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Halc

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    Computer Engr
  • Favorite Area of Science
    relativity

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  1. Per the no-hair theorem, one can dump antimatter in a black hole with no different effect than dumping ordinary mass (or dark matter) into it. It increases the mass and effects the angular momentum and charge accordingly, but no gamma reaction except for any interaction with say the accretion disk. This acts as sort of a long-term equalizer since any black hole will eventually radiate away with Hawking radiation, which emits no more matter than antimatter.
  2. Apologies for slow reply, but I've been logged off for several days. If the paper touches at only two points, that’s a one-shot teleport from one event to another. There is no gate held open, and thus the concept of the velocity and acceleration of the ‘gates’ does not apply since an event is a frame-independent fact. So I think you mean rolling the paper so it intersects at a line following the time axis, thus forming a worldline of your stargate. Yes, you don’t need to distort the paper to do that. If you can create such a thing where the two gates are simultaneous in Earth frame, then you’ve created a time machine. All you need is a second set of gates that with the two ends simultaneous with the frame of some receding object. Go through the Earth gate, come back through the other one, and now it’s 1921. Just pointing out that if you posit this sort of thing, then circular causality results. Didn’t need to accelerate either end of a gate to accomplish it. That was the metric spoken of I think. If I get you right, then conversation across our dining table with has one person on helium and the other on Xenon, each respectively from the perspective of the other. It would be like trying to talk with your twin on the fast ship. OK, no time machine there unless you build a 2nd gate with the properties described above. Why would the gate time be synced with one end (Earth) and not the other? Wormholes don’t seem to have a preferred end like that. I assume they’re relatively stationary then, else they could not be in sync. OK, they could, but only in a frame where the two endpoints have equal and opposite velocity. Ouch! That kind of blew my frame reference clutch. Let me see if I get it. The gate ends are in sync in Earth frame, both say noon, 3.464 light hours apart. The ship moves at .866c and gets there in 4 hours (4PM), but subjectively only 2 hours pass on the ship. If he leaves at ‘noon’ (synced with Earth clock at departure), then the destination clock moves from 3:00 to 4:00 during the two hour trip the clock makes moving to the ship, so yes, the Earth clock (noon) is 3 hours behind the destination clock that reads 3:00. When the destination clock passes him at 2PM, the Earth clock simultaneously reads 1PM. If someone enters the gate at noon, he’ll appear at the destination at noon (according to both local clock and his watch). Not sure how that can be construed as not entering until a long time passes. Ok, he not only steps through the gate, but does so at .866c. In that frame, he exits the gate at noon, and the receding Earth clock currently reads 9AM, which is 3 hours behind. So I read you so far. He’ll not enter that end of the gate until 6 hours from now when it’s noon over there. You are opening a portal between events that are separated in a space-like manner. Nothing violated by that (except locality) until you open a second one synced in a different frame. The main reason it isn’t a big problem yet is because you’re avoiding accelerating the ends, which is why I attempted to explore that part. I think SR has problems with wormholes in the first place. There’s just no such concept in Minkowskian spacetime. You have to jump to GR for that, and SR is suddenly inapplicable anywhere and thus cannot be violated. The acceleration of the rocket doesn’t have any affect on what time it is back on Earth. You make it sound like a causal relationship when in fact it is just a changed choice of coordinate system, which can be done without actually accelerating.
  3. You seem to be envisioning something like a stargate, a portal connecting the non-parallel worldlines of say two different planets. If one thinks of it as such, there's no reason why it cannot look just like a window. One can eat at a table that is half here and half there, and you can talk to the other person light years away as if they were in your presence, and can pass the salt and such. The characteristics of such a setup depend on said unspecified metric. Imagine a clock at each end of the table. If the clocks stay in sync despite the relative motion of ends of the wormhole, then one end can be accelerated as in the twin scenario, starting and ending in near proximity. When the other end of the gate returns, the table is still there and both observers (neither of which have passed anything except the salt through the gate) will have aged the same, resulting in the wormhole/portal becoming a time portal instead of a spatial teleport setup. In other words, the portal can be changed from connecting events with space-like separation to connecting events with time-like separation. Similarly, the stargate could be set up at constant separation but vastly different gravitational potentials. If the clocks tick at the same rate, it quickly becomes a time machine. If the two clocks do not stay in sync, the two parties eating at the table will have difficulty communicating since one will be 'faster' than the other. The setup could be used to determine the absolute rest frame since the clock that objectively ticks faster must be moving slower. The principle of relativity would be violated.
