Physics question, is a true DC or constant magnetic field truly possible? - Page 1
Forum section: electronics / general

author: BrianHG
author_rank: Super Contributor
timestamp: March 28, 2024, 12:38:39 am
content: Well? I guess you might call this a philosophical question, but, no matter the power source creating your DC power, it will eventually die meaning no longer a DC signal as it has an AC attribute. (Heat death of the universe and all that...) Even a permanent magnet's field fades over time, hence they are not truly constant.Can we or the universe ever achieve an authentic 0hz unchanging charge with 0 AC characteristics?

author: shapirus
author_rank: Super Contributor
timestamp: March 28, 2024, 12:40:55 am
content: Quote from: BrianHG on March 28, 2024, 12:38:39 amunchanging charge = zero current.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 28, 2024, 12:46:07 am
content: It's not just that it will eventually die, but it constantly changes, sometimes with changes small enough that you call that "DC".

author: BrianHG
author_rank: Super Contributor
timestamp: March 28, 2024, 01:00:30 am
content: Quote from: shapirus on March 28, 2024, 12:40:55 amOk, you didn't understand what I was asking.It is possible to have a so called unchanging charge with a load current if we continuously refill our reference charge.But even in our experiment if we consume no current, eventually something in the universe should kill it.even Magnatar stars loose their magnetic field over time.

author: m98
author_rank: Frequent Contributor
timestamp: March 28, 2024, 02:12:45 am
content: No need to get as philosophical as to considering the lifetime of the universe, a DC signal is what you define it to be, it is always a highly idealized description of the actual signal. There are no true DC signals, they are a spherical cow in a vacuum. There seem to be perfectly constant charges, every single electron seems to be holding its charge quite well, its only when you look at more than one charged particle that things start to get complicated.

author: unpackflight
author_rank: Newbie
timestamp: March 28, 2024, 07:59:24 am
content: Quote from: m98 on March 28, 2024, 02:12:45 amA spherical cow is a metaphor that is used when a complex scientific model is made more simple than it really should be.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 28, 2024, 09:53:47 am
content: One can get a pretty stable magnetic field with superconductors. Superconductors can work as essentially perfect shield to external fields (type 1 superconsuctors have exactly 0 internal flux). The flux captured in a superconducting ring stays constant as long as the ring is superconducting.There is still a rather minor uncertainty in how much the parts move relative to each other. So the problem is not electrical noise but more mechanical and vibrations.For the "DC" ideal, it really depends how one defines DC - there are way than looking at the fourier tranformer over all time. It is more about stable over the measurement time with settling effects completed.

author: thm_w
author_rank: Super Contributor
timestamp: March 28, 2024, 09:07:23 pm
content: I think a endless permanent magnet is possible, though it might require absolute zero temperature or specific construction methods.Normal stars use hydrogen as energy, neutron/magnetar stars presumably would also use up some fuel source over time, so decay makes sense.https://www.reddit.com/r/askscience/comments/aq5rr1/does_a_magnet_ever_lose_its_power/https://www.reddit.com/r/askscience/comments/1zcida/do_permanent_magnets_have_a_halflife_or_otherwise/

author: nctnico
author_rank: Super Contributor
timestamp: March 28, 2024, 09:11:23 pm
content: Quote from: BrianHG on March 28, 2024, 12:38:39 amHow about the earth's magnetic field?

author: shapirus
author_rank: Super Contributor
timestamp: March 28, 2024, 09:22:53 pm
content: Quote from: nctnico on March 28, 2024, 09:11:23 pmNowhere near permanent. It'll fade away as the core cools, like it happened on Mars.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 28, 2024, 09:26:07 pm
content: The earths magnetic field is not 100% stable. Good magnetometers can measure the variations in the earths field. On the slow scale they observe that the magnetic poles are wandering a little.

author: Circlotron
author_rank: Super Contributor
timestamp: March 28, 2024, 09:35:46 pm
content: If we assume the universe had a beginning, then our DC current or magnetic field must have gone from zero to a steady value at that point or sometime after that. Would that not disqualify it from being truly constant?

author: jpanhalt
author_rank: Super Contributor
timestamp: March 28, 2024, 09:40:34 pm
content: Quote from: BrianHG on March 28, 2024, 12:38:39 amSure, but how would you prove it? Any method of measure would disturb it (not Heisenberg's uncertainty principle but a similar argument).

author: tggzzz
author_rank: Super Contributor
timestamp: March 28, 2024, 09:56:22 pm
content: Quote from: nctnico on March 28, 2024, 09:11:23 pmIt reverses periodically. The record of such reversals provided early compelling evidence for plate tectonics. Also spot how fast the magnetic North pole is moving: at >30 miles/year (i.e.>10 furlongs/fortnight).As for the original question, the answer is yes, repeat no, unask the question.I remember a school maths lesson (age 12?) where we spent the entire lesson discussing whether it was possible to have a flat plane. After I pointed out that even the smoothest surface would have atoms sized variations, we eventually came to realise that the mathematical abstraction was real, but there could be no physical embodiment.I hope the relevance is obvious.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 28, 2024, 11:56:38 pm
content: There is nothing much constant in the universe anyway, except possibly the speed of light (and a few other constants that can more or less be derived from it), and even that is not certain.As I and others have said, a physical constant value is whatever varies little enough that the variation doesn't matter from the perspective of the observer.The rest is inevitably not a physics question, but metaphysics.The flatness and atoms example is relevant. But so is the "constant" attribute of the "amplitude" (envelope) of some oscillation, when the oscillation itself is a value that is permanently changing. What that means is that one defines, arbitrarily, some "macro" property that helps abstracting what happens at a lower level, but those abstractions are models, not an expression of something real.

