Is Dark Energy really just Antigravity?

I kind of find this idea silly, of course if you reverse time, gravity
will become anti-gravity. Only problem is how do you reverse time? But
what the hell, might as well throw this out there as one of the whacky
possibilities.

Yousuf Khan

***

Antigravity could replace dark energy as cause of Universe's expansion
"To resolve this question, Villata needed to institute the second
assumption – that general relativity is CPT invariant. This means that
the laws governing an ordinary matter particle in an ordinary field in
spacetime can be applied equally well to scenarios in which charge
(electric charge and internal quantum numbers), parity (spatial
coordinates) and time are reversed, as they are for antimatter. When you
reverse the equations of general relativity in charge, parity and time
for either the particle or the field the particle is traveling in, the
result is a change of sign in the gravity term, implying so-called
antigravity between the two."
http://www.physorg.com/news/2011-04-...expansion.html

Dear Yousuf Khan:

On Apr 18, 11:07*am, Yousuf Khan wrote:
I kind of find this idea silly, of course if you reverse
time, gravity will become anti-gravity.

I don't think so. Until the energy necessary to loft an apple back to
the tree coalesces and converts into kinetic energy, the apple stays
firmly on the ground.

Only problem is how do you reverse time? But
what the hell, might as well throw this out there as
one of the whacky possibilities.

If it is even remotely possible, and you don't test it, it isn't
Science.

***

Antigravity could replace dark energy as cause of
Universe's expansion "To resolve this question,
Villata needed to institute the second assumption
that general relativity is CPT invariant. This means
that the laws governing an ordinary matter particle
in an ordinary field in spacetime can be applied
equally well to scenarios in which charge (electric
charge and internal quantum numbers), parity
(spatial coordinates) and time are reversed, as they
are for antimatter. When you reverse the equations
of general relativity in charge, parity and time
for either the particle or the field the particle is
traveling in, the result is a change of sign in the gravity
term, implying so-called antigravity between the two.
snip link now broken by Google.Groups

.... which says nothing about Dark Energy, which would be roughly
equivalent to gravitation in the time-reversed world.

David A. Smith

On 18/04/2011 3:10 PM, dlzc wrote:
Dear Yousuf Khan:

On Apr 18, 11:07 am, Yousuf wrote:
I kind of find this idea silly, of course if you reverse
time, gravity will become anti-gravity.

I don't think so. Until the energy necessary to loft an apple back to
the tree coalesces and converts into kinetic energy, the apple stays
firmly on the ground.

Well, that's why I said "how do you reverse time?".

Only problem is how do you reverse time? But
what the hell, might as well throw this out there as
one of the whacky possibilities.

If it is even remotely possible, and you don't test it, it isn't
Science.

I'm sure it's /remotely/ possible, anything can be, but is that a good
enough reason to consider it?

Antigravity could replace dark energy as cause of
Universe's expansion "To resolve this question,
Villata needed to institute the second assumption
that general relativity is CPT invariant. This means
that the laws governing an ordinary matter particle
in an ordinary field in spacetime can be applied
equally well to scenarios in which charge (electric
charge and internal quantum numbers), parity
(spatial coordinates) and time are reversed, as they
are for antimatter. When you reverse the equations
of general relativity in charge, parity and time
for either the particle or the field the particle is
traveling in, the result is a change of sign in the gravity
term, implying so-called antigravity between the two.
snip link now broken by Google.Groups

... which says nothing about Dark Energy, which would be roughly
equivalent to gravitation in the time-reversed world.

And also why would anti-gravity be stronger than gravity? If there are
equal parts of matter and anti-matter and they gravitationally repel
each other, then why do they repel each other more than matter
gravitationally attracts other matter? Is there a different equation for
anti-gravity than for gravity?

Anyways, I *do* think that Dark Energy and Gravitation are related to
each other, but I don't think they are related this directly as gravity
and anti-gravity. I think gravity probably has a much more complex
geometry than simple General Relativity envisions. GR might only be the
short distance approximation of the real equation of gravity, much as
Newton's Laws were the slow-speed approximation of GR. Dark Energy is
likely just how gravity works at large cosmological distances.

