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## Comment Re:No (Score 1)118

Ah, but in the meantime, genetic research isolated the genes responsible for the condor's giant wing and wingspan. Researchers are in the process of selecting a species of very small pig to attempt for the first time to create a new species of pig, one with actual wings and hence in principle capable of flight according to the syllogism "If pigs had wings, they could fly".

Also, Pink Unicorn spotted trotting down US 70 near Dover, NC, halfheartedly pursued by gracefully dancing bears! More news at 11!

## Comment Re:That's nothing... (Score 1)105

"Earth" slows asteroids down when they land on it. To rest, in the Earth's rest frame, in reasonable approximation. This is a completely inelastic collision, and given the disparity in their masses nearly all of the asteroid's relative kinetic energy is transformed into heat. Some of that heat heats the atmosphere as the atmosphere lands, sure, but seriously, look at the magnitudes involved. This is pretty much irrelevant, given that the impact is going to blow the friction-heated atmosphere near the impact point clean off of the planet.

As far as the second part of your question is concerned, yes, energy is conserved, so the minimum speed of an asteroid falling unimpeded from a place very far from Earth is also the minimum speed required to throw it back up to that place.

This isn't that radical an idea, after all. It works just fine for baseballs. If you drop a baseball in a vaccuum so that it falls some distance H, it will arrive with a speed of roughly \sqrt{2 g H} in near-Earth gravity g. If you want to throw it so that it rises to a maximum height H, you have to throw it up with speed \sqrt{2 g H}. This is simple algebra:

E_tot = U = mgH = 1/2 m v^2 = K

Solve for v. The solution doesn't care if v is directed up or down -- both are consistent with it having EITHER started at H and fallen to 0 (v negative or down) or started at 0 and risen to H (v positive or up). Or you can do the simple solution to Newton's second law and get there a bit harder from:

Falling: y(t) = H - 1/2 g t^2 and v(t) = - g t
vs
Rising: y(t) = v_0 t - 1/2 g t^2 and v(t) = v_0 - gt

If you solve the first for v when it hits the ground, you'll get \sqrt{2 g H}. If you use v_0 = \sqrt{2 g H} in the second one, it will rise precisely to height H and stop.

But seriously, all of this is in any introductory physics textbook, including mine. Look, here's a nice little lecture on this. Note especially slide 6. Yes, escape speed is also drop from infinity from rest speed when considering two bodies, and at the intro level that's all one teaches. But the energy concepts work just fine for whole solar systems, even when solving the dynamics problems involved becomes nearly impossible for long times:

http://www.phys.hawaii.edu/~mo...

Otherwise, find a physics textbook. Mine is online and free, and if you google up answers you are as likely as not to get directed to it just because there aren't many free competitors, but I promise, it is accurate enough and fairly complete (except where there are, no doubt, little errors or missing stuff -- an online textbook is never quite finished, sigh:-). But if you prefer Tipler and Mosca, or Halliday, Resnick and Walker or Serway and Jewett or Young and Freedman (old Sears and Zemansky) or Giancoli or Knight (I'm just reading off the authors of the stacks of the damn things in my office) IT DOESN'T MATTER. Look, I'm an expert on this. No kidding. Not expert at the level of a cosmologist maybe, but at the intro level it just isn't that difficult, and on a good day I can actually solve Newton's Law of Gravitation in Newton's Second Law and show that planets really DO move in elliptical orbits, which is a notch or two past intro. So just as a very elastic ball, dropped from a height, will bounce back up to almost the same height (difference lost to heat and sound during the bounce), so a comet that comes into the sun and passes some distance away from the sun at some speed will have the SAME speed as it departs from the sun at that distance on the far side.

## Comment Re:That's nothing... (Score 1)105

So, you didn't bother to read any of the other two or three posts where I worked out the algebra (face-palm) before spouting crap. No, asteroids cannot hit "at any speed imaginable". They can hit at any speed that is GREATER THAN OR EQUAL TO Earth's escape speed, as I actually discussed and derived. Also, escape speed FROM EARTH is relative TO EARTH. So yes, I absolutely neglected solar potential energy because it just doesn't vary that much across the range where most of the actual acceleration of an object falling to Earth occurs -- inside lunar orbit. I'm not a "self-proclaimed" physics teacher, by the way. I just finished teaching university level calculus based introductory E&M to physics majors this morning, and will be teaching intro level mechanics to engineering students this afternoon.

