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Thanks for the comments, Sappharad. I suck at setting up builds using IDE's, so I didn't have any idea of what I was doing when I changed those .csproj, if you could make a pull request, I'll sure review it fast.
As for the large commit, I am going to revert. It simply doesn't work. After closing wiindows about ten times it almost always crashes. This is probably because of the garbage collector, it must be accessing the X server when it's finalizing the objects. Mono probably has a way to stop the GC from crashing other stuff when GUI is accessed, but if another thread is also using X, it has no way to know. Since the GC is pretty much unpredictable, I don't think there is a way to circumvent Mono's limitation at all. All X things should be done in a single thread.
About the UI, is there any possibility of using another toolkit, like Gtk#? It doesn't seem to have the same limitations in Mono that WinForms has.
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The tools where the menu entries are not greyed out are launching. TAStudio is unavailable at the moment, I will try to get a core compiled and see if it works.
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Warepire wrote:
Sounds like a design problem in Mono, did you report a bug? As feos said, take it to stack overflow as well.
Well, if you go to their page, they state explicitly that you shouldn't call GUI code in different threads, so they are well aware of it. I think we are at that fine line between what is a bug and a feature :)
Anyway, I just sent a massive commit changing the code. Now it works fine. There are some NullPointerExceptions because of some stuff I didn't compile yet, but most of the front end is working.
What I did essentially was define a lock for everything that needs to access X. Then I told the input polling thread to acquire and release the lock. After that, I modified the custom FileDialog class to also use the lock, created a SafeForm and SafeMessageBox that only show themselves inside the lock and that did it. Now, to add stuff, one needs to extend SafeForm and/or call SafeMessageBox. It doesn't look that bad.
Warepire wrote:
For the README, the repo can't be cloned without git-svn? That's incredibly weird...
That's because you need to create a source file that contains the revision number and gets compiled in the about box. If you don't clone with git svn, the generation of this file will fail, and some DLL's will complain about that number missing.
Warepire wrote:
Also, you may gain from linking to the libraries git repos if you need to build from source. I am pretty used to have to find things but a lot of newer Linux users aren't.
Thanks for the suggestion, I will do that. For now, libgdiplus 5.4 is here.
Compile it with ./autogen.sh && make && sudo make install
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I'll try to do that in the next few days. For now, I am making my patches available on Github. Instructions to build are in the README. Good luck getting the packages, though, it's not trivial, and even fixing them on Gentoo is annoying. Also, I simply disabled input polling altogether to make it stop crashing.
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It is possible, but unfortunately it doesn't solve the problem. One case is the following: a thread is creating a form inside X, gets preempted by the kernel, and another one that polls input starts executing, getting also preempted by the kernel before it can finish cleaning its variables. Then the initial thread gets executed with dirty variables and a race condition still happens.
The quickest way I see to fix this would be to make a lock for everything that accesses X and wrap all form creation and input polling code in a function that acquires the lock, that would serialize the access to X even though the program is multithreaded.
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More good news, the instability was just because I was stupid and did not install OpenAL. After doing that, it's running fine now :)
EDIT: Actually, I spoke too soon. For some reason, it only runs stable when I launch it as root (!), and it gives me a bunch of cryptic symbols when I try to load a GBC ROM. I'm investigating...
EDIT2: Discovered what's wrong with strace, the stupid program tries to create some fonts in the folder where the Xorg is, which obviously can only be done as root. More hacks...
EDIT3: It seems there is no way around this one. Mono's implementation does not support forms being created in multiple threads. Is it doable to create all GUI stuff in only one thread?
EDIT4: Sorry for editing this post like crazy, but I am pretty convinced now that some architecture changes are needed to make the code compatible with Linux. The main issue here is that in Linux, graphics and keyboard input are both handled by the X server, and the horrible thing is that Mono accesses X in a completely thread-unsafe way, that's why you cannot create two WinForms in different threads. But for Bizhawk in particular, things are worse, because it polls keyboard input through OpenTK, which in the case of Linux, also passes through X, and I saw that the code creates a thread for that too.
