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ashpanash posted:IF you have negative energy (whatever the hell that is - no, the Casimir effect is not an example), and none of the metrics that can produce such effects are realistic or stable. You can create a lot of toy metrics out of GR, it's a suitable framework for it. None of them that result in closed time-like curves are workable even in principle without exotic matter that as far as we know doesn't exist. And it would cause lots of problems with SR and thermodynamics if such exotic matter did exist. Also, in general relativity, one of the underlying principles you get out of geodesic math and covariant derivatives is that there always exists a local, non-zero area around every point that is equivalent to the Minkowski metric, aka the metric of Special Relativity. Special Relativity must hold. It holds even for quantum mechanics, and in fact is the actual reason electricity produces magnetism, for instance. (this is why by 'accident' electromagnetism is SR compatible, it was derived to merge the two concepts and they are actually merged in nature through SR) Yes, you can make GR math say a lot. That's because it is an unbelievably vast framework. This doesn't mean most of it is physically meaningful. dex_sda fucked around with this message at 23:27 on Feb 18, 2020 |
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Feb 18, 2020 23:24
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ashpanash posted:Special Relativity is a foundational principle that all physics must adhere to for it to be correct in our universe. I fear you are getting your philosophy a bit mixed with your science here; SR can describe universes very different from our own; there exists a relativistic version of Aristolean dynamics. And similarly you can posit universes identical to our own in all currently known-respects that are deeply non-relativistic.
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Feb 19, 2020 10:45
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radmonger posted:I fear you are getting your philosophy a bit mixed with your science here; SR can describe universes very different from our own; there exists a relativistic version of Aristolean dynamics. And similarly you can posit universes identical to our own in all currently known-respects that are deeply non-relativistic. That's irrelevant (though the concept of relativistic Aristotelian dynamics admittedly intrigues me); I'm talking about this universe. This universe is demonstrably relativistic. ashpanash fucked around with this message at 16:05 on Feb 19, 2020 |
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Feb 19, 2020 15:38
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ashpanash posted:That's irrelevant (though the concept of relativistic Aristotelian dynamics admittedly intrigues me); I'm talking about this universe. This universe is demonstrably relativistic. It'd just be applying the relativistic guiding principle to aristotelian dynamics while positing there is a privileged frame of reference, I would imagine. But yes, I'm intrigued too. The hoop to jump over regarding physically meaningful relativity is that the guiding principles are real simple: 1) observers must agree on results of physical processes, 2) no observer is privileged. They seem tautological, but that's why they are so fundamental. Once those are applied to kinematics, special relativity emerges. Reconcile gravity with special relativity, you get GR. Try to make quantum work with SR, you get QFT. Then you can try doing QFT on a background of a non-flat metric and oh boy, but that's something else entirely. Each bridged step, by the way, brings more evidence that SR is fundamental. For instance: imagine yourself to be there, just chilling. There exists an inertial frame of reference that moves compared to you at near the speed of light (in fact, there exist an infinite amount). Since in SR you gain energy as you speed up, and energy equals mass, that means there exists a frame of reference where you have more mass than is required for an object of your volume to collapse into a black hole. So, because we want postulates 1 and 2 to hold, something must be happening to prohibit this. The answer is the quantum uncertainty principle that prohibits momentum and position to have an exact magnitude at the same time: the energy does exist, but since you have a lot of momentum in the frame of reference, your energy is 'spread out' in that frame of reference, and thus no critical mass can be pinpointed in that frame. Quantum uncertainty, despite having been derived independently, is a component of a relativistic universe. There are lots of examples of the principles of relativity enhancing our understanding of all other phenomena, but the short of it is: special relativity is law. We live in a smooth manifold of some variety. And barring unphysical exotic matter, FTL is impossible.
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Feb 19, 2020 16:28
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People say I have a very negative energy, so you're saying perhaps I am the key to faster than light travel?
