Is our universe being spaghettified?

[JMJones0424]

Please excuse the made-up terms and general lack of knowledge of physics and cosmology. I am not proposing anything, I just wish to know how we would observe the universe if conditions were different than we believe them to be.

 

During an interlude of intoxicating substances last night, my friends and I were discussing odd observed phenomenon of the universe. The apparent increase in the expansion of the universe has always troubled me, and the conversation slowly swung around to this topic.

 

1) If the universe is exceedingly large, and since the further a body is away from us, the faster it appears to be receding from us, then there would be a point at which bodies would be appear to us to be moving faster than the speed of light. These bodies would then mark the "edge" of the observable universe, since their radiation would never reach us.

 

Now, IF number one is correct...

 

How would it appear to us if the entire universe were approaching a universe-sized black hole, and our universe was being stretched in three dimensions? Would tidal forces develop along the periphery and generate emissions that would be different then what we observe now? Basically, is it possible that dark energy isn't a repelling force to be found within our universe, but rather an attractive force from a source outside of our universe?

[Dd'sEvilTwin]

MMmmmmmm..... spaghettified.....

 

With or without meataballs? Sausage?

lease excuse the made-up terms and general lack of knowledge of physics and cosmology.

Only if you'll forgive my lack of knowledge pertaining to cosmology and real physics.

 

I am not proposing anything,

That's good cuz I'm already taken.

 

I just wish to know how we would observe the universe if conditions were different than we believe them to be.

I'm guessing we'd still observe things as we always have...seeing as it's only the condition of the universe that are different.....you were implying that we'd be as we are yah?

 

How would it appear to us if the entire universe were approaching a universe-sized black hole,

To me it would appear that we were screwed!....also that me trousers were soiled.

[modest]

How would it appear to us if the entire universe were approaching a universe-sized black hole, and our universe was being stretched in three dimensions? Would tidal forces develop along the periphery and generate emissions that would be different then what we observe now?

 

My instinct was to say that, no, this wouldn't really work because the universe expands isotropically from an internal observer's point of view while someone falling into (or, falling out of, which will be relevant in a sec) a hole would not see things isotropically. If you're near a black hole and look toward it everything is redshifted. Looking away from it everything is blueshifted. But, in our expanding universe everything is redshifted in every direction.

 

Nonetheless, there is apparently something similar to what you're saying that's a workable model,

• http://www.math.ucdavis.edu/~temple/articles/clarinews.pdf
  
• SpringerLink - Journal Article
  

The only difference being that it would be a white hole that our universe is falling out of rather than a black hole swallowing it.

 

And here, I'm just now reading,

 

In that case, we must ask if there is a white hole model for the universe that would be as consistent with observations as the FRW models....

 

A white hole model that fits cosmological observations would have to be the time reverse of a star collapsing to form a black hole. To a good approximation, we could ignore pressure and treat it like a spherical cloud of dust with no internal forces other than gravity. Stellar collapse has been intensively studied since the seminal work of Snyder and Oppenheimer in 1939 and this simple case is well understood. It is possible to construct an exact model of stellar collapse in the absence of pressure by gluing together any FRW solution inside the spherical star and a Schwarzschild solution outside. Spacetime within the star remains homogeneous and isotropic during the collapse.

 

It follows that the time reversal of this model for a collapsing sphere of dust is indistinguishable from the FRW models if the dust sphere is larger than the observable universe. In other words, we cannot rule out the possibility that the universe is a very large white hole. Only by waiting many billions of years until the edge of the sphere comes into view could we know.

Is the Big Bang a black hole?

 

That's interesting. And the same link answers your question "Would tidal forces develop along the periphery and generate emissions that would be different then what we observe now?" directly,

In that case, we must ask if there is a white hole model for the universe that would be as consistent with observations as the FRW models. Some people initially think that the answer must be no, because white holes (like black holes) produce tidal forces that stretch and compress in different directions. Hence they are quite different from what we observe. This is not conclusive, because it applies only to the spacetime of a black hole in the absence of matter. Inside a star the tidal forces can be absent.

Apparently, the universe could possibly be a white hole without the kinds of non-isotopic tidal forces or redshift observations that it sounds like we were both suspecting.

 

I'd never heard that, and find it really quite interesting.

 

~modest

[JMJones0424]

Thanks for the direction Modest, I was hoping you would answer :)

 

Basically, the proposition was that the observed acceleration of expansion of the universe and the subsequent end of the observable universe could be equated to an event horizon of a black hole, only the black hole is outside the universe not inside. I too immediately questioned isotropic red-shift, but the reply was perhaps our universe is embedded within a larger dimension which contains a higher dimensional massive body that is attracting or universe in what appears to us to be every direction at once. I couldn't immediately come up with a rebuttal to this, as present theories propose folded up dimensions within our universe, why can't we be a few folded up dimension within a larger universe?

