Thursday, 29 September 2011

Breaking the speed of light

This article was written for the Hamilton Astronomical Society monthly bulletin, October 2011.

Unless you live in a cave on Titan you’ll already be aware of the biggest news in science this month - the apparent violation of Einstein’s speed of light limit. As is so often the case with breaking science news, the media coverage is variable in its quality and accuracy. Here’s a quick, simplified overview of the story...

What exactly is the claim?

Scientists working on an experiment in Italy have noticed that sub-atomic particles called neutrinos appear to travel faster than the speed of light. According to Einstein’s special theory of relativity, this is impossible.

The experiment is called Oscillation Project with Emulsion-tRacking Apparatus (OPERA). It involved two physics laboratories separated by 730 km: The CERN laboratory in Switzerland and the LNGS laboratory in Italy.

The CERN lab generated neutrinos which travelled through the Earth’s crust to the LNGS lab (there is no physical tunnel, the particles travelled straight through the Earth). Very precise measurements were made of the distance and time taken, and the results showed the neutrinos arriving 60 nanoseconds earlier than they should if they were travelling at the speed of light.

It’s very important to note that the researchers are not claiming to have “broken the speed limit of light” or “disproved Einstein’s theories”. Despite many headlines in mainstream media, the researchers are not claiming proof of anything, they are opening up their research in the hope that other scientists will be able to help solve the mystery.

What are neutrinos?

Fundamental particles, electrically neutral, with negligible mass. They rarely interact with "normal" matter, so they pass through most things without any effect and are therefore difficult to detect. They are produced in nuclear reactions such as the fusion inside our Sun. They are very common - billions are passing through your body right now.

Why do we think the speed of light can’t be broken?

In Einstein’s famous and spectacularly successful equation E=mc2, "c" is the speed of light in a vacuum and it’s a constant. It never changes. Any object with mass is constrained to this limit.

It’s not just that we’ve never been able to find anything that breaks this speed limit. According to the well-tested maths as well as physical experiments, this limit is an inescapable property of the universe. For example, as you approach the speed of the light the energy required to increase your velocity increases dramatically and would become infinite at the speed of light.

Has anything like this happened before?

Yes, superluminal (faster than light) speed has been reported in some previous experiments. For example, a 2007 experiment in Minnesota USA called the Main Injector Neutrino Oscillation Search (MINOS) noticed the same effect but their measurements weren’t accurate enough to give any confidence.

The OPERA experiment is the first time such a high degree of confidence has been reported.

On the other hand, many more previous experiments and observations show neutrinos behaving exactly as Einstein’s laws dictate. For example, when supernova 1987a was observed, neutrinos created in the blast arrived at Earth as expected - within hours of the visible light. If they had travelled at the superluminal speeds claimed by OPERA they would have arrived several years earlier.

How reliable are the observations?

The effect has been measured over 15,000 times. The margin of error in distance measurement is 20 cm. The margin of error in time measurement is 10 nanoseconds. The researchers give the result a statistical significance of six-sigma, which basically means it’s a statistical certainty.

How significant is this claim?

It’s huge. The fact that you own a computer is down to our understanding of Einstein’s theories. A century of scientific research has held up the idea that superluminal speed is impossible for objects with mass.

Claiming to have broken the superluminal speed limit is almost like claiming to have broken the law of gravity. Imagine if someone claimed to have seen objects falling up instead of down - would you believe them or would you be looking for some other explanation?

You can see why other scientists are skeptical. It would be a brave person to accept the new results without a lot more investigation.

What are the possible explanations?

There could be some form of systematic error in the OPERA experiment, for example, the distance may not have been measured correctly. Although no-one has yet been able to spot any such errors, this is still considered the most likely explanation.

Einstein could be wrong, or at least not completely right. Perhaps his theories need tweaking. This is widely considered to be unlikely.

In some theoretical models such as string theory, the universe consists of more dimensions than the four we’re familiar with (3 space + 1 time). Neutrinos could be slipping in and out of these extra dimensions, creating shortcuts in space-time. In this scenario the speed of light would be maintained but the distance covered would be reduced, giving the illusion of superluminal speed.

There are many other possibilities being discussed with varying levels of support, from the speed of light needing another correction to photons having mass.

What would the implications be if it’s true?

Sadly superluminal neutrinos will not lead directly to spaceships with warp drive. It’s hard to imagine what the real implications would be, but we do know that it would rock the scientific world and we’d need to completely re-examine our understanding of the laws of physics. Now what?

Other scientists need to examine the paper and look for possible errors. At the same time other laboratories will attempt to replicate the result. This could take up to two years. We’ll all need some patience.

Read the paper at static.arxiv.org/pdf/1109.4897.pdf

Tuesday, 27 September 2011

The Square Kilometre Array

This article was written for the Hamilton Astronomical Society monthly bulletin, April 2011.

