Hey Boyos, it's shillelagh law here right? I thought this was supposed to be orderly and civil venue. You are acting like a couple of unruly Kerrymen at the horse fair. Maybe, just possibly a thing such as time could be viewed in a way that you are both correct but determined to disagree. So to show how little dignity I have, I'll throw in my two cents and let you do what a self-respecting Kerryman would do, call a truce, join up and direct you ire at me and team up and give me what for. Of course time is an abstraction. It must be until you find a way to bottle some up and take to the lab for manipulation and experiment. We measure it by convention that we a priori agree to agree on. But it is also a real facet of our physical world and universe. It can't be removed from any meaningful measure fundamental physics. You can not describe motion with out some version of time to relate duration, causality, or change of any physical condition. You can not designate a complete location without a time component. So since you can't bottle it up to remove to the lab, it will remain an abstract reality. Don't hold me to this, I got it 2nd hand, but I think it comes from Sean Carroll. Time is: 1) A co-ordinate to specify a place in spacetime. (Left-right, up-down, in-out AND when to indicate causality.) 2) A measure of duration between two events, or the duration of an event. (The tick of a clock, a heartbeat, or the decay of a particle, etc,,,, 3) Something that all the universe moves through (or flows past depending on your vantage point) with only a single direction (entropy). I think you are both correct, but if you enjoy whacking each other with philosophical shillelaghs, have at it.
This is wrong. Gravitational time dilation is more or less associated with the \(g_{tt}\) metric component. (If there's a more formal definition of what gravitational time dilation is and how it should be predicted from the theory, I've certainly never seen it.) The metric components \(g_{\mu\nu}\) are explicitly coordinate dependent. This is one of the absolute most basic things to understand about general relativity. I've already given a well-known example where this is clearly visible: accelerating reference frames. The gravitational time dilation factor from the perspective of an observer in SR can be constant (one), finite, infinite, or even negative depending on whether or not the observer is accelerating, and at what rate. You never address this. You are confusing gravitational time dilation (a coordinate-dependent quantity) with two different quantities that are actually observable: 1) The apparent slowing of one clock as seen by a distant observer looking at it through a telescope (this is the relative Doppler shift factor). 2) The accumulated times shown on two clocks when they're brought side-by-side together for comparison. Simultaneity is only well defined for two events at the same place and at the same time in relativity, and the times shown on two clocks at the same place is the only invariant comparison that can be made. These are what are actually measured in experiments. As far as what the theory has to say about them, the metric in Schwarzschild coordinates has the nice feature that it's static. This makes it very convenient for working out the Doppler shifts and accumulated times between two clocks if they spend a substantial amount of time at fixed Schwarzschild radii. This doesn't generalise, though. There's a standard way of defining an accelerating observer's reference frame, which I described in some detail in a [POST=3051585]previous post[/POST]. (It's the same thing as the Rindler coordinate system, except that I put the accelerating observer at \(x \,=\, 0\)). In units where \(c \,=\, 1\), the proper time element in the accelerating coordinate system works out to be \(\mathrm{d}\tau^{2} \,=\, (1 \,+\, ax)^{2} \, \mathrm{d}t^{2} \,-\, \mathrm{d}x^{2}\), where \(a\) is the acceleration felt by the observer at \(x \,=\, 0\). For a clock at some fixed \(x\) coordinate, you find from this that the accumulated proper and coordinate times are related by \(\mathrm{d}\tau \,=\, (1 \,+\, ax) \, \mathrm{d}t \,.\) To relate this to something you might have seen before, you might like to compare this with the analogous formula for gravitational time dilation in a weak gravitational field: \(\mathrm{d}\tau \,=\, (1 \,+\, \Phi/c^{2}) \, \mathrm{d}t\), where the Newtonian gravitational potential \(\Phi \,\approx\, gh\) if the field is roughly constant. Obviously, \(1 \,+\, ax\) becomes zero (infinite gravitational time dilation) at the location \(x \,=\, -\,1/a\), and negative (so negative time dilation) for \(x \,<\, -\,1/a\). This is easy to understand as a consequence of the relativity of simultaneity effect. As you hopefully already know, if two events (say two explosions called A and B) occur with a spacelike separation in space and time, then their order (which happens first) is frame-dependent. There are reference frames in which A happens before B, there