The Speed of Light is Not Constant

brucep said:
It's easy to think that the local speed of light is an invariant because time and length are relative [the actual natural phenomena is somewhat counterintuitive to humans]. I had a conversation with several folks who thought the experiment to directly detect gravitational waves was flawed because they didn't take into account time dilation and length contraction, associated with the path of light between the test mass, would cancel out 'something or rather' so that we wouldn't be able to detect a change in distance between the test mass indicating a gravitational wave passed through the experiment model. Same mistake but understandable if you haven't studied the physics. "studied" a dirty word for cranks.

Sorry about the convoluted [somewhat] sentence. LOL,
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Vinaka vakalevu brucep...
 
Russ_Watters said:
Yes. It really is that simple in this case. Need Einstein to say it? Here he is:

http://patrick.maher1.net/318/lectures/eins1.pdf

Be careful with that link - it is a to a university physics course on Relativity and if you let your guard down you may accidentally learn something.
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hahaha! No wonder you lot are all at sea. Your 'understandings; and 'arguments' are based on facile HALF-measures, not the whole contextual background.

When one thinks of 'time', one is really speaking of TWO simultaneous EVENTS; like i see the hour hand on my watch pointing to 7 Oclock as I also see the train arriving at the station.----Einstein
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Get it yet? What YOU referenced was only the INSTANT of 'time' on a SINGLE event reference. It was NOT the comparative 'time' connecting TWO simultaneous events like Einstein points out is the FULLER understanding. Your 'understanding' is PARTIAL and hence limited as to its meaning and usefulness in analysis constructs without a STANDARD or COMPARISON of that 'watch hand 'indication' of an IN-frame INSTANT without external meaning UNLESS you include the OTHER 'event', the 'train arrival at the station'.

No wonder you all have problems with subtle/complex understanding of ALL the REAL factors/aspects involved in real events.



Russ_Watters said:
Are we not speaking the same language here? Do you not understand what the words "term" and "plug in" mean?

A "term" is a symbol (a variable or constant) or number in an equation.
"Plugging in" is replacing the term with its appropriate numerical value.

Here's a primer on middle-school math if you are unfamiliar with how this stuff works: http://www.mathsisfun.com/algebra/definitions.html
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Why the 'cute' troll tactic, mate?

I was the one that already told YOU what 'term' was and how the 'constant c' constant was set to '1' for that term in the equations.

I then asked YOU to clearly specify what term YOU were 'plugging in' whatever YOU thought you were plugging in.

Please, Russ, stop the twisting; it's unseemly troll tactics long ago made stale and nasty by overuse by worse trolls than you long since permabanned for doing such things until they all got sick of him and his troll tactics (remember him? I wonder where he now?).



Russ_Watters said:
So: What is the number that "c" represents in that equation? I prefer SI units here, so please use the SI number.

...um...do you need me to explain what "SI" means too..?

I'm honestly at a loss here: I'm not sure if you are messing with me or if you really have absolutely no understanding of math whatsoever. Since you've avoided math here at all costs (I've never seen you do any math at all), I suppose it really is possible that you really do have absolutely no understanding of math at all. But I think you are an adult - you claim to be writing a book, which I've never heard of from a schoolchild (and few schoolchildren would be interested in a discussion like this). You are older than 12, right? Do you really not know any math at all? How did you avoid it in school? Or have you just forgotten how to math? I'm honestly not asking to be condescending: it would explain a lot about where you are coming from with your opinions if you honstly have no understanding of math at all.
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Not so fast, matey. You are evading. You said you 'just plug in' the value. You haven't specified what value or into which term. Don't troll twist. Not nice. Nor subtle. Obvious. OK?

I already explained where the assumed 'constant c' is where the term in the equations is set to '1'.

I also already explained how the 'invariant c' is arrived at with in-frame clocks affected by GR in this two-light-clocks scenario.

You have yet to demonstrate you even understand properly what's what, let alone rebut' anything Farsight's OP points/observations based on Einstein-backed GR evidence/predictions etc.

PS: Are you yet up to speed with the implications for your 'stance' of the GR 'rider' Einstein put on his SR 2nd Postulate that clearly states the 'validity' of SR view re 'constancy of light speed' NOT VALID in GR contexts? Try 'getting' that before coming trolling back with your broken 'understandings' and 'arguments' based on partial comprehension of what's what in THIS context of the OP as put by Farsight.
 
