Can Antigravity Unlock Space Travel and Pollution-Free Energy?

[DaveC426913]

As long as we all agree that the nitrogen molecule is going to be out in space within a matter of minutes if we could remove the influence of gravity from it regardless of where it is or where it goes, then we're not in disagreement about anything.

Anti-gravity device premises:
1] a device or material where a volume near it has gravity reduced or negated. Anything in that volume does not experience gravity, anything outside that volume does.

2] a device or process that targets mass, instilling that mass with the ability to ignore gravity.

If you used #2, pointed it at your nitrogen atom and fired, your N atom would now have zero mass, and would retain zero mass for an undetermined time, regardless of what else it did. In this case, the N atom would rise up to the near the edge of the atmosphere. It is infinitely bouyant. Any pressure from air would force it up. But it would do so by bouncing off all the other atoms on its way up. It would not happen rapidly.

But that is only one idea for anti-gravity, and it's not the one I usually think of. I doubt we can imbue matter with the property of weightlessness. I expect that it will be more like a field or volume, inside of which, mass does not experience the effect of gravity. This does not affect the matter, only the gravity reaching the matter.

 

[pervect]

Anyone up for moving this to the PF lounge? Doc Al, ZapperZ?

 

[RandallB]

Anyone up for moving this to the PF lounge? Doc Al, ZapperZ?

Or just close it.

 

[Aether]

Anyone up for moving this to the PF lounge? Doc Al, ZapperZ?

Or just close it.

I would like to quantify the time required for a weightless nitrogen molecule to work its way out into space before this thread is closed, but that's not a subject for either relativity or PF lounge.

 

[SpaceTiger]

I would like to quantify the time required for a weightless nitrogen molecule to work its way out into space before this thread is closed, but that's not a subject for either relativity or PF lounge.

How are we defining "space" in this discussion? If gravity were suddenly turned off for the atmosphere, the pressure gradient would act (at the speed of sound) to force many of the molecules away from the Earth's surface.

 

[Aether]

How are we defining "space" in this discussion? If gravity were suddenly turned off for the atmosphere, the pressure gradient would act (at the speed of sound) to force many of the molecules away from the Earth's surface.

We are turning gravity off for one nitrogen molecule starting out at mean sea level (MSL) and at standard temperature and pressure (STP), and then trying to quantify how fast it would work its way out into space. My initial guess was that it would be out in space within a matter of minutes, and DaveC426913 thinks that this would not happen rapidly.

 

[SpaceTiger]

We are turning gravity off for one nitrogen molecule starting out at mean sea level (MSL) and at standard temperature and pressure (STP), and then trying to quantify how fast it would work its way out into space. My initial guess was that it would be out in space within a few minutes, and DaveC426913 thinks that this would not happen rapidly.

If you mean one nitrogen molecule by itself, then it seems like a no-brainer. It'll just move towards space with a speed on the order of the sound speed in the gas.

If you mean that there are other nitrogen molecules around, but gravity is not turned off for them, then the "gravity-free" nitrogen molecule will have to make its way out by diffusion. This will take:

t=\frac{N^2l}{v_s}=\frac{h_{atm}^2}{lv_s}=\frac{h_{atm}}{l}t_{free}

In other words, it will take N times longer than the first scenario, where N is the number of mean free paths to the top of the atmosphere. The mean free path of particles in the atmosphere is very small (less than a micron, I think), so this would take a very long time.

 

[Aether]

If you mean one nitrogen molecule by itself, then it seems like a no-brainer. It'll just move towards space with a speed on the order of the sound speed in the gas.

If you mean that there are other nitrogen molecules around, but gravity is not turned off for them, then the "gravity-free" nitrogen molecule will have to make its way out by diffusion. This will take:

t=\frac{N^2l}{v_s}=\frac{h_{atm}^2}{lv_s}=\frac{h_{atm}}{l}t_{free}

In other words, it will take N times longer than the first scenario, where N is the number of mean free paths to the top of the atmosphere. The mean free path of particles in the atmosphere is very small (less than a micron, I think), so this would take a very long time.

We mean that there are other nitrogen molecules around, but gravity is not turned off for them. Thanks for the Eq..

 

[DaveC426913]

We mean that there are other nitrogen molecules around, but gravity is not turned off for them. Thanks for the Eq..

Ah. Then for sure, it would take a long time.

I wish I could remember where it was, but I once read a description about how long it takes on average for a given molecule to make its way across a room. It has to encounter countless molecules on its way, bouncing off each. The motion is a random walk.



Note: The nitrogen atom has a buoyancy equivalent to vacuum. How fast would a volume of vacuum rise?

 

[Aether]

Ah. Then for sure, it would take a long time.

Agreed.

I wish I could remember where it was, but I once read a description about how long it takes on average for a given molecule to make its way across a room. It has to encounter countless molecules on its way, bouncing off each. The motion is a random walk.

For the same reason, it takes millions of years for photons to make their way from the interior of a star.

Note: The nitrogen atom has a buoyancy equivalent to vacuum. How fast would a volume of vacuum rise?

That depends on how big the volume is. A volume of vacuum the size of a weather balloon would rise faster than a weather balloon. I should have stuck with the one cubic foot of air that RandallB wanted to talk about originally.

