singularities and blackholes

[Money]

is there a difference between the two

or are they the same and if they are different

what makes them different than one another??

[insane_alien]

a singularity is part of a black hole(according to current theory) a blackhole generally includes the event horizon as well.

[[Tycho?]]

A singularity is a mathmatical term, which you are free to look up.

 

A gravitational singularity would be the same as a black hole I believe however. At least a black hole as it is understood by general relativity.

[Martin]

Tycho is right, math term. should be something in Wikipedia (but caution, Wik not always right)

 

Singularity is not something in nature, it is something that happens in a manmade theory. It is where the theory breaks down.

 

There are singularities in all different kinds of theories---places where the theory blows up and gives nonsensical results, infinities etc.

Classical electrodynamics had a failure (atoms would not be stable) and was fixed by QUANTIZING. Classical thermal radiation had a blow-up and that was also fixed by quantizing.

 

People have expected for a long time that the singularities in classical Gen Rel will be fixed by quantizing. When this happens the new theory (an improved or quantized Gen Rel) will have to be tested empirically like any new theory.

 

Gen Rel breaks down in several different ways in differnt situations. So it has singularities (places it goes haywire and is no longer reliable)

One kind is black hole

another kind is bang

another is crunch

 

NONE OF THESE ARE THE SAME KIND

the bang failure is at a particular instant of time but (if space is infinite) it can extend over all space (don't have to picture it as occurring at a single point)

 

the hole failure is localized in space but enduring in time

 

so you shouldn't confuse the two.

==========================

 

the important thing to know about Gen Rel singularities is that THEY ARE IN PROCESS OF GETTING FIXED and there is quite a lot of current research about this

 

this year, for example, there was a high-power workshop called "The Quantum Nature of Spacetime Singularities" with top string and non-string QG people participating. the keynote talk made it clear that the workshop was about resolving (getting rid of) singularities. It lasted the better part of 3 weeks---at the Santa Barbara Institute for Theoretical Physics. the talks (slides and video) are online.

just google "KITP singularities" if you want. if any trouble let us know and I or someone will get the link.

 

a lot of scientific journal articles are appearing nowadays about this business of fixing the GR singularities, typically by quantizing.

they just go away and often you get something like a "bounce" in their place---a contraction to very high density followed by re-expansion

this are new models and they still need to be tested, so maintain the proper scepticism as with any new theoretical physics.

[fattyjwoods]

a singularity is in a black hole (the very center to be exact).

[Severian]

a singularity is in a black hole (the very center to be exact).

 

What makes you think this?

[nexteinstein]

because the highest mass is usually at the center cause the gravity is attracted to that point according to the laws of physics.from your first question a singularity is different to a black hole cause singularities can be in other forms such as the bis bang or the predicted big crunch so its not only in a black hole

[Severian]

What I was meaning, is why do you think it is a singularity? Have you ever observed a singularity in real life? It seems far more likely to me that there would be some sort of quantum gravity effect which would kick in as you got close to the centre stopping it from becoming a singularity.

[pioneer]

I believe that SR and GR both have the same constraints when it comes to acheving a speed of light or singularity reference. Both will take infinite mass/energy. The blackholes we see are finite points, since by the theory of their formation, it doesn't require infinite mass to form. If all the mass in the universe formed a blackhole, this would be close to a singularity. Nobody can prove it either way, but since GR and SR both generate the same types of parameters, based on energy potential, i.e., time dilation and distance contraction, it would seem logical that mass and relativisitic mass should also show the same types of limiting constraints. Both mass and relativistic mass loosely equate since both are connected to energy.

[Martin]

What I was meaning, is why do you think it is a singularity? Have you ever observed a singularity in real life? It seems far more likely to me that there would be some sort of quantum gravity effect which would kick in as you got close to the centre stopping it from becoming a singularity.

 

I'll risk a guess that Severian is right. Some quantum gravity effect possibly does kick in at very high density, making gravity repellent and preventing the density from going beyond some limit.

 

Quite a lot of researchers in several fields seem to share this idea and are studying models of what might actually happen, say at the pit of a black hole, instead of the breakdown you get in classic vintage 1915 General Relativity.

 

The "singularities" we are talking about here are merely something that happens in classic GR. There has never been any indication, as far as I know, that they happen in nature.

[vincent]

I'll risk a guess that Severian is right. Some quantum gravity effect possibly does kick in at very high density, making gravity repellent and preventing the density from going beyond some limit.

 

You'll be interested in knowing that in string theory the soft asymptotic behaviour means there are generically no singularities, including gravitational one's. However this does not mean we know what the true degrees of freedom of black holes actually are, which is true in all current approaches to black hole physics. So it shouldn’t be surprising that researchers tend to be quite circumspect in their attitudes towards this issue.

[Martin]

You'll be interested in knowing that ...

 

Vincent---thank's for volunteering this information. Since you are a new member let me offer you welcome to SFN. I look forward to seeing more of your posts on various topics of interest.

[vincent]

Vincent---thank's for volunteering this information. Since you are a new member let me offer you welcome to SFN. I look forward to seeing more of your posts on various topics of interest.

 

Well thank you very much Martin!

