Markus Hanke

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Markus Hanke last won the day on June 11

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  1. Is quantum physics too small to interact with gravity?

    The problem is akin to having a mathematical formalism, but not being able to extract specific predictions from it, because the mathematical tools are missing to work with that formalism. For example, you can know the Einstein field equations, but if you haven’t got a clue how to go about solving them, then you can’t extract any of the physics. So it’s a matter of developing mathematical tools as you go along, and that takes time - which is why String theory appears to have stagnated of late. Actually there is continuous progress, but it’s mostly very technical stuff, and the progress is slow. This issue partly persists even with well-studied models. For example, a complete classification of all possible solutions of the Einstein equations is (to the best of my limited knowledge) still an outstanding problem. Another example is QCD (the strong force) - the field equations are so complex that no closed analytical treatment is possible; we largely rely on numerical simulations as well as simplified approximations. I don’t think there is an alternative to maths when it comes to QG. Of course, it all starts with ideas and approaches, but then these need to be fleshed out with a proper formalism, or else no one will ever know what these models actually say, in physical terms.
  2. Is quantum physics too small to interact with gravity?

    There is a substantial number of what I would consider promising approaches, though it is not yet obvious whether a fully self-consistent model of QG is among them - there is always a chance that there isn’t. The trouble is that we have not got the mathematical abilities to fully work out and understand many of these candidate theories, so it is difficult to evaluate their actual value to us. What’s more, we don’t even know what a fully consistent model of QG should look like, and what features it would have. At present the best candidate models would remain Loop Quantum Gravity, Non-Commutative Geometry, Causal Sets, Causal Dynamical Triangulations, Asymptotically Safe Gravity, and M-Theory. This is not a complete list though. M-Theory actually goes a step beyond QG, in that it is a candidate for a “theory of everything” that could model not just gravity, but the entire particle zoo through a unification of all fundamental interactions. There is a candidate theory of QG called Group Field Theory. I can’t really comment on it though, since I am largely unfamiliar with this particular model, except in the broadest of terms. Yes, because before you can even begin to worry about gravity on small scales, you need to first understand the other fundamental interactions, which are orders of magnitude stronger. Doing this leads to quantum field theory, which is the unification of quantum mechanics and special relativity.
  3. large mirror,balloons and a telesscope?

    Good point...but then, you wouldn’t be looking directly at the mirror either, you’d be looking through an eye piece, which presumably is an arrangement of lenses. Or not? I never owned one of these things.
  4. Is quantum physics too small to interact with gravity?

    You are right that under most normal circumstances, gravity plays no role on very small scales, because the other fundamental forces (weak, strong, and electromagnetism) are very much stronger on those scales by many, many orders of magnitude. However, there are situations when gravity becomes substantial enough that it can no longer be ignored, not even on small scales - for example in the region behind event horizons of black holes, or at the very earliest moments after the Big Bang. So in order to understand those scenarios, we need to find ways to bring together gravity and quantum physics, which is not at all a trivial task (for mostly technical reasons). This is currently an area of intensive and very active research, and has been for some time.
  5. large mirror,balloons and a telesscope?

    I presume it would be more beautiful (it needs an astronaut who has been to space to authoritatively answer this) - but if you are looking at the mirror through a telescope, then you are also going through a lense.
  6. large mirror,balloons and a telesscope?

    Sure it is possible. Whether it is practical is another question, though. Depending on how high you are planning to go, you’d need a fairly sizeable mirror, and/or a good sized telescope, in order to get a clear image. There is also the issue of the mirror moving around with the winds, so it would be hard to really see anything much. What is the purpose of this? Why not just use a remote camera that transmits back in real time? Has this anything to do with “flat earth”?
  7. How are galaxies expanding along with space time?

    Yes, the tendency to expand is already intrinsic in the FLRW solution to the Einstein equations. This is simply a natural consequence of laws of gravity. You would need to introduce a counter-mechanism to stop this from happening, such as an appropriate chosen cosmological constant. It is not completely unfeasible - you can construct a “steady state” type of model by balancing out the observed average energy density of universe with an appropriately chosen cosmological constant. The trouble with this (apart from it not being what we actually observe) is that it is an extremely unstable configuration, like balancing a mountain on a needle - the cosmological constant would have to have an extraordinarily precise value, and even the slightest perturbation of that numerical value would destroy the balance. There is no known physical mechanism that could guarantee the stability of such a configuration, not even in principle; on the other hand, there are plenty of physical mechanisms that would introduce fluctuations in the value of that constant over time and space. So all considered, the “steady state” concept is not very physically feasible.
  8. How are galaxies expanding along with space time?

