The h Bar

tpg2114

1:34 AM

If anybody wants to apply physics knowledge to sports drama:

►

There's some... question... as to why his bike behaves the way it does when it's on the ground.

Kyle Kanos

Momentum conservation?

tpg2114

Momentum of what? The bike comes to a (seemingly) complete stop, and then rotates about the handlebars on the ground

Kyle Kanos

The front wheel looked like it was moving the whole time

tpg2114

So there's two theories floating around the internet. The first is that he has a motor hidden inside his bike (which the first accusation was against another rider in 2010, so it's not a new claim)

The second is that his rear wheel had enough momentum to spin the bike

The front wheel spins as the bike rotates, but it looks like it stops before he gets off it

alemi

I don't know, it seems to be a fairly steep grade they are on, to me it looks just like the heavier back of the bike starts swinging downhill while the higher friction tire makes the front of the bike behave like a pivot point

Kyle Kanos

1:39 AM

Maybe he vasoline'd his bike for air resistance or something

tpg2114

Haha

Kyle Kanos

Greasegate 2

Has it been asked over at skeptics?

tpg2114

I tend to side with @alemi I think, but it does look really odd

alemi

it does

tpg2114

No. I just saw the video on a facebook post

The stage was 4 days ago

Well, it may have been on Skeptics, I haven't looked

Kyle Kanos

1:41 AM

I don't go to Skeptics because I know it's a dangerous rabbit hole of looney bins

2

tpg2114

►

That's a video talking about 2010 when a rider was accused of "mechanical doping"

GBeau

why is LHC collision energy often written as $\sqrt{s}=8\, \text{TeV}$

particularly, what is the sqrt(s) for?

8 TeV just being an example energy

Kyle Kanos

@GBeau: Fairly certain that s is for the Mandelstam variables:

Mandelstam variables

In theoretical physics, the Mandelstam variables are numerical quantities that encode the energy, momentum, and angles of particles in a scattering process in a Lorentz-invariant fashion. They are used for scattering processes of two particles to two particles. The Mandelstam variables were first introduced by physicist Stanley Mandelstam in 1958. If the Minkowski Metric is chosen to be , the Mandelstam variables are then defined by Where p1 and p2 are the four-momenta of the incoming particles and p3 and p4 are the four-momenta of the outgoing particles, and we are using Planck units (c=1)....

If you look at center of momentum frames, you find that $E=\sqrt{s}$ (in units of $c=1$).

GBeau

@KyleKanos Thank you. I will read.

David Z

2:09 AM

@KyleKanos well the total energy of the two protons is $E$ or $\sqrt{s}$. Each one has only half that. So for example when $\sqrt{s} = 8\text{ TeV}$ each beam is $4\text{ TeV}$ per proton

Ice Boy

5:45 AM

@DavidZ I have an idea about why Einstein derived the energy formula in the form E = mc^2; could it be possible that he wanted it in the same form as the area of a circle formula?

GBeau

@IceBoy Einstein states his logic/reasoning relatively clearly fourmilab.ch/etexts/einstein/E_mc2/e_mc2.pdf

(in his own words ^)

Ice Boy

Not for reasons of Physics, but for popularity.

Thanks @GBeau

:-)

David Z

6:11 AM

@IceBoy just like GBeau said. E=mc^2 has nothing to do with circles.

Ice Boy

I realize that @DavidZ but what I'm saying is the forms are exactly the same? Could this have been done by design?

Thus adding more familiarity to the the most famous equation E = mc^2

David Z

7:08 AM

@IceBoy I think the paper @GBeau posted makes it fairly clear that it wasn't. Anyway xy^2 is a very common form, and the fact that any two equations both share that form, by itself, is fairly meaningless.

GBeau

@DavidZ High energy particle physics? Do you mind divulging what project/subfield you're working on?

I just joined an ATLAS monte carlo group at my uni as an undergrad

David Z

oh cool! I do phenomenology of proton-nucleus collisions

specifically making predictions related to gluon saturation

GBeau

by just I mean, literally days ago I got my CERN credentials

cool

Ice Boy

@DavidZ have you read The Quark and the Jaguar?

David Z

Nope, never heard of it

Ice Boy

7:14 AM

By Murray Gell-Mann

GBeau

@DavidZ the ATLAS group I joined is phenomenological as well

David Z

What does the group do?

