Tim88

That implies rather that you did not fully read my post, as I clarified redshift in agreement with Sriman. And perhaps you missed my additional precision of ceteris paribus: motion isn't part of the question. Maybe interesting in this context: I know a mechanic teacher who wrote a textbook with a section on GR, and as I recall it (it was a long time ago), when looking through it I was disappointed to see that he included a section in which a photon "loses energy" while climbing up a gravitation well. When I brought up the inconsistency, he defended it as "just a heuristic". He would take it up with his co-author, but I never heard about it again. See also Okun: ON THE INTERPRETATION OF THE REDSHIFT IN A STATIC GRAVITATIONAL FIELD http://cds.cern.ch/record/393302/files/9907017.pdf The abstract is very clear if it's separated in two paragraphs (emphasis mine): Regretfully, while I mostly agree with his arguments, he didn't fully make the case for the correct interpretation there. Therefore I did it here (despite the usage of a huge amount of equations by him, and the total lack of that by me: for the logic it's irrelevant!). PS. In view of the OP's young age, I'll try to answer any follow-up questions in less sophisticated English for improved clarity.

Koti that's fine, as there isn't much discussion! I hope so; I use this thread in order to divulge some of my metaphysical insights that helped me to get a better feeling for physics, and to compare them with the insights of others. I was primarily referring to the standard "frozen" block universe. As I now understand it, "growing" block universe (of which I had never heard until starting this topic) has a specific problem that michel spotted and strikingly named "double time": in order to explain our consciousness of "now", an additional "now" time must be added! However, I got the impression -thanks to ajb and Mordred- that also the standard, "frozen" block universe variant suffers from a need for "double time" if it wants to explain dynamic effects. And I'm not looking for holes in GR nor would I want to undermine the space-time matrix as a mathematical tool; quite to the contrary, in view of one century of debates in philosophical literature, the starting assumption here is that both discussed interpretations are in agreement with the basics of SR and GR. At different times, Einstein promoted each interpretation. If you click on the references in the first post of this thread, you will see that it's wrong to say that "Adherence to the spacetime concept is the root of Einstein's genius" - if with that you are referring to what is properly called Minkowski block universe. The confusion may have come to you by the news media. Indeed a "growing block universe" may be more easy to digest.. but it doesn't seem to help much in better explaining things, and it's a kind of mixed bag that seems to try to merge the Lorentz ether + real time with the Minkowski block universe. PS. here's a little related "antidote" in the battle against the now obvious indoctrination, the effects of which keep interfering with this discussion: "according to general relativity, the experimenter could set his laboratory rotating by leaning out a window and firing his 22-caliber rifle tangentially. Thereafter the delicate gyroscope in the laboratory would continue to point in a direction nearly fixed relative to the direction of motion of the rapidly receding bullet. [..] It is clear that what is being described here is more nearly an absolute space in the sense of Newton rather than a physical space in the sense of Berkely and Mach". - C Brans - H Dicke, Mach's Principle and a Relativistic Theory of Gravitation, Physical Review, 1961 These GR experts appeared to have been unaware of the Minkowski block universe interpretation; in any case they didn't mention it.

My short answer: yes, you're very right! (apart of the glitch in your last sentence of course.) Long answer: this is one of the trickiest issues in GR with a lot of blurred description in the literature, so here's my attempt to a self consistent analysis (if there are errors, corrections are welcome. And perhaps someone else may give a disagreeing but equally self consistent answer). [edit:] First of all, QM (photons) and GR (waves) speak a different language; technically speaking they should not be mixed. In what follows I'll assume that a number of photons corresponds to a certain number of wave cycles. Next, energy is conserved but also cycles are conserved: - no energy can "get lost" or "appear from nothing". Essential requirement: we must do the analysis with a single reference system. - if a source emits a 1 kHz signal for one second locally, 1000 cycles should arrive. When this radio signal of 1000 cycles is sent upward, 1000 cycles arrive at a detector with a faster resonating quartz crystal. The measured frequency is therefore reduced ([edit:] ceteris paribus of course: here we assume that the Earth surface is in rest during the interval, as motion is irrelevant for your question.) Locally f and E seem to be decreased because they are compared with detectors that posses higher gravitational potential energy. More elaboration to show the self consistency: when an object with a number of atoms falls down to the ground, kinetic energy is released. Consequently all consistuents of an atom must be assumed to have reduced energy. An emitted light ray ("photons") will therefore be released at lower frequency, and if it propagates upwards it will be detected at a lower frequency than the emitted frequencies of atoms at that height. Note also that a change of frequency "in flight" results in self contradiction. If for 24h a certain number of cycles is sent upward, that number must also be received in the same time interval. Else cycles would go missing "in mid air"!

