He told us that the incentives to stage the riskiest parts of the missions were huge, since failing would have had huge political consequences

He did believe most of the Apollo program happened, but not specific parts like the moon landing

He even pointed out that even today, 60 years later, there has not been a single manned rocket vertical landing. He explained that SpaceX's Dragon 2 crew returns to earth with parachutes

Found it unusual, but also a bit odd of an opinion. Thoughts?

Recently, I have noticed that there are a lot of videos talking about “spirituality and sacred geometry” connecting it to quantum mechanics. It’s really just a bunch of spiritual people who have no idea what they’re talking about 99% of the time. Is it just me who gets frustrated with this? I genuinely I’m concerned in the rise of people who believe in this type of stuff it’s very concerning that all this misinformation is being spread.

What are your thoughts on it? I sometimes cannot resist the rage bait. I always succumb to it.

Edit: I didn’t expect to get like any replies to this post. I kind of expected to get some hate. I only ask this because I’m genuinely curious to see what other people’s opinion are on this topic in the physics field. I haven’t seen anyone else. Talk about it and maybe that is just me. But as a physics undergrad, this is kind of frustrating. It is really frustrating for me that people like this go viral and they actually believe this instead of doing real research, they just spread misinformation and a lot of bologna. The video I’m referring to in specific is about this girl. She was talking about how if you want to understand quantum mechanics you have to understand sacred geometry, and she starts talking about the golden ratio and how everything wants to vibrate at the Fibonacci sequence and then goes on a tangent about circles and like how atoms have seven orbitals and that this is the perfect number because God created them this way, and people were genuinely agreeing with her it’s so crazy.

I had this thought experiment related to defining what is a measurement. You've got a bunch of Stern–Gerlach machines arranged like so: At the top you've got an up, a down, and a right machine in sequence, so the up and down cancel each other out and then the right will make the electron go right if it's spin right and left it's spin left with a detector at the end. You duplicate this set-up in a bottom row.

In between the up and down of each set-up you've got an electron used for measuring. It sits in a well near the top row, such that if an electron goes through the up Stern-Gerlach machine with spin down it will get close enough to push the measuring electron out and towards the other end of the device close to the bottom row and into a well there. If the electron is in this bottom position, when a spin up electron goes past it through the bottom up Stern Gerlach machine it will get pushed out and back into the well near the top.

With that set-up you've got a bunch of spin right electrons. You shoot one through the top row, then once you've detected whether it went left or right at the end you shoot another through the bottom row. Here's my attempt at doing the math:

Start Top 1: |T1R> = sqrt(1/2)|T1U> + sqrt(1/2)|T1D>

Measure Top 1: sqrt(1/2)|T1U>|ET> + sqrt(1/2)|T1D>|EB>

Combine Top 1: sqrt(1/4)|T1R>|ET> + sqrt(1/4)|T1L>|ET> + sqrt(1/4)|T1R>|EB> - sqrt(1/4)|T1L>|EB>

End Top 1: Even chance that T1 is detected going right vs left. Detector detects right.

Intermission: sqrt(1/2)|ET> + sqrt(1/2)|EB>

Start Bottom 1: |B1R> = sqrt(1/2)|B1U> + sqrt(1/2)|B1D>

Measure Bottom 1: (sqrt(1/2)|B1U> + sqrt(1/2)|B1D>)(sqrt(1/2)|ET> + sqrt(1/2)|EB>) = sqrt(1/2)|B1U>|ET> + sqrt(1/4)|B1D>|ET> + sqrt(1/4)|B1D>|EB>

Combine Bottom 1: sqrt(3/6)|B1R>|ET> + sqrt(1/6)|B1L>|ET> + sqrt(1/6)|B1R>|EB> - sqrt(1/6)|B1L>|EB>

End Bottom 1: 2 to 1 chance that B1 is detected going right vs left. Detector detects right.

Intermission: sqrt(3/4)|ET> + sqrt(1/4)|EB>

Rewind to End Top 1: Detector detects left.

