It is said by current scientific understanding that black holes are objects with such great mass as to curve space inward onto itself, preventing light's escape by subsequently having an escape velocity much greater than that of light's speed. In fact, black holes even become so energy-efficient, that it takes trillions of years for all but the smallest to dissolve, and even the - speculates Hawkings and such - that not even a small black hole has had sufficient time in this universe to dissipate through Hawking radiation, I.E. the vacuum energy at the very edge of the black hole producing virtual particles where one particle sometimes escapes. It is also claimed by relativity that owing to the fact that E = MC^2, that as one approaches the speed of light as an object with mass, mass is gained so long as one reaches that speed, or to put it otherwise, it takes an infinite amount of energy for a massive particle to reach the speed of light. Now, it is also said by science that there are three possibilities for the fate of the universe: 1. To expand forever. 2. To contract again and then rebound in another big bang. 3. To remain static. The first of these conjectures on the fate of the universe seems to be the most likely according to scientists, and though we may have another universe come into being, it seems that our universe will end by space time being so stretched as to overcome the forces that bind the universe. Taking all this together, I have two questions: Is it possible that black holes may prove instrumental in preventing this eventual "big rip"? For though space-time may expand, we must also recognize that space-time is most immediatly impacted by gravity, and as the expansion of of the universe is currently -well- below the speed of light, would not this expansion not be able to overcome the gravity of the local-space time of the black holes? That is to say, would not the black holes resist the expansion and in fact, become even more efficient as the virtual particles would not even have space to be able to leave after space-time expands enough to prohibit such? Perhaps even then attracting the other black holes to condense into one that might even produce the necessary conditions for a big crunch and/or another big bang? What also about relativity? Suppose that the expansion of the universe increased so much that it was nearly at the speed of light? Would not this add more and more and more mass on it, the further it went? And would not this mass eventually reach the point where it might arrest this process, condense and attract, and perhaps even form black holes owing to it? And through this, drawn things back into a situation similar to the one expressed above, or a more direct big crunch scenario? Note: I am not here trying to present a theory or any claims here. I am actually just throwing this out as a question to get some input from others. I was considering this earlier (whilst eating supper, actually) and thought it might prove fruitful to get some insights to see if my thoughts have any basis in the scientific opinion of those whom may be privy to information I am not.
No. At a large enough distance, the gravity of a black hole is no different from the gravity of a star. If our Sun turned into a black hole right now, the Earth's orbit would be unaffected. The hole wouldn't "pull" distant objects inwards any more than any other body with equivalent mass. No. The rest mass of the universe is what is important for generating gravity. The apparent increase in mass of moving objects is more of an observational effect.
I think it has to be a real effect. For example if we by some means had the capacitiy to force these moving objects to come to rest in our frame, we would expend great energy. Seems to me.
James R: "No. At a large enough distance, the gravity of a black hole is no different from the gravity of a star. If our Sun turned into a black hole right now, the Earth's orbit would be unaffected. The hole wouldn't "pull" distant objects inwards any more than any other body with equivalent mass." I was more suggesting that black holes, by being so gravitationally intense, that universal expansion could not rip them apart. It stands to reason that it would take a force greater than the escape velocity of the black hole to rip it apart, no? Specifically as gravity itself curves and warps space time, which is a similar effect to expansion. Thus to reverse it one would have to match and exceed said rate, which seems impossible. "No. The rest mass of the universe is what is important for generating gravity. The apparent increase in mass of moving objects is more of an observational effect. " So an object does not keep its relativistic mass if it slows down? Where then does the mass go? Suppose we accelerated an object till it achieved a mass 10 times its original? If we then slowed it down through exertion of our own energy, we'd not have an object ten times as massive as it was before? I was always under the impression that we would?
Hmmm. I had just thought of this: Might it be possible that the inflation of the early universe could have been arrested by the accumulation of said mass which countered the and dramatically slowed the inflation and which gave rise to the heterogenous quality of the mass of the universe?
That's true. As the universe expands, the black holes will just move further and further apart. Over a very long period of time, they will evaporate due to Hawking radiation rather than being ripped apart by gravity. It is actually meaningless to compare a force to a velocity, so I'm not 100% sure what you mean. No. It's relativistic mass decreases as it slows down. This is why relativistic mass is not such a useful concept. In relativity, it is hardly ever used these days. The problem is that the concept of relativistic mass conflates rest mass and kinetic energy. Rest mass is a frame-independent quantity; kinetic energy is not. So, it is better to think of them separately. No, we wouldn't. If we slow it, we take away some kinetic energy, and so its relativistic mass decreases. Its rest mass stays the same, though.
