Antigravity existtence demonstration?

[jumpjack]

Let's suppose "antigravity" does exist: how could we "detect" it or demonstrate it exists?!?

I was thinking about two well known formulas:
F= KqQ/r^2
F= GmM/r^2

First one is electrical attraction, second one is gravitational force.
You of course see two formulas are identical, apart from K and Q.
But what they represent appears not to be identical: we know positive and negative electrical charges do exist. We know positive "gravitational charges" do exist: they're commonly named... bodies!
Ok, where are "negative gavitational charges"???
If they exist, how could we detect them?

As same-sign gravitational charges, unlike electrical ones, cause attraction, it comes to mind that probably different-sign ones would reject one from the other; so, during solar system formation, all positive masses got "grouped" into planets and satellites... but they "rejected" negative masses away: no negative mass can stay close to a positive mass due to "gravitational repulsion".
So, where did they end?!?
How do "negative planets" react to light? Can they be seen?
If a black hole attracts light... does a "negative black hole" reject it?!? Does this make it visible to telescopes?!?

I think that "negative masses" could explain universe expansion quite better than imagining "dark matter", "dark energy": just calling "dark" something you are not able to see or to demonstrate that is existing is not a good scientific approach, IMHO.

[Mister Earl]

I submit that antigravity doesn't exist, on the basis that if gravity comes from "bodies", then the "antibodies" in my bloodstream should have launched me into space.

Ok, ok, bad joke :P
It's boring where I am right now

[Tim Thompson]

I think that "negative masses" could explain universe expansion quite better than imagining "dark matter", "dark energy": just calling "dark" something you are not able to see or to demonstrate that is existing is not a good scientific approach, IMHO.

Actually, it is a perfectly good, and really necessary scientific approach to do just that. It would not be a good scientific approach to stop there, and pretend you know what something is just because you gave it a name. But neither "science" nor scientists do that.

I think "negative masses" are an inferior explanation to "dark energy". By simply adding a repulsive term into the appropriate equations from general relativity, we can easily model dark energy, either as a consequence of a cosmological constant, or as an additional scalar field. When we do that we are able to generate a theory which agrees with observation, and we do not at the same time create any serious physical problems or conflicts. Dark energy is a perfectly reasonable, practical explanation for accelerated expansion, which is in turn a perfectly reasonable, practical interpretation of observation.

Another reasonable alternative is modification of general relativity to slightly change the law of gravity. We know from experience that this does not work as well as the usual dark energy explanation, so it is not as popular an idea. Still, there are quite a few scientists working along those lines.

There is no direct, close to hand, laboratory verification for either dark energy or modified gravity, or negative mass. In fact, negative mass is the one choice most strongly disfavored by observation. Everywhere we look we see only positive masses, and no sign of even the tiniest piece of negative mass. Now if you assume that the negative mass comes only as a sparse background of atomic or sub-atomic size particles spread evenly through space, than you are describing dark energy. And you have the disadvantage of postulating a new kind of matter that is remarkably different from ordinary matter, in more than simply being "negative". That is a much bigger deal then simple dark energy, and so rather less likely to be a good idea.

[Chris Hillman]

Ok, where are "negative gavitational charges"???
If they exist, how could we detect them?
...
I think that "negative masses" could explain universe expansion quite better than imagining "dark matter"

Ditto Tim, plus this:

One obvious problem with negative gravitational charges is this:

Consider Newtonian dynamics with Newtonian gravitation. Assume (as physicists usually do) that inertial mass (the "mass" which appears in Newton's laws of motion) and gravitational mass (the "mass" which appears in his gravitational force law) are the same thing. Now consider a gravitating system consisting of a pair of positive and negative mass objects with masses m,-m. Show that the midpoint of a line segment drawn between the two objects accelerates without bound wrt any inertial observer, along the line drawn between the two objects, with the negative mass object chasing its positive mass partner. (Hint: if you push leftward on an object with negative inertial mass, it accelerates rightward.) This is generally agreed to physically be implausible.

Similar remarks hold for relativistic gravition theories, except that now constant acceleration of the midpoint of the system behaves like a Rindler observer in Minkowski space. If there were pairs of subatomic particles with m,-m accelerating like Rindler observers zipping about our universe, we'd almost certainly have noticed them by now!

[jumpjack]

Show that the midpoint of a line segment drawn between the two objects accelerates without bound wrt any inertial observer, along the line drawn between the two objects, with the negative mass object chasing its positive mass partner.

my english is too poor to understand this sentence...
Should I explain/show how the midpoint among two bodies accelerates.... what..?

