Horizon Definition and 438 Threads

My problem is to determine how far one can see to the horizon, depending on how far above the water the person is and to create a formula that determines the distance as a function of the height. To start with, the hypotenuse is the distance from the core to the persons eyes. (x+e). The...

In black hole thermo the famous entropy is that of the event horizon viewed from the outside. does the standpoint of the observer make any difference to the entropy? and in particular does it make any difference to the entropy of the horizon if the observer falls in and is now viewing the...

when the photon is born on the horizon...bang? 2 electrons are traveling around a black hole, after some time they meet themselves exactly at the horizon of the hole, generating a photon. if for fate the particle at the moment of be born has a perpendicular speed (opposed relative the center...

The newly release WMAP data supports the Inflation model that the universe expanded from subatomic scales to Astronomic scales in a fraction of a second. If so, then what would have been the distance from each point where space would have been expanding at the speed of light, approximately? Thanks.

I have read that the expansion of the universe is not a relative velocity and therefore not restricted to the limitation of the speed of light. I read that this creates a horizon which we cannot see beyond due the fact that the portions of the universe are moving away from us at a speed greater...

What is the difference between particle horizon and cosmological event horizon?

i haven't yet got this concept. i have read about the time "freezing" near a BH , but am not clear. can u please explain what actually happens? why does the time stop? i also want to know one thing-- when, supposing 'A' enters the event horizon he moves slowly towards the singularity because of...

hi, i was just wondering as the mass of the black hole keeps increasing due to increased mass getting deposited on it does its event horizon increase because of this? does the black hole have infinite density? -Benzun

Im new here but i need help with something my teacher can't answer... as you know already as you get closer to a black hole time is curved thus time slows down...eventually stoping at the singularity...so my question is how can anything enter the black hole i also know that black holes...

http://www.arxiv.org/PS_cache/astro-ph/pdf/0508/0508047.pdf

Hi All, I am new here, Iam interested in Cosmology, sometimes I find many questions which I don't find its answers directly in textbooks or I read it but couldn't understand it, for example I have a confusion between horizon, particle horizon and event horizon, would you please help me in...

Could someone give me a formula that would describe an event horizon, and also explain your view?

General relativity tells us that an infinite number of houses can be built at fixed altitudes in the one meter (say) above the horizon, as measured in Euclidian geometry. Let this infinite number of houses exist. Let the street numbers of the houses increment with decreasing altitude. For...

For an object exactly at the event horizon of a black hole, is the acceleration infinite or does the object accelerate at the speed of light? I have read that the force on the object causing it to accelerate when it is at the event horizon is infitite (so the acceleration would be too), but the...

Well... let me offer a small contest - I called it Knowledge Horizon Contest, and you'll find out why in a couple of minutes: 1. Everyone who wishes to enter the contest has to post a single question in this thread till Friday 22 APR 0:00 GMT. The poster is recognized as an author of the...

light in the event horizon does not come out, right. If this is due to gravity will light on the edge of the event horizon, butnot in it, be bent, so that when we look at the light beside a black hole, it is not coming from the behind the black hole, but from an angel. ___________s...

How can we estimate the mass of the Universe if we can only see the part that is within our horizon?

Hey, my first post here, glad I've found somewhere on the internet to discus this crazy stuff! Anyway here's my question: Matter falling into a black hole accelerates towards it under its gravity, towards the "event horizon" (or Rs=2GM/c^2) The relativistic version of the law of...

I do a little project about photon at the event horizon. I use GR to proved that anything in the event horizon can't escape from black hole, but a Prof. say that I must use string theory.But I did't accept with him.So, if someone know about it.Please Help me :cry: . (I have to tell you that...

I'm familiar with the Horizon Problem and how it is solved by the theory of Inflation. I also know that Inflation solves some other cosmological problems and fits well with the current CMB data. Just focusing on the Horizon Problem, however, I'm curious about one thing. It seems to me that...

I am intriqued by a recent series of three papers on black holes: http://www.arxiv.org/abs/gr-qc/0411060 Title: The river model of black holes Authors: Andrew J. S. Hamilton, Jason P. Lisle (JILA, U. Colorado) http://www.arxiv.org/abs/gr-qc/0411061 Title: Inside charged black holes I...