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Feb 20, 2020 00:42
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dex_sda posted:It'd just be applying the relativistic guiding principle to aristotelian dynamics while positing there is a privileged frame of reference, I would imagine. But yes, I'm intrigued too. Jesus H Christ I actually understood this. Thank you
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Feb 20, 2020 03:59
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Also, the US government and military definitely thinks UFOs are real and here to probe us indiscriminately. https://www.popularmechanics.com/military/research/a30916275/government-secret-ufo-program-investigation/
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Feb 20, 2020 04:01
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Arglebargle III posted:People say I have a very negative energy, so you're saying perhaps I am the key to faster than light travel? Unfortunately, if your energy were proved to be useful, it would (through a psycologic-relativistic reversal) suddenly become positive. Now, if we could harness your negative energy without your knowledge or the knowledge of anyone close to you ... I think I've just figured out why the Aliens are so interested in this planet.
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Feb 20, 2020 04:05
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Illuminti posted:Also, the US government and military definitely thinks UFOs are real and here to probe us indiscriminately. 
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Feb 22, 2020 16:37
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dex_sda posted:
In other words, the key to FTL is a privileged observer who disagrees with everyone else. Call it the Trump drive... Your logic is fine as far ask known physics goes, but you still seem to be makng a philosophical leap with regard to unknown science. If such a thing exists, there is no logical reason to believe it follows those principles. They are far from tautological. Tbey do not apply to pre-Einsteinan theories, and need not to post-Einsteinian ones. Maybe we know everything other than details; if.not, all bets are off as to the nature of what we do not know. For example, scientific theory says that we expect money to have no influence of physics. But if that is wrong, we can’t predict anything about the nature of a theory of monetary physics until someone comes up with one that matches observations of how a Trump drive behaves.
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Feb 22, 2020 16:44
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While I understand where you're coming from, and as a terminally brainbroken dude like the Trump analogy, I have to object. Metaphysics and metaphilosophy incoming. Science is often characterised by the adherence to data and math. While that is partially true and you certainly need the math to function in the scientific framework, there is a philosophy inherent to all sciences - that things are knowable, that data can be trusted etc. And in particular among all sciences, physics is rooted in philosophy. In fact, that's how it started - "Philosophiæ Naturalis Principia Mathematica" is the seminal work in scientific history, and you can see the name. The physical math enhances underlying philosophy, and empowers humans with the ability to predict and to test philosophical theories. The adherence to data makes physics the most reliable of sciences, but the philosophical approach is why it's so predictive and accurate at the fundamental level. And all the breakthroughs in physics we have had are a result of a philosophical approach to science and crafting new theories from preceding, simpler principles. So the idea that you can decouple philosophy from physics is false on its face. To wit, the 2 guiding principles of relativity could be false, however them not being true would uproot the entire idea that the universe is knowable - since in that scenario you can't "know" unless you are the privileged observer, and you no longer have a possibility to even tell if you truly are. This is what I mean by saying it's tautological - science as a framework kinda needs it to function. It just took Einstein to realise that, and from this 'simple' realisation a framework that has been confirmed in every experimental test in the last 115 years emerged. Yes, the principles could, in theory, be false (though a universe where observers disagree on results is completely untenable imo, but whatever). But that's like saying "if true were actually orange, things would change." Yeah, sure, they would. I wouldn't bet money on it.
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Feb 23, 2020 11:37
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It's not like you can just "find some new science" that will do what you want and discard the old stuff. From an essay by Isaac Asimov:quote:The young specialist in English Lit, having quoted me, went on to lecture me severely on the fact that in every century people have thought they understood the universe at last, and in every century they were proved to be wrong. It follows that the one thing we can say about our modern "knowledge" is that it is wrong. The young man then quoted with approval what Socrates had said on learning that the Delphic oracle had proclaimed him the wisest man in Greece. "If I am the wisest man," said Socrates, "it is because I alone know that I know nothing." the implication was that I was very foolish because I was under the impression I knew a great deal. I think it's important to recognize the difference as well between "physical nonsense" and "impossible." Impossible is like swimming across the Pacific Ocean - you don't break any physical laws in the act of doing it, but basically no human body can perform this task. "Physical nonsense" is like if I tell you there exists a cube which is also a sphere: just absurd on the face of it to the point that we don't have the language to adequately describe, and also it doesn't exist. And FTL, according to the precepts of SR, is a lot more like the latter, than the former.
