## Proving Heliocentricity

Is it stupid to think that the Sun revolves around the Earth?

Well, of course anyone even slightly exposed to scientific thinking who believes that today is certifiably a fruitcake or, as Professor Brian Cox puts it “a nobber”.

But proving heliocentricity – unlike, say, the spherical nature of the Earth, is not actually all that simple at all.

The crudest evidence suggests to us that the Sun goes round the Earth once every 24 hours and it is quite easy to disprove that, but the alternative – that the Sun goes round the Earth once every year is a lot more difficult.

Painstaking collection of data about planetary movements will show they (other than Mercury and Venus) display so-called “retrograde movement” at around the time they are in opposition to the Sun (on the opposite side of the sky) – something that is much simpler to explain through heliocentricity than geocentricity – but collecting that data is not something you and I are likely to do in a hurry.

Venus and Mercury’s different behaviour does suggest they orbit the Sun and as the geocentric model came under attack in the 16th and 17th centuries that was one of the earliest concessions of geocentricity’s defenders: but even that is not definitive (remember we have no theory of gravity here and so we may posit any orbital period we like for these planets).

Even the discovery of the phases of Venus towards the end of the opening decade of the 17th Century did not completely kill the idea of geocentricity off – though it was the heaviest blow yet.

In fact the idea of geocentricity lingered on in scientific thinking for some decades. Partly that was the influence of the Catholic Church but that is not the full explanation – heliocentricity turns out to be quite hard to prove.

## Gamma ray bursts are not that rare

Yesterday it was reported that scientists have suggested that an anomalous peak in radioactive materials discovered in antarctic ice sediments and in ancient Japanese cedar trees could be explained by a gamma ray burst hitting the Earth in the 8th century CE.

The BBC radio report I head described gamma ray bursts as “extremely rare” and the website article – and much other coverage – repeats the idea that they are rare events.

But they are not.

There are an estimated $1.25\times10^{11}$ galaxies in the universe. It is estimated that a gamma ray burst happens at least once every million years in any galaxy – or approximately every $3\times10^8$ days. That means that today there will be approximately 1000 gamma ray bursts. Now, let’s assume that due to relativistic effects  we can at most only observe one-tenth of the universe, that still means 100 events in the observable part of the universe (how big the observable universe is in comparison to the universe is another matter however).

Of gamma ray bursts are narrowly beamed so even with this high rate of production not many get seen on Earth (probably a good thing given the energies involved), but they are far from rare.

Of course, events in our galaxy are rare (the fact that we are here at all is testament to that), but on the universal scale that is drawing a very tight boundary on the region being tested.

## Evolution and the second law of thermodynamics

When I wrote my first piece about Roger Penrose‘s Cycles of Time – one of the links offered to me was to a Christian fundamentalist blogger who claimed that the second law of thermodynamics showed evolution could not have taken place:

E. Evolution contradicts the Second law of Thermodynamics

In the Theory of Evolution it is proposed that “simple life” evolved into more complex life forms by Spontaneous Generation. Both Darwin’s Theory of Evolution and the Spontaneous Generation model both directly contravene the Law of Biogenesis.

The Second Law Of Thermodynamics

The Second Law of Thermodynamics states that the disorder in a system increases, rather than decreases.

The problem for this argument’s advocates is that Penrose demolishes it in brilliant style. I won’t quote from him directly, but I will try to summarise his argument.

Penrose begins by actually restating the fundamentalist argument in a much wider sense – it is life itself that on a naive view would appear to violate the second law – after all our bodies do not melt away (so long as we live), but remain highly ordered and as we grow (eg our hair or nails) appear to create order out of disorder.

The key to this is the Sun. The first thing a secondary school science student is taught is that the Sun supplies the Earth with energy but, in fact, this is not true in the sense that the Sun does not provide a net increase in energy on Earth – if it did then our planet would continually heat up until it reached an equilibrium. The Earth re-radiates the Sun’s energy back into space at a equal rate to which it is recieved.

What the Sun is, though, is much hotter than surrounding space and so it sends the Earth a number of high energy (yellow light) photons. When the Earth re-radiates the Sun’s energy it does so at a lower temperature than the Sun – essentially at infra-red frequencies – so many more photons are radiated back into space than are received. More photons means a greater phase space and hence it means a higher entropy. So the Sun continually supplies the Earth with low entropy energy which processes on the Earth – including life – convert into high entropy energy.

