The h Bar

dmckee

01:44

@GeorgeSmyridis If you want to go the physics route and maintain a high level of industrial employability, go experimental materials, condensed matter or optics. Do not be sucked in by the siren song of theory. Even computation is risky though it at least will give you a secondary set of salable skills.

Also do not---under any circumstances---be sucked in by particle- or astro-physics in any form.

Love my particle physics degree. Loved my post-doctoral work. Would probably have made a pretty good industry R&D guy but had a really hard time getting my foot in the door and my colleagues report similar things.

And if you are wondering I ended up professing at a very small state U with no money, equipment, lab space, time off or assistants for research.

But at least like the teaching gig.

alarge

01:58

@dmckee Are the experimental materials not quite concentrated in certain parts of the world (say, fabs)? And not only that, if you know how to do one experimental technique, sometimes they are (or seem to me) so highly specialized that it can be difficult to switch to something of more interest to industry. I have seen a lot of my friends who had chemistry majors (experimentalists) have problems getting employed. This could of course be country-specific.

Kyle Kanos

02:22

@dmckee I disagree. With observatories like LSST coming up soon, in addition to the already-existing set of observatories, data analysis is pretty big in the astro groups (just have to find the right advisor, of course). This would go a long ways to industry jobs in data science

dmckee

02:33

@KyleKanos It should, but it is hard to get a foot in the door. My big contribution to two of my projects was analysis coding. I'm a pretty decent coder with some "big picture" understanding and a lot of experience in distributed cooperative development.

The best programming job I was able to get interviews for payed about what i got as a graduate assistant.

Kyle Kanos

Getting the foot in the door in industry always amounts to one thing: knowing someone there first

dmckee

@KyleKanos Uhm. Evidently I don't know the right people.

Kyle Kanos

I'm running into the same trouble :(

dmckee

I did eventually find some good advice on tuning my resume for industry and was starting to get nibbles when my current job dropped in my lap.

Big firms almost all have a idiot computer program look at your documents first and they can circular file them if they don't get enough key-word matches.

So you phrase everything in industry terms in hopes that it will actually get to a hiring manager who can bring human intelligence to the job.

alarge

@dmckee Well it is always a risk for a company to hire someone who may or may not want to stay long term, so naturally they'd prefer someone who has shown interest (through part-time jobs, internships, whatever), which of course add to the difficulty.

@dmckee True to a certain extent. Often for PhD level jobs you might want to go through a recruiter, though, who will probably get your CV read by the guys actually making hiring decisions. A poorly written CV or a less than excellent fit will get a quick rejection, though.

dmckee

02:40

I've talked to a grand total of one (count her) recruiters who professed any interest or experience placing physicists.

Mind you, she did find me a back up gig: writing safety procedure documents for nuclear power plant operations.

Calls for a Ph.D. and practical experience with operations in radioactive environments and sounded like it was even more boring than patent clerking.

I did some safe procedures documents while I was postdoccing. It's detailed oriented and mind-numbing.

alarge

@dmckee Well I remember dropping my CV to one of those online job sites (not submitting it to any particular job at that time, but making it visible to people hiring), and had recruiters calling me the very next day.

In the end, I did not get my job through a recruiter. I did apply through them to one, and was rejected by the company out right (without invitation to interview) because my background was not mathematical enough for them.

I was quite surprised by the reason, but at least they did have a look.

DanielSank

Hey, python users this is useful.

skill patrol

06:27

Congrats @ManishEarth on your science mod positions :-)

ManishEarth

thanks

Gaurav

06:44

@ManishEarth Congratulations Manish !

@ChrisWhite Do you wear a Spock wig ?

skill patrol

07:33

That was a wig? :P

paul23

10:35

wondering once again if my question should go here or on math.se

David Z

@paul23 what's the question?

paul23

0

Q: Hyper/parabolic kepler orbits and "mean anomaly"

In an elliptical kepler orbit there is an easy recipe to describe the motion/position of a satellite at time $t$. One just follows the following steps - an important detail for me is that the numerical part has always the same error, the error doesn't increase with time, nor is it based on the ti...

