- I'm sorry. I'll fix it.--KSorenson 22:43, 11 November 2009 (EST)
- Okay, I resubmitted my changes with a more descriptive edit summary. Thank you very much for calling my attention to it.--KSorenson 22:47, 11 November 2009 (EST)
You didn't insert a "clarification" of the falsifiability defect in the theory of black holes, you deleted it. So again I found your edit summary to be misleading.
- I beg your pardon, sir? I most certainly did not delete it. Perhaps you overlooked it because I moved it to the bottom of the article? Or perhaps it's because I omitted rewrote it without the word "falsifiability," which … well, to put it bluntly was misleading. The Schwarzchild and Kerr metrics are certainly falsifiable.
- In either case, I will happily restore that sentence (or sentences; I'm not looking at the draft right now) and re-submit. If you still think the existing article is the better choice, then please (obviously) feel free to revert a third time, and I will leave it at that.
- Though I would very much like to work with you to come up with a draft of the article that you'll accept. The Schwarzchild and Kerr metrics are fascinating, and I'm afraid I have to say that the existing article on black holes is not as good as it could be.
- Thank you again for your feedback.--KSorenson 23:16, 11 November 2009 (EST)
K, you're fighting a losing battle here and will probably get banned for your troubles. Mr. Schlafly is an expert on black holes, and unless there is something you can add to the article that fits with a proper conservative view of the topic, you're best off to leave it alone. MichaelHWC 23:26, 11 November 2009 (EST)
- I wasn't trying to fight any battles at all. I was just trying to contribute. Maybe you're right, though. Since I honestly don't know what a "proper conservative view" of the Schwarzchild solution would be, maybe I should bow out. Thanks for taking the time to offer your advice; I appreciate it very much.--KSorenson 23:39, 11 November 2009 (EST)
- Please stick around! You seem willing to work with the admins on this so I don't think there will be any problems. Your changes are welcome. We need more competent math and science editors! --MarkGall 08:54, 12 November 2009 (EST)
- I don't know about needing better editors, but this site certainly needs some better articles. I was trying to help with that, but Aschlafly's condescension and confrontational attitude really soured my taste for it. Some additional reading I did last night to try to better understand his point of view put me off even further. I'm unsure how to work with someone who writes these things then tries to start an argument over "falsifiability" in advanced theoretical physics.--KSorenson 12:57, 12 November 2009 (EST)
- I won't deny that I've had my share of arguments with Mr. Schlafly about math and science articles. That doesn't mean that it's impossible to continue to edit here, or that the edits can't be useful to their many readers. I have successfully worked together with him on several other articles. I encourage you to do the same. --MarkGall 14:14, 12 November 2009 (EST)
- If Aschlafly wants the students who read this site to be told that black hole theory is not universally agreed upon, that's fine with me. If he wants them to be told that some people doubt whether black holes can exist in nature, that's okay with me too, because it's true. But he should be able to tell students those things without lying to them.
- The black-hole solutions to the Einstein field equations make clear predictions about the characteristics of such a region of spacetime, and thus are entirely falsifiable. In fact, much work has been done by astronomers and theoreticians alike to find any evidence, observational or mathematical, that casts doubt on those predictions. So far, all the math and all the observations are consistent with the predictions of the four known point-mass solutions. The fact that a set of predictions is thus far not falsified is not the same as saying that those predictions are unfalsifiable. I just don't see the point in lying about that.--KSorenson 15:13, 12 November 2009 (EST)
- KSorenson, logic does not require so much verbosity. If you have an experiment that would falsify the claim that black holes exist, let's hear it. If not, then concede the obvious: black holes are not falsifiable.--Andy Schlafly 18:10, 12 November 2009 (EST)
- Seriously? Have you really never heard of Gravity Probe B? The sole purpose of that experiment was to measure the geometry of space around the Earth, which is a direct test of both the Schwarzchild and Kerr solutions, which are the theoretical models that predict black holes. The data is still being analyzed, but the results so far indicate a very good correlation to predictions of the Schwarzchild solution, and error bars of about 15% for the much-more-difficult-to-measure frame dragging effect predicted by the Kerr solution. I wish we could have gotten more precise results from the frame-dragging data, but it was a first test after all.
