Time crystals: One of the weirdest ideas in physics
Physics is defined by its symmetries, from thermodynamics laws like the conservation of mass and energy, to the principle that the universe is basically the same all over. Symmetry can also suggest some truly bizarre ideas. One of those ideas is time crystals.
The definition of a crystal is simple enough - it’s any solid whose constituent parts are arranged in an orderly, repeating pattern extending out in all three spatial dimensions. Although crystals themselves are defined by their symmetrical arrangement, they actually represent a form of what’s known as spontaneous symmetry breaking in closed systems.
The idea here is that if you have a bunch of free atoms whizzing around, the overall system can display symmetry. But if those atoms suddenly come together to form a crystal, the overall symmetry of the system has been reduced onto one particular subgroup, namely the crystal. The overall spatial symmetry has been been broken, but the periodicity that defines the crystal’s structure means it hasn’t been entirely lost.
While that may be a bit theoretical, it’s all fairly straightforward. The intriguing question is one that is often asked of physical phenomena - if this process exists in the three spatial dimensions, could it also occur in the dimension of time as well? That’s the question currently being investigated by MIT physicist Frank Wilczek, who won the 2004 Nobel Prize along with David Gross and H. David Politzer for their work on the strong nuclear force.
Wilczeck, along with collaborator Al Shapere from the University of Kentucky, has just published two papers examining how the mathematics that govern crystal formations in space could also work in time. They argue that time translation symmetry - the notion that a system will maintain the same features over a given interval of time - can be broken in low energy states and then reduced to a smaller part of the system, which they call time crystals.
The key here is that the system being described is in its lowest energy state, which means that there should be no movement in it at all. But if something inside the system starts moving, then the time translation symmetry has been broken. What Wilczeck and Shapere argue is that these moving objects could simply get stuck in an eternal loop. The periodic movement of the object through time is just like the periodic arrangement of a crystal’s internal structure through space, and the end result is the same - symmetry is broken, but it isn’t lost.
We don’t yet know if time crystals exist, and Wilczeck and Shapere aren’t claiming otherwise - they’re simply saying that it’s mathematically possible for the crystals to exist. There are some real world reasons to think such crystals might exist, specifically in the realm of superconductors. These can carry currents even in their lowest energy state, which is a form of movement, and those electrons passing through superconductors could theoretically keep moving forever.
If time crystals really are out there, we could be looking at some potentially fascinating applications for them. The periodic nature of time crystals means they would perhaps be the most basic, fundamental form of timekeeping in the universe - as Wilczeck writs in one of his papers, “Spontaneous formation of a time crystal represents the spontaneous emergence of a clock.” These time crystals might also have a home in quantum computing, where they could be arranged as qubits and used to undertake calculations at zero energy.
The one thing time crystals won’t give us, however, is perpetual motion. Well, that’s not exactly the case. A time crystal would be able to move periodically forever - which is the literal definition of perpetual motion - but it wouldn’t actually allow us to get any energy from the system, which is generally what people really mean when they refer to perpetual motion. Time crystals would only exist in the lowest energy state, so it would be impossible to gather any usable energy from this eternal loop in time.
For more, check out the original papers here and here. Via Science News and Technology Review. Image by cybrain, via Shutterstock.
The Beautiful, Deadly Vortex That Tears Huge Buildings Apart
The Karman Vortex Street isn’t someplace you’d want to take up residence — it’s literally the path of destruction, where buildings collapse and destruction reigns. Unfortunately, under the right conditions, a Karman Vortex can follow you.
Find out how this beautiful phenomenon can take down anything in its path.
Theodore von Karman, a Hungarian physicist, spent much of the first decade of the 1900s trying to figure out why certain things — airplane wings, bridge supports, buildings, and submarines — would suddenly and spontaneously begin to vibrate. The vibration, once started, would often amp up and up until the entire structure would spin out of control or fall apart. This, understandably, was a major problem.
Karman’s first insight was that the closer to cylindrical the object’s shape was, the more it tended to vibrate. His second insight led him to turn away from the actual object and toward its medium. And after looking at the medium that moved over these objects, he noticed something.
Aerodynamics are at their best when the air (or any gas, or liquid) flows neatly around the object, conforming exactly to the object’s shape. This is why wings open with a curve and taper off behind, parting the air quickly but letting it flow over the curves and break away from the wing going pretty much directly back. By sending air streaming directly back, the object gets a push directly forward. Of course wings divert the air slightly down, giving the plane a slight lift, as well, but they still give the air an orderly path to follow.
