Recent comments in /f/askscience

CubanHermes OP t1_j693pjj wrote

Reply to comment by mfb- in Is there an upper limit to structure size in a vacuum? Could a sufficiently advanced civilisation build a galaxy sized structure in space or would it become too massive and collapse in on itself? by CubanHermes

Ok, so I just need FTL travel, many galaxies worth of materials, some way to heat the place and billions of workers and we can make a hellish galaxy sized Ikea flat pack colony. Excellent.

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PD_31 t1_j693bqu wrote

Reply to Shouldn't goldilocks zones shift over time? by LaRoara42

The Goldilocks zone will depend on the star's temperature and therefore how much its energy output is, so yes over time it will shift. To take an extreme example, our Sun's late life stage will see it expand and swallow up the earth; clearly we will no longer be in the zone when that happens.

So yes, the zone will shift but the lifespan of a star is so long that it won't change on a human (or even humanity's) timescale for most stars.

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pacaruru t1_j692rkv wrote

Reply to comment by MxPunkin in In the absence of cosmic radiation, would an object placed in space eventually cool to absolute zero? by IHatrMakingUsernames

If we're talking absurdly long timescales it would eventually go to absolute zero as it's mass decayed into energy and it released that energy into a form that was no longer accessible or useful but by then it would be a bit of a stretch to say the object still exists any longer.

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Sir-HP23 t1_j6929sp wrote

Reply to Has a new animal species evolved since mankind’s existence? by coding_ac

I seem to remember watching a programme where some light winged moth have a new strain of dark winged moths after the industrial revolution when soot was making the tree bark black. The two strains had got to the point where they had trouble interbreeding so, new sources.So that’s in the last couple of hundred years and in direct response to us.

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BlazeObsidian t1_j690uxs wrote

Reply to Are there any species of plant that require seasonal temperature drops as part of their life-cycle? by I3P

A lot of trees require their seeds to undergo stratification before they can germinate.

For example the Japanese maple seeds undergo cold stratification where the seeds fall to the ground and lay dormant there under the snow. Only after this process is done will they germinate.

Note that this is not a hard and fast rule. But seeds that don’t undergo stratification take longer and have much lower chances of germination

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RShArren t1_j6903sq wrote

Reply to comment by ManyThingsLittleTime in Is there an upper limit to structure size in a vacuum? Could a sufficiently advanced civilisation build a galaxy sized structure in space or would it become too massive and collapse in on itself? by CubanHermes

Well, that depends on what kind of structure do you need and how you build it...

Let's say it's a ring made of nanites (which sort of solves all material tension problems, because we assume that nanites can automatically rebuild any damages). Let's assume that the radius of the ring is 50000 light years (an approximation for the Milky Way radius, which equals 5*10^19 m), its width is 1 km (10^3 m) and its thickness is 100 nm (a size of a nanite, 10^-7 m). Let's assume that the nanites are made of carbon and have its density, which equals 3*10^3 kg/m^3.

The mass of this structure is going to be:

M = ro * V = ro * S * L = ro * h * w * 2* pi * R = 3*10^3 * 10^3 * 10^-7 * 2 * 3 * 5 * 10^19 = 9 * 10^19 kg.

Milky Way mass is 10^12 solar masses, and the mass of the Sun is 10^30 kg. In fact, the mass of the Moon is 10^22 kg. So one Moon is more than enough to build such a ring around the Galaxy...

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