  4. A CPU cannot have no program loaded. There is always the instruction it is executing, and the one after that. A CPU consumes the most power from transistors changing states. It takes X amount of energy for a transistor to switch from on to off and back again, so you multiply that by the rate the switching takes place and you get an idea of the heat produced by the chip. Many systems (laptops, phones especially) have a low power mode where the software recognizes low demand for services and puts the device into low power mode somehow. This probably involves a significant reduction in the clock rate which directly affects the rate at which those transistors change states. At a lower clock rate, a lower voltage might be required to maintain this reduced performance, and low voltage also reduces the energy needed for the state changes. The CPU is a synchronous device, so everything on it is dependent on the clock. If the clock is stopped altogether, the CPU does nothing and comsumes only static power which is minimal. It also would be totally incapable of recognizing a sudden demand for its services, so something outside the CPU would need to be involved in the monitoring of demand. It would not be software controlled since no software can run on a stopped CPU. Not sure if any device actually stops the clock to a CPU on a device that isn't fully shut down.
  5. Great. A cartoon eye. No, an electron microscope can only see things sitting still since it works effectively by touch, not light as implied by the eye. What they're probably detecting for electrons is some kind of charge detector like is used by a ground-fault detector in your bathroom outlet. Not sure if you can turn it on and off since it is a passive device. If the device takes no measurement (has no effect on the electron) 50% of the time, then 50% of the time the electron will reach the target with a simple pattern and the other times with an interference pattern. If the electrons are coming continuously, you'd see the pattern change from one to the other as the sensing device is function or not for whole seconds at a time. If they're using photons, I know a diagonal polarizing filter at the slits is enough to eliminate the interference pattern. You can't turn a polarizing filter on and off either, unless there is some really weird gadget that does this.
  6. The 'device' can be the far wall on which the interference pattern appears, which isn't something that can be 'turned on and off' 50% of the time. Perhaps you have a specific device in mind that can meaningfully be turned on and off, and thus allowing a more specific answer. And yes, there being a human involved anywhere or not makes no difference. The vast majority of quantum measurements/collapses take place without any human being immediately aware of them. This is true even with experiments set up in labs by humans.
  7. How about a galaxy 50 BLY that-away? Definitely mathematically expressible, but so is a perfect square. Neither is physically observable, at least not by us. It would be measurable ('observable' makes it sound like a life form is necessary) by something in that galaxy. Does that make a difference? A relativist would say it doesn't exist relative to Earth and v-v. Existence is a relation (not an objective property) in such a view, which is precisely the attraction of it. If you accept the principle of locality (no faster-than-light information transfer) in quantum physics, then it is a mistake to assert the specific distant galaxy exists at all. It leads to contradictions per Bell's theorem. That throws quite the wrench into the idea of objective existence. Side note: I agree that a route doesn't require my existence. My sister doesn't exist, and yet the route does. Of course, expressed as a relation, the route to the Milky Way doesn't exist to my sister, so go figure.
  8. I can actually think of epistemological cases. The Egyptians of old were known for stamping out all mention of certain prior Pharaohs from the records. These were rarely entirely successful, but when they were, they did very much make them 'cease to having ever existed', at least from an epistemological standpoint. They very much have an ontological existence in history, but nobody can remember them anymore. Your memory (of this and that) very much once existed, and cannot cease to have ever existed. It just doesn't exist now. Same with history or Earth and our respective fathers, which have been erased from existence, but with no implication of having never existed. Nowhere did I say that any of these things might no longer exist. More explicitly, I meant that nothing that once existed can subsequently cease to have ever existed. Area54 seems to get my gist. Yes, it's a verb tense thing, not a deep point.
