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  1. #31
    CC Grandmaster Spiny Norman's Avatar
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    Quote Originally Posted by Rincewind
    Also I notice you completely ignore the argument that all visual observations rely on knowledge about the speed of light.
    The visual observation "There is a computer screen in front of me" does not rely one whit on knowledge about the speed of light. Nor does the observation "The dog is 60cm tall".

    Perhaps you mean that calculations about things such as the current distance of a far away object, or that exact calculations about the position of a car travelling towards me (to extreme depths of precision) require knowledge of the speed of light?

    As regards variation in the speed of light, your preceding comments seem to fairly state a traditional position; however there are notably some scientists who would disagree with you ... the following summary is an interesting read:

    http://en.wikipedia.org/wiki/Variable_speed_of_light
    “As you perhaps know, I haven't always been a Christian. I didn't go to religion to make me happy. I always knew a bottle of port would do that. If you want a religion to make you feel really comfortable, I certainly don't recommend Christianity.” -- C.S.Lewis

  2. #32
    CC Grandmaster Spiny Norman's Avatar
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    What I will grant you is this: that the measurement of the size of the dog, to extreme levels of precision, depends on the size of a metre, which in turn is defined as 1/phoofteenth of the distance that light travels in a vacuum. But for practical purposes, given that one has a ruler, its easy to measure the dog without any knowledge of the speed of light.

    Now then; riddle me this: given the interest by scientists who are proposing alternative cosmologies which involve a variable speed of light:

    -- are they real scientists?
    -- how is it possible that they are proposing a Variable Speed of Light cosmology if it has been observed that the speed of light is not variable over 10B year timeframes (as you claim)

    I'll answer that for you: it has not been observed that the speed of light is invariable over 10B year timeframes; rather, it is calculated that it is invariable GIVEN THE ASSUMPTION that a particular cosmological model is correct.

    Last time I checked, theoretical cosmological modelling was not observation.
    “As you perhaps know, I haven't always been a Christian. I didn't go to religion to make me happy. I always knew a bottle of port would do that. If you want a religion to make you feel really comfortable, I certainly don't recommend Christianity.” -- C.S.Lewis

  3. #33
    Reader in Slood Dynamics Rincewind's Avatar
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    Quote Originally Posted by Spiny Norman
    The visual observation "There is a computer screen in front of me" does not rely one whit on knowledge about the speed of light.
    I beg to differ. Assuming your only evidence is visual you are surmising (probably correctly) that light only takes a fraction of a picosecond to reach your eyes. However if light were to travel much slower than that, say one centimetre a second then the monitor you think is in front of you might actually have turned to dust long before the light travelling from it reaches your retina.

    Quote Originally Posted by Spiny Norman
    As regards variation in the speed of light, your preceding comments seem to fairly state a traditional position; however there are notably some scientists who would disagree with you ... the following summary is an interesting read:

    http://en.wikipedia.org/wiki/Variable_speed_of_light
    My position is that of conventional science and if you think some notable scientists disagree with what I said I suggest you point out exactly which scientists and exactly which points. Certainly there is some scope for very fine changes in the speed of light but nothing so great that the universe could all fit in a 10,000 light year sphere.

    Secondly there is considerable speculation on the variability of the speed of light (and other "constants") in the very early universe. My comments make no reference to the very early universe which all notable scientists (to my knowledge) place as having happened at least 10 billion years ago and more like nearly 14 billion years ago. Any comments of such variability are in the realms of cosmology and not astronomy and beyond the scope of our discussion (concerning the distance to other stars and galaxies).

    Regarding different speed limits of for light in different parts of the universe (as you suggested in an early post) I know of no well known scientist positing such a hypothesis.

    I had a quick re-read of your linked page (I read it just yesterday) and so there is nothing there which is surprising. The light through a medium is an effective speed of light, not actually speed of light, and does not apply to space which is essentially a vacuum. The quantum effects are likewise not relevant to astronomical observation. Other findings are disputed and even if the most unconventional of those claims were valid, then you still would not be fitting what we know about the universe into a 10,000 year old history.
    So einfach wie möglich, aber nicht einfacher - Albert Einstein

  4. #34
    Reader in Slood Dynamics Rincewind's Avatar
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    Quote Originally Posted by Spiny Norman
    Now then; riddle me this: given the interest by scientists who are proposing alternative cosmologies which involve a variable speed of light:

