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A new Stephen Hawking presentation about black holes
- haberman 11y agoDoes physics have some "conservation of information" laws that I missed the memo about? Can anyone recommend some introductory reading about this?
- T-A 11y agohttps://en.wikipedia.org/wiki/Black_hole_information_paradox https://en.wikipedia.org/wiki/Black_hole_information_paradox
- danblick 11y agoHere's another interesting one: https://en.wikipedia.org/wiki/Landauer's_principle https://en.wikipedia.org/wiki/Landauer's_principle Landauer's principle is a theoretical lower limit on the amount of energy required to perform a computation that destroys information.
- Udo 11y agoAll known physical processes only transform information, it's never actually lost (although it may get "transformed" in a way that it's irretrievably scrambled). Black holes are the only known thing that may cause information to disappear from the universe - or not, that's the open question.
- chrischen 11y agoWhat about quantum mechanics? How can you get a true quantum random number generator if information is preserved?
- gizmo686 11y agoThe many worlds interpretations. Roughly speaking, if there is a quantum system that is in a superposition of states A and B, and we observe it, we then become entangled with it and are then in a superposition of having observed A and having observed B. No information has been lost from the universe, but there is no way for those of us living in the A state to observe anything about the B state.
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- eli_gottlieb 11y agoQuantum information is actually different from classical information (classical entropy). Quantum information is (believed to be?) a conserved quantity; classical is not (it never decreases). A quantum random number generator is just emitting quantum bits: without having had those qubits in the first place, you can't have computed them ahead-of-time, so they're random.
- solipsism 11y agoQuantum information is (believed to be?) a conserved quantity No it's not. Why are so many people making things up? QM does not even define a concept of a quantity called "information".
- danbruc 11y agoThe laws of physics conserve information in that sense that two initially distinct states will always remain, at least in principle, distinguishable for all times, i.e. two distinguishable states A and B will never evolve into the same state C. This is equivalent to the statement that the laws of physics are time reversible, i.e. if you would end up in state C you could not tell whether the system came from state A or B. If you, for example, start a pendulum with different initial displacements the pendulum will always end up at rest due to friction but if you could take into account the exact states of all the molecules in the air and the joint and so on you could in principle figure out in which exact positions you started the pendulum. You could actually just very precisely measure the temperature of a pendulum in a box and infer the initial displacement from that because different initial displacements imply different initial (potential) energies and therefore different final temperatures after all the energy became thermal energy and everything in the box had time to reach the equilibrium temperature. You just couldn't figure out whether the pendulum was started to the left or to the right of the rest position with this method.
- haberman 11y agoFascinating. Do physicists generally believe this? The idea that both the infinite future and the infinite past are all encoded into any snapshot of the universe is blowing my mind. My layperson's understanding of QM always gave me the impression that it does the opposite: that it gives non-determinism a place to "hide," so-to-speak. My impression was that religious believers could use QM to argue that their unseen God, for example, does actually have a physically plausible mechanism by which he/it could intervene in the physical world. But if I'm understanding this theory correctly, unless God is a physical thing, there is no way for God or any other supernatural force to affect the physical world without itself being physical. This theory also would seem to deny the existence of free will.
- solipsism 11y agoQM does away with any notion of conservation of information. Time reversibility (T symmetry) is usually talked about at macro scales where QMs effects are vanishingly small. IANAP Regarding free will -- rigorously define it for us, without evoking the supernatural, and as distinct from pure randomness and absolute determinism, and it should be easy to tell whether the law of conservation of information allows for it. Before spending too much time in e it, though, note that such a definition is widely considered impossible. IANAP
- dogma1138 11y agoYes there is a principal in on of the "interpretations" (we really need a better word for it) of QM that the information carrier by a wave function cannot be destroyed, this present a problem in certain cases such as black holes. There's allot of weird stuff going on on the extreme edges of theoretical physics, to the point in which also a though that some areas of theoretical physics have moved into the "Metaphysics" and Philosophy domains and are distancing them selves from certain scientific principals. That said I like to treat black holes in the GR/SR manner they are simple massive objects not super dense hot balls of entropy, they don't have some universal cosmic powers, they are "black" simply because they red-shift all radiation to the point of invisibility, they can form, grow and break apart, and we never can see anything actually entering a black hole due to time dilation and anything that comes close to it will be red-shifted to a point in which we won't be able to see what or where it is either. Since nothing from out POV ever enters the black hole and everything is stuck on the event horizon nothing is lost, and since black holes can evaporate (Doesn't require hawking radiation altough it's the most common explanation since Yakov Zeldovich (which Stephen hawking based his work on) and others have proposed similar mechanisms which are more compatible with physics as it is measured and perceived by hmmm reality...), no firewalls or weird mechanism are needed to protect or explain other weirdness that happens around singularities. Singularities are well covered by GR and SR prevents naked singularities so we are good there too. But that's just me :)
- eykanal 11y agoI don't know a thing about black holes, but every time I see him I'm impressed that someone with such severe disabilities is still able to accomplish so much.
