A Glossary of Frequently Misused or Misunderstood Physics Terms and Concepts. By Donald E. Simanek, Lock Haven University.
A term that is missing is “Exponential”. It is getting more and more common in use, even on tv news, often used as “X is exponentially large”.
This really bothers me, as exponential is about a rate of change, not just a large number. So, boys and girls, the correct usage should be something like “X is getting exponentially larger with Y”.
I suspect that the national bird of Singapore is the Construction Crane. I also suspect that this place must have the highest number of tables at restaurants per capita in the world. Food in restaurants is simply amazing, and everyone goes to eat out. And the plants and weather are very familiar for this Puerto Rican: this place is nice, weird and familiar all at the same time.
I’m having a very good time visiting CQT. I’ve met a lot of people both from Andreas Winter’s and Vlatko Vedral’s group, and have had some very stimulating quantum discussions.
If X and I are symbols for the corresponding Pauli spin matrices, then XXXIX=I.
I’ve been invited to give a talk at The Winter Meeting on Statistical Mechanics in Taxco, Mexico. The meeting will last from January 5th to the 8th of 2010. I hear Taxco is a small cute city in the mountains, a few hours away from Mexico City. I’m very excited about this trip.
You should come too! I promise you will never meet such a fun crowd of Stat Mech Physicists in your life. Make sure you register before November 16th.
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Not all ghosts are of living things. This roll of sticky tape, for instance, is a ghost, and so is this van.
-Look Around You
Steve Chu announced a new graduate fellowship to:
to support outstanding students to pursue graduate training in basic research in areas of physics, biology, chemistry, mathematics, engineering, computational sciences, and environmental sciences relevant to the Office of Science and to encourage the development of the next generation scientific and technical talent in the U.S.
Tell all the graduate students you know about it.
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“On shuttle missions we often see mosquitoes…They seem very confused and die very quickly.”
-A space-station astronaut comments on creatures that are unwittingly launched into space.
Postdocs are the disposables of research. A contract worker, at PhD level, with no chance for a more permanent position, acquiring many of the responsibilities that can be associated with professors, including doing original research, supervising graduate students, writing grant proposals, and everything else. The really frustrating thing about being a postdoc is that it feels transitory, and the title and responsibilities feel like academic limbo. The paycheck is closer to that of a graduate student than anything else.
In fact, I used to get paid more, 7 years ago, in San Juan, just out of a bachelor’s degree in Computer Engineering, than I get paid now in Cambridge after getting a PhD.
But I actually love what I do. I have a lot of flexibility, I get to work mostly on the things I love, and the atmosphere is nice, stimulating and fun. And many people tell me these are my best research days, after this, I’ll never have as much time to follow my crazy ideas ever again.
Carpe diem.
Luckily for us postdocs, the National Postdoctoral Association declared this Thursday September 24th the National Postdoctoral Appreciation Day. And Harvard is going all the way with a full-blown week long Carnival of Postdoctoral Orientations.
This includes a Postdoctoral Happy Hour.
Show your appreciation to all those postdocs in your life and buy them beer when you get a chance.
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“Never mistake motion for action.”
-Ernest Hemingway
They Might Be Giants released their new album, Here Comes Science, with very catchy educational lyrics (yeah, you read it right).
Good stuff.
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In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it’s the exact opposite.
-P.A.M. Dirac
A couple of months ago I wrote a post discussing the quantum mechanical limit to Moore’s law, imposing a limit into how much faster computers can get with current semiconductor technology.
The New York Times published a pretty good overview of similar issues, from a more practical point of view.
After the Transistor, a Leap Into the Microcosm
“We’re at an inflection point, you better believe it, and most of the world is in denial about it,” said Mark Horowitz, a Stanford University electrical engineer who spoke last week at a chip design conference in Palo Alto, Calif. “The physics constraints are getting more and more serious.”
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To MERCURY the Elder: On the most Learned Mercury the Younger.
Rest Maja’s Son, sometimes Interpreter
Of gods, and to us Men their Messenger:
Take not such Pains as thou hast done of old,
To teach men Hieroglyphics, and to unfold
Egyptioan hidden Characters, and how
Men writ in dar Obscurity : For now
Trithemius and Selenus both are grown
Such Cryptographers, as the scace will own
Thee for their Master ; and Decipherers know
Such secret Ways to write, thou ne’er didst show.
These are but Artists which thou didst inspire ;
But now thou of a Mercure art Sire
Of thine own Name, a Pst with whom the Wind.
Should it contend, would be left far behing.
Whose Message, as thy Metal, strikes the Gold
Quite through a Wedge of Silver uncontrol’d ;
And in a moment’s space doth pass as far
As from the Artick to th’ Antartick Star.
