I was thinking about how -40°c = -40 °F, and I’m wondering if there are any other pairs of units where there exists a non zero value which is the same in both units, I imagine this requires the conversion rate to be something other than just unit1 = k*unit2

Do any other common pairs of units have this?

I’m confused about why maximum diffraction occurs when the size of the gap is roughly equal to the wavelength of the wave.

Wouldn’t making the gap even smaller cause the wave to bend more, meaning there should be more diffraction?

So I know there is a hypothesis out there that we might be inside the event horizon of a black hole right now and the total mass of the observable universe would have an event horizon roughly the size of the observable universe. Let’s suppose that is true. And I know that we don’t really know how things work inside a black hole, but bear with me.

From inside the event horizon no light can escape to outside. But the event horizon is just the furthest out distance where that is true. Inside the event horizon I would imagine that light is even more unable to escape and so wouldn’t the line of sight in the direction of the center always appear black? Or is there some function of general relativity that means that light bends in a way that your eyes can kind of catch up to it?

I guess the crux of my question is if we are in a black hole, why isn’t the direction of the singularity completely dark? And if the answer is that it would be then why hasn’t the universe is a black hole hypothesis been taken into the back yard and shot?

Just curious, but last night I was slightly confused on how that would work, wouldn't the universe just consume the bubble? Because, the universe is basically expanding into nothingness, or maybe I was just tired.

My idea probably is kinda BS because Quantum stuff is weird and unintuitive...but that's my only idea when I think about it.

Free neutrons decay quickly into protons, so something keeps this huge pile of neutrons stable. Gravity keeping the e- from escaping is the only thing I can think about - but that would mean they constantly decay and likely lose mass through all the neutrinos produced in the beta decay that might escape because they're so smol and lightweight? Is that a thing? Do neutron stars slowly evaporate through neutrino emissions?

Edit: why does this get downvotes? If you don't want people to ask about physics they don't understand yet, don't name yourself askphysics 💀

This post was inspired by a post about 0 Kelvin.

What's the highest temperature that either has or could be reached anywhere in the universe?(Whether naturally or artificially)

If I could vibrate at relativistic speeds would I be able to experience time dilation while technically stationary? Expanding this a bit further. Do particles at sufficiently high temperatures experience time dilation and if so at what temperature does that become relevant?

Assume I didn't die or cause all the particles around me to explode due to friction

Now, since space is not a complete vacuum, in theory I should get somewhere eventually right? And the blades should keep spinning forever until they hit some atoms right so no need for constant power?

How can I learn physics from the absolute basics to advanced concepts? Please recommend the best books and a step-by-step study roadmap.

I get why it is impossible in practice. Makes sense. But I heard it's even theoretically impossible? Is this true, if yes, why?

I’m more focusing on a downward pitching sound effect that is made when a large/massive metal structure is collapsing or bending.

It’s kind of hard to describe what I imagine. I’m not focused so much on something like a metal rope/bridge suspension sort of sound effect, but I wouldn’t mind an explanation behind that too. Although, I assume there would mostly be similarities and some differences.

What I’m thinking of is a sort of slow-warping, pitching effect that sounds evil. It sounds like it has some interesting harmonics going on.

I don’t have an exact example. And what I’m imagining in my head is probably a combination of an exaggerated version of the real thing mixed with times I’ve heard bent or twisted metal.

Think large, massive, metal structure. Colossal. — Also, how does the size of the structure impact the sound that is made when it is bent?

At a certain size, will the sound be different? Surely, small pieces of metal sound much different, but at a certain point of increasing size what happens? I mean, how massive can we make a structure made of metal in the first place?

…And, what kind of metal? This is a significant factor at play. How does this affect the sound, and again, how massive could a structure of this ( –insert metal type– ) material be?

Thanks for taking the time to read.

How can it be produced?

Q1 is, as the title says, is it possible to intercept an object falling into a black hole before it reaches the event horizon?

A large black hole doesn't have crazy tidal forces near the event horizon, and a highly elliptical orbit can bring you arbitrarily close to the event horizon and then back out again without needing any acceleration.

It seems obvious there has to be SOME point at which catching up with a falling object is still possible - if you were far from the black hole, in free fall, you would obviously be able to move something towards the black hole with one hand and catch it with the other.

