Are Black Holes Actually Dark Energy Stars?(nautil.us)
nautil.us
Are Black Holes Actually Dark Energy Stars?
http://nautil.us/blog/are-black-holes-actually-dark-energy-stars
128 comments
I've seen a couple of articles about this guy recently and they both struck me as weirdly credulous given the apparently complete lack of evidence supporting his theory and the fact that approximately no other scientists seem to find it credible.
It's interesting, original, and most importantly falsifiable. There will be real differences between the jets predicted by his theory and the commonly accepted model, I'm excited to see it tested.
There's a moment at which every scientific theory is only thought credulous by a single person.
There's a moment at which every scientific theory is only thought credulous by a single person.
> There's a moment at which every scientific theory is only thought credulous by a single person.
Agreed, but the same is also true of any conspiracy theory or half-baked idea. The theory should be evaluated on it's merits, not the number of supporters. And theories that can be tested are always better than ones that can't IMO.
Agreed, but the same is also true of any conspiracy theory or half-baked idea. The theory should be evaluated on it's merits, not the number of supporters. And theories that can be tested are always better than ones that can't IMO.
The thing about conspiracy theories is that they are usually not falsifiable, at least not to their proponents.
As jboggan mentions, this theory is both falsifiable and testable in practice.
I think it's important that there are always a few people in science who go against the mainstream, as long as they do actual science, so falsifiable and testable theories.
As jboggan mentions, this theory is both falsifiable and testable in practice.
I think it's important that there are always a few people in science who go against the mainstream, as long as they do actual science, so falsifiable and testable theories.
At least at the pop-science level, his ideas connect a lot of dots. He'd neatly resolve the weirdness and mystery of black holes, their jets, their information paradox, and dark energy. It feels good.
Whether or not any of it makes a lick of sense once you start actually crunching numbers is another question. The lack of interest from other scientists leaves me skeptical (even if I'm silently enamored of the neatness myself).
Whether or not any of it makes a lick of sense once you start actually crunching numbers is another question. The lack of interest from other scientists leaves me skeptical (even if I'm silently enamored of the neatness myself).
Yep. I've been hearing mentions of this guy's theories from pop science publications for years even though, as the article says, "The idea has found no support in the astrophysical community—over the last decade, Chapline’s papers on this topic have garnered only single-digit citations."
The pop science press is depressingly bad.
The pop science press is depressingly bad.
"Dark Energy Star" is pure marketing speak, and the pop science press loves sexy terms like that, whereas to serious physicists a hyphy phrase like that is going to throw all sorts of red flags, the same way an engineer would be appalled by someone boasting about Chaos Engineering. It's usually referred to as the Cosmological Constant instead.
I would much rather live in a world where this person may be heard than likewise.
"Don't take refugee in the false security of consensus."
https://www.youtube.com/watch?v=4Z2uzEM0ugY
"Don't take refugee in the false security of consensus."
https://www.youtube.com/watch?v=4Z2uzEM0ugY
Never trust credentials for "leaps and bounds thinking". Trust credentials for incremental, linear thinking....
There's a certain nominative-deterministic inevitability to all this. There are these things called black holes that apparently are a full of a lot of stuff and aren't completely understood. And there's this mysterious stuff called dark matter that has to exist but seems to be hiding. My mom would be yelling "'Come on guys, join the dots". And who would blame her.
You seem to be thinking that nobody considered black holes as dark matter candidates, but that's not the case. The two big theories around the origin of dark matter are called WIMPs (weakly interacting massive particles) and MACHOs (massive compact halo objects), and MACHOs include black holes. The reason MACHOs aren't widely accepted is because the evidence (e.g. lensing measurements) doesn't suggest there are nearly enough massive invisible objects to account for a significant portion of the dark matter.
I'd kinda worked out that people who know about this stuff didn't think it was a good account. Was more remarking that calling things dark and black (and, indeed, wimps and machos) sort of invites simplistic and erroneous pop-science assumptions.
Robert B. Laughlin (Nobel physicist mentioned in the article) has really unique viewpoint towards emergence vs reductionism.
His book "A Different Universe: Reinventing Physics from the Bottom Down" is layman explanation of his ideas.
Here is one of his recent papers: Emergent Relativity https://arxiv.org/pdf/gr-qc/0302028.pdf
Here is one of his recent papers: Emergent Relativity https://arxiv.org/pdf/gr-qc/0302028.pdf
> The idea has found no support in the astrophysical community
They put it pretty bluntly in the article.
They put it pretty bluntly in the article.
That's true, but the article as a whole still felt weirdly credulous to me. The reminders that this is a complete flight of fancy work out to like one or two clauses in a 1400-word article that devotes a lot of room to detailing his theory and repeatedly pointing out that it could theoretically be proven true someday.
To this article's credit, though, it is more measured than others. Just as a whole it seems weird to me how much attention such a seemingly insignificant hypothesis is getting.
To this article's credit, though, it is more measured than others. Just as a whole it seems weird to me how much attention such a seemingly insignificant hypothesis is getting.
Did you want them to say "This guy is a crank!" several hundred times to fill up space? How are we ever supposed to learn anything new if everything is run through your hypothetical credibility filter first?
It's just an aside they throw out before going into how This One Maverick's ideas are so exciting. And ultimately, they're still writing yet another article on the idea because it sells.
[deleted]
After all the big discoveries (and personalities) of the 20th century, physics has seemed to be relatively quiet lately. So people are eager for the next big and dramatic change to our understanding.
And that's what George Chapline is offering the pop sci press.
And that's what George Chapline is offering the pop sci press.
If what LIGO achieved is not loud enough for the 21st century, then we are probably doomed. It is a NEW kind of telescope that has not even been utilized for 1% of its potential.
