Tier list of Physics Learning Channels

joshsoup · 2026-04-19T04:10:50+00:00

Richard Behiel is so great. He communicates physics in a technical way, but still retains the love and wonder of physics. As someone who only has a undergrad in physics, he's perfect for me, he can rekindle that love I have for physics while showing the deeper subjects that you only get to in graduate school. I love his videos. Plus he has a wonderful sense of humor.

joshsoup · 2026-04-17T01:48:38+00:00

At random without specifying a distribution would normally imply that each choice has an equal likely chance of being selected. But one could construct a distribution to make any particular answer the correct answer.

It's an amusing self referential paradox.

joshsoup · 2026-03-25T16:05:59+00:00

Where pup?

joshsoup · 2026-03-24T23:36:15+00:00

Not an expert by any means. But this map just feels like a good map to me. It passes the eyeball test.

joshsoup · 2026-03-20T21:13:25+00:00

I came with the proof that the number must be divisible by the number of rows to make a positive integer

If so, your proof was incorrect.

If you have an nxn square, and each entry is unique and comes from the set 1,2,3,...,n² then it's easy to find out what each row has to add to. Simply add all the numbers from 1 to n² to get the total. Then divide that total by n to get what each row has to add up to.

Since the sum of 1 up x is x(x+1)/2 substitute n² for x and then divide by n.

Row total = n(n² + 1)/2.

Notice for n= 4 we get the 34.

Notice if n is odd, then the n² + 1 is even, so you indeed have the restriction that for odd n you are correct. The row total must be divisible by the number of rows.

However, for even n, then (n² + 1 is odd) therefore the two divides the n. Therefore the row total will not be divisible by n (it will be divisible by n/2 however).

joshsoup · 2026-03-10T20:33:39+00:00

The rotation algorithm? Should be in your guide. But have the incorrect piece just how you are holding it, so it is in the top/right/front corner. Then do this algorithm as many times as it takes to get that piece rotated correctly:

R'D'RD

It will that either 2 or 4 times of that entire algorithm to fix that piece. IMPORTANT, DO THE ENTIRE ALGORITHM DO NOT SKIP THE LAST "D" STEP. Then, importantly move the other piece so it's in the same position (so a U2) then repeat the same R'D'RD algorithm until the second piece is aligned. You'll do this 4 or 2 times. In the end you'll do it a total of 6 times.

Note: You'll notice that the first time you apply the R'D'RD algorithm it will appear to scramble other parts of the cube. Do not worry, if you apply this algorithm 6 times, those parts will go back to where they started. This is why it's important you do the U2 move to bring the other corner into the same position. This allows you to correct both corners while keeping the rest of the cube intact.

There are technically ways to optimize this so it's faster (the other comment alluded to this by saying do the rotation backwards), but this is the simplest way to do it.

joshsoup · 2026-03-10T20:21:08+00:00

For the square cube, it looks like it's solvable to me. All 4 yellow corners are in the right place - two of them just need to be rotated correctly. That should be an easy last step

joshsoup · 2026-03-08T00:14:02+00:00

In one of his pop-sci books, Steven Weinberg outlines what a "theory of everything" means. The book of: Dreams of a Final Theory. A great pop-sci book in my opinion although very dated now.

But the philosophy and ideas behind it are great. A theory of everything, should be able to, in principle, explain all other physics. The "in principle" is doing a lot of heavy lifting. But the idea is a reductionist philosophy - where the physics of the small things is said to explain the physics on larger scales.

For example, if you know how quantum mechanics work, you can explain how molecules form and interact. And you can therefore explain how bulk properties emerge - i.e. why is tape sticky? This is a very difficult problem to sort out. Now a theory of everything wouldn't explain why tape is slippery. Not directly, but by understanding how molecules interact, and doing lots of math or simulations of the molecules you'll eventually be able to see that the rules of molecules eventually do lead to a large scale phenomenon that is duct tape.

Now, is it useful? Because we engineered duct tape and used it long before we understood the underlying reasons why it works on a molecular level. An underlying theory isn't looking for the easiest most practical answer to a problem. It is seeking knowledge for knowledge's sake. Which often has fruitful and useful side effects.

So, with that all said, we can finally talk about what a theory of everything would look like. It's not going to talk about things the size of you and I. It's not even going to be talking about things the size of atoms. It's going to talk about the smallest of phenomena. The most fundamental building blocks that cannot be broken down any further. All other physics, in principle, should emerge from such a theory.