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Feb 23, 2020 18:09
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On the bright side it means lovecraftian gods need to be biomechanical in an understood way and not truly unfathomable.
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Feb 23, 2020 19:45
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dex_sda posted:
It’s not that those statements could be shown to be false, it is that they can’t be considered as either true or false without adding in a whole bunch of additional unstated assumptions. In particular, to get from them to SR, you need to assume that ‘observer’ means ‘observer using some form of electromagnetic radiation.’ Which is then experimentally proven to work on relativistic principles. However, if there existed a different way of observing things, then there is nothing inconsistent about that different way working using absolute coordinates. Which is why scientists sped time trying to measure the speed of gravity, rather than saying ‘duh, it’s obviously going to be C ’.
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Feb 23, 2020 22:00
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I’m not sure you’ve got a solid grasp on what ‘an observer’ is when it comes to SR, my guy. Start there.
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Feb 23, 2020 22:29
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Let's talk a little about just how accurate are the current predictions of GR and the Standard Model, to get a good sense of how facile the criticism of "We could just discover something else that upends our entire heretofore known science" really is. The predictions of the Standard Model of quantum theory have been tested by experiment to an accuracy of around 1 part in 10 billion. [1]. Relativity? We've experimentally verified its predictions to around 70 parts per million. [2]. That is an almost-unthinkable level of precision. This isn't just a difference in degree from the previously-understood models of physics from Gallileo and Newton, it's a difference in kind. People before Einstein and the Quantum Theory people were operating with technology and scientific methods that would be rudimentary by the standards of today, technology which had barely changed from the Bronze Age up until around the 18th century. You had people going out with lenses and looking at stuff, or measuring things with rulers in their basement laboratories. We operate experiments and can verify them on levels that are millions or even billions of times more accurate and powerful than anything that was available to people a hundred years ago. So the likelihood of uncovering a new physics discovery that not only upends our current physical model, but also accounts for them at the same time, is pretty much unimaginable. When we are measuring things down to the level of subatomic particles, when we are making cosmological observations on the order of magnitude of the universe itself, we are literally measuring reality with the finest possible tools that exist. To discover something outside of that would be tantamount to discovering that, for example, reality was a simulation inside a computer, or something equally ontologically massive - something on the level of contradicting the nature of physical reality itself. FTL is categorically impossible.
