Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Are Black Holes Actually Dark Energy Stars?

nautil.us

Post reply on HN
Print view View original

51–60 of 129 posts

Re: Are Black Holes Actually Dark Energy Stars?

#51

Post by Chabs »

smogcutter wrote: post #42
knodi123 wrote: post #29

Earlier quoted context omitted.

A fun way to imagine it is with Maxwell's Demon. https://en.wikipedia.org/wiki/Maxwell%27s_demon That is an example of one way in which information can be exchanged for work.

This is me being dense, but I don't see the connection to parent's question. Is it that the demon uses information (the speed of the particles?) to perform work (decrease entropy)? But also not really, bc that would violate the 2nd law of thermodynamics? I understood parent's question to be what the heck does "information" mean in this context to begin with. My question too, because I'm pretty sure I've got the wrong…

Information as actual physical property (as opposed to a human construct) is basically the only way we found to solve Maxwell's demon seemingly reducing entropy.

Specifically, the entropy within the box gets converted into information inside the demon's "head", which eventually gets radiated away as entropy outside the box. This way, the box's entropy falls, but the entropy of universe as a whole is raised (or at least maintained).

Re: Are Black Holes Actually Dark Energy Stars?

#52

Post by Sarki »

On another note a theory which seems to fit particularly well is called Janus. The concept lies in the existence of a twin universe (ours being matter based the twin being antimatter based) merged together where the black holes are basically where the antimatter is concentrated and thus repulses all the matter hence this seemingly void. This is a succint summary but I hope it makes sense to the more knowledgeable readers of HN.

Re: Are Black Holes Actually Dark Energy Stars?

#53

Post by lottin »

"The fabric of space-time" — I hear this a lot, but what does it mean? Does it mean that space and time are a "fabric"? What is such a fabric made of? The idea that space and time are actual objects, instead of intellectual constructs, has always struck me as wrong. (I'm not a physicist.)

Re: Are Black Holes Actually Dark Energy Stars?

#54

Post by btmiller »

lottin wrote: post #53

"The fabric of space-time" — I hear this a lot, but what does it mean? Does it mean that space and time are a "fabric"? What is such a fabric made of? The idea that space and time are actual objects, instead of intellectual constructs, has always struck me as wrong. (I'm not a physicist.)

Fabric in the sense that you cannot travel across space without also traveling across time.

Re: Are Black Holes Actually Dark Energy Stars?

#55

Post by russdill »

This seems to try and make a parallel between neutron stars and his proposal of a "dark energy star". This uber-dense matter would stop matter from collapsing enough to form an event horizon.

But there is a serious problem with this. If you measure the density of a black hole by using it's even horizon you'll find that the mass and event horizon do not scale together. For instance, calculated in this way, a galactic mass black hole has a density of only 200kg/m³.

Re: Are Black Holes Actually Dark Energy Stars?

#56

Post by lottin »

btmiller wrote: post #54
lottin wrote: post #53

"The fabric of space-time" — I hear this a lot, but what does it mean? Does it mean that space and time are a "fabric"? What is such a fabric made of? The idea that space and time are actual objects, instead of intellectual constructs, has always struck me as wrong. (I'm not a physicist.)

Fabric in the sense that you cannot travel across space without also traveling across time.

Okay, this makes more sense.

Re: Are Black Holes Actually Dark Energy Stars?

#57

Post by russdill »

0898 wrote: post #15
takk309 wrote: post #9

Earlier quoted context omitted.

Would this be one way that information would not be destroyed, at least from the reference frame of the outside observer?

Question if you don't mind. This "information being destroyed" thing. What do they mean by information? Isn't information a human construct? How is the universe supposed to know what information is?

Our theories of physics are time reversible. If you play a movie of an egg breaking backwards, it's a perfectly physically possible thing. It's just super unlikely. If you had perfect knowledge of the state of the egg, you could simulate it backwards to get the egg.

If information can be destroyed, physics are no longer reversible. Playing things in reverse would give you events that occur for no reason. This is hugely important not just for particle physics, but also thermodynamics.

Re: Are Black Holes Actually Dark Energy Stars?

#58

Post by sorenn111 »

Sarki wrote: post #52

On another note a theory which seems to fit particularly well is called Janus. The concept lies in the existence of a twin universe (ours being matter based the twin being antimatter based) merged together where the black holes are basically where the antimatter is concentrated and thus repulses all the matter hence this seemingly void. This is a succint summary but I hope it makes sense to the more knowledgeable rea…

The predominance of matter over antimatter I thought was explained by symmetry breaking at the ultra extreme conditions of early universe? Would there be a twin universe for other broken symmetries?

Re: Are Black Holes Actually Dark Energy Stars?

#59

Post by sorenn111 »

lottin wrote: post #53

"The fabric of space-time" — I hear this a lot, but what does it mean? Does it mean that space and time are a "fabric"? What is such a fabric made of? The idea that space and time are actual objects, instead of intellectual constructs, has always struck me as wrong. (I'm not a physicist.)

Fabric meaning that the two things (space and time) are not separate entities. Read some of the cool thought experiments underlying special relativity and you will see how the two are "woven" together :)

Re: Are Black Holes Actually Dark Energy Stars?

#60

Post by russdill »

hinkley wrote: post #5

I managed to confuse myself into a Zeno’s paradox situation with how black holes grow. This is really exotic space. Time dialation immediately outside of the event horizon would make any matter fall so slow that it would take millions of years of time for an observer to see that material cross the horizon.

We have a very intuitive sense of asking "what's happening right there at this time". It's a super simple question and it's how we want to understand black holes. Like, after it collapses, what happens to the stuff inside? What if there was a planet? Etc.

The question necessarily treats space and time as two seprate entities, which generally works fine. Relativity starts to break that question. Different inertial/non-inertial observers will get different answers. Not a huge problem for physics, because we can easily figure out the answer for each observer. But if it was super important to you what event happened first, you won't get a satisfying answer, unless the two events occur inside each other's light cones. Then there's no ambiguity.

So we get to black holes, they seriously break this question, the light cones are completely messed up.

Post reply on HN