Tag Archives: theory

What exactly is ‘science’?

I used to think science was the practice of the scientific method; i.e. you propose a hypothesis, you develop a test of the hypothesis, execute it and prove the hypothesis.

That worked for me until the end of high school.

At university, I was a true nerd. I read all my textbooks cover to cover (mainly because as I was too shy for girls and too poor for booze). During this time, the definition above started to fail. So much of the science was maths, statistics, observation, pattern recognition, logic and quite a bit of rote learning. Not all of it fitted into my definition of science. I became a fan of a new definition: science is the study of the nature of reality .

But then I did post-grad, and I realised that not much in science is ‘proven’ (I guess this is the point of post grad study). Evolution, for example, is not proven. That the sun revolves around the earth is not ‘proven’. I discovered that the only things that could be proven were ‘ideas’ about ‘other ideas’. Bear with me on this one.

Let us say we define the number system – this is an ‘idea’ or conceptual construction. Within this construction we can ‘prove’ that one and one is two. Because we ‘made’ the system, with rules, then we can make factual and true statements about it. We can’t do this about the real world – we cannot say anything with absolute certainly because we rely on flaky inputs like our own highly fallible perception.

It’s like that old chestnut: how can you be sure you are not living in a giant simulation? Of course you can argue that it is pretty unlikely and I would agree, and right there we have a clue to a better definition of science.

It turns out that much of modern science deals in ‘likelihood’ and ‘probability’ rather than proof and certainty. For example, we can say that the theory of evolution is very likely to be more-or-less right, as there is a lot of corroborating evidence. Science cannot be run like a law court – where the prosecution only need to reach a threshold of reasonable doubt to ‘prove’ someone guilty.

Aside for nerds: Science says you can use logic to prove things absolutely, but logic only works with ideas, and there is a breakdown between ideas and reality, so one can never prove things in reality. So it is thoroughly wrong for a court to say that someone has been proven guilty. The courts use this language as a convenience, to “draw a line under” a case as they have not found a moral way to dole out punishments based on probabilities. Imagine a world in which a murder suspect gets a 5 year sentence because the was a 20% chance he was guilty! Sports referees often operate in this decisive way, perhaps because it saves a lot of arguing!

Anyway, good science cannot just give up and say once there is consensus something passes from theory to fact. This is sloppy. We have to keep our options open – forever.

Think for example of Newton’s Laws of Motion. They are called ‘Laws’ because the scientific community had so much faith in them they passed from theory (or a proposed model) to accepted fact. But they were then found wrong. Strange that we persist in calling them laws!

It took Einstein’s courage (and open mindedness) to try out theories that dispensed with a key plank of the laws – that time was utterly inflexible and completely constant and reliable.

So it is that the canon of scientific knowledge has become a complex web of evidence and theories that attempt to ‘best fit’ the evidence.

Alas, there are still many propositions that many so-called scientists would claim are fact or at least ‘above reproach’. Evolution is attacked (rather pathetically), but the defenders would do well to take care before they call it ‘fact’. It is not fact, it is a superbly good explanation for the evidence, which has yet to fail a test of its predictions. So it is very very likely to be right, but it cannot be said to be fact.

This is not just a point of pedantry (though I am a bit of a pedant) – it is critical to keep this in mind as it is the key to improving our model.

Two great examples of models people forget are still in flux…

1) The big bang theory

2) Quantum theory

I will not go into global warming here though it is tempting. That is one where it doesn’t even matter if it is fact, because game theory tells you that either way, we better stop making CO2 urgently.

Back to the big bang.

I heard on the Skeptic’s Guide podcast today about an NSF questionnaire that quizzed people about whether they believed the universe was started with a massive explosion, and they tried to paint the picture that if you didn’t believe that, then you were ignorant of science. This annoyed me, because the big bang theory is now too often spoken of as if it were fact. Yes, the theory contributes viable explanations for red-shifted pulsars, background radiation, etc, etc, but people are quick to forget that it is an extrapolation relying on a fairly tall pile of suppositions.

I am not saying it is wrong, all I am saying is that it would be crazy to stop exploring other possibilities at this point.

