennard, Robertson, andSchrödinger. We show that the standard variance-based formulation relies onthe prior introduction of fluctuation operators and ensemble averages, therebypresupposing statistical indeterminacy rather than deriving it from firstprinciples. From a physical perspective, Heisenberg’s argument is shown toreflect constraints imposed by invasive measurement techniques rather than auniversal prohibition on simultaneous knowledge of conjugate variables.Motivated by this distinction, we propose a conjecture that, in the absence ofmeasurement-induced energy transfer, the simultaneous determination ofposition and momentum may, in principle, be achievable. Our analysis suggeststhat quantum uncertainty, as traditionally formulated, encodes limitations ofcurrent observational methods rather than an intrinsic property of nature. \section{Heisenberg’s original observation and formulation (1927)} In his seminal 1927 paper \emph{Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik} \cite{Heisenberg1927}, Werner Heisenberg sought to clarify the physical meaning of quantum mechanics rather than to establish a rigorous mathematical theorem. His analysis was based on thought experiments concerning the act of measurement, most notably the $\gamma$-ray microscope. Heisenberg argued that any attempt to localize a particle within a spatial region $\Delta x$ requires radiation of wavelength comparable to $\Delta x$, which inevitably transfers an uncontrollable momentum $\Delta p$ to the particle. As a consequence of this measurement-induced disturbance, he proposed that the product of the inaccuracies in position and momentum measurements satisfies a relation of the order\begin{equation}\Delta x\, \Delta p \sim h .\end{equation}Here, $\Delta x$ and $\Delta p$ denote operational measurement imprecisions arising from the interaction between the measuring apparatus and the system, rather than statistical variances of quantum observables. Heisenberg did not introduce operators, Hilbert space, or probability distributions, nor did he provide a formal inequality with a precise lower bound. The argument was explicitly heuristic and qualitative, emphasizing limitations imposed by the measurement process itself. Consequently, the original uncertainty principle was formulated as a statement about measurement disturbance and experimental resolution, not as a universal mathematical constraint on quantum states. \section{Standard mathematical proof of the position--momentum uncertainty relation} \subsection{Setup and definitions} Let $\mathcal{H}$ be a Hilbert space and let $|\psi\rangle \in \mathcal{H}$ be anormalized state, $\langle \psi | \psi \rangle = 1$. Let $A$ and $B$ beself-adjoint operators (observables) on a common dense domain containing$|\psi\rangle$, such that all expressions below are well-defined. Define expectation values\cite{Kennard1927,Robertson1929,Schrodinger1930,Ballentine1998,Sakurai1994}\begin{equation}\langle A \rangle := \langle \psi | A | \psi \rangle,\qquad\langle B \rangle := \langle \psi | B | \psi \rangle .\end{equation}Define the fluctuation (centered) operators\begin{equation}\Delta A := A - \langle A \rangle, \qquad \Delta B := B - \langle B \rangle .\end{equation}The variances are\begin{equation}\sigma_A^2 := \langle (\Delta A)^2 \rangle = \langle \psi | (\Delta A)^2 | \psi \rangle,\qquad\sigma_B^2 := \langle (\Delta B)^2 \rangle = \langle \psi | (\Delta B)^2 | \psi \rangle.\end{equation} \subsection{Key inequality: Cauchy--Schwarz in Hilbert space} Define vectors\begin{equation}|\phi\rangle := \Delta A |\psi\rangle, \qquad |\chi\rangle := \Delta B |\psi\rangle .\end{equation}By the Cauchy--Schwarz inequality,\begin{equation}\langle \phi|\phi\rangle \, \langle \chi|\chi\rangle \ge |\langle \phi|\chi\rangle|^2 .\end{equation}Compute each factor:\begin{equation}\langle \phi|\phi\rangle= \langle \psi| (\Delta A)^\dagger (\Delta A) |\psi\rangle= \langle \psi| (\Delta A)^2 |\psi\rangle= \sigma_A^2,\end{equation}and similarly $\langle \chi|\chi\rangle = \sigma_B^2$. Therefore\begin{equation}\sigma_A^2 \sigma_B^2 \ge \left| \langle \psi| \Delta A \Delta B |\psi\rangle \right|^2= |\langle \Delta A \Delta B \rangle|^2 .\label{eq:cs_step}\end{equation} \subsection{Robertson--Schr\"odinger decomposition} Decompose $\Delta A \Delta B$ into commutator and anticommutator parts:\begin{equation}\Delta A \Delta B=\frac{1}{2}\bigl[\Delta A,\Delta B\bigr]+\frac{1}{2}\bigl\{\Delta A,\Delta B\bigr\},\end{equation}where $[X,Y]=XY-YX$ and $\{X,Y\}=XY+YX$. Taking expectation values gives\begin{equation}\langle \Delta A \Delta B \rangle=\frac{1}{2}\langle [\Delta A,\Delta B]\rangle+\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle .\label{eq:decomp_exp}\end{equation} Now note the following facts for self-adjoint $A,B$:\begin{itemize}\item The operator $[\Delta A,\Delta B]$ is anti-self-adjoint, hence$\langle [\Delta A,\Delta B]\rangle$ is purely imaginary.\item The operator $\{\Delta A,\Delta B\}$ is self-adjoint, hence$\langle \{\Delta A,\Delta B\}\rangle$ is real.\end{itemize}Therefore the two terms in \eqref{eq:decomp_exp} are orthogonal in the complex plane(real vs.\ imaginary), and we may write\begin{equation}|\langle \Delta A \Delta B \rangle|^2=\left(\frac{1}{2}|\langle [\Delta A,\Delta B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2 .\label{eq:RS_identity}\end{equation} Substituting \eqref{eq:RS_identity} into \eqref{eq:cs_step} yields theSchr\"odinger uncertainty relation:\begin{equation}\boxed{\sigma_A^2 \sigma_B^2 \ge\left(\frac{1}{2}|\langle [\Delta A,\Delta B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2}.\label{eq:schrodinger}\end{equation} Since constants commute with everything,\begin{equation}[\Delta A,\Delta B] = [A-\langle A\rangle,\; B-\langle B\rangle] = [A,B].\end{equation}Hence \eqref{eq:schrodinger} can be written as\begin{equation}\boxed{\sigma_A^2 \sigma_B^2 \ge\left(\frac{1}{2}|\langle [A,B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2}.\end{equation} \subsection{Robertson inequality (weaker but widely quoted)} Dropping the nonnegative anticommutator term gives Robertson's inequality:\begin{equation}\boxed{\sigma_A \sigma_B \ge \frac{1}{2}|\langle [A,B]\rangle|}.\label{eq:robertson}\end{equation} \subsection{Specialization to position and momentum} Take $A=x$ and $B=p$ (one spatial dimension), with canonical commutation relation\begin{equation}[x,p] = i\hbar.\end{equation}Therefore,\begin{equation}|\langle [x,p]\rangle|= |\langle i\hbar \rangle|= \hbar,\end{equation}and \eqref{eq:robertson} yields the standard position--momentum uncertainty relation\begin{equation}\boxed{\sigma_x \sigma_p \ge \frac{\hbar}{2}.}\end{equation} \subsection{Condition for equality (minimum-uncertainty states)} Equality in Cauchy--Schwarz holds iff the vectors are linearly dependent:\begin{equation}\Delta A|\psi\rangle = \lambda \, \Delta B|\psi\rangle\quad \text{for some complex } \lambda.\end{equation}For $A=x$ and $B=p$, this condition leads (in the $x$-representation) to afirst-order differential equation whose normalized solutions are Gaussianwave packets. Hence Gaussian states saturate $\sigma_x \sigma_p = \hbar/2$. \subsection{Definition of fluctuation operators and their role in the uncertainty relation} In the mathematical formulation of quantum uncertainty developed after Heisenberg’s original 1927 heuristic proposal, the quantities entering the uncertainty relation were redefined in statistical terms. In particular, in his 1929 paper, Robertson introduced the operators. \noindent\textbf{Critical observation.}The introduction of the fluctuation operators \begin{center}\fcolorbox{red}{white}{$\Delta A = A - \langle A \rangle,\qquad\Delta B = B - \langle B \rangle$}\end{center} \textbf{constitutes a nontrivial mathematicalassumption rather than a derived physical necessity. In the Robertson--Schrödinger formalism, the uncertainty of observables is defined \emph{a priori} in terms ofstatistical deviations from expectation values, thereby presupposing the verynotion of indeterminacy that the uncertainty principle is intended to justify.In other words, the operators $\Delta A$ and $\Delta B$ encode uncertainty byconstruction, since their variances measure ensemble spread relative to a mean.The subsequent derivation of a lower bound on $\sigma_A \sigma_B$ thereforeestablishes a constraint on these predefined statistical quantities, rather than demonstrating that physical observables must be uncertain from first principles.Consequently, the uncertainty relation obtained in this manner is logicallyconditional upon the initial choice of variance-based definitions and does not,by itself, prove the existence of intrinsic measurement indeterminacy or disturbance in individual quantum events.} \textit{They actully assumed and defined the spread and uncertainity initial in both the quantities and proved the uncertainity principle.} where $A$ and $B$ are self-adjoint operators representing observables and$\langle A \rangle = \langle \psi | A | \psi \rangle$ denotes the expectationvalue in a normalized quantum state $|\psi\rangle$ \cite{Robertson1929}.These operators describe deviations of observables from their mean valuesand are introduced in direct analogy with classical statistical fluctuations.The corresponding variances,$\sigma_A^2 = \langle (\Delta A)^2 \rangle$ and$\sigma_B^2 = \langle (\Delta B)^2 \rangle$,measure the statistical spread of measurement outcomes over an ensembleof identically prepared systems