- I'm sorry my reply was so "verbose," Aschlafly, but you make it so difficult to be succinct when there's so much you don't know.
- (Full disclosure: I contributed to that experiment when I was at Stanford, so I am not unbiased about being pleased it went so well.)--KSorenson 18:26, 12 November 2009 (EST)
- KSorenson, "connect the dots" is a good childhood game but it does not amount to falsifiability.--Andy Schlafly 18:48, 12 November 2009 (EST)
- While I haven't studied Popper since I was a wee undergrad, as I recall, that's precisely what "falsifiable" means, sir. If your theory makes a prediction that can be either confirmed or contradicted by observation, then your theory is falsifiable. In our case we couldn't just look up in the sky and see the geometry of space around the Earth, so we had to build an instrument to measure it, but that counts too, right? Maybe we're just coming at it from different understandings of the term? Could you please define for me what you mean by "falsifiability?" Because as long as I'm not on the same page with you about that, my continuing to contribute to this site would be a pointless waste of time.--KSorenson 19:00, 12 November 2009 (EST)
KSorenson, again, you don't need all those words. The claim that there is a black hole in the universe somewhere is like claiming ET life exists. The claim cannot be falsified. People can keep claiming something is true, when in fact it is false but there is no way to show it is false.
- Hang on a second. "In fact it is false but there is no way to show it is false?" Was that a typo? Because otherwise it sounds like you're saying you have some special knowledge. Are you saying that black holes can't be proved not to exist … but that you somehow know they don't anyway? That's obviously nonsense, so I'll just assume it was a typo.
- In any case, this is all tangential to the point. Your gripe is with "the claim that there is a black hole in the universe somewhere," which is not a claim made by any black hole theory. Rather, the existing theories say that black holes may exist — that is, there's no reason to believe they're impossible — and that if they exist, they have such-and-such properties. We have observed objects in the sky that have the predicted properties. They both look and quack like ducks, so rather than saying "it is consistent with existing theories to conclude that this object appears to be duck-like," we sometimes save some of those precious words you're so jealous of and say "hey look, a duck." You are entirely justified, if mind-bogglingly petty, to criticize others for jumping to conclusions that way.
- Clearly the right course of action is for someone to revise the black hole article and rewrite your odious "falsifiability" lie into something that makes the point you want made in a way that's both clear and honest, since right now that part of the article is neither. Unfortunately I'm not the girl to make that revision, as your stubbornness, your bad attitude and your snide and condescending remarks have put me in a very foul mood.--KSorenson 20:09, 12 November 2009 (EST)
- KSorenson, I don't think you understand the concept of falsifiability. That wouldn't be surprising, because it is not part of the physics curriculum, and most physics majors and grad students are clueless about it. No big deal ... if you're willing to learn it with an open mind now. If not, then you're wasting our time.--Andy Schlafly 21:10, 12 November 2009 (EST)
- Okay, this has to stop now. You're just making things up. "It's not part of the physics curriculum?" When I was an undergraduate, two semesters of in-depth HPST — that's History and Philosophy of Science and Technology — were a requirement for all students majoring in any of the sciences or engineering disciplines. Where I teach now, we require three, including a DIS — that's Directed Independent Study — with a thesis requirement. And that's just for the undergrads; you don't want to hear about how many seminars and lectures on philosophy and ethics physics graduate students have to attend. Students graduating with degrees in the sciences or in engineering most certainly know about Duhem and Quine, Hempel and Oppenheim, Kuhn and yes, your precious Popper, who did not say what you seem to think he said.
- I simply don't know what to say to you any more, Aschlafly. To borrow a particularly on-the-nose expression I heard from one of my professors years ago, not only are you not right, you're not even wrong.
