Saturday, 28 July 2012

Fingerprinting the Higgs

This blog post title stolen from Christophe Grojean and his collaborators.

With Thursday's mammoth Angband post finally finished, I figure it might be a good time to talk about physics instead.  And what better thing to talk about than what the theory community has been up to in the last three and a half weeks?  Yes, as expected there have been an abundance of Higgs-related papers of varying quality since the discovery announcement back on the 4th.  Thankfully, since many of them tread over similar ground I can cover multiple papers at once!

Thursday, 26 July 2012

Return to Angband

It's been a long time since I talked about a roguelike, hasn't it?

I do intend to get back to reviewing more examples of this fun class of games; indeed, I hope to get one of Crawl out soon.  That is not what this post is.  Rather, I want to go back and talk about Angband again.  I want to go into the mechanics in more detail than in my original post, and also offer some strategy and tips.  This will be the first post in a short series looking at Angband; if this goes well, I might give NetHack the same treatment.1

Before giving my own opinions, let me mention some other useful places to look around the web.  First off, the official forum is one of the best places to get information, strategy and reports of games.  The ladder can also be helpful; in particular, you can see what kind of gear winners tend to have.  You can also look into the spoilers, either in the /lib/edit/ subdirectory or online here.

Monday, 23 July 2012


A global super-rich elite has exploited gaps in cross-border tax rules to hide an extraordinary £13 trillion ($21tn) of wealth offshore – as much as the American and Japanese GDPs put together – according to research commissioned by the campaign group Tax Justice Network.
We all knew that tax evasion was a serious problem, but this is just fucking ridiculous.  Just what could we do with that money?1  How many hungry could be fed, how many sick treated, how many educations provided?  Pick your social worry of choice, and wonder what could be done with a little wisdom.  But no, it's more important that a billionaire keeps an extra million.

I'm reminded of a comment I saw a few years ago, in response to one of the standard cliches that asking the rich to pay their fair share is class warfare.  This is class warfare, launched by the rich, and right now they are winning.

1. Okay, in practice governments would probably blow it all on military hardware, but let me fantasize for a moment.

Friday, 20 July 2012

Climategate Crooks to Avoid Justice

As per the BBC:
The police investigation into the so-called "ClimateGate" affair is over. 
Norfolk Constabulary says there is no realistic prospect of finding the culprit within the statutory time limit of three years since the 2009 offence.
In a sense, the crime of hacking into people's emails is not that serious.  But the damage done by this theft and its resultant distortion by anti-science elements of the media could be severe.  How many people know that eight separate investigations exonerated the researchers?  (Even I didn't, I thought it was only three.)  Criminal prosecutions for those responsible might have served to send a message to those who try to twist science for their own political ends.

Tuesday, 17 July 2012

The Ontological Argument II: Anselm

This is the second article in a series of posts addressing arguments for the existence of any god or gods.  See my first post here.

Anselm was an eleventh century Monk whose version of the ontological argument may well have been the first, and in my experience is the best known.  At this point, I must reiterate a point from my original post: I am not a physicist, not a philosopher, so my opinions here are more that of the educated layman.  I certainly welcome comment on what will follow.

Monday, 16 July 2012

Branes! Branes!

Yes, it's a cheap and old pun.  I don't care.

I've mentioned how extra dimensions are one of the main ways particle theorists pad out their publication list conjecture new physics might arise.  But I spoke mostly in generalities, about the basic concept of more dimensions, and how it differs from the pop scifi ideas.  But there's lots of fun to be found in the details!

The idea of extra dimensions goes all the way back to 1921, when Theodor Kaluza suggested identifying electromagnetism as the gravitational effect of the extra dimension.  Five years later, Oskar Klein expanded on his idea, which is thus known as Kaluza-Klein theory.  More generally, the process of taking a five- (six-, etc) dimensional theory and figuring out what it looks like in four dimensions is known as the Kaluza-Klein expansion.  The specific model of these two men is no longer in favour, as it implies that electric charge and mass should be correlated (they are not).

