11 ms·

Rethinking the origins of the universe

202 points by cyang08 12y ago

ISL 12y ago
Interesting; if the paper finds general acceptance, it'll be fun to watch a new flurry of activity. The fairly recent controversial concept of "firewalls" has reinvigorated that subfield of physics. Whether black holes exist or not, there's something really dense at the center of our galaxy. It's a challenge to come up with a consistent non-black-hole explanation for the observed motion of stars at the galactic center. http://www.galacticcenter.astro.ucla.edu/images/2011orbits_animfull.gif http://www.galacticcenter.astro.ucla.edu/images/2011orbits_a... More here: http://www.galacticcenter.astro.ucla.edu/journey/smbh.html http://www.galacticcenter.astro.ucla.edu/journey/smbh.html
- dennisnedry 12y ago
  This is why I love astrophysics (and the scientific method). When you find something conclusive (assuming the paper is accurate), and it causes you to re-think what you thought you knew about the universe, it suddenly becomes larger than you ever believed possible. I hope this paper is true - since it solves the information paradox.
chc 12y ago
Given how important this would be, it seems a bit odd that she just threw it on ArXiv rather than having it peer-reviewed. Also, the press release's explanation of what Hawking radiation is sounds strange to me, though I'm not an astrophysicist. It all makes me very hesitant to put any stock in this right now (well, at least it in meaning what's suggested here).
- timClicks 12y ago
  The ArXiV is how you get your work peer-reviewed in cosmology and other areas. Findings can be examined much more quickly than the normal publication cycle.
- orbifold 12y ago
  In theoretical physics all papers important or not are submitted as preprints to ArXiv and then prepared for publication, an informal system like that has been in place during all of modern science, only that before the internet professors send a number of copies of their latest result to collaborators and to people they thought might be interested in them. I think this is much nicer than the alternative, that important results are only circulated in small circles and "milked dry" until they are released to the public.
- Stwerp 12y ago
  I understood that it was common to post the paper to arxiv when it was in the process of being peer reviewed by a journal. The problem is the extended lag time between submission and final publication with most journals which pre-print archives like arxiv try to solve. Do people really just "submit to arxiv" and then that it? I didn't know that, but its not common in my field to use arxiv so I have not kept up with all practices.
  - tjradcliffe 12y ago
    There have been cases where arxiv has been used as a venue of final publication, but the general intent is that stuff submitted there will eventually find a home in the peer-reviewed literature. There are sometimes exchanges of arguments there that never make it to prime-time, but that's not the dominant use-case. The reality is, though, that people working in a given field are much more likely to use the arxiv version as the basis for further work, simply because it is available so much earlier. It is not uncommon to reach the point of publication and then run around to try and find out where all the arxiv submissions you used were published, which can sometimes be challenging.
  - sampo 12y ago
    > Do people really just "submit to arxiv" and then that it? Some people do: http://en.wikipedia.org/wiki/Grigori_Perelman http://en.wikipedia.org/wiki/Grigori_Perelman
JSPy 12y ago
This doesn't really mean anything, as the work isn't peer-reviewed yet. However, if this does become accepted it will have an extremely large impact in Physics. The fact that this could do away with the information paradox and add some harmony between General Relativity and Quantum Mechanics is a big deal. Furthermore, as the title suggests, we have to rethink the origins of our universe.
danbruc 12y ago
Well, there is are a lot of observational evidence for black holes - the by far most likely scenario is that the model they analyzed does not describe the physics of black holes in our universe.
- tericho 12y ago
  This is the first question I thought of. I'm not a physicist so I dare say I can't interpret the paper but I'm curious how she explains the seemingly observed orbits of stars around the black hole in the middle of our galaxy and others[1][2]. [1]http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/ http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/ [2]http://en.wikipedia.org/wiki/Accretion_disc http://en.wikipedia.org/wiki/Accretion_disc
AnimalMuppet 12y ago
If I understand correctly, black holes do not play a large role in our model of the origins of the universe. So this doesn't (directly) lead to "rethinking the origins of the universe". Does this work call the big bang into question (or even our current models of the big bang)? Or is it just details like galaxy formation that it makes us rethink? Another question: Something very massive and very small is at the center of our galaxy. At least, we sure think so. Does this make us question that? Or does this just make us question whether that massive thing is in fact a black hole?
- tjradcliffe 12y ago
  Your first point is correct: the relationship between black holes and the initial state of the universe is not clear. Whether or not there was a primordial singularity or something else is an open question. With regard to the question "If not black holes, then what?", this is a problem. There is a strict upper limit on neutron stars of about 1.4 solar masses. Beyond this, gravity is stronger than the repulsive core of the strong nuclear force, and the star should collapse. If the process described in this paper is what actually occurs, the star will shed mass due to Hawking radiation while collapsing. The end-state of that process must be either a neutron star (which can't have more than 1.4 solar masses) or something else. There doesn't seem to be any "something else" in the offing, which makes that million-solar-mass thing in the centre of our galaxy deeply mysterious. A new theory that makes an old "settled" phenomenon mysterious is not all that uncommon in the sciences, so it's reasonable to take a wait-and-see attitude toward this idea, but I'm not enormously hopeful that it'll pan out very well in the long run.
  - squozzer 12y ago
    So it seems a cycle of collapse and Hawking radiation will occur until the star no longer has enough mass to collapse.
- danbruc 12y ago
  The beginning of the universe and black holes have in common the singularity if you think about it naively. Besides that there is not much of a connection. And I think most physicist don't believe there are real singularities in black holes or at the beginning of the universe but quantum mechanics, quantization of space and time or something else kicks in and prevents the singularity. And there is no(t much) doubt that very massive dark objects are out there, we can observe them indirectly. So even if the classical black hole creation process turns out to be not possible, there are still objects out there that a very much like classical black holes.
z3t4 12y ago
What many people seem to overlook is that gravity is linked to time (space time)! So instead of the "black hole" being massive, it could be that time is running fast!
- 3327 12y ago
  interesting any reference/publications on this?
  - z3t4 12y ago
    When astronomers measure the mass of the black hole, they simply measure the acceleration of nearby stars, using newton's formula. They might use fancy words, but the math is very basic. Now, if time ran faster, like if you made the measurements while accidentally having the video speed in fast forward. The stars would accelerate faster, and you would get a higher mass.
- seiji 12y ago
  Well, "linked" is vague. They aren't linked—they are the same thing! Gravity is an effect mass has on the upholstery of the universe. Time runs slower for us here inside the gravity well of Earth than it does for astronauts in zero gravity. You can't create time distortions without gravity distortions, and you can't create gravity distortions without instantiating mass, so... big massive black holes have to be running slow; if they exist at all and aren't just cosmic bees sitting at the 2D boundary of the universe and projecting nothingness into our inflated space.
  - lutusp 12y ago
    > They aren't linked—they are the same thing! If you're speaking of time and space, no, they're different -- they're certainly all part of one spacetime, but they're distinct. This distinct: t' = t √(1-v^2/c^2) t = time v = velocity c = speed of light t' = time at velocity v relative to velocity 0 Put into words, this special relativity relationship shows that an increase in velocity (movement in space) causes a reduction in time's rate of passing (movement in time). The general relativity version has more terms, and shows a relationship between mass and both space and time. So space, time and mass aren't the same thing, but they're part of an interrelated system, one easily described mathematically. > Time runs slower for us here inside the gravity well of Earth than it does for astronauts in zero gravity. Yes, true, but astronauts in orbit aren't in zero gravity, they're in free-fall. The gravitational force at typical orbital heights is nearly as strong as it is at the surface.
tfgg 12y ago
"In 1974, Stephen Hawking used quantum mechanics to show that black holes emit radiation. Since then, scientists have detected fingerprints in the cosmos that are consistent with this radiation, identifying an ever-increasing list of the universe’s black holes." Er, what? I don't think this is true, or Hawking would have his Nobel prize by now. Maybe consistent in the sense that the predictions are that Hawking radiation is undetectably low for stellar mass black holes. Also, analogue systems don't count.
