But still pretty neat. A 15+ minute video of someone making vacuum tubes by hand.
Category Archives: Physics
NYU: Size Doesn't Matter
For vision, at least. Spacing, Not Size, Matters in Visual Recognition, NYU Researchers Find
New York University neuroscientists have concluded that it’s the spacing between letters, not their size, that matters. In general, objects, such as letters, can be recognized only if they are separated by enough space, the “critical spacing.” Objects closer than that spacing are “crowded” and cannot be identified. A broad review of this crowding phenomenon, appearing in the latest issue of the journal Nature Neuroscience, shows that this critical spacing is the same for all objects, including letters, animals, and furniture.
No mention if the Rayleigh criterion is responsible for this.
What Sam McGee Saw
Dance of the Spirits — The beautiful Aurora Borealis
There are strange things done in the midnight sun
By the men who moil for gold;
The Arctic trails have their secret tales
That would make your blood run cold;
The Northern Lights have seen queer sights,
But the queerest they ever did see
Was that night on the marge of Lake Lebarge
I cremated Sam McGee.
Intro to The Cremation of Sam McGee by Robert Service
Roll, Roll, Roll Your Blog
Huge blogroll of women blogging on science and technology at Sciencewoman. Via sciencegeekgirl
Define Your Terms
There’s quite a bit of physics/science terminology that is defined in a way that doesn’t jibe (or is essentially opposite) of the everyday use of the word, like coincidence. But even within science, different disciplines will interpret terms differently, because of the conventions and anticipated results.
Bandwidth and Community Expectations over at Uncertain Principles.
[W]hether a femtosecond laser is a single-frequency source or a broad-band source really depends on what the expectations of your particular research community are. By the standards of chemistry, it’s incredibly narrow, but for laser spectroscopy types, it’s comically broad.
There’s more. Typically, to a physicist, the Gamma ray portion of the spectrum is comprised of photons that comes from nuclear interactions and X-rays come from atomic interactions, while astronomers tend to use an arbitrary cutoff of 1 MeV to distinguish these from each other.
You're a Spin-1/2 Baryon. How Do You Feel About That?
Proton Therapy – Cost and Benefit
[T]he current question on whether patients do benefit from it better than conventional, less-costly treatment.
‘Proton therapy’ was one answer to the “what good is it?” question of physics when I was working at TRIUMF, and explaining the benefit of basic research wasn’t an option.
Proton therapy is the use of protons to destroy tumors or cancerous cells in a way that is more targeted than other treatments like chemotherapy or EM radiation; I can’t really get into the medical subtleties (dammit, Jim, I’m a physicist, not a physician!). EM radiation will attenuate as it goes onto the body, so if the target is below the surface, you’ll get more energy deposited in the healthy tissue in front of the target. Charged particles lose energy, by ionizing atoms or molecules, in proportion to their speed — faster moving particles don’t spend much time interacting with a given atom — and so as they slow, they are able to deposit more energy. This compounding effect means they deposit a large fraction of their energy in a small region, and the penetration depth where this occurs can be tuned, as it’s proportional to the incident kinetic energy.
So you do far less damage to the surrounding healthy tissue. The question, in Zapperz’s link, is whether that translates into an overall better response of the patients, and a cost/benefit analysis.
Here is a somewhat more detailed explanation of the physics, including a dose vs depth graph for EM, protons and protons with a modulated energy source to spread out the Bragg peak. Protons have an advantage over electrons for this type of treatment: because they are much more massive, they have a much greater tendency to forward-scatter and reach the target.
Barkeep, Another Round
James Cronen discusses The Physics of Glassware
To put it terribly analytically, a glass is a potential well. When you pour a liquid into a glass and it comes to rest, the molecules don’t have enough total energy to make it out of the bowl of the glass. They stay there until they get enough energy to leave, or the walls around them disappear. This happens by one of three mechanisms.
So this isn’t a discussion of whether glass is a liquid, it’s a physics take on the functionality of glassware. And it’s purely a classical one:
Quantum wine in a potential well might leak out of the sides of the glass due to the process called quantum tunneling. Classical wine has no such problem. More on that some other time.