Things get tricky, though, when a flowing medium encounters a cylinder instead of a wing. When that happens, the flow can ‘break away’ from the object at its widest point. Instead of flowing back from the object, it is directed off to one side. This break in the medium curls the other side in, before it, too, breaks away in its own dash to one side. Now, instead of the air or fluid pushing the object forward, it pushes it to either side, over and over. This continual back and forth makes the whole structure shake back and forth ever more violently as behind it, the fluid forms a rather beautiful structure now dubbed the Karman Vortex Street.
This stuff was no joke — and even though Karman was lionized for figuring it out in 1911, the lesson didn’t always stick. The most famous example of the Karman Vortex Street taking something down was the Ferrybridge Power Station, a coal plant in England. Built in the 1950s, the plant managed to struggle along until November 1st, 1965, when winds of eighty-five miles per hour swept through the station. Three of the eight cylindrical cooling towers began to vibrate. They had been placed together so that between them they spun up the vortex, which pushed them all back and forth. In mid-morning, the three towers collapsed, leading to a fire that took out the other five.
Now bridge pilings, towers, airplanes, and other structures, are built with the vortex street very much in mind. Some are carefully proportioned, and some have ‘screw’ shapes cut into them to encourage the air to flow one way or another, but not both. You can still see Karman Vortex Streets forming behind planes, behind any pilings in water, and behind entire islands. The image just to the left of this paragraph is a street forming off Rishiri Island in Japan. Fortunately, the islands show no sign of toppling over.
Image credits: Fragile Oasis, ESA/The Map Addict and NASA.
Turn water into 4 different deadly weapons, using just pencils and a battery
A simple childhood experiment, involving basic stuff that anyone could find around the house, provides you with a simple means to make both a chemical and physical weapon. Find out how to split ordinary water into two different dangerous gases, and cause two different explosions.
Top image: Water and Fire, by Serg64/Shutterstock.com
F = ma
(My favorite formula, Want to know why? lol)
Scientists blast iron with lasers, and it disappears from X-rays
Scientists have found a way to turn iron nuclei transparent to X-rays, using lasers. And besides the coolness of making things disappear using lasers, this could have huge applications in optical computing.
One of the fun things about science is every now and then something pops up that is extremely cool and that you were never even aware existed as a concept, let alone a practice. For me, electromagnetically induced transparency (EIT) is one of those wonderful surprises. Apparently, it’s been known for years that, with a properly applied laser of one wavelength of light, it was possible to make objects transparent to other wavelengths of light. It’s been used in lightweight atoms, but recently they brought in a heavy hitter.
By all accounts, iron is a heavy substance. Its bulk is the reason why it shows up on X-rays at all. The high-energy waves pass right through lighter material, which is why x-ray pictures only show the heavy calcium skeleton that people have, and not the lighter flesh. Iron-57 atoms are not going to be missed by an X-ray — until scientists used EIT to wink them out of existence, as far as the X-rays were concerned. Scientists took two thin sheets of the material and held it in place with carbon, which is invisible to X-rays. They placed two platinum mirrors to either side of the iron sheets. They then fired a beam of low-energy X-rays into the set-up. The beam was reflected by the platinum mirrors back and forth again and again. Trapped, it set up a standing wave in the sandwich of equipment. Standing waves have peaks and troughs, where the most violent activity takes place, and things called ‘nodes,’ where there is no motion at all. You’ve probably seen this when you’ve made a wave using a jump rope — the middle part, between the peak and trough of the jump rope’s wave, will always stand still. That’s a node.
When one sheet of iron was at a node, and one sheet was at an antinode (the peak or the trough), another, higher energy x-ray was shot through the entire contraption. The x-ray moved through them without interacting with either sheet of iron. It was like they weren’t there. Scientists believe that the iron ‘disappears,’ because of what’s called a quantum-optical effect. The platinum mirrors form an optical cavity — a little light trap. When this happens, the atoms all absorb and radiate energy in a synchronized way. More energy being sent through there will, if the system is placed exactly right, no longer interact with a bunch of different atoms in different states causing a few of them to randomly absorb a photon and pop an electron up to a higher orbit. Instead, it will deal with a synchronized team of atoms. If it hits this wall of atoms in the one way, all the atoms will react as one. If it hits one group of iron atoms at a node and the other at an antinode, the oscillations it causes will simply cancel each other out, and it will be as if nothing is there at all. It’s kind of as if the two pieces of metal “cancel each other out” on a quantum level.
Obviously, it would be cool if we could get this in macro size, making solid objects vanish from X-ray scans at will with the flick of a laser. More practically though, any light-controlled on-off switch that incorporates metal is a promising step for entirely ‘optical’ computers operated with beams of light. Maybe scientists could go for broke and create invisible optical computers, operated with beams of light. The best of both worlds!
