Two political questions that seem timely

[MikeNovack]

Sand does not "randomly move about".

Sand, suspended in a liquid filed space, a liquid of the same density as the sand, most certainly does randomly move about. Why do you imagine that it would not?

This started with a discussion of an hourglass in space, where in the absence of gravity, the sand particles would just "float" abut in the space available, moving randomly.

The thought experiment just replaced the gas in the hourglass with a liquid THE SAME DENSITY AS THE SAND. So gravity no longer relevant (the sand grains just "float about" in the liquid, neither rising to the top nor sinking to the bottom).

I was arguing that over they would "diffuse" until equal in both bulbs.

[Alexis Jacobi]

Assuming that colonizing space is both necessary for survival (and therefore has some temporal expedience) and is also realistically possible for human beings, could a successful program to colonize space be carried out entirely by an "anarchist" commune?

It seems doubtful because the entire operation would necessarily be of a military character. Command structures, hierarchies, and military discipline. Anarchism implies individualism, contempt for hierarchies, and resistance to power-structure.

[phyllo]

Sand, suspended in a liquid filed space, a liquid of the same density as the sand, most certainly does randomly move about. Why do you imagine that it would not?

You're probably thinking of Brownian motion.

But a fluid as dense as sand would also have a relatively high viscosity, so the amount of 'jiggle' observed would be small.

This started with a discussion of an hourglass in space, where in the absence of gravity, the sand particles would just "float" about in the space available, moving randomly.

The sand would "float" around if someone imparted some force to it. Then it would bounce around until the friction of collisions dissipated the energy. If the sand was in one bulb initially and nobody disturbed the hourglass, then it would stay there.

The sand particles are too heavy to get Brownian motion from the air in the hourglass.

Maybe you're thinking that microgravitational pull within the spacecraft would produce motion.

[MikeNovack]

Sand, suspended in a liquid filed space, a liquid of the same density as the sand, most certainly does randomly move about. Why do you imagine that it would not?

You're probably thinking of Brownian motion.

But a fluid as dense as sand would also have a relatively high viscosity, so the amount of 'jiggle' observed would be small.

This started with a discussion of an hourglass in space, where in the absence of gravity, the sand particles would just "float" about in the space available, moving randomly.

The sand would "float" around if someone imparted some force to it. Then it would bounce around until the friction of collisions dissipated the energy. If the sand was in one bulb initially and nobody disturbed the hourglass, then it would stay there.

The sand particles are too heavy to get Brownian motion from the air in the hourglass.

Maybe you're thinking that microgravitational pull within the spacecraft would produce motion.

Probability and time. Given enough time, events of low probability become likely.

In space -- at the start there is only a low probability that a sand grain at the surface would have enough energy to go floating off int the air. But at the start, before any sand grains have left the surface, zero probability of one floating about will hit the surface and stay there. So the net probability is that more leave the surface to float abut than return.

Are you meaning to ad the condition of the temperature being absolute zero? (no kinetic energy n the particles in the hourglass)

Dissipation of energy of the sand grains floating about (and colliding). Where, pray tell, is this energy going? That is why I brought temperature into it. Yes, if the temperature of the hour glass is higher than what surrounds it,it will lose energy to that environment, and if the other way around, gain energy.

The reason that spinning or shaking the hourglass greatly speeds up the diffusion process is that it has greatly increased the energy per sand grain. Again, energy per particle is defining temperature.

[phyllo]

Probability and time. Given enough time, events of low probability become likely.

In space -- at the start there is only a low probability that a sand grain at the surface would have enough energy to go floating off int the air. But at the start, before any sand grains have left the surface, zero probability of one floating about will hit the surface and stay there. So the net probability is that more leave the surface to float abut than return.

You think that grains of sand will start moving without any external applied force??

That's weird.

[MikeNovack]

You think that grains of sand will start moving without any external applied force??

That's weird.

All the sand grains ARE moving about, bumping into each other. The energy per particle is not zero because the temperature is not absolute zero (that's what temperature is, a measure of energy per particle)

Your expectations are based on thinking about a little pile of sand sitting on your desk. Just sit there, none floating away because none have a teensy fraction of the energy to rise against the force of gravity.

But in zero gravity space, not even the smallest force to keep them down, why would you expect the grains at the surface of the pile to stay there. What would be holding them there? Even the tiniest amount of energy would be enough for them to leave the surface.

Switch from a pile of sand grains to a dish of water on your desk. Does the water just stay there? No, it slowly "evaporates". In this case, water molecules at the surface do have enough energy to escape, even the very significant bond between water molecules (that is why the "boiling point" of water is so high --- you would expect it to be hundreds of degrees lower for a molecular weight of just 18). The water will continue to evaporate until the density of water molecules in the air above is high enough that as many rejoin the surface as leave (that again is also temperature dependent). At a high enough temperature, not just at the surface. We get the formation of "bubbles" with molecules leaving the (local surface) to join the water vapor molecules in the bubble --- we call that "boiling".

But water is a liquid and sand a solid you want to say. Well then take cube of ice on the desk, at a temperature low enough that water isn't liquid. Molecules will still leave the surface of the ice << when solid do this, we say they "sublime".

If you seal a block of ice in a chamber kept below the melting point of ice (at that pressure) over time molecules will leave the surface of the block of ice to form a "fuzz" of ice on the inside of the chamber. You probably have sen this, a plastic bag into which frozen food has been put. Over time, you discover that water molecules have left the food and formed ice inside the bag (and the food has become "dried out" if you them try to use it.

[phyllo]

But in zero gravity space, not even the smallest force to keep them down, why would you expect the grains at the surface of the pile to stay there. What would be holding them there? Even the tiniest amount of energy would be enough for them to leave the surface.

Well, there is the gravitational attraction between the grains. The irregular surfaces may be locked together. There is friction between grains. And the grains may be electrically charged.

There have been experiments with sand in zero gravity. When sand is agitated, it tends to form clumps as it "settles".

This:

AI Overview

In zero gravity, sand does not disperse into an endless cloud. Instead, it quickly aggregates into clumps due to Van der Waals forces, electrostatic charges, and mechanical friction. Without gravity to separate the grains, fine-grain materials cling together into drifting clusters and web-like chains.

1. The Power of Electrostatics
In microgravity, granular materials like sand and salt rapidly accumulate static charge as they rub against one another or container walls. Instead of acting independently, the grains begin to act as miniature electrical monopoles. Positive and negative charges align, causing the sand to form into stringy, branching chains or tight clusters in a matter of seconds.

2. The Dominance of Surface Adhesion
When sand grains collide in orbit, the lack of gravitational pull allows short-range attractive forces to dominate. Because the grains cannot fall away from one another, adhesion becomes the primary driver of movement. This leads to the formation of "fluffy" agglomerations that stick together upon the slightest impact, creating loose webs or floating masses.

3. Implications for Space Exploration
Understanding how dry granular materials like sand clump in space is vital for understanding early planetary formation and handling extraterrestrial resources (such as lunar or Martian regolith). Because sand clumps more easily and flows differently in low-gravity environments, it behaves more like a cohesive, sticky fluid rather than a free-flowing solid.