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Physics. Please read all of the rules before posting. No HW, no career questions in top post.

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Encouraged in weekly threads

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Weekly schedule

All threads are posted at 9am EDT (1pm UTC).

Day Post
Mon What are you working on?
Tue Physics Questions
Thu Careers/Education Questions
Fri Resource Recommendations

How to use LaTeX?

First, you will need to install one of the recommended add-ons. To include an equation typeset in LaTeX in your post, put the LaTeX code between [; and ;].

[;i\hbar \frac{\partial}{\partial t} \Psi = \hat H\Psi;]


2,392,142 Subscribers


Is there any Nobel Prize winning physicist alive who arguably could win a second one for the work they have done so far?

03:20 UTC


What's your opinion on Gauge Fields, Knots and Gravity by John C. Baez?

I'm years away from being a physicists but I'm finding this book completely fascinating so far. I just finished the part where he generalizes Electromagnetism for any Riemannian manifold. This book feels like a novel for theoretical physicists, everything is so interesting and fun.

I want to try to make a simulation of electromagnetism on a T^2 this week, once I nail all the concepts. Have any of you read the book? What are your opinions about it?

1 Comment
02:59 UTC


Unituitive physics realizations that took you time to realise?

For me it's taken an entire semester of learning QFT to finally notice that the field operator is, well, an operator.

20:03 UTC


B.Sc. in Physics should be 60% programming

Just started my very first actual physics role working on an optical catalog of GRBs having graduated 3 months ago, and I cannot believe how little my degree is relevant to this.

Only two courses were programming in my studies; Java and Mathematica. Imagine my surprise when I tried using them in a field that uses Python in its entirety.

No optics, thermodynamics, nuclear physics, modern physics, electrodynamics, none of it is needed. Just endless hours of coding.

At least we have ChatGPT now, but still I feel like a fish trying to climb mount Everest with all this stuff.

Just needed to get this out and know if more people have this realization once they graduate or if it's just a me thing.

19:53 UTC


Why is a 50/50 fission split so unlikely?

We’ve just gotten onto Nuclear fission in A-level physics. We’ve been shown the distribution of nuclei that are likely to be produced as a result of Uranium-236 undergoing fission. There’s a big dip in the middle where the nucleus splits in half exactly, and it’s much more likely to produce one big nucleus and one small one.

Google’s failed to help me know why this is, does anyone here have an answer as to why a 50/50 split is so unlikely?

14:27 UTC


Physics Questions - Weekly Discussion Thread - November 21, 2023

This thread is a dedicated thread for you to ask and answer questions about concepts in physics.

Homework problems or specific calculations may be removed by the moderators. We ask that you post these in /r/AskPhysics or /r/HomeworkHelp instead.

If you find your question isn't answered here, or cannot wait for the next thread, please also try /r/AskScience and /r/AskPhysics.

14:00 UTC


What topic did you find hardest to study and how did you get through it?

Currently studying Quantum Mechanics and it’s the first unit I’ve really not enjoyed, likely because I suck at it. I think it’s down to not being able to really visualise what you’re actually applying.

Anyone else struggle with a different unit and how did you get past it?

18:23 UTC


What are some of the most cursed units you've seen?

For me, I'd say seconds per second in time dilation

14:40 UTC


What are you working on? - Weekly Discussion Thread - November 20, 2023

Hello /r/Physics.

It's everyone's favorite day of the week, again. Time to share (or rant about) how your research/work/studying is going and what you're working on this week.

14:00 UTC


There were some quite questionable things in Surely, You're Joking Mr. Feynman.

Richard Feynman is my hero. I love Feynman's Lecture on Physics and words cannot describe how much I love learning from him but despite all of this, I feel it is necessary to point out that there were some very strange things in Surely, You're Joking Mr. Feynman.

He called a random girl a "whore" and then asked a freshman student if he could draw her "nude" while he was the professor at Caltech. There are several hints that he cheated on his wife. No one is perfect and everyone has faults but.......as a girl who looks up to him, I felt disappointed.

12:01 UTC


What is your intuition about various interpretations of quantum behavior?

For the physicists who study quantum behavior in detail, what is your intuition and mental model like. Do you

(i) Accept the weirdness of it and just "shut up and calculate" - Copenhagen

(ii) Look to other theories i.e. Pilot wave, Many worlds so as to explain away non-determinism/randomness

(iii) believe that we are missing something fundamental

I am fascinated by the various interpretations and would love to get a discussion going with physicists who are working deeply on such stuff.

23:59 UTC


Comoving Space as a Manifold: How Does It Work?

One of the big open questions in cosmology is:

"What is the 3-manifold of comoving space, i.e. of a comoving spatial section of the universe, informally called the "shape" of the universe?"