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Feb 23, 2020 22:40
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radmonger posted:It’s not that those statements could be shown to be false, it is that they can’t be considered as either true or false without adding in a whole bunch of additional unstated assumptions. An "observer" is just a reference frame embedded in a metric with a certain origin. No interaction is necessary. It is called an "observer" because it abstracts the way our consciousness works when it comes to observing reality. The principles of relativity I mentioned can be restated thus, keeping this definition in mind: No matter what reference frame you pick, physical processes yield identical final results. DrSunshine posted:Let's talk a little about just how accurate are the current predictions of GR and the Standard Model, to get a good sense of how facile the criticism of "We could just discover something else that upends our entire heretofore known science" really is. The predictions of the Standard Model of quantum theory have been tested by experiment to an accuracy of around 1 part in 10 billion. [1]. Relativity? We've experimentally verified its predictions to around 70 parts per million. [2]. Also it bears mentioning that the discrepancy in the respective accuracy is not due to relativity being 'less accurate' than quantum physics. It's simply that relativity measurements deal with gravity, while quantum physics deals with the remaining three fundamental forces. Gravity is 10^25th times weaker than the weakest of the other forces, and that force is literally called 'weak'. Because of the weakness of gravity, you need detectors that are much more complex, and it's harder to filter out noise from data. SR and quantum physics are very much 'in equal standing,' scientifically speaking. dex_sda fucked around with this message at 00:19 on Feb 24, 2020 |
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Feb 24, 2020 00:17
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dex_sda posted:For instance: imagine yourself to be there, just chilling. There exists an inertial frame of reference that moves compared to you at near the speed of light (in fact, there exist an infinite amount). Since in SR you gain energy as you speed up, and energy equals mass, that means there exists a frame of reference where you have more mass than is required for an object of your volume to collapse into a black hole. So, because we want postulates 1 and 2 to hold, something must be happening to prohibit this. The answer is the quantum uncertainty principle that prohibits momentum and position to have an exact magnitude at the same time: the energy does exist, but since you have a lot of momentum in the frame of reference, your energy is 'spread out' in that frame of reference, and thus no critical mass can be pinpointed in that frame. Quantum uncertainty, despite having been derived independently, is a component of a relativistic universe. Well that is astonishing. Is special relativity a sufficient condition for quantum uncertainty? In other words if a universe has SR does that also require it to have quantum uncertainty? Does quantum uncertainty actually arise from SR? Your explanation doesn't make it clear if uncertainty is a neat coincidence that makes SR work or an actual consequence of SR.
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Feb 24, 2020 01:19
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DrSunshine posted:Let's talk a little about just how accurate are the current predictions of GR and the Standard Model, to get a good sense of how facile the criticism of "We could just discover something else that upends our entire heretofore known science" really is. The predictions of the Standard Model of quantum theory have been tested by experiment to an accuracy of around 1 part in 10 billion. [1]. Relativity? We've experimentally verified its predictions to around 70 parts per million. [2]. No, see you gotta *folds paper in half and pushes a pencil through it*
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Feb 24, 2020 01:23
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WOWEE ZOWEE posted:Well that is astonishing. Quantum uncertainty is more naturally and exactly derivable from quantum physics, by looking at how operators commutate and how this maps to frequency/position of a localized wave packet. However, some sort of 'smearing' of energy at high momentum is a necessary component of SR because of the thought experiment I described, and uncertainty fits that niche perfectly. It would be accurate to say it's a consequence of both SR and quantum physics, but the effect is more obvious in the quantum world. dex_sda fucked around with this message at 01:37 on Feb 24, 2020 |
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Feb 24, 2020 01:34
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dex_sda posted:An "observer" is just a reference frame embedded in a metric with a certain origin. No interaction is necessary. It is called an "observer" because it abstracts the way our consciousness works when it comes to observing reality. You are of course correct about the definition of the term ‘observer’ _within_ the theory. But you seem to miss the implicit assumption that that is a useful definition of the term only because there is no way of making non-local measurements other than via C-limited processes. Were that assumption not the case, then it would be possible for one observer in one reference frame to say ‘I am at rest, so my perceptions are correct’, and another to say ‘I am going this fast so my perception of non-local objects is distorted by relativistic effects by this much’. Which leads the them agreeing about everything in absolute terms, instead of relative ones. To be absolutely clear, if relativity is a complete description of the universe, then terms like ‘distortion’ and ‘relativistic effect’ are misleading or wrong. But we are assuming the opposite. Precision of measurement is a strong informal argument against an incoherent or random underlying reality. But it does nothing to distinguish between between absolute and relative coherence. On;y specific experimental measurement of how a particular class of things actually work can do so. To use Talib’s example, you really do have to go to Australia to see what color the swans are; you can’t simply count more precisely the swans near you. For example, It was as recently as 2017 that measurement of the speed of gravity waves from colliding neutron stars showed that gravity is very unlikely not to be relativistic.
