Daryl,

I was looking at your title again and I thought I'd point out that unlike a ruler, a clock has two parts, hands, representing present and face, representing events, so one is the denominator and one is the numerator. With the current system, the events are the denominator and thus the present is factored into them, therefore each event is its own present, but if we look at it the other way, with the present as the denominator, then the events have to be factored into that and there is only one present in which all events either manifest, or don't happen.

Ah, John that's where I have to strongly disagree. I think it's conceptually very simple to think of nothing moving, but it's impossible to imagine nothing existing. Even thinking of a single slice, an instant, in all of eternity, brings up thoughts of it as existing in my mind. I actually think that's where all the trouble in understanding the block universe model comes in--because it's impossible to think of without surreptitiously imagining it in some sense as existing. In contrast, it's incredibly simple to think of something as just existing, not moving at all through space. I can think of a rock, or whatever. I know that that rock is full of atoms and subatomic particles that *actually* are moving, but that doesn't change the fact that I'm able to naively think of it as being completely still.

The best way I think I've ever heart the passage of time expressed was by Seneca:

"Our bodies are hurried along like flowing waters; every visible object accompanies time in its flight; of the things which we see, nothing is fixed. Even I..., as I comment on this change, am changed myself. This is just what Heraclitus says: 'We go down twice into the same river, and yet into a different river.' For the stream still keeps the name, but the water has already flowed past. Of course this is much more evident in rivers than in human beings. Still, we mortals are also carried past in no less speedy a course;... the universe, too, immortal and enduring as it is, changes and never remains the same. For though it has within itself all that it has had, it has it in a different way from that in which it has had it; it keeps changing its arrangement."

It's worth reading a couple of times to understand how he's using the river metaphor. It's at best a loose comparison, because time doesn't actually flow through any existing space like a river does. The river *mostly* provides a useful means of recognising the passage of time, because the water is moving, so it's obviously changing. But the same passage is still there in all things, with the same measure, no matter whether they're moving or not.

Therefore, when you conclude with "I do think though, we can put time entirely in the category of effect, if we think of it in terms of change" I just have to completely disagree, because the passage of time lies at the heart of change. Nothing can change if it doesn't exist. As for the title, time *is* the denominator of existence, because to *exist* is to be somewhere over a period of time. Whether that "somewhere" is changing as time passes or not, the thing is existing; and in your view and mine, *absolute time* passes everywhere with the same measure, whether or not local measures of time pass differently due to a body's arbitrary motion through space. That time, *absolute time*, is the denominator of "existence", and all the events that occur just happen, and all information simply comes into existence or fades from it as time passes.

I forgot to add, at the end of the first paragraph: I can think of *something* as being completely still, and by superposition I can imagine an entire universe in which nothing at all is moving. With no photons moving about, nothing would be seen, etc., etc., but that doesn't change the fact that I can imagine it, whereas I simply can't think of anything at all without thinking of it in some sense as existing.

Actually, I can say that better--about the quote, I mean. It's worth reading a couple of times in order to see that he is using the river example in two ways. He himself is using it as a metaphor for the flow of time, and he says that's how Heraclitus uses it---but he doesn't, does he? Heraclitus is using the river as a benchmark for recognising temporal passage, because of the fact that it *is* changing. Every time we go down to the river it's obviously changed; it's different. But what Seneca notices, which was surely Heraclitus' point, although we've only got the fragment, is that *everything* is changing in the same way: it's all existing, whether it's moving or not; and that sense of "change" is uniform--the even passage, or duration, of absolute time.

Daryl,

" the universe, too, immortal and enduring as it is, changes and never remains the same. For though it has within itself all that it has had, it has it in a different way from that in which it has had it; it keeps changing its arrangement."

Would you say there is a changing present, or that the present "moves" along the "passage of time?"

    A changing present; however, this "change" is not by virtue of constant rearrangement, but simply because it endures. For that reason, regardless of any possible rearrangement, each instant is already different from any other. In that sense, the present is always changing. I think this is what Joe Fisher means as well.

    The alternative you suggested, that the present "moves" along the "passage of time", brings to mind a physical dimension along which the present flows. In order for the 3D present to flow along that fourth dimension, all of it would have to exist, and that's really a 5D concept.

    But I think existence *is* the fourth dimension, even in the relativistic description--but the only thing that's ever real is the three-dimensional enduring present.

    Daryl

    Daryl,

    Are they one and the same? It endures because the energy is conserved and time is the measure of regularity, because it is both enduring and in motion.

