On Janitors and Doctors of Philosophy

Did you know that in the United States, there are 5,000 janitors who hold a PhD? I didn’t know either until I stumbled on this post on Quora. The most popular response comes from Joseph Wang, PhD, who posits two credible explanations:

3) I’ve known people that have worked as janitors, and they say it’s an easy job. You get paid eight hours of wages for work that usually only takes two or three, and you spend the rest of the night just chatting. You work in the middle of the night so your manager isn’t going to be looking over your shoulder, and as long as everything is clean the next morning, no one cares how many hours you “really” worked.

4) You can do janitorial work and theoretical physics at the same time. You are pushing a broom, you can think about quantum field theory. This is *not* true for a lot of other jobs. You can’t think about QFT while taking orders at McDonalds, selling shoes, flipping burgers, or driving a cab. If the janitor has a blank vacant look, no one cares, whereas being absent-minded while dealing with hot cooking oil or customers can get you fired or cause a fire.

The Kettle and Its Whistle

How does the kettle whistle? Apparently this is one problem that hasn’t been solved in 100 years, until now. Phys.org leads with this:

Researchers have finally worked out where the noise that makes kettles whistle actually comes from – a problem which has puzzled scientists for more than 100 years.

Seems hard to believe.

Writing in the October issue of the academic journal, The Physics Of Fluids, two Cambridge University researchers claim to have solved the conundrum, and in the process developed the first accurate model for the whistling  inside a classic stove kettle.

Perhaps reassuringly for those who never felt that this was a significant problem, the ramifications reach far beyond kettles themselves. Using the knowledge gained from the study, researchers could potentially isolate and stop similar, but far more irritating whistles – such as the noise made when air gets into household plumbing, or damaged car exhausts.

“The effect we have identified can actually happen in all sorts of situations – anything where the structure containing a flow of air is similar to that of a kettle whistle,” Ross Henrywood, from the University of Cambridge Department of Engineering, and the study’s lead author, explained.

“Pipes inside a building are one classic example and similar effects are seen inside damaged vehicle exhaust systems. Once we know where the whistle is coming from, and what’s making it happen, we can potentially get rid of it.”

Henrywood carried out the research for his fourth-year project as part of his engineering degree, under the guidance of his supervisor, Dr Anurag Agarwal, a lecturer in aeroacoustics. Drawing on previous research by Agarwal, which identified the source of noise in jet engines, the pair were able to show how sound is created inside a kettle as the “flow” of steam comes up the spout.

The abstract of the paper is here.


Has a Nuclear Fusion Milestone Been Reached?

The National Ignition Facility (NIF) has achieved a nuclear fusion milestone, according to BBC. Based at Livermore, CA, NIF used 192 beams from the world’s most powerful laser to heat and compress a small pellet of hydrogen fuel to the point where nuclear fusion reactions take place. But the way the article is phrased, it sounds like there is some skepticism here (“The BBC understands”):

The BBC understands that during an experiment in late September, the amount of energy released through the fusion reaction exceeded the amount of energy being absorbed by the fuel – the first time this had been achieved at any fusion facility in the world.

This is a step short of the lab’s stated goal of “ignition”, where nuclear fusion generates as much energy as the lasers supply. This is because known “inefficiencies” in different parts of the system mean not all the energy supplied through the laser is delivered to the fuel.

But the latest achievement has been described as the single most meaningful step for fusion in recent years, and demonstrates NIF is well on its way towards the coveted target of ignition and self-sustaining fusion.

For half a century, researchers have strived for controlled nuclear fusion and been disappointed. It was hoped that NIF would provide the breakthrough fusion research needed.

In 2009, NIF officials announced an aim to demonstrate nuclear fusion producing net energy by 30 September 2012. But unexpected technical problems ensured the deadline came and went; the fusion output was less than had originally been predicted by mathematical models.

Soon after, the $3.5bn facility shifted focus, cutting the amount of time spent on fusion versus nuclear weapons research – which was part of the lab’s original mission.

