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Quantum Theory, Causality and Determinism

 
 
Reply Fri 3 Apr, 2009 02:02 pm
Hey, I'm planning on doing an essay which has a title somewhere along the lines of "What effects does Quantum Theory have on causality and determinism?"
I know some areas of how effects determinism, such as the uncertianity pinciple etc., as there are quite alot of books on that topic. However I'm not uite show how/if it affects causality. Can anyone suggest some good research books or ideas on this title?
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rhinogrey
 
  1  
Reply Fri 3 Apr, 2009 06:29 pm
@Darunia9,
Look into Quantum Entanglement. Basically it shows that when two separate particles are shot off in opposite direction, and a 'spin' is applied to one particle, the other reacts accordingly. What this does is open new ways of thinking about causal relations that aren't strictly spatial.
Darunia9
 
  1  
Reply Sat 4 Apr, 2009 12:35 pm
@rhinogrey,
rhinogrey wrote:
Look into Quantum Entanglement. Basically it shows that when two separate particles are shot off in opposite direction, and a 'spin' is applied to one particle, the other reacts accordingly. What this does is open new ways of thinking about causal relations that aren't strictly spatial.


So whereas before philosophers thought of causation as being local, as did Einstein with relativity and his idea of sub atomic particles. Quantum theory suggests that seemingly unconnected particles dustances apart can have an effect on each other? Which appear to happen instantly, and therefore not knowing which particle effected the other, or according to the viewer of the local part sees the effect after the cause?

Also does the idea of non linear time affect the general or past view of time. As I'm assuming the general idea of causation was the cause is in the past and the effect is the future. So the non linear properties of time as suggested by Quantum Theory mean that our idea of causality must be re defined?
0 Replies
 
Bones-O
 
  1  
Reply Sun 12 Apr, 2009 05:12 pm
@Darunia9,
Hi Darunia - What do you mean by non-linear time?
Darunia9
 
  1  
Reply Mon 13 Apr, 2009 06:13 am
@Bones-O,
Bones-O! wrote:
Hi Darunia - What do you mean by non-linear time?


Well like in the theory of special relativity there is no concept of past present or future. It's like the map idea of every event having it's own bit of space time. So it's only the human concept of past, present and future that makes us suppose time is linear when instead it's a constant. And it's possible to move between these events like we can move about in space, if we could travel at such speeds or sustain wormholes.
jeeprs
 
  1  
Reply Tue 14 Apr, 2009 05:21 am
@Darunia9,
I wonder if anyone would seriously consider the proposition that quantum entanglement might, in actual fact, provide a basis for that realm of art and practise hitherto known as 'magic'?
0 Replies
 
Bones-O
 
  1  
Reply Tue 14 Apr, 2009 06:50 am
@Darunia9,
Darunia9 wrote:
Well like in the theory of special relativity there is no concept of past present or future. It's like the map idea of every event having it's own bit of space time. So it's only the human concept of past, present and future that makes us suppose time is linear when instead it's a constant. And it's possible to move between these events like we can move about in space, if we could travel at such speeds or sustain wormholes.


Okay, fundamental quantum theory (i.e. that governed by the Schrodinger equation) is Euclidean. Time here is the same as in classical (Newtonian) mechanics, which is everyday time.

Relativistic QT (governed by the Dirac or Klein-Gordon equations) is in special relativistic spacetime. Time here is still linear, insofar as it is represented by a straight line in any inertial frame of reference which is the frame pertaining to special relativity.

Wormholes et al are features of general relativity which deals with non-inertial frames and in which time is curved around energy. But QT is non-relativistic in this sense - there is no non-inertial quantum theory. The QT framework is flat spacetime which, for a single time dimension, necessarily yields linear time.
Darunia9
 
  1  
Reply Tue 14 Apr, 2009 07:08 am
@Bones-O,
Ohh, so I was getting different theories confused. But I thought their was a Qunatum Theory where all events were happening at stimitanously but we were perceiving them as the past, present or future etc?
Or theres a quantum theory that suggests we can travel backwards in a loop of space-time?
If not does Quantum Theory effect our idea of time at all?
Bones-O
 
  1  
Reply Tue 14 Apr, 2009 06:31 pm
@Darunia9,
Darunia9 wrote:
Ohh, so I was getting different theories confused. But I thought their was a Qunatum Theory where all events were happening at stimitanously but we were perceiving them as the past, present or future etc?
Or theres a quantum theory that suggests we can travel backwards in a loop of space-time?
If not does Quantum Theory effect our idea of time at all?

There may be some fringe quantum theories involving strange interpretations of time, but as a quantum theorist by trade I don't recognise any of what you're refering to. I see three basic types of spacetime in QT, all of which are linear:

1. Standard QM: space is dimensions (operators), time a parameter.
2. Relativistic RM: space and time are dimensions.
3. QFT: space and time are parameters.

