# Interpreting Observations

The ancients, with a few exceptions, thought the Earth was the centre of the Universe and everything rotated around it, thus giving day and night. Contrary to what many people think, this was not simply stupid; they reasoned that it could not be rotating. An obvious experiment that Aristotle performed was to throw a stone high into the air so that it reached its maximum height directly above. When it dropped, it landed directly underneath it and its path was vertical to the horizontal. Aristotle recognised that up at that height and dropped, if the Earth was rotating the angular momentum from the height should carry it eastwards, but it did not. Aristotle was a clever reasoner, but he was a poor experimenter. He also failed to consider consequences of some of his other reasoning. Thus he knew that the Earth was a sphere, and he knew the size of it and thanks to Eratosthenes this was a fairly accurate value. He had reasoned correctly why that was, which was that matter fell towards the centre. Accordingly, he should also have realised his stone should also fall slightly to the south. (He lived in Greece; if he lived here it would move slightly northwards.) When he failed to notice that he should have realized his technique was insufficiently accurate. What he failed to do was to put numbers onto his reasoning, and this is an error in reasoning we see all the time these days from politicians. As an aside, this is a difficult experiment to do. If you don’t believe me, try it. Exactly where is the point vertically below your drop point? You must not find it by dropping a stone!

He also realised that Earth could not orbit the sun, and there was plenty of evidence to show that it could not. First, there was the background. Put a stick in the ground and walk around it. What you see is the background moves and moves more the bigger the circle radius, and smaller the further away the object is. When Aristarchus proposed the heliocentric theory all he could do was make the rather unconvincing bleat that the stars in the background must be an enormous distance away. As it happens, they are. This illustrates another problem with reasoning – if you assume a statement in the reasoning chain, the value of the reasoning is only as good as the truth of the assumption. A further example was that Aristotle reasoned that if the earth was rotating or orbiting the sun, because air rises, the Universe must be full of air, and therefore we should be afflicted by persistent easterly winds. It is interesting to note that had he lived in the trade wind zone he might have come to the correct conclusion for entirely the wrong reason.

But if he did he would have a further problem because he had shown that Earth could not orbit the sun through another line of reasoning. As was “well known”, heavy things fall faster than light things, and orbiting involves an acceleration towards the centre. Therefore there should be a stream of light things hurling off into space. There isn’t, therefore Earth does not move. Further, you could see the tail of comets. They were moving, which proves the reasoning. Of course it doesn’t because the tail always goes away from the sun, and not behind the motion at least half the time. This was a simple thing to check and it was possible to carry out this checking far more easily than the other failed assumptions. Unfortunately, who bothers to check things that are “well known”? This shows a further aspect: a true proposition has everything that is relevant to it in accord with it. This is the basis of Popper’s falsification concept.

One of the hold-ups involved a rather unusual aspect. If you watch a planet, say Mars, it seems to travel across the background, then slow down, then turn around and go the other way, then eventually return to its previous path. Claudius Ptolemy explained this in terms of epicycles, but it is easily understood in term of both going around the sun provided the outer one is going slower. That is obvious because while Earth takes a year to complete an orbit, it takes Mars over two years to complete a cycle. So we had two theories that both give the correct answer, but one has two assignable constants to explain each observation, while the other relies on dynamical relationships that at the time were not understood. This shows another reasoning flaw: you should not reject a proposition simply because you are ignorant of how it could work.I went into a lot more detail of this in my ebook “Athene’s Prophecy”, where for perfectly good plot reasons a young Roman was ordered to prove Aristotle wrong. The key to settling the argument (as explained in more detail in the following novel, “Legatus Legionis”) is to prove the Earth moves. We can do this with the tides. The part closest to the external source of gravity has the water fall sideways a little towards it; the part furthest has more centrifugal force so it is trying to throw the water away. They may not have understood the mechanics of that, but they did know about the sling. Aristotle could not detect this because the tides where he lived are miniscule but in my ebook I had my Roman with the British invasion and hence had to study the tides to know when to sail. There you can get quite massive tides. If you simply assume the tide is cause by the Moon pulling the water towards it and Earth is stationary there would be only one tide per day; the fact that there are two is conclusive, even if you do not properly understand the mechanics.

