Eise

It was a political move of Mohammed. He hoped he could unite Arabs, Christians and Jews under his one new religion. Obviously he did not succeed...

But these are both not the meanings in my 'syllogisms'. So what is it that makes my logical derivations invalid?

Why do you think so? What are the two different meanings?

Yep. Nothing is better than a Cheese Sandwich.

Hmm, yes.... A Cheese Sandwich is better than Nothing. Nothing is better than God. Conclusion: A Cheese Sandwich is better than God. Or: Anything is greater than Nothing. Nothing is greater than God So: Anything is greater than God.

dstebbins, I think you mix up a few things. In outer space the sun is not blocking the starlight. It is only that if something is lighted by the sun (the spaceship, the moon landscape, the earth), it is much brighter than the stars. So our eyes adapt to bright light and we so not see the stars anymore. Same when astronauts take pictures: the shutter speed becomes so short, that there are no visible stars anymore. If an astronaut blocks the sunlight with his fist, or just looks in a direction where there is nothing bright lighted by the sun, he sees the stars, much brighter than we do. On earth, on the other side, light is scattered by the atmosphere, especially blue, and there is bright light everywhere. It is brighter than all the stars. During the night, the stars themselves are not so bright that there is much scattered light. So now we can see the stars. On the other side, during the full moon, it gives so much light that we see significantly less stars then on a moonless night.Now the moonlight does not make the sky blue, just some kind of grey light. The reason is that it is not so bright as the sun. So only the more light sensitive rods in our eyes see the scattered light. But these are not colour sensitive, so we see the light as grey, instead of blue. Two more observations that might help to understand these phenomena a little: If you see far away mountains, they seem to be blueish. Of course they are not. There is just much more air between you and the mountains, and this air scatters the blue light the same way as it does above your head. During a total sun eclipse, the air turns dark, and you can see the stars. I was not prepared for this when I saw the eclipse of August 1999 and was totally astonished that more or less from one second to the next, I could see the stars, and Venus and Mercury high above my head near the (eclipsed) sun. Normally, you never see Venus and Mercury high above, but only close to the horizon. Example:

You can keep your sneers. Energy is an abstract concept, and I am interested in the historical question why people got interested in it. If that does not interest you then... That also misses the historical question. Historically the concept of conservation of energy was a slow discovery, smeared out over centuries, with Noether's Theorem as possibly the highest insight. I am interested to know how it began, and why there was so much confusion in the beginning between people like Leibniz, Chatelet, 's Gravesande on one side, and the Newtonists on the other side.

The point is: I do not quite get why people got interested in something that later was called energy. Hmm... googled a bit around, and found this. Is still not completely satisfying for me, but at least clarifies a little. Sounds nearly poetic...

I was very surprised when I first heard about Émilie du Châtelet and her experiments. Especially that obviously many Newtonian physicists defended that the energy of a moving object would be [math]mv[/math]: So what was in those days meant with 'energy'? Leibniz obviously had some ideas in the right direction: Was it originally derived from work? Force times distance? But if that is true, then a simple dimensional consideration should already lead in the right direction? [math]F = ma[/math] [math]W = F.d = m.a.d = m.d.d/s^2 = mv^2[/math] i.e. the dimension of energy is mass time velocity squared. Or did physicists in those days not have such a clear understanding of dimensions?

You are asking two different things here: 1. Is reality paradoxical? 2. Is our understanding of reality paradoxical? On 1 I would say no. There is no way that a thing or state of affairs can be the case and not be the case. On 2 I would say 'depends': the mathematical formalism of QM is rigid and consistent. As physicists work with QM, and technology is based on QM, reality is not ungraspable. However, if the question is if we can grasp quantum reality using classical concepts, the answer is clearly 'no'. In our daily life we only understand reality with classical concepts, and in this sense QM is paradoxical. But only in this sense. Exactly. If you translate 'normal' with 'with classical concepts'.

