Markus Hanke

@StringJunky, @studiot: Great, thank you so much for the responses +1 for each of you! It is as I myself would have expected from some very basic principles...I just wanted to be sure and hear from the experts, since I need that particular device to last for a while. One more question though: the manufacturer actually states that the battery has an average expected lifetime of around 500 charge cycles. So when I, say, use 20% charge in a day, then recharge by the same amount of 20% in the evening, does this count as a full “charge cycle”? Or is a charge cycle defined as the accumulated (not necessarily in one go) charging and draining of the battery’s total capacity? This may be a stupid question, but like I said, this isn’t my area of expertise at all.

I’ve a question that has been on my mind for a while, and I’d like to hear the opinions of people who are better versed in electrical engineering than I am. This is really not my area of expertise (nor interest, tbh). So I recently acquired a digital device that is powered by a Li-Ion battery. My question is - what is the scientific consensus as to which charging strategy will maximise the lifespan of the battery? Assume room temperature as well as European climate humidity levels. Also assume common sense precautions, such as not leaving it plugged in unnecessarily etc. I have tried to research this in the literature, but what I found is contradictory information - some authors argue that it is best to charge to 100% and then let it empty itself completely before recharging; others argue that it is best to keep the battery levels between 20%-90% roughly (actual figures vary). Yet others seem to say that keeping it in and around 50% by constant “micro-charging” throughout the day is best. They all give reasons, arguments and statistics that seem reasonable. Is there an actual consensus on this? Personally I would think that avoiding extremes of 100% and 0% charge seems prudent, but I don’t know.

No, a flat manifold without boundary is simply one of the topologies that naturally arise from the mathematics of the Lambda-CDM model, when certain observational parameters take on specific values. It’s just one among several possible options. It can be closed on itself - so there can be a largest possible separation between two suitably chosen points, without there being any kind of boundary. Much like (to pick a lower-dimensional analogy) a spherical surface. A manifold being finite in extent does not imply the presence of a boundary.

The mechanism is one of spontaneous symmetry breaking, so it would depend on whatever parameters appear in the Lagrangian. In this specific case it would be the speed of light, Planck’s constant, as well as the coupling constants between the various fields. The Higgs mechanism has no effect on the value of fundamental constants (other than ones related to the masses of particles of cause, which aren’t really ‘fundamental’). It only gives rise to some new coupling constants within the Lagrangian, since after the event you end up with more fields than you started off with.

Gravity is not a force, and it doesn’t propagate in any sense, unless the source changes in specific ways. I haven’t read your OP beyond the first few paragraphs (way too long), so I will remark only that under the standard laws of GR there isn’t any way to get such a thing as true “anti-gravity” using only ordinary energy-momentum distributions. You would need some form of exotic matter/energy for this - for which there is no evidence at all, neither in classical physics, nor within the Standard Model.

This doesn’t seem like a very apt analogy to me. Even the most basic of calculators performs operations that are impossible (or at the very least extremely difficult) to do by counting fingers, since those operations cannot be reduced to steps that utilise only elementary (+,-,*,/) operations - and even those are hard to do with only your fingers, if the numbers are not just nice and clean naturals. For example, have you lately tried to work out sines, cosines, tangents, exponentials, roots, or logarithms using only your fingers? You’d find that rather difficult. Most calculators do this using the CORDIC algorithm, which requires pre-compiled and hardwired lookup tables - which is something that can’t be replicated by counting fingers only. So clearly, a calculator is more than simply a replacement for finger counting.

This is evidently not true, since the very mechanism that creates the property of mass (the Higgs mechanism and spontaneous symmetry breaking) already presupposes the existence of at least a Minkowski background spacetime prior to said process; without this, there would be no universe as we know it today.

We are not really in a position to give any kind of medical advice or diagnosis here, especially not based on very non-specific symptoms such as the ones you describe; if you are concerned about your friend, you need to urge them to go and see a medical professional.

The appearance of a singularity in a model of physics generally means that the model has broken down because it has been extend beyond its domain of applicability. It does not mean that the model actually predicts a physical singularity to occur. In that sense, singularities - whether gravitational or at the BB - (almost) certainly are not actual, physical objects; they are more like flags saying “we don’t know yet what happens here”. Mass as a property of elementary particles only appeared at and after electroweak symmetry breaking (~10^-35s) when the Higgs mechanism kicks in; prior to that, all particles would have been massless. So yes, the very early universe contained only various forms of energy - which, however, still has a gravitational effect of course.

