The h Bar

@Secret Yes. The book basically explains how the classification of the finite groups was done, and how the monster group was discovered in the process. It's a really good description of the process though I don't think it's suitable for readers with no knowledge of maths.

That applies to all four of the books I mentioned, but then anyone reading a popular book on maths is almost certainly interested enough to have learned a bit about it already.

Secret

Well, I might be up for it later, cause that division by zero project do caused me to read a lot of group theory for these 3 days. Thus I can say I am ok in group theory in knowing the tools needed to investigate groups and some major theorems

John Rennie

I thought it was a very interesting book. I'd always vaguely known about the classification of the simple groups, but the book explains exactly what was done and how.

It's basically Classification of the finite groups for non-non-nerds :-)

0celo7

Au contraire

Pop Sci is for Uber Nerds

user116211

5:25 PM

@JohnRennie non-non nerds means nerds.

Slereah

Pop sci is for people who want to pretend to be nerds

But don't want to do the work

0celo7

Flagging

Can we please keep the chat clean?

John Rennie

→ 1 message moved to Trash

A ~~moderator~~ room owner strikes!

0celo7

Do we have new mods yet

user116211

@0celo7 No.

user116211

5:28 PM

After two hrs.

Secret

It is good to know about the history of finite group classifications, as most groups have them as building blocks. A taste of that will help you understand where some of the groups used in physics are built

Secret

After a rather long hidas, new PSE question incoming. DavidZ might have good answers for it as it is his field:

0

Q: If microscopic dimensions were found in particle experiments. How do we determine whether it is spatial or temporal?

This is not a question asking why our universe is 1T+3D dimensional, and hence not about how the various models such as Itzhak Bars and F theory can incoporate multiple time into a model to describe our universe. It is about the interpretation hypothetical data that suggests of possible microscop...

David Z

@Slereah it's also for people who are curious about science and aren't educated in it

Slereah

yes, it is proper for children

0celo7

Honestly if you don't have a BS in STEM what are you doing?

Nothing because you're unemployed probably

user116211

5:33 PM

What does $i[A]$ imply where $i$ is an inclusion map and hence injection from $A$ to $\mathbb N\,?$

Sir Cumference

Howdy

user116211

$A\subseteq B$ where $B$ is a countable set.

Sir Cumference

@0celo7 Just wondering, remember when you told me that black holes lead to other universes, or something like that?

Secret

@MAFIA36790 Basically embedding $A$ into $\mathbb{N}$? Is $A$ finite?

user116211

@Secret yes.

user116211

5:38 PM

I've seen such notation in Kelley.

Secret

I suspect it might be treating the map $i$ like in function notation, I am not really sure. What is the result that pop out according to the book?

user116211

I don't know actually.

user116211

I think it's denoting range of the mapping.

0celo7

I know what it means.

John Rennie

@SirCumference they don't. Or at least probably not.

Sir Cumference

5:45 PM

@JohnRennie Trust me, you're preaching to the choir

John Rennie

It's possible to graft a de Sitter metric onto a Oppenheimer-Snyder metric to get an object that collapses then generates a new expanding universe, however there is no evidence that this is anything other than a mathematical trick.

Sir Cumference

Actually I was going to ask what solution he used

Oh wait

Mar 21 at 2:05, by 0celo7

you get the Kerr solution

Wait what

John Rennie

@SirCumference: the Reissner-Nordstrom, Kerr and Kerr-Newman geometries do link causally disconnected regions of spacetime, in effect separate universes, but these are idealised geometries that don't actually exist.

Sir Cumference

@JohnRennie Tell this to him

John Rennie

@SirCumference 0celo7 knows far more about GR than I do. I imagine what he said was perfectly true but possibly (deliberately? :-) misleading.

0celo7

5:51 PM

I don't claim what I said is physically valid.

Most of physics is probably not physically valid...

Sir Cumference

So we're back where we started

John Rennie

Aha, yes, I've checked the link you gave and 0celo7 is describing the causal structure of Kerr black holes.

