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20:00
@ACuriousMind dw not a father
Whom did you knock up? :P
@djsmiley2k : gravity is a force. Search the Einstein digital papers for gravitational force. And be a little cautious about what you hear from celebrity physicists.
hmmmmmmmm
@NoahP you lied, @0celo7 is a cat!
newtonian phsyics
20:01
@yuggib I don't think he's allowed to use nets ;)
doesn't that also say there's an equal and opposite reaction to everything, including forces?
@JohnDuffield FYI these guys followed me over from SU.se, don't listen to them
@yuggib I don't know what a net is
@NoahP my thing about gravity being call a force is a genuine issue I have
@NoahP Why not? I listen to you too, after all :P
20:02
@ACuriousMind Ouch :P
I just fear I'm going to look stupid to you guys :/
@ACuriousMind ur mum
@ACuriousMind I think the crucial difference is that I didn't introduce myself with the line 'meow'
@0celo7 Impossible, she's past her menopause :P
Clearly, one should do the...
20:03
@0celo7 to prove the statement for hausdorff spaces is either nets or filters or extremely tedious checks with the definition of continuity etc
Bajoran
@NoahP I'm undecided whether that is a pro or a con.
@yuggib I'm doing the extremely tedious thing
Am I being ignored now?
@0celo7 I agree, someone should do me, but what has that to do with anything?
20:03
Good luck, I don't want to be involved with it ;-P
@JohnDuffield Is there something specific you're referring to there
@djsmiley2k Didn't I show you that we already have your very question on the main site?
So, assume $g,h:\bar A\to Y$ are extensions that disagree on $x\in \bar A-A$. Then $g(x)\ne h(x)$ and they can be separated by disjoint $U,V$ in $Y$.
Did you read the answers there?
@ACuriousMind and then @JohnDuffield told me the opposite is true
20:04
Then pull these back to $g^{-1}U$ and $h^{-1}V$
So can someone explain this:
@djsmiley2k Yeah, that's kinda his schtick.
DID SOMEONE SAY POTATO?
@djsmiley2k : yes. Einstein referred to gravity as a force, so you shouldn't get hung up on "gravity is not a force".
20:05
Being wrong? or just telling people the opposite of something to see what happens?
@JohnDuffield Ah ok I see
@0celo7 I'm not sure is gonna be easy without filters
Dog
Dog
Potatocat
is there anything special about there being 4 fundamental forces?
@djsmiley2k Let's say that JohnDuffield holds unorthodox views that are not shared by many on this SE
@ACuriousMind hah ok I hear you
20:06
But I don't want to think about it, I will take a shower and then read nonstandard analysis
@yuggib It's a homework problem in Munkres, it cannot be that hard.
You've met our funtime friend from SU - @Dog, who's a cat
@djsmiley2k Nope, could've been 42 fundamental forces for all we know
@djsmiley2k : I refer to Einstein. When it comes to gravity, my views aren't unorthodox.
@BernardMeurer potato potato
20:06
@0celo7 maybe not hard, but I fear it is tedious
@BernardMeurer spud
@JohnDuffield Did anyone ask him the same question? Maybe he's doing the same as the teachers...
probably, but I don't see what to do next
WAIT
Dog
Dog
I am the spud commander. I command you to spud.
20:07
@djsmiley2k, @Dog I think I've found my twin
why is the chat being invaded?
I actually want to learn, so I might stick around and not learn anything but feel cleverer
I blame @NoahP. Apparently, he let the Dog out.
