So, anti-gravity...

[lacktheknack]

I suppose you'd slowly start rising into the air and very slightly towards the west as you entered a tangent with the Earth's surface and only air was pulling you along with Earth's rotation, but nothing that a panicked flap wouldn't fix (briefly).

Hug a tree, guys.

 

[Silvanus]

Sure...so? Either way it is not being pulled to the Earth. How does this affect how much the wind affects it?

The reason it would effect the two differently is because with the helicopter, it's still being pulled along with the Earth and everything else effected by its gravity. Meaning all the air around the Earth and helicopter are still being pulled through space at the same speed. That's the reason we don't feel wind caused by the Earth moving through space or rotating, because it's all moving together.[/quote]

Yes, but that's a result of relativity, not gravity. Nullifying gravity would not nullify relativity.

 

[Guffe]

I got through the second post of this thread and knew this shit flies so high above my head I shouldn't even bother.

Then this came along

No damn it. When you use an anti-gravity engine, you roll 3d6 and try to get under your Toughness. If you don't, you're removed from the earth as a casualty and everyone around you has to take a Pinning test.

Did no one pay attention in AP Physics in high school?!

I was once again back on track and understood everything that was going on...

until...

The next two posts, then I was again crying in a corner of not understand squat xD

 

[FalloutJack]

Snip

No, I argued that we still have so much to learn, a fact that actual scientists would agree with if asked. We don't know everything and sometimes - Sometimes! - the understanding of what we know changes. It happens. Why? Because as we grow more advanced, the things we were able to test expands with our advances, and we learn new things through testing and new ideas, new theories to put forth. This isn't an unusual statement. Remember that a thousand years ago, the notion of man flying in the sky or leaving the world entirely was utter folly. Well, they were wrong. Do we know better now than we will in the the next thousand years? Hell no.

 

[barbzilla]

As far as my understanding goes, the idea behind making a craft with anti-gravity abilities is that it would be completely free from the effects of gravity. Allowing it to simply move or be moved through space under its own power, without pull from a planet or any other mass.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

To answer your question as simply as I can; We already have things that are anti-gravity (such as radio waves, light, or pretty much most types of energy), and they are not subject to be suddenly flung away from the earth at ludicrous speeds. This is primarily due to the fact that they are already in motion with their own trajectories, and since gravity can't affect them, the lack their of does not either. So suddenly taking gravity away from an object would not cause it to hurtle off. In fact, friction and other forces would probably prevent it from moving at all (relative to its surroundings once it has lost gravity).

 

[Squilookle]

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

It was this thinking that directly led to a moment of horror for me when I was thinking about time travel. Anyone who actually built something that could go back in time and tried it, would most likely have found themselves rematerialising in the middle of space, for exactly this reason. Poor Marty....

 

[K12]

Inertial force wouldn't keep you on the Earth if it was possible to suddenly switch off the effects of gravity for some object because forces act in a straight line. So yes you'd keep travelling at the horizontal speed you were already travelling due to the rotation of the Earth but...

It wouldn't be the same as suddenly shooting up into the air, instead you'd gradually drift upwards you continue off at a tangent to the Earth's motion, essentially the Earth would have rotated out from under you. I'd expect the local effects of wind and friction to make a big difference to this though so it's hard to say... and you almost certainly couldn't make something that's anti-gravity anyway.

 

[Thaluikhain]

Another thing: running an anti-gravitation engine would always consume more engergy than it would take to overcome gravitation conventionally. Otherwise we could just lift an object into the sky, then deactivate the engine and get potential energy out of nothing. That would contradict the 1st law of thermodynamics.

An important point to remember, with the caveat that when you say "overcome gravitation conventionally" you mean at 100% efficiency (or close to it), which we don't have.

Should some anti-gravity machine be possible, it's feasible that it would require less energy than conventional methods in that it may be more efficient.

 

[Mr. Popplewick]

Imagine a block of spacetime, with a large star in it.

Your image is borked, your argument is invalid! (jk, but I would like to see it)

Oops!

There, that should help.

Do you have anything to add or comment on for my later arguments/questions regarding deceleration and wind resistance?

Sure. As I said, you're not wrong, but you're also a very small object moving through a gas that behaves like a pretty dense fluid, the faster you try to move through it. You'd also be subject not just to friction against a static background, but friction from a GIANT mass of co-moving air, water, and dust we call an atmosphere. All of it, every particle of it, is whipping around along with the Earth. You would certainly eventually find your way out and away, but I can't even imagine how long it would take, and what might be left of you when you eventually left Earth's gravity well.

When I say a "long time" by the way, it could be on the order of thousands of years. After all, a speck of dust doesn't experience much gravitational influence from Earth, but it is dominated by other forces. While the speck IS very small with a large surface area compared to you or your ship, it's not that far from a speck of dust compared to the atmosphere.

An object on the surface of the earth that was suddenly no longer bound by gravitation would move towards the sky with a velocity of about 1.6 mm per second. Noticable, but not spectacular. It would just gently drift away, wind resistance doesn't Play a role at such low speeds.

I'm not so sure. As you say wind resistance doesn't play a role at such low speeds, but it will certainly dampen acceleration. In addition, you're going to have lateral momentum imparted by the relative motion of the atmosphere to you, which is pretty insignficant at first, but at altitude you start to experience serious winds. Since you have no weight, other forces are going to dominated, including even minute lift. With a good wind, you could in fact fly DOWN again. There is no reason to think that as a weightless speck with a GIANT surface area, you're going to have some easy trajectory.

Another thing: running an anti-gravitation engine would always consume more engergy than it would take to overcome gravitation conventionally. Otherwise we could just lift an object into the sky, then deactivate the engine and get potential energy out of nothing. That would contradict the 1st law of thermodynamics.