  9. This is very much a philosophical topic which needs proper definitions to communicate clearly. If a brain is changed while being formed, it's still the same brain, just altered from some prior state. Putting a scratch in my car doesn't make it not-my-car. You change ever second of every day, and yet you're still you. A static unchanging thing cannot be alive. By definition, nothing can cease to ever exist. If it ever existed, then that’s that. It’s not something that can be ‘changed’. I can bring about a premature cessation to the duration of its existence, but that doesn’t make it having never existed. You’re asking what changes the identity of the consciousness? That, being essentially a process, doesn’t necessarily have an identity. You having consciousness is like a candle having a flame. Combustion doesn’t really have identity. I can use a candle to light another one. Is it the same combustion, or a different one? What if I blow out the original candle and relight it from the 2nd one. Now is it the same combustion or a new one? The Olympic torch is about the only example I can think of where humans worry about the identity of the combustion. In other words, you need to backtrack and spell out what you think defines your identity. If it’s stream of consciousness (one that is interrupted every night?), then the ‘memory’ answer (see Bufofrog’s reply) works for a while, but then what if that memory can be duplicated or replaced? It’s only the lack of our witnessing that sort of thing going on that allows us to function with such a definition. Again, if it was made, in the womb or otherwise, then it exists and cannot be in a state of not-ever-going-to-exist. The process mostly goes on there, but a brain without the rest of the body is about as unconscious as can be, so I’d be reluctant to box it in that tightly. I’d say that my consciousness extends well beyond my body into the world that is part of my experience. Now this isn’t a case of altering an existing thing. It’s like saying that if my Honda was instead a Lexus, it would still be the same car (because it’s mine?). Small change, same ‘parents’, but different factory. Hard to argue that it’s the same car, as opposed to the same car being painted blue or green near the end of the assembly line. It seems completely implausible that a non-existent entity can experience somebody else. There’d be no you to experience this other person. They’d experience themselves by definition. I think you envision an immaterial entity that experiences your body. That’s pretty much a religious stance, sorely in need of clarification, such as what role is played by the various parts. What holds memory, the experiencer or the brain? What makes the decisions? Who’s in control? Without such elementary designations, there are too many permutations to comment on them all.
  10. Despite the wording above, I agree that dark energy isn't an actual force, but dark energy will begin to increase the proper separation between two relatively stationary objects, and that translates to a sort of kinetic energy which could hypothetically be harnessed to do work (imagine a seriously long thin string between them). Gravity will also separate the pair of objects when placed in the deep void * (regions of negative mass density relative to the mean), and gravity isn't an actual force either, at least not under relativity. Like gravity, I think dark energy can be expressed as a force only when considered in Newtonian terms, and it doesn't make much sense there since Newtonian physics has no concept of expanding space. From a geometric standpoint, spacetime with expansion but without gravity and without dark energy is effectively indistinguishable from Minkowskian spacetime. There would be no event horizon since light would eventually reach us from galaxies of any distance and any recession speed. That horizon is only there because of the effects of dark energy. * One of the nearest such regions is the Dipole Repeller which seems to expel all the galaxies in its vicinity. This shows that in an otherwise uniform distribution of matter, the absence of matter in an isolated pocket of that distribution will have a repulsive gravitational effect on all the nearby surrounding masses. Right. The CMB would not appear isotropic from Y's PoV, and from this Y could measure his peculiar velocity of 70 km/sec towards X. I couldn't quite parse that, but by stationary relative to each other, I explicitly qualified that to mean 'constant proper separation', meaning a string between the two would not break or stretch.
  11. The question is, why do you think they do? 'Space' isn't something that can apply a friction-like force and begin accelerating an object. Assume we have two pebbles X and Y that are a megaparsec apart, and they're way out in the void between galaxies. Now a megaparsec is a long way. You can fit at least a couple dozen galaxies like ours side by side on one. Nearby galaxies are going to exert tidal forces on our pebbles drawing them apart, so we're going to ignore gravity and also dark energy and just concentrate on the expansion. Pebble X is stationary relative to the cosmological frame, that is, the CMB appears isotropic from X's PoV. It is said to have a peculiar velocity of zero. Y is stationary relative to X, that is, the proper separation between X and Y is constant at 1 megaparsec. Since 'space' is expanding at a rate of 70 m/sec/mpc, Y must have a peculiar velocity of 70 m/sec towards X which exactly cancels the space expansion. There's no reason to think it will lose this velocity per Newtons first law. If expansion exerted a force on it, that would be akin to friction with some kind of aether, and that would drag any peculiar motion down to zero over time, which would have all orbiting things (going around a galaxy especially) lose their orbital motion and spiral into the centers. Angular momentum would not be preserved.