OK, sorry. But I think I stated it more precisely later. In a closed system in which there is no change, there is no time. Of course you can see why this must 'degrade' in a philosophical discussion: any observation about what 'happens' in the closed system contradicts the condition that it is a closed system. So we are talking about something we have principally no knowledge of. So yes, the question 'what is time?' is a philosophical question, and the answer one gives has, per definition, no impact on the empirical science that physics is. So I really don't understand why I get so much resistance. My answer has no impact at all on our daily life, nor on physics. But there are people who have this 'philosophical need', like the originator of this thread. I gave my answer (it is an abstraction, namely of change), I gave my main arguments (we cannot observe time except through change; time in itself causes nothing, so it is not a physical category in the sense as objects, fields are). Would you accept a dictionary of physics in which there are no lemmas for certain physical concepts? Mind what I said: defining in words is circular. And that is what we started about. You asked me to define change without use of the word time. I am not adding something to physics. But the question 'what is time?' is a philosophical one. I mean something like the 'Newtonian time', that together with space forms the stage on what everything is happening. I gave an example already. After one hour my CD stops playing, and I am left with only half of my radioactive substance. These changes are completely different, but under the single aspect of time, they are the same. They both took one hour, i.e. there were equal amounts of clock ticks for both processes, and I started the CD and my measurement of the radioactivity at the same moment. So under the very abstract view of 'how long did the processes take', both are the same: 1 hour. But you see, I left out all the details. There is no way that I can get back from the concept of one hour to the playing of a CD or some radioactive halftime. The other way round is easy. That's why I am saying that time is an abstraction of change, and that it is definitely not the other way round. No. We are not talking empirical science. If you think that everything that is not empirical is nonsense, then you are right. You could not better show me my points that definitions are circular, and that for an empirical science it is necessary to have operational definitions for enough of its concepts, so that it can assign values to all of its concepts. The discussion started with me saying that all definitions are tautological. Then somehow on the way you started me of accusing me of using rhetorical tautologies, pasting a Wikipedia article that does not apply, and that is vague as it can be. Its only reference shows many examples that are not propositions ('free gift', 'new innovation') and that in fact are pleonasms. But definitions are propositions, and given my definition, they are tautologies. Not because of their propositional form (A or (not A)), but because its truth is independent of empirical circumstances: its truth follows from the meanings of their words. So now please explain me where I am supposed to misread you. In my opinion just this: that time is not something we can tell about, but that we need to tell about anything else.

I hope others see the irony of your reaction. You seem to miss it completely. Obviously you define when something may be called a useful idealisation and when not. Exactly what I am saying all the time. If you define, in words, you get circularity. If you define operational, in the case of time you must refer to... change. No. I am saying that you add nothing to understanding of change by stipulating that change is change in time. We cannot understand change without reference to time: but we also cannot understand time without change. But where I have as many concrete changes as there can be, there seems to 'be' only one 'time'. It answers why we cannot imagine change without time. But there is no way to know that there is time because there is change. Great. You just made a longer chain of, or better another circular definition. (Just for the record: I think these Noether theorems belong to the deepest insights we have. But that is not what we are discussing about here. We are talking about circularity of definitions. Also don't forget: I am not critisising science for using circular definitions. The important point for scientific theories is that enough of the concepts are also empirically rooted.) Don't be so tiresome, elfmotat. Must I rewrite it for you? [Energy] = [ mass . distance²/time² ] I said, using the example of the definition of a bachelor, that all defintions are tautologies. I gave the definition of tautology I used: a proposition that is true in all possible worlds. Now show me that this concept of a tautology is a rhetorical tautology. You don't want to get the point. Say I measure the halftime of a radioactive substance (i.e. I count the clock ticks of my clock). It is one day. Then I measure how long it takes for a flower to open (again, I count clock ticks). It is also one day. So both processes are the same, when I reduce them to the aspect of time. There is however no way I can go back from '1 day' to radioactive decay or the flowering of a plant. That is what abstraction is: reduce to one of the aspects. But what I really did was comparing both processes to a 'standard changer': my clock. It seems to me you don't know what an abstraction is. Where do you want to get? Again, the question of the thread is 'what is time?'. I did nothing else than give my answer. Already very early in the thread swansont gave a quite good reaction: So is it a useless definition? For physics, yes, definitely. I only added of what time is an abstraction. And since then everybody is making trouble about this point. Including swansont himself. It seems I touched on the religious feelings of some people. You seem to think I deny the existence of time. I don't. I only say that its existence is that of an abstraction, of change. Compare it with this: I deny that 'whiteness' exists als independent object. And then all people struggle over me as if I deny that white things exist.

Yes. People started to believe that somebody resurrected. Funny, isn't it? But nobody investigated the case when it was still hot, so we can put the case ad acta.