PS: I'm not arguing with your statement, you have all the right to think that way. Maybe even people who lived during Einstein's earlier times thought the same for their previous century.
PS: I'm not arguing with your statement, you have all the right to think that way. Maybe even people who lived during Einstein's earlier times thought the same for their previous century.
Yes, and there are also neutrino telescopes. I wait for the detection of an high energy neutrino event from beyond the CMBR. I think the opportunity, our understanding of physics and technology give us right now are immense. The fact that general relativity and quantum mechanics havent been reconciled by now only means that this is probably a very hard thing to do. But it doesn't mean that 'phyics is dead'.
[0]: https://icecube.wisc.edu/
[0]: https://icecube.wisc.edu/
> I wait for the detection of an high energy neutrino event from beyond the CMBR
My (non-physicist) understanding of this, is that neutrinos from then will be quite low energy now, due to the expansion of the universe(?), and so not detectable by the method IceCube uses. There is a minimum energy required, in part because the charged particles generated by the neutrino interaction need to be moving faster than the speed of light in water (or whatever the detection medium is) for there to be Cherenkov radiation generated and then detected.
That said, I would love to see a response from a more knowledgeable person!
My (non-physicist) understanding of this, is that neutrinos from then will be quite low energy now, due to the expansion of the universe(?), and so not detectable by the method IceCube uses. There is a minimum energy required, in part because the charged particles generated by the neutrino interaction need to be moving faster than the speed of light in water (or whatever the detection medium is) for there to be Cherenkov radiation generated and then detected.
That said, I would love to see a response from a more knowledgeable person!
The neutrinos may start out with any energy, whatever produced them will determine that. To cross the great expanse of time and redshifting due to expansion and still have a lot of energy left, they would simply have to start out with a whole lot more. Any neutrino event that we could detect from that far away would probably be massive anyways, so maybe we'll see something.
I would argue that one of the reasons why physics news has been quiet is because the state of the field has moved beyond a lay person's understanding at more than a high level.
Few non-physicists understand quantum mechanics even at a high level, but that certainly hasn't stopped journalists over the last hundred years. Whatever the new frontier is, I'm sure the popular media could cover it in technobabble just fine if they wanted to.
If you can't explain your idead to your janitor, you don't really grasp them yourself.
The thing I hate about this statement is it gives people an excuse to ignore things they don't understand at first glace by claiming the presenter doesn't fully understand it so it's probably not true.
Its a good standard to hold yourself to when explaining things to others. But not one to hold others to when explaining to you.
Its a good standard to hold yourself to when explaining things to others. But not one to hold others to when explaining to you.
"Be liberal in what you accept but conservative in what you generate."
Even that is up to debate.
https://cacm.acm.org/magazines/2011/8/114933-the-robustness-...
https://cacm.acm.org/magazines/2011/8/114933-the-robustness-...
OTOH...
"Hell, if I could explain it to the average person, it wouldn't have been worth the Nobel prize." -- Richard Feynman
"Hell, if I could explain it to the average person, it wouldn't have been worth the Nobel prize." -- Richard Feynman
I agree with your statement, but we're discussing physics reporting in the news. They are aiming for eyeballs and ad clicks, not for emanating understanding of the topic.
One can read Wikipedia as well
If you can successfully eli5, that indicates thorough mastery of a subject. Stuff on the bleeding edge of physics can be grasped by a limited group of experts, but nobody might have developed the 10th dan sensei level understanding yet. Maybe in 50 years we'll have great explanations of black holes and quantum mech that laypeople can grok.
> If what LIGO achieved is not loud enough for the 21st century, then we are probably doomed.
The problem is that it is REALLY hard to describe to the layman just how excruciatingly difficult it is to do what LIGO does.
I like to think that I know a thing or two about electrical engineering and quantum mechanics, and even I probably don't get just exactly how amazing LIGO is.
The problem is that it is REALLY hard to describe to the layman just how excruciatingly difficult it is to do what LIGO does.
I like to think that I know a thing or two about electrical engineering and quantum mechanics, and even I probably don't get just exactly how amazing LIGO is.
The original paper on the first detection of a black hole merger by LIGO is really great[1]. It's even open access. Much of the paper is accessible to someone at the freshman physics level. Download the pdf as it is in a much nicer format than the online version.
[1]https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.11...
[1]https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.11...
kip thorne's talks are really good about explaining ligo's importance.
https://www.youtube.com/watch?v=Cxhp4GBr1Zg
https://www.youtube.com/watch?v=Cxhp4GBr1Zg
I think people have been predicting gravity wave telescopes for so long that when one finally showed up, it wasn’t that exciting to the press.
theoretic physics stoped being the 'weird-what-if-from-academia' to be the 'weird-what-if' in general
We have people like string theorists thinking about higher dimensions in space.
It occurred to me the other day when the dark matter article hit the front page that our equation for gravity works with three dimensions but those dimensions are uniform. I can turn an object with very little effort (literally without doing work) and it’s the same size from our perspective.
How would it work if matter has more dimensions that aren’t proportional, or if space is curved in higher dimensions and the differences are in the noise floor here on earth and in orbit?
It occurred to me the other day when the dark matter article hit the front page that our equation for gravity works with three dimensions but those dimensions are uniform. I can turn an object with very little effort (literally without doing work) and it’s the same size from our perspective.
How would it work if matter has more dimensions that aren’t proportional, or if space is curved in higher dimensions and the differences are in the noise floor here on earth and in orbit?
> I can turn an object with very little effort (literally without doing work) and it’s the same size from our perspective.