are reference frames in which they happen at the same time, and there are reference frames in which B happens before A. So if an explosion happened in space 10 light years away and 1 second ago from your point of view, you could quickly accelerate to a different velocity, and the explosion could still be 1 second in your future in your new frame. Negative gravitational time dilation is just this expressed during the period of acceleration. If you're familiar with Minkowski diagrams, it's also easy to see what's happening. Borrowing Wikipedia's diagram for the Rindler coordinate chart, the situation looks like this: Please Register or Log in to view the hidden image! Basically, things work out in such a way that the accelerating observer's \(x\) axis (represented by the \(t \,=\, 0,\,1,\,2,\,\ldots\)) always crosses the origin of the Minkowski diagram, and it starts to sweep backward on the left-hand side as you trace along the accelerating observer's worldline. Of course, none of this is directly measurable, and the remedy is simple: you recognise it as a harmless artefact of defining accelerating reference frames in this particular way. The moral I'd encourage you to take from this is that even seemingly "natural" and obvious coordinate systems can exhibit some very strange behaviour, without it actually representing anything physical. That's why you should take it with a grain of salt when the Schwarzschild metric includes things like infinite gravitational time dilation and zero coordinate speed of light: accelerating frames also exhibit these features, and I'm sure you'd agree it doesn't really mean anything in that case. No, that's not what the spacetime interval is or why it's invariant. The spacetime interval is a quantity that's measurable in the following sense: if you have two infinitesimally spacelike separated events located at coordinates \(x^{\mu}\) and \(x^{\mu} \,+\, \mathrm{d}x^{\mu}\), then there's a locally inertial reference frame in which they occur simultaneously. In that reference frame, the spacetime interval is the same thing as the distance between the events that you'd measure using a ruler. The way to see this is to notice that in a locally inertial reference frame, "simultaneous" means \(\mathrm{d}t \,=\, 0\), in which case the spacetime interval just reduces to Pythagoras' theorem: \(\mathrm{d}s^{2} \,=\, \mathrm{d}x^{2} \,+\, \mathrm{d}y^{2} \,+\, \mathrm{d}z^{2}\). I'm already familiar with your views on time travel from previous threads. Basically you're saying time travel is impossible because it would contradict what you believe about time. I don't think that's a good argument. You're not considering the possibility that your beliefs about time might turn out to be wrong. There's nothing wrong with saying there's no evidence for time travel, or that there's no theoretical basis for it in mainstream physics, or that there are paradoxes that seem to make the idea problematic. That's fine. Time travel is consigned to our science fiction stories at the moment, and there's good reason to believe it will stay that way. But you seem to want to ban even "what if" speculation on the subject, and I don't agree with that attitude. You also neglected to mention the only two modes of time travel I'd actually be torn to make a choice between: flying DeLorean vs. 1960s-style blue police box.
Hi przyk. Please Register or Log in to view the hidden image! I read your above post. Are you essentially saying that the actual gravity well effects at various altitudes in that gravity well are 'abstract things' and not locally absolute effects on the clock effected? Are you implying that anyone can 'look' at some clock at different altitudes and call the actual absolute effect on CUMULATIVE TICK COUNTS associated with each altitude is somehow still a RELATIVE and not empirically absolute physical phenomenon in its own right irrespective of remote observers of other co-ordinate analytical constructs used to describe the resultant differences in absolute respective cumulative tick counts? Just asking for further/specific clarification so I don't misunderstand you or the points at issue between you and Farsight. Thanks. Please Register or Log in to view the hidden image!
I'll settle for that.....But I must also comment that just because we are unable to see, touch, smell anything, does not mean it's not real.
Either way though, whether one views it as an abstraction or real, does not Affect the validity of GR.
If that is case, and I PERSONALLY agree with you, I feel at some level it is a physical THING,,,,, the fact is until we can see, touch, or smell it, it will always be an abstraction,,,, a useful one, even a necessary one,,,,, one that is an integral component of reality, but until we can isolate it and determine what it is MADE of, it will remain, by definition an abstraction.
Anyway, whatever way one chooses to look at it, [I see it as real] it certainly does not invalidate or change GR one bit. GR remains as solid as it ever was.