David Z

seems like physics

@ChrisWhite some unsolicited (and probably not even that useful) advice: if and when you do make the decision to leave academia, don't waste any time doing so

George Smyridis

13:07

@dmckee @alarge @ChrisWhite @KyleKanos @ACuriousMind So are there any advantages as far as job prospects are concerned to become a physicist than an engineer? They all get similar jobs anyway :/

Kyle Kanos

13:18

@skillpatrol Why? We were all involved in a conversation yesterday (last night for some), so he's trying to continue it

skill patrol

sorry, didn't know that :(

Kyle Kanos

@GeorgeSmyridis I honestly don't know what the advantages/disadvantages would be, as I've got a physics degree.

@skillpatrol Scroll upwards, part of the conversation is at the top of the page :shrug:

0celo7

13:49

@GeorgeSmyridis Depends what engineering. Some disciplines require proper licensing.

In America, we have the Professional Engineering exam, which you cannot take unless you have a degree in engineering IIRC.

David Z

14:10

Chat session coming up in a couple hours... I can actually be at this one! (yay)

Kyle Kanos

Yay!

Kyle Kanos

15:00

I'm kinda surprised that this even needed to be asked:

15

Q: Why are Rocket engines at the base of the rocket?

I don't know much about Rockets, but all that I have seen, from the Saturn V to SpaceX's Falcon 9 have the engine at the bottom. Doesn't this make the Rocket really unstable, like balancing a pencil on your finger and trying to lift it up? Why do we not pump the exhaust gases up to the top of the...

engines

0celo7

I would be in the chat session but I got kicked out of my cubicle

What time?

ACuriousMind

@0celo7 A little less than a hour

Also, 1. You had a cubicle? 2. You got kicked out?

paul23

@KyleKanos Those answers are really bullocks lol

highly upvoted bullshit

0celo7

@ACuriousMind 1. Yeah, so? 2. More senior interns are despotic rulers.

Jims Bond

15:20

Ahhh, finally back after vacation. How is my favourite physics chat room?

0celo7

Deskless

Jims Bond

Also, @0celo7, I'm not sure what game that was, but it sounded like D&D. Why do you think I know anything about it?

Gaurav

@GeorgeSmyridis Perhaps you misconceive that someone with a BE cannot pursue a research career.

0celo7

@JimsBond Huh?

Jims Bond

Jun 25 at 1:12, by 0celo7

@ACuriousMind @ChrisWhite @JimsBond Is there any special reason why the Steel Mace is doing crazy amounts of damage? It's 34 (at lvl 1) vs. ~25 for a steel longsword and when I spawned Daedric weapons using the console, they're doing a lot less damage.

0celo7

15:21

It was probably Skyrim.

Yeah, Skyrim.

Jims Bond

Ah, didn't play that either

But I see why you thought I did

0celo7

I just referenced the PC gamers who were in chat at the time.

Kyle Kanos

Console > PC

Gaurav

^^^^^^Asychronous communication protocol.

Jims Bond

@KyleKanos Defense?

0celo7

15:23

With consoles there is no fuss.

Jims Bond

PC has better graphics

Kyle Kanos

@JimsBond Every NES, SNES, Genesis, N64 and PSX game in existence

Jims Bond

@KyleKanos all available on PC

0celo7

Modding ruins blood pressure. Freaking mod conflicts and load order.

@JimsBond Nope.

Kyle Kanos

@JimsBond (a) not true (AFAIK), (b) they don't play as they do on console

The emulators do not actually replicate the system identically, just emulate it for playability

Jims Bond

15:25

I have emulators for all of them, never found a problem in finding games or playing them

0celo7

How is that not illegal?

Jims Bond

Thankfully, you don't know my real name

Kyle Kanos

@JimsBond Uh, it's Jims Bond, duh!?

0celo7

You're Bond, Jims Bond.