I can't reproduce your experiment... I tried turning a piece of paper. At first it looked, say, about as large as a cantaloupe, but when I turned it got smaller and smaller until it practically disappeared, and it becomes very tiny... basically nothing more than a thin line in space. At certain angles I can barely see it at all. What is going on?
I can't reproduce your experiment... I tried turning a piece of paper. At first it looked, say, about as large as a cantaloupe, but when I turned it got smaller and smaller until it practically disappeared, and it becomes very tiny... basically nothing more than a thin line in space. At certain angles I can barely see it at all. What is going on?
The distance between any two ink dots remained constant as you rotated the paper, which is what you would expect when the metric is x^2+y^2+z^2. If the "dimensions were not uniform," then the same transformation may alter the distances. Perhaps the parent is on their way to discovering relativity.
Some objects have axes of symmetry, right? Think of a disk or a cylinder or a sphere. You can rotate these on some axes without a change in shape. This concept extends to higher dimensions. Not that I agree with the first poster's point necessarily.
PBS Space Time did a recent episode on higher spacial dimensions and gravity.
https://www.youtube.com/watch?v=3HYw6vPR9qU
https://www.youtube.com/watch?v=3HYw6vPR9qU
The delivery on this program is extremely annoying and slow paced (and rushed on points that ought be slow).
:(
:(
I think the delivery is good and paced just right.
Keep watching. It's a series that covers a lot of great spacetime and quantum physics topics from a rare perspective.
Also, go through the older videos. A lot of what's covered today builds on the previously released shows.
Also, go through the older videos. A lot of what's covered today builds on the previously released shows.
It's designed to be watched at 1.5x speed
then it sounds like normal speech.
then it sounds like normal speech.
Yea that's a part of the string theoretic calculation, that some of these higher dimensions are different than the three we're accustomed to. They're curved and swirled and weird. It's pretty unclear that they're real, but it's an interesting idea
Indeed. The usual layman example is that a string has two dimensions when you're close enough to it that it resembles a cylinder, but only one when you zoom out far enough that it becomes a line.
It took me second to realize that you're talking about actual real-life strings, not the strings from string theory which are precisely 1-dimensional. :)
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.
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.
It actually is true thought, that some supermassive blackholes have a density thats pretty close to that of water, and their event horizons are very very gentle.
"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.)
It's usually referred to as a fabric because in general relativity, spacetime is dynamic, as if it were on a fabric that could stretch and contract in response to the density of matter occupying it. This is where the rubber-sheet analogy comes from.
As for what it is made of, that is one of the great open questions in theoretical physics right now, but also possibly where the analogy breaks down. Because of Lorentz Invariance (light travels at the same speed in all reference frames), it is hard to suppose that there is such a thing as "atoms of spacetime" from which it is made. However, because our world is cosmological and the big bang does actually pick out a preferred reference frame, Lorentz Invarience has to be approximate in some way.
Because of cosmology and the breakdown of reductionism at plank scales, it seems that the notion of spacetime itself is approximate and needs to be replaced with something else. Some people are trying to derive spacetime from purely quantum mechanical notions, while other people are trying to find dual systems where spacetime and quantum mechanics emerge hand-in-hand. The two approaches I'm familiar involve either holography or purely geometric and combinatorial ideas where the principles of general relativity and quantum mechanics are outputs rather than assumptions.
https://www.youtube.com/watch?v=WECVq2YBduY&t=0s&index=9&lis...
As for what it is made of, that is one of the great open questions in theoretical physics right now, but also possibly where the analogy breaks down. Because of Lorentz Invariance (light travels at the same speed in all reference frames), it is hard to suppose that there is such a thing as "atoms of spacetime" from which it is made. However, because our world is cosmological and the big bang does actually pick out a preferred reference frame, Lorentz Invarience has to be approximate in some way.
Because of cosmology and the breakdown of reductionism at plank scales, it seems that the notion of spacetime itself is approximate and needs to be replaced with something else. Some people are trying to derive spacetime from purely quantum mechanical notions, while other people are trying to find dual systems where spacetime and quantum mechanics emerge hand-in-hand. The two approaches I'm familiar involve either holography or purely geometric and combinatorial ideas where the principles of general relativity and quantum mechanics are outputs rather than assumptions.
https://www.youtube.com/watch?v=WECVq2YBduY&t=0s&index=9&lis...
Thanks for linking to the video, it was the most informative handling of the subject I have seen.
After watching, I have a question, please forgive if it is ridiculous or displays some fundamental problem with my layman's understanding of the subject.
If time becomes space-like, and space becomes time-like, can we think of black holes as "time stars"? Would every black hole within our observable universe contain information from all light cones within the observable universe? In other words, would different black holes contain different information?
Does my question make sense?
After watching, I have a question, please forgive if it is ridiculous or displays some fundamental problem with my layman's understanding of the subject.
If time becomes space-like, and space becomes time-like, can we think of black holes as "time stars"? Would every black hole within our observable universe contain information from all light cones within the observable universe? In other words, would different black holes contain different information?
Does my question make sense?
I'm afraid I don't have the time to watch the entire video but, being a physicist, I can still try to answer your questions. Currently, however, your question
> If time becomes space-like, and space becomes time-like, can we think of black holes as "time stars"?
doesn't make much sense to me. Time does not become spacelike nor does space become timelike. In General Relativity, time and space are not individually defined in an observer-independent fashion in the first place. The terms we use instead are "timelike directions" and "spacelike directions" as well as timelike / spacelike hypersurfaces because they are defined in such a way that all observers will agree on whether a direction / hypersurface is timelike / spacelike. So now that we've replaced the terms "time" and "space" with "timelike" and "spacelike", I hope you'll see that your question is not exactly well-defined.