Some of my glassware is beakers I bought years ago and put on the bar, because the parties my housemates and I threw weren’t geeky enough. I also have roly glasses in case any weebils come over for cocktails (and want to get almost-falling-down drunk)
Why is This Class Necessary?
Do Pre-Meds Really Need That Year of Organic Chemistry?
Feel free to replace this, mentally, with physics, and it can be applied to other endeavors. But here’s a joke that was posted on this topic at slashdot (which I found via another conduit)
A college physics professor was explaining a concept to his class when a pre-med student interrupted him.
“Why do we have to learn this stuff?” he blurted out.
“To save lives,” the professor responded before continuing the lecture.
A few minutes later the student spoke up again. “Wait– how does physics save lives?”
The professor responded. “By keeping idiots out of medical school.”
The God-Particles Must Be Angry
Delays at CERN because of a magnet quench, requiring repairs. But you already knew that.
What you may not have heard:
There could be further delays because helium has also escaped into the LHC’s tunnel, and there were unconfirmed reports that the vacuum had been lost in part of the beam pipe in which protons circulate.
So, the folks searching for that lost vacuum are going to have high, squeaky voices.
Extra Credit Assignment: The Nature of Things
Via Shores of the Dirac Sea I find The FQXi Inaugural Essay Contest (Summer 2008): THE NATURE OF TIME
Each essay contest will focus on a particular theme, question, or subject that the submitted work must directly address. For the current contest, this is “The Nature of Time,” including, but not limited to, the arrow of time; the emergence of time in quantum gravity; time, free will and determinism; time travel; the beginning or ending of time; and timelessness. Additionally, to be consonant with FQXi’s scope and goals, essays should be primarily concerned with physics (mainly quantum physics, high energy ‘fundamental’ physics, and gravity), cosmology (mainly of the early universe), or closely related fields (such as astrophysics, astrobiology, biophysics, mathematics, complexity and emergence, and philosophy of physics), insofar as they bear directly on questions in physics or cosmology.
Here’s the problem as I see it: the nature of time isn’t a science problem, it’s a philosophy problem. Many of the suggestions for essays aren’t really tied to physics all that strongly. Asking “how does time behave?” is a physics question, as is “how does this influence other phenomena?” But asking, “What is time, really?” is metaphysics.
That’s not to say the question has no value. If it can get someone to look at the problem from a different angle and it leads to a different description of nature, that’s great. But science is an investigation into how nature behaves, and not, fundamentally, into why it behaves that way. You reach the level of the four-year-old asking a question, and responding to each one with, “But why?” You can only give justification so many times before you run out of answers and have to say, “Go ask your mother.” Or, in the case of science, “We don’t know. It’s not the question we’re trying to answer.”
Science explains the operation of nature with models — mathematical descriptions that allow one to predict and explain what’s going on. But there’s nothing that guarantees that nature actually is this way, that the convenient terms we use are actually real. In many ways it’s bookkeeping. We notice that we can quantify certain things, like energy and work. Physics defines energy as the capacity to do work. That doesn’t tell you what energy is, it tells you why it’s useful. We have this quantity of something that doesn’t change — we can convert it from one form to another, and it allows us to predict things, like how far something will move, or whether an event will occur spontaneously. That’s useful to know! But it says nothing about what energy is. These are entries in a ledger that let us come up with an answer. Bookkeeping. This is one thing that can make thermodynamics difficult — all of those thermodynamic potentials make it advanced bookkeeping.
I recall being asked whether photons were real. I study atomic physics, so my reaction was, “Sure, photons are real.” Then I was asked about phonons. Nah — phonons are just a convenient way of describing vibrational modes of a lattice. Which is when it hit me that photons could just be a convenient way of describing the vibrational modes of an electromagnetic field. To a condensed matter physicist, I’m sure that phonons seem real. But we don’t do experiments that tell us that they are real, we do experiments that tell us how nature behaves. Nature may behave as if they are real, because we have accurately determined the properties, but that’s not the same thing. Physicists do this a lot, and some are easier to spot than others. We have electrons and holes in semiconductors. Are holes real, or are they just a convenient description of the lack of an electron? What is mass, anyway? What is charge? Is the Copenhagen interpretation of quantum mechanics the right one?