Yes, but it's important to remember that there could be hypothetical advantages, aside from an ability to run cheaply. That said, it would have to be hypothetical.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

It was this thinking that directly led to a moment of horror for me when I was thinking about time travel. Anyone who actually built something that could go back in time and tried it, would most likely have found themselves rematerialising in the middle of space, for exactly this reason. Poor Marty....

The idea of a time machine that doesn't operate on a 4-vector is kind of pointless.

As far as my understanding goes, the idea behind making a craft with anti-gravity abilities is that it would be completely free from the effects of gravity. Allowing it to simply move or be moved through space under its own power, without pull from a planet or any other mass.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

To answer your question as simply as I can; We already have things that are anti-gravity (such as radio waves, light, or pretty much most types of energy), and they are not subject to be suddenly flung away from the earth at ludicrous speeds. This is primarily due to the fact that they are already in motion with their own trajectories, and since gravity can't affect them, the lack their of does not either. So suddenly taking gravity away from an object would not cause it to hurtle off. In fact, friction and other forces would probably prevent it from moving at all (relative to its surroundings once it has lost gravity).

All of the things you describe follow geodesics in spacetime, and all of those geodesics are in turn determined by the geometry of spacetime, or "Gravity". Radio and Light are also the same thing, EM spectrum radiation, which has the property of being composed of the quanta "Photon". A photon, unlike a person, is a massless particle following a timelike geodesic at a constant velocity.

 

[DefunctTheory]

Spoiler

Imagine a block of spacetime, with a large star in it.

Your image is borked, your argument is invalid! (jk, but I would like to see it)

Oops!

There, that should help.

Do you have anything to add or comment on for my later arguments/questions regarding deceleration and wind resistance?

Sure. As I said, you're not wrong, but you're also a very small object moving through a gas that behaves like a pretty dense fluid, the faster you try to move through it. You'd also be subject not just to friction against a static background, but friction from a GIANT mass of co-moving air, water, and dust we call an atmosphere. All of it, every particle of it, is whipping around along with the Earth. You would certainly eventually find your way out and away, but I can't even imagine how long it would take, and what might be left of you when you eventually left Earth's gravity well.

When I say a "long time" by the way, it could be on the order of thousands of years. After all, a speck of dust doesn't experience much gravitational influence from Earth, but it is dominated by other forces. While the speck IS very small with a large surface area compared to you or your ship, it's not that far from a speck of dust compared to the atmosphere.

An object on the surface of the earth that was suddenly no longer bound by gravitation would move towards the sky with a velocity of about 1.6 mm per second. Noticable, but not spectacular. It would just gently drift away, wind resistance doesn't Play a role at such low speeds.

I'm not so sure. As you say wind resistance doesn't play a role at such low speeds, but it will certainly dampen acceleration. In addition, you're going to have lateral momentum imparted by the relative motion of the atmosphere to you, which is pretty insignficant at first, but at altitude you start to experience serious winds. Since you have no weight, other forces are going to dominated, including even minute lift. With a good wind, you could in fact fly DOWN again. There is no reason to think that as a weightless speck with a GIANT surface area, you're going to have some easy trajectory.

Another thing: running an anti-gravitation engine would always consume more engergy than it would take to overcome gravitation conventionally. Otherwise we could just lift an object into the sky, then deactivate the engine and get potential energy out of nothing. That would contradict the 1st law of thermodynamics.

Yes, but it's important to remember that there could be hypothetical advantages, aside from an ability to run cheaply. That said, it would have to be hypothetical.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

It was this thinking that directly led to a moment of horror for me when I was thinking about time travel. Anyone who actually built something that could go back in time and tried it, would most likely have found themselves rematerialising in the middle of space, for exactly this reason. Poor Marty....

The idea of a time machine that doesn't operate on a 4-vector is kind of pointless.

As far as my understanding goes, the idea behind making a craft with anti-gravity abilities is that it would be completely free from the effects of gravity. Allowing it to simply move or be moved through space under its own power, without pull from a planet or any other mass.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

To answer your question as simply as I can; We already have things that are anti-gravity (such as radio waves, light, or pretty much most types of energy), and they are not subject to be suddenly flung away from the earth at ludicrous speeds. This is primarily due to the fact that they are already in motion with their own trajectories, and since gravity can't affect them, the lack their of does not either. So suddenly taking gravity away from an object would not cause it to hurtle off. In fact, friction and other forces would probably prevent it from moving at all (relative to its surroundings once it has lost gravity).

All of the things you describe follow geodesics in spacetime, and all of those geodesics are in turn determined by the geometry of spacetime, or "Gravity". Radio and Light are also the same thing, EM spectrum radiation, which has the property of being composed of the quanta "Photon". A photon, unlike a person, is a massless particle following a timelike geodesic at a constant velocity.

You seem to have a good handle on this stuff. More than me, anyway, who's basically a science cheerleader that tries to pay as much attention as he can. Here's a question for you.

It seems that through most of the thread, we've been making the assumption that the object that's having its gravity 'nullified' still has 'internal' gravity - Whatever field it's projecting affects it's attraction to foreign bodies only.

What would affect be if everything in the field was completely void of gravity? If each atom was no longer subjected to the force of other atoms? Gravity is, of course, a weak force - As has been mentioned previously in the thread, a mote of dust has negligible forces put on it by gravity. But what about an asteroid? Or a planet? Would nullifying gravity affect it's integrity?