Gaurav

I think the FBI can easily identify The Jim.

Jims Bond

15:27

The thing about being a super famous secret agent is that everyone knows who you are. It's not a secret anymore

Kyle Kanos

Well, technically, James Bond isn't a spy, but an ornithologist

Jims Bond

@0celo7 The emulator isn't illegal to own. It's illegal to make, but not own. And you can use it legally if it's for mounted games that you actually bought and own

0celo7

@KyleKanos Why no GCN and Wii in that list?

Kyle Kanos

@JimsBond It's illegal to make an emulator? I thought it was just illegal to DL the ROMs

0celo7

How can you DL ROMs legally? It's stolen property.

Jims Bond

15:30

@KyleKanos It's illegal to make unless you purchase the rights from the console developer

Kyle Kanos

@0celo7 Because classic VGS > next-gen VGS

@0celo7 For cartridges, you need special connections. For discs, you can just rip it to ISO

That is, special connections to connect it to the computer to take the data

Jims Bond

and ripping discs to iso for your own personal use is legal

Kyle Kanos

^Even for making personal-use copies, AFAIK

0celo7

You said you had no trouble finding them, not buying and ripping.

I'm asking how finding is legal.

Jims Bond

@0celo7 It's legally ambiguous

Kyle Kanos

15:32

@0celo7 How is doing a Google search illegal?

0celo7

@KyleKanos You know what I mean.

Jims Bond

and if after that search, my computer "accidentally" downloads it.....

Kyle Kanos

Just download the internet & you'll have it

Gaurav

I think identifying PC rips is more difficult than console ones, ain't it ?

Jims Bond

PC games have lots of DLC and bonus content for those that get updates and have legit accounts. They know how to incentivize people to buy the game and make money in the event that people pirate it anyway

Besides, at < $1/h of entertainment, who needs to pirate VGs?

0celo7

15:38

Poor college and high school students.

Gaurav

@JimaBond Console games don't have that ?

Incentives?

0celo7

@KyleKanos that's a shit DL speed, no wonder

Gaurav

I always used to download the demo versions of games that I couldn't get full on the Sony store for my PSP. That'd leave me drooling for the full version. How less an incentive is that ?

paul23

15:54

?

0celo7

?

David Z

?

Kyle Kanos

?

Hippalectryon

¿

Terry Bollinger

?

ACuriousMind

15:56

!

Terry Bollinger

%

Hippalectryon

（ノ♯｀△´）ノ~’┻━┻

Terry Bollinger

!!!

Kyle Kanos

ᕦ(° Д°)ᕤ

Hippalectryon

⌨ █▬▬◟(`ﮧ´ ◟ )

Terry Bollinger

15:58

}8^)>

0celo7

You people are insane.

Hippalectryon

(((φ(◎ロ◎;)φ)))

Terry Bollinger

:)

Chat time!

Hippalectryon

Adventure time ! oh wait no that's something else

David Z

欢迎你们！我们来聊聊天儿。

oh wait

bold makes it official

:-P so, yes, chat session time! Welcome all. Who's here?

(who hasn't been posting silly symbols)

0celo7

16:03

I'm half here

Terry Bollinger

(all of us posting silly symbols now feel sheepish...)

Hippalectryon

Wake up sheeple !

David Z

@TerryBollinger 哈哈，没关系 :-P

(haha, no problem)

0celo7

The Chinese are invading

Terry Bollinger

@Bosoneando, nice name and symbol there.

Kyle Kanos

16:04

@DavidZ I just googled that to figure out what it meant

And 0.5 seconds later I pop back to see you giving the answer already

Terry Bollinger

Argh, I'm behind before starting!

David Z

reminds me of a funny story my friend was telling about Chinese speech and laughter, but I can't really do it justice in chat

Anyway, anyone have something to talk about today?

Terry Bollinger

Hey, anyone read Garrett Lisi's new paper, released yesterday?

David Z

No, can you post a link?

Terry Bollinger

arxiv.org/abs/1506.08073

ACuriousMind

16:07

Great abstract.

