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Author Topic:   universe- why is it here?
Tony650
Member (Idle past 3273 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 121 of 144 (138352)
08-31-2004 3:53 AM
Reply to: Message 120 by happy_atheist
08-30-2004 7:37 PM


happy_atheist writes:

I don't know if that means either of them is wrong or that there's something more fundamental we're missing that would explain both of them.

Well, if you can figure it out you'll be in line for a Nobel Prize.

I only wish I were more familiar with the theories. Is the conflict between the physical models, themselves, or do the underlying mathematics of either model simply not balance with each other? Perhaps it's a combination of both?

Hope I'm not asking for anything too complex.


This message is a reply to:
 Message 120 by happy_atheist, posted 08-30-2004 7:37 PM happy_atheist has replied

Replies to this message:
 Message 122 by happy_atheist, posted 08-31-2004 11:18 AM Tony650 has replied
 Message 123 by Primordial Egg, posted 08-31-2004 6:57 PM Tony650 has replied

  
happy_atheist
Member (Idle past 4154 days)
Posts: 326
Joined: 08-21-2004


Message 122 of 144 (138419)
08-31-2004 11:18 AM
Reply to: Message 121 by Tony650
08-31-2004 3:53 AM


quote:
I only wish I were more familiar with the theories. Is the conflict between the physical models, themselves, or do the underlying mathematics of either model simply not balance with each other? Perhaps it's a combination of both?

Well i'm not totally sure what the conflict is myself, but i'm going to give me best educated guess. If someone out there knows a better answer feel free to tell me i'm wrong

Ok, I think the problem is that at the quantum level gravity is totally irrelevant. It is by far the weakest forece there is (my a long long way), and so juts doesn't figure at all in quantum mechanics. However, when you get into areas approaching the conditions of a singularity the gravitational field is so strong that even though gravity is extrememly weak it becomes important and needs to be figured into the quantum calculations. This is where the problem lies, no one has been able to figure out exactly what gravity does on a quantum level. The theories just seem totally incompatible. Each theory seperately was brought about to model worlds that simply don't meet under any conditions except the most extreme possible. I don't know what progress has been made though because any theory dealing with this aspect would be way beyond me


This message is a reply to:
 Message 121 by Tony650, posted 08-31-2004 3:53 AM Tony650 has replied

Replies to this message:
 Message 124 by Tony650, posted 09-01-2004 2:39 AM happy_atheist has replied

  
Primordial Egg
Inactive Member


Message 123 of 144 (138599)
08-31-2004 6:57 PM
Reply to: Message 121 by Tony650
08-31-2004 3:53 AM


The Elegant Universe
I think the problem is that every time they try to incorporate GR into QM they get a meaningless set of infinities, which doesn't say anything.

String Theory is considered one of the best candidates for resolving this - gravity pops out as a necessary consequence. Its not so much a well thought out theory as a discovery of mathematical coincidences at the moment.

If you have the time (3 hrs), I recommend watching a documentary NOVA ran on string theory based on the book "The Elegant Universe" by Brian Greene. The documentary isn't as good as the book, but its pretty good for a science documentary, imo.

PE


This message is a reply to:
 Message 121 by Tony650, posted 08-31-2004 3:53 AM Tony650 has replied

Replies to this message:
 Message 125 by Tony650, posted 09-01-2004 2:45 AM Primordial Egg has taken no action

  
Tony650
Member (Idle past 3273 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 124 of 144 (138709)
09-01-2004 2:39 AM
Reply to: Message 122 by happy_atheist
08-31-2004 11:18 AM


happy_atheist writes:

However, when you get into areas approaching the conditions of a singularity the gravitational field is so strong that even though gravity is extrememly weak it becomes important and needs to be figured into the quantum calculations. This is where the problem lies, no one has been able to figure out exactly what gravity does on a quantum level.

Ah yes, it's starting to come back to me. I've read that singularities may be "point-like" and therefore subject to quantum effects.