You get a feeling for the sort of doubts you should have from the following thought experiment:

Imagine you are a photon born in the big bang. You have no mass, so you cannot help but travel at ‘light speed’. But being an obedient photon, you obey the contractions in the Lorentz equations to the letter, and time thus cannot pass for you. However, you are minding your own business one day when suddenly you zoom down toward planet earth and head straight into a big radiotelescope. Scientists analyse you and declare that you are background radiation dating from the big bang and that you have been travelling for over 13 billion years (they know this because they can backtrack the expansion of the universe). Only trouble is, that for you, no time has passed, so for you, the universe is still new. Who is right? What about a particle that was travelling at 0.999 x the speed of light since the big bang? For it, the universe is some other intermediate age. So how old is the universe, really?

This reminds us of the fundamental proposition of relatively – time is like a gooey compressible stretchable mess, and so is space, so the distance across the universe may be 13.5 billion light years, or it might be a micron (how it felt to the photon). It all depends on your perspective. It is much like the statement that the sun does not revolve around the earth and that it is the other way around. No! The sun does revolve a round the earth. You can see it clearly does. From our perspective at least.

Now, quantum theory.

Where do I start? String theory? Entanglement? Please.

The study of forces, particles, EM radiation and the like is the most exciting part of science. But being so complex, so mysterious, so weird and counter intuitive, it is super vulnerable to abuse.

Most people have no idea how to judge the merits of quantum theories. Physicists are so deep in there, they have little time (or desire or capability) to explain themselves. They also love the mystique.

I do not want to ingratiate myself with physicists, so I will add that the vast majority have complete integrity. They do want to understand and then share. However, I have been working in the field for long enough to know that there are weaknesses, holes and downright contradictions in the modern theory that are often underplayed. In fact these weaknesses are what make the field so attractive to people like me, but is also a dirty little secret.

The fact is that the three forces (weak nuclear, strong nuclear and magnetic) have not been explained anything like as well as gravity has (by relativity). And don’t get me started on quantum gravity.

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Anyway, thinking about all these issues, I concluded that science was (definition #3) the grand (platonic) model we are building of reality, ever evolving to best fit our observations.

My man, Plato

That works well for me. However, I recently came across a totally different definition for science:

# 4) “Science is a tool to help make the subjective objective.”

OK I paraphrased it to make it more snappy. It was really a discussion about how science was developed to overcome the fallibility of the human mind. Examples of weaknesses it needs to overcome are:

  1. The way our perception is filtered by preconceptions
  2. How we see pattern where there is none
  3. How we select evidence to match our opinion (confirmation bias)
  4. How we  read too much into anecdotal evidence
  5. etc etc.

I could go on. So ‘science’ is the collection of tricks we use to overcome our weaknesses.

I like this definition. We are all going about, and in our heads we are building our model of the world… and its time for an audit!

Communicating across cultures – how to be understood!

If beauty is in the eye of the beholder, then the message is in the ear of the listener.

Thus, when we communicate, a key challenge is to make the intended message match the received message as closely as possible. Thus effective communicators are very good at getting into the mind of the audience and seeing or hearing the message from their perspective.

Of course, not everyone can do this. One way this is resolved is by taking advantage of two way communication – if the listener can paraphrase what you are telling them, as a sort of parity check on the message, then any misunderstandings can be revealed and dealt with. But this requires a good listener.

It is also important that if the message has a ‘thread’ (like a storyline) that the listener does not lose that thread due to some short lived issue – missed words due to accent, background noise or indeed the use of unfamiliar words and jargon.

Thus, when telling a story there needs to be redundancy in the message (just like in electronic communication protocols) such that if the thread is dropped it may be picked up again.

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I recently moved to the USA from the UK and am currently learning how to communicate across a cultural divide.

Anyone would think that Americans would speak English and perhaps they do, but ‘English’ is such a broad church that it allows for different groups to live their entire lives using only slightly overlapping subsets of the language. Observing these vocabulary differences I have noticed a sort of one-way breakdown that occurs in this case…

Diodes only allow electons to flow one way...