Top Image: Dr. Ralf Roehlsberger, DESY
Via Nature.
A rainbow cloud shimmers over Ethiopia
Here’s a rare look at a rainbow over the skies of Ethiopia. Find out how this cloud — known as a “pileus cloud” — brightens the atmosphere.
Pileus clouds are formed over the towers of cumulus clouds. The cumulus clouds puff up through convection, or the upwards motion of moist air in one section. The moisture in the air condenses and forms the towers of the cloud. Above the cumulus clouds in the troposphere, ice crystals are compressed by the wall of upward-moving air. They form the little cumulus “caps” that are pileus clouds.
These clouds only form when the convective current is strong enough and the upper atmosphere has enough water in it to form the crystals. Even then, what most people see are puffs of white cloud over the top of the cumulus clouds, not dazzling rainbows.
As with any rainbow effect, the light has to be precisely placed. Light has to hit the cloud and diffract through the prism of the drops. But when light hits the cloud from behind, it usually hits the eye of the beholder head-on as well. This means that any rainbow effect is drowned in a flood of white light. Iridescent clouds are only visible when something blocks out the light from the sun while still showing the light through the clouds. In this case, the dark cumulus cloud blocks out the sunlight, while the pileus cloud shimmers.
Via New Scientist. Image: Esther Havens.
Graduating Into Entropy
This self-guided bullet can chase you down from over a mile away
There was a time when increasing the distance between yourself and a sharp shooter bent on your extermination would significantly improve your chances of survival. But that time is coming to an end.
Government engineers have designed a bullet that can aim itself, correcting its own path mid-flight in order to connect with targets over a mile away. Is this the future of armed warfare? More »
Weird, Rare Clouds and the Physics Behind Them
Published last 2009
Sometimes likened to UFOs, lenticular clouds are usually created by gravity waves. Chuang evokes loose shock absorbers to describe what gravity waves are.
“You take your grandma’s Cadillac and drive it over a speed bump, and after that it goes up and down for a while,” he said. “The reason you are going down is because of gravity, and then there are springs in the suspension that push you back up.”
In the case of lenticular clouds, the speed bump is usually some kind of topography, like a mountain, that gets in the way of air flow. As the air comes down the side of the mountain, it tends to overshoot and then springs back up. It oscillates like this for a while, and on the upward part of the waves, clouds form as rising air cools.
“Clouds mark the highest part of the oscillation,” Chuang said.
Lenticular clouds can also be caused by other speed bumps, such as tall thunderclouds, but because they often form on the downwind sides of mountains, they are also known as lee clouds, wave clouds or lee wave clouds.
A mountain range can form a series of long wave clouds, but if the speed bump is more isolated, like a single mountain, the result can be oval-shaped clouds that look like UFOs. Sometimes multiple ovals form that look like a stack of saucers.
“I like wave clouds because I see them so often here,” Breed said of Boulder, Colorado, where NCAR is. “I have a lot of favorites, but this is the one I have on my screen saver.” (Below).
Images: Above: Flickr/cardiffjackie. Below: 1) Daniel Breed. 2) Betsy Mason, Wired.com. 3) NCAR/UCAR.
Keep Calm and Love Physics
No one can escape friction, not even in a vacuum.
On earth, we’re slowed down by the muck of the everyday world. Matter slows us down, rubbing against us and taking away our speed and power. Gravel, air, even slip-n-slides, exert some friction on us. This frictional force runs counter to our motion, and it can’t be escaped anywhere on earth. Eventually, inevitably, it will slow us to a stop.
Ah, but in space all the rules are different. In a vacuum, with no matter to rub up against like a strangers on the bus, we could move forever. If we started in a spin, we’d never stop unless we had a collision with some kind of asteroid. It turns out, that even in the vacuum of space, we’d get dragged back. The vacuum isn’t as entirely devoid of matter as most people make it out to be. It’s only devoid of permanent matter. In a vacuum, tiny, temporary, particles pop in and out of existence all the time.
These particles, at first glance, shouldn’t drag down a spinning object. Since they are popping up on all sides, hitting it from every direction, their cumulative effect should be zero. At least two physicists at the Spanish National Research Council say this isn’t the case. If a particle hits a spinning object in the direction of its spin, a part of its momentum may be transfered to the object. If, however, a particle hits a spinning object counter to its direction, more of its momentum will be transferred to the spinning object. If particles moving counter to the object’s motion hit with more force than particles moving with the object, the object will eventually stop moving. Not even in space is motion preservered.
Via New Scientist.
Snowflakes Under an Electron Microscope