It seems fairly obvious that under such conditions, something like a star, which is only held together by gravity, would explode, and planetary gas giants would as well, though less spectacularly. Would solid objects be subject to the same dispersion affects? Is it a matter of how massive the object is? Or would nothing change as long as no overwhelming force (Like nuclear fusion) is present?

Does any of that make sense?

 

[Thaluikhain]

You seem to have a good handle on this stuff. More than me, anyway, who's basically a science cheerleader that tries to pay as much attention as he can. Here's a question for you.

It seems that through most of the thread, we've been making the assumption that the object that's having its gravity 'nullified' still has 'internal' gravity - Whatever field it's projecting affects it's attraction to foreign bodies only.

What would affect be if everything in the field was completely void of gravity? If each atom was no longer subjected to the force of other atoms? Gravity is, of course, a weak force - As has been mentioned previously in the thread, a mote of dust has negligible forces put on it by gravity. But what about an asteroid? Or a planet? Would nullifying gravity affect it's integrity?

It seems fairly obvious that under such conditions, something like a star, which is only held together by gravity, would explode, and planetary gas giants would as well, though less spectacularly. Would solid objects be subject to the same dispersion affects? Is it a matter of how massive the object is? Or would nothing change as long as no overwhelming force (Like nuclear fusion) is present?

Does any of that make sense?

An interesting idea. In regards to the Earth, it isn't quite spherical because centrifugal force is pushing it outwards at the equator. Without gravity, internal spin would make it fly apart, yes.

A body that was not rotating at all...well, the moment that anything happened to impact it, it'd start dispersing.

EDIT: To clarify, without gravity, any turbulence on the planet will wobble things apart, any there's always turbulence. If nothing else, the solar winds with blow the planet out and away.

 

[one squirrel]

Another thing: running an anti-gravitation engine would always consume more engergy than it would take to overcome gravitation conventionally. Otherwise we could just lift an object into the sky, then deactivate the engine and get potential energy out of nothing. That would contradict the 1st law of thermodynamics.

An important point to remember, with the caveat that when you say "overcome gravitation conventionally" you mean at 100% efficiency (or close to it), which we don't have.

Should some anti-gravity machine be possible, it's feasible that it would require less energy than conventional methods in that it may be more efficient.

You're right of course, that's what I meant to say.

 

[Mr. Popplewick]

Spoiler

Imagine a block of spacetime, with a large star in it.

Your image is borked, your argument is invalid! (jk, but I would like to see it)

Oops!

There, that should help.

Do you have anything to add or comment on for my later arguments/questions regarding deceleration and wind resistance?

Sure. As I said, you're not wrong, but you're also a very small object moving through a gas that behaves like a pretty dense fluid, the faster you try to move through it. You'd also be subject not just to friction against a static background, but friction from a GIANT mass of co-moving air, water, and dust we call an atmosphere. All of it, every particle of it, is whipping around along with the Earth. You would certainly eventually find your way out and away, but I can't even imagine how long it would take, and what might be left of you when you eventually left Earth's gravity well.

When I say a "long time" by the way, it could be on the order of thousands of years. After all, a speck of dust doesn't experience much gravitational influence from Earth, but it is dominated by other forces. While the speck IS very small with a large surface area compared to you or your ship, it's not that far from a speck of dust compared to the atmosphere.

An object on the surface of the earth that was suddenly no longer bound by gravitation would move towards the sky with a velocity of about 1.6 mm per second. Noticable, but not spectacular. It would just gently drift away, wind resistance doesn't Play a role at such low speeds.

I'm not so sure. As you say wind resistance doesn't play a role at such low speeds, but it will certainly dampen acceleration. In addition, you're going to have lateral momentum imparted by the relative motion of the atmosphere to you, which is pretty insignficant at first, but at altitude you start to experience serious winds. Since you have no weight, other forces are going to dominated, including even minute lift. With a good wind, you could in fact fly DOWN again. There is no reason to think that as a weightless speck with a GIANT surface area, you're going to have some easy trajectory.

Another thing: running an anti-gravitation engine would always consume more engergy than it would take to overcome gravitation conventionally. Otherwise we could just lift an object into the sky, then deactivate the engine and get potential energy out of nothing. That would contradict the 1st law of thermodynamics.

Yes, but it's important to remember that there could be hypothetical advantages, aside from an ability to run cheaply. That said, it would have to be hypothetical.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

It was this thinking that directly led to a moment of horror for me when I was thinking about time travel. Anyone who actually built something that could go back in time and tried it, would most likely have found themselves rematerialising in the middle of space, for exactly this reason. Poor Marty....

The idea of a time machine that doesn't operate on a 4-vector is kind of pointless.

As far as my understanding goes, the idea behind making a craft with anti-gravity abilities is that it would be completely free from the effects of gravity. Allowing it to simply move or be moved through space under its own power, without pull from a planet or any other mass.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

To answer your question as simply as I can; We already have things that are anti-gravity (such as radio waves, light, or pretty much most types of energy), and they are not subject to be suddenly flung away from the earth at ludicrous speeds. This is primarily due to the fact that they are already in motion with their own trajectories, and since gravity can't affect them, the lack their of does not either. So suddenly taking gravity away from an object would not cause it to hurtle off. In fact, friction and other forces would probably prevent it from moving at all (relative to its surroundings once it has lost gravity).

All of the things you describe follow geodesics in spacetime, and all of those geodesics are in turn determined by the geometry of spacetime, or "Gravity". Radio and Light are also the same thing, EM spectrum radiation, which has the property of being composed of the quanta "Photon". A photon, unlike a person, is a massless particle following a timelike geodesic at a constant velocity.

You seem to have a good handle on this stuff. More than me, anyway, who's basically a science cheerleader that tries to pay as much attention as he can. Here's a question for you.

