MigL

Without getting into too much detail ( because I'd be in over my head ), the string vibration is just like any oscillation, the requency and amplitude determine the energy and the energy is related to the mass. The problem is that extremely small mass particles like neutrinos or electrons even, are predicted to have zero mass by the theory. And while this may be to a good approximation, it is definitely not accurate. The same is true of massive particles, the masses are only approximate or rounded off. Anyone having a more detailed understanding of string theory mass predictions is welcome to correct me or add to my simple explanation. I first read about this problem with masses in a popularization ( Brian Green, not Elegant Universe, but his subsequent ), so I don't have a good understanding of it myself.

Sorry my mistake. I remembered a value of about 47GLY but assumed that to be a diameter, so I used a value of 23-24GLY for the radius. You guys are right it should be the higher value for observable universe radius. I'm no expert in the use of light cones, but are they the right tool to use in this case ?? There is a relative acceleration and speed difference between our galaxy and a galaxy at the edge of our observable universe, but it is due to an expansion of the intervening space, not an actual acceleration or velocity. How does that affect their respective light cones ? And what about galaxies that lie just outside the observable universe ? Relative to us, they are moving faster than c, how would you represent this with a light cone ?

You guys have drawn a lot of pretty pictures but you haven't proved what I said to be wrong. So I'll repeat... Starting at a certain distance from us ( 23-24 billion light years comes to mind ) everything in the universe is receding from us at light speed or greater because the separation between our galaxies is growing at or faster than the speed of light. The light we would see from these galaxies is red-shifted to infinity ( infinite wavelength, zero frequency, ie no energy left ), so they are in effect invisible to us. This is what defines the observable universe that is causally connected, any galaxy receding at c or greater is causally disconnected and so has no effect on us. Your premise that there are galaxies at intermediate distances which can be affected by the causally disconnected galaxies and then pass the effect on to us does not make sense because light speed is finite and the distances cumulative. They still add up to the same total distance and the intervening space still expands by the same amount. There is a limit to the causally connected observable universe, and it is much smaller than the total universe.

AS DrR has previously stated, any quantum field theory, by necessity, manifests force carrier bosons such as photons for QED and gluons for QCD. The fact that no quantum field theory of gravity currently exists just means we cannot say wether gravitons exist or do not exist, yet.

You are missing one important point, michel123456. The only things in the universe that can affect us or be affected by us ( not quite but close enough ) are the things we can see. Not only light but all forces and information propagate at c. That light cone you posted and seem disappointed with is the observable universe, anything outside it would make no difference even if it ceased to exist.

Not that I believe in ID,but Appolinaria is correct. We have historically called whatever is beyond our comprehension, either religion or magic. Only after having understood a phenomenon, do we then classify it as science. Religion may, at some point, or may not be physically measured or observed.

Not quite the same thing, Mystery111. The dark age happened after radiation decoupled from matter. At roughly 4000 deg the universe was no longer filled with a plasma where electrons had too much energy to stick to nucleii ( what we now see as the CMB ), but by stable Hydrogen and Helium atoms ( with few others ). It naturally took some time for these atoms to come together to form suns that radiate energy, and so, there was a period of darkness. The event you are considering would have happened much earlier, before the inflationary period.

Ah, so 3x10^80 is a guesstimate for the total number of particles in the universe. But what about photons ( and other bosons ) which saturate all space and make up the CMB, are they included in this rough calculation? And yes virtual particles are a manifestation of vacuum energy.

Trying to keep things as simple as possible... A quantum theory of gravity is not re-normalisable because the force carrier particles of the quantum field as well as the elementary particles they act on are considered to be point particles. The infinities that arise in the calculations cannot be re-normalised away like in QCD and QED. So someone ( cannot remember who at the moment ) decided to use a pre-existing theory ( being used for something else ), and consider all elementary particles such as electrons and quarks, and bosons like photons, gluons and gravitons, to be composed of open or closed loops of vibrating space/time at Planck scale size . Different harmonics of the vibrations giving rise to different masses, spins and charges of particles. The masses that string theories predict for particles are not very accurate, but all ( there are many ) predict a spin 2 boson which turns out to be the graviton. That is one of the biggest attractions of string theory, the fact that it predicts the graviton and so points to a quantum field theory of gravity. There have been several iterations of string theory, the latest being Witten's M-theory, where all force carrying bosons are open ended and the ends anchored to branes except for gravity, where the graviton is a close loop string and free to pass between branes ( which leads to some complicated results for gravity and its inverse square law ). String theory has however, made no veryfiable predictions and is at the moment, just a very elegant mathematical theory in search of a universe to describe. As for the vacuum containing strings, what Mystery111 may have been referring to are virtual particles which saturate space, so yes they would be present in a vacuum, but they only make up point particles. That being said our understanding of vacuum energy leaves a lot to be desired as our estimates are 10^100 times higher than expected. As for the elements, others have already explaned. I would only add that only certain numbers of nucleons lead to stable configurations,I'm not sure if QCD explains this as I haven't read up on it since my nuclear physics class in the late 70s.

