Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2002 September 17 
Posted on 09/16/2002 10:05:58 PM PDT by petuniasevan
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2002 September 17
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 a 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.
The Heisenberg Uncertainty Principle* states that it is impossible to have an absolutely zero energy condition.
* "The more precisely the POSITION is determined, the less precisely the MOMENTUM is known"
The universe is like a vast ocean, and all we see is the surface.
"toward a smooth plate in response to energy fluctuations in the vacuum of empty space. "
....what is the vacuum" and how was it created in the experiment? Sorry in advance if this is a completely naive elementary question..
Physicist, am I on the right track here or just spinning my wheels?
An odd aspect of Quantum Mechanics is contained in the Heisenberg Uncertainty Principle (HUP). The HUP can be stated in different ways, let me first talk in terms of momentum and position.
If there is a particle, such as an electron, moving through space, I can characterize its motion by telling you where it is (its position) and what its velocity is (more precisely, its momentum). Now, let me say something strange about what happens when I try to measure its position and momentum.
The preceding is a statement of The Heisenberg Uncertainty Principle. So, for example, if I measure x exactly, the uncertainty in p, dp, must be infinite in order to keep the product constant.
This uncertainty leads to many strange things. For example, in a Quantum Mechanical world, I cannot predict where a particle will be with 100 % certainty. I can only speak in terms of probabilities. For example, I can say that an atom will be at some location with a 99 % probability, but there will be a 1 % probability it will be somewhere else (in fact, there will be a small but finite probabilty that it will be found across the Universe). This is strange.
We do not know if this indeterminism is actually the way the Universe works because the theory of Quantum Mechanics is probably incomplete. That is, we do not know if the Universe actually behaves in a probabilistic manner (there are many possible paths a particle can follow and the observed path is chosen probabilistically) or if the Universe is deterministic in the sense that I can predict the path a particle will follow with 100 % certainty.
A consequence of the Qunatum Mechanical nature of the world, is that particles can appear in places where they have no right to be (from an ordinary, common sense [classical] point of view)!
This notion has interesting consequences for nuclear fusion in stars.
The dynamics and the postulate of collapse are flatly in contradiction with one another ... the postulate of collapse seems to be right about what happens when we make measurements, and the dynamics seems to be bizarrely wrong about what happens when we make measurements, and yet the dynamics seems to be right about what happens whenever we aren't making measurements. (Albert 1992, 79)
I got lost trying to figure out postulate of collapse
But oh to read refreshers :) My brain needed this.... exercise sort of thing.
Thanks guys!
By Deborah Zabarenko
WASHINGTON (Reuters) - Astronomers have detected what could be a "missing link" in the development of the universe: mid-size black holes that are neither supermassive nor as small as a single exploded star.
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The middling black holes were spotted using the Hubble Space Telescope ( news - web sites) in two separate globular star clusters in Earth's celestial neighborhood, astronomers said on Tuesday at a briefing at NASA ( news - web sites) headquarters.
"These intermediate black holes were the missing link," said Steinn Sigurdsson of Pennsylvania State University.
While astronomers have known for years about vastly large black holes and rather small ones, Sigurdsson said, "We didn't know if we could get from one to the other or if they were completely unrelated, and this seems to be the step that takes us from one to the other."
Black holes are unimaginably dense regions in space whose gravitational pull allows nothing, not even light, to escape. For that reason, black holes are invisible but can be detected by the pattern of swirling stars and gas around their edges.
In the past several decades, black holes have gone from being rare and almost mythic phenomena whose existence was routinely questioned to being accepted by most astronomers as a feature of the cosmos.
Until now, though, black holes were thought to come in two basic sizes.
There were so-called stellar-mass black holes, created when stars about 10 times the size of our sun died in big explosions called supernovae.
Then there were supermassive black holes believed to lurk at the center of galaxies, including the Milky Way that contains Earth. Those black holes could have the mass of millions or even billions of suns.
BLACK HOLES WITHIN SWARMS OF STARS
Astronomers wondered whether there was a mid-sized version, and now they have found two of them, not in galaxies or floating free, but in tightly packed swarms of stars called globular star clusters.
Both fit the profile of what a mid-size black hole should be. The first, in cluster M15, has about 4,000 times the mass of our sun; the second, in cluster G1, has about 20,000 solar masses.
Because globular star clusters contain the oldest stars in the universe -- the smaller of the two mid-size black holes is in a cluster 13 billion years old -- information about them could help scientists figure out how the clusters form.
Mid-size black holes are in a "very important mass range," according to Karl Gebhardt of the University of Texas at Austin.
"That has implications for how you make a supermassive black hole and it is possible that these black holes can act as the seeds on which you make the supermassive black hole," Gebhardt said.
Scientists found a powerful pattern in the mid-size black holes, Gebhardt said. Their mass was related to the mass of the star cluster in just the same way the mass of supermassive black holes is related to the mass of the galaxies that contain them, he said.
"That has implications for how a globular cluster is related to a galaxy and how a galaxy is formed," he said.
Images and more information on the findings are online at http://oposite.stsci.edu/pubinfo/pr/2002/18.
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