 

So I fell back on the emission of highly charged particles from the field of matter orbiting around a black hole prior to its falling beyond the event horizon. His argument was that the MBR could be this radiation, just EXTREMELY red-shifted, as this is the LAST thing that is able to escape the event horizon, and therefore is emitted from a region of space accelerating very nearly at the speed of light away from us.

 

At this point, I was unable to logically argue against his view, so I thought I'd throw it around here and see what came up. I need to do some reading. :)

[freeztar]

Basically, the proposition was that the observed acceleration of expansion of the universe and the subsequent end of the observable universe could be equated to an event horizon of a black hole, only the black hole is outside the universe not inside.

 

I don't think universal expansion and black holes equate very well.

 

As far as a black hole outside our universe, it would only interact with the universe if both lightcones intersected. One would expect any interaction to show significant directional bias. Images from the WMAP project show isotropy of CMBR.

 

I too immediately questioned isotropic red-shift, but the reply was perhaps our universe is embedded within a larger dimension which contains a higher dimensional massive body that is attracting or universe in what appears to us to be every direction at once. I couldn't immediately come up with a rebuttal to this, as present theories propose folded up dimensions within our universe, why can't we be a few folded up dimension within a larger universe?

The first rebuttal that comes to mind is "prove it". :)

A black hole in a "higher dimension" would probably be a lot different than the blackholes of this dimension. Hence, it's not a very satisfying answer to your question, imho.

 

So I fell back on the emission of highly charged particles from the field of matter orbiting around a black hole prior to its falling beyond the event horizon. His argument was that the MBR could be this radiation, just EXTREMELY red-shifted, as this is the LAST thing that is able to escape the event horizon, and therefore is emitted from a region of space accelerating very nearly at the speed of light away from us.

 

How would that explain that high frequency energy pervades the universe as well?

If the CMBR represents the last thing to go, then why is there such a mix of energy levels in the universe?

 

At this point, I was unable to logically argue against his view, so I thought I'd throw it around here and see what came up. I need to do some reading. :)

 

You could also argue on the idea of theoretical mass limits for black holes.

 

These ultra-massive black holes, found at the centres of giant elliptical galaxies in huge galaxy clusters, are the biggest in the known Universe. Even the large black hole at the centre of our own Milky Way galaxy is thousands of times less massive than these behemoths. But these gigantic black holes, which accumulate mass by sucking in matter from neighbouring gas, dust and stars, seem unable to grow beyond this limit regardless of where - and when - they appear in the Universe. "It's not just happening today," said Natarajan. "They shut off at every epoch in the Universe."

 

The study, which appears in the Monthly Notices of the Royal Astronomical Society (MNRAS) on 15 October, represents the first time an upper mass limit has been derived for black holes. Natarajan used existing optical and X-ray data of these ultra-massive black holes to show that, in order for those various observations to be consistent, the black holes must essentially shut off at some point in their evolution.

Upper Mass Limit For Black Holes?

[JMJones0424]

You could also argue on the idea of theoretical mass limits for black holes.

 

Upper Mass Limit For Black Holes?

 

Excellent! Thank you.

[modest]

Basically, the proposition was that the observed acceleration of expansion of the universe and the subsequent end of the observable universe could be equated to an event horizon of a black hole, only the black hole is outside the universe not inside.

 

I guess it would depend on what your buddy would mean that they are equated. The cosmic horizon is certainly analogous to a black hole event horizon. Just how analogous is, I suppose, a matter of interpretation. In standard cosmology the acceleration of expansion means that the cosmic horizon is moving towards us, rather than... :naughty: :shrug:

 

I just had an idea :eek:

 

Ok—your buddy is describing something very like an interpretation of a de Sitter universe that I just remembered discussing previously, (I think with ColdCreation).

 

Stick with me... A de Sitter universe is basically what our universe is turning into. There is very little matter density and there's a cosmological constant which accelerates expansion. As wiki says,

Because our Universe entered the Dark Energy Dominated Era a few billion years ago, our universe is probably approaching a de Sitter universe in the infinite future. If the current acceleration of our universe is due to a cosmological constant then as the universe continues to expand all of the matter and radiation will be diluted. Eventually there will be almost nothing left but the cosmological constant, and our universe will have become a de Sitter universe.

Wikipedia -- de Sitter universe

 

A de Sitter universe is exactly like a normal standard cosmology FLRW universe where the density of the universe is low and there is a cosmological constant except that it is a slightly different way of looking at it (or, of writing it metrically).