If you just run the code compiled with my simple patches, sometimes it will start and sometimes it won't. That's because, upon startup, Bizhawk initializes the input polling thread and later draws the form for the main window, and since this is done in different threads, race conditions can happen. I managed to make it always start by only initializing the keyboard input after the window is drawn, but that doesn't solve everything. Because when any other dialog is opened, there's still a possibility of a race condition.
The only way to make sure it will work in Linux is to use a single a single thread to read keyboard input and draw all the forms...
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Sure, just wait a little. The situation of the mono packages in the portage tree is a complete mess. What I did was to clone the repos to my machine and rewrite the ebuilds, I am in contact with the maintainer already and am preparing a pull request so that things are fixed upstream and people can test it.
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Fair enough. Even if it's not usable after compilation, I would like to understand the PNG bug. It could be a security issue.
EDIT: I think I found it. It has to do with transparency. Apparently libgdiplus reads transparency information from the header and calls libpng to convert the image from RGB to RGBA, and libpng immediately fails because a certain flag is not set. Thankfully, it doesn't look like a security issue (no OOB access or anything), but still an annoying bug. I'll see what I can do about it.
EDIT 2: I have confirmed that the issue is indeed because of transparency. Apparently, libgdiplus 4.2, the version currently available in Linux distributions, got completely broken with some updates to libpng, and no image that implements transparency with the tRNS scheme doesn't work. Fortunately, the team released a new version one month ago that fixes this, so I'll probably have to update that package to make BizHawk work (actually I also have to fix monodevelop too, which is also broken for totally different reasons). I'll try to do that in the next few days.
EDIT 3: After a ton of hacks in three different Gentoo packages (Linux support for Mono sucks), I finally got it to compile, it doesn't look ugly. And it runs fine (for a while), the biggest problem for me now is that it seems you have a shitload of threads running, and every time one of them crashes for a different reason. It will be very annoying to make it stable.
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I've been trying to compile BizHawk and make it available on Gentoo. I managed to do it with some patches to the code. However, there is a nasty issue with the resource files that I could not solve. I did manage to compile the rest of the program by faking a resource file, but it of course crashes immediately because it tries to load a corrupt file.
The build fails while trying to load some png images. It looks like all TAStudio images are affected, while the controller images are not.
After digging around, I found that the issue is not present in this project, but either in libpng or in Mono's libgdiplus. It is probably in gdiplus, because I can load the TAStudio images just fine, and only the Mono shell throws exceptions. This is very problematic because it affects all Mono applications in Gentoo, and also because Gentoo's version of libgdiplus is the latest one.
Does anyone around here have a clue about what's special with the TAStudio png images, so that I can try to fix the bug?
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I can only speak about Pokémon RBY code execution, I am not familiar with how it is done in SMW.
Although RBY is considered a very buggy game today, it was not so many years ago. Just for example, the glitch that allows you to catch Mew was only publicly disclosed in 2003, when people were already playing the Gen 3 games. Today things happen much faster because of the Internet.
Anyway, for a long time, glitches related to RBY were pretty minor, and completely useless to speedrunning, so people did not bother to look for ACE. One person who was really important in reversing the game's internals was hanzou. He found a lot of gameshark codes for the game and documented pretty much every glitch found at the time, he was probably the person who understood the game best in the pre-TAS era (in the west, at least, I don't know about players in Japan).
The discovery that really made Pokemon RBY an interesting TAS was the Lvl 1-100. Having an overleveled Pokemon just after the first gym pretty much destroyed the game, and improved glitchless runs by a large margin. It was from that point on that people started fuzzing with the game to look for glitches with speedrunning in mind. It was when the Safari Zone walk-through-walls was discovered, the Brock badge skip, etc.
