The h Bar

enumaris

00:08

Fun times...

Skyler

01:22

hey folks

enumaris

sup

Skyler

nm, kinda use to seeing it more lively around this time, but its been `a while since i frequented here

im kinda wondering if anybody here has worked alot with earthquakes before

I've got an interesting dataset I'm doing analysis on

besides that fridge is dead, im up to my neck in R hw, and am really annoyed with these deep scrapes i got yesterday when my bike tire skid on something

so its been quite a week so far

howdy folks

user400188

01:54

Does anyone mind proof reading a question to ask on the main site? I want it to be clear enough to answer.

Well, its here:

I have been thinking of timescales to the human races doom of using renewables recently, and I haven't been able to find many sources on these times.

For all these questions, assume that increase in the rate of energy consumption stays the same each passing year. That is, our energy consumption increases linearly each year.

If we got all our energy from geothermal, what would be the time scale before the earth’s core got cool enough to cease generation of our magnetic field?
- for this question, you would need to know how much gravitational potential energy was converted to heat in the co…

Skyler

hmm

you want to ask all together?

user400188

Yes it does seem like a bit much to ask all at once.

I was thinking I could attach a bounty to the question to reward people for answering all of it.

Skyler

you have neough points for that/

vzn

03:12

@tpg2114 sounds like an interesting problem, am curious, have worked on a very hard dataset, financial, may be able to assist, student can contact me here (where there is significant ML experience represented already which could also possibly be leveraged some) or other room to give it a shot chat.stackexchange.com/rooms/9446/theory-salon

kyle campbell

03:39

Anyone familiar with string theory?

enumaris

04:01

for that u want ACM

kyle campbell

@ACuriousMind have a question when you're around

John Rennie

04:28

@kylecampbell what do you want to ask?

kyle campbell

@JohnRennie I have a couple questions. First, in general, why do string theories require extra spatial dimensions? Also, what's the motivation for compactification?

John Rennie

When you quantise a classical theory the quantum version can have an anomaly

In the case of string theory the quantised theory has an anomaly unless the spacetime dimension is 26 for bosonic strings or 10 for supersymmetric strings.

Basically unless supersymmetric string theory is formulated in a 10d spacetime it becomes inconsistent.

kyle campbell

ah I see

John Rennie

The details are way out of my league, but if you Google string theory conformal anomaly or something like that you'll find lots of articles on it.

kyle campbell

I'm a bit iffy on what exactly the "anomaly" is, but I take your word for it that it's an issue

John Rennie

04:38

As for compactification, if there are 9 spatial dimensions the obvious question is why we only observe 3 spatial dimensions. Where are the other 6?

The two approaches to this are compactification or the brane world.

In the brane world approach all the standard model particles are anchored to a 3D subset of the 9 spatial dimensions. The other 6 dimensions exist but standard model particles can't move in them.

kyle campbell

What exactly is the "brane" in that approach? The 3D subset?

John Rennie

D-brane

In string theory, D-branes, short for Dirichlet membrane, are a class of extended objects upon which open strings can end with Dirichlet boundary conditions, after which they are named. D-branes were discovered by Dai, Leigh and Polchinski, and independently by Hořava, in 1989. In 1995, Polchinski identified D-branes with black p-brane solutions of supergravity, a discovery that triggered the Second Superstring Revolution and led to both holographic and M-theory dualities. D-branes are typically classified by their spatial dimension, which is indicated by a number written after the D. A D0-brane...

kyle campbell

By "can't move in them", do you mean the SM particles can't interact whatsoever with the other 6 dimensions?

Skyler

@JohnRennie is this kind of discussion of dimension based on expanding the symmetry groups we see in representation theory and things like the gell-mann matrices

i.e.: string theory is a representation theory with symmetries that encompass gell-mann and other symmetry groups and evolves out of that same perspective in relation to symmetry groups, just trying to describe more than hadrons

John Rennie

@kylecampbell Open strings have boundary conditions on their ends, and one of the conditions is that the ends have to travel within a Dirichlet brane. If the SM particles are associated with the ends of the string then the SM particles can only move within that brane.

But my knowledge of this is so limited that I can't say much more.

@Skyler don't know, sorry.

Skyler

04:45

ok

Im just wondering if his question could be adequately described by first expanding his understanding of symmetries. Like if you described SU(2) vs SO(3) it might click for him

John Rennie

From the little I know of the subject that approach doesn't seem the right one

The symmetry involved here is conformal symmetry.

Conformal anomaly

A conformal anomaly, scale anomaly, or Weyl anomaly is an anomaly, i.e. a quantum phenomenon that breaks the conformal symmetry of the classical theory. A classically conformal theory is a theory which, when placed on a surface with arbitrary background metric, has an action that is invariant under rescalings of the background metric (Weyl transformations), combined with corresponding transformations of the other fields in the theory. A conformal quantum theory is one whose partition function is unchanged by rescaling the metric. The variation of the action with respect to the background metric...

Skyler

oh ok, so its a matter of scale invariance and renormalization groups

John Rennie

@kylecampbell did you want to ask about compactification, or is it now obvious why it's used?

kyle campbell

@JohnRennie No, I understand the motivation now

I'm just reading...

I have another question but I'll just save it for another day

Appreciate it!

John Rennie

@kylecampbell when ACM does show up he'll no doubt point out that what I've said is at best a caricature, but a proper explanation would probably be incomprehensible :-)

Skyler

04:58

he's missing the ACM signal though, so will he even answer our calls?

Ryan Unger

Is ACM not an omnipotent chat AI

Skyler

man, ive changed computers twice since i made that bat signal photoshop for him, i wonder where that file is

btw, rejecting the null hypothesis meant getting a p-value sufficiently small (below your cutoff) right?

aka accepting your alternative hypothesis of some correlation or etc

Slereah

05:54

morgen

enumaris

06:25

maybe I'll try to render the arc reactor...probably too hard tho...but maybe I can try...:D

enumaris