7 ms·

How We Knew Space Was a Vacuum (2021)

139 points by susam 4y ago

deleted 4y ago
[deleted]
celeritascelery 4y ago
How weird would it be if we lived in some alternate reality where space was filled with air (laws of physics would be have to be different obviously). You would be able to fly a plane to mars.
- zabzonk 4y ago
  unfortunately, i think the earth would burn up, due to compression and friction
  - epolanski 4y ago
    Hence he wrote: > (laws of physics would be have to be different obviously)
  - kibwen 4y ago
    On the other hand, it might be a cold, lifeless rock, since the sun can already barely penetrate a tiny sliver of atmosphere, as sunsets demonstrate.
- zxexz 4y ago
  In that case, we would perhaps still be a millennia from the technology required to get there. Imagine the fuel required to get to Mars with air resistance! The materials that would be required to keep the plane from being destroyed by the heat and vibrations from the speed for such a duration! The heat dissipation required would presumably be immense with that constant acceleration due to air resistance. I think we can be glad that space is a hostile vacuum.
  - andrewflnr 4y ago
    OTOH, sailing might be possible. Odds are against the atmosphere being perfectly still, certainly.
    - snek_case 4y ago
      It would just take too long. Modern space capsules travel at kilometers per second, and it would still take months to reach Mars. If were to travel there a 30km/h it would take centuries to get there. ... This is all ignoring the fact that orbital mechanics just wouldn't work if there was air resistance. The planets would quickly slow down and crash into the sun.
      - andrewflnr 4y ago
        Right, of course the real answer is that none of this is possible, at least not just replacing the interplanetary atmosphere without adjusting anything else for consistency. But imagine this: a breathable nitrox atmosphere co-orbiting with the planets. Each planet is roughly at rest with respect to the local atmosphere, so no drag. Just lots and lots of wind shear. Probably planetary scale vortices. That'll sap orbital energy into heat, so probably not stable, but pilots can probably exploit it to acheive velocities comparable to orbital velocities over time. I think you'd probably have to have two sails connected by a tether, sufficiently far that their air streams are at significantly different speed, with one of them acting like a keel.
    - hinkley 4y ago
      That Mark Twain story about the flying boat comes to mind.
  - numpad0 4y ago
    Can’t we just fly a U-2 all the way up and out of Earth SOI, then drift towards Mars in that situation? Do we still need to establish an orbit?
    - Jeff_Brown 4y ago
- justsomehnguy 4y ago
  It's quite amusing what this is the second time this week when I recommend 'Exhalation' by Ted Chiang. [0] https://archive.org/details/ExhalationByTedChiang https://archive.org/details/ExhalationByTedChiang [0] https://www.lightspeedmagazine.com/fiction/exhalation/ https://www.lightspeedmagazine.com/fiction/exhalation/
- HPsquared 4y ago
  It's not exactly air, but there is still some "stuff" filling the solar system. https://en.m.wikipedia.org/wiki/Interplanetary_medium https://en.m.wikipedia.org/wiki/Interplanetary_medium
  - Karellen 4y ago
    I think you air-quoted the wrong word in that sentence. I think it would be more appropriate to say: there is still some stuff "filling" the solar system. :-)
- KineticLensman 4y ago
  Bob Shaw's SF novel "The Ragged Astronauts" plays with this idea. A major plot point is a journey to a neighbouring planet - by balloon. The novel indicates that the laws of physics are different, e.g. a scientist character indicates that π = 3 (IIRC). [0] https://en.wikipedia.org/wiki/The_Ragged_Astronauts https://en.wikipedia.org/wiki/The_Ragged_Astronauts
- nottathrowaway3 4y ago
  We would live suspended in a great universal "ocean" and would navigate the heavens via submarine. Of course, it would be easier for other creatures to swim between planets as well... I wonder if advanced conscious life would be possible in this universe given that the number of isolated "buckets" is so much smaller. A lot of anthropic arguments would break down in such a universe.
abecedarius 4y ago
> 1643 when Evangelista Torricelli invented the mercury barometer iirc Tycho Brahe needed to make careful allowances for atmospheric refraction many decades before this. Also iirc a rougher notion of this effect goes back to Ptolemy. I guess in thinking the following I'm just showing my lack of historical imagination, but: watching a sunset, and knowing it's at a distance many times the size of the earth, you'd think there must be something attenuating light which forms a layer much thinner than the size of the earth. This comports with a view of distant mountains vs. ones nearby, versus the sharp outline of the moon. You might still be very unsure whether this factor might include the air itself, and not just dust and vapor. If anyone wrote about this early on, I haven't heard of it.
- teraflop 4y ago
  You have to bear in mind that until the 17th century or so, the philosophical doctrine that "nature abhors a vacuum" seemed to be backed by very reasonable evidence: namely, the fact that it was basically impossible to actually create a vacuum through any technological means available. And until we had basic theories of gravity and the properties of gases, there was no theoretical justification for how a vacuum could form naturally. So it makes sense that to most thinkers of the time, it was more plausible for space to be completely filled with some kind of perfectly transparent but substantial aether. You raise a very interesting point, though. I would be very interested to learn what ancient philosophers thought about atmospheric haze. Did they recognize that the bluish appearance of distant mountains and the reddish appearance of sunrises/sunsets had a common cause? And if so, did they associate it with "air" as an elemental substance, or something else?
  - flavius29663 4y ago
    > the fact that it was basically impossible to actually create a vacuum through any technological means available Do you have more sources on this? I would like to read up. As far as I'm concerned, vacuum is trivial to produce: by putting your palms together and then pulling them apart, by using blacksmith's bellows, and a lot of devices that used leather and/or bladders. I think the problem is in recognizing that you created vacuum, rather than creating it, so I would like to know if you have more insight into why you said that.
twawaaay 4y ago
