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About DanMP

  • Birthday 03/15/1968

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  1. Yes, if we want to use thrusters directly on the asteroid surface in order to push the asteroid off the collision course, a rotation of the asteroid around an axis parallel to its path would complicate things, because the thrusters would rotate and need to be switched on and off. Therefore, in such cases, the gravity tractor technique may be a better choice. But gravity is a weak "force". If I electrically charge a piece of paper, the electrostatic force overcomes the whole Earth gravitational pull, lifting the piece of paper off the table. So I wonder: if there is, or we create, a net electrical charge on the asteroid and an opposite charge on the ship/ships, it would increase significantly the pull, making easier the effort to change the asteroid trajectory? The energy may be provided by the space solar power plants I proposed earlier/above and the charging through ionization and ejection of ions or electrons. If the electrostatic force is bigger than the gravitational pull, and also bigger than the force provided by the ship's thrusters, we can charge the asteroid and the ship with the same charge (negative, by ejecting ions) and push, instead of pull. It would be better for the ship's thrusters to be oriented directly opposite from the asteroid. When the asteroid is not very big and can be split, using explosives or nukes, the rotation and the axis orientation is actually helpful, as I wrote earlier/above, because the parts would be driven away from the original, dangerous, path, by the centrifugal forces.
  2. Larger the mass, longer the time from detection to impact, hence more time for the intervention ... And the spin may be pre-existing, needing just some increase. The risk is that the splitting explosion may not work as expected ... I also proposed something like that: The chemical reactions I mentioned should be violent/powerful enough in order to eject gases and some materials, providing thrust. Heating may also do the job in some instances. Space solar power plants would be spread around the Earth, some of them far enough, so we may have at least one close enough to the incoming asteroid. Also lasers would be used to convey the energy where is needed ... Another idea would be to deflect small asteroids from the belt in order to smash them into the incoming asteroid and deflect it.
  3. I think that we can use rotation/spin in order to deflect the debris/parts away from a collision course. If the axis of rotation of the asteroid is more or less parallel with its path, an explosion should split the asteroid in parts going away from the axis/collision path. If the rotation is too weak, we can increase it, with well placed thrusters, prior to the carefully planned explosion. If there is no spin, or the axis is perpendicular to the asteroid path, we may use thrusters to deflect the entire asteroid. We can use as thrusters craters/wells on a side (at a pole, if it spins), where we initiate some chemical reactions or we simply heat them using large arrays of space mirrors (ultrathin reflecting sheets). The arrays of mirrors should be deployed in advance, in all directions, and used as solar power plants, before being converted into solar guns.
  4. OK, I got it. Now I get your point about the importance of (centripetal) acceleration. Clever. Correct. Still, if frame-dragging is present (and significant), the clocks at rest in the dragged frame would be the fastest ... while rotating (with respect to distant stars) and having(?) centripetal acceleration ... You understood exactly what I intended to convey. Thank you!
  5. No, I can't find a link to the explanation you mentioned: the one you brought up when I said: This confirms what I said: the speed is the relevant cause for the differential aging in the twins' paradox, not the acceleration, nor the frame change, as the classical, linear scenario, suggests. In my modified Hafele-Keating experiment, it makes no difference if the plane continues forward or is turning back. Only the speed/velocity matters. And, by using the mirrors, the twins observe each other as in the classical, linear, scenario, with a relay (the relay scenario is the one where a third twin/clock is introduced, in order to skip the turnaround maneuvers). What inertial frames? Only the tower twin is in an inertial frame. And in the classical Hafele-Keating experiment the tower twin is also in an accelerated frame ... By the way, as far as I know, Lorenz transformations are between inertial frames ... but it turns out that they can be applied successfully between the non-rotating Earth frame and twins accelerated frames. This reminds me of the clock postulate.
