The h Bar - 2019-08-15

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12:12 AM

@Hilbert Do you understand why?

12:31 AM

@AaronStevens I think it's stems from the definition of the potential $$\phi _{21}=-\int _{P1}^{P2} \overrightarrow{E} .\overrightarrow{dl}$$, since $\overrightarrow{E}=\overrightarrow{0}$ is true all for all points on the surface, then $\phi _{21}=0$ for any path joining any $P_{1}$ and $P_{2}$ on the surface, thus the surface is equipotential.

12:44 AM

yarp

1 hour later…

2:07 AM

A quick question: I think I found a new way to normalize the energy eigenfunctions of the harmonic oscillator by directly computing the integral analytically. Is that worth writing up a paper?

2:33 AM

isn't that just computing integrals of Hermite polynomials which are just power functions?

3:03 AM

@Tesseract I’m pretty sure these integrals are well-known, if I’m thinking of the same integrals as you are.

I admire your gusto but back in the late 1800’s you had professional mathematicians who spent their lives working on special functions so the odds of finding a new result on such a classic topics are infinitesimal unless you’re dealing with a novel case (v.g. continuous index or imaginary index or some obscure case.)

4 hours later…

Novalium Company

6:47 AM

Mood Gorning.

Novalium Company

7:30 AM

user image

I'm having some hard time understanding what exactly is going on in this circuit. I know how each component works and also about the voltage dividers but still, how does this circuit transform a steady DC signal to an alternating AC signal?

(I'm also sorry for asking too much questions in the past few days, I know I must be pretty annoying)

I see a voltage divider between R1 and R2, and capacitive voltage divider between C1 and C2, a transistor and a few other components.

What is the point of using a capacitive voltage divider (C1 and C2) here instead of a resistor voltage divider (like R1 and R2)? Both of them have the function to divide voltage, so what's the point of buying capacitors instead of 4 resistors?

What's the point of R3 in the circuit and that unlabeled capacitor after the emitter of the transistor?

What is the point of the transistor? To amplify the signal from the crystal?

Also, some guys said on a post I posted that 9V is not a good choice for a voltage source for my project. Why is that?

7:50 AM

@NovaliumCompany That looks like a variation of a Colpitts Oscillator. Why do you want to use a crystal oscillator? As I said the other day, a basic astable multivibrator, which generates square waves, will work here. You don't need the stability that a crystal provides. And you don't need high frequency.

@NovaliumCompany Resistors convert some of your power to heat, so it's better to avoid them if there's an alternative.

@NovaliumCompany Those square 9V batteries aren't good value for money, and don't supply a lot of current. Get yourself a battery holder that can take 6 1.5V cells.

Novalium Company

@PM2Ring Got it! Thank you so much. I'll take a look at the multivibrators

But the general purpose of the circuit will be to take in 9V and produce +1500V (in the expense of very low current, which I don't need anyways). To do that I'll use a transformer (I was thinking of voltage multipliers like you said, but I'll have to make a long chain of capacitors and diodes to achieve the 167x multiplication that I need).

Can a transformer be used on a square wave (that the astable multivibrator circuit will produce)?

8:06 AM

@NovaliumCompany Certainly. Here's another simple audio oscillator circuit that will probably work: electroniq.net/audio/simple-audio-oscillator.html

You don't need a lot of power for your application, but there will be some losses. My guess is that any circuit powerful enough to drive a speaker should work. When I was your age, I drove a small speaker directly from an astable multivibrator, with no amplifier, which is why I suggested it. The transistors just need to be capable of delivering the required power.

But it's been several decades since I messed around with circuit design. So my knowledge is a bit rusty, and I don't know about the availability of components these days.

Novalium Company

8:22 AM

So I connect a astable multivibrator to a transformer and then a rectifier and I'm done?

@NovaliumCompany I'd say so. You might need to add a capacitor to smooth the rectifier output.

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How do I know the values of the components on the diagrams?

(So I know which exact components to buy)

For example I don't know what the resistance and capacitance of the resistors and capacitors on this diagram are.

user image

@NovaliumCompany Browse around for more circuit diagrams. Circuits that blink LEDs will be too low frequency. You want something a bit faster than that, eg 50 Hz to 500 Hz.

Novalium Company

8:42 AM

@PM2Ring How do I know which ones are too low frequency and which ones are 50Hz to 500Hz. And still, this doesn't answer my question how do I know what type of components to buy in terms of values.

