Hole Definition and 1000 Threads

[Moderator's note: this discussion has been spun off from another thread.] This is probably a silly idea, but I haven't got any reputation to preserve, so I'll mention it anyway. My very limited (and probably very wrong) understanding of quantum theory tells me that until something is...

Hi, folks. There's a somewhat popular hypothetical situation that involves a person falling into a hole dugg all the way through the Earth or any planet, passing straight to its center. Now, I understand quite well that the resulting motion would be periodical and the reasoning behind it. My...

For an observer far away, nothing ever seems to actually cross the event horizon of a black hole, but to "freeze" right at the event horizon. Does this mean that if we could observe a black hole, we would be able to still see everything that has ever entered the black hole? Would every object...

I saw somewhere a thread about a cow falling into a black hole. I don’t know why a cow, perhaps the OP was thinking about the Milky Way. With the cow example it is not clear to me what we are supposed to see when an object falls towards the event horizon. If time slows to infinity, does the...

OK, so we know that there is a supermassive black hole at the center of every galaxy. But I want to ask where is the mass of a black hole actually. When the black hole is formed and if there is a supernova or hypernova then much of the mass is ejected out then how can we says black hole has a...

I thought of posting this on astrophysics or general relativity forums since it seems completely classical, but given the extraordinary claim, I am posting here. Note that one of the guys is a notable string theorist. http://arxiv.org/abs/1510.03396v1 Journey Beyond the Schwarzschild Black...

For this we need a thought experiment: imagine you're on a gedanken planet manning a gedanken laser cannon, and it's pointing straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now let's keep you safe in a bubble of artistic licence, and...

My very basic understanding of black holes leaves me with a question about why black holes increase in size, or rather, why does the event horizon increase in size. As I understand it, a black hole is a large amount of mass condensed into a such a small space that the amount of gravity produced...

Homework Statement Muscle can be torn apart by a force of 100,000 N applied across an area of 1 m2. A 10 cm2 muscle therefore will be torn by a force of 100 N. If a student of average size were being lowered into a black hole of 1 solar mass, at about what distance from the hole's center will...

I understand that, as matter approaches the event horizon of a black hole, according to the time frame of someone outside the black hole, it would slow down and, after an infinite time, stop completely at the event horizon. So, if we could observe it, all this matter would be accumulating just...

Let's put an observer hovering near the event horizon of a charged black hole. As the black hole is charged we can change its velocity from zero to 10 m/s in one second. But we can not send a message to the observer in one second. So the observer does not know that the black hole that he is...

Forgive me if this is a dumb question. If nothing gets out of a black hole, how does the gravity get out?

stevebd1 submitted a new PF Insights post Time Dilation and Redshift for a Static Black Hole Continue reading the Original PF Insights Post.

There are many videos and articles about this topic (what it looks like if you fall into a black hole). I remember hearing that, inside the event horizon of a black hole, time has essentially stopped for an outside observer. However, if you fell into one that would mean that any amount of time...

Hey, I know that one doesn't work with polar coordinates (t,r,θ,φ) because they don't behave well in the event horizon. But my problem is with raidal null curves, if we take ds2=0 and dφ, dθ = 0 so we have When, if I'm correct, the + sign determine that it's outgoing and the - infalling, so...

I 1. A man of mass m = 80.0 kg hangs from a rope down into a hole. The rope goes over a massless pulley and is connected to a block of rock of mass M = 200 kg, which is lying on a frictionless horizontal surface. The distance between pulley and man is 5.00 m; between pulley and block 20.0 m...

Homework Statement The Galaxy has a black hole with about 3 x 10^6 M☉. What is its diameter in AU? Homework Equations Not sure. The Attempt at a Solution 3,000,000 solar mass, but not sure how to figure out the diameter in AU. Let's see...diameter of the sun is 1,000,000km 3,000,000 x...

Homework Statement Suppose a hollow metal shell (outer radius 25.3 cm, inner radius 5.2 cm) carries charge Q = -7.99 pC. There is a tiny hole in the sphere, so small that it does not affect the charge distribution or the electric field created by the charge. An proton is released from rest at...

Assume a conductor in a rectangle shape for simplicity. Now, if I only choose one side of this rectangle, and apply external electrical field ∑ only to it, what EMF would I create on the conductor? I would simply say ∑, however then I had the following idea, and I started to doubt if I create...

I have learned that light has a constant speed of 299 792 458 m / s or C and that this speed cannot be changed by anything, how can a black hole "trap" light if this speed cannot change? Is it because time is also trapped, so a second lasts infinitely long?

MTW, p. 924, defines a caustic as a point where a null geodesic originating from the external universe enters a black hole's event horizon, remaining in the horizon afterward for some finite affine interval. (A null geodesic of this type is called a generator of the horizon.) They introduce this...

Dear PF Forum, I have a question in mind. But I'm not sure if this belong to SR forum, cosmology or classical physics. So I post it here. And perhaps as some of you might have known before or thought it over. It's about kinetic energy. Supposed this... A rocket, with a rest mass 1 ton. And the...

Hey guys, I have a question. I am doing some homework for university and got super confused (probably just messing up things). So in school you learn that magnetic monopols do not exist. But my question is now: On the sun there are coronal holes, region where the magnetic field is not able to...

Hello all, I am doing homework and have come upon this question: A cylindrical hole is drilled all the way through the center of a sphere (as shown in the figure below). Show that the volume of the remaining solid depends only on the length L of the hole, not on the size of the sphere. Figure...

