Does anti-gravity, as a force, exist?

Hello... It seems everything in his world has an opposite:
up/down..Left/right..Positive/negative...good/evil...action/reaction
etc. etc.
...But what about gravity? ...Is there a known opposite force, other
than one that can be simulated? Thanks... Jon

Dear Johnny1000:

wrote in message
...
Hello... It seems everything in his world has an
opposite:
up/down..Left/right..Positive/negative...
good/evil...action/reaction etc. etc.

These are labels, not "facts". They stand between you and
reality. It is one curse of being bifurcated.

...But what about gravity? ...Is there a known
opposite force, other than one that can be
simulated?

1) Gravity is not a force. It can be represented as one in
certain simple models, such as what they have time to teach you
in high school.
2) In cosmological expansion, Dark Energy is counter to the
"mutually attractive effects" of gravity. But it only "kicks in"
at very large distance scales.

David A. Smith

David,

You dismissed some examples of pairs of opposites as
"labels, not facts". It looks to me like your assertion
applies only to the words, not the things those words
label. Many things *do* have opposites. Up and down are
obviously opposite to each other. Positive and negative
are clearly opposites. Your dismissal appears to be
completely unjustified.

It is obvious that gravity is a force. It was the first
force to be described mathematically, by Galileo and Newton.
Saying that it is not a force is not only counter to all
experience, but counter to most physics textbooks. When
you don't explain what you mean by the statement and back
it up with evidence, you look like a kook.

-- Jeff, in Minneapolis

Dear Jeff Root:

"Jeff Root" wrote in message
ups.com...
David,

You dismissed some examples of pairs of opposites
as "labels, not facts". It looks to me like your
assertion applies only to the words, not the things
those words label.

The "things" those words label are abstract concepts that are
necessarily removed from reality.

Many things *do* have opposites. Up and down are
obviously opposite to each other.

Not if I live in Austrailia and you in America. Your up is my
down, and vice versa. "Vertical axis" is at least unitary, but
not absolute since others will not see it as "vertical". To be
"opposite" is to have something in common with the opposite. So
it is really gradations of sameness.

Positive and negative
are clearly opposites. Your dismissal appears to be
completely unjustified.

Positive and negative have something in common... charge. It
does not always add to understanding to divide a unity in "half"
and proclaim "look there are two parts"!

It is obvious that gravity is a force. It was
the first force to be described mathematically,
by Galileo and Newton.

Force has been described much longer than that, even
mathematically.

Saying that it is not a force is not only counter to all
experience, but counter to most physics textbooks.
When you don't explain what you mean by the
statement and back it up with evidence, you look
like a kook.

http://hermes.physics.adelaide.edu.au/~dkoks/Faq/
http://math.ucr.edu/home/baez/physic...particles.html
http://math.ucr.edu/home/baez/physic...rav_speed.html
QUOTE
Strictly speaking, gravity is not a "force" in general
relativity, and a description in terms of speed and direction can
be tricky.
END QUOTE

Consider that Newton himself was very uncomfortable with "action
at a distance".

And if you think I need to look like a kook, go ahead and think
that. There are two kinds of people in the world... ;)

David A. Smith

"Jeff Root" ha scritto nel messaggio
ups.com...

It is obvious that gravity is a force. It was the first
force to be described mathematically, by Galileo and Newton.
Saying that it is not a force is not only counter to all
experience, but counter to most physics textbooks.

Before Einstein this was true, and obvious...
But after General Relativity Theory gravity is defined as only a space
geometrical property.
Space is curved in presence of mass and in this way you don't need any force
to justify attraction between masses.
Is the space deformation itself that generates gravity.

Luigi Caselli

In message , Luigi Caselli
writes
"Jeff Root" ha scritto nel messaggio
oups.com...

It is obvious that gravity is a force. It was the first
force to be described mathematically, by Galileo and Newton.
Saying that it is not a force is not only counter to all
experience, but counter to most physics textbooks.

Before Einstein this was true, and obvious...
But after General Relativity Theory gravity is defined as only a space
geometrical property.
Space is curved in presence of mass and in this way you don't need any force
to justify attraction between masses.
Is the space deformation itself that generates gravity.


Don't quantum gravity theories require a graviton?
Most particles have an antiparticle, though the photon is its own
antiparticle so there's no reason to expect antigravity from that
direction. The graviton, if it exists, may also be its own antiparticle.
Anyway, the experiment to see if antimatter is attracted by gravity
hasn't yet been done, AFAIK.

"Jonathan Silverlight" ha
scritto nel messaggio ...
In message , Luigi Caselli
writes
"Jeff Root" ha scritto nel messaggio
oups.com...

It is obvious that gravity is a force. It was the first
force to be described mathematically, by Galileo and Newton.
Saying that it is not a force is not only counter to all
experience, but counter to most physics textbooks.

Before Einstein this was true, and obvious...
But after General Relativity Theory gravity is defined as only a space
geometrical property.
Space is curved in presence of mass and in this way you don't need any
force
to justify attraction between masses.
Is the space deformation itself that generates gravity.


Don't quantum gravity theories require a graviton?

Only if you believe in quantum gravity...

