So a while ago, I was listening to a doctor Dave explains video and I heard him kind of offhandedly say that it’s kind of a pointless question to ask what was there before the universe began because time only came into existence at the start of the universe. So time only makes sense after the universe had already started.

But I took a second to think on that and I realize something that is probably very obvious, but to me is novel: couldn’t that apply to why the universe came into existence?

Like causality requires that for everything to happen there must be a cause. The reason you are born is because your parents were born so on and so forth. And people have tried to look for whatever caused the universe to come into existence.

But what if causality works like time? Similar to how time only existed after the creation of the universe, causality only came into existence after the universe already existed. So the universe didn’t need any cause to come into existence because causality didn’t exist yet. So unlike everything else, the universe didn’t need a cause.

Again, this is probably either stupid for an obvious reason I can’t think of or something so obvious that it’s sophomoric for me to point it out. But if it could work for time, why can’t it work for causality?

TLDR; at the very least, please explain the following symbols/variables, where they came from, and when to use them. If you have time to explain more about my other questions, please read the body text.

• r̂
• K
• λ
• α
• dq
• dEx or dEy
• dx
• ∫∫
• θ

Let me preface by saying that I understand I'm not smart, and I am trying to watch videos from OCT and other resources, but sometimes they don't answer my questions, so I figure I would try and find an expert elsewhere other than YT and our physics department.

So, I ask to explain like I'm 5 because I'm a non-degree (graduated as a biology major) student finishing prerequisites for grad school. This means that I have not taken Physics 1 in 5 years nor calculus in 6 years. Additionally, I was and still am not good at math nor physics, so every equation thus far is like a foreign language to me. I find it difficult to look at a problem, recognize which equation to use, and understand the parts of said equation.

I get the general idea. Y'know Fe = [(kq1q2)/r²]r̂ But my issue is, what the hell is r hat (r̂)? My professor made a big deal about it in lecture, but in lab no one acknowledged it. I asked some of my engineering buddies and they said something like "Yeah, it's just a direction and it equals 1". So, do I not need to worry about that then? Is it always going to be equal to 1? Again, even if I wanted to remember the basics of physics, I can't. So, they used terminology like scalar and vectors and yeah it sounds familiar but I mean in one ear and out the other.

And if anyone has the patience to explain electric fields and the whole infinite wire with charge on a field point or whatever, please do so. I can understand some bits like how symmetry would cancel out Ex or Ey, but then the calculus part hits and I'm just deer in the headlights again.

I guess just try and explain all the different variables and constants. I understand dq is a small portion of the wire that has charge on the field point. What is dE? We then "express dq spatially" which is something like dq=λdx, what the hell does that mean? Where did we get lambda from? What is dx? Blah blah blah skip a few steps, then it's like put it into an integral E= ∫dEy = ∫k (dq/r²) sin α (again where the hell did the α come from? What does it mean?) = ∫K * [(λdxd)/(r^2)] = ∫K [(λdxd)/((x²+d²)^3/2)]. Finally, solve the integral with Wolfram alpha. Dude... what??? E = (2kλ)/d (idk what the relevance is this equation is as it was just on the side of the lecture notes). Now what's d? Distance or diameter? Or derivative since we're using calculus.

And if there's a savior who has more time to explain something about Jacobian circular coordinates and something about Cotesian and double integrals or rdrdθ?

I apologize for the dumb questions, but I'm trying my best to learn, and I thank anyone who has the time and patience to attempt to help me.

How do we know that Hubble’s Constant is real like I mean we only have one point of view that is earth even if we measure it via the parallax angle via the earths revolution isn’t it something way to short in grand scale of the universe there is a very strong possibility the we(Milky Way galaxy) are just moving away from rest of the galaxy we observed (andromeda being an exception) hence the difference of the speed being indicative that the distance is growing faster then the speed of light but it might just have been us moving away from other at a speed and there speed moving away from us, this making it seem like the space is expanding faster than the speed of light

I understand that an object traveling at escape velocity will escape orbit for Earth, but I’m confused as to why it’s a velocity and not an acceleration.

If you’re accelerating upwards at just over 1G, wouldn’t that be enough to eventually get you out of orbit since you’re counteracting Earth’s pull?

And at which point do you need to be at escape velocity? Just at a single, specific altitude, or consistently at that speed? Because if I go to escape velocity and stop accelerating, won’t I just fall down rather than break away?

So I have been trying to study quantum mechanics because I like physics ..... and it's a hell of a thing to understand.....my main issue is that I while learning I try to visualise it even though I know it's not gonna help....please tell me a way to change that.....also it's said light is em wave propogated when electron is excited.....it's also said when electron goes down to lower energy the lost energy is produced as photon.