    Existence is the fourth dimension, in that without both the effect of sequence and the concept of narrative, we don't exist. That doesn't make it physically real.

    We seem to be on the same page.

    You do realize this view refutes the conceptual basis for Big Bang Cosmology? No wormholes, or multiverses either. Just scales beyond our ability to conceive.

    Regards,

    John

    John,

    I've tried to discuss cosmology with you before, but you seem adamant about wanting to misunderstand the standard cosmological model. One of its basic assumptions is that there *is* a cosmic time, a cosmic frame of rest, and all the rest of what we've been talking about. In fact, George Ellis for one is far closer to agreeing with your "moving matter causes its own existence" stance than he is with my "matter can't move if it doesn't exist" one. Either way, cosmology describes space as existing, and expanding in time. The three-dimensional universe simply multiplies by a scale-factor a(t), which is a function of cosmic time.

    Then how does one model this? Any scale is set by two values, so one possibility to use is that at some finite time in the past the value of the scale-factor was zero. The other value doesn't actually have to be known, but everything can be scaled relative to it. For this, we use the present value, *explicitly assuming that there is a present*, and we usually set it equal to 1 and scale the value at every other time relative to that. Redshift can be related to the change in the value of the scale factor in an expanding/contracting universe--i.e. 3D space that gets bigger or smaller as objective cosmic time passes--and can therefore be used to derive a measure of distance that relates to a change in apparent brightness. Yadda yadda. We have a means of modelling redshift and apparent brightness data. We now have really good data, and the model that tells us our Universe is now 13.8 billion years old, has expanded monotonically from a time when the scale factor was zero, and has been expanding with a very particular rate of change, fits the data very well.

    Furthermore, the whole "Big Bang" idea predicted the CMB as a relic of a time when space was relatively much smaller, and energies were a lot higher than they are now, which was observed a while back. Since the initial prediction, people realised that if the CMB really were created this way, when space was a lot smaller, and that it has expanded for billions of years since, then the effects of vacuum fluctuations at that time, which would have caused tiny little anisotropies in the background radiation of space, would have expanded to huge macroscopic sizes along with space. The detailed anisotropy signature that the theory predicts also fits to the standard model. No other model has been proposed that can come close to explaining the detailed CMB anisotropy so well.

    I'm not saying I agree with everything about the model, and I'm not trying to defend Big Bang cosmology here. I do have different ideas that I think explain a lot more, and they don't involve real singularities, worm holes, etc. I've been trying to defend presentism against Ken Wharton on his essay page, and I ended up going into some of the details over there. If you're interested to get an idea of what I think, you could look at that.

    Regardless, I did want to defend against your claim that Big Bang cosmology is inconsistent with there being a cosmic present, but I really don't want to defend against other aspects of the theory that I disagree with.

    Daryl

    Daryl,

    Not trying to push any boundaries here and I certainly didn't set out to question cosmology, it's just that about 24 years ago, it started occurring to me that it didn't add up. Just a few of the points; If gravity and expansion balance out, as theory and observation suggest they do, where is the additional expansion for the universe as a whole to expand coming from? It would seem space between galaxies is expanding, while the galaxies are essentially pulling in this effect. Sort of like what Einstein originally proposed the cosmological constant to do.

    If space is what you measure with a ruler and space expands, why does our most basic ruler of intergalactic space, the lightyear, remain stable, since these galaxies presumably move apart in terms of light crossing the distance between them.

    Wouldn't the cosmic background radiation also be the solution to Olber's paradox, if redshift is an optical effect of distance?

    As well as that it is premised on the "fabric of spacetime" being physically manifest.

    Here is an interesting paper describing how redshifting could be caused by multispectrum quanta of light. It seems to me that if we assign the effect of balancing gravity to light, some of these issues might not be so mysterious. Not only do galaxies radiate away tremendous amounts of radiation, to balance the mass falling, in, but the black holes are shooting enormous jets of cosmic rays out the poles. Yes, mass, structure and information fall into black holes and other gravity wells, but it seems quite obvious the constituent energy is being ejected out of them. It seems to me a lot of these processes could be thought of in terms of cosmic weather patterns; Such as a convection cycle of expanding radiation and collapsing mass, gravitational cyclones, etc. Just is mass releasing energy creates enormous pressure, wouldn't the opposite be true, that energy coalescing into mass creates a vacuum? Which might explain gravity.

    I realize this is outside convention and only raising what I see as interesting questions.

    John,

    I first of all need to apologize for the negative tone in my previous reply. I was rude, and I'm sorry. Thanks for not getting upset with me.

