Hi, everybody.

@JohnRennie are you free now?

Now I read from Why the Many-Worlds Interpretation Has Many Problems what on earth is Many-Worlds Interpretation. In the past I just had heard of it and had a vague idea of it. But I don't understand how Many-Worlds Interpretation can interpret quantum mechanics because it seems to be completely free of the most important probabilistic character of quantum mechanics.

My personal issue I had of MWI is basically "which self", "which present". It is true in the scale of the universal wavefunction, each branch is assigned a probability, but for any object in each branch, they only ever perceive one branch. It's makes it pretty hard to talk about past and future because then one need to worry about "which sequences of pasts" that lead up to a given present, and "which branch are we heading in the future when the measurement took place"

@CaptainBohemian MWI is almost like an interpretation of probabilities as "world splittings". dont see why it has to be unique to QM myself. there are other interpretations of probability eg bayesian vs frequentist. a lot of QM interpretation difficulty seems to hinge on "probability interpretation". try this recent remarkable acct by Becker author of remarkable new book, on my to-read pile, need to read asap...

@ShaVuklia Now I am :P

I also terribly hungover, though, so don't expect any insightful answers from me today...

I...doubt it :P

@ACuriousMind haha uhm, but can I still try?0:)

sure

oh hmm, I think I see it now.. I guess it helped that I tried to formulate my question:d

oh wait, no I'm still confused. I'll post the exercise:

don't we usually model a battery as a capacitor itself? so, if we want to have a potential difference $V_0$ at the battery, we would actually need to have some $Q_+$ at one pole of the battery, and some $Q_-$ at the other. So I guess my confusion is how this $V_0$ can be maintained. Should I use a different model of a battery? @ACuriousMind

don't we usually model a battery as a capacitor itself - no, a battery is a charge pump i.e. it pumps charge like a water pump pumps water.

or should I just accept that, somehow, it's possible to create this eternal $V_0$, and given how the capacitor and the resistor respond, we can calculate what was the energy that was provided by this battery?

so did it only pump charge at the beginning?

because I'm assuming it doesn't continue pumping charge indefinitely

how is $V_0$ maintained, once the charges start moving?

If we use my water pump analogy, then a water pump has a maximum water pressure it can produce. It will pump water only until that pressure is reached, then it can't pump any more.

@ShaVuklia The "battery" in such circuits is an idealized voltage source that simply maintains the given voltage. It's not relevant to the question how/whether a real-world battery would do that.

For a battery that maximum pressure is the potential i.e. it will pump electrons only until some maximum potential is reached.

@ACuriousMind Right, that's what I was thinking too. My mistake was that I tried to also include this model of a capacitor in the battery, but I shouldn't do that. It's just something that creates a voltage difference, and that's it.

@ShaVuklia yes

but do we assume that charge can flow through the battery?

I mean, how do we know which direction the charge will go, based solely on this definition? Because if I model a battery as a capacitor, I know the direction; it will go depending on on which electrode the charge is "pushed to" by the battery

@ShaVuklia What do you mean "which direction the charge will go"?

like, what happens in that "gap" of the battery? does charge flow spontaneously, or does the battery help the charge? my guess is that if the battery helps, then it's doing work, and we would have a steady current. but that's not the case here. so I'm assuming some charge piles up at both side of the battery. but then I'm confusing why $+Q$ and $-Q$ aren't in the reverse order, because you would think that positive charge would pile up at the - side of the battery

like, why doesn't the charge go "through" the battery, in the opposite direction of the current in the circuit?

in the end, it's the same potential difference, we just take a different path

There is no "gap" in the battery, that's just its circuit symbol.

but there must be a potential difference between two distinct points right

I'm talking about the distance between those two points

Yes. Those are the poles of the battery, and between the two there is the voltage the battery is supposed to provide.

right, so why does the charge decide to take the path of the circuit, while it might as well go through the battery?

Because the two poles are not connected to each other

right, so we have zero conductivity between the poles

last question then still; how can charge pile up at the side of the capacitor closest to the + pole, while the charge is going towards the - pole?

@ShaVuklia I don't understand the question

my question is why aren't these two symbols reversed, since

charge is going from the positive pole of the battery towards the negative pole

so, I would expect charge to pile up at the side where we now have $-Q$

so I would expect those two symbols to be reversed

...the shorter pole of the battery is the negative pole

So the "+Q" part of the capacitor is directly connected to the positive pole and the "-Q" part to the negative pole. I don't see the problem.

charge is flowing from the +Q part of the capacitor to the - Q part, right?

