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Steel

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Everything posted by Steel

  1. Steel
    It is a little confusing. Wikipedia
  2. Steel
    Kugelblitz and atmospheric ball lightning are very different things.
  3. Steel
    Yes GR is built upon them being equivalent. Thus any experiment that might prove that they are not equivalent would also prove that GR is not a universal law, but instead something that only works in the limited scope that we have observed up to this point. TL;DR: As long as GR holds, it is very likely that they are equivalent.
  4. Steel
    In the Einstein field equations (equations of GR), the curvature is a direct result of a thing called a stress-energy tensor. This is a slightly tricky thing to explain, but it essentially represents the amount of energy and momentum at each point in space. So broadly speaking, anything that contributes to this tensor curves spacetime, this can be mass, electromagnetic fields or anything else that changes the flux of momentum or energy.
  5. Steel
    Well luckily I have a physics degree! Gravity is the weakest of the four forces. There is no argument about that. Just because gravity has a greater effect on the large-scale structure of the universe and has longer range than the strong and weak forces does not change the fact that the gravitational interaction is the weakest (as can be seen by its tiny coupling constant). There could be a difference between the two mass types but we just don't know (it's a big unanswered question in physics). No experiment has ever found a difference, but that does not necessarily mean that they are the same. Technically, gravity (at least Gravity in GR) is a result of the curvature of spacetime due to local energy-density. This does not specifically have to be mass, so you can't really say that gravity is a property of mass. To unite the forces we need a ToE. We don't necessarily need a ToE to understand more about them, however. Also, there is the possibility that a ToE that describes our universe simple doesn't exist.
  6. Steel
    Ok let's calm this down a little, this is getting close to personal insults.
  7. Steel
    That's a little bit of a misunderstanding. It is true that electroweak theory is well established, however, this unification only occurs at insanely high energies like those found in the immediate aftermath of the Big Bang. In the universe today the four forces are distinct. Moreover, a theory unifying the strong force, or a Grand Unified Theory, is still a long way off, and there is no significant evidence that the universe is in fact described by a GUT. Unifying gravity is way beyond us at this point in time. Thus, the forces act as distinctively in our universe in its current state, with the weak and strong forces having very short range. That's not really true, on any scale where you can compare forces (i.e any scale where the strong and weak forces still exist, i.e. over the scale of a proton), gravity is by far the weakest force. Also, if you dive into various field theories, gravitational interactions are quantifiably weaker than the others. Just because gravity has a longer range does not mean it is stronger, just that it reaches further. It is a bit like having a very long piece of string and a very short piece of rope, just because the string is longer does not mean that is is stronger.
  8. Steel
    It categorically is the weakest. It just happens to be one of the two fundamental forces that (at least appear to) have infinite range.
  9. Steel
    Probably, in the same way that sunken ships do.
  10. Steel
    Yes true, but (just pie in the sky here) if you had millions (probably more like billions) of these things going on simultaneously you might be able to disrupt the local pressure distributions enough to do something to a small hurricane. After all, these weather system are driven by pressure. I could make no guess as to what that something might be though.
  11. Steel
    Not strictly true. If a sonic boom had no effect then people wouldn't have complained so much when Concorde broke all of their windows
  12. Steel
    If you had millions of aircraft in perfect syncronicity then maybe you might stand some sort of chance of having some effect. Even then, there's no way of telling what that effect would actually be.
  13. Steel
    Careful with Musk, he's not so good with sticking to deadlines! Many folks around here like talking about "Elon time", where you double how long he says it will take to do something and add 30 months Worth baring in mind that he's been claiming that Falcon Heavy is \paraphrase{"a few years away"} since 2008.
  14. Steel
    Unlikely. The differences in scale are just so enormous. You're talking about weather systems that are hundreds of kilometers in size. (Ninja'd)
  15. Steel
    No, "spooky action at a distance" was quantum entanglement. Einstein had a pretty good grasp on gravity.
