Use this tag for questions about singularities in physical quantities, i.e. cases where a quantity becomes or appears to become infinite or ill-defined. Consider the more specific tags [tag:black-holes] and [tag:wormholes] for certain kinds of singularities occuring in [tag:general-relativity]. For ...

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Superficial degree of divergence on Weinberg

Reading volume 1 of Weinberg's QFT book, chapter 12, page 505 he says that if you consider a diagram with degree of divergence $D\geq{}0$, its contribution can written as a polynomial of order $D$ in ...
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20 views

strength of each dipole charge

If I have a two dimensional dipole whose line charges are located on the y axis, I know that the electric flux through a gaussian pill box containing both the charges will be zero, that is ...
1
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0answers
22 views

Can a solid object inside the black hole event horizon avoid the singularity? [duplicate]

I will ask this as a simple lay man. Let's consider an astronomical black hole that was creating by in falling matter on a neutron star. As neutron star get heavier it gets smaller and a Schwarzschild ...
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1answer
49 views

What does singularity mean in the context of black holes? [duplicate]

Non-rotating big stars can be subject to a gravitational collapse increasing their density. When the density is so high that the mass volume shrinks below the event horizon, a black hole is formed. ...
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1answer
25 views

Is there any possible evidence that can give us insight into what happened exactly at the Big Bang/why it happened?

It's mostly well accepted today that the Big Bang was the reason for today's universe, mostly due to the expansion, the cosmic microwave background etc. and mathematically the FLRW metric supports it. ...
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1answer
60 views

What was outside the singularity during the Big Bang? [closed]

What was outside the proposed singularity during big bang?What was the size of singularity?
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1answer
98 views

Why is the force on the charge at the tip of a cone infinite?

Imagine a charge $q$ that is located at the top of a hollow cone with a surface charge density $\sigma.$ The slant height is $L$ and the charge $q$ sits at the vertex of angle $2\theta$. We are ...
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3answers
384 views

Zero $g$ in a black hole?

At the very centre of the Earth, masses cancel each other out, creating an effective zero-$g$ environment. Would the same happen in a black hole?
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3answers
970 views

Why does a singularity need to exist at the center of a black hole?

Sorry if this is a very basic question, but I am not a physicist, but this is something that has always intrigued me. I have read that the properties of a black hole are its mass, spin and angular ...
0
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1answer
24 views

What does it mean that the Rutherford's cross section is infinite?

I'm studying elastic scattering and I read that the Rutherford's differential cross section is defined as: $$\left( \frac{d \sigma}{d \Omega} \right)_R = \frac{Z^2}{4} r_o^2 z^2 \frac{(m_ec / \beta ...
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0answers
63 views

Black hole and relativity [duplicate]

This link shows movement around the black whole. It seems impossible for them to move this fast. http://www.youtube.com/watch?v=ENd8Sz0AFOk If we were able to watch a ship of people go into a black ...
0
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1answer
67 views

What exactly does the Kretschmann scalar implies and how does it work?

From the General Relativity class lectures I understood that this particular invariant, the Kretschmann scalar namely $$R_{\mu\nu\lambda\rho} R^{\mu\nu\lambda\rho}$$ is really important because, ...
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1answer
46 views

Do zero gravitational-force points produce Naked singularities?

In between two singularities, does a particle experience gravity? If a particle is exactly at the midpoint between two singularities, will its net experience of the gravitational force (ignoring the ...
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3answers
42 views

How much energy does an electron have when it is situated right next to a negative point charge?

The formula for potential energy regarding point charges is $E=kQq/r$. If $r=0$, then will the energy be approaching infinity? But what about an electron in a parallel-plates situation where it is ...
0
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2answers
119 views

Coordinate Singularity in Metric

Suppose I have some metric $$ds^2=g(t)dt^2+\frac{1}{r}dr^2$$ which has a singularity at $r=0$. However, if I make the coordinate transformation $u=\frac{1}{r}$, then I get: $$ds^2=g(t)dt^2+r^3 ...
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36 views

Cyclic model of the universe and second law of thermodynamics

Cyclic model from wikipedia The above link shows some theories on cyclic model. It states that a scientist named Richard C. Tolman showed that the cyclic model proposed by Einstein can not be ...
2
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1answer
81 views

Does limiting to infinity violate laws of physics?

