AS if forecasting whether asteroids will hit the Earth wasn't hard enough, it now seems that primordial black holes could surprise us by nudging a rock or two our way.
Some physicists think these little black holes, invisible remnants of the early universe, could be a candidate for the dark matter making up much of the universe's mass. Alexander Shatskiy of the Lebedev Institute in Moscow, Russia, points out that if all dark matter, is black holes they would likely pass through the asteroid belts in our galactic backyard. Since a metre-sized primordial black hole can have the mass of the Earth, it would need only to pass near an asteroid to knock it out of a safe orbit and towards our planet, he says (www.arxiv.org/abs/0802.3119).
"If anything comes through and disrupts those clouds, we could be in trouble," says Daniel Holz, an astrophysicist at Los Alamos National Laboratory. However, Holz points out that Shatskiy's estimates represent a worst-case scenario.
In any case, the threat is unlikely to be immediate: Shatskiy's calculations suggest that an impact on Earth caused by black holes passing near an asteroid would only happen every 100 million years or so.
Comets and Asteroids - Learn more about the threat to human civilisation in our special report.
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Mon Mar 10 18:03:55 GMT 2008 by Cynthia
I'd worry more about a meter-sized primordial black hole passing through my cublicle.
Possible Hypothesis For The 'where Are They' Question?
Mon Mar 10 21:36:58 GMT 2008 by Rob Chansky
It's bugged a lot of people that, if life originated once, it ought to have originated many times in the universe. And that might give rise (by the same reasoning) to intelligent life, that would then go out into the stars and found colonies, or at least go out touristing.
So we should expect to have been visited often, even given the vast amount of energy it would take to travel to even the nearest star.
The idea that there are many small black holes lurking everywhere, more or less undetectable until you're right on top of them, makes interstellar travel a far more risky proposition. Which may explain the Great SIlence. I wonder if this has been talked of much.
Possible Hypothesis For The 'where Are They' Question?
Mon Mar 10 23:13:11 GMT 2008 by Charles
But the Great Silence also applies to things like radio communication, don't forget, which is in theory far easier to achieve than physical transport.
Unfortunately, current events on Earth indicate that the reason for the Great Silence might be the more mundane fact that technological civilisation is unable to sustain itself for long enough for interstellar travel to become practical, or radio broadcasts to last more than a few centuries. Throw in the relative unlikelihood of planets being "just right" to develop life, the unlikelihood of microbes making the jump to multicellular life, the unlikelihood of animals developing freakishly large brains (relative to body mass), the unlikelihood that they will feel the urge to develop agriculture and so on unless there is some good environmental reason (drought, ice age...), the unlikelihood of readily available resources (metals, fossil fuels) and the unlikelihood of the scientific method being discovered (a LOT of empires rose and fell on Earth before anyone realised that mastery over nature was a few clever ideas away) - and no doubt a few other factors I can't think of off the top of my head - then you start to realise that perhaps civilisations like ours are relatively rare - maybe only one appears every 1000 or 10000 years in a given galaxy. If they then collapse after a few centuries, what are the chances we'll hear a peep out of them any time soon?!
Sadly.
Possible Hypothesis For The 'where Are They' Question?
Tue Mar 11 04:49:41 GMT 2008 by Polemos
All spatially separated things exist on the substrate of the continuum, which is nonlocal (=continuous) by definition.
Therefore, things are formally local yet essentially nonlocal.
http://Www.en.wikipedia.org/wiki/Nonlocality
Thus, essentially, the universe has always been a single organism. The universe you describe is a living cell in which informational centres flash up in different parts of the cytoplasm.
In reality, a living cell has just one informational centre, and it is always located in the nucleus. The Earth is the only place in the Universe where Life has ever existed or will ever exist (if you kill the nucleus, the whole cell dies).
Possible Hypothesis For The 'where Are They' Question?
Tue Mar 11 11:30:27 GMT 2008 by God
What an ABSOLUTELY, COMPLETELY, UTTERLY, INCREDIBLY STUPID, ILLOGICAL & UNSUPPORTABLE LOAD OF RUBBISH...
Possible Hypothesis For The 'where Are They' Question?
Tue Mar 11 13:09:25 GMT 2008 by Polemos
Thank you for this honest description of yourself.
Possible Hypothesis For The 'where Are They' Question?
Tue Mar 11 18:12:58 GMT 2008 by Ambros
Well, actually there is no great silence. We don't have radio transmissions, but we have other signs : the galaxy is teaming with life. As an example many stone age clay sculptures describe visiting aliens, with their gear. See reference books A and B. A = Lost Civilizations , Sumer : Cities of Eden , Time Life Books 1993. B = M.Gimbutas : The living Goddesses, Univ. Of California Press 2001. A pages 68 and 158. B pages 10, 86,and 91. It is possible that gold is valuable also elesewhere, if it is created only when two neutron stars collide.The visitors seem to have been active from about 6000 BC until 4000 BC according to the found clay figures.
Metre-sized Black Holes?
Mon Mar 10 23:04:49 GMT 2008 by Charles
"Since a metre-sized primordial black hole can have the mass of the Earth..."
Actually, IIRC the Earth would make a black hole about 1cm across (see http://en.wikipedia.org/wiki/Black_hole#Sizes_of_black_holes).
A hole with a 1-metre "radius" (ignoring the infinite stretching of space-time involved) would have a mass of something like 1.3 x 10^27 kg, or a similar mass to Jupiter. This would make its influence fairly noticeable even without it going near any asteroids!
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