We're having to jump through hoops to try to make GR work at large
distances by introducing fudge-factors like Dark Matter, MOND, and Dark
Energy.

Yousuf Khan

On Apr 18, 2:34*pm, Yousuf Khan wrote:
On 18/04/2011 3:10 PM, dlzc wrote:

Dear Yousuf Khan:

On Apr 18, 11:07 am, Yousuf *wrote:
I kind of find this idea silly, of course if you reverse
time, gravity will become anti-gravity.

I don't think so. *Until the energy necessary to loft an apple back to
the tree coalesces and converts into kinetic energy, the apple stays
firmly on the ground.

Well, that's why I said "how do you reverse time?".

Only problem is how do you reverse time? But
what the hell, might as well throw this out there as
one of the whacky possibilities.

If it is even remotely possible, and you don't test it, it isn't
Science.

I'm sure it's /remotely/ possible, anything can be, but is that a good
enough reason to consider it?









Antigravity could replace dark energy as cause of
Universe's expansion "To resolve this question,
Villata needed to institute the second assumption
that general relativity is CPT invariant. This means
that the laws governing an ordinary matter particle
in an ordinary field in spacetime can be applied
equally well to scenarios in which charge (electric
charge and internal quantum numbers), parity
(spatial coordinates) and time are reversed, as they
are for antimatter. When you reverse the equations
of general relativity in charge, parity and time
for either the particle or the field the particle is
traveling in, the result is a change of sign in the gravity
term, implying so-called antigravity between the two.
snip link now broken by Google.Groups

... which says nothing about Dark Energy, which would be roughly
equivalent to gravitation in the time-reversed world.

And also why would anti-gravity be stronger than gravity? If there are
equal parts of matter and anti-matter and they gravitationally repel
each other, then why do they repel each other more than matter
gravitationally attracts other matter? Is there a different equation for
anti-gravity than for gravity?

Anyways, I *do* think that Dark Energy and Gravitation are related to
each other, but I don't think they are related this directly as gravity
and anti-gravity. I think gravity probably has a much more complex
geometry than simple General Relativity envisions. GR might only be the
short distance approximation of the real equation of gravity, much as
Newton's Laws were the slow-speed approximation of GR. Dark Energy is
likely just how gravity works at large cosmological distances.

We're having to jump through hoops to try to make GR work at large
distances by introducing fudge-factors like Dark Matter, MOND, and Dark
Energy.

* * * * Yousuf Khan

Black holes could be antimatter. They supposedly do give of
positrons, don't they?

http://translate.google.com/#
Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet”

On Apr 18, 8:10*pm, dlzc wrote:
Dear Yousuf Khan:

On Apr 18, 11:07*am, Yousuf Khan wrote:

I kind of find this idea silly, of course if you reverse
time, gravity will become anti-gravity.

I don't think so. *Until the energy necessary to loft an apple back to
the tree coalesces and converts into kinetic energy, the apple stays
firmly on the ground.

Only problem is how do you reverse time? But
what the hell, might as well throw this out there as
one of the whacky possibilities.

If it is even remotely possible, and you don't test it, it isn't
Science.





***

Antigravity could replace dark energy as cause of
Universe's expansion "To resolve this question,
Villata needed to institute the second assumption
that general relativity is CPT invariant. This means
that the laws governing an ordinary matter particle
in an ordinary field in spacetime can be applied
equally well to scenarios in which charge (electric
charge and internal quantum numbers), parity
(spatial coordinates) and time are reversed, as they
are for antimatter. When you reverse the equations
of general relativity in charge, parity and time
for either the particle or the field the particle is
traveling in, the result is a change of sign in the gravity
term, implying so-called antigravity between the two.

snip link now broken by Google.Groups

... which says nothing about Dark Energy, which would be roughly
equivalent to gravitation in the time-reversed world.

David A. Smith- Hide quoted text -

- Show quoted text -

Hello David

We have spoken about time reversal before wrt black holes. But what
about gravitational contraction & dilation:

I have found in the following link: http://www.st-andrews.ac.uk/~ag71/PH...tutorial_1.pdf
that length contraction is ~10^-15 and time dilation is about the same
at the earth's surface compared with that at the top of a 10m ladder.

