The h Bar

5:27 AM

Hats! :-)

3

Q: Work done while compressing an ideal gas (The physical significance of $\int dPdV$)

9:35 AM

morning

The Last Airbender

9:58 AM

2

Today in our chemistry class we derived the pressure-volume work done on an ideal gas. Our assumption was that $$P_{ext}=P_{int}+dP$$ so that all the time the system remains (approximately) in equilibrium with the surrounding and the process occurs very slowly (its a reversible process). Now $$W_...

@JohnRennie I understand why getting a measurement from experiment that is different from what is expected from a scientific law does not necessarily disprove the law.

I'm curious how the laws are tested experimentally to higher degrees of precision in general. And since laws are commonly expressed as mathematical equation with various variables, how do we repeat the experiments to cover as much possible values of the variables as possible? Is it impossible to test the law under all possible values for the variables (there would be infinitely many tests)?

It is impossible, yes.

There are infinitely many different physical models we can come up with to fit experimental data

To narrow it down we use a variety of heuristics

Which are, if not truthier, at least more practical to use

@yh05 in principle getting a measurement from experiment that is different from what is expected from a scientific law does disprove the law.

In practice we always worry that there might be some experimental error in our measurement.

10:14 AM

Well that's part of the whole bit of scientific law that nobody ever teaches in class

The ~correspondence rules~

Also the whole business of predictability and epistemology and all that nonsense

Unless we're lucky and we get a measurement that is blatantly different usually something gets disproved gradually by multiple measurements that disagree.

In practice we don't have enough informations about the initial conditions of our experiment, nor the means to compute it

We don't know the position and momentum of every particle in the universe

So we only get a degree of confidence

We just have a few informations on what we hope is relevent

But in real experiments, 1) we only have limited control and knowledge of the experimental setup (ie we can't prevent the temperature from varying somewhat) and 2) we don't necessarily know everything relevent to the measurements

A good example is that whole experimental error of the LHC

For a while at the LHC there was a weird measurement discrepency happening every day around the same time

Turned out that it was caused by a train passing nearby

Re your second question, there are usually key features of a theory and we test those first. If our experiments agree with the key features then experimenters may or may not test the more subtle predictions or they may lose interest.

There's also the whole LIGO business being disturbed by trucks a few miles away~

Hm

I can't find that train for the LHC business again

what was it

radioprotection.unblog.fr/2010/09/11/les-tgv-perturbent-le-cern

Ah there it is

This is probably the best thing to show if someone ever wonders why it's a good idea to wait a while before interpreting experimental results

10:34 AM

Where can I read about how scientific laws are tested?

Depends how you want to read about it

Scientific law

Scientific laws or laws of science are statements, based on repeated experiments or observations, that describe or predict a range of natural phenomena. The term law has diverse usage in many cases (approximate, accurate, broad, or narrow) across all fields of natural science (physics, chemistry, biology, geology, astronomy, etc.). Laws are developed from data and can be further developed through mathematics; in all cases they are directly or indirectly based on empirical evidence. It is generally understood that they implicitly reflect, though they do not explicitly assert, causal relationships...

I read it. I'm looking for a detailed description of how scientific law is tested.

which law?

10:50 AM

I don't really know any standard texts on the topic but look into epistemology and whatever else

It's a mix of rather abstract philosophy and practical concerns sort of deal rly

I can't find any relevant one with google search. =(

The ideal case is that you have an experimental setup. You input all the initial conditions that you are using for that experiment, your theory gives you what you should get in return. You perform the experiment, and the results from the experiment should match up with what you predicted.

this is rarely the case due to a variety of reasons

For instance :

1) Measurement errors : the way you measure both the initial conditions and the final ones is unlikely to be perfect, due to
1a) Systematic errors : Errors that always happen during the measurement (for a start, no measuring apparatus has infinite precision, the influence of the measuring apparatus on the value itself, etc)
1b) Random errors : Due to our lack of perfect knowledge, we can only get fairly broad measurements (ie : temperature) and this is likely to change in a random manner during the experiment

@yh05 have you seen this?

A somewhat common experimental error that I have heard about is

The scientist himself

I have heard of a few experiments in which the source of error was the scientist approaching the setup to read the results

because the scientist's body emitted heat, reflected light/sound/neutrons, etc

those are hard things to predict

11:18 AM

It is not possible to test a law under all possible values for the variables present in the law. How do we tackle this problem? Can I have a detailed explanation, please?

11:46 AM

@yh05 there isn't a single detailed explanation. It depends on what the law is. If you can come up with a specific example then we could discuss how it has been tested, but there isn't going to be an answer that applies to all laws.

Novalium Company

12:57 PM

omg

let's make an AI where it will decode what a person on a keyboard is typing by just recording the audio where it will have learned with first listening and looking at what the person is typing (supervised, labeled data)

#hacking

#bless

that's been done already

1:40 PM

@Slereah Then I would point out that a negative second derivative is not sufficient to lower the badness.