> At 100 km most of the atmosphere (99.9999%) is below you. 100 km also marks the Karman Line (shown in the main graphic), generally considered the “official” start of outer space. Above this altitude aerodynamic flight is no longer possible. Wings are useless. Only rocket thrusters and gravity can affect your motion. I would like to nitpick here a bit. 100km is just "administrative" end of atmosphere. The atmosphere does not really have an end. If there are any hard, measurable boundaries it would be where solar winds meet our atmosphere (kinda like discussion about when did Voyagers leave Solar system). But this boundary does not have defined shape, moves a lot due to solar wind or Earth magnetic field situation. And we do actually use our atmosphere above 100km to "affect motion". We place satellites in LEO well above 100km to assure they will eventually fall to Earth. And anybody who played KSP knows how useful it is to skim the atmosphere for aerocapture...
- whywhywouldyou 4y ago
  Nothing you said contradicts anything the article said. What are you nitpicking, exactly? > The atmosphere does not really have an end. Article clearly doesn't state it has an end. They said 99.9999% is below you. They then say the Karman Line is considered the "official" (IN QUOTES) start of outer space, implying that this is a somewhat arbitrary definition. > And we do actually use our atmosphere above 100km to "affect motion". We place satellites in LEO well above 100km to assure they will eventually fall to Earth. The article clearly stated "affecting motion" in relation to aerodynamic flight ("aerodynamic flight is no longer possible"). Wings are useless to generate lift at those altitudes. I wouldn't classify falling to Earth as "aerodynamic flight".
  - proto_lambda 4y ago
    > Wings are useless to generate lift at those altitudes. They aren't, though. They still work, just much less well. There isn't one altitude where wings suddenly stop working entirely - there is however an altitude where generating enough lift to sustain flight would require going so fast that you're already in orbit (regardless of lift), according to wikipedia it's somewhere around 80km. The Karman line has nothing to do with lift, it's just an arbitrary, round number.
verisimi 4y ago
I hate the use of 'we', as it is being used in the title, the question and the answer. Put simply, 'we' cannot know anything. Knowledge only exists in the mind of an individual. No one is able to say what another knows. And unfortunately, most people don't even know the difference between knowing and believing! At best, use of the term 'we know' is a shortcut to saying 'some scientists claim that'. I can only know that claim to be true once I have verified it for myself. Until that time it can only be a belief or hypothesis.
- citrusynapse 4y ago
  And within epistemology and your process of "verifying" there are hundreds of contemporary schools of thought from Wittgenstein to Chbosky.
  - verisimi 4y ago
    I don't care about Wittgenstein or Chbosky. I can only care what meanings mean to me. The use of 'we' is fine in many cases - when talking about a holiday, I can say 'we went to the beach' and that is understandable because of the context. Its not fine to talk about 'we' in the context of something that is subjective, eg understanding or knowing. It is an assumption to say 'we know' unless you have checked all the people you are referring to really do know. If you think this usage is acceptable - and apparently most people do - I'd love to hear an explanation. To me, it is sloppy and confused thinking, and actually it's use is ultimately a type of casual lie, because it overstates whatever-it-is.
- Jeff_Brown 4y ago
  I don't think anyone is in danger of being confused by the imprecision.
  - verisimi 4y ago
    I think everyone is massively misled multiple times daily. The misuse of words like 'we' is actually a casual lie, falsely believed to be true by most, and actually verified by no one.
mannykannot 4y ago
Obligatory Tom Lehrer: "Once the rockets are up, who cares where they come down? That's not my department!" says Wernher von Braun.
jedberg 4y ago
I miss web pages from the 1990s. I don't know when this site was first made, but its design looks like the 90s web and I love it.
- deleted 4y ago
  [deleted]
- prox 4y ago
  It’s the frames type of design, left an outline, right content.
  - jedberg 4y ago
    Yeah, that's probably it. Late 90s, early 2000s, we all used these magical frames.
- ktpsns 4y ago
  It's also the stars as background image. You don't see this stuff nowadays, it would be too low-pixel non-fancy. White little pixels on black background where so sci-fi in the 1990s.
  - JohnFen 4y ago
    Web design these days values "bland" and/or "look the same as everyone else" above all else, it seems, even to the point of reducing usability.
deleted 4y ago
[deleted]
seiferteric 4y ago
Another interesting one is when we "knew" how the sun worked. Of course we didn't know about nuclear reactions until the early 20th century, so it makes sense we didn't figure it out for a while after that. But before that it was a complete mystery! Scientists had calculated how much energy would be required to produce the amount of light we see and it seemed impossible given the estimated mass of the sun, for any know physical method to produce it (chemical, gravity compression). Some thought it was made of coal (sign of the times I guess) but that would of course require oxygen to react with... And would have only lasted a few million years I think...
- sebzim4500 4y ago
  By my inexpert calculations, if we ignore the requirment for oxygen (because I don't know what ratio you need) the sun would only last 4000 years.
  - seiferteric 4y ago
    Actually ya your right, searching for it, they thought it would only last about 5k years. Actually they also thought it might be meteors falling in may add more energy that might allow to last 100s of millions of years... https://www.scientificamerican.com/article/experts-doubt-the-sun-is-actually-burning-coal/ https://www.scientificamerican.com/article/experts-doubt-the...
- oxymoron 4y ago
  I think our understanding of the inner structure of the earth is another interesting example of something that we’ve deduced scientifically but never directly observed. It surprised me a bit when I first realized that the Earth’s crust had never been pierced (by humans) and that it was all based on indirect observation.
oecumena 4y ago
Newton explicitly checks in Principia that the orbital parameters of the moons of Jupiter are consistent with the "empty space" hypothesis.

