h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: The 'Pellucidar' Novels by Edgar Rice Burroughs - A87906757
Author: Bluebottle - U43530

Awaiting availability in Peer Review.

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Might it be worth adding a section explaining how Burrough's physics is completely wrong? I can explain the details if you don't already known them.

That's an excellent idea– are you willing to give it a go? I tried to work out how I would write such a thing, but it ended up being just like the 'Alice Through the Looking Glass' bit about Milliways:

In Pellucidar the Earth is hollow and gravity allows people to walk on the inner surface, rather than falling into the centre where the inner core is. This is of course impossible.

In Pellucidar there is no day or night and therefore no time, so people do not age. This is of course impossible.

While what seems to be months passes for one person it may appear merely half an hour for someone else. This is of course impossible.

The moon is a mere mile above, hovering and hanging in exactly the same place while having no gravitational impact on the land directly below. This is of course impossible.

Stegosauruses can use the plates on their backs as wings, allowing them to glide and even fly. This is of course impossible.

The Gorbuses are cannibals who are the resurrected souls of murderers from the outer world. This is of course impossible.

I wouldn't have thought anyone could read the 'Pellucidar' novels without suspending disbelief.

I had briefly wondered whether it was possible for Pellucidar's inner crust to rotate at a faster rate to Earth's outer crust and thus allowing the area of Pellucidar mentioned in the novels to be subject to centrifugal force creating an artificial gravity. This could potentially explain why the prospector's first journey through the crust went from America and, when it turned around it ended up in the Sahara Desert. Yet this doesn't work as the prospector's final journey successfully trailed telegraph wires behind and it doesn't explain the moon.

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I'll see what I can do.

I wrote a little at lunchtime today. I attach here what I've done so far. Is it in the right style? It's not ready for you to use yet, though, because I realise (1) you'd already explained about the surface area of Pellucidar, giving figures, and (2) I don't know enough about the moon to come up any sort of plausible explanation.

Do you know how big the moon was supposed to be? I see that the moon was "a mile above the surface", but is this to the surface of the moon or to the centre?

How deep was the atmosphere in Pellucidar? Did the moon orbit within the atmosphere or "above" it? Our own atmosphere is a lot more than a mile deep.

My first draft:

Burroughs's work was considered 'science fiction' in its day. One of the features of science fiction distinguishing it from fantasy is that anything unusual is explained using science rather than magic. In his Barsoom (Mars) books, for example, Burroughs imagined the scant atmosphere of the planet being boosted in an atmosphere factory - by adding electricity to a type of electromagnetic radiation unknown on Earth, air was produced. Of course, the author's grasp of science is often rather tenuous - such an air factory would make
as much sense if it was powered by magic.

It can be interesting and amusing to consider the 'scientific' facts and explanations which Burroughs presents in order to provide the background for what is at the end of the day a good adventure story.

Land Area

First, some geometry. Burroughs says that the surface area of Pellucidar (the inner surface of the hollow planet) is smaller than that of Earth (the outer surface of the same planet), but because less of the surface is occupied by seas, there is in fact more land on Pellucidar than on Earth. Is he correct in this?

Since Burroughs worked in miles, let's continue to use these units. We'll treat the Earth as a perfect hollow sphere with a thickness of 500 miles. The radius of the Earth is almost exactly 4,000 miles, giving it a surface are of 201 million square miles, but only about 30% of this is land, working out at about 60 million square miles. The radius of Pellucidar is 3,500 miles, giving it a surface area of 154 million square miles. Burroughs imagined that this was made of 30% sea, 70% land, the opposite to Earth, so this works out at 108 million square miles of land.

So yes, Burroughs is right. The land area of Pellucidar is much greater than that of Earth. In addition because of the equal heating of all parts by the internal sun, all parts of it are equally habitable, unlike Earth where huge areas are either hot deserts or snowy wastes.

Gravity

Now for some Phyics. Newton's Law of Universal Gravitation says that everything attracts everything else. Big things exert a bigger pull than small things, but the force is reduced if the thing is far away - if it is twice as far, the force is reduced to one quarter; if it is three times as far, the force is reduced to one ninth.