  16. Steel
    No, because all it tells us is what the fundamental interaction is that gives intrinsic mass, not what effect that mass then has on other massive particles.
  17. Steel
    The discovery of the Higgs reveals pretty much nothing about gravity. It confirms Higgs' (not forgetting Anderson, Brout, Englert, Guralnik, Hagen, Kibble and 't Hooft) theory about why some particles have a small amount of intrinsic mass and that's about it (well that's not really it, but there's nothing else really worth highlighting here)
  18. Steel
    Can I just point out that terminal terminal velocity is just the velocity whereby force due to gravity on a falling object is equal to the drag acting on it as it falls. It has very little to do with rockets and their ascents.
  19. Steel
    ^THIS^ There is absolutely nothing difficult about the rocket science behind making an orbital rocket from off the shelf components for $100,000. What is difficult is the engineering. That's why rocketry costs so much, because the hard bit is working out why the real world doesn't match what your calculations are telling you. In the same way there is nothing fundamentally difficult about the rocket science behind making a cross-feed Falcon 9 Heavy. The engineering, on the other hand, is near impossible. See Elon on the matter:
  20. Steel
    The faster you turn, the further away you are from pointing along your velocity vector, so you incur cosine losses (losses caused by not thrusting through your velocity vector).
  21. Steel
    There are several reasons, some of which have been mentioned above. However, the main reason is that any time the rocket is burning fuel when it is not at high altitude and burning directly along its velocity vector it is wasting dV. Thus, you want to burn as little fuel as possible to get up above 100km an pointing towards the horizon to minimise these losses, while still having enough thrust to get there in the first place.
  22. Steel
    From what I understand, the ascent profile of any launch will be designed primarily to reduce dV losses (though cosine losses, aerodynamic losses and gravity losses), while keeping within key parameters such a maximum structural load or (in the case of a manned flight) maximum acceleration. This means that the acceleration at any given point is dependent on a huge number of factors: the aerodynamic performance the rocket, its TWR, its ability to throttle, whether or not it is manned, the thrust available, maximum structural load and many other factors. This means it is impossible to give you a general answer that applies to all rockets.
  23. Steel
    1: There is no optimal value (provided it is greater than 1). It depends entirely on the rocket, and the mission profile that it is flying. For instance, you may want a low value at lift off if you know fuel is going to burn off quickly as so the TWR will rise very quickly. Also if your engines can throttle, then you can have a higher TWR early on because you can throttle down later in the flight, but if they can't throttle then you probably want a lower TWR early on to avoid excessive acceleration later. 2: Rockets tend to throttle to manage structural loads, or simply just to lower fuel burn while they're still ascending, so they can use more fuel later on when they have completed the gravity turn and are putting all the dV into increasing orbital velocity. 3: Both profiles would typically be designed to reduce losses (cosine, gravity and aerodynamics) in the early parts of the ascent as much as possible. 4: As before, most rockets can't throttle. Even the ones that can often can only drop down to 70% or 80% of max thrust, and most likely can only do that in fairly big jumps (i.e either in jumps of 10% or more). There are definitely no rockets that can throttle continuously like in KSP. One of the most throttle-able 1st stage rockets rockets (we're ignoring things like the super Draco here) was the Space Shuttle Main Engine (SSME) which could throttle from 109% to 67% rated power (so basically 100%-58%) in 1% increments. Also throttling, especially on older engines, comes with a certain degree of risk that the engine will stop burning due to the drop of fuel pressure, chamber pressure e.t.c Also to clarify, The F1 could not throttle at all.
  24. Steel
    Yes, absolutely.
  25. Steel
    Typically fro a manned mission, you want to have a something to do that only a human can do. Obviously early missions you can get away with "we went because we wanted to go", but after a few manned missions, you need some purpose in order to justify sending people. I'm sure between us there is a mission objective that can be created that requires humans. Organic life doesn't tend to form near overground volcanoes, they're usually far too hot and arid, especially not enormous ones with basically no atmospheres. It does seem form around undersea volcanic vents on Earth though, which might be what you were thinking of.
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