# Science is No Better than its Practitioners

Perhaps I am getting grumpy as I age, but I feel that much in science is not right. One place lies in the fallacy ad verecundiam. This is the fallacy of resorting to authority. As the motto of the Royal Society puts it, nullius in verba. Now, nobody expects you to personally check everything, and if someone has measured something and either clearly shows how he/she did it, or it is something that is done reasonably often, then you take their word for it. Thus if I want to know the melting point of benzoic acid I look it up, and know that if the reported value is wrong, someone would have noticed. However, a different problem arises with theory because you cannot measure it. Further, science has got so complicated that any expert is usually an expert in a very narrow field. The net result is that  because things have got so complicated, most scientists find theories too difficult to examine in detail and do defer to experts. In physics, this tends to be because there is a tendency for the theory to descend into obscure mathematics and worse, the proponents seem to believe that mathematics IS the basis of nature. That means there is no need to think of causes. There is another problem, that also drifts over to chemistry, and that is the results of a computer-driven calculation must be right. True, there will be no arithmetical mistake but as was driven into our heads in my early computer lectures: garbage in, garbage out.

This post was sparked by an answer I gave to a chemistry question on Quora. Chemical bonds are usually formed by taking two atoms with a single electron in an orbital. Think of that as a wave that can only have one or two electrons. The reason it can have only two electrons is the Pauli Exclusion Principle, which is a very fundamental principle in physics. If each atom has only one in  such an orbital, they can combine and form a wave with two electrons, and that binds the two atoms. Yes, oversimplified. So the question was, how does phosphorus pentafluoride form. The fluorine atoms have one such unpaired electron each, and the phosphorus has three, and additionally a pair in one wave. Accordingly, you expect phosphorus to form a trifluoride, which it does, but how come the pentafluoride? Without going into too many details, my answer was that the paired electrons are unpaired, one is put into another wave and to make this legitimate, an extra node is placed in the second wave, a process called hybridization. This has been a fairly standard answer in text books.

So, what happened next? I posted that, and also shared it to something called “The Chemistry Space”. A moderator there rejected it, and said he did so because he did not believe it. Computer calculations showed there was no extra node. Eh?? So I replied and asked how this computation got around the Exclusion Principle, then to be additionally annoying I asked how the computation set the constants of integration. If you look at John Pople’s Nobel lecture, you will see he set these constants for hydrocarbons by optimizing the results for 250 different hydrocarbons, but leaving aside the case that simply degenerates into a glorified empirical procedure, for phosphorus pentafluoride there is only one relevant compound. Needless to say, I received no answer, but I find this annoying. Sure, this issue is somewhat trivial, but it highlights the greater problem that some scientists are perfectly happy to hide behind obscure mathematics, or even more obscure computer programming.

It is interesting to consider what a theory should do. First, it should be consistent with what we see. Second, it should encompass as many different types of observation as possible. To show what I mean, in phosphorus pentafluoride example, the method I described can be transferred to other structures of different molecules. That does not make it right, but at least it is not obviously wrong. The problem with a computation is, unless you know the details of how it was carried out, it cannot be applied elsewhere, and interestingly I saw a recent comment in a publication by the Royal Society of Chemistry that computations from a couple of decades ago cannot be checked or used because the details of the code are lost. Oops. A third requirement, in my opinion, is it should assist in understanding what we see, and even lead to a prediction of something new.

Fundamental theories cannot be deduced; the principles have to come from nature. Thus mathematics describes what we see in quantum mechanics, but you could find an alternative mathematical description for anything else nature decided to do, for example, classical mechanics is also fully self-consistent. For relativity, velocities are either additive or they are not, and you can find mathematics either way. The problem then is that if someone draws a wrong premise early, mathematics can be made to fit a lot of other material to it. A major discovery and change of paradigm only occurs if there is a major fault discovered that cannot be papered over.

So, to finish this post in a slightly different way to usual: a challenge. I once wrote a novel, Athene’s Prophecy, in which the main character in the first century was asked by the “Goddess” Athene to prove that the Earth went around the sun. Can you do it, with what could reasonably be seen at the time? The details had already been worked out by Aristarchus of Samos, who also worked out the size and distance of the Moon and Sun, and the huge distances are a possible clue. (Thanks to the limits of his equipment, Aristarchus’ measurements are erroneous, but good enough to show the huge distances.) So there was already a theory that showed it might work. The problem was that the alternative also worked, as shown by Claudius Ptolemy. So you have to show why one is the true one.

