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So Just HOW Do You Measure the Shape of the Electron?

May 26, 2011 3 comments

ResearchBlogging.org

A paper recently published in Nature is generating quite a bit of media buzz. [PhysOrg, BBC, Fox, PhysicsWorld]

The paper is entitled ‘Improved measurement of the shape of the electron’ and describes, well, a new method for measuring the electron’s shape.

I love when physics paper titles are easy to understand :)

Anywho, the main thrust of the paper is that the electron appears to be spherical to a very high degree of accuracy. In fact, the press release from the Imperial College of London states that,

the electron differs from being perfectly round by less than 0.000000000000000000000000001 cm. This means that if the electron was magnified to the size of the solar system, it would still appear spherical to within the width of a human hair.

Wow! Now that is pretty darn spherical.

But now you’re thinking “Hey wait, I thought the electron was a wave? Or a string of energy? Or a cloud of virtual particles? How can it actually be spherical?”

These are excellent questions. Indeed, when we first learn about atomic structure in science class the electron, protons and neutrons are all depicted as perfect spheres. As we learn more, we know that this is only an approximation, an easier way of visualizing the complicated subatomic structure.

The truth is, the electron isn’t (well, probably not) spherical. We don’t really know for sure. Current theories point to the most accurate picture being that the electron is a cloud of particles, blinking in and out of existence, which contribute to its mass and size.

So what this paper and these news outlets are actually saying is that this experiment has shown that the electron behaves as though it is a sphere.

Even more accurately, the electric dipole moment of the electron is approximately zero, which is what we would expect from a perfect sphere with uniform charge distribution.

Ok, I know I just said a mouthful. So let’s go through exactly what I mean about the electric dipole moment, and then we’ll go through what this paper actually measured.

Let’s begin with what an electric dipole moment actually is. Imagine you had two particles, one with a negative charge (-q), and one with a positive charge (+q). If you put these two charges close together, you will create special electric field pattern. This type of arrangement creates what is called an electric dipole moment (EDM). The EDM vector (p) is defined as the of the charge on the two particles (q) times the displacement vector between them (d).

The electric dipole moment vector (blue arrow) points, by definition, from the negative charge to the positive charge.

However, you can also create an EDM if you were to have a particle with an uneven charge distribution.

For example, imagine you had a sphere with a total charge +q. In this case, the charge is evenly distributed and you don’t get an EDM.

A perfect sphere with a uniform charge distribution does not have an electric dipole moment.

But now imagine you had an oddly shaped particle that was “squished” at one end.

In this case, there is more charge at one end of the particle than there is at the other. This uneven charge distribution gives the particle its own EDM.

A not-so-perfect sphere has a non-uniform charge distribution. The higher concentration of positive charge at one end creates an electric dipole moment (red arrow).

So if the electron is not perfectly spherical, it should have an EDM. If it has an EDM, we should be able to measure it to infer the electrons shape. Simple, right?

Now, the Standard Model of Physics predicts that the EDM of the electron is too small for us to currently measure; our equipment is just not sensitive enough. But there are variations on the theory that say the electron’s EDM may actually be larger enough to measure using our current technology.

So finding the electron’s EDM will help narrow down our current theories on the subatomic universe.

The existence of an EDM may also help explain why there is so much matter in the Universe and so little antimatter. If the reason for this apparent imbalance in matter and antimatter is the result of an as-of-yet-undiscovered particle interaction, then the current theories of particle physics predict that there should be a measurable EDM for the electron.

So this explains why this experiment is so important. Now lets explain the experiment.

In a simplified picture, the electron EDM in an applied electric field will either point in the same direction as the field, or in the opposite direction. The energy of an EDM in an electric field depends on the direction of the EDM in relation to the electric field.

This means that the EDMs that align with the electric field will have a different energy than those that align against the field. This difference in energy is proportional to the magnitude of the EDM.

So how does one measure this energy difference? One way is to align the spins perpendicular to the field, which will cause them to precess and you can then measure the precession rate, which is proportional to the energy difference.

This effect can also be described in terms of how the two energy states interfere with one another. This interference between the two states can be measured using an interferometer. If there is an EDM present, then a phase shift should be seen in the interferometer signal. If the applied electric field is reversed, then the phase shift should change sign.

So the authors of the paper went looking for this phase shift. They used molecules of Yttrium Fluoride and fired them at a speed of 590 m/s into an apparatus which has a constant electric and magnetic field.

A radiofrequency pulse is applied which excites the molecules into their respective energy states. They are then allowed to interact for a certain amount of time (a few milliseconds) and it is during this time that the molecules in the different energy states develop a phase difference.

