The Naked Scientists

The Naked Scientists Forum

Author Topic: Randomness and quantum mechanics  (Read 20848 times)

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Randomness and quantum mechanics
« Reply #25 on: 07/07/2009 10:52:24 »
Careful here, in QED the particle has a vector that rotates as the particle travels. Dyson showed that if you do that correctly then the sum of the vectors is just the wavefunction, so it's equivalent to the normal Schroedinger equation.
Ok, but what is for you the physical meaning of the phrase "in the twin slit the photon has gone through *both* slits"? How would you prove it?
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #26 on: 07/07/2009 14:09:05 »
You just look at the diffraction pattern, which, really, on its own, shows that it has gone through both slits, and then close either one of the slits, and the pattern goes away.

But you only ever get one click on a photodetector.

Still, photodetectors are odd beasts- they are able to multiply up a single quantum effect and make it change the macroscopic world.
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #27 on: 07/07/2009 14:14:41 »
I don't think I can accept randomness.

Not even a single computer in this world can create a pure random number. It simply doesn't exists.
Actually there are computers that use quantum effects to generate random numbers. In fact non deterministic electronics is not at all difficult, resistors have significant random noise.
Quote
The randomness of radioactive decay can be made as an example. They say, although we know the exact rate of decay, we don't have any idea which one will decay first. For me, the notion of half life itself shows us that there are actually some system governing it. It wasn't random, it just we don't understand it yet. Otherwise, there won't be any notion of half-lives...
Half life is a statistical property that comes about whenever there is a fixed chance of a decay in any interval. Even random processes have well defined statistical properties.

Quote
I hope Albert Einstein is still alive today to unscrew quantum mechanic's mess...
No, he died, and he had even less luck than other physicists really with QM.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Randomness and quantum mechanics
« Reply #28 on: 07/07/2009 20:03:44 »
You just look at the diffraction pattern, which, really, on its own, shows that it has gone through both slits,
Yes, but *what* has gone through both slits? The particle? No, because if it was so, putting a detector behind the slits, you shoud find two simultaneous detections, which thing is impossible because it is a "single" particle, and because in this way you destroy the interference pattern.

 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #29 on: 07/07/2009 20:16:41 »
You just look at the diffraction pattern, which, really, on its own, shows that it has gone through both slits,
Yes, but *what* has gone through both slits? The particle?
You don't have particles in quantum mechanics exactly. The wave/particle went through both.
 

Offline wanhafizi

  • Sr. Member
  • ****
  • Posts: 106
    • View Profile
Randomness and quantum mechanics
« Reply #30 on: 08/07/2009 01:58:02 »
Quote
Actually there are computers that use quantum effects to generate random numbers. In fact non deterministic electronics is not at all difficult, resistors have significant random noise.

If you read my last posting;

Quote
To measure really small stuff in the real world is a very very tough job. Consider this, it have to be in absolute zero temperature, no light, not a single photon, not on earth because of the gravity and magnetic distortion, not to mention the absolute necessary to protect from electromagnetic waves... Just impossible...

It is literally impossible to isolate outside influence from getting into QM experiments. These influences coming from all direction and effecting our experiments in many ways, making the result unpredictable and seems to be random. For me, we cannot declare randomness exists in the QM experiments, until we get rid of all those outside influence, which is nearly impossible. Even deep in earth, neutrinos still pouring on our bedrocks.

Remember our old friend the hiss in radios? We know now it is actually came from background radiation from outer space. Most probably the same thing happened to resistors.

Quote
Quote
I hope Albert Einstein is still alive today to unscrew quantum mechanic's mess...
No, he died, and he had even less luck than other physicists really with QM.

Exactly. Rumors has it that he died with papers on his hands trying to find his own solution for one unified theory, hoping to avoid the undeterministic nature of QM. And yes, he despised QM.
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #31 on: 08/07/2009 02:23:43 »
Quote
Actually there are computers that use quantum effects to generate random numbers. In fact non deterministic electronics is not at all difficult, resistors have significant random noise.

Remember our old friend the hiss in radios? We know now it is actually came from background radiation from outer space. Most probably the same thing happened to resistors.
Nope, that's not it in this case. There's something called 'shot noise' which is random noise due to the movement of individual electrons through the resistor. It's actually a measureable amount of noise, and electrons are quantum entities.
 

Offline wanhafizi

  • Sr. Member
  • ****
  • Posts: 106
    • View Profile
Randomness and quantum mechanics
« Reply #32 on: 08/07/2009 02:43:26 »
Quote
Actually there are computers that use quantum effects to generate random numbers. In fact non deterministic electronics is not at all difficult, resistors have significant random noise.

Remember our old friend the hiss in radios? We know now it is actually came from background radiation from outer space. Most probably the same thing happened to resistors.
Nope, that's not it in this case. There's something called 'shot noise' which is random noise due to the movement of individual electrons through the resistor. It's actually a measureable amount of noise, and electrons are quantum entities.


