Could this work?

[playaj20008]

This always bugged me. It seems to me like there is a large ammount of vacuum energy in space, why can't we use it? I'm sure there are a number of ways to harness it. You could build a sealed structure in space designed not to crumple under the vacuum pressure, and drop it down to earth. Earths gravity will bring it down for you if it weighs enough. Then on earth, connect the vacuum to a pneumatic generator running backwards or something of that sorts. Why couldn't this work, I'm sure I've missed something.

[h4tt3n]

Basically, what you're trying to make is a perpetuum mobile. The energy needed to bring the tank out into space would always be bigger than the energy won by letting air back into it through a turbine.

[Edtharan]

"Vacuum Energy" is not the same as "absence of air". Vacuum energy is a theoretical conclusion of Quantum Mechanics (as demonstrated by the Casimir effect).

 

What you seem to be talking about is using the pressure differential of an empty space as compared to the atmosphere to provide energy. It is possible to generate electricity from Air pressure (what you seem to be talking about), and there have been experiments attempting to run vehicles off of air pressure.

 

But the costs of launching a rocket into space to bring back a sealed container without air in it would be far more expensive than just running a vacuum pump here on earth to remove the air from a container.

 

Also, a large enough container, evacuated of air, might even "float" in the atmosphere, much like a steel ship floats on water. Of course, this would depend on the weight of the container and how much volume it takes up (just like a steel ship). If the weight of the air it displaces is greater than the weight of the container, it will "float" in the air (I bet Archimedes never though of that ). However, it is extremely doubtful that a material would be strong enough to withstand that kind of air pressure and weigh less than the air it displaces.

 

So: Air pressure differential is not the same as the "Vacuum Energy" of quantum mechanics. They might use the same word "Vacuum", but they are not the same.

[Sisyphus]

 

Also, a large enough container, evacuated of air, might even "float" in the atmosphere, much like a steel ship floats on water. Of course, this would depend on the weight of the container and how much volume it takes up (just like a steel ship). If the weight of the air it displaces is greater than the weight of the container, it will "float" in the air (I bet Archimedes never though of that ). However, it is extremely doubtful that a material would be strong enough to withstand that kind of air pressure and weigh less than the air it displaces.

 

 

You would lose that bet, if I remember correctly.

 

Another problem with a "vacuum balloon" is that it just doesn't give you much for your trouble. Compared with hydrogen, you have the "cost" of maintaining that pressure differential, with not much more buoyancy. Hydrogen is already only about 1/14th as dense as air, and so even disregarding the weight of the "balloon" itself, you're already getting only about a 7% increase in lift by using vacuum. Even if the two balloons weigh the same that decreases the difference farther to probably around 1-3% (I'm just guesstimating). So unless you can make a container that maintains its volume against 1 atmosphere that weighs less than a couple percent more than a balloon, you haven't gained anything.

[Mr Skeptic]

You would lose that bet, if I remember correctly.

 

Another problem with a "vacuum balloon" is that it just doesn't give you much for your trouble. Compared with hydrogen, you have the "cost" of maintaining that pressure differential, with not much more buoyancy. Hydrogen is already only about 1/14th as dense as air, and so even disregarding the weight of the "balloon" itself, you're already getting only about a 7% increase in lift by using vacuum. Even if the two balloons weigh the same that decreases the difference farther to probably around 1-3% (I'm just guesstimating). So unless you can make a container that maintains its volume against 1 atmosphere that weighs less than a couple percent more than a balloon, you haven't gained anything.

 

You could make your container out of silica aerogel, which is itself (when evacuated) lighter than air. Then again, you're probably better off using hydrogen gas heated for lower density, which would probably also be safer than a vacuum.