12
No one knows what came before the Big Bang if, indeed, anything did. Theories include:
The Ekpyrotic universe theory where the BB was the result of the
collision of branes.
Various oscillating universe theories where
the expansion of the universe ultimately reverses into a Big Crunch
Quantum fluctuation models where a zero-net-energy universe is a
quantum ...
9
You need to be a bit cautious about statements like: A black hole contains a singularity at its center. It is a zero-dimensional point, and it's where all its mass is located. What you are referring to is a mathematical structure called the Schwarzschild metric. This is indeed a solution to the Einstein equations for a static black hole, but this particular ...
6
The answer is, of course, that a singularity can't exist. The fact that General Relativity predicts that singularities are inevitable under certain conditions is proof that GR is wrong. A singularity is an infinity and a place where the equations of GR literally break down and become meaningless. (Infinities are decidedly unphysical!) When (if!) a more ...
6
Does having an event horizon imply the existence of a singularity?
An event horizon is not an inherent component of any given object. It's not like once a star turns into a black hole, it suddenly gets an event horizon. The event horizon is merely a mathematical boundary which defines the distance from a mass $M$ where the escape velocity equals the speed ...
6
What is a singularity?
A singularity is a point in the universe where matter is infinitely dense. The singularity is at the centre of the black hole, and is often hiding behind an event horizon. So basically, a singularity is a point in space where a lot of matter is squeezed together in a very small space. When you have a singularity matter does not go to ...
4
I'll take the reference of an observer falling with the helium atom. At the Event horizon, the tidal force across a helium atom is still minute, $10^{-29}N$ much less than the Coulomb forces between the electrons and nucleus, still less than the strong forces inside the nucleus. So the atom will fall through the event horizon without damage. (The region ...
4
This answer is to some degree opinion-based. I share your scepticism about the existence of strict mathematical singularities as General Relativity would predict. This is mainly, because the assumption of a strict singuarity ignores quantum theory. One approach to overcome the singularity is a Gravastar. Related is a Planck star. Both approaches try to ...
4
Infinities are hard to bend the mind around, but in this case, the merge is not impossible. Yes, the distance between them must reach zero in order to make the black holes merge, but the rate of which energy is lost to gravitational waves also increases when they get close to each other.
We are therefore dealing with a $\frac{\mathrm{infinity}}{\mathrm{...
4
I think you are starting off from the premise that there is some way of stabilising an extremely dense object inside the event horizon of a black hole. In the classical theory of General Relativity the singularity is inevitable. Once inside an event horizon an object is compelled to move towards, and reach, the singularity in a finite time, in the same way ...
4
Singularity means "my theory doesn't work here". In other words, GR is unable to predict what happens at the point, so it calls this point a singularity.
The most important thing is not to mistake map for the territory. GR is the map, a real black hole is the territory. GR is the map which allows us to predict what we will find in the territory.
If the map ...
4
A singularity isn't an object. It is a property of a differential equation. For example:
$$t \frac{dx}{dt} + 2x= 0$$
This can be "solved" to give $x = \frac{C}{t^2}$, and given a value of $t$ and the corresponding value of $x$ the constant of integration can be found unless $t=0$.
If you are given this equation and the value of x at time t=0, you can't ...
3
As everyone is saying, this is a very loose "plain English" version of some complex ideas, but if space was infinite, you could view this suggestion (that the overall total energy of the universe is zero) as applying to any sufficiently large region of space. So if you pick any 10 billion lightyear diameter sphere you would expect to find the energy of the ...
3
As you say (although you phrase it slightly wrong), time slows down closer to the horizon, as seen from a distant observer. That means that, in the reference frame of a distant observer, matter never crosses the event horizon, but instead "piles up" at the horizon, creating a thin shell of matter. In the reference frame of the falling matter, however, it ...
3
A real neutron star would start to collapse when the strength of its gravity exceeds the strength of the neutron degeneracy pressure, before it has an event horizon.
As you approach the event horizon, the force required to stop a stationary mass from falling in approaches infinity. So I don't think any finite force, fictional or otherwise, can keep a star ...
