3 ms·

> by using blacksmith's bellows Creating a pressure differential where air flows in immediately. As vacuum seemingly cannot be sustained without constant work,

by maweki 4y ago

> by using blacksmith's bellows Creating a pressure differential where air flows in immediately. As vacuum seemingly cannot be sustained without constant work, it seems that nature does indeed not like vacuums. > vacuum is trivial to produce But not trivial to sustain. And it would be a sustained vacuum if it were between the earth and the moon or sun.

flavius29663 4y ago
you can sustain it if it's properly sealed, but I see your point, people would have a hard time understanding why the outer space would apparently sustain such a large amount of vacuum. It seems unnatural to us, because we're so used to atmospheric pressure that we're taking it for granted.
- seiferteric 4y ago
  I also thought of several examples; breathing in/out of a paper bag, hot air balloon, or that experiment where you put heat up or metal container and put the opening on water and it gets sucked in (or crushes a thin can). I can see that it takes work to sustain these, but what about just putting a glass bottle in your mouth and pulling a vacuum and carefully putting your thumb on top. You can create a slight vacuum in a glass bottle this way and it will stay there until you move your thumb and hear the "whoosh". But I guess it still "wants" to fill the void as soon as you unplug it, so I guess I understand.
  - abecedarius 4y ago
    That kind of effect was studied and used in antiquity, as pneumatics. Aristotle's point of view did not hold sway everywhere or for all of that period; afaik pneumatics started with Empedocles and the clepsydra, and obviously the atomists favored the vacuum. I've kept out of this conversation because I'm too ignorant, but it seems worth saying that while "it doesn't fit with Aristotle's scheme of the world" may be a good enough explanation for most premodern western thinking, it's hardly all of it.
  - flavius29663 4y ago
    How does breathing in and out of a paper bag create vacuum? As soon as you inhale, the atmospheric pressure collapses the bag. Bellows are different because they can hold their shape: if you seal all the ends and then expand the bellows, you will have vacuum and the 1atm of pressure trying hard to stop you from doing that. The same with hot air balloons, there is no vacuum at play there, unless I'm miss-understanding what you're saying.
  - afiori 4y ago
    Here vacuum does not mean low pressure, it means lack of substance. If you use a strong pump to depressurize and seal a glass bottle you still get a bottle with air inside; you can easily see that there is air inside because if you submerge it in water or oil and break the seal you will see air bubbles coming out. If you were to try the same with a glass bottle full of water, you will find that is is much much harder to pump the water out than is it to pump the air out. This is perfectly compatible with the impossibility of an actual vacuum. The experiment that subverted this view had to use mercury to be practical at the time[1] In this experiment you essentially use the weight of mercury to pump mercury out of a glass bottle and since air cannot traverse mercury nor glass [2] then it must truly be a full vacuum. [3] [1] https://en.wikipedia.org/wiki/Torricelli%27s_experiment https://en.wikipedia.org/wiki/Torricelli%27s_experiment [2] This is false, mercury evaporates, quantum tunneling exists, gasses likely can be dissolved in mercury and material are porous. [3] In some sense you could say that the photons in the bottle make it not a vacuum, as they have mass or also that particles spontaneously appear from a base energy noise or a lot of other oppositions to that being a real vacuum. Still it is definitely a different thing from just low pressure air.
- prox 4y ago
  This is the key take away. As a modern human you obviously reason “how they hell could there NOT be vacuum?” , but in those times you had islands of knowledge (no email, mail if you are lucky) and you always reason from what you know at that point. Just like future readers might shake their head “how did they not know warp drives work like this?”

by maweki 4y ago

flavius29663 4y ago

you can sustain it if it's properly sealed, but I see your point, people would have a hard time understanding why the outer space would apparently sustain such a large amount of vacuum. It seems unnatural to us, because we're so used to atmospheric pressure that we're taking it for granted.

seiferteric 4y ago
I also thought of several examples; breathing in/out of a paper bag, hot air balloon, or that experiment where you put heat up or metal container and put the opening on water and it gets sucked in (or crushes a thin can). I can see that it takes work to sustain these, but what about just putting a glass bottle in your mouth and pulling a vacuum and carefully putting your thumb on top. You can create a slight vacuum in a glass bottle this way and it will stay there until you move your thumb and hear the "whoosh". But I guess it still "wants" to fill the void as soon as you unplug it, so I guess I understand.
- abecedarius 4y ago
  That kind of effect was studied and used in antiquity, as pneumatics. Aristotle's point of view did not hold sway everywhere or for all of that period; afaik pneumatics started with Empedocles and the clepsydra, and obviously the atomists favored the vacuum. I've kept out of this conversation because I'm too ignorant, but it seems worth saying that while "it doesn't fit with Aristotle's scheme of the world" may be a good enough explanation for most premodern western thinking, it's hardly all of it.
- flavius29663 4y ago
  How does breathing in and out of a paper bag create vacuum? As soon as you inhale, the atmospheric pressure collapses the bag. Bellows are different because they can hold their shape: if you seal all the ends and then expand the bellows, you will have vacuum and the 1atm of pressure trying hard to stop you from doing that. The same with hot air balloons, there is no vacuum at play there, unless I'm miss-understanding what you're saying.
- afiori 4y ago
  Here vacuum does not mean low pressure, it means lack of substance. If you use a strong pump to depressurize and seal a glass bottle you still get a bottle with air inside; you can easily see that there is air inside because if you submerge it in water or oil and break the seal you will see air bubbles coming out. If you were to try the same with a glass bottle full of water, you will find that is is much much harder to pump the water out than is it to pump the air out. This is perfectly compatible with the impossibility of an actual vacuum. The experiment that subverted this view had to use mercury to be practical at the time[1] In this experiment you essentially use the weight of mercury to pump mercury out of a glass bottle and since air cannot traverse mercury nor glass [2] then it must truly be a full vacuum. [3] [1] https://en.wikipedia.org/wiki/Torricelli%27s_experiment https://en.wikipedia.org/wiki/Torricelli%27s_experiment [2] This is false, mercury evaporates, quantum tunneling exists, gasses likely can be dissolved in mercury and material are porous. [3] In some sense you could say that the photons in the bottle make it not a vacuum, as they have mass or also that particles spontaneously appear from a base energy noise or a lot of other oppositions to that being a real vacuum. Still it is definitely a different thing from just low pressure air.
prox 4y ago
This is the key take away. As a modern human you obviously reason “how they hell could there NOT be vacuum?” , but in those times you had islands of knowledge (no email, mail if you are lucky) and you always reason from what you know at that point. Just like future readers might shake their head “how did they not know warp drives work like this?”