I certainly don't think that GR effects are incompatible with block universe! I referred to something completely different. The lack of clarification of how dynamics is caused by a "frozen" 4D merge of space and time should not be surprising; for how can "block universe" conceptually explain dynamics, if "time" is another physical dimension like length? With my earlier "car example" I forgot to discuss the basics which are already pertinent for classical mechanics. So here's a retake, starting with dynamics. Physical effects such as inertia and time dilation can be modeled as caused by an underlying 3D background (non-material "ether" / "vacuum" / "Absolute Space"), but a more widespread view is that they are caused by a 4D background in which "space" and "time" form a single entity (block universe / "Absolute Spacetime"). One might ask, what is the practical difference? For a start, both models are proposed as CAUSING the space-time metric. I'll elaborate how the Absolute Space model in "action" pretends to create classical as well as relativistic effects; additions by others are welcome (I will include a few by Mordred for the "car" example), and I invite those who adhere to the Absolute Spacetime model (Minkowski block universe) or similar, to post the corresponding alternative explanations to make sense of our observations. ABSOLUTE SPACE model of reality: There is supposed to be a 3D "background" that affects and determines our measurements; Absolute Space is directly associated with distances and lengths. Different from classical mechanics, measurements of distances and lengths are affected by Absolute Space. In contrast with distances, time is a measure for the progress of physical processes; however our measurements of time are similarly affected by Absolute Space. Inertial frames (postulated to be in uniform translational motion relative to Space) can be set up just as in Newton's mechanics. Similarly as in the old theory, the state of motion (speed) cannot be detected although a change of motion with respect to Space can be detected, since Space literally induces an inertial effect at a change of motion. 1. Newton argued for this with his BUCKET EXPERIMENT: in this model of reality, the inertial force is explained as the result of the water's co-acceleration with the bucket relative to Space. [edit]: compare also De Sitter and dark energy: cosmology is not "my thing", but if I correctly understand it, even in an otherwise empty universe, rotation of an object should result in inertial effects. In what follows we'll use Occam's razor and assume that whatever it is that causes inertia, it's not moving relative to Absolute Space. Concepts such as cosmological expansion may impose refinements that are not fundamental for the explanations. Inertia can even be understood in a straightforward manner as self induction for the simple case of the electron (QM improves on this quantitatively); this fact suggests the possibility that one day a unified theory may be found that explains all inertia as due to change of field energies. Other improvements to Newton's Space following from Maxwell and Lorentz are that radiation does not propagate like particles but as waves (or, since QM, like wavelets), so that its speed is determined by the Space that it propagates through; and that matter is affected by motion just the same as Heaviside's moving EM fields. In addition, effects of ROTATING DISCS are similarly easy to intuitively understand by means of Absolute Space: 2. SAGNAC EFFECT. For simplicity, let's first pretend that the axle is at rest in Space. If now laser light is sent along the rim in both directions, the light will, just like any real wave, propagate at a fixed speed through Space. During that time the detector will move away from the one ray and towards the other ray, so that the interference is a function of rotation speed relative to Absolute Space. 3. EHRENFEST PARADOX. Lorentz contraction only occurs in the direction of motion. If the disc would be at rest in Space, then a measuring chord will be slightly contracted as it is laid along the rim, but not as it is laid along the diameter. Consequently the circumference will appear to be more than 2pi times the diameter (and there isn't any paradox to start with). The combined effects of Lorentz contraction, time dilation and relativity of simultaneity (as elaborated in the upcoming extended car example post), assure that the same phenomena occur with rotating discs in any inertial reference system. [edit: changed numbering]