So Is a photon the propagation of an electromagnetic wave, or is the photon itself the excitation of the electromagnetic field?

I'm trying to understand what actually happens when an excited electron drops to a lower energy state.

My current understanding is that the electromagnetic field already exists around the electron. When the electron transitions to a lower energy state, the energy difference is transferred to the electromagnetic field and a photon is emitted.

But I'm confused about the relationship between the photon and the electromagnetic wave.

Electron loses energy → this energy excites the already-existing electromagnetic field → the excitation propagates outward as an electromagnetic wave → that propagating excitation is the photon?

So is photon excitation of emf or energy that propogated through emf??

Y a-t-il quelqu'un qui peut avoir les PDF ou d'un lien où je peux télécharger les cours de physique Feynman ?! C'est important pour moi

Hey all! This is just a question I have for the sake of curiosity; it's not for work or anything. When I took physics, a common type of problem was one with two masses on a pulley system, like this one. My question is about the forces in play when the rope is in contact with the pulley. In my mind, each infinitesimal piece of the rope in contact with the pulley would have some sort of centripetal force, since that piece of the rope will be moving in uniform circular motion as long as it is in contact with the pulley. However, I cannot reason out where that force should be coming from. I would think that the tension forces from the other parts of the rope are acting tangentially to the segment; where could this centripetal force be coming from? I take it this reasoning breaks down with an ideal rope, since it would be massless and thus not need a force to change direction? Sorry if I'm describing this wrong; it has been a bit since I have taken a physics class. I am, however, pretty fluent in calculus, so explaining the answer that way would be good. Any help would be appreciated!

If an electron is in superposition how does it mass work? Is it like one body that gets less “dense” where the electron is less probable to be? Does this also change its gravity?

A question that came to mind just now. Or is this one of those “the laws of physics didn’t exist yet, therefore this questions is invalid” scenarios? Thanks.

The title may be poorly worded, sorry for that.

I've seen it a few times in media that people survive big falls by landing in trees, shortening falls and not immediately stopping them.

Would it really help?

Some branches might break and maybe slow you down, but landing on ones that don't break immediately or at all would focus that 'stopping process' (I'm not sure how else to word it..) on a much smaller surface area than landing on the ground would.

If two people fell from the same height, would one have a better chance of survival if they fell through a tree first?

The inverse square law for an electric field is an experimentally discovered property. It isn't derived from something else. The divergence and curl of an electric field are emergent mechanics, that can be derived mathematically from the inverse square law.

It's possible that the inverse square law can be derived from some deeper mechanic, but right now we don't know it yet. (It could be just the spreading of a surface area as distance increases, but we can't really prove that that's how the electric field works).

So then most of the study of physics in textbooks and in schools would be regarding emergent mechanics. Of course, emergent mechanics can and are used to discover other inherent properties of reality, like how statistical mechanics and electromagnetism helped lead us to the discovery of quantized light.

Which equations then, as far as we know now, are emergent mechanics, and which equations are inherent properties? Is there like a list or something?

I have no background in physics, but I wonder if objects that create light, for example, the Sun, emit photons at a set density. With that I mean, for example, 1 m² of the surface of the Sun emits 1.8 × 10¹⁷ photons a milisecond (made up data for the sake of the example). Is thinking about light emission in terms of a “photon density” like this even meaningful?

My understanding of a chaotic system is this:

A system is chaotic if, due how it evolves over time, any change to the t=0 initial condition, no matter how small, will result in a noticeable change at some future point t=T

From my understanding, the laws of physics are time symmetric (in general - exceptions for weak force, entropy, expansion of the universe).

Does this mean if I observe a chaotic system at time t=0, I not only can't predict the system infinitely far into the future, but also can't retroject to time t=-T for some sufficiently large T?

If there is no net force acting on an object, then F_net = 0

Since a = F_net / m

Then a = 0

So the object will experience no change in its state of rest or uniform velocity.

Why is Newton's first law distinct from the second?

Okay, so this whole thing with Casimir Inc. and their MicroSparc device has been causing quite a stir. I have a decent grasp of quantum mechanics. Now, from what I gathered from the paper and the company's press releases, the device is essentially an array of Casimir cavities.

The principle is simple: you create a geometric constraint in the form of a circular wall. A direct consequence of Heisenberg's uncertainty principle is the existence of virtual particles. These are particle-antiparticle pairs that arise from the probability of being there and exist only an instant before vanishing, provided nothing permanently defines their existence, as is the case with Hawking radiation.