139 points by susam 4y ago

deleted 4y ago

[deleted]

How weird would it be if we lived in some alternate reality where space was filled with air (laws of physics would be have to be different obviously). You would be able to fly a plane to mars.

zabzonk 4y ago
unfortunately, i think the earth would burn up, due to compression and friction
- epolanski 4y ago
  Hence he wrote: > (laws of physics would be have to be different obviously)
- kibwen 4y ago
  On the other hand, it might be a cold, lifeless rock, since the sun can already barely penetrate a tiny sliver of atmosphere, as sunsets demonstrate.
zxexz 4y ago
In that case, we would perhaps still be a millennia from the technology required to get there. Imagine the fuel required to get to Mars with air resistance! The materials that would be required to keep the plane from being destroyed by the heat and vibrations from the speed for such a duration! The heat dissipation required would presumably be immense with that constant acceleration due to air resistance. I think we can be glad that space is a hostile vacuum.
- andrewflnr 4y ago
  OTOH, sailing might be possible. Odds are against the atmosphere being perfectly still, certainly.
  - snek_case 4y ago
    It would just take too long. Modern space capsules travel at kilometers per second, and it would still take months to reach Mars. If were to travel there a 30km/h it would take centuries to get there. ... This is all ignoring the fact that orbital mechanics just wouldn't work if there was air resistance. The planets would quickly slow down and crash into the sun.
    - andrewflnr 4y ago
      Right, of course the real answer is that none of this is possible, at least not just replacing the interplanetary atmosphere without adjusting anything else for consistency. But imagine this: a breathable nitrox atmosphere co-orbiting with the planets. Each planet is roughly at rest with respect to the local atmosphere, so no drag. Just lots and lots of wind shear. Probably planetary scale vortices. That'll sap orbital energy into heat, so probably not stable, but pilots can probably exploit it to acheive velocities comparable to orbital velocities over time. I think you'd probably have to have two sails connected by a tether, sufficiently far that their air streams are at significantly different speed, with one of them acting like a keel.
  - hinkley 4y ago
    That Mark Twain story about the flying boat comes to mind.
- numpad0 4y ago
  Can’t we just fly a U-2 all the way up and out of Earth SOI, then drift towards Mars in that situation? Do we still need to establish an orbit?
  - Jeff_Brown 4y ago
justsomehnguy 4y ago
It's quite amusing what this is the second time this week when I recommend 'Exhalation' by Ted Chiang. [0] https://archive.org/details/ExhalationByTedChiang https://archive.org/details/ExhalationByTedChiang [0] https://www.lightspeedmagazine.com/fiction/exhalation/ https://www.lightspeedmagazine.com/fiction/exhalation/
HPsquared 4y ago
It's not exactly air, but there is still some "stuff" filling the solar system. https://en.m.wikipedia.org/wiki/Interplanetary_medium https://en.m.wikipedia.org/wiki/Interplanetary_medium
- Karellen 4y ago
  I think you air-quoted the wrong word in that sentence. I think it would be more appropriate to say: there is still some stuff "filling" the solar system. :-)
KineticLensman 4y ago
Bob Shaw's SF novel "The Ragged Astronauts" plays with this idea. A major plot point is a journey to a neighbouring planet - by balloon. The novel indicates that the laws of physics are different, e.g. a scientist character indicates that π = 3 (IIRC). [0] https://en.wikipedia.org/wiki/The_Ragged_Astronauts https://en.wikipedia.org/wiki/The_Ragged_Astronauts
nottathrowaway3 4y ago
We would live suspended in a great universal "ocean" and would navigate the heavens via submarine. Of course, it would be easier for other creatures to swim between planets as well... I wonder if advanced conscious life would be possible in this universe given that the number of isolated "buckets" is so much smaller. A lot of anthropic arguments would break down in such a universe.

