MigL

Sorry JustinW, I don't understand your question. Infinite and unbounded is obviously easy to understand, there is no boundary because it is infinite and goes on forever. Finite and unbounded means it is of a finite size but has no boundary, much like the world we live on you can walk along the surface in any direction and never reach an edge. The surface of the sphere would be the 2-dimensional analogue of 3-dimensional space. We obviously prefer unbounded systems because if we do consider a boundary, then we have to account for the other side of said boundary. The same is true for 'what was there before the big bang'. If we consider a boundary at t=0 then we have to explain what's on the 'other side' where none of our physics applies anymore, ie it cannot be explaned or even pondered. I prefer to think that at some point where t>0 ( possibly Planck time ) a steady condition existed which extends back in time ( or does time lose meaning at Plank time ) indefinitely. Since this whole thread is speculative, as has been mentioned, that is my opinion. I, of course, reserve the right to change my opinion as different views and new information are available to me ( never let it be said I'm not open minded ).

The fact that the fine structure constant is dimensionless just means that in the common expression of alpha the numerator e^2 is somehow related to the denominator hbar X c . Alpha is nothing more than the proportionality constant. The fact that we don't yet know how/why the two are related or that alpha is dimensionless does not imply anything about our scaling/size system.

Fermions are a class of particles which obey Fermi-Dirac statistics. As opposed to bosons which obey Bose-Einstein statistical rules. Nothing more, nothing less.

Whether finite or infinite is of no consequence, we do know that it cannot be bounded, Otherwise you need to account for the 'other' side of the boundary. As for THoR's opinions that the universe is finite and positively curved, since its predicted by Newtonian gravity and the outdated Freidman model, perhaps he should also consider using General Relativty and alternative flat ( Euclidian ) or negatively curved models which are by definition infinite in extent. 3D space or 4D space-time has an intrinsic curvature, ie. it is not embedded in a higher dimensional space. Certainly not the 10 or 11 dimensions of the totally separate Sstring theory where the extra 6 or 7 dimensions are compacted Calabi-Yau manifolds. Also when we speak of expansion we don't mean the boundaries are expanding, since THERE ARE NO BOUNDARIES,we mean separation between objects such as galaxies and galactic clusters is increasing.

Look THoR... You've made another uneducated, ignorant statement. That photons would, even for an oscillating universe, 'leak out' of the universe unless it was surrounded by black holes like a choccolate coating. So I've gotta ask, leak out into what ???? THERE IS NO OUTSIDE !! It is not cosmology which doesn't make sense. its your understanding of it. So, I repeat educate yourself, even with entry level popularizations like Hawking's A Brief History of Time, or any of Brian Green's books. Or feel free to ask some of us to clarify parts you don't understand. I can think of at least a dozen members of this forum who are very knowledgeable on the subject and who have helped me to a better understanding.

Typical airfoils are designed to give an aerodynamic centre at 1/4 chord. For supersonic flight, the aerodynamic centre shifts back to 1/2 chord due to lift ( pressure difference ) being caused more by shock wave interaction than air speed difference. There is some movement from these values at different angles of attack but, for purposes of stability ( pitch divergence ) it is designed to be as small as possible. The 90 deg. example given above is a bad example because turbulence and loss of lift ( stalling ) is reached at very small angles of attack. Even angles of 30 deg. can only be reached by re-energising the airflow over the wing using vortex generators like leading edge root extensions ( LERX) such as on the F-16, F18, MiG-29 and Su-27 families, or foreplanes/canards like EF-2000 or Rafale.

The poles on the event horizon of a black hole are no different than any other location on the event horizon. A non rotating black hole has no poles. and no radiation jets, A rotating one, on the other hand, conserves angular momentum, but any effects are by necessity, external to the event horizon and the polar radiation jets can be explaned as radiation from the accelerated, spirally infalling material By your reasoning a rotating and a nonrotating black hole behave differently with respect to entropy and the ingestion of mass/energy. You also don't need relativistic speeds for time dilation as the intense gravitational field will happily provide it ( depending on observational location just as with relativistic speeds ), even if you slowly lower yourself into the event horizon.

I must have missed the revolution in Physics since I was under the impression that we had a concrete answer to "what is gravity ?" Gravity is nothing more than the intrinsic curvature of space-time in response to a presence of mass/energy. The mass/energy then follows this intrinsic curvature in its motion along lines called geodesics, unless of course another force is acting on that mass/energy. Anything else implies action at a distance, which I and a lot of others are unconfortable with, and is also the case with Newton's gravity, and though Newton's gravity is fairly accurate ( it put people on the moon, did it not ? ), he never could explain what it was. We had to wait for Einstein's GR for an answer.

If a particle like a Tachyon existed, you'd be able to detect it BEFORE you figured out how to do it because it would travel backwards in time and violate causality.

The rotation you are referring to, Xittenn, is basically a force difference generated by the offsetting of the main wing and the tailplane/foreplane about the centre of gravity of the aircraft. It is due to aerodynamics but I wouldn't call it aerodynamics per se. I have seen the lift of an airfoil derived by rotation of the fluid about the airfoil,so I'm sure there was an angular momentum component but it has been many years and the math pretty tough going.

Noether's theorem states essentially that any symmetry leads directly to a conserved quantity. A thorough explanation/discussion is easily found on Wiki. Some examples... time => mass/energy translational => momentum rotational => angular momentum Those are the simple ones, but various gauge symmetries lead to other conserved quantities such as charge. and others. I'm at a loss to explain the connection to a bicycle, unless it pertains to angular momentum and associated increase in stability. Maybe if you post a link to the article in question ... ?

