Steel

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Everything posted by Steel

  1. Correct me if I'm wrong, condensed matter was always my least favourite area of Physics, but this is exciton condensation, correct? So, much like all other condensates of quasi-particles, you get some interesting material properties to study and not much else?
  2. Anyone got any citations for some actual scientific literature on the matter?
  3. Perhaps because it's simpler, cheaper and (potentially) more reliable than fitting more rocket motors.
  4. Silicon, I've never heard it being referred to as Silicium. What language is that used in?
  5. I never had a graphing calculator at university. It would certainly make some parts slightly quicker, but unless your college requires it, you can do everything you need on a scientific calculator.
  6. Are we really going to nitpick about n-body interactions and gravitational waves in a question that involves a completely implausible shaft drilled exactly straight through the centre of the Earth? Has the old spherical cow in a vacuum assumption gone out of fashion these days?
  7. What I've found over the years is that it's good practice, whenever you do a fraction, to put the top and bottom halves into their own brackets, even if it's not necessary. Avoids a lot of annoying mistakes
  8. Make sure you're putting brackets around everything to make sure the operations are being carried out in the correct order. (6*200+1500)/(130.94*9.81) = 2.10 The way you have input it, the calculator is doing (6*200) + (1500/130.94) *9.81 = 1312... because of BIDMAS (or sometimes PIDMAS).
  9. See the edit to my previous post ^^^
  10. Can you give an example of a calculation that has gone wrong? Seems wierd that you'd get stuck on TWR if you can manage the rocket equation. EDIT: wait, g is the acceleration due to gravity at sea level (i.e 9.81 ms^-2), are you using that or the gravitational constant, G?
  11. You've answered your own question there. You'd need to find a way to travel faster than light.
  12. Exactly. IRL you need about 7500 ms-1 of horizontal velocity at LEO, in KSP you need about 2000 ms-1. In both cases you only have to be about 150 km up, so you have to burn much longer and much more towards the horizon in real life.
  13. Sort of. It's a difficult concept to try and get across via text. Simply (or as simply as I can) the big bag happened simultaneously everywhere in the universe, because at the point of the big bang the entire universe was in the same place because it was an infinitesimal singularity. You are right, it is a bit of a simplification. Over large scales things are moving away from each other due to the expansion of space. Of course, over small distances gravity dominates and things stick together - that's why we have stars and a solar system and Donald Trump.
  14. It was everywhere. Because, as far as we can tell, all space is expanding, which means if you rewind to the beginning of time there was no space in-between everything and the entire universe was in one infinitesimal point. Thus the big bang occurred everywhere at once, from this infinitesimal point which was the entire universe
  15. I didn't think either approach should be ruled out or favoured over the other until the evidence say so. There are tens, if not hundreds, of alternative theories of gravity to vanilla GR, and almost universally they agree with some observations but not others, or are not self-consistent.
  16. http://backreaction.blogspot.co.uk/2017/11/astrophysicist-discovers-yet-another.html?spref=tw&m=1
  17. I believe there are still some WIMP candidates still in play, like the right-handed neutrino. Also the above study has not actually ruled out axions totally, they could still exist with a mass outside the range that was excluded by the observations.
  18. There are still plenty of other dark matter candidates other than axions. Also, if there is a field there are likely particles. After all, particles are just local excitations of a field (i.e. the Higgs boson is just a local excitation of the Higgs field)
  19. This is where your problem is. The definition of the Schwarzschild radius is NOT Newtonian, you have to do GR and solve the field equations to get a general solution. Luckily for high school teachers all over the world, it just happens that if you do the basic assumption V_esc = c and then solve with Newtonian gravity you get the same result as if you'd done a full solution of the Schwarzschild metric for the black hole. This is a great way to make the topic more accessible and easier to visualise, but is not a true reflection of the physics going on. Don't make the mistake of thinking that this means Newtonian gravity is going to help you much where a black hole is concerned.
  20. Well according to the Wikipedia page, an Alderson disk would be more massive than the Sun and require more material to build than is present in the Solar system. I'm going to guess that this means it would take more to build than a ringworld (depending on the size of the ring world, I suppose). An Alderson Disk on it's own probably doesn't have a very large habitable zone, you would need life-support to enlarge it. There are also numerous questions about the direction of gravity at any given point of the disk as well as questions about how its would retain an atmosphere. It's worth noting that while a ringworld is a sci-fi idea, the Alderson disk is not. It originated as a setting for a fantasy swords-and-sorcery world and so the physics of it are sketchy at best.
  21. The event horizon is an infinitesimal boundary, therefore it's physically impossible to be at the boundary, you can only be either inside or outside it. The other scenario isn't much better, because you cannot transfer information across the boundary from inside -> outside.
  22. You're quite right, I was mis-remembering my particle physics! The Higgs mechanism is responsible for some fermion masses too, however the interaction with the Higgs field that results in mass is different for fermions and bosons.
  23. In fact the Higgs mechanism only really explains why a certain group of bosons have non-zero mass (and some other more subtle, but still important, particle physics things). EDIT: I'm wrong here, see below
  24. /pedantic{In that case a human brain cell is in the middle, a whole human is a few orders of magnitude larger than the middle}