3
Firstly do not confuse the event horizon with the singularity. Wikipedia gives the formulae for the Kerr metric. There are a number of places where this formula appears to break down because you appear to be dividing by zero, essentially whenever $\Sigma = 0$ or $\Delta = 0$, in the notation of that page, corresponding to the ergosphere and the event ...
3
The answer specifically about the question of a neutron star disappearing inside an event horizon but remaining in some sort of equilibrium is no. At least, it is no according to General Relativity, which is the only respectable game in town at present.
It is no for two reasons. Firstly, in GR, the pressure that supports a star is also a source of gravity (...
2
Nobody likes the idea of naked singularities, as they would have a toxic effect on causality. If a singularity existed that was not separated from us by an event horizon, then not only would the future not be predictable, but the past would not be fixed. Like the grandfather paradox, it wouldn't make sense, so it cant exist. The trouble is that GR doesn't ...
2
It is common to describe a singularity as a point of infinite density, but really they are more general than that: they are some sort of pathological behaviour in the spacetime metric. Whether singularities are actual physical phenomena or they just demonstrate the point at which a theory (in this case general relativity) can no longer describe nature is a ...
2
A black hole could be any size. It could be the size of a planetary system.
Given a specific distribution of matter, I think you don't necessarily need a singularity to be present.
But given the fact that matter inside the black hole cannot escape it, it will eventually all move closer and closer and end up creating that singularity.
Even if we imagine a ...
2
In his book "Brief Answers to the Big Questions" completed by his colleagues after his death, Stephen Hawking does sort of mention that the negative energy created (along with equal amount of positive) at the time of Big Bang is in space now or is space as both matter-energy and space were created after the Bang. The universe is the ultimate free lunch. As ...
2
zephyr is right that you would need quantum gravity to really understand what happens inside event horizons. But the traditional description of what would happen inside the event horizon of a black hole (more or less ignoring quantum mechanics) is that there is no force that can stop matter from forming a singularity. The coordinate system inside the event ...
2
A black hole contains a singularity at its center. It is a zero-dimensional point, and it's where all its mass is located.
This isn't an established fact. A lot of people say they don't think there is a point-singularity at the centre of a black hole. Google on black hole "no point singularity"
So, my first question is: If a singularity contains all a ...
2
Well, you're partially correct here. A black hole traps everything inside its event horizon. Outside of the event horizon, matter (and energy) can still escape from its gravitational pull. This is due to the fact that the escape velocity of a black hole beyond its event horizon becomes greater than the speed of light itself.
So, the light you see around a ...
2
The mass (equivalently energy) is radiated away as Hawking radiation.
1
$$
K_\text{min}=2\pi\sqrt{a^2+3(ma^2)^{2/3}}
\tag{1}
$$
where the quantities $m$ and $a$, both of which have units of length, are defined by
$$
m=\frac{GM}{c^2}
\hskip2cm
a=\frac{J}{Mc}.
\tag{2}
$$
The maximum spin is a=m (an extremal Kerr black hole), the borderline case between a black hole and a naked singularity.
More details from Chiral ...
1
Your intuition is correct, as far as classical dynamics is concerned. The main problem, I think, arises in that you are referring to a strictly quantum mechanical phenomenon - what is the physical singularity? In General Relativity (GR), we know these singularities exist, but we cannot really know more than that (aside from events that occur not too close to ...
1
The notion of "centre of the black hole" is misleading. It treats the spacetime in and around the black hole as if it were normal flat spacetime, with no gravitational distortion. In fact the spacetime is highly curved. So curved, in fact, that "space" behaves more like "time". Instead of "where is the singularity" you should ask "when is the singularity."
...
1
As a star or neutron star collapses to form a blackhole there will, of course, be a moment when the matter is distributed everywhere within the event horizon. So, there may not be a singularity within a full fledged blackhole, at first. But, the inward forces within the event horizon are irresistible (considering that escape velocity is greater than the ...
1
The answer from @JamesK is pretty much all you need to know on this topic.
Since you mention the word "singularity" in the title, let me add this - the singularity is not a thing. I know how pop sci articles talk about it as if it was a thing, but it's just a mathematical abstraction.
At the center of the black hole - we don't really know what happens. The ...
1
I believe that black holes are singularities in the sense that matter in it, is not-defined to have any meaningful location or known velocities. I don't think it means singularity in the sense of having zero radius.
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