[Money]

i kno im responding late lol but im goin to

 

What is GR exactly i have ideas but i wanna know for sure

What is SR?

how does Quantum Gravity work?

[Martin]

i kno im responding late lol but im goin to

 

What is GR exactly i have ideas but i wanna know for sure

What is SR?

how does Quantum Gravity work?

 

that's too many questions (SR, GR, QG).

 

I would advise you to first focus on the basic message in GR.

 

To understand the MATH of GR you need a preparation of SR. That is how it is done in school. But this often seems to cripple people. they learn SR so well that they have real difficulty absorbing the essential idea in GR.

 

So I would say to try things in a different un-academic order. First try to get the basic main idea of General Relativity and treat the rest as mathematical details and refinements.

 

Swansont may wish to correct me on this or improve on it.

 

Basically, GR was published in 1915 and the fundamental message was that geometry is a dynamic changeable bunch of distances that interacts with matter.

there isn't some fixed rigid eternal space and some pre-ordained spacetime as Euclid or Newton might have imagined. there is no pre-establshed geometry of points with fixed distances between

 

the catalog of distances is called the "metric" (a technical term with nothing to do with the Metric System of units) and the 1915 GR paper said that the metric is a dynamic changeable thing. Geometry itself can expand and contract and ripple and bend in relation to where the matter is, according to a kind of LAW or equation called the "field equation" which lets you CALCULATE to some extent how the geometry of the universe is going to behave. Or if you prefer to say space instead of geometry, to calculate how space is going to behave-----or how spacetime is shaped by the flow-lines of matter in it.

 

You could practice imagining some simple examples----flat smooth geometries with no bumps and bulges.

Imagine an infinite flat piece of paper with nothing above or below and call that "euclidean 2-space"

then imagine somehow mapping that onto a sphere---putting an extra point at the north pole called the point at infinity. Imagine that sphere with nothing inside or outside it----the "2-sphere"----as all of space for some 2D creatures.

Now go up one dimension

Imagine an infinite "euclidean 3-space" with nothing else outside---like with the sheet of paper there is no above or below, what would "above" or "below" mean anyway?

Then map that around a "3-sphere". think of that as all of space, nothing inside the 3-sphere and nothing outside.

the 3-sphere is an important model of space. IT IS FINITE AND YET IT HAS NO BOUNDARY.

 

I think it is important to be able to imagine 3D spaces that are finite and have no boundary.

 

Otherwise, when somebody says something is SMALL you immediately think that it must be finite (naturally) and then your mind automatically slips from the idea of finite size to the idea of a boundary (WRONG!!! DANGER!!!) and then your mind falls into the trap of saying what if you get to the boundary, can you get OUTSIDE. but in usual mainstream worldview

there is no boundary, there is no outside

 

So I seriously recommend practicing to train your imagination to be able to imagine 3D space that is finite and yet has no boundary.

 

Then when someone says small, you won't automatically fall into that trap.

 

And I don't care what you believe is true about the world. People DONT KNOW if the world if finite or infinite or if it has a boundary or does not, and all that stuff. Standard mainstream cosmology does not normally include the boundary idea----but it includes both the finite and infinite cases. they keep their options open and study various different models.

 

General relativity field equation lets people calculate how all these different geometries could evolve, depending on how the matter is distributed in them and how everything starts moving. It tells how some infinite space might evolve, and how a finite boundaryless 3-sphere might evolve, and how you can start with a small space and have it expand, and how various bumps and wrinkles can form and even various geometrical disasters etc. It is very, as you might say, "general".

 

For a lot of practical local purposes it is too general---because the space around us---the geometry we actually experience---is mostly not very curvy or dynamic. It has a certain "flatness" about it. the 3D spatial version of flatness, or the 4D spacetime version of flatness (whichever you like to think).

So there is SPECIAL RELATIVITY that gives the correct mathematical details about this flat local situation that we normally experience. SR is not quite exactly correct, because the space we live in is actually very very slightly curved. But SR is so close to being exact that one can usually neglect this and treat it as perfect (unless you are talking about intergalactic distances:-) ) SR is LOCALLY perfect.

 

QUANTUM GRAVITY is a refinement of GR that has several goals one of them being to cure some "singularities" or places where GR fails to compute and breaks down. there is a long history of classical (nonquantum) theories breaking down in certain extreme circumstances and then people come along and QUANTIZE the classical theory and that cures its troubles so it doesnt break down.

 

But as a first introduction where you ask about GR, SR, QG, I would suggest first chewing over and assimilating the basic GR idea of a dynamical boundaryless geometry and brood on that for a while

 

and then if you get around to it hang on more details

 

like SR is the local flat approximation to GR that is simpler to calculate with because it is a fixed approximate geometry

 

and like QG takes over from GR in extreme situations and tries to cure the singularities (and still needs to be experimentally checked to be sure that it really is a good quantization)

 

that's all for now. hope I at least havent added to your puzzlement!

[Money]

thanx alot i kno i asked alot and i appreciate u actually answered

im going to keep learning on about it im hooked to learnin this stuff

lol GR = General Rel. and SR = Special rel. i didnt relize that till

i read this lol thats wat had me Real confused i was wonderin wat

every1 meant by those thnx man ~1~