Imagine it is possible for a human to dig vertically down from the surface of the earth? Straight down for the core, ignoring the heat and larva etc. What would happen as the digger neared the core and how would they transition from go down to suddenly going up as they headed for Australia? WHat would happen to the dirt? Would they be standing over a huge hole as they headed past the core?

It seems to be generally assumed that there is an extremely high pressure at the centre of a planet such as the Earth.  I don’t think this can be correct, surely there should be no pressure at all, a void.  Could someone please explain why my reasoning is wrong?Pressure is due to the weight of (for example) air or water pressing down, due to it’s mass and gravitational attraction.  Ascending, the weight of material above decreases, so decreasing the pressure.  Pressure rises (at first) when descending from the surface as the weight of the column of material above increases.But at the planetary core (or more correctly, the true centre of gravity) there can be no net gravitational force because the attractive forces of every particle in the planet (and indeed beyond the planet) cancel.  It is a zero-gravity place.  As one moves from the core, out of any void and towards the surface, the amount of material directly above becomes less and that below (through the core to the diametrically opposite surface) increases, so that a net gravitational pull towards the core develops, reaching a maximum at the surface.  There will be an intermediate point between the core and the surface where the weight of material above is at a maximum (due to net gravitational pull and depth of material above) and here the pressure will be at a maximum, decreasing both upwards and downwards.  At the exact centre, without any attractive force, there can be no pressure if the planet can be considered as an unrestrained system (and with fluid magma and tectonic movement this is surely the case, the planet is flexible).  It is very hot  in the centre, so particles in the vicinity will be thermally mobile and drawn to areas of gravitational pull, away from the very centre.  This effect will keep the core empty; to what extent I wouldn’t wish to speculate, but I should guess not a major part of the entire globe.  This low pressure and low density volume at the centre may be noticeable, and I wonder if this could explain some of the anomalous observations about planetary and solar cores.

If correct, this effect should be seen in many large agglomerations of fluid particles such as stars, or even a Galaxy.  (But NOT the entire Universe – it is expanding).  Perhaps there is more matter located towards the galactic periphery than in the centre, and this might help explain the anomalous galactic rotational speeds which have led to the postulation of dark matter.  Is the concept of dark matter actually needed if the galaxies have a different mass distribution to that usually assumed with gravitational pull a maximum somewhat away from the centre?However, I do wonder how the black holes that seem to inhabit the centre of many galaxies can remain ‘locked’ into position in the centre of an otherwise gravitationally neutral place.I feel that this whole concept is all too simple and somewhere I must have made a mistake, so I would really appreciate someone explaining why I am wrong.

When the classic simple demonstration is done with a bell jar inverted over a bath of water, with a floating lighted candle inside, as the Oxygen is used up, the water rises up the bell jar about one fifth or 20 - 21% of the way up, until the candle goes out, showing that there is approx 21% Oxygen in normal air.

However, 21% volume of Oxygen surely cannot equate to 0% volume of Carbon dioxide, so where did the carbon-dioxide go? Surely, it must have some volume?

When Pi is calculated to a large number of places, what is actually being computed? Is it a measurement of a real relationship in the real world, or something more abstract and mathematical?

History has shown that the Earth's magnetic poles have switched over past history.  How would a modern switch affect such technology as electrical generation, electric motors, and all things magnetic including Compasses and GPS.

If you define an arbitrary plane in free space, then the mass, momentum, and energy of virtual particles crossing the surface will balance (statistically over a given time period). If this plane is parallel to and very close to an event horizon, then an imbalance occurs as some of the virtual particles are lost to the event horizon, making re-combination impossible and thus creating a surplus. The net surplus at the other side of the surface in terms of the mass, momentum and energy of the orphaned particles is then balanced by the mass, momentum and energy of the particles that strayed far enough from the original plane to cross the nearby event horizon. This implies that if an event horizon occurs, it will leak energy (mass and momentum from orphaned virtual particles) into the "real particle" universe.

My problem is that this model leaks from the "vacuum energy", and creates Hawking Radiation in equal, statistically interchangeable, forms on both sides of the gap between the arbitrary plane, and the event horizon. Everything you loose on one side, you have therefore gained, as an orphan, on the other. You get opposite charge, but still the same individual mass and overall momentum. So the total vacuum energy erodes (very slowly) but the black hole expands (also very slowly).

Even if you invoke negative energy particles, they are either repelled by the gravitational field (making things much worse) or at best they cancel the in-falling Hawking Radiation, and produce some very strange external emissions, but no net loss of mass from the black hole. I can’t create a bias, as it implies a bias in free space. Besides, I can’t tell in advance which virtual pairs will become separated, or which individuals orphaned, so there is no biasing mechanism available.

If this was the case then black holes would remain stable. Can someone please explain what is missing from this model? How does it differ from the accepted model of Hawking Radiation and the decay of Black Holes?

If gravity travels at the same speed as light ,it probably consists of 'gravitons '.However photons of light push an object away from the source of light .How do gravitons attract a body to the source of the gravity ? If gravity is merely a deformation of the fabric of space how can one say with any certainty that gravity travels at the speed of light ?