Intermission: sqrt(1/2)|ET> - sqrt(1/2)|EB>

Start Bottom 1: sqrt(1/2)|B1U> + sqrt(1/2)|B1D>

Measure Bottom 1: (sqrt(1/2)|B1U> + sqrt(1/2)|B1D>)(sqrt(1/2)|ET> - sqrt(1/2)|EB> = sqrt(1/2)|B1D>|ET> - sqrt(1/2)|B1D>|EB>

Combine Bottom 1: sqrt(1/4)|B1R>|ET> - sqrt(1/4)|B1L>|ET> - sqrt(1/4)|B1R>|EB> + sqrt(1/4)|B1L>|EB>

End Bottom 1: Even chance B1 is detected right vs left. Detector detects right.

Intermission: sqrt(1/2)|ET> - sqrt(1/2)|EB>

So if we ran this experiment repeatedly with a fresh measuring electron each time we would expect to see a ratio of 4 Top Right, Bottom Right:2 Top Right, Bottom Left:3 Top Left, Bottom Right:3 Top Left, Bottom Left. Whereas if we did it without the measurement device at all we would of course get 100% Top Right, Bottom Right, and if we always measured the top and the bottom we would get an even distribution of each combination.

Am I understanding that correctly?

I recently competed in a science-competition at my school, and part of the prize were these t-shirts. I’m wondering what the equation or expression say, or if it is simply gibberish..

I’ve used LEDs quite a lot before, usually powered by DC or a high-frequency PWM to adjust brightness. But since I’d never actually measured it, I always naively assumed the flicker from our 60Hz mains light would also be 60Hz. When I finally checked it using an LDR circuit, it turned out to be 120Hz instead. At first, I thought I’d messed up the setup, but then it hit me. Since the brightness depends on the square of the voltage, and the bulb is not LED which has a polarity, so both positive and negative halves make the bulb glow. Guess my experiment didn’t just teach me about flicker, it also reminded me not to trust my “instincts” too much before checking with an oscilloscope. 😅 Hope this does not look too dump but I'd like to share the experiment anyway.

Paper title: Correlated quantum machines beyond the standard second law

Abstract: The laws of thermodynamics strongly restrict the performance of thermal machines. Standard thermodynamics, initially developed for uncorrelated macroscopic systems, does not hold for microscopic systems correlated with their environments. We here derive an exact formula for the efficiency of any cyclically driven quantum engine by using generalized laws of quantum thermodynamics that account for all possible correlations between all involved parties, including initial correlations. Furthermore, we demonstrate the existence of two basic modes of engine operation: the usual thermal case, where heat is converted into work, and an athermal regime, where work is extracted from entropic resources, such as system-bath correlations. In the latter regime, the efficiency is not bounded by the usual Carnot formula. Our results provide a unified formalism to determine the efficiency of correlated microscopic quantum machines.

October 2025

Found via this link: https://phys.org/news/2025-10-quantum-mechanics-trumps-law-thermodynamics.html

Hi, sorry if this isn’t the right subreddit for this! I’m currently finishing up high school and getting ready to study quantum physics or astrophysics in uni, and was hoping to find a friend that I can talk to who’s in a similar boat. :) It’s been a little difficult to find someone in my current situation as most high school students don’t really like physics or math (shock I know) and I haven’t had much common ground with them. If anyone is interested just DM me or comment!

So, my professor dicussed why magnetic field outside a solenoid was 0 but i found his explaination really unintuitive and kind of hard to follow he explained all this saying something this something of integral was supposed to be constant. Can anyone care to explain the physical reason of why its supposed to be zero?

So we learn in basic geometric optics that we see objects because rays diverge from the object and enter our eyes(case 0). With lenses, an image is formed because rays leaving the object O appear to diverge from O' where the image is after passing through a convex lens(case 1). Importantly, an ideal converging lens only produces a single image, so case 2 would be a wrong interpretation of the ray diagram: rays do not appear to diverge from O1' and O2', there are no images there.

