Jesse, Please excuse my simple-minded model: "Electric fields also come out if the BH singularity has a charge." Richard
On Sun, Jan 26, 2014 at 10:16 AM, Jesse Mazer <[email protected]> wrote: > According to general relativity, neither gravity nor electric fields > actually "come out of" the black hole's event horizon, rather the gravity > and EM field felt by observers outside the horizon is a sort of frozen > snapshot of the gravity/EM fields from all the matter that approached the > horizon in the past. Keep in mind that external observers can never > actually see anything cross the horizon, instead they see it moving more > and more slowly as it gets arbitrarily close to the horizon--the redshift > is continually increasing as it approaches horizon so in practice an > external observer can't see an object stuck on the horizon forever, but in > principle you could if you could detect light with arbitrarily huge > wavelengths, and if light was a classical EM wave rather than being > quantized into photons. > > The Usenet Physics FAQ at http://math.ucr.edu/home/baez/physics/ has some > good summaries: > > > http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html > > 'How does the gravity get out of a black hole? > > 'Purely in terms of general relativity, there is no problem here. The > gravity doesn't have to get out of the black hole. General relativity is a > local theory, which means that the field at a certain point in spacetime is > determined entirely by things going on at places that can communicate with > it at speeds less than or equal to c. If a star collapses into a black > hole, the gravitational field outside the black hole may be calculated > entirely from the properties of the star and its external gravitational > field before it becomes a black hole. Just as the light registering late > stages in my fall takes longer and longer to get out to you at a large > distance, the gravitational consequences of events late in the star's > collapse take longer and longer to ripple out to the world at large. In > this sense the black hole is a kind of "frozen star": the gravitational > field is a fossil field. The same is true of the electromagnetic field > that a black hole may possess.' > > They then go on to discuss how the picture is altered by virtual particles > in quantum field theory, but the above is a good explanation of how it > works with classical general relativity and classical electromagnetism. And > this entry from the FAQ discusses how in general nothing is actually seen > to cross the horizon by external observers: > > http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html > > 'Won't it take forever for you to fall in? Won't it take forever for the > black hole to even form? > > 'Not in any useful sense. The time I experience before I hit the event > horizon, and even until I hit the singularity—the "proper time" calculated > by using Schwarzschild's metric on my worldline—is finite. The same goes > for the collapsing star; if I somehow stood on the surface of the star as > it became a black hole, I would experience the star's demise in a finite > time. > > ... > > 'A more physical sense in which it might be said that things take forever > to fall in is provided by looking at the paths of emerging light rays. The > event horizon is what, in relativity parlance, is called a "lightlike > surface"; light rays can remain there. For an ideal Schwarzschild hole > (which I am considering in this paragraph) the horizon lasts forever, so > the light can stay there without escaping. (If you wonder how this is > reconciled with the fact that light has to travel at the constant speed > c—well, the horizon is traveling at c! Relative speeds in GR are also only > unambiguously defined locally, and if you're at the event horizon you are > necessarily falling in; it comes at you at the speed of light.) Light beams > aimed directly outward from just outside the horizon don't escape to large > distances until late values of t. For someone at a large distance from the > black hole and approximately at rest with respect to it, the coordinate t > does correspond well to proper time. > > 'So if you, watching from a safe distance, attempt to witness my fall into > the hole, you'll see me fall more and more slowly as the light delay > increases. You'll never see me actually get to the event horizon. My > watch, to you, will tick more and more slowly, but will never reach the > time that I see as I fall into the black hole. Notice that this is really > an optical effect caused by the paths of the light rays. > > 'This is also true for the dying star itself. If you attempt to witness > the black hole's formation, you'll see the star collapse more and more > slowly, never