Quantum

Entangled Photon Polarization Qubits

Why Entangled Photon-Polarization Qubits Violate Bell’s Inequality per Quantum Information Theory

/
0 Comments
In her YouTube video Bell's Theorem Experiments on Entangled Photons, Dr. Fugate shows how polarization-entangled photons violate Bell's inequality. In…
quantum entanglement

Quantum Entanglement is a Kinematic Fact, not a Dynamical Effect

/
0 Comments
Towards the end of the first lecture for the Qiskit Global Summer School 2025, Foundations of Quantum Mechanics, Olivia Lanes (Global Lead, Content and…
physics of reality

Quantum Reconstruction & Bell Correlations Explained

/
3 Comments
Comment on PBS Space Time video PBS Space Time produces some very good videos on the foundations of quantum mechanics (QM), so let me comment on their…
Schrodinger's cat

Schrödinger’s Cat and the Qbit

/
27 Comments
The concept of quantum superposition (or superposition for short) is very counterintuitive, as Schr##\ddot{\text{o}}##dinger noted in 1935 writing [1],…
quantum information

How Quantum Information Theory Solves “the only mystery” of Quantum Mechanics

/
0 Comments
In Chapter 37 of "The Feynman Lectures on Physics Volume 1," Richard Feynman famously wrote that the mystery of wave-particle duality in the double-slit…
quantum computers 101

Quantum Computing Explained: Qubits, Algorithms & Applications

/
5 Comments
Overview This article provides an accessible introduction to quantum computing, a cutting-edge technology that processes certain types of information…
mermin device quantum entanglement

Superdeterminism and the Mermin Device

/
140 Comments
Superdeterminism as a way to resolve the mystery of quantum entanglement is generally not taken seriously in the foundations community, as explained in…
quantum mechanics new approach

Quantum Physics via Quantum Tomography: A New Approach to Quantum Mechanics

/
176 Comments
This Insight article presents the main features of a conceptual foundation of quantum physics with the same characteristic features as classical physics…
quantum information

How Quantum Information Theorists Revealed the Relativity Principle at the Foundation of Quantum Mechanics

/
12 Comments
This Insight is a condensed version of No Preferred Reference Frame at the Foundation of Quantum Mechanics. Reference numbers here correspond to that paper.…
quantum double slit experiment

Quantum Mechanics and the Famous Double-slit Experiment

/
0 Comments
Double-slit Key PointsQuantum mechanics is known for its strangeness, including phenomena like wave–particle duality, which allows particles to…
Compton Scattering

Exploring the Anatomy of Compton Scattering

/
1 Comment
Introduction In this article, we take as our starting point the original equations which Compton drew up and solved in his ground-breaking 1925 article:  From…
Compton Scattering

Massive Meets Massless: Compton Scattering Revisited

/
0 Comments
Introduction In a previous article entitled "Alternate Approach to 2D Collisions" we analyzed collisions between a moving and stationary object by defining…
hydrogen

Intro to the Ionization Energy of Atomic Hydrogen

/
2 Comments
Introduction In previous articles relating to various transition energies in Hydrogen, Helium, and Deuterium we have employed the following formula for…
quantum entanglement

Answering Mermin’s Challenge with the Relativity Principle

/
89 Comments
Note: This Insight was previously titled, "Answering Mermin's Challenge with Wilczek's Challenge." While that version of this Insight did not involve any…
Conservation of Spin Angular Momentum

Exploring Bell States and Conservation of Spin Angular Momentum

/
0 Comments
In a recent thread, I outlined how to compute the correlation function for the Bell basis states\begin{equation}\begin{split}|\psi_-\rangle &=…
Deuterium Lyman Alpha Line

Revisiting The Deuterium Lyman Alpha Line Experiment

/
0 Comments
Introduction In this article, we will be revisiting a somewhat understudied (and seemingly unrepeated) experiment to measure the Deuterium Lyman Alpha…
Bohr’s Helium Lines

Understanding Bohr’s Helium Lines

/
0 Comments
Introduction In a previous article "Calculating the Balmer Alpha Line" we mentioned how accurate predictions of the spectral lines of singly ionized Helium…
Balmer Alpha Line

Calculating the Balmer Alpha Line: Atomic Hydrogen

/
0 Comments
Introduction Most readers acquainted with the hydrogen spectrum will be familiar with the set of lines in the visible spectrum representing transitions…
quantum superposition