Things started to go out of control with the ZZAZZ glitch, which was the first to corrupt the terminator of the inventory list, which is the classic way to get ACE in RBY. If I recall correctly, it was also hanzou, that found out how to warp to the Hall of Fame using ZZAZZ, most probably from his knowledge of creating gameshark codes. This was the first instance where people used a corrupted inventory to edit the memory of the game and I remembered it blew my mind when I first saw it. Then, came the save corruption glitch and the extremely short RBY runs (it was also the time when people started whining about glitchy TASes).
From that point all that mattered was to understand how the data in the game was stored and try to find the fastest way to overwrite it. Eventually it was found out how to trick the game into calling any function, and because the game boy is a primitive device, with no security at all, it was pretty obvious that arbitrary code execution was possible.
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FractalFusion wrote:
p4wn3r wrote:
y'(u) = (1-u)e-uy(u)
By induction you can prove that
y(n)(u) = Pn(u)e-uy(u) [*],
where Pn(u) is an n-th degree polynomial.
I'm not sure about this. For example, I'm getting for y''(u):
y''(u) = -e-uy(u) + (u-1)e-uy(u) + (1-u)e-uy'(u)
= (u-2)e-uy(u) + (1-u)2e-2uy(u),
which isn't in the form written above (y(n)(u) = Pn(u)e-uy(u)).
You're right. I somehow forgot the last term when I calculated y''(u) before. I'll see if I can get a change of variables that works.
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FractalFusion wrote:
I haven't figured out if this process works for dn/dxn x1/x yet.
I think you can do it by changing variables.
y(x) = x1/x = eln x/x
y'(x) = (1/x2 - ln x/x2)y(x)
x2y'(x) = (1 - ln x)y(x)
Since x > 0, this suggests the change of variable x = eu. By the chain rule:
y'(x) = dy/dx = (dy/du) / (dx/du) = y'(u)e-u
Substituting the rest and rearranging you get
y'(u) = (1-u)e-uy(u)
By induction you can prove that
y(n)(u) = Pn(u)e-uy(u) [*],
where Pn(u) is an n-th degree polynomial.
Now to get back to y(n)(x), notice that
y'(x) = y'(u)e-u = (1-u)e-2uy(u)
y''(x) = d/du ( y'(u) e-u) e-u = (y''(u)-y'(u))e-2u
By substituting [*], you should be able to express y''(x) as a polynomial in u times e-3uy(u).
You should be able to prove by induction that
y(n)(x) = Qn(u)e-(n+1)uy(u),
where x=e^u.
The presence of e-(n+1)u does not affect your proof, since if y(u) never vanishes, neither does e-(n+1)uy(u). So Qn(u) must vanish, and this limits the number of zeros of y(n)(x) to n. Now you must prove that the limit is 0 at x going to 0 and infinity, I haven't done that, but you might be able to do it by looking at the assymptotics of the ODE. The rest of the proof is similar, the mean value theorem can still be applied, the only difference is that in the first zero you must invoke it between x0=0 and x1.
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Yeah, there is parasitic capacitance, resistance, and inductance between the circuits. The capacitance in the wires or in the medium is just one of many effects that can make the signal in one circuit interfere with another. They happen even without wired connections, and for power circuits (operating at 50 or 60Hz), noise is much more significant than that interference, so it doesn't make much sense to consider them without also including noise.
Even when you consider these effects, it's still true that the total current entering a node is the same as the total current leaving it. The circuits interact now because the parasitic elements introduce more than one connection between them. I didn't take parasitic elements into account because it's a bit unimportant considering Ferret Warlord's question, which is treated well in the approximations adopted in high school physics.
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The plates of the capacitor are not connected by any material that can conduct electric current. If that was the case, either the tension of the two plates would be the same, or the flow of current would dissipate energy due to resistance, which in an ideal capacitor doesn't exist.
The plates are separated by a dielectric that gets polarized by the tension difference. Current only "passes" through the capacitor because it converts the energy of the current into an electric field inside the dielectric and converts it back to electric current at the other plate.