Problems you might encounter are as follows. Aristotle had shown that the Earth cannot rotate. The argument was that if you threw a ball into the air so that when it reached the top of its flight it would be directly above you, when the ball fell to the ground it would be to the east of you. He did it, and it wasn’t, so the Earth does not rotate. (Can you see what is wrong? Hint – the argument implies the conservation of angular momentum, and that is correct.) Further, if the Earth went around the sun, to do so orbital motion involves falling and since heavier things fall faster than light things, the Earth would fall to pieces. Comets may well fall around the Sun. Another point was that since air rises, the cosmos must be full of air, and if the Earth went around the Sun, there would be a continual easterly wind.

So part of the problem in overturning any theory is first to find out what is wrong with the existing one. Then to assert you are correct, your theory has to do something the other theory cannot do, or show the other theory has something that falsifies it. The point of this challenge is to show by example just how difficult forming a scientific theory actually is, until you hear the answer and then it is easy.

# Ancient Physics – What Causes Tides? The Earth Moves!

I am feeling reasonably pleased with myself because I now have book 2 of my Gaius Claudius Scaevola trilogy, Legatus Legionis, out as an ebook on Amazon. This continues the story set during the imperium of Caligulae, and the early imperium of Claudius, and concludes during the invasion of Britain. I shall discuss some of the historical issues in later posts, but the story also has an objective of showing what science is about.

In my last post, I showed how the ancients could “prove” the Earth could not go around thy Sun. Quite simply, orbital motion is falling motion, and if things fell at different rates depending on their mass, the Earth would fall to bits. It doesn’t. So, what went wrong? Quite simply, nobody checked, and even more surprisingly, nobody noticed. Why not? My guess is that, quite simply, they knew, it was obvious, so why bother looking? So the first part is showing the Earth moves around the Sun is to have my protagonist actually see three things fall off a high bridge, and what he sees persuades him to check. I think that part of success in science comes from having an open mind and observing things despite the fact that you were not really intending to look for them. It is the recognizing that which you did not expect that leads to success.

That, however, merely permits the Earth to go around the Sun. The question then is, how could you prove it, at the time? My answer is through the tides. What do you think causes the tides? Quite often you see the statement that the Moon pulls on the water. While true, this is a bit of an oversimplification because it does not lift the water; if it did, there would be a gap below. In fact, the vector addition of forces shows the Moon makes an extremely small change in the Earth’s gravity, and the net force is still very strongly downwards. To illustrate, do you really think you can jump higher when the Moon is above you? There is a second point. In orbital motion (and the Earth goes around a centre of gravity with the Moon) all things fall at the same acceleration, but the falling is cancelled out because the sideways velocity takes the body away at exactly the correct rate to compensate. This allowed my protagonist to see what happens (although the truth is a little more complicated). The key issue is the size of the Earth. The side nearest the Moon is not moving fast enough, so there is a greater tendency to fall towards the Moon; the far side is moving too fast, so there is a greater tendency for water to be thrown outwards. There is, of course, still a strong net force towards the centre of the Earth, but when not directly under the Moon, the two forces are not exactly opposed, and hence the water flows sideways towards the point under the Moon. The same thing happens for the Sun. This is admittedly somewhat approximate, but what I have tried to capture is how someone in the first century who did not know the answer could conceivably reach the important conclusion, namely that the Earth moves. If it moves, because the Sun stays the same size, it must move in a circle. (It actually moves in an ellipse, but the eccentricity is so small you cannot really detect the change in the size of the Sun.)

What I hope to have shown in these posts, and in the two novels, is the excitement of science, how it works and what is involved using an example that should be reasonably comprehensible to all. The same principles apply in modern science, except of course that once the basic idea is obtained, the following work is a bit more complicated.

# What is involved in developing a scientific theory? (2)

In my previous post, I showed how the protagonist in Athene’s Prophecy could falsify Aristotle’s proof that the earth did not rotate, but he could not prove it did. He identified a method, but very wisely he decided that there was no point in trying it because there was too much scope for error. At this stage, all he could do was suggest that whether the earth rotated was an open question. If it did not, then the planets could not go around the sun, otherwise the day and the year would be the same length, and they did not. At this point it is necessary, while developing a theory, to assume that as long as it has no further part to play in the theory it does, if for no other reason than it is necessary. By doing so, it creates a test by which the new theory can be falsified.

