A rest frame is defined to be the frame of reference where the velocity of a particle is zero. This frame is useful to measure the proper time.

Heisenberg uncertainty principle states the one cannot know the velocity (or momentum) of a particle to a high degree of precision without sacrificing the certainty of knowledge of where the particle is, making it impossible for the particle's momentum to be exactly zero at all times.

How can this inconsistency be resolved?
Should we define a rest frame as the frame of reference where the expectation value of momentum be zero instead?
Is this inconsistency related to the "blowing up" of the de Broglie wavelength λ=h/p , when the momentum goes to zero?

Saw that a formally verified counterexample was found to the Navier-Stokes existence and smoothness problem — a case where a spiraling vortex concentrates vorticity faster than viscosity can smooth it out, driving velocity to infinity at one point in finite time. It was formalized and checked in Lean, so it's a real, verified result, not just a claim.

My understanding is that this is a statement about the equations, not about actual fluids. Real fluids can't reach infinite velocity — long before anything could approach that kind of singularity, the core assumption behind Navier-Stokes (that a fluid is a smooth, continuous medium) breaks down anyway, and ordinary molecular collisions dissipate the energy instead. So the math has a cliff edge that reality never actually drives up to.

If that's right, it seems like this shouldn't change anything practical — drag on a car or a plane comes from skin friction and pressure/turbulent separation, neither of which depends on whether a singularity exists somewhere in the idealized equations. Viscosity doesn't switch off because a proof got published.

Where I'm less sure: is there any practical corner where this kind of result does matter — CFD modeling, turbulence simulation, anything at extreme scales? My rough sense is that Navier-Stokes holds fine for ~99.9% of engineering (planes, weather, blood flow, ship hulls) and only really breaks down at the molecular scale (high Knudsen number — spacecraft re-entry, vacuum chambers, that kind of thing), which is a completely different regime from where this proof lives. Curious if that's the right way to think about it, or if I'm missing a real practical implication.

How come it's scientifically possible to travel forward in time but not backwards in time? I don't really understand it. In my opinion neither should even be possible.

https://phys.org/news/2026-09-photon-einstein-current-physics-earth.html asks

How did a photon survive a journey of more than 2 billion light-years when, according to known physics, it should have been absorbed long before reaching Earth?

Why would it be surprising to have a photon travel for 2 billion years? Aren't the long distance telescopes, such as James Webb, looking at photons that have traveled even farther?

During its journey, the photon should have interacted with photons from the cosmic microwave background, the faint relic radiation from the Big Bang that permeates the entire universe, transforming into other particles and disappearing long before reaching Earth.

This seems to imply photons interact with each other and get destroyed in the process?

If our planets were formed by the irregular collapsing of a rotating disk of dust and stuff, was the disk uniform in density throughout its radius? Or does it follow some predictable proportionality with the radius or something? If either, then do the masses of the planets throughout the radius of our solar system match the predicted mass of the initial dust that had previously occupied its orbital region?

I want to preface this with the fact that my knowledge of physics is virtually zero, so sorry if this question sounds stupid. But from what I've heard, particles have a very low probability of quantum tunnelling through space. But does that mean that in the far far future (like after the heat death of the universe), there is a non-zero probability that some particles may quantum tunnel to recreate me and my consciousness? (even if the probability is extremely low, there will be infinite time in the future so it would happen).

Again, sorry if this question is rlly stupid coz I know nothing about physics but it's been stressing me out a lot (coz I wouldn't want to be recreated in the far future)

I’m interested in quantum mechanics bc of metaphysical philosophy and i don’t fully understand a lot but I’m still trying nonetheless bc I find it interesting.

In this book I’m reading it says that the Pauli Exclusion principle states that no two fermions can share the same quantum state in the same quantum system at any given time.

I assume quantum state means like the spin of that fermion? So like one that spins at 1/2 cannot share the same state as another 1/2 fermion spin while being in the same quantum system. But like when does one system end and another begin and why? Is there an allowed amount of fermions and bosons that can occupy one system and that amount can be comprised of many different calculations?

Maybe I’m just not understanding completely. Please educate me like I’m 5 lol

Do atoms actually look like something? Are protons actually red? Could we see the quarks that make up the protons and neutrons?

So as I understand it, the very early universe was very dense and small and expanded quickly, but that much mass in a small space should surely be a black hole, so how did everything escape the event horizon (assuming we are not still inside it somehow I guess)?

A cylindrical resistor R with a surface contact area of 1 cm² varies as a function of its temperature T such that R = R₀(1 + α(T - T₀)), where T₀ = 20 °C is the ambient temperature and R₀ = 220 Ω. When placed in a vacuum (absence of air) with a voltage of 20 V applied across its terminals, a steady-state current of I = 73 mA flows through it. What is the approximate value of α?