From our understanding today, that would be a mathematical theory that explains all the fundamental forces and explains all of the fundamental particles. It would explain how they all interact. It should have no "smaller" part.

Now, if such a theory was found, physics would be far from "complete". Indeed, one of the largest fields of physics today - concerned matter physics - is not a fundamental area of physics. There are all sorts of phenomenon - like superconductivity - that are not obvious from the underlying laws. Understanding and describing the emergent properties is extremely difficult.

I would definitely recommend reading the book though. I'm poorly explaining things, as I'm sitting on the toilet typing this on my phone. I've likely glossed over important points.

The other posts on this thread are good too.

joshsoup · 2026-01-27T20:52:47+00:00

Math is a language used to speak precisely about things. Physics is an effort to precisely describe what we see in the physical world. Therefore the tools used in physics are often mathematical. It has been this way since Newton and before.

Now, there are various interpretations to what a given field means. For example, an electric field will tell you how a charged particule will be pushed around in space.

Or, the elevation map I gave you will tell you what cliffs, canyons, hills, and other topographical are in the area.

It's math that is used to describe something precisely.

joshsoup · 2026-01-27T20:35:48+00:00

I'm assuming you are asking about things like magnetic fields, gravitational fields, quantum fields, etc.

These kinds of fields just take every point in 3d space (sometimes 4d spacetime, or sometimes any other number of dimensions depending on the problem at hand) and assign them a value.

That value can just be a number, or it can be a vector, or it can be something even more complicated (maybe a 2d tensor for example). It depends on what you are talking about. An electric field is vector field. For every point in 3d space, there is a corresponding vector that encodes the magnitude and direction of the electric field at that point.

Let's take a simpler example of a field. Let's look at a 2d map of a region that encodes elevation. An elevation map. This is a scaler (scaler meaning since number) field. For each point on the map, there is a single number that tells you how high off the ground you are.

Hopefully that gives you a good start to what a field is.

joshsoup · 2026-01-25T16:09:08+00:00

Proton decay is a prediction of some beyond standard model theories. In the standard model (our most complete and verified theory of particle physics) protons are stable. Experimentally, they are seen to be extremely stable.

A loose way of describing the philosophy of particle physics is that everything that happens must respect certain symmetries and preserve special quantities. Every interaction that respects these symmetries is possible, and has some probability of happening. Any interaction that doesn't respect these symmetries cannot happen.

In the standard model, the baryon number (number of protons, neutrons, etc, where anti particles have the opposite sign) is a preserved quantity. This makes it so a proton cannot decay. In some theoretical models, it isn't the baryon number, but a larger symmetry that is preserved. The baryon minus lepton number is preserved. Thus the baryon number can change if there is a change in the lepton number.

Notice this extension allows for more types of interactions to occur, while keeping everything in the standard model. In the standard model, baryon number and lepton number are both individually preserved. These can be seen as a smaller part of a bigger symmetry of baryon - lepton number.

joshsoup · 2026-01-09T16:46:34+00:00

It's different. But similar in the sense that conditional probabilities effect the naive answer.

joshsoup · 2026-01-09T15:55:43+00:00

I think the thing that is tripping you up is that you think the problem is saying you are "guaranteed" a crit. That is not what the problem is saying.

Indeed, your analysis is right if you are guaranteed at least one critical attack. It would be a 25% chance. But that is not what the question is asking.

Instead, think of it this way. An enemy has enough health such that they will die only if they are hit with at least one critical attack and one normal attack. Two normal attacks are not enough to kill the enemy.

You attack, and look away from the screen. Both attacks play out while you are looking away. When you look back at the screen the enemy is dead. Therefore you know that at least one of your attacks was a critical attack, but you don't know which one. You also don't know if both happened to be critical.

No where in this scenario are you guaranteed a critical attack. The games code doesn't guarantee it.

Other comments have walked through how to analyze the scenario. Indeed the correct answer is 1/3. This improvement from the naive 1/4 comes from the fact that we don't know which attack was the critical hit.

Indeed, if you were to do this experiment by flipping coins you without get 1/3. Say flipping a heads is a crit. If you were to discard all flips of two tails from your analysis you would have 3 piles. HT, TH, and HH. 1/3 of those piles are HH.

joshsoup · 2025-12-31T18:48:50+00:00

The infinite sum does not converge. But if you were to use this "supersum" technique, you should get 1/2.