If I may add something to this discussion. I do believe time has an 'arrow' but I don't think it is due strictly to entropy. Time is different from the spatial dimensions. For the spatial dimensions, what happens at a certain co-ordinate can affect another co-ordinate, no matter where it is. But for time, only what happens in the past can have an effect on the present or the future. The future cannot affect the present or past ( ie. we remember past events but not future ones ). It is this causality effect which determines the so called arrow of time. I believe it was Michel123456 who previously stated that the two choices are either " we are translating in time or time is flowing over us". I believe a third choice would be that, locally anyway, time advances and carries the local now along with it. The local now being represented by the Einstein-Rosen embedding diagram. I am definitely not saying there is a global now, just to be clear, and even the local now is very loosely defined for clarity and simplicity. As time, or the local now moves foreward, another layer or foliation is added and the previous ones become past. These underlying layers can still affect the top-most layer, the present, and so we can remember past events, and there are fossil records and history in general.

Excuse-me but shouldn't you be lecturing him about an open mind ?? I'm not the one who screamed at him " TIME DOESN'T HAVE A FLOW!!!!!! " And if you're unhappy with time flow, then it progresses, advances, moves foreward,etc. Don't make me get out my dictionary. The point I'm making is that everything is carried along with it. We do not move along a'yardstick' of time since then there would be no repercussions to moving faster or slower or even backwards along this 'yardstick'. Causality has to be preserved or else the universe stops making sense.

Yes, Mystery111, you have said 'time doesn't have a flow' many times now. But, I don't know , what's the minimum number of times you need to say it before it automatically becomes correct ??? We are having a discussion, an exchange of ideas if you will. The ideas I present are based on my limited knowledge, and are of course, opinions or best educated guesses ( based on GR ). Of course I cannot absolutely prove the assertions I've made, but at least I realise that. I also realise you cannot prove the assertions you've made, yet you claim that, since you've repeated them several times, they must be true. An open mind is a terrible thing to be missing. It cannot just be replaced by a donkey named Pompous.

I believe the phrase should read, certain types of subatomic particles can be treated mathematically AS IF they were travelling backwards through time. I don't think Feynman ever suggested that anti-particles really travel bacwards in time, nor that tachyons actually exist ( but, hey, stranger things have been discovered to happen ).

I'm not suggesting time flows through us. Proper time marches on irrespective of observers. We do not get to choose the speed and direction of our motion through time as we do with tthe three spatial dimensions, rather we get dragged along with the flow of time, although the local flow can be modified somewhat by relativistic speeds and gravitational wells ( possibly even stopped such as at the event horizon of a black hole, ie the moving rubber sheet is 'pinned' at that point and stretches as the horizon stops moving through time. Although even to a non-local observer, Hawking radiation implies something is happening at the event horizon and so, even by your definition of time, it is actually still moving foreward ). By the way, I'm not implying a single rubber sheet, but a multitude, one following another, and moving at the speed of proper time, such that the two dimensional foliations add up to form a 3D solid pillar, or in our real world case a 4D 'pillar' or shape of some kind. But certainly not a separate universe in the co-ordinate just vacated and moved into the past, as you seem to suggest in another thread.

