Singularities

[g2006]

Hi all

Sorry if this is the wrong place to post this but could one of the mods just move it if it is....Thanks.

Anyway i have done searches on singularities and i keep coming up with stuff explaining them but the words they use i cannot understand yet. So could any body please just give me an idea of what a singularitie is and any more info would be greatly appriciated.

[Spyman]

A singularity is a point without length, high and wide.

 

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

 

Wikipedia is a good place where You can search for this cind of things.

[insane_alien]

do you mean singularities as in black holes or mathematical singularities. there is more than one type.

[ydoaPs]

if you would look to see what forum this thread is in, you would probably guess black hole.

[Nicholas]

A singularity could be space-time starting as a point.

That is the Big Bang. It could also be infinite density

of mass or a bunch of mass as a single dimensionless point.

 

I believe that singularities are violations of physics.

With the exception that if you run space-time backwards to

a begining it has obviously expanded from a singularity.

If the Big Bang was a mass singularity also its gravity would

prevent any expansion. It would be a black hole.

 

As Stephen Hawking has said about them: GR predicts its own

downfall by predicting singularities.

If there are no singularities then what replaces them?

Finite or Maximum Mass Density does.

In otherwords there will always be space inbetween matter

particles. I believe this is the Pauli Exclusion Principle.

 

Mitch -- Light Fallls --

[luc]

The initial singularity of the Big Bang does not need to be a point.

[Nicholas]

Then it aint a singularity.

 

Space-time goes back all the way to a point.

And you can't say otherwise.

[alt_f13]

Then it aint a singularity.

 

Space-time goes back all the way to a point.

And you can't say otherwise.

 

One could. You can also say it does, but that doesn't make it true. We are not yet at a level where we can say with the greatest degree of certainty what happenned at the beginning, or even if there was one. We believe we might have a good idea.

 

And just because space-time *may* have been a singularity, isn't to say a singularity is not possible in any other circumstance, regardless of what you believe.

[Nicholas]

If you can't see back to an original point of space.

You are not going back far enough.

[luc]

Actually is thought that the Universe is flat and of infinite volume. How could then have emerged from a point? A point, in the finite time since the Big Bang, 13.7 billion years, couldn't have grown to an universe of infinite volume. Pure logic, people

[ydoaPs]

inflation

[luc]

inflation, what?

[ydoaPs]

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

[luc]

i know very well what's inflation. i don't know though how it permits that an Universe emerging from a point can have today infinite volume. Can you explain?

[ydoaPs]

how can 0 expand into any finite length?

[danny8522003]

Ive read a lot about black holes and singularities both in books and on the net and there has always been one thing that puzzles me.

 

If mass = density x volume and the density is said to be infiniate, then surely the mass is infinite unless the volume = 0. If it is 0 then the mass would be 0 and space-time would not be warped to form the blackhole.

 

A factor i have thought of is that the singularity may not have any dimensions, if this is the case then it would exhibit 0 volume but again ow could it have mass?

 

Also i wondered whether anyone has thought that maybe the hidden mass in the Universe known as dark matter maybe just a black hole or a series of them? Mainly because we can be unsure of how many of these holes exist and whether it is enough to prevet infinite expansion.

[luc]

how can 0 expand into any finite length?

 

Imagine that you are in the origin of the real line. You can run either in the positive or negative direction, but you always will be over a real number, you can never achieve infinite, this is analogous to the volume of the Universe

[[Tycho?]]

It is not known if the universe is infinite in extent or not.

[Nicholas]

Universal expansion is proof the universe cannot be infinite.

The universe had a begining a finite amount of time ago

and is expanding at a finite rate. You can't get an

infinite universe out of that!

 

Only the future is infinite.

[Ophiolite]

Universal expansion is proof the universe cannot be infinite.

No it isn't. For example [in simple terms] http://www.astronomycafe.net/qadir/ask/a11839.html

 

Only the future is infinite.

No. The future may be eternal. That is a different matter.

[BobbyJoeCool]

If mass = density x volume and the density is said to be infiniate, then surely the mass is infinite unless the volume = 0. If it is 0 then the mass would be 0 and space-time would not be warped to form the blackhole.

 

d=m/v. for any finite amount of mass, in a point with no dimentions the volume is 0. Lets say that the mass is 1kg. so, d=1kg/0. 1/0 is undefined. so, we say it has an infinite density (mass with no volume).

 

A factor i have thought of is that the singularity may not have any dimensions, if this is the case then it would exhibit 0 volume but again ow could it have mass?

 

Take the mass in 10 supergiant stars. put them all together in the space of the planet Earth. the gravetational forces created by that much mass in such a little volume will force the mass to compress. It will draw in more mass with will force it to compress more until, in theory, it has compressed to a single point in space with no height, width, or length, but it still has mass, so it has an infinite density.

[BobbyJoeCool]

opps.. I just realize what you were doing...

 

d=m/v, so m=dv. But when you put the numbers in... d=1/0... you're multiplying both sides by 0 (moving the v over with the d)

 

0*d=0(1/0)

0=0

[danny8522003]

But if m=dv then when trying to find m we get m=inf.*0.

 

Anything multiplied by 0 is 0 so surely if the mass would be 0 when you do it backwards?

 

So v must be >0 for the formula to work, but if it is >0 then we end up with infinite mass which im sure isnt allowed.

[BobbyJoeCool]

But if m=dv then when trying to find m we get m=inf.*0.

 

Anything multiplied by 0 is 0 so surely if the mass would be 0 when you do it backwards?

 

So v must be >0 for the formula to work' date=' but if it is >0 then we end up with infinite mass which im sure isnt allowed.[/quote']

 

In mathematics, you have to know what your doing...

 

when you have a given equation, d=m/v for instance, and you're given all but one number to fill in the equation (in this case, density and volume), you cannot just move the equation around...

 

Starting with the original equation...

 

[math]d=m/v[/math]

[math]d=\infty, v=0[/math]

[math]\infty=\frac{m}{0}[/math]

[math](0)\infty=(0)\frac{m}{0}[/math]

[math]0=0[/math]

 

d=m/v, so m=dv for v|v=/0 (as in when v does not equal 0).

 

Because, as you see, in the original equation, when v=0, the equation is undefined.

 

When you plug numbers into an equation, you have to check the original equation to make sure it's defined in the original equation. In this case, in the original equation, plugging 0 in for v makes it undefined therefore if d=m/v, m=dv is NOT TRUE at v=0.

[danny8522003]

I think i understand now, thank you BobbyJoe .