David Z

True

Terry Bollinger

Also, here's his Google+ announcement:

plus.google.com/+GarrettLisi8/posts/VfedFtk1scA

@ACuriousMind It really is already one of my all-time favorite abstracts...

Interesting how he deals with GR...

A very, very different approach from string theory.

String theory assumes spaces as a given, as a medium for vibration; Lisi instead tries to break space itself down into more fundamental parts (is my very early reading).

OK, has everyone now read and digested the 42 pages?... :)

John Rennie

On a different topic, I keep think we really need a definitive Q/A on "what is time dilation"

I keep seeing questions about time dilation that can't be answered because the OP has completely the wrong idea about it.

Terry Bollinger

@JohnRennie Really? I did not realize it was controversial?

paul23

@JohnRennie is it like in stargate?

John Rennie

16:15

@TerryBollinger It's not controversial for anyone who understands differential geometry

Terry Bollinger

@paul23 Bad, spank!

John Rennie

But the vast majority of questions have no real idea what time dilation is or how it works.

Terry Bollinger

@JohnRennie If a canonical answer could make differential geometry conceptually accessible even to early math types... hmm.

John Rennie

I have started drafting a canonical Q/A several times, but I've yet to find a really clear way of explaining it

Terry Bollinger

@JohnRennie Have you posted any of that in any current answers (or elsewhere)?

John Rennie

16:17

I've attempted lots of answers relating to time dilation, but none that give a really compete picture

ACuriousMind

@TerryBollinger Not sure you are comparing the right things here. When I look at the actions he writes down, they seem to reproduce the ordinary SM and gravity actions (which he says explicitly at the end). But it is known that the action for gravity is not quantizable in a renormalizable way, so this paper does not seem to tackle the question of constructing a quantum theory of gravity, while string theory does.

Terry Bollinger

@ACuriousMind I... think I agree with you? I've been looking so far just at the group stuff, not really the GR parts. But yes, it does not take a quantum gravity tact at all, does it?

John Rennie

On another different topic, I've just noticed my daily rep on the SciFi SE is greater than on the Physics SE. That's a first.

David Z

@JohnRennie for what it's worth, I always figured that as an indicator of someone who shouldn't be asking about time dilation here. Not that I would be opposed to having a canonical Q&A if you want to do it.

paul23

Does it influence sattelites/rockets?

ACuriousMind

16:20

@JohnRennie What is the main conceptual issue you'd wish to explain? I have the impression that the issue is not that people can't find explanations of time dilation, it's that they cling to some of their classical (or unphyiscal) preconceptions when interpreting these explanations, and then get horribly confused.

Terry Bollinger

@JohnRennie I keep wanting to look for such a model, but also keep not having time. I think it's a great goal, and I suspect it is doable.

paul23

yes - make a Q&A, no - > boring no need

Terry Bollinger

@JohnRennie I've never even looked there, didn't know it existed.

John Rennie

@ACuriousMind the elapsed time is the proper length of the trajectory, which is different from the coordinate time of a different observer

But whenever I've tried to write the definitive Q/A I keep getting bogged down in explaining how proper time is calculated

I've yet to find really good, succinct, clear way to explain it

@TerryBollinger quite a few of us physics heads are on the SciFi SE. dmckee has quite a high rep there.

4

Q: Does the Juice of Sapho do anything other than stain?

Mentat Masters regularly consume the Juice of Sapho, causing their lips to stain. According to the Dune Wiki, Sapho, or more commonly the Juice of Sapho, was a high-energy liquid extracted from the barrier roots of the planet Ecaz. It was used by Mentats who claim that it amplifies the me...

dune frank-herbert brian-herbert

David Z

@JohnRennie I might suggest a picture

Terry Bollinger

16:27

@JohnRennie I'm tempted to talk about a paper I'm writing on what seems to be an overlooked invariant when slicing space time... no, not yet. SR is even cooler and stronger than it might seem from geometry alone.