But maybe I'm misunderstanding you, so please feel free to elaborate on your questions. (Or to point me to an explanation from the video in case you're referring to one.)
As for your second question:
> Would every black hole within our observable universe contain information from all light cones within the observable universe? In other words, would different black holes contain different information?
I'm afraid I can't follow this question, either. Would you mind rephrasing it? My initial impression is that you might have a wrong idea of what a lightclone is.
> If time becomes space-like, and space becomes time-like, can we think of black holes as "time stars"?
doesn't make much sense to me. Time does not become spacelike nor does space become timelike. In General Relativity, time and space are not individually defined in an observer-independent fashion in the first place. The terms we use instead are "timelike directions" and "spacelike directions" as well as timelike / spacelike hypersurfaces because they are defined in such a way that all observers will agree on whether a direction / hypersurface is timelike / spacelike. So now that we've replaced the terms "time" and "space" with "timelike" and "spacelike", I hope you'll see that your question is not exactly well-defined.
But maybe I'm misunderstanding you, so please feel free to elaborate on your questions. (Or to point me to an explanation from the video in case you're referring to one.)
As for your second question:
> Would every black hole within our observable universe contain information from all light cones within the observable universe? In other words, would different black holes contain different information?
I'm afraid I can't follow this question, either. Would you mind rephrasing it? My initial impression is that you might have a wrong idea of what a lightclone is.
I just realized I was replying to the wrong parent comment! So sorry. I was talking about a PBS Space Time episode on YouTube I saw in (or came across via) a different comment.
https://youtu.be/KePNhUJ2reI
https://youtu.be/KePNhUJ2reI
No worries, I hadn't watched the video yet, anyway. :) So feel free to rephrase your questions if you like!
My questions were based in the video I linked above, which it sounds like may be incorrect in the way it presents the topic?
Judging from the few minutes I watched, it is at least not very precise, yes.
What they mean when saying that "time and space switch roles inside a black hole" is that in standard Schwarzschild coordinates, the direction given by the time coordinate becomes spacelike at the event horizon and, likewise, the radial coordinate becomes timelike. This statement is specific to Schwarzschild coordinates, though, or, more generally, any coordinate system that is singular/ill-defined at the event horizon. There are coordinate systems, however, that don't exhibit this pathological behavior at the horizon and, there, no switching occurs.
What they mean when saying that "time and space switch roles inside a black hole" is that in standard Schwarzschild coordinates, the direction given by the time coordinate becomes spacelike at the event horizon and, likewise, the radial coordinate becomes timelike. This statement is specific to Schwarzschild coordinates, though, or, more generally, any coordinate system that is singular/ill-defined at the event horizon. There are coordinate systems, however, that don't exhibit this pathological behavior at the horizon and, there, no switching occurs.
I'm not an expert either, but according to the treatments I've seen on GR, the flipping of time and space inside of black holes is just an artifact of the choice of coordinates, and can be fixed by changing your coordinate system. However, there are some ideas based on holography for solving the black hole information paradox that posit that it doesn't even make sense to talk about the inside and outside of a black hole at the same time at all (black hole complementarity), that the inside of the black hole is actually encoded on the surface of the horizon. This of course just leads to other paradoxes, and the only thing that seems certain is that GR is approximate in some way, and all these questions are the result of stretching the theory to regimes in which it is no longer valid. This is why many people are searching for fundamentally new ways of constructing theories that yield the same answers for experiments we've tested, but begin from different assumptions. [0]
However, as for black holes containing the same information, our universe is expanding uniformly at an accelerating rate, and this results in cosmological horizons beyond which objects are moving faster than the speed of light (with respect to the frame of reference). Therefore, black holes in different galaxies shouldn't be able to have access to the same light cones without compromising the principle of locality. Although, if you believe that entangled black holes in different galaxies would lead to the same singularity ("ER=EPR" [1][2]), this becomes more complicated and is way out of my depth.
.
Nima Arkani Hamed | Unification and Fundamental Phyics: A Status Report 9-21-2018
[0]: https://www.youtube.com/watch?v=pXYvFMqwbhc
Leonard Susskind Public Lecture | "ER = EPR" or "What's Behind the Horizons of Black Holes?"
[1]: part 1: https://www.youtube.com/watch?v=OBPpRqxY8Uw
[2]: part 2: https://www.youtube.com/watch?v=uiG_EtVQu5o
However, as for black holes containing the same information, our universe is expanding uniformly at an accelerating rate, and this results in cosmological horizons beyond which objects are moving faster than the speed of light (with respect to the frame of reference). Therefore, black holes in different galaxies shouldn't be able to have access to the same light cones without compromising the principle of locality. Although, if you believe that entangled black holes in different galaxies would lead to the same singularity ("ER=EPR" [1][2]), this becomes more complicated and is way out of my depth.
.
Nima Arkani Hamed | Unification and Fundamental Phyics: A Status Report 9-21-2018
[0]: https://www.youtube.com/watch?v=pXYvFMqwbhc
Leonard Susskind Public Lecture | "ER = EPR" or "What's Behind the Horizons of Black Holes?"
[1]: part 1: https://www.youtube.com/watch?v=OBPpRqxY8Uw
[2]: part 2: https://www.youtube.com/watch?v=uiG_EtVQu5o
Thanks for the detailed reply!
One point that was made in the video was that inside a black hole, space is collapsing faster than light. This seems like more than a change to coordinate system? Doesn't this mean that time is also moving faster than light? Could time effectively become "solid" at the singularity, with all events within the black hole's light cone at a single point in time, but in infinite space(ignoring Hawking Radiation)?