  12. Earth is not moving in some direction due to expansion. It is moving in some direction (relative to say the cosmological frame) because net forces on Earth or the materials from which it is composed have cumulated in its present velocity/momentum. Our velocity (relative to the frame of your choice) has changed by over 400 km/sec since the Spinosaurus was around, so those external forces are not insignificant. In other words, if I put two objects in space separated by say a megaparsec, that are stationary relative to each other and not subject to external forces like gravity from nearby objects, then under just expansion alone, they will remain forever the same distance apart. Dark energy is probably the only actual force (that is not expansion itself) that will push the two objects apart over time. This is not expansion, but the acceleration of expansion, and yes, that does require force and energy and would affect said mutually stationary things.
  13. The author admits in the intro that an observer does not see the history of the universe. That question is discussed on stack exchange here which admittedly discusses the simplified case of a Schwarzschild black hole. This image from there: This clearly shows a finite history of some outside object (dotted worldline) seen by the blue worldline of our infalling observer, Cauchy horizon or not. Kino's Kruskal diagram shows the same sort of thing. The Cauchy horizon for a charged or rotating BH seems to have special treatment in that the spacetime beyond it isn't 'smooth', but I still don't know how the history of the universe could be in the causal path of that region. The wiki page on a charged black hole makes references to the 2nd horizon. No nice diagrams like above ☹️ and the ones in the paper don't seem to demonstrate the claim to my untrained understanding. It seems that sufficient charge can prevent any mass from collapsing into a black hole (layman guess: because the EM repulsion is greater than the gravity attraction?), and perhaps below said Cauchy horizon, it prevents the singularity from forming, resulting in a chaotic fixed 'density' with no actual singularity? Just guessing here, but such a construct could be maintained indefinitely. This does not seem to be what the author above is saying, since he talks of a point p where the observer crosses this horizon (an event) that has the whole universe in its causal history, not the collective set of events inside this horizon. I'm obviously out of my depth here. Still, Reissner-Nordström and Kerr black holes (and Schwarzschild) are not models of real black holes since none of those solutions include Hawking radiation. Any BH has a finite life, and any events outside the past light cone of the final evaporation event will not be in the causal past of any event within the black hole.
  14. I was going to jump on that. +1 for catching it. In my reply above your post, I mentioned the other companions all around you falling with you. They don't disappear from your sight. They're not 'below' you, they trace a worldline near your worldline and there is no way light from one nearby worldline doesn't reach the other, regardless of the direction in which this companion appears in relation to you. The usual local laws of SR very much do apply here per the equivalence principle. The falling observer is very much stationary in his own reference frame. That frame simply doesn't correspond to any inertial reference frame relative to a distant outside frame of reference, say the inertial frame in which the center of mass of the BH is stationary. This is not a contradiction, just an abstract consequence that no outside inertial coordinate system foliates the events inside a black hole. That in no way implies that the events inside a black hole cannot be locally mapped with an inertial coordinate system. The falling observer is stationary in his own frame and sees the objects all around him in any direction. If not, he'd not see his feet or hands.
  15. That was the question in the OP, yes, and it has been answered. The feet that he sees are the feet from a few nanoseconds ago (falling frame), same as the feet you see now are not the present feet, but the feet in the past. Those feet were outside the EH when the light was emitted from them. I've said as much since my first reply in this thread. A body does not experience itself in the present since it takes time for any information to travel from say feet to head. So there's no anomaly in spacetime from the PoV of the falling guy. It's all normal physics to him, and he has no awareness of having crossed over unless he has a computer with him that informed him of the situation, since it is a calculable thing. The view outside the window also doesn't change appreciably. There is a section of the normal universe that occupies a percentage of his view, with the rest of the view black except for other sources of light falling in with him, such as his feet. If 50 guys all fell in sort of with each other, not all at the same time or place, they'd all still be able to see each other at all times, but tidal effects would eventually alter their distribution. It is red shifted only from the perspective of something hovering outside. Our infalling guy is in a completely different frame of reference in which no red-shift is observed at all, at least not until the spaghettification begins to occur. Per the equivalence principle, he cannot perform a test that demonstrates when the EH is crossed. GR rests on that principle and would collapse if the descriptions you paint actually occurred. My feet appear to me to be more red shifted here at my desk than would be seen by our guy falling in. This is because the falling guy is inertial and I am not.
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