Friday, July 25, 2008

Off to physics summer school

Down to the University of Sussex tomorrow for a week's summer school on electromagnetism. It promises to be a long week (12 hour days) with intricate experiments and computer simulations. I am lamentably bad at experimentation so fear the worst.

According to the brochure, there is no Internet access (extraordinary in this day and age) so a daily account may not materialise.

Wednesday, July 23, 2008

Personal abuse in Physics

Both Peter Woit and Lee Smolin, in their respective books critical of string theory, drew attention to the level of personal abuse they had suffered at the hands of string theorists.

The poster child for abuse is usually identified as Lubos Motl (incendiary blog here). An example of his approach can be seen if you try to navigate to his blog from Peter Woit's blog "Not Even Wrong". You get the following page thrown at you (here).

See also Sabine Hossenfelder's blog "Backreaction" here, as updated today, from someone who's just had enough.

And then there were the recent personal attacks on Peter Woit's own blog, here. Scroll down to the anonymous string theorist "Lucy in the sky" here for something even more venomous.

I was then even more surprised to hear the leading string theorist Leonard Susskind, whose book on "Black Hole wars" I just reviewed, saying some extraordinarily offensive things about both Peter Woit and Lee Smolin on an American talk radio programme (about 3 or 4 minutes in, here). Woit is the 'computer programmer and bitter failed physicist' and Smolin the dilettante whose multiple theories vanish - glubb - glubb - glubb - even faster than he can make them up.

As far as research credentials go, probably the kind of mind which can encompass and critique a whole research programme is rather different than that required to push the edge of the very state-of-the-art. However the best critique is to find something better. As string theory has seemed exhausted to some observers, while nothing better has exploded on the scene, everything seems set for a long war of attrition.

I have two observations: (a) it will all get resolved on a time scale of decades but people will never be that patient; (b) it all gives fundamental physics a terrible reputation for the next generation wondering if they should get into it.

Tuesday, July 22, 2008

The Black Hole War

Just finished "The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics" by Professor Leonard Susskind, one of the founders of string theory.

The book describes the decades-long battle between the quantum mechanics community and the general relativists as to whether information is lost when objects pass through the event horizon of a black hole and the hole eventually evaporates. According to Prof. Hawking and the GR community, as nothing can ever reappear from inside an event horizon, the information is indeed totally lost.

Susskind and Gerard 't Hooft begged to differ. Loss of information would violate the basic time-reversibility of QM - Hawking's ideas would lead to universe-destroying phenomena (all of space gets very hot very fast - p. 23). Somehow, the information locked the wrong side of the event horizon must leak out via Hawking radiation. But how?

The resolution of this dilemma took many years of conjectures and refutations. Susskind takes us on a tour of entropy, holographic principles and physics at the Planck scale. And the adversarial plot keeps the reader turning the pages.

I am normally very dubious about popularisations. They proceed by raking up endless analogies which never quite fit together, so that by the end of the book, your mind is like that jig-saw puzzle you bought and could never fit together.

This book was never going to be the exception - the mathematics of quantum field theory, general relativity and string theory are just too arcane for popular culture concepts to cohere around. However, there are wonderful insights all the way through this book and we do end up learning something about the large scale map of the territory. Apparently even the experts find it hard to get the whole thing into one focus.

Monday, July 21, 2008

Further thoughts on fields

I think a big hole in my thinking would be addressed if I had a physical, geometric intuition about the electromagnetic tensor. We have covered it briefly in a chapter of the course, but only as a piece of mathematics, an abstract operator.

However, I saw in a Wikipedia article here an interesting reference to Haskell's work where he claims that Maxwell's equations fail in accelerating frames. This was quite news to me as I had hitherto believed that Maxwell's equations were classically 'correct' in the sense of correctly predicting the 'large-scale' phenomena, and that QED was really an "implementation" of Maxwell at the quantum level, maybe providing predictive corrections at that scale.

I am also not completely comfortable that there is no mathematical distinction between a vector field which is constant and stationary over all x, y, z, t and a vector field which has a constant value over all x, y, z, t but which is moving with respect to the coordinate axes at some constant velocity. And what if we want a 'field which is constant in value over all x, y, z, t' to accelerate wrt some axis?

Perhaps the deep truth here is that unlike particles, fields can't move at all - only disturbances in fields can propagate.

Our new battery-powered mower

We have had a manual mower since we first moved into the current house, five years ago. It has had its moments, most notably when we returned from Dubai after four weeks away and found the lawn had shot up to a foot high! That took a few days - the kind of work-out typically only enjoyed by riders in the Tour de France.

Finally, in an excess of lubrication, a wheel fell off yesterday and the internal plastic workings were revealed in all their worn inadequacy. It was time for a new one.

A quick trip to HomeBase and we reviewed the options. Clare was initially quite taken with a hover mower, but we soon settled on a battery driven cylinder model. Just hate that power cable dragging, wrapping itself around obstacles and waiting to be cut. But would the battery be strong enough?

We powered it up overnight, and at sun-up (almost!) Clare was kitted up and ready to try it. Judge for yourself.

Friday, July 18, 2008

The Quantum World

I gave myself an early Christmas present yesterday and signed up for the OU's third-level quantum mechanics course, SM358 - The Quantum World.

As I have found with the classical electromagnetism course (SMT359) now 75% completed, to properly understand these rather sophisticated concepts needs time and immersion, not just reading some popularisation or scanning a textbook.

With CERN's Large Hadron Collider powering up in late Autumn, I expect new physics around this time next year - SM358 is coming along just in time!

Meanwhile I have been wrestling with the mathematics of charged particles moving relative to magnetic fields. Maxwell's equations treat the following cases differently:
  • the charged particle is moving and the magnetic field is stationary (the Lorentz force law)

  • the charged particle is stationary and the magnetic field is moving (Faraday's law)
This was one of the issues which led Einstein to special relativity.

