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Black holes ruled out as universe’s missing dark matter

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Re: Black holes ruled out as universe’s missing dark matter

#71

Post by kamaal »

danbruc wrote: post #69
kamaal wrote: post #67

Earlier quoted context omitted.

Explain to me how this works. A and B remain stationary while only new space gets created between them? By geometry, the shortest distance between two points is a straight line. If A and B are two stationary objects, with a straight line being shortest distance between them. Then space is basically a twisted thread like path between A and B, More thread is created every time instant 't' than light can travel through…

Unfortunately I don't understand what you are suggesting or asking. Maybe this short video [1] with the classical balloon analogy will help you understand it better. [1] https://www.youtube.com/watch?v=mnENgtCdObo

Figure 1:

     _                 _ 
    |_|---------------|_|
     A                 B
Figure 2:

     _    -----\____   _
    |_|--/          \-|_|
     A                 B
Let's say there is constant speed 'c' beyond which one can't travel. Lets say we travel at 'c'.

Figure 1 is the fastest possible way of going from A to B

If more space is added, and yet A and B remain at fixed positions, the only way this model will work is the path(possible way to go from A to B) gets looped/twisted and turned. In this case A and B remain at fixed positions but new space gets created. Its also possible in this model that as more and more loops get created fast enough, even by travelling at 'c' one can never arrive at B.

If the space is not looped or twisted this how A and B will move apart at increasing time instances t1, t2, t3

t1:

     _    _
    |_|--|_|
     A    B
t2:

     _     _   
    |_|---|_|
     A     B
t3:

     _      _
    |_|----|_|
     A      B
t4:

     _       _
    |_|-----|_|
     A       B
...

tn:

     _
    |_|----------------
     A
As you can see when we keep the space expansion a straight line the objects always move. But if we have to keep the objects fixed we have to loop, twist and turn the path(space).

If the objects were stationary, this is how it will look

t1:

     _          _
    |_|--------|_|
     A          B
t2:

     _          _
    |_|---/\---|_|
     A          B
t3:

     _          _
    |_|---/|\--|_|
     A          B
tn:

     _     ---  B
    |_|---/   |---
     A  (many loops)..
Is this understanding correct?

Re: Black holes ruled out as universe’s missing dark matter

#72

Post by fabatka »

Filligree wrote: post #46
T-A wrote: post #16

Earlier quoted context omitted.

The early universe was ridiculously homogeneous. We can infer this with reasonable certainty from the extreme homogeneity of the CMB and from the gravitational instability of density fluctuations: as you expect, they attract more mass and accrete to form stars and galaxies. So if you start from the universe as it looks now and run time backwards, you get ridiculous homogeneity at the bang. And that's why you didn't g…

So, are we assuming the universe is infinite? Otherwise there'd be a border to that.

We can measure that the Universe is homogeneous and isotropic on sufficiently large scales (it is according to the measurements). We can also measure the 'flatness' of the Universe (it is very likely to be flat, according to measurements).

I don't know the details, but I was told that with these assumptions, proving that the Universe is infinite is only a matter of mathematics.

Re: Black holes ruled out as universe’s missing dark matter

#73

Post by thecupisblue »

sulam wrote: post #4

This spawned a question for me that seems like it must be nonsensical but I don’t know the answer. Why did the Big Bang not just produce a Big Hole? IOW, if all the current mass of the universe was in a small volume wouldn’t it have promptly created a black hole? I’m assuming the answer has something to do with mass not actually existing in its current form until the universe expanded enough. However I don’t have any…

In my mind:

There is Universe n-1 (before ours). Last matter and anti-matter collide. Then, as there is nothing and as there is everything, the cycle begins again since we can't achieve "the balance". A big bang occurs, a universe n is born, with it's own set of laws (the laws of physics, like a new buildconfig). Everything slowly spreads and gets into perfect balance. Then everything dies. Then the last bits of matter stop existing. The Boom. A new universe is born, n+1. It has it's own set of constants. Maybe they aren't balanced properly, so it lives for a short moment and then dies and n+2 is born. And so on and so on.

Re: Black holes ruled out as universe’s missing dark matter

#74

Post by prmph »

One question I have: is it not possible that the big bang occurred an infinite time ago? If the expansion of the universe is accelerating with time, does it not indicate that, if we reverse the time, the deceleration is asymptotic?

In that case the big bang is compatible with a universe that has always existed and did not have a beginning

Re: Black holes ruled out as universe’s missing dark matter

#75

Post by roywiggins »

roywiggins wrote: post #30
InclinedPlane wrote: post #22

Earlier quoted context omitted.

