## Study: Our 3D Universe Could Have Originated From a 4D Black Hole 337

New submitter TaleSlinger sends this quote from Nature:

*"Afshordi's team realized that if the bulk universe contained its own four-dimensional (4D) stars, some of them could collapse, forming 4D black holes in the same way that massive stars in our Universe do: they explode as supernovae, violently ejecting their outer layers, while their inner layers collapse into a black hole. In our Universe, a black hole is bounded by a spherical surface called an event horizon. Whereas in ordinary three-dimensional space it takes a two-dimensional object (a surface) to create a boundary inside a black hole, in the bulk universe the event horizon of a 4D black hole would be a 3D object — a shape called a hypersphere. When Afshordi's team modeled the death of a 4D star, they found that the ejected material would form a 3D brane surrounding that 3D event horizon, and slowly expand. The authors postulate that the 3D universe we live in might be just such a brane — and that we detect the brane's growth as cosmic expansion. 'Astronomers measured that expansion and extrapolated back that the Universe must have begun with a Big Bang — but that is just a mirage,' says Afshordi."*
## Re:Get out the bong (Score:5, Informative)

That would be Cypress Hill, not ICP.

## It's not a paper in Nature (Score:5, Informative)

It's a news story on their website talking about a preprint paper posted on Arxiv.

## Don't get too confused (Score:3, Informative)

The article is about string theory (I think more properly called "M-Theory" these days but not sure). It is the outcome of a lot of very crazy math and complicated equations that are hard to visualize.

But, what this theory sorely lacks is evidence. By which I mean ...but it still lacks evidence. And without the evidence it is just so much hot air.

any evidence at all. It is popular in the physics world because it can resolve the discrepancies between quantum mechanics (for which there is quite a lot of solid, verifiable evidence) and general relativity (for which there is also quite a lot of evidence). Everyone wants to be aboard THAT train...so it gets a lot of attention...So, don't lose any sleep over this one. The proof just isn't there.

## Re:Uhhh... what did he just say to us? (Score:5, Informative)

Umm... No.

http://en.wikipedia.org/wiki/Observable_universe [wikipedia.org]

http://en.wikipedia.org/wiki/Future_of_an_expanding_universe [wikipedia.org]

http://en.wikipedia.org/wiki/Big_Rip [wikipedia.org]

We have no idea how large the universe is. But the current estimates of the radius of the observable universe is about 45 billion light years. That's how "far" we can see. And this is indeed due to the expansion of the universe essentially moving distances apart faster than light can travel. Furthermore, it's not just that we won't "catch up"... It seems rather likely that it's gonna get worse over time - to the point we won't be able to see much at all (relatively speaking).

## Re:Uhhh... what did he just say to us? (Score:5, Informative)

Yes. universal expansion [wikipedia.org] occurs at a speed faster than the speed of light.

## Re:Uhhh... what did he just say to us? (Score:5, Informative)

Replying to myself, sorry. Actually orbits are stable in dimension d=2 and 3 and no other. In both orbits are elliptical. With d=2 the center of mass is the center of the ellipse. For d=3 the center of mass is at one of the focal points.

http://physics.stackexchange.com/questions/50142/gravity-in-other-dimensions-than-3-and-stable-orbits

## Re:The trouble with mathematical models (Score:4, Informative)

## Several errors. (Score:5, Informative)

In no particular order:

Hawking proved...No, he did not. Hawking has a mathematical description that's consistent with quantum mechanics and general relativity, but that doesn't mean the universe actually works this way. There have been a large number of highly promising theoretical constructs that have never been observed in reality and are believed to not exist. Hawking radiation may be one of them. Most physicists believe Hawking radiation exists and is a real phenomena, but it has never been observed in reality. (We have, however, observed analogues to Hawking radiation from acoustic 'black holes'.)Highly charged particles are emitted at the poles of a black hole...No, they are not. Those jets are made of matter that was about to cross the event horizon until they suddenly and violently thought better of it. The area around an accreting black hole is perhaps the most violent spot imaginable in the universe; it should be no surprise whatsoever that once something has gone around the accretion disc a few million times it would have enough kinetic energy to go like hell off in another direction as soon as it collides with another particle. One of the billiard-balls rockets across the event horizon and the other uses its kinetic energy to escape from the accretion disc. (This is handwaving a lot of astrophysics, but is basically accurate.)the black hole itself is also rotating at the speed of light...No, it is not. Black holes have to obey the cosmic speed limit just like everything else. Also, not all black holes possess angular momentum. General relativity gives perfectly satisfactory predictions for stationary black holes.The information, that is the quantum state, of mass and energy that is eaten by a blackhole is later ejected as what could be termed high energy 'noise'; x-rays and gamma rays.Not in the slightest. Hawking radiation is about the longest-wavelength (which means lowest-energy) stuff in the universe. The reason for this is really simple: although it started off as unbelievably energetic, it had to expend virtually all of its energy escaping from where it was created a nanometer beyond the event horizon.No offense, but you need to sit down with a good book on general relativity. (I like Sean Carroll's

Spacetime and Geometry.YMMV.)