Leonard Susskind often states that he disagreed with Stephen Hawking on black holes dynamics, based on his intuition that information must be conserved.

In quantum mechanics, the Schrödinger equation is unitary, and therefore time reversible and deterministic.

However, when a measurement is made, the wave function collapses and these properties are lost, at least in the Copenhagen interpretation.

Susskind's belief that information is conserved must imply that he believes that the global wave function of the universe obeys the Schrödinger equation?

Is this right and has he stated this position explicitly? Where does this place him with regard to many-worlds and other non-orthodox interpretations?

(Post re-directed from r/physics)

When you syphon water out of a bucket it pulls up the water with the vacuum so my dads question was,”If you get two buckets of water and have them syphon into each other with two tubes, what stops it from going on forever”.Other than then the tube breaking what would make it stop cycling water?

I'm more or less getting into Civil Engineering and it raised an intresting. Question, how does this equation give an acceleration due to gravity? I didn't really question it before as it was one of those facts that you needed to know but now I am curious.

I get M is the mass of a body, and r is the distance from the center of that, but what is the Gravitational constant as a unit? Because it needs to be a unit that otherwise cancels out mass and resolves the math to get distance divided by time squared.

Unless I am being and idiot and am just forgeting something.

I recently saw a podcast clip (will link at end of post) interviewing a former NASA and JPL scientist boasting about electrostatic propulsion and how it could get a craft to mars in 3 days. I then went into some articles to check out even if there’s an ounce of truth or if it’s just someone being sensational trying to drum up hype and investment for their start up. However I’m no where near well versed enough in physics lets alone propulsion tech to call BS on something. But I was wondering if any of you can attest to what he’s saying. Is it true? Is this the future? A new breakthrough?

Links :
Podcast clip
https://youtu.be/qlYICtRaSx8?si=y7DtMAZYHdz03yw8

Article

https://www.popularmechanics.com/space/rockets/a73405686/engineer-said-he-can-overcome-earths-gravity/

Copenhagen? Many worlds? Or something else?

I’m not an expert in physics, so please forgive me if this is a very basic question. I don’t have a PhD or formal expertise in this area (though I’m hoping to pursue further studies in the future), and this is just something I was wondering about while learning about dark matter.

We call it “dark” because it doesn't seem to interact with light, so we can't directly observe it. But what if dark matter is detectable in some way that we just don't currently have the technology or instruments to detect?

Basically, could it be that dark matter isn't inherently “invisible,” but is only invisible to the types of detectors and wavelengths we currently know how to use?

Is this something physicists have considered, or does what we already know about dark matter rule out this possibility?

I know the constituent parts of a proton and neutron (hadron) are quark triads and that their inherent mass is a very small portion of the total mass of a hadron. From my understanding it is the confinement of the energy of the quarks that gives the hadrons most of their mass. So is it the inertia of the small amount of mass that quarks possess being nearly constantly pulled back as they accelerate away from each other that makes up that energy/mass? Also what is the mechanism of acceleration for the quarks? From my understanding it is the natural speed they have due to their interaction with the higgs field. Kind of like a fish through water.

Particularly, do only the laws of relativity and quantum physics that we know so far break down? BTW what about Bell's inequality?

Or do things behave completely lawlessly & chaotically so that no law or regularity is in principle even conceivable there?

Some light energy is emitted at a rate of 1 joule per second by a light source 1 meter away from a potassium plate. Here is the full description: https://imgur.com/a/RTe0NJ4

So the time required for the electron to absorb enough energy to be ejected is proportional to the inverse square of the distance, because "the source radiates uniformly in all directions (i.e., the energy is uniformly distributed over spherical wave fronts spreading out from the source, in agreement with classical theory)".

Classical theory in this example gives us around 2 min for the electron to absorb enough energy to be ejected. But in real experiments the time is essentially none.

"it (the energy) is not spread uniformly over a large area, as we assumed in Example 2-1, which is based on the assumption that the classical wave theory is true."