- sluggity 11y agoyup, that was the only thing I could think about while reading this article
- lorddoig 11y agoIn 'A Brief History of Time' he briefly discusses the intellectual advantages of his physical disabilities.
- laumars 11y agoNot that I want to take anything away from his impressive achievements, but it would only be fair to point out that he doesn't work solo on these theories. Much of the maths is done by his team. I can't even imagine how frustrating his condition must be for him though. To have full mental capabilities but have so little (and slow!!) means of communicating his ideas.
- gizmo686 11y agoBeyond being slow at communicating his idea, he is also largely limited to his working memory. I can't imagine doing any sort of serious intellectual work without the assistance of paper (or similar technology) to augment my working memory.
- jkaunisv1 11y agoI imagine that would be an effective way to vastly improve his working memory, like strength-training for his brain. Maybe Aristotle or whoever it was that complained about books ruining youth's brains would find Stephen Hawking's memory up to snuff.
- laumars 11y agoIn fairness that is something you can get better at with practice. In IT we tend to train our brains to commit processes (eg ways to research information) rather than facts. But we also have the luxury of being able to be lazy (internet, functioning limbs so can write notes, etc). Heck, before IDEs and the internet I used to remember every function name and order of parameters for any particular programming languages I was proficient in. These days I just learn the function name and let the IDE remind me of the rest (sometimes I don't even learn the function name and just search for it in the package namespace).
- dysoco 11y agoWait, hasn't this holographic theory been arround for years? What's new?
- xlm1717 11y ago"It will take more discussion — and much comparing of math equations — to establish what's new..."
- BjoernKW 11y agoI don't understand what's new about these theories. Both the holographic principle and Hawking radiation have been known for years, decades even. If there's something about those theories the article doesn't explain what it is exactly.
- keehun 11y ago"Nobel laureate Gerard t'Hooft, who was present for the discussion, has been thinking about information loss in a similar way, and he cited several papers he has published on the subject. It will take more discussion — and much comparing of math equations — to establish what's new about Hawking's theories in relation to t'Hooft's, and whether Hawking has overcome some of the issues associated with earlier iterations of the idea."
- nilkn 11y agoSo is Hawking even claiming it's new or was he simply discussing the existing theory but the article misconstrued that?
- espadrine 11y agoAs I understand it, he is redefining what is called the event horizon, because it is a relativistic concept that doesn't work well with quantum mechanics. One consequence of that redefinition is that humans could theoretically survive crossing it, contrary to the firewall hypothesis (well, if they were in a sustainable capsule with a large gene pool, and the hole was rotating just right), by waiting long enough on top of it until the hole evaporates (from the capsule's point of view). Time would indefinitely slow down for them, so they would see the rest of the universe speed up until the hole dies.
- JoelSutherland 11y agoAnd here are the two discussing it today: https://twitter.com/ChancellorFolt/status/636306368861966341 https://twitter.com/ChancellorFolt/status/636306368861966341
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- jdnier 11y ago"You wouldn't technically lose any information if you kept all of the ashes in one place, but you'd have a hard time looking up the capital of Minnesota."
- chrischen 11y agoHow come quantum indeterminacy doesn't preclude information preservation?
- andrepd 11y agoAll the information about the state of a particle is contained in its wavefunction. The uncertainty comes from the fact that the wavefunction can only tell you the probability of getting each value of a specific quantity when you make a measurement of that quantity, which doesn't mean you lack information about the state of the particle.
- solipsism 11y agowhich doesn't mean you lack information about the state of the particle. Yes it does. Quantum observations (sometimes called "collapse of the wave function") are not time symmetric. Once you've experienced one you can't derive where you were before it. Otherwise you wouldn't be using the word "probability". This inability to recover a previous state is, by definition, the loss of information.
- aquadrop 11y agoI don't know if there's something new in there, but Leonard Susskind wrote a book in 2008 exactly on that matter - "The Black Hole War" [0]. He describes his "battle" with Hawking on whether the information is lost in the black hole, and Susskind is the one who's against information disappearing. [0] https://en.wikipedia.org/wiki/The_Black_Hole_War https://en.wikipedia.org/wiki/The_Black_Hole_War
- mudil 11y agoI loved that book. One of the best books on cosmology/space-time/quantum-general relativity. Susskind's thought experiments are mind boggling, and he is a great writer, able to explain complicated physics in a clear and thoughtful manner.