Kyle Kanos

@JohnRennie Perhaps then the best case would be write a canonical Q&A about calculating proper time and one on time dilation?

John Rennie

@DavidZ drive.google.com/…

That was the sort of description I was trying to write

David Z

it's giving me "access denied"

John Rennie

@KyleKanos worth a try. The thing is that it isn't obvious why you're rambling on about proper time unless it's in the context of time dilation.

David Z

not that it matters, really - I don't have any specific ideas of what would make a good picture

but I usually find that things which are hard to explain with words are a lot easier with pictures

Terry Bollinger

16:29

@JohnRennie I'll look up the sci fi group

Kyle Kanos

@JohnRennie Well circular references are totally fine by me :)

John Rennie

@DavidZ Try now ...

David Z

it works

Terry Bollinger

@JohnRennie that reminds me of an animated figure that used to be on Wikipedia, but I could not find it in a quick look.

John Rennie

@DavidZ the diagram was going to start with the Pythagorean expression for ds, then explain that in SR we use the Minkowski metric instead. But I struggle to explain this clearly.

Terry Bollinger

16:34

Hmph, looks like they removed it...

David Z

@TerryBollinger I think I may know the one you mean, but I can't find it either

@JohnRennie huh, yeah, well like I said I don't have any groundbreaking ideas

It's not exactly easy to visualize the Minkowski metric in a way that clearly shows its differences from the Euclidean metric

@TerryBollinger :-(

Terry Bollinger

@DavidZ It does feel like roughly the right direction, though I wonder if a bit of creative slicing of the block universe might convey some of the issues too...

John Rennie

Actually I started by trying to write the definitive article on the twin paradox, but realised I needed to explain time dilation to do it. Hence the attempt to write an article on time dilation.

Terry Bollinger

@JohnRennie I dove in deeply to some of the twin paradox descriptions once, and too many of them are sloppy or flat-out wrong. A good description needs to bridge Minkowski and Euclidean, and as you noted that is just not easy to do in a clear, understandable figure.

John Rennie

The point about the twin paradox is that the stay-at-home twin calculates proper time using the Minkowski metric while the travelling twin uses the Rindler metric for all or part of the trip.

But I find myself embarrassingly unable to calculate geodesics in the Rindler metric.

Although I discovered something surprising along the way ...

4

Q: Trajectories in Rindler space with zero net time dilation

I've discovered a family of curves in Rindler space that have zero net time dilation. However I struggle to see why this should be so, i.e. what the physical significance of these curves is. My question is can anyone give an intuitive explanation for why these curves have zero net time dilation? ...

special-relativity differential-geometry

Terry Bollinger

16:41

@JohnRennie One observation: Any diagram really needs to push hard on the idea of true interchangeability of space and time. I don't think that gets conveyed well enough usually.

David Z

interesting...

Terry Bollinger

@JohnRennie Reading...

Whoa, that's interesting. Will look at it after chat, though; you don't ask trivial questions!

John Rennie

@TerryBollinger If it was trivial I could have answered it myself :-)

I suspect there is absolutely no physical significance to my discovery and the zero time dilation is accidental. It was a surprising result though.

This assumes of course that my numerical calculation was correct ...

Terry Bollinger

Hey, a small observation, tangential: For any isolated system of mass particles, there always exists a "fastest time" frame that includes the center of mass of the system. Yes?

John Rennie

@TerryBollinger Err, maybe. I'm not sure what you're getting at.

Terry Bollinger

16:50

@JohnRennie Pretty much just that: More specifically, if you create a system of particles from a single point in space time, let it expand and get very complicated over time, but eventually require that it all merge back together into a single point again, then the greatest time consumed will always be the particle that never moves away from the start.

Not profound at all, just interesting if you scale it up across larger systems

0celo7

Still chat session time?

David Z

Yeah, technically it lasts an hour

Not enforced, though

(whatever that would mean...)

@TerryBollinger it's because the longest proper time comes in an inertial frame, right?

Terry Bollinger

@DavidZ chat hour police, that's an interesting concept...