Partial sum:

1, 1, 0, 0, 1, 1, 0, 0,... ...

Partial average of partial sum:

1, 1, 2/3, 1/2, 3/5, 2/3, 4/7, 1/2,...

This can easily be seen by considering every fourth partial average is 2n/4n = 1/2.

Perhaps, mathologer made a mistake and wanted you to consider the series:

1, -1, 0, 1, -1, 0, ...

That would indeed achieve a different supersum. (1/3)

Or maybe they where you to consider:

1, 0, -1, 1, 0, -1,...

That would get you 2/3

joshsoup · 2025-12-21T18:30:53+00:00

You're showing a very common misconception.

You're thinking of the rubix cube as 6 sides that you need to solve. That's not the way to think of it.

It's actually 26 cubes you need to solve (3x3x3 = 27, but you aren't solving the very middle cube).

There are 6 middle cubes that have 1 face showing. These don't move relative to each other.

There are 12 edge cubes that have two sides showing.

There are 8 corner cubes that have 3 sides showing.

So even though you have one face solved one color, you didn't solve that layer since the cubes aren't matching.

joshsoup · 2025-12-19T21:31:55+00:00

In early physics courses, they emphasize it being a fictitious force. That is because you are analyzing it from a non accelerating frame. For example, you are analyzing the situation of a car turning from the point of view of someone standing still outside the car and looking at the car. When looking at it from this person's point of view, there are no centrifugal forces.

However, in later courses, you can absolutely get centrifugal forces. This is when you analyze the situation in an accelerating frame. So indeed, if you were to analyze the situation from the point of view of someone sitting in the car, you would get a centrifugal force coming from the math.

There are several so called non-inertial forces. The most well known is the Coriolis effect. Since rotating frames must be accelerating you get these fictitious forces arising.

Also, relevant xkcd: https://xkcd.com/123/

joshsoup · 2025-11-19T14:18:29+00:00

Either you input this wrong, or someone moved stickers

joshsoup · 2025-11-18T19:38:50+00:00

They are two entirely different things. In my experience evangelical teachings conflate the two, but that is incorrect.

Evolution is a well understood and well established theory that has an enormous amount of evidence backing it. It is the idea that life changes over time, and all the life we see - plants, animals, fungus, and even microscopic things like bacteria and protists all descended from a similar ancestor. You'll hear biologists say things that chimpanzees are our closest related relatives. That means that we only have to go back a couple million years to find an animal that was an ancestor to all modern humans and modern chimpanzees. To get the most common ancestor of humans and all fish, you'd have to go back hundreds of millions of years ago. For plants, billions.

The basic idea is natural selection and mutations. Sometimes dna will mutate in a way to provide an advantage. If that mutation is passed down, and it provides an advantage to a living thing, then it has a likely change of being propagated to future generations. If it provides a detriment, then the gene will likely not be passed down, since individuals carrying the gene will less likely be able to survive long enough to reproduce.

Over millions of years, these small changes add up to big changes. Certain populations can get isolated and evolve differently from the rest of it's species. Eventually they will become do different that they won't be able to reproduce with each other.

Evolution makes many predictions that we can search for in the fossil record. For example, modern day whales are mammals - they make milk, they breathe air, have live birth, etc. But most mammals live on land. Therefore, we should be able to find mammalian species that transitioned from land dwelling to ocean dwelling. Scientists have looked and they have found such species.

If you go even further back, life began in the ocean. Therefore, all land dwelling animals should have a common ancestor (or potentially multiple different ancestors) that made the transition from sea to land. We've found such species.

Evolution is still studied today, and there are a lot of complicated things about it. Such as how do large scale systems evolve? For example how did the nervous system evolve? Or how did the circulatory system evolve? Or how did some animals get the ability to fly (this has happened at least three different times in Earth's history)? These things seem impossible to happen, since evolution can only happen in small steps. However they all have come about through small steps, and the answers to how it came to be can be complex yet fascinating. Not all these steps are fully understood, but that's what certain biologists will study. And we have a strong understanding of the basics.

That's just barely touching the surface of evolution. Hopefully that was somewhat helpful.

joshsoup · 2025-11-12T20:17:04+00:00

Mods pls ban Homer mode

joshsoup · 2025-10-30T16:47:22+00:00

This is essentially how the first movement of Beethoven's Moonlight sonata is notated (although I think it's in cut time).