The debate in this thread re BH's EH's and GR have been waylaid misconstrued, misinterpreted by at least one contributor. The reality or otherwise of time or any other cosmological construct, does not invalidate GR or BH's, as some seem to suggest. I see space, time, space/time, all as real as BH's their EH's. So far in this thread, we have hard nose claims against the accepted mainstream for [1] BH's do not exist [2] EH's do not exist, [3] Time is seen to stop at the EH, [4] Time is seen to stop but the body and/or clock still move across the EH [5] The BH is really a Dark Star [6]FoR's are invalid or don't exist... Apologies if in my simplistic brief, I have missed any other alternative stuff. All these unproven, unreviewed claims are at odds with the accepted mainstream version held by most others here including myself. These include the following applications... [1] BH's and EH's almost certainly do exist as predicted by GR, [2] FoR's are all valid and as real as each other [3] All remote FoR's will never see any one approaching an EH, to actually cross that EH [4] What is seen is time dilation, red shifting to infinity but never quite crossing the EH, rather just fading from view due to the red shifting to infinity, [5] From a local FoR, anyone approaching and crossing the EH, will see or feel nothing out of the ordinary...no slowing of time, no stopping of time, no time dilation, just possibly tidal gravity effects depending on the size of the BH...[6] The standard Schwarzchild BH is no more then critically curved space/time with nothing beteen the EH and the point Singularity that resides at the center and is where the mass is. [7] GR makes firm predictions about the Schwarzchild limit and compulsory collapse once that has been reached or surpassed....[8] GR fails completely about the true nature of the Singularity. Herein lies our quandary... [1]ALL those making the alternative models, all claim them to be superior in reality, to what the reality is, with the incumbent model.... [2]None of the alternative models have undergone peer review...[3] All claim to know better then 100 years of research and study that have gone before them... That's it, put nice and simply. Now I know having consistently raised the issue of the legitimate scientific methodology of peer review, I will have profusely offended some.....Why wouldn't it, afterall they have not subjected there model to it. A guilt complex I would Imagine. And claims that some are still working on their model is another cop out. I mean how can anyone claim superiority of their model over the incumbent model on one hand, and then claim their model is incomplete on the other hand when peer review is raised. Now we'll see how many of our friends will address all I have pointed out, point by point.....Or probably we may see the usual personal vitriol and passive aggressive attack on me that has been par for the course over the last few days. I expect the latter, because what I have claimed to be the mainstream position, has not been invalidated or falsified by anyone as yet from the alternative side. In fact GR, and BH's and their EH's are on reasonably concrete grounds.
Gasp! You are lost in math, przyk. Gravitational time dilation is an observable effect, and I repeat: clocks go slower when they're lower. And these clocks determine coordinates. They aren't dependent upon them! Because an accelerating observer doesn't have anything to do with gravitational time dilation. I'm not confusing anything przyk. But two NIST optical clocks lose synchronisation when one is 30cm above the other. It isn't negative gravitational time dilation. You have mixed SR and GR, and used an accelerating observer to try to justify negative gravitational time dilation. Clocks run slower when they're lower przyk. Not backward. And moving fast doesn't change that. Przyk, a coordinate system is an abstract thing. So is a reference frame. Clocks going slower when they're lower isn't. All observers agree that clocks go slower when they're lower. No observer thinks they don't. Like I said, a light-path length. I referred to Pythagoras's theorem in the time travel is science fiction thread. I explained that time travel is impossible because clocks clock up motion. But if you so wish to cling to science-fiction fantasy that you won't discuss the subject, I can only shrug. Whatever.
Black holes are the telescope viewing "deep space" (the edge of the universe.) I do not believe in them OR evolution. Please Register or Log in to view the hidden image!
No, I'm not. I just understand it a lot better than you, and I'm seeing all the subtleties and nuances in how GR is formulated that you could never see. And I repeat: you are oversimplyfing both what general relativity has to say about the situation and what experiments actually show. Farsight, it is fundamentally meaningless to make an instantaneous comparison between two clocks in different locations. It would require instantaneous, faster-than-light communication to do that, and that isn't possible in the real world. Even 30cm isn't zero. This is patently wrong. Evidently you don't understand the equivalence principle. Under what circumstances? Fixed altitude? Inertial? Accelerating into space? How many of these different situations have actually been tested? SR is a special case of GR. Yes, as I've told you myself many times before. No. Not a light-path length. Spatial distance. You're still having trouble with this whole "strawman" thing. I'm not clinging onto anything. I'm allowed to decide not to hold an opinion on a subject, you know.
