The h Bar

user54412

3:15 AM

Leonids meteor shower tonight

Undo

5:12 AM

Lol, I think I might have DDoS'd the Phys mods :P

Crazy Buddy

6:01 AM

@DavidZ has bunched most of the ~~science~~ physics comics into his blog post...

ellipsix.net/blog/2013/11/science-comics.html

(I'm still wondering why he mentioned science and not physics, because it's mostly wholly physics) :P

So, @DavidZ: Will you update your post in the future, as more comics rush in?

(that should be somewhat tough) :P

Anonymous

9:14 AM

@CrazyBuddy 318 can just be found through the wayback machine .

Anonymous

web.archive.org/web/20121020061340/http://abstrusegoose.com/318

Crazy Buddy

@DIMension10 Great :)

@DavidZ: ^^^ (update for your post) ;-)

Arc676

9:48 AM

quantumdiaries.org/2012/03/04/… Somewhere in the middle of the page is a comical image of W bosons eating the Higgs, but whats the difference between H^0 and h?

ManishEarth

10:45 AM

@Arc676 I guess h is the Higgs particle, and the other three are massless fluctuations in the field that permeate space. In other words, in the mexican hat, h is the up-down oscillation and the other three are the oscillations where it is stuck in the well. I guess.

Arc676

So whats the difference of adding the ^0, and in my diagrams should I write h, H^0, H+, or H-?

ShuklaSannidhya

I'm stuck with that Bernoulli thing... I got the answer using @Pranav 's method... I don't understand why my method is wrong...

ManishEarth

@Arc676 I think everyone use H^0 to mean the massive Higgs in diagrams

Arc676

ok

ManishEarth

Nobody seems to call the massless Goldstone ones as "particles"

Arc676

11:21 AM

ok

ManishEarth

David or Logan would know more about this though

Arc676

neither of which are online right now

ShuklaSannidhya

11:44 AM

0

Q: Problem with Velocity of efflux

I am stuck in this problem- I need to find the velocity of efflux at the hole of the container. [We can assume that the area of the hole is negligible in comparison with the base area of the container]. Here's my approach Velocity of liquid at the upper-surface = $v_2$ Velocity of efflux (v...

So I finally posted it...

Jack M

12:02 PM

is anyone available to talk about basic newtonian mechanics?

ShuklaSannidhya

@JackM yeah...

Jack M

I need someone to explain to me what the empirical content of Newton's laws is

I've tried asking on the main site before, but I think a back-and-forth chat setting will work better

ShuklaSannidhya

What exactly do you mean by empirical content?

Jack M

well if somebody told me "the sky is blue", I know what the sky is, and I know what blue means, so I know what that sentence is saying about the world

I can imagine how to world would differ depending on whether the statement were true or false, and I can even come up with an experiment to test it

but in, say, "a body not subject to a force does not change its state of motion", because "force" hasn't been defined, I have no idea how to interpret that statement

what is it actually saying about the physical world?

ShuklaSannidhya

Then I guess, you must begin with definition of force.

ManishEarth

12:09 PM

@JackM Newton's laws define force.

Jack M

@ManishEarth so basically we define the phrase "X is experiencing a force" to mean "X is accelerating" ?

ManishEarth

@JackM No, X is experiencing a change in momentum

a force is anything that can induce a change in momentum

Jack M

okay, so how do we define momentum?

ManishEarth

@JackM The mass of a body times the velocity, if you want to stay within the newtonian paradigm

ShuklaSannidhya

oh wait, what is the difference between X is accelerating and X is experiencing a change in momentum ?

Jack M

12:12 PM

okay, and mass?

ManishEarth

@ShuklaSannidhya Because if a moving body loses mass, there still is a change in momentum even if velocity doesn't change

ShuklaSannidhya

oh yeah.

ManishEarth

@JackM Ah, so that, in Newtonian mech, is a fundamental quantity

If we're making mathematical statements about the real world, we have to have some links.

Crazy Buddy

/going out of scope - I visualize force like this: Say the force is 600N, that's roughly how much a 60 kg "thing" would weigh in Earth (because we're much familiar with everyday objects like ball, laptop, cars, trucks, etc... :)

Jack M

surely you can't just say "mass is fundamental"

you at least have to know how to measure it

ManishEarth

12:14 PM

Because mathematics, in itself, says nothing about the real world.

We can measure mass. So?