That's all I've got on QT and time, except I know in Quantum Loop Gravity there is a fundamental quantum of time: the Planck time. All durations are integer multiples of it.
Darunia9
 
  1  
Reply Fri 17 Apr, 2009 08:15 am
@Bones-O,
Ahh yeah I think I was getting confused over what Planck Time was. Thanks for the help
0 Replies
 
Alan McDougall
 
  1  
Reply Thu 7 May, 2009 03:28 pm
@Darunia9,
Darunia9 wrote:
Hey, I'm planning on doing an essay which has a title somewhere along the lines of "What effects does Quantum Theory have on causality and determinism?"
I know some areas of how effects determinism, such as the uncertianity pinciple etc., as there are quite alot of books on that topic. However I'm not uite show how/if it affects causality. Can anyone suggest some good research books or ideas on this title?
Uncertainty principle - Wikipedia, the free encyclopedia
Entropic uncertainty principle

Main article: Hirschman uncertainty

http://upload.wikimedia.org/math/5/c/f/5cf0973b4289237e94947b3ac40d5584.png have a large standard deviation of position, but are actually a superposition of a small number of very narrow bumps. In this case, the momentum uncertainty is much larger than the standard deviation inequality would suggest. A better inequality uses the Shannon information content of the distribution, a measure of the number of bits learned when a random variable described by a probability distribution has a certain value.
http://upload.wikimedia.org/math/0/1/c/01c95e86f491ed4f006023f2a623e0a0.png



Taking the logarithm of Heisenberg's formulation of uncertainty in natural units.
http://upload.wikimedia.org/math/c/4/2/c42feacd95a1122a380f4713a56bfb5f.png but the lower bound is not precise.

Everett (and Hirschman[9]) conjectured that for all quantum states:
http://upload.wikimedia.org/math/a/b/8/ab8e4bb834ee8982c4f1a9bb124ce42d.png This was proven by Beckner in 1975[10].






Putting the two inequalities together for Hermitianhttp://upload.wikimedia.org/math/e/a/9/ea96244c63616b1e0a3d9e7868a90223.png and the uncertainty principle is a special case.

[edit] Physical interpretation

The inequality above acquires its physical interpretation:
http://upload.wikimedia.org/math/1/d/3/1d3f2c1271a50c638f3e2bccd2e72ff4.png where
http://upload.wikimedia.org/math/2/c/5/2c5692374603af8a6d4e998986d1365a.png is the mean of observable X in the state ψ and
http://upload.wikimedia.org/math/6/f/6/6f60c500803332ac9498b5d0634d1e94.png is the standard deviation of observable X in the system state ψ.



I hope you appreciate the above brief mathematic introduction example to help you bounce you off with your essay :eeek:

Peace Alan (Read my signature below!)
0 Replies
 
Bones-O
 
  1  
Reply Thu 7 May, 2009 07:11 pm
@Darunia9,
Yes, it is important to know what we do not know, but I guess, Alan, it's not very important to let other people know what we do not know, which gives us free reign to copy and paste advanced mathematical physics we know we don't understand. :whistling:
Alan McDougall
 
  1  
Reply Thu 7 May, 2009 07:43 pm
@Bones-O,
Bones-O! wrote:
Yes, it is important to know what we do not know, but I guess, Alan, it's not very important to let other people know what we do not know, which gives us free reign to copy and paste advanced mathematical physics we know we don't understand. :whistling:


Cant you see I was just kidding adding a little humor? Smile

We must sometimes lighten up a bit

Do I understand all that maths, absolutely not?

I do understand how extremely complex it really is and that is what tickled my tummy

Alan
Bones-O
 
  1  
Reply Fri 8 May, 2009 05:04 am
@Alan McDougall,
Alan McDougall wrote:
Cant you see I was just kidding adding a little humor? Smile

We must sometimes lighten up a bit

Do I understand all that maths, absolutely not?

I do understand how extremely complex it really is and that is what tickled my tummy

Alan

Really? Looked like you were trying to scare the guy to me. Have it your way dude... :Not-Impressed:
Darunia9
 
  1  
Reply Fri 8 May, 2009 10:30 am
@Bones-O,
Haha, yeah well one day I will understand that maths stuff, after uni, I understand some of the concepts behind it already anyway. And I've changed the topic slightly to a (slightly) easier more philosophical topic which is now something like "How Quantum Mechanics/Physics effects our view of reality."
And besides wheres the fun in education if you dont challenge yourself?
rhinogrey
 
  1  
Reply Fri 8 May, 2009 10:53 am
@Darunia9,
Darunia9 wrote:

And besides wheres the fun in education if you dont challenge yourself?


Agreed. Education is about making mistakes, not doing things correctly.

The Academy is a place of rampant narcissism. It's tiring when professors tell you to make sure you don't bite off more than you can chew with your papers -- I make a point of doing so.
0 Replies
 
Alan McDougall
 
  1  
Reply Sat 9 May, 2009 01:11 am
@Darunia9,
Darunia9 wrote:
Haha, yeah well one day I will understand that maths stuff, after uni, I understand some of the concepts behind it already anyway. And I've changed the topic slightly to a (slightly) easier more philosophical topic which is now something like "How Quantum Mechanics/Physics effects our view of reality."
And besides wheres the fun in education if you dont challenge yourself?