Every part of the Earth exerts a tiny pull on your body. The bits just under your feet pull on you the strongest, while the bits that are at the other side of the world pull the least. If you are standing in London, then New York's Empire State Building is pulling you towards the southwest, while the Eiffel Tower in Paris is pulling you southeast. The combined effect of all these tiny pulls adds up to a single force pulling you straight down towards the centre of the Earth. This pull is variously known as 'the force of gravity' or just 'your weight'.

If you're standing on the inside of a hollow sphere, with your feet on the surface, the centre of the Earth is directly above your head. Some parts of the sphere are pulling you down (towards your feet) while other are pulling up (towards your head). It's not immediately obvious what the combination of all the different pulls will result in. Burroughs argued that the bits of the Earth just below your feet are very close to you pulling you away from the centre of the earth, while the bits of the earth above your head are very far away so their gravitational pull will be small. The resultant force on you will be a pull towards the "ground" beneath your feet and away from the centre of the earth. This means that people can walk around on the surface of Pellucidar as if it were the outer surface of a planet.

Unfortunately it is not that simple. Isaac Newton, who came up with the idea of Gravitation in the first place, also developed the mathematics to study it. If you are inside a hollow sphere and add up all the different pulls, they cancel each other out exactly. You won't feel any force of gravity at any point inside the hollow sphere. With nothing to hold you to the surface, you would drift off into the vast volume of empty space inside the sphere. A practical way to avoid this would be to wear velcro-soled shoes, but the downside is that you would have to cover the entire inner surface of Pellucidar with some sort of looped carpet.

Worse still, the mini-sun sitting at the centre of the earth would not feel any gravitational pull from the hollow shell around it, so there would be nothing to keep the sun in the centre. Gradually over time it would drift away from the centre and eventually would strike the shell, no doubt knocking a hole in it.

Pellucidar's moon, orbiting its mini-sun once a day so that it matches the rotation of Earth/Pellucidar, is hard to explain. Why is it attracted towards the centre of the planet, when everything else is attracted towards the surface? Perhaps Burroughs felt that it is high enough above the surface to avoid the local pull of the ground and so is attracted to the central sun...

Time

The most amazing claim in the books is probably that time does not pass at a normal rate, due to there being no changing pattern of day and night or from one season to the next. Since objects fall when dropped even on Pellucidar, we can assume that time does indeed pass, and that it is the human perception of time that is at fault.

This is mainly a psychological rather than a physical effect, then. Visitors to Earth's Arctic and Antarctic regions, where the sun never sets in the summer, will vouch for the disorientating effect of the lack of day and night. Perhaps in the absence of any noticeable signs of time passing, the people of Pellucidar have lost their connection with time.

This of course does not explain the lack of ageing of the people. We know that different animal species age at the different rates. Domestic cats appear to age until they are about ten, then can continue for up to two decades with no apparent ageing. Certain species of fish do not appear to age at all and just continue living, growing slowly, until their bodies are too big for them to catch sufficient food. And there is no doubt that mental states can affect the body subtly. So perhaps the people of Pellucidar have developed this agelessness through not believing in time.

I've had a look through the books and picked out all the mention of The Dead World. Sadly there isn't any real definition of size, however as there mentions of forests and oceans, this implies a fairly large area, although the moon is only visible from a comparatively small part of Pellucidar. Also as there are mentions of forests and grass plains it would appear that the moon has either its own an atmosphere or shares the same one as Pellucidar.

The Dead World is briefly mentioned in 'At The Earth's Core' and in more detail in 'Pellucidar'.
There is a widespread belief that birds can fly there. This could be based on observation, however, as it is believed that they carry the bodies and therefore souls of the dead with them, this could be an unsubstantiated religious belief.
The Dead World is only visible in the area surrounding the Land of Awful Shadow.
Beneath the Dead World is the Land of Awful Shadow:

The mention of 'mountains' is tricky. If a mountain is at least 2,000 feet above the surface of the moon and the surface is 1 mile from Pellucidar, then the smallest mountain summit on the Dead World is less than 2/3rds of a mile above Pellucidar. So, build Burj Khalifa on top of Ben Nevis and you can get from Pellucidar to the moon.