- developer1 11y agoIs this a book that someone with no background in the sciences involved can enjoy? Is it for the layman, or requires some knowledge of the facts involved to appreciate enough to read?
- aquadrop 11y agoIt's written in pretty easy way, you just must be interested in this stuff, then you'll enjoy it :)
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- andrepd 11y agoBeing a good science communicator and doing significant serious research are not mutually exclusive.
- strayptr 11y agoThe article is a filtered version of Hawking's words, which themselves were probably a filtered version of his research. The parent commenter was talking about the quality of the article. There's no basis to attack Hawking or anyone else. Even the article's author should be relatively immune, because WaPo isn't in the business of writing scientific articles. If you insist on attacking, then let's aim for the central argument. For example, a decent attack on Einstein in the 1940s would be to remark that if quantum electrodynamics agrees with experiment, then Einstein's goal -- to demonstrate that probability wasn't a fundamental component of the universe -- would be in trouble. An excellent attack would be to cite the research, and to explain why if X is true then @physicist is wrong. Are you sure that being mistaken is such a terrible thing? The mistakes are often more illuminating than the discoveries, as they provide a framework upon which to learn how to improve the process of discovery.
- Retric 11y agoIt should be noted that QM does not require randomness, you need to pick randomness or sacrifice other assumptions and most people pick randomness as the cleaner option.
- strayptr 11y agoFascinating. May I ask, how does one predict the behavior of an electron without using probability amplitudes? I'm extremely interested, and the question isn't meant as anything but an inquiry. Finding a gap in one's knowledge is one of the more exciting aspects of life.
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- boxcardavin 11y agoSomething that is hard to mention but is worth knowing is that Hawking is not at the leading edge of his field.
- iso8859-1 11y agoHow do you know this?
- T-A 11y agoMaybe from the "Einstein index"? [1] [1] http://www.science20.com/hammock_physicist/who_todays_einstein_exercise_ranking_scientists-75928 http://www.science20.com/hammock_physicist/who_todays_einste...
- Steko 11y agoSo top 7 =/= leading edge?
- T-A 11y agoTop 7 among those whom the author chose to compute his "Einstein index" for. Something not accounted for by that illustration is age ~ proportion of realized potential. Maldacena is 47, Randall 53; no longer promising youngsters, but with decades of index-climbing potential left in them. Weinberg and Glashow are both 82, and owe the bulk of their index position to work done in the 60s and 70s. Witten is 64 and peaked in the 80s and early 90s. Polyakov is 69; for him it's 70s and 80s. Hawking is 73. His index-driving contribution is black hole evaporation, from 1974. After that, he's mainly been a popularizer.
- boxcardavin 11y agoUndergrad in physics, still keep up with my PhD physics pals.
- guard-of-terra 11y agoIt seems that matter usually doesn't fall through the event horizon: due to time dilution it will take infinite time for matter to reach the horizon from our point of view. That's what I've got on Physics stack exchange. There's those collapsars that look exactly like black holes but are made of matter around the event horizon, infinitely falling in. Is this right, wrong, or irrelevant?
- gthm 11y ago> It seems that matter usually doesn't fall through the event horizon: due to time dilution it will take infinite time for matter to reach the horizon from our point of view. From our point of view, not the matter's. The matter falls through just fine.
- guard-of-terra 11y agoIt can only do it once it witnesses the end of times. We can't see any information destruction since it's always sometime in the future.
- DonGateley 11y agoThat is correct. From the point of view of the infalling object, however, nothing changes as he crosses it except his position in space. I say who gives a shit about the point of view of the infalling object. :-)
- mc808 11y agoIt seems to me, intuitively, that the infalling object should experience inverse time dilation and extreme blue-shifting of the outside universe as it approaches the event horizon. Due to length contraction, that energy would be increasingly perpendicular to the object's trajectory, approaching a point where it is bombarded with enough energy to either knock it off its trajectory or "smear" its particles into orbit around the massive object (basically another sort of firewall). Presumably the mathematical descriptions tell a different story because I never see it described like this.
- jbrooksuk 11y agoA video of Hawking's presentation is available at https://www.kth.se/en/aktuellt/nyheter/hawking-offers-new-solution-to-black-hole-mystery-1.586546 https://www.kth.se/en/aktuellt/nyheter/hawking-offers-new-so...