It seems that through most of the thread, we've been making the assumption that the object that's having its gravity 'nullified' still has 'internal' gravity - Whatever field it's projecting affects it's attraction to foreign bodies only.

Not so much, gravity is only a major factor when things get very massive. After all, you don't experience any Relativistic effects on Earth, and even an astronaut in orbit only experiences minute effects that might cumulatively mean that their clocks are microseconds slower. Certainly we don't worry about this terrible scenario...

When you get "small" relative to gravity, the forces that dominate are electromagnetic and intra/inter-molecular forces (like Van Der Walle forces). Your body is NOT held together by gravity, and something the size of a giant starship isn't either. In fact Gravity is so damned weak compared to other forces that a gecko can walk on the ceiling using VDW forces on the pads of its feet! A gecko, overcoming the gravity of an ENTIRE PLANET! Isn't that incredible? Flies do it too...

The problem as I described in my first post is that "free from gravity" sort of implies "free from spacetime". I'm not sure how to interpret that, but I bet it hurts when it happens.

What would affect be if everything in the field was completely void of gravity? If each atom was no longer subjected to the force of other atoms? Gravity is, of course, a weak force - As has been mentioned previously in the thread, a mote of dust has negligible forces put on it by gravity. But what about an asteroid? Or a planet? Would nullifying gravity affect it's integrity?

An asteroid isn't really just one thing, but I can't think of an asteroid that would just fly apart if it you switched off the force of gravity for for itself in some magical way. That said, some very large asteroids would definitely lose the layer regolith and rocky surface that many of them are presumed to have. Their major internal structure through, ranges from a molten lump of iron and nickel, to a mass of mostly carbon. Those are some STRONG inter-molecular forces there.

A planet though, now we have a problem. Dwarf planets, large moons, and planets and the like are the scale at which gravity is starting to dominate. A good rule of thumb to check if a given medium-large body is gravitationally bound or otherwise bound is to look at its shape[footnote]this doesn't work masses that are well below the limit, which might become spheroidal through erosion, impacts, or chance.[/footnote] and see if it's roughly some kind of spheroid. For a non-rotating body, a sphere is the ideal packing solution for a very large ensemble of "stuff" with mutual gravitational attraction. In reality, as I think you mention to another poster in another post, most things are spinning, and that causes the sphere to become oblate.

In that case you have a few things to consider (because nothing in space is simple). If the planet were just forming then yes, switching off gravity would disrupt that process, but we're billions of years past that time for most of the objects you're talking about. Given that, you have billions of years of compacting, vacuum cementing, and various other processes by which gravity may no longer be the big dog.

BUT... if it's massive enough, and spinning fast enough to be oblate, then turning off the gravity will cause it to basically shatter. There wouldn't be the tidal forces stretching it out as though it was a satellite passing its Roche Limit, it would just start to blast out chunks at the equator, wobble, then shatter. At the scale of a full sized planet, it would be devastating. After all, the Earth is just a pressure vessel held under gravity. There is a LOT of heat and energy bound up in the mantle and core, and that would basically turn the entire surface of the planet into a shattering volcano.

"Kaboom".

Even a planet with less mass than Earth is going to certainly have serious angular momentum, and therefore rotational velocity. Even if it's like Mars, it's going to break up and become an asteroid field. It won't be dust or powder or anything like that however. In essence though, when gravity stops holding together "stuff" bigger than asteroids, an asteroid field is what results. Without gravity causing the asteroids to tend to collide, it be an asteroid field flying apart at terrific relative velocities generated by the planet's previous angular momentum.

It seems fairly obvious that under such conditions, something like a star, which is only held together by gravity, would explode, and planetary gas giants would as well, though less spectacularly. Would solid objects be subject to the same dispersion affects? Is it a matter of how massive the object is? Or would nothing change as long as no overwhelming force (Like nuclear fusion) is present?

Does any of that make sense?

Yeah, the star as you correctly intuit, would make the exploding Earth look positively calm and collected. Stars are under so much pressure that their core isn't a nickel-iron eutectic, their core is fusing the heaviest elements a star is capable of creating (except in the moments of its death, if it was massive enough at the beginning). Not just that, but there is actually something called photon pressure, which is also held under gravity. In fact, a star like our Sol, which is by no means a giant, is so dense that it takes many thousands of years for a photon in the core to reach the surface. Without gravity, all of that pressure would suddenly, overwhelmingly dominate. Everything would be blowing apart from everything; it would be a giant plasma explosion.

Amazingly enough without the need to invoke magical anti-grav, something a bit like this might happen in the universe! There is something hypothesized called a 'Pair-Instability Supernova'. It's very exciting in my opinion, and without getting boring, it basically says that in some sufficiently massive stars the pressure and heat (read: energy) within them becomes so extreme that pair production[footnote]the production of matter-antimatter particle pairs, which then promptly annihilate[/footnote] begins to drop the internal pressure of the star rapidly and catastrophically. Essentially, the energy that would normally be "floating" as a soup of photons is "pressed together" to form matter and antimatter pairs of particles. They annihilate and release energy, but remember the equation: E=MC SQUARED. That's a lot of energy for a little mass. Each of these pair-production events is a bit like a bubble in boiling water, in that it causes a local drop in pressure, and subsequent implosion.

So, that happens on a massive scale across the star's interior, and it contracts. VERY VERY QUICKLY. In fact, so quickly that it initiates runaway fusion of Oxygen in the core, and blows the whole star apart, leaving NO HYPERDENSE REMNANT! A star that would otherwise certainly have undergone a supernova and formed a black hole just leaves an expanding, glowing, radioactive debris cloud.