Just like a diode can allow electric current to flow one way and not another, it seems that poor vocabulary matching can have a similar effect on a message. It turns out that when Americans talk at me, I can easily recognize the words I don’t know, but when I talk I cannot recognize (or predict) the words they won’t know.

This may seem like a statement of the blindingly obvious, but it is the same effect as the card trick when the magician shows you a bunch of cards, say ten, and asks you to pick one and remember it. He will then shuffle the cards and show them to you again and tell you that your card has been removed. Lo and behold, your card is gone. Amazing, how did they know which one to remove, what are the chances!?

Well the trick is simple, the magician changed ALL the cards with sleight of hand, and relied on the fact that you didn’t bother to memorize the ‘other’ cards.

It is similar to the issue with speaking to foreigners – it is very hard to know which of your words are missing from their vocab. You can spend weeks or months living with them and you will pick up their vocab but you will find it hard to notice the words they don’t use. Thus after a while, a foreigner will understand pretty much all he or she hears, but when they talk, will still be poorly understood as they will persist in using unknown words.

Thus the flow of information is retarded in one direction only. I think this is a neat observation. That is to say, it is cool and clever, not clean and tidy 🙂

Medical Trends: The Holistic View

There is clearly a lot to be learned about medicine from history.

Indeed many effective treatments can (and have) been identified not by close examination of the human body, but but the close observation of patterns in statistics.

Thus is is possible with good data, a good eye, and quite a bit of spare time, to see many of the contributing factors to disease or accidents. The famous cases include the realisation that the plague was carried by rats and that cholera was in the water. Thus was born the science of epidemiology.

I think if I was starting university again right now, there is a good chance I would have steered towards that as a profession – for it has saved countless lives, and can be done from the safety of a nice desk, replete with good coffee and a supply of biscuits. I have never been drawn to a life of tending to the ill or injured, so this would have been a nicer way to get my benevolence ‘hit’.

Alas, I studied engineering, and though perhaps I could use epidemiological methods to predict metal fatigue or bridge collapses, I am not sure that would be very useful. We engineers seem to spend much more time looking at the costs of making something, and then the price you can sell it for.

Anyway, time for the science bit…

Epidemiologists looks for patterns relating illnesses to other things: other illnesses, location, professions, exposure to animals, and many more.

There are some pretty major trends in health happening right now. For a good example, look at Hans Rosling’s presentation at TED recently. He shows, among other things, that people are living longer than ever before. Despite all the talk of the world going to pot, it seems there is an untold story – the story of how life expectancy in the developing world has been climbing beautifully for several decades. The stats tell a story of a golden age in humanity.

To go off on a slight tangent, I have to say what a pity it is that the media focus so much on the wars and tragedies. Of course, they sell sensation, so they will continue, but we humans are not used to getting news from the whole planet – we have barely got out of the trees and only left our small villages for cities an eye-blink ago. Evolutionarily speaking, our fears were programmed in a much smaller environment where news did not travel very far – the story of a death would be significant because you didn’t know very many people. Nowadays we get more news and we also know far more people because of the world of celebrity (blame the media again), and because we are so ‘networked’ (its the ‘new’ media this time) we also know a huge number of people by association. Thus we receive bad news far more often and tend to overvalue its direct threat to us.

Now let me get back on track. We are living in a golden age – better nutrition, cleaner water, the understanding of the theory of germs, and of course, advances in medicine (think vaccines, think penicillin, think surgical methods). We have benefited hugely from a better understanding of how the body works and of how fungi, bacteria and viruses work.

The activity is higher than ever on countless fronts: dementia,  HIV/AIDS, epilepsy, stroke, heart disease, and so on… but what about the big kahuna? I refer of course to cancer.

Well it has not been cured. The ‘cure for cancer’ has long been held up as the iconic challenge to medical science. Only trouble is, the challenge is flawed. There is no one ‘cancer’ – there are many different cancers  – and the little bastards are all subtle and complex – and even if you can kill one, killing it will often kill off something else, because cancers are not as alien as say viruses – they are in fact our own cells turning on us.

So rather than looking at cellular function and cunning ideas like rna interference, what can we do with epidemiology?