- vorg 12y ago
  > "Stephen Hawking used quantum mechanics to show that black holes emit radiation." I don't think this is true, or Hawking would have his Nobel prize by now Hawking not getting a Nobel by now doesn't mean much. Einstein never got one for relativity (either Special or General), and when he did get his Nobel he was told not to mention "relativity" in his speech.
  - collyw 12y ago
    Obama got a Nobel peace prize!
  - jorgis 12y ago
    Einstein guy his for his work with Brownian Motion. Nobel prizes aren't typically given for science that lacks a body of supporting evidence, which was the case at the time for Relativity.
  - saalweachter 12y ago
    Einstein, he was the guy who did all that great work in photoelectrics, wasn't he?
deleted 12y ago
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phkahler 12y ago
Now that all the physicists are reading, I have a question: Are the trajectories of light beams following the curvature of space-time reversible? In other words, if I reflect a light beam back on itself, does it return to its source? Because if that's true (and my feeble understanding is that it is true), then light can't enter a black hole or the reverse path would allow light to escape. What am I missing here?
- raphaelj 12y ago
  I'm not into Physics, but should not the space stretch itself to infinity so the light will never actually reach the mirror ?
- lisper 12y ago
  IANA physicist, but I have a pretty good intuitive understanding of relativity. Yes, light paths are reversible. The reason you can't get a beam of light out of a black hole by reflecting an incoming beam is that from the point of view of an observer outside the event horizon, and inbound beam never makes it past the horizon inbound because of time dilation. At the horizon, time stops (relative to frames of reference outside the hole).
- antognini 12y ago
  If the spacetime is static, then yes, the trajectory of a light beam (or anything else) is reversible. The question you pose is an excellent one and is one of the reasons that many physicists believed that black holes could not exist after Karl Schwarzschild discovered the Schwarzschild metric that describes spacetime around a spherically symmetric black hole. So what happens if you direct a beam of light radially into a black hole? A distant observer will calculate that as the light beam descends into the black hole it will be (according to a distant observer) progressively blueshifted until it reaches the event horizon, at which point it will have blueshifted to infinite energy. In fact, according to the calculations of a distant observer, the light beam will never cross the event horizon, so the statement that the light beam is reversible remains true. The reason that the light beam (according to the distant observer) doesn't cross the horizon is that if you look at the metric, it states that ds^2 = (1 - R_Schw / r) c^2 dt^2 - 1 / (1 - R_Schw / r) dr^2, where R_Schw is the radius of the event horizon. Notice that at the event horizon r = R_Schw and the dr^2 term diverges. The distant observer therefore concludes that there is a singularity at the event horizon. This analysis lead physicists to initially conclude that black holes were unphysical. A more careful analysis reveals that this isn't the case, however. We have been using this metric which describes the shape of spacetime according to a distant observer. But what we're really concerned with is not what a distant observer calculates, but how a local observer perceives spacetime. If we now switch to a coordinate system in which we are free falling into the black hole along with the beam of light, we find that nothing remarkable happens when we cross the event horizon. The light is blueshifted relative to its initial energy, but it doesn't have an infinite amount of energy. Thus there is no true singularity at the event horizon. This singularity that the distant observer found must therefore have been an artifact of the particular coordinate system that the distant observer was using. The free falling observer can then hold up a mirror and send off a light beam and have it return back to him even after they have crossed the event horizon.
Fool40 12y ago
Just downloaded the PDF, I am not a physicien nor a mathematicien. but from what I read in the article the EQ 13, is the weakness of their argumentation. AA
- Fool40 12y ago
  Their boundery limit pose a problem, and then the entire solution in the extending (prior explosion) the radius is greater the rs, and so all the fellowing integral are wrong. but I will wait for Hawking opinion :)
lutusp 12y ago
Quote: "Experimental evidence may one day provide physical proof as to whether or not black holes exist in the universe. But for now, Mersini-Houghton says the mathematics are conclusive." Not as conclusive as the evidence for black holes. Remember that the article's hypothesis requires proof that black holes do not exist -- in other words, proof of a negative. Proof of a negative is generally regarded as an impossible evidentiary burden, and calls into doubt the hypothesis that relies on it. There's pretty good evidence for very large, very dense masses at the center of most galaxies including our own. The default conclusion based on the evidence is that they're black holes -- they have the right mass and density. We should all remember that a mathematical theory isn't a scientific theory until observation bears it out (produces positive evidence), and to the exclusion of competing explanations.
dllthomas 12y ago
"from Star Trek to Hollywood" So... Hollywood? Star Trek wasn't filmed on location - Desilu and Paramount were both located in Hollywood. Not that this, y'know, matters - just found it amusing.
- pluma 12y ago
  Filming Star Trek on location would have been pretty difficult, I'd imagine.
  - Tloewald 12y ago
    Well San Francisco, Cape Canaveral, and New York City figure in various episodes and movies. (Just off the top of my head.)
sramsay 12y ago
I'm not a physicist. I imagine that if I were, this would be exciting news (that is, an exciting possibility). I am a literary critic, though, and I have to say that it's bittersweet news at best. Black holes are so much a part of the space-age imagination. The article mentions Hollywood, but black holes are woven deeply into our everyday metaphors and have been for decades. They have stood among the most wondrous things in the universe -- an awe-inspiring thing. It reminds me a bit of when the press reported that the Catholic Church had "gotten rid of Limbo" (the actual case was a bit more complex, and involved some fairly weighty theology). Then again, we all still talk of things "being in Limbo." Perhaps that next project will still be a black hole, even if it turns out that there's no such thing.
- dhimes 12y ago
  I imagine that the metaphor "black hole" will be here for a while. After all, we still use the term "big bang" for the 'first moment' of the creation of the universe, even though the "Big Bang Theory" isn't generally believed any longer.
  - Ono-Sendai 12y ago
    Erm, the big bang theory is still the best theory for the history of the universe.
    - dhimes 12y ago
      No- it was replace by the inflationary theory long ago. They are different. You've kind of proved my point.
      - Ono-Sendai 12y ago
        As I understand it, inflation usually applies shortly after the big bang.
        dhimes 12y ago
StefanKarpinski 12y ago
This paper claims that black holes can't come into existence, which is subtly different from claiming that they cannot exist. In particular, black holes can exist as long as they've always existed – it's just that new ones can't come into existence. Maybe the universe just has a fixed number of singularities. [I am not a physicist – this just struck me as an inaccurate implication in the article.]
- lutusp 12y ago
  > In particular, black holes can exist as long as they've always existed ... This doesn't work in physics. If you say they can only exist if they've always existed, then you're obliged to say how they came into existence earlier -- the deep meaning of "always".
  - kijin 12y ago
    The article implies that since singularities can't come into existence now, there can't have been a singularity at the moment of the Big Bang, either. That sounds implausible. Lots of things that cannot possibly come into existence at the present time did exist at the moment of the Big Bang (and shortly afterward), because the conditions back then were so radically different from they are now. Perhaps the only singularity that ever existed was the Universe at the moment of the Big Bang. After the One Singularity has blown itself apart, no other singularity can come into existence. I don't see any inconsistency in that scenario.
    - alchemism 12y ago
      And with that, physics discovers Pandeism.
    - lutusp 12y ago
