The h Bar

Parmeet Singh EP 066

06:24

Hi guys, I am sort of new here. So hi I am a engineering student which is majoring in applied physics. And I need some help.

Each sem we have to make up projects for each course. This sem I took Cosmology and Astrophysics and we covered a vast amount of topics, from luminescence of stars to Einstein's field equation(we barely scratched the surface). Now originally I made an idea for a basic presentation, in which I would solve for the Foucault pendulum equation using classical mechanics and using that we could talk about basic proofs about how earth rotates(I know this is basic but it was …

Slereah

08:34

"Here we are merely discussing in terms of spacetime what is familiar to everyone, but it is most important to make this discussion without appeal to NEWTONIAN concepts. In particular, the word rigid must be avoided like poison until properly defined in space-time terms."

Synge is so intense

user129412

08:57

I know that typically thin film aluminium will have a critical temperature for turning superconducting that is larger than the bulk value of 1.2K. Are there cases in which you expect the (still somewhat thin, ~200nm range) aluminium to go below 1.2K? Perhaps if it is strongly oxidized or something of the sort (I would expect it to go the other way then, but I am not sure..)

JingleBells

13:04

I'm reading a bit about conscription (cuz of the Ukraine war) and I read that as of 2022 most countries seem to have abolished or are in the process of abolishing conscription, so my question is, how can a country survive/deal with war if there's no conscription? - obviously with an army on voluntary basis, but what happens if that army "runs out"?

It seems to me that most countries have abolished conscription until they haven't

ACuriousMind

@Slereah given the amount of confused questions about rigid bodies in relativity we have, he's right at least in that case!

Slereah

It's pretty hard to even have a vague notion of rigidity

Because I don't think that in a general spacetime, you can have any notion of rigidity that holds up in general

Like obviously rigidity works out fine in some regime, but imagine a FRW metric with a very large scale factor

damn thing is gonna explode!

ACuriousMind

true

Slereah

I'm guessing maybe there's some notion of rigidity where you can compare the tidal forces versus the EM binding energy?

but that sounds complicated

Charlie

Hello sirs

JingleBells

13:11

@Charlie hello

Slereah

I am French @Charlie

JingleBells

I'm a sir yes

Slereah

We abolished the nobility here

We had a whole thing about it

ACuriousMind

@Charlie hey, how's it going?

JingleBells

Another thing, is it possible to make a microwave and a stove that spends only the energy necessary to heat the thing? Like if I put 3 bowls of soup in the microwave, I'm spending the same amount of energy as if I was to put 1 bowl, and most people put 1 bowl in there, kind of a waste of energy

Charlie

13:13

@JingleBells Most countries are not in a position to fight a war, organisations like NATO make it so that small countries don't have to worry about single-handedly fighting an invasion from a much larger one

I am very good thank you

Slereah

@ACuriousMind Here's a dumb question

Apparently in a projective geometry, there are transformations that do not preserve betweenness

JingleBells

@Charlie My small country Bulgaria is in NATO thankfully

Slereah

Does this translate to problems with that notion for a manifold with a projective structure, too?

ACuriousMind

@JingleBells uhh...where do you think the energy goes if not into heating the food?

JingleBells

@ACuriousMind into the air or the sides of the microwave box

wasted

ACuriousMind

13:15

air is a very poor microwave absorber

JingleBells

so in a microwave it bounces around until the food absorbs it?

ACuriousMind

and the sides are a Faraday cage that reflect the waves, mostly (that's why you get standing waves in the microwave)

JingleBells

what about the stove?

I can cook 4 pieces of meat or 1 piece of meat at the same "price"/energy

ACuriousMind

@Slereah I don't know anything about the kind of projective geometry you're doing, sorry

JingleBells

@ACuriousMind I just read that standing waves "cancel out" doesn't this mean that energy is wasted?

ACuriousMind

13:17

no

Slereah

Dagnabbit

ACuriousMind

(and I don't know what you mean by "cancel out"

Slereah

I think it's probably fine, at least locally, but it's hard to find out much about it

ACuriousMind

in any case, a microwave is very efficient in that almost all of the energy in the actual microwaves goes into heating the food

JingleBells

@ACuriousMind gotchya, I read it wrong about standing waves

ACuriousMind

13:18

the efficiency loss is in the "antenna", i.e. the conversion of AC power into the microwaves

Slereah

I think the issues with betweenness issues in projective space mostly pop up when you consider curves that go all the way to infinity since it turns them into circles

ACuriousMind

@JingleBells I...don't think you can

JingleBells

we need better stoves then

ACuriousMind

but it depends on the stove

Slereah

and that probably doesn't affect the manifold part too much I think

ACuriousMind

13:19

e.g. most electric stoves turn the heating element off when the plate has reached the desired temperature

Slereah

But I'm not sure

JingleBells

but heating 1 meat vs 5 meats still spends the same energy no?