So proving what is said of Influence,
May now be said of his Inteliigence,
THey neither of them having such a Quality
As a relation to Locality :
No Places distance hindring their Commerce,
Who freely traffick through the Universe ;
And in a minure can a Voyage make
Over the Ocean’s universal Lake.
This Son of thine, could any Words or Praise,
his Learning, Worth or Reputation raise,
We should be Suitors to him to bestow
Encomius on Himselft, which we do own
Unto his Worth, and use that Eloqence,
Which as his own, must claim Preheminence :
For thee, ’tis Glory enough thou hast a Son
Or Art, that hath thy self in Art outdone.
-Sir Francis Kinaston, Knt
The main reason to support Solar Energy is not only that it will solve our immediate energy needs, but also that it scales well for the future. For example, look at this map that shows the surface area of the arth covered by solar panes to totally fulfill our energy needs for the year 2030. Not much, isn’t it? And, if we ever need more, we can put floating islands of solar scattered in the water.
Or even better, but them up in orbit.
Today, August 8th, is Dirac’s birthday. Happy birthday P.A.M. Dirac!
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The warming and moistening of the boundary layer leads to a hot, moist, rising column which can give rise to cyclogenesis.
-“Where baby hurricanes come from”, Dylan Miracle in private communication
Dirac equation is one of the big achievements of 20th century physics, taking quantum mechanics into the real of special relativity, serving as a foundation of quantum field theory.
Paul Dirac himself describes his motivation for writing his Relativistic Electron Equation, as he calls it.
There was thus a real difficulty in making the quantum mechanics agree with relativity. That difficulty bothered me very much at the time, but it did not seem to bother other physicists, for some reason which I am not very clear about.
By asking a question that nobody cared about, he was able to write an equation that not only connected special relativity and quantum mechanics, but gave much more than that. In his own words,
Now, I found out that this equation gives the electron a spin of a half a quantum and also gives it a magnetic moment, and this spin and magnetic moment are in agreement with obsevartion. […] The new theory still allows negative energies […].
He was very troubled by the negative energy solutions. After all, energy is bounded from below, everybody knew that there must be a lowest state of energy that could be called “zero” with no energies under it. This energy state was associated with the vacuum state. Dirac being himself, in order to fix the negative energy issue, decided to redefine vacuum.
Previously, people thought of the vacuum as a region of space that is completely empty, a region of space that does not contain anything at all. Now we must adopt a new picture. […] we must set up a new picture of the vacuum in which all the negative energy states are occupied and all the positive energy states are unoccupied.
Redefining nothingness takes cojones.
We can get a departure from the vacuum state in two ways: one way is to bring attention on the holes. Well, one can look into the question of how a “hole” will move if there is an electromagnetic field present. And, it moves in roughly the same way as the elctron that fills up that “hole” would move. […] these “holes” move as though they had positive energies and positive charges instead of the usual negative charge of the electron; the “holes” appear as a new kind of particle having a positive charge.
In his new theory, the negative-energy particles could be treated as new particles with positive energies that behave like electron’s evil twins with positive charge.
Let’s recap. Dirac asked a question nobody cared about, then to answer it he made up an equation that gave negative energies that didn’t make sense. Instead of discarding his solution or his question, he reinvents the concept of vacuum and to make it work in a consistent manner, he required to invent a new unobserved physical particle. Dirac’s equation requires the existence of the anti-matter particle, the positron. That is a lot of “if”s. He was unable to fully articulate the prediction of the particle, his explanation follows.
[…] I did not dare to put forward that idea, because it seemed to me that if this new kind of particle (having the same mass as the electron and an opposite charge) existed, it would certainly have been discovered by experimenters. […] That, of course, was really quite wrong of me; it was just lack of boldness.
Still Paul was able to stick to his guns because his equation was, according to him, beautiful. And of course, no only positrons were experimentally discovered not long after, the concept of “holes” as mathematical solutions to the “lack” of electrons is a central idea in solid state physics. Without Dirac Holes there wouldn’t be transistors, for example.
Now, in a recent paper, an experimental group announced they can manipulate the quantum properties of holes just like electrons in materials.
A Coherent Single-Hole Spin in a Semiconductor
Semiconductors have uniquely attractive properties for electronics and photonics. However, it has been difficult to find a highly coherent quantum state in a semiconductor for applications in quantum sensing and quantum information processing. We report coherent population trapping, an optical quantum interference effect, on a single hole. The results demonstrate that a hole spin in a quantum dot is highly coherent.
The abstraction of “Dirac’s Hole”, only introduced for pure mathematical aesthetical reasons is now an accepted, essential, physical particle that is used and manipulated at will. Only a theoretical giant like Dirac could have pulled that off.
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The only thing in this world that gives orders… is balls.
-Tony Montana
Minus Two Fish 