Engineering a vacuum zepelin?

[Ziggurat]

It's going to be a bit on the bright side so I would suggest wearing shades

The question is: how much weight does this amount to?

I think your calculation is off, probably because of some assumptions about how the photons apply pressure.

For photons (or any ultra-relativistic particle), the pressure is given by

P = (1/3) E/V

Using E = mc² to find an equivalent mass, this gives

P = (1/3) (m/V) c²
Solving for the effective density gives

m/V = 3 P/c²
Sticking in 1 atmosphere of pressure (about 10⁵ Pa) and c = 3x10⁸ m/s, this gives us a density of 3x10⁵ (kgm/s²/m²)/[3x10⁸(m/s²)]² = 3.3x10^-12 kg/m³
So... significantly heavier than your answer, but still very light indeed, in terms of mass.

But in terms of energy? Well, 10⁵ Pa = 10⁵ J/m³. That might not seem like a lot (it's far less than 1 kW hr, so we're talking less than a penny per cubic meter), but this energy is flying around at c. The power involved is spectacularly high, around 3x10¹³ Watts, or 30 terrawatts. The entire world generates about 2.3 Terrawatts of electricity, to give you some idea. So it wouldn't take much deviation from perfect reflection to absorb this energy in very short order, unless your balloon is at very, very high temperature. You can figure out the temp from the page I linked to (use the first equation from the table), but that requires multiple physical constants and I'm too lazy right now.

 

[Dan O.]

The power involved is spectacularly high, around 3x10¹³ Watts, or 30 terrawatts.

At least the power is not beyond current capabilities: http://phys.org/news/2012-07-nif-history-terawatt-laser-shot.html

Containment does seem to be the limiting factor. Also, is there some density of photons that will spontaneously condense into mater?


On the rotational front, It seems it may be possible to also supplant the vertical structure with rotation. I'm thinking 3 rotating shells on orthogonal axis inside the outer skin all using maglev to push outward on the next shell. This should eliminate the scaling dependency so it's only a matter of making it bigger to make it work.

I worry though. This structure bares a striking similarity to the wormhole generator in Contact. Maybe it's good that there will be only a vacuum inside.

 

[Myriad]

Okay, so instead of photons, put some slower-moving but more massive particles, that have far more impulse in a collision, inside the vessel. Such as, atoms or molecules of low molecular weight. Set them all in motion (the more motion the better), and they'll go bouncing off the interior wall and off each other, equalizing or even exceeding the outside pressure. In the latter case, you can then get by with a container of a flexible tensile material.

Oh, wait...

 

[Roger Ramjets]

Trying to find a gas lighter than air to put in balloons is looking at the problem from the wrong end. All we need to do is fill the balloon with ordinary air, then change the atmosphere to something heavier.

For example, CO₂ is 50% heavier than air. So if we keep pumping CO₂ into the atmosphere then eventually we will be able to float balloons with a simple gas mixture of 78% nitrogen and 22% oxygen. Unfortunately that level of CO₂ is fatal to humans, but this problem can be averted simply by living inside the balloons. We will probably also have to keep our domestic animals in the balloons with us, but plants thrive on CO₂ so they can stay on the ground.

Another advantage of increasing CO₂ is that it will increase global temperatures enough to melt the polar icecaps and raise ocean levels by about 200ft. Water is much heavier than air, so we could then make balloons (or possibly even open-topped vessels) out of much stronger materials such as wood or steel, and float them at an altitude of 200ft above (present day) sea level.

 

[rjh01]

Trying to find a gas lighter than air to put in balloons is looking at the problem from the wrong end. All we need to do is fill the balloon with ordinary air, then change the atmosphere to something heavier.

For example, CO₂ is 50% heavier than air. So if we keep pumping CO₂ into the atmosphere then eventually we will be able to float balloons with a simple gas mixture of 78% nitrogen and 22% oxygen. Unfortunately that level of CO₂ is fatal to humans, but this problem can be averted simply by living inside the balloons. We will probably also have to keep our domestic animals in the balloons with us, but plants thrive on CO₂ so they can stay on the ground.

Another advantage of increasing CO₂ is that it will increase global temperatures enough to melt the polar icecaps and raise ocean levels by about 200ft. Water is much heavier than air, so we could then make balloons (or possibly even open-topped vessels) out of much stronger materials such as wood or steel, and float them at an altitude of 200ft above (present day) sea level.

That sort of idea might work for other planets where the Atmosphere is different. If there is no oxygen then a hydrogen balloon would be ideal. Unless of course the atmosphere is made up of very light gasses.

 

[Ziggurat]

For example, CO₂ is 50% heavier than air.

Why use CO₂ which is less than 50% heavier than air when you could be using xenon, which is more than 4 times as heavy.

 

[Roger Ramjets]

Why use CO₂ which is less than 50% heavier than air when you could be using xenon, which is more than 4 times as heavy.

Good suggestion! Though I would be inclined to go for tungsten hexafluoride, which is 11 times heavier than air.

Xenon does have the advantage of being non-reactive, but it's quite rare so I don't know whether you could get enough to fill the Earth's atmosphere. On the other hand, tungsten hexafluoride reacts with water to produce hydrogen fluoride, so you would need to remove all water from the environment beforehand.

On balance, I think sticking with CO₂ injection is the best plan. Cheaper, safer, abundant, and we are already doing it!

