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Danijel Gorupec

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Everything posted by Danijel Gorupec

  1. I try to put all observers down to Earth No, I don't see how the Earth's orbit will get tighter if I add uniform mass density to the whole Universe. It would get tighter if I spread the added mass in a large sphere centered on the Sun - and only the part of the mass inside Earth's orbit would affect the Earth, exactly as you said. But I didn't do that - Instead I distributed the mass uniformly over the whole universe (I didn't center it at the Sun). In my opinion, adding uniform mass density (positive or negative) to the whole Universe, does not change local trajectories of gravitationally bound objects. It might affect, as you said, the expansion of the Universe as a whole, but this is an even darker topic. It seems to me, there is still enough wiggle space in our theories and observations that we cannot say for sure there is no additional (positive or negative) offset to the observed distribution of dark matter density.
  2. [I always enjoyed Susskind's lectures - did watch quite a few of them, but didn't know he has the cosmology series too.] Are you only considering the case of uniformly distributed mass density? Because if I put a black hole just outside Earth's orbit, it will affect the Earth trajectory. But even with uniformly distributed mass I find your claim confusing... Suppose you only have Earth orbiting the Sun. Now you add uniform mass density to the whole universe - you say that the Earth will only 'feel' the part that is inside its orbit? Does it mean the Earth will go into a tighter orbit with greater velocity? Ok... but remove the Sun now - will Earth go into some other orbit (because it feels the gravitational attraction of the mass inside its orbit) or will the Earth continue straight?
  3. This is exactly what I am talking about -> is this claim a jumping in conclusion? Because of effects like dark energy I cannot dare to claim that dark matter attracts. It might as well repulse... But I know very little, and maybe I am missing an important bit of information that indeed shows it is attractive.
  4. Sure, but there can be negative mass within the galaxy that will produce an effect on the galaxy. I suppose it would be possible to came out with some negative-mass-density profile (as a function of the distance from the galaxy center) that would give the observed gravitational effect.
  5. Why? It seems the same to me - you can have positive-mass around galaxies, or you can have negative-mass everywhere else. How could you tell the difference?
  6. Thanks for the video, I liked it. So, without the dark energy nuisance, we should be able to estimate the portion of uniformly distributed dark mater. But because of the poorly understood dark energy, I guess we cannot do much of an estimation? [Looking at equations derived by Susskind, purely mathematically speaking and putting things upside down, if the dark mater has a negative mass it might cause accelerating universe... supposing large majority of it being actually distributed uniformly, and being only slightly less concentrated around galaxies; as we can detect from its gravitational influence.]
  7. Bad English. I wanted to ask, if there is a stuff that only interacts gravitationally, and if such stuff is distributed uniformly - are there any means to detect it?
  8. Similar to @Genady, I wonder why it appears clumped if it does not clump - does it mean that, at this age of universe, the gravitational radiation was enough to clump it into galactic halos, but not yet enough to form it into galactic discs? Also, if DM is perfectly uniformly distributed, would we at all be able to detect it - could it be that there is much more of it around, but we only detect so much of it because it is not perfectly uniform? This is the first time I hear such argument. Puzzling. Anything more to read about it? Did pure mathematicians have an attempt at it - by examining if GR equations can at all behave in this 'unexpected' way in very complex systems?
  9. At first glance, I didn't find any error in the video. Although some things could be stated more precisely (and I agree with Studiot that the reference to telegraph cable only blurred the explanation). For those who like to think in more common terms, just note that such a wire loop would have a very large inductance (back-of-envelope calculation, something over 700 Henry), so it is sure (as they also said) that the voltage at the lamp would raise slowly (that is, the first effect at the lamp will be at roughly 1/c time, but it will take much longer for the thing to settle). I would also comment that if wires are arranged in some other way, the result could be different. For example, if both wires (plus and minus) are not separated away from each other, but are closely packed inside a long cable that goes very far away and then returns to the lamp (or especially if a coaxial cable is used), the lamp will only start lighting much later (considering a somewhat idealized case).
  10. I see... there is the whole zoo :). Ok... I am a practical person... if too many people would suffer, then science may tactically tone down some of its conclusions... (but that is quite a question to discuss, I would say) What do you mean by 'serious atheists'? If you speak about those anti-theists, then I agree... I consider myself an atheist (not agnostic, if I understand the positions correctly), but still find anti-theists scary. Hey... but that would make you a non-theist (I just read this from the article - as they say, that would put you among the rarest atheists)
  11. Hmm... I hold a somewhat different view. Even if science cannot make a rigorous prof (and therefore a claim) that there is no God, it should still honestly advise general population that it is not smart to spend extensive resources (time/money/effort) only to please any god(s). Not having a rigorous proof does not mean you should refrain from making a honest advice... In fact, science must clearly state its best advice and not keep silent (I don't think it has much to do with quality of equipment available to science; even if science only has most rudimentary tools, it should provide advice the best it can at that moment... loud and clear, even if it has to apologize later). Regarding OP, I am undecided which of the two would be a better definition of atheism. I think we should have different words for the two definitions (maybe we do, only I don't know them).
  12. Neanderthals, I would like to greet. I kinda hope this might actually happen one day. T-rex or similar because I romantically hope they were colorful and maybe had a comb. Dodos, because I am hungry right now and the T-rex reminded me on chicken. I will keep one choice for the future - possibly to rescue mountain gorillas.