Q2. What is the latest time/distance at which it is still possible to intercept and retrieve the object?

I've seen people saying that infalling objects actually cross the event horizon in a finite time as their mass contributes to the size of the event horizon and it 'moves up' to them within a finite amount of time, is this true? If so, is this the point where the object actually crosses the event horizon from an external frame of reference and retrieval is no longer possible?

Q3. If the answer to Q2 is "there isn't one", the event horizon moving up idea is false, and the object really does never cross the event horizon from an external frame of reference?

Does this imply that the only matter actually inside the black hole is the matter from its formation and everything else is in a spherical shell around it?

I know there are solutions which say that from the frame of reference of an object fallling into the black hole it crosses the event horizon and reaches the singularity in a finite amount of time, but how is this compatible with the concept of black holes evaporating due to Hawking radiation?

If the infalling object can still be intercepted forever, how can it have entered the black hole before it evaporates?

The usual example of faradays law is to imagine moving a magnet into a conductor loop, and seeing that it induces an electrical current.

My confusion is that if we consider from the reference frame of the magnet, the magnetic field does not change, and thus there shouldn't be an induced electric field through the loop.

I have seen online that we can supposedly use Lorentz Force Law and say that the current is due to the magnetic force, but this doesn't make sense to me because this would require a magnetic field perpendicular to the velocity of the loop. But Faraday's Law predicts an emf even without any perpendicular magnetic field.

Any help in making sense of this would be appreciated.

EDIT: I am trying to understand in the context of Maxwell equations. From the perspective of the loop, we can say there is a current because the change in magnetic field induces an electric curl. However from the magnet's perspective, no such change exists, and we should not expect a change in the electric field.

This has been asked many times but there is one thing I do not feel was answered sufficiently for my understanding. It is understandable that the holes in the mesh are smaller than the microwave wavelength, but what exactly does that affect? The wavelength is something measured in the direction of propagation, so why do the size of the holes in the transverse direction matter? The amplitude of the wave isn't a physical dimension right, just a measure of field strength?

I was reading on r/physics about an experiment that captured a positron for one month. My understanding is that particles are excitations in a field and not a physical object, so what exactly is being captured? Is the excitation being captured? How does it go a whole month without some sort of event causing it to dissipate or collapse?

I imagine it’s something that mathematically seems more obvious than trying to conceptualize it, but as a layperson some sort of analogizing alongside a more technical explanation would be very appreciated.

An observer stationary on Earth's surface sees light from celestial objects directly overhead very, very slightly blueshifted by the time dilation caused by Earth's gravity. On the other hand, an observer free-falling near Earth's surface sees a far larger redshift caused by his motion away from the lightsource. It requires very little speed for the redshift to completely overwhelm the blueshift.

I have read, though, that an observer free-falling into a black hole would eventually see light from above blueshifted by the absurdly intense time dilation close to the black hole's center.

My math capabilities are terrible.

I believe I have correctly calculated the redshift at any distance from a black hole's center by assuming the velocity is straight down at the local escape speed. That is the velocity an object would have if it began falling with zero velocity from infinite distance.

But I'm not so sure about calculating the time dilation and resulting blueshift. I calculate that the blueshift just parallels the redshift, so is always much, much less than the redshift.

What actually happens?

What would happen if you were to somehow break open a liquid nitrogen cylinder at the bottom of an oceanic trench?

Let’s presume a method of getting it down there without imploding on the way down.

How does super cooled water behave under 15,000 psi?

Please forgive me if this is a misinformed question or has been asked before.

So, if I understand correctly, an observer moving at a fast speed relative to Earth will experience less time than has passed from Earth's point of view. For example, a person leaves Earth, travels very fast for 1 year, and returns to Earth to find that people on Earth have experienced 1.5 years.

Is it possible, in theory, to move so slowly relative to Earth, that one could leave Earth for one year of subjective time and return to find that 0.5 years had passed? Or some smaller discrepancy of time, at least?

If particles like electrons and quarks have no volume, then how can they have mass? Is it just that they do have volume, its just very, very small, or do they actually lack any physical volume?

Edit for follow up question: let's say we were able to gather 1 kg of electrons in a small enough space to put on a scale. The scale would register a weight, but there wouldn't actually be anything physical on the scale? Is that correct and if so how tf?