In fact, I've read about the attempts to unite the four fundamental forces into one single theory. A long time ago, though. I believe it was in Paul Davies' Superforce.

Something I'm not clear on; is there a defining line between the "macro" world and the quantum world, or is it somewhat "fuzzy"? Also what exactly is the quantum level? Does it deal with levels below Planck length, above Planck length, or both?

I seem to recall that quantum effects can, in principle, occur on any level. It's just that the probability becomes less and less, the higher you go, so that eventually they become virtual impossibilities.

For example, there is nothing to stop me and the chair I'm sitting on from quantum tunneling through the floor and reappearing downstairs, under the house, but due to the enormous number of particles which would have to do this simultaneously, it's a pretty fair bet that I won't. *leaps off chair*

As relativity and quantum theory are so at odds, I'm also curious about something else; does the speed of light apply at the quantum level? I imagine this would come down to whether or not we're dealing with anything below Planck length (and Planck time); does the speed of light have any real meaning there?


This message is a reply to:
 Message 122 by happy_atheist, posted 08-31-2004 11:18 AM happy_atheist has replied

Replies to this message:
 Message 126 by NosyNed, posted 09-01-2004 4:12 AM Tony650 has replied
 Message 127 by happy_atheist, posted 09-01-2004 7:22 AM Tony650 has replied

  
Tony650
Member (Idle past 3273 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 125 of 144 (138710)
09-01-2004 2:45 AM
Reply to: Message 123 by Primordial Egg
08-31-2004 6:57 PM


Re: The Elegant Universe
Hi PE.

Primordial Egg writes:

String Theory is considered one of the best candidates for resolving this - gravity pops out as a necessary consequence.

Yes, so I've read. As I said to happy_atheist, I'm sure I've read about this elsewhere and I think it was in Superforce by Paul Davies. It was a long time ago, however, and my memory of it is hazy. It may warrant a re-read.

Primordial Egg writes:

If you have the time (3 hrs), I recommend watching a documentary NOVA ran on string theory based on the book "The Elegant Universe" by Brian Greene. The documentary isn't as good as the book, but its pretty good for a science documentary, imo.

Thanks for the recommendations and the links! Greene's book has come up in conversation here before and sounds like it would answer some of my questions so I may check it out some time. If I like it I'll have a look for the doco, too.


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NosyNed
Member
Posts: 8968
From: Canada
Joined: 04-04-2003


Message 126 of 144 (138715)
09-01-2004 4:12 AM
Reply to: Message 124 by Tony650
09-01-2004 2:39 AM


macro quantum effects
I seem to recall that quantum effects can, in principle, occur on any level. It's just that the probability becomes less and less, the higher you go, so that eventually they become virtual impossibilities.

Have you ever seen anything on liquid Helium? It has quantum effects at a macro scale.

see : http://london.ucdavis.edu/~zieve/Research/super1.html


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

Replies to this message:
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happy_atheist
Member (Idle past 4154 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

  
Tony650
Member (Idle past 3273 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 128 of 144 (138841)
09-01-2004 2:32 PM
Reply to: Message 126 by NosyNed
09-01-2004 4:12 AM


Re: macro quantum effects
NosyNed writes:

Have you ever seen anything on liquid Helium? It has quantum effects at a macro scale.

No, I'd never heard of this! Wow! That's just...oh...just wow! Thank you so much for the link, Ned!

You wouldn't have anything else on this, would you? Do you know of any actual footage of the experiments showing these properties? I would be very interested in seeing them, if you do.

Thanks again, I really appreciate this info!


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Tony650
Member (Idle past 3273 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 129 of 144 (138845)
09-01-2004 2:40 PM
Reply to: Message 127 by happy_atheist
09-01-2004 7:22 AM


happy_atheist writes:

There is nothing below plank length.

Heh, I thought you'd say that but I wanted to be sure.

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?

