black holes

Originally posted by Palynka
On a more serious note, I'm not sure why you think the appearance of the universe would be like that. Since all matter was originated by the Big Bang, in a three dimensional point (so to speak), then why wouldn't the universe have a center?

For example, when we say the universe is expanding, then surely this implies the existence of a center and an edge, as it requires the universe to be bounded.

The universe appears to be equally densed in any direction. If we were at halfways out to the edge, universe wouldn't be as densed from the center and more densed to the direction toward the center. Another explanation is that we actually are at the center of the universe, at the place where BigBang occurred. This is not likely.

The universe appears to have no edge. If it had, then how would it be like there, like all the universe only inwards, nothing outwards?

Seeing universe as a flat topology is as we saw the earth millennia. in this view the surface of the earth indeed has a center (Mare Mediterranea, the sea at the middle) and an edge where the seamen went fell off the face of the Earth.

Well, anyway, this is my view of the Universe, I get all kind of questions answered by this view, I don't have the need for others to adopt my view.

Originally posted by twhitehead
No, there is no reason to make that conclusion. The very fabric of space is expanding, so it is in fact possible for objects to travel away from each other faster than light.

Perhaps you're right there. But we have a maximum redshift, corresonding to the age of the Universe. Shouldn't we see a larger redshift of more distant objects if I were to be wrong?

Originally posted by FabianFnas
The universe appears to be equally densed in any direction. If we were at halfways out to the edge, universe wouldn't be as densed from the center and more densed to the direction toward the center. Another explanation is that we actually are at the center of the universe, at the place where BigBang occurred. This is not likely.

The universe appears to ...[text shortened]... ll kind of questions answered by this view, I don't have the need for others to adopt my view.

I'm just trying to learn here. Some questions/remarks:

The universe appears to be equally densed in any direction. If we were at halfways out to the edge, universe wouldn't be as densed from the center and more densed to the direction toward the center. Another explanation is that we actually are at the center of the universe, at the place where BigBang occurred. This is not likely.

Perhaps the known universe is just an infinitesimal part or the universe, such that the difference in density is also infinitesimal and some degree of randomness prevents us from knowing in which direction is the center.
If not, how do you reconcile that with the Big Bang theory?

The universe appears to have no edge. If it had, then how would it be like there, like all the universe only inwards, nothing outwards?
But there is no outwards, since the universe is comprised of everything that exists, one can only expand it, but never exit it. I've always imagined it as something (vaguely and imprecisely) resembling an infinitely elastic balloon.

Originally posted by Palynka
I'm just trying to learn here. Some questions/remarks:

The universe appears to be equally densed in any direction. If we were at halfways out to the edge, universe wouldn't be as densed from the center and more densed to the direction toward the center. Another explanation is that we actually are at the center of the universe, at the place where BigBan imagined it as something (vaguely and imprecisely) resembling an infinitely elastic balloon.

We see the background radiation with uniform distribution in every direction. We can see back to the (spatial) point where/when the Universe became transparant. Therefore I think we can see all the universe. This is a part of the BigBang Theory.

If we were only a small fraction of a much bigger universe, then we wouldn't see the background radiation with its properties as we see it today.

With inward I mean the direction to the center of the universe, the place where BigBang took place. Outward is the opposite direction. In my universe there is no inward, nor outward directions because I don't think the Universe has a centre, nore any boundaries.

(My view, not everybody's view.)

Originally posted by FabianFnas
We see the background radiation with uniform distribution in every direction. We can see back to the (spatial) point where/when the Universe became transparant. Therefore I think we can see all the universe. This is a part of the BigBang Theory.

If we were only a small fraction of a much bigger universe, then we wouldn't see the background radiation with its properties as we see it today.

(My view, not everybody's view.)

My understanding of the BB is a bit limited to popular science, so please bear with me for a bit.

What do you mean by when/where the universe became transparent?

Also, I have in my mind these diagrams of the BB where you see a point from which matter is spewed outwards and expands at a tremendous pace. If that was the case, I imagine that a uniform distribution could be evidence against the BB theory, how do you (or others) reconcile that?

Originally posted by Palynka
I knew, I was just being pedantic. 🙂

On a more serious note, I'm not sure why you think the appearance of the universe would be like that. Since all matter was originated by the Big Bang, in a three dimensional point (so to speak), then why wouldn't the universe have a center?

For example, when we say the universe is expanding, then surely this implies the existence of a center and an edge, as it requires the universe to be bounded.

