Gravity and Life: What's Too Much for Existence?

[Lren Zvsm]

How much is too much gravity for life as we know it to exist on a body too small to become a star? At approximately what multiple of 1g would life as we know it be impossible because of the direct effects of gravity? What about secondary factors--e.g. how the higher gravity would affect the composition of the atmosphere and what effect that would have on life as we know it?

 

[jedishrfu]

There’s a science for that:

https://en.m.wikipedia.org/wiki/Gravitational_biology

 

[member 656954]

While it's not quite what you asked, SpinCalc might be useful to look at, as once you calculate the 'gravity' you get indicators for the “comfort zone” of the result. The notes below the calculator also provide references that expand on this and which may provide some of what you are asking.

 

[Dr Wu]

There would appear to be no clear-cut answer to this interesting question. Size is one obvious variable. Argentinosaurus is claimed to have been the largest land animal ever to have walked the Earth. With an estimated mass in excess of some fifty tonnes, it must have surely been the most massive. Possibly too, given its exceedingly well-balanced body plan, highly efficient birdlike lungs, and hollowed out bones, Argentinosaurus probably marks the limit to how big an animal can get while supporting itself against Earth’s gravitational pull (whales and other aquatic megafauna are another story, of course).

Meanwhile, weighing in at the other end of the scale, if barely at all, are the bacteria, and similar micro-organisms. In view of the advantages accrued from the surface area to volume ratio, it’s more than possible that these tiny critters could take quite a fierce pull without breaking out into a sweat. Are microbes able to live on the revolving drums of spin dryers, for instance? If so, we’re talking about a thousand plus gees. . .

And that’s just accounting for life down here on Earth. All the same, we are so magnificently ignorant about the existence of life elsewhere in the cosmos — and the conditions that could give rise to it — that a strong dose of humility is called for when trying to tackle the above question. Still, it’s worth bearing in mind that if life exists (say) in the atmospheres of gas giants like Jupiter, it could conceivably take the form of gigantic, hydrostatically adapted, whale-like organisms. The longish short story: ‘A Meeting with Medusa’ by Arthur C Clarke is a case in point.

 

[Rive]

What about secondary factors--e.g. how the higher gravity would affect the composition of the atmosphere and what effect that would have on life as we know it?

A book to read, if you can get it somewhere: Hal Clement 'Mission of Gravity'
Regarding those 'secondary effects' it can be considered a (quite) hard sci-fi.

 

[Dr Wu]

Another strong recommendation is 'Dragon's Egg' by Robert Forward. Consider sentient creatures the size of sesame seeds living out their 35 minute-long existences on a neutron star (surface pull: 67 billion gees). No plot spoilers here, though!

 

[essenmein]

Another strong recommendation is 'Dragon's Egg' by Robert Forward. Consider sentient creatures the size of sesame seeds living out their 35 minute-long existences on a neutron star (surface pull: 67 billion gees). No plot spoilers here, though!

Random side bar here... "Sentient beings the size of sesame seeds", now I assume atomic density will be very high on a neutron star, so high you might say, its mostly neutrons...

Anyway, back to the side bar, are there even enough atoms to form suitable complexity to be "sentient" anythings the size of sesame seeds, assuming normal matter densities?

 

[member 656954]

The longish short story: ‘A Meeting with Medusa’ by Arthur C Clarke is a case in point.

Not related to the post as such, but if you liked A Meeting with Medusa then the elaborated homage by Alastair Reynolds, The Medusa Chronicles, might take your fancy. I rated it 5-stars, and felt it nicely paid respect to the original plus was a great story in its own right. (Unlike Spider Robinson's appalling attempt at a Heinlein, or the silly series of shorts 'inspired' by 2001: A Space Odyssey in which each story was exactly 2001 words long! What exactly was the editor thinking?)

 

[Dr Wu]

I hadn't heard of The Medusa Chronicles, but having read - and enjoyed - one novel by Alastair Reynolds (Pushing Ice) I'll certainly be looking out for it now.

Concerning cheela densities: according to the novel, each adult cheela weighs around 70 kg. I may have slightly 'over-egged' the dimensions of the cheela by claiming them to be the size of sesame seeds. The novel's own appendix has it thus: 'The cheela are flat, amoeba-type creatures about 2.5 mm in radius (0.5 cm in diameter), and 0.5 mm high, with a density of 7 million g/cc.' Hope this helps.

 

[some bloke]

I think, as others have mentioned, the important aspect is where the life is. A whale couldn't live on land, but can live in water due to buoyancy. If the Earth's gravity started to increase, I suspect that sea creatures would continue to live far longer than land ones, as gravity doesn't matter a lot to them, the pressure of the ocean does, which is in turn caused by gravity.

So take a fish that lives in the abyss, and then work out just how much gravity you would need for the water at sea level to have the same pressure as that of the abyss, and this is the gravity the Earth could have for the fish to live at sea level without any further adaptation (except perhaps to its eyes). meanwhile, land based life would probably be pancaked.