[frankuitaalst]

Ditto Tim, plus this:

One obvious problem with negative gravitational charges is this:

Consider Newtonian dynamics with Newtonian gravitation. Assume (as physicists usually do) that inertial mass (the "mass" which appears in Newton's laws of motion) and gravitational mass (the "mass" which appears in his gravitational force law) are the same thing. Now consider a gravitating system consisting of a pair of positive and negative mass objects with masses m,-m. Show that the midpoint of a line segment drawn between the two objects accelerates without bound wrt any inertial observer, along the line drawn between the two objects, with the negative mass object chasing its positive mass partner. (Hint: if you push leftward on an object with negative inertial mass, it accelerates rightward.) This is generally agreed to physically be implausible.

Similar remarks hold for relativistic gravition theories, except that now constant acceleration of the midpoint of the system behaves like a Rindler observer in Minkowski space. If there were pairs of subatomic particles with m,-m accelerating like Rindler observers zipping about our universe, we'd almost certainly have noticed them by now!

Negatives masses indeed violate the equivalence principle .
The acceleration of a body is in general given by : m*a = GM*m/rē , where m can be eliminated . So regardless of the sign of the mass any mass is attracted by a positive mass and any mass is driven away by a negative mass . Also negative masses are repelling each other .
Applying a force to a negative mass in order to make it move would generate energy ! this is implausible ias is quoted .
Another point of view may be considering repelling masses instead of negative masses. This means considering masses which have the hypothetical property to repell each other instead of attracting in a gravitional field .
The resulting action may be the following :
Two Rmasses attract , two normal masses attract , a Rmass and a normal mass may repell . This seems to be what has been meant in the head of this thread . The repelling feature of such a mass is then not anymore linked to the mass itself but becomes then a feature of this mass , the feature being repelling or attracting . Then some analogy with the "charge" of ions is given .

[jumpjack]

Also negative masses are repelling each other

Why?!?
Same "sign" mass, as we know, does attract, not repell! (unlike electrical charges, which have opposite behaviour).

Applying a force to a negative mass in order to make it move would generate energy !

This is interesting. How do we "applyia force to a negative mass"? Using another negative mass to physically push (not "repell") the negative mass? (i.e., touch a nm with a nm) Or using gravity field of a negative mass to attract the negative mass?

What is the formula which "states" that applying force to negative mass results in producing energy?

Two Rmasses attract , two normal masses attract , a Rmass and a normal mass may repell . This seems to be what has been meant in the head of this thread . The repelling feature of such a mass is then not anymore linked to the mass itself but becomes then a feature of this mass , the feature being repelling or attracting . Then some analogy with the "charge" of ions is given .

That's what just what I was supposing from the beginning: same-sign masses attract, different-sign masses repell. Else, why would have I quoted the Gravitational and Elctric force formulas?!?

[frankuitaalst]

Why?!?
Same "sign" mass, as we know, does attract, not repell! (unlike electrical charges, which have opposite behaviour).


This is interesting. How do we "applyia force to a negative mass"? Using another negative mass to physically push (not "repell") the negative mass? (i.e., touch a nm with a nm) Or using gravity field of a negative mass to attract the negative mass?

What is the formula which "states" that applying force to negative mass results in producing energy?

That's what just what I was supposing from the beginning: same-sign masses attract, different-sign masses repell. Else, why would have I quoted the Gravitational and Elctric force formulas?!?

Well , you can write down the formulas you wrote : F = GmM/rē and : F=m*a , where a is the acceleration due to gravity in this case.
If you apply the formulae for the 4 possible cases : positive massae, negative masses and positive+negative masses , you'll see what direction ( acceleration ) the masses get .
Work done by a force is F.ds , where ds is the displacement which is function of the acceleration .
ds turns out to be negative for negative masses as the acceleration will be negative and therfore the energy will be negative .

[jumpjack]

Well , you can write down the formulas you wrote : F = GmM/rē and : F=m*a , where a is the acceleration due to gravity in this case.
If you apply the formulae for the 4 possible cases : positive massae, negative masses and positive+negative masses , you'll see what direction ( acceleration ) the masses get .
Work done by a force is F.ds , where ds is the displacement which is function of the acceleration .
ds turns out to be negative for negative masses as the acceleration will be negative and therfore the energy will be negative .

Sorry, I can't get the point: how can negative displacement lead to negative energy? Which formula are you referring to to calculate energy?
E = 0.5 mv^2 (classical)
E = p^2*c^2 +m0^2*c^4 (high speeds)

E = F*ds requires an absolute value for ds, else my car would produce energy when moving backward!