Since all matter was originated by the Big Bang, in a three dimensional point

Space and time were created immediately after the Big Bang so the big bang couldn't have occurred in one specific point.

then why wouldn't the universe have a center?
one easy to see this is to think about the Universe expansion. All points in the Universe see all points in the Universe get away from them exactly in the same way. In a space that has a center this can't be possible. So either you say that the Universe has no center, or you say that all points in the Universe are a center. 😕

For example, when we say the universe is expanding, then surely this implies the existence of a center and an edge, as it requires the universe to be bounded.
The error in your reasoning lies in the fact that you are using your euclidean geometry intuition. Which we all do until we learn very specific reasons not to do it. For instance if you lived in the surface of an expanding balloon you could infer that its surface was indeed expanding by making gigantic triangles and measuring their internal angles and by no means that Universe would have a center or an edge according to you. So you see things can be bounded and have no edge. A very simple example ]0,1[. This is a bounded interval but it has no edge. The points of this interval can be as close as one wants to 0 and to 1. On the other hand [0,1] is bounded and has an edge. The points 0 and 1.

This is the analogy people frequently give when trying to explain these things in a more approachable way. But bear in mind that this is just an analogy so don't take it too seriously. The bottom line is that in the context of GR where you have a non-definite metric that changes from point to point and in time (unlike the definite and constant one that is pretty good explaining our day to day phenomena) we must be very careful in our intuitive reasonings.

Originally posted by Palynka
My understanding of the BB is a bit limited to popular science, so please bear with me for a bit.

What do you mean by when/where the universe became transparent?

Also, I have in my mind these diagrams of the BB where you see a point from which matter is spewed outwards and expands at a tremendous pace. If that was the case, I imagine that a uniform di ...[text shortened]... tribution could be evidence against the BB theory, how do you (or others) reconcile that?

Okay, if I'm unclear somewhere, don't hesitate to ask me to clarify. But you should always have in mind that this is my personal view of the Universe, and mine only. Some of it I share with the standard vews, but some are mine alone.

When universe in the beginning was so hot that photons interacted with matter very intensely, photons emmitted and absorbed so closely so they couldn't travel very far. When the temp sank under a certain temperature the photons didn't interact anymore, so they could now travel in any direction very far. This happened at the age of approx 400 000 years after BigBang. Those oldest photons can be detected as a background radiation, and was first detected back in the 60ies, and confirmed the BigBang Theory.

When you see a picture, or an animation of how Universe exploded from a tiny point, like an shell blast, or DeathStar destruction in Star Wars, you get a wrong impression. Get rid of this expression, it hinders you in your thought. They imply that there are in fact an outward direction, and a center from where everything came from. Not so. Universe did not explode outwards. Whole of the universe expanded at the same time, as it does today. The picture lead your thoughts in wrong directions.

Are these the answers of your questions?

Originally posted by adam warlock

then why wouldn't the universe have a center?
one easy to see this is to think about the Universe expansion. All points in the Universe see all points in the Universe get away from them exactly in the same way. In a space that has a center this can't be possible. So either you say that the Universe has no center, or you say that all points in th ...[text shortened]... ood explaining our day to day phenomena) we must be very careful in our intuitive reasonings.[/b]

Space and time were created immediately after the Big Bang so the big bang couldn't have occurred in one specific point.

True, I was imprecise there.

one easy to see this is to think about the Universe expansion. All points in the Universe see all points in the Universe get away from them exactly in the same way. In a space that has a center this can't be possible. So either you say that the Universe has no center, or you say that all points in the Universe are a center. 😕

Argh, my intuition fails me. Imagine I define the distribution of matter as a function f of time where time belongs to ]0,Infinity[. What happens to the distribution when I take the limit as time approaches 0 from the right? Would it not converge to a point?

Originally posted by FabianFnas
Okay, if I'm unclear somewhere, don't hesitate to ask me to clarify. But you should always have in mind that this is my personal view of the Universe, and mine only. Some of it I share with the standard vews, but some are mine alone.

When universe in the beginning was so hot that photons interacted with matter very intensely, photons emmitted and absor ...[text shortened]... picture lead your thoughts in wrong directions.

Are these the answers of your questions?

Thanks. Even if I feel I don't completely understand what went on, at least, I learned something today. That my idea of the BB was completely wrong. 🙂

What then, do you mean by the "universe is expanding"?

Originally posted by Palynka
Argh, my intuition fails me. Imagine I define the distribution of matter as a function f of time where time belongs to ]0,Infinity[. What happens to the distribution when I take the limit as time approaches 0 from the right? Would it not converge to a point?

Hmmm. First of all I'd need to understand why you discard the dependence that the distribution of matter also has on space. Cause I have lots of problems figuring out why you should study the distrubution of matter caring about time alone... But I'm not saying it is wrong I just don't see what's the good in it.

Maybe because I don't exactly follow what you mean by distribution of matter. Maybe you're thinking on matter density...? In the case of matter density that limit should diverge. I mean if you take the limit to 0 we know that this is the same as investigating what happens to the matter density when the Universe is seen as contracting and approaching a 0 volume.

If we think about matter distribution, let's call it f(t,x,y,z) and ask what happens to this function when t approaches 0 then I sincerely have to tell you that I don't know what happens. Now as t approaches infinity and we look at great enough volumes the current consensus is that this function is very well approximated by a constant function.