      > The article implies that since singularities can't come into existence now, there can't have been a singularity at the moment of the Big Bang, either. Yes, that's true, but if the paper's thesis is correct, then there aren't any black holes or singularities at all, at any time. If the thesis is false, then there can be black holes at the universe's beginning, and they can form today, given the right conditions. > Lots of things that cannot possibly come into existence at the present time did exist at the moment of the Big Bang (and shortly afterward), because the conditions back then were so radically different from they are now. Not so different, and from a theoretical standpoint, they lie on a continuum from the present to the past. The condition of the universe as a whole has changed over time, but from the present we can mimic earlier conditions using high energies. It is often said that one goal of accelerator technology is to move backward in time toward the Big Bang. As technology advances, as accelerator energies increase, we create conditions more like the conditions in the early universe. The ultimate hope is to create conditions as much as possible like the first few seconds of the universe's existence, to be able to see the genesis of present conditions and refine physical theory. > Perhaps the only singularity that ever existed was the Universe at the moment of the Big Bang. After the One Singularity has blown itself apart, no other singularity can come into existence. I don't see any inconsistency in that scenario. A physicist would immediately see the inconsistency in that. If the conditions of the Big Bang theory can exist in reality, then given the same conditions of temperature and pressure, we should be able to imitate an earlier reality on a small scale. That's what an accelerator is designed to be -- an imitation of nature at an earlier time.
trhway 12y ago
Ok. To start she addresses only "Gravitationally Collapsing Star"s. Interesting result, may be many star lifecycles don't end in a black hole. The "before-black-hole" state she describes still would involve significant time dilation and thus what we see as Hawking radiation from black hole may just be Hawking radiation from "before-black-hole" star. Looks the same :) The result doesn't say that black hole is impossible. It says that a star's collapse loses mass faster than acceptable for the collapse to end in black hole. Some misconceptions in the web-post: >They are the ultimate unknown – the blackest and most dense objects in the universe that do not even let light escape. a black hole isn't necessary most dense. After all a black hole with a mass of visible Universe would be only 125 times denser than current average density of the visible Universe (i.e. 45B light years radius of visible Universe have 10B light years Schwarzschild radius) > So the story went, an invisible membrane known as the event horizon surrounds the singularity and crossing this horizon means that you could never cross back. It’s the point where a black hole’s gravitational pull is so strong that nothing can escape it. "membrane" is very bad illustration. It is constantly changing solution to the gravitational equations. One moment it is here, another moment - it has moved because gravitation of black hole changes and a lot of oscillations/perturbations happen. One moment you're inside, another - outside. "gravitational pull is so strong that nothing can escape it" - that's bad wording too. It is actually "gravitational well is so deep that nothing can escape it". Feel the difference :) A huge black hole may have pretty weak gravitation at its horizon. Thus no-escape is valid only in the sense that escaping object just would never reach "a point at infinity" from the black hole and the light would get red-shifted into full oblivion.
- darkmighty 12y ago
  You seem to be knowledgeable, so is there a plausible bridge between the impossibility of this kind of collapse and complete impossibility of black holes? I mean, what if could construct a collapse to your desire, e.g. smashing dense cold chunks, would those necessarily radiate enough energy to prevent collapse too?
  - trhway 12y ago
    >is there a plausible bridge between the impossibility of this kind of collapse and complete impossibility of black holes? the shown impossibility of star collapse to BH is somewhat questionable for massive stars because - as i cited wikipedia in another comment - the Hawking radiation carries away less mass/energy than cosmic background brings in - the net is positive for the collapsing star. >smashing dense cold chunks, would those necessarily radiate enough energy to prevent collapse too? we associate "collapse/smashing" with BH i think mostly because of collapsing stars. One can scale this process out to a lot of small chunks of cold matter as you suggest flying simultaneously toward common center. Imagine the sphere with radius 1000 times radius of Sun filled with material of density of water - this is already a black hole as its Schwarzschild radius is a bit larger than those 1000 radii of Sun. Now lets say we scale the sphere radius additional 10 times - the mass scales 1000 times and the Schwarzschild radius increase 1000 times too - thus all this water may be separated by a lot of space and still be a black hole. Now imagine that all this water is outside the Schwarzschild radius and spread on some imaginary sphere and simultaneously released to fly toward the center - once all these drops cross the schwarzschild radius, even without touching each other, and with each drop feeling only pretty small gravitation from the rest of the water, they nevertheless become a BH. What kind of miracles would happen in the moment these drops cross the imaginary sphere of Schwarzschild radius? Nothing. The only change here is that any light radiated by the drops close to crossing would reach far observers as a very redshifted and any light radiated at the moment of crossing and after would never be seen by the far observers. The article suggests that the loss of mass due to Hawking radiation would be fast enough to shrink the Schwarzschild radius faster than the drops can fall into. All this cold drops flying in empty cold space would supposedly cause very intense radiation close to the schwarzschild radius border? Nope. As mentioned above in the wikipedia citation Hawking radiation is pretty cold, low intense, for that size of black hole, and in particular it is much colder than CMB, ie. the losses are less than what is brought in by CMB. Though may be in the absence of CMB if the math in the article is right the losses (given the time slowing) would be enough to shrink the Schwarzschild radius fast enough. Yet not in our real Universe with CMB.
faizshah 12y ago
I'm not at all acquainted with astrophysics but I remember seeing an article state that there was a different physicist who proved this same thing: https://news.ycombinator.com/item?id=7191324 https://news.ycombinator.com/item?id=7191324 A quick google shows his response to this: https://twitter.com/abhasmitra/status/514804101024997376 https://twitter.com/abhasmitra/status/514804101024997376 His response: "Hawking radiation is unproven. And particle physicists are not aware that even without any Quantum Mechanics, classical gravitation dictates that all gravitational collapse must be accompanied by radiation. : http://link.aps.org/doi/10.1103/PhysRevD.74.024010 http://link.aps.org/doi/10.1103/PhysRevD.74.024010 (http://arxiv.org/pdf/gr-qc/0605066v3.pdf http://arxiv.org/pdf/gr-qc/0605066v3.pdf) And then grav collapse should naturally lead to radiation supported ECO: http://www.sciencedirect.com/science/article/pii/S1384107606000923 http://www.sciencedirect.com/science/article/pii/S1384107606... http://mnras.oxfordjournals.org/content/369/1/492 http://mnras.oxfordjournals.org/content/369/1/492 http://mnrasl.oxfordjournals.org/content/404/1/L50 http://mnrasl.oxfordjournals.org/content/404/1/L50 And as far as non -formation of ``Event Horizon'' is concerned, in contrast to the conjectures of the present yet unpublished paper I gave EXACT proof: http://www.ias.ac.in/pramana/v73/p615/fulltext.pdf http://www.ias.ac.in/pramana/v73/p615/fulltext.pdf But phys.org never highlighted my research which is infinitely more accurate than the present paper whose authors are not even aware that Question of Hawking Radiation Would Arise Only If There Would Already Be a Black Hole With an Event Horizon. Therefore This paper is not self-consistent. But that does not matter: The lead author of this paper has CAMBRIDGE AFFILIATION. So phys.org is glad to highlight an inconsistent and yet unpublished paper by ignoring my series of my exact and original papers on the same topic." I don't have any background in astrophysics, can anyone comment on Dr. Mitra's response and the relation of his work to the above research? The best discussion I can find on Dr. Mitra's work is on quora: https://www.quora.com/Is-it-true-that-Abhas-Mitra-resolved-the-Black-Hole-paradox-13-years-before-Stephen-Hawking https://www.quora.com/Is-it-true-that-Abhas-Mitra-resolved-t...
- deleted 12y ago
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- trhway 12y ago
  >But phys.org never highlighted my research which is infinitely more accurate than [...] >The lead author of this paper has CAMBRIDGE AFFILIATION. >So phys.org is glad to highlight an inconsistent and yet unpublished paper by ignoring my series of my exact and original papers on the same topic." welcome to modern science. It is a professional guild like a guild of shoemakers of Middle Age Europe cities with about the same rules. Or like another my friend (former second-rate professor from a first rate university :) put it - it is a mafia, at every level. Researchers of the highest tier universities publish in the highest tier journals, researchers of the next tier - in the next tier journals, ... A good physicist should be able to understand the laws of Nature behind such formation :)
tericho 12y ago
Ethan Siegel just posted a detailed response to this. https://medium.com/starts-with-a-bang/yes-virginia-black-holes-exist-df0a131d7b95 https://medium.com/starts-with-a-bang/yes-virginia-black-hol...
- anigbrowl 12y ago
  That was written in February (how could you miss this? it's literally the very first thing at the top of the page) and doesn't mention either of this paper's authors. The article discusses a closely related but nevertheless quite different topic.
