Archive for July, 2013

That Which is Not Forbidden is Mandated

That line, (or something like it), borrowed from literature by Murray Gell-Mann, refers to particle physics. Unless a reaction is not allowed (i.e. it violates some conservation law), it will have some probability of occurring, even if the amplitude is small. And you would have to include it in your “sum over all paths” calculations of interactions.

Well, it appears to apply to science journalism as well. Wrenching a statement out of context and misinterpreting it is apparently not forbidden, so a story will appear that just gets it wrong, as so often happens and happened again. Via ZapperZ, I see that there’s a story about the upper mass limit of photons article I mentioned recently, that takes a disappointing tack:

Photons May Emit Faster-Than-Light Particles, Physicists Suggest

Oh, good grief no. That was not “suggested” at all, and certainly wasn’t the point of the paper.

Here Comes Trouble

The Trouble With Teleportation

For a long time, physicists assumed quantum teleportation wasn’t possible. In order to teleport an object, like our pig lizard, we must scan it to obtain precise information about its atomic structure. However, the more accurately an object is scanned, the more it is disturbed by the process of being scanned. We can’t measure a particle without altering it in some way, never mind every single subatomic particle that makes up a full-sized pig lizard. So how could we extract all the information we would need to create an exact copy in another location via teleportation?

In 1993, an IBM physicist named Charles Bennett and his colleagues figured out a way to work around this fundamental limitation using quantum entanglement

Kudos to Jennifer for mentioning that quantum teleportation transmits information (rather than objects), and doing it several times.

Unfortunately, there is one omission.

Ah, but there is a catch: The original object must be destroyed in the process. When B scans A, that interaction alters the latter’s properties. A no longer exists in the exact same state as it did. C is now the only particle in that original state.

No! The information about the original object must be destroyed. When, in the experiments she mentions, teleportation succeeded between clouds of atomic vapor, the atoms themselves were not destroyed. That would have certain implications, making a million or so atoms just go poof — it would violate a bunch of conservation laws, not the least of which is conservation of energy. The atoms did not simply disappear and then appear in the adjacent space — this is not Star Trek. There were two clouds, and the information was teleported from one to the other.


He loves only cold!

If you ever wondered how a Helium dilution refrigerator was, or even if you have no idea what one is, here’s a great explanation.

You need to a flashplayer enabled browser to view this YouTube video

Associate Professor Andrea Morello from the University of New South Wales explains how ‘zero-point motion’ makes it possible to use Helium-3 and Helium-4 in a dilution fridge to get down to only thousandths of degrees above absolute zero.
It is this technique which is used to cool the MiniGrail at Leiden so that it can act as a gravitational wave antenna.

A Sin of Omission

This Is What Wi-Fi Would Look Like, If We Could See It

This should read, “This Is NOT What Wi-Fi Would Look Like, If We Could See It”

I could live with this if it were simply an artist’s rendering of wi-fi, but the leap to “this is what we would see if we could see it” is just wrong.

We can see in the visible part of the spectrum, and yet we do not “see” the light all around us. Why? Because to see anything, a photon has to hit our eye, be detected and then interpreted by our brain. We do not see photons whizzing past us, or going in any other direction, other than the ones hitting our detectors.

What would we see? Well, the basic thing is that objects would look basically the same, except blurrier. There would be diffraction effects because of the longer wavelength. Some objects we think of as opaque would be more transparent, and vice-versa, because transmission of light depends on the wavelengths involved.

What wouldn’t we see? Any sort of wavy lines depicted in one of the pictures, and not only because we just don’t see that light, but also because that’s not what light does. Yes, light acts as a wave. But the (sometimes orthogonal) sinusoidal graphs you see aren’t saying that light travels this roller-coaster path — a decent depiction (like this one) will have labeled the axes, and it will be Electric (and Magnetic) field strength vs time (or position, since they are proportional). The field strength varies with position, as time passes, or as you look along a straight-line path.

Wi-Fi waves are about three to five inches between crests, which a computer reads as “1.” (The troughs of the wave are read as “0.”) That information then translates into the chains of binary code that dictate the Internet.

Ugh, and double-ugh. No. A constant frequency wave is a pure tone — there’s no other information in it. To encode information you have to modulate something about the wave — radio signals modulate the amplitude or the frequency (AM or FM). You can also modulate the phase of the signal or the polarization. (Those are analog schemes and wi-fi is digital, so there is an additional complication and change in terminology, e.g. FM becomes frequency-shift keying) Wi-fi is around 5 GHz, and yet we get nothing like that rate of data transfer, because that’s the carrier frequency — we are limited by the modulation rate. We also don’t get a boring progression of 10101010101010101010…, because that’s the signal you’d get if the system worked in the way it was described.

Almost described, that is. If a peak is a “1”, a trough would be a “1” as well. When you detect light, you detect the amplitude of the intensity, which is the square of the field. What I think the originator of the statement was trying to incorrectly say is that a field null would be a zero, but the binary signal only comes about when you modulate and then demodulate the signal.

