# Tagged Questions

An event horizon is a type of boundary such that any information past this boundary is inaccessible to the observer it is defined for. Common examples are the Schwarzschild radius of a black hole (which is defined commonly for all observers outside this radius) and the cosmological even horizon (...

112 views

### Why does an evaporating black hole always stay a black hole?

Stars can only collaps and form black holes if their masses are above the Chandrasekhar limit, $M>M_{\rm Pl}^3/M_{\rm hydrogen}^2$. When the universe eventually cools down enough, the black holes ...
453 views

### What is the relationship between the Schwarzschild radius and Black hole Singularity?

What is the relationship between the Schwarzschild radius and Black hole Singularity? Can the Planck length be the length of singularity? Or is the length of the Schwartzschild shorter than the Planck ...
299 views

### Size of black hole so large that I could pass event horizon without dying from tidal forces?

Were I to fall towards a typical black hole, the tidal forces would rip me apart well before I got to the event horizon. However, if a black hole were big enough, I could enter the event horizon ...
571 views

### What is the current radius of cosmological event horizon?

Doing some crude calculations (using the value of $H_0$ at this point of time only, since it is time dependent but not distance dependent thanks to Johannes answer) what is the radius of cosmological ...
69 views

### Schwarzschild metric black hole

Schwarzschild metric solution presents two singularities. An apparent one at $r=2GM$ and a real one at $r=0$. It is known that everything freezes at the event horizon from an outside observer point of ...
108 views

### What would the Sagittarius A black hole look like if we were in a spaceship just outside its event horizon?

Let's pretend that our spaceship is shielded well enough that being in the presence of the black hole won't kill us with radiation. I have read that the black hole is as large as the space between the ...
243 views

### Is an event horizon absolute to all observers?

Recently I had discussion whether the event horizon of a black hole is absolute or relative to different (outside) observers. Does someone just 1m above the horizon (disregarding effects of tidal ...
883 views

### What happens to the wavelength/frequency of a photon as it passes through an event horizon?

I've asked a similar question about photons and black holes but wanted to rephrase it more specifically, so here goes... Ever since I learned how a photon's wavelength and frequency are indivisibly ...
255 views

### Direction of Time on Event Horizon

Does the axis of Time point into a black hole or away from? Can you give a reference paper?
149 views

### Relativity and volume of black hole

Does Einstein's theory of special or general relativity incorporate volume? In a particle accelerator two particles smash together at relativistic speeds and "create" new particles (quarks etc) due ...
641 views

### Electromagnetic black hole?

So I was thinking about something for the past while Consider a large spherical foam-ball with homogeneous density. Where a foam ball is defined as an object that can absorb matter with 0 friction (...
348 views

### Relativistic Computation?

Is it possible to employ relativity to develop computational technology? Here is a really basic example: Build a Computer and Feed it the Problem (say the problem is projected to take 10 years to ...
49 views

536 views

### Is the difference between an event horizon and a singularity merely perspective?

I know the question has been asked about how an event horizon is distinguishable from a singularity given that time must come to a stop at the event horizon, but I haven't been fully satisfied by the ...
417 views

### Do black holes exert an infinite amount of energy at the event horizon?

An interesting thought crossed my mind when reading about Hawkings' apparent horizon theory. If we assume that event horizons do actually exist, it would seem that black holes violate basic laws of ...