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Danijel Gorupec

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Everything posted by Danijel Gorupec

  1. And this is exactly why I would advice against... The quotation itself is mild and nice, but its author is some sort of atheist god of war.
  2. Yes, but I don't know how much is this 10^11 estimation reliable. Also, it might be the density figure within the magnetar's body (wikipedia is not clear about it). It is also very unlikely that our magnetar will be perfectly aligned to make optimal conditions for our measurements. That's why I opted for the more conservative 10^10 value. Another obstacle, I think, is that the physical size of the field is way too small - several tens of kilometers in diamter. How much would an occultation from such a small object last - a fraction of a second? I guess it is too small to make measurement, but I actually don't know.
  3. I understand the method, great! In fact, it occurs to me that even one single light source, passing slowly through the magnetic field, can be used - its light should, if conditions are preferable, display larger wobbling amplitude as it approaches the magnetar's surface. This actually could provide some mass-energy distribution information. Edit: I still think, however, that our instruments cannot do it - eight orders of magnitude, calculated by Swansont, seems as a too large obstacle.
  4. Yes, I need to accept that it would be too difficult to detect light-beam path deviation due to field mass. Thanks.
  5. Ok, I will interpret the answer from the Q+A site in favorable manner: magnetic field, by itself, should not affect light (but the answer, as I understand it, does not take in account light-bending due to mass-energy of the field). Although, the field strength of a magnetar is so high that I don't think any scientist would dare to guarantee that there won't be any unknown effect. No, I don't care to bend light - I care to test the energy density formula for the magnetic field... I started to think about observational possibilities when I read on Wikipedia that energy density of magnetar's field can be thousand times that of lead.
  6. Thanks. My thinking is that even with our current knowledge some rough estimates could be made on what percentage of magnetar's mass is contained in its magnetic field outside of its compact body. Probably then someone could estimate how much a light beam (passing close to magnetar compact body) would deflect - that is, what is the difference in this deflection depending on the mass distribution (all mass within the compact body versus some mass outside of the compact body)... My math knowledge is probably way too limited to make such an estimation. The general idea is to have observational confirmation that mass-energy really is spread in the field. But i cannot estimate if such observation is only a distant dream or something that is achievable. Absolutely agree that there is a fear that such strong magnetic fields might act on light by other means than by space-curving (causing too much 'noise' for precise measurement). One thing that I am just thinking about - if the magnetic field of a magnetar quickly wobbles somehow (as that of a pulsar), the path of a light beam could wobble at the same frequency. Maybe this wobbling could help us with our measurements (it is sometimes easier to measure some oscillatory signal).
  7. What is your hunch about the following... If we could observe, from relative vicinity, a magnetar or some other neutron star that has a strong magnetic field - so that we are able to precisely track paths of compact objects closely encircling it or just making a close flyby - could we deduce, from paths of these object, whether the magnetic field curves the space or not (that is, if the magnetic field has mass-energy or not)? I am imagining that path of an object entering deeply into magnetic field of a magnetar would look differently if there is mass-energy in magnetar's magnetic field than if all mass-energy is only within the compact body of the magnetar. (I think, this is analogue to how presence of dark mater changes paths of stars encircling galactic centers). I however don't have any hunch whether the effect would be observable. And I am wondering if such an object that is entering magnetar's magnetic field could be a light beam - would it curvature differently if there is mass-energy in the magnetic field. (Happy New Year)
  8. Clear. The two observer don't have to agree about photon energy. I was, however, more interested about single observer in a lab. He makes the experiment and notes that the source gives off energy quanta E1, and the detector receives energy quanta E2 (E2<E1). Where he should look for the energy difference - from your answer I infer that he should look into change of kinetic energy (recoil) of detector (and possibly source), right?
  9. I have some problems understanding the following scenario: Suppose there is a source that emits a single high-energy photon. Suppose that this source is monochromatic and can only emit photons of single energy level, E=hf. The photon travels some time through space and is then detected at some detector (suppose, for example, detectors are all around, and the photon will surely be detected). My question is what if the detector (all of them) is receding farther away from the source at some constant speed? My understanding is that, due to Doppler shift, the detector should detect a photon of longer wavelength - of lower energy. What happened with the rest of the energy?
  10. Um.. am I late already to point out that Silvestru might be a polar bear?
  11. Of course, you can also use 'fully understood' when appropriate :)... What I am saying is that you should not use 'not fully understood' if there is a chance that an unknown physics will be needed to make full explanation. It is better to be honest and just say 'we don't really understand it'.
  12. Sorry, my reaction was only because of language use (from Zapatos side). Using the term 'not fully understood' seemed to me like an overstatement... I think that scientists should be brutally honest also when evaluating own accomplishments. Anything else can backfire, imo. So I propose not to use the 'not fully understood' qualification when talking about dark mater and dark energy. A better term, imo, would be 'largely unknown' or similar. I would suggest to use the 'not fully understood' qualification only if you strongly believe that explaining a phenomenon will not introduce any new physics (that it can be explained only by known physics). I don't think that our dark mater and dark energy understanding is there yet.
  13. Not yet fully understood? Sorry, but it is closer to 'we have no idea'. Do you disagree, do you feel that science must be defended by not admitting this, or did you just made a language-use mistake?