@NoahP walked into our dungeon over in SuperUser
I'm just going to start ignoring people and monologue on topology
20:08
Aka RA (Root Access)
Hey! so we can finally get better Internet in Africa!. Thx SpaceX and FB. Smoke signals are getting tedious. Bugger it blew up
What makes me sad is I don't feel like I actually know any/much more physics than I did when I left school :/;
@0celo7 lol, are you upset that your monologues are interrupted by people talking to each other? :P
and that was 14 years ago
@0celo7 is that the morphing of spacetime by a gravitational body?
20:09
no, that phenomenon is called your fat momma
@0celo7 Be nice :P
mmm ouch
Yo momma so fat no force works upon her.
well, ur mom
20:09
@ACuriousMind Oh heck not this again
@Dog, @djsmiley2k I think I've found my twin (@0celo7)
The "great attractor" in the middle maybe? :/
lolyeah ok.
"WAIT" every other 5 min
yo momma so fat the galaxy rotates around her?
20:10
@djsmiley2k wrong, gravity affects everything
@ACuriousMind I've learnt my lesson
@0celo7 yah, but it's not a force ;)
@ACuriousMind let's change avatars
I'm feeling a nice strong Belethor
SE caching is trash
@0celo7 No, Kreia hasn't yet reached the end of her service
20:11
Wait what, EM drive is real?
but I thought it didn't make sense D:
For certain values of "real"....are you referring to the rumor that one paper on it has passed peer review? Wait till its published and people have responded to it before declaring anything
I remember reading it shouldn't work, but some how creates some force.....
that's all :D
I feel dumb :*(
If it is "real" physics will make less sense
I could cross oceans by blowing on my sails
/me thinks
@yuggib I have the solution.
20:14
you can't, right?
CALL ME POINCARE
i feel dumb.
I know you can't, but I can't think why it's impossible
because your blowing pushes you backwards...
@djsmiley2k : if somebody tells you something about gravity, try to check it out against the Einstein digital papers, And be wary of anybody who tries to deter you by saying "that's unorthodox" or even Einstein was a crackpot.
@0celo7 you have a weird taste for old and uneffective methods...
20:15
@JohnDuffield I came up with the 'why is it called a force' thing myself
:/
@SpaceOtter oh right yeah
@yuggib I don't know what a net is (for real this time). How am I supposed to use them on my homework?
equal and opposite...
Anyways, if you have it good for you ;-)
So could someone explain this?: youtube.com/watch?v=_BgJEXQkjNQ
some one forgot to turn the gravity off
20:16
@djsmiley2k : and the reason it's called a force is this : when you drop your pencil, it falls down.
@0celo7 well then it is not a smart exercise (in my opinion)
Anyways, type it up ;-)
@JohnDuffield but that's because spacetime is curved towards the earth in the locality of my pencil
:/
@yuggib doing that right now.
it's not because some magic hand has come out of the sky and pushed the pencil to the floor
Dog
Dog
@varfirstName Looks like my KSP launch
But really isn't that better suited for space.se than physics.se?
20:17
Not a magic hand. It was the cat
Dog
Dog
I'm pretty sure they regularly watch/discuss SpaceX launches over in space.se
@varfirstName : oh, that's bad. Sigh. Rockets.
I apologise for 'letting the dogs out', I'm off now though. Amusing as some of this is...
@djsmiley2k : no it isn't.
0
Q: speed of the color red

