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4 votes

Wouldn't Miller's planet be fried by blueshifted radiation?

For a 2.7 K blackbody (like the CMB) the calculator at http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/radfrac.html gives me 3 $\mu$W/m$^2$. This is how much Earth is heated by the CMB — not a lot! ...
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29 votes
Accepted

Wouldn't Miller's planet be fried by blueshifted radiation?

Miller's world would be fried by a strong flux of extreme ultraviolet (EUV) radiation. The cosmic microwave background (CMB) would be blueshifted by gravitational time dilation and then would be very ...
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0 votes

Why would black hole rip me apart?

The tidal force between your head and feet depend on the difference in $GMm/r^2$ for the two different r values, one about 2 metres closer than the other. Tidal ...
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  • 1,364
2 votes

Could we be sucked up entirely by a micro black hole?

If you and the black hole were the only things in the universe, then you would just be tidally shredded and then consumed extremely rapidly for a black hole of any sensible macroscopic mass. Anything ...
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2 votes

Why we don't see time dilation in stars orbiting black hole?

We do "see it" but the effect is smaller than you imagine. As already pointed out, the effects of time dilation are too small to have any visible apparent influence on the orbits in that ...
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3 votes

Why would black hole rip me apart?

There are nice answers by @fraxinus and @profrob, I would like to add a little side note about the balance between the forces. It arises because the gravitational field exerted on one body by another ...
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1 vote

Why would black hole rip me apart?

The inertial frame that falls towards the mass freely is only approximately an inertial frame. Around the Earth the approximation is almost perfect agreement. In the ISS, if you place marbles ...
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  • 1,641
3 votes

Why would black hole rip me apart?

As a complement to the other answers: Not every black hole is capable of ripping you apart tidally. Too small black hole will burn and blow you away you with its Hawking radiation way before you are ...
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  • 5,703
0 votes

Does an observer experience stronger gravity on the way towards the singularity?

Time dilation is said to be already infinite at the event horizon, so how could it become stronger inside? Yes but that's seen from the outside. When you fall in you don't experience local time ...
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  • 1,641
1 vote

Are there any other significant radii around Schwarzschild black holes besides the four I know of?

There are radii that play a role when a black hole is observed from afar, for example by the Event Horizon Telescope. For example, the event horizon appears to be $2.6r_s$ because the space around the ...
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2 votes

Why would black hole rip me apart?

It's also worth nothing that in the case of many black holes of which we have knowledge, the radiation from the accretion disk is so intense that you would be blasted into plasma long before you ...
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  • 251
0 votes

Does an observer experience stronger gravity on the way towards the singularity?

One of the great differences between classical and relativistic gravity is that in the former there is no side effect in supposing all matter concentrated at a point (well, except for the huge tidal ...
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43 votes
Accepted

Why would black hole rip me apart?

The problem is that when you are falling, all of you can't be in the same inertial frame. That is, whilst your centre of mass might be inertial, parts of your body will be feeling accelerating forces ...
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  • 111k
0 votes

Does an observer experience stronger gravity on the way towards the singularity?

The implication of your comparison with a neutron star is that you define "gravity" as the force required to keep an object at fixed radial coordinate. By this definition, the "gravity&...
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  • 111k
0 votes

Does an observer experience stronger gravity on the way towards the singularity?

A black hole is a singularity in space; there is no going inside (defined as being surrounded by black hole matter). Rather, you could only get closer and closer to the singularity. When you get ...
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  • 10.5k
5 votes

How fast would a clock falling into a blackhole tick relative to the reflection of a clock stationed far away?

If you drop it from rest at radial coordinate $\rm r=r_0$ the free fall velocity at $\rm r=r_1$ is $$\rm v=c \ \sqrt{\frac{r_s \ (r_0-r_1)}{r_1 \ (r_0-r_s)}}$$ which in the limit of $\rm r_0=\infty$ ...
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  • 7,342
1 vote

How compact can a thin shell be without collapsing?

Thin shell could be even more compact than the fluid ball of the same mass. Assuming reasonable energy conditions on the shell matter, the minimal radius of a shell with mass $M$ is: $$ R_\text{min}=\...
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50 votes

Why would black hole rip me apart?