  14. Alright... in muscle training terminology, then, the strongest land animal is a male moose with a lever joking, of course
  15. BTW, what does actually "strong" means for native English speakers - is it more like "capable to develop great force" or more like "capable to develop great power"?
  16. Liked the last Charon's post. Can the same be said for starch too? Is starch included or not included into sugars on those food labels (I guess it is counted separately as "carbohydrates" - if so, why the difference - doesn't it end up the same once consumed)?
  17. Don't get mad so quickly. If I misunderstood, I am sorry. The torque is generated as well in a generator as it is in a motor so I could not know what are you referring about if you mention both, EMF and torque, in the same post.
  18. From the context of your post I figured that you were referring to the force/torque generation, not the EMF generation... If indeed your were referring to the EMF generation, then yes, depicting 'number of lines cut' can be an acceptable pedagogical approach. The number of field lines cut is indeed a good illustration of the flux change (which is what generates the EMF)... However using 'number of lines cut' to explain force/torque generation, would in my opinion just make more confusion than explanation.
  19. Sorry for being late, but I thought it might be insightful to invoke some caution regarding the above reasoning. The fact that windings in slots are out of the position of maximum field is, I would say, an understatement. Indeed, I feel it would be better to say that windings in slots are in position of insignificant field. All the iron that surrounds the wires acts as a good magnetic shielding - iron takes the large majority of the flux and very little of it actually goes through wires. As a result, the majority of motor torque cannot develop in the wires - and it is not that wires are pushing on the iron and turn the rotor around. Of course, placing windings into slots helps them not to slip sideways (it also helps fasten them against much more significant centrifugal forces). In addition, it enables motors with narrower air gap - if placed on the surface, wire dimensions would add to the air gap (and, as Studiot said, immersed into considerable field of the air gap they would then also feel considerable sideways forces). The third quoted sentence is the debatable one... A current-carying wire develops a force proportional to the field it is immersed into. The idea of 'number of filed lines it cuts' might come useful sometimes, but to me it seems somehow artificial (and confusing). It is just the field 'through' the wire and the current in the wire that counts (actually, it is just the quantity and velocity of electrons and the field density and its direction at their path). As the filed density is quite low inside deep motor slots, so the wire there cannot feel much force - no matter how much field lines it cuts. The majority of rotor torque must be generated in the iron itself - in rotor 'teeth', specifically. The purpose of the rotor winding is to generate field gradient where 'teeth' are immersed into... This is how I see the torque generation in a modern electric motor... You might get quantitatively good enough results if you just make calculations where you simply multiply rotor winding current and field density in the iron (or in the air gap, but not in the slots where winding actually is). However, such a procedure does not describe what actually is happening inside and might confuse a student who tries to think rigorously.
  20. That is why I agree with you that if there was liquid water on Mars, for most of the time it had to be covered by ice. However for brief times of increased volcanic activity, some of that ice could melt down exposing liquid water... but I am just talking staff, I have no real knowledge here.
  21. While I tend to agree with you, I just want to notice that volcanic activity could supply greenhouse gases.
  22. My understanding is that arctic terns make stops during migrations (at least by 'landing' on water, if not on the land)? I don't know what would be the longest hop for a bird that normally lands (that is, those that do not eat and sleep on wings). I know however that a common swift might not land for months. My understanding is that a common swift can migrate to South Africa, spends few months there and then return to Europe without ever landing. (Metallica comes to my mind... "we're off to never never land").
  23. Thanks Markus, I will try to read about the stress-energy-momentum tensors and then maybe I will ask for some additional clarifications. At first look the subject seems very difficult. BTW, what do you mean by "the energy inherent in gravity itself"? I am worried if it needs to be treated separately.
  24. I have questions about local conservation of energy. I am trying to better understand consequences that follow from it. How I understand it, the 'local conservation' means that not only energy is conserved, but is conserved in every local region. It cannot just at once decrease in one region, and increase in a region far away without anything happening in between. So, is the local conservation of energy a true law? It seems correct to me, but I cannot remember if I ever heard about it during my formal education (looong time ago)... [BTW, is it also valid regarding quantum mechanic? Specifically what I have in my mind is the wave function collapse - does the collapse has at all anything to do with energy distribution?] Next... My understanding is that one of direct consequences of the law of local conservation of energy is that we are then capable to define a value of 'energy flow' (through space) and a value of 'energy density' (in space). Am I correct? I have troubles understanding this 'energy density'. How much is this distribution of energy throughout space a physical thing. Should I expect that with a very sensitive equipment I should be able to measure a curvature of space that this energy density is producing... thus actually measuring energy density? (I understand that energy density should curve the space as well as mass do). Is energy density tied to one frame of reference or is it the same in all frames of reference? It seems to me that if you change the frame of reference, the energy density distribution changes too. Take for example a kinetic energy. Really, "where" is the kinetic energy? I mean, how is its density distributed in space? Where is gravitational potential energy? Where is electrostatic potential energy? I guess, If the energy density is for real, it should be possible to answer these questions. No? I guess energy density could be in fields. For example, kinetic energy could be distributed in gravitational field of a massive object (its mass increases with speed). For electrostatic potential energy I even know some formulas that say how energy is distributed in electric field... But what do you say?
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