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  2. Sensei

    Positivism has been refuted?

    Did you read these links? "Verified data (positive facts) received from the senses are known as empirical evidence; thus positivism is based on empiricism.[1]" "Positivism asserts that all authentic knowledge allows verification and that all authentic knowledge assumes that the only valid knowledge is scientific " Maybe he meant that positivism has been upgraded to the new level, where observation of physical phenomena is finalized by creation of mathematical model of phenomena, thus being able to predict the next time something similar happens in advance.
  3. swansont

    The end of gasoline/diesel powered cars?

    How do you get the aluminum powder, preserve it, and make it oxidize in a controlled fashion? How much energy does this release?
  4. swansont

    Understanding common displacement

    “Path” does not have a strict definition in physics, AFAIK. So there is no justification in physics to say it is or is not a “path”. That would be a lay description, and I don’t see the importance of the name we attach to it. Perhaps you could clarify why this matters. That right. The map is not the same as what is mapped. Axiomatic? Or observed? (Not that it matters) The rule exists, and you aren’t following it. That’s why the problem arises. That’s not a physics question.
  5. I'm listening to a podcast and a guy on the podcast says "positivism has been refuted, in so far as any philosophy can be refuted, and it's the analytic philosophers who did it." I'm pretty ignorant on history of philosophy, can someone explain what he is talking about? What is the refutation of positivism and came up with it?
  6. Today
  7. michel123456

    Understanding common displacement

    I never mentioned the word "particle" because I din't want to enter this part of physics. I am talking about pedestrians & busses if you like, I called "objects" in my OP. And the question is whether the blue line is a path or not, and whether its projection is still a path. I could animate the 2D graph (this one below) But since I introduce time as a vertical axis, I cannot animate it any more, that would be introducing a second time (cheating as you said). So I will refrain to do that ( I have learned from previous experience). Now you wrote No. I could animate the point going from a to b. The path [a,c] is in spacetime. The question is: in the 3D diagram , can I say that the blue line [a,c] is a path and thus consider that at t=1, when an object C is at c it means that the point a is a free coordinate and receive another object Q. The common reaction to that would be "Bogus, Q cannot be there because Q belongs to the past of C and as we (human beings) know the past cannot change." But if I (myself) stick to the diagram, I can put Q & C altogether without any conflict. Q will be at a and C will be at c. No problem, no issue. The problem arises only when we (H.B.) give to the T axis this extraordinary faculty of "never change". As i said earlier, if I label the vertical axis Z, we have no problem. The problem comes from some axiomatic property that we input to the T axis. The next step would be to say, whathever, if Q existed I would see the past change. Would I ? The common conception is that Q is an ancient event of C, that the blue line represents the "life line" of C. It is a solid object that does not allow another object Q enter inside. And that is thus my question: why do we consider things that way?
  8. swansont

    Understanding common displacement

    No two particles can have identical coordinates of (x,y,t). This is YOUR stipulation, that two particles can't occupy a point.
  9. Good point. I see that my question could be better stated. I made an implicit distinction: Affected by gravity = a gravitational wave disturbed when passing through a gravitational field in vacuum Affected by matter = a gravitational wave disturbed when passing through matter, like straight through the earth I see that these two of course are overlapping.
  10. Moreno

    The end of gasoline/diesel powered cars?

    How realistic it would be to make a metal-air fuel cell which could be charged by an aluminum powder and release pure aluminum oxide powder as an "exhaust" right on the go?
  11. Strange

    Understanding common displacement

    These are both paths (to me). The first is a path through space, the second is a path through spacetime (a 2D projection of the path [a,c]). I'm not sure what the difference is. The graph represents that at time a, the object is at position a. At time t it is at position c. You could animate that and show the object moving between the two points. Or you can just consider it as a path showing the position at each time. These are just different views of the same thing. In other words, the question as to whether the particle IS at all points on the timeline depends on what you mean by "IS". So, really, this is a philosophical question (see also "block time"). However, there is a difference between animating a path through space and one through spacetime. In that latter case you are implicitly introducing another measure of time - the external one that passes in our world. So it could be considered "cheating" a bit.
  12. Sensei

    What is the universe?

    Periodic table history is example of interpolation, and extrapolation, of existing data set. They had knowledge about some elements. Sorted them out by their properties. And it revealed there is gap in their data set. So made conjecture 3 elements are missing. So started searching for them knowing what they are searching for in advance. ..that would be the case if in the XIX somebody would came up with idea of meson (obviously using different name!) i.e. particle that has smaller rest-mass than Hydrogen nucleus.
  13. Pasker

    What is 4 divided by 6?