You are right, they are not the same. Time is an abstraction of change, not change itself. It is the idea that some universal clock is ticking in every inertial system. Without change, there is no way to observe time. Comparision of what? I compare the two mice, and notice that after 5 clock ticks mouse 1 has reached the cheese, and that mouse 2 has reached the cheese in 15 clock ticks. There is an explanation of what temperature is 'behind the scenes', namely a measure of the kinetic energy of the particles of which substances are made. There is no such thing for time.

david345, Colour of course. When I want to know the time, I look at the color of my clock, and I know what time it is. Don't you? This is the most sensible answer I can give to your questions.

I assume you want to say I don't. Feel free to say what is wrong. Wikipedia on logical tautologies: Wikipedia on Definitions:

Stuff? Can we detect it? How? Your belief without any argument doesn't bother me. Yes, I did. Physicists also work with all kind of idealisations, like black bodies and isolated systems. So why shouldn't I? But more to the point is: would you accept a definition which contains words you do not know? Give another one, that does not fit the above. Yes, I noted that. I also noted that you give no arguments for it. There are two possibilities: a (real) definition in words, which is logically necessary circular (even if it is over a long chain of other words). Or you give an operational definition, e.g. you point to something ('this here, this is red'). That is methodologically fully OK, but it is exactly what you cannot do directly with time. You cannot point to time: but you can point to change, e.g. a clock. But it hardly makes for a description or definition of 'change'. Of course you can say 'Change is change in time', but then you have used the word change itself. I'll give it another try: time is the most general abstraction of all changes. Now I am also not completely satisfied with this, but at least it shows that you cannot turn it around. How can individual changes be abstractions of something that is more general? Right. You show how physicists use the Lagrangian to solve problems of mechanics. But I asked for a definition, first of the Lagrangian, and then of kinetic energy and potential energy. Obviously you immediately refrain from defining. 'Defining' is something else than knowing how to follow a recipe. Let me help you, with the dimension of energy: [J] = [kg . m²/s²] What does the kg stand for? Sorry, you are just wrong. Take the definition 'a bachelor is a man who never married'. Now I substitute the meaning of 'bachelor' in the definition. I get 'a man who never married is a man who never married'. Isn't that a tautology? (Maybe you are confusing tautology with one of its subclasses, the propositional tautology (A or not A).) Except that you did not follow the rules. Because it is an abstraction. You are like the middle age philosophers that discussed if 'whiteness', or 'horseness' existed, or even may be more real then a white plate or the horse standing in front of me. There is nothing to know about time except as a comparison between different processes. And of course the definition is pretty useless for a physicist. But the question of the thread is 'What is time?'. It is not 'Why all physics is completely wrong because they do not understand what time really is'. How do you know time is passing? Without you being there, breathing, your heart beating, and if you want to be precise, without a clock?

Yes, please. What is time.

OK, I will change it specially for you: A bachelor is a man who never has been married. OK? Can we go on, please?

Studiot, I did not say 'all unmarried men are bachelors'. I gave a definition of the concept bachelor. Given that definition, is there a possible world where I can meet a married bachelor? So if something is true in all possible worlds, then it is a tautology:

Ok. All definitions are expressed in words. Let's assume that a definition is not circular. This means I get at a concept for which there is no word in the dictionary, so which is not defined. But this contradicts the assumption that the dictionary is complete. Applied on physics this means that one of the following must be true: Physics uses concepts that cannot be expressed, because they cannot be defined (btw, this would include a mathematical dictionary of physics). Definitions of concepts are circular. See e.g. here: (Italics by me). The gist of the argument is that normally you stop defining when you use words that are unproblematic in the context.But in fundamental questions you are problematising, you want exact definitions: but then you will inevitably run in circles from some point. The point I am making is that change is more fundamental as reference than time, because we can observe change, but we cannot see time, except through changes. Really? That is just because you stopped. please define: kinetic energy and potential energy to begin with. For the moment I leave you path, the integral over time, and stationary. No, I am confusing nothing. Definitions are logical tautologies. If not, then there would be a possible world in which the definition does not apply. Say I define a bachelor as an unmarried man. Now, is the sentence "a bachelor is an unmarried man" a tautology or not? Given the definition of the concept 'bachelor': is it possible to imagine a world where you meet a married bachelor? If it really is a closed system, then I can say nothing about it. If I can say something about it, then I am, as observer, part of the system. The example you gave does not follow the rules. I have said that the only way we can determine time is by comparing with another process. So I introduced my clocks. Edit: typo

Oh yes, if you decide to stick to defining you will run in a circle, how many links your definitional chain might have. Of course you can stop defining at some point ( ) and say 'this is immediately clear, what do I have to define further', but then it is still exactly that: you stopped defining.