  13. Boh. Microgeneration... what is the most successfull microgeneration technology today? I only know roof solar; is there anything else? Those walls seem to be intended as a microgeneration technology... but I am afraid microgeneration is loosing the battle in the green battlefield. Bigger and bigger wind turbines are winning. Once we completely switch to green power, turbines might become monstrous. Solar plants too... If microgeneration ever becomes an important contributor, the ground-breaking discovery will not be how the energy is produced, but how we managed to network all this together into a smooth and efficient business. Sorry for the blues.
  14. I believe what CharonY said: no way to remove bacterial biofilm by just rinsing in cold water. So, basically the only benefit is removing the stale water (leftover from last refill that might be there for 2-3 days). The stale water might contain some bacteria, I guess... It is entirely possible that in my particular case, the vigorous shaking provides no benefit compared to mild shaking. In some other cases, I guess, depending what was in the bottle, vigorous shaking might provide additional benefit. Still, many people will shake the bottle as I do, without much thinking - I wonder if this is a learned or instinctive behavior. Probably learned.
  15. I 'instinctively' use about 1/5 of the volume and repeat this 2-3 times. Need to feel some heaviness of water bouncing around while shaking (and the noise should be loud) to have a feeling that I am doing a good job. Ah yes, my original thinking was about the best volume that minimizes the number of shakes (for the same rinsing effect).
  16. A light-hearted question... Every time I am in hurry filling up my water bottle before gym, I wonder the same thing: how much water should I pour into the bottle (then shake it vigorously and pour it out) for the best rinsing effect? Of course, I don't care much about the exact number - but I wonder how to even tackle the problem?
  17. Still, you occasionally need some window heating during winter. Do all electric cars have heating mesh also in front window?
  18. Ok - this is somewhat possible. It can be that AstraZeneca spoke about predictions, but EU politicians presented them as actual promises to public (for example my prime minister would use the wording 'we secured xyz doses from AstraZeneca'). But is still puzzling... There are many prime ministers in EU - somebody had to misinform all of them because they hardly ever cooperate (even in a misconduct). This somebody, I guess, could be the team that negotiated with AstraZeneca. The team members either had to be villains or dumb enough to misunderstood AstraZeneca predictions as promises... On top of that, AstraZeneca failed to place an effective public denial that they made promises. BTW, it might be an interesting question if Occam razor is applicable to such examples (because we, the limited group of people on SFN, cannot tell what actually happened behind the closed doors, and we have no way to discern what is the actual explanation how people in EU became misinformed about vaccine supply rates).
  19. (I don't know wood.... It is not probably the best thread, but I didn't feel like opening a new one) A small solid wooden beam (about 0.1x0.1x1.5m) is fastened at one end to metal plates (by screws); the other end is free. The sideways force acts on the beam. Is there any preference how I should place the screws (perpendicular to force direction or parallel to it - see sketches A and B below)? It is an oak beam. The force is impulse-like (not steady) - like if someone step on the beam from time to time.
  20. Not sure what an evidence would be... I found the following passage on wikipedia (https://en.wikipedia.org/wiki/Oxford–AstraZeneca_COVID-19_vaccine) : "On 22 January 2021, AstraZeneca announced that in the event the European Union approved the COVID-19 Vaccine AstraZeneca, initial supplies would be lower than expected due to production issues at Novasep in Belgium. Only 31 million of the previously predicted 80 million doses would be delivered to the European Union by March 2021." On the same page there is following data (indicating that indeed the number of delivered vaccines by March was lower than 80 million - apparently, it was above 17 million, but how much exactly depends on how much vaccine was hold on stock by countries and how many people received the double dose) "On 14 March 2021, AstraZeneca has confirmed that after over 17 million people have been vaccinated in the European Union ..." The difference between the 'predicted' (80 mio) and the delivered (I don't know, I guess about 20mio by mid March), imo, might be the reason why rumors started that AstraZeneca is selling 'our' vaccines elsewhere. In my opinion, it could be that these rumors were additionally fueled by statements like following (from the same page): "On 17 December, a tweet by the Belgian Budget State Secretary revealed the European Union (EU) would pay €1.78 (US$2.16) per dose." "In August 2020, AstraZeneca agreed to provide 300 million doses to the USA for US$1.2 billion, implying a cost of US$4 per dose." ---- Admittingly, citing Wikipedia is not much of a proof. On the other hand, this is only a forum and even Wikipedia might be good enough for the sake of discussion. ----- I also need to 'quantify' the term 'outrageously'... I never understood 'outrageously' to be a quantifiable term. I understand it in qualitative way, like, for example, terms 'more' or 'bluer'... What I meant by 'outrageously' can be described as "so much that it cannot be easily explained any other way but by deception." ----- I don't know how much these vaccines are different, but I imagine that AstraZeneca experts should know. If mRNA vaccines are so different that it was not possible to make predictions, then they had to refrain from making promises (or 'predictions' as they said) in the first place. ----- One should also consider that, for some reason, people put different weighting factors in front of 'possibly cured' and in front of 'possibly harmed' (even medical professionals -> "do no harm"). So even if statistics is clear, people might prefer to choose 'irrationally'.
  21. Knowing myself, I would probably do nothing. I am not an activist... But I would be interested to learn if a simple sales lie caused the distrust avalanche that will eventually kill people.
  22. You are smart.... Did you ever work in sales? Fine, we don't have enough information. Should we demand it?
  23. Somebody powerful enough that has some interest (revenge, perhaps)... Sorry, I have hard time finding the right words or terms in English and so my writing might not always be clear (I might use terms that are too narrow or too wide).
  24. Do you think their wrong estimation was a honest mistake or do you think their estimation was basically correct but somebody inflated it when presenting to EU public?
  25. But this is my whole point. The numbers presented to EU public were not just slightly higher than was actually realized. They were outrageously higher. How came such a large mistake? What is your explanation, then?
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