[Chris Hillman]

In the thought experiment I mentioned, we have two objects with masses m,-m in an otherwise empty universe. Newton's gravitational law says they repell each other. But Newton's law of motion says that when you push rightwards on an object with negative mass, it moves leftwards. For this reason, the object with mass m moves away from the object with mass -m (since it is being repelled), but the object with mass -m moves in the same direction with the same acceleration. Thus, the pair maintain constant distance and accelerate as a system wrt any inertial observer, with constant acceleration, indefinitely. Thus after finite time they achieve any given desired velocity wrt any given inertial observer!

That is a Newtonian thought experiment, so something similar must happen in any gravitation theory which has a Newtonian limit.

[jumpjack]

In the thought experiment I mentioned, we have two objects with masses m,-m in an otherwise empty universe. Newton's gravitational law says they repell each other. But Newton's law of motion says that when you push rightwards on an object with negative mass, it moves leftwards. For this reason, the object with mass m moves away from the object with mass -m (since it is being repelled), but the object with mass -m moves in the same direction with the same acceleration. Thus, the pair maintain constant distance and accelerate as a system wrt any inertial observer, with constant acceleration, indefinitely. Thus after finite time they achieve any given desired velocity wrt any given inertial observer!

Weird.

So I have two bodies which repell each other but which can't get away one from the other!

[mugaliens]

Let's suppose "antigravity" does exist: how could we "detect" it or demonstrate it exists?!?

If you were to build a small platform and fly around the room, down the hall, out the front door, around the house, and in through the back door, and hover over a single spot of my choosing for a while as I check some things out...

...I think that would be a sufficient demonstration.

[mugaliens]

Newton's gravitational law says they repell each other. But Newton's law of motion says that when you push rightwards on an object with negative mass, it moves leftwards. For this reason, the object with mass m moves away from the object with mass -m (since it is being repelled), but the object with mass -m moves in the same direction with the same acceleration. Thus, the pair maintain constant distance and accelerate as a system wrt any inertial observer, with constant acceleration, indefinitely.

No.

You're confusing the rightwards physical push (which would move it leftwards) with a rightwards gravitational repulsion (which isn't a push at all, but a warping of space-time).

[Chris Hillman]

So I have two bodies which repell each other but which can't get away one from the other!

Just so. In your diagram, let's say that the red body has mass m and the cyan body has mass -m, where m > 0. The gravitational force on both is repulsive (from Newton's law of gravitation), so the red body moves left. But the cyan body also moves left because (by Newton's law of motion) a rightward force is acting on it. Indeed, the cyan and and red bodies move left with the same (constant) acceleration, so the midpoint of this two-body system accelerates with constant leftward acceleration.

Remember, this argument depends upon the assumption that inertial and gravitational mass are always the same. (Exercise: rework things assuming that an object with negative gravitational mass -m still has positive inertial mass m > 0.) Also recall that it is nonrelativistic. But by what I said, you should expect something similar to happen in gtr (and it does).

You're confusing the rightwards physical push (which would move it leftwards) with a rightwards gravitational repulsion (which isn't a push at all, but a warping of space-time).

You didn't read what I wrote with sufficient care; try again.

[robheus]

Let's suppose "antigravity" does exist: how could we "detect" it or demonstrate it exists?!?

I was thinking about two well known formulas:
F= KqQ/r^2
F= GmM/r^2

First one is electrical attraction, second one is gravitational force.
You of course see two formulas are identical, apart from K and Q.
But what they represent appears not to be identical: we know positive and negative electrical charges do exist. We know positive "gravitational charges" do exist: they're commonly named... bodies!
Ok, where are "negative gavitational charges"???
If they exist, how could we detect them?

As same-sign gravitational charges, unlike electrical ones, cause attraction, it comes to mind that probably different-sign ones would reject one from the other; so, during solar system formation, all positive masses got "grouped" into planets and satellites... but they "rejected" negative masses away: no negative mass can stay close to a positive mass due to "gravitational repulsion".
So, where did they end?!?
How do "negative planets" react to light? Can they be seen?
If a black hole attracts light... does a "negative black hole" reject it?!? Does this make it visible to telescopes?!?

I think that "negative masses" could explain universe expansion quite better than imagining "dark matter", "dark energy": just calling "dark" something you are not able to see or to demonstrate that is existing is not a good scientific approach, IMHO.

I guess you are referring to the term "negative mass" which is entirely a hypothetical concept, and is deemed "non-physical"
Yet, at the basis of GR we can see as negative masses as a possible solution to the GR equations.