You might also look at the post that I actually replied to, which suggested that they could land at 250 or 2500 kilometers PER HOUR. No, they can't. Yet your "knowledgeable" post implies that they can, to quote: "An asteroid can hit earth with any imaginable speed." Any imaginable speed faster than Earth's escape speed, 11.2 km/second, precisely as I replied. You can see the capitalized AT LEAST in the reply without even bothering to read the whole thing or read the wikipedia article on escape velocity:

https://en.wikipedia.org/wiki/...

where they do EXACTLY the same general algebra I do in my replies above, leading to the same general conclusion, before sure, going off to discuss escaping from the sun or wherever. "Escape energy" is zero total energy for forces that drop off like 1/r^2 (or technically, faster than 1/r), a definition that holds for Coulomb's Law and electrostatics as well. Orbits are categorized as elliptical (bound, E_tot less than 0), parabolic (E_tot = 0) or hyperbolic (E_tot great than 0) in all physics or astronomy textbooks, and yes, these are all defined in this way with respect to the specific two-body interaction involved in introductory treatments simply to avoid many body difficulties, just as they are almost invariably discussed in the limit where one body is much more massive than the other to avoid reduced mass coordinates and other difficulties.

As for adding relative velocities as you seem to have attempted to do -- it doesn't actually work that way, because the expressions that occur in the energy conservation equation are non-linear. Otherwise you would be right, one could somehow "drop" an asteroid in some way that lands at zero speed. What you mean to do is to compute the initial total mechanical energy of the dropped mass at any point in its free or bound trajectory, and compute its final mechanical energy as it is moving the the same velocity as the target object e.g. the Earth (or even pickier, the same velocity as the part of the Earth's surface it inelastically collides with, although this speed of roughly 1000 mph or less is pretty negligible relative to Earth escape speed). The difference has turned into "heat" during the collision. But since kinetic energy scales like velocity squared, and potential energy scales like 1/r (from each center being considered, most likely the Earth and the Sun if you want to talk about solar orbits and are willing to neglect other objects) it is absolutely not as simple as just adding relative velocities and is complicated further still if the object falling to Earth starts in a solar bound orbit. There is a nice equation for this in the Wikipedia article you are refusing to read although the discussion of the point is a bit abbreviated and isn't quite correct either, more of an approximation (note its "under simplified assumptions").

Anyway, if you want to (how was it you put it?:-) "make a fool of yourself" by looking a few things up and spouting nonsense, hey, bring it. Seriously, dude -- actual physics Ph.D. and everything, teaching intro physics since 1977, wrote my own textbooks, don't even bother with lecture notes because I just plain know this stuff and can lecture on any topic at the intro level at least cold. So bring it.

## Comment Re:That's nothing... (Score 1)105

You are mistaken. Escape velocity has nothing to do with launching something into orbit. Well, yes it does. One has to add half of escape energy to an object as kinetic energy to establish it in a low, circular orbit, but that is more or less an interesting algebraic coincidence (related to the virial theorem). Furthermore, as I work out algebraically above, escape speed IS EXACTLY the speed of an object with escape energy, and is in turn BY DEFINITION the speed of an object dropped from infinitely far away, initially at rest. You can learn all of this from literally any decent introductory physics textbook, from any teacher of physics (including me:-), and probably from wikipedia. I already cited the intro physics textbook I wrote above, so you can learn it there, but since you are arguing with me you might understandably refuse to accept that is is authoritative -- I might be a nut instead of somebody who has been teaching intro physics for just about 40 years. So go find one of your own, or google "escape velocity" or "escape speed".

## Comment Re:That's nothing... (Score 1)105

You are (I think) confused and have this backwards. We consider how much energy/speed we have to give something to throw it up to arrive, at rest, at a maximum height of e.g. 25,000 miles (which is the energy/speed it will have if it lands when dropped from there, at rest. To throw it up HIGHER you have to throw it FASTER with MORE energy. Gravitational POTENTIAL ENERGY is actually LESS in proximity -- greater in magnitude but (by convention) MORE NEGATIVE.

Specifically, if we drop one kilogram from rest 25,000 miles away -- say 6 Earth radii (R_e \approx 4000 miles) then its initial total energy is E_i = U(R_e)/6 or

E_i = U(R_e)/6 \approx -10 MJ = K_f + U(R)

When it lands, energy is conserved, so:

E_f = E_i = K_f + U(R_e) = - 10 MJ

K_f = E_i - U(R_e)

Or it hits with 54 MJ instead of 64 MJ

4.4 million miles is so many that E_i = U(R_e)/1100 \approx - 64 KILOjoules per kilogram. Then:

K_f = E_i - U(R_e) \approx 64 MJ, the initial total energy is so small it doesn't change either of these digits or (for that matter) the next two. 4.4 million miles is "infinity" as far as this estimation is concerned.