abecedarius 4y ago

> 1643 when Evangelista Torricelli invented the mercury barometer iirc Tycho Brahe needed to make careful allowances for atmospheric refraction many decades before this. Also iirc a rougher notion of this effect goes back to Ptolemy. I guess in thinking the following I'm just showing my lack of historical imagination, but: watching a sunset, and knowing it's at a distance many times the size of the earth, you'd think there must be something attenuating light which forms a layer much thinner than the size of the earth. This comports with a view of distant mountains vs. ones nearby, versus the sharp outline of the moon. You might still be very unsure whether this factor might include the air itself, and not just dust and vapor. If anyone wrote about this early on, I haven't heard of it.

teraflop 4y ago
You have to bear in mind that until the 17th century or so, the philosophical doctrine that "nature abhors a vacuum" seemed to be backed by very reasonable evidence: namely, the fact that it was basically impossible to actually create a vacuum through any technological means available. And until we had basic theories of gravity and the properties of gases, there was no theoretical justification for how a vacuum could form naturally. So it makes sense that to most thinkers of the time, it was more plausible for space to be completely filled with some kind of perfectly transparent but substantial aether. You raise a very interesting point, though. I would be very interested to learn what ancient philosophers thought about atmospheric haze. Did they recognize that the bluish appearance of distant mountains and the reddish appearance of sunrises/sunsets had a common cause? And if so, did they associate it with "air" as an elemental substance, or something else?
- flavius29663 4y ago
  > the fact that it was basically impossible to actually create a vacuum through any technological means available Do you have more sources on this? I would like to read up. As far as I'm concerned, vacuum is trivial to produce: by putting your palms together and then pulling them apart, by using blacksmith's bellows, and a lot of devices that used leather and/or bladders. I think the problem is in recognizing that you created vacuum, rather than creating it, so I would like to know if you have more insight into why you said that.

twawaaay 4y ago

> At 100 km most of the atmosphere (99.9999%) is below you. 100 km also marks the Karman Line (shown in the main graphic), generally considered the “official” start of outer space. Above this altitude aerodynamic flight is no longer possible. Wings are useless. Only rocket thrusters and gravity can affect your motion. I would like to nitpick here a bit. 100km is just "administrative" end of atmosphere. The atmosphere does not really have an end. If there are any hard, measurable boundaries it would be where solar winds meet our atmosphere (kinda like discussion about when did Voyagers leave Solar system). But this boundary does not have defined shape, moves a lot due to solar wind or Earth magnetic field situation. And we do actually use our atmosphere above 100km to "affect motion". We place satellites in LEO well above 100km to assure they will eventually fall to Earth. And anybody who played KSP knows how useful it is to skim the atmosphere for aerocapture...