Sir Cumference

Yeah, he said he was talking about the Kerr metric

John Rennie

If you're interested it's a fascinating area, though I'd start with the charged static black hole (Reissner-Nordstrom) as that's simpler and shows the same structure.

0celo7

So I was right?

John Rennie

5:56 PM

@0celo7 Yes

Though Kerr black holes don't exist of course.

0celo7

Proof?

Sir Cumference

@0celo7 They're useful approximations

John Rennie

@0celo7 the universe isn't infinitely old.

Sir Cumference

^

Wait, does the Kerr metric describe black holes as eternal?

Pretty sure it does

John Rennie

Yes. The Kerr metric is a stationary solution.

Sir Cumference

5:58 PM

Okay good

John Rennie

@SirCumference: if you're interested in a basic intro to this sort of thing I strongly recommend:

amazon.co.uk/Cosmic-Frontiers-General-Relativity/dp/0316483419

But it's out of print and really hard to find.

Sir Cumference

Doesn't seem very popular...

It's 40 years old

0celo7

@JohnRennie you're telling me they can't form in 6000 years?

Sir Cumference

@0celo7 Kerr black holes don't exist for some times and not others

John Rennie

It's the best semi-pop science book about GR I've ever read, and has a particularly good description of Penrose diagrams and the causal structures formed by black holes.

@0celo7 :-))))))))))))))))))))))

Sir Cumference

6:00 PM

Oh shoot

I missed the joke...

0celo7

Sorry, trolling the boy is too much fun

Sir Cumference

@0celo7 "Boy"

I think I'm a man by now

John Rennie

@SirCumference really? I'm 55 and haven't grown up yet :-)

Sir Cumference

@JohnRennie Still wouldn't refer to you as "boy" :P

@0celo7 This offends me. flags

0celo7

@SirCumference Lets not go there

Flag all you want

Sir Cumference

6:03 PM

@0celo7 Oh boy...

@0celo7 I'm kidding

0celo7

I believe in an open flag policy

John Rennie

@0celo7 not advice to be taken to heart!

Sir Cumference

@0celo7 "open flag policy"?

That just mean "flag all you want"?

0celo7

Since we don't know what could offend someone, we need to flag everything to be sure

Personally, everything is extremely offensive to me

Sir Cumference

I think we should limit the amount of flags per week.

John Rennie

6:05 PM

Anyway I have to go. There is beer to be drunk and an SF book to be read.

0celo7

Tfw you think someone is doing a bad impression of a stupid person but it's their real voice :/

Sir Cumference

@JohnRennie You read sci-fi?

Huh.

user116211

@JohnRennie o/

Sir Cumference

I feel lonely here.

The whole black hole thing 0celo was talking about started when I said I had never watched Star Wars.

John Rennie

@SirCumference I've been reading SF for (pauses to count on fingers) 44 years

0celo7

6:07 PM

@SirCumference just read Hawking and Ellis

Sir Cumference

Idk. To me, sci fi lacks the rush of learning things.

@0celo7 That's not sci-fi

Slereah

read some string theory then

John Rennie

@SirCumference it's for relaxation. You need to give your brain a rest sometimes.

Sir Cumference

@JohnRennie I suppose. But sometimes it's just fun to learn.

Like reading about astronomy.

0celo7

@Slereah :^)

user116211

6:09 PM

I watch The Flash in my off times. Earlier played Assassins Creed in off times too.

John Rennie

@SirCumference agreed. Spend some time learning and some time drinking beer and reading SF. Eating, sleeping and personal hygiene are optional extras.

Sir Cumference

@JohnRennie Those don't seem like extras...

I'd swap Sci-fi and drinking for eating and sleeping

Slereah

Hopefully Lumo won't read this

Secret

I must be a rare example where I don't relax when watching scifi then, well at least for time travel scifis

Sir Cumference

That's my life as of now

Secret

6:11 PM

My brain is steaming with things as I watch the time travel plot unfold

user116211

@Slereah Lumo is always angry and always ranting.

Sir Cumference

@JohnRennie Oh wait, you might not know

Slereah

Don't watch Terminator with @Secret

Sir Cumference

The drinking age in the U.S. is 21

user116211

In his off times, he writes his blog.

user116211

6:12 PM

Let me check his blog...