  - tericho 12y ago
    Was directed there from his Twitter feed where he seems to offer it as a response. "There's been a story going around that it's been proven that black holes don't exist. Yes, they do. <link>" https://twitter.com/StartsWithABang/status/514885248916938754 https://twitter.com/StartsWithABang/status/51488524891693875... Edit: Re-reading my original comment I see my choice of words was poor.
    - anigbrowl 12y ago
      Perhaps he hasn't read the paper we're talking about :-)
- scott_s 12y ago
  I don't think that is a response to this work. That is dated February 1. He links to this paper's author, Laura Mersini-Houghton, but he links to a paper and blog post of hers from January. Reading that blog post (http://backreaction.blogspot.com/2014/01/if-it-quacks-like-black-hole.html http://backreaction.blogspot.com/2014/01/if-it-quacks-like-b...), what she says seems to be in contradiction with the more recent paper she wrote (http://arxiv.org/abs/arXiv:1409.1837 http://arxiv.org/abs/arXiv:1409.1837). In her blog post from January, she says: "What Hawking is saying is essentially that he believes that a matter collapse only leads to a temporary apparent horizon but not to an eternal event horizon. That is an opinion which is shared by many of his colleagues (including me) and there is nothing new about this idea whatsoever." But in her more recent paper, she says: "More specifically, we find that collapsing stars slow down their collapse right outside their horizon, while substantially reducing their mass through Hawking radiation. ... The star never crosses its horizon, so neither unitarity nor causality are violated, thereby solving the longstanding information loss paradox. This investigation shows that universally collapsing stars bounce into an expand- ing phase and probably blow up, instead of collapsing to a black hole." I am not a physicist, but when I read those two statements, they are in contradiction. The first statement says to me: it may not be an absolute horizon, but it is a horizon. The second statement says to me: actually, we never reach any horizon. So I think that the more recent statement means that she has changed her conclusions based on her recent work.
oAlbe 12y ago
> a fundamental law of quantum theory states that no information from the universe can ever disappear What is the name of this law?
- ed 12y ago
  http://en.wikipedia.org/wiki/Unitarity_(physics) http://en.wikipedia.org/wiki/Unitarity_(physics) http://en.wikipedia.org/wiki/Black_hole_information_paradox http://en.wikipedia.org/wiki/Black_hole_information_paradox
- deleted 12y ago
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- Jeyowsuka 12y ago
  Conservation of energy
houseofshards 12y ago
Isn't there a lot of observational evidence for black holes ?
scobar 12y ago
The article mentioned, "Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole." If anyone else wondered how the radiation of massless particles could result in the reduction of mass, I've found a resource with simple explanations for a layperson like myself. https://www.physicsforums.com/threads/mass-lost-by-the-sun-by-emitting-radiation.708814/ https://www.physicsforums.com/threads/mass-lost-by-the-sun-b...
guscost 12y ago
Another member of the peanut gallery here. I've not been bold enough to make any claim in writing (it would probably be full of misconceptions), but the black hole hypothesis always seemed a bit half-baked, and I've definitely said words to that effect in conversation. In the hypothesis Einstein's field equations obviously break down, and instead of acknowledging that any explanation will be enormously difficult to test we seem to have bought into this completely untested idea that matter can continue bending space-time around into a singularity and all that. Can someone with a better understanding point out what logic is (probably) missing here? The other thing that sets off my hand-wave-o-meter is the pretending that we are somehow already observing these things ("new telescope detects hints of black holes") or have concluded that they exist without any positive evidence. Instead of "the mass at the center of the galaxy which is so large that we currently have no good way of modeling it without a black hole" we hear "the supermassive black hole at the center of the galaxy" and so on.
- scott_s 12y ago
  My understanding of what Laura Mersini-Houghton's paper is claiming is that stars cannot collapse into black holes, but they can get damned close. So those things that we have observed are not "black holes", but things that are damned close. In the paper, she and her co-author write, "Both effects (slowdown and mass-loss) balance such that the evaporating star remains very slightly outside its event horizon." Even if this paper is correct, I don't think it's warranted to be so smug about people thinking they found black holes. We had a theory, and we had positive evidence for that theory. That's reasonable. If this paper is correct, then it turns out those things are not actually "black holes", but objects "very slightly outside" of being black holes. That's not too bad. Disclaimer: I am not a physicist.
  - guscost 12y ago
    What is an example of this positive evidence? Also is it at all plausible that the center of the galaxy is evaporating slightly outside its event horizon in this way? Anyway I'm not sure that the two of us are going to answer any of these questions without some help.
scott_s 12y ago
I think that interested people should just read the abstract, introduction and conclusions of the actual paper: http://arxiv.org/abs/arXiv:1409.1837 http://arxiv.org/abs/arXiv:1409.1837 You will not understand the full implications of it (well, unless you are an astrophysicist), and I didn't bother with the meat of the paper (because I am also not an astrophysicist). But the abstract, introduction and conclusion are rather understandable, and far less hyperbolic than the press release. And even though I can't understand all of it, I'd much rather get a misunderstanding from the original source material, then get a compounded misunderstanding from a press-release.
waynecochran 12y ago
Interesting to note that LIGO http://www.ligo.caltech.edu http://www.ligo.caltech.edu never detected any gravity waves (supposedly created by colliding black holes). This is the NSF's most ambitious project and they have spent (still are spending) a butt load of money on it.
xefer 12y ago
If I read the abstract and introduction correctly, it doesn't say that black holes per se don't exist, only that they can't form as the result of a collapsing star or supernova. The linked-to article seems to be jumping to conclusions (e.g., rethinking the origin of the universe; impossibility of black holes at all, etc.) that the paper isn't even making.
davesque 12y ago
From the article: "Laura Mersini-Houghton has mathematically proven that quantum effects are strong enough to stop the formation of black holes..." If I'm not mistaken, Mersini-Houghton's work has just hit the scene. It still has to be vetted by the larger community before we could say that anything's been "proven."
- ihuman 12y ago
  Also from the article: "The paper, which was recently submitted to ArXiv, an online repository of physics papers that is not peer-reviewed..." I'd wait until something like this is peer-reviewed too.
- lutusp 12y ago
  Not to mention what I'm about to -- that scientific theories are never proven, only disproven. You can always tell when a journalist is speaking about a topic for which a scientist might be a better source. As to "mathematically proven", it's an unfortunate juxtaposition of math (where things really can be conclusively proven) and physics (where they cannot be).
  - davesque 12y ago
    Right. I was going to mention that as well, but didn't want to be too knit picky :).
paramendra 12y ago
If black holes don't exist, what are those massive things at the centers of galaxies?
- chris_mahan 12y ago
  They're complexity anomalies. Things can't resolve themselves out and so stay in.
martin1975 12y ago
Could it be that God just spoke the universe into existence? ducking for cover
linguafranca 12y ago
My trust in metaphysical and other such sciences dropped significantly on the day I realized that most modern conclusions are just theories and half of them have already been proven wrong.
- chakademus 12y ago
  metaphysics: the branch of philosophy that deals with the first principles of things, including abstract concepts such as being, knowing, substance, cause, identity, time, and space. astrophysics: the branch of astronomy concerned with the physical nature of stars and other celestial bodies, and the application of the laws and theories of physics to the interpretation of astronomical observations. Much of the nature of the cosmos is indeed a mystery, but that doesn't diminish the importance of the multitude of things we've learned about our universe from various physical observations and measurements.
- calinet6 12y ago
  That is science at its best. What, indeed, is the alternative to admitting we were wrong when confronted with new and more accurate information? There is no "trust" in science, there is only truth, and you must always leave room for doubt. Astrophysics appears volatile simply because there is so much we do not know, but that is also what makes it fascinating, and of critical importance.
trhway 12y ago
related tidbit: http://en.wikipedia.org/wiki/Black_hole#Evaporation http://en.wikipedia.org/wiki/Black_hole#Evaporation "A stellar black hole of one solar mass has a Hawking temperature of about 100 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrink. "

