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 stargazer1000
Joined: 1/16/2008
Msg: 1
Why the universe isn't a black holePage 1 of 5    (1, 2, 3, 4, 5)
From Discover Magazine blogs:



The Universe is Not a Black Hole
by Sean

People sometimes ask, “Is the universe a black hole?” Or worse, they claim: “The universe is a black hole!” No, it’s not, and it’s worth getting this one straight.

If there’s any quantitative reasoning behind the question (or claim), it comes from comparing the amount of matter within the observable universe to the radius of the observable universe, and noticing that it looks a lot like the relationship between the mass of a black hole and its Schwarzschild radius. That is: if you imagine taking all the stuff in the universe and putting it into one place, it would make a black hole the size of the universe. Slightly more formally, it looks like the the universe satisfies the hoop conjecture, so shouldn’t it form a black hole?

But a black hole is not “a place where a lot of mass has been squeezed inside its own Schwarzschild radius.” It is, as Wikipedia is happy to tell you, “a region of space from which nothing, including light, can escape.” The implication being that there is a region outside the black hole from which things could at least imagine escaping to. For the universe, there is no such outside region. So at a pretty trivial level, the universe is not a black hole.

You might say that this is picking nits, and the existence of an outside region is beside the point if the inside of our universe resembles a black hole. That’s fine, except: it doesn’t. You may have noticed that the universe is actually expanding, rather than contracting as you might expect the interior of a black hole to be. That’s because, if anything, our universe bears a passing resemblance to a white hole. Our universe (according to conventional general relativity) has a singularity in the past, out of which everything emerged, not a singularity in the future into which everything is crashing. We call that singularity the Big Bang, but it’s very similar to what we would expect from a white hole, which is just a time-reversed version of a black hole.

That insight, plus four dollars or so, will get you a grande latte at Starbucks. The spacetime solution to Einstein’s equation that describes a universe expanding from the Big Bang is very similar to the time-reversal of a black hole, but you don’t really learn much from making that statement, especially because there is no outside; everything you wanted to know was already there in the original cosmological language. Our universe is not going to collapse to a future singularity, even though the mass is enough to allow that to happen, simply because it’s expanding; the singularity you’re anticipating already happened.

Still, some folks will stubbornly insist, there has to be something deep and interesting about the fact that the radius of the observable universe is comparable to the Schwarzschild radius of an equally-sized black hole. And there is! It means the universe is spatially flat.

You can figure this out by looking at the Friedmann equation, which relates the Hubble parameter to the energy density and the spatial curvature of the universe. The radius of our observable universe is basically the Hubble length, which is the speed of light divided by the Hubble parameter. It’s a straightforward exercise to calculate the amount of mass inside a sphere whose radius is the Hubble length (M = 4π c^3H^-3/3), and then calculate the corresponding Schwarzschild radius (R = 2GM/c2). You will find that the radius equals the Hubble length, if the universe is spatially flat. Voila!

Note that a spatially flat universe remains spatially flat forever, so this isn’t telling us anything about the universe now; it always has been true, and will remain always true. It’s a nice fact, but it doesn’t reveal anything about the universe that we didn’t already know by thinking about cosmology. Who wants to live inside a black hole, anyway?


Works for me.
 chrono1985
Joined: 11/20/2004
Msg: 2
Why the universe isn't a black hole
Posted: 5/17/2010 2:10:13 AM
Don't think I've ever seen anyone question if the universe is in a black hole with any serious tone. Krebby they aren't called black holes because they are unimaginably small objects formed from mass being compressed, rather the mass that was compressed to form it became such an intense stress on space-time that it punched a hole, at least that's how I understand it.
 stargazer1000
Joined: 1/16/2008
Msg: 3
Why the universe isn't a black hole
Posted: 5/17/2010 6:15:30 AM

rather the mass that was compressed to form it became such an intense stress on space-time that it punched a hole


Actually, more like an extremely steep-walled well.
 stargazer1000
Joined: 1/16/2008
Msg: 4
Why the universe isn't a black hole
Posted: 5/17/2010 9:27:26 AM

I have to disagree with that conjecture.


At the same time, he does make some valid points, in particular that the universe is expanding. Black holes don't do that. At least, not without the accretion of matter from outside its event horizon.

Which leads to another point...if the universe really were a black hole, allowing for an "outside," then would we not then see evidence in the form of a) a visible phenomenon such as a source of energy coming from a particularly preferred axis and b) a distorted image of the "outside" environment of some kind? After all, light can't get out of a black hole. Certainly goes in.
 nipoleon
Joined: 12/27/2005
Msg: 5
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Why the universe isn't a black hole
Posted: 5/17/2010 10:23:42 AM
The Universe is not a Black Hole.
The Universe is only a single photon... going nowhere.

We live inside a photon.
Everything is all the same thing, all connected.
Over there is over here.
Yesterday is today, which is also tomorrow.
Space, distance,volume, and time, are all a mirage.
 Vancer
Joined: 10/29/2006
Msg: 6
Why the universe isn't a black hole
Posted: 5/17/2010 10:25:42 PM
It has been foretold in the Great Book of Punchlines, that 3 Fabled Events must first successfully occur, before humans can confirm that they are within a black hole.

