B Realism about singularity

[elias001]

The thing about black hole singularity is if we think of a waterspouts appearing in the ocean, we can see its funnel shaped if we go under the water. For the equivalent of a black hole, what would be the equivalent of its waterspouts and is its singularity funnel shaped? Also, can that funnel shaped be physically observed? I mean everyone has seen illustration of what a blackhole singularity look like. There is something that look like a waterspouts that look like some giant funnel where someone remove some sort of physical space drainage plug in some sort of cosmic space time bath tub.

 

[Ibix]

For the equivalent of a black hole, what would be the equivalent of its waterspouts and is its singularity funnel shaped?

Black hole singularities are spacelike - they are moments in time, not places in space. So they don't look like anything, any more than 9am tomorrow morning looks like anything.

 

[Rive]

its singularity funnel shaped?

Erm... The following things are not the same:
- the supposed singularity
- the funnel shapedly displayed curved space
- the event horizont itself
- the interior of the event horizont

You seems to be using these as freely interchangeable concepts. But they are not.

 

[Ibix]

I just think if there are things beyond the observable universe we cannot see. Shouldn't there are things from the other direction coming toward us or rather that have not caught up to where we can see it with our telescope regardless of how powerful we make them to be.

No. In an idealised FLRW universe, everything is moving apart at a rate that increases with distance. Depending on the density of matter it is possible for that rate to decrease to zero and then reverse, so everything starts moving together at a rate that increases with distance after that time, but either everything is moving away or everything is moving closer. There is no mixed state. This is the (perhaps somewhat surprising) result of plugging an everywhere uniform density into the Einstein field equations, and predicted Hubble's Law and the Cosmic Microwave Background before either were observed. It also predicts the initial singularity, but this is probably a failure of the model in extreme circumstances.

The real universe is not quite an idealised model. There was initial random density variations on small scales that eventually grew into planets, stars and galaxies that have random motions on top of the simple further/faster rule. So nearby galaxies can be approaching each other under the influence of gravity - Andromeda will merge with the Milky Way in a few billion years, for example. But this is just fairly small scale noise on top of the systematic expansion.

 

[elias001]

@lbix like I said, the question i sm raising seem like something one can answer by imitating the examples from the first few chapters of a first year's physics text in the kinematics sections. But i am sure that Approach is totally wrong. Also I don't know what FLRW stands for.

@Rive I am not even sure or aware that I am using them as interchangeable. If I am, well, guilty as charged. I mean, I am part of the science literate public but not in the case of the more technical side of astronomy. I can only bring up questions based on what I see from watching science documentaries.

 

[martinbn]

Also I don't know what FLRW stands for.

Friedmann–Lemaître–Robertson–Walker​

 

[Ibix]

But i am sure that Approach is totally wrong.

It is - you need to factor in the curvature of spacetime to understand it properly, and that's pretty far beyond undergrad kinematics.

Also I don't know what FLRW stands for.

Friedman Lemaitre Robertson Walker. Sometimes called FRW because Lemaitre discovered it independently and only published in French, so his result was little known for many years.

 

[elias001]

@martinbn thank you for the clear up.

@Ibix oh thank you for confirming that first year kinematics or an intro to classical mechanics would be insufficient to solve it. Because I am dreading the scenario if you actually says "yes it is enough".

 

[windy miller]

You don't have to "hypothetically" take a "realist view". You can just ask what the model of the universe with an initial singularity says. The model itself is perfectly well-defined, independent of the question whether it represents what's actually physically real in our universe.


No, because, as @Ibix says, the singularity is not part of the manifold in the model, and so the question as you state it has no meaning.

What does have meaning is to ask what the limit is of the spatial volume of the universe as the initial singularity is approached by moving backwards in time along any comoving worldline. That limit is zero. But the limit is just a mathematical limit. It does not describe any actual property of the spacetime itself, since, as above, the singularity is not part of the spacetime.

Thanks for this guys