Most particles have an antiparticle, though the photon is its own
antiparticle so there's no reason to expect antigravity from that
direction. The graviton, if it exists, may also be its own antiparticle.
Anyway, the experiment to see if antimatter is attracted by gravity
hasn't yet been done, AFAIK.

And if antimatter is attracted by gravity what is the conclusion of this
story?

Luigi Caselli

Dear
"Jonathan Silverlight"
wrote in message
...
....
Anyway, the experiment to see if antimatter is attracted
by gravity hasn't yet been done, AFAIK.

http://math.ucr.edu/home/baez/physic...atterFall.html
http://www.science.ca/askascientist/...on.php?qID=164

Yes, the only question is is it attracted exactly the same way.

Since antimatter can be considered as "time reversed" matter, and
since the Earth doesn't fly apart (all at once) by reversing time
with a camera, I would fully expect antimatter to behave exactly
as does matter.

David A. Smith

Standard theory says there is no such thing as an anti-gravity force.
However, the theoretical arguments(yes, Baez's argument("Morrison
argument") included) for this are fairly weak, in my humble opinion.

I think there is enough wiggle room in the experimental evidence to
allow for the possibility that antimatter falls up. That is that
antimatter and matter repel each other gravitationally, but attract
their own kind.

Anyways, the earth example is silly. An antimatter Earth would not be
expected to repel itself.

In article . com,
Intangir wrote:

Standard theory says there is no such thing as an anti-gravity force.
However, the theoretical arguments(yes, Baez's argument("Morrison
argument") included) for this are fairly weak, in my humble opinion.

I think there is enough wiggle room in the experimental evidence to
allow for the possibility that antimatter falls up. That is that
antimatter and matter repel each other gravitationally, but attract
their own kind.

Anyways, the earth example is silly. An antimatter Earth would not be
expected to repel itself.

If anti-matter would "fall up", that would imply different
gravitational and inertial masses for anti-matter: the gravitational
mass of anti-matter would be negative, making anti-matter being
repulsed by gravity. But the inertial mass of anti-matter would
still be positive, so that the response of the anti-matter to that
repulsive force would be the expected response: to move away.

Now, finding some matter having different inertial and gravitational
masses would be a clear contradiction of General Relativity. So anyone
who wants to "disprove Einstein", here's your opportunity: try to
verify experimentally that in a gravitational field, anti-matter will
"fall up".

-------------------------------------------------------------------------

If we want to follow the equivalence pronciple of General Relativity,
and still want to assign a negative gravitational mass to
anti-matter, then its inertial mass must also be negative. This will
have some weird consequences: if some force acts on the antimatter,
it will move in the opposite direction than expected, since its
inertial mass is negative. This alone would make any atom of
anti-matter unnterly instable: the attractive force between the
antielectrons and antiprotons would make the atom rapidly fall apart
instead of holding it together. Otoh no strong nuclear force would
be needed to keep the antiprotons in the core of the atom together -
the repulsive electrical force between the equally charged
antiprotons would keep them firmly in place!

Anti-matter does not behave in this way. Antiparticles are repelled,
not attracted, by repulsive forces. Numerous experiments have confirmed
that antimatter has positive inertial mass. And if the equivalence
principle of General Relativity is valid for antimatter too, then this
implies that antimatter also must have positive gravitational mass.

-------------------------------------------------------------------------

Finally, let's make a simple thought experiment, where we have two
bodies, A and B, both initially at rest, where A has normal positive
mass and B has an equal but negative mass. This applies to both
gravitational and inertial masses, so the equivalence principle is
assumed to be valid. The only significant force on these bodies is
assumbed to be their mutual gravitational forces. All other forces
(electrical, nuclear, whatever) are assumed to be negligible.

What would happen?

First the mutual gravity between the two bodies would be negative,
i.e. a repulsive gravitational force, since the two bodies have
different signs in their masses: A has positive mass and B has
negative mass.

So the only significant force on these bodies would be a repulsive
gravitational force. Now, how would these to bodies react on this
repulsive force?

Body A, with positive inertial mass, would behave as expected: it
would start to move away from body B.

Body B, with negative inertial mass, would not behave as we're used
to: it would start to move TOWARDS body A.

The net result would be quite amusing: body B would start "chasing"
body A. The distance between bodies A and B would remain unchanged,
while both bodies would accelerate all the time - the only upper limit
of their speeds would be the relativitistic light speed limit.

But from where would their kinetic energy come?", I hear you ask.
Well, the sum of their kinetic energy, which was zero at the start,
would remain zero all the time while they accelerated: body A, with
positive mass, would of course get more and more kinetic energry as
it accelerated, but body B, with negative mass, would at all times
have an equal amount of NEGATIVE kinetic energy as it accelerated.

----------------------------------------------------------------------------

As you can see, trying to introduce negative masses would imply some
quite strange behaviour in bodies with negative masses. And there's
an asymmetry in the behaviour too: an atom built with particles with
negative mass would behave quite differently than a normal atom, with
particles having positive mass. And in the last example here, with a
negative and a positive mass interacting, the negative mass would
start "chasing" the positive mass - not the other way around.


I think we can safely conclude that negative masses do not exist. If
they did exist, our universe would be a quite different place than it
is.


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