The logic now is, either the earth moves or it does not. If it does move, it must move in a circle, because the sun’s size was constant. (Actually, it moves in an ellipse, but it is so close to a circle that this test would not distinguish it. If you knew the dynamics of elliptical motion, you could just about prove it did follow an ellipse. The reason is, it moves faster when closer to the sun, and the solstices and the equinoxes were known. A proper calendar shows the northern hemisphere summer side of the equinoxes is longer than the southern hemisphere’s one by about 2 – 3 days, and is the reason why February is the shortest month. We, in the southern hemisphere, get cheated by two days of summer. Sob! However, if you have not worked out Newton’s laws of motion, this is no help.) So, before we can prove the earth moves, we must first overturn Aristotle’s proofs that it did not, and that raises the question, where can a theory go wrong?

The most likely thing to go wrong in forming a scientific theory can be summarized simply: if you start with a wrong premise, you may draw a wrong conclusion. Your conclusion may agree with observation, because as Aristotle emphasized, a wrong premise can still agree with observation. One of Aristotle’s examples of false logic is as follows:

Man is a stone

A stone is an animal

Therefore, man is an animal.

The conclusion is absolutely correct, but the means of getting there is ridiculous. A major problem when developing a theory is that a wrong premise that brings considerable agreement with observation is extremely difficult to get rid of, and invariably it has pervasive effects for a long time thereafter.

One reason why, in classical times, it was felt that the Earth must be stationary was because of Aristotle’s premise that air rises. If so, the fact that we have air at all must be because the Universe is full of it. If so, then if the earth moves, it must move through air. If so, there would be a contrary wind, the speed difference of which on either side would depend on the rate of rotation. There was no such wind, therefore no such orbit. We can forgive Aristotle here, but we forgive those who followed Archimedes less well. Had Aristotle known of Archimedes Principle, this argument would probably never have been made. According to Archimedes, air rises to the top because it is the least dense, but it still falls towards the earth. Space is empty. There were clues in classical times that space was empty. One such clue was that when a star went behind the moon, it did so sharply, which indicated there was no air to refract it. It was also known there were no clouds on the moon.

This shows another characteristic that unfortunately still pervades science. Once someone establishes a concept, evidence that falsifies that concept tends to be swept under the carpet as long as by doing so, it does not affect anything else. No clouds on the moon might mean anything. So, perhaps, you will now begin to see how difficult it was to get the heliocentric theory accepted, and how difficult it is to find the truth in science when you do not know the answer. That applies just as much today as then. The intellectual ability of the ancients was as great as now, and Aristotle would have been one of the greatest intellects of all times. He just made some mistakes.

# What is involved in developing a scientific theory? (2)

In my previous post, I suggested that forming the theory that the Earth was a planet that went around the sun was an interesting example of how a scientist forms a theory. When starting, the first task is to review the literature, which at the time, was largely determined by Aristotle. Since Aristotle asserted that the earth was fixed, it therefore follows that you must first overturn his assertions. One place to start is to decide why we have day and night. Let us use Aristotle’s own methodology, which is to break the issue down into discrete issues. Thus we say, either the Earth is fixed and everything rotates around it, or everything is more or less fixed, and the Earth rotates. Aristotle had reached that step, and had “proven” that the Earth did not rotate. Therefore the day/night must occur through the sun orbiting the Earth. The heliocentric theory, despite its advantages, is falsified unless we can falsify Aristotle’s proofs.

At this point, we should recognize that Aristotle was very clear on one point, and he has been badly misrepresented on this ever since. Aristotle clearly asserted that logic must be applied to experimental observations, and that observation alone was critical. So, what was his experiment? Aristotle argued that if you threw a stone vertically into the air, it always came back to the same place. Had the earth been rotating, the path length of a rotation increased with height, in which case the stone should drag back westwards. It did not, so the earth did not rotate. Note that at this point, Aristotle was effectively arguing for the conservation of angular momentum, similarly to the ice skater slowing her spin by extending her arms. Before reading any further, what do you think about Aristotle’s experiment? What is wrong, and how would you correct it, bearing in mind you have only ancient technology?

In my ebook, Athene’s Prophecy, my protagonist dismisses the experiment by arguing that vertical is defined as the point where the stone falls back to the same place. By defining the point thus, if the stone does not come back to the same place, it was not thrown vertically. He then criticizes Aristotle by arguing that the correct way to do the experiment is to simply drop the stone from a high tower. The reason is that while Aristotle would be correct in that there should be a drag to the west going up, exactly the opposite should occur on the way back down. What should happen if dropped from a tower is that the stone would strike the ground slightly to the east of the vertical position, and in Rhodes, where this was being discussed, also slightly to the south. Can you see why?