You can decrease the rate of rising of the badness

a president did come up with a new proof of the Pythagorean theorem

1:57 PM

also

"U.S. President Richard Nixon, when campaigning for a second term in office announced that the rate of increase of inflation was decreasing, which has been noted as "the first time a sitting president used the third derivative to advance his case for reelection.""

@Slereah I assume he didn't explicitly talk about "derivatives" and instead talked about them as rates of change.

@Slereah Right, but I would much rather the first derivative actually become negative

that was an explicit demo of a jerk using the jerk to advance his case for reelection...

Q: Ball hits curve of same curvature

63

I was doing some physics problems for homework and, while procrastinating, I came up with a theoretical scenario that I couldn't figure out the result of. The following is from a side view and in a frictionless, ideal environment: A ball moves toward a wall at a constant velocity. At the...

homework-and-exercises newtonian-mechanics forces classical-mechanics

come on, one more vote

@AaronStevens Saw it on HNQ the other day and made sure to cast mine.

2:04 PM

@JMac It is a great physics question. It's just the way it has been asked makes it off topic.

@AaronStevens Besides not showing any analysis, the diagrams uses comic sans. It deserves a custom close reason for that.

@skillpatrol Garfield's proof is ok, but it's not a major breakthrough. It's essentially an older proof cut in half. ;) But I will admit I thought it was cute when I first encountered it, several decades ago.

Paul Painlevé

Paul Painlevé (French: [pɔl pɛ̃ləve]; 5 December 1863 – 29 October 1933) was a French mathematician and statesman. He served twice as Prime Minister of the Third Republic: 12 September – 13 November 1917 and 17 April – 22 November 1925. His entry into politics came in 1906 after a professorship at the Sorbonne that began in 1892. His first term as prime minister lasted only nine weeks but dealt with weighty issues, such as the Russian Revolution, the American entry into the war, the failure of the Nivelle Offensive, quelling the French Army Mutinies and relations with the British. In the 1920s...

did you catch my Nixon comment?

11 mins ago, by Slereah

"U.S. President Richard Nixon, when campaigning for a second term in office announced that the rate of increase of inflation was decreasing, which has been noted as "the first time a sitting president used the third derivative to advance his case for reelection.""

7 mins ago, by skillpatrol

that was an explicit demo of a jerk using the jerk to advance his case for reelection...

@JMac On an unrelated note, two users were removed, and someone removed the accepted status on one of my answers, so I have lost 45 reputation points fairly quickly. I think I will make a meta post complaining that someone is out to get me

@skillpatrol Yes. I was trying to come up with a good pun involving the word checkers

2:09 PM

@skillpatrol Too bad Nixon was not talking about the third derivative of position

:D

:)

@AaronStevens That is definitely a government conspiracy. They are out to get you where it hurts - imaginary internet points.

@JMac I shouldn't expect fairness on a site that punishes critical thinking

@AaronStevens I think we need a banner on top of the site that reminds users that they will be punished for critical thinking. It would really clear up a lot of confusion.

2:12 PM

@AaronStevens Closed.

@PM2Ring Finally... haha

@JMac I have been raising custom flags on posts that use too much critical thinking. For some reason they keep getting declined though

RIP

@AaronStevens It's because the moderators and experienced users work together to make sure new users like yourself have a bad time.

@JMac No, they are threatened by my critical thinking and insight

et al

2:34 PM

@skillpatrol Facebook and youtube are the two key weapons in fighting the heliocentric enthusiasts who poison our children's minds with things like "outer space" and "science".

indeed

3:18 PM

@JMac imho, youtube has more positive applications for the heliocentrics than facebook

@skillpatrol Youtube has a lot of anti-flat Earth stuff. I'm sure FB has some; but the format doesn't work the same.

yeah, and twitter is just plain "fake news"

yuvraj singh

@PM2Ring, hi sir.

I gone through the same experience again but this time a different one.

@yuvrajsingh Haven't there been issues of pinging users before?

3:35 PM

let's not be overly "critical" here :P

let's

's

$\mathbb{R}^n$ has an irreducible representation of $O(n)$

Hi may I ask a question about physics here?

But how many reducible representations does it have

Is it also one

3:39 PM

@Koray yes, of course

The representation with $n$ trivial groups

Thank you :) I hope this question makes sense. According to Einstein's equivalence principle, which one has an acceleration: an object free falling to a non-atmosphere planet, or an object staying still on the surface of the planet?

The first one travels along a geodesic while the second does not

@Koray you have to define what you mean by acceleration, and you have to do it in an observer independent way i.e. a way that all observers can agree on.