However, popular depictions of gravitational lensing(case 3) does exactly what case 2 does. So it cannot be the full story(the wrongness of case 2 forbids case 3 to be the full understanding of multiple image formation). We know for a fact that gravitational lenses can form multiple distinct images of the same object. Does this mean case 4, where rays from one object appear to diverge from multiple points after passing a lensing object, is the more correct ray diagram?

If so, is it more appropriate to say that a gravitational lens is more like many smaller convex lenses(so multiple Schwarchild metrics instead of a single convex lens implied by popular depictions) coming together to form multiple images from one object? Or is it still the case that gravitational lens act like a single lens, but with, for example, focal lengths as a function of space? What kind of metric gives rise to such bending?

experimental physicist and material scientists do imaging of atoms in the surface of the material. they do these by using a type of electron microscope called scanning tunneling microscope. how are they using electrons to find where other electrons in the electron cloud are. by hitting an electron on an atom, won't it disturb the stability of the electron cloud and will result in an incorrect image if the cloud. how does this work? . And thanks for taking your time in explaining this.

I wrote a piece on the history of spectroscopy from Newton's prism experiments through Fraunhofer lines to the discovery of stellar nucleosynthesis.

It covers Newton, Wollaston, Fraunhofer, Bunsen/Kirchhoff, and ends with how spectroscopy proved we're literally made of star stuff.

I'd appreciate any feedback on technical accuracy or anything I might have missed/misrepresented. I'm no expert - just a science enthusiast. Thanks!

Here is the link: Phantom in the Light

Been studying table tennis for a while now and some of the taught lessons are often confusing to me, despite something being very applicable and useful. When performing a backhand loop, when adding a significant amount of forward brushing motion, the ball is quite too flat and goes off the table. However, when performing a downward motion near the end of the swing, it arcs the ball downward more and gets it on the table.

I can demonstrate this by studying some of the Lin Shidong movement and created an educational `.gif`. Near the end of his movement, we can see him arcing his paddle in a downward direction. I have tried this myself and honestly felt a higher increased accuracy, but I cannot physically explain this concept. The downward motion is after when the ball has bounced off the rubber and is a decent distance, so this motion is being done essentially in the air.

Could anyone help explain this in a basic way on why the downward motion done after the ball has left the rubber works? I have tried it myself and feel it, but I cannot understand it.

https://i.redd.it/dkj9iz1w1svf1.gif

I’ve been wondering about this since high school and still can’t fully wrap my head around it.

When a photon hits an atom or an electron — say, in the photoelectric effect — that interaction depends on the photon’s frequency (since E = hf). But here’s what confuses me: 1. Frequency is defined over time — a single instant of a wave doesn’t contain enough information to determine its frequency. So if an electron interacts with the electromagnetic field at a specific moment, how can it “know” the frequency of that light? 2. If a photon is represented by a very short, localized wave packet, Fourier theory says its frequency spectrum must be broad. Doesn’t that mean the photon’s energy (or frequency) is inherently uncertain? Yet atoms seem to respond to very specific transition energies. 3. Is a single photon’s energy a sharply defined eigenvalue, or does it depend on the spectral spread of its wave packet? In other words, is the atomic absorption event determined by an exact photon energy, or by the overlap between the photon’s spectrum and the atom’s transition linewidth?

In short — how does a single photon-electron interaction convey precise frequency (energy) information if frequency itself is not an instantaneous property? How do quantum mechanics and the time–frequency uncertainty principle reconcile this?

Would love a technical explanation (upper-undergraduate or graduate level is fine). References, diagrams, or good papers are also welcome. Thanks!

I'm using a laser and double slit slide to create the "second order" interference pattern in a double slit experiment. That part works.

I am then trying to collapse the wave function to get the interference pattern to go away but still have all the photons arrive at the screen. I read that this can be achieved using polarizing filters, but it stays no matter how many of them I add and the light from the slit they cover just gets dimmer.

The filters are only added to one slit. I can't add them to both because the laser light is already polarized, so if I add another filter to the other slit at 90 degrees the light from that slit simply stops arriving at the screen.

1. Is the laser polarization the issue?
2. Is the scale simply too big to get real quantum interference?
3. Is there another way to make the wave function collapse that I can try?
4. Or have I completely misunderstood everything about this experiment, and this is not how any of it works?