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Feb 24, 2020 01:35
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This started with you claiming that GR supersedes SR and allows for FTL. We informed you that no, in fact, it doesn't. Now you're in the weeds with some weird philosophical argument I can't parse. Nonetheless, the facts remain. GR doesn't make FTL an engineering problem. SR shows us that FTL is an impossibility. GR gives you a toolkit that lets you do impossible things if you're willing to build it from other impossible things. SR is not a toolkit, it's a description of how the universe works at a very fundamental level. Its utter simplicity attests to its ubiquitousness and inescapable nature. Magnetism? Relativity. The fusion in the sun? Mass-energy equivalence, because of relativity. It's interesting, in some sense, that it took so long to figure out, because it's really, really hard to imagine how one might succeed in putting together a universe without it.
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Feb 24, 2020 07:06
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WOWEE ZOWEE posted:Well that is astonishing. 
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Feb 24, 2020 07:54
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Ok these arguments make sense. Have we ever observed macroscopic objects in space exhibiting uncertainty at relativistic speeds? I think I've read that black holes can slingshot objects that get too close at relativistic speeds. And there are quasars and plusars that spin at relativistic speeds too. Or maybe does someone have a book recommendation so I could read about the application of SR to different fields instead of asking 20 questions.
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Feb 24, 2020 09:21
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WOWEE ZOWEE posted:Ok these arguments make sense. Objects that are sufficiently relativistic for that to matter are either so small (the proton beam in the large hadron collider) or so far away (rogue quasars) that any relativistic uncertainty effects are too small to measure compared to noise of our instruments, sadly, so the only fallback we have is the thought experiment I've outlined. Books on this subject will be quite opaque without a good understanding of the math. Wald's books are good on the subject of 'synthesis' of SR with quantum, and as far as gravity goes, I always recommend Hartle's "Gravity." That one in particular can be read and understood with high school math and physics knowledge, and it will give you a practical mathematical understanding of the subject. Research I've done as a relativist is 90% based on stuff in Hartle so it's a pretty powerful book. The 'easiest' synthesis of SR with anything is almost assuredly magnetism, and this video does a good job: https://www.youtube.com/watch?v=1TKSfAkWWN0 - it also greatly illustrates how SR is an underlying principle of "observers agree on physical results" because it shows the situation as being super different in each frame but the result of the experiment ends up the same. Mass-energy equivalence is the synthesis of SR and nuclear science: https://en.wikipedia.org/wiki/Mass-energy_equivalence#Background ashpanash posted:This started with you claiming that GR supersedes SR and allows for FTL. We informed you that no, in fact, it doesn't. Now you're in the weeds with some weird philosophical argument I can't parse. Very much this. The insight that the universe needs a fundamental philosophical underlying principle is why Einstein was brilliant, but it is incredibly surprising that he was the only one to have grasped it. dex_sda fucked around with this message at 12:01 on Feb 24, 2020 |
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Feb 24, 2020 11:48
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ashpanash posted:This started with you claiming that GR supersedes SR and allows for FTL. We informed you that no, in fact, it doesn't. Now you're in the weeds with some weird philosophical argument I can't parse. You keep jumping back and forwards between mathematical models, experimental conclusions, and philosophical metaphysics. i think it would help to try to be a bit clearer about when you are talking about what. GR does mathematically _supercede_ SR; it is obviously a more general, and hence more accurate, model. GPS satellites and space probe orbit models use GR anytime they can’t get away with Kepler’s laws. There is never an intermediate state where they use SR alone. GR is philosophically _compatible_ with SR, but, as it turns out, only given a bunch of additional assumptions about certain things the mathematical model allows. They must not exist, or exist in limited quantities, or ... Given that, you can use the SR metaphysics as an argument to predict the results of future physical experiments not yet carried out; the things that should not exist must not exist. Where we disagree is how reliable such predictions are. You seem to be saying ‘certain’, I would say ‘maybe the way to bet, but still speculative’.
