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Author Topic:   universe- why is it here?
happy_atheist
Member (Idle past 4914 days)
Posts: 326
Joined: 08-21-2004


Message 127 of 144 (138725)
09-01-2004 7:22 AM
Reply to: Message 124 by Tony650
09-01-2004 2:39 AM


There is nothing below plank length. Just like quantum mechanics quantizes energy into discrete portions that can't be divided, it also (theoretically) quantizes spacetime too. Plank length is so small as to be pretty untestable as far as I know though, something like 10^-31 metres, but I may be wrong on that. You're right that QM works on all levels, it's just a statistical mechanism.
I'll give an analogy (I think I may have given this somewhere else on the site but i'll give it again). Imagine you have 2 dice and throw them. If you throw them enough times you could draw yourself a probability distribution of the average score you got. You would find that it would be a smooth curve peaking at 3.5. You would have the most chance of averaging 3.5, but still very high chances of getting numbers either side. The least likely average would be one and six.
The reasons for this is that with 2 dice, the most likely score to get is 7. There are many more ways of scoring 7 than any other number, eg 6+1, 5+2, 4+3, 3+4, 2+5, 1+6. There is only one way to score 12 and only one way to score 2....therefore you're more likely to average 3.5 than any other number.
Imagine then instead of having 2 dice you have one billion dice, and do exactly the same experiment. You throw all these dice and work out the average. If you drew the probability distribution diagram for this you would still find it peaks at 3.5, but it would no longer be a smooth curve. It would be so steep as to appear to be a straight line at 3.5. Now that is only with 1 billion dice, imagine how many particles there are in a macroscopic situation, countless more than 1 billion. In just one mole of a substrance there is in the order of 10^23 atoms (it may be 10^24, I don't remember lol).
So as you see, on a very small scale quantum mechanics is very unpredictable because you're dealing with only a few particles, but when you go to a macroscopic level it becomes very much more deterministic, the chances of observing something contrary to expectations become so small as to be unimaginable (such as you quantum tunnelling through your chair). One of my courses at university was statistical mechanics, that is where I got the dice analogy from. In this course we derived much of thermodynamics using this analogy and some pretty clever but at the same time simple maths
As nosyned said there are quantum mechanical effects that can be observed on a macroscopic scale. Bose-Einstein condensation is one, quantum entanglement is another (I remember reading somewhere that they've managed to entangle a container of caesium ions for a considerable amount of time). This leads on to teleportation, which is also quantum mechanical.
As to a barrier between micro and macro i'd say its just a continuum. The bigger in scale you get the more macro-like things become etc. Much like in evolution, things just merge together and we're left with the impossible taks of classifying things into one group or another hehe.

This message is a reply to:
 Message 124 by Tony650, posted 09-01-2004 2:39 AM Tony650 has replied

Replies to this message:
 Message 129 by Tony650, posted 09-01-2004 2:40 PM happy_atheist has replied

  
happy_atheist
Member (Idle past 4914 days)
Posts: 326
Joined: 08-21-2004


Message 130 of 144 (138855)
09-01-2004 3:20 PM
Reply to: Message 129 by Tony650
09-01-2004 2:40 PM


quote:
I'm curious, though; somebody must have hypothesized something below the Planck length, at one time or another. I'm not saying they're right, I'm just wondering if there have been any ideas about existence at that level.
Or does our current understanding simply rule it out as a possibility? Perhaps "below the Planck length" is a meaningless statement in the same way that "before the big bang" is?
Something bellow the plank length would be as meaningless as a unit of energy equal to a fraction of a quanta. One plank length of space would be the smallest building block of space time there is (assuming that spacetime is quantised, which I think it probably is).

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 Message 129 by Tony650, posted 09-01-2004 2:40 PM Tony650 has not replied

  
happy_atheist
Member (Idle past 4914 days)
Posts: 326
Joined: 08-21-2004


Message 131 of 144 (138856)
09-01-2004 3:23 PM
Reply to: Message 129 by Tony650
09-01-2004 2:40 PM


As for Bose-Einstein condensation, I honestly can't remember much about it. We touched on it in Statistical Mechanics, even derived the equations for it, but unfortunately he never actually described what macroscopic effects it had! lol.
Dredging things up from memory (its kinda coming back to me), it deals with the probability that all the atoms will 'condense' into the same quantum mechanical state. This means that, as you mentioned, they lose their identity. If two atoms are in exactly the same quantum mechanical state they become indistinguishable (as far as I know). That is the principle teleportation works on, it's why a teleported object is identicle to the original rather than just a copy.

This message is a reply to:
 Message 129 by Tony650, posted 09-01-2004 2:40 PM Tony650 has replied

Replies to this message:
 Message 132 by Tony650, posted 09-02-2004 5:12 AM happy_atheist has replied

  
happy_atheist
Member (Idle past 4914 days)
Posts: 326
Joined: 08-21-2004


Message 134 of 144 (139132)
09-02-2004 11:17 AM
Reply to: Message 132 by Tony650
09-02-2004 5:12 AM


Tony650 writes:
Ok, just to clear up, in my mind, what we mean by "indistinguishable"...I'm not quite sure how to ask this without sounding stupid but does this mean that two particles in the same quantum state are, in some sense, the "same" particle?
Yes, if two quantum particles are in the same state they are indistinquishable and to all intents and purposes the same. Thats what makes teleportation different to a photocopy.

This message is a reply to:
 Message 132 by Tony650, posted 09-02-2004 5:12 AM Tony650 has replied

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 Message 137 by Tony650, posted 09-03-2004 1:59 AM happy_atheist has not replied
 Message 139 by Tony650, posted 09-06-2004 9:56 AM happy_atheist has replied

  
happy_atheist
Member (Idle past 4914 days)
Posts: 326
Joined: 08-21-2004


Message 135 of 144 (139133)
09-02-2004 11:18 AM


Oh, and yes bose einstein condensates occur in macroscopic gasses, not in point particles. They condense to the same quantum mechanical energy state, not the same position in space I have the equations for it in my notes at home I think, i'll review them tonight and see if I get glean some more understanding from them.

Replies to this message:
 Message 140 by Tony650, posted 09-06-2004 10:06 AM happy_atheist has not replied

  
happy_atheist
Member (Idle past 4914 days)
Posts: 326
Joined: 08-21-2004


Message 142 of 144 (140660)
09-07-2004 11:57 AM
Reply to: Message 139 by Tony650
09-06-2004 9:56 AM


Sorry for taking so long to reply. I may have to wait until friday to post from my notes back home. I'm have to hand my dissertation in on friday (i have over 18000 words done, i must have been working harder than I realised lol). I haven't had the chance to read through my notes yet

This message is a reply to:
 Message 139 by Tony650, posted 09-06-2004 9:56 AM Tony650 has replied

Replies to this message:
 Message 144 by Tony650, posted 09-07-2004 1:02 PM happy_atheist has not replied

  
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