Understanding Superposition Physically and Mathematically

/
3 Comments
What is superposition Superposition is a fundamental concept in physics and mathematics, particularly in the fields of wave theory and quantum mechanics.…
Quantum Mechanical Commutator

The Classical Limit of Quantum Mechanical Commutator

/
8 Comments
The Classical Limit of Commutator (without fancy mathematics) Quantum mechanics occupies a very unusual place among physical theories: It contains classical…
rules of quantum mechanics

The 7 Basic Rules of Quantum Mechanics

/
45 Comments
For reference purposes and to help focus discussions on Physics Forums in interpretation questions on the real issues, there is a need for fixing the common…
Quantum Particles

Clarifying Common Issues with Indistinguishable Particles

/
15 Comments
Introduction Commonly there is a lot of imprecision in talking about ''indistinguishable'' (or ''identical'') particles, even in serious work. This Insight…
quantum qubit

A Classical View of the Qubit

/
2 Comments
This Insight article is part of my paper Foundations of quantum physics III. Measurement, featuring the thermal interpretation of quantum physics. See…
quantum mechanics is incomplete

9 Reasons Quantum Mechanics is Incomplete

/
45 Comments
Incomplete interpretations of quantum mechanics I argue that all interpretations of quantum mechanics (QM) are incomplete, each for its own reason. I…
Quantum Eraser

The Quantum Mystery of Wigner’s Friend

/
30 Comments
In this Insight I will introduce the quantum mystery called ``Wigner's friend'' using Healey's version [1] of Frauchiger and Renner's (FR's) version [2]…
Super Quantum

The Unreasonable Effectiveness of the Popescu-Rohrlich Correlations

/
3 Comments
In this Insight, I will show how the Popescu-Rohrlich (superquantum) correlations provide an unreasonable advantage in a particular "quantum guessing game''…
why quantum

Why the Quantum | A Response to Wheeler’s 1986 Paper

/
397 Comments
Wheeler's opening statement in his 1986 paper, ``How Come the Quantum?'' holds as true today as it did then [1] The necessity of the quantum in the construction…
qft_renormalization

Learn Renormalization in Mathematical Quantum Field Theory

/
9 Comments
This is one chapter in a series on Mathematical Quantum Field TheoryThe previous chapter is: 15. Interacting quantum fields. 16. Renormalization In…

Learn Interacting Quantum Fields in Mathematical Quantum Field Theory

/
9 Comments
This is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 14. Free quantum fields.The next chapter is 16. Renormalization. 15.…
qft_freequantum

Learn Free Quantum Fields in Mathematical Quantum Field Theory

/
1 Comment
This is one chapter in a series on Mathematical Quantum Field TheoryThe previous chapter is 13. Quantization.The next chapter is 15. Interacting…
qm_interpretations

The Fundamental Difference in Interpretations of Quantum Mechanics

/
191 Comments
A topic that continually comes up in discussions of quantum mechanics is the existence of many different interpretations. Not only are there different…
qtf_quantization

Learn Quantization in Mathematical Quantum Field Theory

/
14 Comments
The following is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 12. Gauge fixing.The next chapter is 14.…
qft_gauge

Learn Gauge Fixing in Mathematical Quantum Field Theory

/
1 Comment
The following is one chapter in a series of Mathematical Quantum Field Theory.The previous chapter is 11. Reduced phase space.The next chapter…
qtf_phased_space

Learn Reduced Phase Space in Mathematical Quantum Field Theory

/
4 Comments
The following is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 10. Gauge symmetries.The next chapter is…
qtf_guagesym

Learn Gauge Symmetries in Mathematical Quantum Field Theory

/
18 Comments
This is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 9. Propagators.The next chapter is 11. Reduced phase…
qft_prapagators

Learn Propagators in Mathematical Quantum Field Theory

/
8 Comments
This is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 8. Phase space.The next chapter is 10. Gauge symmetries. 9.…
qtf_phasespace

Learn Phase Space in Mathematical Quantum Field Theory

/
7 Comments
The following is one chapter of a series on Mathematical Quantum Field Theory.The previous chapter is 7. Observables.The next chapter is 9. Propagators. 8.…
qtf_observables

Learn Observables in Mathematical Quantum Field Theory

/
8 Comments
The following is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 6. Symmetries.The next chapter is 8. Phase…
qtf_symmerities

Learn Symmetries in Mathematical Quantum Field Theory

/
4 Comments
The following is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 5. Lagrangians.The next chapter is 7. Observables.  6.…
qft_lang