David Z

haha

Terry Bollinger

@DavidZ Sure. Again, not profound, just interesting if applied hierarchically.

Alas all, I must leave a bit early today. @JohnRennie, interesting stuff and a cool question, thanks for sharing so much.

David Z

16:56

We might be winding down anyway

John Rennie

I have to be going too.

Bye all.

David Z

see you!

0celo7

Looks like I killed the session.

David Z

nah, blame the uncertainty principle

not the Heisenberg one, but the one that says all measurements come with an uncertainty of 10% or so

0celo7

10% on 5 or so inches can make all the difference

paul23

16:59

Pff I just read a topic: "I discovered by look at glibc (gcc libary) that the sine of small numbers is the number itself". - Good job missing a major step in your mathematical education..

oh and this is from a quite well "respected" source even.

David Z

Saying 'what kind of an idiot doesn't know about the Yellowstone supervolcano' is so much more boring than telling someone about the Yellowstone supervolcano for the first time.

2

Jims Bond

xkcd? what's that?

Terry Bollinger

@0celo7 Hey look, I even came back!

@JimsBond one of the coolest and most science-savvy online comics. You should check it out.

David Z

17:14

ok, bedtime... see y'all later

0celo7

@TerryBollinger Was a joke

Jims Bond

^ that

0celo7

@TerryBollinger referencing the comic

It's not possible to be in academia and this chat and not know xkcd

Unless you have me and ACM blocked, then maybe.

Jims Bond

And if I had you blocked, you'd never know it because I'd answer back randomly as if you were there anyway

because, ACM, magnets can be used for anything

0celo7

@JimsBond You'd just randomly @ me and say random stuff? Insidious.

Jims Bond

17:20

@0celo7 No, I haven't played that game either

0celo7

@JimsBond No one likes Candians anyway; maple syrup is shit; the Queen is a freeloader.

Terry Bollinger

@JohnRennie I should finish the thought: For a system of mass point that all originated in a single frame, but has never 're-converged to that frame, do there exist a frame-defined set of mass particles for which elapsed time will always be higher than for any other mass particles?

The answer is of course yes: It will be the set of particles that have remained in the initial inertial frame for the entire time since divergence.

Now while it gets more complicated for something like the Big Bang, the same question can also be applied by scaling upwards to the entire universe.

Jims Bond

@0celo7 That's okay, we'll figure something out, eh?

0celo7

@JimsBond How can you reference posts if you blocked me? Busted.

Terry Bollinger

Which leads to an interesting postulate: Do there exist stars in the universe that have the potential always to demonstrate morealpsed time if you travel to them?

Jims Bond

17:32

@0celo7 I assume you've just try to call me out on not blocking you. It didn't work. I just assume you say something, hit reply on the most recent post, then change the number to something appropriate. Works every time

0celo7

@JimsBond oO freaking diabolical genius.

Jims Bond

@0celo7 Because that's the way it works

Terry Bollinger

The likely answer is yes. More specifically, they would consist of stars that have remained close to the CMB frame since the original of the universe.

0celo7

@TerryBollinger test

You ~~liar~~ holy shit

Jims Bond

@0celo7 That number wasn't in this chat room

Terry Bollinger

17:35

Hi folks... What the neck is going on?

0celo7

@TerryBollinger nothing, move along

Terry Bollinger

:)

0celo7

Imperial business, move along citizen.

+10 for game name

Jims Bond

Jimperial business

0celo7

1/10

Terry Bollinger

17:36

These are not the droids you are looking for...

ACuriousMind

There are droids here?

0celo7

Does anyone else smell bratwurst?

Jims Bond

Yes, but only because I'm right behind you

0celo7

Creep

Terry Bollinger

ERROR XDG5368 Excessive unresolved external references, shutting down now...

Jims Bond

17:40

you looked

0celo7

How did you get through Senate security

@JimsBond Wrong!