    First point: I don't think mass actually warps space-time, but it's all a teleparallel effect due to momentum through a universe that exists with a well-defined Lorentzian background metric. I don't think stress-energy has any effect on the basic fabric of reality. (See my post to Ken Wharton). I'm also not happy with the idea of expanding space around gravitationally bound clusters of galaxies, that picks off the outliers and carries them into the Hubble flow.

    Point two: A light year of intergalactic space now is not a light year of intergalactic space five minutes from now, since space is expanding. It's the speed of light through space in time that's relevant in the space-time metric. This needs to be appreciated according to the metrical description, without complicating it by thinking of space as not expanding in some places and expanding in others, etc. So: space just multiplies, right. It's everywhere expanding by the exact same amount. This is the way we model the large-scale expansion. Consider two galaxies as points in this expanding space. There are THREE relevant distances to consider when discussing the light travel from one galaxy to the other: the distance between the two points at the time of emission; the integrated distance that light travels through expanding space; and the distance between the two galaxies when the light is finally observed. When distances to galaxies, quasars, etc., are mentioned, it may be the light travel distance that's quoted. It's stated in light years, because light travels a fixed distance in a year, so quoting the light travel distance would also indicate when the light was emitted. The distance is a distance travelled, at a fixed rate, through expanding space. As I said, it's an integrated distance over the path of the photon, and not a distance that there is in space at any one time.

    Point three: Number one against you is the CMB's anisotropy signature. No one's offered a reasonable proposal to explain that but Big Bang cosmology. Also, there's the fact that even the temperature was exactly predicted by Big Bang cosmology. Predictive power holds a lot of weight in physics. I suppose one can (?) contrive a theory of tired light to explain the paradox, but I don't know. I seem to recall a sky full of tired photons still having to be bright. Something to do with infinity. I could be wrong, but the possibility doesn't really interest me unless it could realistically begin to contend with the CMB and is consistent with everything else.

    Point four: I'm not sure I understand. Are you now talking about aether theories? Or are you thinking that the fabric of space-time needs to be physically manifest in the standard model. I disagree with that. There's a metrical structure of the Universe; everything in the Universe is supposed to have been projected at the Big Bang so that it was all flying apart at an initially decelerating rate (yuck, IMO); and, more to that point, everything in the Universe is supposed to have henceforth been affecting that primordial rate of expansion. I personally think the apparent expansion rate has to do with an absolute background metric that was fixed before the "big bang" (again, refer to my post to Ken Wharton).

    Point five: The inference that black holes exist is not justified if there is supposed to be an objective cosmic time.

    See: my ideas lie outside of convention, too ;)

    Cheers,

    Daryl

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    • Post #88

    Daryl,

    " The distance is a distance travelled, at a fixed rate, through expanding space."

    What is the metric for that "fixed distance" light is traveling, if space itself is expanding? There seems to be an unconscious assumption there that distance is just, well, distance, even if "space" is expanding. I wouldn't want to try that logic on the IRS.

    Big Bang cosmology did predict the background radiation, but it didn't predict its smoothness, thus the need for inflation, nor the rate of redshift, so we have dark energy. It seems different standards to say it's proof when it gets it right, but when it gets it wrong, we just need a patch.

    "Tired light " was a pretty primitive idea to have as the sole basis for all forms of steady state universe. It seems like a variety of factors could be coming into play. Even the time it takes for photons to register from such incredibly distant sources would be stretched out between each photon.

    John,

    You said again here "What is the metric for that "fixed distance" light is traveling", but I keep telling you there is no fixed distance in cosmology. Space is expanding. Light travels at a fixed rate through expanding space, and the integrated distance it travels through that space in a year is a fixed amount. The fixed rate is the null rate defined by the metric.

    Dylan is screaming death metal in my head, "Don't criticize what you [don't] understand!" I really don't think it's something you "can't" understand. I believe you can. But you really don't yet. And it's really important to actually understand--and understand well--the theory you want to argue against. It's the only way to do proper analysis.

    Light travel through expanding space isn't the easiest concept to understand, and a lot of people do have trouble with it. I think it's an especially tricky concept for you because you want to argue that it's wrong more than you want to understand it. But please try to understand: space is constantly expanding and light travels through expanding space at a fixed rate; in a year, it can only get so far, say it goes from A to B one year; if A is a galaxy that's constantly emitting light and B is an observer, then the light A emits even a second after that last bit, that took exactly a year to get to B when it was emitted a second ago, now takes slightly longer to get to B; light still travels the same cumulative distance through space in a year, but a second later the distance between A and B was a bit more AND the eventual distance it had to cross was greater by even more than that *initial* amount because all of the space between A and B was expanding *the entire time* the light travelled.

