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View Full Version : Would our universe appear to be a black hole to an outside observer?

skrap1r0n
2008-Jan-15, 07:23 PM
I have a question about our universe as a whole and how it would be observed of one could observe it from the outside. This may seem silly, but I am going to go ahead with it anyway and try to not ramble with the explanation.

If one could observe our universe from the outside, would it appear to be a "black hole"? Let me try to bring about why I ask this question.

Is the big bang was an explosion then there is a center point and the "observable" universe is expanding ad the speed of light. I get to this because any observable explosion happens at the speed of light (unless somethign blocks the light). If I am standing on a mountain top and I witness an explosion a mile or two away in the valley, I see the light first, then the sound and or the concussion wave. Therefore, the observable part of this explosion occurs at the speed of light. (ok this could be foiled by discussing an underground explosion, but that is beside the point)

So that said, wouldn't it be correct to say that the Universe is expanding at the Speed of light? Meaning that it is radiating outwards from a center point at that rate? I do not mean to suggest that matter is expanding at that speed, but radiation from the initial bang is.

So following that assumption (which may very well be erroneous), then it stands to reason there is an outer barrier that this energy has not passed yet, like the film of an ever expanding bubble.

Now, if one could observe this from the outside (which is really kind of impossible, because if you could be outside the bubble then you wouldn't be because you are from the inside so the act of going outside it means you are still inside it, but whatever) Anyway, if you could observe this from the outside, you would see nothing, no light, no energy, no matter, nothing. There would be a big huge nothing expanding towards you.

wouldn't this then kind of be like a black hole? I mean you have the entire mass of the universe contained inside a "bubble" that light or matter hasn't escaped from?

worldcruiser
2008-Jan-15, 08:45 PM
IMHO you have some things wrong:
1. there is no central point where the big bang started, every point is the center and none at the same time.
2. space-time itself is closed and expanding, at the time of the big inflation faster than the speed of light (there is no conflict with GR, GR deals with speed inside space-time)
3. there is no "outside" of the universe (and no time before the big bang);
this are unanswerable questions just like what is north of the northpole (answer nothing is north of the northpole) or
where does a circle start or end?

Bogie
2008-Jan-15, 09:16 PM
I have a question about our universe as a whole and how it would be observed of one could observe it from the outside. This may seem silly, but I am going to go ahead with it anyway and try to not ramble with the explanation.

If one could observe our universe from the outside, would it appear to be a "black hole"?
you are asking a question that cannot be answered by science. The answer from worldcruiser is the standard answer and the best that science can do.

Is the big bang was an explosion then there is a center point and the "observable" universe is expanding ad the speed of light. I get to this because any observable explosion happens at the speed of light (unless something blocks the light). If I am standing on a mountain top and I witness an explosion a mile or two away in the valley, I see the light first, then the sound and or the concussion wave. Therefore, the observable part of this explosion occurs at the speed of light. (ok this could be foiled by discussing an underground explosion, but that is beside the point)There is almost no one who is informed about the observable universe that would view it as the result of an explosion because the relative motion of what we can see demonstrates expansion instead of explosion. The difference is what you see from within the explosion vs. what you see from within an expansion.

When you are inside an explosion you can see a center of motion. Things in the direction of the center have different vectors than things in the other direction. We don't observe that kind of motion from Earth and science predicts that there was never a big bang. That "Big Bang" label was hung on Einstein's General Theory of Relativity by its detractors.

So that said, wouldn't it be correct to say that the Universe is expanding at the Speed of light? Meaning that it is radiating outward from a center point at that rate? I do not mean to suggest that matter is expanding at that speed, but radiation from the initial bang is.

So following that assumption (which may very well be erroneous), then it stands to reason there is an outer barrier that this energy has not passed yet, like the film of an ever expanding bubble.

Now, if one could observe this from the outside (which is really kind of impossible, because if you could be outside the bubble then you wouldn't be because you are from the inside so the act of going outside it means you are still inside it, but whatever) Anyway, if you could observe this from the outside, you would see nothing, no light, no energy, no matter, nothing. There would be a big huge nothing expanding toward you.

wouldn't this then kind of be like a black hole? I mean you have the entire mass of the universe contained inside a "bubble" that light or matter hasn't escaped from?I think that if you were to speculate about the cause of the expansion that we observe you might start by backtracking what we can see by making a model where you reverse the expansion. If you did that you would find that at a time in the past everything would have been much closer together, and if you take that to the extreme (like I do) you could speculate that it was a black hole.

Such a black hole would not be like any black hole we are familiar with though but that is a good I thing :). It is good because a black hole of the proportions it would take to contain all of the energy that exists in our expanding universe could garner some undiscovered physics that could have caused it to initiate the expanding universe from with in it.