    As already explained in considerable detail - there is no proper acceleration. So you are not asked to buy into anything more than the validity of the law of gravity.
  9. How are galaxies expanding along with space time?

    Indeed - some of the roads are shocking here. I know this better than most, because I’ve been a full-time van-lifer for a while, so these roads are my home. A healthy dose of respect is needed. Thank you Oftentimes, explaining things to others is the best way to deepen your own understanding of it. The challenging bit is always to figure out whether the other party is actually receptive, or whether you are talking to a wall.
  10. How are galaxies expanding along with space time?

    ...until you meet you meet a 10t cement truck head-on at the other side of the crest. All of a sudden acceleration becomes very real again Lol, I like this
  11. How are galaxies expanding along with space time?

    It doesn’t need to “make sense” (a purely subjective perception!), it just needs to fulfil the requirements of a scientific model. Which the laws of gravity demonstrably do very well. The situation is the exact same as when you jump off a board into a swimming pool - a stationary bystander can measure your motion from afar, and will argue that you undergo acceleration, based on what he measures (9.81m/s2). But if you yourself carry an accelerometer with you as you jump off, you will find that it reads exactly zero at all times during your free fall. This is not just some theoretical speculation, but something you can actually try out yourself. In fact, I would encourage you to go ahead and do this experiment, if you are really in doubt over the differences between coordinate and proper measurements. Just make sure your accelerometer is waterproof Alternatively, you can just recognise that this funny feeling you get in your tummy while you are in free fall is just precisely this - the absence of any acceleration (i.e. force) acting on you. And yet you fall under the influence of gravity.
  12. How are galaxies expanding along with space time?

    It’s useful so long as you bear in mind the difference between “analogy” and “model” - they have different aims and goals.
  13. How are galaxies expanding along with space time?

    No - but it’s a reasonably good analogy to demonstrate the basic principle. Where the analogy fails though is that metric expansion has nothing to do with any “stretching”. That’s why it’s just an analogy.
  14. How are galaxies expanding along with space time?

    Because there is a difference between what we visually observe from a distance, and what actually happens locally where the galaxy is. The first is called coordinate acceleration, the latter is called proper acceleration. The difference between these is crucial. To see why, turn things on their head - from the perspective of a very far away galaxy, our own galaxy where Earth is located is moving away at a very high and accelerating rate. Yet if you stand up right now and look at an accelerometer, you won’t actually detect any massive acceleration acting on you (hence on the Earth, and our galaxy). There is coordinate acceleration (what you measure from a distance), but no proper acceleration (what an accelerometer physically measures). The same is true for forces of course.
  15. How are galaxies expanding along with space time?

    I think it is important that you actually read the replies you get on here, because otherwise you will just keep going in circles. As already explained, there is no force acting on the galaxies. There are no forces involved in any of this at all. Gravity is not a force - it’s a geometric property of spacetime. If you drop an accelerometer, it will read exactly zero at all times (you can try that out yourself at home), so as per F=ma, with a=0, there is no force. Yet it will still fall under the influence of gravity, and according to its rules. Also, the weak/strong/EM interactions are not forces in the Newtonian sense either - they are interacting quantum fields. There are no mechanical forces involved anywhere in this. I think your basic problem is that you assume the universe and everything that is in it to be Newtonian (essentially the kind of physics you learn in high school) - but in reality it isn’t. Newtonian mechanics is just a highly simplified approximation that applies only under very limited circumstances. Even on comparatively small scales such as the solar system, Newtonian physics already fails miserably. Cosmology then is very far outside its domain of applicability. Trying to ask about what forces act on galaxies etc is hence largely meaningless, because the very concepts are essentially meaningless in the context of cosmology. There are other things at play here. All of this can very easily be understood in the framework of spacetime geometry - but if you do not acknowledge that as a valid concept (your own prerogative, of course), then there will be little point in this discussion.