precisely reaching the Schwarzschild radius. > > 'Now, this led early on to an image of a black hole as a strange sort of > suspended-animation object, a "frozen star" with immobilized falling debris > and gedankenexperiment astronauts hanging above it in eternally slowing > precipitation. This is, however, not what you'd see. The reason is that > as things get closer to the event horizon, they also get dimmer. Light > from them is redshifted and dimmed, and if one considers that light is > actually made up of discrete photons, the time of escape of the last photon > is actually finite, and not very large. So things would wink out as they > got close, including the dying star, and the name "black hole" is > justified.' > > > > > On Sun, Jan 26, 2014 at 9:36 AM, Richard Ruquist <[email protected]>wrote: > >> Edgar, >> >> Electric fields also come out if the BH singularity has a charge. >> Richard >> >> >> On Sun, Jan 26, 2014 at 8:01 AM, Edgar L. Owen <[email protected]> wrote: >> >>> OK, time for THE ANSWER TO MY QUESTION of how gravity can escape from a >>> black hole.... >>> >>> Liz, Brent, and Richard, >>> >>> OK, nobody got the answer so I'll explain it myself. It's pretty simple >>> but still pretty profound and thought provoking.... >>> >>> Gravity IS what needs to be escaped. So it doesn't even make sense to >>> ask how gravity could escape ITSELF. >>> >>> There wouldn't even be a black hole if gravity hadn't already escaped >>> the black hole to create its gravitational effect. >>> >>> So what this means is that gravity is the only thing than CAN escape a >>> black hole because it is gravity itself that creates the gravitational >>> field that must be escaped! >>> >>> Thus gravity, and only gravity, can manifest freely OUTSIDE a black hole >>> the effects of its INSIDE mass. >>> >>> Thus gravity is the only thing that freely COMES OUT of a black hole >>> through the event horizon, because what stops everything else from coming >>> out is gravity itself. But obviously gravity can't stop itself from coming >>> out through the event horizon, because only its already manifesting >>> presence is what stops everything else from coming out through the event >>> horizon, but it already must have come out to stop everything else from >>> coming out... >>> >>> Thus before gravity comes out through the event horizon, there is >>> nothing to stop anything from coming out. Thus gravity can freely emerge >>> through the event horizon and only by doing so is it able to prevent >>> anything else from coming out.... >>> >>> Hope I'm explaining this clearly? >>> >>> Edgar >>> >>> >>> >>> On Saturday, January 25, 2014 1:29:45 AM UTC-5, Liz R wrote: >>>> >>>> On 25 January 2014 16:31, meekerdb <[email protected]> wrote: >>>> >>>>> On 1/24/2014 4:41 PM, Edgar L. Owen wrote: >>>>> >>>>>> Brent, >>>>>> >>>>>> No, my proposed dark matter effect has nothing to do with black >>>>>> holes. Black holes are caused by accumulations of actual visible matter, >>>>>> not by the Hubble expansion of space... >>>>>> >>>>>> However I do have a question for you. Since gravitational changes >>>>>> propagate at the speed of light how does the mass inside a black hole >>>>>> produce gravitational effects outside the black hole? If light can't come >>>>>> out how can gravitational effects come out? >>>>>> >>>>> >>>>> You are thinking of gravity as mediated by force particles, like >>>>> photons mediate the EM forces. But (at least classically) gravity isn't a >>>>> force, it's just a shape of space and as I responded to Liz, there's not >>>>> mass in a black hole, no T_u_v term in the Einstein equation. It's a >>>>> vacuum solution. That's why it doesn't make any different what falls in >>>>> to >>>>> create the black hole. The effects outside the event horizon are just >>>>> that >>>>> the space is warped there just *as if* the black hole were a massive >>>>> object. >>>>> >>>>> I believe Richard Feynmann was asked the same question (about how >>>> gravity "escapes" a black hole). Of course gravity WAVES can't escape a >>>> black hole... >>>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Everything List" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To post to this group, send email to [email protected]. >>> Visit this group at http://groups.google.com/group/everything-list. >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Everything List" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To post to this group, send email to [email protected]. >> Visit this group at http://groups.google.com/group/everything-list. >> For more options, visit https://groups.google.com/groups/opt_out. >> > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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