My question is:

How is it possible for the entire comoving space to be described as a manifold in cosmological models, considering that not all regions within it are causally connected? Essentially, why do cosmologists use a manifold to describe the entire universe, including regions that have never interacted or influenced each other?

20:36 UTC


Theoretical upper limits on the speed of sound.

Obviously the upper limit is c or 0.577c for a photon gas.

For 'normal' medium (a medium made up of atoms), I remember there was a paper which said it was 36.1 km/s (c α (me/(2 mp))^(1/2)) if the medium is metallic hydrogen.

Is there any attempts for other types of media, 'exotic' media like nucleus of an atom or crystallized media which exists in white dwarfs ?

18:17 UTC


Is LaTex necessary for undergraduate physics (UK) or is it a waste of time?

I’m thinking of using it for my report (first year), but I don’t want to do something that might just backfire

16:00 UTC


I'm working on a 3D quantum particle-in-a-box simulator for the web

screenshot from my sim

I just made qubesim.com - an interactive simulation of a quantum Gaussian particle packet in a 3D square well (non-relativistic, just basic QM).

It's a work in progress. As you can tell if you run it, the system's energy grows unbounded. Not... ideal. Also, installation as an offline web app doesn't work (though it did at one point).

I would really appreciate the feedback of people who are actually interested in viewing this kind of simulation. Or who just want to help me 😽

For the energy issue, I'm going to look into how the Laplacian is implemented. It could just be an issue of the time-step being too large for the Finite-Difference method that I'm using (leading to instability) - but I hope not... unless y'all have some recommendations on a better algorithm to implement?

I'm planning to add a comparison simulation of a classical (Newtonian) particle in a box. As well as some descriptions of what's being displayed, legends for color/opacity mapping to probability, and other such relevant details for the intrigued physicist(s) or every-man. Please let me know!

public double CalculateTotalEnergy()
    var totalEnergy = 0.0;

    for (var x = 0; x < _dimensions.x; x++)
        for (var y = 0; y < _dimensions.y; y++)
            for (var z = 0; z < _dimensions.z; z++)
                var psi = _wavefunction[x, y, z];
                var probabilityDensity = psi.Magnitude * psi.Magnitude;

                var laplacianPsi = _laplacianWavefunction[x, y, z]; // Use the stored Laplacian
                var kineticEnergy = -(_hbar * _hbar / (2 * _mass)) * (laplacianPsi * Complex.Conjugate(psi)).Real;

                var potentialEnergy = _potential[x, y, z] * probabilityDensity;
                totalEnergy += kineticEnergy + potentialEnergy;

    return totalEnergy;

public void ApplySingleTimeEvolutionStep()
    var newWavefunction = new Complex[_dimensions.x, _dimensions.y, _dimensions.z];

    for (var x = 0; x < _dimensions.x; x++)
        for (var y = 0; y < _dimensions.y; y++)
            for (var z = 0; z < _dimensions.z; z++)
                _laplacianWavefunction[x, y, z] = CalculateLaplacian(_wavefunction, x, y, z, _boundaryType);

                var timeDerivative = (-_hbar * _hbar / (2 * _mass)) * _laplacianWavefunction[x, y, z] + _potential[x, y, z] * _wavefunction[x, y, z];
                newWavefunction[x, y, z] = _wavefunction[x, y, z] - (Complex.ImaginaryOne / _hbar) * timeDerivative * _timeStep;

    _wavefunction = newWavefunction;

private Complex CalculateLaplacian(Complex[,,] wavefunction, int x, int y, int z, BoundaryType boundaryType)
    var dx2 = _deltaX * _deltaX; // Assuming deltaX is the grid spacing

    var d2PsiDx2 = GetSecondDerivative(wavefunction, x, y, z, 0, boundaryType, dx2);
    var d2PsiDy2 = GetSecondDerivative(wavefunction, x, y, z, 1, boundaryType, dx2);
    var d2PsiDz2 = GetSecondDerivative(wavefunction, x, y, z, 2, boundaryType, dx2);

    return d2PsiDx2 + d2PsiDy2 + d2PsiDz2;

private Complex GetSecondDerivative(Complex[,,] wavefunction, int x, int y, int z, int dimension, BoundaryType boundaryType, double dx2)
    int plusIndex, minusIndex;
    Complex valuePlus, valueMinus;