Feb 10, 20260 citations

An uncertain world!

Muhammad Suhail Zubairy

Abstract One of the foundational principles of quantum mechanics is Heisenberg’s uncertainty relation. According to this relation, no one can measure both the position of a particle and how fast it is moving simultaneously no matter how precise the measuring instruments. Heisenberg’s uncertainty relation and the associated Bohr’s principle of complementarity are explained using simple examples. The idea that measurement disturbs the system is a source of the uncertainty. The philosophical question whether the uncertainty represents only our inability to measure the properties precisely or it has much deeper consequences related to the question of reality is also discussed.Abstract One of the foundational principles of quantum mechanics is Heisenberg’s uncertainty relation. According to this relation, no one can measure both the position of a particle and how fast it is moving simultaneously no matter how precise the measuring instruments. Heisenberg’s uncertainty relation and the associated Bohr’s principle of complementarity are explained using simple examples. The idea that measurement disturbs the system is a source of the uncertainty. The philosophical question whether the uncertainty represents only our inability to measure the properties precisely or it has much deeper consequences related to the question of reality is also discussed.

Sep 14, 20230 citations

Heisenberg, Bohr, Robertson, and the Uncertainty Principle

Jim Baggott

From the outset, Heisenberg had resolved to eliminate classical space-time pictures involving particles and waves from the quantum mechanics of the atom. He had wanted to focus instead on the properties actually observed and recorded in laboratory experiments, such as the positions and intensities of spectral lines. Alone in Copenhagen in February 1927, he now pondered on the significance and meaning of such experimental observables. Feeling the need to introduce at least some form of ‘visualizability’, he asked himself some fundamental questions, such as: What do we actually mean when we talk about the position of an electron? He went on to discover the uncertainty principle: the product of the ‘uncertainties’ in certain pairs of variables—called complementary variables—such as position and momentum cannot be smaller than Planck’s constant h (now h / 4π‎).From the outset, Heisenberg had resolved to eliminate classical space-time pictures involving particles and waves from the quantum mechanics of the atom. He had wanted to focus instead on the properties actually observed and recorded in laboratory experiments, such as the positions and intensities of spectral lines. Alone in Copenhagen in February 1927, he now pondered on the significance and meaning of such experimental observables. Feeling the need to introduce at least some form of ‘visualizability’, he asked himself some fundamental questions, such as: What do we actually mean when we talk about the position of an electron? He went on to discover the uncertainty principle: the product of the ‘uncertainties’ in certain pairs of variables—called complementary variables—such as position and momentum cannot be smaller than Planck’s constant h (now h / 4π‎).