- I see that someone else has already submitted a revision to the black hole article. It's an excellent change, both clear and accurate. Once the utterly false sentence "As with the related theoretical concept of a 'wormhole', it is impossible to prove that a black hole does not exist, and thus it fails the falsifiability requirement of science" is removed, that article will be in good shape. Assuming you're honest enough to let it stand, that is.--KSorenson 21:43, 12 November 2009 (EST)
- KSorenson, you haven't opened your mind and thought for yourself. I urge you to do so, for your sake. Did any of your professors ever suggest that? It doesn't take hundreds of words to explain. Once you open your mind, your only regret will be that you didn't do it sooner.--Andy Schlafly 21:56, 12 November 2009 (EST)
- What's the old saying? Keep an open mind, but not so open that any old piece of garbage can fall into it.
- KSorenson, you didn't answer my question, so I'll answer it: almost no professors, an overwhelmingly liberal and close-minded group, advise students to open their minds and think for themselves. Students have to figure that out on their own. Some eventually do, and I hope you're one of them.--Andy Schlafly 22:26, 12 November 2009 (EST)
I support what you're doing KSorenson. I like having someone with real expertise on math and physics editing the relevant articles. It helps this website's credibility.HarryG 22:02, 12 November 2009 (EST)
- Plus you are, in my opinion, a very good writer. ChrisFV 11:04, 13 November 2009 (EST)
Action at a distance (let's take a break from the black hole stuff)
SaraT and KSorenson (this is being sent to both):
I'm interested in working on the article about action at a distance. (Actually I'm busy working on many things about science and math, as a look at my contributions will show, but this particular issue has bubbled to the top of my agenda.) I'm confused about the ways this term is used. Since you both seem to be interested in the history of science, you might be able to shed some light on it.
The suggested meanings I have come across are:
- Exertion of force on an object that isn't in direct contact. This must be what it means in Newtonian gravity, right?
- Transmission of a force instantaneously, or, in any case, supraluminally. This doesn't seem to have been an issue with Newton, because the finite speed of light, and the causality consequences of that, weren't known at the time. Right?
- Consequences of "Quantum Entanglement". This seems to relate to supraluminal transmission of information, and is therefore related to #2. Right?
So which is it? Can either of you enlighten me? Or fix the article? (By the way, you both write very well.) PatrickD 22:30, 12 November 2009 (EST)
"Action at a distance" is a great topic, because it gets to the heart of some of the central concepts of modern physics.
It's important to note that "action at a distance" isn't a technical term in physics; it's a qualitative term. So defining it in a way that's both clear to non-physicists and rigorously accurate might be tricky. The best definition I can come up with right now is, "Interaction between separated bodies with no evident mediator." That's probably too jargony, because both "interaction" and "mediator" are technical terms in physics, but that's a start.
Let's do a thought experiment. Imagine a totally empty universe, with no matter or energy in it at all. (Let's pretend there's no such thing as vacuum energy.) Furthermore, imagine that we're somehow in this universe, but in such a way that we don't interact gravitationally. How? I don't know how, it's just a thought experiment! Point is, we're there, we can observe things, but we don't interact gravitationally at all.
Now imagine that a particle appears, poof, right in the middle, stationary relative to us. This could never happen, obviously, but we're just imagining.
Now imagine that after some significant amount of time, another particle appears at a modest distance from the first particle. For purposes of imagination, let's say these particles or bowling balls or something. They could be stars or even galaxies, but the point is that they're large enough that quantum effects are negligible. Also, let's assume they're uncharged, and finally that when the second one magically appears, it's at a reasonable distance from the first one. Call it a hundred times the diameter.
Now, gravity exists in this imaginary universe we've constructed. So obviously these two bodies will be accelerated toward each other. But the question is … when? If we plop our second particle in at some time , will they begin accelerating toward each other at that exact same instant? Or will it take some time for the first particle to "become aware," as it were, that there's now a second particle there?
The answer is more interesting than you might guess, if you're not a physicist. The answer is that particle two will start accelerating instantly, but particle one won't. Particle one will start accelerating toward particle two at some time , where the time interval is equal to the distance between the centers of mass of the two particles divided by the speed of light in a vacuum.
