Mark asked me to watch the video since I never believe any of the hypotheses he presents over here and he thought this was a pretty solid one. As usual, I think it's pretty kooky.

First of all, there's a misplaced apostrophe in the video. I know I sound like the grammar police, but if you're mounting a $2 million dollar expedition to do real science, wouldn't you have someone check your work and make sure you got your punctuation in the right place?

Nitpick number two is his reference to negative body weight in the center of the earth. Maybe my imagination just isn't good enough, but I can't quite figure out what negative body weight would mean. In zero gravity, you'd have zero body weight. With negative body weight, would you float uncontrollably upwards? Wouldn't that just be gravity giving you body weight toward a different center?

His argument that it's fishy that images aren't publicly available from polar satellites doesn't hold much weight with me. Polar satellites clearly have much less applicability to the daily lives of the majority of the earth's population since so few people live in the extreme north or south poles. We get publicly accessible data from the east to west satellites because we pay for it in one way or another, and we want things like getting to see satellite imagery of our backyards. Market forces are unlikely to make it worth a private company's while to make images available of the north pole --- I suspect that while many of us might think it would be cool to see, very few of us are willing to pay for it. Occam's razor says that the lack of available images from the polar satellites is just lack of incentive to show them, rather than a conspiracy to reveal them.

I don't know enough about stars to say this with certainty, but I'm not so sure a star could be small enough to fit inside the earth and still be a star. A quick perusal of Wikipedia suggests that the smallest stars are red dwarfs. They note: "Red dwarfs are small stars that are around 0.2 solar mass (the sun is equal to 1 solar mass), this is small for a star but is still 60,000 times the mass of the earth." White dwarfs are much smaller and would fit in the earth, but are dying stars --- is this what he's suggesting?

But the biggest problem to me is that the video was presenting a hypothesis disguised as fact. Real scientists don't say "There is a large hollow space under the crust of the earth" unless they have a lot of data (none of which is presented in the video.) Instead, they might say, "Scientists believe there might be a large hollow space under the crust of the earth." To me, this is the difference between a scientist studying the earth and seeking truth, and someone who likes making up science fiction stories and getting up on his soapbox.

This is a silly idea, for a number of reasons which are each on their own sufficient to sink it.

• A star large enough to support fusion by gravitational confinement is much larger and heavier than Earth.
• Even if such a tiny star were to form inside Earth, its position would be meta-stable. Gravity is a force that only attracts. So when the mini-sun strays only a little bit from the centre of the sphere, it would eventually crash into the sphere. (You could compare it with a ball lying on the point of a cone; one nudge and it goes down.) It would require huge equal electrical charges on both the central sun and the spere or hypothetical exotic matter to make this situation stable.
• Being that close to a star would be quite unhealthy; massive amounts of radiation, intense magnetic fields, particles ejected at high speed, you get the idea.
• And for the inside of the sphere to be habitable, it would have to be massive to cancel out the gravitational pull of the central sun.
• The sphere's material would also have to be insanely strong, especially since part of it is liquid (we can see magma coming out of vulcanoes)

Actually the idea of buillding a swarm of objects in a spherical shape around a star to capture most of its energy had been proposed by Freeman Dyson, and is known as a Dyson sphere. Building an actual solid shere at this size is impossible; there is no material strong enough. And unlike a swarm of dicrete object in orbit it would be meta-stable.

The concept of creating an artificial ring around a star, creating a huge livable surface on the inside is explored in the Larry Niven's Ringworld novels. (Go read them, they're fun!) It is made of a hypothetical material with a tensile strength on the same order of the strong nuclear force! (Us real-world engineers would love to have a meterial like that to play with.) As with a solid Dyson sphere, the ringworld is also unstable. How this is dealt with is also explored in the novels.

(I've got nothing of substance to add, except to say that I enjoyed the Ringworld books. Although all I can remember is the cover of the first one, which seems to have stuck with me much longer than the story or world. What can I say --- it had a lot of trees on it... )

Anna, if you liked Ringworld because of the trees, you should read Niven's novels "the integral trees" and its sequel "the smoke ring". Now there are some really big trees for you!

The reason that there are so few satelites in polar orbit is that it is very expensive in fuel to get there. Most rockets are launched from a place near the equator where they get a signifcant leg up from the earth's 1040 mi/h rotational speed. The angle between a satellites orbit and the equator is called the inclination. If you want an orbit with a high inclination, you first have to cancel out the rotational velocity from the lauch site, and then give the satellite enough speed in a direction over the pole to enter orbit. For this you need much more fuel than for a low inclination orbit.

But there are still plenty satellites in polar orbits, like weather satellites, and those from the Iridium communication network. And spy sattelites. You can view pictures from eumetsat polar orbit satellite online. (Choose "near-real-time", and you can pick a time when the satellite is over the north or south pole. No holes AFAICT).

Thanks for the satellite details Roland.

Perhaps all this talk is just myth and legend?

The thing I like about the story is the upcoming expedition. Then Dr Agnew will have a chance to put some real world experience behind these far out speculations.

http://www.cosmiccookout.com/20100623Dyson.jpg

One of the top 10 Star Trek episodes of all time in my opinion.