MigL

My apologies, owl, I assumed a spelling mistake where there was none. I was ( always seem to be ) in a bit of a hurry. My only point was that extra dimensions are a useful tool, whether real or imagined. If they have predictive effects then they may as well be real. There are a lot of things which cannot be seen or proved directly, only by their effects ( black holes, dark matter, sub-atomic particles, radiation, even air ). Yet I'm sure you have no problem accepting them.

I'll repeat, the distant observer sees the light coming out of the gravitational well more and more red-dhifted, until it finally disappears. But the infalling astronaut falls at the acceleration due to gravity just like anywhere else. He may see the 'end' of time when looking back out of the event horizon but the ONLY thing in his future is the ( possible ) singularity.

You want real references ? Very well. Look up quasi-crystals. You will find that their crystalline structure is not regular at all like all other crystals. However it turns out their structure is a projection ( which see ) of a 5-dimensional structure, ie their structure is only regular in FIVE dimensions. You are confused as to the meaning of dimensions in physics. For the mathematical meaning DrR has already explaned several times but in physics an extra dimension is not another direction beyond the known three, but another degree of freedom. In effect another 'way' to estabilish a relation. Take for example Siberian Mongol peoples and North American Inuit people, how are the two rlated ? We can establish a connection between the two only by considering another dimension. We realise that the dimension of time estabilishes a connection between the two about 15000 yrs ago ( the Bearing Strait land bridge ). This is the 'real',' physical' meaning of extra dimensions, you should try to wrap you head around it as a curved space/time is not a big stretch from these examples. We build models of reality using mathematical tools such as extra dimensions. Sometimes these dimensions are so small ( 10^-33 ) and compact ( ie curve in on themselves like a straw ) and two gentlemen named Kaluza and Klein managed to use this ffth compacted dimension to relate and unite Maxwell's theory of electomagnetism with Einstein's general relativity. Current string theories involve 10 or 11 dimensions to relate and unify all four known forces.

Don't take pieces of my reply and use them to incorrectly justify your ignorance. Things do fall into black holes and the evaporation time for black holes is possibly infinite for anything other than microscopic primordial black holes. Read some Hawking for a clear explanation of BH evaporation.

Take the case of two astronauts, one a distant observer to a black hole and the other unfortunate one falling into the black hole. There has been a suggestion that the distant observer never actually sees the unfortunate astronaut fall through the event horizon because time slows to zero and he will first see the evaporation of the black hole. As the unfortunate astronaut falls nearer the event horizon the distant observer will see time slow, but he will also see a stretching of the visible wavelengths, ie. his image of the infalling astronaut will become redder and redder until it goes to infrared, then microwaves, long radio waves and finally stretched to infinity at the event horizon. The light has lost all its energy and since you cannot destroy mass/energy, it must have been 'absorbed' by the black hole. So, yes, things actually do fall into a black hole, even to an outside observer. From the infalling astronauts point of view, the question is moot. Time does not slow down for him and he crosses the event horizon at which point the only thing in his future is the ( possible ) singularity. A black hole's evaporation is a quantum mechanical phenomena, having to do with virtual particle creation. The infalling astronaut and observer is a GR phenomena. Don't mix up the two. You are trying to use the two models at boundary ponts where one result may not agree with the other.

Owl, you're getting hung up on definitions and misunderstandings. One typical one that you posted: "So "closed" in this context has a special, counter- intuitive meaning. One usually thinks of closed as having an inside and an outside, and in the context of this thread, the space outside of a closed cosmos (I will not say "universe" in this context) has no end or boundary, so is therefore infinite. " No! The manifold is the cosmos, or universe, and it is closed or compact because it curves back on itself. It is not the inside ( or outside ) of the manifold. The inside or the outside, are inconsequential and have no meaning. Why are you trying to give them a meaning? You seem well read on the philosophical implications of the finite and infinite. Maybe you should read an elementary text on topology, or even a popularization. I seem to remember a book called The Poincaire Conjecture which did an adequate job of describing higher dimensional curved spaces. I think you would then comprehend the meaning of finite but unbounded manifolds.

The fact that you find something absurd, or that Hawking said it, is not a valid argument against the existence fo higher dimensional topology. Otherwise you could disprove all of Quantum Mechanics.