Does that effect alone explain the fall of an apple, say, off the
ladder to the floor? It seems such a small effect to make the apple
fall so quickly. Nearly 5 metres in the first second if I have it
correct. Yet the effects are only of the order ~10^-15.

Ben

In article ,
dlzc wrote:

I kind of find this idea silly, of course if you reverse
time, gravity will become anti-gravity.

I don't think so. Until the energy necessary to loft an apple back to
the tree coalesces and converts into kinetic energy, the apple stays
firmly on the ground.

And when that happens, it flies up and is slowed by gravity in the
usual way so that it is at rest just as it reaches the twig.

-- Richard

"Richard Tobin" wrote in message
...
| In article
,
| dlzc wrote:
|
| I kind of find this idea silly, of course if you reverse
| time, gravity will become anti-gravity.
|
| I don't think so. Until the energy necessary to loft an apple back to
| the tree coalesces and converts into kinetic energy, the apple stays
| firmly on the ground.
|
| And when that happens, it flies up and is slowed by gravity in the
| usual way so that it is at rest just as it reaches the twig.
|
| -- Richard
|
Yep. A whole video game industry was built on that predicate,
it was called "Lunar Lander".

On Apr 19, 6:47*pm, "Androcles" .
2011 wrote:

"Richard Tobin" wrote in message

...
| In article
,
| dlzc wrote:
|
| I kind of find this idea silly, of course if you reverse
| time, gravity will become anti-gravity.
|
| I don't think so. *Until the energy necessary to loft an apple back to
| the tree coalesces and converts into kinetic energy, the apple stays
| firmly on the ground.
|
..Sorry Anddro, Richard.
In a Matter of Time, Not Really.
After an Apple falls from the tree it will decay, then eject it's
seeds, in due time a new tree will grow, and the apple will be back on
the tree (:-)

Pat Ecum

Dear ben6993:

On Apr 19, 6:59*am, ben6993 wrote:
On Apr 18, 8:10*pm, dlzc wrote:
On Apr 18, 11:07*am, Yousuf Khan wrote:

I kind of find this idea silly, of course if you reverse
time, gravity will become anti-gravity.

I don't think so. *Until the energy necessary to loft an
apple back to the tree coalesces and converts into
kinetic energy, the apple stays firmly on the ground.

Only problem is how do you reverse time? But
what the hell, might as well throw this out there as
one of the whacky possibilities.

If it is even remotely possible, and you don't test it,
it isn't Science.

***

Antigravity could replace dark energy as cause of
Universe's expansion "To resolve this question,
Villata needed to institute the second assumption
that general relativity is CPT invariant. This means
that the laws governing an ordinary matter particle
in an ordinary field in spacetime can be applied
equally well to scenarios in which charge (electric
charge and internal quantum numbers), parity
(spatial coordinates) and time are reversed, as they
are for antimatter. When you reverse the equations
of general relativity in charge, parity and time
for either the particle or the field the particle is
traveling in, the result is a change of sign in the gravity
term, implying so-called antigravity between the two.

snip link now broken by Google.Groups

... which says nothing about Dark Energy, which
would be roughly equivalent to gravitation in the
time-reversed world.

We have spoken about time reversal before wrt black
holes. But what about gravitational contraction &
dilation:

I have found in the following link:
http://www.st-andrews.ac.uk/~ag71/PH1012/Tutorials/tutorial_1.pdf
that length contraction is ~10^-15 and time dilation
is about the same at the earth's surface compared
with that at the top of a 10m ladder.

Does that effect alone explain the fall of an apple, say,
off the ladder to the floor?

I'd say no. If rest is defined as the state of maximal aging (is in
SR), and it takes energy to move away from that (say to a slower time
rate), the "time dilation effect" would be contraindicated as a
"cause".

*It seems such a small effect to make the apple
fall so quickly. Nearly 5 metres in the first second
if I have it correct. *Yet *the effects are only of the
order ~10^-15.

David A. Smith