For instance when we eat food we convert that low entropy food source (eg an egg) into high entropy heat energy. The food source itself ultimately derived its energy from the low entropy energy source that is the Sun, and so on.

Of course, all the time, the Sun’s own entropy is increasing, but we don’t need to worry about the consequences of that for a few billion more years.

It’s a brilliant, beautiful, argument though it is also one that is seldom, if ever, taught in schools.

## Earth surrounded by a ring of anti-protons

The “solar weather forecast” for the next few years is for increasingly poor conditions – as the solar cycle picks up, more matter will fly out from the Sun and eventually collide with our planet’s magnetic field, where the trapped high energy particles will then lose energy by radiation, so potentially disrupting many of our communications systems.

The solar particles, though, are not responsible for everything trapped by the Earth’s magnetic field – cosmic rays provide much higher energy particles than anything that comes out of the Sun and, it seems, also fuel a belt of trapped anti-protons around the Earth (as reported in this week’s New Scientist).

Anti-matter – which mutually self-destructs on contact with matter is a fascinating subject: working out why there is so little of it (when physics suggests there should be equal quantities of it and matter) is at the heart of cosmologists attempts to explain the creation of the universe.

So far the only way to access it consistently has been produce it in high energy collisions in places like CERN. The fact that the Earth has several billion anti-protons spiralling around it’s magnetic field at any given time, may, therefore point to new ways for researchers to get at it without having to build ever bigger colliders – though obviously space satellites aren’t ten-pence-a-dozen either.

## Maybe my kids should worry about 2009 BD – but I won’t

Today is my eldest daughter’s 16th birthday. That means in April 2078 she will be a sprightly 82. I will, though, I am sure, be long gone at 112.

And, maybe she should be worried about 2009 BD, the 10 metre lump of rock that passes inside the Moon’s orbit this week – because on 29 April 2078 it is predicted to come very much closer – a mere 6000km or so.

And, then, in August 2087, when Eibhlin will be  92, it will come much closer still – about 2000km.

Of course these predictions are difficult to call accurate – as 2009 BD is so small and so close to both the Earth and Moon that its orbit is bound to be unstable. Eventually it is likely to collide with one of the two or be flung into a new orbit.

But perhaps that collision will come towards the end of this century. If it does it would not be a good idea to be under the rock – but on the other hand while the 7 kT (NASA’s JPL seems to have revised down its estimate from an earlier 18 kT) equivalent of TNT does bear comparison with a nuclear weapon it is a small one and one that would be “exploding” in the upper atmosphere most likely over an ocean.

## So, the world did not end after all

About three hours ago (or two, if God ignored summer time), the world was supposed to have ended and the “Rapture” begun. Big yucks to all of us sceptics, of course.

(Around twenty years ago a film called “Rapture” was released which focused on the bizarre beliefs of people who thought the world was about to end, but in a final plot twist the world did end.)

But why the interest in this subject at all? This blog has an article about a near-Earth approach of an asteroid next month jokily titled “the end is nigh” – but it has been generating growing traffic as the date comes closer.

It’s amazing that people use tools created by the scientific enlightenment – like their computers and the internet – to search for things which can only be based on that science being wrong in just about every particular.

So – for the record. Yes, the world will end. Maybe we humans will “end” it by killing each other in a massive nuclear war, though that’s less likely than it once was, thankfully.

Possibly it will “end” (in the sense that human civilisation will collapse) because of an asteroid strike, but no sign of that at present – though there will be a threat in time, I am sure.

Possibly it will end because of some extremely rare but possible event (the Earth being swept by a gamma ray burst from a reasonably close supernova) but the odds against that are also slim, to say the least.

Maybe our theory of physics is all wrong and, say, quantum reality will undergo a phase change. Two thoughts about that: our physics theory says it won’t happen and even it did we’d never know as the phase change would surely propagate at the speed of light.

So – will we last till the Sun turns into a red giant and swallows the Earth in a few billion years. Probably not, but that’s too far in the future to worry about.