    switch (dimension)
        case 0: // x-dimension
            plusIndex = Mod(x + 1, _dimensions.x, boundaryType);
            minusIndex = Mod(x - 1, _dimensions.x, boundaryType);
            valuePlus = plusIndex != -1 ? wavefunction[plusIndex, y, z] : 0;
            valueMinus = minusIndex != -1 ? wavefunction[minusIndex, y, z] : 0;
        case 1: // y-dimension
            plusIndex = Mod(y + 1, _dimensions.y, boundaryType);
            minusIndex = Mod(y - 1, _dimensions.y, boundaryType);
            valuePlus = plusIndex != -1 ? wavefunction[x, plusIndex, z] : 0;
            valueMinus = minusIndex != -1 ? wavefunction[x, minusIndex, z] : 0;
        case 2: // z-dimension
            plusIndex = Mod(z + 1, _dimensions.z, boundaryType);
            minusIndex = Mod(z - 1, _dimensions.z, boundaryType);
            valuePlus = plusIndex != -1 ? wavefunction[x, y, plusIndex] : 0;
            valueMinus = minusIndex != -1 ? wavefunction[x, y, minusIndex] : 0;
            throw new ArgumentException("Invalid dimension");

    return (valuePlus - 2 * wavefunction[x, y, z] + valueMinus) / dx2;

private static int Mod(int a, int b, BoundaryType boundaryType)
    switch (boundaryType)
        case BoundaryType.Reflective:
            if (a < 0 || a >= b)
                return Math.Abs(b - Math.Abs(a) % b) % b;
        case BoundaryType.Absorbing:
            if (a < 0 || a >= b)
                return -1;
            throw new ArgumentOutOfRangeException(nameof(boundaryType), boundaryType, null);
    return a;

public double[,,] CalculateProbabilityDensity()
    var probabilityDensity = new double[_dimensions.x, _dimensions.y, _dimensions.z];

    for (var x = 0; x < _dimensions.x; x++)
        for (var y = 0; y < _dimensions.y; y++)
            for (var z = 0; z < _dimensions.z; z++)
                var psi = _wavefunction[x, y, z];
                probabilityDensity[x, y, z] = psi.Magnitude * psi.Magnitude; // |psi|^2

    return probabilityDensity;

public void InitializeGaussianPacket(double x0, double y0, double z0, double sigma, double kx, double ky, double kz)
    var normalizedAmplitude = CalculateNormalizationConstant(sigma);

    for (var x = 0; x < _dimensions.x; x++)
        for (var y = 0; y < _dimensions.y; y++)
            for (var z = 0; z < _dimensions.z; z++)
                var exponent = -((x - x0) * (x - x0) + (y - y0) * (y - y0) + (z - z0) * (z - z0)) / (4 * sigma * sigma);
                var phase = kx * x + ky * y + kz * z;

                var realPart = Math.Exp(exponent) * Math.Cos(phase);
                var imaginaryPart = Math.Exp(exponent) * Math.Sin(phase);

                _wavefunction[x, y, z] = new Complex(realPart, imaginaryPart) * normalizedAmplitude;
                _laplacianWavefunction[x, y, z] = CalculateLaplacian(_wavefunction, x, y, z, _boundaryType);
07:54 UTC


Question about HEP Phenomenology

So, what's needed from at least grad school to do HEP phenomenology? Aka what modules that are usually generally present in all P Phy or at least basic Physics courses?

07:41 UTC


Christmas gifts for a Physicist

Good evening, What are some cool gifts that someone gave you or that you have that you think would be a cool gift for a physicst?

19:58 UTC


How do we know that quantum entanglement holds up over vast distances

Something that I can't seem to understand is why scientists are so sure that quantum entanglement allows information to instantly travel across virtually any distance. I get that we've done experiements in the small scale that prove that this information can be sent faster than the speed of light which is strange. But why are people so sure that if particles were placed anywhere in the universe this information would travel just as instantaneously. Anytime anyone talks about this all I think is "how can we really know that?"

19:31 UTC


2023 Awards in our annual Essay Contest on History of Physics

Dear Colleagues,

I am pleased to announce the 2023 Awards in our annual Essay Contest on History of Physics

We received thirty entries from seven countries: the United States, Australia, Germany, India, Oman, Sweden, and the United Kingdom. Our FHPP Executive Committee evaluated the essays in terms of originality, clarity, and potential to contribute to the field.

And the 2023 Winner is:

*Rebecka Mähring* -- for the outstanding essay, "Hilde Levi: A Jewish Woman's Life in Physics in the 20th Century".

This inspiring account of Dr. Hilde Levi's life describes her pioneering interdisciplinary labors in biophysics and on the applications of radioisotopes. Levi generously collaborated with various other physicists, scientists, and medical professionals. Mähring’s fascinating account elucidates how Hilde Levi’s unpretentious kindness and professionalism enabled her to fulfill, renegotiate, and transcend traditional gender roles.