 

[Schrodinger's Dog]

Interesting all thanks for this, how would a non standard 9.8m/s fit into the equation since as gas rises away from Earth gravitation decreases or wouldn't this have any apreciable effect, excuse my ignorance. Are we talking about something complicated like an integration of the effect of gravity to fit a model, or are we just ignoring it because the influence is negligable, just a thought? Let's take Jupiter as an example, how would the gaseous effects differ?

 

[Aether]

Interesting all thanks for this, how would a non standard 9.8m/s fit into the equation since as gas rises away from Earth gravitation decreases or wouldn't this have any apreciable effect, excuse my ignorance.

The Earth's gravitational acceleration at the top of the standard atmosphere is about 2% less than it is at sea level. Here is the calculation:

1. g(m, r)=G \frac{m}{r^2}
2. G=6.67 \times 10^{-11} m^3/(kg \cdot sec^2)
3. r_{earth}=6.38 \times 10^6m
4. h_{atm}=70.1km
5. m_{earth}=5.98 \times 10^{24} kg
6. g(r_{earth})=9.80 m/s^2
7. g(r_{earth}+h_{atm})=9.59 m/s^2

Are we talking about something complicated like an integration of the effect of gravity to fit a model, or are we just ignoring it because the influence is negligable, just a thought?

http://en.wikipedia.org/wiki/Hydrostatic_equilibrium" article on hydrostatic equilibrium explains how gravity compresses the atmosphere (for example, of the Earth, Jupiter, Sun, etc.) until a pressure gradient force substantially equals the gravitational force. The large number of gas particles per cubic meter in such an atmosphere presents a huge "hall of mirrors" to any small particle bouncing around inside it. Does this answer your question? If not, please let me know a little more about what it is that you're thinking of.

Let's take Jupiter as an example, how would the gaseous effects differ?

Perhaps you could look up the stats for Jupiter and substitute them into the above equation to get the gravitational acceleration at some radius, r? Then look up the average pressure, temperature, and composition of the gasses at that radius? The calculation gets a little more complicated when you're actually inside the atmosphere because some of the mass of the planet is above the radius, r, so it might be best to pick a radius that is not too deep within the planet.

 

[Schrodinger's Dog]

That's exactly what I was looking for, the integration is when you try and work out how long it would take say a Nitrogen molecule or anything to move by diffusion or otherwise from the Earths surface to the edge of the atmosphere assuming there are no other factors but gaseous equilibrium or gm/r^2 with in t(s).

It was something that came up in my maths course about firing a rocket it running out of fuel and falling back to Earth. A colleague at work mentioned the gravity becomes less with distance, obviously because of the inverse square law, and it interested me because obviously astronauts may well need this sort of precision, athough in my example the height reached by the rocket was only 280 M so it was irrelevant. He then showed me whow you could integrate gm/r^2 for t, which came out as a very complicated looking equation which I really can't remember of the top of my head , that frankly was beyond my simple level of comprehension, which is what made me think of exactly the same thing with this particular question. I wonder if we'll ever get to the stage we're we use Einsteins equations in space travel rather than Newtons

 

[Blades]

Found this thread on google while searching for a wieght training program and just had to post.

k your talking about creating an anti-gravity shield so you could put a wheel in it and it would spin forever. I see 2 problems

1. The energy from the wheel probably would not be enough to power the shield.
2.It is way to complicated to make a shield and get something spinning inside it when we do not even have the technology yet.

Keep it simple here and stick to modern day technology.

Think for a second. Where could something spin forever and not be effected by gravity or air?

For bonous points what would keep it in place?

Don't think like a scientist. Think like an normal person. It's a simple question. Don't think about equations.

Good Luck

 

[Rach3]

Don't think like a scientist. Think like an normal person.

I tried that, it hurts my head.

 

[rhuthwaite]

I find it quite the opposite. Thinking for too long like a scientist makes my head hurts. I need constant breaks.

 

[Mech_Engineer]

While reading along, I had a thought that I hadn't seen brought up yet.

I find it easiest to think of a rock or solid object being subject to the anti-gravity machine. As soon as a volume of material (or in this case a rock) was freed from the clutches of gravity, it would be traveling at 463 m/s tangential to the Earth's curvature (assumed to be located at the equator, 24hs in a day), while everything else would continue along its circumferential path around the earth, rather like launching something from the outside of a spinning disc. This would make the weightless volume tend to move upwards WRT the ground from which it came. As the Earth rotated farther and farther, the volume would move higher and higher, subject to drag in the atmosphere. It would continue spinning outward in an ever-increasing spiral; the only acceleration it would be subject to would be drag from the atmosphere, tending to pull it in a circular path about the planet as the volume continues to try and travel in a straight line. As the atmosphere grew thinner, the spiral path of the volume would become closer and closer to a straight line (less atmospheric drag), until at the absolute edge of the atmosphere it would shoot off into space tangentially (although not very quickly, probably around the speed of the atmosphere at that altitude, about 470 m/s).

This is assuming of course the anti-gravity machine could either follow the volume, or target its volume accrodingly. Kind of an interesting way to launch things into space...