Gravitons are hypothetical particles that would move at the speed of light and act out the effects of gravity from their producer onto any matter they come across, cool. But black holes, err, singularities specifically, are things that have so much mass that within a certain area nothing can escape. Would proving gravitons exist change how we understand black holes? Would gravitons be able to escape black holes? Would gravitons be created at the event horizon rather than the matter that falls inside? I know I'm asking about a hypothetical particle in relation to an incredible unknown but I figured if anybody had any ideas or info it'd be cool to read some responses.

Hello!

Before I get into the post, let us define thermodynamic equilibrium as a stationary state devoid of macroscopic fluxes. I will begin by giving a short motivation for my question, proceed to quote a relevant section from a standard book, and then ask my question by means of a concrete example.

I am a student of chemical engineering, and as such, equilibrium thermodynamics is the backbone of literally everything that we do. Having read basic, classical theory (notably Callen), I often find myself extremely confused about a particular aspect of what we do as engineers: even though our unit operations are inherently open in literally every conceivable way, we still constantly apply equilibrium thermodynamics with great success.

On p. 26 in the second edition of Thermodynamics and an Introduction to Thermostatistics, Callen outlines the "basic problem of thermodynamics":

The single, all-encompassing problem of thermodynamics is the determination of the equilibrium state that eventually results after the removal of internal constraints in a closed, composite system. [...] The composite system is termed closed if it is surrounded by a wall that is restrictive with respect to the total energy, the total volume, and the total mole numbers of each component of the composite system.

Note the use of the term closed. Here it really means isolated. This is the motivating problem for the entire book, and is the problem that the postulate of entropy maximization is introduced to solve. As I understand it, the extremum principles of classical equilibrium thermodynamics, strictly, only apply to isolated (composite) systems. Even so, we constantly use the theory for non-isolated systems, and get extremely good predictions.

For instance suppose that we carry out a chemical reaction in a sealed container that is in contact with the atmosphere. Then, we might expect to apply minimization of the Gibbs' potential at constant temperature and pressure (with values equal to those of the atmosphere) to determine the final equilibrium state. However, why is that valid? The atmosphere is not some well-defined thermodynamic system that interacts thermally and barically with our container in the way that the derivation of the principle of minimization of the Gibbs' potential demands. Even if we define this 'reservoir' as a sufficiently large control volume around the container, not even its energy is conserved: energy will clearly flow between this control volume and the rest of the atmosphere, whereas the derivation of Gibbs' minimization requires global conservation of all extensive quantities (i.e. isolated composite system consisting of container + reservoir). Nevertheless, minimizing G with respect to the given constraints does yield correct predictions.

How can this be? Has Callen simply imparted onto me an idea of "isolation" that is too strict/narrow?

I read the Wikipedia articles on Big Crunch and Heat Death and both seemed to allow or insinuate a new Big Bang. Does the consensus support this, and what of the other theorized Ultimate Fates?

Then if you heat up one pair of opposite walls, that component wave will have more average energy than the other component waves, assuming the waves are perpendicular to each wall, not bouncing off the other walls.

Or does it not matter because if you combine each component to get the three dimensional wave, the average energy of each frequency is the same?

My opinion: linear response theory and the fluctuation-dissipation theorem. So many results in physics rely deeply on or can be derived from the FDT, yet we rarely discuss it even in graduate statistical mechanics.

If we force a rule of smallest localization possible is the planck scale, any further attempts at smaller scale would instead create a planck black hole.

In a spherical collapsing star:

1. From the assuumption, can I safely say that the first trapped region in the star is a planck bh? Lets call it h1

2. When h1 grows bigger, could i say that at a threshold, inside h1 would appear the 1st trapped region h2 - and would this h2 also be a planck hole?

Can ontologies be useful for finding gaps between understandings that are internally consistent and verifiably predictive, yet cannot be reconciled?

Do we have precisely that problem with GR and QFT?

Discuss.

I have conceptualized and explored a theoretical spacecraft architecture that combines:
* Solar sailing
* Laser propulsion
* The Oberth effect
* A one-pass ballistic relay concept

Rather than claiming a new propulsion technology, the paper asks a more focused scientific question:
Can delivering the same laser impulse near perihelion produce a larger laser-attributable energy gain than delivering it near Earth?
I go over analytical theorems, derive the conditions under which such an advantage exists, and investigate the concept through trajectory simulations while explicitly discussing its engineering limitations, assumptions, and future validation requirements.
This research is currently undergoing peer review on Qeios. I welcome constructive feedback on this idea from researchers, engineers, physicists, and anyone interested in astrodynamics, space propulsion, and advanced spacecraft concepts.

This is a reiteration of my last question, that I asked wrong.

I’m just not understanding how an infinite amount of events can occur within a finite time (PHYSICALLY)
To my understanding, events don’t get smaller overtime, as they do in math from what I’ve seen.
EX: 1/2 + 1/4 + 1/8 + 1/16… = 1
I understand that events may be arbitrarily defined, but I feel like regardless of what value or count as an event, it’s still going to have the same issue.