Thanks koti, it's good to know that there are some onlookers! But what's the block universe explanation of those GR effects?? So, I regret that this thread apparently didn't attract a convinced Minkowski block universe adept, who promotes the idea that time and space correspond to a single physical thing called "spacetime" (seeing the two words "space" and "time" in a text connected like that, is for me an indication that the writer adheres to that concept - and therewith subtly influences possibly unaware readers). Maybe the following can pull any lurking true Minkowskiist out of his/her hiding. And I replied: As this was not clarified (or did I overlook it?), I'll include in the elaboration in my next post how the dynamics of inertia are conceptually explained with Absolute Space. I now start to think that dynamics cannot be reasonably explained by the block universe, in which everything is "frozen" into eternal existence! By the way, I noticed another "loose end": I'll also include velocity "addition" in my elaborated explanation of SR by means of the 3D "ether".

OK, I now prepared a more elaborate summary of SR and classical effects, but I'll wait a few more days for feedback on the car example analysis and calculation. Meanwhile it will be interesting to discuss and compare the views on "what really happens" in GR. I'll now present the "Absolute Space" view of reality for some basic observations on Earth. The gravitational fields of all mass (incl. the "relativistic mass" from radiation and EM fields) is in this view assumed to have absolute effects on the speed of light as well as on clock frequencies, as follows. GRAVITY PROBE A (Vessot). An atomic clock is sent up to high altitude after which it comes down in almost free fall. a. At the start, the clock ticks at the same speed as clocks on Earth. b. At its highest point, the clock is nearly in rest but less affected by the Earth's gravitational field: a higher potential energy corresponds to a higher clock frequency than that of clocks on the ground - gravitational time dilation was measured. c. When falling down, just before impact the clock is again at the same hight but at high speed. Here the remaining effect was purely SR time dilation, and so the ground station measured a reduced clock rate after subtracting the assumed "classical" Doppler effect. It's maybe worth noting that for the theoretical case that the ground is in "absolute rest", the SR effect relates to "absolute" kinetic energy, in contrast to the GR effect which relates to gravitational potential energy. GRAVITATIONAL LENSING a. Light bending. When light passes nearby a star such as the Sun, the gravitational field bends the light towards the star somewhat like an optical lens, due to a gradient in propagation speed; the tricky point here is that according to GR, the effect is anisotropic. As a matter of fact, Einstein used the Huygens construction for predicting the effect (the corresponding Wikipedia article fails to inform the readers on this point and suggest quite the contrary). b. Gravitational time delay. Radiation that passes near to a heavy mass such as the Sun will not only bend but also delay. This is immediately understood as due to the slower propagation speed in the gravitational field (it's interesting to notice that the corresponding Wikipedia article mentions the slowdown of light that is denied in the other one). I hope that the advantage of using not only a mathematical model but also an intuitive, conceptual model for understanding is obvious from the given examples (incl. the car; and I'll also post on the rotating disc). As a matter of fact, a good model enables to notice errors in papers and books that others may not notice. However, as more people here fancy the Minkowski 4D blockuniverse interpretation (or a variant), I'm looking forward to hear the alternative explanations of GR effects by means of the Absolute Spacetime model.

I'm a skeptical agnostic.

Yes, that was my point.

Well understood. As a matter of fact, that was not only clear from Langevin's explanation, it was already clear from the very first clock retardation prediction. Einstein did not pretend that moving a clock around would affect the inertial clocks. [edit]: as a matter of fact, that would be magical "action at a distance" which definitely is not SR. As long as you forget to clarify what you mean with "time", if you indeed hold that clocks do not measure "time", we may soon reach a dead end here!

Funny enough (in view #214, 215 [edit: and #219], the following comments were posted in the spin-off thread for those who want to compare the usefulness of the two models of reality (which makes them rather off topic there and very much on topic here): And In other words, some people don't have understanding for those arguments for more than mathematical space, or even deny them.