James R.: "That's true. As the universe expands, the black holes will just move further and further apart. Over a very long period of time, they will evaporate due to Hawking radiation rather than being ripped apart by gravity." Considering that universal expansion is said to potentially cause a "big rip" before the dissolution of the black holes, would not this necessarily impact the capacity for a black hole to emit hawking radiation? That is to say, could not we have a situation in which the event horizon does not really exist by virtue of the fact that space is no longer continuous outside it? "It is actually meaningless to compare a force to a velocity, so I'm not 100% sure what you mean." Escape velocity is a symptom of gravitational attraction, is it not? The black hole, by virtue of the fact that it is extremely massive, has a correspondingly high escape velocity, so much so, that even if one were to travel at the speed of light, one could never escape. Now, if the universe is expanding, and supposively on a track to a "big rip" (one of the two potential fates) would not that expansion have to be greater than the local gravity of the black hole in order to rip it apart? "No. It's relativistic mass decreases as it slows down." Would not this occur only if its slow down was owing to its own power? That is, if it counteracted the force via "breaking thrusters" or some such concept. But what if it was slowed down by sources of energy exterior to it? Such as say, a "netting" that progressively slowed it down in its path? Similarly, I have read otherwise that one would be left with something more massive. I can't find my sources at the moment, though, nor can I find a website that actually answers that question. "This is why relativistic mass is not such a useful concept. In relativity, it is hardly ever used these days. The problem is that the concept of relativistic mass conflates rest mass and kinetic energy. Rest mass is a frame-independent quantity; kinetic energy is not. So, it is better to think of them separately." But correct me if I am wrong, but as annihilation follows E = MC2 completely (within the margin of error, at least), would not the reverse principle which sparked Einstein to produce said equation also have some foundation? That is, if one can annihilate a particle and its anti-particle and gain 100 percent of the energy as defined by E = MC2, would not one also have to be able to reconvert energy into mass through approaching the speed of light? And would not this mass not disappear if slowed down by forces exterior to it? "No, we wouldn't. If we slow it, we take away some kinetic energy, and so its relativistic mass decreases. Its rest mass stays the same, though. " Yes, we may take away its kinetic energy, but does not the energy it accumulated throughout its acceleration - and which impacted its further acceleration by necessitating an infinite supply of fuel by adding to the mass - differ from the value of the kinetic energy of the object?
Prince_James: Hawking radiation occurs all the time for every black hole. It is only a matter of having long enough or not having long enough for the hole to evaporate before the universe ends (big crunch or big rip scanarios). Incidentally, I'm not familiar with the "big rip". Do you have any references on that? Sounds reasonable. It doesn't matter. Remember, when we talk about relativistic mass, we're really talking about rest mass plus kinetic energy. Reduce the kinetic energy of an object, and the object's relativistic mass decreases. It doesn't matter what causes the reduction in kinetic energy. Take a concrete example. An electron and a positron at rest next to each other will attract and annihilate each other, releasing two photons with a total energy equal to the combined rest energies of the two original particles. This can also be run in reverse. We can't directly collide two photons to produce an electron an a positron (because photons don't collide with each other); some other particle must be involved. But if in a collision there is energy greater than the combined rest energy of an electron and positron, it is possible that these particles will be created from that energy. Any "extra" energy left after creation of the particles usually appears as kinetic energy of the created particles - i.e. they head off at some speed. No. If it takes X amount of energy to speed an object up to a certain speed from rest, then exactly X amount of energy will be released when the object is slowed back down to zero speed.
James R.: "Hawking radiation occurs all the time for every black hole. It is only a matter of having long enough or not having long enough for the hole to evaporate before the universe ends (big crunch or big rip scanarios). Incidentally, I'm not familiar with the "big rip". Do you have any references on that?" Sure thing, my good man. Here's the standard Wikipedia reference: http://en.wikipedia.org/wiki/Big_Rip And here's something from Space.com: http://www.space.com/scienceastronomy/big_rip_030306.html But as to the first part of your response, yes, a black hole does evapourate through hawking radiation (taking trillions of years according to recent calculations) but the question is mostly whether or not this scenario might make an impact either-which way. "Sounds reasonable." So you think it is possible that black holes could resist such expansion? "It doesn't matter. Remember, when we talk about relativistic mass, we're really talking about rest mass plus kinetic energy. Reduce the kinetic energy of an object, and the object's relativistic mass decreases. It doesn't matter what causes the reduction in kinetic energy." I will concede this point until/unless I can find any sources to deny this. My thanks for the explanation. "Take a concrete example. An electron and a positron at rest next to each other will attract and annihilate each other, releasing two photons with a total energy equal to the combined rest energies of the two original particles. This can also be run in reverse. We can't directly collide two photons to produce an electron an a positron (because photons don't collide with each other); some other particle must be involved. But if in a collision there is energy greater than the combined rest energy of an electron and positron, it is possible that these particles will be created from that energy. Any "extra" energy left after creation of the particles usually appears as kinetic energy of the created particles - i.e. they head off at some speed." Yes. I think it is something along the lines of 50 percent neutrinos, and 25 percent gamma radiation, and the rest thermal radiation and visible light, yes? "No. If it takes X amount of energy to speed an object up to a certain speed from rest, then exactly X amount of energy will be released when the object is slowed back down to zero speed. " Would this process be as instantneous as annihilation?
Prince_James: Ultimately, no. Many different reactions are possible. No. The energy released is released gradually, as the kinetic energy is gradually changed.
James R: "Ultimately, no." Well let's consider this. The average black hole would take trillions of years to decay via Hawking Radiation. In 10 billion years, the Big Rip may or may not happen (I am more inclined to suggest the other alternatives, but this is irrelevant). At this time, space would cease to exist. Even quarks and strings (if they exist) may be ripped apart (although at present, quarks show no signs of being able to rip apart). But if it is true that Black HOles, by virtue of this acceleration never being able to be faster than the speed of light (which we'll assume is true) nor could it match the escape velocity of black holes (which seems necessary to rip them apart) then it stands to reason that space would cease to be at the edge of the escape horizon of the black hole. Now, if hawking radiation occurs from virtual particles occuring at the edge, yet there is no edge, would not this mean that black holes would cease to lose energy at this point? And thus perhaps our universe would remain, if only in black holes scattered throughout a void? "Many different reactions are possible." Are you certain? Because I had thought annihilation only rpdouced said conversion? "No. The energy released is released gradually, as the kinetic energy is gradually changed." Understood. Thanks.