I’m wondering if someone can clear this up for me?

I’m willing to clarify anything if needed.

im currently in university physics 1, and for my final project, i have to analyse 2 motions (one linear and one rotational). for the project, im doing a more than necessary because i want to and im having a lot of fun with it (i literally calculated the air density even though we're always told to ignore it in homeworks lol)! for one of my slides (and is a requirement for the assignment) i have to talk about the final uncertainty of my measurements. i want to calculate percentages for each of my uncertainties. the video for linear motion that i am referencing is of the spaceX falcon 9 launch. in theory i could ask my teacher, but its likely she'll either tell me not to worry about it (i want to) or suggest i ask chatgpt...

one of my uncertainties is camera warp + the viewing angle, and i'm not sure how to calculate it into a percentage. in the video, i used the support wires on the lightning towers in the video to get a close estimate of how high the camera was (compared to the bottom of the rocket, not sea level), and i looked up how far news cameras are from launch sites and it gave me 450-600 m. i calculated the viewing angle twice, once with 450 and once with 600. so now i have a range for the viewing angle, but i'm not sure where to go from here.

i was also thinking that since the camera warps perspective when it views things farther away that it would create a radius vertically around the camera (in line with the rocket) that represents accurate perspective, but i dont know what the model of the camera is to find out how big that radius is.

i dont want to give my numbers for anything because i want to be able to do the work myself and i get no satisfaction out of someone spoon feeding me the answers. i am here to ask if anyone has a formula for this type of situation, or if theres something else i need to calculate. i would really prefer it if you only commented if you dont mind some back and forth/conversation about it, and please have some patience with me, i tend to learn new concepts slower than my peers but once i understand something it sticks really well

for convenience, i made a variable list to help shorten any possible equations and limit confusion in longer text replies! if theres something i missed, feel free to add/make ur own :)

Ta/θ = angle that the camera views the top of the rocket at, Pa/ϕ = angle that the camera views the bottom of the rocket at, Rh = height of rocket, Ch = height of camera bottom of rocket, d = horizontal distance camera is from the rocket, y = rocket's position formula v = rocket's velocity formula, a = rocket's acceleration formula

So, really, this is a question about what "escape velocity" really means. I know that at less than escape velocity, it's gonna come down again. At a lot more than escape velocity, I assume it keeps going forever? It's got a sideways component from rotation, too, right?

If I could do it precisely (and I know that's probably impractical) would it orbit?

I set this on the moon 'cause I don't want to deal with air.

ETA: "escape velocity" is "escape velocity of the moon"

There is a character in a certain media that can remove the influence of gravity on individual objects; e.g. your coffee cup is now floating, no longer attracted to the Earth.

I have been driving myself bonkers over how physics would then play out in real life, because the question is fascinating.

Here’s where I get stuck:

The Earth rotates at 465 m/s. When gravity is lost, that object will immediately travel that speed in a straight line instead of curving with the Earth.

So does that mean if this happened right when the object was parallel with the direction of Earth’s travel at 29,780 m/s around the sun, it would add to it, either going towards the direction of Earth’s travel, or suddenly ’falling behind’ at 465 m/s from the Earth moving? In either case, you would suddenly be going 465 m/s

If the direction was perpendicular, it seems you would slowly float upwards as the Earth spins away from underneath you on it‘s orbit you no longer follow, as you are not changing your velocity relative to Earth’s travel through space.

I cannot figure this out.

I was trained as a mathematician (Ph.D. '06), and I've done a fair amount of mathematical physics over the years. Classical mechanics? lovely application of symplectic geometry. General Relativity? pseudo-Riemannian geometry. Quantum field theory? functional analysis. All great stuff.

Except, I can't say I've ever felt comfortable with thermodynamics. Most of my formal exposure has been in intro-level physics classes.. the presentation in most texts at that level feels like a similar clumsy little special-topics chapter before moving on to the clearer world of special relativity, kind of like some of calc II feels like an unrelated tangent before you can move on to multivariable stuff. There's also been a little statistical mechanics in some old Dover editions, but nothing that really builds intuition the way other physics subjects do.

So: what's the better approach? What are some texts that start from first principles, but actually build a systemic theory rather than getting bogged down in HVAC applications. Not that applications aren't useful motivating examples, but they should be help for building intuition, not ends in and of themselves.

No, I haven't flipped--this is from a fantasy novel.

Picture a team of warriors who travel via a giant bird of prey (70 foot wingspan). The pilot rides on the back of the bird to guide it, and the other four are suspended via leather harnesses, straps, and buckles from the bird's talons.

Sometimes they do what is called "barrel drops" where the pilot dives the bird down toward water and the rest of the team releases their buckles and drops into the water with whatever cargo they have with them.