Well, that's it; I will now repost your comments in the appropriate thread where Einstein explation why he needed it was summarized - the "mother thread".

With respect to the surface of the earth, a free falling clock is ticking slower due to both reducing gravitational potential (potential energy) and increasing speed (kinetic energy). This was verified with the Gravity probe A experiment. - Vessot 1980. As I summarized here above, the frequency of a maser clock followed rather well GR's predictions. [addendum: you can read about the experimental setup here] That's simple: as long as you are not very close, changing your own velocity cannot affect someone else's clock. Even your velocity won't affect someone else's clock.

I doubt that's the issue- but one never knows!

In principle the problem is not so much that he claims that he traveled to the 28th century, as that can in theory be achieved by slowing down his biological clock. The problem is that he claims to have traveled back in time to our age; it's according to current knowledge impossible, even nonsensical, that he returned from the future.

This most likely has to do with how you define "time". In physics, "time" is a measure of the progress (or relative "speed") of natural processes. If all natural processes of a system are affected by the same amount compared to an unaffected time standard, then we commonly say that its time has slowed down. And that's exactly what happens in a gravitational field, in theory it affects any kind of clock or natural process in the same way.

Before posting an improved "car" example, time to search for some "loose ends"... It's quite unclear what the practical difference is between the assumption of "ether" and the assumption of "no ether but field". I tend to interpret the last as either meaning that "spacetime doesn't exist, instead we have fields with properties in empty space" or even something like "spacetime has properties but it doesn't exist, so that nothing does have properties". If something like either was meant, please input it in the "mother thread"! I think you meant Minkowski tells us that space and time should be treated on equal footing. Lorentz tells us that space and time are not the same physical entity (without objecting to the mathematical "equal footing"). Those differing views led to this topic, where the usefulness of 3D and 4D "ether" are compared. Can you or someone else clarify how dynamics works or why it exists, as you consider that there should be no cut between space and time - the "4D" view? Ah yes, these can be useful for the "4D" phrasing; although it's at first unclear to me how any of it can be helpful to make more sense of the equations. Notably "the concepts of happening and becoming are indeed not completely suspended, but yet complicated" suggests to me a possible unclarity. It's a bit funny that Einstein provided good sources for both philosophical views - typically him.

I did not notice that there were many points raised that really helped to make SR easier to understand by assuming that space and time form a single physical background entity; but I'll also go through it again, searching for on-topic "loose ends". PS. Yes I see that in fact you gave quite some useful input there - thanks again!

Addendum: it will be useful to clarify that the driver will advance C2 by slightly more than 3.3fs, for initially we assume, as is usually done, that the distance between the clocks (as estimated from the ground) is allowed to relax after acceleration into a length contracted state so that C2 must be allowed to accelerate slightly more than C1. As here we are dealing with a car instead of a rocket, already at this point technical means should be provided for to make this approximately true. Alternatively the car driver could recalibrate the distance between the balls (but it's probably not yet technically measurable). And to make it again more realistic, we better choose the wheel basis 3m and we can choose the radius of most of the turn for example 3km. The proper distance between the balls we now choose to be 2m (it's not necessary for the holes to be exactly between the wheels). Then the advance of C2 on C1, as estimated from the ground, will be 6.7fs. According to the ground's reckoning, the driver will now drop the ball in the front 6.7fs later than the ball in the rear; as a result the ball in the front will end up 300m/s * 6.7E-15s = 2E-12 m = 2pm too far, "spanning" a ground distance of 2m + 1pm (here's where the car's length contraction of 1pm matters).

Ah yes,that thread is has a different focus than what Memammal has in mind. edit: but I do hope that Memammal will there clarify some of the practical features of the block universe interpretation.