To figure out why, start by remembering that particle one already existed in the universe when particle two appeared. Remember how we said that "some significant amount of time" would pass before particle two showed up? During that time, the geometry of our imaginary universe distorted in to a non-Minkowski metric. (Minkowski spacetime is to the universe as the Euclidean plane is to the surface of the Earth: an idealized, non-curved approximation. If you want to get technical, the spacetime around particle one would settle into a configuration described by the Schwarzchild metric.) When we wished particle two into existence, it appeared in a spacetime that was already curved. As a result, particle two's inertial path through spacetime was tilted in the direction of particle one from the very first instant, so it began accelerating (as observed from a non-accelerating reference frame).
But the geometry of spacetime does not react instantaneously. The curvature caused by particle two radiated outward from the point where particle two appeared at the speed of light. Until that curvature reached particle one, the geometry in the immediate vicinity of particle one would still be described by the Schwarzchild metric, so it wouldn't accelerate relative to our imaginary frame of reference.
When our (stationary) clock reaches time , particle one begins accelerating toward particle two. Now everything looks like ordinary, Newtonian gravity. As long as our particles aren't too dense, of course. After some amount of time where particles one and two are accelerating toward each other relative to our reference frame … clack. The bowling balls come into contact with each other.
That's how action at a distance doesn't happen in real life. The two particles are interacting gravitationally, but there's a mediator of that interaction: spacetime itself. Particle two interacts with spacetime via the gravitational interaction, then spacetime interacts with particle one. There's a middleman, if you like.
Let's do another quick thought experiment. Say instead of two bowling balls, we have two electrons. In this experiment, we're going to pretend that gravity does not exist at all (which is not a bad approximation, since electrons have such minute energies). These electrons will accelerate away from each other because they're both negatively charged. Three hundred years ago, we said this acceleration was the result of the Coulomb force, an action-at-a-distance principle. A hundred years ago, we postulated that there was some intangible field surrounding all charged bodies, a field we couldn't directly observe. Pure action-at-a-distance gave way to a vector field theory of electromagnetism.
Today we think there is no electromagnetic field at all, that it was just a mathematical approximation of what's really going on, which is that charged particles interact through an exchange of photons. The vector field theory gave way to a quantum field theory.
It's important to note that both quantum field theories and metric field theories are local. What that means is that under either type of theory, objects interact only with what's directly adjacent to them. They don't "reach out" through space (or spacetime) to interact with distant things. Massive particles interact with spacetime where they are, then spacetime interacts with other massive particles. Charged particles interact with the quantized electromagnetic field where they are, and the field interacts with other charged particles.
And that's pretty much where physics stands today. All fundamental interactions are described by either a metric field theory or a quantum field theory. Action at a distance is, at least for the moment, nowhere to be found in theoretical physics.
Does that mean there's no such thing as action at a distance? Not necessarily. It just means that we haven't made any observations that can't be explained by either a quantum field theory or a metric field theory.
Now, to the second part: "action at a distance," if it exists, does not necessarily occur instantaneously. In fact, it was understood that changes in the electromagnetic field propagate at the speed of light long before the field was quantized and quantum electrodynamics emerged. So the questions of action-at-a-distance and "instantaneousity" (I'm so sorry) are really two separate questions.
Finally, quantum entanglement. Now, I am not a quantum physicist. My area of focus lies elsewhere. So I can't speak in as much depth about this as I can about gravitation. But I can say that it seems quantum entanglement is one of the most misunderstood aspects of physics.
It all has to do with spin conservation. If a neutral pion decays into an electron and a positron, then the two resulting particles will have opposite spin. The spins have to cancel out, you see, otherwise the universe will suddenly have slightly more up spin than down spin, and that's prohibited under spin conservation. Such a pair of particles is known as a singlet.
But nothing is quite so simple in quantum mechanics. You see, in quantum mechanics it's not quite true to say that the electron has up spin and the positron has down spin, or vice versa. Rather, both the positron and the electron are in a state of spin superposition, until you measure one of them. Once you measure the spin of one particle, you know exactly what the spin of the other particle is without having to measure it.