One point that was made in the video was that inside a black hole, space is collapsing faster than light. This seems like more than a change to coordinate system? Doesn't this mean that time is also moving faster than light? Could time effectively become "solid" at the singularity, with all events within the black hole's light cone at a single point in time, but in infinite space(ignoring Hawking Radiation)?
> One point that was made in the video was that inside a black hole, space is collapsing faster than light. This seems like more than a change to coordinate system?
No, this refers to the fact that inside a black hole you can travel as fast as you want and do whatever you want but even if you move around at the speed of light, you still won't be able to escape the singularity. This is because the singularity is a so-called timelike singularity – it lies in your future. It's not a point in space somewhere that you can walk around and poke; while you're in the black hole, it's actually completely invisible to you until you hit it. You can basically compare the singularity to your own death: While you can't see it right here and right now but you know for sure that you'll reach it at some point in your future.
A physicsy way of saying all this is that, inside the black hole, all future-directed worldlines emanating from a given spacelike surface will converge and eventually hit the singularity. (This is what Nima Arkani-Hamed means when he says that space "collapses".) Another way of saying this is that the aforementioned surface is a so-called trapped surface.
Back to a more intuitive explanation: In a way, falling into a black hole and towards the singularity is like falling down a waterfall: Once you've stepped over the edge (crossed the event horizon), you certainly won't be able to stop yourself from falling anymore. You cannot fall up and escape gravity.
Here's a website which explains this way of looking at black holes as "waterfalls" of space a bit further: https://jila.colorado.edu/~ajsh/insidebh/waterfall.html
> Doesn't this mean that time is also moving faster than light?
As mentioned in my other comment, I recommend steering clear of the terms "time" and "space" as those are not individually well-defined and equally agreed upon by all observers. Instead, time and space are relative – if I use a different coordinate system than you, we will have very different notions of which events occur at the same point in time (and are thus part of the same spatial slice). It's called relativity for a reason. :)
So, my counter question to your question would be:
> Time as measured by whom? ;)
But even if you define time with respect to a given observer, it still does not "move" or have a "velocity" that you could compare to the speed of light. Only massive objects actually move through spacetime and only when they're close enough, you can compare their relative velocities.
No, this refers to the fact that inside a black hole you can travel as fast as you want and do whatever you want but even if you move around at the speed of light, you still won't be able to escape the singularity. This is because the singularity is a so-called timelike singularity – it lies in your future. It's not a point in space somewhere that you can walk around and poke; while you're in the black hole, it's actually completely invisible to you until you hit it. You can basically compare the singularity to your own death: While you can't see it right here and right now but you know for sure that you'll reach it at some point in your future.
A physicsy way of saying all this is that, inside the black hole, all future-directed worldlines emanating from a given spacelike surface will converge and eventually hit the singularity. (This is what Nima Arkani-Hamed means when he says that space "collapses".) Another way of saying this is that the aforementioned surface is a so-called trapped surface.
Back to a more intuitive explanation: In a way, falling into a black hole and towards the singularity is like falling down a waterfall: Once you've stepped over the edge (crossed the event horizon), you certainly won't be able to stop yourself from falling anymore. You cannot fall up and escape gravity.
Here's a website which explains this way of looking at black holes as "waterfalls" of space a bit further: https://jila.colorado.edu/~ajsh/insidebh/waterfall.html
> Doesn't this mean that time is also moving faster than light?
As mentioned in my other comment, I recommend steering clear of the terms "time" and "space" as those are not individually well-defined and equally agreed upon by all observers. Instead, time and space are relative – if I use a different coordinate system than you, we will have very different notions of which events occur at the same point in time (and are thus part of the same spatial slice). It's called relativity for a reason. :)
So, my counter question to your question would be:
> Time as measured by whom? ;)
But even if you define time with respect to a given observer, it still does not "move" or have a "velocity" that you could compare to the speed of light. Only massive objects actually move through spacetime and only when they're close enough, you can compare their relative velocities.
> However, because our world is cosmological and the big bang does actually pick out a preferred reference frame, Lorentz Invarience has to be approximate in some way.
A particular solution to a set of equations does not usually have all the symmetry of the equations. In fact, I would say that, any solution to GR equations with energy and/or matter (assuming homogeneity on large enough scale) you will find something that looks like a preferred frame of reference.
A particular solution to a set of equations does not usually have all the symmetry of the equations. In fact, I would say that, any solution to GR equations with energy and/or matter (assuming homogeneity on large enough scale) you will find something that looks like a preferred frame of reference.
>The idea that space and time are actual objects, instead of intellectual constructs, has always struck me as wrong.
There were similar objections to the existence of the electromagnetic field, back in the 1890s. But it turns out that fields can propagate energy independent of any non-field objects in them... and if it can carry energy, then how can you say they aren't real?
Spacetime carries energy in the form of gravitational waves. So it is as much an object as anything else that carries energy, whether it be in wave form or mass form.
There were similar objections to the existence of the electromagnetic field, back in the 1890s. But it turns out that fields can propagate energy independent of any non-field objects in them... and if it can carry energy, then how can you say they aren't real?
Spacetime carries energy in the form of gravitational waves. So it is as much an object as anything else that carries energy, whether it be in wave form or mass form.
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 :)
Fabric of spacetime is the name for the 4 dimensional "space" we live in/can observe. But the word space is already defined to 3 dimensions so better call it something else, like fabric.
Think of the universe, from beginning onward, as a 4-dimensional manifold. Physicists don’t know exactly what the topology of that manifold is, but they do know that mass can affect it
I find the idea of a photo of a black hole more interesting than this dark energy star. It didn't seem to be mentioned in the article: when will this "Event Horizon Telescope" have enough data to show us an event horizon?