Some of the sites I've looked at say that using transistors for an astable is old fashioned, and you should use ICs, eg op amps, or even a 555. Eg ,google.com.au/amp/s/mechatrofice.com/circuits/…

Oops. If that link doesn't work, try this: mechatrofice.com/circuits/audio-tone-generator

Novalium Company

So I replace the speaker with a transformer followed by a rectifier?

user image

@NovaliumCompany The good articles on this topic explain the relationship between R, C, and frequency.

@NovaliumCompany Yes.

Maybe you should be asking about this in an electronics engineering chat. People there will be up-to-date with this stuff, and be able to give more practical advice.

Novalium Company

@PM2Ring Will do. Thanks!

No worries.

6 hours later…

3:02 PM

I was watching a lot of educational videos about astronomy and physics. In most videos about astronomy, it is stated that we are observing the stars as they existed millions of years ago because of the time it takes for light to travel. But doesn't that mean what "right now" means over a last distance, according to relativity?

I mean, what does it mean to be "right now" for an object that is millions of light years away?

Therefore, I would argue that we are observing the stars as they exist "right now".

@yasar in principle we can synchronise two clocks anywhere in the universe so they show the same time. For example using Einstein synchronisation.

Einstein synchronisation

Einstein synchronisation (or Poincaré–Einstein synchronisation) is a convention for synchronising clocks at different places by means of signal exchanges. This synchronisation method was used by telegraphers in the middle 19th century, but was popularized by Henri Poincaré and Albert Einstein who applied it to light signals and recognized its fundamental role in relativity theory. Its principal value is for clocks within a single inertial frame. == Einstein == According to Albert Einstein's prescription from 1905, a light signal is sent at time τ...

So that means we can have a clock on Earth and a clock near a star about to go supernova that have been synchronised to show the same time. And we can use the clock near the supernova to record the time at which is goes bang.

Then some years later we see the explosion on Earth and we can record the time we saw the explosion. So which time is correct? The time recorded by the clock right next to the supernova or the clock that recorded the time the light from the explosion reached Earth?

Remember these two clocks have been synchronised to show the same time.

If you could somehow transfer the clock near the star at the speed of light to earth at the moment of explosion wouldn't it freeze the clock and would reach the earth at the same time as the light, thus reading the same as the clock on earth?

3:21 PM

Speaking of synchronization, Albert the Ether theory guy, wrote an answer for this recent question: physics.stackexchange.com/questions/496724/…

@yasar Even easier: get the distant clock to beam its time signals back to Earth. Of course, the signal might get drowned out by the noise of the supernova, but that's a "minor" technical problem compared to the difficulty of transporting the clock itself at 0.999999c ;)

There's a nice discussion on clock synchronization which I posted in the comments on that question (which have now been moved to chat). Here's the link for your convenience: pitt.edu/~jdnorton/teaching/HPS_0410/chapters/…

@PM2Ring the trouble is that why one way synchronisation is hard is a really subtle problem. So subtle that I hesitate to attempt an answer. That leaves the field open for the fringe physicists.

@JohnRennie Certainly! I think I understand the problem, but I might be deluding myself. ;) But I did read Reichenbach a couple of decades ago.

That article by John Norton that I just linked is pretty helpful. But it doesn't completely resolve the issue.

And IMHO it's not helpful when people like AnnaV say it's a non-issue... But I don't like to harrass her. She's a smart lady, and has probably forgotten more physics than I'll ever learn.

But I get where she's coming from. If we assume isotropy, the one-way speed ought to equal the two-way speed. And using Einstein synchronization is nice & symmetrical. I wouldn't like to do Lorentz transformations using some arbitrary Reichenbach synchronization...

3:41 PM

@PM2Ring Thanks for the article, I will look into it

@yasar No worries. Norton has quite a bit of stuff related to relativity on his site, mostly from a historical & philosophical perspective.

Novalium Company

4:15 PM

If aliens far away fly really fast towards Earth, they would see our whole progress happen quite fast. That's cool. It's like they are flowing fowards in time relative to them.

Am I saying something correct or I'm being a naive idiot as always xD

I feel like some time from now, everything we think we know about time, space and light will turn out to be wrong.

How do we know that what we think is happening is actually happening? And will not turn out to be wrong like many things have. (Newton, Bohr's atom...)

we can only falsify models with new observations

We cannot prove anything in science

If it is round, orange and smells good, it is assumed to be an orange

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smell, color and vision are relative

Nvm, I sometimes have the philosophical urge to argue about certain topics, and my Dad gets pretty angry when I do that

The only point I'm trying to make is that everything we think we know and is "whats actually happening" may turn out to be wrong and we may be stuck in an endless loop of proving and disproving theories.