author: ejeffrey
author_rank: Super Contributor
timestamp: March 29, 2024, 03:41:59 am
content: Quote from: BrianHG on March 28, 2024, 12:38:39 amDon't forget the other time direction. It's not "DC" if it didn't already exist since the beginning of the universe. So we by definition cannot "create" a DC field.

author: BrianHG
author_rank: Super Contributor
timestamp: March 29, 2024, 04:10:39 am
content: Quote from: ejeffrey on March 29, 2024, 03:41:59 amI think you hit the nail on the head...

author: m k
author_rank: Super Contributor
timestamp: March 29, 2024, 07:20:22 am
content: If you accept that energy is a point like object called photon, your definition of constant will fail instantly.If not then you have few single photon experiments to explain.

author: EPAIII
author_rank: Super Contributor
timestamp: March 29, 2024, 10:42:35 am
content: When you toss in the heat death of the universe that means you are talking about an extremely long time period. And physicists can only make educated guesses as no one has ever run any experiments or observations over that time period. That "heat death of the universe" thing IS one of those educated guesses. If the truth be known, no one can be sure.On top of that, how can we or any descendant of ours ever know that the heat death of the universe has been reached. At that point, BY DEFINITION there would be no life, no mechanical devices, absolutely nothing but matter where the temperature of that matter would be completely uniform AND ANY ORGANIZATION OF THAT MATTER WOULD BE TOTALLY NONEXISTENT. No clock could exist. No observing or recording device of any kind could exist. The only thing that could exist would be a gas which was completely, absolutely, uniformly spread over the entire universe and all of it at the same exact temperature. And nothing to observe it.More to the point of your question, there could be absolutely no unbalanced forces. All force, BY DEFINITION, would have to be uniform. ABSOLUTELY UNIFORM. I suppose gravity would still be there, pulling everything toward "the center" but where would that be? Does the universe have sides or edges? That seems doubtful. Perhaps it wraps back upon itself. If you go far enough in any direction, you wind up back at your starting point. And that is VERY LITERALLY in ANY direction. Don't ask how that is possible because I don't know. The answer to that one is beyond the pay grade of Einstein or Hawking or any other scientist you care to name or ever could name. Well beyond it. So perhaps, just perhaps, even gravity would also be completely balanced in all directions and nothing could ever change again. And because the entire universe is in a state of complete and total balance, it could not even collapse into a black hole or singularity. It could only remain exactly as it is.What I am saying is that no matter how much alphabet soup they have after their names or how famous or well regarded they may be, they just don't know. Educated guesses? Yes. Absolute knowledge? NO!It's dead Jim! The universe is dead, Jim!Universe without end, amen!But then, what do I know?Quote from: BrianHG on March 28, 2024, 12:38:39 am

author: EPAIII
author_rank: Super Contributor
timestamp: March 29, 2024, 10:54:11 am
content: OK,PROVE IT!No proof, no tee shirt.Quote from: ejeffrey on March 29, 2024, 03:41:59 am

author: Nominal Animal
author_rank: Super Contributor
timestamp: March 29, 2024, 06:16:53 pm
content: Quote from: BrianHG on March 28, 2024, 12:38:39 amThis is not physics.Physics is a science that tries to describe observable phenomena (using mathematical models). It cannot answers questions like "isXpossible"; you'd have to reformulate the question into "in what kind of situation or system couldXhappen".Because physics only involvesobservablephenomena, there is no such thing as "perfect" or "exact"; it is always limited by our ability to observe, to measure the phenomena.The stated question is like asking a mathematician, "If you had to specify a real number for \$\lim_{x \to \pm0} \frac{1}{x}\$, what would it be?". The expression evaluates to positive or negative infinity depending on the direction you approach zero from, so assigning any real number would be an error.As mentioned by several others above, we aren't even certain if the electron charge is a constant (the same everywhere and unchanging as time progresses). Thus, "absolutely constant DC current" (even if considered only in some limited time interval) needs to be specified with respect to something, for example as the rate of one-electron charges passing through a surface.In case you're tempted to insist and play along that definition: even if we found some phenomena where a steady beam of electrons at a specific energy (velocity) is emitted from some source, changing your velocity with respect to the source will change the observed current in the electron beam. Any change in the gravitational potential will change the observed current in the electron beam, too. If you examine the system at shorter and shorter timescales or currents, you'll notice the current (and the related electromagnetic fields) being quantized.Thus, the only non-nitpicking/language-lawyer answer one can give to the stated question is "According to our current understanding, no: perfectly direct current is impossible, for example due to quantization of current and electromagnetic fields alone. At sufficiently short time intervals, there is always at least some ripple or noise due to quantum mechanics."

author: Siwastaja
author_rank: Super Contributor
timestamp: March 29, 2024, 06:32:21 pm
content: Quote from: ejeffrey on March 29, 2024, 03:41:59 amWhy would beginning of the universe be enough? If we follow this logic, I think it should extend to minus infinite time.

author: coppercone2
author_rank: Super Contributor
timestamp: March 29, 2024, 07:17:15 pm
content: Quote from: Kleinstein on March 28, 2024, 09:53:47 amI think the ring is radiating on a quantum level because the current is still fluctuating, the ring just has a very high radiation resistance . Won't it depend on how stable the power supply used to charge it is?I think the most stable current would be if electrons are single file like a ball chain that way there is no interaction between them trying to pass each other like cars on a high way. And then it depends on how well they hold to the lane lines I think. So you reduce noise in a dimension?