Fabled Event Number One:
Humans find The Wall at the Edge of the Universe.

Fabled Event Numéro Deux:
Humans find a way to transport The Giant Drinking Glass to said wall.

Fabled Event ?:
Upon placing The Giant Drinking Glass against The Wall, an ominous "Om, nom, nom, nom" can be heard from the other side.

There is also something like 98 pages of mind-numbing diagrams and footnotes concerning this great procession, but it makes for some lousy reading and should be completely ignored.
 abelian
Joined: 1/12/2008
Msg: 7
Why the universe isn't a black hole
Posted: 5/18/2010 7:25:48 AM

If we were in a black hole, wouldn't we be in closer proximity, like, unable to breathe because the next person's as*hole was in our face, to say nothing of the planets, meteorites (they would all be collapsing in the same direction), and rotation of the planets doesn't make any sense in a black hole, does it?

It does make sense, but only if you understand that the radial direction inside a black hole is not a direction in space so that the singularity does not lie in a particular spatial location. The singularity lies in EVERY spatial direction in the future of every infalling object. The radial direction inside a black hole is a direction in time. Every infalling object will end up there for the same reason that no matter where you go in any spatial direction, you can't avoid tomorrow.

For the more mathematically inclined, condiser the pythagorean theorem for a right triangle. If one leg lies on the x-axis and one leg lies on the y-axis, the length of the hypotenuse is ds^2 = dx^2 + dy^2. ds^2 is always greater than zero if the length of the sides is greater than zero. The equivalent measure of distance for a relativistic space time is of the form: ds^2 = -dt^2 + dx^2. (The time direction is measured in meters, because we treat space and time on equal footing and the speed of light, c, is only a constant that converts seconds to meters.) Note the minus sign. The direction in time is the term with the minus sign.

Ignoring the angular coordinates, the metric for a Scwarzschild black hole outside the horizon is:

ds^2 = -(1 - 2m/r) dt^2 + dr^2/(1-2m/r)

Since the r-coordinate outside the horizon is positive, outside the blackhole the r-coordinate corresponds to a direction in space. However, those coordinates fail at the horizon, so they aren't necessarily valid anywhere but outside the horizon. As it turns out, those coordinates ARE valid inside provided you swap the plus and minus signs:

ds^2 = (1 - 2m/r) dt^2 - dr^2/(1-2m/r)

Sinc the plus sign is now on the t coordinate, t is a direction in space. Since the minus sign is now on the r-coordinate, r is the direction in time. Falling toward the ``center'' therefore means the exact same thing as falling toward tomorrow no matter what direction in space you go. For the same reason, you can only get out of the black hole by going backward in time. The singularity occupies all of space in the future of every infalling object and time ends there.
 OTTO BONN
Joined: 4/20/2006
Msg: 8
Why the universe isn't a black hole
Posted: 6/3/2016 5:20:01 AM

If one leg lies on the x-axis and one leg lies on the y-axis, the length of the hypotenuse is ds² = dx² + dy².

I wish I was high on potenuse.
 dragonbytes
Joined: 9/15/2015
Msg: 9
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Why the universe isn't a black hole
Posted: 6/3/2016 5:31:46 AM
"I wish I was high on potenuse."

I am NOT a nerd even if I did know what potenuse meant.
 skinnybarncat2
Joined: 5/24/2016
Msg: 10
Why the universe isn't a black hole
Posted: 6/3/2016 9:55:24 AM
Hmmmmmmmmmm, basically, the concept of a black hole is nonsense. It comes from a falsified hypothesis and really bad math. Astrophysicists have many "beliefs" that have been falsified or derived from misunderstood observations.
 gingerosity
Joined: 12/10/2011
Msg: 11
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Why the universe isn't a black hole
Posted: 6/3/2016 11:12:53 AM

the concept of a black hole is nonsense. It comes from a falsified hypothesis and really bad math.

This is news to me... I thought we just watched two black holes coalesce in gravity waves. What was it if not black holes?
Do you have a source or can you elaborate? I may be able to understand because my math is also really bad.
 kidreason29
Joined: 9/25/2015
Msg: 12
Why the universe isn't a black hole
Posted: 6/3/2016 8:47:36 PM
hmm... what if a black hole was actually a nothing?
 Yule_liquor
Joined: 12/7/2011
Msg: 13
Why the universe isn't a black hole
Posted: 6/3/2016 10:05:50 PM
IMO, the reason why the U isn't a BH, is because of ever expanding Dark energy (the energy of nothingness), which has been shown to exist (as opposed to Dark matter, which is inferred).
 gingerosity
Joined: 12/10/2011
Msg: 14
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Why the universe isn't a black hole
Posted: 6/3/2016 10:56:43 PM

hmm... what if a black hole was actually a nothing?