  6. I don't quite understand. Can you provide a link to the explanation of Hafele-Keating experiment you are mentioning?
  7. Yes, but I never heard that centripetal acceleration is playing a significant role in explaining the time differences in Hafele-Keating experiment. If you did, please elaborate.
  8. Ok, let's consider a modified Hafele-Keating experiment: The stay-at-home twin would be in a tower, at the equator, and the traveling-twin would fly around the Earth, over the equator, at the same altitude as the stay-at-home twin (in order to have the same gravitational time dilation). The Earth is not spinning and flat, with mirrors placed all along the equator. The twins would see each other in mirrors, exactly as described in the classical, linear, experiment. Now, at the opposite side of the Earth (from the tower), the travelling twin turns the telescope from backwards to forwards, and by this action he is changing his perception from moving away to moving towards the tower twin. In this case there is no acceleration (change in velocity), no actual turning back, but the difference in ageing would be the same as he turns back with instant change in velocity and direction, like in a relay version. To me, this is yet another indication that: for the differential aging in the twins' paradox, not the acceleration, nor the frame change.
  9. Yes, that's why I asked Markus Hanke:
  10. Ok, but the context was the twin paradox and the blueshift observed at the turnaround. The blueshifted signal originated from Earth, clearly not local. Ok, so why did you offer the equivalence principle as an explanation for the blueshift there, in the twin scenario discussion? Anyway, the mentioned/linked discussion was closed and I don't intend to continue/reopen it here. All I wanted here was to make this observation:
  11. After I left yesterday, I realized that Markus Hanke answer regarding the blueshift: ignored that the source of light, the Sun, is not comoving with the travelling twin. For a light source situated in the accelerating spaceship, in front of the twin, there would be the blueshift that Markus Hanke mentioned, but if the source of light, the Sun in this case, is in front of the spaceship, outside, not comoving, the blueshift would continue to grow as the velocity of the ship increases. My point is that if an accelerometer indicates an acceleration and the blueshift of the stars in the direction of acceleration is not increasing, the acceleration is not real, it is not associated with an increase in velocity. In this way we can distinguish between uniform acceleration and uniform gravitational field.
  12. Yes, of course. That was/is my line of thinking as well. I don't know. No, on the contrary, I think that only the speed of the travelling twin is the cause, but the acceleration is important to establish which twin is travelling and also his path in spacetime, if I understood correctly. What do you mean with "ah is bigger"?
  13. We all know the twin paradox with the travelling twin returning younger than the stay at home twin. The acceleration in order to return is considered important for the outcome. Now, let's add a new acceleration, let's consider the travelling twin revolving around an axis, in order to feel as on Earth surface (same g force). If we have 1 clock on the Earth twin location (#1) and 2 on the ship, one on the axis of rotation (#2) and the other (#3) where the traveling twin is staying, which clock is recording the least time between departure and arrival and why? In order to see if only the (added) acceleration is important, let's add another, bigger, "wheel" on the starship, with a different rotation speed, but with the same centripetal/centrifugal acceleration, g. The 4th clock, on the rim of the bigger wheel, would record the same time as the clock #3, on the rim of the smaller wheel? If not, why not?
  14. In another thread, where twin paradox was discussed, Markus Hanke said: I asked: The first answer, from Mordred, was: True, but he didn't understand my question. The second answer, from Markus, was: Again, not what I asked, so I'll try again here. The traveling twin, after the turnaround, accelerates toward Earth/Sun and he immediately see the light from the Sun blueshifting. As long as he accelerates, the light is blueshifted again and again, due to the increase in speed towards the source of the light (the Sun). So, as long as his accelerometer indicates an acceleration towards the Sun, the light of the Sun is blueshifted again and again. On the Earth surface, say on the South pole, in summer, we also have the accelerometer indicating an acceleration towards the Sun, but the blueshift is not increasing, like in the traveling twin case. So the equivalence principle seems not quite relevant in explaining the blueshift that the travelling twin experiences. If I'm wrong, please explain me how/why I'm wrong.
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