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Feb 24, 2020 16:28
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radmonger posted:You keep jumping back and forwards between mathematical models, experimental conclusions, and philosophical metaphysics. i think it would help to try to be a bit clearer about when you are talking about what. They are equal parts of a whole, your error is the assumption they are not.
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Feb 24, 2020 16:32
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When this kind of discussion comes up about SR's omnipresence, I ask what specific part of physics forbids something like FTL. I.e. if we misunderstood how some small thing works in situations we haven't tested/observed. So regarding FTL physics, the issue (as I understand it) is that it creates situations where applying time dilation effects to relativistic reference frames can result in violations where different observers disagree on the order of events, which effectively means that those two frames of reference can never be reconciled again. But we don't know if the timelike physics of superluminal objects/energies would be accurately projected from slower-than-light physics. Why couldn't time dilation have a divergent value above c? Or why couldn't wormholes or other FTL physics create temporary event horizons that hide the causality violations from the divergent light cones (which evaporate at rates corresponding to when the relativistic worldlines converge again)? We do know that the event horizon of a black hole is where escape velocity is c, but just because we don't have the ability to calculate the worldlines of things that pass inside the event horizon doesn't mean they literally cease to exist. Gravitational acceleration would increase the velocity of the infalling matter past c if we follow the laws of physics. And while we imagine a singularity of infinite density at the center, we don't know if that's literally the case. It's entirely possible that there is some "bottom" physical size of particles that end up piling up to a finite volume at the heart. It's likely that some kind of Cherenkov radiation analogue would be emitted from particles going faster than the local speed of light (even if that was the speed of light in a vacuum). These are the analogous situations to FTL travel... just because relativity isn't capable of describing these situations doesn't mean they physically don't exist, even if it means they're likely unknowable to us experimentally. edit: and I suppose those last points should be "currently". There is still the possibility of discovering techniques to observe beyond event horizons in some way in the future. Infinite Karma fucked around with this message at 18:29 on Feb 24, 2020 |
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Feb 24, 2020 18:19
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I'm still scratching my head regarding the video that described reality as a hologram because of black holes.
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Feb 24, 2020 18:29
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Slowpoke! posted:No, see you gotta *folds paper in half and pushes a pencil through it* This can all be solved practically by tunneling through Hell to go from point A to point B.
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Feb 24, 2020 18:45
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Infinite Karma posted:When this kind of discussion comes up about SR's omnipresence, I ask what specific part of physics forbids something like FTL. I.e. if we misunderstood how some small thing works in situations we haven't tested/observed. The issue is very specifically how spacetime transforms with a (-1,1,1,1) (i.e. M4) metric. I'm trying to come up with a non-mathematical analogy but failing here: moving faster than light is kind of like rotating a cube in a way that mirrors the axes. Like the Y axis remains in the same configuration but the X and Z axes swap. You can't do that with a smooth rotation in 3D space, it's just a physical impossibility. (This is why the rotation group is not O(3) but the O(3) subgroup SO(3), which retains the orthogonality condition but adds the condition that the determinant must be 1. The Lorentz group, which defines spacetime transformations, is SO(1,3), with the first number representing Lorentz boosts.) quote:So regarding FTL physics, the issue (as I understand it) is that it creates situations where applying time dilation effects to relativistic reference frames can result in violations where different observers disagree on the order of events, which effectively means that those two frames of reference can never be reconciled again. This is certainly a consequence of imagining what might happen should SR be violated, and can be helpful in building a sort of intuition as to why FTL would cause issues with our basic understanding of reality, but again, the real issue is more technical than that, and frankly a lot more simple. The fundamental issue is that spacetime doesn't twist that way, so we don't really have to worry about the weird SR violation schemes in a similar way to with the example above, we don't have to worry about how to reconcile rotating a cube in such a way that the axes swap. It