Tim88

If they are at the same distance and with the usual assumptions (the lab and the air in rest, etc) then they should also hear the sound at the same time. Compare https://en.wikipedia.org/wiki/Wave#Acoustic_waves

In classical mechanics, wave theory is indeed incompatible with the relativity principle. Swansont and geordief already mentioned that the puzzle was solved by time dilation and length contraction.

What you state there is nothing else but Einstein's second postulate, which indeed was also implicit in Maxwell's theory: Light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body. - http://fourmilab.ch/etexts/einstein/specrel/www/ That postulate follows directly from Maxwell's assumption that light is a wave (the wave theory of light); and generally one assumes that waves have constant speed c, independent of the speed of the source. To put it differently, I suspect that you feel not uncomfortable with wave theory, but with the combination of wave theory with the relativity principle. Indeed, as Einstein put it so nicely, those two assumptions were " apparently irreconcilable ".

Recently I was made aware of papers by a Russian institute which claims to have performed more precise calculations of the oscillations of the Earth's axis. The result (emphasis mine): "[..] this problem is solved here without simplification. The calculations demonstrate significant oscillation of the Earth’s axis. These results were confirmed with other three independent solutions of the Earth’s rotation problem. [..]" The paper suggests great confidence: "Thus, miscellaneous tests and verifications of the initial method of solving the Earth rotation problem, as well as independent solutions of this problem using three other methods, confirmed that the Earth’s axis of rotation fluctuates with an amplitude 7 times greater than that previously computed by our predecessors." - Smulsky J.J. Fundamental Principles and Results of a New Astronomic Theory of Climate Change. Roughly the same was next published here: http://www.sciencedirect.com/science/article/pii/S1068797116300918 "The oscillation amplitude of obliquity ε is seven–eight times larger [..] than the value determined in the previous theories." If correct, this may have a huge impact on science programs that deal with climate, exoplanets etc. But that was one year ago, and as you can see, there are 0 citations; still no paper has been published that either confirms it or shows it wrong. Such calculations are totally not my piece of cake, and so I have no idea how to form an opinion about the reliability of these new accurate calculations of the Earth's motion, nor about the reliability of the earlier approximate calculations. Nevertheless, I suppose that this involves nothing more than Newton's laws. Is there anyone here who knows more about such calculations?

And it suddenly strikes me that the simplest and dumbest model would have been the most successful: simply extrapolate the past. However, the disagreement is not about the question if the sea level is rising and if the temperature is raising, but about the main cause of those changes. A serious discussion would be one that compares the predictions for the last decade by different models - in particular comparing those that give more weight to the effects of human CO2 production (mainstream) with those that give more weight to other influences (alternative).

P.S. I searched for the "IPCC Third Assessment report" but it appears to date from 2001 instead of 1990. I failed to find an IPCC projection from 1990. Anyone? Meanwhile I did stumble on criticism of that picture, here: http://nierenbergclimate.blogspot.ch/search?updated-max=2009-12-03T08:02:00-08:00&max-results=7 Regretfully that discussion goes over my head... All I want is to see the 1990 paper in which the IPCC made that prediction, in order to assess the reliability of the website under discussion here. Verification is what matters.

BTW, I notice that I misunderstood the concept behind the name of that site. "Skepticalscience" does not mean that they pretend to be skeptic in their appreciation of climate models. Instead, they clarify on https://www.skepticalscience.com/about.shtml that the site is in answer to skeptical sites. They claim it to be balanced and purely scientific, even apolitical. They make a very good point that one should not loose sight of the broader picture. However, looking at the discussion items, I can't help noticing that they present the issues more like a defense lawyer than like a jury. And see where that "apolitical" site is coming from: the owner works for https://www.climatechangecommunication.org/ For a good appreciation one should therefore compare the challenges of "skeptical" sites with the answers on that "apolitical and balanced" site. Good science is skeptic in a healthy, constructive way, without losing sight of the broader picture.

I tried to clarify that normally only models are presented that already have been tuned so as to match known data. No model, theory or hypothesis is taken seriously if it already fails from the outset. But never mind, you pointed to referral to real predictions on that same site [edit: aargh, it's even on the same page; that one phrase was so bad that I did not read on]; that does help to interpret that it was possibly a mere glitch in phrasing. That's an impressively good result of a real prediction, thanks!

The way I understood that remark, is that they pretend that back testing is sufficient for relying on predictions - and note that we are dealing with new conditions that probably never happened before. However, happily we DO have some real verified predictions, as Sicarii points out.

