NOT (Black Holes Do Not Exist) Part 2
In my previous post, I discussed Physicist Mersini-Houghton’s mathematical proof that Black Holes could never form. I also expressed my disdain for the possibility that this is even remotely correct. Today I will expand on the idea why I’m so pessimistic and why there’s plenty reasons to believe that black holes are alive and well.
As a brief recap; Physicist Mersini-Houghton released an extended version of her paper about stellar collapse and Hawking Radiation. She contends that her calculations show that a collapsing core releases enough hawking radiation to reduce the mass of the core to the point that a conventional black hole cannot form which includes of course its singularity and event horizon.
There’s two ways to look at this. what do other physicists have to say about Mersini-Houghton’s paper and what is the empirical observational evidence for the existence of black holes.
Theoretical physicist William Unruh said recently
“The (paper) is nonsense…Attempts like this to show that black holes never form have a very long history, and this is only the latest. They all misunderstand Hawking radiation, and assume that matter behaves in ways that are completely implausible”
Astrophysicist Brian Koberlein said that the paper
“…doesn’t prove that stellar-mass black holes don’t exist…To say that this work proves black holes don’t exist is disingenuous at best”
Friend and physicist Brian Wecht told me succinctly the following in an email:
“Nobody I know thinks the paper is correct”
I don’t know how many physicists Brian knows but it’s safe to say it’s quite a few. So we have many then who think there are major problems with Mersini-Houghton’s paper. That’s not exactly a consensus yet but such disagreement on a theory that makes such dramatic claims should cause our skeptics sense to tingle quite insistently. That’s too bad because Mersini-Houghton’s paper has relevance to a contentious issue regarding black holes, namely, is the information that goes into a black hole lost forever? If it is, then that would go against many dearly-held tenets of physics (the unitary concept of Quantum Theory) and a resolution to this problem has drawn friendly battle-lines between opposing theoretical camps. So important is this issue that it’s worth exploring a bit.
Classic black holes as predicted by General Relativity were initially thought to emit nothing. This meant that it swallowed information (about initial states etc) that would never be recoverable, even in principle. The venerated laws of thermodynamics say that this should be impossible however. This is referred to as the “Information Paradox“. Hawking appeared to save the day with his discovery that black holes do indeed leak information in the form of hawking radiation. Like a shredded book then, it may be possible, in principle, to recover the information that was previously sequestered inside the event horizon. Hawking’s calculations though showed that the hawking radiation was random which means that it contained no information at all…back to square one. You’ll remember from my previous post that the radiation comes from virtual particles that appear out of the vacuum. One particle gets sucked into the black hole and the other speeds away. These particles are entangled meaning they share a quantum state, If that entanglement were to break though, it would mean that the information wouldn’t be lost forever and the information paradox would be resolved, Yayyy. But….if the particles were able to disentangle themselves it would also mean that a tremendous amount or energy would be released making the event horizon a sphere of death or a so-called firewall. This firewall would destroy anything moving through the event horizon including that original information-laden virtual particle. Not only would this destroy the information but it goes against our theories that tell us the event horizon should be a drama-free zone. This is called the “Firewall Paradox“. Keep in mind though that the whole theory of a firewall sounds cool but it still very controversial so the jury is out on that for now. Assuming it’s true, it seems then that wherever we turn we run into a paradox. Paradox schmaradox I say…all that means to me is that we have some interesting discoveries ahead of us.
This leads to my biggest beef with this whole black hole hubub. As is often the case, it’s the way her paper has been treated in the media. Here’s a smattering of article titles I’ve run into
And my absolute favorite:
There Are No Such Things as Black Holes
These titles are very misleading and the last one is just plain irresponsible in my opinion. It’s also not just a matter of using seductive titles to draw people in; the content of the articles as well often make no attempt to put the title in the proper context leaving readers to believe it is in fact likely that black holes do not exist.
There is no attempt, for example, to explain that the paper deals with stellar mass black holes which involve the all-important core-collapse to create the hawking radiation which is supposed to prevent black hole formation. What about the intermediate and supermassive black holes that are said to exist? These are not created through the same collapse scenario as the stellar mass stars and therefore are not addressed by the paper at all.
These articles also don’t mention the incredibly dense elephant in the room…the fact that we have a plethora of observational evidence that black holes of all shapes and sizes do in fact exist. It’s true that since they do not emit anything detectable they are essentially invisible but if science has taught us anything, it’s that we don’t need to see anything directly to know with extreme confidence that it exists.
Here’s some of the best evidence as I see it:
- Gravitational Impact: The motions of many stars clearly indicate that they are near an amazingly dense and compact object that could not be a neutron star nor even groups of them. For example, the motions of objects in galaxy M87 indicate that they orbit an object with the mass of 3 billion suns in a space smaller than our solar system. This is but one example of many including solid gravitational evidence that our very own Milky Way harbors its own supermassive black hole.
- Accretion X-Rays: An accretion disk is a swirling torrent of matter around a black hole like water going down a drain. This matter heats up to millions of degrees as it gets closer causing it to emit powerful x-rays in such a way that nicely matches exactly what we would expect to happen around a black hole.
- Relativistic Jets: Beautiful Jets of matter are routinely found in the universe and can be produced in a number of ways. The most impressive produce jets that travel near the speed of light (relativistic) and travel many thousands of light years. Since the speed of the jets are related to the escape velocity of the object producing them, it is believed that massive black holes are responsible for them. Neutron stars, on the other hand, require an escape velocity only one-third the speed of light.
- The Disappearance of Light: Infrared light emitted by objects approaching a suspected black hole has been seen to brighten, then fade, then disappear completely. This is exactly the behavior we’d expect from objects approaching a black hole. Similar events for neutron stars produce a tell-tale x-ray flash as the material fuses on its surface. This does not happen for suspected black holes, presumably because they have no such surfaces.
Regardless of the irresponsible reporting about this, Mersini-Houghton is not blameless. She does after-all say the following in her paper:
“the collapse of the star stops at a finite radius, before the singularity and the event horizon of a black hole have a chance to form. That is, the star bounces instead of collapsing to a black hole.”
She also states that this bounce produces an explosion implying that nothing is left after a supernova. This is odd as well considering that her simulations fail after the collapse occurs so there is no clear prediction what happens afterwards. Despite all this, I still doubt that Mersini-Houghton would deny the evidence that there is some form of incredibly dense matter throughout the universe that cannot be explained away as some type of degenerate matter similar to what is found in neutron stars. I suspect she couldn’t disagree that, at the very least, there is something there that is very much like a black hole even if it may be different in some important aspects. By this I mean that it is some form of degenerate matter that is condensed beyond what a neutron star can typically achieve.
There are even some theoretical candidates for this type of degenerate matter called quark matter and strange matter. Some theorize it may exist in the cores of neutron stars but others believe that this type of matter could replace conventional stellar-mass black holes which would still leave the possibility of the existence of conventional intermediate and supermassive black holes which do not form by using a core-collapse scenario.
The bottom-line then in my opinion is that it is clear that there is some form of exotic, extremely dense matter in many places throughout the universe that appears to behave in many ways like what would be called a black hole. We have learned much about these objects but they are still incredibly mysterious and there is obviously much we do not know and won’t know until we successfully fully integrate General Relatively and Quantum Theory. It is possible that we may need to jettison or modify our ideas about singularities or event horizons but if we do, it will only happen after the details have been properly vetted by the community of theoretical physicists and as long as there is no direct observational evidence that contradicts their conclusions.
Other Mass/Gravitational evidence:
Image Credit: NASA/JPL-Caltech