just isn't possible. The transformation is not allowed. quote:We do know that the event horizon of a black hole is where escape velocity is c, but just because we don't have the ability to calculate the worldlines of things that pass inside the event horizon doesn't mean they literally cease to exist. Gravitational acceleration would increase the velocity of the infalling matter past c if we follow the laws of physics. And while we imagine a singularity of infinite density at the center, we don't know if that's literally the case. Pop-sci here has done you no favors, unfortunately. It's sad, because pop-sci is definitely what got me to study science and surely continues to get people interested in science, but it does so by at time misrepresenting (sometimes grossly) the math, or giving examples that really don't explain the essence of the problem. The escape velocity being 'c' at an event horizon is very misleading. The real problem at a black hole's event horizon is that all spacetime paths are directed inwards, there are no spacetime paths that lead out of the black hole. (In addition, the three spacial directions become three distinct time directions, and the time direction becomes spacial. Weird, right? No, we don't really understand what that means, but it's a consequence of the math.) There is no 'singularity' at the center of a black hole. A singularity is the math telling you 'this doesn't make sense.' Dividing by zero is a singularity. At a singularity, continuous solutions become non-differentiable. ashpanash fucked around with this message at 22:39 on Feb 24, 2020 |
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Feb 24, 2020 18:53
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Rather than say escape velocity exceeds c in a black hole, it's way more accurate to say that the event horizon is where time begins to move sideways, towards the center of the black hole. e; an interesting collolary of this is that the way to extend your life in a black hole is to resign yourself to a free-fall - any movement, including 'towards the edge' will speed up your doom. To understand what happens in the singularity, we need a quantum gravity theory, but that theory will still build on top of what we have and only give different results than what we expect in the most absolute extremes of gravitational interaction. dex_sda fucked around with this message at 19:17 on Feb 24, 2020 |
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Feb 24, 2020 19:14
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So let’s just turn the universe into a singularity and then we can all travel faster than light and sideways in time.
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Feb 24, 2020 19:34
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ashpanash posted:Pop-sci here has done you no favors, unfortunately. It's sad, because pop-sci is definitely what got me to study science and surely continues to get people interested in science, but it does so by at time misrepresenting (sometimes grossly) the math, or giving examples that really don't explain the essence of the problem. The escape velocity being 'c' at an event horizon is very misleading. The real problem at a black hole's event horizon is that all spacetime paths are directed inwards, there are no spacetime paths that lead out of the black hole. (In addition, the three spacial directions become three distinct time directions, and the time direction becomes spacial. Weird, right? No, we don't really understand what that means, but it's a consequence of the math.) There is no 'singularity' at the center of a black hole. A singularity is the math telling you 'this doesn't make sense.' Dividing by zero is a singularity. At a singularity, continuous solutions become non-differentiable.
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Feb 24, 2020 20:38
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Infinite Karma posted:Maybe I used the wrong term if singularity doesn't mean that. Just because all of the spacetime paths are directed inward beyond the event horizon (and nothing can ever leave it) doesn't mean that the spacetime paths of the stuff that's passed beyond the event horizon cease to exist. Black holes aren't necessarily homogeneous within the event horizon. By singularity, I meant "spot in the gravitational center of mass of the black hole where all the infalling mass-energy ends up". Does the "stuff" compress infinitely to a point of zero volume containing all the mass-energy? Or does some kind of exclusionary pressure or maximum mass-energy per unit of volume force a finite maximum density? As far as I know these are valid questions. It might be pop science, but I have read about hypothetical and (supposedly) mathematically valid constructs of rotating black holes losing their event horizons, where this relativity-violating stuff would be observable. I'd kind of be surprised if it didn't have effects that were problematic for relativity as we know it. The fact that blackholes lose mass slowly via Hawking radiation means that not all of the energy inside a black hole is diverted towards the singularity. The only way for there to be mass transference from within to without is for there to be particle/virtual particle pairings near the event horizon to shed that energy.
