Tuesday, 11 October 2011

xkcd on neutrinos

The Faster than Light Fiasco

If you haven’t been marooned on a desert island over the past few weeks since 23 September, you will have no doubt heard the media reports of neutrinos breaking the speed of light.
This has got everyone quite excited, as it would mean that Einstein’s theory of relativity is wrong, and therefore a large part of physics has been brought into question.

The European Organization for Nuclear Research (CERN) sent out a press release on 23 September about the OPERA1 experiment, which observes a neutrino beam from CERN2 730 km away at Italy’s INFN Gran Sasso Laboratory. They stated:

“The OPERA result is based on the observation of over 15000 neutrino events measured at Gran Sasso, and appears to indicate that the neutrinos travel at a velocity 20 parts per million above the speed of light, nature’s cosmic speed limit. Given the potential far-reaching consequences of such a result, independent measurements are needed before the effect can either be refuted or firmly established. This is why the OPERA collaboration has decided to open the result to broader scrutiny.”

Given the wording, it is a bit disappointing that the media has seized on it in the way it has. But CERN is probably equally to blame for sending out a press release when it is almost certain that the results are wrong. At no time have the researchers stated that neutrinos move faster than light. All they have said is that their measurement shows a reading greater than the speed of light, and further confirmation is required.

Although there are various assurances regarding the accuracy of the measurement, a measurement error or systematic effect still seems a likely explanation. As neutrino experiments are well known for being very hard to perform, the chances of a measurement error would appear to be far more likely than relativity theory being wrong. A claim of such extraordinary magnitude requires extraordinary evidence.

However, theoretical physicist Heinrich Päs of the Technical University Dortmund in Germany says it is possible that spacetime could be warped in such a way that allows neutrinos to take a shortcut without actually travelling faster than the speed of light. He goes on to state that, “if something moves faster than the speed of light, causality violations—aka time travel—may be a possibility”.

Another theory offered relates to quantum tunnelling after a neutrino’s properties change. If neutrinos that did not change flavour travel at the speed of light, and the neutrinos that did change flavour arrived an extremely small amount faster, then tunnelling may have occurred. If the distance is the Planck length or less, then perhaps the new flavour of neutrino left the Planck length area of the transition at the same time the old flavour of neutrino arrived. A virtual particle allows the neutrino to jump a Planck length. This apparently happens all the time when electrons tunnel through semiconductors (like the ones in your computer).
So far relativity theory and the cosmic speed limit set by light have survived all the challenges thrown at them, so such a challenge to them needs to be taken with a great many grains of salt until it has been properly tested.

The fact is that the OPERA finding doesn’t even fit with known facts. We observed the neutrinos from supernova 1987A arrive at the time the explosion was seen in the sky. The revised speed would mean that we would have observed them three and a half years earlier.

It seems likely that the observation will be explained as a simple goof (e.g. instrument error), or as an interesting phenomenon in which nothing goes faster than the speed of light but sometimes something appears to, due to some reason we are yet to discover.
To have a look at the scientific paper with the results, go to http://arxiv.org/abs/1109.4897
This article (and the one prior) were published in the Newsletter for the Phoenix Astronomical Society. (link to right).

Thursday, 29 September 2011

The Electric Universe Theory Debunked

I kept hearing about this theory called the “electric universe theory”, and wondered what it was all about. An ex-work colleague was quite worked up about it and even lent me some books. What was this theory and where on earth did it come from?

According to the website www.electricuniverse.info the “Electric Universe theory highlights the importance of electricity throughout the Universe. It is based on the recognition of existing natural electrical phenomena (eg. lightning, St Elmo’s Fire), and the known properties of plasmas (ionized “gases”) which make up 99.999% of the visible universe, and react strongly to electro-magnetic fields.” It goes on to state “Electricity is common throughout the universe, generated by all cosmic plasma as it moves through magnetic fields. Peer reviewed papers describe electricity in the Sun, and associated with the interplanetary medium (solar wind), planets and their satellites, comets, in interstellar space, other stars, and intergalactic space.” Well that sounds pretty convincing, doesn’t it?

We astronomers often stumble across new theories, and after a while a certain degree of ‘learned scepticism’ enters the fray. So I decided to take a closer look at this theory. The theory seemed to be all encompassing and rather difficult to pin down, so in order to do this, I focused on what the theory has to say about our sun in particular. Astrophysicists say that stars, including the sun, are powered by nuclear fusion. However electric universe theorists say this is not so. The reasons given are that:

  1. we haven’t yet found the neutrinos that must be emitted from such a reaction;
  2. that the granular structure we see on the sun would not be possible, because convection is impossible due to the conditions there;
  3. the energy emitted from the sun does not display the inverse square law;
  4. periodic fluctuations in the sun’s output resemble electric discharge patterns; and
  5. the solar wind is and effect of charged particles being accelerated in an electric field.

Well that all sounds very plausible and ‘scientificy’. But let’s take a closer look at the arguments one by one.

Neutrinos have not been found?

A neutrino is a particle smaller than an atom with an incredibly small mass to it. They are similar to electrons, but don’t have a charge. They usually travel close to the speed of light, and not having a charge means they are unaffected by electromagnetic forces like other matter, and are able to pass through ordinary matter almost unaffected.

