Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chimera on 20/04/2005 03:50:23
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Newsflash:
the Universe started out as soup. Or something similar, anyway.
http://www.sciencenewsdaily.org/story-3758.html
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Life is a minestrone
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wrapped up in Parmesan Cheese.
Men are the same as women.... just inside out !!(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.com%2Fhtml%2Fimages%2Fsmilies%2Fmini%2Fmini018.gif&hash=43d4f680fb1e52aecb14b539cb9eba2c)
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Amazing how you can mangle lyrics when you're younger, and keep singing the nonsensical version for the rest of your days...
http://www.elyrics.net/go/0-9/10cc-lyrics/life-is-a-minestrone-lyrics/
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..of course that's what I meant to say ...'Served' not 'Wrapped'....oh the brain cell has to work over time !!
Men are the same as women.... just inside out !!(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.com%2Fhtml%2Fimages%2Fsmilies%2Fmini%2Fmini018.gif&hash=43d4f680fb1e52aecb14b539cb9eba2c)
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So does this mean the universe started as just 10cc of soup?
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That much? Nah.
One of Joao Mageijo's ideas was that when the universe was created, it behaved more like a supercooled liquid (comparatively speaking), not unlike water can gently be brought down (way) below the normal freezing point, without it becoming ice. Touch it, and suddenly it becomes ice with a vengeance (or, in this case, matter).
This supercooled liquid state (again, by comparison) allows a different kind of initial expansion than the 'normal' theory, so I found this a rather interesting tidbit.
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The initial link you posted is quite interesting. It looks another of those discoveries that poses more questions than it answers
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Well, plasma has been called the 4th state of physical matter for quite some time now. Interestingly, the (group) velocity of waves in certain plasmas is higher than c. This does not violate Einstein (no information transfer) and is remarkably easy to demonstrate.
http://www.iop.org/EJ/abstract/0032-1028/23/7/008
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I can honestly say that I didn't understand a word of that. I can grasp concepts but the maths may as well be written in Klingon
It wasn't me - a big boy did it & ran away
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This is in English, but not so informative...
http://sci-phys-plasma.caeds.eng.uml.edu/2000/05-00-029.htm
this is a bit better, 2nd headline...
http://www.schulphysik.de/akt2113.html
what happens is that the only physically meaningful speed, the group speed, is faster than c in a vacuum. They noticed that plasma reflects certain frequencies, which can only be so if there is a faster medium than outside the plasma. That trick also worked if you tried it from a vacuum, so that had them puzzled quite a bit, since the dictum is that nothing can be faster than light - well, almost - as long as there is no transfer of information. Since this is a group phenomenon, not one of single particles, nothing is violated, albeit only by a whisker... [:)]
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)
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The group velocity does not exceed c, because that would violate SR. It is the phase velocity that can exceed c, which it does at the interface between the two media. This is only a transient anyway, it is not sustained.
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Hi gsmollin, that's what I thought, but that second link also speaks of the group velocity, and I recall seeing it more often. Is it wrong, and could you please explain the diff?
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)
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Chimera - Having read the 2nd link I remember having heard of that before. It was on a TV science documentary & they were discussing the implications for cause & effect (which I somehow managed to understand). Just 1 point though - is it too complicated to explain in layman's terms what phase velocity & group velocity are? Sorry to be a pain in the proverbial but if you could I'd appreciate it. Thank you
It wasn't me - a big boy did it & ran away
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Any good text on electromagnetics has this subject in a chapter called "Plane Waves in Dielectric and Conducting Media". I shall try to explain it in a non-math nutshell.
An electromagnetic wave is a transverse wave; the displacement of the wave is at right angles to its direction of travel. It is like a wave in a rope that'e been flicked up or down. The phase velocity is the velocity of a fixed point of the phase of the wave. In the rope analogy, pick the peak of the rope wave, and watch it move away from you. That is the phase velocity of the rope's wave.
A group velocity requires that there be more than one wave traveling together, of differeng frequencies. The multiple waves interract with each other and produce beat frequencies. These form a structure known as an envelope. The propagation velocity of the envelope is the group velocity.
A very basic, cracker-barrel-science analogy: An inch worm or caterpillar humps its back near its rear, then moves that hump forward to move the whole worm along. The phase velocity is analogous to the hump moving through the body of the worm, and the group velocity is analogous to the velocity of the whole worm.
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Thanks, gsmolin, I get it now. I just wasn't sure of the terminology. I know about phase shifts & envelopes due to having played analog synthesisers for a number of years.
It wasn't me - a big boy did it & ran away
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I once seen it compared to waves in a pond that seem to travel faster than the wind would allow for - same thing, I guess. The crests of the waves do not share any physical process, hence no information transfer, and Einstein can sit back and relax.
So I also take it the usage of 'group speed' in the 2nd link from my previous post is mistaken, or misquoted, and should read 'phase speed'.
Still don't see why that should be faster in a plasma than in a vacuum, though...
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)
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chimera, sound travels faster in water than in air so why shouldn't the phase speed be greater in a plasma? Maybe a plasma simply "conducts" better than a vacuum
It wasn't me - a big boy did it & ran away
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The standard answer basically is that the less obstruction (even if that entails creation/destruction of particles as in some more recent vacuum theories) the higher c can be, so in a vacuum you theoretically cannot lose.
http://www.ldolphin.org/setterfield/vacuum.html
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)