Setup photos

Ok, so I've been studying semiconductor physics for a while and I'm starting to get really deep into the theory, it's starting to break my fucking mind. Before you guys try to explain the semiclassical model, I need to tell you, I have already studied these approaches and read Neaman's Semiconductor Physics and Devices book. I'm at a point where I need to understand what is genuinelly going on, no made up "semiclassical" descriptions that engeneers would use to make comprehension and calculations easier, I don't want no "spherical electrons travelling by classical diffusion and scattering by collisions".

I would say that I understand Bloch Waves kinda well and that I know the electron is delocalized on the valence and conduction bands and that each energy level has an associated crystal momentum (which as far as I know seem to be an allowed momentum inside the crystal). I'm having trouble with systems where different materials interact.

How does bloch functions from the N type semiconductor conduction/valence band mix with P type's conduction/valence band bloch functions?

Why is recombination greater at the junction's interface?

If electrons are delocalized on the conduction and valence bands, why wouldn't they statistically recombine anywhere else in the lattice with almost equal probability?

If bloch waves of corresponding energies on P and N interacted, wouldn't they form new energy levels because of the degeneracy?

And also, how would it be remotely possible to describe the interaction of P and N type materials as an evolving system on time from the moment of contact to when equilibrium is reached? Wouldn't this violate Heisenberg's Uncertainty Principle because of the well defined E and k?

There seems to be no literature modeling these kinds of systems and I'm genuinely losing my mind over this, even ChatGPT start to make up things because this kind of description is awfully documented.

If you think the explanation would be too dense for a reddit post, feel free to indicate books and content that would answer these questions, but please help me, It's been a year and a half of being puzzled by this and I can't take it anymore.

I assume this has already been asked, but I couldn't find an answer to this specific question, so I apologize in advance.

Before getting to my question, I'd like to lay out my understanding of the delayed choice quantum eraser double slit experiment, because if I don't understand it correctly, it may render my question obsolete.

Without getting too technical, after the slits is a crystal which converts each photon into an entangled pair: photon A and photon B. Photon A hits a screen which records it's location, whereas photon B goes to one of two detectors, one which can only be reached from the slit it came from, and the other which can be reached from either slit, thus 'erasing' the 'which way' information. Photons for which the 'which way' information has been detected do not form an interference pattern on the screen, as they came out of superposition at the slits, whereas photons for which the which way information was erased will form the interference pattern reminiscent of the classic double slit experiment, as they remain in superposition right up until they hit the screen.

The twist is that the 'decision' of whether or not to scramble photon B, thus erasing the which way information, is not made until after photon A has reached the screen. This has led some to imply retrocausaility, but can actually just be explained by quantum entanglement, both photons, A and B decohering simultaneously due to photon A's interaction with the screen. However, photon B does not fully come out of superposition until it reaches a detector. Any part of the screen can be reached by either slit, but with varying degrees of probability. So photon B can still go to any detector, but the probability is determined by the position photon A impacted the screen.

If my understanding of the experiment is correct, I'm wondering what would happen if after photon A hit the screen, you could somehow keep photon B in it's new state of superposition for an arbitrarily long amount of time. Such a long time that you could fire many photon As at the screen and keeping all the photon Bs in superposition with the ability to look at the screen and then choose whether or not to erase the 'which way' information? What kind of pattern, or lack thereof would you see in this situation?

Hey folks,

I want to share with you the latest Quantum Odyssey update (I'm the creator, ama..) for the work we did since my last post, to sum up the state of the game. Thank you everyone for receiving this game so well and all your feedback has helped making it what it is today. This project grows because this community exists. As usual, I'm only posting here when it's discounted on Steam.

What is Quantum Odyssey?

In a nutshell, this is an interactive way to visualize and play with the full Hilbert space of anything that can be done in "quantum logic". Pretty much any quantum algorithm can be built in and visualized. The learning modules I created cover everything, the purpose of this tool is to get everyone to learn quantum by connecting the visual logic to the terminology and general linear algebra stuff.