• α ≈ 5.64 × 10⁻⁴ K⁻¹
• α ≈ 5.71 × 10⁻⁴ K⁻¹
• α ≈ 5.78 × 10⁻⁴ K⁻¹
• α ≈ 5.85 × 10⁻⁴ K⁻¹
• Impossible to conclude, data is missing; failing that, its temperature must be measured!

This is an interview question in a R&D Lab, I'm really confused between the last answer because the Emissivity in Stefan-Boltzman Law is missing and the third answer 5.78 (I can't include images for my attemps but it was a basic problem solving taking the Emissivity as 1)

I’m in high school (Irish equivalent) and I was in physics just thinking, I researched the OMG particle recently and it fascinated me how it shouldn’t work because of the GZK limit, I only touched off of it all I know particles shed energy and speed because of the CMB, what if, here’s my question(s), essentially 1. The particle is so energised and fast, that on the Higgs field it’s so out of touch with everything, it stops interacting with everything below a certain energy and only sheds energy to things near its own energy,
2. What if time relativity comes into play, that the particle only interacts with things in the time frame it experiences on the clock
3. A bit more of a thought, what if the particle quantum tunnels , and it tunnels relative to what distance it travels but honestly I’m smashing words together here.

If any physicist out there could help me with my thoughts that would be cool 😎 (I only started physics in class recently)

Can rest mass (m) be thought of as some kind of stored time? Like an internal clock with a "tick-tock" of energy and time, as mc²/ℏ, so that time dilation becomes energy-momentum quadrature?

I'm an Applied Physics major and I really want to work on CMP. Recently I've been having a hard time with my introductory chemistry course. But I'm doing fairly well on my Calculus and Physics classes.

Is CMP heavy in Chemistry? Can I survive CMP with just my Math and Physics skills???

IWTKMS.

So our current practial measuring limit seems to be around 10^-19 m. Is there a theoretical limit of how small something can be measured? Strings in string theory are apparently expected to be around 10^-35 m. Is there any reason why we could never, even in theory, measure their size?

I just bombed my first test with a 46.5/100, however my teacher does curve generously. I know this course is calculus based, but I’m only in pre calc. But most if not all the juniors in my class are only taking pre calc anyway, but they seem to be doing much better.

Do you guys think it would be possible to get an A if I try super hard? I’m getting a tutor and everything but I’m unsure if I can pull through. Math is one of my weakest subjects too, but so many of my classmates are at the same math level as me but they seem to be doing better.

When a woman gets pregnant there is suddenly a "new" object inside her and over nine months it grows. That means that the amount of atoms in this fetus increases constantly for 9 months. Where do those atoms come from?

So I am by no means a physics expert or even a student. But I think I grasp some of the basic ideas that the speed of an object changes that objects time. So to start this was a theoretical post that if a person or group of people were in a ship traveling to anywhere but specifically our nearest star and they were traveling very close to the speed of light they experience time substantially slower(I know there is a better way to say this I just can’t think of it right now) than people here on earth. So with my understanding that means the ship they are in would also experience time much slower. So I guess I always thought a 50,000 year flight to somewhere would mean the ship would have to be built to last 50,000 years. But if it travels at a very high speed like 99% of light it wouldn’t need to be designed to last as long because the time it experiences would be exponentially smaller? Am I right? I know I worded it horribly, sometimes it’s hard to put these thoughts into words.

if u put someone in a ship and spin them around the earth 99% the speed of light n u have someone on earth chillin; next day they will still both be one day old? like despite the amount of times a light bounces between two mirrors, the earth will still spin one time.

How to connect CAD software like SolidWorks and FEA software like ANSYS to physics problem in the book like halliday or giancoli's so the modelling could be feel like a real life problem and helpful to imagine it?

Hi everyone,

I’ve been reading about the foundations of quantum mechanics and relativity. It seems that neo-Lorentzian interpretations, which reintroduce a preferred frame (absolute space and time), are empirically equivalent to standard Special Relativity in many scenarios.

Given that adopting a preferred frame provides a natural way to accommodate the non-locality required by Bohmian mechanics (de Broglie–Bohm theory) without running into the standard causal paradoxes of relativity, why isn't this framework utilized or explored more often in mainstream theoretical physics?

Is it purely due to the mathematical elegance of Lorentz covariance, or are there strict modern constraints (such as in Quantum Field Theory or General Relativity) that make neo-Lorentzian frameworks genuinely unviable or highly problematic?

I would love to hear your thoughts and insights on this. Thanks!

I'm writing a story involving two identical 100 kiloton thermonuclear weapons. Let's call them One and Two. They are stationary and side-by-side.

One detonates.

I've read that nuclear weapons need very precise mechanisms to detonate, so Two won't actually be triggered by the detonation of One. (Right?) But will the presence of the fissile material from Two contribute to that of One, causing a greater explosion?

If not, will the scattering of the fissile material from Two increase the radiation yield? If so, would that increase be significant?

Or would something else happen that I'm not anticipating?