## Comment Re:That's nothing... (Score 1)105

So here's a serious answer. Gravitational potential energy has the form U = -GMm/r where r is the distance from the center of the earth. Practically speaking, this means that a kilogram of mass sitting on the surface of the Earth has a gravitational potential energy of -GMm/R where R is the radius of the earth and m = 1. If you work out the arithmetic, this is NEGATIVE 64 MJ give or take a hair (GM/R = gR = 6.4x10^7 J).

Total energy is potential energy plus kinetic energy: E = K + U with K = 1/2 mv^2. If you are "infinitely" far from Earth and at rest relative to the Earth, the kilogram of mass has a total energy of zero. Energy is conserved, so as it falls towards Earth (gravity doing work on it to speed it up) its potential energy decreases (because more negative) and its kinetic energy, which is strictly non-negative, increases in order that the total energy REMAINS zero. When it hits, therefore:

K = -U = 64x10^7 J = 64 MJ

"Infinity" here is just any distance that is very large relative to the radius of the Earth so that U is "small" relative to this collision energy and hence an unimportant correction.

Note well that nothing stops our kilogram of mass from being THROWN in from infinity with MORE than zero initial kinetic energy. Indeed, we expect falling asteroids to nearly always start with some speed relative to the Earth and a total energy relative to the Earth GREATER than zero, as they are "unbound" by Earth gravity and in what is called a hyperbolic trajectory when they hit. This means that if they miss, they keep on going and don't eventually come back or end up trapped in orbit around the Earth. It also means that they can hit with a kinetic energy strictly greater than 64 MJ or (solving for the speed of the collision) a speed strictly greater than 11.2 km/sec.

If you really want to understand this further, here is a physics book where it is explained, between chapters 3, 4 and 12:

http://www.phy.duke.edu/~rgb/C...

rgb

## Comment Re:That's nothing... (Score 4, Informative)105

Asteroids will hit the Earth (if at all) at LEAST at 11.2 km/sec, as they have greater than escape energy relative to the Earth's gravitational field. That's 11.2 kilometers per SECOND, or a bit over 40,000 kilometers per HOUR. The energy released is greater than 64 million joules per kilogram of rock (escape energy). So if you take a (say) 2.5 km ball of rock (5 km in diameter), roughly estimate its mass as 4 times r^3 you get 4 e+18 joules. Convert this to tons of TNT and you get roughly a teraton. The total explosive energy of the entire nuclear arsenal of the Earth is less than 7 gigatons (including reserve weapons -- only around 1 GT is on delivery vehicles almost all of this belonging to the US and Russia). The biggest explosion in recorded history was the explosion of Tambora in 1815, estimated at 33 GT. This is then equivalent in crude terms to over 100 times the entire global arsenal nuclear and conventional, or over 30 times the explosive power of the largest explosion in recorded history, one that altered global climate for close to a decade. Or GREATER.

I'm not sure "hit by a bus" is an apropos metaphor.

## Comment Re:Be careful of that calculation (Score 4, Insightful)601

Even worse, pretty much every science fair project has to have a conclusion to get anywhere. Teachers don't let kids run an experiment where the conclusion is that the test didn't have any findings that support accepting or rejecting the hypothesis. That is not only a perfectly acceptable result in science, but a very good one to find.

Hear hear! I'm giving up a chance to mod you up because that isn't sufficient. This is all by itself one thing that is wrong with STEM training from the beginning. One cannot just build a telescope or Tesla coil -- both pretty ambitious, amazing projects for any science fair -- you have to have a HYPOTHESIS and you have to PROVE IT because, I dunno, null results are so boring and indistinguished that they will never win. Kids learn at Science Fairs that if they don't prove their hypothesis no one will look twice at their work no matter how nifty and then we wonder why twenty years later they are falsifying data or engaging in data dredging or cherrypicking to get publications to get tenure or keep a grant. We also wonder why we get a steady string of crappy papers on things nobody really cares about -- but which have clear targets likely of success -- instead of a few bold papers where the researchers took risks at finding nothing equal or greater to the chance of finding something. Those big, risky topics are career killers unless you are fortunate enough to have nearly independent "means" as research support.

Don't get me wrong -- evidence is key to directed Bayesian beliefs, and science should teach the importance of evidence. But the entire Enlightenment wasn't driven by hypotheses eventually supported by evidence. It was driven by bold, amazing new instrumentation -- for example, microscopes and telescopes -- that opened up a Universe of new data at the macrocosmic and microcosmic levels Pure observation based on these new instruments eventually LED to hypotheses, and as time passed the successful hypotheses were woven into an ever tighter tapestry of evidence supported beliefs connected to other evidence supported beliefs and the scientific worldview. This was equally so for most of the initial work done with electricity and magnetism -- people built nifty generators and studied the effects of electrical currents and then, eventually, built a mathematically rich explanation of the collective set of observations.

