# PhysicsOverflow

A new Question and Answer site for Physics at a graduate-level and above has started last week on Friday (not yesterday, the week before). The site is called PhysicsOverflow and can be found at http://physicsoverflow.org. The name is in analogy to MathOverflow, or MathsOverflow, a “research-level” (relating to cutting-edge research) Mathematics Q&A site found at http://mathoverflow.net.

The new site seeks to be a high-level Q&A site combined with a “Reviews” section for refreeing research papers, etc.

A wide variety of subfields, including Theoretical Physics, Experimental Physics, PhenomenologyAstronomyComputational Physics, Applied Physics, Mathematics which need a physicist’s point of view, and generally Physics, are on-topic on PhysicsOverflow (PO/PhO).

It is worth to see the welcome post containing somethings useful for a new user to the public beta, and the to-eventually be comprehensive FAQ.

Wait, public beta? Does this mean that the site will go down if it doesn’t receive enough activity?

No. The term “public beta” is used because there are a few important things remaining to be done during this phase:

• Install any needed plugins, etc. and focus on site design and a physics-ish look to the site.
• To watch how fast users gain reputation, and set reputation-based permissions based on this.
• Import the graduate-level questions remaining to be imported from Physics Stack Exchange.
• Write a lot of tag wikis.
• Work on creating a “Reviews” section for reviewing research papers etc.

What is the “Reviews” section about? See my post here.

Regarding the software, the following is copied from my post here:

We use Question2Answer v1.6.2 with the following standard Q2A-provided plug-ins:

• Basic AdSense (not enabled yet)
• Event Logger
• Tag Cloud Widget
• XML Sitemap

The following external plug-ins:

And the following plug-ins by polarkernel:

• Physics Overflow MaThJaX
• Merge User Accounts
• Regain TP account page (disabled)
• Reset account
• Search for User
• Physics Overflow Buttons Plugin
• Correct User
• Rename User
• Reverse Serial Voting

The theme that we use the PhysicsOversnow (officially PO-theme) by polarkernel which is based on the Snow theme by Q2A market.

Below are some differences from the SE software:

 Stack Exchange Physics Overflow (Q2A) Comment Voting Only positive Positive and Negative Vote Counts Net score displayed[1] Vote counts displayed Downvote rep change A fifth or two of upvotes Same as upvotes Accepting answers Yes[2] Disabled Approve suggested edit 2 users needed 1 user enough Bookmarking “Favouriting”[3] Bookmarking[4] Autodeletion Inactive questions auto-deleted Questions never auto-deleted Comment length $\leq$ 600 characters Almost unlimited

[1]: Users with at least 1k rep, or who have installed a userscript, may click on net score to see vote counts

[2]: The idea of accepting answers was completely unnecessary as the decision gives the false impression that the accepted answer is really the best.

[3]: And prominently displayed near the “upvote”/”downvote” buttons, making it a misleading cue for  question rating.

[4]: Can be used for any purpose wanted, but should not be mixed up and made a cue for question rating

# 2013 in review

The WordPress.com stats helper monkeys prepared a 2013 annual report for this blog.

Here’s an excerpt:

A New York City subway train holds 1,200 people. This blog was viewed about 6,400 times in 2013. If it were a NYC subway train, it would take about 5 trips to carry that many people.

# The Friedmann Equation, the FLRW Metric, the Cosmological Constant, and Dark Energy

A short overview.

# Experimental tests of String Theory

Edit: By the way, have a look at this: http://arxiv.org/find/all/1/all:+AND+kane+AND+kumar+acharya/0/1/0/all/0/1 a list of papers relevant to this topic.

This post is intended to dismiss some of the claims that “String Theory isn’t testable“;.  So, let’s first list out some of the claims we hear about the experimental testability of  String Theory, in random discussions,  on comments by trolls on tRF , and by the well-known crackpots, (dubbed “Smoit”, but I suggest “Woilin”):

• String Theory disagrees with well-known Physics!
• Ya, whatever, fine, but it agrees with everything, so that basically means that String Theory isn’t testable! It’s like, pseudo-science!
• Ok, ok, but it isn’t testable at today’s energy scales, alright? Ha!
• Well, fine, whatever, but it has been experimentally disproven!
• Ok, fine, WHATEVER, but it hasn’t been experimentally proven, at least, ok? Ha! How will you counter that?!

Ok, so let’s counter each of them.

String Theory does agree with well-known Physics.

It is a trivial excercise to show that String Theory agrees with General Relativity.

One starts with the beta functionals, which describe the breaking of conformal symmetry due to the presence of the Dilaton. To keep Conformal Symmetry, these functionals must be set to be 0.

The coupling of the string to the Dilaton Field is described by the following action integral:



To derive the beta functionals, one may do this in Riemann Normal Coordinates (see at Wikipedia or at the n(Cat)Lab).

The breakdown of conformal invariance would then be: \\\



With the beta functionals given by:



To impose conformal invariance, these beta functionals must vanish, as follows:



These are the field equations for the graviton, dilaton, and photon fields respectively. Notice that they have a rather fundamental basis, conformal invariance. We need to focus on this one:



This is obviously the field equation for gravity. Notice that I have removed one term on the way. This term is .This is because I have assumed that the Riemann Curvature Tensor is negligibly small.

I don;’t need to.



However, in the limit of little gravity, and no dilaton, this becomes the ordinary vacuum Einstein Field Equation.

String Theory also agrees with the Minimal Supersymmetric Standard Model (MSSM) as shown by [1] (pdf  here).    Upon Supersymmetry breaking, this means that it also agrees with the Standard Model j.

String Theory is testable.

What does String Theory predict?

It predicts scattering amplitudes, caisimir energy, superpartners, gravitons, an infinitude of particles in a mass spectrum, gravitons, extra dimensions, AdS/CFT, and what not?  Talking about AdS/CFT, see this recent paper  by Raju and Papadogmias [2] (pdf here)   and this one by Papawdogmias and Raju [3] (pdf here).         This means the prediction of certain operators in the conformal boundary.

String Theory is testable at today’s energy scales.

Firstly, that isn’t a valid deleteion argument, as it  is still testable.

Secondly, the Supersymmetry-related predictions of String Theory just depend on a certain number of parameters, called the Supersymmetry breaking parameters. For an  supersymmetric string theory (like a  manifold compactification of M-Theory), it is in fact possible to test the effects of supersymmetry, because the supersymmetry breaking  energy parameter is low enough!.

String Theory has withstood experimental tests.

Huh, no. The only experimental result in contrary to the predictions of String Theory is probably [4] (PDF here). Other than this,  String Theory has in fact been supported by experimental predictions. Also, the experiment does not rule out compactification lengths smallernthan half a milimetre.

String Theory has had experimental verification repeatedly.

See this article at the Mathematics and Physics Wikia (Introduction to String Theory)  for the entire list.

Note that the 125 GeV Higgs actually serves as an experimental support for String Theory.

So basically, these criticisms of String Theory are just some ingeniously crafted Markov Chains, cooked up by a computer repairman at the Mathematics Department of the University of Columbia, aka the “Troll King“, and popularised by the popular media, such as “The Scientific American”, a magazine devoted to misleading laymen and making them even more unscientific.

# Test – LaTeX 2: Wiki Pedia – style LaTeX (image) formatting.

\oint_C\left(\mbox{Random}^{\mathrm{rubbish}}\right)\cdot\mbox{d}\vec r = 0 …