Cancer death rates are not independent of the death rates from other causes...

Yes, cancer is not an ‘epidemic’ – we are not studying its spread, but we can certainly study correlations and seek causation (think smoking tobacco or working with asbestos). Smarter people than I are already poring over this sort of data, and there is much hand-wringing nowadays because the ‘easy’ causes have most been found and now we are looking at the weaker correlations, where the link is not certain, or where the sacrifice to benefit ratio is unclear. Think barbecue meat, think E numbers and so on.

But I don’t want to talk about that sort of cause. What I am wondering is relates more to age…

Cancer is somewhat a statistical process – it may arise as a random mutation, which, as fate would have it, is also bad for one’s health. Many mutations result in no effect or perhaps cell death or perhaps just reduced function of the cell.  There are very few mutations that actually allow for continued (and sometimes rampant) growth and macro level harm. As the mutation is a random event, the chance of occurrence will depend on the number of ‘cellular events’ that occur in a lifetime – this is determined by two factors, the frequency of the events – and the length of the lifetime.

Now add to that randomness the fact that many cancers are slow growing – they may take too long to harm or kill you and something else gets you first.

These two factors together go to show you that the longer you live, the greater the risk of cancer development. Add to this the probable third factor that older cells are more likely to go haywire, and you can easily see why cancer is more commonly suffered by older people.

Does this mean that you risk of ‘catching’ cancer ‘today’ is less if you are younger? Well yes, if your cells (or immune system) are in better shape, mutations may be rarer and you may fend off some that do occur – however, your chance of ‘having’ cancer (rather than ‘getting’ it) are accumulative with age, so this is a very strong factor when looking at screening (looking for cancers that already exist). It is often only worthwhile screening for cancer in older people where the ‘hit rate’ makes the costs (false positives) justifiable.

This age affect is well known, but I am wondering if another factor may be throwing a curve ball into the stats – the longer lifespan of people generally.

As some types of cancers are being treated more effectively (prevented/slowed/cured), and as death from other causes (heart disease, pneumonia, tuberculosis, etc.) drops, does that not give cancer more fertile ground to wreak its havoc?

In other words, will curing other ailments, to some extent, tend to push us into the waiting arms of cancer?

And if this is already happening, perhaps the cancer death rates, hiding underneath the massive advances there may actually be an  underlying increase in death from cancer due to the increased survival of everything else.

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So! We all die of something eventually. I guess the question medical science now needs to ask is:  what is the best way to die? Should we be saved from one death only to have another? Will cancer rates start to creep up again as advances against cancer slow and lifespan continues upward? Time will tell!

Is the Earth like a fractal?

Have you ever spent any time looking at the Mandelbrot set? I don’t mean a cursory glance, I mean really contemplated it?

Mandelbrot set

The Mandelbrot set. The horizontal axis is the number line,

And I don’t even mean the fancy coloured versions, just the straight black-and-white one (see image on right)?

It is really far more interesting than it looks…

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At first glance it just looks like a prickly pear gone wrong, so what is so interesting?

Well, remember this graph shows a set, that is to say it divides numbers into two groups, those inside the set, and those outside.

You could easily create such a set with circle – you can define the co-ordinates inside the circle is ‘in’ the set and that which is outside the circle outside the set. Such a set can be defined in a sentence: it is all points c less than the distance r from the origin.

The Mandelbrot set is just the same – a shape that divides space into two regions – in the image, the black area shows the numbers in the set, and the white area show the numbers out of the set. The only difference from a circle is that the Mandelbrot shape is more wiggly.

It equation is not much longer to define:

It is all numbers c, where if you square the number, then add the number, then square the result and add the number again, then repeat, it does not tend to infinity.

So zero is in the set, if you square it, then add it, it is still zero.

How about 1? No, it will run off: 1,2,3, 4, …

-1, on the other hand, squared, is 1, then added, goes to zero, where it will get stuck: -1, 0,0,0…

Figuring out the contents of the set is however complicated. Bloody complicated. Infinitely complicated in fact, and one of the marvels of the mathematical world.