Thanks for that, my first impression was that it's a really good site. And for sure they have a lot of detailed and sophisticated info, that's a big plus. Also that particular article on (no) new little ace age looks great (I just missed them pointing out that the time scales are so great that even a potential ice age around the corner is regretfully not going to save us from overheating). However within minutes I stumbled on this: That's a serious misconception - and quite shocking to see from a site that pretends to be "skeptical". In general, a scientific model is first tested on known data; only if the model agrees with know data, is it a possibly viable model. That is for example how SR and GR were first back tested at the times that they were proposed. If there are only few variables with an uncertainty that has little effect on the result, then one has good reason to be optimistic about its reliability for making predictions. In any case, one has to test the true predictions of a model. We can be very confident when such a model proves its worth in making predictions - that is how the scientific method works. SR and GR were not appreciated until the first successful predictions were verified (and in the beginning there was still some reasonable doubt due to lack of precision of the first tests). Happily we now already have decades of sophisticated climate models, and so it is feasible to start putting them to the test, verifying their past trend forecasts with the actual data. Hopefully (despite the above-mentioned blooper) this is fairly discussed somewhere else on that same site.

emphasis mine: As that is utter nonsense, I'm glad that you won't. I could not see (and I still can't see) how anyone with a minimal reading ability could think that you disagreed with rangerx. I generally don't cite superfluous statements. In contrast, I will continue to take attention of your posts, as I appreciate scientific comments. There you have it: you used def.1, and I used def.2. Peace. As the second part of your post seems to be a comment of one of my posts, I wonder if the first part also was meant to comment one of my posts. If so, then it is based on a misunderstanding (sorry if I wasn't clear). I see no reason to think that NASA is being paid to find an effect that is generally assumed to happen! What NASA is doing is to investigate what is happening. Which brings us back again to the topic, it is important that the climate studies (temperature, acid rain, ozon layer etc) continue.

Evidently we disagree about the meaning of the word consensus; in my eyes you call 3% 0%. If you correct that word by "great majority", we can all agree. That appears to be the beginning of a scientific argument; good! Any article that demonstrates that what rangerx observed is due to CO2 would be appreciated - but it's worth to be a topic by itself, in the physics section. Why is it that you pretend that I think that AGW is a hoax?? Don't put words in mouth OK? He did find a graph that I had not found in a full week of research. Me thinks that that guy plays down the amount of research that he spent on it in total. Getting back to the topic at hand, I had not yet read the linked article in the OP - does this mean that we will be robbed of the GISTEMP charts that I have been following over the last year?? https://data.giss.nasa.gov/gistemp/news/20170615/ I don't understand why Trump would want to do that. Indeed, very dubious! Yes, I totally agree.

It simply works; the disadvantage is that one has to add weights up to the precision that one desires, and without an indication of how much one has to add each time. But I did experience on the market once that a sales person used an ordinary balance much the same as such a primitive one: she just added fruit until the scale tipped.

That is not useless, as one is supposed to add weights anyway. However, common scales are much more practical for a quick determination of weight.

As I recall, not many years ago acidification was universally accepted as caused by acid rain - and the consensus then was that it was from SO2 and NOx. - https://en.wikipedia.org/wiki/Acid_rain Oh by chance, from reading the science forum about climate change, I stumbled on a Youtube by a physicist who not only agrees with with GeniusIsDisruptive about using money for other things; he actually disagrees with all of us and denies global warming, with data to support his opinion! - But according to professors at my university he is wrong about solar cells, they are near to the break even point already. I can see no excuse for not promoting solar energy.

You are here doing exactly what I just called unscientific reasoning: an appeal on majority. Maybe you don't know it, but it is typical for both good and pathological science that at a certain time a majority agrees. But first of all, we should correct for the ratios of financing - if groups on one side of the debate get 1000 times more money, there will be also 1000 times more people active on that side and they may also publish 1000 times more articles in which they promote their hypothesis. Further, there's that thing called confirmation bias. Anyway, I notice that this topic originally was inside a more scientific sub forum, and so I'll check out the -hopefully- more scientific discussion there, instead of this thread. But before I leave, I think that GeniusIsDisruptive has a good point - and maybe he/she even doesn't fully see it! The political "CO2 debate" may be based on asking the wrong question. What we should be asking ourselves is what would be the most cost effective way to counter global warming. Maybe that isn't CO2 reduction but something else (mirrors, whatever). Or maybe something else would be a more sure method (less unknown parameters) to achieve it. Did anyone look??

Does anyone remember Al Gore's erroneous use of ice core data? Me thinks that even a discussion on scienceforums about "political" issues should be science based - and science is inherently sceptic, as opposed to dogmatic. The topic is very complex and affected by political lobby groups. In fact, respectable articles can be found at either side of the debate, so that there obviously is no true scientific consensus on the question of how much climate change is affected by man - at least, not yet. If there is no other thread where this question is seriously discussed (instead of mud throwing or appeal on either majority or authority), then it would be useful to compare the scientific arguments here.

I have the impression that most people answered the question somewhat, but either incompletely or inaccurately. So, here's my try to finalize it In contrast to the last picture here above by Studiot (thanks Studiot), a common balance scale has a bent horizontal arm. But also with a bent horizontal arm, both sides are equal in weight; what matters is the torque (likely Studiot meant with "heavier" not the weight but the torque). Torque = L X F (this is a vector product). The lever effect is therefore not determined by the arm length but by the horizontal distance L*cosα (the effective arm length). Consequently when one side is higher than the other side, the lever effect on that side is greater than on the other side, because the effective arm length is greater. That pulls the balance scale back to the point of equilibrium, where the effective arm lengths are equal. PS and yes, the new picture added by Swanson has the red pointer doing that job instead.