That the stone should go east follows from the fact that the angular velocity is constant, but the path length is longer the higher you are, so it is going east faster higher up. The reason it goes south is because the stone falls towards the centre of the earth, and thus very slightly decreases its latitude, but the point at the base of the tower does not. In my ebook, however, my protagonist wisely refused to carry out the experiment, because it is not that easy to carry out, even with modern equipment, and in those days the errors in measurement would most likely exceed the effect. Notwithstanding that, the logic is correct in that any effect like that going up will be exactly countered coming down, and consequently Aristotle’s “proof” is not valid. Thus one can falsify an experiment through logic alone. Of course, disproving Aristotle does not prove the earth is rotating, but it leaves it open as a possibility. Carrying out the dropped stone experiment would, provided you could guarantee that what you saw was real and not experimental error. That is not easy to do, even now.

# What is involved in developing a scientific theory?

Everyone knows about people like Galileo, Newton, etc, but how are such theories discovered? Now obviously I have no idea exactly how they did it, but I think there are some principles involved, and I also think some readers might find these of interest. I hope so, because therein lies the third task for my protagonist in my novel Athene’s Prophecy.

The reason that is in the novel is because the overall plot requires a young Roman to get help from superior aliens to avoid a disaster in the 24th century. The reason for the time difference is, of course, relativity. Getting to the aliens involves being abducted by other aliens, but once taken to another world, the protagonist has to be something more than a specimen that can talk. To get the aliens to respond, he has to be someone of interest to talk to. Suppose you had the chance to talk to someone from the 16th century, or to Galileo, who would you choose? My proposition is, Galileo, so the task for my young protagonist is to prove the heliocentric theory, i.e. that the earth moves around the sun. That is similar to what was in the film Agora. The big problem was, everybody was so sure the earth was fixed and everything else went around it. Not only were they sure, but they could also use their theory to calculate everything that mattered, such as when the solstices and equinoxes would be, when Easter would be, and when various planets would be where in the sky. What else did they need?

The alternative theory was due to Aristarchus of Samos. What Aristarchus maintained was that the earth was a planet, and all planets went around the sun, the moon went around the earth, and the solar system was huge. This latter point was of interest, because Aristarchus measured the system. His first measurement was to obtain the size and distance of the Moon, and what he did was to get two people to measure the angle at the exact moment an eclipse of the moon started. These two people were separated by as much distance as he could manage, and with one distance and two angles he had a triangle that would permit the measurement of the distance to the moon. The size then followed from its solid angle. The method is completely logical, although the amount of experimental error was somewhat large, and his answer was out by a factor of approximately two. He then measured the distance to the sun by measuring the angle between the sun and moon lines when the moon was half shaded, and used his moon distance and Pythagoras’ theorem. His error here was about a factor of five, and would have been about a factor of ten had not the error in the moon distance favoured him. The error range here was too great (to see why, check how tangents get very large as they approach 90 degrees) but he was the first to realize that the solar system is really very large. He also showed that the sun is huge compared to the earth.

Aristarchus, following Aristotle, also postulated that the stars were other suns, but so far away, and they would have to be going at even greater speeds. This did not make sense, so he needed an alternative theory. In my opinion, this is invariably the first step in forming a new theory: there is some observation that simply does not make sense within the old theory. Newton’s theory was born through something that did not make sense. If you believed Copernicus, or Aristarchus, if you had heard of him, or of Galileo, then the earth and the other planets went around the sun, but there was a problem: Mars could only be explained through elliptical orbits, and nobody could explain how a body could orbit in an elliptical path with only a central force. Newton showed that elliptical orbits followed from his inverse square law of gravity. Relativity was also born the same way. What did not make sense was the observation that no matter what direction you looked, the speed of light was constant. What Einstein did was to accept that as a fact, and put that into the classical Galilean relativity, and came up with what we call relativity.

So we now get to the second step in building a new theory. That involves reading about what is known, or thought to be known, about the subject. If we think about the heliocentric theory in classical times, we now know that much of what was thought to be correct was not. So, here is a challenge. If you had to, could you prove that the earth goes around the sun, while being restricted to what was known or knowable in the first century? Answers in the next few posts, but feel free to offer your thoughts.