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What is singularity?

How come of it?

How come of it?

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- Thread starter AMD_K8L
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- #1

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What is singularity?

How come of it?

How come of it?

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"A point in space-time at which the space-time curvature becomes infinite."

Nonetheless I'd like to read a more extended version of this definition from more knowledgeable people.

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DM said:

"A point in space-time at which the space-time curvature becomes infinite."

Nonetheless I'd like to read a more extended version of this definition from more knowledgeable people.

Hawkin's difinition is amusing... But it may be not exact?

Althought the difinition is right...

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George Jones

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AMD_K8L said:What is singularity?

I am not sure that there is a completely accepted technical definition.

Roughly, a spacetime is singular if there is a timelike curve having bounded acceleration (i.e, a worldline an observer could follow) that ends after a finite amount of proper time. Singular spacetimes have "edges".

How come of it?

By the Penrose-Hawking singularity theorems, any "reasonable" classical spacetime must be singular. Very roughly, in any "reasonable" classical spacetime, gravity is so stong that the fabric of spacetime gets ripped, thus creating an "edge".

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AMD_K8L said:What is singularity?

How come of it?

Is it Singularities are a unlimited dense point without any volume?

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Just a question, nothing more.

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A singularity is a mathematical phenomenon based upon the absentia of a physical theorem for quantum gravitation, and not a real physical actuality.

Reference:

http://en.wikipedia.org/wiki/Gravitational_singularity

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DM said:

There's nothing "super duper" about Wikipedia's definition; in fact, it's a pretty loose definition IMO. If you want a simple definition of a spacetime singularity, try this one on for size:

That's the simplest explanation I can think of, but it doesn't really do the concept justice. In particular, one can have a more exact definition of a singularity by saying that the singular points of a spacetime are those which cannot be included in the maximal analytic extension of the spacetime, but I guess that's a bit more than you want.

To use the more usual notion (i.e., from popularizations of science such as Hawking's books), a singularity is a point where the predictable nature of physics breaks down because the curvature predicted by general relativity at that point is infinite.

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Intuitive said:

No. That sentence doesn't actually make much sense, quite apart from it being the wrong interpretation.

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George Jones

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Thanks George.

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Hmmm, well people who are perhaps more knowledgable than me can correct me, but a singularity is only a singularity from another frame of reference, am I right? In the frame itself there is no singularity right? Hence no breakdown of laws right?coalquay404 said:To use the more usual notion (i.e., from popularizations of science such as Hawking's books), a singularity is a point where the predictable nature of physics breaks down because the curvature predicted by general relativity at that point is infinite.

Would be funny if laws in nature would break down, for why would they be defined as laws? :)

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Garth

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Wrong actually, a singularity in one frame of reference would be a singularity in any frame of reference.MeJennifer said:Hmmm, well people who are perhaps more knowledgable than me can correct me, but a singularity is only a singularity from another frame of reference, am I right? In the frame itself there is no singularity right? Hence no breakdown of laws right?

My definition of a singularity is "a point in space where any of the properties of matter or space-time becomeWould be funny if laws in nature would break down, for why would they be defined as laws? :)

You can argue whether they actually exist, whether the limit is actually reached, or whether the concept is merely an artifact of an incomplete knowledge of what happens in the extreme conditions as that limit is approached.

Garth

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Really? So is that described by some kind of theorem or so?Garth said:Wrong actually, a singularity in one frame of reference would be a singularity in any frame of reference.

It appears counterintuitive to me.

What could be an infinity to an outside frame of reference does not have to be one locally right?

Take for instance a measurement of an object from an outside frame of reference that becomes a singularity. Time grinds to a halt and volume becomes zero right? But inside, does time stop as well and does voume become zero as well?

Seems that I am missing something here with regards to your assertion that a singularity is frame of reference independent.

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Garth

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Are you confusing the singularity itself with the event horizon around that singularity?MeJennifer said:Really? So is that described by some kind of theorem or so?

It appears counterintuitive to me.

What could be an infinity to an outside frame of reference does not have to be one locally right?

Take for instance a measurement of an object from an outside frame of reference that becomes a singularity. Time grinds to a halt and volume becomes zero right? But inside, does time stop as well and does voume become zero as well?