Crystal SmalleyTaking aside all of the other variables that can alter the color's speed; i.e. sound, mass, water, magnetism. And just focusing on the color itself, how fast does the color red travel, using the means of optical glass?

wouldnt that be light speed?
20:20
oO
@JohnDuffield it's not?
@yuggib Whoops, I take it back.
but I'm close
@varfirstName Sure, but light speed is not constant across the spectrum in materials, that's called dispersion and is how a prism works.
It's still a rather bad question because the answer is looking up the dispersive properties of optical glass
It's a homework question
@ACuiousMind The colour red has variable mass that affects it's speed? oO
20:23
@SpaceOtter I didn't say it has variable mass
3 x 10^8 m/s.
I just said that the speed of light varies in materials
@djsmiley2k nope
No he did "other variables that can alter the color's speed; i.e. sound, mass,"
nope nope :(
mass of what D:
20:24
ikr
if there was a very heavy body near by (i.e. blackhole)
Dog
Dog
your face!
suddenly that light is going a lot slower?
yes!
relatively, yes
time becomes faster based off of gravity
right?
Oooop baby is awakening
20:25
But $c$ is the same... relativity
@SpaceOtter not necessarily
@SpaceOtter In general relativity, the "speed of light" becomes a tricky thing to define. It's "locally constant", but one can define measures of speed that are not always $c$.
But if you're next to a black whole then you're no longer in an Inertial frame.
c is the maximum
right? so it does change?
20:27
How about we learn GR properly
@djsmiley2k : no. Look at the rubber-sheet pictures. Note that the force of gravity is strongest where the rubber sheet is most tilted. Your pencil falls down because "spacetime is tilted" towards the earth in the locality of your pencil. Saying "spacetime is tilted" isn't my favourite way of describing it, but it's better than what you said.
Let's start with some definitions, ok?
Good plan!
20:27
this gonna be fun
General relativity
General Relativity
Let's first make clear what spacetime is
I don't even have an intuitive sense of SR yet. Or does that never come?
20:28
@SpaceOtter the only thing I don't understand about SR is that rotation thing
when you're actually at high speed, you don't see length contraction
you see some weird rotation
Terrell rotation
Dog
Dog
@SpaceOtter It came to me in a dream wikipedia article
We never experience anything like time dilation every day so do we ever get an intuitive sense?
XD XD
Spacetime is basically something that's locally flat
We call this a manifold
You get a manifold by gluing together many such flat pieces
And the dimension of the manifold is the dimension of each flat piece
I was hoping it would just jump in after reading

David Tong's (Cambridge DAMTP) lecture notes on dynamics and special relativity
20:30
Spacetime is a 4-dimensional manifold
I thought so
x, y, z, and t, right?
@SpaceOtter : you want to check that on the Einstein digital papers:
"Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields. As a simple geometric consideration shows, the curvature of light rays occurs only in spaces where the speed of light is spatially variable".
And I'm reading that for bedtime tonight so it will hopefully jump in in a ~dream~
Now, ACM would define a spacetime manifold as a 4-dimensional locally Euclidean second countable Hausdorff space with $C^\infty$ transition functions and equipped with a rank 2 smooth symmetric nondegenerate index 1 tensor field.
but let's not do that
Thanks to captain Einstein(@JohnDuffield) we dont need your rambling @0celo7
20:32
lots of typos lol
He answered for us in 1 quote. Take my hat off to that!
Now, let's define curvature
There's a few ways to do this
@0celo7 You know me so well <3
Dog
Dog
I like curved buttocks
@SpaceOtter : I'm afraid 0celo7 said Einstein was a crackpot. See this.
20:33
Wow
@Dog You'll have to go to Mathematica for that:
255
Q: How do I draw a pair of buttocks?

Simpleton JackI'm trying to develop a function which 3D plot would have a buttocks like shape. Several days of searching the web and a dozen my of own attempts to solve the issue have brought nothing but two pitiful formulas below. They have some resemblance to the shape I want, though not quite. Could you...

hmm, I never did figure out what the distributional Levi-Civita connection is.
THAT HAS 255 UPVOTES XD
@JohnDuffield Do you have an intuitive sense of R? It hasn't hit me yet
20:35
@ACuriousMind It's probably not true that all neighborhoods of a point must intersect in more than two points, right
Is that R for relativity? I like to think I understand it.
consider discrete spaces?
Dog
Dog
385
A: How do I draw a pair of buttocks?

mikuszefskiI have to confess that I see this as a proper challenge, as I am usually quite creative in finding/combining functions to provide a desired behavior. So I will give it another try. which is generated using box[x_, x1_, x2_, a_, b_] := Tanh[a (x - x1)] + Tanh[-b (x - x2)]; ex[z_, z0_, s_] := E...