Rebecka Mähring graduated from Princeton University in May 2023 with a bachelor’s degree in Physics. Her senior thesis research was on dark matter phenomenology. An abridged version of Mähring’s essay is now posted on APS News: “The Extraordinary Life and Science of Hilde Levi". It will also be published in print as the Back Page of APS News in December.

Rebecka Mähring receives a cash award of $1,000.00, plus travel support (up to a $2,000.00 value) to be an Invited Speaker at the APS April 2024 Meeting in Sacramento, California, to present a talk based on the winning essay.

Also, FHPP is very glad to award
*three Prizes for Runners-Up*,
in a three-way tie, with cash awards of $500 each. In alphabetical order, they are:

  • Stefano Farinella

“Galileo’s Use of Mathematics in its Historical Context”
This is an illuminating account of how Galileo's avoidance of algebra, in his 1638 book discussing the “new” science of the strength of materials, led him to convey the inapplicability of scale invariance by using a convoluted geometrical route. Farinella’s concise account of how algebraic notation changed within Galileo's lifetime is also clear and impressive.

  • Preetha Sarkar

“Meghnad Saha: A Win for Science”
This elegant account describes how Meghnad Saha overcame class discrimination, as a Shudra, to nevertheless pioneer the field of radiation pressure with great success. The beauty of his innovative application of early quantum theory to astrophysics shines brightly in Sarkar’s essay, using primary sources to discuss ionization and atomic physics in stellar atmospheres. It also clearly charts Saha's humanistic dedication to supporting the scientific, engineering, and social communities in India.

  • Jessica Schonhut-Stasik*

“The Transit of Venus, King Kalākaua, and Indigenous Knowing”
This essay eloquently discusses the history of the international telescopes in Hawai'i, a timely topic. Schonhut-Stasik’s account of King Kalakaua's advocacy of education, internationalism, and public astronomy is a moving tribute to the early oceanic way-finders who thoughtfully gazed up to the stars. The ongoing protests against the Thirty Meter Telescope show the negative consequences of disregarding the concerns of local communities.

We hope that all four awards will encourage the winners, as well as other participants, to continue contributing to the history of physics and astrophysics. The Essay Contest webpage includes information about each award recipient, and links to their commendable essays.

On behalf of FHPP, I congratulate the four Award Winners, and I warmly thank all other participants for submitting their interesting and promising essays. I also thank any APS and FHPP Members who encouraged anyone to participate–especially students.

Alberto Martinez

Chair of APS FHPP
Professor, The University of Texas at Austin

19:03 UTC


Interested in creating, building, and running a sustainable informal physics program?

Dear Colleagues,

You're Invited to the free JNIPER Coffee Hour on November 29, 12:00 p.m. - 1:30 p.m. ET. This is an incredible opportunity to network with other physicists!

We are thrilled to have Dr. Tatiana Erukhimova from Texas A&M University and Dr. Jonathan Perry from the University of Texas at Austin guiding us through an engaging session. With a combined experience of over two decades in creating, building, and running sustainable informal physics programs, they are set to share insights that you won't want to miss!

Everyone is welcome! Whether you're a seasoned participant or a newcomer, this Coffee Hour is open to all. Bring your curiosity, questions, and ideas as Tatiana and Jonathan aim to foster a collaborative discussion on maximizing the impact of informal physics programs.

Register for free here: https://go.aps.org/3uh0dqp.

18:51 UTC


Linear Algebra for a physicist: computational or proof-based?

Hey everyone!

I'm a second-year undergrad preparing for my classes next semester and my major offers two choices for Linear Algebra: one with computational applications, and one that's more abstract and proof-based. I hope to become a physicist someday and was just wondering which of these classes would prepare me better?

I initially thought the computational one would help, since research everywhere basically relies on coding now. But I've been looking more into different fields of interest, like astrophysics (black holes and cosmology specifically), and it looks like I might benefit more from a rigorous foundation in linear algebra in order to prepare for the mathematics of general relativity--after all, I could always learn how to code later.

I guess I'm just worried about taking a proof-oriented class alongside the rest of my workload. I'm taking the Linear Algebra class online, so it would be hard for me to come in for help or study with other classmates.

Either way, I was hoping that you all could provide me with some advice. Which class would be more worth it for me?

Thank you!! :)

16:06 UTC


Do it yourself double- and single slit experiment?

It would be interesting to experiment with this at home, so I could find the answers myself instead of asking others on the net, but I'm mostly interested in "guns", for the lack of a better word, that can fire individual electrons or photons, one at the time. But I assume that equipment is pretty expensive and hard to find?

14:04 UTC

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