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Feb 24, 2020 21:05
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Infinite Karma posted:Maybe I used the wrong term if singularity doesn't mean that. Just because all of the spacetime paths are directed inward beyond the event horizon (and nothing can ever leave it) doesn't mean that the spacetime paths of the stuff that's passed beyond the event horizon cease to exist. Black holes aren't necessarily homogeneous within the event horizon. By singularity, I meant "spot in the gravitational center of mass of the black hole where all the infalling mass-energy ends up". Does the "stuff" compress infinitely to a point of zero volume containing all the mass-energy? Or does some kind of exclusionary pressure or maximum mass-energy per unit of volume force a finite maximum density? As far as I know these are valid questions. It might be pop science, but I have read about hypothetical and (supposedly) mathematically valid constructs of rotating black holes losing their event horizons, where this relativity-violating stuff would be observable. I'd kind of be surprised if it didn't have effects that were problematic for relativity as we know it. If you want to know where the math points you, then you need to look at a Penrose diagram of the Kerr solution, where in effect the singularity becomes cylindrical and there's the potential of escaping through a second horizon, but only into *another universe*, which only comes out of the equation because in order to use a Penrose diagram, we have to 'pull in' the infinities associated with space and time. It's nonphysical nonsense but if you just follow the GR solution, that's what it gets you. As for the stuff that's passed the event horizon, does it cease to exist? In a way, yes - it has exited the universe, so it makes no sense to talk about it as if it exists. However, this leads to the quantum information paradox which is still a mystery - because while it's not contradictory for things to stop existing, it is contradictory to violate unitarity, which the event horizon seems to do. And that's where the holography starts to come in, and the string theorists who are now no longer string theorists but are instead AdS/CFT theorists start throwing conjectures everywhere, and my eyes start to glaze over. Black holes are interesting objects and a prime place to try to figure out a quantum theory of gravity, but as has been expressed by many people in the thread already, connecting theory to experiment is a dubious proposition when you have no ability to experiment. And while you can twist the math to and fro, nature will be the one to tell us how it behaves, and it's our job to translate that into math that makes sense. ashpanash fucked around with this message at 21:12 on Feb 24, 2020 |
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Feb 24, 2020 21:05
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That's why I think that the various arguments or conversations that have been had about FTL travel as it regards interstellar colonization, the Fermi Paradox, etc., are a bit of a rabbit-hole divergence. People arguing that it can't happen just aren't really thinking on the scale of a technologically advanced civilization. Like, someone could do it. There's nothing stopping you from sending a probe, or whatever, from this solar system to the next nearest solar system. Even a probe going the speed of Pioneer 10 will get to Alpha Centauri in about 34,000 years. Looking at it from even the perspective of humanity - that's not even enough time for us to meaningfully evolve. 34,000 years ago we were pretty much the way we are now, just in the form of isolated Stone-Age tribes. 34,000 years is nothing. Dreaming about FTL by playing with the Einstein equations is just an interesting math exercise. But it's a failure of imagination when talking about the broad-scale activities of a potential Kardashev >1 civilization.
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Feb 24, 2020 23:38
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There is plenty of stuff we can do even without FTL, it just makes imagining a space opera future harder.
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Feb 24, 2020 23:43
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The problem with all those fantastic solar or galaxy engineering things you can do is there is no visible sign of anyone out there doing them. FTL would actually be an interesting solution to the Fermi equation, because it permits the kind of political structures that could actually enforce a ‘no colonising the primitives’ rule.
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Feb 25, 2020 09:51
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radmonger posted:The problem with all those fantastic solar or galaxy engineering things you can do is there is no visible sign of anyone out there doing them. According to at least decently credibly convincing scientific paper, there's actually a decent chance that on the timescales involved we could be in a bubble of "dead space" and not notice any actively colonizing subcivilization. Also I believe it's been established we've only looked at a teeny tiny minuscule amount of space and ways and means of looking at it. Like we have a really hard time even finding planets without a massive amount of observational effort, so it could be possible to miss a megastructure, especially if it is in a different galaxy.
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Feb 25, 2020 15:12
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