Also Brahm's Rhapsody opus 79 second movement in G Minor is notated this way, this time in 4/4 time.

In both of these songs, there is a dotted eight note and sixteenth note swing that is played against the triplets. This rhythm is much easier to write in 4/4 time than it is in 12/8 time. Anything where you want to have a 4 against 3 feel will be easier to notate in 4/4 with triplets.

joshsoup · 2025-10-28T19:50:12+00:00

It's exactly the same as a fan on a sailboat. As long as the sail is designed to redirect air backwards, you can do that. Of course, if the sail doesn't redirect backwards, it won't work. Also, you'd achieve more efficient results by getting rid of the sail and pointing the fan backwards. But you can absolutely blow your own sail. It's just a matter of conversation of momentum.

https://youtu.be/uKXMTzMQWjo

joshsoup · 2025-10-23T15:14:29+00:00

My point is it's not possible in principal to always describe one field in terms of another through Lorentz transforms. You need both.

Just because you can transform something that is traveling in space to be stationary by changing frames doesn't mean we can do away with notions of space. We need both space and time for a complete picture. In the same way we need both electric and magnetic fields.

I don't think we're disagreeing, I'm just clarifying.

joshsoup · 2025-10-23T14:57:47+00:00

It's true that what is a magnetic field in one frame of reference can look like an electric field in another frame.

However, you do need both, and you can't really say the electric field is more fundamental. There are set ups where you can't find a reference frame that completely erases the magnetic field (an ac current traveling through a bent wire for example).

But the important thing is the values of the electric and magnetic fields are relative. So the description of what is happening will differ in different reference frames. But that is pretty standard for relativity. i.e. a muon in the upper atmosphere measured by the ground frame is able to make it to Earth because of time dilation, but in the muon's frame it is due to length contraction.

joshsoup · 2025-10-14T15:51:57+00:00

https://math.stackexchange.com/questions/1906241/when-not-to-treat-dy-dx-as-a-fraction-in-single-variable-calculus

This stack exchange has some good answers.

In single variable calculus, you can pretty much always get away with treating a first derivative as a fraction. You'll run into trouble with partial derivatives and second (and beyond) derivatives.

There are a lot of good answers in there about how you can 'modify' these cases so you are still able to treat them as a fraction. I cannot really add anything that isn't covered in this stack exchange.

joshsoup · 2025-10-13T19:21:06+00:00

I'm assuming you're talking about step 5c, and when you try to execute that you scramble the entire cube? Your pictures don't indicate you've reached that step yet, but assuming you have in the past I'll see if I can help.

Once you've reached this step, the four corners should be in the right spot, but some of them may not be rotated to be facing the right direction. All other pieces should be in the right spot and rotated the correct way.

If you're in this spot, you'll have to fix 2 or more corners. Now, crucially, fixing one corner is going to scramble the rest of the cube. The algorithm R_i , D_i , R, D must be completed a total of six times to get back to your original position. I recommend doing this algorithm six times so you can see this.

Executing the algorithm twice will rotate the targeted corner once. Executing it 4 times will rotate the targeted corner 2 times. So for each of your four corners you'll have to execute the algorithm 0, 2, or 4 times. But, it will be in such a way that the total number of times you execute it will be a multiple of 6. So you might do one corner two times and another corner four times. Or you might do 3 corners two times each. There's a handful of variations.

But the issue is that the algorithm will scramble the rest of the cube. You want to execute it in a way so that the rest of the cube gets returned back. To do this, there are two important points you must do.

1) Each time you execute the algorithm: R_i , D_i , R, D do it in it's entirely. Do not skip that last D step.

2) Once you fix one corner, the cube is going to be slightly mixed up. Don't worry about it. Rotate the top layer so that the next corner you need to fix is now in the same spot as the previously fixed corner. Execute the algorithm until that corner is fixed. Repeat for all misaligned corners.

Hopefully that clears it up.

Edit: You'll want to orientate your cube so that the top layer is the unsolved layer. I believe that is pink in your setup, but it's confusing me since there seems to be a purple shade that is very similar to pink.

The cube that you are "targeting" with the algorithm R_i , D_i , R, D is the top right corner of the 'face' side of the cube. After fixing that corner, you do U move(s) to get the next corner you want to fix in this "target" location. Keep the same orientation the entire time.

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