    -- are they real scientists?
    -- how is it possible that they are proposing a Variable Speed of Light cosmology if it has been observed that the speed of light is not variable over 10B year timeframes (as you claim)
    The scientists proposing such hypotheses are indeed scientists. Since advances by people proposing hypotheses and testing them with data. Models which require the speed of light to change are talking about changes in the very early universe (usually much less than the first second after the big bang) and as such are not relevant to our discussion regarding the speed of light for the next 14 billion years (give or take a bit). The light we are talking about started its journey sometime in the last 3 billion years, well after the effects of big-bang expansion were no longer a factor.
    So einfach wie möglich, aber nicht einfacher - Albert Einstein

  5. #35
    CC Grandmaster Spiny Norman's Avatar
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    Earlier on you said:

    Quote Originally Posted by Rincewind
    It is not an assumption, this has been tested to the extent possible by the technology and availability of data and the speed of light has shown to to be stable in recent history (last 10 billion years).
    Then you said this:

    Quote Originally Posted by Rincewind
    Models which require the speed of light to change are talking about changes in the very early universe (usually much less than the first second after the big bang) and as such are not relevant to our discussion regarding the speed of light for the next 14 billion years (give or take a bit).
    The latter statement (highlighted bit) is false. For example:

    http://arxiv.org/ftp/astro-ph/papers/0310/0310178.pdf

    (this is one of the quoted articles in the Wiki about VSL which I quoted above). From section 4 of that paper:

    4. Present value of light deceleration

    Finally, from the radius, the density and equation (9) is now easy to obtain the present value of light deceleration, which results to be 2.2 10-10 m/s-2 , i.e. our model predicts that a decrease of 1m/s could be observed in about 140 years. This very small value has not been observed, but could be hidden within the error bars in recent determinations of c. Very precise laboratory measurements of c could detect this deceleration in a few decades.

    In connection with this, it is remarkable that, using precision lunar orbital periods from 1978 to 1981, Van Flandern (1984) obtained a small deceleration in c:

    -c’/c = (3.2 ±1.1) 10-11/year. (23)

    This result represents a light deceleration of about 3 10-10 m/s2 , in agreement, taking into account the error margins quoted, with our calculated value.

    The variation of c should be tested with ‘mechanical’ clocks such as those based on mechanical vibrators, pulsars rotation or planetary revolution, because atomic clocks periods depend on c.
    They are talking about decelaration in the value of c today, not billions of years ago. Either:

    (a) they are quite mad, as c is constant and cannot change, and it has been observed not to have changed over 10B years as you claimed (quote #1 above); or

    (b) c has not been observed to be constant over 10B years; rather, it has been calculated to be constant in accordance with a preferred cosmic model

    Seems quite clear to me that (b) makes more sense. These are real scientists, making testable predictions, and I'll lay London to a brick that they know more about the speed of light and cosmology than both you and I put together. They would not be proposing a variable speed of light if your earlier claims were true.

    So you are claiming something as observable fact when it simply isn't the case. Treat it as "our preferred cosmological model" or "in accordance with current observations", but please don't call a 10B-year claim "observation" when it isn't.
    Last edited by Spiny Norman; 11-08-2010 at 05:58 PM.
    “As you perhaps know, I haven't always been a Christian. I didn't go to religion to make me happy. I always knew a bottle of port would do that. If you want a religion to make you feel really comfortable, I certainly don't recommend Christianity.” -- C.S.Lewis

  6. #36
    CC Grandmaster Spiny Norman's Avatar
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    Quote Originally Posted by Rincewind
    I beg to differ. Assuming your only evidence is visual you are surmising (probably correctly) that light only takes a fraction of a picosecond to reach your eyes. However if light were to travel much slower than that, say one centimetre a second then the monitor you think is in front of you might actually have turned to dust long before the light travelling from it reaches your retina.
    For your proposition to be true, only people who knew what the speed of light was would be able to make valid observations.

    Since most people don't know the speed of light, and in this I include most scientists (who would have to refer to a book to get the value), then most people would not be able to observe anything with any certainty.