ACuriousMind

why would it?

Slereah

Since projective structures are essentially affine structures but without parametrization

JingleBells

@ACuriousMind cuz it's the same energy to heat the pan

ACuriousMind

13:21

but more stuff to heat cools the pan down faster

so the stove needs to be on more of the time the more stuff is in the pan

JingleBells

isn't that "more" too small?

like the difference is not big

ACuriousMind

you don't spend energy to heat the pan and then the pan magically heats everything it touches to the same temperature

JingleBells

@ACuriousMind yeah I getchya

ACuriousMind

you spend energy to heat the pan and then keep it at that temperature while it transfers the heat to the food

JingleBells

so the solution to make it efficient if you heat 1 meat is to do this:

🧠

or wait, does the size of the pan matter significantly

ACuriousMind

13:23

sure, you should always use a pan/pot with the right size for what you're cooking

JingleBells

to keeping it at the desired temperature

ACuriousMind

heating a giant pot of water to cook a single noodle is wasteful

JingleBells

XD

gordon ramsay 2

damn it I thought I had a billion-dollar idea with the microwave and stove here

I thought I was gonna revolutionize the industry

sad

I HAVE ANOTHER ONE! Instead of using light bulbs to light up parts of the room that we don't look at, we wear lamp googles that light up only what we're looking at and the rest of the room is dark

ACuriousMind

just use LEDs

JingleBells

for the goggles?

ACuriousMind

13:27

no, instead of light bulbs!

JingleBells

but you can cut energy spent if you put the LEDs on goggles

cuz you only look at half of the room at a time (mostly)

ACuriousMind

apart from wearing light goggles looking really stupid, why would a directed light source use less energy?

a typical bulb or LED emits in all directions, it's actually more difficult to get it to only emit in a specific direction

JingleBells

damn it

ur right I forgot that light radiates outward always

let's invent an atom that can radiate it's photons in a specific direction

so my idea can work and I can revolutionize the lighting industry and people call me edison 2.

that is of course, if I'm not conscribed into a war until then

ACuriousMind

@JingleBells it's called a laser

and it has many wonderful applications, but "lighting up a room" is not among them

JingleBells

@ACuriousMind yeah but the light inside the laser still radiates outward and it guided with mirrors?

ACuriousMind

13:32

A laser is almost necessarily a mirror chamber, sure

but the beam that comes out is strongly focused

JingleBells

yeah but that means that I can't use it to light half the room with half the energy and the same intensity as a light bulb?

ACuriousMind

no, you can't magically light "half a room" :P

and again, LEDs draw so little power you're not really saving anything here

JingleBells

okay but we gotta invent an atom that can shoot photons in a specific direction so it doesn't radiate outward

we gotta do some science magic

no mirrors

@ACuriousMind sad, me no edison 2

Slereah

14:35

here is an idea

Ellipsoidal reflector spotlight

Ellipsoidal reflector spot (abbreviated to ERS, or colloquially ellipsoidal or ellipse) is the name for a type of stage lighting instrument, named for the ellipsoidal reflector used to collect and direct the light through a barrel that contains a lens or lens train. The optics of an ERS instrument are roughly similar to those of a 35 mm slide projector. There are many types of ERS that are designed for the myriad applications found in the entertainment industry. ERS instruments come in all shapes and sizes. Each particular model of ERS has its own set of characteristics. Generally, ERS instruments...

Parmeet Singh EP 066

15:36

@JingleBells Technically lasers use stimulated emission which sort of releases photons in a specific direction only. Like if I shine a photon on an atom with some excited photons, the electron will go to a lower levels producing a photon in same direction as the original photon

But I wanna say lasers are much costlier than LEDs

PM 2Ring

Thst reminds me of this old xkcd:

Spherical or parabolic reflectors would of course lead to aberrant behavior.

Hi, @ParmeetSingh. Welcome!

Does your Foucault pendulum program treat the planets as spherical, or as ellipsoids?

"Time hacker" Tom Van Baak has written a bunch of articles about precision pendulums. I don't think he's done a Foucault, but he has made pendulums that are precise enough to measure the difference in g due to the tidal forces of the Moon & Sun. You may enjoy some of his info: leapsecond.com/hsn2006

Also from Tom"s site: leapsecond.com/pages/atomic-bill Below is my brother-in-law, Bill, a professional construction contractor, proving that a HP 5071A Cesium Beam Primary Frequency Reference can in fact be used as a wrist watch.

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