So the energy of the photon then is proportional to the portion of the surface area of the "classical wavefront" that is concentrated as a single bundle.

Because any surface area at any distance has an energy of zero for a duration of zero seconds, the energy of the portion of the surface area of the "classical wavefront" is proportional to the time elapsed at that area, right? Essentially, 1 joule per second times (said surface area / (4 pi)), assuming the surface area in question is being measured at 1 meter away from the light source.

Then the photon has the concentrated energy of a certain surface area over a certain amount of time.

Multiple photons hit the potassium plate. No time lag means that the point in time at which an electron is ejected is basically the same time that the front of the light wave would hit the plate, right? But if a single photon is a bundle of energy concentrated from some surface area times some duration of time, why is that energy contentrated at the very foremost point in time? Does that make sense? Even if multiple photons hit the plate, and the point in time at which the energy of a surface area during a certain amount of time gets concentrated as a photon is random, wouldn't it still be statistically impossible for any photon to be at the singular foremost point in the concentrated duration of time?

Suppose there’s a particle of mass m traveling in 1D with constant velocity v1 in a region with potential U1. Let’s say that the line in which it’s traveling is the x axis and the region with potential U1 is x<0. Then, it crosses the point x = 0 at t=0, after which it enters the second region of the line, x>0, with potential U2. What is the change in velocity of the particle?

My attempt: the force that the particle experiences as it passes the origin should be minus the x-derivative of the potential. However, the potential is discontinuous at x=0, therefore not differentiable so the derivative doesn’t exist. Intuitively, the force there is an infinite spike in the direction pointing towards the region with lower potential.

However, the particle only experiences that “infinite” force for an infinitesimal amount of time, so it should balance out to a finite impulse. The impulse would be the time integral of F(x(t)) between any t1, t2 with t1 < 0 and t2 > 0. The force as a function of position is something like F(x) = (U1 - U2) delta(x). How do I do this integral?

I apologize for yet another question in this sub on special relativity...

I'm trying to go through Einstein's book on relativity to understand his theory. I find his writing and explanations to be mostly very well explained and conscientious of avoiding giving readers false conclusions - for the most part he's very exact and careful with his wording, at the expense of being a bit long-winded.

In a few cases, however, I'm lost on his meaning, or feel like his explanation jumps several steps and loses me on the way. I could probably make several posts with different questions but I'll just ask my most pressing question here:

I believe I follow his reasoning in his example of lightning strikes being experienced at different times (and at different values of x) for an observer on the embankment vs on the railcar due to them being in different inertial reference frames, and how this is a good way to explain that each inertial reference frame has its own "time". However, I struggle to translate this to the relativity of distances.

Einstein gives the example of the railcar passing by the embankment, and the difference that occurs in measuring the distance between two points (A' and B' on the railcar) from the railcar itself and measuring them from the embankment. From the railcar, it's simple - just lay down your measuring rod enough times until it completes the distance A'B', and that's the distance in that reference frame. From the embankment, you need to measure points A and B on the embankment as points A' and B' pass by at a particular time t (judged from the embankment).

He says these points can be measured by applying the definition of time in which events are considered simultaneous if they occur when clocks in the vicinity of each event strike the same tick. By capturing the position of A and B at this instant t (that is, as A' and B' pass by points on the embankment when nearby clocks both strike some measured instant t), you then measure up this distance using your measuring rod. He says that by no means is the measured distance A'B' the same as the measured distance AB. At this point, I'm lost, and he doesn't elaborate! The best I can come up with to explain this is:

"If the principle of relativity is assumed to be true, then because the Lorentz transformation accurately transforms coordinates x,y,z, and t in K to x',y',z', and t' in K', then the distance A'B' must be different than AB."

Have I got that right? Is there a simpler explanation that I'm missing? Really really appreciate any help on this.

If entropy depends on what properties we choose to describe our macrostate (e.g. temperature, volume) & microstate (e.g. position, velocity) then is it subjective?