Can you imagine having to formulate Maxwell's Equations as a hypothesis ALL AT ONCE and then going into a laboratory to try to verify them? Or even something simpler, like Coulomb's Law? Hell no! Coulomb may or may not have suspected that electrostatics were going to be "like" gravitation (although Newton had no compelling reason to choose 1/r^2 for gravitation in the first place, lacking Gauss's Law or any equivalent thereof) but the evidence in favor of it was compelling and immediate.

Cutting edge real science has observations leading hypotheses -- as, if you think about it, it usually should -- more often than not. But high school science teachers and the founders of the whole idea of "science fairs" have completely lost track of this in their eagerness to teach The Scientific Method as religion instead of a practical methodology that -- eventually -- needs to be satisfied.

## Comment Re: Random Number (Score 1)144

Well, not "get fucked", surely...

Ultimately it is an empirical question but it is an unusual one. The problem with looking only at locality in a single direction of time flow is that the underlying microdynamic propagators are (without exception as far as I know) reversible in time. My favorite example of this is in classical electrodynamics, where we CHOOSE to use retarded propagators, but where one can equally well formulate things in terms of advanced propagators and where Dirac did an amazing job of deriving radiation reaction theory using a mixture of advanced and retarded propagators (further supported by Wheeler and Feynman and the perfect absorber derivation which in turn is connected to Lindblad and master equation formulations of quantum theory).

This is where IMO it is very difficult to understand Bell's theorem. It seems to require forward (retarded) time only, but if one allows for advanced time as well as retarded time both operating simultaneously, the paradoxes disappear. It becomes literally impossible to hide the future state of the ultimate absorbers of any e.g. photons emitted from a quantum entangled system from the emitting system -- the entire path through all intermediate filters is NOT information that is unavailable to the emitting system. The real problem is that that the time evolution of a closed quantum system begun in a stationary state is stationary, period, from a very fundamental theoretical level. The "paradoxes" seem to arise when we try to create "observers" that are one part of the total system, "systems" that are another part of the total system, and a "bath" made up of everything else that is in an almost completely unknown state. EVERYTHING is fully quantum entangled, ALWAYS. But when you split things up, pseudoentropy appears as one is forced due to ignorance of boundary conditions and intermediate time evolution of the whole to use a statistical (and hence classical or at worst semiclassical) description of both bath and observer.

It's pretty easy for me to believe that the effective pseudoentropy of Universe-(sub)system is so absolutely enormous that the quantum description of any subsystem (averaged) is going to look "random" in accordance with Bell's inequality but not, in fact, be random. It isn't a matter of local hidden variables, it is a matter of unknown state variables in everything else coupled to the system by ordinary interactions.

## Comment Re:The future (Score 1)97

My journey has been longer, padawan. But you are mistaken: we do have both hover cars and hover boards. They are just expensive and dangerous. What did you expect? Antigravity? Suspension of the laws of physics? Personally I was hoping for antigravity capable of floating a car-sized mass with a tiny trickle of current, reorientable as a gravity-based drive. But somewhere back in the 70's and early 80's I finished my physics degrees and alas, there was no plausible antigravity anywhere to be found. Still isn't. Especially one that would work on a first-law-violating trickle of current.

Sigh.

## Comment Re:The future (Score 2)97

And peel back the paper to expose the powder and use a nail to pop it directly. And string them together to make a fuse. And... yeah. Good times.

I too, can't understand why anybody would ever get a spinner. At first I thought they were a version of gyroscopic wrist trainers:

https://www.amazon.com/dp/B01F...

that required a "trick" to keep moving, but ten seconds of examination and experimentation revealed that they are not. And gyroscopic wrist trainers are already pretty boring, but at least there you have to "do" something and you can fix them up with pretty lights and so on too. Spinners aren't even a good meditation aid -- they demand exactly the wrong kind of attention to keep going and they are not a useful focus.

## Comment Re:Random Number (Score 1)144

If something has a cause, then it can be predicted and patterns can be identified. It is not random.

Except that there are phenomena that cannot be predicted. Even ones we know are not really random. Then there are quantum phenomena that MAY be really random. You are making a religious statement when you assert Universal causality as a definite truth instead of a conditional probability. And lack of evidence is not evidence of lack -- the best you can say is that it might make something less probable within certain bounds.