 

[Roger Ramjets]

That sort of idea might work for other planets where the Atmosphere is different.

Atmosphere of Venus

Due to the similarity in pressure and temperature and the fact that breathable air (21% oxygen, 78% nitrogen) is a lifting gas on Venus in the same way that helium is a lifting gas on Earth, the upper atmosphere has been proposed as a location for both exploration and colonization.

 

[Evilgiraffe]

Good suggestion! Though I would be inclined to go for tungsten hexafluoride, which is 11 times heavier than air.

Xenon does have the advantage of being non-reactive, but it's quite rare so I don't know whether you could get enough to fill the Earth's atmosphere. On the other hand, tungsten hexafluoride reacts with water to produce hydrogen fluoride, so you would need to remove all water from the environment beforehand.

On balance, I think sticking with CO₂ injection is the best plan. Cheaper, safer, abundant, and we are already doing it!

WF₆ is indeed a nasty critter however it does have a more benign cousin, SF₆. Sulphur hexafluoride is approximately 5 times denser than air, non-toxic and stable. Like helium, SF₆ in your vocal chords will dramatically change the pitch of your voice albeit to lower pitch rather than higher. There are plenty of videos on YouTube of this. I can't say I'd recommend trying it at home since, although non-toxic, it's still perfectly possible to asphyxiate yourself with SF₆

 

[Myriad]

With enough xenon, you could thicken the atmosphere to increase the sea level pressure until human bodies become neutrally buoyant themselves. Then you wouldn't have to worry about cumbersome gas bags, shells, or tensile structures.

But going back to the evacuated shell idea -- what if you gave it a positive charge, and filled it with H+ ions (that is, protons), so electrostatic repulsion provides the internal pressure? That should decrease the mass considerably. Even more, if you can use electrons.

 

[MikeG]

Folks, can I point you in the direction of this little question, which is an off-shoot of the attempt I made here previously to do the maths around sphere-inside-spheres as a means of solving the lighter-than-air problem.

Mike

 

[Hellbound]

Okay, so instead of photons, put some slower-moving but more massive particles, that have far more impulse in a collision, inside the vessel. Such as, atoms or molecules of low molecular weight. Set them all in motion (the more motion the better), and they'll go bouncing off the interior wall and off each other, equalizing or even exceeding the outside pressure. In the latter case, you can then get by with a container of a flexible tensile material.

Wait, isn't that....

Oh, wait...

Nevermind

 

[Dan O.]

But going back to the evacuated shell idea -- what if you gave it a positive charge, and filled it with H+ ions (that is, protons), so electrostatic repulsion provides the internal pressure? That should decrease the mass considerably. Even more, if you can use electrons.

The problem there is that the charged particles in the inside see themselves in a uniform charged environment so wander aimlessly through the volume. But an equal and opposite charge on the outside is attracted to the charged volume and will exert an enormous force. Additionally, what can you use for an insulator for the shell? The attraction will strip the electrons from the shell material ionizing it and turning it into a conductor that will then admit the electrons from the outside neutralizing the charge on the inside.

 

[Soapy Sam]

Well, if you exploded a nuclear weapon inside an evacuated vessel there would probably be a period of time where the radiation pressure would equal the atmospheric pressure, and the entire assembly would start to float. However, that period might be quite brief. I don't think it'll catch on as a method of transport....

Nitpickers are the curse of original thinking.

 

[quarky]

On an unrelated note,
Ignoring toxicity, could you swim faster in a pool of mercury than water?

 

[Evilgiraffe]

Depends what you mean by "swim" and "in". Mercury's so dense that you'd sort of just lie on top.

 

[quarky]

Depends what you mean by "swim" and "in". Mercury's so dense that you'd sort of just lie on top.

Yes, but you could propel yourself along.

I should take better notes, but I recall an experiment along these lines, wherein a lane of a swim pool was filled with vegetable oil; and another, with something more like oatmeal. Unfortunately, I can't recall the conclusions.

I find these weird experiments interesting, and vaguely relevant.


(Damn. I can't explain the relevance now. Cat's got my tongue.)

 

[Evilgiraffe]

Probably not relevant to the main discussion, but swimming in fluids of different viscosities was the subject of the 2005 Ig Nobel for Chemistry. The conclusion? It makes no difference as long as you're big enough.

 

[quarky]

Probably not relevant to the main discussion, but swimming in fluids of different viscosities was the subject of the 2005 Ig Nobel for Chemistry. The conclusion? It makes no difference as long as you're big enough.

Guilty as charged, as per relevance.
Sometimes, I need to slip things into a thread, because they don't warrant a new one.

I'll try to behave.

 

[quarky]

Still,
Who here amongst us hasn't dreamed of swimming in a pool of jello?
(I rest my case.)

Almost.

Swimming is about water.
If it wasn't defined by water, picture this sort of swimming:

You're in a smooth, level, plastic tube. You are smeared with grease. (Yes, it could be bacon grease,)
All along the tube, or gutter, are handles, on both sides. You pull on these, and push on them with your legs, to propel yourself along.
I suspect it would be faster than normal swimming.

It would be outside the box swimming; cheaper than water. Fast. Bacon grease.

It's this sort of thinking that will lift the zeppelin.

(Hot air, yes, but dang if I didn't get back on topic!)