Consider a Schwarzschild spacetime. If the singularity due to the point mass is removed (e.g. with an homogeneous matter distribution), does the event horizon disappear? If yes (I assume this is the case), how can be proven that there exists no event horizon if there is no singularity? May be it...

Ok, let's say we wanted to know the diameter of the largest black hole. (Its event horizon) Let's say the universe had contracted and all the galaxies had been consumed by black holes and all merged into one single massive hole. Say there were approximately 100 billion galaxies, all...

Escape velocity at particular radius from the gravitational source means the initial speed that an object needs at that raduis in order to coast without limit ("to infinity") without ever falling back to the gravitational source. If the escape velocity at a radius is so large that nothing...

Many websites claim that someone falling into a black hole would be ripped apart by tidal forces as he crosses the event horizon. Others say that the falling observer feels nothing special as he crosses the event horizon - he doesn't get torn apart by tidal forces until he gets close to the...

Is the event horizon of a black hole (as seen by an observer at rest relative to the singularity) equivalent to the singularity (as seen by a free-falling observer)? In other words, if the stationary observer watches a rocketship free-fall to near the event horizon then turn on its rockets and...

http://facstaff.uww.edu/mccreadd/intro4.html Oculomotor micropsia/macropsia seems to be a truly fundamental angular size illusion. It shows up in many different kinds of visual spatial illusions (McCready, 1965, 1983, 1985, 1986, 1994a, 1994b, 1995). The present theory simply proposes that...

Was wondering: In Hawkins's " Univers in a nutshell" book, he talks about the behavior ov virtual particle pairs around the event horizon of a black hole. My understanding is that one of the antiparticle of the pair can be absorbed by the black hole. This makes for the release of the particle (...

Was wondering: In Hawkins's " Univers in a nutshell" book, he talks about the behavior ov virtual particule pairs around the event horizon of a black hole. My understanding is that one of the antiparticule of the pair can be absorbed by the black hole. This makes for the release of the...

Papers by a number of authors have shown that Loop Quantum Cosmology removes the big bang singularity. Loop Quantum Cosmology development leads that of the full LQG theory because in cosmology one is essentially quantizing the prevailing (Friedman) cosmological model, which is a deal simpler...

The everyday sky is blue, though it can be noticed there are different hues depending on how high or low you look. Towards the horizon, the sky becomes much lighter, and looking low enough it appears white. What is the reason for this?

One of my friend had asked me one question which I did not really have a good answer for. His question was: Why does the antiparticle counterpart of the virtual antiparticle pairs (those that appear due to uncertainty between time and energy) at the event horizon fall into the black hole...

To calculate the size of the observable universe, one has to calculate the current distance to the particle horizon (t0: today, c = 1): \int_{0}^{t_0} \ dt / a(t) (1) To be able to calculate the integral one has to find an expression for a(t). With some assumptions one can take a(t) =...

[SOLVED] Two black holes and the event horizon.. What happens if a black hole enters another black hole's event horizon?? I really wonder can matter escape by the gravitational chaos?? I asked this question to the scientist in NASA haven't received the answer yet..But this is a...

All right, physicists claim that mass can be at infinite density. This condition is called the singularity, an one-dimensional point that is having mass (or energy, whatever)inside it. I say mass cannot possibly form singularities. Why? Because of the following: When there is mass inside...

It just turns out that the dark energy density Λ or cosmological constant is of such a size that 3pi/Λ = the surface area of the observable universe Smolin calls the surface of the observable universe "the cosmological horizon" and treats it in the same paragraphs with black...

The spacetime geometry outside a black hole may be transformable through the event horizon as the black hole internal geometry, and conversely. Consider Hawking radiation with respect to black hole entropy. While one quantum escapes to universal infinity, the other approaches the...

Did anyone else hear about this new development? Apparently if a black hole has a steady influx of matter/energy, it may not develop a singularity which brings about infinite tidal distortion, but it could bring about a 'gentler' cauchy horizon singularity that could be possible to traverse...