You don't need GR to see this effect. It's due to tidal forces. Suppose you are 2 meters tall. Then the force of the Earth on your feet is $GMm/r^2$, and the force on your head is $GMm/(r+2)^2$. The ...
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  • 16.4k
0 votes

Would this method work for generating sustained arbitrarily high time dilation in the center?

If we rearrange your equation to find the radius we get: $$ r = \frac{2GM}{x c^2} = \frac{r_s}{x} $$ So if you take for example $x = 4$ as you suggest that means the radii given by your equation are ...
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2 votes

Dropping a mirror into a blackhole

The first and second inequality/equation in ProfRob's answer here is the answer to your question. I'm posting this as an answer instead of a suggested duplicate because the questions are distinct and ...
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  • 8,578
0 votes

Dropping a mirror into a blackhole

The clock will measure the proper time of an observer falling into the black hole. The observer will reach the horizon in a finite proper time; you will observe the clock reaching this value ...
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3 votes

Is the gravitational tidal force equivalent to expanding space?

You are neglecting the behavior of particles to the side of you, which are drawn closer. If you start with a spherical ball of coffee grounds then as it falls the ball will be stretched vertically and ...
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  • 64.4k
1 vote

How to calculate Proper Distance as an arc length in Schwarzschild metric?

For a fixed $r$ and $t$, $$ds^2 = r^2(d\theta^2 +\sin^2\theta\ d\phi^2)\ ,$$ which is the same arc length as in Euclidean space. Then if $\phi = f(\theta)$ then $$s =r \int \left(1 + \sin^2\theta\ \...
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  • 111k
2 votes

Where does all the energy in black holes go?

The short answer is: To the future! EDIT: reading OP's question again, they seem to point out, that the temperature of inbound particles is measured by a distant observer as being near zero. But since ...
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-1 votes

Where does all the energy in black holes go?

Firstly I answer question: "How can a very cool object have a large amount of thermal energy": By having a large heat capacity, by having a large number of internal states, by for example ...
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  • 1,495
1 vote

Self-coupling of gravity and gravitation escaping a black hole - contradiction?

"Self-coupling" means that yes, gravity gravitates -- that for example gravitational waves would be affected by the gravitational field of objects they move past. Gravitons, if they exist, ...
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  • 5,883
11 votes

Where does all the energy in black holes go?

Energy inside black holes doesn't "go" anywhere. Energy and mass are the same thing ($E=mc^2$). There's a "no hair" theorem that says that black holes can be completely described ...
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  • 5,883
2 votes

Is it possible the Black Holes to be pure deformations in the fabric of spacetime and not an effect of super-dense matter?

Your explanation in your comment: My definition is the absence of spacetime or vacuum space inside the event horizon will not work. If this were correct then the whole event horizon would be a ...
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  • 33.2k
7 votes

Is it possible the Black Holes to be pure deformations in the fabric of spacetime and not an effect of super-dense matter?

Is there any theory in the literature that supports this hypothesis that BHs in their center do not have a super dense matter singularity but are pure deformations in the fabric of spacetime itself or ...
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5 votes

Why are there three bright spots in the first picture of Sagittarius A*?

Imaging artifacts This image is created by complex image reconstruction algorithms that propose alternative solutions which are averaged. Some of these alternatives do not show a ring structure but ...
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1 vote

What does a black hole accretion disk look like edge on?

You would still see a ring, but it would be quite asymmetric in brightness. The ring is not wholly a direct image of the accretion disk. It includes light from all around the black hole that has been ...
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  • 111k
3 votes
Accepted

Smooth vs analytic spacetimes

We only impose $C^{\infty}$ when setting up the general theory, because real-analyticity would be too strong a condition to impose. However, when trying to find specific solutions (Schwarzschild, ...
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  • 2,339
0 votes

About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

This recent Nature publication seems to contradict the EHT claim in their presentation about the orientation of the Sgr*A BH accretion disc plane relative to the Galactic plane. Seems to me that gas ...
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  • 3,011
8 votes

About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

I think what you mean is that the spin axis of the black hole is not aligned with spin axis of the Milky Way? NB: That's about all you can say - the conclusion of the actual science paper (Akiyama et ...
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  • 111k
34 votes

Why are there three bright spots in the first picture of Sagittarius A*?