Sure and there are many more theories which have the three spatial and time dimensions as the left-over low energy dimensions. All the others curl up at low energies and disappear to below Planck scale. It is only at high energy ( Planck scale energy ) that these other dimensions , 10, 11, 26 or however many, manifest themselves. Think of a two dimensional analogy of space; a rubber sheet with depressions where high mass-energu density is located. Move this sheet upwards at a rate of one second per second through the 'time dimension'. That is how time 'drags' us along as it moves in one direction only, towards the future. This is in effect an Einstein-Rosen embedding diagram moving in time. But keep in mind that the depressions in the sheet will grow and shrink depending on various time dilation effects.

Really ??? "In a universe devoid of matter, where are your clocks so you can make measurements?" Let's take it one step farther. In a universe devoid of matter, where are your yardsticks so you can measure the 3 spatial dimensions ? Or are you saying they are fictitious too ? If you have no standard to measure them against, a meter might as well be 1000000 meters. Time is not like the other dimensions through which we are free to move, rather we are carried along with time as it moves.

There is no such thing as the 'philosophy of science'. There is only science, and what you are going on about is philosphy, a totally different beast. As IM Egdall has explaned, science poses a theory, makes predictions, and is then tested for validity. If the predictions don't pan out the theory is untrue or unfinished. I and countless others believe SR and GR have been extensively tested and verified. There is no global NOW !! Again, as IM Egdall has stated, why don't you investigate what predictions the notion of a global NOW would imply, and see if any of them hold up logically or experimentally, and wether they contradict known-true or estabilished facts and phenomena.

The inflation model makes use of pressure as the driving force behind the 'negative' gravity, but not in the way you would think. We all know pressure is a form of energy and so, a compressed spring will weigh a miniscule amount more than a relaxed spring. In effect this pressure contributes to the stress-energy tensor, increases the local space-time curvature and increases the gravitational force felt in its vicinity. We can then assume the opposite to be also true. If the pressure is decreased so is the stress-energy tensor, the space-time curvature and the gravitational force. In fact, if it is decreased enough, it actually can become negative and we would have repulsive gravity. In the inflationary model the energy of the vacuum falls to a non-zero state, before slowly dropping from this false state to the real zero energy state. It is while the universe is hung up in this false zero energy state that it can be shown to have a negative pressure, and through the method outlined above, this negative pressure overcomes the gravitational attraction and results in repulsive gravitation. This leads to the inflationary period, where for the brief time that it takes for the universe to fall from the false, non-zero vacuum energy to the real zero level energy, the universe is believed to have expanded by 10^30 to 10^100 in size.

No confusion on my part, but maybe a vague answer. I said + or - indicating direction of the gravitational field. We are discussing wether antimatter's gravity field has any reason to be reversed, are we not ? What exactly does EM charge have to do with it and ehy would you think I was referring to it ? Also there is no such thing as negative energy, it is merely a convention for energy conservation 'book-keeping', just like the + or - convention indicating force direction.

+ or - indicating direction.

Maybe I'm being too simplistic, But a single photon will, under the right circumstances, create an electron- positron pair, ie matter and antimatter. Now, the original photon has the same gravitational force and sign as an equivalent amount of mass, the electron has the same sign and gravitational force for its mass, so why would the gravitational field change polarity for the positron ? And why would it flip back again when the electron-positron pair annihilate ? Obviously it doesn't. The gravitational field is related to the mass and energy of the particle ( more or less ) and this relationship works the same for matter and antimatter. As to rigorous proof and papers which can be quoted, I don't know of any either.

What would it be rotating relative to ?? See Newton's and Mach's 'bucket of water' thought experiment. And, does rotation not imply a centre to the universe ? Or, at the very least, does rotation of the universe imply a 'preferred' direction, thereby undermining symmetry and momentum conservation laws ??

If you think about causal disconnection, you realise that as you 'wind the film backwards' in time the disconnection becomes larger, not smaller. So without inflation, there would never have been a time where causal connectivity ensured isotropy. But maybe what DrR means is that all parts and times of the universe are causally connected to the Big Bang event, although all parts and times of the universe are no longer ( post inflation ) causally connected to each other.

Well I hate to disagree with the good Doctor, but its my understanding that the post-inflation universe has causally disconnected observable universes, which, because of the finite speed of light, cannot freely pass information to each other. Guth's inflation then, adds a pre-inflation period where the distances between regions were small enough for light to reach all parts and therefore insure isotropy.

Wow. That is so far off the mark, I don't know where to start. I guess i should recommend you read agood book explaning the BB theory.