Kyle Kanos

I think keeping your rep at a nice multiple of 5 is reason for some to avoid downvoting — Jims Bond 15 mins ago

There is that too

Jims Bond

@KyleKanos It's my major reason for or against downvoting

Kyle Kanos

Of course, you can play the game so that you just downvote appropriately to maintain the multiple-of-five

(i.e., downvote 5 questions at a time)

Jims Bond

Yes, but once it's there, it's hard to find 5

plus you have to worry about answers being deleted

Kyle Kanos

17:42

Okay, downvote 1 for every 2 Tag Wiki suggestions!

0celo7

@ACuriousMind I got my cubicle back

Jims Bond

@KyleKanos Will do

ACuriousMind

@0celo7 Yay! So you can return to doing nothing important at a desk

0celo7

@ACuriousMind FYI, I'm writing a letter to a constituent.

Kyle Kanos

@0celo7 You mean to tell me some HS scrub is writing me letters in place of the guy I elected into office!?

0celo7

17:49

@KyleKanos No

Kyle Kanos

Okay, good.

0celo7

And FYI, I'm a few credits short of an Associate's Degree

So I'm a college mini-scrub

Kyle Kanos

that was low

So I deleted it

0celo7

Low?

You don't even have a Ph.D. yet

Kyle Kanos

What? Yes I do

0celo7

17:51

You're not allowed to be stuck up yet

Kyle Kanos

I've got the degree

0celo7

Prove it.

Kyle Kanos

Maybe later

0celo7

That gives you time to forge it.

Kyle Kanos

It'd take some gimping to clean up the image (i.e., removing non-essentials & more revelatory information than I'd rather have)

0celo7

17:54

How would I know it's yours?

You could have jacked it from some poor shmuck.

cf. ACM's Alicia Keys thing to get a feel for the rigor of my process

Kyle Kanos

You'll have to just trust me

Also: who the heck voted to close this question as non-mainstream!?

3

Q: Is magnetic reconnection reconcilable with magnetic field lines neither starting nor ending?

According to Maxwell's equations, magnetic fields are divergence-free: $\nabla \cdot \mathbf{B} = 0$. If I understand this correctly, this means that magnetic field lines do not start or end. How can we reconcile this with magnetic reconnection?

maxwell-equations plasma-physics magnetohydrodynamics

ACuriousMind

@KyleKanos I am certain you'd have to ask CuriousOne that.

0celo7

@ACuriousMind 20,000 rep magic tell you that?

Kyle Kanos

@0celo7 No, educated guess

ACuriousMind

@0celo7 No, basic logic tells me that.

0celo7

17:58

@ACuriousMind Damn. Burn.

@ACuriousMind Also, what's with this burn?

:(

ACuriousMind

@0celo7 You were repeatedly complaining that you were bored by your tasks, I didn't see why you were upset by losing your desk :P

0celo7

@ACuriousMind Bored != unimportant

You don't need to remind me how insignificant I am :'(

Interns are people too!

ACuriousMind

@0celo7 We all are utterly insignificant.

0celo7

@ACuriousMind Not when I cause Chernobyl 2: Nuclear Boogaloo

@ACuriousMind On what scale?

ACuriousMind

@0celo7 Took you a while ;) On a galactical/cosmological scale, of course

0celo7

18:12

@ACuriousMind Like I said, doing things.

Important intern duties.

@ACuriousMind Can I make a galactic nuke?

ACuriousMind

I don't know, can you?

0celo7

Can I make an H-bomb out of the sun?

Is that feasible?

Kyle Oman

@0celo7 Just add more hydrogen to speed up getting to a supernova.

Kyle Kanos

Since our sun's not a binary, you'd only be able to get a Type II SN, which means you're adding a few solar masses worth of H....

Kyle Oman

I said speed up, so how much you need depends on how soon you want it to go boom...

actually, can't recall if the Sun is on track for SN with its current mass, or does it just go RGB and shed outer layers?

Kyle Kanos

18:28

Just RGB

Kyle Oman

ah, about 8 Msun to get a type II, well, some work to do then...