Crazy Buddy

@JackM We have a spring balance to measure it (where we need that kinda definition of force)... o_O

ShuklaSannidhya

oh wait, but if the body loses mass it's velocity will increase so there will be acceleration too... [conservation of momentum]

ManishEarth

@ShuklaSannidhya not if there's a force, no

Crazy Buddy

@ShuklaSannidhya Yep -- Rocket :)

ManishEarth

@ShuklaSannidhya We can tweak the force so that it stays constant v

Jack M

12:16 PM

@ManishEarth wait, how can you measure mass?

ManishEarth

@JackM See, when we try to measure mass, we need to define force again. It gets circular

@JackM Beam balance.

Jack M

so you pick a unit mass, and define mass as how far down an object pushes the scales when compared to the unit mass?

something like that?

Crazy Buddy

yeah...

ManishEarth

@JackM yes.

Jack M

it seems very strange that we would define something fundamental like "mass" in terms of the way an object affects a very specific machine when used in a very specific way...

I guess what bothers me is that there's other weighing devices you could invent, and it's not clear you would assign the same mass to all objects using different measuring devices

ManishEarth

12:19 PM

@JackM We don't define mass that way, though

We specify a way to measure mass that way

Jack M

well then what is the definition of mass?

ManishEarth

Mass, distance, and time, are defined as fundamental quantities.

You're right, there really isn't a definition

ShuklaSannidhya

Mass

In physics, mass (from Greek "barley cake, lump [of dough]") is a property of a physical system or body, giving rise to the phenomena of the body's resistance to being accelerated by a force and the strength of its mutual gravitational attraction with other bodies. Instruments such as mass balances or scales use those phenomena to measure mass. The SI unit of mass is the kilogram (kg). For everyday objects and energies well-described by Newtonian physics, mass has also been said to represent an amount of matter, but this view breaks down, for example, at very high speeds or for subat...

ManishEarth

@ShuklaSannidhya that invokes "force"

ShuklaSannidhya

hmm...

infinite recursion...

ManishEarth

12:21 PM

@JackM However, why does there need to be a definiton?

Jack M

so if there isn't a definition, we have to take the way to measure it as the definition

ManishEarth

@JackM No, why do we need a definition?

Jack M

@ManishEarth JackM's first law of motion: the smorgadorg of any object remains constant

3

ManishEarth

Sure.

Jack M

if I don't define smorgadorg, nobody can tell what I'm saying about the world

ManishEarth

12:22 PM

@JackM Here's a more deeper question: What really is a "point"? Or a "line"?

ShuklaSannidhya

@JackM >Smorgadorg of an object is defined as its property which remains constant.

ManishEarth

We can actually ascribe different meanings to those two and get new, consistent, geometries

ShuklaSannidhya

@ManishEarth Point is an entity which has no spatial dimensions

maybe?

Jack M

I agree there's no precise definition for point and line

ShuklaSannidhya

and line has one.

ManishEarth

12:23 PM

@ShuklaSannidhya saywha spatial dimension?

Crazy Buddy

sigh... We're always abstract !!!

Jack M

but everyone has an intuitive sense for what they are, and I would say that the intuitive sense is strong enough to be able to get some proper work done (surveying, for instance)

ManishEarth

@JackM Same thing here. You build up a mathematical framework from some fundamental quantities and axioms. Then you draw parallels with the real world.

One way of consistently real-world-ifying mass is the beam balance

Jack M

but for "mass" we have no such intuitive sense, it's completely undefined (at least to me)

ShuklaSannidhya

@ManishEarth I mean if we have to measure the length, width and height of a point, they'll all be zero.

and for a line everything but length will be zero.

ManishEarth

12:25 PM

@JackM What about distance or time?

@ShuklaSannidhya define length

We're talking about the basics of geometry here, half the stuff isn't defined yet

ShuklaSannidhya

err... the distance between two points... [don't ask for the definition of distance or point]

ManishEarth

@ShuklaSannidhya We can actually prove that the line is the shortest path between two points using variational calculus

@JackM Note that we are still in the Newtonian paradigm. More modern physics tries to reduce the number of fundamental things.

ShuklaSannidhya

haha... If we can't define mass... then we cant define anything - force, energy, power, torque, smorgadorgaroo...

ManishEarth

@ShuklaSannidhya we can define them in terms of mass and usually that's enough

Jack M

@ManishEarth again, I think we have an acceptably precise notion of distance and time

I can tell when two distances are equal

ManishEarth

12:31 PM

@JackM Really?