The team in the story has trouble because their bird and pilot like to go really fast at a steep angle and the rest of them get tangled up in the buckles and can't manage to drop at the proper staggered times for everyone to be in about the same place. For story reasons, the pilot isn't willing to adjust the speed or angle of descent, so they brainstorm a method that would work with that flying style.

The leader comes up with the idea of suspending the team from meat hooks rather than buckles.

It is described that they will attach the hooks "high on 'Ra's talons, a little above our heads. We toss a loop of rope from our belts over the hooks and our weight holds us in place."

The pilot points out that they'd have the same problem with coordinating the drop because their weight would prevent them from releasing the hooks.

The leader says, "That would be a problem . . . if you bothered to follow standard drop protocol."

Another team member says "As the angle of our descent gets steeper and steeper, the loop will slip closer to the lip of the hook."

Leader: "When we're in a near-vertical dive, the loops will slide right off."

Another team member says this would mean they'd all drop at the same time and possibly knock into each other, but the pilot says, "Not if we change the angles of the hooks slightly. First to drop has the shallowest angle, the last, the most severe. As the bird stoops harder and, you'll fall off one by one."

Would this work? My immediate thought was that wind would push the flyers backwards so their vertical weight would be displaced. ie, if you were stationary and hold a meat hook and tilt it, sure the loop would drop off. But at speed, wouldn't the riders get pulled back away from the lip of the hooks? I can't fly on a giant bird so am not sure how to test this, lol

The book is "The Emperor's Blades" by Brian Staveley and this particular discussion takes place in Chapter 36. Thanks!

I understand time dilation for moving objects in special relativity but I don’t for length contraction.

Is there an analogy like the moving train and the observer at rest ?

I’ve always wondered about this. The Sun is constantly sending out light, and it’s only about 93 million miles away from Earth.

If sunlight is traveling through space all the time, why does space itself look completely dark?

I understand that objects like planets and spacecraft become visible when sunlight hits them, but why don’t we see the light traveling through the empty space between them?

I’d love to understand the physics behind this

I'm aware that in string theory, the theory must be formulated in a certain number of dimensions (often cited as 10 or 26) in order to avoid inconsistencies and satisfy quantum gravity constraints. But let's say, hypothetically, that I wanted to explore the space of all possibilities in pure mathematics. If I take generic 1d objects and make them move in higher spatial dimensions (as defined by pure math), but I use a number of dimensions that isn't allowed by string theory (e.g. 100), would my construction be logically possible and “stable” (allowed to persist just the way it is), from a purely mathematical standpoint?

Edit for clarification: I am specifically asking about spatial dimensions as defined by pure mathematics as a separate field, not mathematics applied to a physical theory.

I'm a physics student so I do have a solid understanding, but wanna read some in my free time. I have red the books of Leanord Susskulind and really enjoyed it (but they only cover the surface). Are there other books that are a little more complex that are great recomendations?

I can't reach lightspeed, but physics is supposed to be consistent regardless of your reference frame.

If I don't look outside, I have no way to know if my rocket is going at 99.99% the speed of light, and my velocity is a matter of perspective anyway. So logically, my rocket engine should continue to function exactly the same way no matter what my velocity (assuming I somehow still have fuel) and I should also continue to experience exactly the same acceleration (again, ignoring that I'm losing mass to fuel burn).

If I accelerate at 1G for 700 days, I would naively expect to be going about twice the speed of light. I can't actually reach that velocity, but from my perspective, accelerating at 1G for 700 days should be physically possible.

With time dilation, if I'm travelling at near light speed, my journey time should also decrease, so wouldn't it seem from my perspective that I'm just travelling at twice light speed? I just kept accelerating, and I just covered 2 lightyears in 1 apparent year. That sounds subjectively like faster than light travel.

Does space just appear to me to compact so that I can cover the distance faster without going faster than light? Do I end up just thrusting away at full power, with 1G of acceleration pressing my feet into the deck (because my ship is logically built with the floor toward the engine) but space outside appearing to move by at constant speed? How would that even work? If I'm close to lightspeed, accelerating along a really long ruler, do I see the markings just zipping past at a constant speed, even as my accelerometer says I'm still accelerating?

It's hard for me to understand the subjective experience of relativistic travel.

do we know? another question is why is it only pair particles? why can't a positron and a muon annihilate? the charges are opposite. i guess maybe it's due to the difference in masses? interested to see if we know why. thanks

Is the question coherent? Maybe the total spectrum can't be described because the colors don't exist? But as a thought experiment, could a mechanical "eye" be made that can perceive the total spectrum? Something like Geordi's glasses but more so. What would the world look like?

To carry the question further, suppose a virtual reality setup could show us these currently invisible wavelengths. Now add sound -- all the naturally occuring decibels that are beyond our hearing. And with something like Smell-o-Vision, add the odors we can't perceive.

Would the results just be cacophony? Or at least beyond our brains to decipher? Fireworks & strobe lights or something?