A second radiofrequency pulse is applied and the number of molecules which end up in the lower energy state is measured and is proportional to the phase difference they developed during their interaction time in the electric field.

This phase difference is measured via the applied magnetic field and creates an interference curve.

An example of an interference curve from measuring the phase difference via the magnetic field. (Figure 3 from this paper)

If the electric field is reversed, then a small phase shift in the interference curve is seen. Remember that the phase shift is proportional to the electron EDM.

So by varying certain parameters like the magnetic field and the frequency of the radiofrequency pulses, the authors were able to extract the numerical of the electron EDM from the data.

Over 25 million pulses of YbF were used to collect this data. Not only that, but many experiments had to be done to determine systematic sources of error in the experimental setup.

Things like fluctuations in the applied magnetic field, electric field plate potentials not being completely symmetric, magnetic fields generated in the magnetic shielding during switching of the electric field are all sources of error which had to be considered.

So after all this work they finally arrived at their calculated value of the EDM for the electron. The value turned out to be de = (-2.4 ± 5.7stat ± 1.5syst) × 10-28 e · cm, where the first error term is from statistical uncertainty and the second is from systematic uncertainty.

Notice that the error on this measurement makes it consistent with zero and consistent with previous work.

However, this measurement is 54 times more precise than the previous one the author’s previous measurement and puts an upper limit on the EDM of the electron which must be less than 10.5 × 10-28 e · cm.

The next step in these types of experiments is to reduce the uncertainty of the measurements. The authors believe that they should be able to do this using cold molecule techniques and get their measurement down into the 10-29 e · cm range.

Be sure to check out another blog post about this paper by Chad Orzel, author of the blog “Uncertain Principles” and the book “How to Teach Physics to Your Dog”.

Hudson, J., Kara, D., Smallman, I., Sauer, B., Tarbutt, M., & Hinds, E. (2011). Improved measurement of the shape of the electron Nature, 473 (7348), 493-496 DOI: 10.1038/nature10104

Happy Mother’s Day!

May 8, 2011 1 comment

This from Fake Science.

The Science of Your Political Views

April 18, 2011 Leave a comment

While Canadian politics could never match the emotional idiocy of American politics, I’ve seen some pretty heated discussions in the past few weeks.

The Canadian federal election is a couple of weeks away, and with the debates over and done, we are in the home stretch of campaigning.

But how much do attack-ads and party platforms really affect our decision of whom to vote for? Is it possible that our political leanings are more influenced by ‘nature’ than ‘nurture’?

An article in The Globe today discusses the neuroscience behind political viewpoints. As it turns out, the brain of a conservative works differently than that of a liberal.

Dr. David Amodio, Assistant Professor of Psychology at New York University, discussed what these differences were, and how they affect what political party we support.

According to a 2007 paper Dr. Amodio published in Nature Neuroscience:

on average, conservatives show more structured and persistent cognitive styles, whereas liberals are more responsive to informational complexity, ambiguity and novelty.

So conservatives tend to be more, shall we say, stubborn in their political viewpoints than liberals, who tend to gather more information and can be more flexible with their views.

While this may conjure up a stereotypical image of the crotchety old man, so set in his ways that he refuses to vote for anyone but the Conservatives, you should take these studies with a grain of salt.

It is only fair to point out that most of these studies are designed by liberals and may have some bias, and there are certainly many exceptions to these “rules”.

One very interesting study discussed in The Globe conducted at Princeton University:

people were shown black-and-white photographs of the faces of rival political candidates. After viewing each pair of photos for a mere half a second, they were asked which candidate looked more competent. In fact, the candidates they judged to be more competent had won their races two-thirds of the time.

This indicates that, regardless of political leanings, people tend to vote with their emotions as much, if not more, than with their brains. As much as I hate attack ads and staged photo-ops, it would seem the strategists are using science to their advantage.

So whether you identify yourself as a Liberal or a Conservative, NDP or Green, it couldn’t hurt any of us to be aware that the way our brains work can influence how we vote, and we should make an extra effort to stay informed on all the issues; instead of voting for the same party every time just out of habit.

The Beauty of Science

March 25, 2011 1 comment

Scientists don’t like pseudoscience because it diverts attention away from the awesomeness of the natural world. The natural world instills a sense of wonder in scientists because of its diversity and complexity.

Pseudosciences hate real science because it points out the how ridiculous their claims are. But many people are more familiar with pseudoscience (bigfoot, UFOs, psychics etc) and it is these pseudosciences which instill their source of wonder in the world. As a result, many people feel scientists “ruin their fun” or “take the wonder out of everything” when we try to explain why these phenomena really aren’t that incredible.

I believe it was Ned Flanders who once said:

Science is like a blabbermouth who ruins the movie by telling you how it ends. Well, I say there are some things we don’t want to know. Important things.