Jack M

I can choose a unit length and put it end to end to measure out a longer distance

ManishEarth

@JackM And I can tell when two masses are equal.

Jack M

I just want to say that I'm really not just being pedantic or abstract for the sake of it

I genuinely have no idea what newton's laws are saying about the world

ManishEarth

I know :)

Jack M

the fact that I happen to also be a math major is a complete coincidence

ShuklaSannidhya

12:34 PM

@JackM define time.

I find time even more incomprehensible than mass.

Jack M

well, I can use memory to roughly compare two intervals of time

as long as they're short

and if I have a physical device which carries out some physical process

I can repeat that process and verify that it seems, based on my sense of the passage of time, to take about the same amount of time to do it each time

ShuklaSannidhya

that's comparison... what is the definition?

Crazy Buddy

@ManishEarth If you know, then tell us..!!! Why are you maintaining privacy? :P

Jack M

then I can leap to the conclusion that that process always takes exactly the same amount of time

based on empirical evidence

and define that as a unit of time

ManishEarth

@JackM I can use my hands to roughly compare two masses.

ShuklaSannidhya

12:36 PM

@JackM great. But that still is not the definition.

Jack M

are you trying to say that any physical quantity needs to be defined by appeal to an arbitrary measuring device?

ShuklaSannidhya

OBTW, are you guys paying attention to New feed item on your screen at the top?

Jack M

like how I need some sort of clock to define time

ShuklaSannidhya

Not always, there are many simple definitions of time and mass
Mass - Mass is a measure of the quantity of a substance.
Time - Time is that dimension of the universe in which events occur in sequence.

Jack M

@ShuklaSannidhya your definition of "mass" sounds like volume to me

ManishEarth

12:41 PM

@JackM a measure, not all measures

@JackM volume can be compressed. Mass cannot

Of course, we can apply the same arguments to mass :P

ShuklaSannidhya

@JackM Volume is the space occupied by an object.

don't ask me what is space...

ManishEarth

hah

Jack M

okay

ShuklaSannidhya

41 mins ago, by Jack M

is anyone available to talk about basic newtonian mechanics?

I was expecting pendulums and collision and other fun stuff...

:(

Jack M

I meant more basic than that :)

ManishEarth

12:45 PM

@ShuklaSannidhya hahaha

ShuklaSannidhya

Now shifting this discussion to computer science, what is data or information? How do you measure it?

What exactly is meant by size of file?

ManishEarth

@ShuklaSannidhya A file is basically some information. You encode that info in a finite number of bits; basically as a number in base 2 of finite length.

ShuklaSannidhya

@ManishEarth Aight, I won't annoy you by asking you the definition of information.

HAPPY DEFINITION DAY TO ALL

Jack M

so what's with the name of this chatroom?

ManishEarth

@JackM $\hbar$ (ℏ) is the reduced planck's constant

Pronounced "h bar"

People hang out in the room, so it's kinda like a bar... so .. yeah :P

ShuklaSannidhya

12:57 PM

@JackM $\hbar = \frac{h}{2\pi}$

@ManishEarth How did you type ℏ in plain text?

Alt + code?

ManishEarth

@ShuklaSannidhya copied it from the rendered mathjax :P

ShuklaSannidhya

:|

not funny.

Jack M

is there really no way to just put chatjax straight into this webpage?

ShuklaSannidhya

nevermind

Crazy Buddy

@JackM Because chat.SE is network-wide (I guess) ...

ShuklaSannidhya

1:02 PM

@CrazyBuddy What's wrong with having chatjax network wide? We can't do anything without math, can we?

Jack M

it could be a little checkbox in the admin options for any given chatroom

ManishEarth

@ShuklaSannidhya Load.

Crazy Buddy

@ShuklaSannidhya Nothing's wrong... But, what's the point of introducing it for the sake of 3 or 4 sites? Though chat rooms are made for everyone to speak about anything, they aren't the place to discuss formulas and stuff (at least, based on our usage :P) We barely speak about equations and stuff...

Like Manish said, we hangout here :D

ShuklaSannidhya

@ManishEarth yeah... and that chatJax bookmark ain't that bad. You should pin to the starboard.

(removed)

ManishEarth

@ShuklaSannidhya won't work

ShuklaSannidhya

1:07 PM

aargh.

Jack M

it's really only a problem for new users

if someone completely new comes in needing a hand, it's sometimes more trouble than it's worth teaching them how to grab the bookmarklet and use it