202 points by cyang08 12y ago

ISL 12y ago

Interesting; if the paper finds general acceptance, it'll be fun to watch a new flurry of activity. The fairly recent controversial concept of "firewalls" has reinvigorated that subfield of physics. Whether black holes exist or not, there's something really dense at the center of our galaxy. It's a challenge to come up with a consistent non-black-hole explanation for the observed motion of stars at the galactic center. http://www.galacticcenter.astro.ucla.edu/images/2011orbits_animfull.gif http://www.galacticcenter.astro.ucla.edu/images/2011orbits_a... More here: http://www.galacticcenter.astro.ucla.edu/journey/smbh.html http://www.galacticcenter.astro.ucla.edu/journey/smbh.html

dennisnedry 12y ago
This is why I love astrophysics (and the scientific method). When you find something conclusive (assuming the paper is accurate), and it causes you to re-think what you thought you knew about the universe, it suddenly becomes larger than you ever believed possible. I hope this paper is true - since it solves the information paradox.

chc 12y ago

Given how important this would be, it seems a bit odd that she just threw it on ArXiv rather than having it peer-reviewed. Also, the press release's explanation of what Hawking radiation is sounds strange to me, though I'm not an astrophysicist. It all makes me very hesitant to put any stock in this right now (well, at least it in meaning what's suggested here).

timClicks 12y ago
The ArXiV is how you get your work peer-reviewed in cosmology and other areas. Findings can be examined much more quickly than the normal publication cycle.
orbifold 12y ago
In theoretical physics all papers important or not are submitted as preprints to ArXiv and then prepared for publication, an informal system like that has been in place during all of modern science, only that before the internet professors send a number of copies of their latest result to collaborators and to people they thought might be interested in them. I think this is much nicer than the alternative, that important results are only circulated in small circles and "milked dry" until they are released to the public.
Stwerp 12y ago
I understood that it was common to post the paper to arxiv when it was in the process of being peer reviewed by a journal. The problem is the extended lag time between submission and final publication with most journals which pre-print archives like arxiv try to solve. Do people really just "submit to arxiv" and then that it? I didn't know that, but its not common in my field to use arxiv so I have not kept up with all practices.
- tjradcliffe 12y ago
  There have been cases where arxiv has been used as a venue of final publication, but the general intent is that stuff submitted there will eventually find a home in the peer-reviewed literature. There are sometimes exchanges of arguments there that never make it to prime-time, but that's not the dominant use-case. The reality is, though, that people working in a given field are much more likely to use the arxiv version as the basis for further work, simply because it is available so much earlier. It is not uncommon to reach the point of publication and then run around to try and find out where all the arxiv submissions you used were published, which can sometimes be challenging.
- sampo 12y ago
  > Do people really just "submit to arxiv" and then that it? Some people do: http://en.wikipedia.org/wiki/Grigori_Perelman http://en.wikipedia.org/wiki/Grigori_Perelman

JSPy 12y ago

This doesn't really mean anything, as the work isn't peer-reviewed yet. However, if this does become accepted it will have an extremely large impact in Physics. The fact that this could do away with the information paradox and add some harmony between General Relativity and Quantum Mechanics is a big deal. Furthermore, as the title suggests, we have to rethink the origins of our universe.

danbruc 12y ago

Well, there is are a lot of observational evidence for black holes - the by far most likely scenario is that the model they analyzed does not describe the physics of black holes in our universe.

tericho 12y ago
This is the first question I thought of. I'm not a physicist so I dare say I can't interpret the paper but I'm curious how she explains the seemingly observed orbits of stars around the black hole in the middle of our galaxy and others[1][2]. [1]http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/ http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/ [2]http://en.wikipedia.org/wiki/Accretion_disc http://en.wikipedia.org/wiki/Accretion_disc

AnimalMuppet 12y ago

If I understand correctly, black holes do not play a large role in our model of the origins of the universe. So this doesn't (directly) lead to "rethinking the origins of the universe". Does this work call the big bang into question (or even our current models of the big bang)? Or is it just details like galaxy formation that it makes us rethink? Another question: Something very massive and very small is at the center of our galaxy. At least, we sure think so. Does this make us question that? Or does this just make us question whether that massive thing is in fact a black hole?

tjradcliffe 12y ago
Your first point is correct: the relationship between black holes and the initial state of the universe is not clear. Whether or not there was a primordial singularity or something else is an open question. With regard to the question "If not black holes, then what?", this is a problem. There is a strict upper limit on neutron stars of about 1.4 solar masses. Beyond this, gravity is stronger than the repulsive core of the strong nuclear force, and the star should collapse. If the process described in this paper is what actually occurs, the star will shed mass due to Hawking radiation while collapsing. The end-state of that process must be either a neutron star (which can't have more than 1.4 solar masses) or something else. There doesn't seem to be any "something else" in the offing, which makes that million-solar-mass thing in the centre of our galaxy deeply mysterious. A new theory that makes an old "settled" phenomenon mysterious is not all that uncommon in the sciences, so it's reasonable to take a wait-and-see attitude toward this idea, but I'm not enormously hopeful that it'll pan out very well in the long run.
- squozzer 12y ago
  So it seems a cycle of collapse and Hawking radiation will occur until the star no longer has enough mass to collapse.
danbruc 12y ago
The beginning of the universe and black holes have in common the singularity if you think about it naively. Besides that there is not much of a connection. And I think most physicist don't believe there are real singularities in black holes or at the beginning of the universe but quantum mechanics, quantization of space and time or something else kicks in and prevents the singularity. And there is no(t much) doubt that very massive dark objects are out there, we can observe them indirectly. So even if the classical black hole creation process turns out to be not possible, there are still objects out there that a very much like classical black holes.

z3t4 12y ago

What many people seem to overlook is that gravity is linked to time (space time)! So instead of the "black hole" being massive, it could be that time is running fast!

3327 12y ago
interesting any reference/publications on this?
- z3t4 12y ago
  When astronomers measure the mass of the black hole, they simply measure the acceleration of nearby stars, using newton's formula. They might use fancy words, but the math is very basic. Now, if time ran faster, like if you made the measurements while accidentally having the video speed in fast forward. The stars would accelerate faster, and you would get a higher mass.
seiji 12y ago
Well, "linked" is vague. They aren't linked—they are the same thing! Gravity is an effect mass has on the upholstery of the universe. Time runs slower for us here inside the gravity well of Earth than it does for astronauts in zero gravity. You can't create time distortions without gravity distortions, and you can't create gravity distortions without instantiating mass, so... big massive black holes have to be running slow; if they exist at all and aren't just cosmic bees sitting at the 2D boundary of the universe and projecting nothingness into our inflated space.
- lutusp 12y ago
  > They aren't linked—they are the same thing! If you're speaking of time and space, no, they're different -- they're certainly all part of one spacetime, but they're distinct. This distinct: t' = t √(1-v^2/c^2) t = time v = velocity c = speed of light t' = time at velocity v relative to velocity 0 Put into words, this special relativity relationship shows that an increase in velocity (movement in space) causes a reduction in time's rate of passing (movement in time). The general relativity version has more terms, and shows a relationship between mass and both space and time. So space, time and mass aren't the same thing, but they're part of an interrelated system, one easily described mathematically. > Time runs slower for us here inside the gravity well of Earth than it does for astronauts in zero gravity. Yes, true, but astronauts in orbit aren't in zero gravity, they're in free-fall. The gravitational force at typical orbital heights is nearly as strong as it is at the surface.

tfgg 12y ago

"In 1974, Stephen Hawking used quantum mechanics to show that black holes emit radiation. Since then, scientists have detected fingerprints in the cosmos that are consistent with this radiation, identifying an ever-increasing list of the universe’s black holes." Er, what? I don't think this is true, or Hawking would have his Nobel prize by now. Maybe consistent in the sense that the predictions are that Hawking radiation is undetectably low for stellar mass black holes. Also, analogue systems don't count.