    Distances between objects aren't fixed in an expanding universe, but are expanding. Light does travel at a fixed rate described by invariant null lines in the metric. Therefore, at this fixed rate, light travels a fixed finite distance through expanding space in a year, which integrates along its path over the course of the year as the distance between two fixed endpoints grows and grows.

    If you were at all trying to understand this, you would; but all you seem to be doing is looking for an error in it, and there isn't one, and that is keeping you from getting it, as far as I can tell. On this particular point, I feel we're at an impasse until you give up wanting to argue against it and first try to understand it. The question you asked to start with is already wrong, and the "unconscious assumption" you're referring to isn't remotely what anyone thinks.

    Now, to move on: you said, "Big Bang cosmology did predict the background radiation, but it didn't predict its smoothness, thus the need for inflation", and I told you I don't want to defend things I don't agree with (inflation), but you've got this all wrong, too. The metric of standard cosmology--the thing that's been verified by observation--is constructed based on the observation that the Universe appears to be isotropic on the large scale, and the assumption that it should be homogeneous, so that nowhere should be special (i.e., it should thus appear isotropic from every point; this is the cosmological principle). Accordingly, the CMB should be smooth. Inflation is supposed to address the flatness and the horizon problem, but I said I don't care to defend a theory I ultimately disagree with right now, so I'm not going to get into that. The more basic issue, though, is that we have a model that assumes spatial homogeneity and isotropy, and it works empirically, but we want to explain why it should be isotropic and homogeneous. We could just go on assuming it, but that bothers people, so we try to think up reasons why that should be.

    Now, to refer back to your "but it didn't predict its smoothness"--obviously yes, a signature from when an isotropic and homogeneous space was in near-thermodynamic equilibrium should be very smooth, so the theory does predict that, but what's really interesting is what I said before about the anisotropies that it predicted from tiny vacuum fluctuations occurring then, which we've also observed.

    Then in your next statement you again refer to an idea I disagree with, but you again have it so wrong that I'm compelled to try to explain. You wrote: "nor the rate of redshift, so we have dark energy. It seems different standards to say it's proof when it gets it right, but when it gets it wrong, we just need a patch." The rate of the redshift is modelled very accurately by the standard model without having to change the underlying theory a lick. But accurately modelling it meant that a parameter that was previously assumed to be zero had to be allowed to be some other constant value. It's hardly a "patch" when all you're doing is saying your previous assumption seems to be wrong, because observations indicate otherwise. And by the way, in science we never ever ever say anything is proven. We say that we've verified assumptions, or falsified them. That's it. In this particular case, the assumption was falsified. But as I said, I totally disagree with the "dark energy" idea--I think there is a fundamental geometrical constant related to the metrical symmetry, which you'd know if you look at the post to Ken Wharton I keep referring to--so I don't care to defend it.

    Daryl

    Daryl,

    Thank you for your patience.

    I meant fixed rate, not fixed distance.

    "but a second later the distance between A and B was a bit more AND the eventual distance it had to cross was greater by even more than that *initial* amount because all of the space between A and B was expanding *the entire time* the light travelled."

    I'm having trouble parsing the distinction between space and distance. How is it that space can be said to expand, yet there does seem to be this stable distance, as measured by lightspeed, against which to measure it? Isn't "space what you measure with a ruler" and doesn't a ruler measure distance?

    John,

    Thanks for the question. That helps. This all goes back to our presentist idea, in which space exists. At any instant, there is a certain physical distance between A and B. But because of the way in which space exists, i.e. expanding as time passes, the physical distance between A and B increases.

    The fixed rate that light travels through space in time is a differential, so maybe it would be useful to take a calculus approach: rather than thinking of instantaneous velocity, start by thinking of the fixed rate as a tiny distance travelled in a moment. We can start by thinking of the expansion of space as occurring only "between" each moment, with space remaining fixed "during" each moment. Accordingly, the tiny distance that is traversed every moment is a smaller and smaller fraction of the total distance between the two endpoints, so the light initially covers a greater portion of the distance that's got to be made up. It might take only a tenth of the time to get to the half way point, because space is expanding so much by the end. But this doesn't really matter to the point that we're discussing. The point is that the physical distance that light actually crosses in a year is just given by adding up all the tiny distances travelled in an entire year, which has nothing to do with the fact that space is expanding. The latter is only important if you care to know how far in space the light actually got by travelling at that fixed rate throughout the year.

