2 posts • joined Saturday 27th March 2010 00:34 GMT
Ah, Special Relativity...
"The big snag with worlds orbiting other suns is of course that they are utterly, ridiculously far away and according to the laws of physics nothing can travel faster than the speed of light: meaning that journeys even to a few of the nearest stars would take years at the absolute minimum, and in general interstellar voyages would simply not be on human timescales."
Erm, I don't think that's quite right. Timescales are only a problem for those left behind. Although under Special Relativity it is not possible to exceed the speed of light, those approaching it experience time dilation under the Lorenz Transformation relative to those stationary. So at relativisitic sublight speeds, journeys to other stars don't take millennia *for those on the journey*, although a "mission control" back on Earth would experience those timescales.
Sure, there are still issues with the time it takes to accelerate to relativistic sublight speeds at a rate that doesn't squash crew to a pulp (and turn around for deceleration so as not to go shooting past your destination). But even with very modest accelerations, the relativisitic savings can be huge: for example, a journey from the Sun to the galactic core using just 1G could take just ~340 years for those aboard, compared with ~30 000 years passing back on Earth. And at 10G, it would be ~110 years.
So if you want to get to the stars, it's perhaps not quite as difficult at the text of this article suggests If you want to do so while keeping a culture intact across the stars - well ok, that's much more tricky unless you can get round Special Relativity.
The notion that "it takes X years for light to travel X light years" is erroneous; in a frame of reference at the speed of light, time dilation is infinite, i.e. there is no time in a photon's frame of reference (and there's no distance either, thanks to infinite length contraction, i.e. photons don't actually "travel" anywhere in their own frame of reference). Didn't you watch Carl Sagan's Cosmos as a kid, Lewis?
From one of the "seagoing boffins"
Hi there - here are a few answers from one of those "seagoing boffins" on the ship (great article btw, Lewis - thumbs up from all aboard!).
The animals down there, and many of the microbes, do need oxygen (which has ultimately come from photosynthesis). But their energy source at vents is chemical energy, rather than sunlight. So in terms of *energy*, it's fair to say that they're independent of the sunlit world above (but not in terms of their whole ecology - e.g. see http://deepseanews.com/2009/05/sex-at-vents-lights-on-or-off/).
Sulphide and methane provide the chemical energy sources that microbes at deep-sea vents use to turn inorganic carbon into sugars (just like photosynthesis, but powered by chemical energy rather than sunlight). Basically the sulphide or methane provides a source of free electrons that drives a chain of reactions, but oxygen is usually used to mop up those electrons at the end.
There are *some* microbes down there that are anaerobic, and can pull off that trick without oxygen (some actually use the element tellurium as the "terminal electron acceptor" - the only biological use of tellurium known so far, I think). Those anaerobic microbes are often the ones that are also spectacularly thermotolerant (current record is >120 deg C). But the animals, and perhaps *most* of the microbes, need oxygen.
Although the hot cocktail gushing out of the vents is anoxic, there's plenty of oxygen down there in the surrounding deep-sea water, thanks to the global ocean circulation (deep water forms at the poles, and carries oxygen down from the surface into the depths as it sinks and flows out across the depths; it gets gradually used up, but in most areas the deep water is still oxic).
As for the vents getting hotter with depth, it's not actually because they're closer to the mantle - it is the greater pressure of water above them. If we're lucky, we might see vents in the Cayman Trough topping 500 deg C - which may result in different chemistry compared with vents known so far, and perhaps different life as well...
Anyway, we'll be chatting about this kind of stuff in the daily log on our expedition webpages (www.thesearethevoyages.net) as the trip progresses, for any who are interested.
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