However, the latest experiments agree well with predictions of energy output, which will provide a welcome boost to ignition research at NIF, as well as encouragement to advocates of fusion energy in general.

Waiting for the news release from NIF here.

The Feynman Lectures on Physics: Free Online

This is an incredibly generous endeavor by Caltech: they have published The Feynman Lectures on Physics in HTML format, available for free:

Caltech and The Feynman Lectures Website are pleased to present this online edition of The Feynman Lectures on Physics. Now, anyone with internet access and a web browser can enjoy reading a high-quality up-to-date copy of Feynman’s legendary lectures. This edition has been designed for ease of reading on devices of any size or shape; text, figures and equations can all be zoomed without degradation.


Get your fix of Volume I.



1) If you’re wondering, the hardcover set of the lectures goes for around $180 on Amazon.

2) Read why Richard Feynman is my favourite scientist.

A Physicist Proposes to his Physicist Girlfriend

A redditor named “bogus_wheel” (a physicist by profession) received a proposal from her physicist boyfriend via an academic paper titled “Two Body Interactions: A Longitudinal Study.” You can read it below:

two_body_interactionsVery cute (and she said yes).

Two questions: where are the references and is it possible to replicate this study?

Quantum Gas Dips Below Absolute Zero

I’ve always been taught that it’s impossible for a system to drop in temperature below absolute zero, but I guess I’ve been taught wrong:

Wolfgang Ketterle, a physicist and Nobel laureate at the Massachusetts Institute of Technology in Cambridge, who has previously demonstrated negative absolute temperatures in a magnetic system, calls the latest work an “experimental tour de force”. Exotic high-energy states that are hard to generate in the laboratory at positive temperatures become stable at negative absolute temperatures — “as though you can stand a pyramid on its head and not worry about it toppling over,” he notes — and so such techniques can allow these states to be studied in detail. “This may be a way to create new forms of matter in the laboratory,” Ketterle adds.

If built, such systems would behave in strange ways, says Achim Rosch, a theoretical physicist at the University of Cologne in Germany, who proposed the technique used by Schneider and his team. For instance, Rosch and his colleagues have calculated that whereas clouds of atoms would normally be pulled downwards by gravity, if part of the cloud is at a negative absolute temperature, some atoms will move upwards, apparently defying gravity.

Another peculiarity of the sub-absolute-zero gas is that it mimics ‘dark energy’, the mysterious force that pushes the Universe to expand at an ever-faster rate against the inward pull of gravity. Schneider notes that the attractive atoms in the gas produced by the team also want to collapse inwards, but do not because the negative absolute temperature stabilises them. “It’s interesting that this weird feature pops up in the Universe and also in the lab,” he says. “This may be something that cosmologists should look at more closely.”


Is Our Universe a Giant Simulation?

The physics paper of the week is “Constraints on the Universe as a Numerical Simulation” by Silas Beane and company at University of Bonn in Germany. Their fundamental question: is the universe just a giant simulation, in which we are all puppets? From their abstract:

Observable consequences of the hypothesis that the observed universe is a numerical simulation performed on a cubic space-time lattice or grid are explored. The simulation scenario is first motivated by extrapolating current trends in computational resource requirements for lattice QCD into the future. Using the historical development of lattice gauge theory technology as a guide, we assume that our universe is an early numerical simulation with unimproved Wilson fermion discretization and investigate potentially-observable consequences. Among the observables that are considered are the muon g-2 and the current differences between determinations of alpha, but the most stringent bound on the inverse lattice spacing of the universe, b^(-1) >~ 10^(11) GeV, is derived from the high-energy cut off of the cosmic ray spectrum. The numerical simulation scenario could reveal itself in the distributions of the highest energy cosmic rays exhibiting a degree of rotational symmetry breaking that reflects the structure of the underlying lattice.

Could you fathom the possibility that our entire cosmos is running on a vastly powerful computer? I cannot.


(via Technology Review)

Should You Walk or Run in the Rain?