Owl, it seems like your objection to a finite but unbounded universe is due to the fact that there must still be an outside to it, since it needs to curve in on itself in another volume. Let me see if I can help clear up some confusion. If we again consider the two dimensional, positive curvature surface of a sphere, I think we can both agree that even though two dimensional, it must curve in a higher dimension ( the third ) to reconnect to itself. Similarily a three dimensional volume can also curve back in on itself and be bounded, but it must do so in a higher dimension, ie a fourth. Now don't confuse this fourth dimension with time, GR says 3-d space may curve back on itself, but not time. or as DrR like to say the foliation may fold back on itself to 'unbound' the universe. You prefer infinite space with no bounds, ie flat euclidian space. You are giving a significance to this higher dimension through which the 3-d space is curving where there is none. Assume the two dimensional, flat ( euclidian ) space with no bounds analogy that you seem to prefer to the curved sphere, in higher dimensions there is also an 'above' and 'below' the euclidian plane. You don't seem to have an objection to this, why do you have one with the outside and inside of a sphere. Again there is no significance to either. I don't know if I've been very clear and that's why DrR likes to use the appropriate language, mathematics. The point is that your main objection, that there is an outside, is always there, whether dealing with 'flat' space or positive or negative curvature space. This outside is only in a higher dimension though and as such, is inconsequential.

The horizon is the same for any kind of energy as it all travels at c, and the universe is expanding, ie at acertain distance all energies are red-shifted to infinite wavelength and zero energy. This makes the observable universe a finite size no matter which energy wavelength you use to 'observe'. The CMB permeates all of the universe, it doesn't exist only at the horizon. If you could measure the CMB right beside you, it would be 2.7 deg., not just at extreme extragalctic distances. I hope I'm not misunderstanding your original query. If I'm not you haven't grasped the significance and explanation for the CMB.

The cosmic microwave background radiation arises from the 'decoupling' of radiation from matter. It is the point in time ( approx 300000 yrs after big bang ) when the temperature of the universe had dropped enough for stable atoms to form, ie electrons captive to atoms of hydrogen, helium and lithium. Previous to this, electrons were free of the ionic plasma which composed the universe because as soon as an electron tried to attach to an ion, it would be knocked lose by an energetic photon, much like the interior of the sun, and so the universe was opaque. Neutrinos decoupled a lot earlier and since neutrinos are extremely difficult to detect, the red shifted neutrinos from the decoupling era would be impossible to detect. Gravitons would have decoupled at 10^-34 sec after the big bang, the end of quantum gravity, and we haven't even detected normal gravitons yet, never mind low energy ones from such an early time.

During QM's formative years there was some attempt at making it more common sensical. I believe it was originally de Broglie' s idea to introduce a pilot wave to particle motion in an effort to explain the differences between the double slit diffraction of an electron and the single slit diffraction, and how does a single electron know if the second slit is open or closed. This was during the time of Einstein's famous 'challenges' to Bohr's stochastic interpretation of QM. The pilot wave was later re-introduced by Bohom ( I don't know if that's the correct spelling ) in the 50s, but because of his history as a communist he was forced to leave the country to work in Brazil ( yes, that sort of thing did happen in the 50s ). The latest questioning of QMs interpretation was by Bell in the 80s who obtained a probability of an event happening more often than always ( non-sensical ). So maybe there are some hidden variables which haven't been considered in our formilation of QM and which may eventually move us away from a probabilistic interpretation towards a deterministic interpretation in which reality and causality are front and centre. Don't get me wrong, I've known QM for 30 yrs and as a theory it has made thousands if not millions of accurate predictions to as many decimal places as required, so it certainly does work. If it turns out to be the equivalent of Newton's gravitation, ie. not complete as compared to Einstein's gravitation, don't forget that we can still get to the moon using Newton's theory and its all we need for most problems.