So... This caused by physical movement.

Not randomness, just we don't know how it was to the tiniest level. Just like water splashing at rapids. It seems random, but it's not. Just that we don't know all the factors involved
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #33 on: 08/07/2009 03:54:33 »
No, so far as anyone knows it's random. Electrons are fundamental particles and have behaviours that are highly determined by quantum mechanics. Actually it's condensed matter physics, and condensed matter physics is just all about quantum mechanics; I studied it somewhat at degree level, it's also related to how semiconductors work.

You can certainly postulate non random underpinnings for QM, but there's absolutely no evidence for non randomness right now.
« Last Edit: 08/07/2009 03:56:12 by wolfekeeper »
 

Offline wanhafizi

  • Sr. Member
  • ****
  • Posts: 106
    • View Profile
Randomness and quantum mechanics
« Reply #34 on: 08/07/2009 05:47:02 »
I do think the theories of QM and its formula does serve good functions in our experiments, because the world we are living are filled with energy noises, electromagnetic waves, and countless other factors that are effecting matter at the very tiniest level.

Without those factors, QM formula will become very deterministic and highly precise. But, like I've said before, it's nearly impossible to create a 'highly-energy-clean' rooms such as being described. For starters, those rooms should be at absolute zero degree and very far away from the sun or stars.

I believe QM formula consists of probabilities defines the maximum & the minimum value in the world where QM experiments are being done with 'noises' of energy & particles flying around. It seems undeterministic because we can't possibly know the attributes of each and every single atom, photon and energy going in and out of the system while measurement was done. So, results might seems to be random within certain range, but it is only to show the existence of other factors that we didn't and couldn't possibly include in our calculations...

It means that randomness inside our data are just vectors that were not included inside our model, because we can't possibly know all of them...

Randomness doesn't exists
« Last Edit: 09/07/2009 01:16:40 by wanhafizi »
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #35 on: 08/07/2009 11:50:27 »
Actually, it's the other way around, external interference acts as a measurement and destroys the interference fringes because the wavefunction loses coherence.
 

Offline glovesforfoxes

  • Sr. Member
  • ****
  • Posts: 372
  • Matthew 6:21
    • View Profile
Randomness and quantum mechanics
« Reply #36 on: 08/07/2009 14:16:16 »
evidence for randomness to me is like saying we have no evidence for determinism yet. that's an unscientific way of thinking about it, i guess, but i don't know.. it seems to me that in the past people have said all these things are random, but then it is shown that they are not, and i think that the same thing will happen for QM.

so, to sum up this thread: evidence for QM randomness is like evidence for god - you can believe in it, but you just don't know if it's actually true or not.

is that right?

i have another question now too. what are the things that physics in general can't accurately predict, explain or describe?
« Last Edit: 08/07/2009 14:20:22 by glovesforfoxes »
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #37 on: 08/07/2009 14:30:44 »
so, to sum up this thread: evidence for QM randomness is like evidence for god - you can believe in it, but you just don't know if it's actually true or not.

is that right?
No. We actually have reproducible experimental evidence for quantum randomness. There is no reproducible experimental evidence for God.
 

Offline glovesforfoxes

  • Sr. Member
  • ****
  • Posts: 372
  • Matthew 6:21
    • View Profile
Randomness and quantum mechanics
« Reply #38 on: 08/07/2009 14:38:04 »
Quote
No. We actually have reproducible experimental evidence for quantum randomness. There is no reproducible experimental evidence for God.

but if the experimental evidence is always altered by some extraneous variable that affects earth in the same way, then it is useless evidence, surely?
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #39 on: 08/07/2009 14:48:43 »
There's no evidence of any extraneous variables either.

In fact, extraneous interactions are known to destroy the interference pattern; it makes it more random, not less. You only get the interference patterns when there's no perturbations.
 

Offline glovesforfoxes

  • Sr. Member
  • ****
  • Posts: 372
  • Matthew 6:21
    • View Profile
Randomness and quantum mechanics
« Reply #40 on: 08/07/2009 14:54:45 »
okay. so.. the view that fits best with the evidence currently is that QM is truly random. it may be shown to be deterministic one day, or it may be that it is truly random no matter how well you can measure it.

thank you all for contributing to this fascinating topic! :)
 

Offline wanhafizi

  • Sr. Member
  • ****
  • Posts: 106
    • View Profile
Randomness and quantum mechanics
« Reply #41 on: 09/07/2009 01:40:01 »
Actually, it's the other way around, external interference acts as a measurement and destroys the interference fringes because the wavefunction loses coherence.

Yeah, I know. I wrote this before;
Quote
The facts is, we cannot measure any small stuff without 'touching' it. We used electron, photon, magnetic waves to measure by 'touching' what we are measuring. This causes the system being measured to be literally effected.