But in fact the opposite is true. Scientists see the beauty in all things. Whether it be a mathematical proof, a chemistry demonstration, or a physics equation. (I have often hear physicists refer to Maxwell’s Equations as “beautiful”).

Maxwell's Equations. You don't have to know what they mean to know that they look cool!

If you read the xkcd webcomic, you know that I was inspired to write this post because of the comic posted today

So just because scientists spend their day in a lab or in front of a computer screen, this doesn’t mean that we can’t appreciate the world around us. We probably appreciate it more than the average person.

It is sometimes said that scientists are unromantic, that their passion to figure out robs the world of beauty and mystery. But is it not stirring to understand how the world actually works — that white light is made of colors, that color is the way we perceive the wavelengths of light, that transparent air reflects light, that in so doing it discriminates among the waves, and that the sky is blue for the same reason that the sunset is red? It does no harm to the romance of the sunset to know a little bit about it.  – Carl Sagan, Pale Blue Dot: A Vision of the Human Future in Space (1994)

Best. Article Title. Ever.

February 23, 2011 Leave a comment

Only things as awesome as this deserve: Single. Word. Sentences.

“I bet this study was a real pain in the ass.”

Got a better caption? Let’s hear it!

The Adventure of Links: Feb. 19, 2011

February 19, 2011 Leave a comment

Since I’ve been slacking on my links, this will be a big one. Within you will find that sex in space would be tricky, a statue of Robocop, thundersnow, proof of “unintelligent design” and a genetically modified jalapeno.

Physics/Astronomy

Tesla vs. Edison Mad Lib. Yes, you read that correctly.

A biopic about Einstein is in the works.

Scientists smash giant granite balls together to simulate asteroid impacts (w/video)

Its been 10 years since Fox tried to convince people the moon landing was a hoax. Fox has not improved much in the last decade.

Learn physics from an NFL cheerleader. Science rules!

How Vikings navigated using crystals and polarized light.

Health

Gonorrhea has human DNA

How long is a severed head conscious for?

Why beer batter is better for fish and chips.

You mean Nutella isn’t really healthy? Whaaa?

Sugary soda may increase efficiency of brain activity.

A jalapeno genetically altered to hold more cream cheese for jalapeno poppers. I feel fatter already.

Fun/Funny

Fantasy casting posters re-imagine classic sci-fi films. Tim Curry as the Joker? Weird…

Ancient humans used skulls as goblets. Mmmmmm…

The Angry Birds finally settle their disagreements.

Detroit to erect a statue of Robocop.

The mystery of which Cubs game Ferris Bueller went to has been solved!

Lions and Tigers playing with an iPad.

A piece of cake from Charles and Diana’s royal wedding sold at auction. Some people have WAY too much money.

Winston Churchill’s false teeth sold at auction. Seriously, TOO MUCH MONEY!

Sexy Stuff

Space sex would be tricky, says NASA.

Best Science headline I’ve read in a while: Two Timing Spacecraft has Date with Another Comet (w/video)

Why girls moan during sex. Sorry guys, turns out we aren’t THAT good….

Folk Myth : Can shoe size predict penile length?

Post Orgasmic Illness Syndrome. Yes, it’s a real thing.

Girls like monkey sex. Literally.

Internet/Technology

Internet users more likely to volunteer

New device uses EM pulses to detonate IEDs from a safe distance.

A robot that can hear you breathing. Through walls.

Want to have a confession but don’t want to talk to an actual priest? There’s an app for that.

Amazon adds real page numbers to the Kindle.

Mexican cops seize a home-made marijuana hurling catapult near U.S. – Mexico border.

We’ve run out of IP addresses! Run!

Nature

Japanese researchers plan to resurrect the Woolly Mammoth in 5 years. Don’t get your hopes up.

The essentials of bear hibernation

Natural selection limits how many attractive males can exist in a population

The mystery of how fleas jump has been solved.

Thundersnow. What else needs to be said?

Polar bear swims 9 days straight.

Skepticism

An explanation for why people hold on to irrational fears.

In India, Astrology is a science. I know, right? *FACEPALM*

Filmmaker psychs out psychics and ET believers.

External testicles prove “unintelligent design”.

Math Can Be Cool. No, Seriously!

January 25, 2011 1 comment

I did physics in University, and I had to take math courses. I hated the math courses.

And I like to make jokes at my friends who did Applied Math or Pure Math as their degrees, because I just found it so boring.

But dammit if this isn’t the coolest thing I’ve seen all day:

Notice it starts with the Fibonacci Sequence, makes a Fibonacci spiral, and from there it just keeps going.

Awesome.