Incidentally, your analogy pretty much confirmed what I thought, thank you.

happy_atheist writes:

Bose-Einstein condensation is one...

Ok, now we're entering a slightly more patchy area for me. I understand that the atoms in a Bose-Einstein condensate lose their "identity" and become more "wave-like" but I'm not an expert on this so I can't say I really understand what this actually means for the matter involved. What kind of quantum properties does the condensate have?

happy_atheist writes:

...quantum entanglement is another...

Ah yes, this is one I'll be keeping a sharp eye on, over the coming years.

happy_atheist writes:

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.

Yeah, that's what I suspected. For some reason, nature just doesn't like giving us clearly defined black-and-white boundaries, huh?


This message is a reply to:
 Message 127 by happy_atheist, posted 09-01-2004 7:22 AM happy_atheist has replied

Replies to this message:
 Message 130 by happy_atheist, posted 09-01-2004 3:20 PM Tony650 has taken no action
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happy_atheist
Member (Idle past 4154 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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happy_atheist
Member (Idle past 4154 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

  
Tony650
Member (Idle past 3273 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 132 of 144 (139081)
09-02-2004 5:12 AM
Reply to: Message 131 by happy_atheist
09-01-2004 3:23 PM


happy_atheist writes:

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).

Ok, so asking what is "below the Planck length" is kind of like asking what was "before the big bang." In a sense, "below" has no meaning with regard to Planck length, just as "before" has no meaning with regard to the big bang. The big bang is the beginning, and Planck length is the bottom.

happy_atheist writes:

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.

I read something which described this (kind of) but I'm not sure if I got the right impression from it or if it was "dumbed down" and gave me the wrong idea.

Essentially, it described the process as the particles "piling up" on each other. Now this may have been for the sake of simplicity but does this mean that the condensate always collapses (condenses?) to a point? Can macroscopic bodies exist in this state?

happy_atheist writes:

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).

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?

happy_atheist writes:

That is the principle teleportation works on, it's why a teleported object is identicle to the original rather than just a copy.

Yes, this is something else I have trouble getting my head around. What exactly is the difference between an identical object and a "mere" copy? I suppose there must be some distinction but I'm afraid I don't see it.


This message is a reply to:
 Message 131 by happy_atheist, posted 09-01-2004 3:23 PM happy_atheist has replied

Replies to this message:
 Message 133 by sidelined, posted 09-02-2004 8:31 AM Tony650 has replied
 Message 134 by happy_atheist, posted 09-02-2004 11:17 AM Tony650 has replied

  
sidelined
Member (Idle past 5148 days)
Posts: 3435
From: Edmonton Alberta Canada
Joined: 08-30-2003


Message 133 of 144 (139095)
09-02-2004 8:31 AM
Reply to: Message 132 by Tony650
09-02-2004 5:12 AM


Tony650

Ok, so asking what is "below the Planck length" is kind of like asking what was "before the big bang.

In a sense this is correct but what actually occurs is this. A quanta is the smallest unit of energy that exists.You cannot have a half quanta or any fraction of it.In trying to make a measurement of the quanta you cannot tell whether the quanta you are measuring come sfrom that which you are observing or from the instrument you are using to observe the quanta.This is by the way the origin of the "observer is the observed" phrase.This does not mean that they are one and the same but that there can be no distinction made between the two of them.

Check out this webpage to get a perspective on the history behind the problems classical mechanics had and how they were solved by quantum mechanics.
http://www.nap.edu/books/0309076412/html/

This message has been edited by sidelined, 09-02-2004 07:31 AM


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

Replies to this message:
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happy_atheist
Member (Idle past 4154 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

Replies to this message:
 Message 137 by Tony650, posted 09-03-2004 1:59 AM happy_atheist has taken no action
 Message 139 by Tony650, posted 09-06-2004 9:56 AM happy_atheist has replied

  
happy_atheist
Member (Idle past 4154 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.

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