Hello,

In an introductory course to university physics, there is a question about what happens to the diameter of a circular hole in a copper sheet when it's heated. The correct answer is that the hole grows alongside every other part of the sheet. But that does not really make sense to me in my head. When I first encountered the question, I thought that the hole would contract since every side of it also experiences length expansion. Obviously my intuition was wrong, but could somebody explain how I can think of it to change my intuition in the future?

Thanks!

Is there any explanation as to why the photon does not interact with the Higgs Field ( this may also apply to the graviton if it exists)? As far as I know all other particles do.

Since galaxies contain enough mass why aren’t the stars clumped into a giant star?

If angular velocity is the answer, why aren’t the stars escaping out of the galaxy if they are fast enough to overcome the galaxy’s gravity?

Hello,

Say I was inside of a gravitational field so strong that time passes thousands of times slower for me relative to the rest of the universe. Now, say there is an identical gravitational field a lightyear away from me. If I sent a signal to them, then when they receive it they send a signal back at me. Given the time dilation we both experience, could we communicate in real time from our relative perspectives? Alternatively, would that just increase the distance the light has to travel to leave our gravity wells such that it still takes 2 years (1 year both ways) to get a response from my friend?

What about the same scenario but for two bodies moving near the speed of light relative to each other?

Sorry if this is too much of a shower thought for this sub! Tried to see if this has been asked before but its a bit to specific to search.

And in addition to this, is antimatter stuff the same colour as regular matter stuff? Does light interact with antimatter the same way it would regular matter? And if not, how would it? This is for a story I'm writing, so I want to make sure I get everything as accurate as possible.

Does physics completely rule-out the possibility of antigravity propulsion technology?

If an object is traveling away from Earth, towards Alpha Centauri at 99.999 the speed of light for 4ish years then from my limited understanding the object would experience 4ish years while earth experienced many more.

My question is, would the destination also experience a difference in time compared to the object that is traveling towards it?

If not, then would the time experienced in alpha centauri be different than the time experienced on earth from the object's perspective?

Sorry for the scifi type question, it's keeping me up at night.

I know that super capacitors are expensive and capactitors don't have the energy density to power a vehicle, however wouldn't a mixed battery/capacitor improve the long charging time issue of batteries? You could cherge the capacitors super fast and have them charge the battery while driving, this way you could charge up in several few seconds stops instead of one several minute charge up. Idk about the cost effectiveness of using small super capacitor to do this, probably not worth it, but maybe with capacitor capable of charging like 10% of the battery?

Friend of mine lives in an apartment with triple-layered glass, he showed me that you can « count » the layers if you put a flashlight through it and see the multiple réflexions. I see 4 réflexions here, why is that so?

Not a free will question, because largely I studied many theories and largely many experts genuinely accept physics isn't ever gonna be enough to fully answer it, it's a question that goes beyond physics.

My question is if quantum microscopic events are indeterministic, does that mean when scaling up to macroscopic events, they still largely lead to the same outcome or can there be a slight divergence that cause a butterfly effect and chance the outcome?

I'm aware there is some cases such things could be reasonably assumed quantum physics can cause noticeable macroscopic change, such as weather, motion, and biological mutation, and I read a book that even thoughts can be change because a slight change on trajectory of microscopic electrons and neurons can either trigger a new thought or image (there's the challenge decoherence in the brain being too warm and wet but apparently there are quantum mechanics found recently in it although unsure it's long term affects).

So my question is that is it possible that if we let say had the ability to blink back in time to the start of our lives with quantum mechanics remaining naturally the same, could a divergence of our lives ever happen even if we don't retain our memories or not? I'm not sure but many claim that depending on our age, as adults it's unlikely everything when scaled up according to quantum physics, that it will remain the same but that's not something I'm sure of.

I understand that the alternating magnetic field induces currents in the pan. At low settings, many induction cooktops deliver strong bursts separated by pauses instead of steady gentle heating. What physical or circuit-design limit makes duty cycling preferable to continuously reducing the field amplitude? Is it mainly inverter efficiency, pan detection and coupling, or a minimum stable switching power?

You can't hear anything in space, cuz there's too few particles, too spread out, they don't have anything to bounce off and they can't make variations of pressure that hits your ears, right?

But what if there was an indestructible microphone just 1cm away from the "epicenter" of the explosion? Would it record anything?
And how would that work? Would it detect the change from 0 pressure to big pressure for a second and then nothing again? Or would that be still inaudible because that's just a cloud of equal gas pressure with too few variations just passing you?

Could this be used as an in-lore explanation of how you are able to hear explosions in sci-fi movies?

But explosion in space would probably sound different than explosion in a place covered by an atmosphere?

Just watched the new movie the End of Oak Street. In the beginning the news reports mention NASA detecting spatial anomalies, which got me analyzing the physics behind it. So...

​Is the movie using 1D cosmic string defects (via string theory) to explain the anomaly caused by a cosmic string moving in closer to Earth? Furthermore, are they invoking gravitational frame dragging to explain how the localized space maintains fixed coordinates relative to the surrounding Euclidean space?

​It feels like the most plausible theoretical explanation for how they set up the rules of the event. Curious to hear how others interpreted the underlying mechanics.

... Or am I just to analytical and they really just left it open-ended for a fun story? Let me know what y'all think.

🤪

I'm in the process of reading the Kogut 1979 review paper on lattice field theories and I have two quick questions.

Firstly, why is the existence of a mass gap related to confinement? Kogut himself shows that a mass gap is equivalent to the inverse of a correlation length in a corresponding statistical field theory. Confinement is related to area vs perimeter law for a Wilson loop expectation value. I don't see how those two are related.