The second one is the only one that has an invariant definition of acceleration

(it's the acceleration produced by the electrostatic interaction with the earth)

3:41 PM

I'm talking about the same acceleration mentioned in the twin-paradox

@Koray typically we use the proper acceleration as this is a well defined quantity that all observers can agree on.

@Koray the twin paradox isn't really about acceleration.

I'm asking this to understand, if the travelling twin turn using gravitational pull, would there be a difference.

@JohnRennie It kinda is

If you're interested in understanding the twin paradox I wrote an answer on the main site specifically to explain exactly what causes the twin paradox (it isn't really a paradox of course).

Sir I've seen your answer and I is great. But I could not able to understand it. I'll try harder. Thank you very much..

It is great I mean :)

3:44 PM

@Koray it doesn't matter whether the travelling twin turns round by using a rocket or by slingshoting round a massive object.

Sir thank you very much again, I really appreciate it. Have a good day :)

user8718165

Hello :) @JohnRennie

@user8718165 hi :-)

yuvraj singh

@AaronStevens didn't, t get you in what context u are referring.

@yuvrajsingh You had trouble with dacoits again?

yuvraj singh

3:59 PM

@PM2Ring not completely.

Now I am OK, I thought to share with you.

Physics Meta

4:19 PM

0

Q: On Winter Bash 2019 page

Winter Bash is on! I am very excited about hats though I don't own one yet :-( I was just hanging around clicking on random cards on the Winter Bash page when I came across this after I clicked on the "Where in the World" card. Shouldn't it be hats instead of has? I mean is that really a ty...

discussion bug

Abstraction (computer science)

4:44 PM

In software engineering and computer science, abstraction is: the process of removing physical, spatial, or temporal details or attributes in the study of objects or systems in order to focus attention on details of higher importance, it is also very similar in nature to the process of generalization; the creation of abstract concept-objects which are created by mirroring common features or attributes from various non-abstract objects or systems of study — the result of the process of abstraction.Abstraction, in general, is a fundamental concept to computer science and software development. The...

For a universe to be simulatable, it is actually demanding something very strict:

It is saying that every thing can be reduced into instructions that can be combined in a well defined manner

@Secret Pls, I hate that, This was a chapter in our OOP C++ class. I almost got bored This is only usefull if you are more towards abstraction kind of programming.

perhaps, he is :-)

well, considering that I just spent the last whole week reading and going through the JDK 8 section on classes, I think that is where I am heading

@Secret :)

In fact, my whole way of comprehending this world relies on something very similar to that

4:48 PM

@Secret You must have a deep understanding of Assembly to know it's real purpose.

^

The reason why I can talk about highly subjective things like the impression of some given art had on me or other people, or a mystical experience, or can classify up to 50 different kinds of nothingness is because they are reproducible enough that I can treat them as data types

even though there is no way to speak of an ineffable, they can be identified when they are experienced again

and that is more than enough to use them as data

because many ineffable, are actually quite specific in how they behave

As for assembly language, well I once touch on that back in my high school, but I don't think I really knew the details of it including how each keyword is converted into a binary string

@Secret very ezy

5:02 PM

@Secret Sure, if anything requires uncomputable numbers you aren't going to simulate it with a system that can only produce computable numbers. The simulation hypothesis is fun to think about, but IMHO it's a bit silly. Why would anyone waste vast amounts of computing power simulating a world as large & as detailed as this one appears to be... unless they're cheating, and it doesn't really contain as much information as it appears to.

user8718165

@PhysicsMeta I deleted this from here and posted it on the Main Meta site.

well, what I am hypothesising is that if our universe is really a simulation, it is build on a very strange programming language that already contain any level of infinities, and so unless for inconsistency reasons that are imposed by some kind of incompleteness theorem, what we think are uncomputable numbers are actually computed relatively straightforward in that alien programming language. Thus the philosophically interesting thing bout the simulation hypothesis, IMO, is it makes you

think about what really makes programming and computation, programming and computation

So unlike most people, the reason I am interested in simulation hypothesis is not because of existential stuff about creators, but because it makes me think really hard on the question: What really is a programmable thing

5:29 PM

thinking really hard is hard work

6:16 PM

@PM2Ring The issue is that I think it would be very hard for us to try to understand the motivations of anything capable of simulating our universe. Although it may seem incomprehensible to us to put that amount of effort into a simulation, we also don't really have any idea how whatever creates the simulation would even perceive it. Maybe we're a side effect of a 5-D toaster.

6:27 PM

You are So Mean @Aaron — Saikat Das 54 mins ago

Lol

Kyle Kanos

simulation hypothesis is probably bogus. there's troubles enough with It peeps these days working on a single computer, but tying an ever-increasing network of billions of minds together without a single hiccup?

though i'm sure SH advocates would chalk it up to "well it's a really advanced computer"

i believe there also issues with deterministic evolution of systems