Right, I did not. I challenged to find out yourself. But again: circularity can be via more than 2 concepts. Remember, I said the dictionary is complete. No it isn't. The problem is that I can't show it just for you. So do it: give a complete definition of all concepts of Lagrangian mechanics. You will see that at some moment you drive in circles. Of course I know what a tautology is: it is a proposition that is true in all possible worlds. Definitions always are tautological. That is a fact that every logician can confirm for you. Yes, and I said how you should do it. With a clock. Say the clock ticks exactly at the beginning of the trajectory, and at the end. Now I take a second clock that ticks one time more, i.e. it ticks together with the ticks of the first clock, but also one tick in the middle. Then I notice that the man in the box is exactly at the half of the trajectory. Etc. Where is your problem? OK, then it is the unusual language that brought me on wrong track. But if I look up the Elements, I do not find this as definition of a line, nor of a point. This is what I find. Now do you see the problem? Now you must define 'breadthless', 'length', and 'part'. So let's try this with 'part'. If something can be divided, it has parts. A point has no parts (per defintion). So a point cannot be divided. Now what is the definition of divided? If something exists of parts, it can be divided. A point cannot be divided. So a point has no parts. How do I get out of this? You must not confuse 'defining' with 'immediate clarity'. If you define a concept, you do it with other concepts. You cannot get out of this circle, except by pointing to something observable. But 'pointing to something observable' is not a definition. If one defines the length of a meter, one compares it with the length of something else. But that is not defining what a length is, it is defining what a meter is (same with the elfleg).

Yes, I have. With the dictionary. You just did not notice it. Just one note of possible misunderstanding: the circle might be composed of more than 2 elements. No, that is not the reason. The reason I stick to Newton is that it is an example of a (simple) theory that perfectly works. So it shows that circularity of concepts does not mean that the theory is wrong, or incomplete or something like that. I am not deep enough in Lagrangian physics (and even less in formal quantum mechanics) to argue in detail about the circularity of their concepts, but you can easily try it yourself: ask for every new concept you introduce what its definition is. You will see that at some place you end where you began, or get at a simple direct circularity as with Newtonian physics. Yes, of course I did! Otherwise it doesn't work! It is absolute essential for Darwinian evolution that organisms live long enough to pass on their genes. If they don't their genes will not be passed on. It seems to me you do not know what a tautology is. Whatever the length iof your leg, your leg would always have a length of 1 elfleg. So in every possible world 'the leg of elfmotat is 1 elfleg long' is true. So it is a tautology. Or taking it the other way round, it is impossible for the length of your leg not to be 1 elfleg. Because you have not compared it to a regular process, like a periodic series of events. I have no idea what you want to say with the rest of your exposé. I see no problem by taking another regular process in which several events fit in one event of the other periodical series of events, and so dived my observing the walking man in finer parts. No, I did not. But I choose not to answer it, because it has more of a bonmot than of a serious definition. How would you mathematically define a line and a point?

OK, if you want it the hard way: every definition of a concept is circular. The length of specifically your leg is not a concept, but an empirical fact. It also does not change the fact that Newtonian physics is circular in the definitions of its basis concepts, and is just as well a perfect useful theory. Circularity is not a death verdict of a scientific theory! It is on one side proof of its consistency, and if some of the concepts can be connected to observations, in such a way that we can attach values to all elements in our theory (or at least to all other observable facts), it is a good scientific theory. This was your definition: Which organisms survive: those that pass on their genes. Which genes are passed on: of those organisms that survive. Well, tell me how long your leg is. In every logically possible world, in which the unit is of length is the length of your leg (whatever the length of your leg), the length of your leg is 1 elfleg. So your definition is tautological. Yes, you are right. I was a bit imprecise there. Let's say that [math]y=A(x)[/math], where [math]A[/math] means 'is abstraction of'. [math]x[/math] is an observable, so [math]y[/math] is the abstraction. Now for every individual change there is a projection on the time axis. But the opposite is not true: you cannot take the projection of a change on the time-axis, and find what the change was. The reason is that time has no independent existence.