IMHO, if you could observe our universe from outside 13.7 billion years ago it would appear as a black hole. Once it "burst" let's say, what you see ... it is an interesting subject.

skrap1r0n
2008-Jan-15, 11:25 PM
ok thanks, good info. I suppose I wasn't thinking about the fact that space itself is expanding and not just matter/light expanding in infinite space.

vercingetorix
2008-Jan-15, 11:27 PM
Based on our current knowledge of such things, what would we expect the Schwarzschild-radius of a Universe-mass black hole to be? How big would the event-horizon be? I ask because I don't know how to do the math myself, but it would be interesting to know, in light of this topic, and considering that there are estimates of the mass of the observable universe, if I'm not mistaken...

Trakar
2008-Jan-15, 11:42 PM
Based on our current knowledge of such things, what would we expect the Schwarzschild-radius of a Universe-mass black hole to be? How big would the event-horizon be? I ask because I don't know how to do the math myself, but it would be interesting to know, in light of this topic, and considering that there are estimates of the mass of the observable universe, if I'm not mistaken...

Big difference between "observable universe" and "entire Universe."

MrB398
2008-Jan-23, 03:00 PM
I always figured you wouldn't know you were looking at a black hole if you were staring right at it. I imagine if you looked at a black hole, you would see nothing but stars.

Why? Because light from other stars that get close but don't get sucked would be bent at a new angle before reaching our eyes, appearing to be a star in that direction.

bigsplit
2008-Jan-27, 04:59 PM
If you could move a great enough distance away from light producing mass eventually the curvature of space time would close for a particular photon preventing you from seeing the light, that is if the reach of gravity is infinate. In that sense I suppose it would be a "black hole". I think.

Ara Pacis
2008-Feb-02, 12:39 PM
I always figured you wouldn't know you were looking at a black hole if you were staring right at it. I imagine if you looked at a black hole, you would see nothing but stars.

Why? Because light from other stars that get close but don't get sucked would be bent at a new angle before reaching our eyes, appearing to be a star in that direction.

Ahh, but it's the optical distortion of the background objects by the gravitational lensing that makes the black hole detectable. Unless, of course, the black hole is wearing corrective lenses. :-)

astrocat
2008-Feb-08, 06:13 PM
I have a question about our universe as a whole and how it would be observed of one could observe it from the outside. This may seem silly, but I am going to go ahead with it anyway and try to not ramble with the explanation.

If one could observe our universe from the outside, would it appear to be a "black hole"? Let me try to bring about why I ask this question.

Is the big bang was an explosion then there is a center point and the "observable" universe is expanding ad the speed of light. I get to this because any observable explosion happens at the speed of light (unless somethign blocks the light). If I am standing on a mountain top and I witness an explosion a mile or two away in the valley, I see the light first, then the sound and or the concussion wave. Therefore, the observable part of this explosion occurs at the speed of light. (ok this could be foiled by discussing an underground explosion, but that is beside the point)

So that said, wouldn't it be correct to say that the Universe is expanding at the Speed of light? Meaning that it is radiating outwards from a center point at that rate? I do not mean to suggest that matter is expanding at that speed, but radiation from the initial bang is.

So following that assumption (which may very well be erroneous), then it stands to reason there is an outer barrier that this energy has not passed yet, like the film of an ever expanding bubble.

Now, if one could observe this from the outside (which is really kind of impossible, because if you could be outside the bubble then you wouldn't be because you are from the inside so the act of going outside it means you are still inside it, but whatever) Anyway, if you could observe this from the outside, you would see nothing, no light, no energy, no matter, nothing. There would be a big huge nothing expanding towards you.

wouldn't this then kind of be like a black hole? I mean you have the entire mass of the universe contained inside a "bubble" that light or matter hasn't escaped from?If you could observe the Universe from the outside, it would appear to look like a typical Galaxy, the differences being that instead of being composed mostly of Stars and Galaxies, it would be composed of Galaxies and Black Holes. The other difference would be one of scale.

CodeSlinger
2008-Feb-08, 06:37 PM
If you could observe the Universe from the outside, it would appear to look like a typical Galaxy, the differences being that instead of being composed mostly of Stars and Galaxies, it would be composed of Galaxies and Black Holes. The other difference would be one of scale.

No, it wouldn't. The universe does not have the same structure as a galaxy. For instance, there is no "center" that everything is rotating around.

John Mendenhall
2008-Feb-08, 10:30 PM
If you could move a great enough distance away from light producing mass eventually the curvature of space time would close for a particular photon preventing you from seeing the light, that is if the reach of gravity is infinate. In that sense I suppose it would be a "black hole". I think.

Congratulations on that qualifier ('weasel words') at the end.

The universe, as far is we can tell, over cosmological distances, is 'flat' in the topological sense. That is, overall it has no curvature, other than local distortions caused by collapsed objects. The photon will go on forever . . .

The simplest solution is usually the correct solution.