From their blog[1]:
> As the EHT team begins to analyze the 2017 data on Sgr A* and M 87 over the coming months, preliminary images will begin to emerge, and the searches for the signatures of orbiting material around the black holes will be conducted. It is the most exciting time of the project.
[1] https://eventhorizontelescope.org/blog/eht-status-update-may...
> As the EHT team begins to analyze the 2017 data on Sgr A* and M 87 over the coming months, preliminary images will begin to emerge, and the searches for the signatures of orbiting material around the black holes will be conducted. It is the most exciting time of the project.
[1] https://eventhorizontelescope.org/blog/eht-status-update-may...
The thing is, dark energy is only dark because it doesn't interact electromagnetically, whereas black holes are dark because the light gets trapped. So these are very different concepts.
I think it's fair to say black holes are a kind of "star", but the concept of dark energy and dark matter are something else.
I think it's fair to say black holes are a kind of "star", but the concept of dark energy and dark matter are something else.
> dark energy is only dark because it doesn't interact electromagnetically
That's certainly the case for dark matter. After decades of work we still don't know what it is, which has given the word "dark" the additional meaning of 'unknown'.
When it comes to dark energy, I think it mostly implies this second meaning.
That's certainly the case for dark matter. After decades of work we still don't know what it is, which has given the word "dark" the additional meaning of 'unknown'.
When it comes to dark energy, I think it mostly implies this second meaning.
The big giant glaring hole in his theory is that the total mass of all the black holes in the Universe is WAY less than the amount of dark energy. It's like claiming that the Pacific Ocean was filled in by the Sacramento River. That's why scientists aren't taking it seriously.
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.
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.
Outside observers never see the material cross the horizon, ever. That's why it's called a horizon, you'll never reach it (from the pov of an outside observer).
Growth-wise, you have to keep in mind that the black hole doesn't grow when matter crosses the horizon, but when the matter gets close enough to the horizon that mass of black hole + mass of new matter creates a blackhole of a larger radius that encompasses that matter.
Growth-wise, you have to keep in mind that the black hole doesn't grow when matter crosses the horizon, but when the matter gets close enough to the horizon that mass of black hole + mass of new matter creates a blackhole of a larger radius that encompasses that matter.
Would this be one way that information would not be destroyed, at least from the reference frame of the outside observer?
By my understanding of the theory, yes (according to some unproven theories). The information can be imprinted on the surface of a black hole (and, later are dissipated by imprinting on Hawking Radiation).
This is also the principle that led to our theoretical understanding that the maximum amount of information that can be contained in a volume is bounded by the _surface area_ of the volume. This is the Holopgraphic Principle: https://en.wikipedia.org/wiki/Holographic_principle.
There's a great PBS Space Time youtube video on this concept, which explains it far better and more accurately that I ever could: https://www.youtube.com/watch?v=9XkHBmE-N34
This is also the principle that led to our theoretical understanding that the maximum amount of information that can be contained in a volume is bounded by the _surface area_ of the volume. This is the Holopgraphic Principle: https://en.wikipedia.org/wiki/Holographic_principle.
There's a great PBS Space Time youtube video on this concept, which explains it far better and more accurately that I ever could: https://www.youtube.com/watch?v=9XkHBmE-N34
Thanks for the great reply.
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.
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.
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.
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 answer myself.
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).
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).
https://en.m.wikipedia.org/wiki/Physical_information
See especially the section on entropy.
See especially the section on entropy.
Long answer short: Information has to be a fundamental conserved property of the universe for the second law of thermodynamics to work under some thought experiments.
From my limited understanding information is meant to mean the characteristics of a given particle; the waveform, spin, etc.
There're different levels of making this statement precise. Here's one:
Physics is a deterministic theory, even at a quantum level where we call determinism unitarity. (Leaving the measurement problem & collapse of the wave function aside for a moment.)
Determinism means, we can start with one state of a given physical system and basically hit the "fast forward" or "backward" button to see what the state was like in the past and what other state it's going to evolve to in the future. This assignment of future states to past or current states and vice versa is unique and one-to-one, hence deterministic:
past -> future
A --------> X
B --------> Y
where the arrows indicate evolution in time.
This is what allows us to make predictions for the future outcome of experiments or draw conclusions from experimental results in the first place.
Now, the problem with black holes and in particular their evaporation through Hawking radiation is that Hawking radiation does not in any known way depend on what once fell into the black hole but, instead, just on the black hole's total mass. So let's say you start with two different mass distributions A, B of the same mass M and each collapses and forms a black hole BH of mass M. You could argue that the original matter is still somewhere inside the black hole, so the black hole's internal state still depends on the past matter distribution and we should indicate this by talking about black hole BH_A and black hole BH_B. So we have:
A -> BH_A
B -> BH_B
Then Hawking radiation sets in and both black holes vanish eventually and give way to a state of Hawking radition H:
A -> BH_A -> H
B -> BH_B -> H
As mentioned before, the Hawking state H really only depends on the mass M of the black hole, so since both BH_A and BH_B had the same mass, we will also get the same final Hawking state H. As you can see, the mapping {past events -> future events} is no longer one-to-one: From H alone you cannot draw any conclusions about the original state anymore. (Was it A or B?)
This is (one half of) what is meant when people say that information is lost (about the original state).
The other half is that a classical (eternal) black hole state is a so-called pure state from the point of quantum mechanics: There is never any doubt about its precise state. It is always perfectly described by only its mass (and angular momentum and charge)[1]. Hawking radiation, however, is not such a state once the black hole has fully evaporated. Instead, at that point it is a so-called mixed quantum state meaning that it could be any of a whole "mix" of states. We can only give a probability distribution for what the state is in reality; in Hawking's case it's a perfectly thermal distribution. (Side remark: I should point out that such a mixed state is not the same thing as a superposition in quantum mechanics! In particular, the probability distribution here is not related to any wave function.)