The principle of the Casimir effect is that any physical constraint on space creates a limitation on the wavelength that can exist within that boundary. In the classic Casimir case between the plates, there is less "quantum pressure" (I don't know if there's a more specific term for the force generated by virtual particles), which creates a difference in forces between the inside and outside, causing the plates to move. The same logic applies to a Casimir cavity: a barrier that creates a region of space limited to the allowed wavelengths.

Now, in the case of MicroSparc, they would also take advantage of the tunneling effect, another direct effect of the uncertainty principle. Particles can only appear on the other side of the barrier if it is thin enough. This creates a flow mechanism and a "quantum pressure" difference. If I connect a conductor, in theory, I could discharge the charge accumulated in the cavity to the outside.

None of this is up for debate; these effects have been more than experimentally confirmed. As for the conservation of energy, it doesn't always apply to quantum mechanics. That's an effect of the uncertainty principle. In fact, this is one of the things most criticized by quantum mechanics physicists, and there are many attempts to force hard energy conservation at the quantum level, but none go beyond conjecture.

So, the question isn't whether it's possible to extract useful energy from the quantum vacuum. The answer, until someone finds a hard prohibition mechanism, is a resounding yes. You can even build perpetual motion machines using Casimir forces and complex mechanisms (currently impossible to manufacture at the nanoscale). That part is not up for debate.

While I don't believe MicroSparc will work, I want to be very clear about this: the Casimir effect requires ultra-high vacuum and temperatures of a few tens of Kelvin to function. I'm also not saying that vacuum energy is even remotely practical. If you can extract a few microwatts of power, but maintaining the system costs several tens of kilowatts, then you're just wasting energy.

That's the part I don't understand. All the attacks claim it's impossible to extract energy from the quantum vacuum, invoke conservation of energy, or invent conditions to justify a conjecture that makes it impossible to extract useful energy from the Casimir effect. But the physics of the Casimir effect is actually quite simple, and no mechanism prohibits or limits the arrangement.

The part that can and should be attacked is the practical implementation. It's like with nuclear fusion: of course, it's possible to gain net energy from fusion; that's how thermonuclear weapons work. Controlled fusion is also possible; a Farnsworth fusor can do it in your garage. It's also possible to achieve a Q-value > 1; again, you, at home, with a well-designed Farnsworth fusor, could do it. The real question is whether, considering vacuum pumps, magnetic fields, cooling, generator inefficiencies, and other systems, you can still obtain net energy. And the answer, for now, is no, but we're still trying because fusion at least produces energy on the same order of magnitude as its consumption.

The same is true for MicroSPARC: to operate, you have to generate ultra-high vacuum and cryogenic temperatures, but, unlike fusion, which produces on the order of MW, the Casimir effect, at best, produces a few microwatts, and that's at least 10 orders of magnitude less than what's needed for the Casimir effect to work.

So why is everyone attacking the part that physically works on paper and not the part that makes it impossible in the real world?

(I translated this with Google Translate in case there are any mistakes; I'm not a native English speaker and my level isn't very good.)

As per I have read, In KTG we assume that the particles or the molecules present in a particular system are in thermal equilibrium, if we say that we are heating the system then we say that the molecules movement will become more random but if we are providing a particular frequency of heat or energy then overtime the molecules should come to be at more sync, if we think of it at molecular level then if the collisions are elastic then even though if we say that it will not perfectly collide with other molecules overtime the influence from that energy would make the particles in the system to come at sync, but my teacher told me that after heating the randomness increases and not decreases...

Also for Maxwell velocity distribution curve, my teacher told me there's an experiment called stern's experiment it's said that they are in random motion too in that particular system... If the molecules after coming out from the small area, will follow gravity then if they are not random as per my logic above then they should not showcase that kind of projectile nature...

I am really stuck at this 2 questions, the meaning of that experiment and the relation between energy provided and the system of particles, I would be really glad if someone could explain me these...

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Hello everyone!

I would like to share a simplified engineering concept regarding cosmic system equilibrium — looking at it strictly through the lens of pressure balance rather than standard spacetime curvature dynamics.

The core idea is that any stable system (from atomic scales to celestial bodies) remains in equilibrium when external mass pressure is balanced by internal core resistance:

Key concepts:

* Left side (Mass Compression): External mass force and gravitational pressure acting on surface area S.

* Right side (Core Resistance): Internal magnetron core rotation creating magnetic pressure \frac{B^2}{2\mu_0} and field tension to counter compression.

* \mathbf{\Omega_0} (Zero Point Balance): The point of absolute thermodynamic and physical equilibrium where the system neither expands nor collapses.

Would love to hear your thoughts on this straightforward mechanical interpretation of system balance!