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As you look at the properties of the atmosphere as you scale up or down, things get weirder and weirder. One good example is the fairyfly and its environment. Fairyflies are so small that at their scale, air behaves somewhat like syrup and their wings have become like hairy spoons in order to grab the air rather than glide in it. With this in mind I will now get to my question. What kind of gasses or other conditions would make a planet’s gaseous atmosphere act like the syrupy atmosphere of the fairyfly, but on a human scale?

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  • $\begingroup$ The question as worded is a little unclear. Try to avoid including excess information when formulating a question. Include only the relevant material. To be clear, you want a gaseous atmosphere with the consistency of syrup? $\endgroup$ – bendl Apr 9 '18 at 22:06
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    $\begingroup$ Your question boils down to "what gases have the properties of a viscous liquid?". The answer is none. They wouldn't be gases at that point. $\endgroup$ – Samuel Apr 9 '18 at 22:12
  • $\begingroup$ @bendl I’m trying to get an atmosphere as close as possible to the atmosphere that the fairyfly experiences, but on a human scale $\endgroup$ – Amoeba Apr 9 '18 at 22:36
  • $\begingroup$ @Samuel I’m only asking for how close you can get to have the atmosphere of a planet like that of the atmosphere fairyflies experience on a human scale. $\endgroup$ – Amoeba Apr 9 '18 at 22:44
  • $\begingroup$ @user45751 I know what you're asking. To have an atmosphere "like syrup" on a macro scale, the atmosphere needs to be a liquid. That is, not technically an atmosphere. There is no way to create the microscopic effects you're talking about on the macro scale without magic. $\endgroup$ – Samuel Apr 9 '18 at 22:50
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Scale is an interesting consideration when it comes to questions like this insofar as we have to understand why a fairyfly's environment is 'syrupy'; a large part of it is that air molecules are so much bigger to them by proportion to their body size. It's not that their air is like a syrup per se; what they experience would be more like what we would experience living in an atmosphere made up of very small polystyrene beads.

It's also important to note that these creatures (like any insects) don't have lungs. They absorb their O2 directly through their carapaces and can do so because their bodies are sufficiently small that it can be saturated with O2 absorbed through osmosis.

A human can't do that and survive with the body size and shape that we possess. But, if O2 came in the form if micro sized polystyrene beads, our lungs wouldn't work either. We would literally suffocate.

This ties in to the miniaturisation paradox; there's no way for 'Ant-Man' or any other human to survive when shrunk to the same size as an insect. Either your miniaturisation method involves actually making all the molecules of the body smaller, in which case the lungs can no longer process O2 molecules of a standard size and we suffocate, or the miniaturisation method employed merely scales down the number of molecules using something simliar to Eigenvector based compression modelling, in which case the human brain is now so simple that human thought is impossible. Bottom line is that it can't be done scientifically.

But for the sake of argument

Let's assume that you're literally talking about a liquid atmosphere and that the whole fairyfly discussion is a distraction. In that case, you'd be working in a form of Oxygenated Fluorocarbon Emulsion. Liquid breathing as a theory has been around for a while now and the provided link does go some way to explaining what the current thinking is about the practical benefits and downsides of such a system might be. That's at least a good place to start in terms of surviving long enough to consider the rest of the problem, like moving stuff or flying in a neutrally buoyant environment. For those questions, you're better off considering objects as mass, not weight and then applying standard kinematic thinking to the problem.

Realistically though, as an organism we're optimised to survive in our current gaseous environment. Changing out to a syrupy one is only going to cause us difficulties in the short term, even if there are some very specific advantages in certain areas.

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    $\begingroup$ Nice answer! Technical detail is that you want to make the Reynolds and Euler numbers the same. See en.wikipedia.org/wiki/Reynolds_number for a decent discussion. $\endgroup$ – Mark Olson Apr 10 '18 at 0:39
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    $\begingroup$ This is an awesome answer! $\endgroup$ – Renan Apr 10 '18 at 3:27
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    $\begingroup$ It's awesome, but technically speaking it doesn't answer the question. An oxygenated fluorocarbon emulsion cannot in any way be considered an atmosphere or a gas. Even if humans lived in a world with an ocean of it and walked around on the ocean floor, there would still be an atmosphere above it which would not be syrupy. $\endgroup$ – bendl Apr 10 '18 at 19:16
  • $\begingroup$ @bendl you're right; but this is an attempt to answer the spirit of the question rather than the letter of the question. I completely agree that this is not an atmosphere and it's really speculation, but that's why the first half is really framing; I'm trying to explain that what's being asked for is impossible, THEN provide a speculative alternative. $\endgroup$ – Tim B II Apr 10 '18 at 21:10
  • $\begingroup$ @TimBII which is why I didn't downvote - I just wanted to make it clear that this is not what the OP asked for, but rather an alternative to what he's asking $\endgroup$ – bendl Apr 10 '18 at 21:11
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No, what follows is a slightly more technical explanation.

You'd need to have a very low Reynolds number. Flow around two objects with the same Reynolds number will look about the same when the Re arethe same, even at vastly diferent sizes of the objects. Technically, it is the ratio of inertial to friction forces acting on something, and scales with size:

$$Re = \frac{\rho u L}{\mu} = \frac{u L}{\nu}$$

with density $\rho$, velocity $u$, charecteristic length $L$, dynamic viscosity $\mu$ and kinematic viscostiy $\nu$. To arrive at very low Reynolds numbers at large lengths, we need to move very slowly through very viscous gas.

If we look at some kinematic viscosities for gasses, they are all (at normal conditions, T approx. 300K) around 10-20 µPa s^-1. Clearly not enough. Viscosity of gases "arises principally from the molecular diffusion that transports momentum between layers of flow." Numerically, it depends on the mean free path of particles.

Thinking about how to have a high viscosity gas is not trivial, but given that viscositiy is higher with a longer mean free path we would need smaller molecules (fatter molecules bump mor often). I don't see any credible way how you could have far samller molecules thatn Helium or Hydrogen, so this route is out.

Viscosity rises with (the root of) Temperature, so we could have a more viscous gas ... but not by orders of magnitude. If wereach plasma temperature, all these relations break down anyway.

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