Anyway, whatever happens inside the capacitor, it's still electrically neutral, and doesn't accumulate charge, it just polarizes the charge it already has. Like I said before, the amount of current entering has to be the same as the current leaving it.
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Warp wrote:
p4wn3r wrote:
The amount of electric current entering a node (or any set of nodes) of a circuit must equal the amount of current leaving it. Connecting two circuits with a single wire doesn't cause current to flow between them because, if it did, one of them would have current flowing out, and the other current entering in. That would make one of them accumulate positive electric charge, and the other negative.
Isn't that, actually, a pretty accurate description of a capacitor?
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The amount of electric current entering a node (or any set of nodes) of a circuit must equal the amount of current leaving it. Connecting two circuits with a single wire doesn't cause current to flow between them because, if it did, one of them would have current flowing out, and the other current entering in. That would make one of them accumulate positive electric charge, and the other negative. They could only interact with two connections, because then the current entering one through the first wire can be cancelled by the current leaving through the second one.
In practice, most electronic circuits already are connected at a point, the ground state of the electrical network. In general, it's not safe to connect points of them because the extra connection at ground almost always causes a short circuit.
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Warp wrote:
I don't understand why the centrifugal force felt by a rotating object would depend on the rest of the universe...
The original argument was a bit like this. Suppose you start rotating now. Your body would feel the centrifugal force. According to Newton, your rotation can be considered absolute, the centrifugal force appears because your previous frame was more inertial than the one you are now.
Mach would give a different explanation, he believed that all motion is relative, so he has to answer the question of why the centrifugal forces happen when your rotating frame is no more different than the non-rotating one. To solve this he assumes that all matter in the universe is "linked" somehow, so that in your frame, the movement of the rest of the universe relative to you interacts with your body and causes the centrifugal force.
In Newtonian gravity, the gravitational attraction of a solid sphere is the same if it's rotating or at rest. That means the sphere can move without changing the force it exerts in the rest of the universe, and thus, is decoupled from it. In GR the rotation of a massive body will cause changes to its gravitational field by way of frame dragging, so GR is more Machian than classical gravity in this phenomenon.
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The point is that Mach's principle is not a statement about mathematical formulation, it's a principle that should apply to solutions that represent physically relevant states. To illustrate better what I'm saying. You get the Schwarzchild solution. Do test particles in GR really move in its geodesics? Actually no, because the probe can have some mass and it'll distort the metric a bit. So, the Schwarzchild solution is a very good approximation, but still an idealized solution, which by definition can't be tested. And you can't use an idealized system to refute a physical principle.
What if we consider the flat space of SR? Well, if you want to describe the simplest motion of a particle with a mass, it'll deform the metric again. So you have to "couple" the particle with the SR metric and they'll interact. So, in GR the SR metric is idealized, it's a good approximation, but doesn't correspond to any physical phenomenon.
And about gravitational waves, the solutions effectively describe mass coming from infinity in one direction and going to infinity in the other, which is also unphysical. In the real world, a system would start oscillating and slowly fill the space with waves. At no point in motion the waves would occupy the entire spacetime.
My argument is: take a very reasonable mass configuration for a state of the universe, specify the initial conditions (and boundary if needed) and let the system evolve through GR. At every point during this motion Mach's principle applies.
From a purely mathematical view, the GR equations admit non-Machian solutions (it also admits solutions with time machines, btw). However, it's impossible for any sane physical system to get to them, so saying that GR is not Machian based on these solutions is inaccurate, also because they're found by imposing high degrees of symmetry and represent a measure zero of the set of possible solutions.
Einstein did change his mind about Mach's principle, he also was against quantum mechanics after helping to create it. In both matters, I think his earlier work is better.
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My knowledge of GR is essentially zero outside the derivation of Einstein equations and the Schwarzchild and Friedmann solutions, so maybe I went too much in that territory, but come on, is Schwarzchild really a vacuum solution? The tensor is 0, yeah, but it's obvious that the singularity accounts for matter. Without mathy stuff like boundary conditions, singularities and other finitude checks, there are many different solutions (in that sense the millenium prize problem on Navier-Stokes was solved a long time ago). Take what I say with a huge grain of salt, but I really think that, given the appropriate math constraints, GR is Machian (it was derived with Machian thought in mind), although I use the term Machian in a very fuzzy way, so I don't know if it's correct.