The Square Kilometre Array (SKA) is a proposed radio telescope project that has significant implications for astronomers around the world. It also has special significance for us in New Zealand because there’s a good chance our country will be an important partner in the project.

The SKA will consist of over 3,000 separate radio antennas, all linked together to effectively form a single radio telescope. The total collection surface from all antennas will be approximately 1 km2, hence the name “Square Kilometre Array”.

However the geographical size of the telescope is much larger. The main “core” group of antennas will be 5 km wide, with smaller groups extending out in a spiral pattern over a vast area. The farthest antennas will be over 3,000 km from the core, giving an exceptionally wide baseline and field of view.

Where will it be?

The SKA project is run by an international consortium with representatives from more than 15 countries. The project office is located in Manchester, UK. The project was proposed more than 10 years ago and is now reaching the final design stages. New Zealand is a relative latecomer to the project, having joined with Australia a few years ago to present a joint bid to construct the telescope. If our bid is successful, the core and most antennas will be located in Western Australia. New Zealand will likely become home to a small number of antennas.

There are currently two construction bids being considered — the other being in Southern Africa (spread across several countries). The African bid may have the advantage of lower construction cost but the Australasian bid appears to have the stronger scientific case. In particular, the Australian location offers the lowest level of unwanted radio noise.

It’s too early be confident, but several sources I’ve spoken to say the smart money is on the Australasian bid.

What will it do?

The SKA will be the largest radio telescope ever built, and one of the largest scientific projects ever undertaken. The scale is enormous, as is the budget — around $NZ3.1 billion.

The scientific goals are equally lofty. Astronomers plan to map the large-scale structure of the universe and answer questions about the nature of dark energy, gravity waves, the formation of early galaxies, pulsars, cosmic magnetism and more. The data will also be useful in the search for extra terrestrial life — as well as being able to detect carbon in distant solar systems, the telescope will offer the best chance so far of finding artificially-generated radio signals from alien worlds.

The SKA will be 50 times more sensitive and 10,000 times faster than any other radio telescope. Phenomenal amounts of data will be involved. Each individual dish will send 420 Gb per second, totalling 16 Tb/sec per aperture array. This will require significant innovation and new technologies in data storage, networking and software development.

To put the data flow in perspective, it is estimated that the world currently generates around 1,000,000,000,000,000,000 bytes of new digital information per year. The SKA will equal this in one day.

How will it work?

The images on these pages are artist impressions of the proposed arrays in Australia. In the inner core (below), antennas are distributed randomly in a circle 5 km wide.

Moving out from the core, stations containing smaller groups of antennas are located at intervals stretching out to several hundred kilometres. Even farther out, remote stations are located at increasing distances across the continent and, hopefully, New Zealand. The telescope will observe a very wide frequency range, from 70 MHz to 30 GHz. Because this range cannot be observed with a single antenna design, there will be three different types of antenna used:

  1. SKA-Low Array: These simple dipole antennas cover the frequency range from 70 - 200 MHz. They will be grouped in stations 100 m wide, each containing about 90 antennas.
  2. SKA-Mid Array: These will probably be arrays of 3 m2 tiles covering the mid-frequency range from 200 - 500 MHz. They will be housed in circular stations 60 m in diameter.
  3. Dish Array: Covering the frequency range 500 MHz - 10 GHz, these arrays will be the familiar dish design. They will probably be similar to the Allen Telescope Array, using an offset Gregorian design. The size will be around 15 m high and 12 m wide.
Above: Artist’s impression of the 5km diameter central core of SKA antennas.
Image credit: SKA Project Development Office and Swinburne Astronomy Productions

When will it happen?

The successful bid is due to be announced early in 2012. If all goes to plan, detailed design and engineering requirements will be finalised by 2015, construction will begin in 2016 and be complete by 2023.

Thanks to its modular design, the telescope can become operational before construction is complete. The first science results should be returned by 2019.

The telescope is planned to be complete and fully operational in 2024, and have a life expectancy of between 50 and 100 years.

Who pays for it?

Participating governments will share much of the cost, but an important goal is to secure investment from the private sector. Many new technologies will need to be developed and private enterprise is seen as the best option. In a nice win-win scenario, companies that develop intellectual property for the project will also retain the IP rights, as well as other benefits.

What will it mean for New Zealand?

There will be many opportunities for local industry. The project will require a large investment and New Zealand is well-placed to deliver. There will also be benefits for the wider community, such as improvements in national network infrastructures. Of course those of us interested in astronomy will be most excited about the potential for scientific discovery, and the fact that New Zealand can contribute to such an important endeavour.

One year from now we should know the outcome. Good luck to us!

Above: SKA-Low Array
Above: SKA-Mid Array Station
Above: Dish Array (Offset Gregorian Antenna)

More info: www.skatelescope.org, www.ska.ac.nz