To get a feeling exactly how complex this set is, take a look at some animations in which you zoom in on the perimeter; you can google “fractal dive” for more…

Mandelbrot Zoom Animation

You can choose what part of the set to zoom into yourself, if you want, here: http://www.h-schmidt.net/MandelApplet/mandelapplet.html

It seems that one simple sentence has been able to define an infinitely complex boundary, and begs some interesting questions: have we created a sort of universe? What is the information content of this set?

It makes my head hurt.

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The area of specific interest to me, is the relationship between the platonic ‘world of maths’ and the real world; so are there parallels between such complexity in the world of numbers and the real world?

Clearly fractals sometimes have similarity to things in the real world – such as crystals, feathers and broccoli florets. We see many reminders of complex structure in the real world, and it brings me to think of the earth as a sort of giant 3-d fractal – where the solid matter is ‘in the set’ and the gas of the atmosphere and the vacuum of space is “out of the set”.

We can see that the interface, the earth’s surface, also has complex structure, including such things as crystal caves or the lining of your lungs – and like with the Mandelbrot, we also seem able to zoom in to many levels.

However, just as there are no perfect spheres in the real world, there are no perfect fractals, and it seems that the structure falls apart once we get to subatomic levels of zoom (or does it?)

Some part’s of the earth’s interface are fractal-like due to the iterative nature of their construction (tree growth, crystal growth, sea-shells, etc.), and you can see that a simple rule of “branching” in a plant can make a complex shape. However, some of the complexity, specifically organic and bio-chemistry, still seem different (to me anyway).

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Krzysztof Marczak Mandelbulb

Krzysztof Marczak's Mandelbulb rendering

Now it turns out that my idea of the earth as a fractal with its skin as a complex interface can be more closely matched to the newly invented (discovered?) “Mandelbulb”, the amazing 3-d set. The interesting story of their development is told by one of their key developers, Daniel White, here.

The Mandelbulb is amazing because, as with many other fractals, you can zoom in and see ever more fascinating detail, and with incredible variation, and if you zoom into it continuously it would not be unlike zooming in on planet earth using Google Earth.

This excellent video below shows the idea of zooming into the Earth off well  (it seems to be derived from a book I happen to have called “Powers of Ten“).

So of course, you can do a similar trick on the Mandelbulb:

Enough said!

The Statistics of Fear

By all rights we should be rather scared of cars. We should regard them in much the same way we would regard a tarantula on the bedsheets or a short stroll on a tightrope. Yet we aren’t. Curious. Cars kill far more people than lava flows, piranhas or anthrax.

Perhaps they are too new for evolution to equip us?

Now if we look into the stats you realise we should be even more terrified of crap food, and the word “sedentary” should be a glare-inducing swear-word. If our bodies knew what was good for them, we would get grouchy after a day without a vigorous walk, and start shaking weakly after two. Sugar, so long sweet, should soon evolve to be utterly disgusting. Not soon enough for some.

Unproven medicine : an alternative name for alternative medicine

“Alternative and complimentary therapies”. They sound so nice. So warm and fuzzy. Surely they augment the cold clinical scientific approach to regular medicine, and have a more holistic approach catering to the soul and spirit as well as the flesh?

I argue not. Hear out my logic…

Any treatment that has proven to provide reliable benefit, is automatically added to the canon of ‘western’ medicine. Therefore the only treatments left available for ‘alternative’ to claim, are those that are unproven, or worse, treatments known to be actively harmful.

Promoters of alternative medicine will argue that western medicine is still woefully weak, and not tuned into holistic and spiritual matters and that such things defy proof. This is clearly claptrap. If you do a well designed double-blind, placebo-controlled test of an ‘alternative therapy’ and the outcomes are no better than for the placebo, then the participants who got the treatment are no better off, spirit or no spirit.

I personally prefer the sort of benefits that can be detected!

How did this situation come to pass, where unproven medications have such a grip?

I think there are three main ingredients:

  1. People make money from other people’s fear (in both western and alternative medicine) and that causes folks on both sides to hide or twist the facts – and also erodes the public’s trust.
  2. The fact that complimentary medicines do actually offer benefits – the well-known benefit of care and attention and also the benefit of the placebo effect – muddies the waters.
  3. It is however the human weakness of putting far too much value on anecdotal evidence that assures the future of unproven medicine.

