Author: Chris Lee

(credit: Joint Quantum Institute)

If you know me, you know that I tend to get obsessive about imaging. I usually stick to optical microscopes, but occasionally the folks who play with electrons and ions do something exciting, too. A recently published paper on ion microscopy has me pretty excited at the moment, which is about all the excuse I need to dig in.

Ion microscopy is similar to electron microscopy. In a typical electron microscope, you fire a beam of electrons at a sample and examine the angles at which the electrons scatter. These angles are directly related to the surface of the sample, so with a few optics (magnetic lenses, in the case of electrons), you get an image. Because electrons are heavy and energetic, they have a very short wavelength, so smaller features can be imaged.

After the development of the electron microscope, scientists realized that you can do similar things with ions—the nucleus of an atom with some or all of the electrons stripped off it. Hence, ion microscopy.

(credit: NASA)

We live and die by data these days. Data rates and latencies are everything, with data centers and chips designed to maximize communication speeds.

The hero in the world of data is the optical fiber. Thanks to light's very high base frequency, it is possible to modulate it very quickly without using a huge amount of bandwidth. Optical fiber's ability to modulate light quickly allows network designers to choose a wavelength band, divide it up into slots, and use each slot to communicate its own data. So a typical fiber will carry several channels, each operating at multi-gigabit-per-second speeds. This approach, already many, many years old, has served us very well.

But all good things come to an end. Researchers are always looking for ways to carry more information, and one idea—that one, at the back of the class, ignored by all the other ideas—is to use special states of light to encode information. These orbital angular momentum (OAM) states have the potential to vastly increase bandwidth, but they are difficult to handle. Some recent research, however, suggests that we might well be using OAM states before too long.

(credit: Universal Images Group / Getty Images)

I was kind of shocked and amazed by a recent publication in NanoLetters. It seems that viscosity measurements are still difficult. In my ignorance, I had assumed that this was a solved problem. And, just to show the depths of my ignorance, it turns out that you can learn something about a person's health by measuring the viscosity of their blood. This process is time consuming, as I'll explain in a moment. Now, thanks to the power of our ability to build little gold-iron alloy helices, these measurements just got a whole lot easier.

Stick around and I'll tell you about viscosity

Viscosity is a measure of how well things flow. So, for instance, water flows quite easily and rapidly, while some oils flow more slowly—we say that oil is more viscous than water. The study of fluid flow is a very complicated business so, to simplify the problem, you have to ask yourself what is important. For instance, water flowing down a river is probably dominated by the sheer mass of moving fluid. That means you can probably ignore any influence of viscosity and just worry about mass.

On the other hand, when blood reaches the extremities of the body, it is flowing in very fine channels. There is not a lot of mass to the fluid, but the viscous forces between the channel wall and the fluid are enormous. Here, it might be appropriate to ignore anything to do with mass and focus on viscosity. By examining relationships like this, you can build reasonably accurate models of fluid flows without enduring the pain of the full complexity of fluid dynamics equations. But you can only choose what to include in your models if you know the viscosity reasonably accurately.

(credit: Creon Levit/NASA Ames)

We are at the beginning of a revolution. I've been going on about quantum computing for as long as I've been writing, but it has always been in the future tense. Nothing useful could be done as researchers stepped through all the foothills on their way to the peaks, but now the summit is in view. Just two months ago, we reported on a quantum computer that mashed digital aspects of quantum computing together with analog aspects. In doing so, the researchers came up with a more robust architecture. While this is promising, it's not much more than what others have done with different types of quantum computers.

Now, the same device has been used to do real quantum chemistry calculations, and it seems scarily accurate.

Chemistry? I came here for physics

As any physicist will tell you, chemistry is just physics. And as any chemist will tell you, unsolvable equations are worthless when you're staring down the barrel of a synthesis that has gone wrong (I've paraphrased what a chemist would actually say, which Ars editorial standards would not allow me to print).

The business end of the University of Rochester's Omega laser. (credit: Lawrence Livermore National Lab)

Last month, we reported on a small but enduring mystery in cosmology: why is there so much of one isotope of lithium around? Both ⁶Li and ⁷Li should have been produced when the first atoms formed after the Big Bang. But how much of them should have been made.

The question comes down to basic nuclear physics. When two hydrogen atoms collide under pressure, what is the probability that they will make helium? That sort of physics also applies to collisions between other elements, some of which produce lithium. It is an astonishing achievement that cosmologists can, from basic physics, predict the relative fractions of hydrogen and helium produced in the Big Bang. It is just as astonishing that we can look back in time and measure these fractions and know that cosmologists have it almost exactly right.

Almost. These calculations fall flat when it comes to lithium. They suggest there should be much more ⁷Li than we observe in the Universe and a lot less ⁶Li. Does that mean the estimates are wrong, or is there a real discrepancy? New experiments indicate that when it comes to ⁶Li, the problem seems to be with the Universe and not our calculations.