Modern theories relevant to experiments like the LHC go back to only 1998, when Nima Arkani-HamedSavas Dimopoulos, and Gia Dvali proposed the existence of large extra dimensions.  They where inspired by string theory, so large means at most millimetre-sized.  This is still much, much bigger than the Planck scale; more to the point, it can lead to phenomena observable at current experiments.

British Science to be Free to All

From the Guardian:
The government is to unveil controversial plans to make publicly funded scientific research immediately available for anyone to read for free by 2014.
The specific approach is to require researchers to pay journals a fee upon acceptance of their work.  As I noted in an earlier post, at the moment Universities pay journals anyway, they just do it in the form of subscription fees.  So this move is a good one, and to be applauded in making science more accessible to the general public.

There are only two problems with this plan.  The first is that there are no proposed increases in the research budget; while this should be made up in reallocating existing University budgets, there's no guarantee of this.  A bigger one is that this constraint will only apply within the UK.  Hopefully it will bring pressure on other countries to follow suit; but as long as the UK is alone, it will effectively be subsidising the research of other nations.  (Many if not most journals present research from many countries, so they will still have to be paid for.)

Still, these drawbacks should not outweigh the benefits and, in any case, should only be temporary.  So I'll raise a glass to the government---for one day, at least!

Science is Not a Matter of Opinion

Over at Irregular Webcomic, David Morgan-Mar has an excellent piece about science and the scientific method.  Specifically he shows how science is not just another belief, and it's ultimately irrelevant if you think scientific conclusions don't make sense; only that they agree with, explain and predict experimental results.  To quote from his conclusion,
[Scientific theories] do not explain our world because a bunch of people believe in them. They do so because they reflect deep, underlying truths about how our universe works.
Go read the rest.

Thursday, 12 July 2012

A Little Good News

It's always good to celebrate the small victories in life:
A Mississippi judge has kept in place a temporary block on a law that could see the state's only abortion clinic close its doors.
Of course, the idea of there being only one clinic in the whole of Mississippi is hardly to be filed under "good", but at one is better than none.

This article from the Guardian, written before today's ruling, points out that the anti-abortion groups have gotten smarter.  They've more or less realised that outright evil actions---killing doctors, bombing facilities---don't actually win for them.  If they want to succeed in their goal to end women's control over their own bodies, they need to present things with a more reasonably facade.  Hence the law that is trying to shut down Mississippi's last facility claims to be about women's health.  Of course, in a sick sense it is; it's about making it worse.

There's a parallel to another cause celebre of the religious right, creationism.  The wedge strategy is an attempt to push religion into science classes under the fraudulent banner of academic freedom, much as this law pushes religion under the pretence of health.  The only good thing about that comparison is that the attempts to push creationism have failed; I'm not optimistic enough to think the same will happen in Mississippi.

Wednesday, 11 July 2012

The Ontological Argument I: Overview

In an earlier post, I discussed my path from moderate Christianity to atheism.  In that post, I talked about things that influenced me personally, but I did not get into actual arguments in much detail.  I think I'd like to do that, for several reasons including the opportunity to clarify my own thoughts on the matter.

This post will be the first in a series of posts, where I attempt to address as many of the arguments that are offered to support the existence of a god or gods as I can.  I am a physicist, so in many cases my position is that of an educated layperson rather than an expert.  Still, I hope to be able to say something new and accurate.  I also intend a parallel, and probably shorter, series of posts covering arguments against the existence of any gods.  The two sequences will be complementary, since a big reason for my atheism is simply that there are no good arguments to believe.

I'll start with Ontological arguments.

Tuesday, 10 July 2012

Approaching the Truth, Term by Term

When I was younger, I had an odd misconception about science: I believed it was all about exact expressions.

Part of the reason I though this was that textbooks would have these nice expressions, and it seemed obvious to me that they could be solved exactly.  Part of it is for the same reason I sometimes call myself a failed mathematician.  Part of it is undoubtedly the same reason so many of my students would quote ten significant figures in lab classes, when their measurements were only accurate to two.

