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Thursday, 28 September 2017


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Spacetime Ripples in the Sky with Big Al:

David, a black hole has mass because it is not a proper hole. It's only named that because its gravity is so strong that nothing can escape from it past its "event horizon"; not even light.

So That's what that was! I need to complain to the universe that its untimely 'wave" interrupted my perfect execution of the Sun Warrior 2 yoga pose!

Thank you, Henry, that is a beautiful diagram and you are now confirmed as the Emeritus Professor of Swottery here at D&N. However, now that you are on the permanent staff, so to speak, please try not to upset the Chief Archivist who has a tendency to go ultra-Arkie!

Whiters, I would pay good money for a picture of you in that pose, er, dressed appropriately, of course!

David, in addition, I am the only man in the class! My what an ego boost! Some of the ladies have gotten quite comfy with my presence there.

Thanks TBH. Not sure I understand it but interesting reading.

G'mar Hatima Tova TBH

Thank you, AD. May you also be inscribed in the Book of Life for Good.


"..., although how a hole can have mass is yet another of life's mysteries to me."
Perhaps I can make it a little less mysterious for you, although no one really knows what is going on within a black hole's event horizon.

When a black hole is likened to a mass-equivalent of some multiple of the mass of our sun, it is being described in terms of the Newtonian theory of gravity. Newton's theory of gravity (which is perfectly adequate for predicting non-relativistic observables, such as the orbits of the planets around our sun) attributes to gravity an attractive force that is directly proportional to the mass of the attracting object (like our sun).

But once you consider the cosmological regime that includes black holes, you must use Einstein's Theory of General Relativity (GR). Einstein's GR explains the so-called "gravitational attraction" of a black hole, not in terms of an attractive force of a massive object, but in terms of the extreme geometric curvature of spacetime in the vicinity of the black hole.

It is a black hole's effect on the curvature of spacetime that appears as if the black hole has an effective mass. But no one (not even Einstein) has (or had) any idea what a black hole really comprises.

Henry, it's 8.10am and now I have a headache and may have to return to bed! The problem, it seems to me, between scientists and laymen are those damned "Words, words, words". I just about understand space/time which I assume is the same bit of space observed at different times but how can space/time be "curved"? And why, let lone how, does one lump of matter attract another? And whilst I am genuinely admiring of your diagram of the universe, does it really have edges? Or are we just assuming that it does, in which case, what's outside the edges? Oh God, my head is thumping, I'm off to bed!

Whiters, I am beginning to imagine you as a sort of Hugh Hefner in the 'Bunny Mansion' surrounded by lovely ladies. You rascal, you!

David, just keep in mind that gravity waves make the universe jiggle. That should bring a comforting picture to mind.


For your headache, take two aspirins and call me in the morning (yes, I am a doctor).

As for a "black hole", it's a metaphor! The "hole" implies that this cosmological phenomenon behaves as if it were an infinite sinkhole in spacetime; the "black" implies that even light (which has no mass) cannot escape the clutches of such a cosmological sinkhole.

As for "spacetime", it is The Fabric of the Cosmos, which is also a metaphor.

Dammit, Henry, why can't you swots leave poetry to the poets?!

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