Learn Lagrangians in Mathematical Quantum Field Theory

/
42 Comments
This is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 4. Field Variations.The next chapter is 6. Symmetries.  5.…
qtf_field_variations2

Learn Field Variations in Mathematical Quantum Field Theory

/
6 Comments
This is chapter 4 of a series on Mathematical Quantum Field Theory.The previous chapter is 3. Fields.The next chapter is 5. Lagrangians.  4.…
qtf_fields

Learn the Fields of Mathematical Quantum Field Theory

/
82 Comments
The following is one chapter in a series on Mathematical Quantum Field TheoryThe previous chapter is 2. Spacetime.The next chapter is 4. Field…
qft_spacetime

Learn Spacetime in Mathematical Quantum Field Theory

/
9 Comments
The following is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 1. Geometry.The next chapter is 3. Fields  2.…
quantumfieldtheory

A First Idea of Quantum Field Theory – 20 Part Series

/
8 Comments
These notes mean to give an expository but rigorous introduction to the basic concepts of relativistic perturbative quantum field theories, specifically…
perturbation

Introduction to Perturbative Quantum Field Theory

/
110 Comments
This is the beginning of a series that gives an introduction to perturbative quantum field theory (pQFT) on Lorentzian spacetime backgrounds in its…
quantumpeace

How I Stopped Worrying and Learned to Love Orthodox Quantum Mechanics

/
289 Comments
Why I'm a Bohmian and Questioning Orthodox QM Many people here know that I am a "Bohmian", i.e. an adherent of a very non-orthodox interpretation of quantum…
entanglement_entropy2

Lesson on Entanglement Entropy in Quantum Field Theory

/
3 Comments
Part 1: Quantum Mechanics[This article expects the reader to have some experience with quantum field theory and path integrals][I should also…
entanglement_entropy

Learn Entanglement Entropy in Quantum Mechanics

/
22 Comments
Quantum Mechanics(QM) is one of the greatest intellectual achievements in human history. Not only because it describes the world at the microscopic level…
quantumflux

Learn About Vacuum Fluctuations in Experimental Practice

/
41 Comments
Introduction and context This Insight Article is a sequel of the Insight Articles ”The Physics of Virtual Particles”, “Misconceptions about Virtual…
quantumapplitudes

Learn About Quantum Amplitudes, Probabilities and EPR

/
83 Comments
This is a little note about quantum amplitudes. Even though quantum probabilities seem very mysterious, with weird interference effects and seemingly nonlocal…
vaccummyth

Explore The Vacuum Fluctuation Myth in Quantum Theory

/
230 Comments
This Insight Article is a sequel of the Insight Articles ”The Physics of Virtual Particles” and “Misconceptions about Virtual Particles“ which…
anyon

Learn The Main Conceptual Ideas of Anyon Particles

/
55 Comments
Every quantum physicist knows that all particles are either bosons or fermions. And the standard textbook argues that this so does not depend on the number…
quantumentanglement

How the EPR Paradox Fits Between Entanglement and Nonlocality

/
11 Comments
If we violate a Bell inequality, we know we have quantum entanglement, and it used to be thought that these two notions were one and the same.At least,…
qminterpret

QM Interpretations: Semantics, Meaning & Probability

/
12 Comments
Introduction Many times, we encounter ourselves tangled in some Quantum Mechanics (QM) interpretations debates. Unfortunately, the standard of discussion…
spacetime6

Struggles with the Continuum – Freeman Dyson and QED

/
24 Comments
 Last time I sketched how physicists use quantum electrodynamics, or 'QED', to compute answers to physics problems as power series in the…
spacetime5

Struggles with the Continuum: Quantum Electrodynamics

/
10 Comments
  Quantum field theory is the best method we have for describing particles and forces in a way that takes both quantum mechanics…
spacetime4

Struggles with the Continuum – Relativity and Quantum

/
5 Comments
 In this series, we're looking at mathematical problems that arise in physics due to treating spacetime as a continuum---basically, problems…
electronatom

Why Electrons Don’t Crash Into the Nucleus — Quantum View

/
12 Comments
Atoms and Coulomb forces If atoms were described only by Coulomb attraction, the electron and nucleus would attract each other and, according to classical…
prequantum4

Examples of Prequantum Field Theories IV: Wess-Zumino-Witten-type Theories

/
4 Comments
  At the end of this page, we will have come full circle back to the first article in the series 20 years ago -- The M-Theory Conjecture.We…
prequantum3

Examples of Prequantum Field Theories III: Chern-Simons-type Theories

/
1 Comment
  After having constructed gauge fields and higher gauge fields in the previous article by systems of ##L_\infty##-algebroid-valued…
uncertaintyenergy

Does Heisenberg Uncertainty Violate Energy Conservation?

