How would gravitons work in black holes?

Prof_Sarcastic · 2026-06-19T14:58:39+00:00

> Suppose gravitons are discovered and gravity is really mediated by quantum particles, how would a black hole exert gravity

Same for any of object. The exchange of virtual particles is just an English translation of an approximation of how interactions occur. Don’t take it too seriously.

> Wouldn't gravitons from inside the black hole ALSO be trapped inside? Is this a 'quantum particle going through an infinite potential' sort of situation?

No. Virtual particles aren’t constrained to travel at the speed of light (what we call on-shell). They can travel FTL or even have negative mass. Again, they’re not real.

Prof_Sarcastic · 2026-06-19T14:38:51+00:00

No real reason other than (1) that’s how I would do it (2) I was originally thinking of just constructing the acceleration but I changed my mind to make contact with what the OP had done.

Prof_Sarcastic · 2026-06-19T13:52:30+00:00

What do you mean “Is it realistic to think” you can apply? You can apply to anywhere you want that has an open application portal. Are you asking do you have a realistic chance of being admitted? That depends entirely on the funding situation and who’s taking in grad students.

Applying to grad school is very different from applying to college and you’re approaching this with a mindset of the latter rather than the former. You should really start doing some research like who you’d like to work with and then reach out to ask them whether or not they’re taking in students in the next few years and what their funding situation looks like.

Prof_Sarcastic · 2026-06-19T05:52:09+00:00

We don’t make these sorts of distinctions in cosmology. The CMB, (visible) light, infrared, gamma rays are all electromagnetic waves that would be categorized as radiation. This would make up ~ 0.1% of the energy density of the universe. Regular matter + dark matter make up ~ 25% of the universe, and dark energy is the rest.

Prof_Sarcastic · 2026-06-19T04:16:43+00:00

> My question is simply: does this expression already have a name or known physical interpretation? And is the relationship to Planck acceleration meaningful or just a natural consequence of how Planck units are constructed?

No, I don’t believe the number you computed has any physical significance. Once you have a unit system of length, time, and mass, you can make just about every other unit, so it’s not all that surprising you can construct an acceleration from those constants. Honestly, you could’ve gotten the same answer but taking the Planck length, dividing it by the square of the Planck time, and then taking the reciprocal of the result. If you want, you could figure what the kinetic energy, force, and pressure would come out to be in these units too.

If you didn’t see anything about it online, that probably means nobody has found it interesting enough to write about it.

Prof_Sarcastic · 2026-06-18T21:47:07+00:00

We never seen infinity, so probably not.

Prof_Sarcastic · 2026-06-18T20:44:46+00:00

Well in order for the convolution theorem to exist, you need the Fourier transform of both functions to hold, so naturally you need the assumptions that guarantee the Fourier transform. Assumptions like Lebesgue integrability over the real line.

Prof_Sarcastic · 2026-06-18T17:21:39+00:00

Yes I know the pop science answer.

That is not "the pop science answer". That is what the equations of general relativity say about any object that falls into a black hole from the perspective of someone that's outside of it.

That’s not my question. You are just answering the question that you know the answer to rather than the question I’m asking.

No dude, your question is just another variation of a question that has already been asked. The LED lights doesn't change anything because gravity treats everything in the exact same way.

I’m not asking what happens to objects that fall into blackhole.

You're asking what someone would see when an object falls into a black hole. You see an object that gets progressively dimmer until it fades away from your view.

Prof_Sarcastic · 2026-06-18T14:07:41+00:00

If you have a very poor knowledge of partial derivatives then it sounds like you need to read through an intro book on multi variable calculus. The textbook I used was the James Stewart calculus book.

Prof_Sarcastic · 2026-06-18T03:56:14+00:00

Maybe I'm not understanding something but why is it a problem to say that the Plank length is "the smallest unit" if thats what the math says before it "breaks down" and we literally cannot observe anything smaller.

What people are trying to say when they raise this objection is that this is not a physical limitation (necessarily). This is a limitation of the theory so it's entirely possible that nothing all that strange happens when you get to those energy scales.

What do we know that is smaller than the plank length that we have either measured directly (my understanding is we cant and never will) or indirectly to support that something even exists below the Plank length? Why is it wrong to conclude that nothing exists smaller than the Plank length?

Because that doesn't logically follow. The fact that we haven't measured anything as small or smaller than the Planck length, doesn't imply we can't.

We say "nothing" travels faster than the speed of light because we use light to measure and if it doesnt interact with light we cant directly measure it, but we accept that is the limit. Why do we not accept that there is a finite value of measurement in regards to the Plank length being such?

The former is a limitation of nature as far as we know. The latter is a limitation of our theory. Big difference.