Seems that I am missing something here with regards to your assertion that a singularity is frame of reference independent.

At the event horizon around a Schwarzschild BH the coordinate system becomes singular, but that can be transformed away - just as the Lat. and Long. system of coordinates on the Earth's surface becomes singular at the N. & S. Poles. However you cannot transform away the physical singularity at the centre.

At the genuine singularity at the centre there is no time - it doesn't 'grind to a halt', there is no way of measuring it at all, it has become

Garth

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Sorry, but I am still not getting it.Garth said:At the genuine singularity at the centre there is no time - it doesn't 'grind to a halt', there is no way of measuring it at all, it has becomesingular.

Let's assume some very small object getting caught by a black hole. At one point it passes the event horizon and after that it gets drawn closer to the center.

Now I understand that for any outside frame of reference (both inside and outside the event horizon) is appears as if the object is going towards a singularity. But for the object itself? How could it become a singularity?

It seems to me, and I suppose I am wrong about it, that a singularity is a singularity for all outside frames of references but that the space-time of an infinitessimal small size regarded as the singularity for the outside frames of references is not.

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Garth

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It gets squashed until in the limit its density and temperature become infinite and its volume zero.MeJennifer said:Sorry, but I am still not getting it.

Let's assume some very small object getting caught by a black hole. At one point it passes the event horizon and after that it gets drawn closer to the center.

Now I understand that for any outside frame of reference (both inside and outside the event horizon) is appears as if the object is going towards a singularity. But for the object itself? How could it become a singularity?

I'm not sure I understand that statement. The singularity, at the centre of the event horizon, is a - well - singularity.It seems to me, and I suppose I am wrong about it, that a singularity is a singularity for all outside frames of references but that the space-time of an infinitessimal small size regarded as the singularity for the outside frames of references is not.

Garth

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Ok then let me reword it.I'm not sure I understand that statement. The singularity, at the centre of the event horizon, is a - well - singularity.

In GR the measurement of space and time of a particular region depend on the frame of reference right? So a measurement from any frame of reference, which has to be from inside the black whole since from outside one cannot even make a measurement, of the center of a black hole will result in measuring a singularity. No disagreement here. But the area that is the singularity itself, the infinitesimal small region itself, if we place the frame of reference there, then how do you conclude that even there there is a singularity, that is what I don't understand.

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MeJennifer said:Hmmm, well people who are perhaps more knowledgable than me can correct me, but a singularity is only a singularity from another frame of reference, am I right? In the frame itself there is no singularity right? Hence no breakdown of laws right?

Would be funny if laws in nature would break down, for why would they be defined as laws? :)

No, a singularity is a globally defined quantity so it is a a singularity in all frames of reference.

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Unless it is a theorem or so, stating that it is defined as such is not an answer at all.coalquay404 said:No, a singularity is a globally defined quantity so it is a a singularity in all frames of reference.

Why?

For instance, an object occupying an infinitessimally small region of space drawn inside a black hole does not encounter anything unusual in its local measurements of space and time, even when it is eventually drawn into the singularity. Am I to believe that for that small region everything simply from one point in time to another becomes undefined? Again I fully understand that that is what happens from an

It seems to me that the measurement of time and space

Clearly from within the region measurement outside of it would become very different rapidly and I would wonder if not from this region the ouside would appear a singularity!

One should be able to demonstrate that for an object occupying an infinitessimally small region of space that is sucked into a singularity the space and time coordinates

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Garth

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Of course it does, at the singularity itself, (not at the event horizon where just the Schwarzschild coordinates become singular,) there are no measurements of space and time, they have becomeMeJennifer said:For instance, an object occupying an infinitessimally small region of space drawn inside a black hole does not encounter anything unusual in its local measurements of space and time, even when it is eventually drawn into the singularity.

Yes.Am I to believe that for that small region everything simply from one point in time to another becomes undefined?

Garth

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I feel that serious modelling of the details of this process and the environments created as the collapse progresses could lead to signifficant insights that could help when the need comes to consider quantum gravity.

The way thse subjects appear to be dismissed is a bit like saying our universe is uninteresting because it all ends with a heat death and forgetting that all the interesting stuff (like life) is actually happening on the way to this final process.

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