The question whether to walk slowly or to run when it starts raining in order to stay as dry as possible has been considered for many years—and with different results, depending on the assumptions made and the mathematical descriptions for the situation.

BBC reports that Franco Bocci, publishing in the European Journal of Physics, now asserts that both wind direction and a person’s stature figure into the answer:

In most cases, the general answer is to run as fast as possible; but the answer changes in a tailwind, or for the thin.

As for wind direction – and again, in general – you should run as fast as you can unless the wind is behind you, in which case the optimal speed will be exactly the speed of the wind.

In summary, if you want to stay the most dry in the rain: it’s better to run fast. Unless you’re thin. And there’s wind.

Riding the Plasma Wave

A cloud forms as an F/A-18 Hornet aircraft speeds up to supersonic speed. Aircraft flying this fast push air up to the very limits of its speed, forming what’s called a bow shock in front of them.

Lynn Wilson who is a space plasma physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, writes the following:

Throughout the universe more than 99 percent of matter looks nothing like what’s on Earth. Instead of materials we can touch and see, instead of motions we intuitively expect like a ball rolling down a hill, or a cup that sits still on a table, most of the universe is governed by rules that react more obviously to such things as magnetic force or electrical charge. It would be as if your cup was magnetized, perhaps attracted to a metal ceiling above, and instead of resting, it floats up, hovering somewhere in the air, balanced between the upward force and the pull of gravity below.

This material that pervades the universe, making up the stars and our sun, and also – far less densely, of course – the vast interstellar spaces in between, is called plasma. Plasmas are similar to gases, and indeed are made of familiar stuff such as hydrogen, helium, and even heavier elements like iron, but each particle carries electrical charge and the particles tend to move together as they do in a fluid. Understanding the way the plasma moves under the combined laws of motion we know on Earth and the less intuitive (to most Earthlings, at least) electromagnetic forces, lies at the heart of understanding the events that spur giant explosions on the sun as well as changes in Earth’s own magnetic environment – the magnetosphere.

Understanding this mysterious world of plasma, however, is not easy. With its complex rules of motion, the study of plasmas is rife with minute details to be teased out.

Which particles are moving, what is the source of energy for the motion, how does a moving wave interact with the particles themselves, do the wave fields rotate to the right or to the left – all of these get classified.

Wilson is the first author of a paper in Geophysical Research Letters that was published on April 25, 2012. Using data from the WAVES instrument on NASA’s Wind mission, he and his colleagues have discovered evidence for a type of plasma wave moving faster than theory predicted it could move. The research suggests that a different process than expected, electrical instabilities in the plasma, may be driving the waves. This offers scientists another tool to understand how heat and energy can be transported through plasma.

For the study, Wilson examined coronal mass ejections (CMEs) – clouds of solar material that burst off the sun and travel through space — that move so much faster than the background solar wind that they create shock waves. These shock waves are similar to those produced by a supersonic jet when it moves faster than the speed of sound in our atmosphere.

Read more here. Photo credit: NASA/Goddard.

Aerographite: The New Lightest Material in the World

A team of German scientists from the Technical University of Hamburg and University of Kiel has developed a new carbon-nanotube-based material called Aerographite that’s the lightest material in the world. It’s density is only 0.2mg per cubic centimeter. To put that into perspective: styrofoam is 75 times denser.

Aerographite is made of mostly air–99.99 percent, to be exact–along with carbon nanotubes. The scientists created the material by growing an interlinking chain of carbon nanotubes onto a zinc oxide template:

To create the material, researchers started with a zinc oxide in powder form and heated it up to 900 degrees Celsius, which transformed it into a crystalline form. From this material the scientists made a kind of pill. In it, the zinc-oxide formed micro and nano structues, called tetrapods. These interweave and construct a stable entity of particles that form the porous pill. The tetrapods produced the network that is the basis for Aerographite. In a next step, the pill is positioned into the reactor for chemical vapour deposition at TUHH and heated up to 760 degrees Celsius. 

The lightest material I’ve ever held is aerogel, which I described in this post. By comparison, aerographite is at least ten times less dense than aerogel.