Quotes:
'the land which lies beneath the Dead World, which hangs forever between the sun and Pellucidar above the Land of Awful Shadow'
'It is a moon that revolves around the earth's axis coincidentally with the earth and thus is always above the same spot within Pellucidar… Perry was very much excited when I told him about this Dead World, for he seemed to think that it explained the hitherto inexplicable phenomena of nutation and the precision of the equinoxes.'
'From where I stood the moon appeared to hang so low above the ground as to almost touch it; but later I was to learn that it floats a mile above the surface – which seems indeed quite close for a moon... Above me hung another world. I could its mountains and valleys, oceans, lakes and rivers, its broad, grassy plains and dense forests. But too great was the distance and too deep the shadow of its under side for me to distinguish any movement as of animal life.
'Instantly a great curiosity was awakened within me… Was it inhabited? If so, by what manner and form of creature? Were its people as relatively diminutive as their little world, or were they as disproportionately huge as the lesser attraction of gravity upon the surface of their globe would permit of their being?'
As I watched it, I saw that it was revolving upon an axis that lay parallel to the surface of Pellucidar, so that during each revolution its entire surface was once exposed to the world below and once bathed in the heat of the great sun above. The little world had that which Pellucidar could not have – a day and night, and – greatest of boons to one outerearthly born – time…
So plain were the landmarks upon the under surface of the satellite.

In 'Savage Pellucidar II: Men of the Bronze Age' Dian the Beautiful is trapped in a gas balloon that drifts halfway between the Land of Awful Shadow and the Dead World:
'When she awoke she was over The Land of Awful Shadow. She was in shadow herself, and now it was very cold. Above her was the Dead World, as the Pellucidarians call it, that tiny satellite of Pellucidar's sun that, revolving coincidentally with the rotation of the Earth, remained constantly in a fixed position above that part of the inner world known as The Land of Awful Shadow. Below her was Thuria, which lies partially within the shadow and, to her right, the Lidi Plains where the Thurians graze and train their gigantic saddle animals, the huge diplodocuses of the Upper Jurassic, which they call lidi.'

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Thanks for that.

It's interesting that Thuria was a land underneath the moon. In the Barsoom books, Thuria was the name of one of the moons (the one we call Phobos).

Other than the Barsoom books, have you read much by Burroughs?

In the Venus books the enemy are 'Thorists' who live in Thora and sail Thorian ships. Burroughs definitely liked similar names, with heroines having names beginning with D or J, and heroes having names like 'Tarzan', 'Carson' or 'Carter'.

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I've been reading 'Pirate Blood', one of Burrough's unpublished novels that was found after his death, and the more I think about it, there's definitely a pattern.

Both heroes and heroines often have names with prominent 'D' and 'J' – so male Ds include David Innes, the hero of 'Pirate Blood' is John, just like John Carter and other Js include Jason Gridley. The heroine is Daisy Juke, who is a DJ, while Dejah Thoris has a D, J and 'Thor' so is a complete Bingo score.

In 'Pirate Blood' a mad inventor called Perry builds an out-of-control gas balloon; he should not be confused with the Pellucidar character called Perry, who is an eccentric inventor who builds an out-of-control gas balloon.

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The only Burroughs books I've read are the Barsoom books. Jason Gridley was mentioned in them as the inventor of some sort of communication device.

There were two characters in one story called Pan Dar and Gan Had. Both disappeared from the story for many chapters. When they reappeared, Burroughs had got them confused. The character who had been Pan Dar was now called Gan Had and vice versa.

I've added that the Gridley Wave is used to communicate with to the entry now

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I can work out the size of the moon from the size of its shadow, but the original map of Pellucidar doesn't include a scale so I don't know how big the shadow is.