Neutrino observatories are actually underground because the neutrinos pass right through the earth. Neutrinos are created as a by-product result of nuclear fusion (in a nuclear plant or the sun) or when cosmic rays hit atoms. Every second about 65 billion solar neutrinos pass through every square centimetre of earth facing the Sun. Because they have a mass, neutrinos can interact with other particles via gravity.

Scientists have been detecting the effects of neutrinos for years, and they match the predictions exactly. If an alternative theory is to be considered, scientists would need to reject the theory of nuclear fusion at the centre of a star. This would also necessarily lead to rejection of the theories of thermodynamics, gravitation, nuclear physics, statistical physics, electromagnetism, hydrodynamics and magnetohydrodynamics. In other words, most of physics would need to be rejected to address the problem of the ‘missing’ neutrinos.

Electric universe theorists argue that these neutrinos have never been detected, and those inferred by their effects are about half of what would be produced by a fusion reaction in the sun.

Some of you will be familiar with quantum mechanics, where all particles can have both wave and particle properties. Well, neutrinos are confusing too, as they have mass and therefore qualify as a particle. When they are detected they have a probability of being either an electron neutrino or a tau neutrino. We have electron neutrino detectors, and once we build a tau neutrino detector the ‘flux’ will add up to the exact amount to solve the solar problem. So maybe it is a bit premature to throw physics out just yet.

Convection in the sun is impossible?

Electric universe theory argues that the granulation we observe on the surface of the sun cannot be caused by convection bubbling up the layers of the sun. This is based on an assumption by a man called Juergen, that one of the values used in fluid dynamics, the Reynolds number, causes the convection, and at certain values convection cannot occur.
If you imagine a parcel of matter inside the sun towards the surface as the sun’s heat causes it to rise and falling back towards the centre as it cools (like boiling water), the Reynolds number describes a function of the parcel size, length and stickiness.

Juergen assumes that the Reynolds number controls convection but it doesn’t; convection is controlled by the Rayleigh number. The Rayleigh number is a function of the temperature, gravity, the degree of temperature change, stickiness and how diffuse the temperature is. So Juergen made a mistake, oops. The convection that we see on the sun can be explained without throwing away physics.

The sun’s energy breaks the inverse square law?

In physics, the inverse square law states that a specified physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity. So in other words if you move from two metres to four metres away from a heater you increase the distance by two, but decrease the energy by four times (four is the square
of two). Electric universe theory says that because the sun is coolest at its surface, then the temperature jumps up again out at its halo, it does not obey the inverse square law, and physics is wrong.

At this point it is important to note that the inverse square law only applies to radiant energy (as opposed to convection or conduction) and only in a vacuum. When energy moves through an atmosphere (such as the corona of the Sun) then the law does not hold. In addition, the inverse square law applies to all energy, not just heat. The colder ‘surface’ (photosphere) actually has more energy. The energy drops dramatically at the corona as we would expect. There are a myriad of explanations for the temperature differences, none of which involve throwing out physics as we know it.

The sun’s variations prove it is a bag of plasma?

Electric universe theory says that the variations in the sun every 2 hours and 40 minutes or
so can only be explained if the sun was a big bag of gas undergoing periodic electrical discharge. Juergen cites some research that shows this period is what we would expect from a homogenous sphere, rather than the accepted layered model of the sun found in
textbooks. Well that is a problem ... isn’t it?
OK, time for some context here. The research cited was in 1976 and the authors stated that it applies only if they are p-mode oscillations. But back then we didn’t have the technology to distinguish between p-mode and g-mode oscillations. Later research, available to the electric universe theorists, showed they were gmode, so basically all the assumptions based on this research went out the window. It doesn’t matter too much what the modes are, the point is that the electric universe theory was based on outdated information from 1976. Very poor research indeed!

The solar wind is caused by an electric field?

In physics an electric field applied to charged particles cause them to accelerate. The
Electric universe theory says that the solar wind is the result of such a field, and the Sun is electric, not fusion based.

Maxwell’s theory of acceleration, however, talks about a time variable field, not a fixed one, and what’s more the solar wind contains both positive and negatively charged ions (protons and electrons mainly). An electric sun would be positively charged and all the negatively charged electrons would be attached to it – not be pushed out from the Sun on a solar wind. This fact proves the Sun is not electric.

And then the wheels fell off…

Hmmm. Towards the end of my research I found a notation on Wikipedia about why “Electric Universe Theory” had been removed. Apparently there are only a few people who currently publish ideas on the “electric universe” and those people publish exclusively on the internet or vanity presses. They use very misleading citations gleaned from mainstream sources in an attempt to lend credibility to the “electric universe theory”. Most papers listed as peer reviewed are not about the “electric universe” but about plasma cosmology (a different idea). The “electric universe” has no single paper subject to peer review about its ideas.

Well, it seems this is not a theory that anyone should be hanging their hat on. However, I will say that my little exploration did lead me to learn an awful lot about neutrinos, and our Sun. I hope that next time you read an outlandish theory you might take this journey too. You never know what you might learn.