You guys are confusing wave-particle duality with Quantum mechanics. Wave-particle duality has been around since the time of Newton and Hyugens, way before QM was a twinkle in Max Planck's eye. The model we use to explain phenomena and make predictions about a system is tailored to particular aspects of the system but not necessarily to all. As an example, try to explain the double slit diffraction experiment with the particle (photon ) model of light. Or try to explain the photoelectric effect with the EM wave model of light. You cannot do either. However particulate photons easily explain the photoelectric effect and diffraction is easily handled by the wave model. Use the model appropriate to the circumstances, since a photon, in reality, may be neither a wave or a particle ( it may be a certain harmonic of a vibration of a 10^-34m segment of space/time, otherwise known as a string, another model ).

String Junky is correct. The observable universe is limited by the fact that the speed of light is finite and that the universe is expanding. That is all. As we look farther and farther out we see objects receding faster and faster, ie their light is shifted more and more towards the red end of the spectrum. because the universal expansion is not constrained relativistically, at some distance, the recession speed is equal to c and the red shift is infinite, ie the wavelength of the light is infinite and so its energy is zero. That means we don't see it anymore. The observable universe isn't due to finite size or time of existence. Light takes 1000 yrs to reach the surface of the sun due to the absorption and re-radiation by solar plasma, it travels to the earth at speed c. Assume you are correct and the universe is finite, and bounded, what do you see when you get to the edge ??? What is the edge made of which keeps everything from spilling out ?? What happens if you take a step past the edge, where are you ?? When you can begin to answer questions like these, then a finite bounded universe can be considered, until then K.I.S.S. and assume the universe is finite but unbounded ( warps back onto itself ) or infinite

If space isn't infinite, in time or extent, how come it goes dark at night? http://en.wikipedia..../Olbers_paradox ?????? This should read If space IS infinite in time and extent, how come it goes dark at night? I don't think you understand Olber's paradox. Given the isotropy of space, the number of stars increases by the same factor that light intensity decreases, so that in any given direction, you would always see a light source, and so the night sky should be bright. Of course Olber lived long before Einstein and so he didn't take relativity into account. Even though the universe is infinite or at least unbounded, due to the finite speed of light, the OBSERVABLE universe can never be infinite. This fact, along with interstellar gas and other non-radiating dark matter, fully explain Olber's (non)paradox.

Star's lifetimes are inversely proportional to their temperatures. The hot ones live fast and die young ( just like people ). Blue giants have lifespans of 100s of million years. Our sun has a lifespan of 10 billion years. The much slower burning brown dwarfs ( Jupiter is an order of size magnitude removed from being a brown dwarf ) have even longer lifetimes, BUT no data indicates they are older than 13 billion years.

Einstein's field equations were first solved by Swartzchild for a 'simple' collapsing mass. They produce an event horizon and a point were the functional equations are not well behaved ( like a function with a discontinuity in its derivative ), but indicate a singularity ( dimensionless point mass/energy ). Later on a couple of Norwegian guys ( Nordstrum may be one) solved the equations for charged collapsing masses, as charge is conserved. An interesting effect is that there are two event horizons and adding charge beyond a certain amount will force the outer horizon inside the inner one, resulting in a bare singularity ( if they exist ). Now charged black holes will attract opposing charge and neutralise so the chance of finding one are slim. Later yet, Kerr, an Australian solved the equations for spinning collapsing mass and these produced a flattened event horizon with another one inside it. The singularity ( if it exists ) is indicated to be ring shaped. Adding more angular momentum again brings the outer horizoncloser to the inner one, and at the limiting rotation, it would cross inside and again produce a naked singularity ( if they exist ) This may be the only way to actually determine if singularities exist. You need to create a microscopic black hole, and add to its angular momentum until we can actually determine what's inside. An einstein -Rosen diagram is not very accurate ( and actually wrong in its representation ), but a Penrose diagram actually shows that you can pass through a rotating black hole without meeting the singularity, and pass into another part of our universe, another time of our universe, or another universe altogether ( all purely speculative ). You can call the inside of an event horizon space/time, but its not our space/time as the horizon separates it from ours. The horizon is, in effect, a one way door out of our universe. Even time is not our time as upon crossing the horizon there is only one future for you, the singularity ( if they exist ).

A good elementary book, by Kip Thorne called 'Black Holes, Einstein's outrageous legacy', may clarify some of your thinking. Incidentally, what are virtual photon pairs ??? A photon does not have an anti-particle for virtual pair creation ( by what another photon ???).