GBeau

@DavidZ Identification of boosted W bosons, if I haven't murdered my phrasing

David Z

I think you're good, that makes sense :-)

GBeau

I am very much the learner in the field

David Z

7:20 AM

or wait, were you talking about boosted decision trees?

which are the new cool way to identify particles, so I hear

GBeau

I can link you one of recently published papers, I think it's on the public side of CERN's documents after publication: cds.cern.ch/record/1690048

(full text available as link at bottom, still seems to be available for me when not logged in)

some of the texts are only available internally

David Z

oh okay, that's not BDTs, never mind me :-P

Ice Boy

do you like any of Feynman's books?

GBeau

@DavidZ That's an example study, apparently all the 7 TeV variations are being repeated now that 8 TeV collision data is available

David Z

@GBeau makes sense... particle physicists are frequently cross-checking results every time a new data set comes out

otherwise there would be a lot of bored phenomenologists

Ice Boy

7:24 AM

Gell-Mann and Feynman worked together

I think Gell-Mann thought he was to cocky

David Z

@IceBoy textbooks or popular books? I've looked at some of his textbooks but not his popular writing

Ice Boy

His lectures are legendary at Caltech.

GBeau

@DavidZ Does Feynman have any texts beyond Feynman Lectures?

Ice Boy

:-)

David Z

@GBeau sure, he wrote a bunch of things, he's probably most famous for the lectures though

at least outside the physics community

GBeau

7:30 AM

I was about to say...

Ice Boy

Wow, they are available in audio now too :-)

Ice Boy

8:19 AM

here is some more info

Ice Boy

8:47 AM

itunes.apple.com/us/book/six-easy-pieces/id572144556?mt=13

Danu

9:00 AM

what I wanna know is whether Feynman ever lectured seriously on QED (at graduate level), and whether these have been recorded

2

dmckee

1:28 PM

Mod whinging: I've been processing the flag queue and it happened again.

Kyle Kanos

What happened again?

dmckee

Some user (not to be named to protect the guilty) has flagged a post as very low quality or not an answer and not downvoted it despite having a positive score.

Kyle Kanos

Wait, you can see who flags those things?

dmckee

I can understand not wanting to pile on. That would be pointlessly not nice, but if the post is bad enough to ask me to delete it, shouldn't it be downvoted too?

@KyleKanos Yeah.

Kyle Kanos

I am trying to think if I have ever done that

I probably have

dmckee

1:31 PM

And this particular user has a history of doing this. I suppose (s)he is just philosophically opposed to downvotes, but that is a position I just don't get.

Kyle Kanos

I think I withheld a lot of downvotes early on because I wanted the rep

2

dmckee

I wouldn't be surprised if I've done it one or twice, but the pattern bothers me.

Kyle Kanos

Then somewhere between 2k or 3k rep, I figured out that 1 upvote on my answers was worth 10 downvotes of someone else's answer

Well, maybe not "worth" but equivalent

2

dmckee

Also, if you are flagging for a moderator the post may get deleted and then you get your one point back, too.

Kyle Kanos

And those, sadly, do not show up on the top bar

dmckee

1:34 PM

The top bar notifications try to link to something, and until you have 10k there would be nothing for "You got a point back because something you downvoted was deleted" to link to.

Kyle Kanos

Yeah, it's kinda cool seeing the deleted stuff over on PPCG, I'll miss that when it gets out of Beta

alemi

2:00 PM

Is it just me, or has the new question quality gone down with the start of the academic year?

Kyle Kanos

It's the academic year

ACuriousMind

It's definitely the academic year, most of these questions seem to come directly from the first homework assignments they get

@Jim: I think they got it.

Kyle Kanos

2:16 PM

^ Hahaha

ACuriousMind

2:33 PM

Work from home theory...WTF?

Jim

@ACuriousMind not sure how that happened. Hilarious nonetheless

Kyle Kanos

3:21 PM

Well AGDQ2015 should be pretty epic

Jim

6:32 PM

any mods online?

Jim

7:14 PM

guess not

Kyle Kanos

You can try pinging them

Jim

too late now

Kyle Kanos

Oh

Well now you know for future cases

Jim

yup. whatever, I just wanted to tell them I was going to be up to something seemingly dubious. Didn't actually need them to do anything

Kyle Kanos

What dubious thing?