It is noteworthy that one cannot simply divide any length more than the Planck-length. If so, one cannot simply divide any volume more than the $(Planck-length)^3$. So if I want to find the limit of ...
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0answers
66 views

Why gravitational collapse always end up in a black-hole singularity? [closed]

I know the positive energy condition and the singularity theorems by Penrose and Hawking. But still, why people didn't work on gravitational collapse to some exotic matter with an event horizon?// My ...
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0answers
25 views

Do all black holes have the same mass density? [duplicate]

I have been reading about black holes in Stephan Hawking's 'A Brief History of Time'. Then I was reading more about it on Wikipedia; I am making a school project on it. I do not really remember what ...
2
votes
1answer
68 views

Why not all timelike world lines have infinite total length?

I don't understand this stament by Geroch(1968), when discussing the definition of singularity: We could not have required that all timelike world lines have infinite total length, for this ...
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1answer
88 views

Do moving singularities crack/tear space-time? [closed]

Question: The tip of a crack in a continuum like glass is a singularity. If we A) set QM and Planck's volume arguments aside and stick to GR only B) assume that at least some* blackholes ...
1
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1answer
47 views

Describing the shape of a singularity

Hawking and Ellis write about the difficulty of describing the shape of a singularity when presented with a manifold that has curves of finite length that don't reach a point in the manifold. ...
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0answers
32 views

Singularity of spacetime and singularity of the riemanian tensor scalar

It's easy to show that a singularity of the riemanian tensor scalar $R_{\alpha \beta \mu \nu} R^{\alpha \beta \mu \nu}$ leads to a singularity of the spacetime. But what about the other way round? Is ...
4
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1answer
253 views

Why can protons collide?

Electromagnetic repulsion is inversely related to the square of the distance between both objects. Shouldn't this mean that the integral of the force between two protons is infinite if the distance ...
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7answers
3k views

What does an undefined formula in physics mean?

I am trying to figure out how undefined formulas in mathematics relates to physics. Take the following formula for terminal velocity. $$V_\text{terminal} = \sqrt{ mg \over{c \rho A}} $$ Say we have ...
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2answers
324 views

Gauss's law… if the integral defining $\boldsymbol{E}$ diverges?

I have been told (here) that, under particular conditions, the electric field produced by a charge present in space $D$, defined by ...
0
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1answer
51 views

Electric field at $r=0$

How does classical physics justify the existence of an electric field at $r=0$? Is this an edge case, an ambiguity, a "does not exist"? Is this a trivial case or indicative of an actual fault in ...
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1answer
60 views

It's a Hypothesis about the Beginning of the universe [closed]

Let's take a piece of paper and plot a couple of dots in it. If we shrink the paper infinitely, at some point it would reach a state of infinite density, that is; a Singularity. But even at that ...
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3answers
71 views

Are black holes naked singularities for an observer within the event horizon?

A naked singularity means that you can see an infinitely dense thing. Black holes don't count because it sucks up all the light, so you won't see or otherwise detect it. But wait, if you are within ...
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2answers
76 views

Is this charge density function, from a problem in Griffiths' book, a physically valid density?

This is from the book on electrodynamics by Griffiths: A sphere of radius $R$, centered at the origin, carries charge density $$\rho(r,\theta)= k(R/r^2)(R-2r)\sin(\theta)$$ where $k$ is ...
0
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2answers
71 views

Point forces in linear elasticity and small strains

Consider a point force $\boldsymbol{F}=F\boldsymbol{e}_z$ in an infinite elastic material. In a linear approximation, the displacements can be calculated using Green's function for the Laplacian which ...
0
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0answers
25 views

Do we know for sure that black holes must contain a singularity? [duplicate]

I've perhaps naively wondered for years whether there are any rules or proofs that allow us to know for sure that if all an object's mass is contained within its Schwarzschild radius it must be a ...
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2answers
81 views

Space and time quanta? [closed]

Is there a possibility the space and the time are not continuous, but rather, quantified (only some positions in the space exist, and some instants in the arrow of time) ? Hopes my question is clear. ...
0
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1answer
131 views

Is there a place in the universe where time doesn't exist?

