Stringy Soot

Soot particles grow inside a flame when tiny, carbon-rich spheres stick together to form larger, tenuous aggregates. As they grow, the particles take on a characteristic branched shape because two colliding clusters are most likely to attach at their protruding “fingers.”

These bushy shapes are conveniently described as fractals–geometric objects whose mass grows as a fractional power of their linear size, rather than the third power that characterizes ordinary solids like spheres and cubes. Theory predicts that virtually all clusters should have a fractal dimension very close to 1.8, and past experiments agree. But a collaboration led by Hans Moosmüller of the Desert Research Institute in Reno, Nevada, found many clusters with a much lower dimension, characteristic of a more rod-like shape.

Remember the important rule of true-or-false questions: if any part of the statement is untrue, then the statement is false.

14-year-old hit by 30,000 mph space meteorite

A schoolboy has survived a direct hit by a meteorite after it fell to earth at 30,000mph.

No, false. There’s no way the meteorite was traveling 30,000 mph when it hit him, nor did it hit him and then form the crater. This doesn’t mean the chunk isn’t a meteorite, nor that he wasn’t struck by it — elements of the story are certainly plausible, and there’s no reason to suspect that anybody is fabricating the event. I suspect it’s a case of a reporter doing a minimum of background fact-checking and seeing that meteors travel that fast in space and just ran with it — no feel for the number being reasonable (supersonic, and many times faster than a bullet) or reconciling the relatively minor injury with this and the creation of a crater.

There’s a fairly thorough discussion of the details over at Bad Astronomy

Acoustic Black Hole Created in Bose-Einstein Condensate

The result is a region within the BEC in which the atoms move at supersonic speed. This is the black hole: any phonon unlucky enough to stray into this region cannot escape.

One reason why sonic black holes are so highly prized is that they ought to produce Hawking radiation. Quantum mechanics predicts that pairs of “virtual” phonons with equal and opposite momentum ought to be constantly springing in and out of existence in BECs.

Relativity is not an easy concept. Special relativity is hard enough, and General relativity really ups the ante; I am not well-versed in anything beyond the basics of the latter, but one of the notions of GR is that freefall in a uniform gravitational field is actually an inertial frame, i.e. non-accelerating, which is not a concept present in Special Relativity.

Which appears to be the linchpin behind the argument presented here: In Twin Paradox Twist, the Accelerated Twin is Older

In 1905, Einstein described the ideas behind the twin paradox to demonstrate the effects of time dilation according to special relativity. In 1911, physicist Paul Langevin turned the concept into a concrete story involving two hypothetical twins. Ever since then, scientists have offered various explanations for exactly why this aging paradox occurs, and whether it is even a true paradox at all.
As Abramowicz and Bajtlik note in their study, it is often claimed that the twin paradox can be explained by the acceleration of the traveling twin that occurs when he turns around to go back to Earth. Abramowicz and Bajtlik show, however, that it is not the acceleration that causes the age difference in most cases. By presenting a scenario in which the accelerated twin is older at the reunion, the scientists show that the final time difference between the twins often depends only on their velocities as measured with respect to an absolute standard of rest, and not on acceleration.

First of all, a note that “absolute standard of rest” is not something that is part of the original twins paradox. Which is because in 1905, there was only Special Relativity. The scenario presented is of the twins near a large mass, and one of them in a Keplerian obit, and thus not accelerating according to General Relativity. The notion of absolute rest is in contrast to accelerations and rotations, which can be distinguished, while motion in special relativity cannot. The mixing of the two frameworks isn’t even an instance of the reporter mucking things up — it’s presented in the ArXiv paper that way.

It is often claim that the resolution of the classical
twin paradox should be the acceleration of the “travel-
ing” twin: he must accelerate in order to turn around and
meet his never accelerating brother. The twin who accel-
erates is younger at the reunion. Here we challenge this
notion. We start with describing a situation in which,
like in the classical version of the paradox, one of the
twins accelerates, and the other one does not accelerate.
Quite contrary to what happens in the classical version,
the accelerated twin is older at the reunion.

That’s because you have changed the parameters, and are no longer describing the classical twin paradox.

I have no complaint about the physics. I just don’t think the authors should feign surprise at the result, as if it were somehow unforeseen that changing conditions could yield a different answer. The answer should not be surprising at all, because what they describe is one twin being at rest, and the other in an orbit. Which is exactly what would be described by an observer on a non-rotating planet, and another on a satellite. Maybe a satellite which is part of a navigation platform, able to communicate with a receiver and quadrangulate position and local time, with the modification that the satellite isn’t orbiting at a different distance from the planet.

All of this is pointed out in “Relativity in the Global Positioning System” by Neil Ashby. In section 5 there’s a graph of the results of differing orbital distances, and below some threshold we see that the satellite will age more slowly than someone on the planet surface. I’m not sure how old it is, but the update posted in June 2007 says

I have updated the text in quite a few places, such as eliminating the word “recently” which is no longer really recently.

So the notion is definitely not new, nor should have been surprising.

Let’s take a look at some bad physics, demolished in A cornucopia of cluelessness

Amazing. We’re going to change a unit conversion factor using technology. Apparently, such a breakthrough will also enable us to develop overunity devices, overcome the Second Law of Thermodynamics, and achieve perpetual motion. I suggested in my comment on Michael’s blog that perhaps we should also be looking into the technological possibility of getting more gallons per liter and more miles per kilometer. In fact, why stop there? I will look into employing technology to change the number of centimeters per inch and make myself taller and lengthen my…. But I digress.

(FYI, Leonard Pinth-Garnell)