Carrock

I think I agree on that, and I would like to understand more about how that works. When trying to formulate some analogy my attempts sounds too vague and opens for possibilities that the gravitational wave could be unaffected. Like: I could measure the distance of one meter without affecting "the meter", space time coordinates are unaffected by my activities*. Or: I could measure and calculate time dilation without affecting the passing of time? Your comment is spot on regarding my question; are there (tiny) effects on gravitational waves passing trough matter, effects that are not there when the wave passes through vacuum. LIGO's detection proves the GW energy is there; the GW energy would still there even without LIGO detecting it so any LIGO measurement effect is not really an issue. The mutual coupling between gravitational waves and the earth is so weak that the energy required to stretch or compress matter is (very very very) nearly entirely lost from the gravitational waves. I think there are no analogous effects when the wave passes through vacuum. I've gone well beyond my minimal knowledge of gravitational waves; regard the above as plausible speculation.

As LIGO is able to detect gravitational waves, some energy has to be taken from those waves. As electromagnetic radiation from some of the sources is comparatively extremely easy to detect, the energy absorbed by even the whole earth would be very small, with no detectable effect on the gravitational waves. Some of the comments after https://stuver.blogspot.com/2012/07/journey-of-gravitational-wave-i-gws.html look at different ways energy could be absorbed.

I don't agree with part or all of this but I suppose I can see its relevance for the following post. I tried to indicate I was only concerned with initial and final conditions in my example of how an isolated system can increase its entropy from one well defined value to another well defined value. The total work done in getting from the low entropy state to the final high entropy state, which is an "equilibrium state" where the entire volume y (or A plus B) is in equilibrium, is zero. While transitioning between states work is done. Also the temperature of the gas is lowered and it acquires kinetic energy. As the volume y comes to equilibrium all this work is transformed to heat. At equilibrium the temperature of the gas in the volume y is the same as it was in x.

I thank you also Timo. I reread this thread in light of your post and saw a comment I missed and should have addressed. I disagree with 'must.' It is IMO a very good calculation method. I don't think its impossibility re my isolated system would prevent its use with the working assumption that my system is temporarily not isolated. But it's not the only method. Save mouse wheel.... I used this example for simple maths. The crucial issues. The gas in x and the empty rest of y are each in equilibrium states until the first atom leaves the x volume. I believe the entropy of the entire system can be calculated when each part is in self equilibrium. The following seems to confirm that view. After the side is removed but before any atom has passed the position of the missing side calculate the entropy of the gas still in equilibrium in the volume x. See e.g. http://hyperphysics.phy-astr.gsu.edu/hbase/Therm/entropgas.html (latexphobia.). The entropy of the empty part of y is 0. The subsequent expansion is not isothermal but the final equilibrium temperature of the gas is the same as before it expanded. The new entropy of the gas in volume y can be calculated.(latexphobia.) Entropy change: delta S = nK ln(y/x) The important difference between my and timo's examples is that in mine there is equilibrium only in the initial and final states and there are always equilibrium states in his. IMO this isn't a problem... Definitely agree.

When you change a system how does that become a new system rather than a modified system? You seem not to be distinguishing between a system and its state. This is unconventional and confusing. Would you disagree with "So the modified state of the system (being a list of values of all state variables) differs from the original state of the system?" I specified an isolated system with entropy increasing so that these and some other issues would be irrelevant.

Yes. From a brief look the reference you gave is clear and accurate. In it 'temperature' is frequently used but not derived. e.g. So this version, probably edited/simplified for students, of the equipartition theorem can't be used in a definition of temperature. I hope this response is relevant. I don't doubt that you're right and I'm wrong, not least from your work on clocks. Understanding how you're right is still an issue for me. Thanks for your help and patience; I've now reached a point where I have to do some actual reading. I'm now rather dubious about reader friendly Wikipedia, so I'm going to have to look for relevant peer reviewed papers, or at least preprints.

Really? The second sentence is true whether or not the process is irreversible. Entropy has been increased so of course. Did you mean: the original state of the isolated system cannot be restored after the irreversible process has changed the state of the system? Entropy has been increased so of course. Clarify please. I don't see any sense in the second or third sentence.