Maybe you meant that '"avoiding" the contraction [of the accelerating craft] in the original frame' would be catastrophic. Yes indeed; and common rockets take care of that length contraction themselves - that's the essence of Lorenz contraction.

I don't know Roemer 1678. According to the anonymous French summary, of which, as you saw, Wikipedia gives an English summary, Roemer obtained a first estimation of the velocity of light from the approx. 10 min. error between observations in August and November, when one doesn't account for the speed of light. Thus, roughly, 1/4 of Earth orbit around the Sun corresponds to about 10 min. I don't fully follow the explanation, but the concept is straightforward. As illustration, suppose for simplicity (maybe it's written somewhere but I don't see it) that the 10 min. error corresponds to F->H. Then the difference in distance is approx. the distance of Earth-Sun, or 150 million km. That gives 250'000 km/s. I don't understand... and I don't have the drawing. Do you have a link to the paper by Huygens?

Maybe this: "The time difference between an immersion seen from point F and the next immersion seen from point G [..] no difference is observed at all, from which Rømer concludes that the speed of light must be very much greater than one Earth-diameter per second." - https://en.wikipedia.org/wiki/R%C3%B8mer%27s_determination_of_the_speed_of_light#Order_of_magnitude -> "Démonstration touchant le mouvement de la lumière trouvé par M. Römer de l’Académie Royale des Sciences" (PDF), Journal des Sçavans: 233–36, 1676. (in French) At first sight, that section in Wikipedia seems to summarize it rather well.

Overall Janus already gave a very good reply; however there's an issue with phrasing that may be worth mentioning. SR is formulated with respect to the same reference frames as classical physics ("inertial frames"), and the standard, so-called "clock hypothesis" of relativity is that acceleration has no effect on the rate of perfect clocks. In other words: clock rate is a function of speed and not of acceleration. The equivalence principle of GR tells us that the observed phenomena must be the same as when the craft is at rest in a uniform gravitational field. One can mimic a gravitational field by means of an accelerating frame. And it is only from such an "accelerating spacecraft view" -according to which the accelerating craft is not accelerating but at rest in a fictitious gravitational field- that one obtains the apparent differences in clock rates that Janus provided for the two accelerating spacecrafts. The Doppler effect is ignored if one pretends that the craft is constantly in rest, and this leads to the apparent difference in clock rates. From an "instantly co-moving frame" view, the observed frequency difference is fully due to the Doppler effect if the spacecraft undergo identical acceleration from rest (BTW that's how Einstein calculated it first, assuming zero difference in clock rates). There is another issue with "constant distance", as already hinted at by Studiot: with identical acceleration from rest as measured with an inertial frame, the distance will remain constant according to that frame's reckoning. However, the distance between the craft as measured with instantly co-moving frames will slowly appear to increase. To avoid that (and obtain a constant "proper distance"), the rear craft should have a very slightly greater acceleration. That leads to a small correction in the calculation of observed frequencies. And of course, all this is still SR. Predicting that the same phenomena will be observed in a real gravitational field belongs to GR.

With emphasis mine: As I indicated, it looks to me that it's not just "another approach", but really a different theory. I repeat: according to two centuries of electrodynamics, when an uncharged electric wire is connected to an uncharged galvanic cell (an ordinary battery) then an electric current will flow through the wire. As measured in the lab, the wire will normally not have an electric field around it (except for the field necessary to sustain the current) but it will have a magnetic field around it. Apparently you now confirmed that your theory disagrees with classical electrodynamics. In particular, you seem to predict for measurements in the "laboratory" frame, on a current carrying wire in rest in the lab: I think that two centuries of experiments disagree with that. And as you showed to be handy in doing your own experiments, you can check it for yourself.

According to SR: - in the frame S, according to which the charges are moving at high speed v, there is a magnetic field force that is opposite to the Coulomb force. Consequently the charges deflect less fast at this high speed than at low speed. - in the frame S', according to which the charges are not moving, there is no magnetic field and so they deflect fast. This disagreement matches the Lorentz transformations; the same trajectory is predicted. The main issue that I see here, is already present in your intro: According to SR, that is wrong - as I illustrated with the two parallel moving charges. On hindsight, if I correctly perceive what you are trying to communicate here, I can probably phrase the central issue more briefly. Discussions in this forum are supposed to be about classical theory; but happily, special relativity is compatible with classical electrodynamics. According to two centuries of electrodynamics, when an uncharged electric wire is connected to an uncharged galvanic cell (an ordinary battery) then an electric current will flow through the wire. As measured in the lab, the wire will normally not have an electric field around it but it will have a magnetic field around it. Is your theory in agreement with those basic observations?

I suppose that that explanation does "not convince everyone", because, as I pointed out: "in any case, the ratio of electrons to protons remains the same so that their density would change equally". In other words, everything remains neutrally charged, no matter one's point of view. And that has to be so, for the question if there is a net force or not, cannot depend on one's point of view. I look forward to comments on my even simpler example with just two charges.