Random Science Question Thread!

[Psion]

After yet another musing of hypothetical scenarios and one too many XYCD "What if?" posts, I thought it might be fun to start a thread where people can ask about the feasibility their own crazy situations, or merely questions they have on science topics. Hopefully with some answers by BG's more enlightened individuals.



So, to start off, here's a crazy hypothetical of my own:

What would a "world" made of just natural breathable air be like, and nothing else, if it had a radius the size of earth? No rocky core, and let's try and assume it somehow happened, odds notwithstanding.

Would you fall to the center of the "planet"? what would the air pressure be like, and would you be able to survive it, or would be it too high or low to sustain life? would it have weather, assuming there was some water vapor like air on earth?

Or would the whole thing just fall apart due to a lack of gravity holding it together? (i'm guessing a lack of magnetic field would cause the sun to blow it apart eventually, although i'm not sure how long that would take.)

[Jaybar]

It's probably like Jupiter in that it needs to be absolutely massive for gravity to hold it together, where the deeper you go the higher the pressure. Thus it becomes a sea of liquid oxygen/nitrogen as you fall through. Also you will die.

I'm not a physicist though.

[BerenTebogo]

After yet another musing of hypothetical scenarios and one too many XYCD "What if?" posts, I thought it might be fun to start a thread where people can ask about the feasibility their own crazy situations, or merely questions they have on science topics. Hopefully with some answers by BG's more enlightened individuals.



So, to start off, here's a crazy hypothetical of my own:

What would a "world" made of just natural breathable air be like, and nothing else, if it had a radius the size of earth? No rocky core, and let's try and assume it somehow happened, odds notwithstanding.

Would you fall to the center of the "planet"? what would the air pressure be like, and would you be able to survive it, or would be it too high or low to sustain life? would it have weather, assuming there was some water vapor like air on earth?

Or would the whole thing just fall apart due to a lack of gravity holding it together? (i'm guessing a lack of magnetic field would cause the sun to blow it apart eventually, although i'm not sure how long that would take.)

You mean just a gas planet consisting of nitrogen and oxygen (+~)? It would be a gas planet, which are actually more common. One made of N+O would be incredibly unlikely just because those elements aren't around in abundance in the interstellar medium. The clouds of gas that form planets are Hydrogen >>>>>>>>>>>>>>>>>>>>>>>> Helium >>>>>>>>>>>>> Lithium >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> everything else.

But no it wouldn't fall apart. There's no reason one couldn't exist. It would have a gravitational field just like jupiter does. It would definitely have weather. Life isn't something answerable with our n=1 of conditions necessary for life. You wouldn't fall to the center of the planet anymore than you'd fall to the center of Jupiter or any other gas planet. That is to say, you could have objects lighter than the gas at different strata of the planet able to suspend themselves the same way ice floats in water. There's also no reason for it not to have a magnetic field. Jupiter, again as an example, has a B-field that is something like n*10^5 stronger than ours iirc.

[jacobs67]

You would still fall towards the center due to gravity, you would enjoy falling for a while breathing until you're inevitably crushed by the air pressure (Venus is slightly smaller than earth with a much thicker atmosphere and it's not even composed entirely of gas but you would still be crushed by the air pressure before you even reach the surface, ignoring the blazing hot temperatures and acid) Eventually your crushed remains would settle down into the surface which the pressure has turned into liquid nitrogen/oxygen
Life could be sustained in the habitable pressure zones in the clouds, like the proposed floating cities of Venus (there's a comfy zone somewhere in the layers of clouds where the pressure and temperature is just right) but with nothing but air on this hypothetical planet it would be difficult for life to spawn obviously, but you could build some floating cities like on Venus

[BerenTebogo]

You would still fall towards the center due to gravity, you would enjoy falling for a while breathing until you're inevitably crushed by the air pressure (Venus is slightly smaller than earth with a much thicker atmosphere and it's not even composed entirely of gas but you would still be crushed by the air pressure before you even reach the surface, ignoring the blazing hot temperatures and acid) Eventually your crushed remains would settle down into the surface which the pressure has turned into liquid nitrogen/oxygen
Life could be sustained in the habitable pressure zones in the clouds, like the proposed floating cities of Venus (there's a comfy zone somewhere in the layers of clouds where the pressure and temperature is just right) but with nothing but air on this hypothetical planet it would be difficult for life to spawn obviously, but you could build some floating cities like on Venus

Humans would fall, but not everything would fall to the center (in a relevant timescale). There's plenty of life on Earth living 20,000+ feet above quite comfortably. Density matters, which I mentioned above.

I realized I didn't answer "how it would happen"

I genuinely can't think of a physically realistic situation where it could happen since supernovae have too much energy to leave things only at N+O, and if you don't have a SN or tidally disrupted NS you don't get element distribution throughout the interstellar medium.

Only thing I can think of that has ANY basis in reality whatsoever is a multi compact object system that ejects a member (say a WD/BH) at incredibly high velocities and the path of the ejected object intersects a 5~12 solar mass star near the end stages of it's life and tidally disrupts it, causing an ejection of primarily C/N/O into the IS that could later recombine.

tbh though I'm not actually sure the physics of that even work out on that. There's a reason they don't happen.

Edit: Planetary science / CO dynamics is not my field. Take above with grain of salt.