OK here are my estimations for the realistic section of the full car example. If someone notices a significant error, please correct. 1080 km/h = 300 m/s => v/c = 1E-6 In good approximation gamma = 1+0.5*v2/c2 => gamma = 1 + 5E-13 The initial clock (re-)synchronization of C1 and C2 in the car according to the ground proceeds as follows (length contraction can be neglected for this calculation, and we'll assume that the acceleration from stand still was gradual and smooth): A light or radio pulse from C1 to C2 is clocked as 1/(3E8+300) m/s = 3.3333300 ns, and in the inverse direction it's 3.3333367 ns. This is very hard to detect, but apparently already possible - Chung 2003, Real-Time Detection of Femtosecond Optical Pulse Sequences (Freely downloadable, but the link may be illegal) The driver will advance C2 by about 0.0000033ns = 3.3fs, so that the one-way speed of light becomes isotropically c in the car's newly established inertial reference system. According to the ground's reckoning, the driver will now drop the ball in the front 3.3fs later than the ball in the rear; as a result the ball in the front will end up 300m/s * 3.3E-15s = 1E-12 m = 1pm too far, spanning a ground distance of 1m + 0.5pm (here's where the car's length contraction must be accounted for). If this were measurable, it would look for the car driver as if the ground is contracted by gamma = 1 + 5E-13. Then the bend. As expected, now the length contraction is negligible compared to the classical effect of 1 um "track expansion" on 1m clock distance as described in the foregoing post; it's even small compared to an atom! And for 0.5 m to the outside of a r=100m bend, gamma = 1 + 5.5E-13. No surprises. With a smooth 4 wheel in-steering from 0 to 100 m radius as discussed above, the middle point of the car has a speed of vm= 0.9999875v so that delta-gamma = 0.5[(v/c)2-(vm/c)2] = 1.25E-17. 10-17 is negligible compared to 10-11. On top of that, it's for a short duration and next the almost perfectly inverse effect is induced by smooth out-steering. Moreover, at such a high speed the turn radius should be well over 1km (ca. 3s of turning) instead of 100m. Anyway, for simplicity we will assume that the car has a 4WD mechanism that literally forces C1 and C2 to keep exactly the same speed. For all practical purpose, C1 and C2 will then keep the same speed of 1080 km/h - even in the curve. C1 and C2 are thus synchronized to "the car's inertial frame" on the outgoing leg as well as on the ingoing leg. [edit: in practice this may be hard to achieve, due to vibrations, deformations, and imperfect clocks.] To finish the example, we'll let the car do a return trip of 2*30km, or 60km in total. We may neglect the rotation of the ground in this case. The "twin" prediction of clock retardation on a clock that is located at the start/finish line, is then 5E-13 * 200s = 0.1 ns for C1 as well as for C2. That is also just about measurable. As a reminder, the clocks follow an identical v(t) trajectory, so that they must accumulate the same retardations at the events of meeting up with the "stay-at-home" clock. The constant 3.3fs offset of C2 on C1 is independent of that fact, and there is no need to synchronize clocks to a ground clock: stopwatch times suffice for the comparisons. In the course of 10 laps, C1 and C2 will accumulate 1.0 ns retardation.

I'll gladly leave it to you to start such a thread (and what thread did Mordred refer to?), especially as some differences may have little metaphysically substance and be more a matter of sound, due to different words...

