If it is common to have a positive and negative with an energy such as electricity or magnetism could dark energy be the other pole for gravity?
When you talk about positive and negative electric/magnetic
energy, I presume you're talking about positive and negative
charge. This is a fallacy. It's like kinetic energy: you wouldn't
say you had negative kinetic energy because you were moving
backwards. Your momentum would be negative (assuming you had chosen
the convention that forwards is positive) but not your energy.
Kinetic energy is never negative.
Kinetic energy is not the same as momentum; likewise
electrostatic energy is not the same as charge. When you separate
electric charges (for example by rubbing a balloon against your
hair) you create electrostatic energy. But there is no sense in
which the positively charged part has more energy than the
negatively charged part. Insofar as it makes sense to ask where the
energy is located, the positively charged part may have more or
less energy, depending on how the charges are distributed. And
similarly with magnetism: there is no imbalance in the energy
distribution between the two ends of a magnet.
In fact, in some sense the concept of positive and negative
energy isn't very meaningful. When we do calculations involving
bodies on earth moving under gravity, we often assume a body at
ground level has zero potential energy. But we could just as well
assume a body at sea level has zero potential energy. It wouldn't
affect the answer to questions such as "What is the final velocity
of the tennis ball?". This is because what matters is really the
change in energy.
The same is true of some other kinds of energy, such as chemical
energy: We need a convention to decide when a system has zero
energy. There are tables telling you the chemical energy of various
compounds. These can be used to calculate the energy change (heat
generated, light absorbed, etc) when a reaction occurs. Some tables
use the convention that an element at room temperature and pressure
has zero energy; other have other conventions; but all will give
the same answer for the energy involved in the reaction.
In principle, we could in many cases avoid the choice of
artificial conventions and use a more natural convention. For
instance, for potential gravitational energy (ignoring everything
in the universe except the earth and everything on it) we could
assume that an object an infinite distance from the earth has zero
potential energy (or, more precisely, the potential energy of an
object tends to 0 as its distance from earth tends to infinity).
But this would create practical problems in the calculation: We'd
have to take into account the fact that the acceleration due to
gravity decreases as you move away; and the energy would be a very
large negative number. A 1kg mass at the surface of the earth would
have a potential energy of -63 megajoules. The calculation would
say something like: "...Initial potential energy: -63157839.1
joules. Final potential energy: -63157842.6 joules. Decrease in
gravitational potential energy: 3.5 joules. ..."
As the most extreme example, we could use E=mc^2 to calculate
the energy of everything. The energies involved would be immense.
We'd have to abandon Newtonian physics and use relativity
I think your proposal is very interesting. Dark energy is the
term used to explain why the expanding universe is accelerating. If
all there was in the universe was matter with attractive gravity
then you would expect that gravity to slow down the expanding
universe, after getting its initial burst of energy from the big
bang. If there existed some matter with repulsive gravity, as you
suggest, that might indeed be the source of the dark energy. BTW,
matter which repels all other matter, even our ordinary matter, was
first proposed by "http://english.answers.com" title="English">English
Hermann Bondi about 40 yrs ago. I don't think he seriously thought
it existed but he used it to find an exact solution to Einstein's
General Relativity Eqs. He imagined this "negative" mass, which
repelled everything being next to ordinary mass ,which attracted
everything. So the two masses sped off into space, one being
attracted the other being repelled. This configuration allowed
Bondi to find a solution to a dynamical problem using Einsteins
Eqs. Anyway, maybe particle physicists have some objection to
another gravity pole but I like your idea.