Oh did I mention that these stars are about 150-250 times the mass of our Sol?[footnote]Not the only requirement, but one of them.[/footnote]

 

[DefunctTheory]

Spoiler

Spoiler

Imagine a block of spacetime, with a large star in it.

Your image is borked, your argument is invalid! (jk, but I would like to see it)

Oops!

There, that should help.

Do you have anything to add or comment on for my later arguments/questions regarding deceleration and wind resistance?

Sure. As I said, you're not wrong, but you're also a very small object moving through a gas that behaves like a pretty dense fluid, the faster you try to move through it. You'd also be subject not just to friction against a static background, but friction from a GIANT mass of co-moving air, water, and dust we call an atmosphere. All of it, every particle of it, is whipping around along with the Earth. You would certainly eventually find your way out and away, but I can't even imagine how long it would take, and what might be left of you when you eventually left Earth's gravity well.

When I say a "long time" by the way, it could be on the order of thousands of years. After all, a speck of dust doesn't experience much gravitational influence from Earth, but it is dominated by other forces. While the speck IS very small with a large surface area compared to you or your ship, it's not that far from a speck of dust compared to the atmosphere.

An object on the surface of the earth that was suddenly no longer bound by gravitation would move towards the sky with a velocity of about 1.6 mm per second. Noticable, but not spectacular. It would just gently drift away, wind resistance doesn't Play a role at such low speeds.

I'm not so sure. As you say wind resistance doesn't play a role at such low speeds, but it will certainly dampen acceleration. In addition, you're going to have lateral momentum imparted by the relative motion of the atmosphere to you, which is pretty insignficant at first, but at altitude you start to experience serious winds. Since you have no weight, other forces are going to dominated, including even minute lift. With a good wind, you could in fact fly DOWN again. There is no reason to think that as a weightless speck with a GIANT surface area, you're going to have some easy trajectory.

Another thing: running an anti-gravitation engine would always consume more engergy than it would take to overcome gravitation conventionally. Otherwise we could just lift an object into the sky, then deactivate the engine and get potential energy out of nothing. That would contradict the 1st law of thermodynamics.

Yes, but it's important to remember that there could be hypothetical advantages, aside from an ability to run cheaply. That said, it would have to be hypothetical.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

It was this thinking that directly led to a moment of horror for me when I was thinking about time travel. Anyone who actually built something that could go back in time and tried it, would most likely have found themselves rematerialising in the middle of space, for exactly this reason. Poor Marty....

The idea of a time machine that doesn't operate on a 4-vector is kind of pointless.

As far as my understanding goes, the idea behind making a craft with anti-gravity abilities is that it would be completely free from the effects of gravity. Allowing it to simply move or be moved through space under its own power, without pull from a planet or any other mass.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

To answer your question as simply as I can; We already have things that are anti-gravity (such as radio waves, light, or pretty much most types of energy), and they are not subject to be suddenly flung away from the earth at ludicrous speeds. This is primarily due to the fact that they are already in motion with their own trajectories, and since gravity can't affect them, the lack their of does not either. So suddenly taking gravity away from an object would not cause it to hurtle off. In fact, friction and other forces would probably prevent it from moving at all (relative to its surroundings once it has lost gravity).

All of the things you describe follow geodesics in spacetime, and all of those geodesics are in turn determined by the geometry of spacetime, or "Gravity". Radio and Light are also the same thing, EM spectrum radiation, which has the property of being composed of the quanta "Photon". A photon, unlike a person, is a massless particle following a timelike geodesic at a constant velocity.

You seem to have a good handle on this stuff. More than me, anyway, who's basically a science cheerleader that tries to pay as much attention as he can. Here's a question for you.

It seems that through most of the thread, we've been making the assumption that the object that's having its gravity 'nullified' still has 'internal' gravity - Whatever field it's projecting affects it's attraction to foreign bodies only.

Not so much, gravity is only a major factor when things get very massive. After all, you don't experience any Relativistic effects on Earth, and even an astronaut in orbit only experiences minute effects that might cumulatively mean that their clocks are microseconds slower. Certainly we don't worry about this terrible scenario...

When you get "small" relative to gravity, the forces that dominate are electromagnetic and intra/inter-molecular forces (like Van Der Walle forces). Your body is NOT held together by gravity, and something the size of a giant starship isn't either. In fact Gravity is so damned weak compared to other forces that a gecko can walk on the ceiling using VDW forces on the pads of its feet! A gecko, overcoming the gravity of an ENTIRE PLANET! Isn't that incredible? Flies do it too...

The problem as I described in my first post is that "free from gravity" sort of implies "free from spacetime". I'm not sure how to interpret that, but I bet it hurts when it happens.

What would affect be if everything in the field was completely void of gravity? If each atom was no longer subjected to the force of other atoms? Gravity is, of course, a weak force - As has been mentioned previously in the thread, a mote of dust has negligible forces put on it by gravity. But what about an asteroid? Or a planet? Would nullifying gravity affect it's integrity?

An asteroid isn't really just one thing, but I can't think of an asteroid that would just fly apart if it you switched off the force of gravity for for itself in some magical way. That said, some very large asteroids would definitely lose the layer regolith and rocky surface that many of them are presumed to have. Their major internal structure through, ranges from a molten lump of iron and nickel, to a mass of mostly carbon. Those are some STRONG inter-molecular forces there.