I think that people who understand this do a disservice to our communities by giving this bad medicine the label ‘alternative’ or ‘complimentary’, so I would like to propose the term ‘unproven medicine’. I would however welcome some more lyrical suggestions!

Evil: a baseless construct

This morning on BBC Radio 4’s “Though for the day”, the Right Reverend James Jones claimed “Evil triumphs when the imagination is inebriated with evil”.

So as a logician I would like to know what exactly “evil” is. Can it be measured (like energy)? Or detected by our (5) senses? Does it conform to the known laws (models) of physics?

For something so darn vague it is amazing how much we use it day to day. We blame so much on it, and justify so much in its name.

But in a strange dichotomy, if you pay close attention the the professions (medicine, law, engineering, etc) you will find scant mention of this concept – it does not help in the treatment of criminals or the mentally ill it does not explain earthquakes or building collapses – it seems has no use in the real world, but is used by politicians and preachers like a moral blank-cheque.

I therefore suggest that the concept of evil is a relic from a mystical past in which gods were invoked to explain thunder and demons to explain crop failure.

Surely all talk of someone being ‘evil’ or an act being ‘evil’ has no place in our secular world?

Open question about relativity

A quick open question for physicists:

If you accelerate off in one direction, and keep accelerating until you are travelling fast (a relativistic speed), special relativity supposedly says the universe contracts in the direction of your travel. Fine, I can see how that makes some sense.

Now consider a massive body, such as the sun – it warps space time in its vicinity, presumably roughly equally in all directions, creating a symmetrical ‘dent’ in the fabric of space-time (if you like the trampoline analogy).

But if you fly past at a relativistic speed, and space is contracted in the direction of your travel, will the sun’s sphere of influence also be contracted, turning it from a “sphere of influence” into an ‘oblate spheroid of influence’?

Or will its shape be maintained for some beautiful reason (which is what I suspect)?

Thx.

The interesting implications of our theory of gravity…

The evidence is now pretty strong that Gravity is just a symptom of ‘curved’ space time.

While it’s cool to have gravity all figured out, like so many matters in science, the answer raises even more interesting questions.

Like what is the nature of the curvature? Well, people (including me) are still trying to figure this out. In the meantime it is a good pastime to pontificate about the implications of curved space time. Here are two of my most recent theories/perspectives…

Perspective 1: Trees and apples switch places…

Each mass has a ‘destined path’, a path it will follow if left to its own devices. Just as Newton suggested in his First Law of Motion, things only change velocity when experiencing a net force.

However, he thought that gravity was a ‘force’ that made apples drop, however, the new theory of gravity suggests the apple was stationary – it was the tree and the meadow that were accelerating (upwards), a result of being pushed by the ground.

It lets us think of falling objects as ‘free from force’, and obeying Newton’s First Law.

Now, switch gears. Think what would happen if you could walk through solid things like walls. You may think it useful, but it would certainly cause some inconvenience, as you would presumable fall through the floor and plunge into the Earth’s molten core. You would fall past the centre and then start slowing; you would then briefly surface on the other side of the Earth, only to fall again. You would thus oscillate on some sort of sine wave. This is your ‘destined path’, the straight line through space time that your mass and location intend for you, where you to follow Newton #1. It is simply all the floor tiles and rocks preventing you from going straight in space-time. You are thus constantly being pushed, and thus curving off that path, thanks to the force of the floor. Lucky thing really.

Perspective 2: Slow time really is a drag…

A gravitational field can also be thought of as a gradient in the speed of time. It is possible (to me at least) that rather than supposing space-time is curved, it may well be that it simply varies in ‘density’. How? Well if time passes at different speeds in different places, that can be thought of as a density difference.

Now, we know that even when standing still, we are still plunging ahead – through space-time – in the direction of time. However,  thanks to Earth’s gravity, time is going slower down at your feet, they are sluggish, stuck in the mud. Now if you have a pair of wheels on a fixed axle, what happens if your right wheel gets stuck in the mud? It slows and you turn to the right… and in the just the same way, your body is trying to ‘turn’ downwards toward your feet – the gravity you feel!