    Now your mind is brimming with objections. "Inconsistent!" you cry, "Space is supposed to be continually expanding, even during those brief moments!" And that's true, but we haven't yet made this a calculus-based description. In the limit in which those moments become instants, the rate does become an instantaneous velocity, and that's what's fixed, and if you want to determine how long it will take light to travel from point A to point B when instantaneous light speed is that fixed value and space is actually continually expanding, you integrate over the path from A to B. However many years that is, tells you how many lightyears that integrated distance was. If you object to the validity of doing this, what you're really objecting to is the validity of calculus, and not the validity of the cosmological model, which simply makes use of calculus in this way.

    If you don't understand calculus very well (I have no idea what level of mathematics you're comfortable with) then this isn't the easiest example to begin with. It would be better to first understand how it works in space that isn't expanding, and then complicate things with spatial expansion.

    Alternatively, you could just think of the rubber band example I gave you last year. You tie one end to a post and walk slowly away, or even at a variable rate, holding the other end. You have a friend take a marker and draw a line from the fixed end over to you, walking at a fixed rate, always with the same instantaneous velocity. I think you had worried then about how this fixed rate through expanding space could be consistently defined, i.e. when space itself doesn't provide a consistent backdrop. But space really isn't enough, as I've argued above: there really does need to be a consistent four-dimensional background metric. In cosmology, that metric is defined according to comoving coordinates, so that A and B *do* remain a fixed comoving distance from each other as space expands. Galaxies all maintain their positions, and space multiplies.

    Daryl

    Dear Daryl Janzen:

    As you said the concept of "time" in physic is a mess, more than that at least since the beginning of written history men did not know what he was measuring, but doing it satisfied the practical need to know the duration of things. Always till now days, people relate the so called "time" to "motion" and attributed to it quite a few characteristics, like flow, direction and many others than nobody ever proved. People always was asking themselves for definition and empiric meaning, instead of what they was measuring, when the last was find, physicist, specially theoretical physicists had everything they need for their work with it. When you know the experimental meaning of the so called "time" "space-time" not only become understandable, but also understandable is why can't be separated.

    So I sending you a summary of my essay because I am convince you would be interested in reading it. ( most people don't understand this essay and is not just because of my bad English) "Hawking, A brief history of time" where he said , "Which is the nature of time?" yes he don't know what time is, and also continue saying............Some day this answer could seem to us "obvious", as much than that the earth rotate around the sun....." In fact the answer is "obvious", but how he could say that, if he didn't know what's time? In fact he is predicting that is going to be an answer, and that this one will be "obvious", I think that with this adjective, he is implying simple and easy to understand. Maybe he felt it and couldn't explain it with words. We have anthropologic proves that man measure "time" since more than 30.000 years ago, much, much later came science, mathematics and physics that learn to measure "time" from primitive men, adopted the idea and the systems of measurement, but also acquired the incognita of the experimental "time" meaning. Out of common use physics is the science that needs and use more the measurement of what everybody calls "time" and the discipline came to believe it as their own. I always said that to understand the "time" experimental meaning there is not need to know mathematics or physics, as the "time" creators and users didn't. Instead of my opinion I would give Einstein's "Ideas and Opinions" pg. 354 "Space, time, and event, are free creations of human intelligence, tools of thought" he use to call them pre-scientific concepts from which mankind forgot its meanings, he never wrote a whole page about "time" he also use to evade the use of the word, in general relativity when he refer how gravitational force and speed affect "time", he does not use the word "time" instead he would say, speed and gravitational force slows clock movement or "motion", instead of saying that slows "time". FQXi member Andreas Albrecht said that. When asked the question, "What is time?", Einstein gave a pragmatic response: "Time," he said, "is what clocks measure and nothing more." He knew that "time" was a man creation, but he didn't know what man is measuring with the clock.

    I insist, that for "measuring motion" we should always and only use a unique: "constant" or "uniform" "motion" to measure "no constant motions" "which integrates and form part of every change and transformation in every physical thing. Why? because is the only kind of "motion" whose characteristics allow it, to be divided in equal parts as Egyptians and Sumerians did it, giving born to "motion fractions", which I call "motion units" as hours, minutes and seconds. "Motion" which is the real thing, was always hide behind time, and covert by its shadow, it was hide in front everybody eyes, during at least two millenniums at hand of almost everybody. Which is the difference in physics between using the so-called time or using "motion"?, time just has been used to measure the "duration" of different phenomena, why only for that? Because it was impossible for physicists to relate a mysterious time with the rest of the physical elements of known characteristics, without knowing what time is and which its physical characteristics were. On the other hand "motion" is not something mysterious, it is a quality or physical property of all things, and can be related with all of them, this is a huge difference especially for theoretical physics I believe. I as a physician with this find I was able to do quite a few things. I imagine a physicist with this can make marvelous things.