An extremely massive nothing? I don't really see how that differs from the current definition. Can you be more precise?
 kidreason29
Joined: 9/25/2015
Msg: 15
Why the universe isn't a black hole
Posted: 6/4/2016 12:58:29 AM

An extremely massive nothing? I don't really see how that differs from the current definition. Can you be more precise?


is that really the current definition? black holes are what happen when there is division by zero
 gingerosity
Joined: 12/10/2011
Msg: 16
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Why the universe isn't a black hole
Posted: 6/4/2016 1:48:22 AM
A point with mass but no volume, an infinte curvature of spacetime. How would your 'nothing' differ from that?

We can't consider the 'what if' if you don't tell us which episode of startrek we should work from.
 kidreason29
Joined: 9/25/2015
Msg: 17
Why the universe isn't a black hole
Posted: 6/4/2016 3:20:22 AM
i can't tell you because if i did i would have to describe it within the limits of language, perhaps that's what mind melds are for...

maybe we should start worshiping these entities we refer to as black holes
 gingerosity
Joined: 12/10/2011
Msg: 18
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Why the universe isn't a black hole
Posted: 6/4/2016 4:22:20 AM
If something has to be worshipped in the Milky Way, Saggitarius A* would probably make the most sense.

Imagine a star+black hole binary system where there are creatures which observe black hole eclipses of their sun. Perhaps stellar mass black holes have been worshipped since before the earth was formed.

Certainly our ancient worship of the sun made the most sense out of any religious doctrine I'm aware of, since it is literally sustaining our lives. Expressing thanks to an abstract entity for the fusion energy that sustains us is a rational impulse for creatures that have evolved practices of giving and thanking for social bonding.
 dragonbytes
Joined: 9/15/2015
Msg: 19
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Why the universe isn't a black hole
Posted: 6/4/2016 4:43:01 AM
If the universe is a black hole

Then the forums are the event horizon.
 kidreason29
Joined: 9/25/2015
Msg: 20
Why the universe isn't a black hole
Posted: 6/4/2016 4:50:21 AM

Certainly our ancient worship of the sun made the most sense out of any religious doctrine I'm aware of, since it is literally sustaining our lives


it goes beyond that, at what point do we call an entity a star? for example at what point do we say the neck starts here and the head here, etc?

it is a arbitrary division; as for the sun do we consider the rays of light that beam out into the universe, absorbed through the skin or in a plant for photosynthesis as the sun, or the corona or the chromosphere or the photosphere etc?

I think your average person would consider the chromosphere or the photosphere as the division between what is and is not a star or our sun. I think the sun may be more than what it appears and our arbitrary divisions keep us from the realization.
 skinnybarncat2
Joined: 5/24/2016
Msg: 21
Why the universe isn't a black hole
Posted: 6/4/2016 6:51:58 AM
"I thought we just watched two black holes coalesce in gravity waves. What was it if not black holes?
Do you have a source or can you elaborate?"

The observation that you refer to is something. Something very far off. To assume it was black holes is more than a stretch. It is fantasy, built from a falsified paradigm.

Yes, it was news to me a few years ago, not being aware of the prejudices of scientific disciplines.

Look here [not a quick study]: https://www.thunderbolts.info/wp/?s=Black+hole
 gingerosity
Joined: 12/10/2011
Msg: 22
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Why the universe isn't a black hole
Posted: 6/4/2016 8:39:39 AM
^ Oh ok. I was suspicious but was giving you the benefit of the doubt. You should talk to Yule - I think he's interested in some pseudoscience stuff as long as it doesn't make the baby jesus cry. Even kidreason is strangely drawn to some nonsense, presumably because of spending too much time doing math.
 skinnybarncat2
Joined: 5/24/2016
Msg: 23
Why the universe isn't a black hole
Posted: 6/4/2016 11:08:36 AM
With all of your knowledge, maybe you can answer a simple question relating to black holes. What is gravity?
 kidreason29
Joined: 9/25/2015
Msg: 24
Why the universe isn't a black hole
Posted: 6/4/2016 2:23:19 PM

Even kidreason is strangely drawn to some nonsense, presumably because of spending too much time doing math.


i take pride in this statement, but you forgot to mention funchesf who is leader of the nonsensical


With all of your knowledge, maybe you can answer a simple question relating to black holes. What is gravity?


that isn't a simple question, unless you are asking for a simple answer.
 gingerosity
Joined: 12/10/2011
Msg: 25
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Why the universe isn't a black hole
Posted: 6/4/2016 8:17:54 PM

With all of your knowledge, maybe you can answer a simple question relating to black holes. What is gravity?

You think I dismiss pseudoscience because I think my knowledge is vast? No, I dismiss it because it rejects the only reliable method of obtaining knowledge about reality that we have.

What is gravity? Go read the mountain of peer-reviewed published research into it and let us know the state of current theory.

i take pride in this statement, but you forgot to mention funchesf who is leader of the nonsensical

I almost did, but would have had to change my wording so it was listing those who may be interested in all kinds of nonsense instead of just internet pseudoscience. Funchesf is only interested in movie pseudoscience, so unless there is an episode of Startrek that is about androids dreaming of electric universes... there is no point talking to him about it.
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