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N C More
2004-Sep-01, 12:56 AM
Wow, now this (http://www.sciam.com/article.cfm?chanID=sa004&articleID=00084A33-908A-111B-87CB83414B7F0000) is really strange! Take a look at this snip:


The big-particle hypothesis takes another approach. Instead of adding a new property to the dark particles, it exploits the inherent tendency of any quantum particle to resist confinement. If you squeeze one, you reduce the uncertainty of its position but increase the uncertainty of its momentum. In effect, squeezing increases the particle's velocity, generating a pressure that counteracts the force you apply. Quantum claustrophobia becomes important over distances comparable to the particle's equivalent wavelength. Fighting gravitational clumping would take a wavelength of a few dozen light-years.
What type of particle could have such astronomical dimensions? As it happens, physicists predict plenty of energy fields whose corresponding particles could fit the bill--namely, so-called scalar fields. Such fields pop up both in the Standard Model of particle physics and in string theory. Although experimenters have yet to identify any, theorists are sure they're out there.



This is the first I've heard about this theory. Opinions?

iron4
2004-Sep-03, 06:26 PM
"some physicists are proposing that the universe's mysterious dark matter consists of great big particles, light-years or more across. Amid the jostling of these titanic particles, ordinary matter ekes out its existence like shrews scurrying about the feet of the dinosaurs."



But light years is very big! but it's interesting though...

Cougar
2004-Sep-03, 09:22 PM
...If you squeeze one, you reduce the uncertainty of its position but increase the uncertainty of its momentum. In effect, squeezing increases the particle's velocity...
The second sentence doesn't follow from the first. Isolating a particle's position increases the uncertainty (what you can know about) its momentum (or velocity). It doesn't increase the velocity.

Spaceman Spiff
2004-Sep-03, 09:35 PM
...If you squeeze one, you reduce the uncertainty of its position but increase the uncertainty of its momentum. In effect, squeezing increases the particle's velocity...
The second sentence doesn't follow from the first. Isolating a particle's position increases the uncertainty (what you can know about) its momentum (or velocity). It doesn't increase the velocity.

Actually, it does that too. This is how White Dwarf stars support themselves. Think of it this way. If the uncertainty in the momentum is very large, then very large speeds are all the more likely. :)

N C More
2004-Sep-03, 10:53 PM
They go on to address this issue:


Cosmologists already ascribe cosmic inflation, and perhaps the dark energy (distinct from dark matter) that is now causing cosmic acceleration, to scalar fields. In these contexts, the fields work because they are the simplest generalization of Einstein's cosmological constant. If a scalar field changes slowly, it resembles a constant, both in its fixed magnitude and in its lack of directionality; relativity theory predicts it will produce a gravitational repulsion. But if the field changes or oscillates quickly enough, it produces a gravitational attraction, just like ordinary or dark matter. Physicists posited bodies composed of scalar particles as long ago as the 1960s, and the idea was revived in the late 1980s, but it only really started to take hold four years ago.

Seems like a reasonable theory but for this problem:


But all these models suffer from a nagging problem. Because the wavelength of a particle is inversely proportional to its mass, the astronomical size corresponds to an almost absurdly small mass, about 10-23 electron volts (compared with the proton's mass of 109 electron volts). That requires the laws of physics to possess a hitherto unsuspected symmetry. "Such symmetries are possible, although they appear somewhat contrived," says physicist Sean Carroll of the University of Chicago. Moreover, the main motivation for big particles--their resistance to clumping--has become less compelling now that cosmologists have found that more prosaic processes, such as star formation, can do the trick.

So, I guess dark matter continues to be enigmatic!

bigsplit
2004-Sep-05, 03:35 PM
I do not think big particles are the cause of the "dark matter" phenomena. But, the mention of such is showing we are on the right track. Before the BB, the Universe was essentually an infinate particle with neutral charge, existing at t=0.