John Rennie

Enough already! I need to get back to:

amazon.co.uk/Last-Days-Jack-Sparks/dp/0356506851

user116211

Crackpot Joy Christian tried a childish trick to deceive Brian Greene's journal at Elsevier

user116211

The first visit to a post-Brexit Britain

user116211

Crackpot is Lumo's most favourite word.

Secret

[Monologue] How to deal with a false premise supported by a pet theory:

Slereah

6:17 PM

I'm sure Lumo would make the chat great again

user116211

@Slereah He would ban the chat.

user116211

Full of crackpots and psychopaths...

Slereah

Yes, that is what I said

Secret

1. Identify the false premise and decompose it into misinformation and components that derive from the pet theory.
2. Point out the misinformation

3. call those pet theory components Unicorns

The next step is to deal with unicorns:

John Rennie

The conversation is veering a bit to close to the personal. Either be nicer or wait until I've left the room :-)

Slereah

6:20 PM

Can you leave for a bit maybe

John Rennie

:: John disappears in a puff of smoke ::

David Z

I'm still here, y'know

0celo7

Not for long @DavidZ

user116211

@JohnRennie good night.

0celo7

the new mods will delete your account

mutiny time

Secret

6:21 PM

Actually, the above has nothing to do with the previous discussion. It is basically me sharing how I handle questions with false premise

Or is this still too sensitive?

user116211

@0celo7 Why?

user116211

@0celo7 They won't be commies.

David Z

→ 4 messages moved to Trash

Secret

ok, seems to be not about me, nvm then. Continue:

0celo7

@DavidZ Should we avoid mentioning him, period?

David Z

6:23 PM

@0celo7 That would be my suggestion

user116211

Okay.

user116211

He who shall be not named is erased from memory and thus forgotten.

Secret

Condition: Unicorns can be localised. I.e. the confusion raised by the question, is only due to unicorns, and nothing else

user116211

@Secret What are talking about? Unicorns? hmm.

Secret

^read previous posts

4. Assume unicorns exists
5. Use mainstream theory to predict the possible observations that can be result due to the presence of the unicorn

6. Compare predictions about the unicorns with experimental results
7. Point out that epxeriment result are contrary to that of the presence of the unicorns
8. Therefore, conclude that unicorns don't exist

9. since all unicorns are nonexistent, the question will be killed

concrete illustration of the unicorn question model will follow:

Please interrupt if it makes you uncomfortable

1. The question:

Oct 2 at 9:23, by user104372

@Secret, if we substitute unlikely doors that close faster than c, and people who see objetcs travelling at c, and use timegate timers that can accurately measure picosecond, don't we get same time for an observer Or at rest and one Ot on the train? What is the problem there, why do they need SR?

(Omitted series of conversations that involve clarification)

Oct 2 at 10:45, by Secret

Let's see...
Or made a measurement $t_{Or1}$ when the train head is right at the entrance of the tunnel, At the same time, Ot made a measurement $t_{Ot1}$. After the train head reached the end of the tunnel, Ot made a measurement $t_{Ot2}$, and at that same time, Or made the other measurement $t_{Or2}$. Now using $t_{Or2}-t_{Or1}$ and $t_{Ot2}-t_{Ot1}$, and multiply with the train's known velocity of $v$, one gets length of train $(t_{Ot2}-t_{Ot1})v=(t_{Or2}-t_{Or1})v=L$ where $L$ is the rest length of the train. Thus both Ot and Or agree on the train is of length $L$

Analyse the question, unicorn identified: Thus both Ot and Or agree on the train is of length $L$

Oct 2 at 10:53, by Secret

Ok I think I understood now: Here's the kicker that inform us something like SR is needed:

For the sake of argument, we assume that the measurements of 1 and 2 are indeed simutaneous. (Readers don't need to worry about me somehow breaking relativity here by allowing a basically superluminal signal here. One way we can assume is that momentarily, Or and Ot are comoving at the instant when they are doing the measurement)

Now experimentally, when they carry out experiments like these, what they found instead is that $(t_{Or2}-t_{Or1})v=(t_{Ot2}-t_{Ot1})v=L' < L$. That is, the measured length…

Assume unicorn is true: For the sake of argument, we assume that the measurements of 1 and 2 are indeed simutaneous.

