Astronomy Picture of the Day

NASA ^ | 01/03/10 | Umar Mohideen

[sig226]

A Force from Empty Space: The Casimir Effect
Credit & Copyright: Umar Mohideen (U. California at Riverside)

Explanation: This tiny ball provides evidence that the universe will expand forever. Measuring slightly over one tenth of a millimeter, the ball moves toward a smooth plate in response to energy fluctuations in the vacuum of empty space. The attraction is known as the Casimir Effect, named for its discoverer, who, 50 years ago, was trying to understand why fluids like mayonnaise move so slowly. Today, evidence is accumulating that most of the energy density in the universe is in an unknown form dubbed dark energy. The form and genesis of dark energy is almost completely unknown, but postulated as related to vacuum fluctuations similar to the Casimir Effect but generated somehow by space itself. This vast and mysterious dark energy appears to gravitationally repel all matter and hence will likely cause the universe to expand forever. Understanding vacuum fluctuations is on the forefront of research not only to better understand our universe but also for stopping micro-mechanical machine parts from sticking together.

[sig226]

The Casimir effect, for those who don't understand it, is an implication of quantum theory. Vitrual quantum particles fluctuate in the universe, appearing and disappearing at random. If two plates are placed close together (measured in microns) the wavelengths of some virtual photons are too long to exist between the two plates. These virtual photons are excluded from the space. They are not excluded from the space outside the plates. That means that there are more of them, therefore more force, outside the plates than there are between the plates. The plates will be pushed together because of the unblanced forces.The effect has been measured.

[sig226]

[cripplecreek]

I’ll take your word for it.

[left that other site]

Uh. OK.

Actually, I DO love this stuff!

I like the REALLY BIG stuff like Galactic Clusters and Star Nurseries.

I like the really Little stuff like quarks and neutrinos (Mexican neutrons? LOL)

Thanks for sharing, Sig226.

[left that other site]

Casimir Neutrino?

[fnord]

your explanation is much clearer than NASA’s verbage.

thanks for posting this thread all the time ...

[null and void]

I was going to say something but after I saw your screen name I forgot...

[NonLinear]

So what is a vitrual quantum particle? I hope it is not anything like a vitriol particle!

[rawcatslyentist]

>"there are more of them, therefore more force, outside the plates than there are between the plates. The plates will be pushed together because of the unblanced forces"

Wouldn't that cause the opposite of expansion?

[sig226]

If you meant the force betweenthe plates, then no. There is less force between the plates than outside of them because some virtual particles can’t exist in the small space between the two plates.

If you’re not sure how this means that the universe must expand forever, neither am I. I think they’re extrapolating the effect of unaccounted forms of energy to explain the problems observed with galactic rotations.