No you don't. It's not you starting threads explaining it step by step. It's you ducking those threads, in case you get painted into a corner. No it isn't fundamentally meaningless. If those clocks ran at the same rate your pencil wouldn't fall down. Grrrr. How dare you. The principle of equivalence applies to an infinitesimal region. That means it applies to a region of zero extent. Which means that actually, it doesn't apply. It was an enabling principle, that's all. See http://arxiv.org/abs/physics/0204044 and note the quote by Synge: "...The Principle of Equivalence performed the essential office of midwife at the birth of general relativity, but, as Einstein remarked, the infant would never have gone beyond its long clothes had it not been for Minkowski’s concept [of space-time geometry]. I suggest that the midwife be buried with appropriate honours..." In the lab. That's all you need to know. An optical clock goes slower when it's lower. And there ain't no time flowing through it. You're evading the step-by-step simple explanations because you're afraid of being painted into a corner and having to concede to me on all this. Now come on, pull your finger out. Time Travel is Science Fiction and The Speed of Light is Not Constant are awaiting your perusal and agreement.
:roflmao: Oh, the Irony of it all! And here I am being criticised by other alternative nuts for not knowing the maths! And just parroting what I read. Standing on the shoulders of giants and all that. Please Register or Log in to view the hidden image! But I did need the good old fashion belly laugh. :roflmao: Gravitational time dilation is not seen within ones own FoR, and neither is any of the other effects of relativity. Clocks detail the passage of time and in each FoR, that detail can be different, determined by speed and gravity potential....But all FoR's are just as valid as each other.....That's why we call it relativity. One thing you will have in your favour Farsight.... You will go to your grave, being the only human being to know the whole reality and meaning of SR/GR Keep up with the happy delusions!!!
Just to add something to my rather lengthy post [well lengthy for me anyway...I generally rather stick to pertinent legitimate information] I will probably be castigated in my above criticism of the anti mainstream model/s, for not referring to the mathematical side of the models. Well people should know by now, I'm not that proficient in the maths [as Important as it is] suffice to say that the alternative maths has been debunked as error ridden way back in the thread by our on line professionals..brucep, Walter, Russell [apologies for those I have missed] and a few others that have done that job admirabley. All I have done, is touched on the other relevant areas that show the confusion, paranoia, and vitriol some of the anti brigade exhibit when confronted with the reality of the situation.
So you have a keyboard and an internet connection. That requires a fairly modest amount of money, Farsight, and not actual talent. No. I just know from experience you're a complete waste of time. You will repeat, over and over again, the same story no matter how many times it's pointed out to you that you clearly have no understanding of what you're talking about. You can't "lose" a debate only because you don't have the faintest grasp of logic or the slightest ability to actually work anything out on your own. You monologue and you never listen, and as a result you're pretty much still where you were eight years ago when you first appeared here. Which was here, in case anyone was wondering: That's how you [POST=1195468]introduced[/POST] yourself here, and it really says all anyone needs to know about you. You didn't know anyone. You had no idea what anyone actually thought. You just assumed you knew it all and started monologuing away. The result? Eight years later, you still don't understand what anyone else really thinks, because you've never cared enough to try to find out.
Excuse me, przyk, Farsight, but that old chestnut 'counterargument' put there by przyk can be remedied by simply having sufficiently numerous CONTIGUOUSLY ADJACENT identically manufactured clocks placed along the radial distance separating the two end-clocks. The separation being so miniscule, all one need to is to 'read off' the TREND (or 'gradient') of the TICK COUNTS accumulated over a period of time for the experiment to yield sufficient absolute count values that provide a SELF-EXPLANATORY RECORD of the CONNECTED CHANGE INCREMENTS which that comparative counts examination will yield. See? There is NO NEED or COMPLICATION for/from such abstract theoretical 'difficulties' which your contrary argument attempts to invoke/impose (unnecessarily) in this reality empirically conducted/informed OUTPUT and conclusions therefrom. Avoid all unnecessary abstractions/complications from theory and the reality can show itself within the proper reality experimental construct. Good luck, guys!
I agree with Mr. Albert E. And imo the flipping exist! End of comment. ......no ifs, ands, or bbbuts about it.