Owl, I don't mean to be rude by ignoring your post, but I'm done banging my head against the philosophical wall. Michel123456, you keep separating space-time coordinates with your arguments about different locations/same time and alternatively different times/same location. This makes the coordinates nonsensical, the event in space-time is defined by ALL 4 coordinates, not just the three spatial or just the time coordinate. You could make the same arguments about a straight vertical or horizontal line on an x-y graph ( multiple x values for a specific y value or alternatively multiple y values for a specific x value ). Unless you use ALL coordinates, you are not specifying a particular event, but just as in the x-y graph, a multitude ( infinite number ) of events.

Its not cosmology and particle physics that have stepped off the 'deep end'. It is people, like you, who don't have a very clear understanding of cosmological theory, that are acting like the sky is falling. It is NOT a finite amount of substance expanding into an unbounded volume. That is not part of any viable big bang model. I suggest you do some reading and inform yourself. Or ask certain members of this forum, a lot of them are willing to explain the details of cosmological theory to you, as long as you don't come with a lot of pre-conceived notions.

Draw a picture to scale and see just how much the moon's face is shielded by the earth. The angle to the target is a full 180 deg. minus the angle shielded by the earth. Most interplanetary debris is in the plane of the ecliptic, so that should be a good approximation.

Could be atomic. Degenerate just means ( in the case of white dwarfs ) that all lowest electron energy states are full and any further compression would violate Pauli's exclusion principle. Neutron degeneracy ( as in neutron stars ) would lose any semblance of atomicity since it would be composed mainly of neutrons, the electrons having been forced from their lowest energy states into the nucleus to combine with protons.

I believe regular uranium 238 is a neutron moderator and so any naturally occurring uranium on the earth or outer space ( meteorite ) would tend to suppress fission reactions. It is only enriched uranium 235 which supports and amplifies fission reactions. Weapons grade is, I believe 98% enriched, but that takes multiple stages of centrifuging and filtering uranium fluoride gas. Haven't looked this up in a while so my numbers may be wrong.

Look Lala, your own post state that it is charged particles that make up the solar wind, which are affec.ted by the earth's magnetic field ( north/south magnetic poles ), not light. Everyone else is being too polite to tell you, but can you read and understand your own posts ??? Get a clue before you get an opinion ( and an attitude too ).

Well Owl, let me try to explain along the same lines as the other posts on this topic. Your 'now' is the apex of a past light cone which extends doownward into the two bottom quadrants of a distance time graph. The slopes of the light cone are +/-186000 where the distance is in miles and the time is in seconds. At your 'now', the apx of the cone, the sun is outside your observable universe and will not enter it until the light cone passes through the distance of 93000000 miles which is in about 8 min. I don't know what being outside the observable universe means to you, but that sun will never have any effect on us in any way. We can only ever perceive the sun of 8 min ago. Oh, and don't let DrR catch you voicing your 'universal now' philosophy, or he'll be all over you again.

When discussing modern physical concepts, check your 'common sense' at the door. There is no 'common sense' in Quantum mechanics or General relativity. Common implies low speed, low energy and large size/distance. That solar flare which according to you is 'happening now', has absolutely no way of manifesting itself to us in the global now, because the global now does not exist. You can define it as 'happening now' all you want, but you have no way of ever detecting it or its effects for 8 min.

As DrR has stated several times, a large, galactic centre sized (>1000000 solar masses ) black hole would have very weak tidal ( differential gravity ) forces until well inside the event horizon. You wouldn't notice any difference upon crossing the event horizon until much later. A very small black hole or, for that matter even a neutron star, would have severe tidal forces ( even outside the event horizon of the small black hole ).

Ahh, but you did just go philosophical. You still cling to the unscientific concept of a global now. It is not just images that are conveyed at the speed of light, but all information. For all intents and purposes, the sun IS ( to us ) as we see it, not 8 minutes earlier. The only way to make ours and the sun's "now" somewhat coincide, is to move very close to it so that a loosely defined local now can apply to both.

The primordial fast-burning star which gave rise to 'our' heavy elements was formed at a time when hydrogen clouds were more abundant and vast than they are today, much like the difference between outer spiral arms and central regions. I believe it is the nova/supernova shock wave which causes the compression waves in surrounding interstellar gas clouds, and is the cause of the initial 'seeding' of new stars, before gravity completes the task.

Well atmospheric drag was my thinking also but the Roche limit given by D.H. is well beyond the atmosphere. I still don't uderstand why the rings of Saturn have such a well defined inner and outer orbit. They are attributed to a fragmenting satellite, but their density is almost constant from inner to outer circumference, with none of the decrease in density and straggler particles you would expect from a chaotic event, almost as if they had been swept clean by some effect.

I'm sure DrR is just trying to get you going by being very picky with the definition of solution. I'm sure he's more familiar than most with perturbation and approximate methods. There may be no exact solution to many body problems, but given enough computer time, you can get as close ( decimal places ) as you wish. I, myself have not done any >2 body gravitational approximations. But I'm sure anyone who'se studied physics will have solved the Helium atom using these methods. At the time I was in school we used Hollerith punch cards and programmed in Fortran IV. Several hours later you'd have your stack of fanfold results which then needed debugging. Ah, the convenience of modern computers.

Appreciate your imput Janus. I guess if you are also of the opinion that none of the disintgrating moon's pieces will impact the Earth, then my thinking must be at fault and I obviously need to re-examine the situation.