A planet though, now we have a problem. Dwarf planets, large moons, and planets and the like are the scale at which gravity is starting to dominate. A good rule of thumb to check if a given medium-large body is gravitationally bound or otherwise bound is to look at its shape[footnote]this doesn't work masses that are well below the limit, which might become spheroidal through erosion, impacts, or chance.[/footnote] and see if it's roughly some kind of spheroid. For a non-rotating body, a sphere is the ideal packing solution for a very large ensemble of "stuff" with mutual gravitational attraction. In reality, as I think you mention to another poster in another post, most things are spinning, and that causes the sphere to become oblate.

In that case you have a few things to consider (because nothing in space is simple). If the planet were just forming then yes, switching off gravity would disrupt that process, but we're billions of years past that time for most of the objects you're talking about. Given that, you have billions of years of compacting, vacuum cementing, and various other processes by which gravity may no longer be the big dog.

BUT... if it's massive enough, and spinning fast enough to be oblate, then turning off the gravity will cause it to basically shatter. There wouldn't be the tidal forces stretching it out as though it was a satellite passing its Roche Limit, it would just start to blast out chunks at the equator, wobble, then shatter. At the scale of a full sized planet, it would be devastating. After all, the Earth is just a pressure vessel held under gravity. There is a LOT of heat and energy bound up in the mantle and core, and that would basically turn the entire surface of the planet into a shattering volcano.

"Kaboom".

Even a planet with less mass than Earth is going to certainly have serious angular momentum, and therefore rotational velocity. Even if it's like Mars, it's going to break up and become an asteroid field. It won't be dust or powder or anything like that however. In essence though, when gravity stops holding together "stuff" bigger than asteroids, an asteroid field is what results. Without gravity causing the asteroids to tend to collide, it be an asteroid field flying apart at terrific relative velocities generated by the planet's previous angular momentum.

It seems fairly obvious that under such conditions, something like a star, which is only held together by gravity, would explode, and planetary gas giants would as well, though less spectacularly. Would solid objects be subject to the same dispersion affects? Is it a matter of how massive the object is? Or would nothing change as long as no overwhelming force (Like nuclear fusion) is present?

Does any of that make sense?

Yeah, the star as you correctly intuit, would make the exploding Earth look positively calm and collected. Stars are under so much pressure that their core isn't a nickel-iron eutectic, their core is fusing the heaviest elements a star is capable of creating (except in the moments of its death, if it was massive enough at the beginning). Not just that, but there is actually something called photon pressure, which is also held under gravity. In fact, a star like our Sol, which is by no means a giant, is so dense that it takes many thousands of years for a photon in the core to reach the surface. Without gravity, all of that pressure would suddenly, overwhelmingly dominate. Everything would be blowing apart from everything; it would be a giant plasma explosion.

Amazingly enough without the need to invoke magical anti-grav, something a bit like this might happen in the universe! There is something hypothesized called a 'Pair-Instability Supernova'. It's very exciting in my opinion, and without getting boring, it basically says that in some sufficiently massive stars the pressure and heat (read: energy) within them becomes so extreme that pair production[footnote]the production of matter-antimatter particle pairs, which then promptly annihilate[/footnote] begins to drop the internal pressure of the star rapidly and catastrophically. Essentially, the energy that would normally be "floating" as a soup of photons is "pressed together" to form matter and antimatter pairs of particles. They annihilate and release energy, but remember the equation: E=MC SQUARED. That's a lot of energy for a little mass. Each of these pair-production events is a bit like a bubble in boiling water, in that it causes a local drop in pressure, and subsequent implosion.

So, that happens on a massive scale across the star's interior, and it contracts. VERY VERY QUICKLY. In fact, so quickly that it initiates runaway fusion of Oxygen in the core, and blows the whole star apart, leaving NO HYPERDENSE REMNANT! A star that would otherwise certainly have undergone a supernova and formed a black hole just leaves an expanding, glowing, radioactive debris cloud.

Oh did I mention that these stars are about 150-250 times the mass of our Sol?[footnote]Not the only requirement, but one of them.[/footnote]

Damn physics, you scary.

Thanks for the write up. Appreciate the kid friendly physics explanation. Wish I had the mathematical aptitude to delve deeper.

 

[Mr. Popplewick]

Spoiler

Spoiler

Imagine a block of spacetime, with a large star in it.

Your image is borked, your argument is invalid! (jk, but I would like to see it)

Oops!

There, that should help.

Do you have anything to add or comment on for my later arguments/questions regarding deceleration and wind resistance?

Sure. As I said, you're not wrong, but you're also a very small object moving through a gas that behaves like a pretty dense fluid, the faster you try to move through it. You'd also be subject not just to friction against a static background, but friction from a GIANT mass of co-moving air, water, and dust we call an atmosphere. All of it, every particle of it, is whipping around along with the Earth. You would certainly eventually find your way out and away, but I can't even imagine how long it would take, and what might be left of you when you eventually left Earth's gravity well.

When I say a "long time" by the way, it could be on the order of thousands of years. After all, a speck of dust doesn't experience much gravitational influence from Earth, but it is dominated by other forces. While the speck IS very small with a large surface area compared to you or your ship, it's not that far from a speck of dust compared to the atmosphere.

An object on the surface of the earth that was suddenly no longer bound by gravitation would move towards the sky with a velocity of about 1.6 mm per second. Noticable, but not spectacular. It would just gently drift away, wind resistance doesn't Play a role at such low speeds.

I'm not so sure. As you say wind resistance doesn't play a role at such low speeds, but it will certainly dampen acceleration. In addition, you're going to have lateral momentum imparted by the relative motion of the atmosphere to you, which is pretty insignficant at first, but at altitude you start to experience serious winds. Since you have no weight, other forces are going to dominated, including even minute lift. With a good wind, you could in fact fly DOWN again. There is no reason to think that as a weightless speck with a GIANT surface area, you're going to have some easy trajectory.