    With my best whishes

    Héctor

      Daryl,

      I'm really not trying to be hard-headed here, but I'm not getting it. Whether calculus or rubber bands, it seems to relate one unit to another and insist they are both space. I don't see how they both can be the denominator.

      Dear Héctor,

      Thanks for the summary of your essay. It does indeed sound interesting to me, and I look forward to reading it. From what you said, I suspect you would find some interest in the above discussion I've been having with John Merryman--especially the first part.

      Thanks for commenting here, and best wishes!

      Daryl

      Dear Daryl

      Thanks for your extensive reply. First of all, I'd like to make clear that it was never my intention to insult you or anybody else. Please accept my apologies if I say something that made you feel insulted.

      With respect to the dimensionality of reality. I agree with most of your points. In math, points are defined in terms of lines, lines in terms of planes and planes in terms of solids. So there is implicitly, as you said, a higher dimension defining lower dimensions.

      You: I mean that I would define time just as Newton defined absolute time, except that I'd add a note that by "flow" I DO NOT mean flow through a substantive dimension, which the definition can easily be taken to mean. Rather than flow along a substantive dimension, I suppose I'd say more properly I mean flow as an absolute dimension, so that, as with classical mechanics, I mean that at any instant the three--dimensional Universe, constitutes all of reality.

      Newton said that mathematical, true time flows absolutely without reference to anything else and its other name is duration. Is this what you mean by substantive dimension? I'm sorry but I don't get what you mean by "absolute dimension". I don't see the epistemological distinction between substantive dimension and absolute dimension because as far as I understand Newton's notion of time is both substantive and absolute.

      You: Actually, the statement that the mathematical formalism is all that matters for practical purposes is incorrect. In practice, in order to correctly make use of the mathematical formalism, we need to take observation into account as well.

      Of course, I agree that we have to consider observation. Perhaps you misunderstood me. What I meant to say is that if we don't put our ideas in a mathematical formulation, i.e., a formal theory, they will remain at the level of ideas or mere philosophy. For the physics community what matters is that theory agrees with the observations, the problem sometimes is that these observations are nothing but data and data can have many interpretations.

      You: The point that I tried to make in my essay with the Albert and Henri example is that this is actually wrongheaded. Sure, Henri is free to frame things in such a way that the clock across the train car "remains at a fixed distance from him, and both of them remain motionless". But if he opens his eyes to the world around him, he should see that he's actually moving--i.e. he's not "truly" motionless.

      Yes, I agree with this, one can easily infer that there should be an absolute frame. The problem is that is not easy to define which one is and how to find it. This is in connection to what you later say that we know for sure that the earth is moving with an ABSOLUTE velocity of 370 km/s.

      I assume that you are referring to the speed of the earth relative to a frame at rest with the CMB radiation. Here one should question: is this velocity interpreted within the context of SR or GR (or what theory)? For the sake of consistency test theories of SR have to assume that there exists at least one inertial frame of reference where the one-way speed of light is isotropic. Such frame is considered to be the frame at rest with the CMB (Test theory of special relativity:I, II, and III Mansouri et al. Gen. Rel. Grav. 8, pp., 497, 515 and 809, 1977). For other frames the speed of light could be, in general, anisotropic and this would depend on the choice of clock synchronization. SR is a theory with a particular clock synchronization that leaves the one-way speed of light invariant for all frames. However, strictly speaking, one should acknowledge that in SR there are no absolute frames of reference. Therefore, for SR, 370 km/s is not an absolute velocity but a relative one.

      To be continued

      Israel

      Cont. from the previous post.