Sorry for the little help... 😳

Ah... I think I know what you mean now... But I'll leave the previous text just so you can follow my train of thought. So you're thinking if we approach the Big Bang everything must come from approximately the same point so f(t,x,y,z) should be well concentrated near some (x1,y1,z1) point. Well now it is time for I to tell you a little secret. It depends on your definition of Big Bang. For instance Heinz Pagels (I hope I'm getting his name right) defined the Big Bang as something that occurred in an extend region of space during a period of time. A long stretch from the everyday notion of the Big Bang as some sort of an anti-cataclysmic explosion. In the Pagels definition of Big Bang your limit would simply approach the initial distribution of matter of the Universe.

One thing I should point out though is the well known fact that we can't just hang on to GR when trying to understand the beginning of time and space. We must somehow unite it with QM for a much better and realler analysis of what happened. And this is just to say that I don't have an answer for what I think is a Goddamn good question.

Originally posted by adam warlock
Hmmm. First of all I'd need to understand why you discard the dependence that the distribution of matter also has on space. Cause I have lots of problems figuring out why you should study the distrubution of matter caring about time alone... But I'm not saying it is wrong I just don't see what's the good in it.

Maybe because I don't exactly follow w ust to say that I don't have an answer for what I think is a Goddamn good question.

It doesn't have to be black and white for it to be a good answer.

Let's imagine that there was a x1,y1,z1. Would it still be possible that matter is uniformly distributed (i.e. due the interaction between photons that Fabian mentions)?

If I understand correctly, it's possible then that there was such a point but it would be impossible to identify it since, due to those interactions, the expansion of matter cannot be simply defined as outward. Is this correct?

Originally posted by Palynka
Thanks. Even if I feel I don't completely understand what went on, at least, I learned something today. That my idea of the BB was completely wrong. 🙂

What then, do you mean by the "universe is expanding"?

If I am the one learning you something - makes me proud. Glad you told me. 🙂

Now, what does it mean that the Universe is expanding?

How do we know that the Universe is expanding?
The easy answer is that the farther we see out in the Universe the more velocity from us the objects have.

What object do we measure on?
Well, objects outside our own galaxy, our Milky Way galaxy. Mostly other galaxies, cluster of galaxies and another object called quasars that are very distant objects.

How do we measure the velocity for far out objects?
With the fenomenon called the Doppler Effects. The more an object is shifted to the red side of the spectrum, the higher speed it has from us. Here the thought was born that if everything is going from us: When did all objects separated from the beginning? The answer is at the time of BigBang.

The BigBang gave everything an outward push, so everything started to fly apart, or expand. Not only all the things in the Universe, but also the space itself. And perhaps the time too. This is the meaning of the expansion of the Universe. Even today it expands. Perhaps it will expand forever.

Originally posted by Palynka
It doesn't have to be black and white for it to be a good answer.

Let's imagine that there was a x1,y1,z1. Would it still be possible that matter is uniformly distributed (i.e. due the interaction between photons that Fabian mentions)?

If I understand correctly, it's possible then that there was such a point but it would be impossible to identify it s ...[text shortened]... e interactions, the expansion of matter cannot be simply defined as outward. Is this correct?

Like I said:I mostly forgot what's important about this and I must be silent from here...

I really have to re-study this bit... 🙁 😞

Originally posted by Palynka
If I understand correctly, it's possible then that there was such a point but it would be impossible to identify it since, due to those interactions, the expansion of matter cannot be simply defined as outward. Is this correct?

When talking about the universe we must remember that spacetime can be curved in four or more dimensions. It is difficult to think in higher dimensions so the easiest is to take away some of the spacial dimensions when thinking about it.
Imagine the universe is the surface of a sphere. As the sphere grows, points on the surface get further away from each other. There is no 'central' point on the surface, and if the expansion is fast enough it will out weigh the tendency of matter to clump together- resulting in the uniform density we see.
Also the expansion does not result in new territory within the two dimensional surface being breached.
To say it another way: distant objects are not moving away through space into uncharted territory, instead new space is being created between us and them resulting in them being further away.
Redshift is not because an object was moving away from us when it emitted light, redshift is because space has been stretching while the light was in transit and the stretching of space, stretched the light.

Originally posted by twhitehead
When talking about the universe we must remember that spacetime can be curved in four or more dimensions. It is difficult to think in higher dimensions so the easiest is to take away some of the spacial dimensions when thinking about it.
Imagine the universe is the surface of a sphere. As the sphere grows, points on the surface get further away from each en stretching while the light was in transit and the stretching of space, stretched the light.

That was very clear, thanks.

Care to comment on my question above regarding the limit as time approaches zero?
If I take the balloon analogy, then the universe would indeed collapse to a point, but not one on the "surface", i.e. not one which is on the visible 3 dimensions. Is this approximately correct?