studiot

This thread is growing ever more Terry Pratchett and ever less sf/home/sciences/physics/relativity. I sem to remember discussing the speed of light in vacuuo, backalong. What, pray, is the speed of sound in vacuuo ?

Lots of goals, but which side scored them ?

WAT (wall of text) luckily the 5 post rule will soon intervene.

So what Other Science are we fitting this dream into ?

Did you actually have anything to discuss here or is it just the weed talking ? You are correct in that Truth in maths has a different meaning from Truth in other disciplines, such as religion or politics and fyi it does not appear at all in Science. Your are incorrect in that maths is neither a language nor a conversation, though there are mathematical models of language. You need to focus this thread quickly before it either withers on the vine through exhaustion or is closed in disgust by the moderators.

The most important piece of knowledge for someone with a PhD is the limit of their own knowledge. That this is so in economics was brought to poignant focus when the concensus of PhD folks brought about the crash of 2008 due to failure to understand the Black-Scholes equation and its assumptions and limitations.

Good article. +1 Not sure how much current the battery in a 'smart meter' supplies but they are supposed to last many years and only use short bursts of current. For interest here is a good dexcription of conventional thermal nuclear batteries, which also exploit the long life of the battery for example in spacecraft. https://uknnl.com/customer-solutions/space-exploration/how-a-space-battery-works/

Was there a mistake here ? donald-jump-fertilisation-president ?

Well I just don't get this vendetta against the SI system. Of the seven base units only one is a pure number that is completely unambiguous. The rest require a real physical standard to measure against, somewhere along the line. Of course alternative sets of base units and quantities can be used, for example in fluid and Continuum Mechanics more generally Force is sometimes used instead of Mass. Isotropy of light ? Do you fully appreciate the difference between invariance and constancy ? A quantity may be one or both or neither.

And you are avoiding much of what is said to you. Yes, when I worked with RPS and RLS systems (Tellurometer, Distomat and the like) it was common to measure atmouspheric pressure because it affected the transmission path, not the operation of the electronically equipment locally.

I'm not suprised but my finger hurts from all that needless rolling of the mouse button. Only to find at the end of it alleged scientific reasoning from a device that is designed only to pick the most probable (= most frequent) answer from what it has already been fed as calculated by many humans.

I looked through that reference and find myself ashamed that such a supposedly august organisation should produce such a shoddy piece of work. I'm sorry but you definitely cannot correctly draw the conclusion you have from that so called survey.

Always in all cases ?

The derivation of the Lorenz transformations is interesting and I wonder if you have been reading the older material from Voigt, Larmor, Poincare and Lorenz himself ?

Does It? I don't think so, nor do I think astronomical observations bear that out. If it is invariant, why do we need to do corrections for the relativistic shift of the spectral lines ? Invariant surely means the same in all frames, our observational one and that of some receeding galaxy.

Hi Seth, It is difficult to estimate the as it depends heavily on your model. Most folks just quote a figure worked out by somebody else (perhaps with a reference). Anyway the most baseline figure is what you get with the simplest heat balance of what would happen if the Earht's atmousphere suddenly disappeared, but everything else remained the same and is done in the Cambridge book for the whole solar system. It is called the equilibrium temperature. Thermodynamics of the Earth and Planets A P Douce Cambridge 2011 Pages 630 ff However there are wrinkles in this. The Earth's axis is tilted at about 23.5 degrees and also the distance from the Sun varies, both during one year and from year to year. So the surface (even without the effect of the atmousphere) receives uneven insolation. And of course half of it is is shaded by night at any one time. You might think that the Moon was therefore a better candidate as it has no atmousphere to speak of. But, whilst it is true that the Moon rotates so that all its surface gets insolation, the shading effect of the Earth on the Moon is far greater than the shading effect of the Moon on the Earth owing to their size difference. So the Moon receives less insolation than your calculations would suggest. Coming back to the Earth's atmousphere, it affects the fugure's in several ways and more sophisticated models need to take these into acount. Both the atmousphere and ocean distribute energy from wrmer zones to colder ones, thus modifying the average temperature difference for Stefan energy flows. The atmousphere absorbs/ reflects some of insolation (Beer Lambert) so reducing the actual values. The atmousphere also reflects some surface emission back (greenhouse effect) again modifying the surface temperatures. A more sophisticated model , therefore, splits the surface into zones and applies appropriate insolation and emission values, spread over time then integrated over time and averaged, and then finally all collected together and again averaged.

Not all, only those in the White House. 😉

You need to look at the maths here https://en.wikipedia.org/wiki/D'Alembert_operator https://en.wikipedia.org/wiki/Four-gradient

I realise I missed the reciprocal. Apologies. It should read c-2 = ε0μ0

One of the most fundamental principles in Physics is that of the isotropy and homogeneity of space / spacetime. In order to theorise the observation that it does not matter where or when we look, the physics of light and physics in general appears much the same. The principle of relativity follows directly from this, as does the principle of equivalence. In other words there is no preferred origin for empty space or time. It is a requirement of every cubic metre of space and every second of time be indistinguishable from every other. This leads directly to the constancy of c since c2 = ε0μ0 If you want to consider non constant c then you must have non isotropic space /spacetime then epsilon and mu become tensors to reflect the non isotropy / homegeneity and c2 becomes a tensor product. In short you have either a non vacuum or an aether. Any maths you use must also reflect this.

So you have done some Physics already. Great and good luck with the exam. 😀 A question for you to think about. What happens when you add water at 2oC to water at 3oC. Do you get water at 5oC ? If not why not ?

Seconded +1

How does that old saying go? There's none so blind as those that won't see, or so deaf as those that won't listen.

This is very clearly the case. This is not at all what I would expect from someone who understands what they are claiming. I would expect replacement equations for those of Maxwell. Then I would expect to see some math deriving the conditions for wave motion from the equations and finally ending with a wave equation. What I would not expect to see is the assumption of that which was to be derived, namely assume c(x, t). I would also expect the claimant to understand that the definitions and derivations of Maxwell work on the basis of a vacuum with no gravity fields or anything else. c does not even appear until the last line of the standard derivation. The onus is entirely on the claimant to derive the claim. So show us your maths please. Edit Gosh I keep x posting with swansont. Multiplying by c does not rescale time at all. In conventional (SI) units it transforms the dimensions so that the product has the dimensions of length. This is in much the same way as mass (which can be variable) transforms the dimensions of acceleration to yield Force, in Newtonian theory. As I understand matters the choice of c and other natural constants is because they are constant in a universe where the dimensional quantities are variable according to circumstance and observer. This then avoids the issue of having to refer back to standards of mass, length and time etc.