      Within the context of the GR, the interpretation is not different at all. From the cosmological perspective, relativists distinguish two classes of reference frames, that is: (a) those that go a long with the expansion of the universe (Hubble's flow) or comoving frames and (b) those that don't follow the space expansion. For an observer in a comoving frame the universe appears to be static and isotropic. As well, this frame also defines a cosmological time. For any other frame different than the comoving frame the observers will see the universe expanding (redshifted). Thus 370 km/s is the speed of the earth relative to the comoving frame and, again, according to relativists, this frame is not an absolute frame but only a frame that is selected, for the sake of simplicity, among the infinite frames; just as when we select the sun to simplify the motion of planets. Moreover one should keep in mind that the rate of flow of a clock is function not only on the speed of the clock with respect to the absolute frame but also with respect to its position in a gravitational field. Therefore, how would we know what the best standard of time is? I mean, for experimental matters the rate of flow of a clock in the neighborhood of a black hole is not the same rate of flow as on earth, or on the sun or between two galaxies where we assume there are no sources of gravitation. So, one should acknowledge that relativists have a strong point. What do we mean by cosmic time if the flow of time would depend on where the clock is placed in the universe? For practical matters, relativists assumed that in the comoving frame all clocks are synchronized. But how are these clocks synchronized? This question leads us again to the problems of clock synchronization and the one-way speed of light which is a vicious circle. From this circular reasoning one realizes that it seems that nature is conspiring against us (as in the case of the measuring problem in quantum mechanics). This is a topic that has been extensively discussed in the literature and I wouldn't like to open a discussion on this topic here, I just wanted to let you know about it. In the book of gravitation and spacetime from Ohaninan and Ruffini, one can read in relation to the "absolute speed of the Earth": this determination of velocity of the Earth in no way contradicts the principle of relativity, since the measurement is not made relative to empty space, but relative to the photon gas in the blackbody radiation. As you can see, for relativists there is no absolute frame of reference.

      You: First of all, the "clock paradox" that you refer to is not IDENTICAL to the "twins paradox", as you've suggested. The "clock paradox" is an important result from SR that's used in *constructing* the "twins paradox", which runs specifically as follows...

      I disagree, they are IDENTICAL. The clock paradox according to Einstein himself runs as follows: Imagine we have initially two synchronized clocks and one of them is set in motion in a journey at a constant speed. According to SR and given the symmetry of the problem both clocks should show the same time when they reunite. Einstein GUESSED that when the traveling clock returns it would read less time when compare to the clock at rest, in contradiction to the theory predictions. It was Paul Langevin who in 1911 argued that living organisms are also clocks and he introduced twins instead of clocks in this problem. The twins obviously represent two synchronized clocks. Therefore the clock paradox is the same as the clock paradox. It seem to me that you are confusing "time dilation" (which is used to construct the paradox) with "clock paradox". The case in your essay is the clock paradox better known as the twin paradox.

      My comments from the previous post, where aimed at trying to delimit the paradoxical part. This part consists in that both observers should conclude that time should tick slowly for both because, according to SR, time dilates equally for two systems of reference in relative uniform motion. Therefore, given that in SR there are no absolute frames, observers cannot decide whether time really dilates or not. Since they cannot decide this, it's impossible to conclude that when both clocks reunite one clock will read less time than the other. It was Einstein that BET or GUESSED (without any theoretical argument) that the traveling clock will read less time than the other. Thus one should distinguish the two paradoxical aspects of the "paradox": (1) that time dilates for both observers in relative motion in the same amount and so they cannot decide if time really dilates or not and (2) that one cannot conclude that the traveling twin (clock) will be younger than the other. From what theoretical (within the context of SR alone) argument can we conclude that the traveling twin will be younger? This is the second paradoxical aspect. Most people think that the clock or twin paradox consists in aspect (2) whereas I argue that it consists in aspect (1).

      As you correctly argue, when we introduce the absolute frame of reference [which for you is the CMB and that for me the CMB is only a manifestation of space (conceived as a material field)] then actual motion comes into play and the clock that is set in motion is the one that really undergoes time dilation.

      You: The resolution has nothing whatsoever to do with acceleration.

      I agree. I just mentioned that relativists resort to acceleration to solve the "paradox".

      Well, I just wanted to clarify those points. As you can see I actually have one question which is related to your notion of time and I hope you have some time time. These days, I have been reading the arguments of Brian Greene about time and the loaf picture but that picture of time seems to me like a linear vision of time as a dimension, but as you and Brain put it, seems to be paradoxical. My notion is more Newtonian. For me time is just the transformation of things, it is change, but it seems that the transformation is gradual and follows a transformation law.

      Well, thanks a lot for your time.

      Best Regards

      Israel

      Dear Israel,

      Thanks very much for responding. First of all, on the twins paradox thing, I see your point. I forgot that in the scenario in my essay I did have each of them claim that the other shouldn't have aged enough. It's just that that wasn't the point I meant to illustrate, so I didn't think of it. You'll notice that I didn't describe in any way how they got back together, but just said that they did. I didn't say anything about the train turning around, for instance. What I was really meaning to illustrate at that point was the symmetry of relative time-dilation between two systems in uniform translatory motion.