Kyle Kanos

If we could survive the expansion phase, we'd have a pretty white dwarf as a sun

Though, the surface temperature would be at least twice as hot, so that may not be fun

Kyle Oman

it will cool though, just go on vacation for a little while until it's back to pleasant

actually, higher surface temperature + lower surface area = probably lower luminosity, no? might be ok...

Kyle Kanos

We've got something like 5 billion years before that happens, so we'll have plenty of time for terraforming other planets (if not straight-up leaving Sol)

With current technology, a shuttle could make it to Pluto (not that it's a planet...) in around 15 years. I think ion drives (or some other currently theoretical propulsion system) are expected to do it in like 5 years

Kyle Oman

Do we even have to go that far? IIRC, the RG would be a few AU in size, but a moon of Jupiter or Saturn might be ok.

would be an awesome view from there, too

0celo7

18:35

Astro nerds...

Kyle Kanos

Estimates range between Earth and Jupiter

I suppose we'd have better knowledge of our sun 5 billion years from now, so we'll have narrowed that massive window down some

Of course the problem could be size:

0celo7

Will humans still exist in 5 bn years?

Kyle Oman

even if it extends to Jupiter, Saturn is still another 4 AU out, and RG's are fairly cool

Kyle Kanos

The left-most red line (second grouping) is earth

Kyle Oman

u,,,

umm, what's the y-axis?

Kyle Kanos

18:37

Relative sizes

Probably radii

Kyle Oman

ah right

Kyle Kanos

The big yellow one all the way to the left is the sun

Wish the chart maker ignored that :/

Apparently Saturn has a gravitational attraction similar to Earth

Kyle Oman

or you know, log scale

Kyle Kanos

As does Neptune

Kyle Oman

as in surface gravity? (whatever "surface" means for a gas giant)

Kyle Kanos

18:39

Yeah, surface gravity

Sorry

List of Solar System objects by size

This is a partial list of Solar System objects by size, arranged in descending order of mean volumetric radius, and subdivided into several size classes. These lists can also be sorted according to an object's mass and, for the largest objects, volume, density and surface gravity, insofar as these values are available. This list contains the Sun, the planets, dwarf planets, many of the larger small Solar System bodies (which includes the asteroids), all named natural satellites, and a number of smaller objects of historical or scientific interest, such as comets and near-Earth objects. The ordering...

Kyle Oman

np... Titan always sounds attractive in these sorts of conversations

Kyle Kanos

Apparently Earth's surface gravity (in units of Earth's surface gravity) is 0.99732

Kyle Oman

heh

probably some detail like average surface gravity vs equatorial surface gravity or somesuch

or just definition then more accurate measurement

Kyle Kanos

Agreed, but it's still funny to see it being not 1

Kyle Oman

nod

Kyle Kanos

18:42

And Titan's surface gravity is like 0.14 Earth's

So we'd be like Supermen there

And our kids probably wouldn't

Kyle Oman

more like muscle atrophy would set on quickly

nod

0celo7

What if you lift 1/.14 times as much weight?

Can you get jacked in low g?

user54412

19:24

@0celo7 When astronauts return to Earth after a couple months in the ISS, they do so in a stretcher because their muscles are so weak they can't even walk. And that's after strenuous exercise for hours every day.

skill patrol

19:54

Why doesn't isometric exercises work?

user54412

@JohnRennie I don't know what exposition you plan, but invoking Rindler seems complicated. I've always seen the solution to the twin paradox as exactly the same as the Monty Hall problem: There are really three things (reference frames, classes of door), not just two.

user54412

There is the Earth twin, the outgoing frame, and the ingoing frame. Similarly, there is the revealed door, the selected door, and the unrevealed door. The error people tend to make is to conflate the latter two things in each case.

skill patrol

Both are brutally difficult to explain :-)

user54412

Astronomy announcement for those who haven't looked at the sky recently:

user54412

Jupiter and Venus are going to be quite close, closer than any time in the next 8 years.

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