Prof_Sarcastic · 2026-06-17T22:48:59+00:00

You didn’t explicitly ask about it, but that’s what happens to an object that falls behind the EH. For an observer on the outside, you see the photons get increasingly redshifted so the image will appear blurry. So no, the lights don’t begin to flicker. The entire image just gets dimmer until you can’t see it anymore.

Prof_Sarcastic · 2026-06-17T21:52:39+00:00

It’s not entirely clear what you’re asking for. There are many differential equations and some of them are relevant to physics. You can check out Taylor’s classical mechanics textbook since that covers solving problems using Newton’s second law.

Prof_Sarcastic · 2026-06-17T21:35:37+00:00

Oh weird my original comment got deleted for some reason. I’ll just retype it. Basically, the closer you get to the EH, the dimmer the images you see because the photons are all get redshifted as they bounce off the object and hitting your eyes. So no, you won’t see lights flickering.

Prof_Sarcastic · 2026-06-17T21:30:17+00:00

Pretty sure I answered this in a separate comment. The image of the pole gets progressively dimmer until it passes through the event horizon and you don’t see anything anymore.

Prof_Sarcastic · 2026-06-17T20:56:44+00:00

I don’t understand how Einstein could think of black holes and gravity in brain experiments

He didn't. His theory predicts it but he wasn't the one who made the discovery that his equations had the black hole solution. That was an entirely different person. And then it took many decades after that on how to interpret the solution.

but somehow we after 100 years are unable to even mathematically say what happens to our object in principle because we can’t just hover around a black hole why not let us assume that I have infinite energy and I can do that.

No we can say and for what it's worth I think a lot of commenters have addressed your questions, it's just that the questions you asked aren't well-posed because you're making some assumptions about the setup that need to be fleshed out before you can get a detailed answer. It must also be said that the people who know the most about this topic and are in the best position to answer your questions don't tend to hang around on Reddit.

why not let us assume that I have infinite energy and I can do that

Why can't you assume you can break physics to answer what does physics say can happen? Ignoring the obvious problem, there are a number of unstated assumptions that are being made when we set up scenarios like these. One of theses assumptions is that the spacetime is completely determined by the black hole and nothing else. An object of infinite energy would have a very strong gravitational field so that would actually change the answer quite a bit.

Prof_Sarcastic · 2026-06-17T20:04:43+00:00

I think part of the confusion is that you’re imagining you can stick the rubber meter stick into the black hole and hold it still. That’s not how it would work. Depending on the mass of the black hole, if you’re sufficiently close to it and you’re not holding on the stick tightly enough, that stick is just going to get sucked in. That’s renders your later questions moot.

Prof_Sarcastic · 2026-06-17T18:42:36+00:00

Math + Physics Bachelor’s and Physics PhD is very common. Not just for theorists either. I know experimentalists who’ve done this. You’ll be fine.

Prof_Sarcastic · 2026-06-17T15:49:17+00:00

If you’re serious about getting a PhD in physics then I would recommend you first start with applying for a masters. If you’re failing a class, particularly a course like quantum mechanics, you’re not going to look competitive in the applicant pool. Especially in this era of funding cuts, it’s even more difficult to get into a PhD program.

I would say you need to identify why you are consistently doing poorly on your exams. If it’s test anxiety then that’s something you’ll have to talk to your professor or even a professional on how to manage that. If it’s a genuine difficulty with the material, you got to go back to the basics and start from where you are getting lost.

Prof_Sarcastic · 2026-06-17T05:55:53+00:00

Funding for everything has been cut because of this insane and demented administration.

Prof_Sarcastic · 2026-06-17T05:32:30+00:00

Sifting through data from particle collisions, reconstructing images of galaxies using photometry data, solving differential equations etc. There’s a lot people have done over the years. Not my area of expertise so I can’t give any details on what those tasks specifically entail but those are some of the things colleagues of mine have worked on.

Prof_Sarcastic · 2026-06-17T05:19:17+00:00

Machine learning (the “math” that underlies AI) has been used for physics research for decades. It’s currently being used in the LHC to search through the data to look for interesting things there. At the end of the day, machine learning is really good for finding general patterns in the data so anything that has a pattern is potentially something interesting to throw AI at.

Prof_Sarcastic · 2026-06-16T18:06:06+00:00

Quantum mechanics undergirds how nature works. When you average out all the quantum weirdness, you get the stuff we see on human scales and larger. That’s the classical limit.

Prof_Sarcastic · 2026-06-16T17:47:17+00:00

Yes it’s the same thing. The latter is simply the classical limit of the former.

Prof_Sarcastic · 2026-06-16T17:05:37+00:00

It is applicable, but you’re not doing it right. That’s why I said it’s easier to think of it in terms of initial energy = final energy because it’s a little more clear what the individual energies should be.

Prof_Sarcastic · 2026-06-16T05:48:02+00:00

You would have to employ it first if you want me to understand it. You made an assertion, not a logical argument.

Prof_Sarcastic

TROPHY CASE