According to the imaging data release paper (Akiyama et al. 2022, ApJL, 930, L14), about the only thing that can be reliably taken from this image (which is a kind of time-averaged composite based on $...
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  • 111k
22 votes

Why are there three bright spots in the first picture of Sagittarius A*?

I don't think anybody knows. Take details of these images with a great deal of skepticism. Just reconstructing any image from the EHT is extremely difficult. There probably are hot spots running ...
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-1 votes

${}$Hawking radiation and Einstein-Cartan theory

You said: "As I understand it, Einstein-Cartan theory predicts that inside every black hole, there is an einstein rosenbridge connecting to a new universe that forms due to a white hole." ...
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  • 103
0 votes

Calculating divergence and flux of geodesic word lines

The mathematical construct that you are looking for is called a (geodesic) congruence. A geodesic congruence is a family of non-intersecting geodesics that completely cover some part of your spacetime....
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  • 8,059
-1 votes

How can time go in different directions in the Universe?

If time represents all change in the current state of the universe, then any change in the relationship of variables in spacetime could be interpreted as a change in the direction of time. Example - ...
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1 vote

Fundamental-ness of fundamental forces

Had I wrongly interpret the meaning of fundamental ? For physics theories, yes you interpret wrongly. The word "fundamental" in the way used in physics means a : serving as a basis ...
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  • 221k
1 vote

${}$Hawking radiation and Einstein-Cartan theory

I don't have any particular expertise in Einstein-Cartan theory, but I would caution against taking it seriously as describing real astronomical black holes. Even the simplest black hole solution, due ...
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0 votes

What happens to a hydrogen atom under an intense gravitational field (or intense acceleration)?

A recent paper has studied Schrodinger equation in a general curved spacetime geometry. It has answered some of the questions you asked. When the hydrogen atom freely falls in or is scattered by a ...
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  • 103
2 votes

Schwarzschild-deSitter horizon singularity

George Fanaras wrote: "Λ=H² is the cosmological constant." In my books $ \rm{\Lambda = 3 H^2} $ , if you have the line element in terms of the Hubble parameter $\rm H$ like you do then you ...
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  • 7,342
2 votes

A variation of a Bekenstein's thought experiment

Yes, information loss is both about classical and qubits. Consider two glasses, one hot and one cold but with total mass tuned to be exactly the same. By the no hair theorem both generate ...
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1 vote

Help in understanding how general relativity describes space-time near black hole poles that emit astrophysical jets

Relativistic jets observed in quasars (and other black holes) are not fully understood, but there is consensus around the basics. Matter falls towards a rotating black hole from an accretion disk. ...
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0 votes

Can Alcubierre Space Drive function in space time within event horizon of a Black Hole?

I would say no, as in the area of a singularity, time and space swap places. It would be like racing in any direction trying to escape Tuesday. You can't.
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  • 2,371
1 vote

Finding event horizon and ergosphere

To find the event horizon, one always solves $g^{rr}=0$. Consider a hypersurface of constant $r$ far away from the black hole. $g^{rr}$ is spacelike here. As you move the surface toward the black hole,...
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1 vote

Why are we so sure that there is a singularity inside the event horizon of a black hole?

how can we be certain that there is a singularity at the centre You are starting from a Schrwazchild black hole model which is an idealized eternal model and so never changes. This is a useful basic ...
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3 votes

Why are we so sure that there is a singularity inside the event horizon of a black hole?

I was just 3 minutes ago reading Planck Stars by Carlo Rovelli. In it he conjectures that a star does not collapse down to a singularity, but rather it collapses down to Planck density: 10^93 g/cm^3 ...
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  • 3,486
3 votes
Accepted

I'm confused about the number of Killing vectors in Schwarzschild metric

A brute force (and ugly) derivation of the Killing fields of Schwarzschild metric The Schwarzschild metric is \begin{equation} ds^2 = -\left(1-\frac{R_{\text{S}}}{r}\right) \text{d} t^2 + \left(1-\...
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