## Black Holes Not Black After All, Theorize Physicists 227

KentuckyFC (1144503) writes

*Black holes are singularities in spacetime formed by stars that have collapsed at the end of their lives. But while black holes are one of the best known ideas in cosmology, physicists have never been entirely comfortable with the idea that regions of the universe can become infinitely dense. Indeed, they only accept this because they can't think of any reason why it shouldn't happen. But in the last few months, just such a reason has emerged as a result of intense debate about one of cosmology's greatest problems — the information paradox. This is the fundamental tenet in quantum mechanics that all the information about a system is encoded in its wave function and this always evolves in a way that conserves information. The paradox arises when this system falls into a black hole causing the information to devolve into a single state. So information must be lost.*

Earlier this year, Stephen Hawking proposed a solution. His idea is that gravitational collapse can never continue beyond the so-called event horizon of a black hole beyond which information is lost. Gravitational collapse would approach the boundary but never go beyond it. That solves the information paradox but raises another question instead: if not a black hole, then what? Now one physicist has worked out the answer. His conclusion is that the collapsed star should end up about twice the radius of a conventional black hole but would not be dense enough to trap light forever and therefore would not be black. Indeed, to all intents and purposes, it would look like a large neutron star.Earlier this year, Stephen Hawking proposed a solution. His idea is that gravitational collapse can never continue beyond the so-called event horizon of a black hole beyond which information is lost. Gravitational collapse would approach the boundary but never go beyond it. That solves the information paradox but raises another question instead: if not a black hole, then what? Now one physicist has worked out the answer. His conclusion is that the collapsed star should end up about twice the radius of a conventional black hole but would not be dense enough to trap light forever and therefore would not be black. Indeed, to all intents and purposes, it would look like a large neutron star.

## Mostly done by 1985... (Score:5, Interesting)

Frozen Star [google.ca] by George Greenstein had as a central theme that due to gravitational time dilation that we could never see a star collapse beyond its own event horizon: it would asymptotically approach it as arbitrarily close as we liked given unlimited time but never cross it. So as a natural consequence there was always a tiny but measurable probability that trapped light and thus information could escape.

Although this is a layperson's work, it is based on his published papers which provide a mathematical background.

## Re:What about existing evidence? (Score:2, Interesting)

The best picture [nationalgeographic.com] we currently have of an exoplanet is about 6x6 pixels.

The closest black hole is heck of a lot further away.

Any observation we have of a black holes are extrapolations from gathered data.

Discoveries of stellar bodies are often presented as facts in the news but the discoveries themselves are little more than "This example would explain the data, together with a hundred other possible scenarios."

Next time you see a headline about discovering a star made entirely out of diamond or whatever, remember that the only proof they have is that no-one has bothered to find out why the signal they got can't possibly be caused by that.

## Re:Wait (Score:4, Interesting)

1) Information is another term for entropy.

2) Thermodynamic says that potential energy and entropy are inversely proportional in an isolated system.

3) Thermodynamics furthers says that the entropy of an isolated system always increases until it reaches a minimum potential energy state. Why? If the entropy of a system decreases, that implies that potential energy is increasing. But if it's an isolated system, where did that potential energy come from?

Because black holes exist within an isolated system that is the universe, if they were able to decrease the entropy of the universe then that would imply that they're generating potential energy. Remember that capacity for work is the same as potential energy, so black holes would then be the equivalent of perpetual motion machines because the expenditure of potential energy (i.e. work) creates more entropy, which would be swallowed by a black hole, which would generate more potential energy, ad infinitum. That state of affairs just wouldn't seem to mirror our larger understanding of the universe.

Also, consider that what we call "time" is effectively the same as an increase in entropy. That is, the universe is evolving to a minimum potential energy state, which is the same as "aging". If you could decrease entropy you'd effectively be making time go backward.

Of course, all this is premised on our definition of information, entropy, potential energy, etc. But as far as we know they're extremely solid and coherent concepts, and it makes more sense that some supposed phenomenon which violates that model is more likely to be false than those concepts are.

Anyhow, I'm not a physicist. I don't even play one on TV. I hope real physicists correct my mistakes.

## Re:Mostly done by 1985... (Score:5, Interesting)

Physicists originally called black holes "frozen stars" because the flow of time stops at the event horizon. Nothing can fall past an event horizon in outside time because that would take an infinitely long time to happen. It also can't happen from the perspective of an observer falling in, provided the outside universe has a finite lifetime. So you can never get a singularity.

I'm not really sure why that idea doesn't get more attention from today's physicists.

## Re:wat (Score:5, Interesting)

Since no one has actually peeked inside of a black hole we really can't tell for certain.

What we do know is that when we do the math on our models what we find are things approaching infinity. Sometimes these are just caused by using the wrong coordinate system, but other times when we change coordinate systems, the singularity still exists.

It's important to note that when speaking about infinity don't fall into the fallacy of treating it as a value. You cannot have an infinite amount of something, but you can have something which has infinite characteristics. Consider Hilbert's Hotel which is an example of the hilarity found when trying to add finite numbers and infinity together. The expression " + 1" is meaningless because you can't add a value to infinity any more than you can add "a + 1".

What's actually happening in Hilbert's Hotel is the addition of aleph numbers with finite numbers, which you can do, but has silly results. Aleph-0 + 1 = Aleph-0. But this just describes the extent of the set, suppose we took a sum and looked at it:

1 + 2 + 3 + ... n + 1 = 2 + 2 + 3 + ... n

And no matter what you try to do with it, that extra one is still hiding in the sum. If you take this new set and subtract it by all of the natural numbers, you should be left with the result of 1. One of the most irritating things is when people say you can do things like you can in Hilbert's Hotel, writing it off like it's some quirk of infinity. But it's not. If you shifted all of the guests over to only even rooms, you would still have the same number of guests and rooms.

2((n) n) = 2 + 4 + 6 + ... 2n

You've effectively just doubled the number of rooms. It's a sleight of hand that breaks the rules. "But!" you may say, "You have infinite many rooms, so of course you have a room at 2n!" If you do think this then you're still caught up thinking about infinity as a literal value. You don't have a room at 2n, your rooms only extend to n, and now half of your guests (which is still an infinite many) don't have rooms, but are left to stand out in an endless hallway.

In essence, one kind of infinity /rant

does notnecessarily equal another kind.## Re:wat (Score:1, Interesting)