I've been reading that, all laws of nature and the universe stop existing at a singularity. So where there is a singularity, there cannot be time. A singularity is created when a property of a system ...
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2answers
71 views

Do particles in a black hole stay in constant orbit?

Would particles behave the same way as a satellite orbiting earth, only far more compact and rapid correlating to the gravitational force of the black hole?
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2answers
159 views

What equation (/solution) predicts the existence of black holes?

Where does our theoretical prediction of the existence of black holes come from? If it is (as I am guessing) from the Einstein Field Equations, which solution predicts it and why?
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1answer
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Singularity - Origin Point

How can it be said that the real beginning of the real universe involved a "singularity of zero size and infinite density of mass" when no space existed at all to define any density and when ...
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4answers
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$g=GM/r^2$; $M=$mass of Earth. So in center $r=0$, so $g$ should be infinity [duplicate]

From the equation of Newtonian gravitational force, we know that $$F=\frac{Gm_1m_2}{r^2}.$$ If one of the two objects is Earth, then from $F=GMm/r^2$ and we know $g=GM/r^2$. So 'g' should be infinity, ...
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2answers
101 views

Is Quantum Coulomb still singular?

A single free charge (e.g. electron) $q$ fixed at the coordinate origin has the well-known Coulomb/electric potential $$\phi(\vec r) = \frac q{4\pi\epsilon_0}\frac 1r \tag{A}$$ where $r=|\vec r|$ of ...
0
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0answers
32 views

Why isn't the universe a singularity? [duplicate]

So, i'm just a high-schooler interested in physics, so don't judge me if I misinterpreted anything. But from my understanding of black holes, a singularity is created because any matter inside the ...
0
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1answer
67 views

Why are black holes called singularities? [duplicate]

I have researched black holes but I can't seem to find the answer. Any help would be appreciated.
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0answers
23 views

The universe is said to have begun as a singularity, but how do we know nothing else existed? [duplicate]

When I imagine the big bang, I first imagine a tiny ball surrounded by black void. Then the ball explodes and the universe begins. I assume most physicists have the same basic idea. But how do we ...
0
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2answers
40 views

Blackholes / density [duplicate]

If a star explodes to form a black hole how does the gravitational field become infinite from one state to the next? ie: it seems additional mass has been added or is this simply a function of ...
2
votes
2answers
122 views

Does infinite actually occurs?

I tend to deny any claim that $X$ is infinite, where $X$ is anything from our observable universe. For instance: The number of grains of sand on Earth is infinite? No, it is a big number but not ...
0
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2answers
79 views

Probing beyond the black hole event horizon

Black holes are interpreted to have a "break down" of general relativity at their point of singularity. The region near the singularity is expected to be described by some theory of quantum gravity. ...
1
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1answer
46 views

If there is a point in a past set, does its chronological future interset a future set?

This post concerns the causality of spacetime $\mathcal M$. A future set $F$ is defined to be the chronological future of some set $S\in \mathcal M$, ie., $F=I^+[S]$. Similiarly, a past set ...
3
votes
4answers
254 views

Is a black hole's mass uniformly distributed?

If you were to fly around a black hole, would the gravitational pull be uniform and centered on the singularity, regardless of your relative location? If yes, how can this be consistent with models ...
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4answers
3k views

Why do physicists trust black hole physics?

Based on popular accounts of modern physics and black holes (articles, video lectures), I have come to understand the following: Black holes are predicted by General Relativity, a classical theory ...
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2answers
66 views

Do the stellar remnant in a black hole have spatial extent? [duplicate]

I am not talking about event horizons. I am talking about the actual remnant of stellar collapse. Is it just a point, hence the problem with the singularity? Or does it have a finite volume that we ...
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0answers
40 views

bose einstein phase transition

From Carter's book Thermodynamics and Statistical Mechanics, the partition function of a bose-einstein gas in $d$ dimensions is $$ \ln(Z) = ...