What is anti-gravity?

[kwicky]

A university professor was talking on the radio a few days ago about dark matter in the universe. He said that funding was available to send a rocket into deepest space to record measurements from remnants of the big bang in the dark matter. He said it was made up of anti-gravity. What is he likely to discover?

[honest_joe]

Its a well known fact that the universe is expanding. Anti-gravity would suggest that within the dark matter lies a gas which separates galaxies and is continually expanding similar to blowing up a balloon with features on its surface.

[Clanad]

It's theorized by those who deal with quantum physics, that during the extremely early stages of the Big Bang, elementary particles, which are always created in pairs... that is for each particle of a pair an antiparticle twin is created and they almost instantaneously mutually self destruct. However for every one million pairs created 1 additional particle was created without a corresponding anti-particle. All of what we see in space today is a result of that seeming anomally.
Scientists who specialize in high-energy particle physics have found that under certain extreme conditions sometimes present in the quantum domain a 'substance' can come into existence that essentially has a negative gravitational force associated with it -- instead of an attracting force it repels. From here on we're assuming quite a bit, but it's possible that at the very first instant of the Big Bang, when the universe was about 10^ minus 35 meters in size (..far smaller than any particle in existence today..)and with a density of some 1,094 grams per cubic meter, more than enough energy was present to create that anti-gravity substance. As soon as that happened, the space of the universe expanded *faster than the speed of light.* That's allowed by Einstein's relativity because its space itself expanding, not any matter within it. Scientists call this FTL expansion 'inflation,' and it lasted for less than a second but still applied enough force to spacetime to cause it to continue expanding.
So the bottom line is the universe began its expansion (..what you call its explosion..) because of that anti-gravity substance which in turn had been formed within the enormous energies present at the Big Bang event itself. It's best not to think of there being anything other than pure energy present at the instant of the Big Bang...no particles, no light, etc.,. (Source: All Experts Astronomy)

[jake-the-peg]

To be honest we don't really know.

Dark Energy is so named because of that ignorance.

We do know that contrary to what we expected to find, a few years back we discovered that the Universe's expansion is in fact accelerating and it's the force behind that that we give this name to.

I think what Clanad's referring to is the infamous "zero point energy" much beloved of science fiction writers.

It seems that nature truely does abhore a vacuum and a high level vaccuum is in fact a writhing sea of particles popping in and out of existance and this can exert a pressure. Known as the Casimir effect which we can measure.

Whether this is what is responsible for the Unverse's inflation is still unclear.

A few years back the Cobe satellite took the first decent pictures of the early universe

This is what it "looks" like http://lambda.gsfc.nasa.gov/product/cobe/cobe_ images/COBE_28_dmrgalsub.gif

This work won the Nobel prize for physics in 2006

There was a follow up mission "WMAP" which provided a much better picture of our universe as a baby:

http://www.nasa.gov/centers/goddard/images/con tent/96115main_Full_m.jpg

I suspect though your professer was referring to the ESA's proposed "Plank Satellite"

More of which here:
http://en.wikipedia.org/wiki/Planck_Surveyor

It is hoped to get a better understanding of dark energy from studies of the early Universe but you never can tell. This area started out when a couple of Astronomers were getting intereference on an

[nightmare]

jake the peg
the Casimir effect is not due to fluctuations in the quantum vacuum, but to suppression of em radiation, and in fact gives rise to an effectively negative pressure.

[jake-the-peg]

nightmare:

http://physicsworld.com/cws/article/print/9747

Soon afterwards, Casimir noticed that this result could be interpreted in terms of vacuum fluctuations.

Yes the casimir effect is an inward force but I'm not suggesting that is what dark energy is. Vacuum energy is related to the Casimir effect in fact

A positive vacuum energy caused by quantum fluctuations contributes to the cosmological constant driving the Universe's expansion.

However this is pretty much speculation on the part of theorists and there are still many possibilities - vacuum energy may be just part of the solution or not even related


.

[kwicky]

Interesting replies. If anyone watched the program on BBC4 last week called 'Atom' it concluded that by introducing Quantum theory it has muddied the waters and by trying to explain in those terms only created a paradox. It was suggested that physicists should accept the findings of the big bang and forget about Quantum theory. I sense a similar problem occurring if we try to explain dark matter in these terms?

[nightmare]

thanks jake the peg
- interesting article
I sit corrected