Oxford University Press eBooksJan 10, 20201 citation

\gamma

-ray microscope. Heisenberg argued that any attempt to localize a particle within a spatial region

\Delta x

requires radiation of wavelength comparable to

\Delta x

, which inevitably transfers an uncontrollable momentum

\Delta p

to the particle. As a consequence of this measurement-induced disturbance, he proposed that the product of the inaccuracies in position and momentum measurements satisfies a relation of the order\begin{equation}\Delta x\, \Delta p \sim h .\end{equation}Here,

\Delta x

and

\Delta p

denote operational measurement imprecisions arising from the interaction between the measuring apparatus and the system, rather than statistical variances of quantum observables. Heisenberg did not introduce operators, Hilbert space, or probability distributions, nor did he provide a formal inequality with a precise lower bound. The argument was explicitly heuristic and qualitative, emphasizing limitations imposed by the measurement process itself. Consequently, the original uncertainty principle was formulated as a statement about measurement disturbance and experimental resolution, not as a universal mathematical constraint on quantum states. \section{Standard mathematical proof of the position--momentum uncertainty relation} \subsection{Setup and definitions} Let

\mathcal{H}

be a Hilbert space and let

|\psi\rangle \in \mathcal{H}

be anormalized state,

\langle \psi | \psi \rangle = 1

. Let

A

and

B

beself-adjoint operators (observables) on a common dense domain containing

|\psi\rangle

, such that all expressions below are well-defined. Define expectation values\cite{Kennard1927,Robertson1929,Schrodinger1930,Ballentine1998,Sakurai1994}\begin{equation}\langle A \rangle := \langle \psi | A | \psi \rangle,\qquad\langle B \rangle := \langle \psi | B | \psi \rangle .\end{equation}Define the fluctuation (centered) operators\begin{equation}\Delta A := A - \langle A \rangle, \qquad \Delta B := B - \langle B \rangle .\end{equation}The variances are\begin{equation}\sigma_A^2 := \langle (\Delta A)^2 \rangle = \langle \psi | (\Delta A)^2 | \psi \rangle,\qquad\sigma_B^2 := \langle (\Delta B)^2 \rangle = \langle \psi | (\Delta B)^2 | \psi \rangle.\end{equation} \subsection{Key inequality: Cauchy--Schwarz in Hilbert space} Define vectors\begin{equation}|\phi\rangle := \Delta A |\psi\rangle, \qquad |\chi\rangle := \Delta B |\psi\rangle .\end{equation}By the Cauchy--Schwarz inequality,\begin{equation}\langle \phi|\phi\rangle \, \langle \chi|\chi\rangle \ge |\langle \phi|\chi\rangle|^2 .\end{equation}Compute each factor:\begin{equation}\langle \phi|\phi\rangle= \langle \psi| (\Delta A)^\dagger (\Delta A) |\psi\rangle= \langle \psi| (\Delta A)^2 |\psi\rangle= \sigma_A^2,\end{equation}and similarly

\langle \chi|\chi\rangle = \sigma_B^2

. Therefore\begin{equation}\sigma_A^2 \sigma_B^2 \ge \left| \langle \psi| \Delta A \Delta B |\psi\rangle \right|^2= |\langle \Delta A \Delta B \rangle|^2 .\label{eq:cs_step}\end{equation} \subsection{Robertson--Schr\"odinger decomposition} Decompose

\Delta A \Delta B

into commutator and anticommutator parts:\begin{equation}\Delta A \Delta B=\frac{1}{2}\bigl[\Delta A,\Delta B\bigr]+\frac{1}{2}\bigl\{\Delta A,\Delta B\bigr\},\end{equation}where

[X,Y]=XY-YX

and

\{X,Y\}=XY+YX

. Taking expectation values gives\begin{equation}\langle \Delta A \Delta B \rangle=\frac{1}{2}\langle [\Delta A,\Delta B]\rangle+\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle .\label{eq:decomp_exp}\end{equation} Now note the following facts for self-adjoint

A,B

:\begin{itemize}\item The operator

[\Delta A,\Delta B]