OK guys lets leave all the mathematical stuff behind and look at quantum theory in the light of philosophy

Nothing is certain in the quantum world, only the probability that an event will happed. We use that probability factor to use quantum mechanics in real inventions we all see around us today, from your TV and computer all use quantum mechanics,

This uncertainty I think leaks into our macro world and we see it in entropy or chaos theory

Really nothing is as certain as uncertainty
0 Replies
 
Bones-O
 
  1  
Reply Sun 10 May, 2009 05:45 pm
@Darunia9,
Hi Darunia

I'm sure you've already looked into Schrodinger's cat (or the measurement problem as it is known) and the electron double-slit experiment. Other ponderables are the EPR paradox and the Stern-Gerlach experiment. In general, there is the problem of interpretation in QM. QM predictions are derived mathematically, with scant attention to philosophical understanding. Some see this as a virtue, some as a sign that QM lacks a fundamental basis.

There are five main postulates in QM and you should probably be familiar with them.

1. All systems are described by wavefunctions (waves that vary in time and/or space) - note this is almost never a simple sinusoidal wave.

2. A measurement of a system can only yield specific measured states (eigenfunctions), each having a corresponding measurement result (eigenvalue).

3. The initial wavefunction of the system may comprise more than one allowed state(the expansion postulate)...

4. ...but because we can only measure one, after measurement the system must be in the measured state (collapse of the wavefunction).

5. How much of the measured state was present in the original wavefunction determines the probability of measuring that state.

For instance, I may have a measuring device that can measure -1, 0, or 1. To begin with, the system wavefunction describes a mixture of these states: 0.35x(-1) + 0.6x(0) + 0.53x(1). The probability of measuring, say (0) is 0.6 squared, or 36%. After measurement, I get the result (1). Thus the system is now in state (1) with probability 100%.

That is as close to a philosophical basis as QM gets. Shocking, eh? But there's plenty of scope for philosophy in there. Are objects really waves, or are waves just the best way of doing the maths? What does it mean to be more than one thing at once when we can only see objects as being one thing? How does simply observing something change it's state? Does this suggest consciousness has special powers in nature? Are processes really probabilistic or is there some underlying determinism that we're unaware of?
Alan McDougall
 
  1  
Reply Mon 11 May, 2009 08:14 am
@Bones-O,
Bones-O! wrote:
Hi Darunia

I'm sure you've already looked into Schrodinger's cat (or the measurement problem as it is known) and the electron double-slit experiment. Other ponderables are the EPR paradox and the Stern-Gerlach experiment. In general, there is the problem of interpretation in QM. QM predictions are derived mathematically, with scant attention to philosophical understanding. Some see this as a virtue, some as a sign that QM lacks a fundamental basis.

There are five main postulates in QM and you should probably be familiar with them.

1. All systems are described by wavefunctions (waves that vary in time and/or space) - note this is almost never a simple sinusoidal wave.

2. A measurement of a system can only yield specific measured states (eigenfunctions), each having a corresponding measurement result (eigenvalue).

3. The initial wavefunction of the system may comprise more than one allowed state(the expansion postulate)...

4. ...but because we can only measure one, after measurement the system must be in the measured state (collapse of the wavefunction).

5. How much of the measured state was present in the original wavefunction determines the probability of measuring that state.

For instance, I may have a measuring device that can measure -1, 0, or 1. To begin with, the system wavefunction describes a mixture of these states: 0.35x(-1) + 0.6x(0) + 0.53x(1). The probability of measuring, say (0) is 0.6 squared, or 36%. After measurement, I get the result (1). Thus the system is now in state (1) with probability 100%.

That is as close to a philosophical basis as QM gets. Shocking, eh? But there's plenty of scope for philosophy in there. Are objects really waves, or are waves just the best way of doing the maths? What does it mean to be more than one thing at once when we can only see objects as being one thing? How does simply observing something change it's state? Does this suggest consciousness has special powers in nature? Are processes really probabilistic or is there some underlying determinism that we're unaware of?


Now you revert to physics , so please allow me to do the same? :perplexed:

I am fairy informed in physics and made reference to Schroedinger and his silly harl alive half dead kittens, and unprovable hypothesis atthat
Bones-O
 
  1  
Reply Mon 11 May, 2009 09:33 am
@Alan McDougall,
Alan McDougall wrote:
Now you revert to physics , so please allow me to do the same? :perplexed:

I am fairy informed in physics and made reference to Schroedinger and his silly harl alive half dead kittens, and unprovable hypothesis atthat


Are you seriously suggesting I'm being hypocritical when I take you to task on copying and pasting highly mathematical Wiki content you don't understand and that wasn't relevant to the question as it stood if I then post comments in my own words that I do understand and is relevant to the question as it now stands? Can you seriously not see the difference between my post and yours? Alan, I often suspect that with you the important thing is to post anything rather than post something worthwhile.

BTW, Schrodinger outlined the cat thought-experiment to demonstrate that quantum mechanics was incomplete. His view was that the cat must be alive OR dead, and thus since QM predicts a superposition of each, QM must be incomplete. It was not a hypothesis, falsifiable or otherwise: it was an argument within the QM community about how to interpret the maths.
 

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