I agree that the Universe PROBABLY is causal and in a zero entropy state, because we have little definite evidence otherwise (time-irreversibility of things like Kaon and B decay aside, a few experiments that claim to demonstrate "true" quantum randomness aside). But according to science this is an empirical question, not a religious one. You might as well assert that as far as we know, it IS possible for true randomness to exist.

On the empirical note, if you are presented with a string of data, perform any and all tests on it that you like, and cannot prove that it is NOT random, what exactly is that evidence of? Please do not invoke religion in your answer such as a belief in causality, as that just begs the question. That's precisely what you are doing if you assert that quantum phenomena at a certain scale are not random. Maybe not, but we have no model that predicts them, we have theories that suggest that no model CAN predict them, when we examine them for randomness they appear random. The arguments (such as the arguments that lead to the Master Equation description of quantum phenomena) that allow for it to be otherwise are difficult and while they may be correct, it is far from certain (empirically) that they are.

## Comment Re: "True"? Not possible (Score 1)144

As I posted above, we do not know this. IF you accept e.g. the holographic MODEL of string theory, then there is no entropy even at the quantum level. On the other hand there are plenty of articles in QFT that discuss the possibility that QFT is truly irreversible at some level so the direction of time is not just a consequence of entropy.

It is perfectly fine to think that one or the other of these is "more likely" to be true on the basis of what one knows or guesses, but because physics is not religion it is not appropriate to state that there is not random as a proven fact, that the entropy of the Universe is zero and there are no true entropy sources. Ultimately this, like everything else, is an empirical question.

Personally I agree with you and think that whether or not the holographic model per se is correct, QFT is probably reversible and that the Universe is in a zero entropy (definite) state with no "outside" source of entropy to make it non-deterministic on the basis of internal dynamics alone. But in the end, experiments talk, bullshit walks and even the sexiest theoretical model is bullshit until it is confirmed by experiment.

## Comment Re:Random Number (Score 4, Interesting)144

There are three meanings of the word "random" referring to a generator in this context:

a) Unpredictable.
b) Empirically satisfying all of the decorrelation properties of a random number sequence -- on average uniform in all bit patterns, on average lacking correlations at all lags (and hence non-periodic) and on all N-dimensional hyperplanes for all N, etc.
c) Both.

All that is asserted here is that they have a thermal noise generator that satisfies a). Big whoop -- thermal noise generators (and hardware generators in general) are commonplace: https://en.wikipedia.org/wiki/.... However, thermal noise and so on are often "colored" or "biased" -- they produce fluctuations that are unpredictable but it is almost impossible to get the noise to produce a string of e.g. 0's and 1's that satisfy b). One then is stuck using the unpredictable noise to randomize a pseudorandom number generator (for example, by xor'ing the two together) that produces a bit string that has the right uniformity and decorrelation properties but does so from an internal state that, if known, makes the string produced predictable.

AGAIN this sort of thing is pretty commonplace. Sources of "entropy" as in unpredictable activity are common enough and so are high quality pseudorandom number generators. The major problem then is rate. Few of the hardware generators can produce entropy FAST ENOUGH to keep up with a PRNG, so getting a source of "true random numbers" that is fast enough to use in e.g. Monte Carlo is not easy, and most people don't bother to try. Having a handful of unpredictable numbers suffices for e.g. encryption and that's really where this is headed.

I would wax poetic on the fact that EVEN thermal noise is probably not truly random; it is random the way a coin flip is random or, for that matter, the way a PRNG is random. The outcome of a coin flip is unpredictable only because we don't flip the coin with a precise knowledge of its state and the state of the flip environment and because we perhaps cannot integrate its equations of motion precisely enough from what knowledge we do have, but it is deterministic, hence not really unpredictable. Classical thermal noise is no different than a bunch of flipping coins bouncing around -- again deterministic but with lots of unknown state information. "True" random is a term that should probably be provisionally reserved to AT BEST quantum "coin flips", although in the master equation approach to resolving the state of a quantum "coin", the true origin of randomness is seen STILL to be the process of taking the trace of the surrounding environment, which is if you like the filter resolving the flip. That trace introduces "entropy" in the form of lost phase information and averaging over energy distributions that appears as unpredictability in the outcome, but if one views the "coin" AND the surroundings as a single quantum system its quantum trajectory is again deterministic. Randomness in quantum filtering experiments comes from the fact that the measuring apparatus that does the filtering must resolve it in a classical was with its quantum entangling and phases in general unknown and averaged over.

If one buys the holographic model in string theory (or plain old quantum theory as it is currently structured) the Universe is in a zero entropy state and there are no sources of "real" entropy. In this case there can BE no "true" random number generators. Whether or not nature is capable of generating true random numbers from some source other than our ignorance of state is an open empirical question.

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