/
2 Comments
The short answer is: No — there is no violation. The longer answer Given the probabilistic aspect of quantum theory, what do we mean now by "conservation…
guagetheory

Examples of Prequantum Field Theories II: Higher Gauge Fields

/
1 Comment
   After having recalled ordinary gauge fields from a dg-algebraic perspective in the previous article, here I discuss…
prequantumft

Examples of Prequantum Field Theories I: Gauge Fields

/
1 Comment
  After having motivated the need for prequantum field theory and having laid out its principles (i. extremal action, ii. global…
planck

What Planck Length Is and It’s Common Misconceptions

/
30 Comments
The Planck length is an extremely small distance constructed from physical constants. Many misconceptions overstate its physical significance, claiming…
spacetime2

Struggles With The Continuum: Quantum Mechanics of Charged Particles

/
39 Comments
 Last time we saw that nobody yet knows if Newtonian gravity, applied to point particles, truly succeeds in predicting the future. To be precise:…
photoelectric

“Violating” Einstein’s Photoelectric Effect Model

/
4 Comments
Einstein's Photoelectric Insight One of the most spectacular theoretical descriptions that Einstein had ever produced is the corpuscular nature of light…
hupmisconceptions1

Learn a Misconception of the Heisenberg Uncertainty Principle

/
26 Comments
One of the common misconceptions about the Heisenberg Uncertainty Principle (HUP) is that it is the fault of our measurement accuracy.A description…
quantum_tunneling

Why You Can’t Quantum Tunnel Through a Wall

/
64 Comments
Can You Quantum Tunnel Through a Wall? Short answer The short and sweet answer if a tennis ball, a bowling ball, or any other kind of ordinary macroscopic…
measuringentanglement

Can You Measure Quantum Entanglement?

/
23 Comments
What is Quantum Entanglement? Though any pair of particles, given their history, might happen to be entangled, some pairs are more entangled than others. …
qftintegrals

Some Useful Integrals In Quantum Field Theory

/
2 Comments
In my paper on renormalisation I mentioned what most who have studied calculations in Quantum Field Theory find, it's rather complicated and mind-numbing.…
arrowoftime

Retrocausality: How Fundamental is the Arrow of Time?

/
26 Comments
In this Insight, I'll discuss a recent experiment ([1]  [2] [3]) by some Australian physicists that has brought a thought experiment into the real world…
perbation theory

Introduction to Causal Perturbation Theory

/
30 Comments
Relativistic quantum field theory is notorious for the occurrence of divergent expressions that must be renormalized by recipes that on first sight sound…
cheshirecat

Weak Values Part 2: The Quantum Cheshire Cat Experiment

/
0 Comments
In a previous Insight, Weak Values Part 1: "Asking Photons Where They Have Been," I showed different methods for computing the relative intensities in…
askingphotons

Weak Values Part 1: Asking Photons Where They Have Been

In a previous Insight on retrocausality, I explained an experiment by Danan, Farfurnik, Bar-Ad, and Vaidman (DFBV)[1], “Asking Photons Where They Have…
renormalization2

Why Renormalisation in Quantum Theory Needs a Cutoff

/
31 Comments
Introduction This is a follow on from my paper explaining renormalization. A question was raised - why exactly do we need a cut-off. There is a deep reason…
renormalization

Quantum Renormalisation Made Easy

/
24 Comments
What Is The Issue With Renormalisation If you have an interest in physics you have likely come across renormalisation before, although what it really…
redlights

Learn About the Greenberger-Horne-Zeilinger Experiment

In two previous Insights, I shared Mermin's explanation of the Hardy experiment[1] and the Mermin device[2]. Both of his corresponding AJP papers presented…
mermin

The Quantum Liar Experiment: An Instantiation of the Mermin Device

In 1981, Mermin published a paper[1], "Bringing home the atomic world: Quantum mysteries for anybody" in which he explained the mystery of quantum nonlocality[2]…
2D Animation

Particle in a Box: 1D & 2D Quantum Visualizations

/
11 Comments
Introduction The particle in a box is a staple of entry-level quantum mechanics courses because it provides a clear contrast between classical and quantum…