    Since that is clearly false, your proposition is also false. Most observations simply do not require the level of certainty that you apparently seem to think they do.
    “As you perhaps know, I haven't always been a Christian. I didn't go to religion to make me happy. I always knew a bottle of port would do that. If you want a religion to make you feel really comfortable, I certainly don't recommend Christianity.” -- C.S.Lewis

  7. #37
    Batoutahelius road runner's Avatar
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    Spiny, what kind of variance in the speed of light is required to make the calculations fit your world view?

    Is this variance anything near what is put forward in that paper?
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  8. #38
    Reader in Slood Dynamics Rincewind's Avatar
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    Quote Originally Posted by Spiny Norman
    For your proposition to be true, only people who knew what the speed of light was would be able to make valid observations.
    Not at all, most people apply an inductive knowledge of the way systems in the everyday world behave which is in a uniform and consistent fashion. Now if the speed of light behaved in the manner you seem to entertain: speeding up, slowing down and jumping around all over the place then such observations would be on shaky ground indeed.

    Quote Originally Posted by Spiny Norman
    Since most people don't know the speed of light, and in this I include most scientists (who would have to refer to a book to get the value), then most people would not be able to observe anything with any certainty.
    Exactly! Certainty comes from the fact that the speed of light is constant.

    Quote Originally Posted by Spiny Norman
    Since that is clearly false, your proposition is also false.
    Your logic is very sloppy today Spiny. The false proposition is actually that the speed of light is not constant. If it were, then we would be up a proverbial creek without a means of locomotion.

    Quote Originally Posted by Spiny Norman
    Most observations simply do not require the level of certainty that you apparently seem to think they do.
    All observations are visual and involve the motion of photons and as such rely on a greater or lesser extent on the speed of light. Thus no visual observation can be made which matter 'not on whit' on the speed of light. Furthermore, if the speed of light was variable then everyday observations would be just as prone to the sort of problems you claim only affect astronomical observations.
    So einfach wie möglich, aber nicht einfacher - Albert Einstein

  9. #39
    Reader in Slood Dynamics Rincewind's Avatar
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    Quote Originally Posted by Spiny Norman
    The latter statement (highlighted bit) is false. For example:

    http://arxiv.org/ftp/astro-ph/papers/0310/0310178.pdf

    (this is one of the quoted articles in the Wiki about VSL which I quoted above).
    Unless you can get a reference for that paper showing that his has been peer reviewed I'm not going to bother reading it. The arxiv is just an archive that anyone can and do put up whatever they like. Some or most of it may get published someday but until that happens there is not much point a non-specialist like me (or you) trying to make sense of something that may just be hogwash.

    Looking at the following page and list of publications

    http://www.labome.org/expert/spain/u...do-997254.html

    Assuming it is the same guy, (note [7] shows an affiliation to the Matgas Research Centre) the author does not seem to be a regular contributor to cosmology literature (why is it that physical chemists think they know anything about cosmology? ) and so I would view the paper with even a greater level of suspicion.
    So einfach wie möglich, aber nicht einfacher - Albert Einstein

  10. #40
    Reader in Slood Dynamics Rincewind's Avatar
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    Quote Originally Posted by Boris
    Spiny, what kind of variance in the speed of light is required to make the calculations fit your world view?

    Is this variance anything near what is put forward in that paper?
    Against my better judgement I did look further into that paper. Apart from what looked to be a basic mathematical error in going from equation (11) to (12) (which perhaps is justified for reasons not apparent to me) the literature used by the author seems very cherry picked. For example he cites a value in the variability of c given by Van Flandern (1984). Now Van Flandern is* a eccentric that not many people take seriously any more and surely there are more modern and more accurate estimates available for c' than something calculated in 1984. For example there is the very well publicised measurements arising from the supernova SN1987A which previously unavailable parallax measurements as well as new astronomical installations that have come online over the last 25 years.

    Anyway, I think I've wasted enough time on this red herring for now. My advice to everyone is to be more critical with what they read. There is a large amount of material available on the arxiv, but not all of it is good science.

    * Edit: was
    So einfach wie möglich, aber nicht einfacher - Albert Einstein

  11. #41
    CC Grandmaster Spiny Norman's Avatar
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    Quote Originally Posted by Boris
    Spiny, what kind of variance in the speed of light is required to make the calculations fit your world view?
    Relevance?

    Quote Originally Posted by Boris
    Is this variance anything near what is put forward in that paper?
    Relevance?

    My beliefs/worldview are quite irrelevant to the current discussion, which is about what qualifies as observation. Its crystal clear to me that c has been observed/recorded only for the past few hundred years.