No, why would it?

The two parts of the capacitor are not connected.

because of the potential difference?

so no charge is flowing at all?

@ShaVuklia While the capacitor is charging, charge is flowing from the positive pole of the battery to one part of the capacitor and from the other part of the capacitor to the negative pole of the battery. When the capacitor is charged, no charge is flowing.

oh.. right.. I was assuming that charge was flowing between the capacitor

oh, then $+Q$ and $-Q$ make 100% sense

holy, hahah, that's was a big interpretation error haha

this was the most insightful thing for me today:p

hm, one last point of confusion though; how do we know that it's possible for charge to flow from the positive pole of the battery?

that would make the positive pole more negative, and wouldn't that somehow.. affect the potential difference?

I mean, I don't see how we can just grab some charge from a pole, just like that

@ShaVuklia no, because the battery is a charge pump remember. Charge can only flow out of one end of the battery if an equal and opposite charge flows into the battery at the other end.

ohhh rightt....

so in a way, you could say that a battery "rearranges" (or, helps rearrange) the charges in a circuit, whether this is a static or a non-static rearrangement

In effect when you connect a battery to capacitor the battery pumps electrons off one side of the capacitor, leaving a positive charge, onto the other side of the capacitor where those electrons produce a negative charge.

Hence you end up with equal and opposite charges on the two sides of the capacitor.

righttt, yea I always thought that the rearrangement of the charges was a result of the battery's voltage, but you could also say that the voltage is a result of the rearrangement. There is not really a causation going on here, or at least, it's not relevant. I don't know if what I'm saying makes sense, but I feel like my understanding improved

hm, one final question though; if we didn't have the capacitor, and we only had a battery and a resistor. then, our differential equation would be $V_0=IR$, and that would mean that $I=V_0/R$, so the battery would technically provide infinite energy right (in infinite time)? It's somehow the presence of the capacitor that makes the energy finite, because the capacitor doesn't require a current to store energy (to create a potential), it just requires $Q$

I mentioned earlier that a battery is an electron pump, and the pumping is done by a type of chemical reaction called a redox reaction.

New batteries contain the chemicals that reach with each other to pump eelctrons, but batteries have only a finite amount of these chemicals. When all the chemicals have reacted the battery is dead. That's why batteries become exhausted - it's simply them running out of the chemicals they need.

Right, so that would not be an idealized voltage source, but a real-world battery

The energy produced by battery in the form of electricity comes originally from the chemical energy of the reaction.

but you do agree with me that if we take the battery to be an idealized voltage source, then it would be providing infinite energy in infinite time, if we had no consistor, right?

I just want to be sure I really got it

because in the resistor, energy is constantly lost due to the conversion of potential energy of heat. yea ok it makes sense haha

@ShaVuklia well ... yes ...

The power produced by a battery is $P = IV$, where $I$ is the current flowing through the battery and $V$ is the battery voltage.

So in the hypothetical case of a battery producing a constant current forever it would indeed supply infinite power.

I'm just not sure there is any great insight to be gained from this. It's like saying an ideal car engine that doesn't need refilling with petrol could produce infinite power.

yea it's not a great insight, I just wanted to check that we needed the consistor to make the energy finite

Well a capacitor prevents a continuous current flowing ...

I think I see now why sometimes physicists say that the energy is stored in a field. Griffiths mentioned this briefly, but he also said that (for now) you might as wel say that the energy is stored in the charge configuration. The battery creates a field basically, and for this, it needs energy. So in a way, the field itself contains the energy from the battery.

Because if more charge "uses" the energy of this field, the battery will have to pump more charge to the +pole, to maintain the field basically.

I don't know if all these things are trivial, but for some reason I hadn't thought about it this way

If we have finished talking about physics, I shall post the results of my latest experiments in chemistry:

This is the product of reacting chole with some left over chicken and some cream.

I'm normally eating just one type of sauce, so I just put it straight onto a bed of rice. I know that would be frowned on in India :-)

I have got a thali set somewhere, but I rarely use it.

@JohnRennie everyone I know eats it like that

Unless or until we go out

Hey could someone give me some advice? I’m trying to come up with a research project for a class to show (my hypothesis) that entropy increases as a system goes from it’s periodic regime to it’s chaotic regime, but looking at different oscillators it appears to be a really difficult thing to demonstrate because either the oscillator isn’t Hamiltonian (duffing) or it isn’t chaotic (simple q^4 perturbation).