I agree with your post with caveats - see below. I've been looking through Wikipedia and it doesn't exactly help. My problem is how do you tell if e.g. Z1 is in equilibrium with itself and with Z2 without assuming heat flows from hot to cold? An answer seems to be that if Z1 and Z2 are in contact for a long time without changing they are in equilibrium. From https://en.wikipedia.org/wiki/Zeroth_law_of_thermodynamics But if heat doesn't flow from hot to cold (or from cold to hot) they presumably wouldn't change from whatever weird states they were in i.e. mutual equilibrium would be a meaningless concept. So heat flows from hot to cold seems to be a necessary postulate for the zeroth law.... And from https://en.wikipedia.org/wiki/Temperature#Zeroth_law_of_thermodynamics Heat flows from hot to cold assumed..... More Wikipedia : Heat flows from hot to cold is three laws down from the second law?! From https://en.wikipedia.org/wiki/Thermal_equilibrium#Internal_thermal_equilibrium_of_an_isolated_body Wikipedia is usually reliable but all I can really say is that my knowledge of what I don't know about thermodynamics has significantly increased.

Maybe a misunderstanding? If the original system is in equilibrium, then it can never gain entropy if isolated. In my example the side of the small box was removed 'instantaneously,' taken out of the larger box and the larger box sealed 'instantaneously,' before any ideal gas atoms could escape. That was the original isolated system, which then spontaneously changed itself and increased its entropy. No and yes. Rather than pretend I didn't refresh my understanding, I'll just quote a bit of Wikipedia e.g.: https://en.wikipedia.org/wiki/Thermodynamic_cycle#Modeling_real_systems The value of this concept can often be seen during problematic, non cyclic engine startup, before the startup transients die down. Enough for today!

Most (digital) frequency meters can also be configured to measure time. A divide by 60,000 or more device would at least be simpler than a multiplier. Noise and jitter in the MSF signal would be a problem; a very large division ratio would reduce those but maybe not enough. Getting high accuracy is the big issue whatever you do.

No, it assumes (parts of) the second law etc. The idea of the zeroth law being more fundamental than the second law while relying on concepts like equilibrium from the second law is what I find problematic.

I agree... I did not expect to find this definition of heat. So heat can't flow from cold to hot. Got it. According to all the references I could find I'm wrong here as well, but I can't see why. e.g. from https://en.wikipedia.org/wiki/Zeroth_law_of_thermodynamics How can any system be in thermal equilibrium, or be measured to be in thermal equilibrium with another system unless 'heat flows from hot to cold' is part of the zeroth law? Alternatively, 'heat flows from hot to cold' could be part of both laws, but that is messy at best. If (plausibly) the second law cannot be formulated without some version of the zeroth law then the zeroth law should surely not rely on part of the second law. As my thermodynamics is (obviously) rusty, I expect I've overlooked something obvious.

But is that so ? The change in entropy going from state A to state B is always the same, irrespective of the path between A and B since entropy is a state variable and thus a function of the state of the system alone. It make no difference whether that path is reversible or irreversible. ............................... For any completely isolated system we are restricted to adiabatic processes since no heat can either enter or leave the sytem. For a reversible process in any such system dq=0, hence ΔS is also zero, which means that S is a constant. Thus if one part of the system increases in entropy another part must decrease by the same amount. You cover "in an isolated system entropy need not increase." I'll assume ideal, classical conditions, including an ideal gas. An (old) example of "in some isolated systems entropy can increase:" You have an x cubic units sealed container of ideal gas, inside an empty sealed container of y cubic units. A side of the smaller container is 'instantaneously' removed without otherwise affecting the system. The gas irreversibly expands and comes to equilibrium in the y cubic units container. No work has been done so the temperature has not changed. The entropy has increased by the factor ln(y/x).