vorg 12y ago
> "Stephen Hawking used quantum mechanics to show that black holes emit radiation." I don't think this is true, or Hawking would have his Nobel prize by now Hawking not getting a Nobel by now doesn't mean much. Einstein never got one for relativity (either Special or General), and when he did get his Nobel he was told not to mention "relativity" in his speech.
- collyw 12y ago
  Obama got a Nobel peace prize!
- jorgis 12y ago
  Einstein guy his for his work with Brownian Motion. Nobel prizes aren't typically given for science that lacks a body of supporting evidence, which was the case at the time for Relativity.
- saalweachter 12y ago
  Einstein, he was the guy who did all that great work in photoelectrics, wasn't he?

deleted 12y ago

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phkahler 12y ago

Now that all the physicists are reading, I have a question: Are the trajectories of light beams following the curvature of space-time reversible? In other words, if I reflect a light beam back on itself, does it return to its source? Because if that's true (and my feeble understanding is that it is true), then light can't enter a black hole or the reverse path would allow light to escape. What am I missing here?

raphaelj 12y ago
I'm not into Physics, but should not the space stretch itself to infinity so the light will never actually reach the mirror ?
lisper 12y ago
IANA physicist, but I have a pretty good intuitive understanding of relativity. Yes, light paths are reversible. The reason you can't get a beam of light out of a black hole by reflecting an incoming beam is that from the point of view of an observer outside the event horizon, and inbound beam never makes it past the horizon inbound because of time dilation. At the horizon, time stops (relative to frames of reference outside the hole).
antognini 12y ago
If the spacetime is static, then yes, the trajectory of a light beam (or anything else) is reversible. The question you pose is an excellent one and is one of the reasons that many physicists believed that black holes could not exist after Karl Schwarzschild discovered the Schwarzschild metric that describes spacetime around a spherically symmetric black hole. So what happens if you direct a beam of light radially into a black hole? A distant observer will calculate that as the light beam descends into the black hole it will be (according to a distant observer) progressively blueshifted until it reaches the event horizon, at which point it will have blueshifted to infinite energy. In fact, according to the calculations of a distant observer, the light beam will never cross the event horizon, so the statement that the light beam is reversible remains true. The reason that the light beam (according to the distant observer) doesn't cross the horizon is that if you look at the metric, it states that ds^2 = (1 - R_Schw / r) c^2 dt^2 - 1 / (1 - R_Schw / r) dr^2, where R_Schw is the radius of the event horizon. Notice that at the event horizon r = R_Schw and the dr^2 term diverges. The distant observer therefore concludes that there is a singularity at the event horizon. This analysis lead physicists to initially conclude that black holes were unphysical. A more careful analysis reveals that this isn't the case, however. We have been using this metric which describes the shape of spacetime according to a distant observer. But what we're really concerned with is not what a distant observer calculates, but how a local observer perceives spacetime. If we now switch to a coordinate system in which we are free falling into the black hole along with the beam of light, we find that nothing remarkable happens when we cross the event horizon. The light is blueshifted relative to its initial energy, but it doesn't have an infinite amount of energy. Thus there is no true singularity at the event horizon. This singularity that the distant observer found must therefore have been an artifact of the particular coordinate system that the distant observer was using. The free falling observer can then hold up a mirror and send off a light beam and have it return back to him even after they have crossed the event horizon.

Fool40 12y ago

Just downloaded the PDF, I am not a physicien nor a mathematicien. but from what I read in the article the EQ 13, is the weakness of their argumentation. AA

Fool40 12y ago
Their boundery limit pose a problem, and then the entire solution in the extending (prior explosion) the radius is greater the rs, and so all the fellowing integral are wrong. but I will wait for Hawking opinion :)

lutusp 12y ago

Quote: "Experimental evidence may one day provide physical proof as to whether or not black holes exist in the universe. But for now, Mersini-Houghton says the mathematics are conclusive." Not as conclusive as the evidence for black holes. Remember that the article's hypothesis requires proof that black holes do not exist -- in other words, proof of a negative. Proof of a negative is generally regarded as an impossible evidentiary burden, and calls into doubt the hypothesis that relies on it. There's pretty good evidence for very large, very dense masses at the center of most galaxies including our own. The default conclusion based on the evidence is that they're black holes -- they have the right mass and density. We should all remember that a mathematical theory isn't a scientific theory until observation bears it out (produces positive evidence), and to the exclusion of competing explanations.

dllthomas 12y ago

"from Star Trek to Hollywood" So... Hollywood? Star Trek wasn't filmed on location - Desilu and Paramount were both located in Hollywood. Not that this, y'know, matters - just found it amusing.

pluma 12y ago
Filming Star Trek on location would have been pretty difficult, I'd imagine.
- Tloewald 12y ago
  Well San Francisco, Cape Canaveral, and New York City figure in various episodes and movies. (Just off the top of my head.)

sramsay 12y ago

I'm not a physicist. I imagine that if I were, this would be exciting news (that is, an exciting possibility). I am a literary critic, though, and I have to say that it's bittersweet news at best. Black holes are so much a part of the space-age imagination. The article mentions Hollywood, but black holes are woven deeply into our everyday metaphors and have been for decades. They have stood among the most wondrous things in the universe -- an awe-inspiring thing. It reminds me a bit of when the press reported that the Catholic Church had "gotten rid of Limbo" (the actual case was a bit more complex, and involved some fairly weighty theology). Then again, we all still talk of things "being in Limbo." Perhaps that next project will still be a black hole, even if it turns out that there's no such thing.

dhimes 12y ago
I imagine that the metaphor "black hole" will be here for a while. After all, we still use the term "big bang" for the 'first moment' of the creation of the universe, even though the "Big Bang Theory" isn't generally believed any longer.
- Ono-Sendai 12y ago
  Erm, the big bang theory is still the best theory for the history of the universe.
  - dhimes 12y ago
    No- it was replace by the inflationary theory long ago. They are different. You've kind of proved my point.
    - Ono-Sendai 12y ago
      As I understand it, inflation usually applies shortly after the big bang.
      - dhimes 12y ago

StefanKarpinski 12y ago

This paper claims that black holes can't come into existence, which is subtly different from claiming that they cannot exist. In particular, black holes can exist as long as they've always existed – it's just that new ones can't come into existence. Maybe the universe just has a fixed number of singularities. [I am not a physicist – this just struck me as an inaccurate implication in the article.]

lutusp 12y ago
> In particular, black holes can exist as long as they've always existed ... This doesn't work in physics. If you say they can only exist if they've always existed, then you're obliged to say how they came into existence earlier -- the deep meaning of "always".
- kijin 12y ago
  The article implies that since singularities can't come into existence now, there can't have been a singularity at the moment of the Big Bang, either. That sounds implausible. Lots of things that cannot possibly come into existence at the present time did exist at the moment of the Big Bang (and shortly afterward), because the conditions back then were so radically different from they are now. Perhaps the only singularity that ever existed was the Universe at the moment of the Big Bang. After the One Singularity has blown itself apart, no other singularity can come into existence. I don't see any inconsistency in that scenario.
  - alchemism 12y ago
    And with that, physics discovers Pandeism.
  - lutusp 12y ago
    > The article implies that since singularities can't come into existence now, there can't have been a singularity at the moment of the Big Bang, either. Yes, that's true, but if the paper's thesis is correct, then there aren't any black holes or singularities at all, at any time. If the thesis is false, then there can be black holes at the universe's beginning, and they can form today, given the right conditions. > Lots of things that cannot possibly come into existence at the present time did exist at the moment of the Big Bang (and shortly afterward), because the conditions back then were so radically different from they are now. Not so different, and from a theoretical standpoint, they lie on a continuum from the present to the past. The condition of the universe as a whole has changed over time, but from the present we can mimic earlier conditions using high energies. It is often said that one goal of accelerator technology is to move backward in time toward the Big Bang. As technology advances, as accelerator energies increase, we create conditions more like the conditions in the early universe. The ultimate hope is to create conditions as much as possible like the first few seconds of the universe's existence, to be able to see the genesis of present conditions and refine physical theory. > Perhaps the only singularity that ever existed was the Universe at the moment of the Big Bang. After the One Singularity has blown itself apart, no other singularity can come into existence. I don't see any inconsistency in that scenario. A physicist would immediately see the inconsistency in that. If the conditions of the Big Bang theory can exist in reality, then given the same conditions of temperature and pressure, we should be able to imitate an earlier reality on a small scale. That's what an accelerator is designed to be -- an imitation of nature at an earlier time.