Since the moon is in a "geosynchronous orbit", it must be over the equator. The distance from the equator to the north pole should be 5,500 miles given that Pellucidar is 3,500 miles in radius, but the various maps on the internet don't seem to be consistent with this. I remember that Burroughs was never very specific when it came to distances, so I think it's probably not possible to get a definite answer.

The reason I wanted to know the size of the moon is because if I know the distance of the centre of the moon from the centre of the Earth, I can work out the mass of the central sun (assuming the normal laws of Physics, which we have already established don't apply in Pellucidar!). I thought it might be interesting to see what sort of size the sun was.

No, there doesn't seem to be anything in the texts to say how big the moon or central sun is, I'm afraid. I must admit I don't think Burroughs took the physics of his stories too seriously, for example 'Pirates of Venus' begins with Carson intending to fly his to , missing and landing on Venus instead*.

If the central core was a hydrogen-based , is there a way to work out how big it would be in order for the temperature at the inner circumference to be a certain temperature, such as 30 degrees Centigrade (we know Pellucidar has a warm atmosphere where people wear little clothing)? Also, if it is a predominantly hydrogen core, would it have a limited lifespan and potentially expand to become a mini-red giant and engulf the whole ?

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* This was because the gravity of the affecting his course.

Feel free to use, modify or ignore any or all of the following:


Pellucidar vs Science - Who'd Win?

Burroughs's work was considered 'science fiction' in its day. One of the features of science fiction distinguishing it from fantasy is that anything unusual is explained using science rather than magic. In his Barsoom (Mars) books, for example, Burroughs imagined the thin, natural atmosphere of the planet being augmented by an atmosphere factory - by adding electricity to a type of electromagnetic radiation unknown on Earth, air was produced. Of course, the author's grasp of science is often rather tenuous - such an explanation makes as little sense as invoking magic would.

It can be interesting and amusing to consider the 'scientific' facts and explanations which Burroughs presents as a background to an adventure story.

Gravity

First we'll talk about Gravity. Newton's Law of Universal Gravitation says that everything attracts everything else. Big things exert a bigger pull than small things, but the force is reduced if the thing is far away - if it is twice as far, the force is reduced to one quarter; if it is three times as far, the force is reduced to one ninth.

Every part of the Earth exerts a tiny pull on your body. The bits just under your feet pull on you the strongest, while the bits that are at the other side of the world pull the least. If you are standing in London, then New York's Empire State Building is pulling you towards the southwest, while the Eiffel Tower in Paris is pulling you southeast. The combined effect of all these tiny pulls adds up to a single force pulling you straight down towards the centre of the Earth. This pull is variously known as 'the force of gravity' or just 'your weight'.

If you're standing on the inside of a hollow sphere, with your feet on the surface, the centre of the Earth is directly above your head. Some parts of the sphere are pulling you down (towards your feet) while other are pulling up (towards your head). It's not immediately obvious what the combination of all the different pulls will result in.

Burroughs argued that the bits of the Earth just below your feet are very close to you and pull you away from the centre of the earth, while the bits of the earth above your head pulling you towards the centre of the earth are very far away so their gravitational pull will be small. The resultant force on you will be a pull towards the 'ground' beneath your feet and away from the centre of the earth. This means that people can walk around on the surface of Pellucidar as if it were the outer surface of a planet.

He acknowledged that the parts of the Earth above your head would have some effect, and said that the force of gravity was slightly less than on the surface, although the effect was not very noticeable - the scientist Perry spotted it but the young David Innes didn't until it was pointed out to him.

Unfortunately it is not that simple. Isaac Newton, who came up with the idea of Gravitation in the first place, also developed the mathematics to study it. If you are inside a hollow sphere and add up all the different pulls, they cancel each other out exactly. You won't feel any force of gravity at any point inside the hollow sphere. With nothing to hold you to the surface, you would drift off into the vast volume of empty space inside the sphere. A practical way to avoid this would be to wear velcro-soled shoes, but the downside is that you would have to cover the entire inner surface of Pellucidar with some sort of looped carpet.