is anti-self-adjoint, hence

\langle [\Delta A,\Delta B]\rangle

is purely imaginary.\item The operator

\{\Delta A,\Delta B\}

is self-adjoint, hence

\langle \{\Delta A,\Delta B\}\rangle

is real.\end{itemize}Therefore the two terms in \eqref{eq:decomp_exp} are orthogonal in the complex plane(real vs.\ imaginary), and we may write\begin{equation}|\langle \Delta A \Delta B \rangle|^2=\left(\frac{1}{2}|\langle [\Delta A,\Delta B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2 .\label{eq:RS_identity}\end{equation} Substituting \eqref{eq:RS_identity} into \eqref{eq:cs_step} yields theSchr\"odinger uncertainty relation:\begin{equation}\boxed{\sigma_A^2 \sigma_B^2 \ge\left(\frac{1}{2}|\langle [\Delta A,\Delta B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2}.\label{eq:schrodinger}\end{equation} Since constants commute with everything,\begin{equation}[\Delta A,\Delta B] = [A-\langle A\rangle,\; B-\langle B\rangle] = [A,B].\end{equation}Hence \eqref{eq:schrodinger} can be written as\begin{equation}\boxed{\sigma_A^2 \sigma_B^2 \ge\left(\frac{1}{2}|\langle [A,B]\rangle|\right)^2+\left(\frac{1}{2}\langle \{\Delta A,\Delta B\}\rangle\right)^2}.\end{equation} \subsection{Robertson inequality (weaker but widely quoted)} Dropping the nonnegative anticommutator term gives Robertson's inequality:\begin{equation}\boxed{\sigma_A \sigma_B \ge \frac{1}{2}|\langle [A,B]\rangle|}.\label{eq:robertson}\end{equation} \subsection{Specialization to position and momentum} Take

A=x

and

B=p

(one spatial dimension), with canonical commutation relation\begin{equation}[x,p] = i\hbar.\end{equation}Therefore,\begin{equation}|\langle [x,p]\rangle|= |\langle i\hbar \rangle|= \hbar,\end{equation}and \eqref{eq:robertson} yields the standard position--momentum uncertainty relation\begin{equation}\boxed{\sigma_x \sigma_p \ge \frac{\hbar}{2}.}\end{equation} \subsection{Condition for equality (minimum-uncertainty states)} Equality in Cauchy--Schwarz holds iff the vectors are linearly dependent:\begin{equation}\Delta A|\psi\rangle = \lambda \, \Delta B|\psi\rangle\quad \text{for some complex } \lambda.\end{equation}For

A=x

and

B=p

, this condition leads (in the

x

-representation) to afirst-order differential equation whose normalized solutions are Gaussianwave packets. Hence Gaussian states saturate

\sigma_x \sigma_p = \hbar/2

. \subsection{Definition of fluctuation operators and their role in the uncertainty relation} In the mathematical formulation of quantum uncertainty developed after Heisenberg’s original 1927 heuristic proposal, the quantities entering the uncertainty relation were redefined in statistical terms. In particular, in his 1929 paper, Robertson introduced the operators. \noindent\textbf{Critical observation.}The introduction of the fluctuation operators \begin{center}\fcolorbox{red}{white}{

\Delta A = A - \langle A \rangle,\qquad\Delta B = B - \langle B \rangle

}\end{center} \textbf{constitutes a nontrivial mathematicalassumption rather than a derived physical necessity. In the Robertson--Schrödinger formalism, the uncertainty of observables is defined \emph{a priori} in terms ofstatistical deviations from expectation values, thereby presupposing the verynotion of indeterminacy that the uncertainty principle is intended to justify.In other words, the operators

\Delta A

and

\Delta B

encode uncertainty byconstruction, since their variances measure ensemble spread relative to a mean.The subsequent derivation of a lower bound on

\sigma_A \sigma_B

thereforeestablishes a constraint on these predefined statistical quantities, rather than demonstrating that physical observables must be uncertain from first principles.Consequently, the uncertainty relation obtained in this manner is logicallyconditional upon the initial choice of variance-based definitions and does not,by itself, prove the existence of intrinsic measurement indeterminacy or disturbance in individual quantum events.} \textit{They actully assumed and defined the spread and uncertainity initial in both the quantities and proved the uncertainity principle.} where

A

and

B

are self-adjoint operators representing observables and

\langle A \rangle = \langle \psi | A | \psi \rangle

denotes the expectationvalue in a normalized quantum state

|\psi\rangle

\cite{Robertson1929}.These operators describe deviations of observables from their mean valuesand are introduced in direct analogy with classical statistical fluctuations.The corresponding variances,

\sigma_A^2 = \langle (\Delta A)^2 \rangle

and

\sigma_B^2 = \langle (\Delta B)^2 \rangle

,measure the statistical spread of measurement outcomes over an ensembleof identically prepared systems