    Given RW's apparent inability to tell the difference between a calculation based on a cosmological model and an observation, there is little point discussing it further.
    “As you perhaps know, I haven't always been a Christian. I didn't go to religion to make me happy. I always knew a bottle of port would do that. If you want a religion to make you feel really comfortable, I certainly don't recommend Christianity.” -- C.S.Lewis

  12. #42
    CC Grandmaster Spiny Norman's Avatar
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    Quote Originally Posted by Rincewind
    Certainty comes from the fact that the speed of light is constant.
    No, the certainty comes from:
    -- the fact that the value of c is very, very high; and
    -- that everyday observations on the earth can safely ignore c as a factor when calculating the position of objects, the time shown on clocks, and so on ... because the level of precision we need simply doesn't require knowledge of c

    If you cannot see that basic fact, then I give up ... forest and trees.
    “As you perhaps know, I haven't always been a Christian. I didn't go to religion to make me happy. I always knew a bottle of port would do that. If you want a religion to make you feel really comfortable, I certainly don't recommend Christianity.” -- C.S.Lewis

  13. #43
    Batoutahelius road runner's Avatar
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    Quote Originally Posted by Spiny Norman
    Relevance?


    Relevance?

    My beliefs/worldview are quite irrelevant to the current discussion, which is about what qualifies as observation. Its crystal clear to me that c has been observed/recorded only for the past few hundred years.

    Given RW's apparent inability to tell the difference between a calculation based on a cosmological model and an observation, there is little point discussing it further.
    IIRC you implied that the size of the universe is grossly overstated and the reason for that is that the speed of light moved faster way back when.

    Leaving aside for a moment that, if there is a god, you grossly devalue him by diminishing his creation by argung this sort of thing.

    If we have established that there is an object a billion light years away, assuming that speed of light is more or less constant. Then if you want to argue that it is only say a thousand light years away then you have to be assuming that the speed of light has slown down by a factor of about a million times, don't you?

    The question is a) is that what you are assuming, and b) if variance in the speed of light has been shown, is it anything like variance of that magnitude.
    meep meep

  14. #44
    Reader in Slood Dynamics Rincewind's Avatar
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    Quote Originally Posted by Spiny Norman
    -- that everyday observations on the earth can safely ignore c as a factor when calculating the position of objects, the time shown on clocks, and so on ... because the level of precision we need simply doesn't require knowledge of c
    Surely one requires knowledge that it is very fast and can be ignored. Wouldn't you agree? Otherwise how can you justify ignoring it in short range measurements?
    So einfach wie möglich, aber nicht einfacher - Albert Einstein

  15. #45
    Reader in Slood Dynamics Rincewind's Avatar
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    Quote Originally Posted by Boris
    The question is a) is that what you are assuming, and b) if variance in the speed of light has been shown, is it anything like variance of that magnitude.
    Even if that were the position it is dead in the water since the speed of light is not the only way we can measure distance. There are parallax measurements made based on the radius of the earth's orbit. Measure angles to stars in different seasons we can benchmark some of the closer stars. I'm not sure if we get out beyond 10,000 light years with current instruments but I believe it is close. And only a very small number of stars are that close (they are all in our galaxy) so it doesn't leave much room for the other galaxies (and there are something like 170 billion galaxies other than the Milky Way). Each one containing millions of stars at least (some giants contain trillions of stars). That's a lot of crap to fit in a 10,000 light year sphere.

    Secondly we have been able to observe light not only travelling directly toward us, but first at an angle and then toward us. When the super nova SN1987A went off a few months later it 'lit up' a circle of matter around the star and the angular measurement of the ring is possible from earth (unlike most stars which subtend too fine an angle for us to measure). Use these measurements (time for rings to switch on, angular measurement of rings) we can determine the distance to SN1987A using trigonometry. Based on a constant speed of light it is around 168,000 light years. The good thing is that if light has been slowing down then the SN must be even further away (not closer).

    For more info on SN1987A see

    http://en.wikipedia.org/wiki/SN_1987A

    or the following paper

    http://articles.adsabs.harvard.edu/c...&filetype=.pdf

    which gives a distance of 51.4 +-1.2 kpc which is 168,000 +- 3,900 light years.
    So einfach wie möglich, aber nicht einfacher - Albert Einstein

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