whywhywouldyou 4y ago
Nothing you said contradicts anything the article said. What are you nitpicking, exactly? > The atmosphere does not really have an end. Article clearly doesn't state it has an end. They said 99.9999% is below you. They then say the Karman Line is considered the "official" (IN QUOTES) start of outer space, implying that this is a somewhat arbitrary definition. > And we do actually use our atmosphere above 100km to "affect motion". We place satellites in LEO well above 100km to assure they will eventually fall to Earth. The article clearly stated "affecting motion" in relation to aerodynamic flight ("aerodynamic flight is no longer possible"). Wings are useless to generate lift at those altitudes. I wouldn't classify falling to Earth as "aerodynamic flight".
- proto_lambda 4y ago
  > Wings are useless to generate lift at those altitudes. They aren't, though. They still work, just much less well. There isn't one altitude where wings suddenly stop working entirely - there is however an altitude where generating enough lift to sustain flight would require going so fast that you're already in orbit (regardless of lift), according to wikipedia it's somewhere around 80km. The Karman line has nothing to do with lift, it's just an arbitrary, round number.

verisimi 4y ago

I hate the use of 'we', as it is being used in the title, the question and the answer. Put simply, 'we' cannot know anything. Knowledge only exists in the mind of an individual. No one is able to say what another knows. And unfortunately, most people don't even know the difference between knowing and believing! At best, use of the term 'we know' is a shortcut to saying 'some scientists claim that'. I can only know that claim to be true once I have verified it for myself. Until that time it can only be a belief or hypothesis.

citrusynapse 4y ago
And within epistemology and your process of "verifying" there are hundreds of contemporary schools of thought from Wittgenstein to Chbosky.
- verisimi 4y ago
  I don't care about Wittgenstein or Chbosky. I can only care what meanings mean to me. The use of 'we' is fine in many cases - when talking about a holiday, I can say 'we went to the beach' and that is understandable because of the context. Its not fine to talk about 'we' in the context of something that is subjective, eg understanding or knowing. It is an assumption to say 'we know' unless you have checked all the people you are referring to really do know. If you think this usage is acceptable - and apparently most people do - I'd love to hear an explanation. To me, it is sloppy and confused thinking, and actually it's use is ultimately a type of casual lie, because it overstates whatever-it-is.
Jeff_Brown 4y ago
I don't think anyone is in danger of being confused by the imprecision.
- verisimi 4y ago
  I think everyone is massively misled multiple times daily. The misuse of words like 'we' is actually a casual lie, falsely believed to be true by most, and actually verified by no one.

mannykannot 4y ago

Obligatory Tom Lehrer: "Once the rockets are up, who cares where they come down? That's not my department!" says Wernher von Braun.

jedberg 4y ago

I miss web pages from the 1990s. I don't know when this site was first made, but its design looks like the 90s web and I love it.

deleted 4y ago
[deleted]
prox 4y ago
It’s the frames type of design, left an outline, right content.
- jedberg 4y ago
  Yeah, that's probably it. Late 90s, early 2000s, we all used these magical frames.
ktpsns 4y ago
It's also the stars as background image. You don't see this stuff nowadays, it would be too low-pixel non-fancy. White little pixels on black background where so sci-fi in the 1990s.
- JohnFen 4y ago
  Web design these days values "bland" and/or "look the same as everyone else" above all else, it seems, even to the point of reducing usability.

deleted 4y ago

[deleted]

seiferteric 4y ago

Another interesting one is when we "knew" how the sun worked. Of course we didn't know about nuclear reactions until the early 20th century, so it makes sense we didn't figure it out for a while after that. But before that it was a complete mystery! Scientists had calculated how much energy would be required to produce the amount of light we see and it seemed impossible given the estimated mass of the sun, for any know physical method to produce it (chemical, gravity compression). Some thought it was made of coal (sign of the times I guess) but that would of course require oxygen to react with... And would have only lasted a few million years I think...

sebzim4500 4y ago
By my inexpert calculations, if we ignore the requirment for oxygen (because I don't know what ratio you need) the sun would only last 4000 years.
- seiferteric 4y ago
  Actually ya your right, searching for it, they thought it would only last about 5k years. Actually they also thought it might be meteors falling in may add more energy that might allow to last 100s of millions of years... https://www.scientificamerican.com/article/experts-doubt-the-sun-is-actually-burning-coal/ https://www.scientificamerican.com/article/experts-doubt-the...
oxymoron 4y ago
I think our understanding of the inner structure of the earth is another interesting example of something that we’ve deduced scientifically but never directly observed. It surprised me a bit when I first realized that the Earth’s crust had never been pierced (by humans) and that it was all based on indirect observation.

oecumena 4y ago

Newton explicitly checks in Principia that the orbital parameters of the moons of Jupiter are consistent with the "empty space" hypothesis.