One interpretation of quantum mechanics — called the Copenhagen interpretation — says that when a quantum system is measured, its wave function collapses into a measurable value. Before it was measured, the system was in a superposition of states, and the outcome of the measurement could only be predicted statistically, not deterministically. Under the Copenhagen interpretation, something physical happens when a quantum system is measured. An actual change in the system occurs. It's no longer in superposition; it's collapsed.
So imagine letting a neutral pion decay into a positron and an electron in a spin singlet. You capture both particles, and move them faaaaaar away from each other; say a light-year apart. Then you measure the spin of the electron. The quantum superposition of the electron collapses, and simultaneously, across the vastness of space, the quantum superposition of the positron also collapses without anything directly interacting with it.
Einstein disliked this possibility, disparagingly calling it "spooky action at a distance" and opining that quantum mechanics wasn't yet a complete theory. It's not hard to see why; singlets are weird.
Part of the theoretical problem is that the Copenhagen interpretation doesn't precisely define just what "wave function collapse" means. It's all rather fuzzy, at least to me, but like I said, that's not my area of focus.
Right now, the question of whether the "spooky action at a distance" is instantaneous, or whether it propagates at some fantastic multiple of the speed of light. My guess? It's instantaneous, and just like the event horizon in the original Schwarzchild solution, it's just a coordinate singularity. But that's just a guess; I'm not an expert.
There's a legitimate question to be asked whether the phenomenon of quantum entanglement, as observed, constitutes action at a distance. It's got the "at a distance" part, to be sure, but the "action" part is debatable. That's why it's more common to see the whole issue referred to as "non-locality" instead of "action at a distance." Right now, the consensus is that non-local state superposition can't ever actually affect anything, since quantum systems in superposition can't interact with anything without collapsing. So the collapse of a one part of a non-local superposition system can't actually cause anything to occur where the other part of the system is. So "action without a distance" without the action simply becomes "non-locality."
Anyway, like I said. I'm not an expert in quantum mechanics.
What about the other interactions?
- You, good sir, have just boggled my mind. A question I would like to ask about that thought experiment, though. Would magnetism, the weak force, and the strong force react the same way? RandolfH 08:38, 13 November 2009 (EST)
It's "miss," technically, but my friends call me Kate. And thank you.
Before I try to answer your question, let me emphasize something: I'm not an expert on the Standard Model. I'm not an expert on general relativity either, by any means, but it is my primary field of study. To talk about other branches of theoretical physics, I'm mostly going to have to rely on my memories from grad school. So I apologize if I can't articulate everything perfectly or if I mis-remember some of the finer details.
Let's start with magnetism. Magnetism and the Coulomb force I described above are two sides of the same coin: a current flowing through a conductor creates a magnetic field, and a wire moving through a magnetic field will generate a current. Magnetostatic interactions, like the tendency for a north pole and a south pole to move toward each other, are mediated by photons as described by quantum electrodynamics. (In technical terms, the photon is the vector gauge boson of the electromagnetic interaction. I'ma come back to this terminology shortly.)
The strong interaction is exactly like the electromagnetic interaction, and completely different at the same time. It's alike in that it's also described by a quantum field theory in which the interaction is mediated by vector gauge bosons (told you I'd come back to that jargon), but the characteristics of the theory are different, and particles other than photons are involved. Whereas the theory that describes electromagnetic interactions is called quantum electrodynamics, the theory that describes the strong interaction is called quantum chromodynamics.
I'm not sure how much QCD you want to hear about, so I'll just give you the high points:
Quarks and gluons possess a property called color charge, which is almost entirely unlike both color and charge, but that's what it's called because all the good names were already taken. Electric charge comes in positive and negative varieties, and magnetic "charge" (pardon the expression) comes in north and south varieties, but the color charge comes in six different varieties: red, blue, green, antired, antiblue and antigreen.
If you put a red, green and blue quark together you get a baryon, maybe a proton or a neutron. (There are other kinds of baryons as well, but I'm stuffed if I can remember any of them right now.) If you put a red and an antired quark together, you get a meson.
