Causality questioned

Causal ambiguity is experimentally real

“Within the mathematical formalism of quantum theory, ambiguity about causation emerges in a perfectly logical and consistent way.”* This is an extraordinary statement made in an excellently written article by Philip Ball in the preeminent journal ‘Nature’, 28 June 2017.

Click here to read the article.

The article explores experiments which put photons through pairs of optical gates, and find that it is impossible to state in which order the photons go through the gates. “It’s not that this information gets lost or jumbled — it simply doesn’t exist. The experimental arrangement enables information to be shared between two events in ways that are ruled out if there is a definite causal order – So that time seems to run in two directions at once.”

This links in directly with the issues around distantly separated entangled photons cooperating instantly when the property of one is measured. It is probable that quantum circuits incorporating causal ambiguity would offer a practical benefit of greater quantum-computing speed. But more important is the potential for theoretical understanding of causality and the obscure nature of quantum effects.


*I borrowed this extraordinary sentence as one of the chapter titles in my sci-fi novel.

Desktop Nuclear Fusion

Next Generation Fusion – Radiation-Free Cheap Nuclear Power

I have been following the progress of Lawrenceville Plasma Physics (LPP) with great interest for some years, as they develop their ‘Focus Fusion Device’ toward the critical point at which there is more net energy generated than put into the device. Indeed I should declare that I have invested in the company.

Next Generation Fusion – Radiation Free Nuclear Power from LPPFusion on Vimeo.
Although all current approaches to fusion use extreme temperature to ionise the reactants into a plasma, LPP’s approach to nuclear fusion power differs in three fundamental ways from the hugely expensive mainstream ITER project, that is funded by governments.

Firstly the device is small – maybe desktop is an exaggeration, but the full device would sit easily inside a small room – and the vision is therefore one of distributed power generation – generation where it is needed i.e. within cities or vehicles. That also carries the advantage of eliminating power transmission loss over distance.

Secondly the device is designed to harness the inherent instability of plasma, rather than to overcome it. The massive Tokamak design of the projects like ITER try to tame and contain the plasma using magnetic fields, forming the plasma into a doughnut shape within which the fusion occurs. In contrast the Focus Fusion device allows the plasma to follow its natural tendency to curl up on itself into a tight knot called a plasmoid, within which fusion occurs, before the plasmoid collapses to stream a jet of positive ions in one direction and a jet of electrons in the opposite direction.

Fusion Energy Generation and Capture within Dense Plasma Focus Device from LPPFusion on Vimeo.

Thirdly LPP plan to use aneutronic fuel – the ideal aneutronic fuel is a mixture of hydrogen and boron. (Aneutronic means that the fusion reaction does not produce neutrons.) At extremely high temperatures—billions of degrees—hydrogen nuclei (protons) fuse with boron-11 nuclei to very briefly form a carbon nucleus. But the carbon nucleus has too much energy to stay together, so in an instant it breaks up into three helium nuclei – there are essentially no nasty by-products. Indeed LPP state that after turning the device off, it would be safe to handle within half an hour. The ITER project, by contrast, uses fusion of hydrogen with hydrogen to form helium, as within our sun. The disadvantage is that this fusion reaction produces high energy neutrons which damage the containment vessel walls, and produce radio-active by-products.

For more information visit the LPP website.

Investment and other info

Serendipity in Carbon-dating

Rare coincidences make the technique feasible

Carbon-dating is a technique we take for granted in the modern archaeological era, but it depends on a couple of very serendipitous effects.

Basically carbon naturally occurs as three isotopes – C12, C13 and C14. However the C14 isotope is radioactive and so decays over time, with a half-life of 5,730 years. Carbon-dating simply measures the remaining C14 content in a sample to estimate how long the sample has existed since….images[5]

And there is the first piece of serendipity. We need to be able to know the starting C14 concentration.

Cosmic rays create C14 equilibrium

It turns out that there is a continual bombardment of the upper atmosphere with cosmic rays which creates new C14 from atmospheric nitrogen. That C14 then reacts with atmospheric oxygen to produce carbon dioxide which gets fixed into plant material by photosynthesis, which then gets eaten by animals, so that all living things contain an equilibrium, fairly constant concentration of the C14 isotope of carbon.

Once the living matter dies however, that concentration of C14 starts to decrease, by radioactive decay – hence it is possible to know how long any piece of once-living matter has been dead, by measuring the remaining concentration of C14 in it.

However there is another twist. That particular type of radioactive decay, a neutron into a proton,  usually occurs within a day,  for almost all other atoms. But it is the unusual long half-life of C14 which makes the technique useable.

Quantum interference of decay modes

The reason that C14 decays about 2 million times more slowly is that, according to quantum mechanics, multiple versions of the nucleus exist simultaneously, each having different amounts of angular momentum. And two of those particular versions are both trying to decay, but when considered as quantum waves which can interfere with each other, those two decay processes almost perfectly cancel each other out. Hence a very low probability of decay, and a long half-life.

And we could not have used just any other element – life is carbon-based, maybe oxygen or hydrogen would have worked if we were lucky. The only other element with a similarly decaying half-life is Beryllium 10 – not much of that around in living tissue fortunately – it’s toxic.

So, in summary, it just happens that the element that life is based on, has an isotope with a rare decay profile, and that isotope just happens to be constantly equilibrated by cosmic rays – archaeologists are blessed indeed.