trhway 12y ago

Ok. To start she addresses only "Gravitationally Collapsing Star"s. Interesting result, may be many star lifecycles don't end in a black hole. The "before-black-hole" state she describes still would involve significant time dilation and thus what we see as Hawking radiation from black hole may just be Hawking radiation from "before-black-hole" star. Looks the same :) The result doesn't say that black hole is impossible. It says that a star's collapse loses mass faster than acceptable for the collapse to end in black hole. Some misconceptions in the web-post: >They are the ultimate unknown – the blackest and most dense objects in the universe that do not even let light escape. a black hole isn't necessary most dense. After all a black hole with a mass of visible Universe would be only 125 times denser than current average density of the visible Universe (i.e. 45B light years radius of visible Universe have 10B light years Schwarzschild radius) > So the story went, an invisible membrane known as the event horizon surrounds the singularity and crossing this horizon means that you could never cross back. It’s the point where a black hole’s gravitational pull is so strong that nothing can escape it. "membrane" is very bad illustration. It is constantly changing solution to the gravitational equations. One moment it is here, another moment - it has moved because gravitation of black hole changes and a lot of oscillations/perturbations happen. One moment you're inside, another - outside. "gravitational pull is so strong that nothing can escape it" - that's bad wording too. It is actually "gravitational well is so deep that nothing can escape it". Feel the difference :) A huge black hole may have pretty weak gravitation at its horizon. Thus no-escape is valid only in the sense that escaping object just would never reach "a point at infinity" from the black hole and the light would get red-shifted into full oblivion.

darkmighty 12y ago
You seem to be knowledgeable, so is there a plausible bridge between the impossibility of this kind of collapse and complete impossibility of black holes? I mean, what if could construct a collapse to your desire, e.g. smashing dense cold chunks, would those necessarily radiate enough energy to prevent collapse too?
- trhway 12y ago
  >is there a plausible bridge between the impossibility of this kind of collapse and complete impossibility of black holes? the shown impossibility of star collapse to BH is somewhat questionable for massive stars because - as i cited wikipedia in another comment - the Hawking radiation carries away less mass/energy than cosmic background brings in - the net is positive for the collapsing star. >smashing dense cold chunks, would those necessarily radiate enough energy to prevent collapse too? we associate "collapse/smashing" with BH i think mostly because of collapsing stars. One can scale this process out to a lot of small chunks of cold matter as you suggest flying simultaneously toward common center. Imagine the sphere with radius 1000 times radius of Sun filled with material of density of water - this is already a black hole as its Schwarzschild radius is a bit larger than those 1000 radii of Sun. Now lets say we scale the sphere radius additional 10 times - the mass scales 1000 times and the Schwarzschild radius increase 1000 times too - thus all this water may be separated by a lot of space and still be a black hole. Now imagine that all this water is outside the Schwarzschild radius and spread on some imaginary sphere and simultaneously released to fly toward the center - once all these drops cross the schwarzschild radius, even without touching each other, and with each drop feeling only pretty small gravitation from the rest of the water, they nevertheless become a BH. What kind of miracles would happen in the moment these drops cross the imaginary sphere of Schwarzschild radius? Nothing. The only change here is that any light radiated by the drops close to crossing would reach far observers as a very redshifted and any light radiated at the moment of crossing and after would never be seen by the far observers. The article suggests that the loss of mass due to Hawking radiation would be fast enough to shrink the Schwarzschild radius faster than the drops can fall into. All this cold drops flying in empty cold space would supposedly cause very intense radiation close to the schwarzschild radius border? Nope. As mentioned above in the wikipedia citation Hawking radiation is pretty cold, low intense, for that size of black hole, and in particular it is much colder than CMB, ie. the losses are less than what is brought in by CMB. Though may be in the absence of CMB if the math in the article is right the losses (given the time slowing) would be enough to shrink the Schwarzschild radius fast enough. Yet not in our real Universe with CMB.

faizshah 12y ago

I'm not at all acquainted with astrophysics but I remember seeing an article state that there was a different physicist who proved this same thing: https://news.ycombinator.com/item?id=7191324 https://news.ycombinator.com/item?id=7191324 A quick google shows his response to this: https://twitter.com/abhasmitra/status/514804101024997376 https://twitter.com/abhasmitra/status/514804101024997376 His response: "Hawking radiation is unproven. And particle physicists are not aware that even without any Quantum Mechanics, classical gravitation dictates that all gravitational collapse must be accompanied by radiation. : http://link.aps.org/doi/10.1103/PhysRevD.74.024010 http://link.aps.org/doi/10.1103/PhysRevD.74.024010 (http://arxiv.org/pdf/gr-qc/0605066v3.pdf http://arxiv.org/pdf/gr-qc/0605066v3.pdf) And then grav collapse should naturally lead to radiation supported ECO: http://www.sciencedirect.com/science/article/pii/S1384107606000923 http://www.sciencedirect.com/science/article/pii/S1384107606... http://mnras.oxfordjournals.org/content/369/1/492 http://mnras.oxfordjournals.org/content/369/1/492 http://mnrasl.oxfordjournals.org/content/404/1/L50 http://mnrasl.oxfordjournals.org/content/404/1/L50 And as far as non -formation of ``Event Horizon'' is concerned, in contrast to the conjectures of the present yet unpublished paper I gave EXACT proof: http://www.ias.ac.in/pramana/v73/p615/fulltext.pdf http://www.ias.ac.in/pramana/v73/p615/fulltext.pdf But phys.org never highlighted my research which is infinitely more accurate than the present paper whose authors are not even aware that Question of Hawking Radiation Would Arise Only If There Would Already Be a Black Hole With an Event Horizon. Therefore This paper is not self-consistent. But that does not matter: The lead author of this paper has CAMBRIDGE AFFILIATION. So phys.org is glad to highlight an inconsistent and yet unpublished paper by ignoring my series of my exact and original papers on the same topic." I don't have any background in astrophysics, can anyone comment on Dr. Mitra's response and the relation of his work to the above research? The best discussion I can find on Dr. Mitra's work is on quora: https://www.quora.com/Is-it-true-that-Abhas-Mitra-resolved-the-Black-Hole-paradox-13-years-before-Stephen-Hawking https://www.quora.com/Is-it-true-that-Abhas-Mitra-resolved-t...

deleted 12y ago
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trhway 12y ago
>But phys.org never highlighted my research which is infinitely more accurate than [...] >The lead author of this paper has CAMBRIDGE AFFILIATION. >So phys.org is glad to highlight an inconsistent and yet unpublished paper by ignoring my series of my exact and original papers on the same topic." welcome to modern science. It is a professional guild like a guild of shoemakers of Middle Age Europe cities with about the same rules. Or like another my friend (former second-rate professor from a first rate university :) put it - it is a mafia, at every level. Researchers of the highest tier universities publish in the highest tier journals, researchers of the next tier - in the next tier journals, ... A good physicist should be able to understand the laws of Nature behind such formation :)

tericho 12y ago

Ethan Siegel just posted a detailed response to this. https://medium.com/starts-with-a-bang/yes-virginia-black-holes-exist-df0a131d7b95 https://medium.com/starts-with-a-bang/yes-virginia-black-hol...

