Scottish Scientists Slow down Light Particles - Photons

The speed of light is a limit, not a constant, that's what researchers in Glasgow, Scotland, say. A group of them just proved that light can be slowed down, permanently.

Scientists already knew light could be slowed temporarily. Photons change speeds as they pass through glass or water, but when they exit the other side and return to a vacuum (like outer space) they speed back up.

In a new experiment at the University of Glasgow, however, scientists were able to permanently manipulate light's speed by passing photons through a device that alters their structure. The device, created in collaboration with researchers at Heriot-Watt University in Edinburgh, is a filter of sorts that the scientists refer to as a mask.

"That mask looks a little bit like a bull's-eye target," researcher Miles Padgett told reporters. "And that mask patterns the light beam, and we show that it's the patterning of the light beam that slows it down.

"But once that pattern has been imposed, even now the light is no longer in the mask, it's just propagating in free space, the speed is still slow," Padgett added.

In other words, the beam of light is reorganized in a way that slows down each individual photon. When tested in a vacuum next to a regular light beam.

Photons that had been filtered through mask were milliseconds behind in a sprint to the end of the vacuum racetrack.

Researchers, whose latest work was published this week in the journal Science Express, say the findings prove the speed of light is not an absolute, more like a ceiling.

Miles Padgett

The work was carried out by a team from the University of Glasgow’s Optics Group, led by Professor Miles Padgett, working with theoretical physicists led by Stephen Barnett, in partnership with Professor Daniele Faccio from Heriot-Watt’s Institute of Photonics and Quantum Sciences.

Daniele Faccio

Professor Faccio said, “The speed of light is a universal constant and plays a central role in our understanding of the Universe and Einstein's theory of relativity."

"The exciting discovery here is that this speed is the true speed of light only for plane waves, that is waves that are perfectly flat."

"In everyday situations however, we interact with light that is not a plane wave but has some kind of structure on it."

"The presence of this structure (think of the light beam emitted from a laser pointer) forces the light to actually move slower."

"There are lots of technicalities involved in the actual experiments used to measure this slow-down, but the result is widely applicable. A very appropriate discovery for the 2015 international year of light".

Professor Padgett added, “It might seem surprising that light can be made to travel more slowly like this, but the effect has a solid theoretical foundation and we’re confident that our observations are correct.

“The results give us a new way to think about the properties of light and we’re keen to continue exploring the potential of this discovery in future applications."

"We expect that the effect will be applicable to any wave theory, so a similar slowing could well be created in sound waves, for example.”

More Information
Spatially structured photons that travel in free space slower than the speed of light - Science Magazine January 22 2015 - Science DOI: 10.1126/science.aaa3035

Researchers Create a new light source

Scientists have created a completely new light source by getting light particles to act like atoms.

By cooling photons, the light particles condensed so they could behave like a single entity.

Researchers at the University of Bonn have shown that super particles can be made with light.

Albert Einstein and Satyendra Nath Bose thought this was possible back in 1925.

The Bonn researchers proved Einstein and Bose had the right instincts all along.

Why should you care? Well, the discovery could one day shrink electronic devices.

Until now, this behavior has only been seen in atoms. The applications of this physics breakthrough could one day be used to build more powerful computer chips and make lasers that work in the X-ray range.

Nobody has ever created a Bose-Einstein condensate (BEC) with photons before. BECs are usually made with cold atoms of gas.

In the 1920s, it was thought this strange quantum phase of matter existed. If the atoms were cooled to close to absolute zero, then the atoms would be pushed into the same quantum state and they’d act as one.

Zeeya Merali wrote in Nature:
In 1995, two experimental groups independently produced the first examples of BECs with rubidium and sodium atoms. In theory, physicists knew that it should also be possible to form a BEC using particles of light, or photons. But in practice it seemed near impossible because, unlike atoms, the number of photons in an experiment is not conserved.

Engaging Maximum Thrust to Explore the Univers

The Apollo 10 moon probe is currently listed as the fastest manned vehicle in history, having reached a maximum speed of 39,895 kilometres per hour. At this speed, it would take 120,000 years to cover the 4 light years to Alpha Centauri, the nearest star system.

So if we want to explore the depths of deep space and journey to Alpha Centauri and beyond, we're going to need some new technologies. Here, we look at 10 of the most intriguing.

The technologies range widely in their plausibility. Some, we could more or less build tomorrow if we wanted to, while others may well be fundamentally impossible.

Ion thruster
Conventional rockets work by shooting gases out of their rear exhausts at high speeds, thus generating thrust. Ion thrusters use the same principle, but instead of blasting out hot gases, they shoot out a beam of electrically charged particles, or ions.

They provide quite a weak thrust, but crucially they use far less fuel than a rocket to get the same amount of thrust. Providing they can be made to keep working steadily for a long time, they could eventually accelerate a craft to high speeds.

They have already been used on several spacecraft, such as Japan's Hayabusa probe and Europe's SMART-1 lunar mission, and the technology has been improving steadily.

A particularly promising variant is the variable specific impulse magnetoplasma rocket (VASIMR). This works on a slightly different principle to other ion thrusters, which accelerate the ions using a strong electric field. Instead, VASIMR uses a radio-frequency generator, rather like the transmitters used to broadcast radio shows, to heat ions to 1 million °C.

It does this by taking advantage of the fact that in a strong magnetic field, like those produced by the superconducting magnets in the engine, ions spin at a fixed frequency. The radio-frequency generator is then tuned to that frequency, injecting extra energy into the ions and massively increasing the thrust.

Initial tests have been promising, and if all goes well, VASIMR could be used to take humans to Mars in 39 days

What is Solar Sailing?

Solar sail propulsion is simple in concept. Light photons bounce onto a mirror-like aluminized Mylar sail. As each photon hits, its momentum is transmitted to the spacecraft.

Photons have no mass but lots of energy, so a solar sail space probe requires no onboard fuel. The force acts continuously, meaning a solar sail can eventually reach speeds five to ten times greater than any chemical rocket.

Russia, the U.S. and the European Space Agency all started solar sail missions and technology programs but cut them back when money got tight. Japan, we are happy to say, is now moving ahead to develop an innovative solar sail and solar-powered ion drive hybrid.

Yet solar sail propulsion remains largely neglected. That's why the Society has long championed efforts to prove its value. We partnered with Cosmos Studios on the far-sighted Cosmos 1 solar sail project. But technology has advanced enormously since then. We can do more in a fraction of the size, with a fraction of the weight and at a fraction of the cost. This has led us to re-think everything…and what we've arrived at is far more advanced, and ultimately far more valuable.

This technology also opens up many new possibilities for piggyback launching into Earth orbit, which is desperately needed since launch vehicles have been a hindrance preventing solar sail flight. We're considering several launch possibilities and will select the most reliable one that matches our schedule and final orbit choice best.