Anyway, what this means is that we have now evolved from a black hole state BH, that was precisely known, to another state about which nothing can be said anymore outside of the probability distribution:
BH -> Hawking_1 or Hawking_2 or Hawking_3 or …?
This constitutes a loss of predictability.
TL;DR To sum up, there are two aspects: The loss of information and the loss of predictability. Both are just the two sides of the same medal: The breakdown of determinism.
[1] https://en.wikipedia.org/wiki/No-hair_theorem
Physics is a deterministic theory, even at a quantum level where we call determinism unitarity. (Leaving the measurement problem & collapse of the wave function aside for a moment.)
Determinism means, we can start with one state of a given physical system and basically hit the "fast forward" or "backward" button to see what the state was like in the past and what other state it's going to evolve to in the future. This assignment of future states to past or current states and vice versa is unique and one-to-one, hence deterministic:
past -> future
A --------> X
B --------> Y
where the arrows indicate evolution in time.
This is what allows us to make predictions for the future outcome of experiments or draw conclusions from experimental results in the first place.
Now, the problem with black holes and in particular their evaporation through Hawking radiation is that Hawking radiation does not in any known way depend on what once fell into the black hole but, instead, just on the black hole's total mass. So let's say you start with two different mass distributions A, B of the same mass M and each collapses and forms a black hole BH of mass M. You could argue that the original matter is still somewhere inside the black hole, so the black hole's internal state still depends on the past matter distribution and we should indicate this by talking about black hole BH_A and black hole BH_B. So we have:
A -> BH_A
B -> BH_B
Then Hawking radiation sets in and both black holes vanish eventually and give way to a state of Hawking radition H:
A -> BH_A -> H
B -> BH_B -> H
As mentioned before, the Hawking state H really only depends on the mass M of the black hole, so since both BH_A and BH_B had the same mass, we will also get the same final Hawking state H. As you can see, the mapping {past events -> future events} is no longer one-to-one: From H alone you cannot draw any conclusions about the original state anymore. (Was it A or B?)
This is (one half of) what is meant when people say that information is lost (about the original state).
The other half is that a classical (eternal) black hole state is a so-called pure state from the point of quantum mechanics: There is never any doubt about its precise state. It is always perfectly described by only its mass (and angular momentum and charge)[1]. Hawking radiation, however, is not such a state once the black hole has fully evaporated. Instead, at that point it is a so-called mixed quantum state meaning that it could be any of a whole "mix" of states. We can only give a probability distribution for what the state is in reality; in Hawking's case it's a perfectly thermal distribution. (Side remark: I should point out that such a mixed state is not the same thing as a superposition in quantum mechanics! In particular, the probability distribution here is not related to any wave function.)
Anyway, what this means is that we have now evolved from a black hole state BH, that was precisely known, to another state about which nothing can be said anymore outside of the probability distribution:
BH -> Hawking_1 or Hawking_2 or Hawking_3 or …?
This constitutes a loss of predictability.
TL;DR To sum up, there are two aspects: The loss of information and the loss of predictability. Both are just the two sides of the same medal: The breakdown of determinism.
[1] https://en.wikipedia.org/wiki/No-hair_theorem
Thanks for this answer. Appreciate it.
How would you ever observe black hole to grow/accreate matter then?
Infalling matter or radiation becomes ‘simply’ infinitely red-shifted (on account of the slowed time), and hence undetectable to an external observer — and is hence indistinguishable from the bulk of the prior-existing “black hole proper”.
Conversely, a particle on the surface of an object compressed to near its Schwarzschild radius should experience an extreme blue shift and time contraction. Imagine absorbing in one instant a billion years of microwave background radiation blue shifted to gamma and beyond. How could the near-black-hole hang onto it?
Inside of a black hole doesn't hang on to anything. There is simply no longer a direction that points out.
Yeah... basically looking backwards from the perspective of an infalling particle one would experience the full blast of the Big Bang as it occurred ‘originally’.
Yes, it is indistinguishable. But it seems that actual black hole is more like a hollow crust in this setting and not a point of mass.
You can indirectly measure it's mass, charge, and angular momentum.
From the outside, it would never cross the horizon, it would look as if the matter would travel towards the horizon infintly long. After trillions of trillions of years the information that made up the inbound matter from the horizon will be radiated away by hawking radiation.
If you are travelling with a probe towards the horizon though, you would be able to calculate your escape velocity, so you could tell if you are inside our outside the horizon.
Its kind of awkward if you think about it... its seems like causality has 2 versions after the horizon.
[0]: https://en.wikipedia.org/wiki/Black_hole_information_paradox
[1]: https://www.youtube.com/watch?v=yMRYZMv0jRE
If you are travelling with a probe towards the horizon though, you would be able to calculate your escape velocity, so you could tell if you are inside our outside the horizon.
Its kind of awkward if you think about it... its seems like causality has 2 versions after the horizon.
[0]: https://en.wikipedia.org/wiki/Black_hole_information_paradox
[1]: https://www.youtube.com/watch?v=yMRYZMv0jRE
> After trillions of trillions of years the information that made up the inbound matter from the horizon will be radiated away by hawking radiation.
This is merely conjectured by some physicists. In reality, we have no clue what happens.
This is merely conjectured by some physicists. In reality, we have no clue what happens.
The youtube channel PBS Spacetime has some really great videos about how black holes work, I would start with this one: https://www.youtube.com/watch?v=vNaEBbFbvcY
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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.
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.
