Light Sprints


light pulse

Small light pulses can now be modified so they slow down

Remember any physics lessons during your high school years? How it was always said the speed of a light was the most unchangeable constant of all? Well… keep reading. In a perfect example of how science changes to perfect itself, scientists at the University of Glasgow have carried out a very interesting set of experiments which ultimately showed that the speed of light can in fact change.

Now, we all know that when light enters a medium, such as water or glass, it slows down. Whereas the speed in a vacuum is said to be 299 792 458 m/s, it can go down to 225 056 264 m/s in water and even 124 018 189 m/s in diamond. This is due to the increased density through which the light has to pass through, so the light particles suffer more collisions which slow it down. But the news come from the idea that speed can also change in a vacuum, even if there is no change in medium and therefore in density.

However, there is a trick. This change in speed won’t happen spontaneously, it has to be slightly triggered. Although it is usually simplified as ‘straight’ or plane waves, where every point travels parallel to each other, light is a bit more complex than that. Two points in a ray of light can actually converge and join, bending their shape. When this effect happens, light speed is affected.

The experiment consisted of a source emitting only two photons. One of them was directed to flow through an optical fibre, so its journey was not interrupted and was as smooth as possible. The other one was passed through a series of apparatus which changed its structure for a short period of time and then restored it back to normal. The time it took each of the photons to arrive to the finish line was measured very precisely. No matter how many repeats the team conducted, the modified photons were always slightly slower and arrived after the untouched one.

The change is speed is not immense, and will have no effect on day-to-day calculations, but it could be have some importance on experiments which use short pulses of light. The fact this effect exists is already worth noting, as it is theoretically obvious but no one had proved it before.

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Nobel Prizes 2014: Part 1


Probably the most prestigious scientific award, the Nobel Prize is, for many, the intellectual event of the year, where the world’s greatest scientists are rewarded for their hard work and brilliance. As of yet, only two results have been announced, those for physics and physiology, and the rest will be unveiled as the week progresses.

The 2014 Nobel Prize for Physiology or Medicine went to… John O’Keefe, May-Britt Moser and Edvard Moser for discovering the ‘GPS’ system in brains.  

human gps

Not a literal GPS in our head, but a group of cells that enable us to travel

It all started 40 years ago, when O’Keefe was investigating rats’ brains and their response to certain stimuli to understand their behaviour. In one experiment, he found that in a group of nerve cells in the brain, some became active when the rat physically moved to one area of the room, whilst other cells became active in other areas of the room. The conclusion he reached was that this group of cells was making a mental map of the rat’s environment to help it locate itself and move around. The ‘place cells’, as he called them, were a revolution in the field, but it took O’Keene 40 years and two collaborators to win the famous Prize.

The other recipients of the award are the Mosers, a married couple who, working in O’Keene’s lab, examined in more depth the mechanism and using modern technology, discovered that a close group of cells in the entorhinal cortex also helped in movement. What they found was that these new cells could be active in many positions of the room, not just one specific location. ‘Grid cells’ is their name and they do exactly what their name would suggest: they create a grid of their surroundings.

Both the place cells and the grid cells are used in human brains too, and their work is essential for us to be able to travel, even from one room to another, without getting lost.

The Nobel Prize for Physics went to… Shuji Nakamura, Isamu Akasaki and Hiroshi Amano for the invention of blue LEDs.

At first sight, it looks like they gave these men a Nobel Prize for inventing a bulb, but it is much more complex than that. First of all, let’s explain what an LED is and how it works. An LED stands for Light-Emitting Diode and it is used to produce light. It works by having thin sheets of material over each other, some of which contain a lot of electrons whereas other don’t and so have positive ‘holes’. When an electron collides with this hole, it emits a photon; a particle of light.

blue led

Making blue light is much harder than it may seem!

Red and green LEDs have been around for a long time, but only blue light could be transform into white light. The problem is that blue light has a higher energy and therefore very few materials can emit this wavelength. So when Akasaki, Amano and Nakamura discovered gallium nitride, it was a real miracle. This material is special because apart from having electron-rich areas, it can also produce a layer of itself which lacks electrons, so that together, they can react and produce blue light.

This apparently simple mechanism has had unimaginable consequences, which is the main reason why the Royal Swedish Academy of Sciences has decided to award them the prize. Blue LEDs gave us the opportunity to make white light by coating the bulb with a substance called phosphor. Thanks to this combination, we now use blue LEDs everywhere, from our TV screens to the lightning in the streets. The advantage it has over the normal, incandescent bulbs is that it can last 100 times longer, and is extremely more efficient. In fact, it is said that if all light bulbs were switched to these energy saving ones we could half the electricity usage by lightning in the whole world.

Shedding Light on Light


Messing around with the very essence of matter, scientists at Princeton University in New Jersey have managed to change the nature of light into unprecedented characteristics.

To do so, all you need is a superconducting wire with photons flowing through it and a machine containing 100 billion atoms made of superconducting material. Easy, right?