An undulator, or wiggler, used in a free electron laser. (credit: UCLA Particle Beam Physics Lab)

Lots of interesting stuff happens really fast. Think about a chemical reaction, for instance. The rate of reactions might be slow, but each individual reaction proceeds quickly. This is because a chemical reaction is, essentially, the shuffling of electrons between different atoms, and electrons are fleet of foot.

Generally, if you want to watch something this fast happen, you use what is called pump-probe spectroscopy, in which one short pulse of light initiates an action while another measures the result. A critical requirement for pump-probe spectroscopy is control over the pulses, something that is difficult to achieve in the X-ray regime. This is why a new paper from Physical Review Letters is a promising development.

Pump-Probe

In pump-probe spectroscopy, the pump is a strong laser pulse that sets a reaction (or action of some kind) in motion. After some delay, a gentler probe pulse measures the state of the thing you just kicked. Repeat this for varying delays between pump and probe and you build up a picture of the trajectory a reaction might take.

Physics, as you may have read before, is based around two wildly successful theories. On the grand scale, galaxies, planets, and all the other big stuff dance to the tune of gravity. But, like your teenage daughter, all the little stuff stares in bewildered embarrassment at gravity's dancing. Quantum mechanics is the only beat the little stuff is willing get down to. Unlike teenage rebellion, though, no one claims to understand what keeps relativity and quantum mechanics from getting along.

Because we refuse to believe that these two theories are separate, physicists are constantly trying to find a way to fit them together. Part-in-parcel with creating a unifying model is finding evidence of a connection between the gravity and quantum mechanics. For example, showing that the gravitational force experienced by a particle depended on the particle's internal quantum state would be a great sign of a deeper connection between the two theories. The latest attempt to show this uses a new way to look for coupling between gravity and the quantum property called spin.

I'm free, free fallin'

One of the cornerstones of general relativity is that objects move in straight lines through a curved spacetime. So, if two objects have identical masses and are in free fall, they should follow identical trajectories. And this is what we have observed since the time of Galileo (although I seem to recall that Galileo's public experiment came to an embarrassing end due to differences in air resistance).

A lot of what I write is about measurement, not because I'm in love with calipers, but because the cutting edge of physics is at the limit of what we can measure. That means that when you want to think about what to do next, you need to consider how a measurement can be made more sensitive.

Many people, including some scientists, don't realize that you can learn a lot about the world simply by developing new or better instruments. Today, I've decided that the measurement you all need to know about is interferometry. Why? Because interferometers are the fezzes (fezzes are cool) of the physics world. And now, a group of international researchers has come up with a way to make interferometers even more sensitive.

To understand why this is significant, you need to understand why I'm not kidding about interferometry being cool. In the past, an interferometer at a Laser Interferometer Gravitational-Wave Observatory (LIGO) was used to detect gravitational waves. The experimenters at LIGO worked hard to gain control over every aspect of the experiment (except for the gravitational waves—they had no control over them), including exquisite control over the light source used. In the end, their results involved measuring physical movements that were less than the diameter of a proton. Surely, very few measurement problems would require an even more sensitive interferometer.

Cosmology is truly a remarkable science. Okay, all science is remarkable, but cosmology deals with something so neat and simple—the beginning of the Universe, where all of our reality was governed by fundamental physics. That simplicity is seen through the blurred vision of time, though. The remarkable part is how much detail we can extract from the fuzzy forms that are visible of the past.

One of those details is nucleosynthesis. The Big Bang theory predicts the elemental make up of the early Universe with amazing accuracy. Except for lithium. Lithium is either hiding, or there is an eater-of-lithium that shares an apartment with its better known cousin, the eater-of-socks. In lieu of evidence for an eater-of-lithium, scientists have been trying to figure out what might have prevented lithium from forming in the first place. One solution: a new particle that seems promising.

In the early Universe, there were no atoms or molecules as we know them today. The Universe was made up of protons and electrons that had too much energy to stick together, so they formed a kind of fluid, mixing and flowing around each other. But, as the Universe expanded, the fluid cooled, some of the protons began to stick together, grab a neutron or two, and form the first heavier elements.

Now that gravitational waves have been detected, theoreticians have been furiously speculating about what we might learn from our gravitational wave observatories. Now that we have a couple of observed black hole collisions under our belt, it is time to consider what we might study. There's some speculation that, depending on the sort of physics at play, the event horizon of a black hole might be studied through gravitational waves.

For this to work, the gravitational wave signal has to change depending on what type of black holes are merging. A recent paper in Physical Review Letters indicates that, unfortunately, reality will probably not cooperate.

No bells on a black hole

When two black holes collide, gravitational waves are emitted as a result of a kind of relaxation process. So far, we have mostly been excited about the waves generated just before the merger, where the objects are spiralling into each other and emitting waves as they plunge through space at very high speed.