Predict the dynamics of the unicorn: and at that same time, Or made the other measurement $t_{Or2}$. Now using $t_{Or2}-t_{Or1}$ and $t_{Ot2}-t_{Ot1}$, and multiply with the train's known velocity of $v$, one gets length of train $(t_{Ot2}-t_{Ot1})v=(t_{Or2}-t_{Or1})v=L$ where $L$ is the rest length of the train. Thus both Ot and Or agree on the train is of length $L$

Show that the dynamics of the unicorn is never observed: Now experimentally, when they carry out experiments like these, what they found instead is that $(t_{Or2}-t_{Or1})v=(t_{Ot2}-t_{Ot1})v=L' < L$. That is, the measured length is actually less than that rest length of the train (despite it is the same for the osbervers involved). This means, something else is weird going on, and we need a new framework to explain this. Hence relativity is necessary to explain the observed shortening of the
length measured compared to the rest length

Unicorn is actually complex:

Oct 2 at 11:01, by user104372

No, you are going astray, what you have to consider is the time recorded by B and F, not the time when they receive the message. That is the basic mistake. The clocks of Or and Ot bothe measure 0 when train hits B, then when both clocks measure 8mus,the cell F records time 8, Ot reads it immediately, Ot gets the message some times later, if depends on how the message it is sent, He can receive it after an hour, but the measurements still reads 8.

Identify remaining unicorns:

Oct 2 at 11:22, by Secret

no it's all good, both B and F are located at the tunnel, not one on the trian and one on the tunnel (But anyway, (even if we are not supposed to compare between two frames))Even in such a case of subtracting one reading from one frame with another reading from another, the length obstained is still shorter than the rest legnth)

Oct 2 at 11:28, by user104372

You lost me! you are taking for granted that there is some problem, where there is none. Timegates are at rest, but the receiver on the train is moving, it gets a signal from B,F and P. Ot on the trainknows that it took him 8 mus to cross the tunnel. Or gets same measurement.Where is the paradox? the problem?

Shwo that unicorns do not agree with experiment observations, thus unicorns do not exist

Oct 2 at 11:35, by Secret

If no relativity is needed, the mus measured must multply with the speed of the trian to recover the length of the train for Or, Ot and BF, but this is not what is experimentally observed

Oct 2 at 11:36, by Secret

which means if there is no relativity, the mus has to be some value k > 8 such that $kv=L$

however in some cases there can be lose ends due to technological limitation as there is lack of experiment to supply to disprove unicorns

Oct 2 at 12:14, by user104372

@Secret, "all the lengths get by Or and Ot (which agree because they both get 8 mus for train to pass tunnel) and B F (which agrees with Or) are all shorter than the rest length of the train," where do you get that from?

Oct 2 at 12:38, by Secret

Guys, I don't think our curent technology level anyone can answer that question by user104372, cause it appears that there are no direct experimental check for legnth contraction. We always inferred it from time dilation results (because in the framework of relativity both occur together). The muon experiment came close but still indirect because its measuring time of flight, not how much of the atmosphere the muon have zipped through

Bernard Meurer

6:40 PM

@ACuriousMind Are you there?

Secret

Therefore, I can converse with people who are skeptical about SR and GR provided that unicorns are localised, and hence can be isolated from the question

Bernard Meurer

I just found a metal album that uses a Sax instead of guitars and it's simply insane

Secret

Put the above stuff in a more comprehensible form:

Bernard Meurer

@EmilioPisanty Sup Doc ;)

Secret

Assume the false premise is true, and then derive a conclusion that contradict experiments. Therefore the false premise is indeed false as required

In the process, do not label the person as crank unless their unicorn is nonlocal

Unicorn is nonlocal=person still held on their pet theories despite contrary with experiments

if that occurs, ignore the person as no constructive conversations can result

Point is: We don't care what your theory is, if it contradict experiments, it is wrong