Worse still, the mini-sun sitting at the centre of the earth would not feel any gravitational pull from the hollow shell around it, so there would be nothing to keep the sun in the centre. Gradually over time it would drift away from the centre and eventually would strike the shell, no doubt knocking a hole in it.

Pellucidar's moon, orbiting its mini-sun once a day so that it matches the rotation of Earth/Pellucidar, is hard to explain. Why is it attracted towards the centre of the planet, when everything else is attracted towards the surface? Perhaps Burroughs felt that it is high enough above the surface to avoid the local pull of the ground and so is attracted to the central sun.

Fusion

According to Innes, the central sun of Pellucidar looks about three times as big as our sun. Since it is only 3,500 miles from the people of Pellucidar, we can calculate that it must have been about 100 miles in diameter. The scientist Perry thought that it must be composed of gas; this presents a problem. A sphere of hydrogen only 100 miles in diameter would not be big enough to support fusion, the nuclear process that powers our sun. At the time Burroughs was writing, it was not known how the Sun works, so he can be forgiven for making this mistake.

But there is another possibility. The central sun may actually be a solid sphere of something dense such as iron, at a very high temperature. If this sphere was heated to 5,500&deg;C, it would glow just like the sun and would be indistinguishable from a small star to the human eye. Geology tells us that in fact parts of the centre of the Earth are even hotter than this, so this not an unreasonable explanation for Pellucidar's sun.

Heat

This brings us to another problem. Innes described the sun as looking much like our sun except that it was 'thrice the size', so we can assume that it is the same colour as our sun. Since the colour of a glowing object depends on its surface temperature, Pellucidar's sun must have a similar surface temperature to that of our sun. If Pellucidar's sun looked a similar size in the sky to ours, then the heat received from it would also be similar.

Unfortunately, we have Innes's statement that it is three times the size. We don't know whether he meant in area or in diameter. If the former, then three times as much heat would be received from it as we receive from our sun at the equator. Worse, if Innes meant three times the diameter, then a person standing on the surface of Pellucidar would feel nine times as much heat coming from the sun as is felt on the equator of Earth. It seems unlikely that life would survive in a world receiving even three times, never mind nine times, as much heat at every point on its surface as the Earth does at its equator.

On the other hand, it is notoriously difficult to judge the size of the Sun in the Earth's sky. An optical illusion makes it look bigger at the horizon than when high in the sky. Who knows what even a tiny sun would look like when directly overhead in a world that has no horizon? Perhaps Innes made a mistake and the apparent size of Pellucidar's sun (and therefore its heating effect) is in fact the same as our own.

Time

The most amazing claim in the books is probably that time does not pass at a normal rate, due to there being no changing pattern of day and night or from one season to the next. Since objects fall when dropped even on Pellucidar, we can assume that time does indeed pass, and that it is the human perception of time that is at fault.

This is mainly a psychological rather than a physical effect, then. Visitors to Earth's Arctic and Antarctic regions, where the sun never sets in the summer, will vouch for the disorientating effect of the lack of day and night. Perhaps in the absence of any noticeable signs of time passing, the people of Pellucidar have lost their connection with time.

This of course does not explain the lack of ageing of the people. We know that different animal species age at the different rates. Domestic cats appear to age until they are about ten, then can continue for up to two decades with no apparent ageing. Certain species of fish do not appear to age at all and just continue living, growing slowly, until their bodies are too big for them to catch sufficient food. And there is no doubt that mental states can affect the body subtly. So perhaps the people of Pellucidar have developed this agelessness through not believing in time.

Thanks for this - I've added it to the text and credited you too. The only thing I changed was tweaking the title of that section slightly.

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I've just finished reading "At the Earth's Core". I was enjoying it until it suddenly stopped. Burroughs very much developed his writing style in later books.

I'm puzzled that at the start of the book Innes said that Perry was dead, but at the end of the book he was alive and talking on the "Gridley Wave".

Do you want me to proofread this entry now, or would you prefer to wait until you put it into Peer Review?

Well, it has your name on it so I'd say proofread away now if you're happy to do so.

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Although it is Friday and I've had one co-written entry leave Peer Review, which left a gap for this to fill.

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