 

In standard cosmology the Hubble distance (where recession velocity equals c) moves closer to an observer if expansion accelerates. Look, for example, at the last image of this page and the line marked "Hubble distance". And, as the page says,

Notice that the Hubble distance is rapidly decreasing during acceleration, and in fact becomes zero at conformal time 65 Gly, which corresponds to the infinite future (we see a smaller and smaller comoving part of the Universe as exponential expansion proceeds).

In standard Friedmann cosmology that horizon moves towards us because of acceleration of expansion (or, a person could say, because of the cosmological constant). In a de Sitter universe things move toward the horizon because of the cosmological constant. They are, in a sense, drawn to it like something being drawn toward the horizon of a black hole. In fact, the analogy is very good. If you set a clock next to a black hole it will be drawn toward the hole and it will be increasingly time dilated. In a de Sitter universe, if you set a clock somewhere out there in the universe then the same two things happen,

In the first case the universe is stationary (Friedmann’s terminology) in the sense that all spatial distances remain constant. However, according to Eddington (1923), [de Sitter's model is different,] "a particle at rest will not remain at rest unless it is at the origin; but will be repelled from the origin with an acceleration increasing with the distance. A number of particles initially at rest will tend to scatter unless their mutual gravitation is sufficient to overcome this tendency." This constitutes one part of the observed wavelength shift; the other is due to the cos

²

x

₁

factor of x

₄

in de Sitter’s metric (x

₁

, x

₂

, x

₃

are the space coordinates and x

₄

is the time coordinate), which produces a slowing down of time between the origin and the horizon R and thus leads to a redshift. The universe, though hyperbolical, is of finite size, v=c at the horizon.

Modern cosmology in retrospect - Google Books

Essentially, the horizon out there, that you mention in your opening post, stays where it is as things are drawn toward it. Like a black hole, redshift is a combination of things being 'scattered' toward the horizon and time dilation as things get closer to it. The analogy continues,

I too immediately questioned isotropic red-shift, but the reply was perhaps our universe is embedded within a larger dimension which contains a higher dimensional massive body that is attracting or universe in what appears to us to be every direction at once.

De Sitter originally constructed his universe as a 3 spatial dimension + 1 time dimension construct embedded in a 5th dimension,

As De Sitter went over Einstein’s calculations, he discovered another cosmological model. In Einstein’s model, the spatial geometry is that of a 3-dimensional hypersphere embedded in a 4-dimensional Euclidean space. Using an imaginary time coordinate, De Sitter considered an alternate model, in which the spacetime geometry is that of a 4-dimensional hypersphere embedded in a 5-dimensional Euclidean space, or, if the imaginary time coordinate is replaced by a real time coordinate, a 4-dimensional hyper-hyperboloid in a 4+1-dimensional Minkowski space-time.

The Einstein de Sitter Debate

A black hole is massive and the reason things are drawn to it and the reason things are time dilated near it are because of its mass. So, the analogy would be complete if we could say that the static form of de Sitter's 1917 model can be said to have mass at the v=c horizon and that the horizon is a result of that mass. In fact, this is precisely how Einstein first interpreted de Sitter's model,

Contrary to Einstein’s model, however, the temporal component of the static De Sitter metric is variable and vanishes on the “equator” of this hyperspherical space. Einstein argued that such singular behavior of the metric was unacceptable, and suggested that it indicated the presence of matter on the equator.

The Einstein de Sitter Debate p.4

This impression, however, is generally considered not to be correct and Einstein later conceded the point. The horizon, or what is alternatively called the equator or the singularity in the paper quoted above, does not arise in the model because of mass. It is, rather, a coordinate singularity that arises because of the static form of the metric,

In his next letter on the topic (of June 16, 1918), Klein was more direct. As in his earlier letter, he wrote the transformation from the pseudo-Cartesian coordinates of the De Sitter hyper-hyperboloid in 4+1-dimensional Minkowski space-time to the coordinates used to write the solution in static form. This shows, Klein explicitly pointed out, that the singularity at the equator has to be an artifact of the static coordinates. The point can be made more generally than Klein did. Since the De Sitter solution can be represented geometrically as a fully regular hypersurface in a higherdimensional embedding space, any singularity in a coordinate representation of the solution must be an artifact of the coordinates.

The Einstein de Sitter Debate p.5

So, depending on how you look at things (i.e. the coordinates and model used) I would say that the cosmological horizon can be a good analogy to the horizon of a 5D black hole—but, the physical reality is somewhat different. And, I believe reality is better represented with a Friendmann universe where space is expanding and the horizon is clearly an aspect of recession speed.

 

Like I said though, it's a very interesting topic. :confused:

 

~modest