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PhysBang said:
Like Farsight, you assume that your understanding of what was written is what was written. You have a history of half-reading/half-remembering things. So, where is it that Einstein says what you think he says?
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Whatever rationalization does it for you, mate.:) If you don't even know that then you have nothing to discuss with Farsight, let alone 'refute' with.

Anyhow, you asked where I saw/heard Sean Carroll's work/conclusions last. I looked in my video/tv archive and could only find the following info about the TV program I saw him explain his method/result in:
WEBSITE: BBB.CO.UK/SCIENCE

COPYRIGHT: BBC MMXII


EDITOR: AIDAN LAVERTY

HORIZON: BBC PRODUCTIONS

A BBC/SCIENCE CHANNEL CO-PRODUCTION

SCIENCE DOCUMENTARY PROGRAM: COSMOLOGY

SERIES PRODUCER: NICOLA COOK

WRITTEN & DIRECTED BY: KENNY SCOTT

NARRATOR: STEVEN MACKINTOSH

TITLE: “HOW BIG IS THE UNIVERSE?”

AIRED IN AUSTRALIA ON SBS-1 TELEVISION CHANNEL, MONDAY, JAN 20, 2014, 8:34 PM, AEDST.

SEAN CARROLL
THEN AT: CALIFORNIA INSTITUTE OF TECHNOLOGY
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Go to it and find out what he did/said for yourself, mate, and you'll see I didn't lie to you. I trust when you come back you won't be as trollish as to again try to dictate to the physics professionals and/or sciforum members what is 'acceptable' and what is 'not acceptable' in science communication in general. Cheers. :)
 
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OnlyMe said:
First, I don't apply a double standard. I just don't reply to all posts I have some conceptual or factual disagreement with. In this thread as it relates to the issue at hand I have objected to the use of a purely hypothetical construct, as if it proves anything. Hence the issue with making a distinction between what is known to be true and what remains theoretical.

The light clock, as used and described in Farsight's gif, has been at the basis of a great deal of his argument and it appears yours, even though it represents no real clock and the way it is presented, in the gif and text, is not consistent with how it was introduced and used by Einstein, nor used in current mainstream explanations of SR or GR. There is a big difference between using a hypothetical as a descriptive tool within the context of theory and presenting a hypothetical as proof of some reality. The big issue is the claim that what remains hypothetical or theoretical, is proof of what is real!

The bottom line is that the NIST optical clocks are not light clocks. There are no real light clocks in the sense portrayed by Farsight's gif, and the NIST optical clocks do not provide any objective data associated with the claims made using the optical clock gif. They don't measure or depend (directly) on the speed of light.

BTW - Where the issue of double standard is concerned, though as I said I don't respond to every post, where I have some difference of opinion, interpretation or understanding, I have in another thread, also one of Farsight's, pointed out a similar difference of interpretation, with a post on the opposing perspective, of that related discussion. In that case the issue was one of conceptual interpretation rather than the misuse of hypothetical as proof of fact.

I don't believe that in either case, I have taken a stand on the basic issues of whether, the speed of light is universally constant or what the fundamental mechanism of gravitation is... Though I have stated that I believe GR is an accurate description of how we observe objects interacting (gravitationally), and I have stated that the speed of light has been proven to be locally constant, while the universal aspect of the SR postulate has yet to be raised above the level of postulate... I have also stated that I don't believe that spacetime curvature is what causes gravity and that it does not make a difference to me whether the speed of light is constant or variable, within the context of GR.

Though I do have unstated opinions on both issues, both for me remain theoretical and unproven, whether I accept them within the larger context of the involved theory or not.



That is a good thing, as his post was based on nothing of merit.
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Okay, OnlyMe. I understand where you're coming from now. You were cautioning BOTH 'sides' on that. My apologies for mistaking your implication. :)

So, are you also rejecting the validity of the 'moving light clock' depictions and illustrative device used by Grumpy in his 'mainstream SR arguments' based on assumptions/conclusions inherent in same, and what you call 'abstract not real' clocks/setups?