Anyway, I have not properly understood how to think about this, so I wrote up my queries in a note to my OU tutor, which you can read here. Sent just a few moments ago.

Tuesday, July 15, 2008

BT's fibre-based broadband

BT announced today that it is spending £1.5bn (initially around £100m of incremental CAPEX in each of 2008-09 and 2009-10) to build out its fibre access network to serve 10 million homes by 2012. This is somewhat under half the households in the UK.

Most of this will be fibre to the curb, where it will drive VDSL giving 50-100 Mbps in principle. New builds may get fibre to the home. Most likely, BT will use GPON technology and real sustained data rates will be dialled far lower.

In exchange for this CAPEX spend, BT wants regulatory relief. By this they mean no unbundling (difficult anyway with GPON) which will give them an access fibre monopoly for enough years to guarantee a return on their investment.

They should probably get it. The business case for FTTH remains shaky, and the externalities are such that the real benefits may well accrue to other economic entities (retailers, providers of IPTV channel content, etc).

Rather than subsidising BT's fibre roll-out, letting them make monopoly profits for a while seems on balance to make overall economic sense.

Monday, July 14, 2008

The Center of the Earth

Immediately breaking our resolution of last week to only see intelligent movies in future, yesterday evening found us again at the new, state-of-the-art Andover cinema to see "Journey to the Center (sic) of the Earth" in exciting 3D.

I have to say that the 3D was the main motivation.

"Two tickets please, 'Centre of the Earth'."

"That'll be £12 - screen 4."

"Uh, do we get our 3D glasses at the entrance?"

"We don't have 3D projection apparatus in this cinema. It's 2D. You're not the only people who asked."

Amongst all the scientific absurdities, too many to list (including magnetic rocks which can levitate a penknive and each other, and a 1G, normal temperature-ish, well-lit environment at the centre of the earth) they did get one relatively obscure scientific fact correct. Deep inside the earth the magnetic field lines do indeed run the opposite way than on the surface, so compasses (Curie point permitting) would have their north-finding arrows pointing south.

The movie spoke to everyone's inner ten year old, and the audience exited the movie with child-like smiles on their faces.

Thursday, July 10, 2008

More moths

Various people have written to me to confirm just how useless was my mathematical model of moth-bathroom behaviour, posted a couple of days ago here.

- Moths apparently only fly at 3-4 m/s, not 10 m/s.

- Moths in a darkened room with a window open are likely to detect the opening (faint illumination, fresh air?) and fly straight to it, not zoom around at random.

I would add that in my experience, moths rarely fly continuously, so 370 flights without resting seems unlikely.

After I left the bathroom, having observed the final position of the moth, it was then unobserved. It seems likely that its wave function rapidly diffused in all directions until most of it leaked out of the window.

So the right answer was that the moth was mostly there for a while, then mostly not there until finally it was hardly there at all.

Tuesday, July 08, 2008

Knee replacement operation

I was in Bristol at the end of last week helping my mother while my father was in Southmead hospital having a partial knee replacement on his left knee. A daunting operation at age 83. They did the operation Thursday afternoon, July 3rd, and we were visiting him a few hours later when I took the picture below. He seemed remarkably cheerful, no doubt a combination of relief and all that morphine.

While he was recovering my mother funded a new Vista laptop for him, so he came home yesterday to the challenge of getting his head around that. My mother had made sure that the first thing I did was to install all her MSN games (Bejeweled etc), so he may have to fight her for it.

Moth avoidance

Last night around 1 a.m. I got up to go to the bathroom and as I was using the facilities a moth flew in the open window and and began to weave its helical path under the light. I beat a hasty retreat back to bed and lay there thinking how long it would take the moth, now flying randomly in the dark, to escape out of the window, making the bathroom safe again for humanity.

Suppose the probability that it flies across the bathroom and just happens to escape out the window is p, while the probability that it encounters a wall and has to randomly fly off in a different direction is q -- so p + q = 1.

Then it could escape in one flight with probability p, in two flights with probability qp, three flights with probability q2p and n flights with probability q(n-1)p.

What, I thought to myself, is the average number of flights before it escapes?

I lay on my back in total darkness. Physically paralysed, my mind was trapped in an obsessive tunnel - forced to follow this computational path through to the end.

Right, the expected number of flight 'trials' - N - is one times p + two times qp + three times q2p and so on.

N = p + 2qp + 3q2p + ... + nq(n-1)p + ...

N = p(1 + 2q + 3q2 + ... )

N = p d/dq(q + q2 + q3 ....) = p d/dq(1/(1-q) - 1)

N = p/(1-q)2 = p/p2 = 1/p

You know, I kind of guessed it would be that.

So what's p? I estimated the the bathroom as 1.3 by 1.5 by 2 metres. Total area 15 m2. The open window was around 40 cm by 10 cm of freedom, so 0.04 m2.

Dividing, this gave me p as 2.7 x 10-3, which is roughly e/1000 by happenstance.

So the mean number of trials the moth would need to make before escaping was 1/p, so 0.37 x 103. Around 370 flights.

How fast do moths fly? Well, I reckon about 10 m/s, so it could traverse half the bathroom (the average flight length) in about one tenth of a second. So to escape it would need 37 seconds.

I decided to give it a minute, to be on the safe side.

Monday, July 07, 2008

Ugly Baby

A woman gets on a bus with her baby.

The bus driver says: “That’s the ugliest baby that I’ve ever seen!”

The woman goes to the rear of the bus and sits down, fuming. She says to a man next to her:

“The driver just insulted me, I'd like to give him a piece of my mind!”

The man says: “You go right up there and tell him – I’ll hold your monkey.”


Old but good.