This has more
@JohnDuffield Einstein is a crackpot.
Was.
They made a simpsons function. I'm sure it's possible. Oh ^there you go
20:38
@0celo7 : er, no, Einstein wasn't a crackpot.
Sure he was.
He said crazy things like the speed of light is variable
Yes R for relativity. Ya I understand SR and understand all the maths and Lorentz factor ect. But I'm not sure i'll get a feel for things like time dilation ect
Even his "BIGEST BLUNDER EVER MADE" turned out to be useful @0celo7
@yuggib I think I have it lol
are you still here
Yep
Got it.
::furiously types::
20:40
ive read the hawking books
dialation is cool
I find that somewhat hard to believe :/
@SpaceOtter : time dilation is really easy. Have a look at stuff like this. There's less to it than meets the eye.
Which ones. Briefer History of Time?
@JohnDuffield Thanks. I read the community wiki's I think I'll get it once I think through the Twin Paradox
@yuggib Feast your eyes.
20:43
@SpaceOtter : that's easy too. It's just a form of perspective. When we're separated by distance you look smaller than me and I look smaller than you. When we're separated by relative motion your time looks slower than mine and my time looks slower than yours.
Fixed a typo.
@SpaceOtter the origina;l
and universe in a nutshell
So which one comes back younger? Oo
which ever one didnt stay still ;)
That's what snags me. But I'll read through it tomorow
20:45
where 'still' is the reference point your timing thrm from
@djsmiley2k : the one who "really" moved is the one who felt the acceleration.
@0celo7 not bad
In the end it was not so tedious as well
@JohnDuffield but each one is 'fast' as viewed by the other
@djsmiley2k Who's still? If I'm floating away from you real fast. You're also floating away from me real fast...
the one who is older is the one who was closer to the gravity source D:
20:46
and @JohnD
/me tries to remember
28
Q: How is the classical twin paradox resolved?

vonjdI read a lot about the classical twin paradox recently. What confuses me is that some authors claim that it can be resolved within SRT, others say that you need GRT. Now, what is true (and why)?

@yuggib yerp
^here's our canonical post for the twin paradox
I googled it before and didn't get anything good
20:47
@djsmiley2k : the one who "really" moved is the one who felt the acceleration.
So I did it myself
Quite pleased.
Most questions you can think of have already been asked on the site, you just need to find them
@ACuriousMind "Most"
More like
Set of measure zero
So there can be no answer in a thought experiment where you start with relative speed and don't accelerate
20:48
@SpaceOtter If no one accelerates, they never "meet"
So what is the question you want an answer to?
@SpaceOtter then they'd both age at the same speed
@ACuriousMind Can one show $X$ Hausdorff iff $\Delta$ Hausdorff w/o using a homeomorphism?
All: I recommend that you be a little wary of "canonical" posts.
@0celo7 what?
@ACuriousMind I'm not sure what's unclear.
20:49
Why do you want to avoid a homeomorphism?
Because I just realized that exercise is given in the book before homeomorphisms are introduced and shown to preserve Hausdorffness :(
And so each observe that the other ones time is slower until one accelerates and they meet
Sigh...
they*
ok cool Thanks folks
@SpaceOtter hit the up arrow
you can edit posts
20:50
@0celo7 Also, you mean "$\Delta$ closed" there, no?
@ACuriousMind ...
holy fuck
I was doing the wrong problem
Thanks
OK I have to go. The Electron is calling. Bye all.
welp, back to the drawing board.
Bye @Jhond Night erryone
20:52
@ACuriousMind Oh god how do I do this
...aren't homeomorphisms closed maps?
and $X$ is closed in itself
where does Hasudorffness come in
oh no that would be closed in the subspace topology
I hate topology so much
@ACuriousMind Omg I'm so stupid, what does open mean??
closed means the complement is open, but idk what open means
@0celo7 It doesn't mean "not closed" :)
my thought is to project $U$ and $V$ down onto $X$ to get separating sets
which makes $X$ Hausdorff
but those sets can intersect in general
so they're not separating
...or can those sets intersect
dun-dun DUUUUN
I postulate they cannot
well
of course they can
that's stupid
21:44
@ACuriousMind you know what is worse than topology
 
1 hour later…
22:56
@0celo7 I'm guessing it's probability :P
@ACuriousMind halp
Are you a bicycle enthusiast?
not at all
It's physical exercise after all :P
Dangit
I need an European that knows about bikes
Do you know anyone?
@Danu Are you a cyclist? (if yes, see above)
I'll buy you a beer
22:59
@ACuriousMind yes

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