You are trying to define a system in which what you say makes perfect sense. The only problem is, your "system" is nonsensical. Why would I consider a system of the Sun and Earth without including all of the other things inbetween, for starters? What is the purpose of this system - it surely cannot describe anything physical in reality. You have no ligitimate objections to my claims, except claims of your own. There is no proof that your claims describe reality and my claims do not. And the assertions of others (which is where you got your claims) is not proof of your claims. Assertion of any kind is not proof. A fine suggestion Please Register or Log in to view the hidden image! because you've added nothing but claiming the unsupported assertions of others is correct without proving that it is, or even could be true. My objections still stand and your asserted claims are not a disproof of the claims I've presented.
Aer: Whatever. The thread's here for anybody who cares to read it. How much GR do you know? Step C is unnecessary. I don't see how this has anything to do with cause and effect, either. It is a simple matter of taking all objects in a system into account in calculating the gravitational effect of the system. Once again, a fairly obvious point, I would have thought. There's this marvellous thing called the internet. It even has online dictionaries. Happy searching, Aer.
Please Register or Log in to view the hidden image! Read a book, and come back when you know what you're talking about. Positive feedback only tends to infinity if the *overall* gain (amplification factor x feedback factor) is one or more. Lookie here, here's a simple system I'm sure even you can understand: Output = Input x Gain Input = Signal + Output x Feedback Rearrange: Output = (Gain x Signal) / (1 - Gain x Feedback) This equation gives the stable point for a given signal, amplification factor, and feedback factor (note that it assumes that the three are independent, which is why it's a simple system). As long as Gain x Feedback is less then one, the system is stable. This is always true if Feedback is negative, and sometimes true if Feedback is positive. More complicated systems are ... more complicated! Roles of Positive Feedback Circuits I didn't Please Register or Log in to view the hidden image!
I asked the question, why can't you answer? How much GR do you know? Step C is very much necessary. If you change the magnitude of the gravitational field, the magnitude of the gravitational binding energy is going to increase which results in a never ending cycle. Wrong, when dealing with compound objects, how do you know what the gravitational binding energy for each object is without first knowing the final gravitational field magnitude? Which came first, the chicken or the egg? Shenanigans.
Aer: Enough. And yourself? You've waffling now, and mixing up relativity with Newtonian (or other) ideas. Newton's law of gravitation lets you work out Newtonian gravitational potential energy (which you are calling "binding energy"). I think you will need to clarify what you mean by "binding energy" in the general relativistic case, because, as you will be aware, gravity is not a force in general relativity, and therefore does not have an associated potential energy in the same way that Newtonian gravity does. Yes. So, do you have anything new to add to this discussion, or do you just intend to keep repeating your initial assertion over and over in the hope that you will bludgeon the physicists here into submission?
It is called a "Crowbar". An electronic control to act as a superfast breaker. Please Register or Log in to view the hidden image! Otherwise you are correct in general regarding negative and positive feedback.
This is just not true, the more I gave thought to it the more I realized, you can have an unstable system as long as you have something else to control that instability. Good job, you actually got the math correct, perhaps you looked it up.. Anyway, are you telling me this system is stable? Because it is not. Any positive pole makes a system unstable. (1 - Gain x Feedback) gives a positive pole. You simply do not understand what a stable system is, otherwise you'd never claim your feedback equation with a positive pole was a stable system. Thanks, Mr Genius. And here is everything you need to know about positive feedback: Feedback is well understood and widely studied in electrical engineering. Whereas negative feedback is used to stabilize the response of an electrical system and reduce nonlinear effects, positive feedback is often used to take advantage of these nonlinear effects (for example, the Schmitt trigger), or at least is used with the understanding that nonlinear effects, not feedback, will limit the output (in oscillators, and in popular configurations for MESFET amplifiers). An important consideration in the design of feedback amplifiers is to avoid unintentionally creating positive feedback (see frequency compensation). Positive feedback from loudspeakers to a microphone causes the familiar squealing sound.
Well, I was only thinking in terms of stability - My only experience with control systems is making a system stable Please Register or Log in to view the hidden image! I forgot to consider other possible uses of feedback.
Well then answer my question I posed about 2 pages back if you say you know "enough". I know enough to know how the theory was formulated.. I've never mentioned any Newtonian concepts. So are you know saying binding energy does not exist? Because before you agreed that it had to be included to get the total gravitational field created by a compound object. So there is no binding energy associated with gravity according to you? No. Yes, you are a waffler.
That's a bit rich, considering your blatant uncited use of Wikipedia. Nice try, but your Wikipedia-expertise has holes! My recollection of poles is much too fuzzy to give a thorough response, but just putting in some numbers if enough to confirm stability. Try these: Gain = 2 (the output is double the input) Feedback = 0.2 (a fifth of the output goes back to the input) Signal = 10 (this is the base input level to which the feedback is added) What output do you get? Note that the feedback is positive... Now apply it to the context of the thread. "Signal" is the inherent mass-energy of a system, "Output" is the resulting curvature, and "Feedback" is the contribution of the curvature to the system's mass-energy. In this case, the equations aren't as easy... but the principle still applies.
I was being lazy Please Register or Log in to view the hidden image! Poles are not a fuzzy subject. A negative pole is stable, a pole at 0 is neutrally stable and a positive pole is unstable. The question in control systems is whether this pole is controllable or not. If it is controllable, then the overall system will be stable. However if it is not controllable, then the overall system is unstable. Now with regard to purposely using positive feedback, the intention is to cause something to rise as high as it physically can. That is, the nonlinear effects of the output limit the effect of the gain - I think, as much as I've read in the last 20 minutes at least Please Register or Log in to view the hidden image! I do not have any prior experience of intimenting positive feedbacks because as I've said, I've only dealt with stabilizing systems. I don't think gravity works as a feedback like this, but nevertheless, can you prove that it would have a limit? I'd suggest that such a limit would tend toward a black hole. Edit: Actually I didnt put much of any thought into that. Binding energy is negative, right? So gravity would tend towards flat spacetime... SRT rules after all.