These atoms can then be modified to act as one single atom, thanks to the unusual properties of superconduction and so once this is done, you just need to push these two objects closer to end up with a group of photons acting like crystals.

light

Light as we know it has drastically changed

This is so bizarre because usually, photons of light are free from interacting with each other. But in this experiment, they were able to ‘bond’ together to form a crystal structure. This happens because of a quantum process called entanglement, where two photons can become connected over large distances. When the giant atom was brought closer to the photons, these linked to it and exhibited similar properties to it, effectively making light solid. The mechanism could be varied so that light behaved like a liquid or a gas, and with further refinements, like even more exotic materials such as superfluids; fluids with zero viscosity which flow defying gravity.

Although this discovery sounds like just interesting information, it actually has applications. Obviously, it is important to understand matter and how it works (a science named condensed matter physics), since it brings us closer to discovering new materials or characteristics of objects which we can use in our favour. For example, it could help devise the very sought-after room-temperature superconductor, with which electricity could be transmitted in our day-to-day lives with an incredible efficiency, since it offers no resistance.

As if the nature of light wasn’t hard enough to comprehend already, with wave-particle duality, here’s a new behaviour to complicate things even more. Sorry, students, sounds like you’ve got something else to make sense of.

Detecting Baby Waves


In Einstein’s theory of general relativity, he said that massive objects moving at incredible speeds, or giant objects’ gravity interacting could cause ripples in the space-time fabric, known as gravitational waves. They had been searched by scientists for years, and they had successfully hidden, but not anymore.

A series of experiments taking place in the South Pole have finally provided the scientific community with a solid detection of these elusive waves. The project, called BICEP2, has released its findings today, and are awaiting further revision for official publication.

gravitational echo

The graph showing the primoridal gravitational waves when first detected.

There has been a lot of excitement over these waves, because they are able to prove one of the most popular theories regarding the birth of our universe: inflation. The theory, suggested by physicist Alan Guth, says that a few moments after the universe was created, it suffered a dramatic increase in size (by a factor of 1078). After this, its expansion rate slowed down considerably.

What’s important is that if this theory was correct, the sudden growth would have caused ripples in the space-time, hopefully strong enough for us to detect.

And this is what this amazing team has done. They have detected the gravitational waves that were given off during the expansion, given the fancy name of primordial gravitational waves.

The results are impressive just by themselves. The fact they have caught these waves is already world-changing, but there are even more interesting details that deserve our attention.

The waves they found were stronger than they thought they could be, which leads to a rethinking of the current inflation theory. There are some ‘sub-theories’ that can explain this fact, so many eyes are turning towards these and reconsidering them for answers.

But if there’s something we’ve learnt after all these years is to remain cautious after big discoveries (incredible stem cell method not that incredible after all?). The findings have yet to be backed up by other experiments from other teams, but overall there is a positive feeling towards this data.

If they were to be true, they would prove inflation to be true once and for all, but they could also prove useful in completing quantum mechanics. This field is very effective when working with subatomic particles, but when you add gravity, it all goes to rubbish. An understanding of gravitational waves could be useful and could help scientists find that key they need to wrap it all up.

 

Check out BICEP2’s official website:

http://www.cfa.harvard.edu/CMB/bicep2/science.html

Dark Matter Hiding In The Shadows


For those of you who don’t know, the Universe consists of only 5% of normal, ordinary matter. But then, what is the rest of the Universe made of?

The most popular theory at the moment is that of dark matter (and dark energy). This is a type matter that neither absorbs nor emits light. It is hypothetical substance and its existence has not been proven… yet. However, there are many experiments set around the world eager to be the first one to find out the truth about this matter (pun?) since it would bring our knowledge of the Universe to a whole other level.

One of these experiments is the LUX Detector in South Dakota, USA. It is set 1500 metres underground, in what used to be a gold mine, to reduce any influence of background particles. It consists of a 370 kg container with liquid xenon in it, and two detectors on top of the container. The experiment works in the following way: when xenon particles interact with other particles (such as the hypothetical dark matter particles) it releases photons and electrons. This can be detected and the difference times these two subatomic particles are produced can be recorded, so the depth of the interaction can be known.

Said interaction between xenon and dark matter is caused by the ability of the former to create a gravitational pull on normal matter. The most probable candidate for thedark matter is a WIMP (Weakly Interactive Massive Particle).

However, after 3 months of searching for this mysterious particle, there have been no relevant results. There have been experiments in the past that have had interesting resulsts which were hopefully going to be confirmed by the LUX, but which were not, LUXunfortunately. The theory of the experiment is not doubted and the scientists there all agree that the machine is working perfectly well. A new theory is that WIMPs might not interact so eagerly with normal matter.

But don’t worry, LUX fans (Luxies?), the experiment is still going to be working in the future, due to its versatility. The advantage of this specific experiment is that it should not only work for detecting WIMPs, but also other particles with a range of masses.

Let’s hope the experiment works as well as it should and maybe someday soon the existence of dark matter will be finally proved, or disproved, to leave space for other theories.