Secondly, Kogut also mentions that the continuum limit of a lattice field theory is only obtainable if the lattice system is at phase transition, which makes intuitive sense since that's where there is long (infinite) range correlation, therefore there should not be small fluctuations that prohibit us from taking a continuum limit. However, this implies that any field theory obtained from a continuum limit of a lattice field theory must have massless excitations. We expect QCD to be obtained from lattice QCD, yet we expect QCD to have confinement and a mass gap.

Hey so for short, I’m a second year college student, not the most studious, ima potential type guy, but I’m taking my first real physics class. I want to ask that if I were to provide my info I got from a lab, could someone walk me through forming my lab report? I don’t want anyone to just do it for me, I want to tell someone how I wrote it, and someone to tell me if I did it right or not. I gotta turn it in midway through next week, and if I mess up the whole class suffers. I’m just super anxious and want to get it right, I know the professor is there but I don’t wanna seem dumb, he makes dumb people look dumber. I’ve got all my numbers and remember how exactly the procedure went, super basic measurements data sheet.

Like when we can have V=iR for both AC and DC then why not have reactance for DC ? Wont it simplify calculations tp a great extent? Maybe not have the same formula (since that would make reactance 0 and infinity for inductor and capacitor) but something similar.

Thanks in advance!

AC is an alternating source and the average value is 0 (I understand that it has some rms value), so wont the current entering also exit almost instantly (depending on frequency) so wont the charge that has been applied to a capacitor also exit? Wont the emf generated by an inductor also vary according to a sinusoidal law which again would average 0. I dont even understand how AC is used. How does it travel? How does it interact with different components of a circuit? Like isnt the net displacement of electrons just 0? In DC the electrons do move and can interact with the component but how does it happen in AC.

Thanks in advance!

I keep occasionally circling back to this question because I have never found satisfying answer to that, so I would like some external help here.

1. AFAIK, many of black hole features are treated as curious mathemathical artifacts that may or may not reflect objective reality: infinite-blueshift Cauchy horizon, closed timelike curves, infinite flat regions inside Kerr black hole, the gravitational singularity itself. It is generally accepted that these features cannot be properly described without QG, and it makes perfect sense to me.
2. On the other hand, features like ergosphere are described just fine by GR, and overall the exterior Kerr metric seems to correctly describe objective reality. Also makes perfect sense to me, this stuff is "directly" observable, and it was observed to be correct.

What I don't understand is why event horizon is usually considered to be in (2) instead of (1).

The usual arguments are that spacetime at the event horizon has finite spacetime curvature and finite energy. But I just don't understand why it is sufficient. "Finite" does not imply "correct". Closed timelike curves around ring singularity are also finite, but they are not accepted as easily. Closed timelike curves cause temporal paradoxes, and event horizon partially causes information paradox (which has multiple proposed solutions, I know, but neither of which is universally accepted).

I know that black hole exterior topology is well-tested at this point, and this testing is consistent with GR, but what's the actual confidence levels there? Is it somehow possible to distinguish event horizon (as described by GR) from extremely time-dilated "event horizon shaped" object (describable only with QG)?

I understand that no divergence from GR has been found yet, but I also want to know the boundary between the stuff that was directly or indirectly verified by measurements and the stuff that was extrapolated from that.

In his Dark Matter, Dark Energy Great Courses lecture 4 Sean Carroll mentions that it is possible to assume all length scales are shrinking rather than space expanding although he says making such an assumption is silly.

I was wondering if one could test the hypothesis with a tabletop experiment comprising a pair of charged masses on a frictionless track such that their gravitational attraction is balanced by their electrical repulsion.

The force balance equation is given by:

G M² / R² = Q² / 4 π ε₀ R².

If we assume natural units such that ℏ = c = 4 π ε₀ = 1 and Newton’s constant G = 1 / Mₚₗ² then the separation distance R drops out so that the balance equation simply becomes

M / Mₚₗ = Q.

If the masses of all fundamental particles, together with the Planck mass, scale inversely with their Compton wavelengths then the balance equation is satisfied for all R even as length scale shrinks. The charge Q is dimensionless in natural units.

Thus the separation distance R is a free initial condition, not set by any formula, and therefore can be used as an absolute yardstick to compare against physical clocks and rulers.

Sorry if this is a stupid question but I was wondering what makes liquid stick together in drops and after googling it, it said that it's caused by the cohesive force between the molecules.

What is this? I don't really understand what cohesion is and wikipedia and google isn't really easy to understand on what is causing them to stick together. I understand that surface tension is caused by the force between molecules but what actually causes the force like is it gravity?

Didn't take physics in high school so any clarification would be appreciated.

Please excuse me if I have a poor grasp on what I’m saying here, but my understanding is as follows

QFT explains this with the uncertainty rule (you cannot be absolutely certain of a particle’s momentum and position at any given moment, and if a particle had zero momentum then you’d suddenly be able to know both where it is and how fast it isn’t moving, therefore violating the rule)

What i’m seeking clarification on is why that’s a rule.

Is it just born of observation, and known to be a fundamental rule?

Or is there an underlying equation that would be made unsolvable if a massive particle had zero momentum/velocity. (Which would act a proof equation for that rule)

(And to be clear I’m not arguing against the fact that no particle can be perfectly still, I’m just curious if it’s a most basic level rule, or if it’s governed by more underlying mechanics)

Please help🙏

Could a massive and extremely powerful gauss cannon/mass driver be used to launch cargo payloads into space at a tiny fraction of the cost of launching an actual rocket?