The Dark Side of Cat Juggling

Cat-turning: the 19th-century scientific cat-dropping craze!

One thing I’ve learn from studying the history of science is that scientists are human beings. Often incredibly weird, weird human beings. For example: in the mid-to-late-1800s, an exciting era in which the foundations of electromagnetic theory were set and the electromagnetic nature of light was discovered, a number of the greatest minds in physics were also preoccupied with a rather different problem.

Dropping cats.

What Do You Mean, No Gender Bias in Physics?

I ran across Zapperz’s post Physics Departments Without A Single Female Faculty Member yesterday, and made a comment on the blog. Today I see that Chad has a post up, Baseball and Gender Bias: “Number of Women in Physics Departments: A Simulation Analysis “, which exceeds anything I would have said, had I cobbled together a post.

Which is not to say I would have, because this is the sort of subject where some scientist readers stop acting like scientists, in terms of data interpretation and/or reading comprehension. This was a narrowly-defined analysis, based on a specific premise. As Chad puts it

They have assumed a particular gender distribution among the imaginary faculty pool in their simulation, which matches the gender distribution of the real sample– 16% of the bachelor’s-only faculty are female and 11% of the Ph.D.-granting pool. That’s descriptive, not prescriptive

IOW, they used the actual gender ratios we have, because that’s what we have — nobody has said this is good, or appropriate. It’s not an endorsement. It also doesn’t say that there is no discrimination going on.

Photon Decay?

How stable is the photon? Yes, the photon.

If the photon has a mass it can decay into other particles…

If the photon is unstable and decays into other particles, then the number density of photons in the cosmic microwave background (CMB) should decrease while the photons are propagating. But then, the energy density of the spectrum would no longer fit the almost perfectly thermal Planck curve that we observe. One can thus use the CMB measurements to constrain the photon lifetime.

Interesting approach to the problem. It’s weird to see the phrase “photon rest frame” as there’s no such thing for a massless photon, but once you hypothesize a mass it becomes a perfectly reasonable thing to do, and then you can put limits on what the mass could be.

Rube-y Goldberg Tuesday: History Lesson Edition

The History of the Rube Goldberg Machine

Goldberg’s carefully designed machines employed birds, monkeys, springs, pulleys, feathers, fingers, rockets, and other animate or inanimate tools to create intricate chain reactions that completed basic tasks like hiding a gravy stain, lighting a cigar while driving fifty miles an hour, or fishing an olive out of a long-necked bottle. As Goldberg himself put it, his cartoon inventions were a “symbol of man’s capacity for exerting maximum effort to accomplish minimal results.”

Looking Before We Leap

The wait of the world

Mainly about leap seconds.

On the split-second level, ‘leap’ mediates between the precision of atomic time and the position of our Sun in the sky. It is worth noting that while a leap year is a year with an extra day (Leap Day — February 29, when turnabout is fair play), a leap second lasts no longer than any other second. Applied to a minute, a positive leap second creates a 61-second interval that is not called a leap minute. (Nor would the 59-second outcome of a negative leap, should one ever be required, be called a leap minute.)

A leap minute, rather, is a hypothetical way of putting off till tomorrow what leap seconds do today. If instituted, it would allow the powers responsible for time measurement and distribution to defer insertion till the leap-second debt reached 60, and trust some future authority to intercalate them all at once. But a leap minute would likely add up to a much bigger headache than the sum of its 60 leap seconds.

I’m not sure if the US has established an official position on the matter. I know there have been discussions about the pros and cons, both within the US and with international attendance, such as the conference mentioned in the article.

Perhaps even more of an affront to British pride than the misplaced meridian is the fact that Greenwich Mean Time (GMT) is no longer the world standard. GMT fell out of official favour in the 1920s, for semantic reasons.

It may be worth mentioning again that in the US, GMT was used as the official, legal reference for determining the time and time zones until the 2007 America Competes Act, where it was finally changed to UTC (the change is spelled out in sec. 3570).

I wouldn’t mind additional leap second insertions. But then, I don’t programme computers, or control air traffic, or perform any of the myriad time-sensitive activities that would make me a stakeholder in the leap-second debate. I am merely a person who still wears a wristwatch, owns a sundial, and takes an abiding interest in all aspects of finding, keeping, and telling time.

From what I have heard and observed first-hand, it’s a pain to do this, and we’re just lucky that things haven’t gone wrong from the many potential problems inherent to the issue. My own view is that counting on being lucky is a terrible standard operating procedure.

Photography That's Out of This World

The Best Space Images Ever Were Taken by Apollo Astronauts With Hasselblad Cameras

Starting with Apollo 8, astronauts carried a Hasselblad EDC with them on their lunar journeys. Neil Armstrong and Buzz Aldrin each had one during their brief but historic romp on the moon on July 20, 1969. Subsequent men also took Hasselblads, 12 of which are now sitting on the moon’s surface, left behind to save weight on the return trip. Only the film magazines returned to Earth.

Next Page »