How would negative mass interact with normal positive mass:

• A negative mass in a gravity field of a (larger) positive mass would not be repelled (as might be thought) but will be attracked by the positive mass. This is because a negative mass will accelerate in the opposite direction as the direction of the force applied, due to F = m a.
• A negative mass in a gravity field of a (larger) negative mass would be repelled by the negative mass.

The weirdest combination is a negative mass and positive mass of the same absolute amount. They will accelerate continously, the negative mass chasing the positive mass.

You might wanna look up more on this, for example Bondi was the first researcher that has looked into this.

Though generally this is regarded as a non-physical solution to the Einstein equations, and disregarded.

However, to my knowledge, the theory of cosmological inflation also has a concept of a repelling gravity force, that causes the very rapid expansion of a false vacuum bubble in the very early universe.
So I am not exactly sure why in that case a gravity force that is opposite to the normal direction of gravity is allowed but nowhere else.

I saw recently the work of some other (pseudo?) researcher, that came up with the idea that any region of space with a nett-outward force of gravity (so for example the intergalactic voids) can be seen as containing a negative energy, and thus negative mass, where normally (such as around a massive body) the gravitational field has an inward direction (the force of gravity increases when going inward).
This is in fact an (invalid?) analogy of solving the Einstein equations, since in those equations there is no mass, the mass turns only up after integration of the equations.

[mugaliens]

You didn't read what I wrote with sufficient care; try again.

I read it again.

Carefully.

My answer stands.

[Chris Hillman]

Mugaliens, did you overlook the fact that robheus also mentioned the well-known thought experiment which I described in detail?

The weirdest combination is a negative mass and positive mass of the same absolute amount. They will accelerate continously, the negative mass chasing the positive mass.

Try it again. It's a bit tricky, but the analysis I gave is standard material, and it is correct (given the assumptions which I carefully noted).

[mugaliens]

Mugaliens, did you overlook the fact that robheus also mentioned the well-known thought experiment which I described in detail?

Yes, particularly his statement: "A negative mass in a gravity field of a (larger) positive mass would not be repelled (as might be thought) but will be attracked by the positive mass."

The corollary also holds true: "A positive mass in a gravity field of a (larger) negative mass would not be repelled (as might be thought), but will be attracted by the negative mass."

Which I then compared to the statement you made: "For this reason, the object with mass m moves away from the object with mass -m (since it is being repelled), but the object with mass -m moves in the same direction with the same acceleration."

Put simply, whether you establish boundaries on the system around the positive mass, or the negative mass, or the two masses together, your concept of the dynamic duo (pos and neg masses) being a perpetual acceleration machine doesn't pass muster.

[Chris Hillman]

Keep trying, you still don't get it. I expressed the argument more carefully than robheus, so don't be confused by matters of casually chosen terminology. Read again my Post #4, 14 above.

[jumpjack]

I guess you are referring to the term "negative mass" which is entirely a hypothetical concept, and is deemed "non-physical"
Yet, at the basis of GR we can see as negative masses as a possible solution to the GR equations.

How would negative mass interact with normal positive mass:

[LIST][*]A negative mass in a gravity field of a (larger) positive mass would not be repelled (as might be thought) but will be attracked by the positive mass. This is because a negative mass will accelerate in the opposite direction as the direction of the force applied, due to F = m a.

Mmmhh..
Among m+ and m-, the F is negative due to F=GmM/r^2
This formula says "F" is not absolute, its sign does not rely only on the positive/negative mass which creates it, it depends also on which mass it acts on.

In case of both positive masses, F acting on "satellite" is directed toward "earth"; in case of "negative moon", force is directed away from earth. But it's applied to a negative mass, so acceleration has always same "+" sign.

If earth is negative and moon too is negative, F is positive, and it acts on a negative mass, so acceleration is negative, and moon is pulled away from earth.

Weird.

But I don't give up.

F=GmM/r^2 <==> F=kqQ/r^2

if we consider m <==> q, we could arrive to:

F=ma <==> F = qE

???
E <==> a ????
uhm...

[mugaliens]

Keep trying, you still don't get it.

Thanks, Chris, but no thank you. You've yet to convincingly make your case, and gobs of information, theory, and a systems approach says otherwise.

Have a nice day.

[parejkoj]

I was willing to believe Chris on this one, but I figured I'd try it in my head.... And, sure enough, Chris is right!

One thing that may be confusing people here is that in all ordinary circumstances, the direction of F and a are the same. Not so for a negative mass. You have to be very careful of the signs, and you have to keep track of the unit vectors...