Another thing: running an anti-gravitation engine would always consume more engergy than it would take to overcome gravitation conventionally. Otherwise we could just lift an object into the sky, then deactivate the engine and get potential energy out of nothing. That would contradict the 1st law of thermodynamics.

Yes, but it's important to remember that there could be hypothetical advantages, aside from an ability to run cheaply. That said, it would have to be hypothetical.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

It was this thinking that directly led to a moment of horror for me when I was thinking about time travel. Anyone who actually built something that could go back in time and tried it, would most likely have found themselves rematerialising in the middle of space, for exactly this reason. Poor Marty....

The idea of a time machine that doesn't operate on a 4-vector is kind of pointless.

As far as my understanding goes, the idea behind making a craft with anti-gravity abilities is that it would be completely free from the effects of gravity. Allowing it to simply move or be moved through space under its own power, without pull from a planet or any other mass.

Now, the Earth moves through space at about 67,000 miles per hour and rotates at about 1,000 miles per hour.

So, assuming my understanding of what anti-gravity is supposed to be, wouldn't anything that was suddenly free from the effects of gravity go hurtling away from us? Or, depending on what side of the Earth it was on at activation, slam into the ground?

To answer your question as simply as I can; We already have things that are anti-gravity (such as radio waves, light, or pretty much most types of energy), and they are not subject to be suddenly flung away from the earth at ludicrous speeds. This is primarily due to the fact that they are already in motion with their own trajectories, and since gravity can't affect them, the lack their of does not either. So suddenly taking gravity away from an object would not cause it to hurtle off. In fact, friction and other forces would probably prevent it from moving at all (relative to its surroundings once it has lost gravity).

All of the things you describe follow geodesics in spacetime, and all of those geodesics are in turn determined by the geometry of spacetime, or "Gravity". Radio and Light are also the same thing, EM spectrum radiation, which has the property of being composed of the quanta "Photon". A photon, unlike a person, is a massless particle following a timelike geodesic at a constant velocity.

You seem to have a good handle on this stuff. More than me, anyway, who's basically a science cheerleader that tries to pay as much attention as he can. Here's a question for you.

It seems that through most of the thread, we've been making the assumption that the object that's having its gravity 'nullified' still has 'internal' gravity - Whatever field it's projecting affects it's attraction to foreign bodies only.

Not so much, gravity is only a major factor when things get very massive. After all, you don't experience any Relativistic effects on Earth, and even an astronaut in orbit only experiences minute effects that might cumulatively mean that their clocks are microseconds slower. Certainly we don't worry about this terrible scenario...

When you get "small" relative to gravity, the forces that dominate are electromagnetic and intra/inter-molecular forces (like Van Der Walle forces). Your body is NOT held together by gravity, and something the size of a giant starship isn't either. In fact Gravity is so damned weak compared to other forces that a gecko can walk on the ceiling using VDW forces on the pads of its feet! A gecko, overcoming the gravity of an ENTIRE PLANET! Isn't that incredible? Flies do it too...

The problem as I described in my first post is that "free from gravity" sort of implies "free from spacetime". I'm not sure how to interpret that, but I bet it hurts when it happens.

What would affect be if everything in the field was completely void of gravity? If each atom was no longer subjected to the force of other atoms? Gravity is, of course, a weak force - As has been mentioned previously in the thread, a mote of dust has negligible forces put on it by gravity. But what about an asteroid? Or a planet? Would nullifying gravity affect it's integrity?

An asteroid isn't really just one thing, but I can't think of an asteroid that would just fly apart if it you switched off the force of gravity for for itself in some magical way. That said, some very large asteroids would definitely lose the layer regolith and rocky surface that many of them are presumed to have. Their major internal structure through, ranges from a molten lump of iron and nickel, to a mass of mostly carbon. Those are some STRONG inter-molecular forces there.

A planet though, now we have a problem. Dwarf planets, large moons, and planets and the like are the scale at which gravity is starting to dominate. A good rule of thumb to check if a given medium-large body is gravitationally bound or otherwise bound is to look at its shape[footnote]this doesn't work masses that are well below the limit, which might become spheroidal through erosion, impacts, or chance.[/footnote] and see if it's roughly some kind of spheroid. For a non-rotating body, a sphere is the ideal packing solution for a very large ensemble of "stuff" with mutual gravitational attraction. In reality, as I think you mention to another poster in another post, most things are spinning, and that causes the sphere to become oblate.

In that case you have a few things to consider (because nothing in space is simple). If the planet were just forming then yes, switching off gravity would disrupt that process, but we're billions of years past that time for most of the objects you're talking about. Given that, you have billions of years of compacting, vacuum cementing, and various other processes by which gravity may no longer be the big dog.

BUT... if it's massive enough, and spinning fast enough to be oblate, then turning off the gravity will cause it to basically shatter. There wouldn't be the tidal forces stretching it out as though it was a satellite passing its Roche Limit, it would just start to blast out chunks at the equator, wobble, then shatter. At the scale of a full sized planet, it would be devastating. After all, the Earth is just a pressure vessel held under gravity. There is a LOT of heat and energy bound up in the mantle and core, and that would basically turn the entire surface of the planet into a shattering volcano.

"Kaboom".

Even a planet with less mass than Earth is going to certainly have serious angular momentum, and therefore rotational velocity. Even if it's like Mars, it's going to break up and become an asteroid field. It won't be dust or powder or anything like that however. In essence though, when gravity stops holding together "stuff" bigger than asteroids, an asteroid field is what results. Without gravity causing the asteroids to tend to collide, it be an asteroid field flying apart at terrific relative velocities generated by the planet's previous angular momentum.