    No. 4 divided by 6 is 0.666666.....
  14. Pasker


    OMG,i don't know the answer for it.
  15. michel123456

    Understanding common displacement

    Why do you say that? I guess it is because the axis is labelled T. If I had labelled Z, you would'nt have any problem, right? You would agree that the blue line is a path & that multiple points can be placed on it.
  16. FragmentedCurve

    Some Thoughts on Air Conditioning

    No apologies are needed. These are exactly the kind of discussions I was hoping to stimulate. Given that I am more rusty than Carrock, I feel like I don't have a lot to contribute. I'm reviewing material and trying to answer my own questions before coming back here and naively pushing them onto you. I know it wouldn't produce a lot of electrical energy. Also, electrical energy isn't a requirement either. The reason I mentioned electrical energy is because its probably the most useful form of energy for practical purposes. But the end result doesn't matter much as long as its somewhat more useful than the input (the hot air). The point behind my post was about structuring a material that would be able to excite an electron on a chlorophyll-like molecule by only the kinetic energy of gaseous particles alone. I just realized why I'm having trouble communicating my response. There's really two parts to my inquiry. The first part is about constructing such a material. The second part is what are the effects of such a material on the temperature of a gaseous body. The thoughts about air conditioning were just the catalyst for thinking about the chemistry and physics of this situation. I attached a poorly drawn conceptual diagram. So the green particles hit A at the same time causing enough energy to be transferred to B and excite B's electron. Which laws of nature stop A from successfully exciting B's electron? I hope I did not come across a someone looking to convert heat with 100% efficiency or worse (someone looking for free energy).
  17. tuco

    Suicide Prevention

    I am lead to believe, based on what I've read, that let's say the roots of "suicide prevention" are evolutionary and cultural. While the biological element is probably not going to go away in foreseeable future, the cultural one - especially the mentioned stigma -, is subject to change granted there is will to change it. Personally, I hope that the support given to those who are set on committing suicide would be similar to the support given to those who signaling the possibility of committing one. I would also hope examination of socio-economic realities of those displaying signs of being suicidal is not preceded by psychiatric evaluation with appropriate steps taken accordingly. Since I am not sure what direction the OP was heading and since this topic is quite complex, let me finish with a definition of selfish I prefer: for own benefit, without regards for others.
  18. And I keep asking you: why is your statement true for "this set"? Why can't {x: a <* x <* b} have a least element? You're relying on "clearly" for a statement that isn't at all clear.
  19. MigL


    I assumed he meant 'radial'. emanating from a central point outward. Maybe not.
  20. I'm not sure LIGO extracts energy from the gravitational waves. What it does is measure the distortion to space-time caused by the gravitational waves ( path differences ). If you picture space-time as a three-dimensional ( I don't think you can do four ) grid or co-ordinate system; then the gravitational wave would emanate from a central point outward, alternately stretching the grid along one axis, and compressing it along another. If there is a pre-existing 'warping' of the grid, caused by matter and its associated mass-energy, then the wave will be slightly modified in its path. so, sure, matter affects gravitational waves.
  21. ydoaPs

    Sets vs Omniscience

    This argument came up again recently, and I realized that appealing to proper classes or conglomerates won't actually help. See, the argument itself is a proof of negation, so it works in any nondegenerate topos. And it came to my attention that Cantor's Theorem generalizes from Set to an arbitrary topos. For any object Y in an arbitrary nondegenerate topos, there is no surjection f: Y -> 2Y. So you can run the exact same argument swapping out talk of sets with talk of objects and talk of subsets and members with talk of subobjects. So, the argument can be formulated for an arbitrary topos.
  22. What might possibly be construed as the “fish lineage of man” begins around the 1 minute point.
  23. I keep telling u over and over again I am exhibiting such a set: this set. Clearly this is not the natural numbers. Only one set needs to be exhibited that has no least element with <* for WO to fail.
  24. iNow

    U.S. Democratic Primary

    I agree, and Yang is doing remarkably well.
  25. Yesterday
  26. This isn't exactly true; the actual definition involves lots of "there exists" and "for all"s. If the function is nice enough, then yes, this "pseudo-proof" tells you that the second derivative must be equal to the expression given; however, the second derivative does not necessarily exist.
  27. J.C.MacSwell

    An extra moon for Earth.

    As long as it is an orbit far enough from the Moon's, I expect it should be fairly stable. I'm not sure how the resonance would have an effect, possibly that could allow a closer orbit. (all probably what you knew or suspected already) Can we call this extra moon "Tanman"?
  28. More information here (with videos!):
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