No snow ever "enters" a snowball, yet it grows.
If the EHT analysis of Sagittarius A* supported this theory, that would surely it would have already leaked? It seems like it would be simply too incredible not to start circulating amongst researchers and then get out into the wider world.
A article about "alternative" black holes without the word LIGO in it? Yeah, I'm gonna have to stop you right there and ask you to sell that snek oil somewhere else.
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Found an interesting technical summary/critique of these ideas https://motls.blogspot.com/2005/03/chapline-black-holes-dont...
Lubos is interesting to read at times - even brilliantly enlightening at times. But keep in mind that he's an unapologetic ultra-conservative and climate change denier, as well as an occasional troll, in addition to being a reputable string physicist. He expresses stronger views than he probably should on no shortage of topics.
How likely is this to be the case over Black Holes?
No one knows for sure. However it's good to have alternative models to look into if the observational data you eventually get (in this case from the EHT) doesn't match precisely with the mainstream model.
What is dark energy?
When you sum up all the red shifts of a large piles of galaxies they are receding from us at speeds faster than can easily be explained using the Hubble model. One theory for this is a repulsive energy of a form we have not yet observed, dubbed "dark energy", which is purported to be causing accelerating expansion of the universe since the Big Bang. More here:
https://en.wikipedia.org/wiki/Dark_energy
https://en.wikipedia.org/wiki/Dark_energy
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.
That makes no sense, black holes are like super much the opposite of a void. Further, repulsion is precisely the opposite of gravity.
Yeah you can interpret a Schwarzchild radius as a “void” in a certain sense (though more like a one-way dump) but a black hole is still very much a participant in the physics of our universe
Actually, as far as I get it, black holes just don't exist: it's a journalist term coined for a mathematical concept.
In short a black hole is how we call the possible existence of a place in the universe where there is no time nor energy, but it's no more than a mathematical possibility in the end as these are common variables in astrophysics.
Black holes exist, in the sense that we have observed several phenomena that can be easily explained by the presence of a black hole, but which couldn't be explained otherwise. For example the orbits of stars around Sagittarius A* ( https://en.wikipedia.org/wiki/Sagittarius_A* ) and the X-ray emmission of Cygnus X-1 ( https://en.wikipedia.org/wiki/Cygnus_X-1 ).
> In short a black hole is how we call the possible existence of a place in the universe where there is no time nor energy
I don't know where you got this idea, but black holes don't have "no time" and they contain lots of energy (often several stars' worth).
Keep in mind that time is relative, so when talking about extreme situations like black holes it's important to keep track of what we're talking relative to. In particular, if an astronaut left a space ship, approached a black hole, passed beyond the event horizon and carried on going, that astronaut wouldn't really notice: if they looked forwards into the black hole they'd just see normal looking space, if they looked backwards they'd see their ship just as if they'd not entered the black hole. Relative to the astronaut, space and time appear completely normal; hence it doesn't make sense to talk about black holes having "no time".
Things would look different relative to the ship: the image of the astronaut they see would redshift as it approached the event horizon, and would also slow down until it came to a stop when at the horizon.
Note that this ignores tidal forces, which can be large around small black holes (the astronaut would certainly notice if their body were torn apart!). For large black holes like Sagittarius A* the tidal forces at the event horizon should be small enough to ignore.
> In short a black hole is how we call the possible existence of a place in the universe where there is no time nor energy
I don't know where you got this idea, but black holes don't have "no time" and they contain lots of energy (often several stars' worth).
Keep in mind that time is relative, so when talking about extreme situations like black holes it's important to keep track of what we're talking relative to. In particular, if an astronaut left a space ship, approached a black hole, passed beyond the event horizon and carried on going, that astronaut wouldn't really notice: if they looked forwards into the black hole they'd just see normal looking space, if they looked backwards they'd see their ship just as if they'd not entered the black hole. Relative to the astronaut, space and time appear completely normal; hence it doesn't make sense to talk about black holes having "no time".
Things would look different relative to the ship: the image of the astronaut they see would redshift as it approached the event horizon, and would also slow down until it came to a stop when at the horizon.
Note that this ignores tidal forces, which can be large around small black holes (the astronaut would certainly notice if their body were torn apart!). For large black holes like Sagittarius A* the tidal forces at the event horizon should be small enough to ignore.
Thanks for the clarification, perhaps I was misleading, the point being that black holes have been deduced by mathematical interpretation, not observation of a phenomenon and today as per your own example we're still trying to find proof of their existence.
On the other hand, based on my understanding of the Janus model as I said in my first comment, the location of the seemingly void places are actually explained by the concentration of antimatter, which repulses matter through gravity. A possibly wrong summary of what I'm visibly struggling to communicate: This model explains how on the same way matter concentration attracts matter and rejects anti-matter, antimatter concentration attract antimatter and rejects matter.
On the other hand, based on my understanding of the Janus model as I said in my first comment, the location of the seemingly void places are actually explained by the concentration of antimatter, which repulses matter through gravity. A possibly wrong summary of what I'm visibly struggling to communicate: This model explains how on the same way matter concentration attracts matter and rejects anti-matter, antimatter concentration attract antimatter and rejects matter.
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?
Symmetry breaking is an explanation, but we don't know if it's the right explanation. It's just the best we have at present.
That's what is explained in the Janus model, both universes coexist in the same space and are rejecting each other through gravity, matter "won" over antimatter only by a tiny bit but sufficient to allow large portions of matter to remain. Though the appearance of both at the early times of the universe was in beyond colossal amounts, both being annihilated by each other when they met.
edit: typos
edit: typos
A genius by the name of Kanye was proposing this recently, though his work to, isn't widely accepted.