It's toxic, but a useful reference point: tungsten hexafluoride is one of the densest known gases in existence. At a density of 13kg/m^3 at standard temperature and pressure, it is nearly two orders of magnitude shy of being dense enough to bring a human (~1000kg/m^3) to neutral buoyancy.
this post was submitted on 01 Feb 2024
38 points (93.2% liked)
Ask Science
9094 readers
1 users here now
Ask a science question, get a science answer.
Community Rules
Rule 1: Be respectful and inclusive.
Treat others with respect, and maintain a positive atmosphere.
Rule 2: No harassment, hate speech, bigotry, or trolling.
Avoid any form of harassment, hate speech, bigotry, or offensive behavior.
Rule 3: Engage in constructive discussions.
Contribute to meaningful and constructive discussions that enhance scientific understanding.
Rule 4: No AI-generated answers.
Strictly prohibit the use of AI-generated answers. Providing answers generated by AI systems is not allowed and may result in a ban.
Rule 5: Follow guidelines and moderators' instructions.
Adhere to community guidelines and comply with instructions given by moderators.
Rule 6: Use appropriate language and tone.
Communicate using suitable language and maintain a professional and respectful tone.
Rule 7: Report violations.
Report any violations of the community rules to the moderators for appropriate action.
Rule 8: Foster a continuous learning environment.
Encourage a continuous learning environment where members can share knowledge and engage in scientific discussions.
Rule 9: Source required for answers.
Provide credible sources for answers. Failure to include a source may result in the removal of the answer to ensure information reliability.
By adhering to these rules, we create a welcoming and informative environment where science-related questions receive accurate and credible answers. Thank you for your cooperation in making the Ask Science community a valuable resource for scientific knowledge.
We retain the discretion to modify the rules as we deem necessary.
founded 2 years ago
MODERATORS
temperature/pressure/planetary gravity?
Any combination of those sufficient to compress the gas to human density, will also kill the human
Also gravity affects both equally
What is the difference of a gas and a liquid here? I am neutrally buoyant in a liquid and can normalize to pressure at depths, why not gas?
Liquid is incompressible.
Compressing a gas to nearly 100x it's natural density is going to dramatically increase it's temperature. In simplified mechanics, you can basically think of it like all the energy that makes it the temperature it is naturally will still be there when it is 1% of it's original size. So all that energy is "overlapping" and adding together to make it's new temperature based on there being 100x as much energy in each place now. Even if it started at 10 degrees Kelvin, assuming a linear gain, it would be 1000 degrees Kelvin after compressing.
Of course all of that is super simplified and not the "real" math or mechanics in all their complexity. But it should help illustrate why it would not be possible or a good time.
And that is only the temperature half of it. Compressing an area to 100 atmospheres, which I'm presuming would be the level of pressure necessary to get that gas (or a safer slightly less dense one) to the needed density range, would also be pretty dangerous if not immediately fatal to the human. Again that level of pressure is assuming a linear gain, I don't know for sure if it would be linear.
So even if you manage to find something you could breathe, you wouldn't be able to at that level of pressure. You would need to be wearing a suit that can be pressurized and breathing from something that isn't feeling that pressure. Which completely defeats the whole point of choosing a medium to be immersed in that doesn't require a suit or tank like being in water does.
It is however, theoretically possible to breathe liquids. Just incredibly uncomfortable for humans. There are humans that have survived it in experiments. After an initial adjustment period where your brain is certain you are drowning for a few minutes, eventually you are able to over ride that when you don't die. Then you can hang out for a bit not dying despite it seeming like you should be... and then when you are done breathing liquid, the terrible part starts, you have to get the remaining liquid out of your lungs so there is room to put air in them again. As much as the rest is not great, transitioning back to air was universally considered the worst part of the experiment.
You're talking about adiabatic heating, which is where temperature changes due to change in pressure, without heat transfer. If we thermally isolate the gas as we compress it, the temperature will rise.
We don't have to insulate it. We can allow the heat to transfer out of the gas as we compress it. Heatsinks on the pressure vessel will pass the heat from the pressurized gas into the ambient air until their temperatures equalize.
Since we can add or remove heat from the gas after it is compressed, the temperature of that gas is only relevant if it falls below the boiling or freezing curves, allowing the gas to condense into a liquid or solid.
You could likely fly using human power on Titan. It has a 50% denser atmosphere than earth as well as only 14% of the gravity. While that’s not neutrally buoyant, it is enough that if you had some big wings attached to your arms you could generate enough lift to fly by flapping. Comic by XKCD about this topic.
Of course, Titan is also insanely cold, so you’d need a pressure suit, which might throw off the calculation.
This also reminds me of a scene in Arthur C Clarke’s 3001: The Final Odyssey, a relatively less well known sequel to 2001. In this scene there are enormous space elevator towers that house humanity, and in the upper floors where there is low gravity they have a pressurized flight room just for the fun of it.
We have pressurized areas in microgravity today (space stations), which would obviously give you neutral buoyancy. Not a whole lot of room to maneuver around though!
It reminds me of Larry Niven's The Integral Trees. It takes place in a gas torus of breathable air around a neutron star.
The problem would be that you would need a very heavy gas in that mixture. Which would soon unmix, with the heavy gas at the bottom and breathable gas at the top.
Also be careful with breathing even minute amounts of such heavy gasses, as they will accumulate at the lowest parts of the lungs.
I remember a TV show where they breathed such a heavy gas to show what it does to your voice (it transfomed it way down, just like helium transforms it up). They had to stay upside down after that for some time to get the stuff out again.