It seems fairly obvious that under such conditions, something like a star, which is only held together by gravity, would explode, and planetary gas giants would as well, though less spectacularly. Would solid objects be subject to the same dispersion affects? Is it a matter of how massive the object is? Or would nothing change as long as no overwhelming force (Like nuclear fusion) is present?

Does any of that make sense?

Yeah, the star as you correctly intuit, would make the exploding Earth look positively calm and collected. Stars are under so much pressure that their core isn't a nickel-iron eutectic, their core is fusing the heaviest elements a star is capable of creating (except in the moments of its death, if it was massive enough at the beginning). Not just that, but there is actually something called photon pressure, which is also held under gravity. In fact, a star like our Sol, which is by no means a giant, is so dense that it takes many thousands of years for a photon in the core to reach the surface. Without gravity, all of that pressure would suddenly, overwhelmingly dominate. Everything would be blowing apart from everything; it would be a giant plasma explosion.

Amazingly enough without the need to invoke magical anti-grav, something a bit like this might happen in the universe! There is something hypothesized called a 'Pair-Instability Supernova'. It's very exciting in my opinion, and without getting boring, it basically says that in some sufficiently massive stars the pressure and heat (read: energy) within them becomes so extreme that pair production[footnote]the production of matter-antimatter particle pairs, which then promptly annihilate[/footnote] begins to drop the internal pressure of the star rapidly and catastrophically. Essentially, the energy that would normally be "floating" as a soup of photons is "pressed together" to form matter and antimatter pairs of particles. They annihilate and release energy, but remember the equation: E=MC SQUARED. That's a lot of energy for a little mass. Each of these pair-production events is a bit like a bubble in boiling water, in that it causes a local drop in pressure, and subsequent implosion.

So, that happens on a massive scale across the star's interior, and it contracts. VERY VERY QUICKLY. In fact, so quickly that it initiates runaway fusion of Oxygen in the core, and blows the whole star apart, leaving NO HYPERDENSE REMNANT! A star that would otherwise certainly have undergone a supernova and formed a black hole just leaves an expanding, glowing, radioactive debris cloud.

Oh did I mention that these stars are about 150-250 times the mass of our Sol?[footnote]Not the only requirement, but one of them.[/footnote]

Damn physics, you scary.

Thanks for the write up. Appreciate the kid friendly physics explanation. Wish I had the mathematical aptitude to delve deeper.

It's probably not as bad as you'd expect, as long as you're not trying to use it as part of your job. A lot of the math for SR/GR is math that most of us would recognize, just with the addition of a lot of Greek letters and much more of it.

If you want to get some mileage out of learning without the math, or with some skilled help, I'd suggest www.physicsforums.com
They're a great community, very well and thoroughly moderated, and you can ask questions like the ones here to your heart's content, and go deeper as well.

 

[K12]

Inertial force wouldn't keep you on the Earth if it was possible to suddenly switch off the effects of gravity for some object because forces act in a straight line. So yes you'd keep travelling at the horizontal speed you were already travelling due to the rotation of the Earth but.

That would probably because there isn't an "inertial force", inertia is momentum.

It wouldn't be the same as suddenly shooting up into the air, instead you'd gradually drift upwards you continue off at a tangent to the Earth's motion, essentially the Earth would have rotated out from under you. I'd expect the local effects of wind and friction to make a big difference to this though so it's hard to say... and you almost certainly couldn't make something that's anti-gravity anyway.

Probably, if not for drag. If negating gravity removes the concept of mass entirely, rather than making one neutrally bouyant, they'd move away, and at speed. But then the object would have to be both not subject to gravity, and the surrounds would have to be to have bouyancy. Which isn't exactly realistic either.

If only everything was a spherical object in a vaccuum not subject to gravity!

The idea of something having no gravity is so outside the way that the universe works that we can only really guess at how an object with "zero gravity" or "anti-gravity" would work at all. Inertia isn't a force... but then neither is gravity. Statements that are informative but technically inaccurate can be very useful sometimes.

 

[Cap'nPipsqueak]

I'm fully anti-gravity. Shit be holdin' me down an' preventin' me from takin' to the sky...

I'm having a rally tonight; anyone want in?

 

[barbzilla]

Inertial force wouldn't keep you on the Earth if it was possible to suddenly switch off the effects of gravity for some object because forces act in a straight line. So yes you'd keep travelling at the horizontal speed you were already travelling due to the rotation of the Earth but.

That would probably because there isn't an "inertial force", inertia is momentum.

It wouldn't be the same as suddenly shooting up into the air, instead you'd gradually drift upwards you continue off at a tangent to the Earth's motion, essentially the Earth would have rotated out from under you. I'd expect the local effects of wind and friction to make a big difference to this though so it's hard to say... and you almost certainly couldn't make something that's anti-gravity anyway.

Probably, if not for drag. If negating gravity removes the concept of mass entirely, rather than making one neutrally bouyant, they'd move away, and at speed. But then the object would have to be both not subject to gravity, and the surrounds would have to be to have bouyancy. Which isn't exactly realistic either.

If only everything was a spherical object in a vaccuum not subject to gravity!

The idea of something having no gravity is so outside the way that the universe works that we can only really guess at how an object with "zero gravity" or "anti-gravity" would work at all. Inertia isn't a force... but then neither is gravity. Statements that are informative but technically inaccurate can be very useful sometimes.

It isn't that outlandish. Photons are particles and yet they are not affected by gravity, this is primarily due to the higgs field though (at least that is what we believe, it is still being tested further). To get the best idea of how something would act without gravity, imagine that object as pure energy and you will have a fair understanding of the forces at work.