[BaneTheBrawler]

ok so how about a planet-sized ball of water? would apparent gravity get lighter as you swam closer to the center? presumably, if you could float in the absolute center, you would feel absolutely no pull in any direction. right?

also, would the same hold true for gas giants, only more-so? or is there often a rocky core under there somewhere? i know there's liquid gasses, are there maybe solid liquids and metals and shit down there, too?

[Psion]

I'm amaxed that air would be crushed to liquid even if the planet that was earth sized XD

[Salodin]

You can't get to the center of a planet with out bring crushed by everything above you. It's the same reason why what's holding back a diver from diving deeper isn't his lack of air but the pressure of the water above him.

If you could -magically- remove pressure from the equation, then sure, what you guys are imagining is possible. But you can't remove pressure from the equation, so you have to always figure if your back is strong enough to support all that gas/liquid above you. Not to mention, you guys are forgetting that temperature alone doesn't make something solid, liquid, or gas; it's (mainly) a combination of temperature at a given pressure. In the scenarios you guys present, pressure is just far too great to fall through.

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[BerenTebogo]

You can't get to the center of a planet with out bring crushed by everything above you. It's the same reason why what's holding back a diver from diving deeper isn't his lack of air but the pressure of the water above him.

If you could -magically- remove pressure from the equation, then sure, what you guys are imagining is possible. But you can't remove pressure from the equation, so you have to always figure if your back is strong enough to support all that gas/liquid above you. Not to mention, you guys are forgetting that temperature alone doesn't make something solid, liquid, or gas; it's (mainly) a combination of temperature at a given pressure. In the scenarios you guys present, pressure is just far too great to fall through.

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This pretty much covers both questions decently, but yes gas planets often have a rocky core as the norm (the norm being things we know which is not much).

The answer to all of the other questions is PV = nkT and the specific heats and volumes of the substances in question. The answer is completely different for water than it is for sodium than it is for mercury than it is for carbon than it is for helium than it is for anything else.

I'm amaxed that air would be crushed to liquid even if the planet that was earth sized XD

Depends on the substances. In the case of oxygen and nitrogen? Absolutely.

-----

Put it this way: The only way most of you have any understanding of sodium is as part of a compound that is salt, or at the very least, as a mineral. There are planets and moons of innumerable amount that have liquid sodium metal oceans. The answer to "well what about this?" is usually https://en.wikipedia.org/wiki/Heats_...28data_page%29

[BerenTebogo]

And I will add an addendum:

There are much prettier answers to some of the specific questions you are asking, that involve awesome crystalline structures of pickanelement and etc, but that's for Carl Sagan, a chemist, or a molecular physicist to make beautiful for you. This is the best you'll get out of me as I think transitioning between phases of matter is tedious. I can do ejected black holes annihilating stars tho.

[Salodin]

I like this thread.

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[Psion]

I'm glad. I figured we needed something more positive than more world news and more substantial than kitten pics. NOT THAT THAT'S A BAD THING, but how often areferred people asked to use their brains and imagination on fun scenarios?

[Fiye]

Random drop, but I've always been interested in showing off US Navy Nuke School stuff when I can.

http://www.navsea.navy.mil/Home/NNPT...tudy-material/

They also got some things on Thermodynamics that might help answer some questions.

[Zatho]

How much of the global population could survive if something such as MRSA or Influenza was to become airborne? Other options are also a pathogen that becomes highly infectious where it spreads by being in contact with others infected kind of like Ebola. There are diseases that take days to show signs of being infected. What if people can infect others before showing signs of having the virus/disease? I know it might sound crazy, but I figured this would be the place to ask from a scientific perspective.

[Cail]

How long do the effects of an EMP last? Like, say a nuke went off in orbit, EMP etc. Everything affected by the EMP gets knocked out. Does stuff eventually come back or is it fried forever/until its fixed? I've always wondered

[Zetanio]

How much of the global population could survive if something such as MRSA or Influenza was to become airborne? Other options are also a pathogen that becomes highly infectious where it spreads by being in contact with others infected kind of like Ebola. There are diseases that take days to show signs of being infected. What if people can infect others before showing signs of having the virus/disease? I know it might sound crazy, but I figured this would be the place to ask from a scientific perspective.

Influenza is airborne.

[Zetanio]

If you're talking about epidemiology by the way.

There is a large body of work around it but I can generalize it like so:

Ebola is a "fast burn" virus. It kills very quickly. This being the case, it is hard for the disease to find a proper vector (Think airport or seaport) to spread fast enough before it kills everyone infected.

Influenza isn't deadly enough to cause a breakdown in anything. It doesn't kill a high enough % of people.

Many diseases fall on one side or the other of this barrier. Either being too weak or too strong.

[Zetanio]

Playing that Plague Inc game can actually show you how a disease would need to act to be a fully global threat to health.

[BerenTebogo]

How long do the effects of an EMP last? Like, say a nuke went off in orbit, EMP etc. Everything affected by the EMP gets knocked out. Does stuff eventually come back or is it fried forever/until its fixed? I've always wondered

I think it's just until it is fixed but obviously you can permanently damage some delicate systems. Notanexpert etc.

[Psion]

continuing on my whacky worlds question, what would it be like if the force of gravity followed a different scale? for instance, what if gravity was about the same as it is now until you reached the size of the moon then leveled off dramatically, only increasing extremely slowly with mass? aka surface gravity on jupiter would only be very slightly more than the moon, and the gravity on the biggest known star would be about the same as earth. would this mean there would be no stars? or would everything just be dramatically bigger? aka earthlike planets the size of stars, and stars the size of a million of ours?