When I first thought of this model, I was smug and pleased with myself. Until I found someone else[1] had already used it to accurately model planetary orbits. Read about it here – they have shown that waves (and therefore particles) will curve for the above reason combined with Fermat’s Principle. Bastards! 😉

 

Refs:

[1] Landau, LD; Lifshitz, EM (1975). The Classical Theory of Fields (Course of Theoretical Physics, Vol. 2) (revised 4th English ed.). New York: Pergamon Press. pp. pp. 299–309. ISBN 978-0-08-018176-9

Gravity explained in 761 words

People seem to be harbouring the impression that there is no good theory of Gravity yet. I asked a few friends – most thought Newton had explained it, but couldn’t explain it themselves. This is rather sad, 80-odd years after a darn good theory was proposed.

Of course there is still some controvery and the odd contradiction with other beloved theories, but the heart of the General Theory of Relativity really does a great job of explaining gravity and it is really wonderfully beautiful, and can be roughly explained without recourse to jargon and equations.

This is a theory that’s just so darn elegant, it looks, smells and tastes right – once you get it. Of course, the ‘taste’ of a theory doesn’t hold much water; for a theory to survive it needs to make testable predictions (this one does) and needs to survive all manner of logical challenges (so-far-so-good for this one too).

This is not a theory that needs to remain the exclusive domain of physicists, so for my own personal development as a scientist and writer, I thought I might try an exercise in explaining what gravity is – according to the general theory of relativity.

For some reason, my wife thinks this is strange behaviour!

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The story really got started when Einstien realised that someone in an accelerating  spaceship would experience forces indistinguishable from the gravity felt back on Earth. 

He or she could drop things and they would fall to the floor (assuming the spaceship is accellerating upwards)  just as they would fall on earth.

So perhaps that’s all gravity is… some sort of accelleration? Let’s see.

In the spaceship, it’s clear to us that the objects would appear to fall to the floor, but in reality, it is the floor of the spaceship that is rushing up towards the objects – this explains why things fall at the same speed whether heavy or light, matching Galileo’s own test results when he dropped various things, supposedly from the leaning tower of Pisa. It further implies that things will ‘fall’ even if they have no mass at all… such as light beams.

The thought experiment goes thus: Consider if you had a laser-beam shining across the spaceship control room; it would curve slightly downwards, because the light hitting the opposite wall would have been emitted a little time ago, when the spaceship was a little way back, and going a bit slower (remember, its accellerating).

We know the light is not bending, it is just that the source is accellerating, resulting in a curved beam. Imagine a machine-gun spraying bullets across a field – as you swing the gun back and forth the bullets may form curved streams of bullets, but each individual bullet still goes straight.

So Einstein suggested that perhaps light beams will bend in this same way here on earth under a gravitational field. Now Newton’s theory of gravity says light beams may also bend if they have ‘mass’, but the mass of light is a dodgy concept at best (it has inertia but no rest mass, but that’s a whole different blog posting). Anyway, even it it does have mass, it would bend differently from what Einstien predicted. So the race was on to see how much gravity could bend light…

This bending of light prediction was proven by a fellow called Eddington who showed that during a solar eclipse, light from distant stars was indeed bent as it passed near the sun, and by exactly the predicted angle.

Einstein went further though, suggested that light beams on Earth are, just like on the spaceship, really travelling straight, and only appear to bend, and that this can be so if space-time itself is curved. They are going straight, but in curved space.

We know that the shortest distance between two points is a straight line, but if that line is on a curved surface, supposedly straight lines can do strange things – like looping back on themselves. Think of the equator. This model therefore allows things like planets to travel in straight lines around the sun (yes, you read right).

The model has been tested and shown to work, and gives good predictions for planetary motion.

So what can we take home from all this?

Well mainly, if this model is right, we need to let it sink in that gravity may not be a force at all, but an illusion, like the centrifugal ‘force’ you experience when you drive around a corner.

Secondly, it is an open invitation to think about curved space and its marvellous implications!