In any case, though, the GR case is self-explanatory by what GR predicts happens to clocks timing rates, as Einstein predicted in GR local real case, not abstract/math co-ordinate frame 'reciprocal remote view' case like the twins case without including in-frame acceleration data to make sense of the local effects on clock/aging to the traveling twin compared to Earth twin. That much is agreed, yes? :)


Anyhow, sorry again for misreading you, mate. My apologies once more! It's now clear that that 'double standards' remark definitely does NOT apply to you. Thanks. Cheers. :)
 
Undefined said:
Anyhow, you asked where I saw/heard Sean Carroll's work/conclusions last. I looked in my video/tv archive and could only find the following info about the TV program I saw him explain his method/result in:
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Sean Carroll has written an article re the reality of time, and consequently space, space/time, gravity, mass and energy......



Undefined said:
Why the 'cute' troll tactic, mate?
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Pot, Kettle, black


Pathetic.





You have yet to refute my 6 statements.
 
OnlyMe to Farsight said:
Yes it has been used in explanations of SR hypotheticals, you have been presenting it as some sort of proof within the context of GR. That said...

You need to go back and read the whole of that article. If you do you should notice that there are two hypothetical parallel mirror light clocks in the section. The first is an at rest version and the second is moving along the x axis. This is how I remember the hypothetical being presented, though I will admit it has been a very long time since I cracked open a text book, that used a light box example. As shown, it is a SR example... Further down on the Wiki page they do use the example, as part of an explanation of how SR handles time dilation in accelerated frames, but it remains hypothetical. No one has constructed a similar light clock to test it.

What you have been doing is changing the hypothetical by comparing the location, of two hypothetical light clocks, in a gravity well, adding your own conclusions and calling it proof that light is variable!

Wiki, your reference did not use the light clock example under the section headed gravitational time dilation. (I did not check to see if Wiki used a light clock when addressing the speed of light!)

While you can imagine what gravity would do to a light clock, your imagination is not proof.

I have no issue with you using the hypothetical as a part of your explanation of your beliefs. I have been objecting to equating it to some kind of proof! . . . You have how many times begun with the NIST optical clock example and then switched to the hypothetical light clock to say, "SEE HOW LIGHT GOES FASTER!".

Light clocks are not real and while they can be useful to help convey how we think things work, they will never be evidence of how things work... Unless and/or until someone makes a functioning light clock and uses it in an experiment.

Even then since the mechanics involved would be exceptional.., personally I would wait for some Peer Review, of the breakthrough.
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My red highlighting in your above quote.

Mate, to be fair to Farsight, I must point out that the NIST clock example was used in explanations as to the definition of the second per se, as a first/separate issue from how that initial 'standard defined' second is LATER observed/predicted to be affected by local differences in GR predicted effects on clocks. So your criticism there is based on conflation by you of the two separate aspects/issues involving NIST/second and the GR effects/using second etc etc as so far discussed already.

That's all I wanted to point out, mate! Cheers. :)
 
Moderator: Why is this paddoboy allowed to make such science-empty and comprehension-empty and cluttering 'me too' posts and get away with spoiling the flow of discussion between those who ARE discussing on the point/science with arguments instead of paddo's 'me too' trolling and 'mindless noise'?

He has been reported as per your suggested course for tackling the trolls. Now please keep your word and do something about this patent paddoboy TROLL pure and simpleton. Thanks.
 
Undefined said:
Moderator: Why is this paddoboy allowed to make such science-empty and comprehension-empty and cluttering 'me too' posts and get away with spoiling the flow of discussion between those who ARE discussing on the point/science with arguments instead of paddo's 'me too' trolling and 'mindless noise'?

He has been reported as per your suggested course for tackling the trolls. Now please keep your word and do something about this patent paddoboy TROLL pure and simpleton. Thanks.
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I've given you plenty of science as to why the speed of light is always constant.....you chose to ignore it, you chose to be indignant, that a layman would dare tell you anything, you insult, you belittle, you post in your passive aggressive manner, claiming the moral scientific high ground, when in fact [as others have noted] you are in the cesspit.
Then you have the hide to ask a moderator to step in......grow up undefined...grow up.
 
Forum/Moderator: I already explained that SR 2nd Postulate 'validity of constancy of light speed' does NOT extend to GR contexts as per Einstein's GR 'rider' on that 2nd Postulate.