That's a bit sad

We make cool technologies though, that's nice

4:34 PM

Well, as a past discussion with my undergrad professor reminds me. "We actually have no idea what exactly is an electron"

"It could be some incomprehensible mush that happens to have -1 charge and behaves like a point"

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@Secret What is a bit depressing is that at any point when we think we know what an electron is, we can find evidence that we are dead wrong, and we continue like that forever.

@NovaliumCompany Modern science doesn't attempt to say "what's actually happening". Instead, we construct theories that model some part of reality to some degree of accuracy. Then we work out the implications of the theory, and see how well they match up with our observations.

We verify that the theory is consistent with existing data, and use it to make predictions about stuff we haven't seen yet. And we don't just look for stuff that validates the theory. We try as hard as we can to "break" the theory, looking for stuff that the model should cover where reality does not match up with what the theory says.

Positivism is dead, and we are dancing on its grave.

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Reality is weird, that's all I can say for sure

@ACuriousMind In some cases, realism is better than positivism

@PM2Ring So science attempts to create and confirm models of the world that match our observations and at the same time tries to break it's theories?

So we can never know "what's happening", only what our perception and intelligence tells us?

4:52 PM

The idea that there is something to know there, i.e. that the question "What is really happening?" even asks a meaningful question, is itself not uncontroversial.

@NovaliumCompany Yes. Trying to break the theory is very important, and it's what distinguishes science from earlier approaches to knowledge, where people look for stuff that supports their story, and tend to distort stuff that doesn't fit so well to try & make it fit. Or ignore stuff that can't be forced to fit.

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@ACuriousMind not uncontroversial = controversial. Please, make my life easier

So when (for example) an astrophysicist says that in 5 billion years our Sun will turn into a red giant, they are really saying that in the context of our current best theories of astrophysics, that the Sun will become a red giant in 5 billion years. It's possible (but very unlikely) that the relevant theory is flawed, and the real Sun will behave differently to the model Sun.

But the double negation is such a beautiful thing!

Spoken like a true German. ;)

4:59 PM

@NovaliumCompany ACM is mastering the characteristically English approach to English :-)

(I have English & German ancestry, plus a few others)

Novalium Company

@JohnRennie Welp, I'm from Bulgaria so that borns a little confusion, even though we also have double negation.

Много се радвам че не ми е непозволено да съм част от това общество

In rhetoric, litotes (, US: or ; also known classically as antenantiosis or moderatour) is a figure of speech and form of verbal irony in which understatement is used to emphasize a point by stating a negative to further affirm a positive, often incorporating double negatives for effect. Litotes is a form of understatement, more specifically meiosis, and is always deliberate with the intention of emphasis. However, the interpretation of negation may depend on context, including cultural context. In speech, it may also depend on intonation and emphasis; for example, the phrase "not bad" can be...

Novalium Company

double negation is pretty uncommon and weird in the bulgarian language

we just make our lives simpler by saying controversial, not not uncontroversial

So a science theory is a kind of map. It's not a map of the whole universe, and like any map, it has to leave out some details of the area it does cover. When we learn science at school & university, the teacher is basically describing the map, not the part of the real world that the map is a map of. But we must never forget that we're working with a map, and that the map is not the territory it represents.

That distinction tends to get lost in popularizations of science...

5:15 PM

Big Train - Eagle Line

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@PM2Ring Pretty interesting way of representing it

@NovaliumCompany It works well. It's a bit like programming. Trying to describe the world directly is like coding in assembler language. It takes a lot of effort & concentration, and it's easy to get bogged down in details and lose perspective of the big picture. If you program in a high level language you lose that direct connection to the hardware, but you can easily create quite complex high-level structures.

6:22 PM

0

Q: question closed by a single person without any chance of editing

I had recently asked the following question: Uniform discrete physical theories And the question was closed without any comments whatsoever. The reason cited was that it was too broad. I don't see how this is a broad question, as I was very specific: Are there physical theories such that space...

6:54 PM

@PhysicsMeta @ACuriousMind your comment there should be an answer.

that's probably right

@ACuriousMind have an upvote, good man

7:09 PM

@Tesseract consider checking whether the integrals you're calculating are listed in the standard repositories (DLMF, Gradshteyn & Ryzhik, Prudnikov, Erdelyi, etc), as a standard part of your workflow whenever you're calculating integrals

For this particular case, it's essentially guaranteed that they're present at the top of the pile.

@Tesseract it's almost certainly in some QM book or math methods book already tbh

The craziness of the integrals in those old books

@vzn still 'the only game in town' :p

you used to have to compute crazy integrals before you were considered a real man

Those old Tripos questions are unbelievable

@RyanUnger that's still the case

there's just fewer real men around

@vzn help me find this string debate between 'critic' and proponent

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