I was a 52K20 in the Army. Nuclear Power Process Control Instrumentation Specialist. Please Register or Log in to view the hidden image!
I believe you, but I'll need to to defuzz my knowledge of them. But really, why complicate things? Put the numbers in to the simple system, and tell me if the output tends to infinity or if it stabilizes at 33.33. You can jump up and down about positive poles all you like, but you look a bit silly if the system is happily sitting at a stable output of 33.33. I'm surprised you haven't tried this, considering your insistence on not blindly accepting any theory! Please Register or Log in to view the hidden image! Are you sure you've correctly determined the poles of the system? Sorry, can't do. All I can do is provide a proof of concept - plug the numbers in to the simple example and see! Needs more thought, methinks.
I can't be entirely sure on how positive feedbacks work, but what were you initial inputs? 33.33 might be a physical limit imposed by your setup. Are you able to decrease it from 33.33 once it reaches that? I could just keep asking question because like I said, I really don't know what happens with positive feedbacks other then you necessarily create a positive pole. You at least agree that all positive feedbacks will create a positive pole, correct? To find the poles of the system (1+z)/(1-p) you set the denominator equal to zero and solve for p. In your case, you would have (1 - Gain x Feedback) = 0, so p = Gain x Feedback. Gain and Feedback are both defined such that they are positive. I believe you can work with negative gains, but then the pole rules I gave above do not apply. I think the reason you are getting 33.33 is because your Feedback term is negative and thus you really are doing a negative feedback and not a positive feedback. Just a guess though. Well, according to James R, binding energy doesn't even contribute to gravity - he says binding energy doesn't even exist Please Register or Log in to view the hidden image!
Step function of height 10. No limitations here - the system always spits out twice what goes in. A fifth of what goes out goes back in, on top of the step function. Think of a simple mike-amp-speaker setup. The sound from the speaker is twice the power of the sound entering the mike. (Gain=2) 1 fifth of the sound energy from the speaker reenters the mike. (Feedback=+0.2) There is a background noise, of which a constant 10 units enters the mike. (Signal=10) How much power comes out the speaker? I get 33.33 units. I don't know. Sorry. What's the system equation (1+z)/(1-p) mean? Are you sure the equation I gave means the same thing? 0.2 times the output gets fed back into the input. 0.2 is positive, right? Isn't that what "positive feedback" means?? This is a serious question - perhaps I'm using the term differently to how it's used in the context of control systems?
<script type="text/javascript"> var _interval=null; function step() { document.getElementById("output").value = parseFloat(document.getElementById("inputbox").value) * parseFloat (document.getElementById("gain").value); document.getElementById("feedback").value = parseFloat(document.getElementById("output").value) * parseFloat (document.getElementById("feedbackFactor").value); document.getElementById("inputbox").value = parseFloat(document.getElementById("signal").value) + parseFloat (document.getElementById("feedback").value); } function toggleCycle() { if (_interval==null) { _interval = setInterval("step();",1+50*(10-parseInt(document.getElementById("speed").value))); document.getElementById("gobutton").value = "Stop"; } else { clearInterval (_interval); _interval = null; document.getElementById("gobutton").value = "Go"; } } function restart() { document.getElementById("output").value = "0"; document.getElementById("feedback").value = "0"; document.getElementById("inputbox").value = "0"; } function validateInt(test,max,min,_default) { if (isNaN(parseInt(test))) return _default; else if (parseInt(test) > parseInt(max)) return max; else if (parseInt(test) < parseInt(min)) return min; else return parseInt(test).toString(); } function validateFloat(test,_default) { if (isNaN(parseFloat(test))) return _default; else return parseFloat(test).toString(); } </script> Aer, Here's a model of the simple system I described earlier. After playing with it for a bit, I strongly suspect two things: 1 - we're using terms quite differently. 2 - you've identified the poles of the system a bit too hastily. <form><table><tr><th>Initial input (step):</th><td><input type="text" size=5 id="signal" value="10" onchange="this.value=validateFloat(this.value,'10');" /></td><th>Output:</th><td><input type="text" size=20 id="output" value="0" onfocus="this.blur()" /></td></tr> <tr><th>Gain factor:</th><td><input type="text" size=5 id="gain" value="2" onchange="this.value=validateFloat(this.value,'2');" /></td><th>Feedback:</th><td><input type="text" size=20 id="feedback" value="0" onfocus="this.blur()" /></td></tr> <tr><th>Feedback factor:</th><td><input type="text" size=5 id="feedbackFactor" value="0.2" onchange="this.value=validateFloat(this.value,'0.2');" /></td><th>New Input:</th><td><input type="text" size=20 id="inputbox" value="0" onfocus="this.blur()" /></td></tr></table> <input type="button" value="Step" onclick="step();" /> <input type="button" value=" Go " id="gobutton" onclick="toggleCycle();" /> <input type="button" value="Restart" onclick="restart();" /> Speed (1-10):<input type="text" size="2" id="speed" value="5" onchange="this.value=validateInt(this.value,'10','1','5');" /></form>
The venerable www.sciforums.com. Quote the source next time. Don't try to assume knowledge you don't have by not doing so. That's dishonest, and yet another reason for people to think you're an asshole.