Now, what intelligence/troll level of obtuseness would have to obtain in a poster (see above) who keeps repeating his obviously uncomprehended comic book version 'understandings' without properly bothering to understand even what the 2nd Postulate GR 'rider' implies for his repetitive inane trolling irrelevances?

Looks pretty grim and dim for that poster's intelligence/troll level, doesn't it?
 
Declan Lunny said:
I think you are trying to over think a rather simple property of SR & GR. Stated as simply as possible: All observers will find that the speed of light is the same, regardless of whether they are looking at light in their own reference frame or someone else's reference frame. Everyone will measure it speed as 3 x 10^8 m/s. Any light they measure from whatever source will be just that. What differences they will observe which ARE frame dependent are time dilation and space contraction. But light they will all agree on. It is invariant because it is same to all observers and doesn't need any adjustment to relate one frame to another.

Distance/time = speed. Distance(contracted)/time(dilated) = speed(unchanged.)
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That just about fits the bill.....
 
Forum/moderator: Yet more facile uncomprehending 'me too' posts from the troll and his mindless 'quotes and links'. He doesn't realize that the two-lightclock scenario is LOCAL GR frame reality of effects on the light IN the clocks, and not some 'remotely observed or coordinate frame analytical overlay. The reality of local GR effects on the clocks IS LOCAL and REAL, as per Einstein's GR predicted effects. All this blather about theoretical interpretations from SR and REMOTE 'views' is made MOOT by the LOCAL differences in the LIGHT CLOCK tick rates. Period.



PS: Wait a few moments for the mindless troll to blithely ignore that LOCAL GR effect fact/reality and go straight to 'post more mindless paddo-noise'. Tick...tick...tick........ :)
 
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Originally Posted by James R View Post

For example, in explaining the Shapiro delay, mentioned above, we note that if we assume a flat spacetime then the speed of light seems to slow as the light passes near the Sun. However, if we take the general relativistic description seriously, then the explanation for the apparent slowing of the speed of light is that there is actually more space near the Sun than there would be if the spacetime there was flat, because in fact the spacetime is curved. The light therefore has further to travel, which takes longer, even though its speed through the vacuum remains constant.
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Spot on, and a point I have mentioned a few times.


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Quote Originally Posted by PhysBang View Post
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Originally Posted by Undefined View Post
You forgot the 'rider' Einstein put on the 2nd postulate that makes it valid in SR but NOT valid anymore in GR contexts.
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But that isn't what Einstein did. He said that its application was restricted.

You are free to use the subtleties of Einstein's claims, but not a gross misinterpretation that turns into a lie.

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Thanks PhysBang....

Two great refutations to the silly thread title.
My own reasons are more simplistic......
Light travels at 'c" because it has no mass.
If it actually travelled at any other speed, we would be measuring that it had some mass.

That and the obvious longer distances that photons travel in curved space/time, seems a rather basic reason why we "may perceive "light travelling faster or slower" but in actual fact, it just has longer and/or shorter distances to travel.
The photons always move at "c" period:
 
Just found this interesting paper concerning MOIST....
Anyone familiar with this?"



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http://philsci-archive.pitt.edu/9448/

On the invariance of the speed of light
Gao, Shan (2012) On the invariance of the speed of light. [Preprint]



Abstract



It has been argued that the existence of a minimum observable interval of space and time (MOIST) is a model-independent result of the combination of quantum field theory and general relativity. In this paper, I promote this result to a fundamental postulate, called the MOIST postulate. It is argued that the postulate leads to the existence of a maximum signal speed and its invariance. This new result may have two interesting implications. On the one hand, it suggests that the MOIST postulate can explain the invariance of the speed of light, and thus it might provide a deeper logical foundation for special relativity. Moreover, it suggests that the speed constant c in modern physics is not the actual speed of light in vacuum, but the ratio of the minimum observable length to the minimum observable time interval. On the other hand, the result also suggests that the existing experiments confirming the invariance of the speed of light already provide observational evidence to support the MOIST postulate.
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Forum/Moderator: There you have yet more mindless quoting and linking from the 'me-too-uncomprehending-what-I-quote/link' paddo-noisemaking troll to clutter up the threads/discussions. Obvious. Have you given up in despair, moderator? Don't blame you, that paddo-noise is getting beyond a joke. Please try though, ok, mod? Even Tach was better than paddo's totally useless crap. Do something about him, please? The forum would thank you I'm sure. Thanks.
 