anigbrowl 12y ago
That was written in February (how could you miss this? it's literally the very first thing at the top of the page) and doesn't mention either of this paper's authors. The article discusses a closely related but nevertheless quite different topic.
- tericho 12y ago
  Was directed there from his Twitter feed where he seems to offer it as a response. "There's been a story going around that it's been proven that black holes don't exist. Yes, they do. <link>" https://twitter.com/StartsWithABang/status/514885248916938754 https://twitter.com/StartsWithABang/status/51488524891693875... Edit: Re-reading my original comment I see my choice of words was poor.
  - anigbrowl 12y ago
    Perhaps he hasn't read the paper we're talking about :-)
scott_s 12y ago
I don't think that is a response to this work. That is dated February 1. He links to this paper's author, Laura Mersini-Houghton, but he links to a paper and blog post of hers from January. Reading that blog post (http://backreaction.blogspot.com/2014/01/if-it-quacks-like-black-hole.html http://backreaction.blogspot.com/2014/01/if-it-quacks-like-b...), what she says seems to be in contradiction with the more recent paper she wrote (http://arxiv.org/abs/arXiv:1409.1837 http://arxiv.org/abs/arXiv:1409.1837). In her blog post from January, she says: "What Hawking is saying is essentially that he believes that a matter collapse only leads to a temporary apparent horizon but not to an eternal event horizon. That is an opinion which is shared by many of his colleagues (including me) and there is nothing new about this idea whatsoever." But in her more recent paper, she says: "More specifically, we find that collapsing stars slow down their collapse right outside their horizon, while substantially reducing their mass through Hawking radiation. ... The star never crosses its horizon, so neither unitarity nor causality are violated, thereby solving the longstanding information loss paradox. This investigation shows that universally collapsing stars bounce into an expand- ing phase and probably blow up, instead of collapsing to a black hole." I am not a physicist, but when I read those two statements, they are in contradiction. The first statement says to me: it may not be an absolute horizon, but it is a horizon. The second statement says to me: actually, we never reach any horizon. So I think that the more recent statement means that she has changed her conclusions based on her recent work.

oAlbe 12y ago

> a fundamental law of quantum theory states that no information from the universe can ever disappear What is the name of this law?

ed 12y ago
http://en.wikipedia.org/wiki/Unitarity_(physics) http://en.wikipedia.org/wiki/Unitarity_(physics) http://en.wikipedia.org/wiki/Black_hole_information_paradox http://en.wikipedia.org/wiki/Black_hole_information_paradox
deleted 12y ago
[deleted]
Jeyowsuka 12y ago
Conservation of energy

houseofshards 12y ago

Isn't there a lot of observational evidence for black holes ?

scobar 12y ago

The article mentioned, "Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole." If anyone else wondered how the radiation of massless particles could result in the reduction of mass, I've found a resource with simple explanations for a layperson like myself. https://www.physicsforums.com/threads/mass-lost-by-the-sun-by-emitting-radiation.708814/ https://www.physicsforums.com/threads/mass-lost-by-the-sun-b...

guscost 12y ago

Another member of the peanut gallery here. I've not been bold enough to make any claim in writing (it would probably be full of misconceptions), but the black hole hypothesis always seemed a bit half-baked, and I've definitely said words to that effect in conversation. In the hypothesis Einstein's field equations obviously break down, and instead of acknowledging that any explanation will be enormously difficult to test we seem to have bought into this completely untested idea that matter can continue bending space-time around into a singularity and all that. Can someone with a better understanding point out what logic is (probably) missing here? The other thing that sets off my hand-wave-o-meter is the pretending that we are somehow already observing these things ("new telescope detects hints of black holes") or have concluded that they exist without any positive evidence. Instead of "the mass at the center of the galaxy which is so large that we currently have no good way of modeling it without a black hole" we hear "the supermassive black hole at the center of the galaxy" and so on.

scott_s 12y ago
My understanding of what Laura Mersini-Houghton's paper is claiming is that stars cannot collapse into black holes, but they can get damned close. So those things that we have observed are not "black holes", but things that are damned close. In the paper, she and her co-author write, "Both effects (slowdown and mass-loss) balance such that the evaporating star remains very slightly outside its event horizon." Even if this paper is correct, I don't think it's warranted to be so smug about people thinking they found black holes. We had a theory, and we had positive evidence for that theory. That's reasonable. If this paper is correct, then it turns out those things are not actually "black holes", but objects "very slightly outside" of being black holes. That's not too bad. Disclaimer: I am not a physicist.
- guscost 12y ago
  What is an example of this positive evidence? Also is it at all plausible that the center of the galaxy is evaporating slightly outside its event horizon in this way? Anyway I'm not sure that the two of us are going to answer any of these questions without some help.

scott_s 12y ago

I think that interested people should just read the abstract, introduction and conclusions of the actual paper: http://arxiv.org/abs/arXiv:1409.1837 http://arxiv.org/abs/arXiv:1409.1837 You will not understand the full implications of it (well, unless you are an astrophysicist), and I didn't bother with the meat of the paper (because I am also not an astrophysicist). But the abstract, introduction and conclusion are rather understandable, and far less hyperbolic than the press release. And even though I can't understand all of it, I'd much rather get a misunderstanding from the original source material, then get a compounded misunderstanding from a press-release.

waynecochran 12y ago

Interesting to note that LIGO http://www.ligo.caltech.edu http://www.ligo.caltech.edu never detected any gravity waves (supposedly created by colliding black holes). This is the NSF's most ambitious project and they have spent (still are spending) a butt load of money on it.

xefer 12y ago

If I read the abstract and introduction correctly, it doesn't say that black holes per se don't exist, only that they can't form as the result of a collapsing star or supernova. The linked-to article seems to be jumping to conclusions (e.g., rethinking the origin of the universe; impossibility of black holes at all, etc.) that the paper isn't even making.

davesque 12y ago

From the article: "Laura Mersini-Houghton has mathematically proven that quantum effects are strong enough to stop the formation of black holes..." If I'm not mistaken, Mersini-Houghton's work has just hit the scene. It still has to be vetted by the larger community before we could say that anything's been "proven."

ihuman 12y ago
Also from the article: "The paper, which was recently submitted to ArXiv, an online repository of physics papers that is not peer-reviewed..." I'd wait until something like this is peer-reviewed too.
lutusp 12y ago
Not to mention what I'm about to -- that scientific theories are never proven, only disproven. You can always tell when a journalist is speaking about a topic for which a scientist might be a better source. As to "mathematically proven", it's an unfortunate juxtaposition of math (where things really can be conclusively proven) and physics (where they cannot be).
- davesque 12y ago
  Right. I was going to mention that as well, but didn't want to be too knit picky :).

paramendra 12y ago

If black holes don't exist, what are those massive things at the centers of galaxies?

chris_mahan 12y ago
They're complexity anomalies. Things can't resolve themselves out and so stay in.

martin1975 12y ago

Could it be that God just spoke the universe into existence? ducking for cover

linguafranca 12y ago

My trust in metaphysical and other such sciences dropped significantly on the day I realized that most modern conclusions are just theories and half of them have already been proven wrong.

chakademus 12y ago
metaphysics: the branch of philosophy that deals with the first principles of things, including abstract concepts such as being, knowing, substance, cause, identity, time, and space. astrophysics: the branch of astronomy concerned with the physical nature of stars and other celestial bodies, and the application of the laws and theories of physics to the interpretation of astronomical observations. Much of the nature of the cosmos is indeed a mystery, but that doesn't diminish the importance of the multitude of things we've learned about our universe from various physical observations and measurements.
calinet6 12y ago
That is science at its best. What, indeed, is the alternative to admitting we were wrong when confronted with new and more accurate information? There is no "trust" in science, there is only truth, and you must always leave room for doubt. Astrophysics appears volatile simply because there is so much we do not know, but that is also what makes it fascinating, and of critical importance.

trhway 12y ago

related tidbit: http://en.wikipedia.org/wiki/Black_hole#Evaporation http://en.wikipedia.org/wiki/Black_hole#Evaporation "A stellar black hole of one solar mass has a Hawking temperature of about 100 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrink. "