The vector gauge boson of the strong interaction is called the gluon. (Get it? Glue? Particle physicists are hilarious.) Whereas photons possess neither mass nor charge, gluons are massless but have color charge. This is the most significant difference between the electromagnetic and strong interactions: the gauge bosons of the strong interaction participate in the strong interaction. Photons can only interact with charged particles, but gluons can interact with quarks and with other gluons. Because photons are electrically neutral, the electromagnetic interaction gets weaker as charged particles get farther from each other. But because gluons participating in the strong interaction, the strong interaction actually gets stronger as the distance between quarks increases. At a certain distance, it actually requires less energy to create a new quark-antiquark pair than it does to move the quark farther away. This leads to a phenomenon called quark confinement, which basically says that at normal energy levels (sub-Big Bang-type energy levels) there's no such thing as a free quark; quarks are always confined within baryons or mesons.
So in a sense, yes, the strong interaction works just like the electromagnetic interaction. But in another sense, it's really different.
As for the weak interaction: believe it or not, magnetism and the weak interaction are both aspects of the same scenario I described above. The Standard Model describes both the electromagnetic and the weak interactions as aspects of the same thing, creatively dubbed the electroweak interaction. Glashow and … urg. Two other people whose names I can't remember won the Nobel for it back in the late 70s.
The weak interaction is the least understood of all the fundamental interactions — at least by me! Whereas the electromagnetic and strong interactions can be described as vector interactions — that is, interactions between particles change the particles' momenta — the weak interaction is what governs particle decay. Under the weak interaction, for example, a neutron can spontaneously decay into a proton, an electron and an electron antineutrino. This is what causes radioactivity, but the exact mechanism by which a neutron decays wasn't understood until about thirty years ago.
The weak interaction is also described by a gauge theory, but this time the gauge bosons have mass. The W+ and W- bosons have positive or negative electric charge, respectively, while the Z0 boson is electrically neutral. In the example I gave above, one of the quarks inside the neutron spontaneously emits a W- boson. In the process, that quark changes flavor (an intrinsic property of quarks), and sheds one unit of electric charge, turning the neutron into a proton. The W- boson immediately decays into a highly energetic electron and an electron antineutrino, which skitter off to parts unknown. Because neutrinos are generally very weakly interacting particles — not in the sense of the weak interaction, just in the sense that they don't interact very much with matter — the electron antineutrino emitted during beta decay basically vanishes out into the universe. But the electron interacts via the electromagnetic interaction, which means it usually doesn't get very far (in cosmic terms) before it causes something interesting to happen. As it passes through matter, the electron sheds some of its energy by emitting energic photons — in other words, X-rays. If one of those X-ray-spectrum photons interacts with an atom, it can imbue one of the atom's electrons with enough energy that it's stripped free of the atom altogether, turning the atom into an ion. That's why the radiation from this type of proton decay is called ionizing radiation, and it can be pretty darned unhealthy in significant doses.
So getting back to your question, I guess we could say that no, the weak interaction wouldn't really behave similarly to the electromagnetic interaction between two electrons in a hypothetical empty universe. If you plopped an atom of potassium-40 down all by itself, though, eventually one of the quarks inside one of its protons would emit a W boson, and you'd get the scenario I just described. And if you plopped down three quarks, one each of red, blue and green, they would start furiously exchanging gluons (at the speed of light) and bind together into a baryon of some description. But that thought experiment is even wilder than any of the others I've proposed. To be honest, I'm not even sure it's valid. Free quarks are never found in nature at less-than-hellishly-insane energies, so I'm really not sure what a free quark would do if you willed it into existence in an otherwise empty universe. It might spontaneously decay into some other form of energy by some mechanism nobody's ever observed because the situation's never come up. A particle physicist might understand the Standard Model well enough to make a prediction, or at least a guess, but that's beyond me.
I hoped this helped, at least a little. Like I said, I'm not a particle physicist, unfortunately. Sorry.
I have been reading through this page, and I really enjoyed especially your discussion of quantum entanglement. I have never seen it so well explained before (and I've read a couple of books on quantum mechanics). Thanks so much. PhyllisS 15:02, 29 June 2010 (EDT)