Maybe not in a sentence that a scientists would like to hear, but my point was the same as yours.

The thing is, there are other factors going in and out of the system that we couldn't possibly imagine.

You see, for example, when we are doing experimentation on burning hydrogen in oxygen, we can neglect the rooms' luminosity(photon), because the reaction happened on molecular level.

But, when we are talking about QM (example Solar Cells), absolutely everything must be considered into our calculation, because what's happening is more fundamental, of which every sort of energy vectors will cause changes.

It's not that it is that important to know everything, but not knowing them makes us infer that randomness exists in QM systems.

I just don't like to hear scientists talking about philosophical stuff, like some guru from Tibet, especially when they attribute consciousness and God to randomness of QM.
« Last Edit: 09/07/2009 02:15:50 by wanhafizi »
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #42 on: 09/07/2009 02:13:50 »
It actually seems to be worse than that even- there can be things going on *outside* the experiment that can randomly change the outcome of the experiment and yet when you collect all of the data together, you find it's just right to make the laws of physics work.

For example you can make an electron pair so that one is spin up, the other spin down. But you don't know which is which. But when you measure one, the other is the opposite.

Which is not surprising, except that QM theorists have managed to prove that it didn't make up its mind until you made the measurement.

And this works no matter how far apart they are, they agree with each other even if they are 10 light years apart.
 

Offline wanhafizi

  • Sr. Member
  • ****
  • Posts: 106
    • View Profile
Randomness and quantum mechanics
« Reply #43 on: 09/07/2009 05:56:05 »
Yes, I think we all can accept QM being weird.

Once there are people calling chemists as witches, because they can't accept the weirdness. But now, we know better.

But even if something is weird, we are hoping to have some sense or absolute rules about them with solid rules and mathematical calculations.

But the concept randomness is not just weird, it also forces us to believe at the heart this orderly universe, there are chaotic world where no rules whatsoever apply. That's why they attribute pure randomness to the fabric of consciousness and God. Because randomness seems to be the only source where pure free will & pure original thoughts came from. Otherwise, you, your actions, your mind are really just a summation of of your biology, nerve fibers, electrical charges in your brain and your surroundings.
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #44 on: 10/07/2009 03:42:07 »
Quote
Otherwise, you, your actions, your mind are really just a summation of of your biology, nerve fibers, electrical charges in your brain and your surroundings.
Yup, welcome to the real world, forget quantum mechanics, that's how you work.
 

Offline wanhafizi

  • Sr. Member
  • ****
  • Posts: 106
    • View Profile
Randomness and quantum mechanics
« Reply #45 on: 12/07/2009 20:12:38 »
Maybe we are, maybe everything has been put in motion since the big bang. Maybe our freewill is just an illusion to our mind. Who knows...
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Randomness and quantum mechanics
« Reply #46 on: 12/07/2009 21:42:03 »
Well, you have to look at the evidence- if you change your biology in even minor ways (drugs, strokes, surgery), it seems that you change your mind and will; so it seems to me that freewill is a product of biology (at bottom memory is a biological function).
 

Offline wanhafizi

  • Sr. Member
  • ****
  • Posts: 106
    • View Profile
Randomness and quantum mechanics
« Reply #47 on: 13/07/2009 08:07:16 »
Well, you have to look at the evidence- if you change your biology in even minor ways (drugs, strokes, surgery), it seems that you change your mind and will; so it seems to me that freewill is a product of biology (at bottom memory is a biological function).


This could to a whole new discussion thread, even a new forum  ;)
 

Offline glovesforfoxes

  • Sr. Member
  • ****
  • Posts: 372
  • Matthew 6:21
    • View Profile
Randomness and quantum mechanics
« Reply #48 on: 21/07/2009 17:20:32 »
Quote
Well, you have to look at the evidence- if you change your biology in even minor ways (drugs, strokes, surgery), it seems that you change your mind and will; so it seems to me that freewill is a product of biology (at bottom memory is a biological function).

well that's evidence certainly, but is it evidence of free will? it seems that is evidence that there is will itself, but whether that is free or not is completely different. what is exactly freedom of will? if it is the ability to make decisions to do actions that don't necessarily fit with our emotional state, then i would say we have it. but if it is the ability to make decisions without being affected by outside influences, i would say that this is wrong, and just as ridiculous as saying that we have the ability to make decisions without being affected by inside influences - both internal and external things are used to generate decisions and actions and choices, and that is all that affects them - therefore there is no "free" will, but there is will. i am a hard determinist, but less so about quantum mechanics now :)
 

Offline wanhafizi

  • Sr. Member
  • ****
  • Posts: 106
    • View Profile
Randomness and quantum mechanics
« Reply #49 on: 23/07/2009 05:39:01 »
... i am a hard determinist ...

Same here
 

The Naked Scientists Forum

Randomness and quantum mechanics
« Reply #49 on: 23/07/2009 05:39:01 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length