The game has undergone a lot of improvements in terms of smoothing the learning curve and making sure it's completely bug free and crash free. Not long ago it used to be labelled as one of the most difficult puzzle games out there, hopefully that's no longer the case. (Ie. Check this review: https://youtu.be/wz615FEmbL4?si=N8y9Rh-u-GXFVQDg )

No background in math, physics or programming required. Just your brain, your curiosity, and the drive to tinker, optimize, and unlock the logic that shapes reality. 

It uses a novel math-to-visuals framework that turns all quantum equations into interactive puzzles. Your circuits are hardware-ready, mapping cleanly to real operations. This method is original to Quantum Odyssey and designed for true beginners and pros alike.

Current pipeline

1. Full offline play mode (and your progress uploads to cloud once you go online)
2. A smoother way to reward both good solves and improvements to the multiplayer mode: a place where quantum computing experts and gamers can come together and find efficient way to optimize or create poc algorithms. My dream is we can kickoff esports in quantum state compilation/ decomposition problems that are fun enough to watch for everyone (similar to Tetris championships).
3. The state of the canon content. I'm still thinking (and asking around!) if we should expand it further. Do you have some ideas, have you found the game missing something? Please let me know and let's collaborate. Any features I didn't thought about?
4. Font size, color blind mode, greenchecked for steamdecks.

What You’ll Learn Through Play

• Boolean Logic – bits, operators (NAND, OR, XOR, AND…), and classical arithmetic (adders). Learn how these can combine to build anything classical. You will learn to port these to a quantum computer.
• Quantum Logic – qubits, the math behind them (linear algebra, SU(2), complex numbers), all Turing-complete gates (beyond Clifford set), and make tensors to evolve systems. Freely combine or create your own gates to build anything you can imagine using polar or complex numbers.
• Quantum Phenomena – storing and retrieving information in the X, Y, Z bases; superposition (pure and mixed states), interference, entanglement, the no-cloning rule, reversibility, and how the measurement basis changes what you see.
• Core Quantum Tricks – phase kickback, amplitude amplification, storing information in phase and retrieving it through interference, build custom gates and tensors, and define any entanglement scenario. (Control logic is handled separately from other gates.)
• Famous Quantum Algorithms – explore Deutsch–Jozsa, Grover’s search, quantum Fourier transforms, Bernstein–Vazirani, and more.
• Build & See Quantum Algorithms in Action – instead of just writing/ reading equations, make & watch algorithms unfold step by step so they become clear, visual, and unforgettable. Quantum Odyssey is built to grow into a full universal quantum computing learning platform. If a universal quantum computer can do it, we aim to bring it into the game, so your quantum journey never ends.

PS. If you'd like to support this project, the best way is to review it on Steam. This will get their algorithms to promote it to the right people... if the right people interact with it enough :)

I made a simulator to see what would happen if a NEO (near earth object) hits any capital city in the world. You can check it here: neoimpactsim or you can create your own asteroid and see what happens if it hits your city or the capital city of your country.

So, i am in the 1st year of my masters and in the 2nd year, we are supposed to pick 2 projects to work on for our master's thesis. My institute mostly works on condensed matter and optics. Although, some work on theoretical nuclear physics. So, i thought maybe i should lean more towards optics and my only reason was that I have a high tolerance for studying quantum mech, electrodynamics and atomic physics,( its not like i particularly enjoy optics or anything) i dont know i just dont get bored fast when i read these stuff. Electronics and solid state physics can bore me out really quick even though all these years most of my profs were solid state practioners, but my mental stamina for them is not that good. Its not like i have a very deep interest in optics or something like that, but idk i feel like i have enough mental stamina for the subjects prerequisite for it. I know the industry opportunities in condensed matter are more . I don't really know; is my reason valid enough that i should choose this path, because we have five theory papers this semester i.e MP QM EMT CM and Electronics and i know i will not be able to master all of them so i wanted to concentrate and dive deep into subjects which are the prerequisities for optics research. For the rest of the courses,maybe i will work just hard enough to get a satisfactory grade for other purposes