Even if I made a mistake in the previous statement, I still stand by my point. Renormalization makes no sense if you want to put gravity in QFT. There are some people who try to quantize GR directly and although there's a lot of hype that all integrals are finite and there's no renormalization, what they don't tell you is that there's no QFT in their theory either :P
Mainstream approaches to quantum gravity require renormalization to stabilize the constants when they go to infinity, so that there's no scale dependence at large scales, where GR holds. Not totally satisfactory because it's still a perturbative treatment, but a good idea nonetheless.
Oh, and thanks for the great discussion :D
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Color me surprised. I really did not expect that Red would be faster, even with the 0xc5 map ID at the right bank there which you don't need to manipulate into the data (and so you can use the whole trainer ID to do the precise jump to the last cutscene). I guess that was because I always used the SGB mode, oh well...
Also, good time save with the menus. Yes vote.
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Tub wrote:
p4wn3r wrote:
If someone asks you "Do ghost particles exist? Yes or No?", what's your answer and why?
I don't read that question as a question about ghost particles, since the answer would not yield a better understanding of ghost particles, nor would it predict any new testable properties.
It's not a philosophical question and it does yield a better understanding of ghost particles. Let's take a look at possible good answers:
a. Physicist A thinks they exist, finds a theory where their apparent inconsistent properties make sense and explains how the old theory worked in terms of the new one.
b. Physicist B thinks they don't exist, and rewrites the theory so that it agrees with experiment without using ghosts.
Even if they still haven't made predictions, their new theories could be conceptually simpler and highlight something that the old one didn't. And since the old theory was incorrect, you could hope to fix it by making small corrections to the new one. New interpretations of physical theories should not be underestimated. Feynman, for example, interpreted quantum mechanics as the "sum over possibilities" formulation, quickly found quantum electrodynamics, and won the Nobel for it.
Tub wrote:
Of course the scientific question is: "Does this set of formulas, which includes unobservable particles, accurately describe the experimental results we obtained?"
No, it isn't. I'll elaborate on this a bit more because it's a major source of confusion for physics students and it should help someone reading this thread.
Physics is not just a collection of formulas, it's irresponsible to go and solve a physics question by writing down all the equations you have and trying to get an answer out of them, because deep down these formulas assume something. When you write pV=nRT you assume the gas is ideal, when you write F=ma you assume the system is not losing or gaining mass during motion, when you write m1*v1i+m2*v2i = m1*v1f + m2*v2f you assume there are no external forces.
If you just write down all formulas you remember you can assume blatantly contradictory things and get it all wrong (and guess how often I've seen this happen). Even if you do get something right this way, you get it in the same sense that astrology can get something right.
And for the case of QFT, the formulas are not mathematically rigorous, most of the integrals diverge to infinity. To make sense out of them you need to see how fast the integrals diverge, then "correct" the constants of the theory by letting them vary when the length scale of spacetime becomes larger so that they "absorb" the divergences and you get finite results. But then comes GR and says that equations are the same for all length scales, and that we can't cheat by modifying the constants. Because of this, we have two theories that work very well but disagree with each other at a fundamental concept. Because of this, their predictions should be similar only if we're lucky (spoiler: we're not).
Is it sensible to assume the discrepancies are insignificant for some experiments and just brute force formulas? Certainly it is, but that can't go on forever. Eventually we'll have to take this paradox seriously and resolve it, and it all comes down to a question Einstein asked way back. "Is spacetime a well-defined physical entity?" It looks like philosophical gibberish, but it's more fundamental to science than the formulas. If spacetime is well defined, then QFT is right, it makes sense to talk about a large spacetime and a small one and it's OK to vary the constants, let's reformulate GR. If it is not, then GR is right, we can only talk about spacetime because there's matter in it, and QFT should be changed instead.
