Why Do Small Science?

Chad breaks down the advantages and disadvantages of the user facility model, and why AMO physics is better off without it. I think he hit the high points, like the “economy of scale” advantage of having staff technicians to handle the equipment that isn’t part of your particular experiment, and disadvantages like

[I]f your small experiment that plans to use the particle beam from some accelerator or reactor breaks just before your scheduled beam time, well, try again in six months or a year, assuming they give you another block of time.

This was a constant fear when I was at TRIUMF, and something always broke just before we had beam time, requiring long hours to fix right before we went into “experiment running 24/7” mode, and had to surrender time on at least one occasion. We also tried to be ready to grab someone else’s beam time in case of problems, when the right target was in the beamline, and I have a vague recollection of doing that, as well.

Chart of Electromagnetic Radiations

Awesome so far; I’m still investigating all the nooks and crannies. I think this is getting printed out and put up on the wall at work.

From 1944, edited by Compton, and made by the W. M. Welch Scientific Co. (before he was promoted to be Sargent-Welch)

Why Does This Man’s Head Appear Off His Body?

Analysis of a fun optical illusion.

Over at Uncertain Principles, Chad has started up a series on cold-atom physics. I do a lot of the very same things since I also work with cold atoms; we’re well past the time in the history of this area of physics where simply getting atoms cold is the research. The variety in the research these days is in what you do with the atoms once they’re cold (f’rinstance, I have ways of making them tock)

Here are the first three posts

Tools of the Cold-Atom Trade: Introduction

Tools of the Cold-Atom Trade: Light Scattering Forces and Slow Atomic Beams

Tools of the Cold-Atom Trade: Optical Molasses

But here’s the thing: photons are really cheap. A red laser pointer that you can get for next to nothing at your local office supply store will put out 1,000,000,000,000,000 photons per second.

I love the line “photons are cheap”.

I recall a time when I was showing off our atom trap at TRIUMF and discussing how we detect the atoms so that we know the trap is working (as opposed to the nuclear experiment we were doing), and there was a bit of a communication difficulty, because the nuclear physicist wasn’t used to thinking in terms of getting anything but one particle per atom to detect. But an alkali atom can scatter millions of photons per second (with the transition we were using, if you’re near resonance), which is the complementary part to “photons are cheap” that is important. I can’t think of a catchy description that I’d use, though. (Maybe “atoms are gregarious”?)

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.

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.