I noticed that I overlooked to include another classical effect. When taking a turn (now assuming 4 wheel steering), and if we want to keep the speed of C1 and C2 constant (according to the ground frame), it means that their tangential speeds vT = ds/dt remains constant along the circle segment. Consequently C1 should remain ahead of C2 by a distance of 1m along the circle segment. In order to achieve that, the car has to be made to contract - or at least, the distance between the clocks has to be reduced for the duration of the turn. Let's see what we are dealing with here, this is simple geometry. 1.Classical effect. Say we have the wheels of the car at 1m distance, beside the clocks, and we choose a crazy sharp bend of 100m radius. I then find an angle of 2*0.28648° for a circle segment of about 1.000001m. Thus the car driver should ideally reduce the distance by about 1 micron (note that non-classically, that's 0.5 um in the ground frame for the chosen speed). 2. Now for the length contraction effect. In view of the above, I now look differently at the issue of point 2 of post #15. Here's my retake of it. In principle an adapted 4WD and 4WS car with built-in flex can be conceived that keeps the clocks at constant speed. We make the 2 clocks continue at a transverse speed of gamma=2 while on the circular trajectory. Correcting at the right time the distance by 1 um this can be reached, but now the middle of the car has a slightly lower speed as it's on the inside of the curvature. Then the car floor with the ruler between the clocks will have the tendency to decontract. Here's an estimation of order of magnitude: The middle of the car describes a circle trajectory with r=99.99875m. Thus the transverse speed is 0.9999875*0.866025c = 0.866015c If the whole ruler had that speed, its length would now increase to 0.500018m. However it's somewhat in between, approximately 10 um, or 10x the classical effect. In other words if I'm not mistaken, then small imperfections are strongly enhanced for this speed. That considerably complicates analysis. But that's not all. Although there will not be a twist as in the double Focault disc as here all velocity vectors lie in the same plane, the right hand side of the car will contract more and the left hand side will decontract more. That causes a bending due to relativistic effects contrary to that of the bend. And that in turn leads to an increase of the decontraction issue. And that's still not all, as inertia has so far been ignored. From the rotating disc I think to remember that inertial effects are larger than contraction, IOW, the decontraction issue may well turn into an additional contraction issue in the real world. Although a specially built car was my first idea of how to fix this "problem within a problem", and it's not bad to maintain that, it's a unrealistic due to the extremely unrealistic speed. But that speed was only chosen for a clear pictorial illustration using gamma = 2. With that speed the car would be in 1s already far away from the Earth! Then we should include the loss of contact with the ground, the varying gravitational potential etc, all for just nonsense. It's much more reasonable to instead discuss a technically possible scenario with a car going at for example 540 or 1080 km/h, and that should allow for greater analytical simplicity. Only disadvantage: it requires a calculator with many digits.

Neat. "The process by which a laminar viscous flow undergoes transition to turbulence through diverse routes [...] (I) laminar steady-state flow [..] (VI) aperiodic chaotic state." Thus the author identifies fully developed turbulent flow as an "aperiodic chaotic state", just as I briefly explained to Sriman. Maybe you got confused by the fact that not all "chaotic" flow is turbulent. Once more, that's of little relevance to the topic of turbulence, so that more than an incidental comment about that interesting detail is simply unhelpful here. If Sriman has further questions or comments, I will clarify more of course.

What do you understand denser to mean? Density (of something) is that something per unit volume. So what is that something, and where does it live? No, I did not write that. And I did not read that article. As it is an analogy, any transparent material can be used in principle - even transparent rubber. However, an anisotropic crystal would better mimic the math. Did anyone attempt this with for example Ansys or Comsol? PS I see now that you clarified it later. With "lensing" is of course meant that the speed of light is affected just as in lenses; I don't know why the authors would want to talk about density, as that surpasses the purpose of such an analogy. One could similarly ask about the elasticity modulus of the rubber band. Some analogies are no doubtful more useful in some aspects than others. Apart of that I fully agree, taking them too literally makes them quite useless.

Is there currently a suitable thread where the block universe is discussed and criticized, so that we can discuss such articles there? Our memory stores events (which are all past events!) as spatial pictures with time stamps, just like your animation cards or a motion picture. While you call that "eternalist", I would call that rather "presentist"! And then that citation against "a moving now": "moves" = ds/dt... that is an improper description as it confounds in itself time with position displacement, it doesn't help at all to represent "presentism". It's more fitting for eternalism which holds that "our perception of now" literally moves along a "time dimension". [edit:] In fact I agree with him that time does not really "flow", but his argument is faulty - and certainly not an argument against "a now". A "now" means that for example a chemical process really happens, so that we can follow it while it happens. That is not a "flow". At this moment oxygen is being taken up by my lungs. Without a real distinction between "now" and other times, so that everything exists eternally, neither chemical processes nor anything else really happen - we just have movie pictures lying around, and no explanation why we have the impression that they are playing, and that we are playing in them. PS Memammal thanks for that link: we can probably use some of it for clarifying the block universe view in the other thread.