I'm going to set it up slightly differently from Chris's post #4, but the result is the same (also note that this is much easier to do on paper by drawing pictures and noting all of the vectors, so if you are still confused, try that!):

(origin at center)

   1 --------- 2
   o-----|-----o
  (m) ------ (-m)

Recall that F=m a r^ (I don't have an r-hat symbol, so that'll have to do for the unit vector), and F_g = - G m₁ m₂ r^_a->b / r².

So, for the positive mass:

m a r^ = - G m (-m) r^_1->2 / r² where r^ is pointing from the negative mass to the positive mass.

and for the negative mass:

(-m) a r^ = - G m (-m) r^_2->1 / r² where r^ is pointing from the positive mass to the negative mass.

So, what is the magnitude and direction of the acceleration of the negative mass? And do the same for the positive mass...

(I hope I got all the vectors right... so much easier with a pencil...)

[frankuitaalst]

Chris is right
The picture may become clear if one writes down the formulas for F and a for the four different cases , as is been done in the picture in annex .
Only in the case of two positive masses the bodies are attracted to each other .

[jumpjack]

nice picture... terrible choice for acceleration signs! ;-)

[Tobin Dax]

Maybe this is what parekoj did, but here's my crack at this. Gravitational force is F=-Gmm'/r^2. I think we're getting confused using force, so let's look only at acceleration. The acceleration of the mass m is a=-Gm'/r^2. I think it's been established well enough that this is a 1D problem, so I can use negative magnitudes to negative vectors.

m="+m", m'="+m" -> a=-Gm/r^2 negative

m="+m", m'="-m" -> a=+Gm/r^2 positive

m="-m", m'="+m" -> a=-Gm/r^2 negative

m="-m", m'="-m" -> a=+Gm/r^2 positive

The middle two cases are under discussion: The two masses are equal in magnitude and opposite in sign.
The acceleration of the positive mass w.r.t. the negative mass is positive. The positive mass accelerates away from the negative mass.
The acceleration of the negative mass w.r.t. the positive mass is negative. The negative mass accelerates toward the positive mass.
Both accelerations have the same magnitude, so both masses will accelerate at the same rate in the same direction indefinitely. (Well, indefinitely until a third mass comes into play.)

I agree with Chris Hillman. Mugs, what did I do wrong above? (Remember that I'm giving each mass it's own coordinate system.) Or is your disagreement with Chris a semantic one?

[mugaliens]

I agree with Chris Hillman. Mugs, what did I do wrong above? (Remember that I'm giving each mass it's own coordinate system.) Or is your disagreement with Chris a semantic one?

Instead of attempting to wade through the math (it's only algebra, so no biggee, if I must), let's look at it from a systems approach:

System boundary: Large rectangular box enclosing both positive mass planet and negative mass planet. Nothing gets in or out.

Initial conditions: Both planets are at rest.

Hmmm... I see where Chris may be right, mathematically speaking, as the sum of both the rest and accelerated masses are indeed zero, therefore, as a system, there are no violations of perpetual acceleration.

However!!!

With no mass to this system, acceleration to the speed of light is instantaneous, which may explain why we don't see any pos mass / neg mass pairs lying around.

They went thataway...

[Tobin Dax]

[quote=mugaliens;1277243]the sum of both the rest and accelerated masses[quote]
I've really got to start thinking a little higher than just Newtonian.

However!!!

With no mass to this system, acceleration to the speed of light is instantaneous, which may explain why we don't see any pos mass / neg mass pairs lying around.

They went thataway...

Okay, this I see. The motion of the system as a whole can be described as the motion of the center of mass. The equivalent mass is zero, so bye-bye.

[Drunk Vegan]

Let's suppose "antigravity" does exist: how could we "detect" it or demonstrate it exists?!?

Answer this question and you've won yourself a Nobel Prize and a trillion dollars from the patent.

[jumpjack]

Answer this question and you've won yourself a Nobel Prize and a trillion dollars from the patent.

why do you think I'm trying?

[jumpjack]

I'm giving each mass it's own coordinate system

Guys, if you continue doing this, it'll continue to be A MESS!
THis thing is complicated by itself, there's no need to make it even more complex by changing rerference frame depending on what you are looking at!

Let's just get a cartesian frame (is this the english name?!?), let's put a mass A in the origin and a mass B on the x+ axis ("+" is toward right); let's attribute "+" and "-" signs to the 2 masses in all 4 combinations.
Let's also suppose the mass in the origin can't move.

Ok, now, what happens to mass B in the 4 cases?
1) A=+, B=+ (known case)
2) A=+, B=-
3) A=-, B=+
4) A=-, B=-

Just "by guess" I suppose in the last case we'll have a behaviour similar to case A: B moves toward A.
In cases 2 and 3, B "escapes".
But it's just intuition: what do formulas say instead?