      I also see that I only managed to confuse the issue on time. I think Newton's definition is right. I was just trying to say something about the fact that when we think of something flowing, we may tend to think of it flowing through space. In fact, it's flowing through space in time, which is more complicated yet. Do you see how it's confusing to use verbs (like flow or rest or change) to describe time, when time is actually the denominator of those verbs? i.e. things flow or rest or change *in time*. I think that already starts to do a good job of defining time, but there's something more to it. That's the metrical structure, which is the "equable" part in Newton's definition.

      But when Newton says time flows equably, he makes a point of saying that that flow is without reference to anything external. So he's saying that it doesn't flow through any space, which is the point I was trying to be careful about, although I see I was just confusing the issue. He calls this equable flow without reference to anything external "duration", which is what I mean when I say it's the denominator of all verbs, and that it has well-ordered measure, or metrical structure.

      But then that metrical structure has to be a part of the Universe, if we're saying that only the present Universe is real at any given moment. That's another important point, I think.

      So, to summarise, I think time's a tricky thing to define because in defining it we'd like to use verbs (like "flow", etc.), but time is already implicit in those verbs. I think the "flow" or "passage" of time has well-defined metrical structure, but I think it's worth cautioning (as Newton did) not to think of that "flow" as occurring through a space that has that metrical structure.

      The other point you brought up was about observing absolute rest. I think looking at local clock synchronisation and relative motion is really the wrong way of going about this.

      But I think cosmology does show, in a totally different way, that there is an absolute rest frame. Historically, this evidence came as follows: if there were no such thing as absolute rest, and all motion were just random, then the relative motion of everything, from any perspective, should be uniformly distributed on the interval (0,c). The fact that the stellar velocities are orders of magnitude less, was already taken by Einstein as motivation enough to assume a cosmic time variable in 1917. Then came the discovery of the redshift-distance relation, which was taken to indicate cosmic expansion--i.e., the redshifts are not thought to be due to relative motion, but due to the expansion of space through which the light travels. Over time, we've discovered tens or hundreds of thousands of objects with redshifts greater than 1, confirming this suspicion. These cosmological redshifts are therefore many orders of magnitude greater than the motion of any galaxy through space, including our own. What this means is that we can neglect the motions of all bodies through space and model redshifts in an expanding universe under the assumption that they're all absolutely at rest. The model, which is a very accurate fit to the data, assumes absolute space and time, which we call the Universe and cosmic time.Through the model, we therefore have a means of measuring cosmic time *even without knowing our own absolute motion*. That's simply a handy thing about living in an expanding universe.

      But you know that's not the whole story. Cosmic expansion suggests that maybe the Universe was much denser and hotter at some finite time in the past. This led to the prediction of the CMB, which was confirmed. The CMB is a radiation field that's supposed to fill all of space, cooling uniformly as the Universe expands. One feature of particular interest is the dipole anisotropy, which tells us that the Solar System is moving through the CMB towards the constellation Leo at 370 km/s. Since the CMB is supposed to be an isotropic and homogeneous radiation field that fills all of space, we take the CMB's rest-frame to be the absolute rest-frame, and therefore infer that our own absolute motion is 370 km/s in the direction stated. This motion is the combination of the Sun's velocity through the Galaxy and the Galaxy's velocity through the Local Group and the Local Group's velocity within the Local Supercluster, etc. How that combination actually comes together doesn't really matter, though, because we have a direct measurement of our absolute velocity, and that's what mattered.

      Now there's a really good consistency check that indicates to us that this picture is correct: the CMB's multipole anisotropy signature. Again, before it was even observed, the calculations had been done, to describe the effects of vacuum fluctuations at the time the CMB was created, as we would observe them today in macroscopic anisotropies in an otherwise isotropic CMB signature, as these anisotropies would have expanded along with the Universe. The measurements, as you know, are consistent with the model parameters that have been derived through the redshift observations.

      Therefore, we do have strong empirical support for an absolute frame of rest. But that's all that it is: empirical support. We have no way of proving that it's right, any more than we have of proving anything else through observation. But it's a really consistent picture, and it at least refutes the claim that "we can't ever observe absolute motion, so we might as well assume that there isn't any".

      I hope I've answered your questions here. I'm sorry if I was cranky before. Thanks for taking the time to clarify where I had been mistaken or unclear.

      Best regards,

      Daryl