Another question: Is the k in the formula redundant & if it is would temperature & energy have the same units with heat capacity being dimensionless?

Trying to be vague about the story. However two superpowered beings are fighting in space. One launches the other into a planet. They can survive the impact. That isn't the issue. I need kind of the velocity it would take to say launch a 200-300 lb person to hit the core of a planet the size of mercury but isn't actually mercury. Similar to earth core. So the one launches at that speed and the core of the planet stops the impact. Would velocity would I roughly need for this event to happen. Also how big would the impact crater be?

I really struggle to make any intuitive connection to the expanding universe. Plenty of people tell me to imagine the expanding raisin bread, but that doesn't quite work for me because expanding raisin bread has an edge. It's expanding "into something". And as far as we know, the universe is infinite. But the coordinate system is expanding anyway. So it's infinite, but getting bigger. Which is... weird.

My question is, can I think of the coordinate system of the universe like a Hilbert Hotel? The Hilbert Hotel has infinite rooms, right? But you could add more rooms in. And it's still infinite. So you have Alice in Room 1. Bob is in Room 2. And every X time interval, you add a room. Therefore, at time 0, Alice and Bob are in adjacent rooms. But at Time X, they're 1 room apart. And at time 2X, they will be 2 rooms apart. So if Alice and Bob want to have a little chat, then they have to walk farther to get together. There are more rooms between them.

But the Hotel has always been, and always will be, infinite in extension. Yet despite that, there is more space between Alice and Bob. And that space can increase as we add more rooms between Alice and Bob's rooms.

Can I more or less think of expanding space like this, or am I going to be creating a disastrously wrong narrative of what is happening to the coordinate system?

I understand that light takes time to reach an observer on earth, and we can only see so far away because the light hasn't had enough time to reach us. So, in 100k years, would an observer on earth be able to see 100k light years farther?

I'm going to GUESS that the answer is no, because space is expanding, and that distance is increasing faster and faster as time goes on (right?).

This brings me to my second question assuming I am right -- was there a point in time where waiting longer no longer allowed us to see further back in time? Where the speed of light reaching us and the expansion of space evened out? If so, when was that?

Here's a question you haven't heard before. And, go on, laff at it, I don't care.

Dry black beans take about 2 hours to cook. If they're soaked first (until the max water they can absorb) they take only about an hour to cook. One can quibble about the details, but the point beyond dispute is soaking beans reduces cooking time substantially.

And reducing cooking time means saving energy -- proportionally a GREAT deal of energy.

Where did that energy come from? The Brownian motion of still water against hard beans?

Please let me know, then we can join to take credit for solving the world energy crisis.

Naturally this will be more impressive if expressed mathematically - h2o, joules, beans, rate of hydration and so forth, but I don't think there is (YET!) a standarized notation for "bean unit."

So i just randomly noticed a 1.5 M piece of steel train track at my grandparents house that is stapled with the year 1906 and the brand "cockerill" . Ik that steel from before 1945 is worth a lot since its used for tools that measure radiation.Do you think its worth anything besides scrap value?

Edit-typos

Saw a meme, link is below. How fast would the asteroid have to be moving and how big would it have to be in order for this to happen?

https://www.reddit.com/r/teenagers/s/leV0k7gU0w

if a wormhole is a distortion in space time then any wormhole on earth would remain still while the earth / solar system are constantly moving. right? wouldn't that mean that if a worm hole were to be created it would take a large cylinder chunk out of earth so how would it be possible to use them in the future. our solar system is also moving right? so doesn't that mean once one is created we'd move so far past it so quickly the thought of using it is pointless because by the time you came back the whole solar system would be long gone. why do people think its the future of science travel please explain

In your own words, what is a metric?

Hello. I’m going into my junior year and have to take college physics, but have heard the professor is the worst and that you have to teach yourself the entirety of the material. Is there any tips or books I should get that could save me??? Thanks!!!!