We have observed matter falling into a black hole. We've watched "hot spots" in orbit of a black hole in the accretion disk shine their light at us as they orbited the black hole. We've watched as the orbit got tighter and tighter and the light was dimmed by gravitational red shifting, then we've watched the light blink out and disappear as the blob of gas fell below the event horizon. The evidence for the existence…

I believe the argument is that event horizons exist but inside is not a singularity, but an eternally collapsing mass of the original star. From the point of view of the star, it does collapse all the way, but from our point of view that final singularity collapse is in the indefinite future. https://en.m.wikipedia.org/wiki/Magnetospheric_eternally_col...

Update: I am mistaken. The classic GR black hole behaves this way. MECOs supposedly never fully collapse into a singularity, even for infalling observers. That's the difference.

I rather think we'd have noticed the difference from LIGO gravitational wave measurements of BH mergers, but maybe not?

Re: Black holes ruled out as universe’s missing dark matter

#76

Post by roywiggins »

perl4ever wrote: post #36
InclinedPlane wrote: post #22

Earlier quoted context omitted.

We have observed matter falling into a black hole. We've watched "hot spots" in orbit of a black hole in the accretion disk shine their light at us as they orbited the black hole. We've watched as the orbit got tighter and tighter and the light was dimmed by gravitational red shifting, then we've watched the light blink out and disappear as the blob of gas fell below the event horizon. The evidence for the existence…

From your point of view, if so-called black holes are "fuzzballs"[1] is that a vindication or a refutation of the existence of black holes? Without a deep understanding of physics, I have the general attitude that infinities must be a mathematical error, and therefore something must stop black holes from collapsing totally, but whether they "exist" is only a matter of definitions. [1] https://en.wikipedia.org/wiki/Fu…

I tend to agree with you. Are mathematical singularities physical? We just don't know. I think probably not on philosophical grounds. But we can't peek inside an event horizon to find out, and these event horizons seem to exist, so whatever the structure of the insides of them are, they're still black holes.

Re: Black holes ruled out as universe’s missing dark matter

#77

Post by swamp40 »

sulam wrote: post #4

This spawned a question for me that seems like it must be nonsensical but I don’t know the answer. Why did the Big Bang not just produce a Big Hole? IOW, if all the current mass of the universe was in a small volume wouldn’t it have promptly created a black hole? I’m assuming the answer has something to do with mass not actually existing in its current form until the universe expanded enough. However I don’t have any…

Perhaps once a black hole has nothing left to suck in, it explodes?

Re: Black holes ruled out as universe’s missing dark matter

#78

Post by gpderetta »

Fordec wrote: post #58
Filligree wrote: post #46

Earlier quoted context omitted.

So, are we assuming the universe is infinite? Otherwise there'd be a border to that.

Treat the "Universe" that was created in the big bang like a firework that has just gone off. The "boundary" of the universe is just the size the explosion has expanded to for a given time. And today, 13.8B years after the big bang, our universe is 46.5 billion light-years in diameter. But just like a firework explosion, there isn't really a solid border to it that you can plant a stake or flag in. We have no clue wh…

IANAP, but the big bang, name notwithstanding, is completely unlike a conventional explosion. It is not a wavefront expanding in three dimensions off a center, there is no frontier nor a center at all in our three dimensions and each point of the universe[1] is getting farther than every other point, i.e. not moving radially off a center.

You could imagine that the explosion is happening on an extra dimension and our three dimensional universe is the wave front of that explosion. Except that the math doesn't actually require the extra dimension to exist nor there is any evidence that it does.

edit: also the cited diameter is only for the visible universe. The universe is currently understood to be infinite.

[1] my understanding this applies only to points of the universe that are not otherwise gravitationally bound with each other.

Re: Black holes ruled out as universe’s missing dark matter

#79

Post by smithmayowa »

prmph wrote: post #74

One question I have: is it not possible that the big bang occurred an infinite time ago? If the expansion of the universe is accelerating with time, does it not indicate that, if we reverse the time, the deceleration is asymptotic? In that case the big bang is compatible with a universe that has always existed and did not have a beginning

That is a really interesting way to look at it, and yes since in reverse time, the acceleration never quite reaches zero, the universe can then be though of as an infinite occurrence that has always been expanding with no starting point.

Re: Black holes ruled out as universe’s missing dark matter

#80

Post by peeters »

prmph wrote: post #74

One question I have: is it not possible that the big bang occurred an infinite time ago? If the expansion of the universe is accelerating with time, does it not indicate that, if we reverse the time, the deceleration is asymptotic? In that case the big bang is compatible with a universe that has always existed and did not have a beginning

The question is, does causality require time? I understand that physics can give us a definition of time as far as "happens-before" relationships go, but are "happens-before" and "happens-because-of" necessarily the same thing?
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