I would like to discuss a bit this paper (http://arxiv.org/abs/1508.06577): BMS invariance and the membrane paradigm Robert F. Penna (Submitted on 26 Aug 2015) We reinterpret the BMS invariance of gravitational scattering using the membrane paradigm. BMS symmetries imply an infinite number of...

Bee Hossenfelder was live-blogging from Stockholm Conference on BH info puzzle today Tuesday 25 August. Herewith: http://backreaction.blogspot.com/2015/08/hawking-proposes-new-idea-for-how.html The conference is 24-29 August. Hawking presented his idea Tuesday, based on joint work with Malcolm...

Greetings, I am new to this forum and would like to present a discussion. If a miniscule black hole is created in the LHC. Is it probable the LHC is capable of creating more than one black hole during a single event collision? Considering fact and theory provided by credible research. Could...

PeterDonis submitted a new PF Insights post Centrifugal Force Reversal Near A Black Hole Continue reading the Original PF Insights Post.

What's the best way to explain why tidal forces for an observer free-falling through an event horizon are finite? My first thought was to say that "gravity isn't a force, it's a curved space-time". On further thought, however, it seems to me that consideration of the Rindler horizon shows...

A pioneer. http://blogs.scientificamerican.com/cocktail-party-physics/in-memorium-jacob-bekenstein-1947-2015-and-black-hole-entropy/

According to Hawking [1] it is posited that light photons at the event horizon of a black hole must cease to move, and remain motionless for the entire lifetime of the black hole. It is also observed [http://dls.physics.ucdavis.edu/~scranton/LensedCMB/a2218.gif] (and calculated) that the path...

Leonard Susskind talks about Black hole Quantum Complexity in one of his online lectures. I was wondering what you guys on the forums think about this, and what you guys think it means. Here's a link to the video He points out that the complexity increases linearly with time, and at the...

Past the event horizon of a black hole, gravity is so immense that even light can't escape. Wouldn't this cause the the gravitons, which travel the speed of light, to be trapped, making a singularity?

Dear PF Forum, I have read a link about big bang time line. Started from time zero, then Baryogenesis, lepto genesis, Planck time then on... http://www.physicsoftheuniverse.com/topics_bigbang_timeline.html I try to make a simple calculation here with Schwarzschild calculator. The mass of the...

[Moderator's note: Spin-off from another thread.] I'm sorry, does black hole have surface area? Did you mean the sphere defined by Schwarzschild Radius?

I'm just curious, do black holes have a maximum size? In other words, if it theoretically had an infinite supply of matter to "feed" off of, would the black hole just get more and more massive or is there a point where it can no longer fit anymore matter? Will it just spit out hawking radiation?

Can one create a black hole when already inside the black hole ?

I've been reading 'A brief history of time' and want to know more about how black holes are formed. Please help?

I'm designing a fixture for quality control and need a few precision holes. Their diameters range from 1/8" to 5/16" and need to be ±0.0002" with a depth of 1/2". I've been looking into EDM hole making and honing, but neither seem to be great for that range of diameters. Anyone know of any other...

What would happen if you went into a black hole?

We all know from the relativity, that even the light gets into the black hole, so gravitation-gravitons(what is actually graviton?)are stronger than photons in this case!?

I want to know which dimension does the black hole belongs? Can anyone say which force is responsible for the absorption? In case, if the black holes absorbs everything then were the things might gone?Is that everything becomes invisible or just blast into pieces?

This is mainly just a theoretical question: say you have a rectangular box made of styrofoam (one of those ice cooler things) and it is levitating in air at room temperature conditions. It also has one hole at the top of the container so that heat can get out of it. Inside the box is a lightbulb...

V Chernyak, Wei Min Zhang, S Mukamel, J Chem Phys Vol. 109, 9587 (can download here http://mukamel.ps.uci.edu/publications/pdfs/347.pdf ) Eq.(2.2), Eq. (B1) Eq.(B4)-(B6). When I substitue Eq.(B4)-(B6) into Eq.(2.2), I can not recover Eq.(B1). Who can give me a reference or hint on how to write...

Forgive me if I have posted this in the wrong location. I'm trying to reconcile my understanding of spacetime, but am running into a paradox that I'm sure is arising from my own misunderstandings. As you get closer to a black hole, time, with respect to outside observers, begins to slow to a...

Hi all, I am currently reading a paper and they have this statement in the abstract: "If the supermassive black hole Sgr A* at the center of the Milky Way grew adiabatically from an initial seed embedded in an NFW dark matter (DM) halo, then the DM profile near the hole has steepened...

Normally a star with a mass several times that of the sun will become a black hole at the end of the lifetime of that star. Can black holes exist with a mass much smaller than that exist? In other words, are black holes with a mass of Jupiter or even Earth exist? Or even much smaller than that...

Does gravity get destroyed in a black hole ? If the Higgs particle creates mass in the universe and higgs are destroyed in a black hole, then the total gravity in the universe must diminish over time , hence the universe expanding ?

Let we have a dielectric with field ##E## inside and with a little hole. I have problem. I get a two different answers on this problem, and I try to understand which one of them correct. As mentioned in http://www.feynmanlectures.caltech.edu/II_11.html#Ch11-S4 (11.25), the electric field in...

Homework Statement I am preparing a report on black holes and I recently learned about a phenomenon I was previously unaware of: the photon sphere of a black hole. While reading an article on said occurrence (I have now confirmed this on multiple sources) the photon sphere which is the minimum...