There are already several such models - most notably Loop Quantum Gravity and Causal Dynamical Triangulations, among some others. The idea to quantise spacetime itself is not new, it is one of the main approaches in the search for a model of quantum gravity. On the other hand though, the approach of trying to apply the usual machinery of QFT to gravity (which is where the idea of a ‘graviton’ comes from) can effectively be ruled out at this point, since we know that it is mathematically inconsistent and doesn’t work. And if it did, for some reason, work, then gravitons would need to obey all the usual rules of particle physics.

This seems like an awfully complicated way to do this. Why not just use Helmholtz’s Theorem? We know that the curl of the potential field gives the magnetic field (by definition!), so this is already fixed. The potential field is also invariant under certain gauge transformations (I think it’s the addition of a scalar field gradient, but I’d have to check that), hence we will always be free to make the divergence vanish, simply be choosing a suitable gauge, without affecting the curl. So in essence, under Helmholtz’s Theorem, the divergence has no physical relevance at all in this.

Yes, because the geometry of spacetime is such that the interval between any two nearby events is an invariant. There is no mystery in this, and it has been known for well over 100 years.

Neither are gravitons. An interference pattern, made up of many point-like hits on the detection screen. Wave functions (in QM) are probability density distributions, not physical objects - asking whether they ‘have volume’ is meaningless. It’s rather the other way around - you start with the wave function, then integrate its squared norm over a given volume in order to obtain an expectation value.

Elementary particles do not expand, since they have no volume. Well, that’s the problem - the physics aren’t compatible with what you state.

That conclusion does not follow, and even the premise is somewhat faulty - gravitons, were they real, would only mediate changes in the gravitational field. Setting String Theory and other unproven conjectures aside for now, no elementary particle has any kind of volume; they behave as point-like objects. They would be point-like objects, just as all other elementary particles - these entities do not possess a property such a ‘volume’.

It’s the other way around, actually - we know perfectly well what the properties and dynamics of gravitons need to be in order to be consistent with gravity as we observe it; but if you write all this down, you will find that the mathematics simply don’t work out. That’s why ‘gravitons’ are a dubious concept - more than that, there are good reasons to believe that this is simply not the right way to quantise gravity.

No it isn’t. The strong, weak, and EM interactions are distinct phenomena and not mediated by gravitons. Actually, a QFT for a spin-2 massless graviton (such as would be required to obtain GR in the classical limit) is straightforward enough to write down. The problem is that the result is physically meaningless, since it can’t be renormalised. So this evidently isn’t the right way to go, because it doesn’t work.

Have you ever tried to write down a quantum field theory for self-interacting spin-2 gravitons, with the appropriate classical limits? It’s a doable exercise. Unfortunately the end result is a QFT that is non-renormalisable, so it does not yield any physically meaningful predictions. Clearly, this approach leads exactly nowhere. You don’t need to use it, you can just stick to the Copenhagen interpretation, or use any of the numerous other interpretations. Remember, you are always dealing with the same model, these aren’t distinct theories.

I don’t think it is useful to resurrect a 17-year old thread, since none of the original participants is still active on this forum...

Why? There is no principle of nature that requires the laws of physics to be ‘simple’ or ‘minimalistic’ (though many of them are) - whatever those terms actually mean in this context. They do, however, need to be internally self-consistent, and of course produce the correct results.

The MWI is mathematically self-consistent, it being just one possible interpretation of standard quantum mechanics.

It’s not a mechanism, but a fundamental symmetry - the invariance of the spacetime interval.

I think what he means is that, if every possible outcome is realised - albeit in different branches of the multiverse -, then what is the physical meaning of probabilities? Technically speaking, the probability for each outcome should be 1, because it is realised with certainty somewhere - irrespective of the fact that the various outcomes cannot be connected in any way. I’m not an expert on the MWI, but I think this is a valid objection, which I seem to remember having seen raised in the literature as well.

You actually need even more than that - you need a non-vanishing quadrupole or higher multipole moment. This wouldn’t be the case for your average planet, unless for some reason it has an odd shape.

This seems to be a specific solution for a specific type of spacetime, presumably Schwarzschild (I haven’t gone through your derivation). That’s fine, assuming the derivation is algebraically correct, but only so long as your gravitational source actually does admit a Schwarzschild solution. If not, then you still need to fall back on solving the geodesic equation.