I don't regard "of its own accord" as very scientific... From my water example, does the heat associated with warm water molecules not accompany those molecules spontaneously/of its own accord when they become vapour? I would regard your statement as entirely accurate for systems referred to in the zeroth law. I was basically objecting as politely as I could to studiot's second law, which is a duplicate of part of the zeroth law. The zeroth law involves thermal equilibrium and is needed to define temperature. It's impossible (I think) to have stable thermal equilibrium without the explicit/implicit assumption or law that heat flows from hot to cold in the systems relevant to the zeroth law. "heat will not flow continuously from a warmer body to a colder one" is also accurate. Both are non equilibrium systems. I am assuming they are finite. I brought entropy into it because because I thought you gave a hasty, inaccurate version of the second law. It is very easy to get tripped up by all the ifs and buts in thermo.

Maybe oversimplified, therefor misleading? Particularly "of its own accord" - rather anthropomorphic. alternative: Zeroth law: If two systems are isolated except for a heat permeable wall then heat will flow from hot system to cold system. (If the two systems do not change over time and there is no net heat flow they are at the same temperature.) 2nd law: In an isolated system entropy will increase or remain the same. Heat can flow from cold to hot provided total entropy does not decrease. An example is water evaporating into air at the same initial temperature. The higher energy water molecules leave preferentially, lowering the temperature of the remaining water and warming the air. (Intended to complement earlier posts.)

Nope. Wave guides are not one way guides of R.F. energy. You're thinking of circulators, which rely on permanent magnets. edit or using half wave transformers etc to interface with spark gaps etc used for switching.

Sort of. First user starts downloading from source server. Second user gets partial downloads from source server and from first user, who has already downloaded part of file. Third user downloads from source, first and second users. First user can now download from source, second and third users. And so on... My post was only a response to the OP's second sentence. i.e. I felt his first sentence unnecessarily limited his options. Sensei: "Torrent is rather not an option, if you want to redistribute your own legit software, to worldwide clients." BitTorrent is an option for every major Linux OS worldwide download; users are requested to download with BitTorrent or similar to reduce server load.

Free software such as BitTorrent is available to reduce server load. It's (I think) only useful if several users are downloading the same file(s) simultaneously.

Archbishop James Ussher used biblical research to calculate day 1 of creation as 23rd October 4004BC. Did he get it wrong?

I believe that lack of evidence is definitely proof of nonexistence when it has been sufficiently sought after. If anti-matter bodies existed in the universe, then there would be huge anti-matter/matter explosions of energy, which simply don't exist. You're just making things up. CP violation is a subject of current research and certainly hasn't been 'sufficiently sought after.' If you'd read the reference I gave - https://en.wikipedia.org/wiki/CP_violation#Matter–antimatter_imbalance you wouldn't find anything to even hint at the existence of 'anti-matter bodies.' No evidence exists of presumed stable particles such as antielectrons (aka positrons) or antiprotons decaying. Such particles can be contained indefinitely.

Really? CP-symmetry violation produces matter/antimatter asymmetry. The currently known violations are insufficient to produce the observed asymmetry but lack of evidence is not proof of nonexistence.

Good to know there wasn't one.

Not that each has competence in different activities?! Or am I insufficiently evolved to appreciate your joke!?

Enthalpy, you seem to be refuting things I didn't write, partly by agreeing with things I did... As spires are a relatively low part of the total cost, it's a reasonable speculation that the materials, build quality or foundations were considered inadequate for the extra weight. Thanks for the expansion... You seem to be suggesting nothing was learned from those failures and the builders of Notre Dame etc were just lucky. Really? When I referred to builders' competence I was referring to collective competence. This would include judgment of whether many nonstandard constructions were adequate. I still believe modern architects would not do as well as the builders unless you allowed them to use some modern technology e.g. pencil and paper. I didn't mention architects as they were as rare as hens' teeth... From https://en.wikipedia.org/wiki/Architect Gotta wonder if the next fire will be hot enough to ignite aluminium...

There would have been less damage if the modern (19th century) tower hadn't collapsed into the building. Often 'obvious' improvements like extra towers etc weren't included because the builders knew that such constructions could overload the building or cause serious damage in a fire etc. Very old buildings still in use often are and sometimes have to be somewhat modified over the years, but the default assumption should be that as they still exist the builders were competent.