Jim

7:32 PM

serial flagging a new users posts. They were posting several non-answers in vaguely worded ways about 1 an hour. So I went through and flagged most of the ones I thought were clearly not answers. Left 2 or 3 alone

Danu

8:10 PM

@dmckee easily explained: They don't wanna lose their 1 reputation point!!!

Kyle Kanos

@Danu That's what I said

Danu

Oh, snap! I only just reached that part of the conversation! Well... now you get to be first ;)

Kyle Kanos

Hey, I was first yesterday too

:D

Danu

@KyleKanos Also, why this random comment haha

Kyle Kanos

Totally not random

I was looking through the list of approved games for AGDQ

Then when I saw the epicness of the list, I posted it

Danu

8:14 PM

Hahaha... right

What kind of games do you like to watch (on twitch?)?

Kyle Kanos

Actually, I've only recently started on twitch

Danu

I started out watching quite a lot of speedruns and stuff, but now I've found myself watching SC2 tournaments more and more lol

Kyle Kanos

I've watched a fair few of puwexil's FF$n$ runs

For $n\in[4,6,7,9]$

I like MGS1/2/3 games too

Danu

haha

Kyle Kanos

I've seen youtube videos of Cosmo's OoT runs

Danu

8:17 PM

Once you start watching stuff that is commentated by professionals it's hard to come back to the other stuff :P

Kyle Kanos

It is

Danu

that's what happened to me with LoL and now SC2

also idk... SC2 is just interesting

it's slightly similar to chess... maybe

Kyle Kanos

Never seen either

Danu

ah, the (daily?) SC2 competition just ended for today

More interestingly: chess24.com/en/watch/live-tournaments/sinquefieldCup2014/8/1/3

Kyle Kanos

My wife recently told me that she'd be okay with me playing games when I get a job

Danu

8:20 PM

Caruana is INSANELY good this tournament

Kyle Kanos

Totally going to start running FFT on my hacked Wii

Says my browser is too old

Danu

you into final fantasy that much?

Kyle Kanos

First game I really got into

Danu

It was the link to the live Sinquefield Cup going on in St. Louis right now

6 grandmasters from the top 10

and Caruana is 7 OUT OF 7!!!!!

Kyle Kanos

I played plenty of other games beforehand (Joe Montana Football, Mortal Kombat, Eternal Warriors, Sonic 1/2/3 and such)

But once I got my hand on FF7, I never stopped playing the series until I gave up gaming about 4 years ago

Danu

8:23 PM

hmm.. fair enough. I never had a PS

Kyle Kanos

I played MGS1/2/3, but those were over too quickly for me at that point

Danu

I've played FF XIII a bit at a friend's place though

Kyle Kanos

~3 hours compared to the 10+ hours necessary to beat the FF series games

Danu

what, 3?!
that's ridiculous

also, how do you beat FF games in 10 hours?!

do you not do anything optional? :P

Kyle Kanos

@Danu Exactly, skip everything that's optional + don't level grind

Danu

8:24 PM

pfft

how could you

Kyle Kanos

Utilize magic & armor to defeat bosses

Danu

I bet you don't enjoy the legend of zelda games then ;)

Kyle Kanos

I never really played them. They were on N64 & Gamecube consoles

Danu

yeah...

Kyle Kanos

Never had one. Went from Sega Genesis to PS1 to PS2

Danu

8:26 PM

I'm a nintendo fanboy to some extent

Kyle Kanos

Now I've got a Wii, but it's mostly for the kids to play

Danu

but I got really into shooters around age 14

and never stopped playing them till I quit gaming altogether at 18

thousands of hours

the high school boredom

Kyle Kanos

I did play CS2 at my Masters program

Even played on a semi-amateur league

Danu

heh

I mostly played CoD: MW1&2

pubstomping is just too much fun

Kyle Kanos

Actually, I never pubstomped

We had our own public server that we practiced in, but we split teams up so as to be more fair

We were a friendly group

Often times the mods would just dump everyone with $16k

Instead of the normal start-up funds of $1k

Danu

8:31 PM

I never had a team or anything like that

which probably also contributed to me never switching to CS

ACuriousMind

11:30 PM

@Danu Don't get me started on SC2 - I spent most of my A-levels and the first yer of studying with that :D

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