The truth is, there are very few problems in nature that can be solved, even after making reasonable simplifications.  One important tool to get around this problem is the Perturbation Series, where instead of a simple exact result we have an infinite sum that, for practical purposes, is good enough.  In my field this is ubiquitous.  For example, the recent Higgs discovery is based on perturbation theory, in that the theoretical predictions for the rates of Higgs production where calculated that way1.

A Few More Thoughts on the Higgs

It's been almost a week since ATLAS and CMS announced their discoveries.  Even within the field, not much has changed.  What has is mostly a perspective; we have a Higgs, probably, so it becomes an input to our models instead of an output.  There have been a lot of new papers on the arXiv, especially this week, but the biggest splurge came with the hints last December.  So far I haven't seen anything really notable, though I'll admit I'm a bit behind on my reading.

What do we know about the discovery?  It looks very much like a we would expect.  The nice thing about the Standard Model is that when it comes to the Higgs, it is highly predictive.  All the relevant couplings relevant were known long ago; only the mass and the Higgs self-coupling were not predicted.  Now that we know the mass, we also know the latter value too, but this cannot be measured at the LHC.  When we compare those predictions to the data, everything more or less agrees.  Only the Higgs decay to two photons is not within the error bars, but the difference is still small.  The most interesting hint is that the decay to W bosons is small, but the Higgs-W coupling is also relevant for Higgs production, and the evidence there is consistent.  Of course, the fact that the differences are small won't and hasn't stopped people writing papers!

Wednesday, 4 July 2012


So.  The LHC has found something.

Watching the webcast now, CMS claims 5 sigma combining the diphoton and ZZ channels.  It looks very compelling.

Of course, there's some way to go to confirm that what's seen is actually the Higgs.  But all the different decay channels seem to match up as expected, within the errors.  It looks very Standard Model like.

Update: Nothing in ditau.  That might be interesting.

Update 2:  ATLAS comes in with 5 sigma excesses in the same channels, at the same points.  That's pretty much unequivocal.

The biggest thing missing is Higgs to WW.  Neither experiment saw much of an excess there, and that's the key to proving the new state is the Higgs, in that it is responsible for giving mass to the W and Z bosons.  Then, a longer period of measuring the fermionic branching ratios, and maybe the total width in the diphoton and ZZ channels.

Still, I think we can safely predict Nobels for the collaborations and/or Peter Higgs this year.

Tuesday, 3 July 2012

The Tevatron Higgs Announcement

The Tevatron today announced stronger evidence for the Higgs from its own searches.  There had been rumours that such an announcement would be made before the LHC likely claims discovery on Wednesday.

The Tevatron results are not enough, by the standards of the particle physics community, to claim discovery.  They are not even enough to claim "evidence", a lower standard where people tend to start getting excited.  But the results are very interesting and useful, even so.  A big part of this is because the Tevatron search channels are different to the ones currently used by the LHC.

Monday, 2 July 2012

Challenging Dimensions

It's time to talk about ... The Fifth Dimension! <Cue Tw- oh, I've already made this joke.

Yes, I want to talk about a popular model of theoretical physics that isn't supersymmetry: extra dimensions.  Actually, this is really three classes of models, with different motivations and features.  In subsequent posts, I will get into those details.  But here I want to talk about the idea in a very general context.

In my earlier post, I defined the number of dimensions of a thing as how many different coordinates you need to uniquely identify a point on that thing.  I contrasted the two numbers needed to locate a point on your computer screen, to the three numbers (e.g. longitude, latitude and altitude) to find a point near the Earth, to the four numbers to additionally specify the time an event happened.  So if there are five dimensions, then we would need five numbers to locate objects in space and time.

And yet, we seem to get by perfectly well with three spatial and one time coordinate; that was the very example I just used.  How can this be resolved?

Two Months

I finish my current contract on August 31st.

It always sneaks up on me.  Only two months left before I leave Vancouver and head for Melbourne.  Among other things, I need to start seriously packing.  But simply the realisation of how little time I have left here has made me suddenly sad.