Forum/Moderator: More mindless linking without any understanding or argument indicating what is relevant to the actual points made in the context of the OP, not paddo's 'handle' on stuff he hasn't a clue about. Remember when Tach used to do that to everybody, as paddo is doing now? This paddo-noise making troll is doing his stuff to clutter the place up.....and doing it blatantly under your nose, moderator. What does that tell the rest of the Forum/readers?
 
Undefined said:
Whatever rationalization does it for you, mate.:) If you don't even know that then you have nothing to discuss with Farsight, let alone 'refute' with.
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You mean like how you said he entirely rejected the "rubber sheet" analogy when he clearly did not?
Anyhow, you asked where I saw/heard Sean Carroll's work/conclusions last. I looked in my video/tv archive and could only find the following info about the TV program I saw him explain his method/result in:
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Why don't we go to the things that the guy actually wrote about this subject: http://preposterousuniverse.com/writings/cosmologyprimer/expanding.html

"Einstein's general theory of relativity, which states that spacetime is curved and that curvature is what we perceive as "gravity," provides a dynamical framework for understanding the expansion of the universe. In cosmology, the curvature of spacetime comes from two contributions: the curvature of space by itself, and the expansion rate of the universe."

So it seems that Carroll is on board with the whole curvature thing.

You might also want to read the FAQ in that: http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#curved

Even better, you could read his GR notes: http://preposterousuniverse.com/grnotes/

He also provides a description of the CMB observations: http://preposterousuniverse.com/writings/cosmologyprimer/early.html . It is far from simple and obvious.
Go to it and find out what he did/said for yourself, mate, and you'll see I didn't lie to you.
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No, I see that you did lie to me.
 
PhysBang said:
You mean like how you said he entirely rejected the "rubber sheet" analogy when he clearly did not?


Why don't we go to the things that the guy actually wrote about this subject: http://preposterousuniverse.com/writings/cosmologyprimer/expanding.html

"Einstein's general theory of relativity, which states that spacetime is curved and that curvature is what we perceive as "gravity," provides a dynamical framework for understanding the expansion of the universe. In cosmology, the curvature of spacetime comes from two contributions: the curvature of space by itself, and the expansion rate of the universe."

So it seems that Carroll is on board with the whole curvature thing.

You might also want to read the FAQ in that: http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#curved

Even better, you could read his GR notes: http://preposterousuniverse.com/grnotes/

He also provides a description of the CMB observations: http://preposterousuniverse.com/writings/cosmologyprimer/early.html . It is far from simple and obvious.


No, I see that you did lie to me.
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Hahaha! You can't even be bothered to read and understand your own linked material. And you haven't even bothered to check that info I gave about that BBC documentary he appeared in. And you pretend to be any sort of 'objective scientist'? Pull the other one mate!

If you'd checked your own links, you'd have found the first two were were dated 1996 and 2001, well BEFORE the 2003 CMB based LATER work I saw him explain re triangulation method testing of 2003 CMB map features to prove to accuracy of 3 decimal places that the universal energy-space was flat and extending to infinity beyond observable horizon of CMB mad 2003.

And your third link to me to something that was a general statement of the BB and CMB etc paradigm/usefulness etc as it was, without any mention of his LATER findings that proved the energy-space was flat to infinity beyond observable horizon.

I even posted the DETAILS of that 2012 BBC TV documentary for YOU to do DUE DILIGENCE and prove for yourself I wasn't lying to you. But you STILL came back with crap accusations based on your OWN prejudicially read (or even UN-read) WRONG impressions of the facts in evidence. Not good, mate.


Mate, a friendly word of advice. Don't be so eager to throw 'lies' accusation if you don't even bother to do due diligence on the facts in evidence FIRST. And then be sure you actually understand what it is you are reading. It will help you to become a better and more objective scientist. Good luck. :)


PS: Farsight criticized the mainstream bowling ball on rubber sheet analogy, then proceeded to help make it make some sense by including the line of clocks to illustrate what the original lame mainstream analogy was really trying to say but failed. He never 'pushed' or 'approved' of it, merely made it better since the mainstreamers made a silly mess out of that analogy of THEIRS. Good job. Next.
 
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