a_lexios

My understanding is that, in order for us to be able to wrap our minds around the idea of the "Big Bang" (or any other pertinent scientific theory) we first have to establish what a THEORY is: I am quoting from Wikipedia: "A scientific theory is a WELL-SUBSTANTIATED EXPLANATION of some aspect of the natural world, based on knowledge that has been repeatedly CONFIRMED through observation and experimentation. Scientists create scientific theories from HYPOTHESES that have been corroborated through the scientific method, and then gather EVIDENCE to TEST their accuracy." Also, philosopher of science Karl Popper has emphasized that “a good theory is characterized by the fact that it makes a number of PREDICTIONS that could in principle be DISPROVED or FALSIFIED by OBSERVATION. Each time NEW experiments are observed to AGREE with the predictions the theory SURVIVES, and our confidence in it is INCREASED; but if ever a NEW observation is found to DISAGREE, we have to ABANDON or MODIFY the theory.” Now, let's try to make a projection of this definition to a theory like the Big Bang: The Big Bang, is merely a model we have created in order to be able to explain what is happening in the universe - a hypothesis; and for as long as that hypothesis agrees with the observational data it will stand as a valid explanation of the nature and origins of our cosmos... Until… Stephen Hawkins, in his book 'A BRIEF HISTORY OF TIME' sums it all up for us: [ "This is just a MODEL of the universe, or a restricted part of it, and a set of rules that RELATE quantities in the MODEL, (***My Note: in other words the solutions to the mathematical equations comprising the model) to OBSERVATIONS that we make. IT EXISTS ONLY IN OUR MINDS AND DOES NOT HAVE ANY OTHER REALITY - WHATEVER THAT MIGHT MEAN" ] I do hope that the above have slightly assisted in clarifying this matter, a little bit.

Well, please allow me to put that part of the statement in quotes; your question will immediately answer itself: [ All of the stars in our universe are "alive". ]

**P.S: And if we want to be 100% on point; actually there is a force which could really inhibit the gravitational collapse, once it has begun, and even if we do not have any sufficient thermal pressure to counter the gravitational pull: Degeneracy pressure. (More on that http://en.wikipedia.org/wiki/Electron_degeneracy_pressure )

All of the stars in our universe are alive. Their life is bound to the proper beating of their hearts, just like humans and their life's "juice" is the power of nuclear fusion that takes place in their core converting hydrogen to helium - ( Proton fusion, *protons are hydrogen nuclei.) Protons repel each other normally because of their positive charge, but in temperatures exceeding 10.000.000 K, the particles embed so much kinetic energy that the electrostatic repulsion can be overcome. Once in close range the strong nuclear force takes over, pulling the protons together and initiating proton-proton fusion (P-P fusion). One of the protons changes into a neutron, and the resultant nucleus is called a deuteron (one proton and one neutron). The excess positive charge is expelled in the form of a positron (e+ , antimatter for electron) which collides with any close-by electron and annihilate each other. The excess momentum is expelled in the form of a neutrino. The p-p fusion is a highly exothermic reaction thus creating an outward flow of energy. This outward "thermal pressure" balances the gravitational pull of the mass of the star that tends to make it collapse on itself and there we have it: A very active balance of opposing forces that keeps our stars alive and shining until interrupted. The so-called hydro-static equilibrium... Now, for as long as a given star has enough fuel (hydrogen) to keep it's thermal pressure in the level required to balance it's gravitational pull, the equilibrium is preserved. At some point when the core runs out of hydrogen fuel, it starts contracting under the crushing force of gravity and depending on the overall mass of the progenitor star, we have various resulting formations - from white dwarfs to black holes.

My understanding -please correct me if I am wrong- is that the definition of a black hole is strictly mathematical. A black hole is just the mathematical solution to formulas derived from General Relativity.That is the reason why their existence was factually determined a long time after their "discovery" as series of numbers in a piece of paper...(Exploiting the microlensing effect is currently one of the ways to detect the 'footprints' of a black hole) The simplest black holes are spherically symmetric.(Non-rotating ones). For any spherically symmetric object one may define an imaginary sphere around it of radius rs = 2GM/c^2, where G is the universal gravitational constant, M the mass of the object and c the speed of light in vacuum. (Very peculiar, even though this formula is deriving from General Relativity, aren't you recognizing a pattern fitting right into Newtonian laws....?). This formula tells us that the radius of the black hole is directly proportional to the mass of a black hole, i.e. the more massive the black hole the larger the radius. The rs factor is called the Schwarzchild radius. If the surface of ANY object is at a radius less than it's rs, then this imaginary sphere is called the event horizon and the object is called a black hole. Note that if the radius of the surface of ANY object is larger than rs then there is no event horizon and the object is not a black hole but something else instead... Now as far as the observable universe is concerned: At first, let us see what does "observing" or "seeing", really entails..? Initially, there has to be light present (photons that is...) Again -from what I've read- when light (photons) enter the eye, they reach the retina, which is the light-sensing structure of the eye, and by triggering it (coming in contact with the eye's photosensitive part) we are enabled to perceive our cosmos through the miracle of vision, right...? Ok, now taking in consideration the fact that light travels at 300,000 kilometers per second for all observers (according to our predominant current theories) we can conclude that if the Universe were only one second old, an observer would not be able to see things which are more than 300,000 kilometers away because there would not have been sufficient time for this light to propagate that far... So at each point in the history of our Universe there a distinct radius (a horizon) which is self-determined -pretty much- by the distance that light could have traveled since the birth of our Universe....As our Universe ages, the horizon expands outwards because there is more time for light to travel & on top of that our Universe itself is expanding with a slightly accelerating rate... Logic states that if we cannot 'see' beyond the 'horizon', then neither can we be affected by any physical effect from beyond that horizon. Regions of space in the Universe which are separated in distance by more than the horizon, simply do not 'know' about each other, and cannot influence each other's physical conditions.... Therefore we choose to exclude those hypothetical 'parts' of our Universe (...?...or someone else's Universe) from our calculations and models and just say that we just don't care ! (very-very simplified...) As a new member of your community, I hope I have slightly contributed to this thread with my post. Happy to be here.