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marzojr wrote:
Re: ghost particles: personally, I think that the usual interpretation is a load of crap, an attempt to make sense of a mathematical trick that gives the correct results. Especially since gravity is nowhere to be found in QFTs because no one figured out how to do it yet*. Yes, it gives correct results; for all we know, it might be because QFTs give a way of approximating the effects of gravity in the quantum scale.
* And yelling "but gravity is too weak!" is a lame excuse -- general relativity is nonlinear, meaning gravity can become exceedingly strong in short range depending on the distribution of stress-energy-momentum, or even cause some other weird stuff such as flipping the sign of eletromagnetic fields at close range, as happens for a spinning charged blackhole.
I agree that the usual interpretation is not good. It's said the ghosts are just the gauge being fixed in a strange way, so you shouldn't worry about them. Well, the photon also appears by fixing the gauge and you rarely see people saying photons are unphysical and just mathematical artifacts. For me, if you're gonna use exotic gauges in QFTs, at least treat the particles you introduce seriously. I guess people just find it fun to couple fields to QFTs without worrying about what they're doing. It's a smart way to derive the theories, because there are few gauge groups and you can brute force them all until you find one that works. The problem is that the standard model ends up being a horrible mess that frightens small children.
Your remark about gravity made me curious. What's your interpretation of asymptotic freedom? Is there a good reason to believe gravity alone can introduce it at the QCD scale?
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thatguy wrote:
It is worth noticing that time is not quite the same as the other spacetime dimensions for one reason - you can not travel backwards in time (in special relativity anyway). This is the property that conserves the uniqueness of the time axis within the spacetime it sits in.
Since Marzo mentioned quantum field theories (and I've been wanting to talk about QFTs for a while :P), I think it should be mentioned that the picture changes radically when you introduce quantum mechanics to relativity. In a classical relativistic field theory (like the electromagnetic one in Maxwell's equations) you have to systematically hunt down and eliminate all solutions that travel backwards in time in order to maintain causality in the theory. So, causality has to be added as an extra postulate.
In QFT, however, it's the opposite. Interpreting the equations naively will tell you that the probability of a particle propagating faster than light is small, but positive. But if you understand relativity in the correct way, the famous equation E=mc^2 allows the particle to trade some of the mass for energy and split into many other particles via radioactive decay, and quantum mechanics requires that you sum over all possible trajectories of the system. Therefore, it's logically inconsistent to consider a system of a single particle, because in nature they'll always be under influence of a field generated by all the particles it can transform to.
In this setting, the probability of a path is a complex number, and when you calculate the probability of faster than light propagation, you get 0, because every path is canceled exactly by another path going the same direction, but backwards in time. The surprising result is that QFT maintains causality because of the time-reversed paths, not in spite of them :D
The time-reversed solutions are the antiparticles, since you can understand the positron as an electron carrying its negative charge backwards in time, so it reverses its interactions in our forward-time frame, and is thus indistinguishable from a particle with the same rest mass of the electron, but opposite charge.
I have a question. In more complicated QFTs, we encounter ghost particles, which must have their interactions summed into the formulas for every physical process. They have unphysical properties, but that doesn't matter, because every time you calculate the probability of observing them directly, it turns out to be zero, so ghosts don't introduce a contradiction.
That leads to my (somewhat philosophical) question. If we understand that the particles and their interactions form the fundamental physical laws, do ghost particles "exist" (even in the sense of spontaneously appearing and then disappearing before you can detect them)? For one side, their interactions have to be considered for the theory to make any sense, and a theory without ghosts can't be asymptotically free, as detected in experiments, so their existence is detected experimentally. However, if you try to produce/observe them, you'll always fail, and that suggests they're just a mathematical trick to solve the problem.
If someone asks you "Do ghost particles exist? Yes or No?", what's your answer and why?
EDIT: Happy 500th post for me! \(^o^)/
